THERMEDICS INC
SC TO-T, 2000-03-03
MISC INDUSTRIAL & COMMERCIAL MACHINERY & EQUIPMENT
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<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                             -----------------------

                                   SCHEDULE TO

                                 (Rule 14d-100)

            TENDER OFFER STATEMENT UNDER SECTION 14(d)(1) OR 13(e)(1)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                             -----------------------

                               THERMO SENTRON INC.
                            (Name of Subject Company)

                            SENTRON ACQUISITION, INC.
                                    (Offeror)

                                   CORPAK INC.
                                   (Offeror)

                                 THERMEDICS INC.
                                   (Offeror)

                          THERMO ELECTRON CORPORATION
                                   (Offeror)

                     COMMON STOCK, PAR VALUE $0.01 PER SHARE
                         (Title of Class of Securities)

                                CUSIP 883593 10 5
                      (CUSIP Number of Class of Securities)

                             Seth H. Hoogasian, Esq.
                                 General Counsel
                           Thermo Electron Corporation
                                 81 Wyman Street
                        Waltham, Massachusetts 02454-9046
                                 (781) 622-1000

            (Name, Address and Telephone Number of Person Authorized
       to Receive Notices and Communications on Behalf of Filing Persons)

                                 with a copy to:

                             David E. Redlick, Esq.
                                Hale and Dorr LLP
                                 60 State Street
                           Boston, Massachusetts 02109
                                 (617) 526-6000

                             -----------------------
<PAGE>   2

                            CALCULATION OF FILING FEE

<TABLE>
<S>                       <C>                <C>                      <C>
Transaction Valuation(1): $31,834,396.00     Amount of Filing Fee(2): $6,366.88
- --------------------
</TABLE>

(1)      For purposes of calculating fee only. This amount is based upon (a) the
         maximum number of Shares to be purchased pursuant to the Offer and (b)
         the price offered per Share.

(2)      The amount of the filing fee, calculated in accordance with Regulation
         240.0-11 under the Securities Exchange Act of 1934, as amended, equals
         1/50 of one percent of the Transaction Valuation.

[ ]      Check the box if any part of the fee is offset as provided by Rule
         0-11(a)(2) and identify the filing with which the offsetting fee was
         previously paid. Identify the previous filing by registration statement
         number, or the Form or Schedule and the date of its filing.

<TABLE>
<S>      <C>                                         <C>
         Amount Previously Paid:                     Not applicable
         Form or Registration No.:                   Not applicable
         Filing Party:                               Not applicable
         Date Filed:                                 Not applicable
</TABLE>

[ ]      Check the box if the filing relates solely to preliminary
         communications made before the commencement of a tender offer.

         Check the appropriate boxes below to designate any transactions to
         which the statement relates:

         [X]      third-party tender offer subject to Rule 14d-1.

         [ ]      issuer tender offer subject to Rule 13e-4.

         [X]      going-private transaction subject to Rule 13e-3.

         [X]      amendment to Schedule 13D under Rule 13d-2.

         Check the following box if the filing is a final amendment reporting
         the results of the tender offer: [ ]


                            SCHEDULE 13D INFORMATION
         -----------------------------------------------------------------------

         1.       NAMES OF REPORTING PERSONS
                  I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

                  Thermo Electron Corporation
                  IRS No. 04-2209186
         -----------------------------------------------------------------------

         2.       CHECK THE APPROPRIATE BOX IF  A MEMBER OF A GROUP*     (a) [ ]
                                                                         (b) [X]
         -----------------------------------------------------------------------

         3.       SEC USE ONLY
         -----------------------------------------------------------------------

         4.       SOURCE OF FUNDS*

                  WC
         -----------------------------------------------------------------------
<PAGE>   3
         5.       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS
                  REQUIRED PURSUANT TO ITEM 2(d) or 2(e)                     [ ]
         -----------------------------------------------------------------------


         6.       CITIZENSHIP OR PLACE OF ORGANIZATION

                  State of Delaware
         -----------------------------------------------------------------------

         NUMBER OF                  7.      SOLE VOTING POWER
         SHARES
         BENEFICIALLY                       8,171,157
         OWNED BY          _____________________________________________________
         EACH
         REPORTING                  8.      SHARED VOTING POWER
         PERSON WITH
                                            0
         -----------------------------------------------------------------------

         9.       SOLE DISPOSITIVE POWER

                  8,171,157
         -----------------------------------------------------------------------

         10.      SHARED DISPOSITIVE POWER

                  0
         -----------------------------------------------------------------------

         11.      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                  8,171,157
         -----------------------------------------------------------------------

         12.      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
                  CERTAIN SHARES                                             [ ]
         -----------------------------------------------------------------------

         13.      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

                  86.6%
         -----------------------------------------------------------------------

         14.      TYPE OF REPORTING PERSON*

                  CO
         -----------------------------------------------------------------------
<PAGE>   4
         This Tender Offer Statement on Schedule TO relates to the offer by
Sentron Acquisition, Inc., a Delaware corporation (the "Purchaser") and an
indirect wholly-owned subsidiary of Thermedics Inc., a Massachusetts corporation
("Thermedics"), to purchase all outstanding shares of common stock, par value
$0.01 per share (the "Shares"), of Thermo Sentron Inc., a Delaware corporation
(the "Company"), at a purchase price of $15.50 per Share net to the seller in
cash, without interest thereon, upon the terms and subject to the conditions set
forth in the Offer to Purchase dated March 3, 2000 (the "Offer to Purchase"), a
copy of which is attached hereto as Exhibit 12(a)(1), and in the related Letter
of Transmittal (which, together with the Offer to Purchase, constitute the
"Offer"), a copy of which is attached hereto as Exhibit 12(a)(2). The
information in the Offer to Purchase under the captions "Summary",
"Introduction", "Special Factors", "The Tender Offer", "Certain Federal Income
Tax Consequences", "Price Range Of The Shares; Dividends", "Certain Information
Concerning The Company", "Certain Information Concerning The Purchaser, Corpak,
Thermedics And Thermo Electron", "Source And Amount Of Funds" and "Fees And
Expenses" and Schedules I, II and III to the Offer to Purchase are incorporated
herein by reference as set forth below.

ITEM 1.   SUMMARY TERM SHEET.

         See the section of the Offer to Purchase captioned "Summary".

ITEM 2.   SUBJECT COMPANY INFORMATION.

         (a) See the section of the Offer to Purchase captioned "Certain
Information Concerning The Company".

         (b) See the section of the Offer to Purchase captioned "Introduction".

         (c) See the section of the Offer to Purchase captioned "Price Range Of
The Shares; Dividends".

ITEM 3.   IDENTITY AND BACKGROUND OF FILING PERSON.

         (a) See the section of the Offer to Purchase captioned "Certain
Information Concerning The Purchaser, Corpak, Thermedics And Thermo Electron"
and Schedule I to the Offer to Purchase ("Members Of The Boards Of Directors And
Executive Officers Of The Purchaser, Corpak, Thermedics And Thermo Electron").

         (b) See the section of the Offer to Purchase captioned "Certain
Information Concerning The Purchaser, Corpak, Thermedics And Thermo Electron"
and Schedule I to the Offer to Purchase ("Members Of The Boards Of Directors And
Executive Officers Of The Purchaser, Corpak, Thermedics And Thermo Electron").

                                      -1-
<PAGE>   5
         (c) See the section of the Offer to Purchase captioned "Certain
Information Concerning The Purchaser, Corpak, Thermedics And Thermo Electron"
and Schedule I to the Offer to Purchase ("Members Of The Boards Of Directors And
Executive Officers Of The Purchaser, Corpak, Thermedics And Thermo Electron").

ITEM 4.   TERMS OF THE TRANSACTION.

         (a) See the sections of the Offer to Purchase captioned "Summary",
"Introduction", "Special Factors - The Merger", "Special Factors - Other
Possible Purchases Of Shares", "The Tender Offer - Terms Of The Offer;
Expiration Date", "The Tender Offer - Acceptance For Payment And Payment For
Shares", "The Tender Offer - Procedures For Accepting The Offer And Tendering
Shares", "The Tender Offer - Withdrawal Rights" and "Certain Federal Income Tax
Consequences".

ITEM 5.   PAST CONTACTS, TRANSACTIONS, NEGOTIATIONS AND AGREEMENTS.

         (a) See the sections of the Offer to Purchase captioned "Special
Factors - Conflicts Of Interest - Executive Officers And Directors of the
Company" and "Certain Information Concerning The Purchaser, Corpak, Thermedics
And Thermo Electron - Certain Transactions" and Schedule I to the Offer to
Purchase ("Members Of The Boards Of Directors And Executive Officers Of The
Purchaser, Corpak, Thermedics And Thermo Electron").

         (b) See the sections of the Offer to Purchase captioned "Special
Factors - Background To The Offer And The Merger", "Special Factors - Conduct Of
The Company's Business After The Offer And The Merger", "Certain Information
Concerning The Purchaser, Corpak, Thermedics And Thermo Electron - Certain
Transactions" and Schedule II to the Offer to Purchase ("Information
Concerning Transactions in the Common Stock of the Company").

ITEM 6.   PURPOSE OF THE TRANSACTION AND PLANS OR PROPOSALS.

        (a) and (c)(1)-(7) See the sections of the Offer to Purchase captioned
"Introduction", "Special Factors - Background To The Offer And The Merger",
"Special Factors - Purpose and Reasons For The Offer And The Merger", "Special
Factors - The Merger", "Special Factors - Other Possible Purchases Of Shares",
"Special Factors - Certain Effects Of The Offer And The Merger", "Special
Factors - Conduct Of The Company's Business After The Offer And The Merger",
"Special Factors - Conduct Of The Company's Business If The Offer Is Not
Completed" and "The Merger; Appraisal Rights".

ITEM 7.   SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

         (a), (b) and (d) See the section of the Offer to Purchase captioned
"Source And Amount Of Funds".

                                      -2-

<PAGE>   6
ITEM 8.   INTEREST IN SECURITIES OF THE SUBJECT COMPANY.

         (a) See the section of the Offer to Purchase captioned "Introduction"
and Schedule I to the Offer to Purchase ("Members Of The Boards Of Directors And
Executive Officers Of The Purchaser, Corpak, Thermedics And Thermo Electron").

         (b) See Schedule II to the Offer to Purchase("Information Concerning
Transactions In The Common Stock Of The Company").

ITEM 9.   PERSONS/ASSETS RETAINED, EMPLOYED, COMPENSATED OR USED.

         (a) See the sections of the Offer to Purchase captioned "Introduction"
and "Fees And Expenses".

ITEM 10.  FINANCIAL STATEMENTS.

         (a) The financial statements of the Purchaser, Corpak Inc., a
Massachusetts corporation ("Corpak") and a wholly-owned subsidiary of
Thermedics, Thermedics and Thermo Electron Corporation, a Delaware corporation
("Thermo Electron"), are not material to the Offer.

         (b) The pro forma financial statements of the Purchaser, Corpak,
Thermedics and Thermo Electron are not material to the Offer.

ITEM 11.  ADDITIONAL INFORMATION.

         (a)(1) None.

         (a)(2) See the sections of the Offer to Purchase captioned
"Introduction", "The Tender Offer - Acceptance For Payment And Payment For
Shares" and "The Tender Offer - Certain Legal Matters; Regulatory Approvals".

         (a)(3) See the section of offer to Purchase captioned "Certain Legal
Matters; Regulatory Approvals".

         (a)(4) See the sections of the Offer to Purchase captioned "Special
Factors - Certain Effects Of The Offer And The Merger".

         (a)(5) None.

         (b) The information set forth in the Offer to Purchase and the Letter
of Transmittal is incorporated herein by reference.

ITEM 12.   EXHIBITS.

         (a)(1)   Offer to Purchase dated March 3, 2000.

         (a)(2)   Letter of Transmittal.

         (a)(3)   Notice of Guaranteed Delivery.

                                      -3-
<PAGE>   7
         (a)(4)   Letter from the Dealer Managers to Brokers, Dealers,
Commercial Banks, Trust Companies and Nominees.

         (a)(5)   Letter to Clients for use by Brokers, Dealers, Commercial
Banks, Trust Companies and Nominees.

         (a)(6)   Summary Advertisement as published on March 3, 2000.

         (a)(7)   Guidelines for Certification of Taxpayer Identification Number
on Substitute Form W-9.

         (a)(8) Press Release issued by Thermedics on January 31, 2000
(incorporated herein by reference to Exhibit 99 to the Current Report on Form
8-K of Thermedics filed with the Commission on February 1, 2000).

         (a)(9)   Press Release issued by Thermo Electron on January 31, 2000
(incorporated herein by reference to Exhibit 99 to the Current Report on Form
8-K of Thermo Electron filed with the Commission on February 1, 2000).

         (a)(10)  Press Release issued by Thermedics on March 3, 2000.

         (b)      Loan Agreement dated as of March 1, 2000 between Thermo
Electron and Thermedics.

         (d)      None.

         (g)      Slide Presentation of Thermo Electron to Financial Analysts.

         (h)      None.

ITEM 13.   INFORMATION REQUIRED BY SCHEDULE 13E-3.

         Item 2.  Subject Company Information.

                  (d)      See the section of the Offer to Purchase captioned
"Price Range Of The Shares; Dividends".

                  (e)      See the section of the Offer to Purchase captioned
"Certain Information Concerning The Company".

                  (f)      See Schedule II to the Offer to Purchase
("Information Concerning Transactions In The Common Stock Of the Company").

         Item 4.  Terms of the Transaction.

                  (c)      None.

                  (d)      See the section of the Offer to Purchase captioned
"The Merger; Appraisal Rights".

                  (e)      See the section of the Offer to Purchase captioned
"Certain Information Concerning The Company".

                  (f)      Not applicable.

                                      -4-
<PAGE>   8
         Item 5.  Past Contacts, Transactions, Negotiations and Agreements.

                  (c)      See the sections of the Offer to Purchase captioned
"Introduction" and "Special Factors - Background To The Offer And The Merger".

                  (e)      See the sections of the Offer to Purchase captioned
"Special Factors - The Merger" and "Source And Amount Of Funds".

         Item 6.  Purposes of the Transaction and Plans or Proposals

                  (b)      See the section of the Offer to Purchase captioned
"Special Factors - The Merger".

                  (c)(8)   See the section of the Offer to Purchase captioned
"Special Factors - Certain Effects Of The Offer And The Merger".

         Item 7.  Purposes, Alternatives, Reasons and Effects.

                  (a), (b) and (c)     See the sections of the Offer to Purchase
captioned "Introduction", "Special Factors - Background To The Offer And The
Merger", "Special Factors - Purpose and Reasons For The Offer And The Merger"
and "Special Factors - Position Of Thermedics And Thermo Electron As To
Fairness Of The Offer And The Merger".

                  (d)     See the sections of the Offer to Purchase captioned
"Special Factors - Certain Effects Of The Offer And The Merger", "Special
Factors - Conduct Of The Company's Business After The Offer And The Merger",
"Special Factors - Conduct Of The Company's Business If The Offer Is Not
Completed", "Certain Federal Income Tax Consequences" and "The Merger; Appraisal
Rights".

         Item 8.  Fairness of the Transaction.

                  (a), (b), (c), (d), (e) and (f)     See the sections of the
Offer to Purchase captioned "Special Factors - Background To The Offer And The
Merger", "Special Factors - Position Of Thermedics And Thermo Electron As To
Fairness Of The Offer And The Merger", "Special Factors - Summary Of The
Advisors' Analysis And Opinion", "Special Factors - Certain Projected Financial
Data", "Special Factors - Other Possible Purchase Of Shares" and "Special
Factors - The Merger."

         Item 9.  Reports, Opinions, Appraisals and Negotiations.

                  (a), (b) and (c)     See the sections of the Offer to Purchase
captioned "Special Factors - Summary Of The Advisors' Analysis And Opinion" and
"Special Factors - Certain Projected Financial Data".

         Item 10.  Source and Amount of Funds or Other Consideration.

                  (c)      See the section of the Offer to Purchase captioned
"Fees And Expenses".

                                      -5-
<PAGE>   9
         Item 12.  The Solicitation or Recommendation.

                  (d)      See the section of the Offer to Purchase captioned
"Special Factors - Conflicts Of Interest".

                  (e)      Except for the positions of the members of the
Special Committee of the Board of Directors of the Company and the Boards of
Directors of Thermo Electron and Thermedics as set forth in the sections of the
Offer to Purchase captioned "Special Factors - Background To The Offer And The
Merger" and "Special Factors - Position Of Thermedics And Thermo Electron As To
Fairness Of The Offer And The Merger", the filing persons are not aware of any
officer, director or affiliate of the Company or any person listed on Schedule I
to the Offer to Purchase who has made a recommendation either in support of or
against the Offer.

         Item 13.  Financial Statements.

                  (a)      (1) The audited consolidated financial statements of
         the Company as of and for the fiscal years ended January 2, 1999 and
         January 3, 1998 are incorporated herein by reference to the
         Consolidated Financial Statements of the Company included as Exhibit 13
         to the Company's Annual Report on Form 10-K for the fiscal year ended
         January 2, 1999 filed with the Securities and Exchange Commission (the
         "Commission") on March 15, 1999.

                           (2) The unaudited consolidated financial statements
         of the Company for the three and nine month fiscal periods ended
         October 2, 1999 are incorporated herein by reference to Item 1
         ("Financial Statements") of Part I of the Company's Quarterly Report on
         Form 10-Q for the quarter ended October 2, 1999 filed with the
         Commission on November 5, 1999.

                           (3) See the section of the Offer to Purchase
         captioned "Certain Information Concerning the Company - Selected
         Consolidated Financial Information".

                  (b)      Pro-forma financial statements of the Company are not
material to the Offer.

         Item 14. Persons/Assets Retained, Employed, Compensated or Used.

                  (b)      None.

         Item 16. Exhibits.

                  (c)      Opinion of J.P. Morgan Securities Inc. and The
Beacon Group Capital Services, LLC dated January 29, 2000.

                  (f)      Statement of Appraisal Right. See the section of the
Offer to Purchase captioned "The Merger; Appraisal Rights".

                                      -6-
<PAGE>   10
                                    SIGNATURE

After due inquiry and to the best of my knowledge and belief, I certify that the
information set forth in this Statement is true, complete and correct.

                                            SENTRON ACQUISITION, INC.


                                            By: /s/ John T. Keiser
                                               -----------------------------
                                                Name:  John T. Keiser
                                                Title: President

                                            CORPAK INC.


                                            By: /s/ Sandra L. Lambert
                                               -----------------------------
                                                Name:  Sandra L. Lambert
                                                Title: Clerk

                                            THERMEDICS INC.


                                            By: /s/ John T. Keiser
                                               -----------------------------
                                                Name:  John T. Keiser
                                                Title: President and Chief
                                                        Executive Officer

                                            THERMO ELECTRON CORPORATION


                                            By: /s/ Theo Melas-Kyriazi
                                               -----------------------------
                                                Name:  Theo Melas-Kyriazi
                                                Title: Vice President and Chief
                                                        Financial Officer


Date: March 3, 2000

                                      -7-
<PAGE>   11
<TABLE>
<CAPTION>
                                 EXHIBIT INDEX


EXHIBIT                      DESCRIPTION
<S>                          <C>
12(a)(1)                     Offer to Purchase dated March 3, 2000

12(a)(2)                     Letter of Transmittal

12(a)(3)                     Notice of Guaranteed Delivery

12(a)(4)                     Letter from the Dealer Managers to Brokers,
                             Dealers, Commercial Banks, Trust Companies and
                             Nominees

12(a)(5)                     Letter to Clients for use by Brokers, Dealers,
                             Commercial Banks, Trust Companies and Nominees

12(a)(6)                     Summary Advertisement as published on March 3, 2000

12(a)(7)                     Guidelines for Certification of Taxpayer
                             Identification Number on Substitute Form W-9

12(a)(8)                     Press Release issued by Thermedics on January 31,
                             2000 (incorporated herein by reference to
                             Exhibit 99 to the Current Report on Form 8-K of
                             Thermedics filed with the Commission on February 1,
                             2000)

12(a)(9)                     Press Release issued by Thermo Electron on January
                             31, 2000 (incorporated herein by reference to
                             Exhibit 99 to the Current Report on Form 8-K of
                             Thermo Electron filed with the Commission on
                             February 1, 2000)

12(a)(10)                    Press Release issued by Thermedics on March 3, 2000

12(b)                        Loan Agreement dated as of March 1, 2000 between
                             Thermo Electron and Thermedics

12(c)                        Opinion of J.P. Morgan Securities Inc. and The
                             Beacon Group Capital Services, LLC dated January
                             29, 2000

12(d)                        Not applicable

12(e)                        Not applicable

12(f)                        Summary of Appraisal Rights (Included in Exhibit
                             12(a)(1) in the section captioned "The Merger;
                             Appraisal Rights")

12(g)                        Slide Presentation of Thermo Electron to Financial
                             Analysts

12(h)                        Not applicable
</TABLE>


<PAGE>   1

                           OFFER TO PURCHASE FOR CASH

                     ALL OUTSTANDING SHARES OF COMMON STOCK

                                       OF

                              THERMO SENTRON INC.

                                       AT

                              $15.50 NET PER SHARE

                                       BY

                           SENTRON ACQUISITION, INC.

                     AN INDIRECT WHOLLY-OWNED SUBSIDIARY OF

                                THERMEDICS INC.

- --------------------------------------------------------------------------------

  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
        TIME, ON THURSDAY, MARCH 30, 2000, UNLESS THE OFFER IS EXTENDED.

- --------------------------------------------------------------------------------

     THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY
TENDERED AND NOT WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT NUMBER OF
SHARES OF COMMON STOCK OF THERMO SENTRON INC. (THE "COMPANY") WHICH, TOGETHER
WITH SHARES OWNED BY THERMO ELECTRON CORPORATION AND ITS SUBSIDIARIES, INCLUDING
THERMEDICS INC., CONSTITUTES AT LEAST NINETY PERCENT (90%) OF THE OUTSTANDING
SHARES OF THE COMPANY ON THE EXPIRATION DATE. AS OF JANUARY 28, 2000, THERMO
ELECTRON CORPORATION AND ITS SUBSIDIARIES OWNED AN AGGREGATE OF 8,171,157 SHARES
OF THE COMPANY'S OUTSTANDING COMMON STOCK, WHICH CONSTITUTED 86.5% OF THE
OUTSTANDING SHARES OF COMMON STOCK ON SUCH DATE. THE OFFER IS ALSO SUBJECT TO
OTHER IMPORTANT TERMS AND CONDITIONS CONTAINED IN THIS OFFER TO PURCHASE.
                            ------------------------

     NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THIS OFFER, PASSED UPON THE FAIRNESS
OR MERITS OF THE OFFER OR DETERMINED WHETHER THIS OFFER TO PURCHASE IS ACCURATE
OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A CRIME.
                            ------------------------

                     The Dealer Managers for the Offer are:

                          J.P. MORGAN SECURITIES INC.

                                      AND

                     THE BEACON GROUP CAPITAL SERVICES, LLC

March 3, 2000
<PAGE>   2

                                    SUMMARY

     Before you make any decision with respect to the tender offer, you should
read the following summary together with the more detailed information included
elsewhere in this Offer to Purchase. This summary and the remainder of this
Offer to Purchase include information regarding the tender offer, the proposed
subsequent short-form merger, Thermo Sentron Inc. and the position of Thermedics
Inc. and Thermo Electron Corporation regarding the fairness of the terms of the
tender offer and the merger.

- - PRINCIPAL TERMS OF THE TENDER OFFER AND THE MERGER.

     - Tender Offer For All Outstanding Shares (page 32).  Sentron Acquisition,
       Inc., an indirect wholly-owned subsidiary of Thermedics Inc., is offering
       to purchase in a tender offer all of the outstanding shares of common
       stock of Thermo Sentron Inc. that Thermo Electron Corporation and its
       subsidiaries, including Thermedics, do not currently own.

     - Affiliation of Thermo Sentron, Sentron Acquisition, Corpak, Thermedics
       and Thermo Electron (pages 7 and 26).  Thermo Sentron is a majority-owned
       subsidiary of Corpak Inc., which in turn is a wholly-owned subsidiary of
       Thermedics. Sentron Acquisition is a wholly-owned subsidiary of Corpak.
       Thermedics is a majority-owned subsidiary of Thermo Electron. Certain
       officers and directors of Thermedics and Thermo Electron are also
       officers or directors of Thermo Sentron. See "Certain Information
       Concerning The Company" and "Certain Information Concerning The
       Purchaser, Corpak, Thermedics And Thermo Electron."

     - Tender Offer Price (pages 7 and 43).  The consideration being offered in
       the tender offer is $15.50 per share in cash. This price is equal to a
       premium of approximately 73.4% over the last reported sale price of
       Thermo Sentron common stock on the American Stock Exchange on the last
       trading date prior to the initial announcement, on December 10, 1998, of
       our intention to take Thermo Sentron private. The last reported sale
       price of Thermo Sentron common stock on the American Stock Exchange on
       January 28, 2000, the day prior to the date that the tender offer was
       announced, was $14.4375 per share. The last reported sale price of Thermo
       Sentron common stock on the American Stock Exchange on February 29, 2000
       was $15.00 per share. For more information regarding the trading range of
       Thermo Sentron common stock, see "Price Range Of The Shares; Dividends."

     - Conditions to the Tender Offer (page 37).  The tender offer is subject to
       a number of conditions, including the condition that enough shares of
       Thermo Sentron common stock are tendered and not withdrawn so that on the
       expiration date of the tender offer Thermo Electron and its subsidiaries,
       including Thermedics, will together own at least 90% of Thermo Sentron's
       outstanding shares. Assuming that no outstanding Thermo Sentron stock
       options are exercised, this 90% tender condition will be met if at least
       330,886 shares of Thermo Sentron common stock are validly tendered and
       not withdrawn prior to the expiration date of the tender offer. See "The
       Tender Offer--Certain Conditions Of The Offer."

     - Thermo Sentron Shares Outstanding; Ownership by Thermo Electron and Its
       Subsidiaries (page 7). As of January 28, 2000, Thermo Sentron had
       9,446,714 shares of common stock outstanding. In addition, options to
       purchase 647,450 shares of Thermo Sentron common stock were outstanding
       at such date. Thermo Electron and its subsidiaries owned in the aggregate
       8,171,157 shares of Thermo Sentron common stock, or approximately 86.5%
       of the outstanding shares of Thermo Sentron common stock, on January 28,
       2000.

     - Expiration of the Tender Offer (page 32).  The tender offer will expire
       at 12:00 midnight on March 30, 2000. We can elect at any time to extend
       the tender offer. If we extend the tender offer, we will issue a press
       release announcing the extension. See "The Tender Offer--Terms Of The
       Offer; Expiration Date."

     - Procedures for Accepting the Tender Offer and Tendering Shares (page
       34).  In order for your shares of Thermo Sentron common stock to be
       purchased in the tender offer, you must follow the procedures

                                        2
<PAGE>   3

       described in "The Tender Offer--Procedures For Accepting The Offer And
       Tendering Shares" and in the accompanying Letter of Transmittal prior to
       the expiration of the tender offer.

     - Payment for Tendered Shares (page 33).  If all of the conditions of the
       tender offer are satisfied or waived and your shares of Thermo Sentron
       common stock are accepted for payment, we will pay you for your shares
       promptly after the expiration of the tender offer. See "The Tender
       Offer--Acceptance For Payment And Payment For Shares."

     - Withdrawal Rights (page 37).  You may withdraw shares that you have
       tendered at any time on or prior to March 30, 2000, or, if the tender
       offer is extended, prior to the expiration of the tender offer. Unless
       accepted for payment on or prior to May 1, 2000, you may also withdraw
       shares you have tendered at any time after that date. In order for a
       withdrawal to be effective, American Stock Transfer & Trust Company, the
       depositary for the tender offer, must receive your notice of withdrawal
       prior to the expiration of the tender offer at one of the addresses on
       the back cover of this Offer to Purchase. For more information on your
       withdrawal rights, see "The Tender Offer--Withdrawal Rights."

     - Subsequent Merger (pages 27 and 52).  The tender offer is the first step
       in Thermedics' plan to take Thermo Sentron private. If the tender offer
       is completed, Thermo Electron and its subsidiaries, including Thermedics,
       will together own at least 90% of Thermo Sentron's outstanding shares.
       Promptly following the closing of the tender offer, Corpak and Thermo
       Electron plan to contribute their shares of Thermo Sentron common stock
       to Sentron Acquisition in exchange for common stock of Sentron
       Acquisition. Corpak and Thermo Electron would then cause Sentron
       Acquisition to merge with and into Thermo Sentron in a so-called
       "short-form" merger. After the merger, Thermo Sentron would be owned
       exclusively by Thermedics, through its ownership of Corpak, and Thermo
       Electron. Sentron Acquisition does not intend to enter into a merger
       agreement with Thermo Sentron or to seek the approval of the board of
       directors of Thermo Sentron for such merger. Stockholders of Thermo
       Sentron who do not tender their shares of Thermo Sentron common stock in
       the tender offer will not be entitled to vote their shares with respect
       to this merger, but will have a statutory right to demand a judicial
       appraisal of the fair value of their shares of Thermo Sentron common
       stock. See "The Merger; Appraisal Rights." The consideration in the
       merger would be the same $15.50 per share in cash as is payable in the
       tender offer. See "Special Factors--The Merger."

     - Other Possible Purchases of Thermo Sentron Common Stock (page 27).  If,
       after the tender offer is completed but prior to consummation of the
       merger, the aggregate ownership by Thermo Electron and its subsidiaries
       of the outstanding shares of Thermo Sentron common stock should fall
       below 90% due to the exercise of outstanding options or for any other
       reason, Sentron Acquisition intends to acquire additional shares of
       Thermo Sentron common stock on the open market or in privately negotiated
       transactions to the extent required for the aggregate ownership of Thermo
       Sentron common stock by Thermo Electron and its subsidiaries to equal or
       exceed 90%. These purchases would be made at the market prices or
       privately negotiated prices at the time of purchase, which may be higher
       or lower than the price of $15.50 per share in the tender offer and the
       merger. See "Special Factors--Other Possible Purchases of Shares."

     - Source of Funds (page 51).  The total amount of funds required for
       Sentron Acquisition to purchase all of the outstanding shares of Thermo
       Sentron common stock pursuant to the tender offer and merger, assuming no
       outstanding options are exercised, and to pay related expenses is
       estimated to be approximately $21.3 million. Sentron Acquisition will
       obtain the funds to purchase the Thermo Sentron common stock in the
       tender offer and the merger from Thermedics as a loan or a capital
       contribution. Thermedics intends to use a combination of its own working
       capital and borrowings from Thermo Electron to fund this loan or capital
       contribution. Thermo Electron has committed to provide any required loan
       financing to Thermedics. Because the tender offer and the merger are for
       cash and Thermedics and Thermo Electron have access to sufficient cash to
       fund the tender offer and the merger, we do not believe that the
       financial condition of Thermedics, Thermo Electron, Corpak or

                                        3
<PAGE>   4

       Sentron Acquisition is relevant to your decision whether to tender your
       shares in the tender offer. See "Source And Amount Of Funds."

- - THERMEDICS' AND THERMO ELECTRON'S POSITION ON THE FAIRNESS OF THE OFFER AND
THE MERGER (PAGE 16).

     - Determinations of Boards of Directors of Thermedics and Thermo
       Electron.  The boards of directors of Thermedics and Thermo Electron
       determined that the terms of the tender offer and the merger are fair to
       the stockholders of Thermo Sentron. In considering the fairness of the
       tender offer and the merger from a financial point of view to Thermo
       Sentron's stockholders, the boards of directors of Thermo Electron and
       Thermedics reviewed and relied in part upon an analysis of the ranges of
       potential values of the shares of Thermo Sentron common stock that
       resulted from the application of several accepted valuation
       methodologies. This analysis, including the selection of valuation
       methodologies, was prepared by J.P. Morgan Securities Inc. and The Beacon
       Group Capital Services, LLC. J.P. Morgan and The Beacon Group are the
       financial advisors to Thermedics and Thermo Electron in connection with
       the tender offer and the merger and the reorganization of Thermo Electron
       and its subsidiaries described below. For a discussion of the factors
       that the boards of directors of Thermedics and Thermo Electron considered
       in making their determinations as to the fairness of the tender offer and
       the merger and a summary of the financial analysis prepared by J.P.
       Morgan and The Beacon Group, see "Special Factors--Position Of Thermedics
       And Thermo Electron As To Fairness Of The Offer And The Merger" and
       "Special Factors--Summary Of The Advisors' Analysis and Opinion."

     - Negotiation with Special Committee of Thermo Sentron Board of
       Directors.  The boards of directors of Thermo Electron and Thermedics
       determined to proceed with the tender offer and short-form merger after
       negotiations with a special committee of the board of directors of Thermo
       Sentron with respect to a long-form going private merger did not result
       in an offer price that the special committee was prepared to recommend to
       Thermo Sentron's stockholders as a fair price for their shares. This
       special committee has advised Thermedics that it expects to recommend
       that Thermo Sentron stockholders not tender their shares in the tender
       offer. See "Special Factors--Background To The Offer And The
       Merger--Going Private Merger Discussions."

     - Potential Conflicts of Interest.  Thermedics is the majority stockholder
       of Thermo Sentron. Thermo Electron is the majority stockholder of
       Thermedics. Some of the officers and directors of Thermedics and Thermo
       Electron are also officers or directors of Thermo Sentron and own shares
       of common stock of, or hold options to purchase shares of common stock
       of, Thermo Electron, Thermedics and/or Thermo Sentron. As a result, there
       are various potential or actual conflicts of interest in connection with
       the tender offer and the merger. See "Special Factors--Conflicts Of
       Interest."

- - CONSEQUENCES OF THE OFFER AND THE MERGER (PAGE 28).

     Completion of the tender offer and the merger would have the following
consequences:

     - Thermedics and Thermo Electron would have complete control over Thermo
       Sentron's business.

     - Thermedics and Thermo Electron would own 100% of the equity interest in
       Thermo Sentron's business and would solely have the benefit or detriment
       of any change in Thermo Sentron's value.

     - The shares of Thermo Sentron would no longer be listed on the American
       Stock Exchange.

     - Thermo Sentron would no longer be subject to the requirements of the
       Securities Exchange Act of 1934, including requirements to file annual
       and other periodic reports or to provide the type of going-private
       disclosure contained in this offer to purchase.

     If you do not tender your shares of Thermo Sentron common stock and the
tender offer is completed, your shares will remain outstanding until the
subsequent merger of Sentron Acquisition and Thermo Sentron. After the merger,
each of your shares will, subject to statutory appraisal rights, be converted
into the right to receive $15.50 in cash, without interest.

                                        4
<PAGE>   5

- - APPRAISAL RIGHTS (PAGE 52).

     If you tender your shares of Thermo Sentron common stock in the tender
offer, you will not be entitled to exercise statutory appraisal rights under the
Delaware General Corporation Law. If you do not tender your shares in the tender
offer, upon the subsequent merger of Sentron Acquisition and Thermo Sentron, you
will have a statutory right to dissent and demand payment of the judicially
appraised fair value of your Thermo Sentron shares plus a fair rate of interest,
if any, from the date of the merger. This value may be more or less than the
$15.50 per share cash consideration in the tender offer and the merger. See "The
Merger; Appraisal Rights."

- - PURPOSE OF THE TENDER OFFER (PAGE 9).

     On January 31, 2000, Thermo Electron announced that its board of directors
had authorized its management to proceed with a major reorganization of the
operations of Thermo Electron and its subsidiaries. As part of this
reorganization, Thermo Electron plans to acquire the public minority interests
in most of its subsidiaries that have minority investors, spin off its
separation technologies and fiber-based products business and its medical
products business and divest a variety of non-core businesses. The primary goal
of the reorganization is for Thermo Electron and each of its spun-off
subsidiaries to focus on its core business. The purpose of this tender offer and
the proposed subsequent merger is to acquire the minority public interest in
Thermo Sentron as part of Thermo Electron's overall reorganization and to
provide Thermo Sentron's stockholders with $15.50 in cash for each of their
shares of Thermo Sentron common stock. Following the tender offer and the
merger, Thermo Electron plans to retain Thermo Sentron as part of Thermo
Electron's core instrument business.

- - FOR MORE INFORMATION (PAGE 44).

     More information regarding Thermo Sentron, Thermedics and Thermo Electron
is available from their public filings with the Securities and Exchange
Commission. See "Certain Information Concerning the Company" and "Certain
Information Concerning the Purchaser, Corpak, Thermedics and Thermo Electron."

     If you have any questions about the tender offer, please call the
information agent, D.F. King & Co., Inc. If you are a banker or broker, call
collect at (212) 269-5550. All others should call toll-free at (800) 290-6433.

                                        5
<PAGE>   6

                                   IMPORTANT

     Any stockholder of the Company desiring to tender all or any portion of
such stockholder's Shares (as defined herein) should either (1) complete and
sign the accompanying Letter of Transmittal (or a facsimile thereof) in
accordance with the Instructions in the Letter of Transmittal, have such
stockholder's signature thereon guaranteed if required by the Instructions to
the Letter of Transmittal, mail or deliver the Letter of Transmittal (or a
manually signed facsimile) or, in the case of a book-entry transfer effected
pursuant to the procedures set forth in "The Tender Offer--Procedures For
Accepting The Offer And Tendering Shares," an Agent's Message (as defined
herein), and any other required documents to the Depositary (as defined herein),
and either deliver the certificates representing such Shares to the Depositary
along with the Letter of Transmittal (or a manually signed facsimile) or deliver
such Shares pursuant to the procedures for book-entry transfer set forth in "The
Tender Offer--Procedures For Accepting The Offer And Tendering Shares" or (2)
request such stockholder's broker, dealer, commercial bank, trust company or
other nominee to effect the transaction for such stockholder. Any stockholder
having Shares registered in the name of a broker, dealer, commercial bank, trust
company or other nominee must contact such broker, dealer, commercial bank,
trust company or other nominee if such stockholder desires to tender such
Shares.

     A stockholder who desires to tender Shares and whose certificates
representing such Shares are not immediately available, or who cannot comply in
a timely manner with the procedures for book-entry transfer, may tender such
Shares by following the procedures for guaranteed delivery set forth in "The
Tender Offer--Procedures For Accepting The Offer And Tendering Shares."

     Questions and requests for assistance or for additional copies of this
Offer to Purchase, the Letter of Transmittal or other tender offer materials may
be directed to the Information Agent or the Dealer Managers, at their respective
addresses and telephone numbers set forth on the back cover of this Offer to
Purchase. Stockholders may also contact their broker, dealer, commercial bank or
trust company for assistance concerning the Offer.

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                              PAGE
                                                              ----
<S>                                                           <C>
SUMMARY.....................................................    2
INTRODUCTION................................................    7
SPECIAL FACTORS.............................................    9
THE TENDER OFFER............................................   32
CERTAIN FEDERAL INCOME TAX CONSEQUENCES.....................   42
PRICE RANGE OF THE SHARES; DIVIDENDS........................   43
CERTAIN INFORMATION CONCERNING THE COMPANY..................   44
CERTAIN INFORMATION CONCERNING THE PURCHASER, CORPAK,
  THERMEDICS AND THERMO ELECTRON............................   47
SOURCE AND AMOUNT OF FUNDS..................................   51
THE MERGER; APPRAISAL RIGHTS................................   52
FEES AND EXPENSES...........................................   55
MISCELLANEOUS...............................................   56
</TABLE>

SCHEDULE I    MEMBERS OF THE BOARDS OF DIRECTORS AND EXECUTIVE OFFICERS OF THE
              PURCHASER, CORPAK, THERMEDICS AND THERMO ELECTRON

SCHEDULE II   INFORMATION CONCERNING TRANSACTIONS IN THE COMMON STOCK OF THE
              COMPANY

SCHEDULE III  SECTION 262 OF THE DELAWARE GENERAL CORPORATION LAW

                                        6
<PAGE>   7

TO THE HOLDERS OF COMMON STOCK OF THERMO SENTRON INC.:

                                  INTRODUCTION

     Sentron Acquisition, Inc. (the "Purchaser"), a Delaware corporation and an
indirect wholly-owned subsidiary of Thermedics Inc., a Massachusetts corporation
("Thermedics"), hereby offers to purchase all outstanding shares of common
stock, par value $.01 per share (the "Shares"), of Thermo Sentron Inc., a
Delaware corporation (the "Company"), at a purchase price of $15.50 per Share
(the "Offer Price"), net to the seller in cash, without interest thereon, upon
the terms and subject to the conditions set forth in this Offer to Purchase and
in the related Letter of Transmittal (which, together with any amendments or
supplements hereto or thereto, collectively constitute the "Offer"). The
Purchaser is a wholly-owned subsidiary of Corpak Inc., a Massachusetts
corporation ("Corpak"). Corpak is a wholly-owned subsidiary of Thermedics.
Thermedics is a majority-owned subsidiary of Thermo Electron Corporation, a
Delaware corporation ("Thermo Electron").

     THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY
TENDERED AND NOT WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT NUMBER OF
SHARES WHICH, TOGETHER WITH THE SHARES OWNED BY THERMO ELECTRON AND ITS
SUBSIDIARIES, INCLUDING THERMEDICS, CONSTITUTES AT LEAST NINETY PERCENT (90%) OF
THE OUTSTANDING SHARES ON THE EXPIRATION DATE OF THE OFFER (THE "MINIMUM
CONDITION"). THE OFFER IS ALSO SUBJECT TO OTHER IMPORTANT TERMS AND CONDITIONS
CONTAINED IN THIS OFFER TO PURCHASE. SEE "THE TENDER OFFER--CERTAIN CONDITIONS
OF THE OFFER."

     As of January 28, 2000, there were 9,446,714 Shares outstanding and 647,450
Shares reserved for issuance pursuant to options (the "Options") outstanding as
of such date under the Company's option plans. As of such date, Corpak owned
6,999,250 Shares, or approximately 74.1% of the outstanding Shares (69.3%
assuming all outstanding Options are exercised). Of the Shares owned by Corpak,
56,250 Shares have been reserved for issuance under stock options granted by
Thermedics under its stock option plans. As of January 28, 2000, Thermo Electron
owned 1,171,907 Shares, or approximately 12.4% of the outstanding Shares (11.6%
assuming all outstanding Options are exercised). Of the Shares owned by Thermo
Electron, 74,575 Shares have been reserved for issuance under stock options
granted under Thermo Electron's stock option plans.

     Based upon the number of outstanding Shares as of January 28, 2000 and
assuming no Options are exercised, 330,886 Shares must be tendered in the Offer
in order to satisfy the Minimum Condition. Assuming all outstanding Options are
exercised, 913,591 Shares must be tendered in the Offer in order to satisfy the
Minimum Condition.

     Tendering stockholders will not be obligated to pay brokerage fees or
commissions or, except as otherwise provided in Instruction 6 of the Letter of
Transmittal, stock transfer taxes with respect to the purchase by the Purchaser
of Shares pursuant to the Offer. The Purchaser will pay all fees and expenses of
J.P. Morgan Securities Inc. ("J.P. Morgan") and The Beacon Group Capital
Services, LLC ("The Beacon Group"), which are acting as the Dealer Managers (the
"Dealer Managers"), American Stock Transfer & Trust Company, which is acting as
the Depositary (the "Depositary"), and D.F. King & Co. Inc., which is acting as
the Information Agent (the "Information Agent"), in connection with the Offer.
See "Fees And Expenses."

     This Offer to Purchase and the documents incorporated by reference in this
Offer to Purchase include certain forward-looking statements. These statements
appear throughout this Offer to Purchase and include statements regarding the
intent, belief or current expectations of Thermedics and Thermo Electron and
their Boards of Directors, including statements concerning Thermedics' and
Thermo Electron's strategies following completion of the Offer and their plans
with respect to the acquisition of all of the equity interests in the Company.
Such forward-looking statements are not guarantees of future performance and
involve risks and uncertainties. Actual results may differ materially from those
described in such forward-looking statements as a result of various factors.

                                        7
<PAGE>   8

     THIS OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN
IMPORTANT INFORMATION THAT SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE
WITH RESPECT TO THE OFFER.

     If the Offer is completed, Thermo Electron, Corpak and the Purchaser
together will own at least 90% of the Shares. Promptly following the closing of
the Offer, Corpak and Thermo Electron plan to contribute their Shares to the
Purchaser in exchange for common stock of the Purchaser. Thermo Electron and
Corpak would then cause the Purchaser to merge with and into the Company in a
so-called "short-form" merger between the Company and the Purchaser (the
"Merger"). After the Merger, the Company would be owned exclusively by
Thermedics, through its ownership of Corpak, and Thermo Electron. Stockholders
of the Company who do not tender their Shares in the Offer would not be entitled
to vote on the Merger. The consideration per Share in the Merger would be the
same as the Offer Price.

     If, after the Offer is completed but prior to consummation of the Merger,
the aggregate ownership by Thermo Electron and its subsidiaries of the
outstanding Shares should fall below 90% due to the exercise of outstanding
Options or for any other reason, the Purchaser intends to acquire additional
Shares on the open market or in privately negotiated transactions to the extent
required for such ownership to equal or exceed 90%. Any such purchases would be
made at market prices or privately negotiated prices at the time of purchase,
which may be higher or lower than the Offer Price. For a discussion of other
actions Thermedics and Thermo Electron may take if the Offer is not completed,
see "Special Factors--Conduct Of The Company's Business If the Offer Is Not
Completed."

     The Purchaser, Corpak, Thermedics and Thermo Electron have filed with the
Securities and Exchange Commission (the "Commission") a Tender Offer Statement
on Schedule TO (including the information required by Schedule 13E-3) (the
"Schedule TO") under the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), relating to the Offer, the Merger and other potential purchases
of Shares.

                                        8
<PAGE>   9

                                SPECIAL FACTORS

BACKGROUND TO THE OFFER AND THE MERGER

     THE THERMO ELECTRON REORGANIZATION.  On January 31, 2000, Thermo Electron
announced that its Board of Directors had authorized its management to proceed
with a major reorganization of the operations of Thermo Electron and its
subsidiaries. As part of this reorganization, Thermo Electron plans to acquire
the public minority interest in most of its subsidiaries that have minority
investors, spin off its separation technologies and fiber-based products
business and its medical products business and divest a variety of non-core
businesses. The primary goal of the reorganization is for Thermo Electron and
each of its spun-off subsidiaries to focus on their respective core businesses.
The purpose of the Offer and the Merger is to acquire the minority public
interest in the Company as part of Thermo Electron's overall reorganization and
to provide the public stockholders of the Company with $15.50 per Share in cash.
Following the Offer and the Merger, Thermo Electron plans to retain the Company
as part of Thermo Electron's core instrument business.

     THE COMPANY.  The Company develops, manufactures and markets high-speed
precision-weighing and inspection equipment for industrial production and
packaging lines. Each of the Company's segments serves two principal markets:
packaged-goods and bulk materials. The Company's products for the packaged-goods
market include a broad line of checkweighing equipment and metal detectors that
can be integrated at various stages in production lines for process control and
quality assurance, as well as hot foil and thermal printers and X-ray inspection
equipment. The product-monitoring businesses design, manufacture and distribute
specialized packaged-goods equipment, including checkweighers and metal
detectors, for the food and pharmaceutical industries. The Company's
bulk-materials product line includes conveyor-belt scales, solid
level-measurement and conveyor-monitoring systems, sampling systems and
small-capacity feeders.

     The business of the Company was acquired by Thermedics from Baker Hughes
Incorporated in March 1994. Thermedics operated the Company's business under the
name Ramsey Technology Inc. until November 1995, at which time the Company was
incorporated and Thermedics transferred the operations of Ramsey Technology to
the Company. Until 1996, the Company was a wholly-owned subsidiary of
Thermedics. The Company completed its initial public offering in April 1996. In
the initial public offering, the Company sold 2,875,000 Shares to the public at
a price of $16.00 per Share (for net proceeds of $42.3 million).

     GOING PRIVATE MERGER DISCUSSIONS.  In August 1998, Thermo Electron
determined that it would benefit from a corporate restructuring that would
simplify its corporate structure, consolidate and strategically realign certain
businesses and increase the liquidity in the public stock of certain of its
publicly traded subsidiaries. Thermo Electron subsequently refined and expanded
this proposal and on January 31, 2000 announced the proposed reorganization
described above under "--The Thermo Electron Reorganization."

     As part of the initial restructuring plan, Thermo Electron proposed on
August 12, 1998 that Thermedics' majority ownership of the Company be
transferred to Thermo Electron in exchange for a portion of the shares of
Thermedics common stock held by Thermo Electron. Thermo Electron proposed to
then transfer its equity interest in the Company to Thermo Instrument Systems
Inc. ("Thermo Instrument"), another majority-owned subsidiary of Thermo
Electron, which would have merged the Company with Metrika Systems Corporation
and ONIX Systems Inc., each of which is a public subsidiary of Thermo
Instrument.

     On December 10, 1998, Thermo Electron issued a press release announcing
revisions to its August 12, 1998 proposal. This revised proposal contemplated
that Thermo Electron would take the Company private as a wholly-owned subsidiary
of Thermo Electron. To this end, Thermedics proposed to transfer its Shares to
Thermo Electron as part of an exchange for Thermo Electron's wholly-owned
biomedical group, with Thermo Electron offering the stockholders of the Company
other than Thermo Electron and its subsidiaries (the "Public Stockholders") cash
in exchange for their Shares.

     In May 1999, the Board of Directors of the Company formed a special
committee (the "Special Committee"), consisting of Messrs. Peter Richman and
William Hoover, the Directors of the Company who are not otherwise affiliated
with Thermo Electron, Thermedics or any of their subsidiaries other than the

                                        9
<PAGE>   10

Company. The Special Committee was authorized to negotiate the terms of the
proposed going private transaction with Thermo Electron and Thermedics. The
Board of Directors also authorized the Special Committee to retain its own
counsel and financial advisor. In July 1999, the Special Committee retained
Nutter, McClennen & Fish, LLP as its legal counsel.

     During the week of July 26, 1999, the Special Committee engaged HSBC
Securities (USA) Inc. ("HSBC") as its financial advisor in connection with the
proposed transaction. During August 1999, Thermo Electron and Thermedics
provided HSBC with certain financial and other information that HSBC had
requested on July 28, 1999. On August 26, 1999, the Company and Thermo Electron
entered into an engagement letter with HSBC, pursuant to which HSBC agreed to
provide financial advisory services to the Special Committee in connection with
the proposed transaction. During August 1999, HSBC conducted a financial due
diligence review of the Company and the proposed transaction.

     On September 8, 1999, Mr. Theo Melas-Kyriazi, the Chief Financial Officer
of Thermo Electron, Thermedics and the Company, provided the Special Committee
with a written proposal from Thermo Electron (the "September 8 Proposal") to
acquire all of the outstanding Shares through a merger to be submitted to the
Board of Directors and stockholders of the Company for their approval (a
"long-form merger") at a price of $15.50 per Share in cash. The proposal was
subject to the approval of the Boards of Directors of Thermo Electron and
Thermedics. Mr. Melas-Kyriazi indicated that the price of $15.50 per Share was
based upon the following considerations:

     - The price represented a 73% premium over the price of the Shares on
       December 9, 1998, the day before Thermo Electron announced the proposed
       going private transaction involving the Company.

     - The price was higher than the range of values per Share calculated by
       Thermo Electron using a discounted cash flow analysis. Thermo Electron
       calculated the cash flows that the Company expected to generate during
       fiscal years 1999 through 2003 based upon financial projections for
       fiscal 1999 and 2000 prepared by the Company (the "1999-2000
       Projections") in August 1999 as part of the Company's normal operations
       and projections prepared by Thermo Electron, with the assistance of
       management of the Company, for 2001 through 2003 (the "2001-2003
       Projections"). Thermo Electron also calculated a range of terminal asset
       values of the Company at the end of the five-year period ending in fiscal
       2003 by applying a multiple of 10 times earnings before interest and
       taxes ("EBIT"), a multiple of 8 times earnings before interest, taxes,
       depreciation and amortization ("EBITDA") and a multiple of 15 times net
       earnings. The cash flows and the range of terminal asset values were then
       discounted to present values using discount rates of 12.5%, 15% and
       17.5%. The present value of the cash flows and the range of terminal
       asset values were then adjusted for the Company's estimated 1999 fiscal
       year-end excess cash, option exercise proceeds, the acquisition of a
       building and total debt. This discounted cash flow analysis prepared by
       Thermo Electron indicated a range of values of between $11.98 and $14.53
       per Share based on an EBIT discounted cash flow analysis, $11.67 and
       $14.16 per Share based on an EBITDA discounted cash flow analysis and
       $11.85 and $14.38 per Share based on a net earnings discounted cash flow
       analysis, resulting in an average discounted cash flow range of values of
       between $11.83 and $14.36 per Share. See "--Certain Projected Financial
       Data."

     - The price exceeded the high end of the range of values per Share of $4.97
       to $14.32 that was calculated by Thermo Electron using an analysis of
       multiples of EBIT, EDITDA, book value, net earnings and revenues of the
       following publicly traded companies that Thermo Electron considered
       comparable to the Company: Mettler-Toledo International, Inc. ("MTD"),
       Milltronics, Ltd., K-Tron International, Inc. and TSI, Inc.

     By a letter to Mr. Melas-Kyriazi dated September 13, 1999, HSBC on behalf
of the Special Committee responded to the September 8 Proposal by proposing a
price of $20.83 per Share with the condition that any merger be approved by a
majority of the Public Stockholders. HSBC's proposal included an analysis of
discounted cash flows that indicated a range of values from $20.17 to $24.54 per
Share, an analysis of comparable merger and acquisition transactions which
indicated a range of values between $18.66 and $20.63

                                       10
<PAGE>   11

per Share and an analysis of comparable spin in transactions which indicated a
range of values between $19.39 and $21.76 per Share.

     During the week of September 22, 1999, Mr. Melas-Kyriazi prepared and
provided to HSBC an additional valuation analysis of the Company based upon a
comparison with MTD, a principal competitor of the Company, using enterprise
valuation methodologies and comparing after-tax EBITDA, revenues, EBIT, EBITDA
and earnings per share for the two companies.

     In late September and early October 1999, HSBC informally explored with Mr.
Melas-Kyriazi the possibility of a price between $16.875 and $18.00 per Share.

     On October 12, 1999, Mr. Melas-Kyriazi orally informed HSBC he was willing
to propose, subject to approval by the Boards of Directors of Thermedics and
Thermo Electron, a price of $16.25 per Share (the "October 12 Offer").

     In connection with the Company's closing of its books for the third quarter
of 1999 during the week of October 11, 1999, Mr. Melas-Kyriazi learned that the
Company's sales in the third quarter were below projected levels and that
bookings for the third quarter fell substantially short of the Company's
expectations. As a result of this shortfall in bookings, the Company anticipated
lowering the Company's projections of revenue and net income for the fourth
quarter of 1999 and calendar year 2000 as part of its normal November budgeting
process. See "--Certain Projected Financial Data." On October 13, 1999, Mr.
Melas-Kyriazi informed HSBC that, as a result of the Company's lower than
expected bookings and downward revisions of its sales estimates for the fourth
quarter and the fiscal year, Thermedics and Thermo Electron were reducing the
October 12 Offer to a range of between $15.25 to $15.75 per Share.

     On October 26, 1999, in a letter to Mr. Jonathan Wilk, Deputy General
Counsel of Thermo Electron, counsel for the Special Committee stated that the
Special Committee was "increasingly concerned about the course and progress of
the negotiations" and had determined that "further discussions concerning an
appropriate price to be paid for the Thermo Sentron shares should be suspended."
The Special Committee stated in this letter that it intended to have HSBC
analyze the Company's actual results for the third quarter and any revised
forecasts for the fourth quarter and for future periods. Following such
analysis, the Special Committee would "decide whether it will want to reopen
negotiations or whether it wants to await year end results."

     On November 4, 1999, Thermo Electron provided counsel to the Special
Committee with the additional financial information requested by the Special
Committee, including updated projections prepared by the Company for the
remainder of fiscal 1999 and 2000 (the "2000 Projections"). The operational
management of Thermedics directed the management of the Company and Thermedics'
other subsidiaries to apply a higher level of certainty in formulating the 2000
Projections in light of the Company's and the other subsidiaries' failure to
achieve their targets reflected in the prior projections, including the
1999-2000 Projections. On November 12, 1999, Mr. Melas-Kyriazi spoke with the
Special Committee to determine whether they were prepared to proceed with
negotiations rather than await year-end results. On November 19, 1999, Mr.
Melas-Kyriazi orally informed HSBC that Thermedics and Thermo Electron were
willing to offer, subject to the approval of the Thermo Electron and Thermedics
Boards of Directors, $16.00 per Share in order to get the deal done.

     On November 23, 1999, in a telephone conversation with Mr. Melas-Kyriazi,
counsel for the Special Committee indicated that the Special Committee would not
accept the $16.00 per Share offer.

     On December 8, 1999 at a meeting of the Company's Board of Directors,
management of the Company described to the Company's Board of Directors the
further downward revision of its projected fourth quarter revenues and bookings.

     On December 10, 1999, counsel for the Special Committee sent Mr.
Melas-Kyriazi and Dr. George N. Hatsopoulos, then chairman of the Board of
Directors of Thermo Electron, a letter (the "December 10 Letter") on behalf of
the Special Committee setting forth the Special Committee's position with
respect to an acceptable price for the Shares. In the December 10 Letter,
counsel for the Special Committee stated that the

                                       11
<PAGE>   12

Special Committee believed that the offer price in a going private transaction
should be based upon a premium to market value for the minority interest. The
December 10 Letter further advised that the Special Committee did not believe
that the then current market price of the Shares reflected the anticipation of a
buyout premium. The December 10 Letter stated that the Special Committee
proposed a price of $19.25 per Share, reflecting a premium of 29.5% over the
closing price of the Shares on December 9, 1999. In support of the Special
Committee's position:

     - The December 10 Letter compared the $16.00 per Share offer to buyout
       premiums paid in 24 other buyout transactions, including eight
       transactions involving Thermo Electron subsidiaries. The December 10
       Letter pointed out that the average premium paid in the 24 other buyout
       transactions was 38.5% and the average premium paid in the eight
       transactions involving Thermo Electron subsidiaries was 36.8%. The
       December 10 Letter also analyzed the relative market values of the Shares
       and the common stock of three other subsidiaries of Thermo Electron for
       which going private transactions had been announced on October 20, 1999.
       These comparable companies were The Randers Killam Group Inc., Thermo
       TerraTech Inc. and ThermoRetec Corporation (the "Comparable Companies").
       In the case of both the Company and the Comparable Companies, Thermo
       Electron announced its intention to take the companies private
       substantially in advance of the date on which the financial terms of the
       transactions were disclosed. The December 10 Letter compared the premiums
       that the offer prices in the going private transactions for the
       Comparable Companies represented over the market prices of the shares of
       the Comparable Companies immediately prior to the dates on which the
       offer prices were announced. The December 10 Letter stated that premiums
       for the Comparable Companies were approximately 30% and that a similar
       premium over the then current market price should be paid for the Shares.
       The December 10 Letter took the position that an analysis of the value of
       an offer for the Shares in comparison with the market price of the Shares
       immediately prior to the December 10, 1998 announcement of Thermo
       Electron's intention to take the Company private was not relevant based
       upon the trading histories of the Company and the Comparable Companies
       since that date.

     - The Special Committee also maintained in the December 10 Letter that,
       although it believed that Thermo Electron's comparison of the Company
       with MTD was not the best way to determine a fair price for the Shares,
       such a comparison supported a higher price for the Company than $16.00
       per Share. The Special Committee noted that Thermo Electron had indicated
       that it was willing to pay a premium of 10% to 15% above the levels
       implied by MTD's market valuation. Using the 1999-2000 Projections, an
       implied value per Share ranging from $16.58 to $19.92 was obtained by
       applying the MTD multiple to the Company's projected after-tax EBITDA,
       revenues, EBIT, EBITDA and earnings per share. Applying a 12.5% premium,
       that analysis produced a value for the Shares ranging from $18.65 to
       $22.41. Using the 2000 Projections, an implied value per Share ranging
       from $15.22 to $19.92 was obtained by applying the MTD multiple to the
       Company's projected after-tax EBITDA, revenues, EBIT, EBITDA and earnings
       per share. Applying a 12.5% premium, that analysis produced values for
       the Shares ranging from $17.12 to $22.41. The Special Committee
       maintained that it considered the use of the 1999-2000 Projections to be
       more appropriate than the 2000 Projections.

     On December 23, 1999, Mr. Melas-Kyriazi sent counsel to the Special
Committee a letter responding to the December 10 Letter as to the following
matters:

     - Mr. Melas-Kyriazi disagreed with the Special Committee's premise that the
       correct way to value the Shares is based upon an appropriate premium to
       market. Mr. Melas-Kyriazi stated that all relevant factors should be
       considered in valuing the Shares, of which an appropriate premium over
       market value was only one indicator, and that the starting point should
       be an analysis of the intrinsic value of the Shares.

     - Mr. Melas-Kyriazi disagreed with the Special Committee's conclusion that
       the current market price of the Shares did not reflect a premium in
       anticipation of a buyout.

     - Mr. Melas-Kyriazi disputed the Special Committee's characterization of
       MTD as a model and also pointed out that such a comparison was not very
       meaningful, particularly given the differences between the strong
       operating results of MTD and recent operating results for the Company.
                                       12
<PAGE>   13

     Mr. Melas-Kyriazi had several telephone conversations with representatives
of the Special Committee after sending this letter. He was advised by those
representatives that a response would be forthcoming.

     In December 1999, Thermo Electron retained J.P. Morgan and The Beacon Group
as its financial advisors for the purpose of advising Thermo Electron in
connection with its strategic alternatives, including advising Thermo Electron
and Thermedics in connection with the acquisition of the minority interest in
the Company.

     On a number of occasions on or about January 14, 2000, J.P. Morgan and The
Beacon Group discussed with the management of Thermo Electron the preliminary
results of their analysis of the ranges of potential values of the Shares that
resulted from the application of several accepted valuation methodologies. J.P.
Morgan and The Beacon Group subsequently presented the results of their analysis
to the Thermo Electron Board of Directors on January 18, 2000 and January 28,
2000 and to the Thermedics Board of Directors on January 25, 2000 and January
29, 2000. J.P. Morgan's and The Beacon Group's analysis indicated an estimated
range of equity values for the Shares of approximately $11.75 to $15.75 per
Share based on an analysis of the trading value of comparable companies, between
$12.25 and $17.00 per Share based on an analysis of comparable buy-out
transactions and between $12.50 and $15.50 per Share based on an analysis of
discounted cash flows. See "--Summary Of The Advisors' Analysis and Opinion."

     On January 17, 2000, Mr. Wilk sent a letter to counsel for the Special
Committee that confirmed the terms of an oral offer made by Mr. Melas-Kyriazi
earlier that day to the Special Committee. In this offer, Thermedics and Thermo
Electron proposed to acquire, by merger, the minority interest in the Company at
a price of $15.50 per Share conditioned upon the approval of the merger by a
majority of the Shares held by the Public Stockholders. Mr. Wilk's letter stated
that the offer would expire at noon on January 21, 2000.

     On January 20, 2000, counsel to the Special Committee sent Mr. Wilk a
letter (the "January 20 Letter") that described the Special Committee's basis
for not accepting the proposed price of $15.50 per Share. In general, the
January 20 Letter restated the analysis with respect to the Comparable Companies
and MTD set forth in the December 10 Letter.

     On January 21, 2000, counsel to the Special Committee sent Mr. Wilk another
letter (the "January 21 Letter"). In the January 21 Letter, counsel reiterated
the Special Committee's position that it would not be able to "recommend to the
public stockholders of Thermo Sentron . . . that they accept an offer of $15.50
[per Share] for their Thermo Sentron shares." However, the January 21 Letter
stated that the Special Committee "would not oppose" a merger at such a price if
completion of the merger was conditioned upon the approval of a majority of the
Shares held by the Public Stockholders.

     Because the Special Committee did not accept the terms proposed in Mr.
Wilk's letter of January 17, 2000, Thermedics determined not to proceed with
negotiation of a long-form merger with the Special Committee, but instead
elected to initiate the Offer and the Merger.

     On January 29, 2000, the Company's Board of Directors held a meeting by
telephone conference call at which representatives of Thermedics and Thermo
Electron described their intention to initiate the Offer and the Merger.

     On February 29, 2000, the Board of Directors of the Company held a meeting
at which the authority of the Special Committee was expanded to delegate to the
Special Committee the response to be made to the Offer on behalf of the Company.

     On March 3, 2000, the Purchaser commenced the Offer.

REASONS FOR THE OFFER AND THE MERGER

     ACTIONS OF THERMEDICS' BOARD OF DIRECTORS.  On January 25, 2000 and January
29, 2000, the Board of Directors of Thermedics held meetings at which the
proposed plan to acquire the minority stockholder interest in the Company
through the Offer and the Merger were presented and discussed. Messrs. George N.
Hatsopoulos, John N. Hatsopoulos, John T. Keiser and John W. Wood, Jr., members
of Thermedics' Board of Directors, initially took part in each of these
meetings, but recused themselves from discussions of the terms of


                                       13
<PAGE>   14

the Offer and the Merger and from voting to approve the Offer. These directors
recused themselves because they were also officers or directors of the Company
or hold Shares or options to purchase Shares. No director of Thermedics present
for the vote approving the Offer objected to or abstained from such vote.

     BENEFITS AND DETRIMENTS TO THE COMPANY OF THE OFFER AND THE MERGER.  In
determining whether to make the Offer and thereafter effect the Merger, the
Thermedics Board of Directors considered several factors, including the
financial performance and profitability of the Company and the potential
benefits to the Company's business if the Company were to become part of a
larger business unit. Thermedics' Board of Directors also considered the
following factors:

     - the prospect of achieving greater marketing, operating and administrative
       efficiency as a result of the Company's operations being conducted in a
       more coordinated manner with Thermo Electron's other instruments
       subsidiaries;

     - the reduction in the amount of public information available to
       competitors about the Company's businesses that would result from the
       termination of the Company's obligations under the reporting requirements
       of the Commission;

     - the elimination of additional burdens on management associated with
       public reporting and other tasks resulting from the Company's public
       company status, including, for example, the dedication of time by and
       resources of the Company's management and Board of Directors to
       stockholder and analyst inquiries and investor and public relations;

     - the decrease in costs, particularly those associated with being a public
       company (for example, as a privately-held entity, the Company would no
       longer be required to file quarterly, annual or other periodic reports
       with the Commission or publish and distribute to its stockholders annual
       reports and proxy statements), that Thermo Electron and Thermedics
       anticipate could result in savings of approximately $450,000 per year,
       including fees for an audit by an independent accounting firm and legal
       fees;

     - the greater flexibility that the Company's management would have to focus
       on long-term business goals, as opposed to quarterly earnings, as a
       non-reporting company, particularly in light of the potential volatility
       in the Company's quarterly earnings; and

     - recent public capital market trends affecting small-cap companies,
       including perceived lack of interest by institutional investors in
       companies with a limited public float.

     The Board of Directors of Thermedics also considered the advantages and
disadvantages of certain alternatives to acquiring the minority stockholder
interest in the Company, including:

     - a sale of its equity interest in the Company; and

     - leaving the Company as a majority-owned, public subsidiary.

     The first alternative, selling Thermedics' equity interests in the Company,
was briefly considered. It was not an alternative that was pursued at length,
given that Thermo Electron did not want to sell, and did not want Thermedics to
sell, its equity interest in the Company, but rather intended to retain the
Company as a part of Thermo Electron's core instruments businesses.

     In the view of the Board of Directors of Thermedics, the principal
advantage of leaving the Company as a majority-owned, public subsidiary of
Thermedics was the ability of Thermedics to invest the cash that would be
required to buy the minority stockholder interest in the Company for other
purposes. The disadvantages of leaving the Company as a majority-owned, public
subsidiary which were considered by the Board of Directors of Thermedics
included the inability to achieve many of the benefits of taking the Company
private discussed above. The Board of Directors of Thermedics concluded that the
advantages of leaving the Company as a majority-owned, public subsidiary of
Thermedics were significantly outweighed by the disadvantages of doing so, and
accordingly that alternative was rejected.

                                       14
<PAGE>   15

     Thermedics and Thermo Electron have determined to make the Offer and effect
the Merger at this time as part of the larger reorganization of Thermo Electron
and its subsidiaries. The Company's stock price was not a significant factor in
the timing of Thermedics' and Thermo Electron's decision to acquire the minority
stockholder interest in the Company.

     CONSIDERATION OF LIQUIDITY AND SHARE PRICE; TIMING.  The Board of Directors
of Thermedics also considered the relatively low volume of trading in the Shares
and considered that the Offer and the Merger would result in immediate, enhanced
liquidity for the Public Stockholders. The Board of Directors of Thermedics
considered trends in the price of the Shares in the past twelve months and
during the period between the Company's initial public offering and the
announcement of Thermedics' intention to take the Company private.

     ALTERNATIVE STRUCTURE CONSIDERED.  The Board of Directors of Thermedics
also considered whether to structure the transaction as a tender offer followed
by a short-form merger or as a long-form merger. In determining to structure the
transaction as a tender offer followed by a short-form merger, the Board of
Directors considered the following:

     - The discussions with the Special Committee with respect to a long-form
       merger were progressing at a pace that the Thermedics Board of Directors
       did not consider acceptable. See "--Background To The Offer And The
       Merger--Going Private Merger Discussions."

     - Unless at least 90% of the outstanding Shares are owned by the Purchaser,
       it could not effect a short-form merger. Unlike a long-form merger, the
       approval of the Company's Board of Directors is not required to complete
       a short-form merger. Consequently, once the Special Committee determined
       not to recommend the long-form merger contemplated by the January 17,
       2000 letter, the Offer and the Merger potentially enabled Thermedics and
       Thermo Electron to acquire all of the Shares without the approval of the
       Board of Directors of the Company or the Special Committee.

     - A tender offer followed by a short-form merger would permit Thermedics
       and Thermo Electron to acquire the minority interest in the Company on an
       expeditious basis and provide the Public Stockholders with a prompt
       opportunity to receive the Offer Price of $15.50 per Share.

     - In the Offer, each Public Stockholder would individually determine
       whether to accept the Offer Price of $15.50 per Share.

     - Public Stockholders who do not tender their Shares in the Offer could
       preserve their appraisal rights in the Merger under state law.

     After discussing the advantages and disadvantages of acquiring the minority
stockholder interest in the Company, including the alternative method of
acquiring such interests through a long-form merger, the Thermedics Board of
Directors authorized taking the Company private through a tender offer for all
of the Shares of the Company that Thermo Electron and its subsidiaries,
including Thermedics, did not already own, at a price per Share of $15.50 in
cash, to be followed by a short-form merger at the same price.

     ACTIONS OF THERMO ELECTRON'S BOARD OF DIRECTORS.  On January 18, 2000 and
January 28, 2000, the Board of Directors of Thermo Electron held special
meetings at which Thermo Electron's management presented the proposal for
Thermedics to acquire all of the Shares that Thermo Electron and its
subsidiaries did not already own as a part of the proposed corporate
reorganization of Thermo Electron and certain of its subsidiaries. Messrs.
George N. Hatsopoulos, John N. Hatsopoulos and Robert A. McCabe, members of
Thermo Electron's Board of Directors, initially took part in each of the
meetings, but recused themselves from discussions of the terms of the Offer and
the Merger and from taking action with respect to the Offer. These directors
recused themselves because they hold Shares or options to purchase Shares. The
Board of Directors of Thermo Electron considered all of the factors relating to
the Offer and the Merger referred to above that were considered by Thermedics'
Board of Directors. The Board of Directors of Thermo Electron also discussed the
fact that the acquisition by Thermedics of the minority stockholder interest in
the Company would advance the goal of Thermo Electron's proposed corporate
reorganization. After consideration of these factors, the Board of Directors of
Thermo Electron resolved that it would not object if Thermedics determined

                                       15
<PAGE>   16

to take the Company private through Thermedics' acquisition for cash through the
Offer and the Merger of all of the Shares held by the Public Stockholders at a
purchase price of $15.50 per Share. No director of Thermo Electron present to
vote on the resolution not to object if Thermedics determined to effect the
Offer and the Merger objected to or abstained from such vote.

POSITION OF THERMEDICS AND THERMO ELECTRON AS TO FAIRNESS OF THE OFFER AND THE
MERGER

     Because Corpak and Thermo Electron together currently own a majority of the
Shares, Thermo Electron, Thermedics, Corpak and the Purchaser are deemed
"affiliates" of the Company under Rule 12b-2 of the Exchange Act. Accordingly,
in compliance with Rule 13e-3 under the Exchange Act, the Boards of Directors of
Thermedics and Thermo Electron have considered the fairness of the Offer and the
Merger to the Public Stockholders.

     DETERMINATIONS OF THE BOARDS OF DIRECTORS OF THERMEDICS AND THERMO
ELECTRON.  In authorizing the Offer and the Merger, the Board of Directors of
each of Thermedics and Thermo Electron determined that the Offer and the Merger
are fair to the Public Stockholders. In reaching their determinations that the
terms of the Offer and the Merger are fair to the Public Stockholders, the
Boards of Directors of Thermedics and Thermo Electron considered the factors set
forth under this section captioned "Position Of Thermedics And Thermo Electron
As To Fairness Of The Offer And The Merger," which constitute all of the
material factors considered by the Boards of Directors of Thermedics and Thermo
Electron in making their determinations. The Boards of Directors of Thermedics
and Thermo Electron determined that each of the following factors supported
their belief that the Offer and the Merger are fair to the Public Stockholders:

     - Financial analysis.  In considering the fairness of the Offer and the
       Merger from a financial point of view to the Company's stockholders,
       including the Public Stockholders, the Boards of Directors of Thermedics
       and Thermo Electron reviewed and relied in part upon an analysis of the
       ranges of potential values of the Shares that result from the application
       of several accepted valuation methodologies. This financial analysis,
       including the selection of valuation methodologies, was prepared by J.P.
       Morgan and The Beacon Group (the "Advisors") to assist the Boards of
       Directors of Thermedics and Thermo Electron with their evaluation of the
       Offer and the Merger. Thermo Electron retained J.P. Morgan and The Beacon
       Group as its financial advisors for the purpose of advising Thermo
       Electron in connection with its strategic alternatives, including
       advising Thermo Electron and Thermedics in connection with the
       acquisition of the minority interest in the Company. The financial
       analyses undertaken by the Advisors included an analysis based upon
       public trading multiples, comparable buy-out transactions and discounted
       cash flows. The analysis of trading multiples of companies engaged in
       businesses which the Advisors judged to be analogous to the Company's
       business indicated an estimated range of equity values for the Shares of
       approximately $11.75 to $15.75 per Share. The analysis of other buyout
       transactions indicated an estimated range of equity values for the Shares
       of between $12.25 and $17.00 per Share. The analysis based upon
       discounted cash flows indicated an estimated range of equity values for
       the Shares of between $12.50 and $15.50 per Share. See "--Summary of The
       Advisors' Analysis and Opinion."

     - Information concerning the financial performance, condition, business
       operations and prospects of the Company.  The Boards of Directors of
       Thermedics and Thermo Electron believed the Offer Price to be attractive
       in light of the Company's current financial performance, profitability
       and growth prospects. In addition, the Offer and the Merger would shift
       the risk of the future financial performance of the Company from the
       Public Stockholders, who do not have the power to control decisions made
       as to the Company's business, entirely to Thermedics and Thermo Electron,
       who do have the power to control the Company's business and who have the
       resources to manage and bear the risks inherent in the business over the
       long term. See "--Certain Projected Financial Data."

     - The premium reflected in the Offer Price of $15.50 per Share.   The
       Boards of Directors of Thermedics and Thermo Electron considered the
       current and historical trading prices of the Shares. The market price of
       the Shares had declined from $16.125 on March 27, 1996, the date of the
       Company's initial public offering, to $8.9375 on December 9, 1998, the
       trading date immediately prior to Thermedics'

                                       16
<PAGE>   17

      announcement of its intention to take the Company private. The Offer Price
      represented a premium of 73.4% over the closing price of $8.9375 on
      December 9, 1998. The purchase by Thermedics would eliminate the exposure
      of the Public Stockholders to any future or continued declines in the
      price of the Shares. The Boards of Directors of Thermedics and Thermo
      Electron believed that the market price of the Shares after the December
      10, 1998 announcement reflected the financial markets' anticipation of the
      consideration that would be paid to the Public Stockholders in a going
      private transaction. See "--Certain Effects Of The Offer And The Merger."

    - Terms of the Offer.  The Boards of Directors of Thermedics and Thermo
      Electron considered the terms of the Offer and the Merger, including (1)
      the amount and form of the consideration, (2) the limited number of
      conditions to the obligations of the Purchaser, including the absence of a
      financing condition, (3) the tender offer structure, which would provide
      an expeditious means for the Public Stockholders to receive the Offer
      Price and (4) the Minimum Condition.

    - The market price and relative lack of liquidity for the Shares and the
      liquidity that would be realized by the Public Stockholders from the
      all-cash Offer.  The Boards of Directors of Thermedics and Thermo Electron
      believed that the liquidity that would result from the Offer and the
      Merger would be beneficial to the Public Stockholders because Thermedics'
      and Thermo Electron's combined significant ownership of Shares (1) results
      in a relatively small public float that necessarily limits the amount of
      trading in the Shares and (2) decreases the likelihood that a proposal to
      acquire the Shares would be made by an independent entity without the
      consent of Thermedics and Thermo Electron.

    - Thermo Electron's and Thermedics' determination to retain their majority
      ownership of the Company and not to seek a third party buyer for the
      Company.  Thermedics and Thermo Electron stated their current intention to
      retain their majority holdings in the Company, which foreclosed the
      opportunity to consider an alternative transaction with a third party
      purchaser of the Company or otherwise provide liquidity to the Public
      Stockholders. Accordingly, it is unlikely that finding a third party buyer
      for the Company was a realistic option for the Public Stockholders.
      Neither Thermedics nor Thermo Electron solicited or received an offer for
      the Company from a third party in the prior two years.

     PROCEDURAL FAIRNESS.  The Boards of Directors of Thermedics and Thermo
Electron also determined that the Offer and the Merger are procedurally fair to
the Public Stockholders. In making such determination, the Boards of Directors
considered the following factors:

    - Each Public Stockholder can individually determine whether to tender
      Shares in the Offer.

    - The Offer provides the opportunity for the Public Stockholders to sell
      their Shares without incurring brokerage and other costs typically
      associated with market sales.

    - In determining the Offer Price, the Boards of Directors of Thermedics and
      Thermo Electron relied in part upon an analysis prepared by the Advisors
      of the ranges of potential values of the Shares that resulted from the
      application of several accepted valuation methodologies. See "--Summary
      Of The Advisors' Analysis and Opinion."

    - Public Stockholders who believe that the terms of the Offer and the
      Merger are not fair can pursue appraisal rights in the Merger under state
      law.

     CERTAIN NEGATIVE CONSIDERATIONS.  The Boards of Directors of Thermedics and
Thermo Electron also considered the following factors, each of which they
considered negative, in their deliberations concerning the fairness of the terms
of the Offer and the Merger:

    - Termination of participation in future growth of the Company.  Following
      the successful completion of the Offer and the Merger, the Public
      Stockholders would cease to participate in the future earnings or growth,
      if any, of the Company or benefit from increases, if any, in the value of
      their holdings in the Company.

    - Conflicts of Interest.  The financial interests of Thermo Electron and
      Thermedics are adverse as to the Offer Price to the financial interests
      of the Public Stockholders. In addition, officers and directors of

                                       17
<PAGE>   18

       the Company have actual or potential conflicts of interest in connection
       with the Offer and the Merger. See "--Conflicts Of Interest."

     - No Public Stockholder Approval.  The Offer and the Merger do not provide
       the Public Stockholders with an opportunity to vote on the proposed
       transaction.

     - Inability to Reach Agreement with Special Committee.  The Boards of
       Directors of Thermedics and Thermo Electron considered the negotiations
       that had taken place with the Special Committee concerning a possible
       long-form merger, the proposals the Special Committee had made for the
       terms of such a merger and the fact that the Special Committee determined
       not to recommend such a merger at the Offer Price. See "--Background To
       The Offer And The Merger--Going Private Merger Discussions."

     - No Unaffiliated Representative or Independent Director Approval.  The
       majority of the members of the Board of Directors of the Company who are
       not employees of the Company have not retained an unaffiliated
       representative to act solely on behalf of the Public Stockholders for
       purposes of negotiating the terms of the Offer and the Merger or
       preparing a report concerning the fairness of the Offer and the Merger.
       In addition, such majority of the independent members of the Company's
       Board of Directors have not approved the Offer or the Merger. The Board
       of Directors of the Company has delegated to the Special Committee the
       authority to make a recommendation to the Public Stockholders with
       respect to the Offer and to prepare a Solicitation/Recommendation
       Statement on Schedule 14d-9, as required by the rules of the Commission.
       The Special Committee retained HSBC to act as financial advisor to the
       Special Committee.

     OTHER FACTORS.  The Boards of Directors of Thermedics and Thermo Electron
did not consider the net book value of the Company as a relevant factor in
assessing the Company's value and, accordingly, did not evaluate the fairness of
the Offer Price in relation to the Company's net book value. The Company's net
book value at January 1, 2000 was approximately $94 million, which would have
yielded a per Share valuation for the Company of $9.97. The Boards of Directors
relied in part upon valuation methodologies selected by the Advisors for the
purpose of their financial analysis, and the Boards of Directors of Thermedics
and Thermo Electron noted that the Advisors did not employ net book value in
their financial analysis. Moreover, the Boards of Directors of Thermedics and
Thermo Electron do not believe that an analysis based upon net book value was
appropriate for an instruments business. The Boards of Directors of Thermedics
and Thermo Electron believe that net book value is a valuation methodology more
typically used in the banking, utilities, real estate and financial services
industries.

     The Boards of Directors of Thermedics and Thermo Electron also did not
consider "shopping" the Company to prospective purchasers. Shopping the Company
would not only entail substantial time delays and allocation of management's
time and energy, but would also disrupt and discourage the Company's employees
and create uncertainty among the Company's customers and suppliers. Furthermore,
Thermedics and Thermo Electron do not intend to sell the Company, but rather
intend to continue to operate the Company as part of Thermo Electron's core
instruments businesses.

     The Boards of Directors of Thermedics and Thermo Electron did not consider
the Offer Price as compared to any implied liquidation value because it was not
contemplated that the Company be liquidated, whether or not the Offer and the
Merger were completed. See "--Conduct Of The Company's Business After The Offer
And The Merger."

     RECENT PURCHASES OF SHARES BY THERMO ELECTRON AND THERMEDICS.  See Schedule
II to this Offer to Purchase for information on purchases of Shares by Thermo
Electron and Thermedics (as well as by the Company) during the past two years.

     CONCLUSIONS OF THE BOARDS OF DIRECTORS.  The Thermedics and Thermo Electron
Boards of Directors concluded that, given the performance of the Shares between
the Company's initial public offering and the announcement of Thermedics'
intention to take the Company private, the uncertainties surrounding the
Company's future growth prospects and the limited trading market for the Shares,
the Offer and Merger would result in a fair treatment of the Public
Stockholders. In determining that the Offer and the Merger are


                                       18
<PAGE>   19

fair to the Public Stockholders, the Boards of Directors of Thermedics and
Thermo Electron considered the above factors as a whole and did not assign
specific or relative weights to them, other than that the Offer Price of $15.50
per Share in cash was considered the most important factor.

     In making the determination as to fairness, Thermedics and Thermo Electron
also had access to the 2000 Projections and the 1999-2000 Projections. See
"--Certain Projected Financial Data."

SUMMARY OF THE ADVISORS' ANALYSIS AND OPINION

     Thermo Electron retained J.P. Morgan and The Beacon Group as its exclusive
financial advisors for the purpose of advising Thermo Electron in connection
with its strategic alternatives, including advising Thermo Electron and
Thermedics in connection with the acquisition of the minority interest in the
Company. On a number of occasions on or about January 14, 2000, the Advisors
discussed with the management of Thermo Electron the preliminary results of
their analysis of the ranges of potential values of the Shares that resulted
from the application of several accepted valuation methodologies. The Advisors
subsequently presented the results of their analysis to the Thermo Electron
Board of Directors on January 18, 2000 and January 28, 2000 and to the
Thermedics Board of Directors on January 25, 2000 and January 29, 2000. This
financial analysis, including the selection of valuation methodologies, was
prepared by the Advisors to assist the Boards of Directors of Thermedics and
Thermo Electron with their evaluation of the Offer and the Merger. At the
January 28, 2000 and January 29, 2000 meetings of the Boards of Directors of
Thermo Electron and Thermedics, respectively, the Advisors also orally delivered
their opinion (the "Opinion"), subsequently confirmed in a written opinion dated
January 29, 2000, that, as of such date and based upon and subject to the
various factors, assumptions and limitations set forth in their Opinion, the
consideration of $15.50 net per Share in cash to be paid pursuant to the Offer
and the Merger was fair from a financial point of view to Thermedics and Thermo
Electron.

     THE ADVISORS' FINANCIAL ANALYSIS AND RELATED OPINION WAS PROVIDED TO THE
BOARDS OF DIRECTORS OF THERMEDICS AND THERMO ELECTRON. THE OPINION IS DIRECTED
ONLY TO THE FAIRNESS OF THE CONSIDERATION FROM A FINANCIAL POINT OF VIEW TO
THERMEDICS AND THERMO ELECTRON (AND NOT TO THE PUBLIC STOCKHOLDERS) AND DOES NOT
CONSTITUTE A RECOMMENDATION AS TO WHETHER OR NOT THE PUBLIC STOCKHOLDERS SHOULD
TENDER THEIR SHARES IN THE OFFER.

     In conducting their financial analysis and rendering their Opinion, the
Advisors reviewed, among other things:

     - the audited financial statements of the Company, Thermedics and Thermo
       Electron for the fiscal year ended January 2, 1999;

     - the unaudited financial statements of the Company, Thermedics and Thermo
       Electron for the period ended October 2, 1999;

     - current and historical market prices of the Shares;

     - certain publicly available information concerning the business of the
       Company and of certain other companies engaged in businesses deemed by
       the Advisors to be comparable to those of the Company;

     - the reported market prices for securities of certain other companies
       deemed by the Advisors to be comparable to the Company;

     - publicly available terms of certain transactions involving companies
       deemed by the Advisors to be comparable to the Company and the
       consideration paid for such companies;

     - the terms of other business combinations deemed relevant by the Advisors;

     - the 2000 Projections; and

     - certain agreements with respect to outstanding indebtedness or
       obligations of the Company, Thermedics and Thermo Electron.

                                       19
<PAGE>   20

     The Advisors also held discussions with certain members of the management
of Thermedics and Thermo Electron with respect to certain aspects of the Offer
and the Merger. In addition, the Advisors held discussions with certain members
of management of Thermedics and Thermo Electron with respect to the past and
current business operations of the Company, the financial condition and future
prospects and operations of the Company and certain other matters believed
necessary or appropriate to the Advisors' inquiry. In addition, the Advisors
reviewed such other financial studies and analyses and considered such other
information as the Advisors deemed appropriate for the purposes of their
financial analysis and Opinion. The 2000 Projections were the only information
prepared by the Company which was reviewed by the Advisors, and the Advisors did
not hold any discussions with management of the Company. No limitation was
placed upon the scope of the Advisors' investigation or valuation methodologies
by Thermedics or Thermo Electron.

     The Advisors relied upon and assumed, without independent verification, the
accuracy and completeness of all information that was publicly available or that
was furnished to, or discussed with, the Advisors by Thermedics, Thermo Electron
and the Company or otherwise reviewed by the Advisors, and the Advisors have not
assumed any responsibility or liability therefor. The Advisors also assumed that
there have been no material changes in the Company's condition, results of
operations, business or prospects since the date of the most recent financial
statements made available to the Advisors. The Advisors have not conducted, and
did not assume any responsibility for conducting, any valuation, appraisal or
physical inspection of any of the Company's assets or liabilities (contingent or
otherwise), nor have any valuations or appraisals been provided to the Advisors.
In relying on the financial analyses, projections and estimates provided to, or
discussed with, the Advisors, the Advisors have assumed that they have been
reasonably prepared based on assumptions reflecting the best currently available
estimates and judgments by management as to the expected future financial
performance of the Company.

     The 2000 Projections used by the Advisors were prepared by management of
the Company. None of the Company, Thermedics or Thermo Electron publicly
discloses internal management projections of the type used by the Advisors in
connection with the Advisors' analysis of the Offer and the Merger, and such
projections were not prepared with a view toward public disclosure. The 2000
Projections and the additional projections prepared by the Advisors were based
on numerous variables and assumptions that are inherently uncertain and may be
beyond the control of the management of the Company, Thermo Electron and
Thermedics, including, without limitation, factors related to general economic
and competitive conditions and prevailing interest rates. Accordingly, actual
results could vary significantly from those set forth in such projections. See
"--Certain Projected Financial Data."

     The Advisors' financial analysis and Opinion are necessarily based on
economic, market and other conditions as in effect on, and the information made
available to the Advisors as of, the date of their Opinion. Subsequent
developments may affect the financial analysis and the conclusions in the
Opinion, and the Advisors do not have any obligation to update, revise or
reaffirm their financial analysis or Opinion.

     In accordance with customary investment banking practice, the Advisors
employed generally accepted valuation methods in conducting their financial
analysis and reaching their Opinion. The following is a summary of the material
financial analyses undertaken by the Advisors with respect to the Company and
presented to the Boards of Directors of Thermo Electron and Thermedics:

          Public Trading Multiples.  Using publicly available information, the
     Advisors compared selected financial data of the Company with similar data
     for selected publicly traded companies engaged in businesses which the
     Advisors judged to be analogous to the Company's business. The companies
     selected by the Advisors were Mettler-Toledo International, Inc., Fairey
     Group plc, Milltronics and K-Tron International. These companies were
     selected, among other reasons, because they compete in similar industries
     with fairly similar competitive dynamics and growth potential. For each
     comparable company, publicly available financial performance through the
     most recent last twelve months was measured. In addition, the Advisors
     derived estimates of sales, EBITDA, EBIT and net income for the year ended
     December 31, 2000 for each comparable company from the Institutional
     Brokers Estimates System.

                                       20
<PAGE>   21

          The Advisors applied a range of multiples derived from such analysis
     to the Company's estimated (based upon the 2000 Projections) sales, EBITDA,
     EBIT and net income for calendar years 1999 and 2000, and arrived at an
     estimated range of equity values for the Shares of approximately $11.75 to
     $15.75 per Share.

          Selected Transaction Analysis.  Using publicly available information,
     the Advisors examined seven selected transactions in which companies
     engaged in businesses which the Advisors judged to be analogous to the
     Company's were acquired within the last three years. Specifically, the
     Advisors reviewed the following transactions (indicated as
     target/acquiror): Milltronics/Siemens, Drexelbrook Engineering/Ametek,
     Smiths Industries (Product Monitoring)/Thermo Sentron, Computational
     Systems/ Emerson Electric, BIE Technologies/Shareholders, NDC
     Systems/Fairey Group plc, and Core Industries/United Dominion. The Advisors
     applied a range of multiples derived from such analysis to the Company's
     estimated (based upon the 2000 Projections) sales, EBITDA, EBIT and net
     income for calendar year 1999, and arrived at an estimated range of equity
     values for the Shares of between $12.25 and $17.00 per Share.

          No company or transaction used in the comparable public trading
     multiple analysis or the selected transaction analysis is identical to the
     Company or the Offer and the Merger. Accordingly, an analysis of the
     results of the foregoing necessarily involves complex considerations and
     judgments concerning differences in financial and operating characteristics
     of the Company and other factors that could affect the public trading value
     of the companies to which they are being compared. In evaluating the
     comparable companies, the Advisors made judgments and assumptions with
     regard to industry performance, general business, economic, market and
     financial conditions and other matters, many of which are beyond the
     control of the Company.

          Discounted Cash Flow Analysis.  The Advisors conducted a discounted
     cash flow analysis for the purpose of determining the fully diluted equity
     value per Share. The Advisors calculated the unlevered free cash flows that
     the Company is expected to generate during fiscal years 2000 through 2004
     based upon financial projections prepared by the Advisors after discussions
     with the management of Thermedics and Thermo Electron. The Advisors also
     calculated a range of terminal asset values of the Company at the end of
     the 5-year period ending 2004 by applying a perpetual growth rate ranging
     from 2.0% to 3.0% to the unlevered free cash flow of the Company during the
     final year of the 5-year period. The unlevered free cash flows and the
     range of terminal asset values were then discounted to present values using
     a range of discount rates from 9.5% to 10.5%, which were chosen by the
     Advisors based upon an analysis of the Company's weighted average cost of
     capital. The present value of the unlevered free cash flows and the range
     of terminal asset values were then adjusted for the Company's estimated
     1999 fiscal year-end excess cash, option exercise proceeds and total debt.
     Based on this analysis, the Advisors calculated an estimated range of
     equity values of between $12.50 and $15.50 per Share.

          Historical Common Stock Performance.  The Advisors conducted a
     historical analysis of the closing price of the Shares over the 52-week
     period prior to the date of their Opinion and also reviewed the closing
     price of the Shares as of the date two weeks prior to the date of their
     Opinion. During the 52-week period, based on trading prices on the American
     Stock Exchange, the Company's Shares achieved a high trading price of
     $15.625 on August 31, 1999 and a low trading price of $9.625 on April 26,
     1999. On January 11, 2000, the closing price of the Shares was $14.3125 and
     on January 25, 2000 the closing price of the Shares was $14.50.

     The summary set forth above does not purport to be, and is not, a complete
description of the financial analyses or data undertaken or presented by the
Advisors. The summary of the Advisors' Opinion set forth in this Offer to
Purchase is qualified in its entirety by reference to the full text of the
written Opinion. The full text of the Advisors' written Opinion, which sets
forth among other things the assumptions made, procedures followed, matters
considered and limitations on the scope of the review undertaken by J.P. Morgan
and The Beacon Group in conducting their financial analysis and in rendering
their Opinion, is attached as Exhibit 12(c) to the Schedule TO. The written
Opinion should be read carefully and in its entirety. A copy of the Advisors'
written Opinion will be made available for inspection and copying at the
principal office of

                                       21
<PAGE>   22

Thermo Electron during its regular business hours upon request from any record
holder of the Shares or a representative of such person designated as such in
writing or may be obtained from the Schedule TO filed with the Commission.
Requests to have the Opinion made available should be directed to the Corporate
Secretary of Thermo Electron at the address set forth under "Certain Information
Concerning The Purchaser, Corpak, Thermedics And Thermo Electron."

     The preparation of the financial analysis and the related fairness Opinion
is a complex process and is not necessarily susceptible to partial analysis or
summary description. In arriving at their Opinion, the Advisors considered the
results of all of their analyses as a whole and did not attribute any particular
weight to any analysis or factor considered by them. The Advisors believe that
the summary set forth above and their analyses must be considered as a whole and
that selecting portions thereof, without considering all of their analyses,
could create an incomplete view of the processes underlying their analyses and
Opinion. In addition, the Advisors may have given various analyses and factors
more or less weight than other analyses and factors, and may have deemed various
assumptions more or less probable than other assumptions so that the ranges of
valuation resulting from any particular financial analysis described should not
be taken as the Advisors' view of the actual value of the Company. The Advisors
based their analyses on assumptions that they deemed reasonable, including
assumptions concerning general business and economic conditions and
industry-specific factors. The other principal assumptions upon which the
Advisors based their analyses are set forth above under the description of each
such analysis. The Advisors' analyses are not necessarily indicative of actual
values or actual future results that might be achieved, which values may be
higher or lower than those indicated. Moreover, the Advisors' analyses are not
and do not purport to be appraisals or otherwise reflective of the prices at
which businesses actually could be bought or sold.

     As described above, the Advisors' financial analysis and Opinion was only
one of many factors considered by the Boards of Directors of Thermedics and
Thermo Electron in their determination that the terms of the Offer and the
Merger are fair to the Public Stockholders and should not be viewed as
determinative of the views of the Boards of Directors of Thermedics and Thermo
Electron with respect to the value of the Company.

     J.P. Morgan and The Beacon Group advised the Boards of Directors of Thermo
Electron and Thermedics in connection with the Offer and the Merger in part
because the Advisors had been retained to advise Thermo Electron in connection
with the overall reorganization of Thermo Electron and its subsidiaries. The
Boards of Directors of Thermo Electron and Thermedics also considered J.P.
Morgan's and The Beacon Group's experience and expertise. J.P. Morgan is an
international corporate and investment bank, and The Beacon Group is a
nationally recognized private investment banking firm. As part of their
investment banking businesses, J.P. Morgan and The Beacon Group are regularly
engaged in the valuation of businesses and securities in connection with mergers
and acquisitions, investments for passive and control purposes, negotiated
underwritings, competitive biddings, secondary distributions of listed and
unlisted securities, private placements and valuations for estate, corporate and
other purposes.

     J.P. Morgan has advised Thermo Electron and Thermedics that, in the
ordinary course of its business, it or its affiliates may actively trade the
debt and/or equity securities of the Company, Thermedics, Thermo Electron and
their affiliates for their own account and for the accounts of customers and,
accordingly, may at any time hold a long or short term position in such
securities.

     In October 1999, Thermo Electron engaged The Beacon Group as its financial
advisor in connection with Thermo Electron's proposed acquisition of the
outstanding shares held by public stockholders in certain subsidiaries. Thermo
Electron paid The Beacon Group $500,000 in fees for services rendered pursuant
to that engagement in connection with the acquisition of the outstanding
publicly-held shares of common stock of ThermoTrex Corporation and ThermoLase
Corporation.

     As noted above, J.P. Morgan and The Beacon Group have acted as financial
advisors to Thermo Electron for the purpose of advising Thermo Electron in
connection with its strategic alternatives, including the proposed
reorganization of Thermo Electron and its subsidiaries. As part of the proposed
reorganization, it is contemplated that Thermo Electron will acquire the
publicly-held minority interest in Thermedics and that J.P. Morgan and The
Beacon Group will act as financial advisors to Thermo Electron in connection
with such acquisition.

                                       22
<PAGE>   23

     Pursuant to a letter agreement among Thermo Electron and J.P. Morgan and
The Beacon Group, dated January 17, 2000, Thermo Electron has agreed to pay each
of J.P. Morgan and The Beacon Group a fee of $500,000 for its services in
connection with the Offer and the Merger. In addition, J.P. Morgan and The
Beacon Group will be reimbursed for expenses incurred in connection with these
transactions. The letter agreement also relates to the overall proposed
reorganization of Thermo Electron and provides for separate fees for services
with respect to other elements of Thermo Electron's reorganization. These other
fees include a minimum retainer for each of J.P. Morgan and The Beacon Group of
$1.25 million, and the engagement letter provides for substantial additional
compensation if some or all of the other elements of Thermo Electron's
reorganization are completed. Thermo Electron has agreed to indemnify J.P.
Morgan and The Beacon Group and their affiliates against certain liabilities,
including liabilities under the federal securities laws, in connection with
their engagement.

CERTAIN PROJECTED FINANCIAL DATA

     The Company does not, as a matter of course, make public forecasts or
projections as to future sales, earnings or other income statement data, cash
flows or balance sheet and financial position information. However, Thermedics
and Thermo Electron had access to the 1999-2000 Projections and the 2000
Projections, made the 1999-2000 Projections and the 2000 Projections available
to the Special Committee and made the 2000 Projections available to the
Advisors. The 1999-2000 Projections and the 2000 Projections were prepared by
the Company's management in the regular course of its financial planning. The
2001-2003 Projections were prepared by Thermo Electron, with the assistance of
the Company's management, for the sole purpose of preparing the discounted cash
flow analysis included in the September 8 Proposal. The 1999-2000 Projections,
the 2000 Projections and the 2001-2003 Projections are collectively referred to
herein as the "Projections".

     The following summaries of the 1999-2000 Projections and the 2000
Projections are included in this Offer to Purchase because the 1999-2000
Projections and the 2000 Projections were made available to Thermedics, Thermo
Electron and the Special Committee, and the 2000 Projections were made available
to the Advisors. The 2001-2003 Projections are included in this Offer to
Purchase because they were provided to the Special Committee. The Projections do
not reflect any of the effects of the Offer, the Merger or other changes that
may in the future be deemed appropriate concerning the Company and its assets,
business, operations, properties, policies, corporate structure, capitalization
and management in light of the circumstances then existing. Thermedics and
Thermo Electron believe that the assumptions upon which the Projections are
based were reasonable at the time the Projections were prepared, given the
information known by management of the Company or Thermo Electron at such time.

     The Projections were not prepared with a view toward public disclosure or
compliance with published guidelines of the Commission or the American Institute
of Certified Public Accountants regarding forward-looking information or
generally accepted accounting principles. Neither the Company's independent
auditors, nor any other independent accountants, have compiled, examined or
performed any procedures with respect to the prospective financial information
contained in the Projections nor have they expressed any opinion or given any
form of assurance on such information or its achievability, and they assume no
responsibility for, and disclaim any association with, such prospective
financial information. Furthermore, the Projections necessarily make numerous
assumptions, many of which are beyond the control of Thermedics and Thermo
Electron and may prove not to have been, or may no longer be, accurate.
Additionally, this information, except as otherwise indicated, does not reflect
revised prospects for the Company's businesses, changes in general business and
economic conditions, or any other transaction or event that has occurred or that
may occur and that was not anticipated at the time such information was
prepared. Accordingly, such information is not necessarily indicative of current
values or future performance, which may be significantly more favorable or less
favorable than as set forth below, and should not be regarded as a
representation that they will be achieved.

     THE PROJECTIONS ARE NOT GUARANTEES OF PERFORMANCE. THEY INVOLVE RISKS,
UNCERTAINTIES AND ASSUMPTIONS. THE FUTURE FINANCIAL RESULTS AND STOCKHOLDER
VALUE OF THE COMPANY MAY MATERIALLY DIFFER FROM THOSE EXPRESSED IN THE
PROJECTIONS. MANY OF THE FACTORS THAT WILL DETERMINE


                                       23
<PAGE>   24

THESE RESULTS AND VALUES ARE BEYOND THE COMPANY'S ABILITY TO CONTROL OR PREDICT.
STOCKHOLDERS ARE CAUTIONED NOT TO PLACE UNDUE RELIANCE ON THE PROJECTIONS. THERE
CAN BE NO ASSURANCE THAT THE PROJECTIONS WILL BE REALIZED OR THAT THE COMPANY'S
FUTURE FINANCIAL RESULTS WILL NOT MATERIALLY VARY FROM THE PROJECTIONS. THE
COMPANY DOES NOT INTEND TO UPDATE OR REVISE THE PROJECTIONS.

     The following are the 1999-2000 Projections:

                             1999-2000 PROJECTIONS
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                             PROJECTEDQ3    PROJECTEDQ4      PROJECTED       PROJECTED
                                                1999           1999             1999           2000
<S>                                          <C>            <C>            <C>               <C>
SELECTED INCOME STATEMENT DATA:
Revenues...................................    $28,000        $29,000         $111,662       $118,054
                                               -------        -------         --------       --------
Costs and Operating Expenses:
  Cost of revenues.........................     17,086         17,291           68,041         70,439
  Operating expenses.......................      7,866          8,050           31,926         32,887
                                               -------        -------         --------       --------
                                                24,952         25,341           99,967        103,326
                                               -------        -------         --------       --------
Operating Income...........................      3,048          3,659           11,695         14,728
Interest Income............................        107            121              498            442
Interest Expense...........................       (269)          (381)          (1,252)        (1,100)
Equity in Earnings of Unconsolidated
  Subsidiary...............................         --             --              126             --
                                               -------        -------         --------       --------
Income Before Provision for Income Taxes...      2,886          3,399           11,067         14,070
Provision for Income Taxes.................      1,126          1,326            4,317          5,488
                                               -------        -------         --------       --------
Net Income.................................    $ 1,760        $ 2,073         $  6,750       $  8,582
                                               =======        =======         ========       ========
SELECTED BALANCE SHEET DATA:
Accounts Receivable, Net...................    $24,131        $24,412         $ 24,712       $ 25,292
Inventories................................     16,768         16,225           16,420         17,223
Prepaid Income Taxes and Other Current
  Assets...................................      4,564          4,533            4,413          4,396
                                               -------        -------         --------       --------
Total Current Assets Excluding Cash and
  Investments..............................     45,463         45,170           45,545         46,911
Property, Plant, and Equipment:
  Balance, beginning of period.............      3,102          3,064            3,757          8,996
  Additions................................        277          6,326            7,431          1,519
  Depreciation expense.....................       (331)          (388)          (1,350)        (1,435)
  Sales....................................         16             (6)            (842)            (8)
                                               -------        -------         --------       --------
  Balance, end of period...................      3,064          8,996            8,996          9,072
Cost in Excess of Net Assets of Acquired
  Companies................................     71,731         71,237           71,477         69,243
</TABLE>

                                       24
<PAGE>   25

     The following are the 2000 Projections:

                                2000 PROJECTIONS
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                                            PROJECTEDQ4    PROJECTED    PROJECTED
                                                               1999          1999         2000
<S>                                                         <C>            <C>          <C>
SELECTED INCOME STATEMENT DATA:
Revenues..................................................    $27,416      $109,232     $116,000
                                                              -------      --------     --------
Costs and Operating Expenses:
  Cost of revenues........................................     16,660        65,975       69,714
  Selling, general, and administrative expenses...........      6,777        28,768       29,292
  Research and development expenses.......................        876         3,379        3,680
  Gain on sale of property, plant, and equipment..........         --            87           --
                                                              -------      --------     --------
                                                               24,313        98,035      102,686
                                                              -------      --------     --------
Operating Income..........................................      3,103        11,197       13,314
Interest Income...........................................        109           455          339
Interest Expense..........................................       (273)       (1,136)        (663)
Equity in Earnings of Unconsolidated Subsidiary...........         --           157           --
                                                              -------      --------     --------
Income Before Provision for Income Taxes..................      2,939        10,673       12,990
Provision for Income Taxes................................      1,145         4,200        5,067
                                                              -------      --------     --------
Net Income................................................    $ 1,794      $  6,473     $  7,923
                                                              =======      ========     ========
SELECTED BALANCE SHEET DATA:
Accounts Receivable, Net..................................    $24,112      $ 24,112     $ 25,162
Inventories...............................................     16,025        16,025       17,040
Prepaid Income Taxes and Other Current Assets.............      5,164         5,164        5,519
                                                              -------      --------     --------
Total Current Assets Excluding Cash and Investments.......     45,301        45,301       47,721
Property, Plant and Equipment:
  Balance, beginning of period............................      3,143         3,757        3,264
  Additions...............................................        464         1,640        1,450
  Depreciation expense....................................       (338)       (1,340)      (1,435)
  Sales...................................................         (5)         (793)          --
                                                              -------      --------     --------
  Balance, end of period..................................      3,264         3,264        3,279
Cost in Excess of Net Assets of Acquired Companies........     72,211        72,211       70,213
</TABLE>

                                       25
<PAGE>   26

     The following are the 2001-2003 Projections:

                             2001-2003 PROJECTIONS
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                         FISCAL YEAR
                                                             -----------------------------------
                                                               2001         2002          2003
<S>                                                          <C>         <C>            <C>
Revenues...................................................  $123,928     $130,124      $136,631
  Growth Rate..............................................      5.0%         5.0%          5.0%
Gross Profit...............................................  $ 49,943     $ 52,961      $ 56,702
  Gross Profit Margin......................................     40.3%        40.7%         41.5%
EBIT (without goodwill amortization).......................  $ 18,589     $ 20,169      $ 21,861
  EBIT Margin..............................................     15.0%        15.5%         16.0%
EBIAT -- Earnings Before Interest After Taxes..............  $ 11,154     $ 12,102      $ 13,117
NOA -- Net Operating Assets................................  $ 34,700     $ 35,784      $ 36,890
  NOA/Sales................................................     28.0%        27.5%         27.0%
Increase (Decrease) NOA....................................  $  1,298     $  1,084      $  1,106
Operating Cash Flows.......................................  $  9,855     $ 11,017      $ 12,010
</TABLE>

CONFLICTS OF INTEREST

     THERMO ELECTRON AND THERMEDICS.  The financial interests of Thermo Electron
and Thermedics are adverse as to the Offer Price to the financial interests of
the Public Stockholders.

     DIRECTORS OF THERMO ELECTRON AND THERMEDICS.  The members of the Boards of
Directors of Thermo Electron and Thermedics own common stock of, or hold options
to purchase the common stock of, Thermo Electron, Thermedics and/or the Company.
In addition, certain members of the Boards of Directors of Thermo Electron and
Thermedics are also officers of the Company. These positions and equity
interests present these directors with actual or potential conflicts of interest
in determining the fairness of the Offer and the Merger to the Public
Stockholders. See Schedule I to this Offer to Purchase for a listing of the
positions that the members of the Boards of Directors of Thermo Electron and
Thermedics hold with Thermo Electron, Thermedics and the Company and their
ownership of the common stock of Thermo Electron, Thermedics and the Company. To
the knowledge of each of the Purchaser, Corpak, Thermedics and Thermo Electron,
all of the directors and executive officers of Thermo Electron and Thermedics
who own Shares have advised Thermedics that they intend to tender their Shares
in the Offer.

     EXECUTIVE OFFICERS AND DIRECTORS OF THE COMPANY.  In considering any
position that the Board of Directors of the Company may take with respect to the
Offer, the Public Stockholders should be aware that the executive officers and
certain directors of the Company have interests in connection with the Offer and
the Merger that present them with actual or potential conflicts of interest, as
summarized below.

     Following consummation of the Offer and the Merger, Thermedics anticipates
that the board of directors of the Company, as the corporation surviving the
Merger (the "Surviving Corporation"), will be comprised solely of members of the
Company's and Thermedics' management. Officers and directors of the Company who
own Shares will receive the Offer Price in the Offer or the Merger on the same
terms as the Public Stockholders.

     As of January 28, 2000, the members of the Board of Directors and executive
officers of the Company owned in the aggregate 7,500 Shares and will receive a
payment for their Shares in the aggregate amount of $116,250, assuming that they
tender all of their Shares in the Offer or their Shares are acquired in the
Merger. Except as set forth below, to the knowledge of the Purchaser, Corpak,
Thermedics and Thermo Electron, all of the directors and executive officers of
the Company who own Shares have advised Thermedics that they intend to tender
their Shares in the Offer. Mr. Peter Richman, a director of the Company, has
indicated that he intends to hold his Shares and not tender such Shares in the
Offer.

                                       26
<PAGE>   27

     In addition, as of January 28, 2000, such Board members and executive
officers of the Company held Options to acquire an aggregate of 268,800 Shares,
with exercise prices ranging from $9.53 to $16.00. Unvested Options held by such
persons will be assumed by Thermo Electron in the Merger and converted into
options to acquire shares of Thermo Electron's common stock on the same terms as
are applicable to all the other holders of Options. In the case of vested
Options held by such persons, the holders will be given the opportunity to elect
in the Merger either to convert the Options into options for Thermo Electron
common stock or to receive cash for their Options at the Offer Price less the
applicable exercise price. See "--Certain Effects Of The Offer And The
Merger--Assumption of Options by Thermo Electron."

     Further, as of January 1, 2000, deferred units equal to 298, 2,573 and 485
Shares had accumulated under the Company's deferred compensation plan for
directors for the benefit of Mr. William W. Hoover, Mr. Donald E. Noble and Mr.
Peter Richman, respectively, which units will be converted into the right to
receive the Offer Price in the Merger per unit for an aggregate cash payment of
$4,619, $39,881 and $7,517, respectively. See "--Certain Effects Of The Offer
And The Merger--Deferred Compensation Plan for Directors."

     Certain members of the Board of Directors of the Company and certain
executive officers of the Company are directors or officers of Thermo Electron
and/or Thermedics. All of such directors and executive officers in the Company
hold equity interests in Thermo Electron and Thermedics. Mr. Melas-Kyriazi, the
chief financial officer of the Company, is also the chief financial officer of
Thermo Electron and Thermedics. Mr. John T. Keiser, a director of the Company,
is chief operating officer, biomedical of Thermo Electron and is president and
chief executive officer of Thermedics. Mr. Paul Kelleher, the chief accounting
officer of the Company, is also the chief accounting officer of Thermo Electron
and Thermedics. Consequently, certain of these directors and officers receive or
have received compensation not only from the Company but also from Thermo
Electron, Thermedics and their affiliates.

     INDEMNIFICATION AGREEMENTS.  Thermo Electron has entered into separate
indemnification agreements with each of the Company's officers and directors
providing for indemnification of and advancement of expenses to such persons
directly by Thermo Electron in the event that such person, by reason of his or
her status as a director or officer of the Company (or service as a director,
officer or fiduciary of another enterprise at the request of Thermo Electron),
is made or threatened to be made a party to any threatened, pending, or
completed action, suit or other proceeding, whether civil, criminal,
administrative or investigative, if the indemnitee acted in good faith and in a
manner the indemnitee reasonably believed to be in or not opposed to the best
interests of Thermo Electron, and, with respect to any criminal action or
proceeding, had no reasonable cause to believe his or her conduct was unlawful.
In the case of any threatened, pending or completed action, suit or proceeding
by or in the right of Thermo Electron, indemnification shall be made to the
maximum extent permitted under Delaware law.

OTHER POSSIBLE PURCHASES OF SHARES

     If the Offer is successfully completed, Thermo Electron and its
subsidiaries will collectively own at least 90% of the outstanding Shares. If,
after the Offer is completed but prior to the effective date of the Merger (the
"Effective Date of the Merger"), as a result of the exercise of Options or for
any other reason, Thermo Electron and its subsidiaries collectively own less
than 90% of the outstanding Shares, the Purchaser intends to acquire additional
Shares in the open market or in privately negotiated transactions to the extent
required for Thermo Electron and its subsidiaries' collective ownership of
Shares to equal or exceed 90%. If the Offer is not completed, the Purchaser may
make open market or privately negotiated purchases of Shares to the extent
necessary in order for Thermo Electron and its subsidiaries collectively to own
at least 90% of the outstanding Shares. Such open market or privately negotiated
purchases would be made at market prices or privately negotiated prices at the
time of purchase, which may be higher or lower than the Offer Price.

THE MERGER

     If the Offer is successfully completed, Corpak and Thermo Electron plan to
contribute the Shares they own to the Purchaser in exchange for capital stock of
the Purchaser and to cause the Purchaser to merge into

                                       27
<PAGE>   28

the Company in a short-form merger. The short-form merger would occur as soon as
possible after completion of the Offer. After the short-form merger, the Company
would be owned exclusively by Thermo Electron and Corpak. Under the Delaware
General Corporation Law (the "DGCL"), if the Purchaser owns at least 90% of the
outstanding Shares, the Purchaser would have the power to approve, adopt and
consummate the Merger without a vote of the Company's stockholders (other than
the Purchaser) or Board of Directors.

     On the Effective Date of the Merger, each outstanding Share (other than
Shares held by stockholders, if any, who are entitled to and perfect their
appraisal rights under Section 262 of the DGCL) would be cancelled and converted
into the right to receive the Offer Price in cash, without interest. After the
Merger, Thermedics and Thermo Electron will, directly or indirectly, own 100% of
the equity interest in the Surviving Corporation.

CERTAIN EFFECTS OF THE OFFER AND THE MERGER

     GENERAL.  Upon completion of the Offer and the Merger, Thermedics and
Thermo Electron would have complete control over the conduct of the Company's
business and together would have a 100% interest in the net book value and net
earnings of the Company. In addition, Thermedics and Thermo Electron would
receive the benefit of complete control over any future increases in the value
of the Company and would bear the complete risk of any losses incurred in the
operation of the Company and any decrease in the value of the Company. Thermo
Electron's and its subsidiaries' aggregate ownership of the Company prior to the
transactions contemplated by the Offer and the Merger was approximately 86.5%.
Upon completion of the Offer and the Merger, Thermo Electron's and its
subsidiaries' aggregate interest in the Company's net book value of
approximately $94 million on January 1, 2000 and net earnings of $6.4 million
for the year ended January 1, 2000 would increase from approximately 86.5% of
such amounts to 100% of such amounts.

     BENEFITS AND DETRIMENTS TO THE PUBLIC STOCKHOLDERS.  Upon completion of the
Offer and the Merger, the Public Stockholders would no longer have any interest
in, and would not be stockholders of, the Company and therefore would not
participate in the Company's future earnings and potential growth and would no
longer bear the risk of any decreases in the value of the Company. In addition,
the Public Stockholders would not share in any distribution of proceeds after
any sales of businesses of the Company, whether contemplated at the time of the
Offer or thereafter. See "--Conduct Of The Company's Business After The Offer
And The Merger." All of the Public Stockholders' other incidents of stock
ownership, such as the rights to vote on certain corporate decisions, to elect
directors, to receive distributions upon the liquidation of the Company and to
receive appraisal rights upon certain mergers or consolidations of the Company
(unless such appraisal rights are perfected in connection with the Merger), as
well as the benefit of potential increases in the value of their holdings in the
Company based on any improvements in the Company's future performance, would be
extinguished upon acceptance of Shares tendered in the Offer or, if not
tendered, upon completion of the Merger.

     Upon completion of the Offer and the Merger, the Public Stockholders would
also not bear the risks of potential decreases in the value of their holdings in
the Company based on any downturns in the Company's future performance. Instead,
the Public Stockholders would have immediate liquidity in the form of the Offer
Price in place of an ongoing equity interest in the Company in the form of the
Shares. In summary, if the Offer and the Merger are completed, the Public
Stockholders would have no ongoing rights as stockholders of the Company (other
than statutory appraisal rights in the case of Public Stockholders who are
entitled to and perfect such rights under Delaware law).

     POSSIBLE EFFECT OF THE OFFER AND OPEN MARKET PURCHASES ON THE MARKET FOR
SHARES.  Following the completion of the Offer and prior to the Effective Date
of the Merger, the purchase of Shares by the Purchaser pursuant to the Offer or
any subsequent open market or privately negotiated purchases would reduce the
number of Shares that might otherwise trade publicly and may reduce the number
of holders of Shares. This could adversely affect the liquidity and market value
of the remaining Shares held by the public.

     AMERICAN STOCK EXCHANGE LISTING.  If the Offer and Merger are consummated,
the Shares would not meet the requirements for continued listing on the American
Stock Exchange and would be delisted. Assuming that the Merger occurs shortly
after the completion of the Offer, Thermo Electron and Thermedics do not expect
the American Stock Exchange to delist the Shares until after the Effective Date
of the Merger.
                                       28
<PAGE>   29

     Following the closing of the Offer and prior to the Effective Date of the
Merger, depending upon the aggregate market value and the number of Shares not
purchased pursuant to the Offer or any subsequent open market or privately
negotiated purchases, as well as the number of Public Stockholders who are not
affiliated with Thermedics or Thermo Electron, the Shares may no longer meet the
quantitative requirements for continued listing on the American Stock Exchange.
The listing requirements of the American Stock Exchange require that an issuer
have at least 200,000 publicly held shares, held by at least 300 stockholders,
with a market value of at least $1,000,000 and have stockholders' equity of at
least $2,000,000 or $4,000,000 (depending on profitability levels during the
issuer's four most recent fiscal years).

     In the event that the Shares no longer meet the requirements for listing on
the American Stock Exchange, it is possible that the Shares would continue to
trade in the over-the-counter market prior to the Effective Date of the Merger
and that price or other quotations might still be available from other sources.
The extent of the public market for the Shares and the availability of such
quotations would, however, depend upon such factors as the number of holders
and/or the aggregate market value of such Shares remaining at such time, the
interest in maintaining a market in such Shares on the part of securities firms,
the possible termination of registration of such Shares under the Exchange Act,
as described below, and other factors. The Purchaser cannot predict whether a
reduction in the number of Shares that might otherwise trade publicly would have
an adverse or beneficial effect on the market price for or marketability of the
Shares or whether it would cause future market prices to be greater or less than
the price paid in the Offer and the Merger.

     EXCHANGE ACT REGISTRATION.  The Shares are currently registered under the
Exchange Act. If the Offer and the Merger are completed, however, the Company's
reporting obligations under the Exchange Act would terminate.

     Prior to the Effective Date of the Merger, the purchase of Shares pursuant
to the Offer or open market or privately negotiated purchases following
consummation of the Offer may result in the Shares becoming eligible for
deregistration under the Exchange Act. Registration of the Shares may be
terminated upon application by the Company to the Commission if the Shares are
not listed on a national securities exchange (see "--American Stock Exchange
Listing") and there are fewer than 300 record holders of the Shares. Thermedics
presently intends to seek to cause the Company to terminate the registration of
the Shares under the Exchange Act as soon after the consummation of the Offer or
the Merger as the requirements for termination of registration are met.

     The termination of the registration of the Shares under the Exchange Act
would substantially reduce the information required to be furnished by the
Company to holders of the Shares and would make certain provisions of the
Exchange Act, such as the short-swing profit recovery provisions of Section
16(b), the requirement of furnishing a proxy statement in connection with
stockholders' meetings pursuant to Section 14(a) and the requirements of Rule
13e-3 under the Exchange Act with respect to "going private" transactions, no
longer applicable to the Shares. Furthermore, "affiliates" of the Company and
persons holding "restricted securities" of the Company may be deprived of the
ability to dispose of the securities pursuant to Rule 144 under the Securities
Act. If registration of the Shares under the Exchange Act were terminated, the
Shares would no longer be "margin securities" or eligible for listing on the
American Stock Exchange.

     MARGIN REGULATIONS.  The Shares are currently "margin securities" under the
rules of the Board of Governors of the Federal Reserve System (the "Federal
Reserve Board"), which has the effect, among other things, of allowing brokers
to extend credit on the collateral of such Shares for the purpose of buying,
carrying or trading in securities ("purpose loans"). If the Offer and the Merger
are completed, the Shares would no longer be "margin securities." Following the
purchase of Shares pursuant to the Offer or any subsequent open market or
privately negotiated purchases and prior to the Effective Date of the Merger,
depending upon factors such as the number of record holders of the Shares and
the number and market value of publicly held Shares, the Shares might no longer
constitute "margin securities" for purposes of the Federal Reserve Board's
margin regulations and therefore no longer be used as collateral for purpose
loans made by brokers. In addition, if registration of the Shares under the
Exchange Act were terminated, the Shares would no longer constitute "margin
securities."

                                       29
<PAGE>   30

     TREATMENT OF THERMO SENTRON OPTIONS.  The Company has, from time to time,
issued Options to acquire Shares pursuant to the Company's Equity Incentive
Plan, Directors Stock Option Plan and Employees Equity Incentive Plan (the
"Plans"). On the Effective Date of the Merger, each outstanding unvested Option
under the Company's Plans will be assumed by Thermo Electron and converted into
options to acquire shares of Thermo Electron common stock as provided below. In
the case of vested Options, the holders will be given the opportunity to elect
in the Merger either to convert the Options into options for Thermo Electron
common stock or to receive cash from Thermedics in an amount equal to the number
of Shares that have vested under such Option multiplied by the difference
between the Offer Price and the exercise price per Share of such Option. Each
Option assumed by Thermo Electron will continue to have, and be subject to, the
same terms and conditions, including the vesting of shares issuable upon the
exercise thereof, as were applicable to the Option immediately prior to the
Effective Date of the Merger, except that:

     - each Option will be exercisable (or will become exercisable in accordance
       with its terms) for that number of whole shares of Thermo Electron common
       stock equal to the product of the number of Shares that were issuable
       upon exercise of such Option immediately prior to the Effective Date of
       the Merger multiplied by the Exchange Ratio (as defined below), rounded
       down to the nearest whole number of shares of Thermo Electron common
       stock, and

     - the per share exercise price for the shares of Thermo Electron common
       stock issuable upon exercise of such assumed Option will be equal to the
       quotient determined by dividing the exercise price per Share at which
       such Option was exercisable immediately prior to the Effective Date of
       the Merger by the Exchange Ratio, rounded up to the nearest whole cent.

The "Exchange Ratio" is a fraction, the numerator of which is the Offer Price
and the denominator of which is the closing price of the Thermo Electron common
stock on the day immediately preceding the Effective Date of the Merger as
reported on the consolidated transactions tape.

     DEFERRED COMPENSATION PLAN FOR DIRECTORS.  On the Effective Date of the
Merger, the Company's deferred compensation plan for directors (the "Deferred
Compensation Plan") will terminate, and the Company will distribute to each
participant cash in an amount equal to the balance of stock units credited to
his deferred compensation account under the Deferred Compensation Plan as of the
Effective Date of the Merger multiplied by the Offer Price. Based on the units
accumulated as of January 1, 2000, Mr. William W. Hoover will receive $4,619 for
his units, Mr. Donald E. Noble will receive $39,881 for his units and Mr. Peter
Richman will receive $7,517 for his units.

     ACCOUNTING TREATMENT.  The Offer and the Merger would be accounted for as
the acquisition of a minority interest by Thermedics, using the purchase method
of accounting.

     TAX CONSEQUENCES.  For federal income tax purposes, the receipt of the cash
consideration by holders of the Shares pursuant to the Offer or the Merger will
be a taxable sale of the holder's Shares. See "Certain Federal Income Tax
Consequences."

CONDUCT OF THE COMPANY'S BUSINESS AFTER THE OFFER AND THE MERGER

     Following Thermo Electron's reorganization, Thermo Electron plans to retain
the Company as part of Thermo Electron's core measurement and detection
instruments businesses. In connection with the reorganization of Thermo Electron
and its subsidiaries, Thermo Electron intends to evaluate ways in which its
instruments businesses, including the Company's business, can be more
efficiently integrated and operated. Thermedics and Thermo Electron do not
currently have any commitment or agreement for the sales of any of the Company's
businesses. Additionally, Thermo Electron and Thermedics do not currently
contemplate any material change in the composition of the Company's current
management, except that Thermedics intends to appoint a Board of Directors of
the Company comprised solely of members of the Company's and Thermedics'
management after the Merger.

     In connection with its reorganization, Thermo Electron currently intends to
acquire all of the outstanding common stock of Thermedics that it does not
currently own. If such transaction is completed, the Company will become an
indirect wholly-owned subsidiary of Thermo Electron.

                                       30
<PAGE>   31

     Except as otherwise described in this Offer to Purchase, the Purchaser,
Corpak, Thermedics and Thermo Electron do not have, as of the date of this Offer
to Purchase, any specific plans or proposals for:

     - any extraordinary corporate transaction involving the Company after the
       completion of the Offer and the Merger;

     - any sale or transfer of a material amount of assets currently held by the
       Company after the completion of the Offer and the Merger;

     - any change in the Board of Directors or management of the Company;

     - any material change in the Company's dividend rate or policy; or

     - any other material change in the Company's corporate structure or
       business.

CONDUCT OF THE COMPANY'S BUSINESS IF THE OFFER IS NOT COMPLETED

     If the Offer is not completed because the Minimum Condition or another
condition is not satisfied or waived, Thermo Electron and Thermedics expect that
the Company's current management will continue to operate the Company's business
substantially as presently operated. See "--Conduct Of The Company's Business
After The Offer And The Merger." However, Thermedics and Thermo Electron
anticipate that if the Offer is not completed, Thermedics and Thermo Electron
will re-evaluate the role of the Company within the overall reorganization
strategy being pursued by Thermo Electron. In particular, Thermedics and Thermo
Electron may consider:

     - engaging in open market or privately negotiated purchases of Shares to
       increase Thermo Electron's and its subsidiaries' aggregate ownership of
       Shares to at least 90% of the outstanding Shares and then effecting a
       short-form merger;

     - proposing that the Purchaser and the Company enter into a long-form
       merger agreement, which would require the approval of the Company's Board
       of Directors, and voting all of their Shares in favor of such merger;

     - keeping outstanding the public minority interest in the Company, in which
       case the Public Stockholders would receive no cash for their Shares and
       would bear the risk that the trading price per Share could decline to a
       price that is less than the Offer Price; or

     - selling their interests in the Company or pursuing a sale of the entire
       Company to a third party.

     If Thermedics and Thermo Electron were to pursue any of these alternatives,
it may take considerably longer for the Public Stockholders to receive any
consideration for their Shares (other than through sales in the open market)
than if they had tendered their Shares in the Offer. Any such transaction may
result in proceeds per Share to the Public Stockholders that are more or less
than the Offer Price.

                                       31
<PAGE>   32

                                THE TENDER OFFER

TERMS OF THE OFFER; EXPIRATION DATE

     Upon the terms and subject to the conditions of the Offer (including, if
the Offer is extended or amended, the terms and conditions of any such extension
or amendment), the Purchaser will accept for payment and pay for all Shares
validly tendered prior to the Expiration Date (as defined below) and not
properly withdrawn as provided in "--Withdrawal Rights." The term "Expiration
Date" means 12:00 midnight, New York City time, on Thursday, March 30, 2000,
unless and until the Purchaser, in its sole discretion, shall have extended the
period during which the Offer is open, in which event the term "Expiration Date"
shall mean the latest time and date at which the Offer, as so extended by the
Purchaser, shall expire.

     Subject to the applicable rules and regulations of the Commission, the
Purchaser expressly reserves the right, in its sole discretion, at any time and
from time to time, to extend the period during which the Offer is open for any
reason, including the failure to satisfy any of the conditions specified in
"--Certain Conditions Of The Offer," and thereby delay acceptance for payment
of, and payment for, any Shares, by giving oral or written notice of such
extension to the Depositary. There can be no assurance that the Purchaser will
exercise its right to extend the Offer. During any such extension, all Shares
previously tendered and not properly withdrawn will remain subject to the Offer,
subject to the rights of a tendering stockholder to withdraw such stockholder's
Shares. See "--Withdrawal Rights."

     Subject to the applicable rules and regulations of the Commission, the
Purchaser also expressly reserves the right, in its sole discretion, at any time
and from time to time, to (1) terminate the Offer and not accept for payment (or
pay for) any Shares if any of the conditions referred to in "--Certain
Conditions Of The Offer" has not been satisfied or upon the occurrence and
during the continuance of any of the events specified in "--Certain Conditions
Of The Offer," and (2) waive any condition or amend the Offer in any respect, in
each case by giving oral or written notice of termination, waiver or amendment
to the Depositary and by making a public announcement thereof. The Purchaser
acknowledges (a) that Rule 14e-1(c) under the Exchange Act requires the
Purchaser to pay the consideration offered or return the Shares tendered
promptly after the termination or withdrawal of the Offer and (b) that the
Purchaser may not delay acceptance for payment of, or payment for, any Shares
upon the occurrence of any of the conditions specified in "--Certain Conditions
Of The Offer" without extending the period during which the Offer is open.

     If the Minimum Condition or any other condition specified in "--Certain
Conditions Of The Offer" is not fulfilled by the Expiration Date, the Purchaser
reserves the right (but shall not be obligated) to (1) decline to purchase any
of the Shares tendered, return all tendered Shares to tendering stockholders and
terminate the Offer, (2) extend the Offer and retain all tendered Shares until
the expiration of the Offer, as extended, subject to the terms and conditions of
the Offer (including any rights of stockholders to withdraw their Shares), or
(3) waive or reduce the condition and, subject to complying with applicable
rules and regulations of the Commission, accept for payment and purchase all
Shares validly tendered.

     Any extension, termination or amendment will be followed as promptly as
practicable by a public announcement thereof, such announcement, in the case of
an extension, to be made no later than 9:00 a.m., New York City time, on the
next business day after the previously scheduled Expiration Date. Without
limiting the manner in which the Purchaser may choose to make any public
announcement, except as provided by applicable law (including Rules 14d-4(c),
14d-6(d) and 14e-1 under the Exchange Act, which require that material changes
be promptly disseminated to holders of Shares), the Purchaser will have no
obligation to publish, advertise or otherwise communicate any such public
announcement other than by issuing a release to the Dow Jones News Service.

     If the Purchaser makes a material change in the terms of the Offer or the
information concerning the Offer, or waives a material condition of the Offer,
the Purchaser will disseminate additional tender offer materials (including by
public announcement as set forth above) and extend the Offer to the extent
required by Rules 14d-4(d), 14d-6(d) and 14e-1 under the Exchange Act. The
minimum period during which the Offer must remain open following material
changes in the terms of the Offer or information concerning the Offer, other
than a change in price, a change in percentage of securities sought or a change
in any dealer's
                                       32
<PAGE>   33

soliciting fee, will depend upon the facts and circumstances, including the
relative materiality of the changes. With respect to a change in price or,
subject to certain limitations, a change in the percentage of securities sought
or a change in any dealer's soliciting fee, a minimum ten business day period
from the date of such change is generally required to allow for adequate
dissemination of such change to stockholders. Accordingly, if, prior to the
Expiration Date, the Purchaser decreases the number of Shares being sought,
increases the consideration offered pursuant to the Offer or adds a dealer's
soliciting fee, and if the Offer is scheduled to expire at any time earlier than
the period ending on the tenth business day from the date that notice of such
increase, decrease or addition is first published, sent or given to
stockholders, the Offer will be extended at least until the expiration of such
ten business day period. For purposes of the Offer, a "business day" means any
day other than a Saturday, Sunday or a federal holiday and consists of the time
period from 12:01 a.m. through 12:00 midnight, New York City time.

     The Company has provided the Purchaser with the Company's stockholder list
and security position listings for the purpose of disseminating the Offer to
holders of Shares. This Offer to Purchase and the related Letter of Transmittal
and, if required, other relevant material will be mailed to record holders of
Shares and will be furnished to brokers, dealers, commercial banks, trust
companies and similar persons whose names, or the names of whose nominees,
appear on the Company's stockholder list or, if applicable, who are listed as
participants in a clearing agency's security position listing for subsequent
transmittal to beneficial owners of Shares.

ACCEPTANCE FOR PAYMENT AND PAYMENT FOR SHARES

     Upon the terms and subject to the conditions of the Offer (including, if
the Offer is extended or amended, the terms and conditions of any such extension
or amendment), the Purchaser will purchase by accepting for payment, and will
pay for, all Shares validly tendered prior to the Expiration Date and not
properly withdrawn (including Shares validly tendered and not withdrawn during
any extension of the Offer, if the Offer is extended, subject to the terms and
conditions of such extension), promptly after the Expiration Date. In addition,
subject to complying with Rule 14e-1 under the Exchange Act, the Purchaser
expressly reserves the right, in its sole discretion, to delay the acceptance
for payment of, or payment for, Shares in order to comply, in whole or in part,
with any applicable law.

     In all cases, payment for Shares tendered and accepted for payment pursuant
to the Offer will be made only after timely receipt by the Depositary of:

     - certificates evidencing Shares ("Share Certificates") or timely
       confirmation of a book-entry transfer of such Shares ("Book-Entry
       Confirmation") into the Depositary's account at The Depository Trust
       Company (the "Book-Entry Transfer Facility") pursuant to the procedures
       set forth in "--Procedures For Accepting The Offer And Tendering Shares";

     - the Letter of Transmittal (or a facsimile thereof), properly completed
       and duly executed, with any required signature guarantees, or an Agent's
       Message (as defined below) in connection with a book-entry transfer; and

     - any other documents required by the Letter of Transmittal.

     Accordingly, payment may be made to tendering stockholders at different
times if delivery of the Shares and other required documents occurs at different
times.

     The term "Agent's Message" means a message transmitted by the Book-Entry
Transfer Facility to, and received by, the Depositary and forming a part of a
Book-Entry Confirmation, which states that the Book-Entry Transfer Facility has
received an express acknowledgment from the participant in the Book-Entry
Transfer Facility tendering the Shares which are the subject of such Book-Entry
Confirmation, that such participant has received and agrees to be bound by the
terms of the Letter of Transmittal and that the Purchaser may enforce such
agreement against such participant.

     For purposes of the Offer, the Purchaser will be deemed to have accepted
for payment, and thereby purchased, Shares validly tendered and not properly
withdrawn if, as and when the Purchaser gives oral or

                                       33
<PAGE>   34

written notice to the Depositary of the Purchaser's acceptance for payment of
such Shares pursuant to the Offer. Upon the terms and subject to the conditions
of the Offer, payment for Shares so accepted for payment pursuant to the Offer
will be made by deposit of the aggregate purchase price therefor with the
Depositary, which will act as agent for tendering stockholders for the purpose
of receiving payment from the Purchaser and transmitting such payment to
stockholders whose Shares have been accepted for payment. UNDER NO CIRCUMSTANCES
WILL INTEREST ON THE PURCHASE PRICE FOR SHARES BE PAID, REGARDLESS OF ANY
EXTENSION OF THE OFFER OR DELAY IN MAKING SUCH PAYMENT. Upon the deposit of
funds with the Depositary for the purpose of making payment to validly tendering
stockholders, the Purchaser's obligation to make such payment shall be satisfied
and such tendering stockholders must thereafter look solely to the Depositary
for payment of the amounts owed to them by reason of the acceptance for payment
of Shares pursuant to the Offer.

     If any tendered Shares are not accepted for payment pursuant to the terms
and conditions of the Offer for any reason, or if Share Certificates are
submitted for more Shares than are tendered, Share Certificates representing
Shares not purchased or not tendered will be returned, without expense, to the
tendering stockholder (or, in the case of Shares tendered by book-entry transfer
of such Shares into the Depositary's account at the Book-Entry Transfer Facility
pursuant to the procedures for book-entry transfer set forth in "--Procedures
For Accepting The Offer And Tendering Shares," such Shares will be credited to
an account maintained at the Book-Entry Transfer Facility), as soon as
practicable following expiration or termination of the Offer.

     If, prior to the Expiration Date, the Purchaser increases the consideration
to be paid per Share, the Purchaser will pay such increased consideration for
all Shares purchased pursuant to the Offer, whether or not such Shares have been
tendered or purchased prior to such increase in consideration.

     The Purchaser reserves the right to transfer or assign, in whole or in part
from time to time, to one or more of its affiliates, the right to purchase the
Shares tendered pursuant to the Offer, but any such transfer or assignment will
not relieve the Purchaser of its obligations under the Offer, nor will any such
transfer or assignment in any way prejudice the rights of tendering stockholders
to receive payment for Shares validly tendered and accepted for payment pursuant
to the Offer.

PROCEDURES FOR ACCEPTING THE OFFER AND TENDERING SHARES

     GENERAL.  Except as set forth below, in order for Shares to be validly
tendered pursuant to the Offer, the Letter of Transmittal (or a facsimile
thereof), properly completed and duly executed, together with any required
signature guarantees, or an Agent's Message in connection with a book-entry
delivery of Shares, and any other documents required by the Letter of
Transmittal, must be received by the Depositary at one of its addresses set
forth on the back cover of this Offer to Purchase prior to the Expiration Date,
and either (l) Share Certificates evidencing tendered Shares must be received by
the Depositary at such address or such Shares must be tendered pursuant to the
procedures for book-entry transfer set forth below (and a Book-Entry
Confirmation must be received by the Depositary), in each case prior to the
Expiration Date, or (2) the guaranteed delivery procedures set forth below must
be complied with.

     No alternative, conditional or contingent tenders will be accepted and no
fractional Shares will be purchased. All tendering stockholders, by execution of
the Letter of Transmittal (or a facsimile thereof), waive any right to receive
any notice of the acceptance of their Shares for payment.

     THE METHOD OF DELIVERY OF SHARE CERTIFICATES, THE LETTER OF TRANSMITTAL AND
ALL OTHER REQUIRED DOCUMENTS, INCLUDING DELIVERY THROUGH THE BOOK-ENTRY TRANSFER
FACILITY, IS AT THE SOLE OPTION AND RISK OF EACH TENDERING STOCKHOLDER AND,
EXCEPT AS OTHERWISE PROVIDED UNDER THIS HEADING "--PROCEDURES FOR ACCEPTING THE
OFFER AND TENDERING SHARES," THE DELIVERY WILL BE DEEMED MADE ONLY WHEN ACTUALLY
RECEIVED BY THE DEPOSITARY. IF DELIVERY IS MADE BY MAIL, REGISTERED MAIL WITH
RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED. IN ALL CASES,
SUFFICIENT TIME SHOULD BE ALLOWED TO ENSURE TIMELY DELIVERY.

                                       34
<PAGE>   35

     BOOK-ENTRY TRANSFER.  The Depositary will make a request to establish
accounts with respect to the Shares at the Book-Entry Transfer Facility for
purposes of the Offer within two business days after the date of this Offer to
Purchase. Any financial institution that is a participant in the system of the
Book-Entry Transfer Facility may make book-entry delivery of Shares by causing
the Book-Entry Transfer Facility to transfer such Shares into the Depositary's
account at the Book-Entry Transfer Facility in accordance with the Book-Entry
Transfer Facility's procedures for such transfer. Although delivery of Shares
may be effected through book-entry transfer into the Depositary's account at the
Book-Entry Transfer Facility, the Letter of Transmittal (or a facsimile
thereof), properly completed and duly executed, together with any required
signature guarantees, or an Agent's Message, and any other documents required by
the Letter of Transmittal, must, in any case, be received by the Depositary at
one of its addresses set forth on the back cover of this Offer to Purchase prior
to the Expiration Date in order for such Shares to be validly tendered pursuant
to the Offer, or the tendering stockholder must comply with the guaranteed
delivery procedures described below.

     DELIVERY OF DOCUMENTS TO THE BOOK-ENTRY TRANSFER FACILITY IN ACCORDANCE
WITH THE BOOK-ENTRY TRANSFER FACILITY'S PROCEDURES DOES NOT CONSTITUTE DELIVERY
TO THE DEPOSITARY.

     SIGNATURE GUARANTEES.  Signatures on all Letters of Transmittal must be
guaranteed by a firm that is a bank, broker, dealer, credit union, savings
association or other entity which is a member in good standing of the Securities
Transfer Agents Medallion Program, the Stock Exchanges' Medallion Program or the
New York Stock Exchange, Inc. Medallion Signature Program (an "Eligible
Institution"), unless Shares tendered thereby are tendered (1) by a registered
holder of Shares who has not completed either the box entitled "Special Delivery
Instructions" or the box entitled "Special Payment Instructions" on the Letter
of Transmittal or (2) for the account of an Eligible Institution. See
Instruction 1 of the Letter of Transmittal.

     If the Share Certificates are registered in the name of a person other than
the signer of the Letter of Transmittal, or if payment is to be made, or Share
Certificates for unpurchased Shares are to be returned, to a person other than
the registered holder(s), then the tendered Share Certificates must be endorsed
or accompanied by appropriate stock powers signed exactly as the name(s) of the
registered holder(s) appear(s) on the Share Certificates with the signature(s)
on such Share Certificates or stock powers guaranteed by an Eligible Institution
as provided above and in the Letter of Transmittal. See Instructions 1 and 5 of
the Letter of Transmittal.

     GUARANTEED DELIVERY.  If a stockholder desires to tender Shares pursuant to
the Offer and such stockholder's Share Certificates are not immediately
available or time will not permit all of the required documents to reach the
Depositary prior to the Expiration Date, or the procedure for book-entry
transfer cannot be completed on a timely basis, such Shares may nevertheless be
tendered, provided that all of the following conditions are satisfied:

     - such tender is made by or through an Eligible Institution;

     - a properly completed and duly executed Notice of Guaranteed Delivery,
       substantially in the form provided by the Purchaser with the Letter of
       Transmittal, is received by the Depositary, in accordance with the
       procedure set forth as provided below, prior to the Expiration Date; and

     - the Share Certificates (or a Book-Entry Confirmation) for all tendered
       Shares, in proper form for transfer, in each case together with the
       Letter of Transmittal (or a facsimile thereof), properly completed and
       duly executed, with any required signature guarantees or, in the case of
       a book-entry transfer, an Agent's Message, and any other documents
       required by the Letter of Transmittal, are received by the Depositary
       within three American Stock Exchange trading days after the date of
       execution of such Notice of Guaranteed Delivery.

     The Notice of Guaranteed Delivery may be delivered by hand or transmitted
by telegram, facsimile transmission or mail to the Depositary and must include a
guarantee by an Eligible Institution in the form set forth in the Notice of
Guaranteed Delivery.

     Notwithstanding any other provision of this Offer, payment for Shares
accepted for payment pursuant to the Offer will in all cases be made only after
timely receipt by the Depositary of Share Certificates therefor (or

                                       35
<PAGE>   36

Book-Entry Confirmation of the transfer of such Shares into the Depositary's
account at the Book-Entry Transfer Facility), a properly completed and duly
executed Letter of Transmittal (or a facsimile thereof), together with any
required signature guarantees or, in the case of a book-entry transfer, an
Agent's Message, and any other documents required by the Letter of Transmittal.
Accordingly, payment may not be made to all tendering stockholders at the same
time and will depend upon when Share Certificates or Book-Entry Confirmations of
such Shares are received by the Depositary.

     BACKUP FEDERAL INCOME TAX WITHHOLDING.  Under the U.S. federal income tax
laws, the Depositary may, under certain circumstances, be required to withhold
31% of the amount of any payments made to certain stockholders pursuant to the
Offer. To prevent such backup federal income tax withholding with respect to
payments made to certain stockholders of the purchase price of Shares purchased
pursuant to the Offer, each such stockholder must provide the Depositary with
such stockholder's correct taxpayer identification number and certify that such
stockholder is not subject to backup federal income tax withholding by
completing the Substitute Form W-9 included in the Letter of Transmittal. See
Instruction 9 of the Letter of Transmittal.

     APPOINTMENT AS PROXY.  By executing the Letter of Transmittal, a tendering
stockholder irrevocably appoints designees of the Purchaser as such
stockholder's attorneys-in-fact and proxies in the manner set forth in the
Letter of Transmittal, each with full power of substitution with respect to any
Shares tendered thereby (and with respect to any and all other Shares or other
securities issued or issuable in respect of such Shares on or after January 31,
2000). All such powers of attorney and proxies shall be considered irrevocable
and coupled with an interest in the tendered Shares. Such appointment will be
effective when, and only to the extent that, the Purchaser accepts the tendered
Shares for payment and deposits the purchase price therefor with the Depositary.
Upon such deposit, all prior powers of attorney and proxies given by such
stockholder at any time with respect to such Shares (and other Shares and
securities issued or issuable in respect of the tendered Shares on or after
January 31, 2000) will, without further action, be revoked, and no subsequent
powers of attorney or proxies may be given nor any subsequent written consents
be executed by such stockholder (and, if given or executed, will not be deemed
effective). Upon such deposit by the Purchaser, the designees of the Purchaser
will, with respect to such Shares and other securities, be empowered to exercise
all voting and other rights of such stockholder as they in their sole discretion
may deem proper at any annual or special meeting of the Company's stockholders,
or any adjournment or postponement thereof, or by written consent in lieu of any
such meeting or otherwise. The Purchaser reserves the right to require that, in
order for Shares to be deemed validly tendered, immediately upon the Purchaser's
payment for such Shares, the Purchaser must be able to exercise full voting and
other rights of a record and beneficial holder, including, without limitation,
voting at any meeting of stockholders or by written consent in lieu of any such
meeting.

     DETERMINATION OF VALIDITY.  All questions as to the validity, form,
eligibility (including the time of receipt) and acceptance for payment of any
tendered Shares pursuant to any of the procedures described above will be
determined by the Purchaser, in its sole discretion, which determination will be
final and binding on all parties. The Purchaser reserves the absolute right to
reject any and all tenders of any particular Shares determined by it not to be
in appropriate form or for which the acceptance of or payment may, in the
opinion of its counsel, be unlawful. The Purchaser also reserves the absolute
right to waive any of the conditions of the Offer or any defect or
irregularities in the tender of any particular Shares, whether or not similar
defects or irregularities are waived in the case of any other Shares. The
Purchaser's interpretations of the terms and conditions of the Offer (including
the Letter of Transmittal and Instructions thereto) will be final and binding.
No tender of Shares will be deemed to have been validly made until all defects
and irregularities have been cured or waived. None of the Purchaser, any of its
affiliates or assigns, the Dealer Managers, the Information Agent, the
Depositary or any other person will be under any duty to give notification of
any defects or irregularities in tenders or incur any liability for failure to
give any such notification.

     THE PURCHASER'S ACCEPTANCE FOR PAYMENT OF SHARES TENDERED PURSUANT TO THE
OFFER WILL CONSTITUTE A BINDING AGREEMENT BETWEEN THE TENDERING STOCKHOLDER AND
THE PURCHASER UPON THE TERMS AND SUBJECT TO THE CONDITIONS OF THE OFFER.

                                       36
<PAGE>   37

WITHDRAWAL RIGHTS

     Except as otherwise provided in this Section, tenders of Shares made
pursuant to the Offer are irrevocable. Shares tendered pursuant to the Offer may
be withdrawn at any time prior to the Expiration Date and, unless previously
accepted for payment as provided herein, may also be withdrawn at any time after
May 1, 2000.

     If the Purchaser extends the Offer, is delayed in, or delays, its
acceptance for payment or payment for Shares or is unable to accept for payment
or pay for Shares for any reason, then, without prejudice to the Purchaser's
other rights under the Offer, tendered Shares may nevertheless be retained by
the Depositary, on behalf of the Purchaser, and may not be withdrawn except to
the extent tendering stockholders are entitled to and duly exercise withdrawal
rights as described in this Section. Any such extension or delay will be
accompanied by an extension of the Offer to the extent required by law.

     In order for a withdrawal to be effective, a written, telegraphic or
facsimile transmission notice of withdrawal must be timely received by the
Depositary at one of its addresses set forth on the back cover of this Offer to
Purchase. Any such notice of withdrawal must specify the name of the person who
tendered the Shares to be withdrawn, the number of Shares to be withdrawn and
the name of the registered holder of the Shares to be withdrawn, if different
from that of the person who tendered such Shares. If Share Certificates to be
withdrawn have been delivered or otherwise identified to the Depositary, then,
prior to the physical release of such Share Certificates, the tendering
stockholder must also submit the serial numbers shown on such Share Certificates
to the Depositary, and the signatures on the notice of withdrawal must be
guaranteed by an Eligible Institution, unless such Shares have been tendered for
the account of an Eligible Institution. If Shares have been tendered pursuant to
the procedures for book-entry transfer, as set forth in "--Procedures For
Accepting The Offer And Tendering Shares," any notice of withdrawal must specify
the name and number of the account at the Book-Entry Transfer Facility to be
credited with the withdrawn Shares and must otherwise comply with the procedures
of the Book-Entry Transfer Facility.

     Withdrawals may not be revoked and any Shares properly withdrawn will
thereafter be deemed not to have been validly tendered for purposes of the
Offer. However, withdrawn Shares may be re-tendered at any time prior to the
Expiration Date by following the procedures described in "--Procedures For
Accepting The Offer And Tendering Shares."

     All questions as to the form and validity (including the time of receipt)
of any notice of withdrawal will be determined by the Purchaser, in its sole
discretion, which determination will be final and binding on all parties. None
of the Purchaser, its affiliates or assigns, the Dealer Managers, the
Information Agent, the Depositary or any other person will be under any duty to
give notification of any defects or irregularities in any notice of withdrawal
or incur any liability for failure to give any such notification.

CERTAIN CONDITIONS OF THE OFFER

     Notwithstanding any other provisions of the Offer, and in addition to (and
not in limitation of) the Purchaser's rights to extend and amend the Offer at
any time in its sole discretion, the Purchaser shall not be required to accept
for payment or, subject to any applicable rules and regulations of the
Commission, including Rule 14e-1(c) under the Exchange Act (relating to the
Purchaser's obligation to pay for or return tendered Shares promptly after
termination or withdrawal of the Offer), pay for, and may delay the acceptance
for payment of or, subject to the restriction referred to above, the payment
for, any tendered Shares, and may amend or terminate the Offer if (1) the
Minimum Condition has not been satisfied or (2) at any time on or after March 3,
2000 and before the time of acceptance of the Shares for payment pursuant to the
Offer, any of the following events shall occur:

          (a) any change shall have occurred in the business, properties,
     assets, liabilities, capitalization, stockholders' equity, financial
     condition, cash flows, operations, licenses, franchises or results of
     operations of the Company or its subsidiaries which has a material adverse
     effect on the Company and its subsidiaries taken as a whole; or

                                       37
<PAGE>   38

          (b) any government or governmental authority or agency, whether
     domestic, foreign or supranational (a "Governmental Entity"), shall have
     instituted or threatened any action, proceeding, application, claim or
     counterclaim, sought or obtained any judgment, order or injunction, or
     taken any other action, which (i) challenges the acquisition by Thermo
     Electron, Thermedics, Corpak or the Purchaser (or any other affiliate of
     Thermo Electron) of any Shares pursuant to the Offer or the Merger,
     restrains, prohibits or materially delays the making or consummation of the
     Offer or the Merger, prohibits the performance of any of the contracts or
     other arrangements entered into by Thermo Electron, Thermedics, Corpak or
     the Purchaser (or any other affiliate of Thermo Electron) in connection
     with the acquisition of the Shares or the Company, seeks to obtain any
     material amount of damages, or otherwise directly or indirectly adversely
     affects the Offer or the Merger, (ii) seeks to prohibit or limit materially
     the ownership or operation by the Company, Thermo Electron, Thermedics,
     Corpak or the Purchaser (or any other affiliate of Thermo Electron) of all
     or any material portion of the business or assets of the Company or of
     Thermo Electron and its affiliates, or to compel the Company, Thermo
     Electron, Thermedics, Corpak or the Purchaser (or any other affiliate of
     Thermo Electron) to dispose of or to hold separate all or any material
     portion of the business or assets of Thermo Electron or any of its
     affiliates or of the Company or any of its subsidiaries as a result of the
     transactions contemplated by the Offer or the Merger, (iii) seeks to impose
     any material limitation on the ability of the Company, Thermo Electron,
     Thermedics, Corpak or the Purchaser (or any other affiliate of Thermo
     Electron) to conduct the Company's or any subsidiary's business or own such
     assets, (iv) seeks to impose or confirm any material limitation on the
     ability of Thermo Electron, Thermedics, Corpak or the Purchaser (or any
     other affiliate of Thermo Electron) to acquire or hold, or to exercise full
     rights of ownership of, any Shares, including the right to vote such Shares
     on all matters properly presented to the stockholders of the Company, (v)
     seeks to require divestiture by Thermo Electron, Thermedics, Corpak or the
     Purchaser or any of their affiliates of all or any of the Shares or (vi)
     otherwise has resulted in or has a reasonable likelihood of resulting in, a
     material adverse effect on the business, financial condition, results of
     operation or prospects of the Company, Thermo Electron, Corpak or
     Thermedics (a "Material Adverse Effect"); or

          (c) there shall have been entered or issued any preliminary or
     permanent judgment, order, decree, ruling or injunction or any other action
     taken by any Governmental Entity or court, whether on its own initiative or
     the initiative of any other person, which (i) restrains, prohibits or
     materially delays the making or consummation of the Offer or the Merger,
     prohibits the performance of any of the contracts or other arrangements
     entered into by Thermo Electron, Thermedics, Corpak or the Purchaser (or
     any other affiliate of Thermo Electron) in connection with the acquisition
     of the Shares or the Company or otherwise directly or indirectly materially
     adversely affects the Offer or the Merger, (ii) prohibits or limits
     materially the ownership or operation by the Company, Thermo Electron,
     Thermedics, Corpak or the Purchaser (or any other affiliate of Thermo
     Electron) of all or any material portion of the business or assets of the
     Company and its subsidiaries taken as a whole or of Thermo Electron,
     Thermedics, Corpak or the Purchaser (or any other affiliate of Thermo
     Electron), or compels the Company, Thermo Electron, Thermedics, Corpak or
     the Purchaser (or any other affiliate of Thermo Electron) to dispose of or
     to hold separate all or any material portion of the business or assets of
     Thermo Electron or any of its affiliates or of the Company or any of its
     subsidiaries as a result of the transactions contemplated by the Offer or
     the Merger, (iii) imposes any material limitation on the ability of the
     Company, Thermo Electron, Thermedics, Corpak or the Purchaser (or any other
     affiliate of Thermo Electron) to conduct the Company's or any subsidiary's
     business or own such assets, (iv) imposes or confirms any material
     limitation on the ability of Thermo Electron, Thermedics, Corpak or the
     Purchaser (or any other affiliate of Thermo Electron) to acquire or hold,
     or to exercise full rights of ownership of, any Shares, including the right
     to vote such Shares on all matters properly presented to the stockholders
     of the Company, (v) requires divestiture by Thermo Electron, Thermedics,
     Corpak or the Purchaser or any of their affiliates of all or any of the
     Shares or (vi) otherwise has resulted in, or has a reasonable likelihood of
     resulting in, a Material Adverse Effect; or

          (d) there shall have been instituted or be pending before any
     Governmental Entity or court any action, proceeding, application, claim or
     counterclaim or any judgment, order or injunction sought or any other
     action taken by any person or entity (other than a Governmental Entity)
     which (i) challenges the
                                       38
<PAGE>   39

     acquisition by Thermo Electron, Thermedics, Corpak or the Purchaser (or any
     other affiliate of Thermo Electron) of any Shares pursuant to the Offer or
     the Merger, restrains, prohibits or materially delays the making or
     consummation of the Offer or the Merger, prohibits the performance of any
     of the contracts or other arrangements entered into by Thermo Electron,
     Thermedics, Corpak or the Purchaser (or any other affiliate of Thermo
     Electron) in connection with the acquisition of the Shares or the Company,
     seeks to obtain any material amount of damages, or otherwise directly or
     indirectly adversely affects the Offer or the Merger, (ii) seeks to
     prohibit or limit materially the ownership or operation by the Company,
     Thermo Electron, Thermedics, Corpak or the Purchaser (or any other
     affiliate of Thermo Electron) of all or any material portion of the
     business or assets of the Company or of Thermo Electron and its affiliates,
     or to compel the Company, Thermo Electron, Thermedics, Corpak or the
     Purchaser (or any other affiliate of Thermo Electron) to dispose of or to
     hold separate all or any material portion of the business or assets of
     Thermo Electron or any of its affiliates or of the Company or any of its
     subsidiaries as a result of the transactions contemplated by the Offer or
     the Merger, (iii) seeks to impose any material limitation on the ability of
     the Company, Thermo Electron, Thermedics, Corpak or the Purchaser (or any
     other affiliate of Thermo Electron) to conduct the Company's or any
     subsidiary's business or own such assets, (iv) seeks to impose or confirm
     any material limitation on the ability of Thermo Electron, Thermedics,
     Corpak or the Purchaser (or any other affiliate of Thermo Electron) to
     acquire or hold, or to exercise full rights of ownership of, any Shares,
     including the right to vote such Shares on all matters properly presented
     to the stockholders of the Company, (v) seeks to require divestiture by
     Thermo Electron, Thermedics, Corpak or the Purchaser (or any other
     affiliate of Thermo Electron) of all or any of the Shares or (vi) otherwise
     has resulted in or, in the Purchaser's reasonable discretion, has a
     reasonable likelihood of resulting in a Material Adverse Effect; and which
     in the case of clause (i), (ii), (iii), (iv) or (v) is successful or the
     Purchaser determines, in its reasonable discretion, has a reasonable
     likelihood of being successful; or

          (e) there shall be any statute, rule or regulation enacted,
     promulgated, entered, enforced or deemed applicable to the Offer or the
     Merger, or any other action shall have been taken by any Governmental
     Entity or court that results in, directly or indirectly, any of the
     consequences referred to in clauses (i) through (vi) of paragraph (b)
     above; or

          (f) there shall have occurred any general suspension of trading in, or
     limitation on prices for, securities on the New York Stock Exchange,
     American Stock Exchange or in the over-the-counter market (other than any
     temporary suspension pursuant to a circuit breaker procedure then in effect
     and lasting for not more than three trading hours), any declaration of a
     banking moratorium by federal or New York authorities or general suspension
     of payments in respect of lenders that regularly participate in the United
     States market in loans, any material limitation by any federal, state or
     local government or any court, administrative or regulatory agency or
     commission or other governmental authority or agency in the United States
     that materially affects the extension of credit generally by lenders that
     regularly participate in the U.S. market in loans, any commencement of a
     war involving the United States or any commencement of armed hostilities or
     other national or international circumstance involving the United States
     that has a material adverse effect on bank syndication or financial markets
     in the United States or, in the case of any of the foregoing occurrences
     existing on or at the time of the commencement of the Offer, a material
     acceleration or worsening thereof; which in the reasonable judgment of the
     Purchaser, in any such case, and regardless of the circumstances giving
     rise to such condition, makes it inadvisable to proceed with the Offer, the
     Merger and/or with such acceptance for payment or payments.

     The foregoing conditions are for the sole benefit of the Purchaser and its
affiliates and may be asserted by the Purchaser regardless of any circumstances
giving rise to any condition and may be waived by the Purchaser, in whole or in
part, at any time and from time to time in the reasonable discretion of the
Purchaser. The failure by the Purchaser (or any affiliate of the Purchaser) at
any time to exercise any of the foregoing rights will not be deemed a waiver of
any right, and each right will be deemed an ongoing right which may be asserted
at any time and from time to time.

                                       39
<PAGE>   40

CERTAIN LEGAL MATTERS; REGULATORY APPROVALS

     GENERAL.  Except as described below, none of Thermo Electron, Thermedics,
Corpak or the Purchaser is aware of any license or regulatory permit that
appears to be material to the business of the Company and its subsidiaries that
might be adversely affected by the Purchaser's acquisition of Shares as
contemplated herein.

     Except as described in this section, none of Thermo Electron, Thermedics,
Corpak or the Purchaser is aware of any other material filing, approval or other
action by any federal or state governmental or administrative authority that
would be required for the acquisition of Shares by the Purchaser as contemplated
herein. Should any such other approval or action be required, it is currently
contemplated that such approval or other action would be sought. There is,
however, no present intention to delay the purchase of Shares tendered pursuant
to the Offer or the Merger pending the outcome of any such other approval or
action. There can be no assurance that any such other approval or action, if
needed, would be obtained without substantial conditions or that adverse
consequences might not result to the Purchaser's, Corpak's, Thermedics', Thermo
Electron's or the Company's business in the event that such other approvals were
not obtained or such other actions were not taken. The Purchaser's obligation
under the Offer to accept for payment and pay for Shares is subject to certain
conditions, including conditions relating to the legal matters discussed in this
section. See "--Certain Conditions Of The Offer."

     ANTITRUST.  The Purchaser believes that the Offer and the Merger are exempt
from the reporting requirements contained in the Hart-Scott-Rodino Antitrust
Improvements Act of 1976. Nevertheless, there can be no assurance that a
challenge to the Offer and the Merger on antitrust grounds will not be made, or,
if such challenge is made, what the result will be.

     FOREIGN APPROVALS.  The Company conducts business in a number of foreign
countries and jurisdictions. In connection with the acquisition of the Shares
pursuant to the Offer or the Merger, the laws of certain of those foreign
countries and jurisdictions may require the filing of information with, or the
obtaining of the approval or consent of, governmental authorities in such
countries and jurisdictions. The governments in such countries and jurisdictions
might attempt to impose additional conditions on the Company's operations
conducted in such countries and jurisdictions as a result of the acquisition of
the Shares pursuant to the Offer or the Merger. If such approvals or consents
are found to be required, the Purchaser intends to make the appropriate filings
and applications. In the event such a filing or application is made for the
requisite foreign approvals or consents, there can be no assurance that such
approvals or consents will be granted and, if such approvals or consents are
received, there can be no assurance as to the date of such approvals or
consents. In addition, there can be no assurance that the Purchaser will be able
to cause the Company or its subsidiaries to satisfy or comply with such laws or
that compliance or noncompliance will not have adverse consequences for the
Company or any subsidiary after purchase of the Shares pursuant to the Offer or
the Merger.

     STATE ANTI-TAKEOVER STATUTES.  Section 203 of the DGCL prohibits business
combination transactions involving a Delaware corporation (such as the Company)
and an "interested stockholder" (defined generally as any person that directly
or indirectly beneficially owns 15% or more of the outstanding voting stock of
the subject corporation) for three years following the time such person became
an interested stockholder, unless special requirements are met or certain
exceptions apply, including that prior to such time the board of directors of
the subject corporation approved either the business combination or the
transaction which resulted in such person being an interested stockholder. The
Purchaser believes that neither the Offer nor the Merger is prohibited by
Section 203 of the DGCL.

     A number of other states have adopted laws and regulations applicable to
attempts to acquire securities of corporations which are incorporated, or have
substantial assets, stockholders, principal executive offices or principal
places of business, or whose business operations otherwise have substantial
economic effects, in such states. In 1982, in Edgar v. MITE Corp., the Supreme
Court of the United States invalidated on constitutional grounds the Illinois
Business Takeover Statute, which, as a matter of state securities law, made
takeovers of corporations meeting certain requirements more difficult. However,
in 1987 in CTS Corp. v. Dynamics Corp. of America, the Supreme Court held that
the State of Indiana may, as a matter of corporate law, and, in particular, with
respect to those aspects of corporate law concerning corporate governance,
constitutionally disqualify a potential acquiror from voting on the affairs of a
target corporation without the prior approval of


                                       40
<PAGE>   41

the remaining stockholders. The state law before the Supreme Court was by its
terms applicable only to corporations that had a substantial number of
stockholders in that state and were incorporated there.

     The Company, directly or through subsidiaries, conducts business in a
number of states throughout the United States, some of which have enacted
takeover laws. None of Thermo Electron, Thermedics, Corpak or the Purchaser
knows whether any of these laws will, by their terms, apply to the Offer or the
Merger, and the Purchaser has not necessarily complied with any such laws.
Should any person seek to apply any state takeover law, the Purchaser will take
such action as then appears desirable, which may include challenging the
validity or applicability of any such statute in appropriate court proceedings.
In the event it is asserted that one or more state takeover laws is applicable
to the Offer or the Merger, and an appropriate court does not determine that it
is inapplicable or invalid as applied to the Offer or the Merger, the Purchaser
might be required to file certain information with, or receive approvals from,
the relevant state authorities. In addition, if enjoined, the Purchaser might be
unable to accept for payment any Shares tendered pursuant to the Offer or be
delayed in continuing or consummating the Offer. In such case, the Purchaser may
not be obligated to accept for payment any Shares tendered. See "--Certain
Conditions Of The Offer."

DIVIDENDS AND DISTRIBUTIONS

     If, on or after January 31, 2000, the Company should declare or pay any
dividend or other distribution (including, without limitation, the issuance of
additional Shares pursuant to a stock dividend or stock split or the issuance of
rights for the purchase of any securities) with respect to the Shares that is
payable or distributable to stockholders of record on a date occurring prior to
the transfer to the name of the Purchaser or its nominees or transferees on the
Company's stock transfer records of the Shares purchased pursuant to the Offer,
then, without prejudice to the Purchaser's rights described in "--Certain
Conditions Of The Offer," (1) the purchase price per Share payable by the
Purchaser pursuant to the Offer will be reduced in the amount of any such cash
dividend or distribution, and (2) the whole of any non-cash dividend or
distribution (including, without limitation, additional Shares or rights as
aforesaid) will be required to be remitted promptly and transferred by each
tendering stockholder to the Depositary for the account of the Purchaser
accompanied by appropriate documentation of transfer. Pending such remittance or
appropriate assurance thereof, the Purchaser will be entitled to all rights and
privileges as owner of any such non-cash dividend, distribution or right, and
may withhold the entire purchase price or deduct from the purchase price the
amount of value of such non-cash dividend, distribution or right, as determined
by the Purchaser in its sole discretion.

     If, on or after January 31, 2000, the Company should split the Shares or
combine or otherwise change the Shares or its capitalization, then, without
prejudice to the Purchaser's rights described under the heading "--Certain
Conditions Of The Offer," appropriate adjustments to reflect such split,
combination or change may be made by the Purchaser in the purchase price and
other terms of the Offer, including, without limitation, the number or type of
securities offered to be purchased.

                                       41
<PAGE>   42

                    CERTAIN FEDERAL INCOME TAX CONSEQUENCES

     The following is a general summary of the material U.S. federal income tax
consequences of the Offer and the Merger to the beneficial owners of Shares.
This summary is based upon the provisions of the Internal Revenue Code of 1986,
as amended (the "Code"), applicable treasury regulations thereunder, judicial
decisions and current administrative rulings as in effect on the date of this
Offer to Purchase. The discussion does not address all aspects of U.S. federal
income taxation that may be relevant to particular taxpayers in light of their
personal circumstances or to taxpayers subject to special treatment under the
Code (for example, life insurance companies, foreign corporations, foreign
partnerships, foreign estates or trusts, or individuals who are not citizens or
residents of the United States and beneficial owners whose Shares were acquired
pursuant to the exercise of warrants, employee stock options or otherwise as
compensation) and does not address any aspect of state, local, foreign or other
taxation.

     The receipt of cash for Shares pursuant to the Offer or the Merger will be
a taxable transaction for federal income tax purposes under the Code, and may
also be a taxable transaction under applicable state, local or foreign income or
other tax laws. Generally, for federal income tax purposes, a beneficial owner
of Shares that tenders Shares pursuant to the Offer or surrenders Shares
pursuant to the Merger will recognize gain or loss equal to the difference
between the amount of cash received by the beneficial owner and the aggregate
tax basis in the Shares sold pursuant to the Offer or canceled and converted to
cash pursuant to the Merger. Gain or loss will be calculated separately for each
block of Shares purchased pursuant to the Offer or canceled and converted to
cash pursuant to the Merger.

     Gain or loss on the disposition of Shares will be capital gain or loss,
assuming that the Shares are held as capital assets. Capital gains of
individuals, estates and trusts generally are subject to a maximum federal
income tax rate of (i) 20% if, at the time the tendered Shares are accepted for
payment (in the case of the Offer) or the Effective Time of the Merger (in the
case of the Merger), the beneficial owner held the Shares for more than one year
or (ii) 39.6% if, at the time the tendered Shares are accepted for payment (in
the case of the Offer) or the Effective Time of the Merger (in the case of the
Merger), the beneficial owner held the Shares for not more than one year.
Capital gains of corporations generally are taxed at the federal income tax
rates applicable to corporate ordinary income. In addition, the ability of both
corporate and non-corporate beneficial owners to use capital losses to offset
ordinary income is limited.

     In general, cash received by Public Stockholders who exercise statutory
appraisal rights ("Dissenting Stockholders") in respect of such appraisal rights
will result in the recognition of gain or loss to the Dissenting Stockholders.
Any such Dissenting Stockholder should consult with its tax advisor for a full
understanding of the tax consequences of the receipt of cash in respect of
appraisal rights pursuant to the Merger.

     A beneficial owner may be subject to backup federal income tax withholding
at a rate of 31% with respect to the amount of cash received pursuant to the
Offer or the Merger unless the owner provides its tax identification number
("TIN") and certifies that such number is correct or properly certifies that it
is awaiting a TIN, or unless an exemption applies. A beneficial owner that does
not furnish its TIN may be subject to a penalty imposed by the Internal Revenue
Service. See "The Tender Offer--Procedures For Accepting The Offer And Tendering
Shares--Backup Federal Income Tax Withholding."

     If backup withholding applies to a beneficial owner, the Depositary is
required to withhold 31% from payments to such owner. Backup withholding is not
an additional tax. Rather, the amount of the backup withholding can be credited
against the federal income tax liability of the person subject to the backup
withholding, provided that the required information is given to the Internal
Revenue Service. If backup withholding results in an overpayment of tax, a
refund can be obtained by the beneficial owner upon filing an income tax return.

     EACH BENEFICIAL OWNER OF SHARES IS URGED TO CONSULT SUCH BENEFICIAL OWNER'S
TAX ADVISOR AS TO THE SPECIFIC TAX CONSEQUENCES TO SUCH BENEFICIAL OWNER OF THE
OFFER AND THE MERGER, INCLUDING THE APPLICATION OF STATE, LOCAL, FOREIGN AND
OTHER TAX LAWS.

                                       42
<PAGE>   43

                      PRICE RANGE OF THE SHARES; DIVIDENDS

     PRICE RANGE OF SHARES.  The Shares are listed on the American Stock
Exchange under the symbol "TSR". The following table sets forth the high and low
sales prices per Share on the American Stock Exchange, as reported in publicly
available sources for each of the periods indicated.

<TABLE>
<CAPTION>
                                                              HIGH           LOW
                                                              ----           ---
<S>                                                           <C>            <C>
Fiscal Year Ended January 2, 1999:
  First Quarter.............................................  $12 1/16       $ 9 1/4
  Second Quarter............................................  $12 5/8        $11 3/8
  Third Quarter.............................................  $12 1/2        $ 8 3/8
  Fourth Quarter............................................  $10            $ 8 1/8
Fiscal Year Ended January 1, 2000:
  First Quarter.............................................  $11 3/8        $ 9 3/4
  Second Quarter............................................  $13 7/8        $ 9 5/8
  Third Quarter.............................................  $15 5/8        $12 3/4
  Fourth Quarter............................................  $15            $13 1/2
Fiscal Year Ending December 30, 2000:
  First Quarter (through March 1, 2000).....................  $15 1/4        $14 1/8
</TABLE>

     As of January 28, 2000, there were 79 holders of record of the Shares and
in excess of 500 beneficial owners of the Shares.

     On January 28, 2000, the last full trading day prior to the public
announcement of the Purchaser's intention to commence the Offer, the closing
sale price per Share, as reported on the American Stock Exchange, was $14 7/16.
On February 29, 2000, the closing sale price per Share, as reported on the
American Stock Exchange, was $15.00.

STOCKHOLDERS ARE URGED TO OBTAIN CURRENT MARKET QUOTATIONS FOR THE SHARES.

     DIVIDENDS.  The Company has never declared or paid any cash dividends in
respect of the Shares.

                                       43
<PAGE>   44

                   CERTAIN INFORMATION CONCERNING THE COMPANY

     Stockholders are urged to review the publicly available information
concerning the Company before acting on the Offer.

     GENERAL.  The Company develops, manufactures and markets high-speed
precision-weighing and inspection equipment for industrial production and
packaging lines. Each of the Company's segments serves two principal markets:
packaged-goods and bulk materials. The Company's products for the packaged-goods
market include a broad line of checkweighing equipment and metal detectors that
can be integrated at various stages in production lines for process control and
quality assurance, as well as hot foil and thermal printers and X-ray inspection
equipment. The product-monitoring businesses design, manufacture and distribute
specialized packaged-goods equipment, including checkweighers and metal
detectors, for the food and pharmaceutical industries. The Company's
bulk-materials product line includes conveyor-belt scales, solid level-
measurement and conveyor-monitoring systems, sampling systems, and
small-capacity feeders. The principal executive offices of the Company are
located at 501 90th Avenue, N.W., Minneapolis, Minnesota 55433, and its
telephone number is (781) 622-1000.

     The Company is subject to the disclosure requirements of the Exchange Act
and in accordance therewith is required to file reports, proxy statements and
other information with the Commission relating to its business, financial
condition and other matters. In addition, the Company is required to file within
10 business days of the commencement of this Offer, and to distribute to the
Company's Stockholders, a statement on Schedule 14D-9 regarding its
recommendation to the Company's stockholders with respect to the Offer. Such
reports, proxy statements, Schedule 14D-9 and other information are available
for inspection at the Commission's public reference facilities at 450 Fifth
Street, N.W., Washington, D.C. 20549 and should also be available for inspection
at the regional offices of the Commission located at 7 World Trade Center, Suite
1300, New York, New York 10048 and Citicorp Center, 500 West Madison Street,
Suite 1400, Chicago, Illinois 60661. Copies may be obtained at prescribed rates
from the Commission's principal office at 450 Fifth Street, N.W., Washington,
D.C. 20549. The Commission also maintains a web site that contains reports,
proxy and information statements and other information regarding registrants
that file electronically with the Commission at http://www.sec.gov. In addition,
certain material filed by the Company may also be available for inspection at
the offices of the American Stock Exchange, 86 Trinity Place, New York, NY
10006-1881.

     None of Thermo Electron, Thermedics, Corpak or the Purchaser intends to
grant unaffiliated stockholders special access to the Company's records in
connection with the Offer. None of Thermo Electron, Thermedics, Corpak or the
Purchaser intends to obtain counsel to or appraisal services for unaffiliated
stockholders of the Company.

     FINANCIAL INFORMATION.  Set forth below is certain selected consolidated
financial information with respect to the Company and its subsidiaries excerpted
or derived from the audited consolidated financial statements contained in the
Company's Annual Report on Form 10-K for its fiscal year ended January 2, 1999
and the unaudited financial statements contained in the Company's Quarterly
Reports on Form 10-Q for the quarters ended October 2, 1999 and October 3, 1998
(collectively, the "Company Reports"). More comprehensive financial information
is included in the Company Reports and in other documents filed by the Company
with the Commission (which may be inspected or obtained in the manner set forth
above), and the following financial information is qualified in its entirety by
reference to the Company Reports and other documents and all of the financial
information (including any related notes) contained therein or incorporated
therein by reference.

     The selected financial information presented below as of and for the fiscal
years ended January 2, 1999, January 3, 1998, December 28, 1996, December 30,
1995 and as of and for the periods from March 16, 1994 through December 31, 1994
and October 1, 1993 through March 15, 1994 has been derived from the Company's
Consolidated Financial Statements, which have been audited by Arthur Andersen
LLP. The selected financial information as of and for the nine months ended
October 2, 1999 and October 3, 1998 has not been audited. The results of
operations for the nine months ended October 2, 1999 are not necessarily
indicative of results for the entire year.

                                       44
<PAGE>   45

                  SELECTED CONSOLIDATED FINANCIAL INFORMATION

<TABLE>
<CAPTION>
                                                                    THE COMPANY                         PREDECESSOR(A)
                                               ------------------------------------------------------   --------------
                                                                                             MAR. 16,      OCT. 1,
                          NINE MONTHS ENDED                                                    1994          1993
                         -------------------                                                 THROUGH       THROUGH
                         OCT. 2,    OCT. 3,                                                  DEC. 31,      MAR. 15,
                           1999     1998(B)      1998(B)     1997(C)    1996(D)     1995       1994          1994
                         --------   --------   -----------   --------   --------   -------   --------   --------------
                                                    (IN THOUSANDS EXCEPT PER SHARE AMOUNTS)
<S>                      <C>        <C>        <C>           <C>        <C>        <C>       <C>        <C>
STATEMENT OF OPERATIONS
  DATA:
Revenues...............  $ 81,816   $ 69,660    $ 98,763     $ 78,695   $ 70,027   $67,474   $50,116       $24,300
Net Income (Loss)......     4,679      4,338       5,719        6,488      5,152     3,830     1,260        (1,269)
Earnings (Loss) per
  Share:
  Basic................       .50        .45         .59          .66        .56       .55       .18          (.18)
  Diluted..............       .49        .45         .59          .66        .56       .55       .18          (.18)
Weighted Average
  Shares:
  Basic................     9,431      9,690       9,625        9,875      9,156     7,000     7,000            --
  Diluted..............     9,467      9,693       9,627        9,878      9,162     7,000     7,000            --
BALANCE SHEET DATA (AT
  END OF PERIOD):
Working Capital........  $ 14,050   $  5,859    $  9,176     $ 45,005   $ 41,394   $  (853)  $  (250)      $13,409
Total Assets...........   137,699    141,612     140,164      115,101    107,186    61,960    62,527        28,494
Long-term Obligation...        --         --          --           --         --        --     1,849            --
Shareholders'
  Investment...........    93,423     87,774      88,993       87,931     82,365    34,687    34,600        15,781
OTHER DATA:
Book Value per Share...  $   9.90   $   9.31    $   9.44     $   8.91
Cash Dividends.........        --         --          --           --         --        --        --            --
Ratio of Earnings to
  Fixed Charges(e).....     6.42x      7.24x       6.38x       11.96x
</TABLE>

- ---------------
(a) On March 16, 1994, Thermedics acquired Ramsey Technology Inc. ("Ramsey"),
    the Company's predecessor, from Baker Hughes Incorporated. Periods prior to
    March 16, 1994, represent the results of Ramsey as included in Baker Hughes
    Incorporated's financial statements. Periods subsequent to March 15, 1994,
    represent the results of Ramsey as included in Thermedics' consolidated
    financial statements. The principal difference in the basis of accounting
    between Ramsey and the Company relates to the cost in excess of net assets
    of acquired companies, the amortization of which approximates $860,000 per
    year.

(b) Reflects the June 1998 acquisition of the product-monitoring group of
    Graseby Limited, a subsidiary of Smiths Industries plc.

(c) Reflects the February 1997 acquisition of the business of RCC Industrial
    Electronics Pty. Limited and the July 1997 acquisition of Westerland
    Engineering Ltd.

(d) Includes the net proceeds of the Company's initial public offering in April
    1996, and reflects the January 1996 acquisition of Hitech Electrocontrols
    Limited and the April 1996 acquisition of the solids flow-measurement
    product line of Endress + Hauser, Inc.

(e) For purposes of computing the ratios of earnings to fixed charges,
    "earnings" represent income before taxes, plus fixed charges. "Fixed
    charges" consist of interest on indebtedness and one-third of rental
    expense, which is deemed to be the interest component of such rental
    expense.

                                       45
<PAGE>   46

     RECENTLY RELEASED FINANCIAL DATA.  The selected financial information of
the Company presented below for the three and twelve month periods ended January
1, 2000 and January 2, 1999 were publicly released by the Company on February
17, 2000. With the exception of the financial information for the twelve months
ended January 2, 1999, this financial information is not audited and full
financial statements reflecting such information have not yet been filed with
the Commission.

                        CONSOLIDATED STATEMENT OF INCOME

<TABLE>
<CAPTION>
                                                     THREE MONTHS ENDED    TWELVE MONTHS ENDED
                                                     ------------------    -------------------
                                                     JAN. 1,    JAN. 2,    JAN. 1,     JAN. 2,
                                                      2000       1999        2000       1999
                                                     -------    -------    --------    -------
                                                      (IN THOUSANDS EXCEPT PER SHARE AMOUNTS)
<S>                                                  <C>        <C>        <C>         <C>
Revenues...........................................  $25,970    $29,103    $107,786    $98,763
                                                     -------    -------    --------    -------
Costs and Operating Expenses:
  Cost of revenues.................................   15,475     18,293      64,790     61,621
  Selling, general, and administrative expenses....    6,997      7,569      28,901     25,438
  Research and development expenses................      889        836       3,392      2,823
                                                     -------    -------    --------    -------
                                                      23,361     26,698      97,083     89,882
                                                     -------    -------    --------    -------
Operating Income...................................    2,609      2,405      10,703      8,881
Interest Income....................................      122        227         468      1,398
Interest Expense...................................     (273)      (380)     (1,136)    (1,060)
Other Income.......................................      315         75         472        186
                                                     -------    -------    --------    -------
Income Before Provision for Income Taxes...........    2,773      2,327      10,507      9,405
Provision for Income Taxes.........................    1,079        946       4,134      3,686
                                                     -------    -------    --------    -------
Net Income.........................................  $ 1,694    $ 1,381    $  6,373    $ 5,719
                                                     =======    =======    ========    =======
Earnings per Share:
  Basic............................................  $   .18    $   .15    $    .68    $   .59
                                                     =======    =======    ========    =======
  Diluted..........................................  $   .18    $   .15    $    .67    $   .59
                                                     =======    =======    ========    =======
Weighted Average Shares:
  Basic............................................    9,438      9,428       9,432      9,625
                                                     =======    =======    ========    =======
  Diluted..........................................    9,506      9,428       9,477      9,627
                                                     =======    =======    ========    =======
</TABLE>

                                       46
<PAGE>   47

             CERTAIN INFORMATION CONCERNING THE PURCHASER, CORPAK,
                         THERMEDICS AND THERMO ELECTRON

THE PURCHASER

     The Purchaser is a newly organized, wholly-owned subsidiary of Corpak
formed for the purpose of making the Offer. The Purchaser is organized under the
laws of the State of Delaware. The Purchaser's principal executive offices are
located at 81 Wyman Street, P.O. Box 9046, Waltham, Massachusetts 02454-9046,
and its telephone number is (781) 622-1000.

     The name, business address, principal occupation, employment history and
citizenship of each of the executive officers and directors of the Purchaser are
set forth on Schedule I hereto.

     During the past five years, the Purchaser has not been convicted in a
criminal proceeding (excluding traffic violations or similar misdemeanors) or
been a party to any judicial or administrative proceeding (except for any
matters that were dismissed without sanction or settlement) that resulted in a
judgment, decree or final order enjoining the Purchaser from future violations
of, or prohibiting activities subject to, federal or state securities laws, or a
finding of any violation of federal or state securities laws.

CORPAK

     Corpak, a Massachusetts corporation and a wholly-owned subsidiary of
Thermedics, designs, manufactures and markets enteral feeding systems that
introduce special nutritional solutions into the stomach or the small intestine
through tubes entering the nose or stomach. Enteral therapy is used for patients
who are unable to eat or digest food normally or who require high levels of
nutritional support. Corpak's products include bags for nutritional fluids,
delivery pumps, associated pump sets that hook up to the pumps and feeding
tubes. In addition, Corpak markets catheters for peritoneal dialysis. Corpak's
principal executive offices are located at 81 Wyman Street, P.O. Box 9046,
Waltham, Massachusetts 02454-9046, and its telephone number is (781) 622-1000.

     The name, business address, principal occupation, employment history and
citizenship of each of the executive officers and directors of Corpak are set
forth on Schedule I hereto.

     During the past five years, Corpak has not been convicted in a criminal
proceeding (excluding traffic violations or similar misdemeanors) or been a
party to any judicial or administrative proceeding (except for any matters that
were dismissed without sanction or settlement) that resulted in a judgment,
decree or final order enjoining Corpak from future violations of, or prohibiting
activities subject to, federal or state securities laws, or a finding of any
violation of federal or state securities laws.

THERMEDICS

     Thermedics, a Massachusetts corporation, develops, manufactures and markets
diverse product lines, including implantable heart assist devices and other
biomedical products, security instruments and equipment, that assure the quality
of a wide variety of consumer products and bulk materials.

     Thermedics' businesses operate in the following segments: Quality Assurance
and Security Products, Precision Weighing and Inspection Equipment, Heart Assist
and Blood Testing Devices, Power Electronics and Test Equipment and Respiratory
Care Products.

     Quality assurance and security products.  Through Thermedics Detection
     Inc., Thermedics' Quality Assurance and Security Products segment develops,
     manufactures and markets high-speed detection and measurement instruments
     used in a variety of on-line industrial process and security applications,
     and for laboratory analysis.

     Precision weighing and inspection equipment.  Thermedics' Precision
     Weighing and Inspection Equipment segment includes the Company, which
     develops, manufactures and markets high-speed precision-weighing and
     inspection equipment for industrial production and packaging lines.

     Heart assist and blood testing devices.  Thermedics' Heart Assist and Blood
     Testing Devices segment consists of the Thermo Cardiosystems Inc.
     subsidiary, which has developed two implantable left ventricular-assist
     systems (LVAS): a pneumatic, or air-driven, system and an electric version.
     Thermo
                                       47
<PAGE>   48

     Cardiosystems' International Technidyne Corporation subsidiary is a leading
     manufacturer of near-patient, whole-blood coagulation testing equipment and
     related disposables and also manufactures premium-quality, single-use
     skin-incision devices.

     Power electronics and test equipment.  Thermedics' Power Electronics and
     Test Equipment segment, through the Thermo Voltek Corp. subsidiary,
     designs, manufactures and markets a range of products related to power
     amplification, conversion and quality.

     Respiratory Care Products.  Erich Jaeger, GmbH, acquired in July 1999,
     develops and manufactures equipment for lung function, cardio-respiratory
     and sleep disorder diagnosis and monitoring.

     Thermedics' common stock is listed on the American Stock Exchange under the
symbol "TMD". The principal executive offices of Thermedics are located at 470
Wildwood Street, P.O. Box 2999, Woburn, Massachusetts 01888-1799, and its
telephone number is (781) 622-1000.

     Thermedics is subject to the disclosure requirements of the Exchange Act
and in accordance therewith is required to file reports, proxy statements and
other information with the Commission relating to its business, financial
condition and other matters. Such reports, proxy statements and other
information are available for inspection and copying at prescribed rates at the
offices of the Commission and the American Stock Exchange as set forth under
"Certain Information Concerning The Company."

     The name, business address, principal occupation, five-year employment
history and citizenship of each of the directors and executive officers of
Thermedics are set forth in Schedule I hereto.

     During the past five years, Thermedics has not been convicted in a criminal
proceeding (excluding traffic violations or similar misdemeanors) or been a
party to any judicial or administrative proceeding (except for any matters that
were dismissed without sanction or settlement) that resulted in a judgment,
decree or final order enjoining Thermedics from future violations of, or
prohibiting activities subject to, federal or state securities laws, or a
finding of any violation of federal or state securities laws.

THERMO ELECTRON

     Thermo Electron, a Delaware corporation, and its subsidiaries develop and
manufacture a broad range of products that are sold worldwide. Thermo Electron
is a world leader in monitoring, analytical and biomedical instrumentation;
biomedical products including heart-assist devices, respiratory-care equipment
and mammography systems; and paper recycling and papermaking equipment. Thermo
Electron also develops alternative-energy systems and clean fuels, provides a
range of services including industrial outsourcing and environmental-liability
management and conducts research and development in advanced imaging, laser and
electronic information-management technologies. Thermo Electron performs its
business through wholly-owned subsidiaries and divisions, as well as majority
owned subsidiaries that are partially owned by public or private investors.

     On January 31, 2000, Thermo Electron announced that its Board of Directors
had authorized its management to proceed with a major reorganization of the
operations of Thermo Electron and its subsidiaries. As part of this
reorganization, Thermo Electron plans to acquire the public minority interest in
most of its subsidiaries that have minority investors, spin off its separation
technologies and fiber-based products business and its medical products business
and divest a variety of non-core businesses. The primary goal of this
reorganization is for Thermo Electron and each of its spun-off subsidiaries to
focus on its respective core business. The purpose of the Offer and the Merger
is to acquire the minority public interest in the Company as part of Thermo
Electron's overall reorganization and to provide the Public Stockholders with
$15.50 per Share in cash. Following the Offer and the Merger, Thermo Electron
plans to retain the Company as part of Thermo Electron's core instrument
business.

     Thermo Electron's common stock is listed on the New York Stock Exchange
under the symbol "TMO". The principal executive offices of Thermo Electron are
located at 81 Wyman Street, P.O. Box 9046, Waltham, Massachusetts 02454-9046,
and its telephone number is (781) 622-1000.

                                       48
<PAGE>   49

     Thermo Electron is subject to the disclosure requirements of the Exchange
Act and in accordance therewith is required to file reports, proxy statements
and other information with the Commission relating to its business, financial
condition and other matters. Such reports, proxy statements and other
information are available for inspection and copying at prescribed rates at the
offices of the Commission as set forth under "Certain Information Concerning The
Company." In addition, certain material filed by Thermo Electron may also be
available for inspection at the offices of the New York Stock Exchange, 20 Broad
Street, New York, New York 10005.

     The name, business address, principal occupation, five-year employment
history and citizenship of each of the directors and executive officers of
Thermo Electron are set forth in Schedule I hereto.

     During the past five years, Thermo Electron has not been convicted in a
criminal proceeding (excluding traffic violations or similar misdemeanors) or
been a party to any judicial or administrative proceeding (except for any
matters that were dismissed without sanction or settlement) that resulted in a
judgment, decree or final order enjoining Thermo Electron from future violations
of, or prohibiting activities subject to, federal or state securities laws, or a
finding of any violation of federal or state securities laws.

CERTAIN TRANSACTIONS

     Except as otherwise set forth in this Offer to Purchase, none of the
Purchaser, Corpak, Thermedics or Thermo Electron or, to the best knowledge of
the Purchaser, Corpak, Thermedics and Thermo Electron, any of the persons listed
on Schedule I hereto, has any contract, arrangement, understanding or
relationship with any other person with respect to any Shares or other
securities of the Company, including, but not limited to, any contract,
arrangement, understanding or relationship concerning the transfer or voting of
any such Shares or other securities, joint ventures, loan or option
arrangements, puts or calls, guaranties of loans, guaranties against loss or the
giving or withholding of proxies.

     PRIOR CONTACTS.  Except as set forth in this Offer to Purchase
(particularly the section entitled "Special Factors--Background To The Offer And
The Merger"), since January 1, 1998, there have been no contacts, negotiations
or transactions between the Purchaser, Corpak, Thermedics, Thermo Electron, any
subsidiary of the Purchaser, Corpak, Thermedics or Thermo Electron or, to the
best knowledge of the Purchaser, Corpak, Thermedics and Thermo Electron, any of
the persons listed on Schedule I hereto, on the one hand, and the Company or any
of its officers, directors or affiliates, on the other hand, concerning a
merger, consolidation or acquisition, a tender offer or other acquisition of
securities, an election of directors, or a sale or other transfer of a material
amount of assets, other than votes cast by Thermo Electron or Thermedics for the
election of directors of the Company in the normal course.

     PRIOR BUSINESS RELATIONSHIPS.  Except as set forth in this Offer to
Purchase, none of the Purchaser, Corpak, Thermedics or Thermo Electron or, to
the best knowledge of the Purchaser, Corpak, Thermedics or Thermo Electron, any
of the persons listed on Schedule I hereto has, since January 1, 1998, had any
business relationships or transactions with the Company or any of its executive
officers, directors or affiliates that would require disclosure herein under the
rules and regulations of the Commission applicable to the Offer or the Merger.

     INTERCOMPANY SALES AND BORROWING.  In June 1998, the Company borrowed
$21,000,000 from Thermo Electron pursuant to a promissory note due December
1998, bearing interest at the 90-day Commercial Paper Composite Rate plus 25
basis points, set at the beginning of each quarter. The Company entered into
this note in order to partially finance its acquisition of the three businesses
that constituted the product-monitoring group of Graseby Limited, a subsidiary
of Smiths Industries plc ("Graseby"), for $44,000,000 in cash, net of cash
acquired, and the assumption of certain liabilities. In December 1998, the
Company repaid $2,000,000 of this amount and issued Thermo Electron a new
promissory note for $19,000,000 in exchange for the initial note. Subsequently,
in June 1999, the Company repaid $6,000,000 of this amount and issued Thermo
Electron a new promissory note for $13,000,000 in exchange for the December 1998
note. The Company repaid an additional $1,000,000 of the amount owed under the
note in each of the third and fourth quarters of 1999. The new note is due March
2000 and bears interest at the 30-day Dealer Commercial Paper Rate plus 150
basis points, set on the second business day of each fiscal month of the
Company.
                                       49
<PAGE>   50

     MINNEAPOLIS LEASE.  The Company has entered into a fifteen-year lease
arrangement with Thermo Electron, effective as of January 1, 2000, with respect
to the Company's principal executive offices in Minneapolis, Minnesota. Thermo
Electron purchased the building in December 1999 from Baker Hughes Corporation
for $5.5 million. The rent payable by the Company to Thermo Electron under this
lease is $50,000 per month for the first five years of the lease term, $55,000
per month for the second five years of the lease term and $60,000 per month for
the third five years of the lease term.

     FINANCIAL INFORMATION.  Because the Offer Price will be paid in cash, the
Purchaser, Corpak, Thermedics and Thermo Electron do not believe that financial
information with respect to the Purchaser, Corpak, Thermedics, Thermo Electron
and their subsidiaries would be material to a stockholder's evaluation of the
Offer and the Merger. Financial information concerning Thermedics, Thermo
Electron and their subsidiaries is filed by Thermedics and Thermo Electron with
the Commission (which may be inspected and copies thereof obtained at the
offices of the Commission as set forth in "Certain Information Concerning The
Company").

                                       50
<PAGE>   51

                           SOURCE AND AMOUNT OF FUNDS

     The total amount of funds required by the Purchaser to purchase all of the
outstanding Shares pursuant to the Offer and the Merger, and to pay related fees
and expenses, is estimated to be approximately $21.3 million. The Purchaser will
obtain the funds to purchase the Shares in the Offer and the Merger from
Thermedics as a loan or capital contribution. Thermedics will use a combination
of its own working capital and borrowings from Thermo Electron to fund this loan
or capital contribution. Thermo Electron has committed to provide any required
financing to Thermedics. Any loan by Thermo Electron to Thermedics will be
evidenced by an unsecured note due September 1, 2000 that will bear interest at
a floating rate equal to the 30-day Dealer Commercial Paper Rate (the "DCP
Rate") plus 150 basis points, adjusted at the beginning of each fiscal month of
Thermedics. The interest rate of the note will be reduced to the DCP Rate plus
50 basis points to the extent of any funds invested by Thermedics'
majority-owned subsidiaries in Thermo Electron's cash management arrangement.

                                       51
<PAGE>   52

                          THE MERGER; APPRAISAL RIGHTS

THE MERGER

     Following the consummation of the Offer, subject to the terms and
conditions and in accordance with the DGCL, Thermedics plans to cause the
Purchaser to merge with and into the Company. Upon the Effective Date of the
Merger:

     - each Share issued and outstanding immediately prior to the Effective Date
       of the Merger (other than Shares held by Public Stockholders, if any, who
       are entitled to and who properly exercise their dissenters' rights (See
       "--Appraisal Rights" below) under the DGCL) will be cancelled and
       extinguished and be converted into and become a right to receive the
       Offer Price per Share; and

     - each outstanding share of the Purchaser's capital stock issued and
       outstanding immediately prior to the Effective Date of the Merger will be
       converted into one validly issued, fully paid and nonassessable share of
       common stock of the Surviving Corporation. As a result of the Merger,
       Corpak and Thermo Electron will own all of the outstanding equity
       interests in the Company.

     Under the DGCL, if the Purchaser holds at least 90% of the outstanding
Shares, the Purchaser would have the power to effect the Merger without a vote
of the Company's Board of Directors or the Company's other stockholders. The
Purchaser intends to take all necessary and appropriate action to cause the
Merger to become effective as soon as reasonably practicable after the
consummation of the Offer and without a meeting of the Company's stockholders.

APPRAISAL RIGHTS

     Stockholders who tender their Shares in the Offer are not entitled to
appraisal rights under the DGCL. If the Purchaser effects the Merger, then
Company stockholders who do not tender their Shares to the Purchaser pursuant to
the Offer would have the right to demand an appraisal of the fair value of their
Shares in accordance with the provisions of Section 262 of the DGCL ("Section
262"), which sets forth the rights and obligations of Company stockholders
demanding an appraisal and the procedures to be followed.

     Under the DGCL, record holders of the Shares who follow the procedures set
forth in Section 262 will be entitled to have their Shares appraised by the
Court of Chancery of the State of Delaware and to receive payment of the fair
value of such shares together with a fair rate of interest, if any, as
determined by such court. The fair value as determined by the Delaware court is
exclusive of any element of value arising from the accomplishment or expectation
of the Merger. The following is a summary of certain of the provisions of
Section 262 of the DGCL and is qualified in its entirety by reference to the
full text of Section 262, a copy of which is attached to this Offer to Purchase
as Schedule III.

     The Surviving Corporation would notify the Public Stockholders of record as
of the Effective Date of the Merger, and of the approval and consummation of the
Merger and the availability of appraisal rights under Section 262 within ten
days of the Effective Date of the Merger (the "Merger Notice"). Any Public
Stockholder entitled to appraisal rights would have the right, within 20 days
after the date of mailing of the Merger Notice, to demand in writing from the
Surviving Corporation an appraisal of his Shares. Such demand will be sufficient
if it reasonably informs the Surviving Corporation of the identity of the
stockholder and that the stockholder intends to demand an appraisal of the fair
value of his Shares. Failure to make such a timely demand would foreclose a
Public Stockholder's right to appraisal.

     Only a holder of record of Shares at the time of the Merger is entitled to
assert appraisal rights for the Shares registered in that holder's name. A
demand for appraisal should be executed by or on behalf of the holder of record
fully and correctly, as the holder's name appears on the holder's Share
Certificates. Holders of Shares who hold their shares in brokerage accounts or
other nominee forms and wish to exercise appraisal rights should consult with
their brokers to determine the appropriate procedures for the making of a demand
for appraisal by such nominee. All written demands for appraisal of the Shares
should be sent or delivered to Sandra L. Lambert, Secretary, Thermo Sentron
Inc., c/o Thermo Electron Corporation, 81 Wyman Street,

                                       52
<PAGE>   53

P.O. Box 9046, Waltham, Massachusetts 02454-9046, so as to be received within
the 20 days after the mailing of the Merger Notice.

     If the Shares are owned of record in a fiduciary capacity, such as by a
trustee, guardian or custodian, execution of the demand should be made in that
capacity, and if the Shares are owned of record by more than one person, as in a
joint tenancy or tenancy in common, the demand should be executed by or on
behalf of all joint owners. An authorized agent, including one or more joint
owners, may execute a demand for appraisal on behalf of a holder of record;
however, the agent must identify the record owner or owners and expressly
disclose the fact that, in executing the demand, the agent is agent for such
owner or owners.

     A record holder such as a broker holding Shares as nominee for several
beneficial owners may exercise appraisal rights with respect to the Shares held
for one or more beneficial owners while not exercising such rights with respect
to the Shares held for other beneficial owners; in such case, the written demand
should set forth the number of shares as to which appraisal is sought and where
no number of shares is expressly mentioned the demand will be presumed to cover
all Shares held in the name of the record owner.

     Within 10 calendar days after the Effective Date of the Merger, the
Surviving Corporation must send a notice as to the effectiveness of the Merger.
Within 120 calendar days after the Effective Date of the Merger, the Surviving
Corporation, or any stockholder entitled to appraisal rights under Section 262
and who has complied with the foregoing procedures, may file a petition in the
Delaware Court of Chancery demanding a determination of the fair value of the
Shares of all such stockholders. The Surviving Corporation is not under any
obligation, and has no present intention, to file a petition with respect to the
appraisal of the fair value of the Shares. Accordingly, it is the obligation of
the stockholders to initiate all necessary action to perfect their appraisal
rights within the time prescribed in Section 262.

     Within 120 calendar days after the Effective Date of the Merger, any
stockholder of record who has complied with the requirements for exercise of
appraisal rights will be entitled, upon written request, to receive from the
Surviving Corporation a statement setting forth the aggregate number of Shares
with respect to which demands for appraisal have been received and the aggregate
number of holders of such Shares. Such statement must be mailed within 10
calendar days after a written request therefor has been received by the
Surviving Corporation or within 10 calendar days after the expiration of the
period for the delivery of demands for appraisal, whichever is later.

     If a petition for an appraisal is timely filed, after a hearing on such
petition, the Delaware Court of Chancery will determine the stockholders
entitled to appraisal rights and will appraise the fair value of the Shares,
exclusive of any element of value arising from the accomplishment or expectation
of the Merger, together with a fair rate of interest, if any, to be paid upon
the amount determined to be the fair value. Holders considering seeking
appraisal should be aware that the fair value of their Shares as determined
under Section 262 could be more than, the same as or less than the amount per
share that they would otherwise receive if they did not seek appraisal of their
Shares. The Delaware Supreme Court has stated that "proof of value by any
techniques or methods that are generally considered acceptable in the financial
community and otherwise admissible in court" should be considered in the
appraisal proceedings. In addition, Delaware courts have decided that the
statutory appraisal remedy, depending on factual circumstances, may or may not
be a dissenter's exclusive remedy. The Court will also determine the amount of
interest, if any, to be paid upon the amounts to be received by persons whose
Shares have been appraised. The costs of the action may be determined by the
Court and taxed upon the parties as the Court deems equitable. The Court may
also order that all or a portion of the expenses incurred by any holder of
Shares in connection with an appraisal, including, without limitation,
reasonable attorneys' fees and the fees and expenses of experts used in the
appraisal proceeding, be charged pro rata against the value of all the Shares
entitled to appraisal.

     The Court may require stockholders who have demanded an appraisal and who
hold Shares represented by certificates to submit their certificates for Shares
to the Court for notation thereon of the pendency of the appraisal proceedings.
If any stockholder fails to comply with such direction, the Court may dismiss
the proceedings as to such stockholder.

                                       53
<PAGE>   54

     Any stockholder who has duly demanded an appraisal in compliance with
Section 262 will not, after the Effective Date of the Merger, be entitled to
vote the Shares subject to such demand for any purpose or be entitled to the
payment of dividends or other distributions on those shares (except dividends or
other distributions payable to holders of record of Shares as of a date prior to
the Effective Date of the Merger).

     If any stockholder who demands appraisal of shares under Section 262 fails
to perfect, or effectively withdraws or loses, the right to appraisal, as
provided in the DGCL, the Shares of such holder will be converted into the right
to receive the Offer Price, without interest. A stockholder will fail to
perfect, or effectively lose, the right to appraisal if no petition is filed
within 120 calendar days after the Effective Date of the Merger. A stockholder
may withdraw a demand for appraisal by delivering to the Surviving Corporation a
written withdrawal of the demand for appraisal and acceptance of the Merger,
except that any such attempt to withdraw made more than 60 calendar days after
the Effective Date of the Merger will require the written approval of the
Surviving Corporation. Once a petition for appraisal has been filed, such
appraisal proceeding may not be dismissed as to any stockholder without the
approval of the Court.

     For federal income tax purposes, stockholders who receive cash for their
Shares upon exercise of Dissenters' Rights will realize taxable gain or loss.
See "Federal Income Tax Consequences."

     THE FOREGOING SUMMARY DOES NOT PURPORT TO BE A COMPLETE STATEMENT OF THE
PROCEDURES TO BE FOLLOWED BY STOCKHOLDERS DESIRING TO EXERCISE THEIR DISSENTING
APPRAISAL RIGHTS AND IS QUALIFIED IN ITS ENTIRETY BY EXPRESS REFERENCE TO THE
DELAWARE APPRAISAL STATUTE, THE FULL TEXT OF WHICH IS ATTACHED HERETO AS
SCHEDULE III. STOCKHOLDERS ARE URGED TO READ SCHEDULE III IN ITS ENTIRETY SINCE
FAILURE TO COMPLY WITH THE PROCEDURES SET FORTH THEREIN WILL RESULT IN THE LOSS
OF APPRAISAL RIGHTS.

                                       54
<PAGE>   55

                               FEES AND EXPENSES

     The Advisors are acting as financial advisors to Thermedics and Thermo
Electron in connection with the Offer and the Merger. The Advisors are also
acting as Dealer Managers in connection with the Offer. For a discussion of the
fees to be paid to the Advisors in connection with Offer and the Merger, see
"Special Factors--Summary Of The Advisors' Analysis and Opinion."

     The Purchaser has retained D.F. King & Co., Inc. to act as the Information
Agent and American Stock Transfer & Trust Company to act as the Depositary in
connection with the Offer. The Information Agent may contact holders of Shares
by mail, telephone, telex, telecopy, telegraph and personal interview and may
request brokers, dealers, commercial banks, trust companies and other nominees
to forward the Offer material to beneficial owners. Each of the Information
Agent and the Depositary will receive reasonable and customary compensation for
its services and will be reimbursed for certain reasonable out-of-pocket
expenses and will be indemnified against certain liabilities and expenses in
connection with the Offer, including certain liabilities under U.S. federal
securities laws.

     The Purchaser will not pay any fees or commissions to any broker or dealer
or any other person for soliciting tenders of Shares pursuant to the Offer
(other than to the Dealer Managers and the Information Agent). Brokers, dealers,
commercial banks and trust companies will, upon request, be reimbursed by the
Purchaser for customary mailing and handling expenses incurred by them in
forwarding materials to their customers.

     The following is an estimate of fees and expenses to be incurred by the
Purchaser in connection with the Offer:

<TABLE>
<S>                                                           <C>
Financial Advisors..........................................  $1,000,000
Legal.......................................................     250,000
Printing....................................................     100,000
Advertising.................................................      25,000
Filing......................................................       6,367
Depositary..................................................       7,500
Information Agent (including mailing).......................      12,000
Miscellaneous...............................................      99,133
                                                              ----------
                                                              $1,500,000
                                                              ==========
</TABLE>

     The Company will not pay any of the fees and expenses to be incurred by the
Purchaser in connection with the Offer.

                                       55
<PAGE>   56

                                 MISCELLANEOUS

     The Offer is being made solely by this Offer to Purchase and the related
Letter of Transmittal and is being made to all holders of Shares. The Offer is
not being made to (nor will tenders be accepted from or on behalf of) holders of
Shares in any jurisdiction in which the making of the Offer or the acceptance
thereof would not be in compliance with the laws of such jurisdiction. In any
jurisdiction where the securities, blue sky or other laws require the Offer to
be made by a licensed broker or dealer, the Offer shall be deemed to be made on
behalf of the Purchaser by the Dealer Managers or one or more registered brokers
or dealers licensed under the laws of such jurisdiction.

     Thermo Electron, Thermedics, Corpak and the Purchaser have filed with the
Commission a Schedule TO together with exhibits, pursuant to Rule 14d-3 and Rule
13e-3 promulgated by the Commission under the Exchange Act, furnishing certain
additional information with respect to the Offer. Such statement and any
amendments thereto, including exhibits, may be examined and copies may be
obtained at the same places and in the same manner as set forth with respect to
information about the Company in "Certain Information Concerning The Company"
(except that such statement and amendments may not be available in the regional
offices of the Commission).

     NO PERSON HAS BEEN AUTHORIZED TO GIVE ANY INFORMATION OR MAKE ANY
REPRESENTATION ON BEHALF OF THE PURCHASER NOT CONTAINED HEREIN OR IN THE LETTER
OF TRANSMITTAL AND, IF GIVEN OR MADE, SUCH INFORMATION OR REPRESENTATION MUST
NOT BE RELIED ON AS HAVING BEEN AUTHORIZED.

March 3, 2000

                                       56
<PAGE>   57

                                   SCHEDULE I

                     MEMBERS OF THE BOARDS OF DIRECTORS AND
          EXECUTIVE OFFICERS OF THE PURCHASER, CORPAK, THERMEDICS AND
                                THERMO ELECTRON

DIRECTOR AND EXECUTIVE OFFICER OF THE PURCHASER

     Mr. John T. Keiser is the president and sole director of the Purchaser.
Biographical and other information with respect to Mr. Keiser is set forth below
under "--Directors and Executive Officers of Thermedics."

DIRECTORS AND EXECUTIVE OFFICERS OF CORPAK

     The name, business address, position with Corpak, present principal
occupation or employment and five-year employment history of each of the
directors and executive officers of Corpak, together with the names, principal
businesses and addresses of any corporations or other organizations in which
such principal occupations are conducted, are set forth below. Unless otherwise
indicated, each occupation set forth refers to Corpak, each individual is a
United States citizen and each individual's business address is 81 Wyman Street,
Waltham, Massachusetts 02454. Unless otherwise indicated, to the knowledge of
each of the Purchaser, Corpak, Thermedics and Thermo Electron, no director or
executive officer of Corpak beneficially owns any Shares (or rights to acquire
Shares). Unless otherwise indicated, to the knowledge of each of the Purchaser,
Corpak, Thermedics and Thermo Electron, no director or executive officer of
Corpak has been convicted in a criminal proceeding during the last five years
(excluding traffic violations or similar misdemeanors) and no director or
executive officer of Corpak was a party to any judicial or administrative
proceeding during the last five years (except for any matters that were
dismissed without sanction or settlement) that resulted in a judgement, decree
or final order enjoining the person from future violations of, or prohibiting
activities subject to, federal or state securities laws, or a finding of any
violation of federal or state securities laws.

JOHN T. KEISER               Mr. Keiser, 64, has been a director and chairman of
                             the board of Corpak since March 1998. Biographical
                             and other information with respect to Mr. Keiser is
                             set forth below under "--Directors and Executive
                             Officers of Thermedics."

THOMAS I. KUHN               Mr. Kuhn, 45, has been a director of Corpak since
                             May 1996 and its president and chief operating
                             officer since August 1992. Mr. Kuhn's business
                             address is 100 Chaddick Drive, Wheeling, IL 60090.

     STOCK OWNERSHIP.  The following table sets forth the beneficial ownership
of common stock of the Company, as well as the common stock of Thermedics and
Thermo Electron, as of January 31, 2000, with respect to each director and
executive officer of Corpak. No director or executive officer of Corpak
beneficially owns any shares of capital stock of the Purchaser or Corpak. While
certain directors and executive officers of Corpak are also directors and
executive officers of Thermo Electron or its subsidiaries, all such persons
disclaim beneficial ownership of the shares of common stock beneficially owned
by Thermo Electron.

<TABLE>
<CAPTION>
                                                      THERMO                              THERMO ELECTRON
NAME(1)                                           SENTRON INC.(2)   THERMEDICS INC.(3)    CORPORATION(4)
<S>                                               <C>               <C>                   <C>
John T. Keiser................................        19,500             194,693              331,636
Thomas I. Kuhn................................             0              38,941                5,626
All directors and current executive officers
  as a group (2 persons)......................        19,500             233,634              337,262
</TABLE>

- ---------------
(1) Except as reflected in the footnotes to this table, shares beneficially
    owned consist of shares owned by the indicated person or by that person for
    the benefit of minor children, and all share ownership includes sole voting
    and investment power.

(2) Shares of the common stock of the Company beneficially owned by Mr. Keiser
    and all directors and current executive officers as a group include 19,500
    and 19,500 shares, respectively, that such person or

                                       I-1
<PAGE>   58

    group has the right to acquire within 60 days of January 31, 2000 through
    the exercise of stock options. No director or current executive officer
    beneficially owned more than 1% of the Company's common stock outstanding as
    of January 31, 2000; all directors and current executive officers as a group
    beneficially owned less than 1% of such common stock outstanding as of such
    date.

(3) Shares of the common stock of Thermedics beneficially owned by Mr. Keiser,
    Mr. Kuhn and all directors and current executive officers as a group include
    187,900, 34,100 and 222,000 shares, respectively, that such person or group
    had the right to acquire within 60 days of January 31, 2000 through the
    exercise of stock options. No director or current executive officer
    beneficially owned more than 1% of the Thermedics common stock outstanding
    as of January 31, 2000; all directors and current executive officers as a
    group beneficially owned less than 1% of such common stock outstanding as of
    such date.

(4) Shares of the common stock of Thermo Electron beneficially owned by Mr.
    Keiser, Mr. Kuhn and all directors and current executive officers as a group
    include 263,230, 4,950 and 268,180 shares, respectively, that such person or
    group has the right to acquire within 60 days of January 31, 2000 through
    the exercise of stock options. No director or current executive officer
    beneficially owned more than 1% of the Thermo Electron common stock
    outstanding as of January 31, 2000; all directors and current executive
    officers as a group beneficially owned less than 1% of such common stock
    outstanding as of such date.

DIRECTORS AND EXECUTIVE OFFICERS OF THERMEDICS

     The name, business address, position with Thermedics, present principal
occupation or employment and five-year employment history of each of the
directors and executive officers of Thermedics, together with the names,
principal businesses and addresses of any corporations or other organizations in
which such principal occupations are conducted, are set forth below. Unless
otherwise indicated, each occupation set forth refers to Thermedics, each
individual is a United States citizen and each individual's business address is
81 Wyman Street, Waltham, Massachusetts 02454. Unless otherwise indicated, to
the knowledge of each of the Purchaser, Corpak, Thermedics and Thermo Electron,
no director or executive officer of Thermedics beneficially owns any Shares (or
rights to acquire Shares). Unless otherwise indicated, to the knowledge of each
of the Purchaser, Corpak, Thermedics and Thermo Electron, no director or
executive officer of Thermedics has been convicted in a criminal proceeding
during the last five years (excluding traffic violations or similar
misdemeanors) and no director or executive officer of Thermedics was a party to
any judicial or administrative proceeding during the last five years (except for
any matters that were dismissed without sanction or settlement) that resulted in
a judgement, decree or final order enjoining the person from future violations
of, or prohibiting activities subject to, federal or state securities laws, or a
finding of any violation of federal or state securities laws. Mr. John N.
Hatsopoulos resigned from the Boards of Directors of Thermedics and Thermo
Electron on February 21, 2000.

T. ANTHONY BROOKS            Mr. Brooks, 60, has been a director of Thermedics
                             since September 1998. Mr. Brooks was a managing
                             director and member of the operating committee of
                             Lehman Brothers Inc., a financial services firm
                             located at 3 World Financial Center, New York, NY
                             10285 from 1991 until his retirement in 1997. While
                             at Lehman Brothers Inc., Mr. Brooks was the head of
                             the European equity division from 1995 to 1996.

PETER O. CRISP               Mr. Crisp, 67, has been a director of Thermedics
                             since 1983. Mr. Crisp was a general partner of
                             Venrock Associates, a venture capital investment
                             firm located at 30 Rockefeller Plaza, New York, NY
                             10112, for more than five years until his
                             retirement in September 1997. He has been the vice
                             chairman of Rockefeller Financial Services, Inc.
                             since December 1997. Mr. Crisp is also a director
                             of American Superconductor Corporation, Evans &
                             Sutherland Computer Corporation, Thermo Electron,
                             ThermoTrex Corporation and United States Trust
                             Corporation.

PAUL F. FERRARI              Mr. Ferrari, 69, has been a director of Thermedics
                             since 1991. Mr. Ferrari was a vice president of
                             Thermo Electron from 1988 until his

                                       I-2
<PAGE>   59

                             retirement at the end of 1990. Mr. Ferrari is also
                             a director of General Scanning Inc. and ThermoTrex
                             Corporation.

GEORGE N. HATSOPOULOS        Dr. Hatsopoulos, 73, has been a director of
                             Thermedics since 1983. He served as president,
                             chief executive officer and chairman of the board
                             of Thermo Electron from 1956 until January 1997,
                             June 1999 and January 2000, respectively. Dr.
                             Hatsopoulos is also a director of Photoelectron
                             Corporation, Thermo Ecotek Corporation, Thermo
                             Electron, Thermo Fibertek Inc., Thermo Instrument
                             Systems Inc. and ThermoTrex Corporation.

JOHN T. KEISER               Mr. Keiser, 64, has been a director of Thermedics
                             since April 1997. He has been the president and
                             chief executive officer of Thermedics since March
                             1998 and December 1998, respectively. From 1994
                             until March 1998, Mr. Keiser served as a senior
                             vice president of Thermedics. Mr. Keiser has been
                             the chief operating officer, biomedical, of Thermo
                             Electron since September 1998, and a vice president
                             from April 1997 until his promotion. He has also
                             been the president of Thermo Electron's wholly
                             owned biomedical group, a manufacturer of medical
                             equipment and instruments, since 1994. Mr. Keiser
                             is a director of Metrika Systems Corporation,
                             Thermedics Detection Inc., Thermo Cardiosystems
                             Inc., ThermoLase Corporation, the Company,
                             ThermoTrex Corporation and Trex Medical
                             Corporation.

RICHARD F. SYRON             Dr. Syron, 56, has been a director of Thermedics
                             since June 1999. He has been the president and
                             chief executive officer of Thermo Electron since
                             June 1999 and has been chairman of the board since
                             January 2000. From April 1994 until May 1999, Dr.
                             Syron was the chairman and chief executive officer
                             of the American Stock Exchange Inc. located at 86
                             Trinity Place, New York, NY 10006-1881. Dr. Syron
                             is also a director of Dreyfus Corporation, John
                             Hancock Life Insurance Company, John Hancock
                             Financial Services, Inc., Thermo Electron, Thermo
                             Fibertek Inc. and Thermo Instrument Systems Inc.

JOHN W. WOOD JR.             Mr. Wood, 56, has been a director of Thermedics
                             since 1984 and chairman of the board since March
                             1998. Mr. Wood was president and chief executive
                             officer of Thermedics from 1984 to March 1998. Mr.
                             Wood has been a senior vice president of Thermo
                             Electron since December 1995, and, prior to that
                             promotion, was a vice president of Thermo Electron
                             from September 1994 to December 1995.

NICHOLAS T. ZERVAS           Dr. Zervas, 70, has been a director of Thermedics
                             since 1987. Dr. Zervas has been Chief of
                             Neurosurgical Service, Massachusetts General
                             Hospital, located at 55 Fruit Street, Boston, MA
                             02114, since 1977. Dr. Zervas is also a director of
                             Thermo Cardiosystems Inc., ThermoLase Corporation
                             and ThermoTrex Corporation.

PAUL F. KELLEHER             Mr. Kelleher, 57, has been the chief accounting
                             officer of Thermedics since March 1986. Mr.
                             Kelleher also has served as the senior vice
                             president, finance and administration, of Thermo
                             Electron since June 1997, and served as its vice
                             president, finance from 1987 until 1997. Mr.
                             Kelleher served as Thermo Electron's controller
                             from 1982 until January 1996. Mr. Kelleher is a
                             director of ThermoLase Corporation.

THEO MELAS-KYRIAZI           Mr. Melas-Kyriazi, 40, has been the chief financial
                             officer of Thermedics since January 1999. Mr.
                             Melas-Kyriazi also has served as a vice

                                       I-3
<PAGE>   60

                             president of Thermo Electron since March 1998 and
                             its chief financial officer since January 1999.
                             Prior to his appointment as a vice president of
                             Thermo Electron, Mr. Melas-Kyriazi served as
                             president and chief executive officer of
                             ThermoSpectra Corporation from its inception in
                             August 1994 until March 1998. He is a director of
                             ThermoRetec Corporation. Mr. Melas-Kyriazi is a
                             citizen of Greece.

VICTOR L. POIRIER            Mr. Poirier, 58, has been a senior vice president
                             of Thermedics since 1985. He has also been
                             president and chief technical officer of Thermo
                             Cardiosystems Inc., a majority-owned subsidiary of
                             Thermedics located at 470 Wildwood Street, Woburn,
                             Massachusetts 01888-2697 since 1990 and 1999,
                             respectively, and was its chief executive officer
                             from 1991 to November 1998.

     STOCK OWNERSHIP.  The following table sets forth the beneficial ownership
of common stock of the Company, as well as the common stock of Thermedics and
Thermo Electron, as of January 31, 2000, with respect to each director and
executive officer of Thermedics. No director or executive officer of Thermedics
beneficially owns any shares of capital stock of the Purchaser or Corpak. While
certain directors and executive officers of Thermedics are also directors and
executive officers of Thermo Electron or its subsidiaries, all such persons
disclaim beneficial ownership of the shares of common stock beneficially owned
by Thermo Electron.

<TABLE>
<CAPTION>
                                                      THERMO                              THERMO ELECTRON
NAME(1)                                           SENTRON INC.(2)   THERMEDICS INC.(3)    CORPORATION(4)
<S>                                               <C>               <C>                   <C>
T. Anthony Brooks.............................              0              5,367                     0
Peter O. Crisp................................              0             37,076               106,767
Paul F. Ferrari...............................              0             11,050                16,482
George N. Hatsopoulos.........................         17,000             63,681             3,909,357
John T. Keiser................................         19,500            194,693               331,636
Paul F. Kelleher..............................          5,000             20,360               213,530
Theo Melas-Kyriazi............................              0             11,861               458,532
Victor L. Poirier.............................          7,500             69,455                53,880
Richard F. Syron..............................              0                  0             1,074,006
John W. Wood Jr...............................         35,000            233,200               293,550
Nicholas T. Zervas............................              0             22,064                     0
All directors and current executive officers
  as a group (11 persons).....................         84,000            668,807             6,457,740
</TABLE>

- ---------------
(1) Except as reflected in the footnotes to this table, shares beneficially
    owned consist of shares owned by the indicated person or by that person for
    the benefit of minor children, and all share ownership includes sole voting
    and investment power.

(2) Shares of the common stock of the Company beneficially owned by Dr.
    Hatsopoulos, Mr. Keiser, Mr. Kelleher, Mr. Poirier, Mr. Wood and all
    directors and current executive officers as a group include 15,000, 19,500,
    5,000, 7,500, 31,000 and 78,000 shares, respectively, that such person or
    group has the right to acquire within 60 days of January 31, 2000 through
    the exercise of stock options. No director or current executive officer
    beneficially owned more than 1% of the Company's common stock outstanding as
    of January 31, 2000; all directors and current executive officers as a group
    beneficially owned less than 1% of such common stock outstanding as of such
    date.

(3) Shares of the Thermedics common stock beneficially owned by Mr. Brooks, Mr.
    Crisp, Mr. Ferrari, Mr. Keiser, Mr. Kelleher, Mr. Poirier, Mr. Wood, and all
    directors and current executive officers as a group include 1,000, 9,000,
    8,950, 187,900, 10,000, 25,000, 174,150 and 416,000 shares, respectively,
    that such person or group had the right to acquire within 60 days of January
    31, 2000 through the exercise of stock options. Shares beneficially owned by
    Dr. Hatsopoulos, Mr. Kelleher, Mr. Melas-Kyriazi and all directors and
    current executive officers as a group include 1,635, 1,294, 1,119 and 4,048
    shares,

                                       I-4
<PAGE>   61

    respectively, allocated through January 31, 2000 to their respective
    accounts maintained pursuant to Thermo Electron's employee stock ownership
    plan (the "ESOP"), of which the trustees, who have investment power over its
    assets, are executive officers of Thermo Electron. Shares beneficially owned
    by Mr. Brooks, Mr. Crisp, Dr. Zervas and all directors and current executive
    officers as a group include 1,367, 9,971, 10,364 and 21,702 shares,
    respectively, that had been allocated through January 1, 2000 to their
    respective accounts maintained under the Deferred Compensation Plan. Shares
    beneficially owned by Dr. Hatsopoulos include 654 shares held by Dr.
    Hatsopoulos' spouse and 50,000 shares that a family limited partnership
    indirectly controlled by Dr. Hatsopoulos has the right to acquire within 60
    days of January 31, 2000 through the exercise of stock options. Dr.
    Hatsopoulos disclaims beneficial interest in the shares owned by the family
    limited partnership except to the extent of his pecuniary interest therein.
    Shares beneficially owned by Mr. Wood include 2,600 shares held in custodial
    accounts for the benefit of two minor children. No director or current
    executive officer beneficially owned more than 1% of the Thermedics common
    stock outstanding as of January 31, 2000; all directors and current
    executive officers as a group beneficially owned 1.59% of the Thermedics
    common stock outstanding as of such date.

(4) Shares of the common stock of Thermo Electron beneficially owned by Mr.
    Crisp, Dr. Hatsopoulos, Mr. Keiser, Mr. Kelleher, Mr. Melas-Kyriazi, Mr.
    Poirier, Dr. Syron, Mr. Wood and all directors and current executive
    officers as a group include 10,596, 25,448, 263,230, 179,359, 384,361,
    46,123, 1,011,000, 249,298 and 2,169,415 shares, respectively, that such
    person or group has the right to acquire within 60 days of January 31, 2000
    through the exercise of stock options. Shares beneficially owned by Dr.
    Hatsopoulos, Mr. Kelleher, Mr. Melas-Kyriazi and all directors and current
    executive officers as a group include 2,266, 1,426, 1,071 and 4,763 shares,
    respectively, allocated to their respective accounts maintained pursuant to
    Thermo Electron's ESOP, of which the trustees, who have investment power
    over its assets, are executive officers of Thermo Electron. Shares
    beneficially owned by Mr. Crisp, Dr. Syron and all directors and current
    executive officers as a group each include 49,277, 2,506 and 51,783 shares
    allocated through January 1, 2000 to their respective accounts maintained
    pursuant to Thermo Electron's deferred compensation plan for directors.
    Shares beneficially owned by Dr. Hatsopoulos include 144,437 shares held by
    his spouse, 311,708 shares held by a family trust of which his spouse is the
    trustee and 566,262 shares held by a family limited partnership indirectly
    controlled by Dr. Hatsopoulos. Shares beneficially owned by Dr. Hatsopoulos
    also include 50,000 shares that a family trust, of which Dr. Hatsopoulos'
    spouse is the trustee, has the right to acquire within 60 days of January
    31, 2000 and 2,149,500 shares that a family limited partnership indirectly
    controlled by Dr. Hatsopoulos has the right to acquire within 60 days of
    January 31, 2000 through the exercise of stock options. Dr. Hatsopoulos
    disclaims beneficial interest in the shares owned by the family limited
    partnership except to the extent of his pecuniary interest therein. Except
    for Dr. Hatsopoulos, who beneficially owned 2.44% of the Thermo Electron
    common stock outstanding as of January 31, 2000, no director or current
    executive officer beneficially owned more than 1% of such common stock
    outstanding as of such date; all directors and current executive officers as
    a group beneficially owned approximately 4.08% of the Thermo Electron common
    stock outstanding as of such date.

DIRECTORS AND EXECUTIVE OFFICERS OF THERMO ELECTRON

     The name, business address, position with Thermo Electron, present
principal occupation or employment and five-year employment history of each of
the directors and executive officers of Thermo Electron, together with the
names, principal businesses and addresses of any corporations or other
organizations in which such principal occupations are conducted, are set forth
below. Unless otherwise indicated, each occupation set forth refers to Thermo
Electron, each individual is a United States citizen and each individual's
business address is 81 Wyman Street, Waltham, Massachusetts 02454. Unless
otherwise indicated, to the knowledge of each of the Purchaser, Corpak,
Thermedics and Thermo Electron, no director or executive officer of Thermo
Electron beneficially owns any Shares (or rights to acquire Shares). Unless
otherwise indicated, to the knowledge of each of the Purchaser, Corpak,
Thermedics and Thermo Electron, no director or executive officer of Thermo
Electron has been convicted in a criminal proceeding during the last five years
(excluding traffic violations or similar misdemeanors) and no director or
executive officer of Thermo Electron was a party to any judicial or
administrative proceeding during the last five years (except for any matters
that were dismissed without

                                       I-5
<PAGE>   62

sanction or settlement) that resulted in a judgement, decree or final order
enjoining the person from future violations of, or prohibiting activities
subject to, federal or state securities laws, or a finding of any violation of
federal or state securities laws. Mr. John N. Hatsopoulos resigned from the
Boards of Directors of Thermedics and Thermo Electron on February 21, 2000.

SAMUEL W. BODMAN             Mr. Bodman, 61, has been a director of Thermo
                             Electron since May 1999. Since 1988, Mr. Bodman has
                             served as the chairman and chief executive officer
                             of Cabot Corporation, a manufacturer of specialty
                             chemicals and materials located at 75 State Street,
                             Boston, MA 02109. Mr. Bodman is also a director of
                             Cabot Corporation, John Hancock Life Insurance
                             Company, John Hancock Financial Services, Inc.,
                             Security Capital Group Incorporated and Westvaco
                             Corporation.

PETER O. CRISP               Mr. Crisp, 67, has been a director of Thermo
                             Electron since 1974. Mr. Crisp was a general
                             partner of Venrock Associates, a venture capital
                             investment firm located at 30 Rockefeller Plaza,
                             New York, NY 10112, for more than five years until
                             his retirement in September 1997. He has been the
                             vice chairman of Rockefeller Financial Services,
                             Inc. since December 1997. Mr. Crisp is also a
                             director of American Superconductor Corporation,
                             Evans & Sutherland Computer Corporation, NovaCare
                             Inc., Thermedics, ThermoTrex Corporation and United
                             States Trust Corporation.

ELIAS P. GYFTOPOULOS         Dr. Gyftopoulos, 72, has been a director of Thermo
                             Electron since 1976. Dr. Gyftopoulos is Professor
                             Emeritus of the Massachusetts Institute of
                             Technology, where he was the Ford Professor of
                             Mechanical Engineering and of Nuclear Engineering
                             for more than 20 years until his retirement in
                             1996. Dr. Gyftopoulos is also a director of Thermo
                             BioAnalysis Corporation, Thermo Cardiosystems Inc.,
                             ThermoLase Corporation, ThermoRetec Corporation and
                             Trex Medical Corporation.

GEORGE N. HATSOPOULOS        Dr. Hatsopoulos, 73, has been a director of Thermo
                             Electron since he founded Thermo Electron in 1956.
                             He served as president, chief executive officer and
                             chairman of the board of Thermo Electron from 1956
                             until January 1997, June 1999 and January 2000,
                             respectively. Dr. Hatsopoulos is also a director of
                             Photoelectron Corporation, Thermedics, Thermo
                             Ecotek Corporation, Thermo Fibertek Inc., Thermo
                             Instrument Systems Inc. and ThermoTrex Corporation.

FRANK JUNGERS                Mr. Jungers, 73, has been a director of Thermo
                             Electron since 1978. Mr. Jungers has been a
                             consultant on business and energy matters since
                             1977. His business address is 822 N.W. Murray
                             Boulevard, Suite 242, Portland, OR 97229. Mr.
                             Jungers is also a director of The AES Corporation,
                             Donaldson, Lufkin & Jenrette, Inc., Georgia-Pacific
                             Corporation, ONIX Systems Inc., Statia Terminals
                             Group N.V., Thermo Ecotek Corporation and
                             ThermoQuest Corporation.

ROBERT A. MCCABE             Mr. McCabe, 65, has been a director of Thermo
                             Electron since 1962. He has been the chairman of
                             Pilot Capital Corporation, located at 444 Madison
                             Avenue, Suite 2103, New York, NY 10022, which is
                             engaged in private investments, since 1998. Mr.
                             McCabe was the president of Pilot Capital
                             Corporation from 1987 to 1998. Mr. McCabe is also a
                             director of Atlantic Bank & Trust Company, Burns
                             International Services Corporation, Church & Dwight
                             Company and Thermo Optek Corporation.

                                       I-6
<PAGE>   63

HUTHAM S. OLAYAN             Ms. Olayan, 46, has been a director of Thermo
                             Electron since 1987. She has served since 1995 as
                             president and a director of Olayan America
                             Corporation, a member of the Olayan Group, and as
                             president and a director of Competrol Real Estate
                             Limited, another member of the Olayan Group, from
                             1986 until its merger into Olayan America
                             Corporation in 1997. The surviving company, which
                             is located at 505 Park Avenue, Suite 1100, New
                             York, NY 10022, is engaged in private investments,
                             including real estate, and advisory services. Ms.
                             Olayan is also a director of Trex Medical
                             Corporation. Ms. Olayan is a citizen of Saudi
                             Arabia.

ROBERT W. O'LEARY            Mr. O'Leary, 56, has been a director of Thermo
                             Electron since June 1998. He has been the president
                             and chairman of Premier, Inc., a strategic alliance
                             of not-for-profit health care and hospital systems
                             located at 12225 El Camino Real, San Diego, CA
                             92130, since 1995. Mr. O'Leary is also a director
                             of Eco Soil Systems, Inc.

RICHARD F. SYRON             Dr. Syron, 56, has been a director of Thermo
                             Electron since September 1997, its president and
                             chief executive officer since June 1999 and
                             chairman of the board since January 2000. From
                             April 1994 until May 1999, Dr. Syron was the
                             chairman and chief executive officer of the
                             American Stock Exchange Inc. located at 86 Trinity
                             Place, New York, NY 10006-1881. Dr. Syron is also a
                             director of Dreyfus Corporation, John Hancock Life
                             Insurance Company, John Hancock Financial Services,
                             Inc., Thermedics, Thermo Fibertek Inc. and Thermo
                             Instrument Systems Inc.

ROGER D. WELLINGTON          Mr. Wellington, 73, has been a director of Thermo
                             Electron since 1986. Mr. Wellington serves as the
                             president and chief executive officer of Wellington
                             Consultants, Inc. and Wellington Associates Inc.,
                             international business consulting firms he founded
                             in 1994 and 1989, respectively, each of which is
                             located at P.O. Box 8186, 5555 Gulf of Mexico
                             Drive, Unit 302, Longboat Key, FL 34228. Mr.
                             Wellington is also a director of Photoelectron
                             Corporation and Thermo Fibergen Inc.

BRIAN D. HOLT                Mr. Holt, 51, became the chief operating officer,
                             energy and environment, of Thermo Electron in
                             September 1998. Mr. Holt has been the president and
                             chief executive officer of Thermo Ecotek
                             Corporation, a majority-owned subsidiary of Thermo
                             Electron located at 245 Winter Street, Waltham, MA
                             02451, that is involved in clean-power resources,
                             clean fuels, and naturally derived products for
                             protecting crops since February 1994. From March
                             1996 to September 1998, he was a vice president of
                             Thermo Electron. Mr. Holt is also a director of The
                             Randers Killam Group Inc., Thermo Ecotek
                             Corporation, ThermoRetec Corporation and Thermo
                             TerraTech Inc.

JOHN T. KEISER               Mr. Keiser, 64, became chief operating officer,
                             biomedical, of Thermo Electron in September 1998
                             and was a vice president from April 1997 until his
                             promotion. Mr. Keiser has been the president and
                             chief executive officer of Thermedics since March
                             1998 and December 1998, respectively, and served as
                             a senior vice president of Thermedics from 1994
                             until his promotion to president. He has also been
                             the president of Thermo Electron's wholly owned
                             biomedical group, a manufacturer of medical
                             equipment and instruments, since 1994. Mr. Keiser
                             is a director of Metrika Systems Corporation,
                             Thermedics, Thermedics Detection

                                       I-7
<PAGE>   64

                             Inc., Thermo Cardiosystems Inc., ThermoLase
                             Corporation, the Company, ThermoTrex Corporation
                             and Trex Medical Corporation.

PAUL F. KELLEHER             Mr. Kelleher, 57, has been the senior vice
                             president, finance and administration, of Thermo
                             Electron since June 1997, and served as its vice
                             president, finance from 1987 until 1997. Mr.
                             Kelleher served as Thermo Electron's controller
                             from 1982 until January 1996. Mr. Kelleher is a
                             director of ThermoLase Corporation.

EARL R. LEWIS                Mr. Lewis, 56, became chief operating officer,
                             measurement and detection, of Thermo Electron in
                             September 1998, and served as senior vice president
                             of Thermo Electron from June 1998 to September 1998
                             and vice president from September 1996 to June
                             1998. Mr. Lewis has been president and chief
                             executive officer of Thermo Instrument Systems
                             Inc., a manufacturer of measurement and detection
                             instruments, since March 1997 and January 1998,
                             respectively, and was chief operating officer from
                             January 1996 to January 1998. Prior to that time,
                             he was executive vice president of Thermo
                             Instrument Systems Inc. from January 1996 to March
                             1997 and senior vice president from January 1994 to
                             January 1996. Mr. Lewis served as chief executive
                             officer of Thermo Optek Corporation, a
                             majority-owned subsidiary of Thermo Instrument
                             Systems Inc. and a manufacturer of analytical
                             instruments that measure energy and light for
                             purposes of materials analysis, characterization
                             and preparation, from its inception in August 1995
                             to January 1998. Mr. Lewis is a director of FLIR
                             Systems Inc., Metrika Systems Corporation, ONIX
                             Systems Inc., SpectRx Inc., Spectra-Physics Lasers,
                             Inc., Thermo BioAnalysis Corporation, Thermo
                             Instrument Systems Inc., Thermo Optek Corporation
                             and ThermoQuest Corporation.

THEO MELAS-KYRIAZI           Mr. Melas-Kyriazi, 40, has been a vice president of
                             Thermo Electron since March 1998 and its chief
                             financial officer since January 1999. Prior to his
                             appointment as a vice president of Thermo Electron,
                             Mr. Melas-Kyriazi served as president and chief
                             executive officer of ThermoSpectra Corporation from
                             its inception in August 1994 until March 1998. He
                             is a director of ThermoRetec Corporation. Mr.
                             Melas-Kyriazi is a citizen of Greece.

WILLIAM A. RAINVILLE         Mr. Rainville, 58, became chief operating officer,
                             recycling and resource recovery, of Thermo Electron
                             in September 1998. Mr. Rainville was a senior vice
                             president of Thermo Electron from March 1993 to
                             September 1998, and a vice president of Thermo
                             Electron from 1986 to 1993. He has been president
                             and chief executive officer of Thermo Fibertek
                             Inc., a majority-owned subsidiary of Thermo
                             Electron located at 245 Winter Street, Waltham, MA
                             02451 that develops and manufactures equipment and
                             products for the papermaking and paper-recycling
                             industries, since its inception in 1991. Mr.
                             Rainville is also a director of Thermo Ecotek
                             Corporation, Thermo Fibergen Inc., Thermo Fibertek
                             Inc., ThermoRetec Corporation and Thermo TerraTech
                             Inc.

     STOCK OWNERSHIP.  The following table sets forth the beneficial ownership
of common stock of the Company, as well as the common stock of Thermedics and
Thermo Electron, as of January 31, 2000, with respect to each director and
executive officer of Thermo Electron. No director or executive officer of Thermo
Electron beneficially owns any shares of capital stock of the Purchaser or
Corpak. The directors and executive

                                       I-8
<PAGE>   65

officers of Thermo Electron disclaim beneficial ownership of the shares of
common stock beneficially owned by Thermo Electron.

<TABLE>
<CAPTION>
                                                      THERMO          THERMEDICS        THERMO ELECTRON
NAME(1)                                           SENTRON INC.(2)       INC.(3)          CORPORATION(4)
<S>                                               <C>               <C>                <C>
Samuel W. Bodman..............................             0                  0               12,599
Peter O. Crisp................................             0             37,076              106,767
Elias P. Gyftopoulos..........................             0              8,298               76,399
George N. Hatsopoulos.........................        17,000             63,681            3,909,357
Brian D. Holt.................................         2,000                  0              322,941
Frank Jungers.................................             0              3,000              156,021
John T. Keiser................................        19,500            194,693              331,636
Paul F. Kelleher..............................         5,000             20,360              213,530
Earl R. Lewis.................................         2,000                  0              215,477
Robert A. McCabe..............................         2,000              2,498               51,326
Theo Melas-Kyriazi............................             0             11,861              458,532
Hutham S. Olayan..............................             0                  0               34,568
Robert W. O'Leary.............................             0                  0               28,830
William A. Rainville..........................         7,000                  0              361,499
Richard F. Syron..............................             0                  0            1,074,006
Roger D. Wellington...........................             0                  0               40,795
All directors and current executive officers
  as a group (16 persons).....................        54,500            341,467            7,394,283
</TABLE>

- ---------------
(1) Except as reflected in the footnotes to this table, shares beneficially
    owned consist of shares owned by the indicated person or by that person for
    the benefit of minor children, and all share ownership includes sole voting
    and investment power.

(2) Shares of the common stock of the Company beneficially owned by Dr.
    Hatsopoulos, Mr. Holt, Mr. Keiser, Mr. Kelleher, Mr. Lewis, Mr. Rainville
    and all directors and current executive officers as a group include 15,000,
    2,000, 19,500, 5,000, 2,000, 7,000 and 50,500 shares, respectively, that
    such person or members of the group have the right to acquire within 60 days
    of January 31, 2000 through the exercise of stock options. No director or
    current executive officer beneficially owned more than 1% of the Company's
    common stock outstanding as of January 31, 2000; all directors and current
    executive officers as a group beneficially owned less than 1% of the
    Company's common stock outstanding as of January 31, 2000.

(3) Shares of the common stock of Thermedics beneficially owned by Mr. Crisp,
    Dr. Gyftopoulos, Mr. Keiser, Mr. Kelleher, and all directors and current
    executive officers as a group include 9,000, 2,750, 187,900, 10,000 and
    209,650 shares, respectively, that such person or members of the group have
    the right to acquire within 60 days of January 31, 2000 through the exercise
    of stock options. Shares beneficially owned by Dr. Hatsopoulos, Mr.
    Kelleher, Mr. Melas-Kyriazi and all directors and current executive officers
    as a group include 1,635, 1,294, 1,119 and 4,048 shares, respectively,
    allocated to their respective accounts maintained pursuant to Thermo
    Electron's ESOP, of which the trustees, who have investment power over its
    assets, are executive officers of Thermo Electron. Shares beneficially owned
    by Mr. Crisp and all directors and current executive officers as a group
    include 9,971 shares allocated to Mr. Crisp's account maintained pursuant to
    Thermedics' deferred compensation plan for directors. Shares beneficially
    owned by Dr. Hatsopoulos include 654 shares held by his spouse and 50,000
    shares that a family limited partnership indirectly controlled by Dr.
    Hatsopoulos has the right to acquire within 60 days of Janaury 31, 2000
    through the exercise of stock options. Dr. Hatsopoulos disclaims beneficial
    interest in the shares owned by the family limited partnership except to the
    extent of his pecuniary interest therein. No director or current executive
    officer beneficially owned more than 1% of the Thermedics common stock
    outstanding as of January 31, 2000; all directors and current executive
    officers as a group beneficially owned less than 1% of the Thermedics common
    stock outstanding as of January 31, 2000.

                                       I-9
<PAGE>   66

(4) Shares of the common stock of Thermo Electron beneficially owned by Mr.
    Bodman, Mr. Crisp, Dr. Gyftopoulos, Dr. Hatsopoulos, Mr. Holt, Mr. Jungers,
    Mr. Keiser, Mr. Kelleher, Mr. Lewis, Mr. McCabe, Mr. Melas-Kyriazi, Ms.
    Olayan, Mr. O'Leary, Mr. Rainville, Dr. Syron, Mr. Wellington and all
    directors and current executive officers as a group include 11,000, 10,596,
    12,442, 25,448, 284,948, 9,673, 263,230, 179,359, 212,278, 12,442, 384,361,
    12,442, 12,000, 294,630, 1,011,000, 9,673 and 2,745,522 shares,
    respectively, that such person or members of the group have the right to
    acquire within 60 days of January 31, 2000 through the exercise of stock
    options. Shares beneficially owned by Dr. Hatsopoulos, Mr. Kelleher, Mr.
    Melas-Kyriazi and all directors and current executive officers as a group
    include 2,266, 1,426, 1,071 and 4,763 shares, respectively, allocated to
    their respective accounts maintained pursuant to Thermo Electron's ESOP, of
    which the trustees, who have investment power over its assets, are executive
    officers of Thermo Electron. Shares beneficially owned by Mr. Bodman, Mr.
    Crisp, Dr. Gyftopoulos, Mr. Jungers, Mr. McCabe, Ms. Olayan, Mr. O'Leary,
    Dr. Syron, Mr. Wellington and all directors and current executive officers
    as a group include 1,599, 49,277, 1,378, 80,427, 34,725, 19,876, 3,830,
    2,506, 26,342 and 219,960 shares, respectively, allocated to accounts
    maintained pursuant to Thermo Electron's Deferred Compensation Plan. Shares
    beneficially owned by Dr. Hatsopoulos include 144,437 shares held by his
    spouse, 311,708 shares held by a family trust of which his spouse is the
    trustee and 566,262 shares held by a family limited partnership indirectly
    controlled by Dr. Hatsopoulos. Shares beneficially owned by Dr. Hatsopoulos
    also include 50,000 shares that a family trust, of which Dr. Hatsopoulos'
    spouse is the trustee, has the right to acquire within 60 days of January
    31, 2000 and 2,149,500 shares that a family limited partnership indirectly
    controlled by Dr. Hatsopoulos has the right to acquire within 60 days of
    January 31, 2000 through the exercise of stock options. Dr. Hatsopoulos
    disclaims beneficial interest in the shares owned by the family limited
    partnership except to the extent of his pecuniary interest therein. Shares
    beneficially owned by Ms. Olayan do not include 6,150,000 shares owned by
    Crescent Holding GmbH, a member of the Olayan Group. Crescent Holding GmbH
    is indirectly controlled by Suliman S. Olayan, Ms. Olayan's father. Ms.
    Olayan disclaims beneficial ownership of the shares owned by Crescent
    Holding GmbH. Except for Dr. Hatsopoulos, who beneficially owned 2.44% of
    the Thermo Electron common stock outstanding as of January 31, 2000, no
    director or current executive officer beneficially owned more than 1% of the
    Thermo Electron common stock outstanding as of such date; all directors and
    current executive officers as a group beneficially owned 4.68% of the Thermo
    Electron common stock outstanding as of January 31, 2000.

                                      I-10
<PAGE>   67

                                  SCHEDULE II

                      INFORMATION CONCERNING TRANSACTIONS
                       IN THE COMMON STOCK OF THE COMPANY

     The following table sets forth information with respect to purchases of the
Company's common stock by the Company, Corpak, Thermedics, the Purchaser and
Thermo Electron since January 4, 1998 (the commencement of the Company's second
full fiscal year preceding the date of this Offer to Purchase).

<TABLE>
<CAPTION>
                                             NUMBER OF
                                              SHARES         RANGE OF PRICES        AVERAGE PURCHASE
                                             PURCHASED        PAID PER SHARE         PRICE PER SHARE
     QUARTER/YEAR           PURCHASER     DURING QUARTER    DURING QUARTER(1)    PAID DURING QUARTER(1)
     ------------           ---------     ---------------   ------------------   -----------------------
<S>                      <C>              <C>               <C>                  <C>
1(st) Quarter 1998.....  Thermo Electron       64,900       $    9.75 - 12.00           $11.3052
1(st) Quarter 1998.....  Thermo Sentron         9,100          9.4375 - 12.00            10.1315
2(nd) Quarter 1998.....  Thermo Sentron       256,800        11.375 - 12.5625            12.0877
3(rd) Quarter 1998.....  Thermo Sentron       172,199           8.625 - 11.25             9.4939
3(rd) Quarter 1998.....  Thermo Electron      147,424          8.6875 - 9.125              8.957
4(th) Quarter 1998.....  Thermo Electron      241,900            8.75 - 10.00             9.2918
1(st) Quarter 1999.....  Thermo Electron       41,700        10.0625 - 10.875            10.5114
</TABLE>

- ---------------
(1) Prices per share of the Company's common stock are net of commissions paid
    by the respective purchasers.

     There were no transactions in the Company's common stock effected during
the 60 days preceding the date of this Offer to Purchase by Corpak, Thermedics,
the Purchaser, Thermo Electron or, to the best knowledge of the Purchaser,
Corpak, Thermedics and Thermo Electron, the Company or the directors and
executive officers of any of the Company, Corpak, Thermedics, the Purchaser or
Thermo Electron, except for the option exercise described in the table below.

<TABLE>
<CAPTION>
                                                                                   NUMBER OF
                                                                                SHARES RECEIVED   EXERCISE PRICE
             NAME                        RELATIONSHIP           EXERCISE DATE    UPON EXERCISE      PER SHARE
             ----                        ------------           -------------   ---------------   --------------
<S>                              <C>                            <C>             <C>               <C>
John W. Wood Jr. ..............  Director and Chairman of the      2/17/00            400             $9.80
                                 Board, Thermedics
</TABLE>

                                      II-1
<PAGE>   68

                                  SCHEDULE III

              SECTION 262 OF THE DELAWARE GENERAL CORPORATION LAW

262. APPRAISAL RIGHTS.

     (a) Any stockholder of a corporation of this State who holds shares of
stock on the date of the making of a demand pursuant to subsection (d) of this
section with respect to such shares, who continuously holds such shares through
the effective date of the merger or consolidation, who has otherwise complied
with subsection (d) of this section and who has neither voted in favor of the
merger or consolidation nor consented thereto in writing pursuant to sec.228 of
this title shall be entitled to an appraisal by the Court of Chancery of the
fair value of the stockholder's shares of stock under the circumstances
described in subsections (b) and (c) of this section. As used in this section,
the word "stockholder" means a holder of record of stock in a stock corporation
and also a member of record of a nonstock corporation; the words "stock" and
"share" mean and include what is ordinarily meant by those words and also
membership or membership interest of a member of a nonstock corporation; and the
words "depository receipt" mean a receipt or other instrument issued by a
depository representing an interest in one or more shares, or fractions thereof,
solely of stock of a corporation, which stock is deposited with the depository.

     (b) Appraisal rights shall be available for the shares of any class or
series of stock of a constituent corporation in a merger or consolidation to be
effected pursuant to sec.251 (other than a merger effected pursuant to sec.251
(g) of this title), sec.252, sec.254, sec.257, sec.258, sec.263 or sec.264 of
this title:

          (1) Provided, however, that no appraisal rights under this section
     shall be available for the shares of any class or series of stock, which
     stock, or depository receipts in respect thereof, at the record date fixed
     to determine the stockholders entitled to receive notice of and to vote at
     the meeting of stockholders to act upon the agreement of merger or
     consolidation, were either (i) listed on a national securities exchange or
     designated as a national market system security on an interdealer quotation
     system by the National Association of Securities Dealers, Inc. or (ii) held
     of record by more than 2,000 holders; and further provided that no
     appraisal rights shall be available for any shares of stock of the
     constituent corporation surviving a merger if the merger did not require
     for its approval the vote of the stockholders of the surviving corporation
     as provided in subsection (f) of sec.251 of this title.

          (2) Notwithstanding paragraph (1) of this subsection, appraisal rights
     under this section shall be available for the shares of any class or series
     of stock of a constituent corporation if the holders thereof are required
     by the terms of an agreement of merger or consolidation pursuant to
     sec.sec.251, 252, 254, 257, 258, 263 and 264 of this title to accept for
     such stock anything except:

           a. Shares of stock of the corporation surviving or resulting from
              such merger or consolidation, or depository receipts in respect
              thereof;

           b. Shares of stock of any other corporation, or depository receipts
              in respect thereof, which shares of stock (or depository receipts
              in respect thereof) or depository receipts at the effective date
              of the merger or consolidation will be either listed on a national
              securities exchange or designated as a national market system
              security on an interdealer quotation system by the National
              Association of Securities Dealers, Inc. or held of record by more
              than 2,000 holders;

           c. Cash in lieu of fractional shares or fractional depository
              receipts described in the foregoing subparagraphs a. and b. of
              this paragraph; or

           d. Any combination of the shares of stock, depository receipts and
              cash in lieu of fractional shares or fractional depository
              receipts described in the foregoing subparagraphs a., b. and c. of
              this paragraph.

          (3) In the event all of the stock of a subsidiary Delaware corporation
     party to a merger effected under sec.253 of this title is not owned by the
     parent corporation immediately prior to the merger, appraisal rights shall
     be available for the shares of the subsidiary Delaware corporation.

                                      III-1
<PAGE>   69

     (c) Any corporation may provide in its certificate of incorporation that
appraisal rights under this section shall be available for the shares of any
class or series of its stock as a result of an amendment to its certificate of
incorporation, any merger or consolidation in which the corporation is a
constituent corporation or the sale of all or substantially all of the assets of
the corporation. If the certificate of incorporation contains such a provision,
the procedures of this section, including those set forth in subsections (d) and
(e) of this section, shall apply as nearly as is practicable.

     (d) Appraisal rights shall be perfected as follows:

          (1) If a proposed merger or consolidation for which appraisal rights
     are provided under this section is to be submitted for approval at a
     meeting of stockholders, the corporation, not less than 20 days prior to
     the meeting, shall notify each of its stockholders who was such on the
     record date for such meeting with respect to shares for which appraisal
     rights are available pursuant to subsections (b) or (c) hereof that
     appraisal rights are available for any or all of the shares of the
     constituent corporations, and shall include in such notice a copy of this
     section. Each stockholder electing to demand the appraisal of such
     stockholder's shares shall deliver to the corporation, before the taking of
     the vote on the merger or consolidation, a written demand for appraisal of
     such stockholder's shares. Such demand will be sufficient if it reasonably
     informs the corporation of the identity of the stockholder and that the
     stockholder intends thereby to demand the appraisal of such stockholder's
     shares. A proxy or vote against the merger or consolidation shall not
     constitute such a demand. A stockholder electing to take such action must
     do so by a separate written demand as herein provided. Within 10 days after
     the effective date of such merger or consolidation, the surviving or
     resulting corporation shall notify each stockholder of each constituent
     corporation who has complied with this subsection and has not voted in
     favor of or consented to the merger or consolidation of the date that the
     merger or consolidation has become effective; or

          (2) If the merger or consolidation was approved pursuant to sec.228 or
     sec.253 of this title, each constituent corporation, either before the
     effective date of the merger or consolidation or within ten days
     thereafter, shall notify each of the holders of any class or series of
     stock of such constituent corporation who are entitled to appraisal rights
     of the approval of the merger or consolidation and that appraisal rights
     are available for any or all shares of such class or series of stock of
     such constituent corporation, and shall include in such notice a copy of
     this section; provided that, if the notice is given on or after the
     effective date of the merger or consolidation, such notice shall be given
     by the surviving or resulting corporation to all such holders of any class
     or series of stock of a constituent corporation that are entitled to
     appraisal rights. Such notice may, and, if given on or after the effective
     date of the merger or consolidation, shall, also notify such stockholders
     of the effective date of the merger or consolidation. Any stockholder
     entitled to appraisal rights may, within 20 days after the date of mailing
     of such notice, demand in writing from the surviving or resulting
     corporation the appraisal of such holder's shares. Such demand will be
     sufficient if it reasonably informs the corporation of the identity of the
     stockholder and that the stockholder intends thereby to demand the
     appraisal of such holder's shares. If such notice did not notify
     stockholders of the effective date of the merger or consolidation, either
     (i) each such constituent corporation shall send a second notice before the
     effective date of the merger or consolidation notifying each of the holders
     of any class or series of stock of such constituent corporation that are
     entitled to appraisal rights of the effective date of the merger or
     consolidation or (ii) the surviving or resulting corporation shall send
     such a second notice to all such holders on or within 10 days after such
     effective date; provided, however, that if such second notice is sent more
     than 20 days following the sending of the first notice, such second notice
     need only be sent to each stockholder who is entitled to appraisal rights
     and who has demanded appraisal of such holder's shares in accordance with
     this subsection. An affidavit of the secretary or assistant secretary or of
     the transfer agent of the corporation that is required to give either
     notice that such notice has been given shall, in the absence of fraud, be
     prima facie evidence of the facts stated therein. For purposes of
     determining the stockholders entitled to receive either notice, each
     constituent corporation may fix, in advance, a record date that shall be
     not more than 10 days prior to the date the notice is given, provided, that
     if the notice is given on or after the effective date of the merger or
     consolidation, the record date shall be such effective date. If no record
     date is fixed and the notice is given prior to the effective date, the
     record date shall be the close of business on the day next preceding the
     day on which the notice is given.

                                      III-2
<PAGE>   70

     (e) Within 120 days after the effective date of the merger or
consolidation, the surviving or resulting corporation or any stockholder who has
complied with subsections (a) and (d) hereof and who is otherwise entitled to
appraisal rights, may file a petition in the Court of Chancery demanding a
determination of the value of the stock of all such stockholders.
Notwithstanding the foregoing, at any time within 60 days after the effective
date of the merger or consolidation, any stockholder shall have the right to
withdraw such stockholder's demand for appraisal and to accept the terms offered
upon the merger or consolidation. Within 120 days after the effective date of
the merger or consolidation, any stockholder who has complied with the
requirements of subsections (a) and (d) hereof, upon written request, shall be
entitled to receive from the corporation surviving the merger or resulting from
the consolidation a statement setting forth the aggregate number of shares not
voted in favor of the merger or consolidation and with respect to which demands
for appraisal have been received and the aggregate number of holders of such
shares. Such written statement shall be mailed to the stockholder within 10 days
after such stockholder's written request for such a statement is received by the
surviving or resulting corporation or within 10 days after expiration of the
period for delivery of demands for appraisal under subsection (d) hereof,
whichever is later.

     (f) Upon the filing of any such petition by a stockholder, service of a
copy thereof shall be made upon the surviving or resulting corporation, which
shall within 20 days after such service file in the office of the Register in
Chancery in which the petition was filed a duly verified list containing the
names and addresses of all stockholders who have demanded payment for their
shares and with whom agreements as to the value of their shares have not been
reached by the surviving or resulting corporation. If the petition shall be
filed, by the surviving or resulting corporation, the petition shall be
accompanied by such a duly verified list. The Register in Chancery, if so
ordered by the Court, shall give notice of the time and place fixed for the
hearing of such petition by registered or certified mail to the surviving or
resulting corporation and to the stockholders shown on the list at the addresses
therein stated. Such notice shall also be given by or more publications at least
week before the day of the hearing, in a newspaper of general circulation
published in the City of Wilmington, Delaware or such publication as the Court
deems advisable. The forms of the notices by mail and by publication shall be
approved by the Court, and the costs thereof shall be borne by the surviving or
resulting corporation.

     (g) At the hearing on such petition, the Court shall determine the
stockholders who have complied with this section and who have become entitled to
appraisal rights. The Court may require the stockholders who have demanded an
appraisal for their shares and who hold stock represented by certificates to
submit their certificates of stock to the Register in Chancery for notation
thereon of the pendency of the appraisal proceedings; and if any stockholder
fails to comply with such direction, the Court may dismiss the proceedings as to
such stockholder.

     (h) After determining the stockholders entitled to an appraisal, the Court
shall appraise the shares, determining their fair value exclusive of any element
of value arising from the accomplishment or expectation of the merger or
consolidation, together with a fair rate of interest, if any, to be paid upon
the amount determined to be the fair value. In determining such fair value, the
Court shall take into account all relevant factors. In determining the fair rate
of interest, the Court may consider all relevant factors, including the rate of
interest which the surviving or resulting corporation would have had to pay to
borrow money during the pendency of the proceeding. Upon application by the
surviving or resulting corporation or by any stockholder entitled to participate
in the appraisal proceeding, the Court may, in its discretion, permit discovery
or other pretrial proceedings and may proceed to trial upon the appraisal prior
to the final determination of the stockholder entitled to an appraisal. Any
stockholder whose name appears on the list filed by the surviving or resulting
corporation pursuant to subsection (f) of this section and who has submitted
such stockholder's certificates of stock to the Register in Chancery, if such is
required, may participate fully in all proceedings until it is finally
determined that such stockholder is not entitled to appraisal rights under this
section.

     (i) The Court shall direct the payment of the fair value of the shares,
together with interest, if any, by the surviving or resulting corporation to the
stockholders entitled thereto. Interest may be simple or compound, as the Court
may direct. Payment shall be so made to each such stockholder, in the case of
holders of uncertificated stock forthwith, and the case of holders of shares
represented by certificates upon the surrender to the corporation of the
certificates representing such stock. The Court's decree may be enforced as

                                      III-3
<PAGE>   71

other decrees in the Court of Chancery may be enforced, whether such surviving
or resulting corporation be a corporation of this State or of any state.

     (j) The costs of the proceeding may be determined by the Court and taxed
upon the parties as the Court deems equitable in the circumstances. Upon
application of a stockholder, the Court may order all or a portion of the
expenses incurred by any stockholder in connection with the appraisal
proceeding, including, without limitation, reasonable attorney's fees and the
fees and expenses of experts, to be charged pro rata against the value of all
the shares entitled to an appraisal.

     (k) From and after the effective date of the merger or consolidation, no
stockholder who has demanded appraisal rights as provided in subsection (d) of
this section shall be entitled to vote such stock for any purpose or to receive
payment of dividends or other distributions on the stock (except dividends or
other distributions payable to stockholders of record at a date which is prior
to the effective date of the merger or consolidation); provided, however, that
if no petition for an appraisal shall be filed within the time provided in
subsection (e) of this section, or if such stockholder shall deliver to the
surviving or resulting corporation a written withdrawal of such stockholder's
demand for an appraisal and an acceptance of the merger or consolidation, either
within 60 days after the effective date of the merger or consolidation as
provided in subsection (e) of this section or thereafter with the written
approval of the corporation, then the right of such stockholder to an appraisal
shall cease. Notwithstanding the foregoing, no appraisal proceeding in the Court
of Chancery shall be dismissed as to any stockholder without the approval of the
Court, and such approval may be conditioned upon such terms as the Court deems
just.

     (1) The shares of the surviving or resulting corporation to which the
shares of such objecting stockholders would have been converted had they
assented to the merger or consolidation shall have the status of authorized and
unissued shares of the surviving or resulting corporation. (Last amended by Ch.
339, L. '98, eff. 7-1-98.)

                                      III-4
<PAGE>   72

     Manually signed facsimile copies of the Letter of Transmittal will be
accepted. The Letter of Transmittal and certificates evidencing Shares and any
other required documents should be sent or delivered by each stockholder or his
broker, dealer, commercial bank, trust company or other nominee to the
Depositary at one of its addresses set forth below:

                        The Depositary for the Offer is:

                    AMERICAN STOCK TRANSFER & TRUST COMPANY

<TABLE>
<S>                              <C>                              <C>
           By Mail:                                                By Hand or Overnight Courier:

        40 Wall Street                                                    40 Wall Street
          46th Floor                                                        46th Floor
   New York, New York 10005                                          New York, New York 10005
Attn: Reorganization Department                                   Attn: Reorganization Department
                                   By Facsimile Transmission:
                                         (718) 921-8200
                                      Confirm by Telephone:
                                         (718) 921-8200
</TABLE>

     Questions and requests for assistance or for additional copies of this
Offer to Purchase, the Letter of Transmittal or other tender offer materials may
be directed to the Information Agent or the Dealer Managers at their respective
addresses and telephone numbers set forth below. Stockholders may also contact
their broker, dealer, bank or trust company for assistance concerning the Offer.

                    The Information Agent for the Offer is:

                             D.F. KING & CO., INC.
                          77 Water Street, 20th Floor
                               New York, NY 10005
                Bankers and Brokers Call Collect (212) 269-5550
                    All Others Call Toll-Free (800) 290-6433

                     The Dealer Managers for the Offer are:

                          J.P. MORGAN SECURITIES INC.
                                 60 Wall Street
                               New York, NY 10260
                                 (877) 869-0656

                     THE BEACON GROUP CAPITAL SERVICES, LLC
                                399 Park Avenue
                               New York, NY 10022
                                 (212) 339-9100

<PAGE>   1

                             LETTER OF TRANSMITTAL
                        TO TENDER SHARES OF COMMON STOCK

                                       OF

                              THERMO SENTRON INC.
                       PURSUANT TO THE OFFER TO PURCHASE
                              DATED MARCH 3, 2000

                                       BY

                           SENTRON ACQUISITION, INC.
                     AN INDIRECT WHOLLY-OWNED SUBSIDIARY OF

                                THERMEDICS INC.

  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
        TIME, ON THURSDAY, MARCH 30, 2000, UNLESS THE OFFER IS EXTENDED.

                        The Depositary for the Offer is:
                    AMERICAN STOCK TRANSFER & TRUST COMPANY

<TABLE>
<S>                                                        <C>
                 By Mail:                                         By Hand or Overnight Courier:
              40 Wall Street                                             40 Wall Street
                46th Floor                                                 46th Floor
            New York, NY 10005                                         New York, NY 10005
      Attn: Reorganization Department                            Attn: Reorganization Department
</TABLE>

                           By Facsimile Transmission:

                                 (718) 234-5001

                             Confirm by Telephone:

                                 (718) 921-8200

     DELIVERY OF THIS LETTER OF TRANSMITTAL TO AN ADDRESS OTHER THAN AS SET
FORTH ABOVE, OR TRANSMISSIONS OF INSTRUCTIONS VIA A FACSIMILE NUMBER OTHER THAN
AS SET FORTH ABOVE, WILL NOT CONSTITUTE A VALID DELIVERY. YOU MUST SIGN THIS
LETTER OF TRANSMITTAL IN THE APPROPRIATE SPACE PROVIDED THEREFOR AND COMPLETE
THE SUBSTITUTE FORM W-9 SET FORTH BELOW.

     THE INSTRUCTIONS ACCOMPANYING THIS LETTER OF TRANSMITTAL SHOULD BE READ
CAREFULLY BEFORE THIS LETTER OF TRANSMITTAL IS COMPLETED.

     This Letter of Transmittal is to be completed by holders of Shares (as
defined below) either if certificates evidencing Shares ("Share Certificates")
are to be forwarded herewith or, unless an Agent's Message (as defined in the
section of the Offer to Purchase dated March 3, 2000 (the "Offer to Purchase")
captioned "The Tender Offer -- Acceptance For Payment And Payment For Shares")
is utilized, if delivery of Shares is to be made by book-entry transfer into the
account of American Stock Transfer & Trust Company, as Depositary (the
"Depositary"), at The Depository Trust Company ("DTC") pursuant to the
procedures set forth in the section of the Offer to Purchase captioned "The
Tender Offer -- Procedures For Accepting The Offer And Tendering Shares."
Stockholders who tender Shares by book-entry transfer are referred to herein as
"Book-Entry Stockholders."

     Stockholders whose Share Certificates are not immediately available or who
cannot deliver their Share Certificates and all other documents required hereby
to the Depositary prior to the Expiration Date (as defined in the section of the
Offer to Purchase captioned "The Tender Offer -- Terms Of The Offer; Expiration
Date"), or who cannot complete the procedures for delivery by book-entry
transfer on a timely basis, may tender their Shares according to the guaranteed
delivery procedures set forth in the section of the Offer to Purchase captioned
"The Tender Offer -- Procedures For Accepting The Offer And Tendering Shares."
See Instruction 2. DELIVERY OF DOCUMENTS TO DTC IN ACCORDANCE WITH DTC'S
PROCEDURES DOES NOT CONSTITUTE DELIVERY TO THE DEPOSITARY.
<PAGE>   2
- --------------------------------------------------------------------------------
                         DESCRIPTION OF SHARES TENDERED
- --------------------------------------------------------------------------------

                NAME(S) AND ADDRESS(ES) OF REGISTERED HOLDER(S)
(PLEASE FILL IN, IF BLANK, EXACTLY AS NAME(S) APPEAR(S) ON SHARE CERTIFICATE(S))
- --------------------------------------------------------------------------------



- -----------------------------------------------------------
              DESCRIPTION OF SHARES TENDERED
- -----------------------------------------------------------
        SHARE CERTIFICATE(S) AND SHARE(S) TENDERED
      (ATTACH ADDITIONAL SIGNED LIST, IF NECESSARY).
                    SEE INSTRUCTION 3.
- -----------------------------------------------------------
                         TOTAL NUMBER
                           OF SHARES
         SHARE            REPRESENTED           NUMBER
      CERTIFICATE          BY SHARE            OF SHARES
      NUMBER(S)*        CERTIFICATE(S)*       TENDERED**

- -----------------------------------------------------------

- -----------------------------------------------------------

- -----------------------------------------------------------

- -----------------------------------------------------------

- -----------------------------------------------------------

     TOTAL SHARES


- --------------------------------------------------------------------------------
 *  Need not be completed by Book-Entry Stockholders.
 ** Unless otherwise indicated, all Shares represented by Share Certificates
    delivered to the Depositary will be deemed to have been tendered. See
    Instruction 4.
 IF ANY SHARE CERTIFICATES HAVE BEEN LOST OR DESTROYED, SEE INSTRUCTION 11.
- --------------------------------------------------------------------------------

[ ] CHECK HERE IF SHARES ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER MADE TO AN
    ACCOUNT MAINTAINED BY THE DEPOSITARY WITH DTC AND COMPLETE THE FOLLOWING
    (ONLY PARTICIPANTS IN DTC MAY DELIVER SHARES BY BOOK-ENTRY TRANSFER):

   Name of Tendering Institution:______________________________________________

   DTC Account Number:_________________________________________________________

   DTC Transaction Code Number:________________________________________________

[ ] CHECK HERE IF SHARES ARE BEING DELIVERED PURSUANT TO A NOTICE OF GUARANTEED
    DELIVERY PREVIOUSLY SENT TO THE DEPOSITARY AND COMPLETE THE FOLLOWING
    (PLEASE ENCLOSE A PHOTOCOPY OF SUCH NOTICE OF GUARANTEED DELIVERY):

   Name(s) of Registered Holder(s):_____________________________________________

   Window Ticket Number (if any):_______________________________________________

   Date of Execution of Notice of Guaranteed Delivery:__________________________

   Name of Institution that Guaranteed Delivery:________________________________

   If delivered by Book-Entry Transfer:_________________________________________

   DTC Account Number:__________________________________________________________

   DTC Transaction Code Number:_________________________________________________

                    NOTE: SIGNATURES MUST BE PROVIDED BELOW.
              PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY.

Ladies and Gentlemen:

     The undersigned hereby tenders to Sentron Acquisition, Inc. (the
"Purchaser"), a Delaware corporation and an indirect wholly-owned subsidiary of
Thermedics Inc., a Massachusetts corporation ("Thermedics"), the above-described
shares of common stock, par value $0.01 per share (the "Shares"), of Thermo
Sentron Inc., a Delaware corporation (the "Company"), pursuant to the
Purchaser's offer to purchase all of the outstanding Shares at a price of $15.50
per Share, net to the seller in cash, without interest thereon, upon the terms
and subject to the conditions set forth in the Offer to Purchase and in this
Letter of Transmittal (which, together with any amendments or supplements
thereto or hereto, collectively constitute the "Offer"), receipt of each of
which is hereby acknowledged. The undersigned understands that the Purchaser
reserves the right to transfer or assign, in whole or from time to time in part,
to one or more of its affiliates, the right to purchase all or any portion of
the Shares tendered pursuant to the Offer.

     Subject to, and effective upon, acceptance for payment of the Shares
tendered herewith in accordance with the terms and subject to the conditions of
the Offer, including, if the Offer is extended or amended, the terms and
conditions of any such extension or amendment, the undersigned hereby sells,
assigns and transfers to, or upon the order of, the Purchaser all right, title
and interest in and to all of the Shares that are being tendered hereby and any
and all dividends and distributions, including, without limitation,
distributions of additional Shares or rights declared, paid or issued with
respect

                                        2
<PAGE>   3

to the tendered Shares on or after January 31, 2000 (collectively,
"Distributions"), and irrevocably constitutes and appoints the Depositary the
true and lawful agent and attorney-in-fact of the undersigned with respect to
such Shares and any Distributions with full power of substitution (such power of
attorney being deemed to be an irrevocable power coupled with an interest) to
(a) deliver such Share Certificates and any Distributions, or transfer ownership
of such Shares and any Distributions on the account books maintained by DTC,
together in either case with appropriate evidences of transfer and authenticity,
to, or upon the order of, the Purchaser, upon receipt by the Depositary, as the
undersigned's agent, of the purchase price, (b) present such Shares and any
Distributions for transfer on the books of the Company, and (c) receive all
benefits and otherwise exercise all rights of record and beneficial ownership of
such Shares and any Distributions, all in accordance with the terms and subject
to the conditions of the Offer.

     The undersigned hereby irrevocably appoints John T. Keiser, Kenneth J.
Apicerno, Sandra L. Lambert and Seth H. Hoogasian in their respective capacities
as officers of the Purchaser or one of its affiliates, and any individuals who
shall hereafter succeed to any such office of the Purchaser or one of its
affiliates, and each of them or any other designees of the Purchaser, as
attorneys-in-fact and proxies of the undersigned, each with full power of
substitution, to the full extent of the undersigned's rights with respect to the
Shares tendered by the undersigned and accepted for payment and paid for by the
Purchaser and any Distributions. This power of attorney and proxy shall be
considered irrevocable and coupled with an interest in the tendered Shares. Such
appointment will be effective when, and only to the extent that, the Purchaser
accepts such Shares for payment and deposits the purchase price therefor with
the Depositary. Upon such deposit, all prior powers of attorney and proxies
given by the undersigned at any time with respect to such Shares and any
Distributions will, without further action, be revoked, and no subsequent powers
of attorney or proxies may be given nor any subsequent written consents executed
by the undersigned (and, if given or executed, will not be deemed effective).
Upon such deposit by the Purchaser, the designees of the Purchaser will, with
respect to such Shares and any Distributions, be empowered to exercise all
voting and other rights of the undersigned as they in their sole discretion may
deem proper at any annual or special meeting of the Company's stockholders, or
any adjournment or postponement thereof, by written consent in lieu of any such
meeting or otherwise. The Purchaser reserves the right to require that, in order
for Shares to be deemed validly tendered, immediately upon the Purchaser's
payment for such Shares, the Purchaser must be able to exercise full voting
rights and other rights of a record and beneficial owner with respect to such
Shares and any Distributions, including, without limitation, voting at any
meeting of stockholders or by written consent in lieu of any such meeting.

     The undersigned hereby represents and warrants that (a) the undersigned has
full power and authority to tender, sell, assign and transfer the Shares
tendered hereby and any Distributions and (b) when the Shares are accepted for
payment by the Purchaser, the Purchaser will acquire good, marketable and
unencumbered title to the Shares and any Distributions, free and clear of all
liens, restrictions, charges and encumbrances, and the same will not be subject
to any adverse claim. The undersigned, upon request, shall execute and deliver
any additional documents deemed by the Depositary or the Purchaser to be
necessary or desirable to complete the sale, assignment and transfer of the
Shares tendered hereby and any Distributions. In addition, the undersigned shall
promptly remit and transfer to the Depositary for the account of the Purchaser
any Distribution in respect of the Shares tendered hereby, accompanied by
appropriate documentation of transfer, and, pending such remittance or
appropriate assurance thereof, the Purchaser shall be, subject to applicable
law, entitled to all rights and privileges as record and beneficial owner of any
such Distribution and may withhold the entire purchase price of Shares tendered
hereby or deduct from the purchase price the amount or value of any such
Distribution, as determined by the Purchaser in its sole discretion.

     No authority herein conferred or agreed to be conferred shall be affected
by, and all authority herein conferred or agreed to be conferred shall survive,
the death or incapacity of the undersigned and any obligation of the undersigned
hereunder shall be binding upon the heirs, personal representatives, successors
and assigns of the undersigned.

     Except as otherwise provided in the Offer to Purchase, tenders of Shares
made pursuant to the Offer are irrevocable. Shares tendered pursuant to the
Offer may be withdrawn at any time prior to the Expiration Date (as defined in
the section of the Offer to Purchase captioned "The Tender Offer--Terms Of The
Offer; Expiration Date") and, unless theretofore accepted for payment by the
Purchaser pursuant to the Offer, may also be withdrawn at any time after May 1,
2000. See the section of the Offer to Purchase captioned "The Tender Offer
 -- Withdrawal Rights."

     The undersigned understands that tenders of Shares pursuant to any of the
procedures described in the section of the Offer to Purchase captioned "The
Tender Offer -- Procedures For Accepting The Offer And Tendering Shares" and in
the Instructions hereto will constitute the undersigned's acceptance of the
terms and conditions of the Offer. The Purchaser's acceptance of such Shares for
payment will constitute a binding agreement between the undersigned and the
Purchaser upon the terms and subject to the conditions set forth in the Offer.

     The undersigned understands that the Offer is conditioned upon, among other
things set forth in the Offer to Purchase, there being validly tendered and not
withdrawn prior to the expiration of the Offer that number of Shares

                                        3
<PAGE>   4

which, together with the Shares held by Thermo Electron Corporation and its
subsidiaries, including Thermedics, constitutes at least ninety percent (90%) of
the Shares outstanding on the Expiration Date.

     The undersigned understands that, under certain circumstances set forth in
the Offer to Purchase, the Purchaser may terminate or amend the Offer or may not
be required to accept for payment any of the Shares tendered herewith.

     Unless otherwise indicated herein under "Special Payment Instructions,"
please issue the check for the purchase price of all Shares accepted for payment
and issue or return any Share Certificate(s) for Shares not tendered or not
purchased in the name(s) of the registered holder(s) appearing under
"Description of Shares Tendered." Similarly, unless otherwise indicated herein
under "Special Delivery Instructions," please mail the check for the purchase
price of all Shares accepted for payment and return any Share Certificate(s) for
Shares not tendered or not purchased (and accompanying documents, as
appropriate) to the address of the registered holder(s) appearing under
"Description of Shares Tendered." In the event that both the "Special Delivery
Instructions" and the "Special Payment Instructions" boxes are completed, please
issue the check for the purchase price of all Shares accepted for payment and
return any Share Certificate(s) for Shares not tendered or not purchased in the
name(s) of, and deliver such check and return such Share Certificate(s) to, the
person(s) so indicated. Please credit any Shares tendered herewith by book-entry
transfer that are not purchased by crediting the DTC account designated above.
The undersigned recognizes that the Purchaser has no obligation pursuant to the
"Special Payment Instructions" to transfer any Shares from the name(s) of the
registered holder(s) thereof if the Purchaser does not accept for payment any of
the Shares tendered hereby.

- ------------------------------------------------------------

                          SPECIAL PAYMENT INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 5, 6 AND 7)

        To be completed ONLY if Share Certificate(s) evidencing Shares not
   tendered or not purchased or the check for the purchase price of Shares
   accepted for payment are to be issued in the name of someone other than
   the undersigned.

   Issue:  [ ] check     [ ] certificates to:

   Name:
   ----------------------------------------------------
                                    (PLEASE PRINT)

   Address:
   --------------------------------------------------

   ------------------------------------------------------------
                               (INCLUDE ZIP CODE)

   ------------------------------------------------------------
                  (TAX IDENTIFICATION OR SOCIAL SECURITY NO.)
                        (SEE SUBSTITUTE FORM W-9 BELOW)
   ------------------------------------------------------------
   ------------------------------------------------------------

                         SPECIAL DELIVERY INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 5, 6 AND 7)

        To be completed ONLY if Share Certificate(s) evidencing Shares not
   tendered or not purchased or the check for the purchase price of Shares
   accepted for payment are to be sent to someone other than the undersigned
   or to the undersigned at an address other than that shown above.

   Mail:  [ ] check     [ ] certificates to:

   Name:
   ----------------------------------------------------
                                    (PLEASE PRINT)

   Address:
   --------------------------------------------------

          ------------------------------------------------------------
                               (INCLUDE ZIP CODE)

   ------------------------------------------------------------

                                        4
<PAGE>   5

<TABLE>
<S>     <C>                                                                 <C>
        -------------------------------------------------------------------
SIGN                                 IMPORTANT                              SIGN
HERE             SIGN HERE AND COMPLETE SUBSTITUTE FORM W-9 BELOW           HERE
[ARROW] X                                                                   [ARROW]
[ARROW]   ----------------------------------------------------------------- [ARROW]
        X
          -----------------------------------------------------------------
                             SIGNATURE(S) OF HOLDER(S)

        Dated:
               ------------------------------------------, 2000

        (Must be signed by the registered holder(s) exactly as name(s)
        appear(s) on Share Certificate(s) or on a security position listing
        or by person(s) authorized to become registered holder(s) by
        certificates and documents transmitted herewith. If signature is by
        a trustee, executor, administrator, guardian, attorney-in-fact,
        officer of a corporation or other acting in a fiduciary or
        representative capacity, please provide the following information.
        See Instruction 5.)

        Name(s):
                 ----------------------------------------------------------

        -------------------------------------------------------------------

        -------------------------------------------------------------------
                                  (PLEASE PRINT)

        Capacity (Full Title):
                               --------------------------------------------

        -------------------------------------------------------------------

        -------------------------------------------------------------------

        Address:
                 ----------------------------------------------------------

        -------------------------------------------------------------------

        -------------------------------------------------------------------
                                (INCLUDE ZIP CODE)

        Area Code and Telephone Number:
                                        -----------------------------------

        Tax Identification or Social Security No.:
                                                   ------------------------

        Dated:
               ---------------------------, 2000

                             GUARANTEE OF SIGNATURE(S)
                            (SEE INSTRUCTIONS 1 AND 5)

        Authorized Signature:
                              ---------------------------------------------

        Name:
              -------------------------------------------------------------
                                  (PLEASE PRINT)

        Title:
               ------------------------------------------------------------

        Name of Firm:
                      -----------------------------------------------------
                                  (PLEASE PRINT)

        Address:
              -------------------------------------------------------------
                                (INCLUDE ZIP CODE)

        Area Code and Telephone Number:
                                        -----------------------------------
        Dated:
               ---------------------------, 2000
        -------------------------------------------------------------------
</TABLE>

                                        5
<PAGE>   6

                                  INSTRUCTIONS

             FORMING PART OF THE TERMS AND CONDITIONS OF THE OFFER

     1.  Guarantee of Signatures.  No signature guarantee is required on this
Letter of Transmittal (a) if this Letter of Transmittal is signed by the
registered holder(s) of Shares (which term, for purposes of this document, shall
include any DTC participant whose name appears on a security position listing as
the owner of Share(s)) tendered herewith, unless such holder(s) has (have)
completed either the box entitled "Special Payment Instructions" or the box
entitled "Special Delivery Instructions," or (b) if such Share(s) are tendered
for the account of a firm which is a commercial bank, broker, dealer, credit
union, savings association or other entity which is a member in good standing of
the Securities Transfer Agents Medallion Program, the Stock Exchanges' Medallion
Program or the New York Stock Exchange, Inc. Medallion Signature Program (each
of the foregoing being referred to as an "Eligible Institution"). In all other
cases, all signatures on this Letter of Transmittal must be guaranteed by an
Eligible Institution. See Instruction 5.

     2.  Delivery of Letter of Transmittal and Certificates.  This Letter of
Transmittal is to be completed by stockholders either if Share Certificates are
to be forwarded herewith or, unless an Agent's Message is utilized, if delivery
of Shares is to be made by book-entry transfer pursuant to the procedures set
forth in the section of the Offer to Purchase captioned "The Tender
Offer -- Procedures For Accepting The Offer And Tendering Shares." In order for
Shares to be validly tendered pursuant to the Offer, this Letter of Transmittal
(or a facsimile hereof), properly completed and duly executed, together with any
required signature guarantees, or an Agent's Message in connection with a
book-entry delivery of Shares, and any other documents required by this Letter
of Transmittal, must be received by the Depositary at one of its addresses set
forth on the front cover hereof prior to the Expiration Date and either (i)
Share Certificates evidencing tendered Shares must be received by the Depositary
at such address or such Shares must be tendered by book-entry transfer and a
timely confirmation of such book-entry transfer (a "Book-Entry Confirmation")
must be received by the Depositary, in each case prior to the Expiration Date or
(ii) the guaranteed delivery procedures described in the following sentence must
be complied with. Stockholders whose Share Certificates are not immediately
available or who cannot deliver their Share Certificates and all other required
documents to reach the Depositary prior to the Expiration Date or who cannot
complete the procedure for delivery by book-entry transfer on a timely basis may
tender their Shares by properly completing and duly executing a Notice of
Guaranteed Delivery pursuant to the guaranteed delivery procedures set forth in
the section of the Offer to Purchase captioned "The Tender Offer -- Procedures
For Accepting The Offer And Tendering Shares." Pursuant to such procedures: (i)
such tender must be made by or through an Eligible Institution; (ii) a properly
completed and duly executed Notice of Guaranteed Delivery, substantially in the
form made available by the Purchaser, must be received by the Depositary prior
to the Expiration Date; and (iii) the Share Certificates (or a Book-Entry
Confirmation) evidencing all tendered Shares, in proper form for transfer,
together with this Letter of Transmittal (or a facsimile hereof), properly
completed and duly executed, with any required signature guarantees (or, in the
case of a book-entry delivery, an Agent's Message), and any other documents
required by this Letter of Transmittal, must be received by the Depositary
within three American Stock Exchange trading days after the date of execution of
such Notice of Guaranteed Delivery.

     THE METHOD OF DELIVERY OF THIS LETTER OF TRANSMITTAL, SHARE CERTIFICATES
AND ALL OTHER REQUIRED DOCUMENTS, INCLUDING DELIVERY THROUGH DTC, IS AT THE SOLE
OPTION AND RISK OF THE TENDERING STOCKHOLDER AND THE DELIVERY WILL BE DEEMED
MADE ONLY WHEN ACTUALLY RECEIVED BY THE DEPOSITARY. IF DELIVERY IS BY MAIL,
REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED.
IN ALL CASES, SUFFICIENT TIME SHOULD BE ALLOWED TO ENSURE TIMELY DELIVERY.

     No alternative, conditional or contingent tenders will be accepted. All
tendering stockholders, by execution of this Letter of Transmittal (or a
facsimile hereof), waive any right to receive any notice of the acceptance of
their Shares for payment.

     If Share Certificates are forwarded to the Depositary in multiple
deliveries, a properly completed and duly executed Letter of Transmittal must
accompany each such delivery.

     3.  Inadequate Space.  If the space provided herein is inadequate, the
Share Certificate numbers, the number of Shares and any other required
information should be listed on a separate signed schedule attached hereto and
referenced in the box entitled "Description of Shares Tendered."

     4.  Partial Tenders.  (Not Applicable to Book-Entry Stockholders.)  If
fewer than all the Shares evidenced by any Share Certificate submitted to the
Depositary herewith are to be tendered, fill in the number of Shares which are
to be
                                        6
<PAGE>   7

tendered in the box entitled "Number of Shares Tendered." In such cases, new
Share Certificate(s) evidencing the Shares that were evidenced by the Share
Certificate(s) delivered to the Depositary herewith, but which were not tendered
hereby, will be sent to the registered holder(s) shown above, unless otherwise
provided in the box entitled "Special Delivery Instructions," as soon as
practicable after the expiration or termination of the Offer. All Shares
represented by Share Certificates delivered to the Depositary will be deemed to
have been tendered unless otherwise indicated.

     5.  Signatures on Letter of Transmittal, Stock Powers and Endorsements.  If
this Letter of Transmittal is signed by the registered holder(s) of the Shares
tendered hereby, the signature(s) must correspond with the name(s) as written on
the face of the Share Certificate(s) without alteration, enlargement or any
change whatsoever.

     If any of the Shares tendered hereby are owned of record by two or more
persons, all such persons must sign this Letter of Transmittal.

     If any of the tendered Shares are registered in the names of different
holders, it will be necessary to complete, sign and submit as many separate
Letters of Transmittal as there are different registrations of Share
Certificates.

     If this Letter of Transmittal or any Share Certificate or stock power is
signed by a trustee, executor, administrator, guardian, attorney-in-fact,
officer of a corporation or other person acting in a fiduciary or representative
capacity, such person should so indicate when signing, and proper evidence
satisfactory to the Purchaser of such person's authority so to act must be
submitted.

     If this Letter of Transmittal is signed by the registered holder(s) of the
Shares listed and tendered hereby, no endorsements of Share Certificates or
separate stock powers are required, unless payment is to be made to, or Share
Certificates evidencing Shares not tendered or not purchased are to be issued in
the name of, a person other than the registered holder(s), in which case, the
Share Certificate(s) evidencing the Shares tendered hereby must be endorsed or
accompanied by appropriate stock powers signed exactly as the name(s) of the
registered holder(s) appear(s) on such Share Certificate(s). Signatures on such
Share Certificate(s) or stock powers must be guaranteed by an Eligible
Institution.

     If this Letter of Transmittal is signed by a person other than the
registered holder(s) of the Share Certificate(s) listed and tendered hereby, the
Share Certificate(s) must be endorsed or accompanied by appropriate stock
powers, in either case signed exactly as the name(s) of the registered holder(s)
appear on such Share Certificate(s). Signature(s) on such Share Certificate(s)
and stock powers must be guaranteed by an Eligible Institution.

     6.  Stock Transfer Taxes.  Except as set forth in this Instruction 6, the
Purchaser will pay or cause to be paid any stock transfer taxes with respect to
the transfer and sale of Shares to it or its order pursuant to the Offer. If,
however, payment of the purchase price of Shares accepted for payment is to be
made to, or if Share Certificate(s) evidencing Shares not tendered or not
purchased are to be issued in the name of, any person other than the registered
holder(s), or if tendered Share Certificates are registered in the name of any
person other than the person(s) signing this Letter of Transmittal, then the
amount of any stock transfer taxes (whether imposed on the registered holder(s)
or such person or otherwise) payable on account of the transfer to such other
person will be deducted from the purchase price unless satisfactory evidence of
the payment of such taxes, or an exemption therefrom, is submitted.

     EXCEPT AS SET FORTH IN THIS INSTRUCTION 6, IT WILL NOT BE NECESSARY FOR
TRANSFER TAX STAMPS TO BE AFFIXED TO THE SHARE CERTIFICATE(S) TENDERED HEREBY.

     7.  Special Payment and Delivery Instructions.  If a check for the purchase
price of Shares accepted for payment is to be issued in the name of, or Share
Certificate(s) evidencing Shares not tendered or not purchased are to be issued
or returned to, a person other than the signer of this Letter of Transmittal or
if a check or such Share Certificate(s) are to be returned to a person other
than the signer of this Letter of Transmittal or to an address of the signer
other than that shown in this Letter of Transmittal, the appropriate boxes on
this Letter of Transmittal must be completed.

     8.  Waiver of Conditions.  The conditions of the Offer may be waived by the
Purchaser, in whole or in part, at any time and from time to time in its sole
discretion.

     9.  Substitute Form W-9.  Under U.S. federal income tax law, a stockholder
whose tendered Shares are purchased is required to provide the Depositary with
such stockholder's correct taxpayer identification number ("TIN") (e.g., social
security number or employer identification number) on Substitute Form W-9 below
and to certify whether such

                                        7
<PAGE>   8

stockholder is subject to backup withholding of federal income tax. If a
tendering stockholder has been notified by the Internal Revenue Service (the
"IRS") that such stockholder is subject to backup withholding, such stockholder
must cross out item 2 of the Certification box (Part 2) of the Substitute Form
W-9, unless such stockholder has since been notified by the IRS that such
stockholder is no longer subject to backup withholding. Failure to provide the
information on the Substitute Form W-9 may subject the tendering stockholder to
federal income tax withholding at the rate of 31% on the payment of the purchase
price of all Shares purchased from the stockholder. If the Depositary is not
provided with the correct TIN, the IRS may subject the stockholder or other
payee to a $50 penalty.

     Certain stockholders are not subject to these backup withholding and
reporting requirements. Exempt recipients, such as corporations, are also
requested to provide their TIN and check the "Exempt" box in Part 3. Foreign
individuals or entities must submit a Form W-8 or W-8BEN, signed under penalties
of perjury, attesting to their foreign status. A Form W-8 or W8-BEN can be
obtained from the Depositary. See the enclosed "Guidelines for Certification of
Taxpayer Identification Number on Substitute Form W-9" for more instructions.

     IF BACKUP WITHHOLDING APPLIES, THE DEPOSITARY IS REQUIRED TO WITHHOLD 31%
OF ANY PAYMENTS MADE TO THE STOCKHOLDER OR OTHER PAYEE. BACKUP WITHHOLDING IS
NOT AN ADDITIONAL TAX. RATHER, THE TAX LIABILITY OF PERSONS SUBJECT TO BACKUP
WITHHOLDING WILL BE REDUCED BY THE AMOUNT OF TAX WITHHELD. IF WITHHOLDING
RESULTS IN AN OVERPAYMENT OF TAXES, A REFUND MAY BE OBTAINED FROM THE IRS.

     The "Awaiting TIN" box in Part 3 of the Substitute Form W-9 may be checked
if the tendering stockholder has not been issued a TIN and has applied for a TIN
or intends to apply for a TIN in the near future. If the "Awaiting TIN" box in
Part 3 is checked, the stockholder or other payee must also complete the
Certificate of Awaiting Taxpayer Identification Number below in order to avoid
backup withholding. If the "Awaiting TIN" box in Part 3 is checked and the
Certificate of Awaiting Taxpayer Identification Number is completed, the
Depositary will withhold 31% of all payments made unless a properly certified
TIN is provided to the Depositary within 60 days.

     The stockholder is required to give the Depositary the TIN of the record
owner of the Shares or of the last transferee appearing on the transfers
attached to, or endorsed on, the Shares. If the Shares are in more than one name
or are not in the name of the actual owner, consult the enclosed "Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9" for
additional guidance on which number to report.

     10.  Questions and Requests for Assistance or Additional Copies.  Questions
and requests for assistance may be directed to the Dealer Managers or the
Information Agent at their respective addresses and telephone numbers set forth
below. Additional copies of the Offer to Purchase, this Letter of Transmittal
and all other tender offer materials may be obtained from the Information Agent
or from brokers, dealers, commercial banks or trust companies at the Purchaser's
expense.

     11.  Lost, Destroyed or Stolen Certificates.  If any Share Certificate has
been lost, destroyed or stolen, the stockholder should promptly notify the
Depositary. The stockholder will then be instructed as to the steps that must be
taken in order to replace such Share Certificate. This Letter of Transmittal and
related documents cannot be processed until the procedures for replacing lost,
destroyed or stolen Share Certificates have been followed.

     IMPORTANT: THIS LETTER OF TRANSMITTAL (OR A FACSIMILE HEREOF), PROPERLY
COMPLETED AND DULY EXECUTED, OR, IF APPROPRIATE, AN AGENT'S MESSAGE, TOGETHER
WITH SHARE CERTIFICATES OR CONFIRMATION OF BOOK-ENTRY TRANSFER AND ALL OTHER
REQUIRED DOCUMENTS, OR A PROPERLY COMPLETED AND DULY EXECUTED NOTICE OF
GUARANTEED DELIVERY, MUST BE RECEIVED BY THE DEPOSITARY PRIOR TO THE EXPIRATION
DATE.

                                        8
<PAGE>   9

<TABLE>
<S>                                <C>                                                    <C>
- ----------------------------------------------------------------------------------------------------------------------------
PAYER'S NAME: AMERICAN STOCK TRANSFER & TRUST COMPANY
- ----------------------------------------------------------------------------------------------------------------------------
 SUBSTITUTE                         PART 1 -- PLEASE PROVIDE YOUR TIN IN THE BOX AT RIGHT  -------------------------------
 FORM W-9                           AND CERTIFY BY SIGNING AND DATING BELOW:                    Social security number
 DEPARTMENT OF THE TREASURY
 INTERNAL REVENUE SERVICE                                                                                 or
                                                                                           -------------------------------
 PAYER'S REQUEST FOR                                                                           Employer identification
 TAXPAYER IDENTIFICATION                                                                                number
 NUMBER (TIN)                                                                              (If Awaiting TIN, write "Applied
                                                                                                         For")
                                   -----------------------------------------------------------------------------------------
                                    PART 2 -- CERTIFICATION -- Under penalties of                     PART 3 --
                                    perjury, I certify that:                                       [ ] Awaiting TIN
                                    (1) The number shown on this form is my correct                [ ] Exempt
                                        Taxpayer Identification Number (or I am waiting
                                        for a number to be issued to me); and
                                    (2) I am not subject to backup withholding because:
                                        (a) I am exempt from backup withholding, or
                                        (b) I have not been notified by the Internal
                                            Revenue Service (the "IRS") that I am subject
                                            to backup withholding as a result of a failure
                                            to report all interest or dividends, or
                                        (c) the IRS has notified me that I am no longer
                                            subject to backup withholding.
                                   -----------------------------------------------------------------------------------------
                                    CERTIFICATION INSTRUCTIONS -- You must cross out Item (2) above if you have been
                                    notified by the IRS that you are subject to backup withholding because of underreporting
                                    interest or dividends on your tax return. However, if after being notified by the IRS
                                    that you are subject to backup withholding you received another notification from the
                                    IRS that you are no longer subject to backup withholding, do not cross out such item
                                    (2).
- ----------------------------------------------------------------------------------------------------------------------------

          SIGN HERE                SIGNATURE
                                   --------------------------------------   DATE _______________, 2000
- ----------------------------------------------------------------------------------------------------------------------------
</TABLE>

NOTE: FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP WITHHOLDING
      OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO THE OFFER. PLEASE REVIEW
      THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
      NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS.

                                        9
<PAGE>   10

               YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU
        CHECKED THE "AWAITING TIN" BOX IN PART 3 OF SUBSTITUTE FORM W-9.

             CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER

     I certify under penalties of perjury that a Taxpayer Identification Number
has not been issued to me, and either (1) I have mailed or delivered an
application to receive a Taxpayer Identification Number to the appropriate
Internal Revenue Service Center or Social Security Administration Office, or (2)
I intend to mail or deliver an application in the near future. I understand that
if I do not provide a Taxpayer Identification Number, 31% of all reportable
payments made to me may be withheld until I provide a Taxpayer Identification
Number with required certifications, which should be provided within 60 days.

Signature:
- --------------------------------------------------

Dated:________________________, 2000

                                       10
<PAGE>   11

                    The Information Agent for the Offer is:

                             D.F. KING & CO., INC.
                          77 Water Street, 20th Floor
                               New York, NY 10005
                Bankers and Brokers Call Collect (212) 269-5550
                    All Others Call Toll-Free (800) 290-6433

                     The Dealer Managers for the Offer are:

                          J.P. MORGAN SECURITIES INC.
                                 60 Wall Street
                               New York, NY 10260
                                 (877) 869-0656

                     THE BEACON GROUP CAPITAL SERVICES, LLC
                                399 Park Avenue
                               New York, NY 10022
                                 (212) 339-9100

<PAGE>   1

                         NOTICE OF GUARANTEED DELIVERY
                                      FOR

                        TENDER OF SHARES OF COMMON STOCK
                                       OF

                              THERMO SENTRON INC.

     As set forth in the section captioned "The Tender Offer -- Procedures For
Accepting The Offer And Tendering Shares" in the Offer to Purchase described
below, this Notice of Guaranteed Delivery or one substantially in the form
hereof must be used to tender shares of common stock, par value $0.01 per share
(the "Shares"), of Thermo Sentron Inc., a Delaware corporation (the "Company"),
pursuant to the Offer (as defined below) if certificates evidencing Shares are
not immediately available or the certificates evidencing Shares and all other
required documents cannot be delivered to American Stock Transfer & Trust
Company (the "Depositary") prior to the Expiration Date (as defined in the Offer
of Purchase), or if the procedures for delivery by book-entry transfer cannot be
completed on a timely basis. This instrument may be delivered by hand or
transmitted by facsimile transmission, overnight courier or mail to the
Depositary.

                        The Depositary for the Offer is:

                    AMERICAN STOCK TRANSFER & TRUST COMPANY

<TABLE>
<S>                                                 <C>
                     By Mail:                                  By Hand or Overnight Courier:
                  40 Wall Street                                      40 Wall Street
                    46th Floor                                          46th Floor
             New York, New York 10005                            New York, New York 10005
          Attn: Reorganization Department                     Attn: Reorganization Department
</TABLE>

                           By Facsimile Transmission:
                                 (718) 234-5001

                             Confirm by Telephone:
                                 (718) 921-8200

     DELIVERY OF THIS NOTICE OF GUARANTEED DELIVERY TO AN ADDRESS OTHER THAN AS
SET FORTH ABOVE, OR TRANSMISSIONS OF INSTRUCTIONS VIA A FACSIMILE NUMBER OTHER
THAN AS SET FORTH ABOVE, WILL NOT CONSTITUTE A VALID DELIVERY.

     This Notice of Guaranteed Delivery is not to be used to guarantee
signatures. If a signature on a Letter of Transmittal is required to be
guaranteed by an Eligible Institution (as defined in the Offer to Purchase)
under the instructions thereto, such signature guarantee must appear in the
applicable space provided in the signature box in the Letter of Transmittal.

              THE GUARANTEE ON THE REVERSE SIDE MUST BE COMPLETED.
<PAGE>   2

Ladies and Gentlemen:

     The undersigned hereby tenders to Sentron Acquisition, Inc., a Delaware
corporation and an indirect wholly-owned subsidiary of Thermedics Inc., a
Massachusetts corporation, upon the terms and subject to the conditions set
forth in the Offer to Purchase dated March 3, 2000 (the "Offer to Purchase") and
in the related Letter of Transmittal (which, together with any amendments or
supplements thereto, collectively constitute the "Offer"), receipt of each of
which is hereby acknowledged, the number of Shares indicated below pursuant to
the guaranteed delivery procedures set forth in the section of the Offer to
Purchase captioned "The Tender Offer -- Procedures For Accepting The Offer And
Tendering Shares."


- --------------------------------------------------------------------------------
<TABLE>
<S>                                                     <C>
 Signature(s):                                          Address:
               -------------------------------------             ------------------------------------------
 Name(s) of Record Holder(s):
                              ----------------------    ---------------------------------------------------
                                                                                                   Zip Code
 ---------------------------------------------------    Area Code and Tel. No.(s):
                Please Type or Print                                               ------------------------

 Number of Shares:                                      Check box if Shares will be tendered by book-entry
                   ---------------------------------    transfer:  [ ]

 Share Certificate No(s).(if available):                DTC Account Number:
                                         -----------                        -------------------------------

 ---------------------------------------------------

 ---------------------------------------------------
 Dated:                                       , 2000
        --------------------------------------
</TABLE>

                                   GUARANTEE
                   (Not to be used for signature guarantees)

      The undersigned, a firm which is a commercial bank, broker, dealer,
 credit union, savings association or other entity which is a member in good
 standing of the Securities Transfer Agents Medallion Program, the Stock
 Exchanges' Medallion Program or the New York Stock Exchange, Inc. Medallion
 Signature Program, hereby guarantees to either deliver to the Depositary
 certificates evidencing all the Shares tendered hereby, in proper form for
 transfer, or to deliver such Shares pursuant to the procedure for book-entry
 transfer into the Depositary's account at The Depository Trust Company, in
 either case together with the Letter of Transmittal (or a facsimile thereof),
 properly completed and duly executed, with any required signature guarantees
 or an Agent's Message (as defined in the Offer to Purchase) in the case of a
 book-entry transfer, and any other required documents, all within three
 American Stock Exchange trading days after the date hereof.

 Name of Firm:
              -----------------------------------------------------------------
 Address:
          ---------------------------------------------------------------------

 ------------------------------------------------------------------------------
                                                                       Zip Code
 Area Code and Tel. No.:
                         ------------------------------------------------------
 Authorized Signature:
                       --------------------------------------------------------
 Name:
       ------------------------------------------------------------------------
 Title:
        -----------------------------------------------------------------------
 Dated:                                                                  , 2000
        -----------------------------------------------------------------

     NOTE: DO NOT SEND CERTIFICATES WITH THIS NOTICE OF GUARANTEED DELIVERY.
         CERTIFICATES SHOULD BE SENT WITH YOUR LETTER OF TRANSMITTAL.


- --------------------------------------------------------------------------------

                                        2

<PAGE>   1

<TABLE>
<S>                                                    <C>
             J.P. MORGAN SECURITIES INC.                          THE BEACON GROUP CAPITAL SERVICES, LLC
                   60 WALL STREET                                      399 PARK AVENUE, 17TH FLOOR
                 NEW YORK, NY 10260                                         NEW YORK, NY 10022
                   (877) 869-0656                                             (212) 339-9100
</TABLE>

                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF

                              THERMO SENTRON INC.
                                       AT

                              $15.50 NET PER SHARE
                                       BY

                           SENTRON ACQUISITION, INC.
                     AN INDIRECT WHOLLY-OWNED SUBSIDIARY OF

                                THERMEDICS INC.

  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
        TIME, ON THURSDAY, MARCH 30, 2000, UNLESS THE OFFER IS EXTENDED.

                                                                   March 3, 2000

To Brokers, Dealers, Commercial Banks,
  Trust Companies and Other Nominees:

     We have been appointed by Sentron Acquisition, Inc., a Delaware corporation
(the "Purchaser") and an indirect wholly-owned subsidiary of Thermedics Inc., a
Massachusetts corporation ("Thermedics"), to act as Dealer Managers in
connection with the Purchaser's offer to purchase all outstanding shares of
common stock, par value $0.01 per share (the "Shares"), of Thermo Sentron Inc.,
a Delaware corporation (the "Company"), at a purchase price of $15.50 per Share,
net to the seller in cash, without interest thereon, upon the terms and subject
to the conditions set forth in the Offer to Purchase dated March 3, 2000 (the
"Offer to Purchase") and in the related Letter of Transmittal (which, together
with any amendments or supplements thereto, collectively constitute the "Offer")
enclosed herewith.

     THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS DESCRIBED IN THE OFFER TO
PURCHASE, THERE BEING VALIDLY TENDERED AND NOT WITHDRAWN PRIOR TO THE EXPIRATION
OF THE OFFER THAT NUMBER OF SHARES WHICH, TOGETHER WITH SHARES OWNED BY THERMO
ELECTRON CORPORATION AND ITS SUBSIDIARIES, INCLUDING THERMEDICS, CONSTITUTES AT
LEAST NINETY PERCENT (90%) OF THE OUTSTANDING SHARES ON THE EXPIRATION DATE (AS
DEFINED IN THE SECTION OF THE OFFER TO PURCHASE CAPTIONED "THE TENDER
OFFER -- TERMS OF THE OFFER; EXPIRATION DATE"). THE OFFER IS ALSO SUBJECT TO
OTHER IMPORTANT TERMS AND CONDITIONS CONTAINED IN THE OFFER TO PURCHASE.

     Enclosed for your information and for forwarding to your clients for whose
accounts you hold Shares registered in your name or in the name of your nominees
are copies of the following documents:

          1. The Offer to Purchase dated March 3, 2000.

          2. The Letter of Transmittal to tender Shares (for your use and for
     the information of your clients).

          3. The Notice of Guaranteed Delivery for Shares (to be used to accept
     the Offer if certificates evidencing Shares ("Share Certificates") are not
     immediately available or if such Share Certificates and all other required
     documents cannot be delivered to American Stock Transfer & Trust Company
     (the "Depositary") prior to the Expiration Date or if the procedures for
     book-entry transfer cannot be completed on a timely basis).

          4. A printed form of letter which may be sent to your clients for
     whose accounts you hold Shares registered in your name or in the name of
     your nominees, with space provided for obtaining such clients' instructions
     with regard to the Offer.

          5. Guidelines for Certification of Taxpayer Identification Number on
     Substitute Form W-9.

          6. A return envelope addressed to the Depositary.

     YOUR PROMPT ACTION IS REQUESTED. WE URGE YOU TO CONTACT YOUR CLIENTS AS
PROMPTLY AS POSSIBLE. PLEASE NOTE THAT THE OFFER AND WITHDRAWAL RIGHTS WILL
EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON THURSDAY, MARCH 30, 2000,
UNLESS THE OFFER IS EXTENDED.
<PAGE>   2

     In all cases, payment for Shares tendered and accepted for payment pursuant
to the Offer will be made only after timely receipt by the Depositary of (i)
certificates evidencing Shares ("Share Certificates") or timely confirmation of
a book-entry transfer of such Shares into the Depositary's account at the
Book-Entry Transfer Facility (as defined in the section of the Offer to Purchase
captioned "The Tender Offer -- Acceptance For Payment And Payment For Shares")
pursuant to the procedures set forth in the section of the Offer to Purchase
captioned "The Tender Offer -- Procedures For Accepting The Offer And Tendering
Shares," (ii) the Letter of Transmittal (or a facsimile thereof), properly
completed and duly executed, with any required signature guarantees, or an
Agent's Message (as defined in the section of the Offer to Purchase captioned
"The Tender Offer -- Acceptance For Payment And Payment For Shares") in
connection with a book-entry transfer, and (iii) any other documents required by
the Letter of Transmittal.

     If a stockholder desires to tender Shares pursuant to the Offer and such
stockholder's Share Certificates are not immediately available or such
stockholder cannot deliver the Share Certificates and all other required
documents to reach the Depositary prior to the Expiration Date, or such
stockholder cannot complete the procedure for delivery by book-entry transfer on
a timely basis, such Shares may nevertheless be tendered by following the
guaranteed delivery procedures specified in the section of the Offer to Purchase
captioned "The Tender Offer -- Procedures For Accepting The Offer And Tendering
Shares."

     No fees or commissions will be paid to brokers, dealers or any other
persons (other than to the Dealer Managers and D.F. King & Co., Inc. (the
"Information Agent"), as described in the Offer to Purchase) for soliciting
tenders of Shares pursuant to the Offer. The Purchaser will, however, upon
request, reimburse you for customary mailing and handling expenses incurred by
you in forwarding any of the enclosed materials to your clients.

     The Purchaser will pay or cause to be paid any transfer taxes payable on
the purchase of Shares by the Purchaser pursuant to the Offer, except as
otherwise provided in Instruction 6 of the Letter of Transmittal.

     Questions and requests for assistance or for additional copies of the
enclosed materials may be directed to the Dealer Managers or the Information
Agent, at their respective addresses and telephone numbers set forth on the back
cover of the Offer to Purchase.

                                        Very truly yours,

                                        J.P. Morgan Securities Inc.
                                        The Beacon Group Capital Services, LLC

     NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
OR ANY OTHER PERSON THE AGENT OF THERMO ELECTRON CORPORATION OR ANY OF ITS
SUBSIDIARIES (INCLUDING WITHOUT LIMITATION THERMEDICS AND THE PURCHASER), THE
COMPANY, THE DEALER MANAGERS, THE DEPOSITARY OR THE INFORMATION AGENT, OR ANY
AFFILIATE OF ANY OF THEM, OR AUTHORIZE YOU OR ANY OTHER PERSON TO MAKE ANY
STATEMENT OR USE ANY DOCUMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE
OFFER OTHER THAN THE ENCLOSED DOCUMENTS AND THE STATEMENTS CONTAINED THEREIN.

<PAGE>   1

                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK

                                       OF

                              THERMO SENTRON INC.
                                       AT

                              $15.50 NET PER SHARE

                                       BY

                           SENTRON ACQUISITION, INC.
                     AN INDIRECT WHOLLY-OWNED SUBSIDIARY OF

                                THERMEDICS INC.

  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
        TIME, ON THURSDAY, MARCH 30, 2000, UNLESS THE OFFER IS EXTENDED.

To Our Clients:

     Enclosed for your consideration is an Offer to Purchase dated March 3, 2000
(the "Offer to Purchase") and the related Letter of Transmittal (which, together
with any amendments or supplements thereto, collectively constitute the "Offer")
relating to an offer by Sentron Acquisition, Inc., a Delaware corporation (the
"Purchaser") and an indirect wholly-owned subsidiary of Thermedics Inc., a
Massachusetts corporation ("Thermedics"), to purchase all outstanding shares of
common stock, par value $0.01 per share (the "Shares"), of Thermo Sentron Inc.,
a Delaware corporation (the "Company"), at a purchase price of $15.50 per Share,
net to the seller in cash, without interest thereon, upon the terms and subject
to the conditions set forth in the Offer.

     We are the holder of record of Shares held by us for your account. A TENDER
OF SUCH SHARES CAN BE MADE ONLY BY US AS THE HOLDER OF RECORD AND PURSUANT TO
YOUR INSTRUCTIONS. THE LETTER OF TRANSMITTAL IS FURNISHED TO YOU FOR YOUR
INFORMATION ONLY AND CANNOT BE USED BY YOU TO TENDER SHARES HELD BY US FOR YOUR
ACCOUNT.

     We request instructions as to whether you wish to have us tender on your
behalf any or all of the Shares held by us for your account, pursuant to the
terms and subject to the conditions set forth in the Offer.

     Your attention is directed to the following:

     - The tender price is $15.50 per Share, net to the seller in cash, without
       interest thereon.

     - The Offer and withdrawal rights will expire at 12:00 midnight, New York
       City time, on Thursday, March 30, 2000, unless the Offer is extended.

     - The Offer is made for all of the outstanding Shares.

     - The Offer is conditioned upon, among other things described in the Offer
       to Purchase, there being validly tendered and not withdrawn prior to the
       expiration of the Offer that number of Shares which, together with Shares
       owned by Thermo Electron Corporation and its subsidiaries, including
       Thermedics, constitutes at least ninety percent (90%) of the outstanding
       Shares on the Expiration Date (as defined in the section of the Offer to
       Purchase captioned "The Tender Offer -- Terms Of The Offer; Expiration
       Date"). The Offer is also subject to other important terms and conditions
       contained in the Offer to Purchase.
<PAGE>   2

     - Tendering stockholders will not be obligated to pay brokerage fees or
       commissions or, except as set forth in Instruction 6 of the Letter of
       Transmittal, transfer taxes on the purchase of Shares by the Purchaser
       pursuant to the Offer.

     - In all cases, payment for Shares tendered and accepted for payment
       pursuant to the Offer will be made only after timely receipt by American
       Stock Transfer & Trust Company (the "Depositary") of (i) certificates
       evidencing Shares or timely confirmation of a book-entry transfer of such
       Shares into the Depositary's account at the Book Entry Transfer Facility
       (as defined in the section of the Offer to Purchase captioned "The Tender
       Offer -- Acceptance For Payment And Payment For Shares") pursuant to the
       procedures set forth in the section of the Offer to Purchase captioned
       "The Tender Offer -- Procedures For Accepting The Offer And Tendering
       Shares," (ii) the Letter of Transmittal (or a facsimile thereof),
       properly completed and duly executed, with any required signature
       guarantees, or an Agent's Message (as defined in the section of the Offer
       to Purchase captioned "The Tender Offer -- Acceptance For Payment And
       Payment For Shares") in connection with a book-entry transfer and (iii)
       any other documents required by the Letter of Transmittal.

     The Offer is being made solely by the Offer to Purchase and the related
Letter of Transmittal and is being made to all holders of Shares. The Offer is
not being made to (nor will tenders be accepted from or on behalf of) holders of
Shares in any jurisdiction in which the making of the Offer or the acceptance
thereof would not be in compliance with the laws of such jurisdiction. In any
jurisdiction where the securities, blue sky or other laws require the Offer to
be made by a licensed broker or dealer, the Offer shall be deemed to be made on
behalf of the Purchaser by J.P. Morgan Securities Inc., The Beacon Group Capital
Services, LLC or one or more registered brokers or dealers licensed under the
laws of such jurisdiction.

     If you wish to have us tender any or all of the Shares held by us for your
account, please instruct us by completing, executing and returning to us the
instruction form contained in this letter. If you authorize a tender of your
Shares, all such Shares will be tendered unless otherwise specified in such
instruction form. YOUR INSTRUCTIONS SHOULD BE FORWARDED TO US IN AMPLE TIME TO
PERMIT US TO SUBMIT A TENDER ON YOUR BEHALF PRIOR TO THE EXPIRATION OF THE
OFFER.

                                        2
<PAGE>   3

                            ------------------------

                        INSTRUCTIONS WITH RESPECT TO THE
                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF

                              THERMO SENTRON INC.

     The undersigned acknowledge(s) receipt of your letter enclosing the Offer
to Purchase dated March 3, 2000 (the "Offer to Purchase") and the related Letter
of Transmittal (which, together with any amendments or supplements thereto,
collectively constitute the "Offer") pursuant to an offer by Sentron
Acquisition, Inc., a Delaware corporation and an indirect wholly-owned
subsidiary of Thermedics Inc., a Massachusetts corporation, to purchase all of
the outstanding shares of common stock, par value $0.01 per share (the
"Shares"), of Thermo Sentron Inc., a Delaware corporation.

     This will instruct you to tender the number of Shares indicated below (or,
if no number is indicated below, all Shares) that are held by you for the
account of the undersigned, upon the terms and subject to the conditions set
forth in the Offer.

<TABLE>
<CAPTION>
<S>  <C>                                                 <C>
     ------------------------------------------------
     Number of Shares to be
     Tendered(1):
     ------------------------------------------------
     Dated: ------------------------------, 2000

                                            SIGN HERE    x
                                                         ------------------------------------------------
                                                         Signature(s):
                                                         ------------------------------------------------
                                                         Please type or print name(s):
                                                         ------------------------------------------------
                                                         Address:
                                                         ------------------------------------------------
                                                         Area Code and Telephone Number:
                                                         ------------------------------------------------
                                                         Tax Identification or Social Security No:

  (1) Unless otherwise indicated, it will be assumed that all of the Shares held by us for your account
      are to be tendered.
</TABLE>

                                        3

<PAGE>   1
This announcement is neither an offer to purchase nor a solicitation of an offer
to sell Shares. The Offer is being made solely by the Offer to Purchase dated
March 3, 2000 and the related Letter of Transmittal and is being made to all
holders of Shares. The Offer is not being made to (nor will tenders be accepted
from or on behalf of) holders of Shares in any jurisdiction in which the making
of the Offer or the acceptance thereof would not be in compliance with the laws
of such jurisdiction. In any jurisdiction where the securities, blue sky or
other laws require the Offer to be made by a licensed broker or dealer, the
Offer shall be deemed to be made on behalf of the Purchaser by J.P. Morgan
Securities Inc., The Beacon Group Capital Services, LLC or one or more
registered brokers or dealers licensed under the laws of such jurisdiction.

NOTICE OF OFFER TO PURCHASE FOR CASH

ALL OUTSTANDING SHARES OF COMMON STOCK

OF

THERMO SENTRON INC.

AT

$15.50 NET PER SHARE

BY

SENTRON ACQUISITION, INC.

AN INDIRECT WHOLLY-OWNED SUBSIDIARY OF

THERMEDICS INC.

Sentron Acquisition, Inc., a Delaware corporation (the "Purchaser") and an
indirect wholly-owned subsidiary of Thermedics Inc., a Massachusetts
corporation ("Thermedics"), is offering to purchase all outstanding shares of
common stock, par value $0.01 per share (the "Shares"), of Thermo Sentron Inc.,
a Delaware corporation (the "Company"), at a purchase price of $15.50 per Share,
net to the seller in cash, without interest thereon, upon the terms and subject
to the conditions set forth in the Offer to Purchase dated March 3, 2000
(the "Offer to Purchase") and in the related Letter of Transmittal (which,
together with any amendments or supplements thereto, collectively constitute the
"Offer"). The Purchaser is a wholly-owned subsidiary of Corpak Inc. ("Corpak"),
a Massachusetts corporation and wholly-owned subsidiary of Thermedics. Thermo
Electron Corporation, a Delaware corporation ("Thermo Electron"), owns a
majority of the outstanding shares of common stock of Thermedics.


 -------------------------------------------------------------------------------
                         THE OFFER AND WITHDRAWAL RIGHTS
                  WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
                 TIME, ON THURSDAY, MARCH 30, 2000, UNLESS THE
                               OFFER IS EXTENDED.
 -------------------------------------------------------------------------------

THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY TENDERED
AND NOT WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT NUMBER OF SHARES
WHICH, TOGETHER WITH SHARES OWNED BY THERMO ELECTRON AND ITS SUBSIDIARIES,
INCLUDING THERMEDICS, CONSTITUTES AT LEAST NINETY PERCENT (90%) OF THE
OUTSTANDING SHARES OF THE COMPANY ON THE EXPIRATION DATE. THE OFFER IS ALSO
SUBJECT TO CERTAIN OTHER IMPORTANT TERMS AND CONDITIONS CONTAINED IN THE OFFER
TO PURCHASE.



<PAGE>   2
The Offer is the first step in Thermedics' plan to take the Company private. The
purpose of the Offer is to acquire the minority interest in the Company as part
of an overall reorganization of Thermo Electron. If the Offer is completed,
Thermo Electron, Corpak and the Purchaser together will own at least 90% of the
Shares. Promptly following the closing of the Offer, Corpak and Thermo Electron
plan to contribute their Shares to the Purchaser and cause the Purchaser to
merge with and into the Company in a so-called "short-form" merger between the
Company and the Purchaser (the "Merger"). Stockholders of the Company who do not
tender their Shares in the Offer will not be entitled to vote on the Merger. The
consideration per Share in the Merger (other than with respect to Shares held by
stockholders, if any, who are entitled to and perfect their appraisal rights
under Delaware law) would be the same as the Offer price of $15.50.

For purposes of the Offer, the Purchaser will be deemed to have accepted for
payment, and thereby purchased, Shares validly tendered and not properly
withdrawn if, as and when the Purchaser gives oral or written notice to American
Stock Transfer & Trust Company (the "Depositary") of the Purchaser's acceptance
for payment of such Shares pursuant to the Offer. Upon the terms and subject to
the conditions of the Offer, payment for Shares so accepted for payment pursuant
to the Offer will be made by deposit of the aggregate purchase price therefor
with the Depositary, which will act as agent for tendering stockholders for the
purpose of receiving payment from the Purchaser and transmitting such payment to
stockholders whose Shares have been accepted for payment. UNDER NO CIRCUMSTANCES
WILL INTEREST ON THE PURCHASE PRICE FOR SHARES BE PAID, REGARDLESS OF ANY
EXTENSION OF THE OFFER OR ANY DELAY IN MAKING SUCH PAYMENT. In all cases,
payment for Shares tendered and accepted for payment pursuant to the Offer will
be made only after timely receipt by the Depositary of (i) certificates
evidencing Shares ("Share Certificates") or timely confirmation of a book-entry
transfer of such Shares into the Depositary's account at the Book-Entry Transfer
Facility (as defined in the section of the Offer to Purchase captioned "The
Tender Offer -- Acceptance For Payment And Payment For Shares") pursuant to the
procedures set forth in the section of the Offer to Purchase captioned "The
Tender Offer -- Acceptance For Payment And Payment For Shares," (ii) the Letter
of Transmittal (or a facsimile thereof), properly completed and duly executed,
with any required signature guarantees, or an Agent's Message (as defined in the
section of the Offer to Purchase captioned "The Tender Offer -- Acceptance For
Payment And Payment For Shares") in connection with a book-entry transfer and
(iii) any other documents required by the Letter of Transmittal.

The term "Expiration Date" means 12:00 midnight, New York City time, on
Thursday, March 30, 2000, unless and until the Purchaser, in its sole
discretion, shall have extended the period during which the Offer is open, in
which event the term "Expiration Date" shall mean the latest time and date at
which the Offer, as so extended by the Purchaser, shall expire.

Subject to the applicable rules and regulations of the Securities and Exchange
Commission, the Purchaser expressly reserves the right, in its sole discretion,
at any time and from time to time, to extend the period during which the Offer
is open for any reason, including the failure to satisfy any of the conditions
specified in the section of the Offer to Purchase captioned "The Tender Offer --
Certain Conditions Of The Offer," and thereby delay acceptance for payment of,
or payment for, any Shares, by giving oral or written notice of such extension
to the Depositary. Any such extension will be followed as promptly as
practicable by a public announcement thereof, such announcement to be made no
later than 9:00 a.m., New York City time, on the next business day after the
previously scheduled Expiration Date. During any such extension, all Shares
previously tendered and not properly withdrawn will remain subject to the Offer,
subject to the right of a tendering stockholder to withdraw such stockholder's
Shares.

Except as otherwise provided in the section of the Offer to Purchase captioned
"The Tender Offer -- Withdrawal Rights," tenders of Shares made pursuant to the
Offer are irrevocable. Shares tendered pursuant to the Offer may be withdrawn at
any time prior to the Expiration Date and, unless previously accepted for
payment by the Purchaser pursuant to the Offer, may also be withdrawn at any
time after May 1, 2000. In order for a withdrawal to be effective, a written,
telegraphic or facsimile transmission notice of withdrawal must be timely
received by the Depositary at one of its addresses set forth on the back cover
of the Offer to Purchase. Any such notice of withdrawal must specify the name of
the person who tendered the Shares to be withdrawn, the number of Shares to be
withdrawn and the name of the registered holder of the Shares to be withdrawn,
if different from that of the person who tendered such Shares. If Share
Certificates to be withdrawn have been delivered or otherwise identified to the
Depositary, then, prior to the physical release of such Share Certificates, the
tendering stockholder must also submit the serial numbers shown on such Share
Certificates to the Depositary, and the signatures on the notice of withdrawal
must be guaranteed by an Eligible Institution (as defined in the section of the
Offer to Purchase captioned "The Tender Offer -- Procedures For Accepting The
Offer And Tendering Shares"), unless such Shares have been tendered for the
account of an Eligible Institution. If Shares have been tendered pursuant to the
procedures for book-entry transfer, as set forth in the section of the Offer to





<PAGE>   3
Purchase captioned "The Tender Offer -- Procedures For Accepting The Offer And
Tendering Shares," any notice of withdrawal must specify the name and number of
the account at the Book-Entry Transfer Facility to be credited with the
withdrawn Shares and must otherwise comply with the procedures of the Book-Entry
Transfer Facility. Withdrawals may not be revoked, and any Shares properly
withdrawn will thereafter be deemed not to have been validly tendered for
purposes of the Offer. However, withdrawn Shares may be retendered at any time
prior to the Expiration Date by following the procedures described in the
section of the Offer to Purchase captioned "The Tender Offer -- Procedures For
Accepting The Offer And Tendering Shares." All questions as to the form and
validity (including the time of receipt) of any notice of withdrawal will be
determined by the Purchaser, in its sole discretion, whose determination will be
final and binding.

The information required to be disclosed by Rule 14d-6(d)(1) and Rule
13e-3(e)(1) of the General Rules and Regulations under the Securities Exchange
Act of 1934, as amended, is contained in the Offer to Purchase and is
incorporated herein by reference.

The Company has provided the Purchaser with the Company's stockholder list and
security position listings for the purpose of disseminating the Offer to holders
of Shares. The Offer to Purchase, the related Letter of Transmittal and, if
required, other relevant material will be mailed to record holders of Shares
whose names appear on the Company's stockholder list and will be furnished to
brokers, dealers, commercial banks, trust companies and similar persons whose
names, or the names of whose nominees, appear on the Company's stockholder list
or, if applicable, who are listed as participants in a clearing agency's
security position listing for subsequent transmittal to beneficial owners of
Shares.

The receipt of cash for Shares pursuant to the Offer will be a taxable
transaction for U.S. federal income tax purposes.

THE OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN IMPORTANT
INFORMATION WHICH SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE WITH
RESPECT TO THE OFFER.

Tendering stockholders of record who tender Shares directly will not be
obligated to pay brokerage fees or commissions or, except as set forth in
Instruction 6 of the Letter of Transmittal, stock transfer taxes on the purchase
of Shares by the Purchaser pursuant to the Offer. Stockholders who hold their
Shares through a bank or a broker should check with such institution as to
whether it charges any service fees. The Purchaser will pay the expenses of the
Depositary, D.F. King & Co., Inc., who is acting as the information agent (the
"Information Agent"), and J.P. Morgan Securities Inc. and The Beacon Group
Capital Services, LLC, who are acting as dealer managers (collectively, the
"Dealer Managers"), in connection with the Offer.

Questions and requests for assistance or for additional copies of the Offer to
Purchase, the Letter of Transmittal and all other tender offer materials may be
directed to the Information Agent or the Dealer Managers as set forth below, and
copies will be furnished promptly at the Purchaser's expense. No fees or
commissions will be paid to brokers, dealers or any other persons (other than
the Dealer Managers and the Information Agent) for soliciting tenders of Shares
pursuant to the Offer.

The Information Agent for the Offer is:

D.F. King & Co., Inc.
77 Water Street, 20th Floor
New York, NY 10005
Bankers and Brokers call collect: (212) 269-5550
All Others Call Toll Free: (800) 290-6433

The Dealer Managers for the Offer are:

J.P. Morgan Securities Inc.
60 Wall Street
New York, NY 10260
(877) 869-0656

The Beacon Group Capital Services, LLC
399 Park Avenue

<PAGE>   4
New York, NY 10022
(212) 339-9100


March 3, 2000




<PAGE>   1

            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9

GUIDELINES FOR DETERMINING THE PROPER IDENTIFICATION NUMBER TO GIVE THE
PAYER.--Social Security numbers have nine digits separated by two hyphens: i.e.,
000-00-0000. Employer identification numbers have nine digits separated by only
one hyphen: i.e., 00-0000000. The table below will help determine the number to
give the Payer.

<TABLE>
<C>  <S>                                 <C>
- ------------------------------------------------------------
                                         GIVE THE
              FOR THIS TYPE OF ACCOUNT:  SOCIAL SECURITY
                                         NUMBER OF--
- ------------------------------------------------------------

 1.  An individual's account             The individual
 2.  Two or more individuals (joint      The actual owner of
     account)                            the account or, if
                                         combined funds, the
                                         first individual on
                                         the account(1)
 3.  Husband and wife (joint account)    The actual owner of
                                         the account or, if
                                         joint funds, the
                                         first individual on
                                         the account(1)
 4.  Custodian account of a minor        The minor(2)
     (Uniform Gift to Minors Act)
 5.  Adult and minor (joint account)     The adult or, if
                                         the minor is the
                                         only contributor,
                                         the minor(1)
 6.  Account in the name of guardian or  The ward, minor or
     committee for a designated ward,    incompetent
     minor or incompetent person         person(3)
 7.  (a) The usual revocable savings     The grantor-
         trust account (grantor is also  trustee(1)
         trustee)
     (b) So-called trust account that    The actual owner(1)
         is not a legal or valid trust
         under State law
 8.  Sole proprietorship account         The owner(4)
- ------------------------------------------------------------
- ------------------------------------------------------------
                                         GIVE THE EMPLOYER
              FOR THIS TYPE OF ACCOUNT:  IDENTIFICATION
                                         NUMBER OF--
- ------------------------------------------------------------

 9.  A valid trust, estate or pension    The legal entity
     trust                               (Do not furnish the
                                         identifying number
                                         of the personal
                                         representative or
                                         trustee unless the
                                         legal entity itself
                                         is not designated
                                         in the account
                                         title.)(5)
10.  Corporate account                   The corporation
11.  Religious, charitable or            The organization
     educational organization account
12.  Partnership account held in the     The partnership
     name of the business
13.  Association, club or other tax-     The organization
     exempt organization
14.  A broker or registered nominee      The broker or
                                         nominee
15.  Account with the Department of      The public entity
     Agriculture in the name of a
     public entity (such as a State or
     local government, school district,
     or prison) that receives
     agricultural program payments
- ------------------------------------------------------------
</TABLE>

(1) List first and circle the name of the person whose number you furnish.
(2) Circle the minor's name and furnish the minor's social security number.
(3) Circle the ward's, minor's or incompetent person's name and furnish such
    person's social security number.
(4) Show the name of the owner.
(5) List first and circle the name of the legal trust, estate or pension trust.

NOTE: If no name is circled when there is more than one name, the number will be
      considered to be that of the first name listed.
<PAGE>   2

            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9

                                     PAGE 2

OBTAINING A NUMBER
If you don't have a taxpayer identification number or you don't know your
number, obtain Form SS-5, Application for a Social Security Number Card (for
individuals), or Form SS-4, Application for Employer Identification Number (for
businesses and all other entities), at the local office of the Social Security
Administration or the Internal Revenue Service and apply for a number.

PAYEES EXEMPT FROM BACKUP WITHHOLDING
Payees specifically exempted from backup withholding on ALL payments include the
following (Section references are to the Internal Revenue Code):
  - A corporation.
  - A financial institution.
  - An organization exempt from tax under section 501(a), or an individual
    retirement plan, or a custodial account under section 403(b)(7).
  - The United States or any agency or instrumentality thereof.
  - A State, the District of Columbia, a possession of the United States, or any
    subdivision or instrumentality thereof.
  - A foreign government, a political subdivision of a foreign government, or
    any agency or instrumentality thereof.
  - An international organization or any agency, or instrumentality thereof.
  - A registered dealer in securities or commodities registered in the U.S. or
    possession of the U.S.
  - A real estate investment trust.
  - A common trust fund operated by a bank under section 584(a).
  - An exempt charitable remainder trust, or a non-exempt trust described in
    section 4947(a)(1).
  - An entity registered at all times under the Investment Company Act of 1940.
  - A foreign central bank of issue.
Payments of dividends and patronage dividends not generally subject to backup
withholding include the following:
  - Payments to nonresident aliens subject to withholding under section 1441.
  - Payments to partnerships not engaged in a trade or business in the U.S. and
    which have at least one nonresident partner.
  - Payments of patronage dividends where the amount received is not paid in
    money.
  - Payments made by certain foreign organizations.
  - Payments made to a nominee.
Payments of interest not generally subject to backup withholding include the
following:
  - Payments of interest on obligations issued by individuals.

  NOTE: You may be subject to backup withholding if this interest is $600 or
more and is paid in the course of the payer's trade or business and you have not
provided your correct taxpayer identification number to the payer.
  - Payments of tax-exempt interest (including exempt-interest dividends under
    section 852).
  - Payments described in section 6049(b)(5) to nonresident aliens.
  - Payments on tax-free government bonds under section 1451.
  - Payments made by certain foreign organizations.
  - Payments made to a nominee.
Exempt payees described above should file the Substitute Form W-9 to avoid
possible erroneous backup withholding. FILE THIS FORM WITH THE PAYER, FURNISH
YOUR TAXPAYER IDENTIFICATION NUMBER, WRITE "EXEMPT" ON THE FACE OF THE FORM,
SIGN AND DATE THE FORM AND RETURN IT TO THE PAYER.

Certain payments other than interest, dividends, and patronage dividends that
are not subject to information reporting are also not subject to backup
withholding. For details, see sections 6041, 6041A(a), 6042, 6044, 6045, 6049,
6050A and 6050N, and the regulations under those sections.

PRIVACY ACT NOTICE.--Section 6109 requires most recipients of dividend,
interest, or other payments to give taxpayer identification numbers to payers
who must report the payments to the IRS. The IRS uses the numbers for
identification purposes and to help verify the accuracy of tax returns. Payers
must be given the numbers whether or not recipients are required to file a tax
return. Payers must generally withhold 31% of taxable interest, dividend, and
certain other payments to a payee who does not furnish a taxpayer identification
number to a payer. Certain penalties may also apply.

PENALTIES
(1) PENALTY FOR FAILURE TO FURNISH TAXPAYER IDENTIFICATION NUMBER.--If you fail
to furnish your taxpayer identification number to a payer, you are subject to a
penalty of $50 for each such failure unless your failure is due to reasonable
cause and not to willful neglect.
(2) FAILURE TO REPORT CERTAIN DIVIDEND AND INTEREST PAYMENTS.--If you fail to
include any portion of an includible payment for interest, dividends or
patronage dividends in gross income, such failure is strong evidence of
negligence. If negligence is shown, you will be subject to a penalty of 20% on
any portion of an underpayment attributable to that failure.
(3) CIVIL PENALTY FOR FALSE INFORMATION WITH RESPECT TO WITHHOLDING.--If you
make a false statement with no reasonable basis which results in no imposition
of backup withholding, you are subject to a penalty of $500.
(4) CRIMINAL PENALTY FOR FALSIFYING INFORMATION.--Willfully falsifying
certifications or affirmations may subject you to criminal penalties including
fines and/or imprisonment.

 FOR ADDITIONAL INFORMATION CONTACT YOUR TAX CONSULTANT OR THE INTERNAL REVENUE
                                    SERVICE.

<PAGE>   1
           THERMEDICS COMMENCES CASH TENDER OFFER FOR THERMO SENTRON

WOBURN, Mass., March 3, 2000 - Thermedics Inc. (ASE-TMD), a Thermo Electron
company, announced today that it has commenced its previously announced cash
tender offer of $15.50 per share for all outstanding shares of its Thermo
Sentron Inc. subsidiary. The offer and withdrawal rights will expire at midnight
on Thursday, March 30, 2000, unless the offer is extended. The tender offer is
part of a major reorganization plan under which Thermedics' parent company,
Thermo Electron Corporation (NYSE-TMO), will spin in, spin off, and sell various
businesses to focus solely on its core measurement and detection instruments
business.

The complete terms and conditions of the offer are set forth in the offer to
purchase, letter of transmittal, and other related materials being filed today
with the Securities and Exchange Commission (SEC). Copies of the offer and
transmittal letter are being distributed to Thermo Sentron shareholders.

The goal of the tender offer is to bring Thermedics' and Thermo Electron's
combined equity ownership in Thermo Sentron to at least 90 percent. If
Thermedics and Thermo Electron achieve this 90-percent-ownership level, Thermo
Sentron would then be spun into Thermedics through a "short-form" merger at the
same cash price as the tender offer. Thermedics expects to complete the spin-in
of Thermo Sentron in the second quarter of 2000.

The tender offer and proposed subsequent short-form merger require SEC clearance
of necessary filings. The short-form merger would not require Thermo Sentron
board or shareholder approval.

Thermedics Inc. develops, manufactures, and markets diverse product lines,
including implantable heart-assist devices and other biomedical products,
security instruments, and equipment that assures the quality of a wide variety
of consumer products and bulk materials. Thermedics is a public subsidiary of
Thermo Electron Corporation. More information is available on the Internet at
http://www.thermo.com/subsid/tmd1.html.

The following constitutes a "Safe Harbor" statement under the Private Securities
Litigation Reform Act of 1995: This press release contains forward-looking
statements that involve a number of risks and uncertainties. Important factors
that could cause actual results to differ materially from those indicated by
such forward-looking statements are set forth under the heading "Forward-looking
Statements" in Exhibit 13 to the company's annual report on Form 10-K for the
year ended January 2, 1999. These include risks and uncertainties relating to:
government regulation and industry standards, competition and technological
change, intellectual property rights, reimbursement by insurers for medical
procedures, medical community acceptance of medical devices, availability of
materials and components, product liability, international operations, and the
company's spinout and acquisition strategies.



<PAGE>   1

                                                                   March 1, 2000

Thermedics Inc.
470 Wildwood Street
Woburn, MA 01888
Attn:  John Keiser

Dear Jack:

     Reference is made to Thermedics Inc.'s proposed acquisitions of the
minority interest investment in each of its majority owned subsidiaries, Thermo
Sentron Inc. and Thermedics Detection Inc. In connection with those
transactions, Thermo Electron Corporation intends to loan Thermedics up to
$20,000,000 for the acquisition of such interests in each of Thermo Sentron and
Thermedics Detection. This loan will be available at an interest rate equal to
the 30-day Dealer Commercial Paper Rate plus 150 basis points, set at the
beginning of each month, provided such rate shall be reduced to the Dealer
Commercial Paper Rate plus 50 basis points to the extent of any funds invested
by Thermedics' majority owned subsidiaries in Thermo Electron's cash management
arrangement. Interest will be due and payable on a monthly basis and the loan
will be payable in full on September 1, 2000. If these terms are acceptable to
you, please sign the letter as indicated below to evidence your acceptance of
the terms.


                                     Sincerely,

                                     THERMO ELECTRON CORPORATION

                                     /s/Theo Melas-Kyriazi


                                     Theo Melas-Kyriazi
                                     Vice President and Chief Financial Officer


ACCEPTED AND AGREED TO:

THERMEDICS INC.



John T. Keiser
/s/John T. Keiser
President and CEO



<PAGE>   1
January 29, 2000


Board of Directors
Thermo Electron Corporation
81 Wyman Street
Post Office Box 9046
Waltham, MA  02454-0946

Attention:  Dr. Richard Syron
            Chairman and Chief Executive Officer


Board of Directors
Thermedics Inc.
470 Wildwood Street
Woburn, MA  01888

Attention:  Mr. John Keiser
            President and Chief Executive Officer


Ladies and Gentlemen:

J.P. Morgan Securities Inc. ("J.P. Morgan") and The Beacon Group Capital
Services, LLC (collectively "we", "us" and "our") understand that Thermedics
Inc. ("Thermedics"), a subsidiary of Thermo Electron Corporation ("Thermo
Electron"), proposes to acquire all of the outstanding common stock, par value
$.01 per share, (the "Shares") of Thermo Sentron Inc. (the "Company") not
currently held by Thermo Electron or its subsidiaries from the holders thereof
at a purchase price of $15.50 per Share, net to the seller in cash (the
"Consideration"), pursuant to (i) an offer (the "Offer") by Sentron Acquisition,
Inc. (the "Purchaser"), an indirect wholly-owned subsidiary of Thermedics, to
purchase all of the outstanding Shares and (ii) the subsequent merger (the
"Merger") of the Purchaser with and into the Company. You have requested our
joint opinion as to the fairness, from a financial point of view, to Thermedics
and to Thermo Electron of the Consideration proposed to be paid pursuant to the
Offer and the Merger.

In arriving at our opinion, we have reviewed (i) certain publicly available
information concerning the business of the Company and of certain other
companies engaged in businesses deemed to be comparable to those of the Company;
(ii) the reported market prices of the securities of certain other companies
deemed by us to be comparable to the Company; (iii) publicly available terms of
certain transactions involving companies deemed
<PAGE>   2
                                      -2-


by us to be comparable to the Company and the consideration paid for such
companies; (iv) current and historical market prices of the Shares; (v) the
audited financial statements of Thermedics, Thermo Electron and the Company for
the fiscal year ended January 2, 1999 and the unaudited financial statements of
Thermedics, Thermo Electron and the Company for the period ended October 2,
1999; (vi) certain agreements with respect to outstanding indebtedness or
obligations of Thermedics, Thermo Electron and the Company; (vii) the terms of
other business combinations that we deemed relevant; and (viii) projections for
the the period from October 2, 1999 through December 31, 1999 and for fiscal
2000 prepared by the Company in November 1999 (the "2000 Projections").

In addition, we have held discussions with certain members of the managements of
Thermedics and Thermo Electron with respect to certain aspects of the Offer and
the Merger, the past and current business operations of the Company, the
financial condition and future prospects and operations of the Company and
certain other matters we believed necessary or appropriate to our inquiry. We
did not hold any discussions with the management of the Company. We have
reviewed such other financial studies and analyses and considered such other
information as we deemed appropriate for the purposes of this opinion. However,
the 2000 Projections were the only information prepared by the Company which we
reviewed.

In giving our opinion, we have relied upon and assumed, without independent
verification, the accuracy and completeness of all information that was publicly
available or was furnished to, or discussed with, us, by Thermedics, Thermo
Electron or the Company or was otherwise reviewed by us, and we have not assumed
any responsibility or liability therefor. We have also assumed that there have
been no material changes in the Company's financial condition, results of
operations, business or prospects since the date of the most recent financial
statements made available to us. We have not conducted, and we have not assumed
any responsibility for conducting, any valuation, appraisal or physical
inspection of any assets or liabilities (contingent or otherwise), nor have any
such valuations or appraisals been provided to us. In relying on the financial
analyses, projections and estimates provided to, or discussed with, us, we have
assumed that they have been reasonably prepared based on assumptions reflecting
the best currently available estimates and judgments by management as to the
expected future financial performance of the Company. We have relied as to all
legal matters relevant to rendering our opinion upon the advice of counsel.

Our opinion is necessarily based on economic, market and other conditions as in
effect on, and the information made available to us as of, the date hereof. It
should be understood that subsequent developments may affect the conclusions in
this opinion and that we do not have any obligation to update, revise or
reaffirm this opinion.

We have acted as financial advisors to Thermedics and Thermo Electron with
respect to the proposed Offer and Merger and will receive a fee from Thermo
Electron for our services. We have also acted as financial advisors to Thermo
Electron for the purpose of advising

<PAGE>   3

                                      -3-


Thermo Electron in connection with its strategic alternatives, including the
proposed reorganization of Thermo Electron and its subsidiaries. As part of the
proposed reorganization of Thermo Electron, it is contemplated that Thermo
Electron will acquire the publicly-held minority interest in Thermedics. We will
receive separate fees for services with respect to other elements of Thermo
Electron's reorganization, including acting as financial advisors to Thermo
Electron in connection with the acquisition of the publicly-held minority
interest in Thermedics. These other fees include a minimum retainer for each of
us and additional compensation if some or all of the other elements of Thermo
Electron's reorganization are completed. In the ordinary course of their
businesses, J.P. Morgan and its affiliates may actively trade the debt and
equity securities of Thermedics, Thermo Electron or the Company and their
affiliates for their own account or for the accounts of customers and,
accordingly, they may at any time hold long or short positions in such
securities.

On the basis of and subject to the foregoing, it is our opinion as of the date
hereof that the Consideration to be paid pursuant to the Offer and the Merger is
fair, from a financial point of view, to Thermedics and to Thermo Electron.

This letter is provided to the Boards of Directors of Thermedics and Thermo
Electron in connection with and for the purposes of their evaluation of the
Offer and the Merger. This opinion does not constitute a recommendation to any
stockholder of the Company as to whether such stockholder should tender its
Shares in the Offer. This opinion may not be disclosed, referred to, or
communicated (in whole or in part) to any third party for any purpose whatsoever
except with our prior written consent in each instance. We hereby consent to the
filing of this opinion as an exhibit to the Tender Offer Statement on Schedule
TO to be filed by Thermedics, Thermo Electron and certain of their subsidiaries
and to the provision of this opinion to persons who request it as contemplated
by the Schedule TO.


Very truly yours,


/s/ J.P. Morgan Securities Inc.

J.P. Morgan Securities Inc.



/s/ The Beacon Group Capital Services, LLC

THE BEACON GROUP CAPITAL SERVICES, LLC





<PAGE>   1

                             [LOGO] Thermo Electron
                             ---------------------------------------------------


<PAGE>   2


THE NEW THERMO ELECTRON
- ---------------------------------------------------------------------------


                                   > Vision

                                   > Focus

                                   > Clarity

                                   > Growth


1                                                         [LOGO] Thermo Electron
<PAGE>   3


SHAREHOLDER VALUE
- ---------------------------------------------------------------------------

Medical    >   Dividend
Products

                                      Existing
  New      >   Stock          >    Thermo Electron
Thermo                               Shareholders


 Thermo
Fibertek   >   Dividend


2                                                         [LOGO] Thermo Electron
<PAGE>   4


OUR GOAL
- ---------------------------------------------------------------------------

                         To channel all our resources -

                                   financial,

                                     human,

                                technological -

                            to become the preeminent

                        instrument company in the world.


3                                                         [LOGO] Thermo Electron
<PAGE>   5


WHY INSTRUMENTS?
- ---------------------------------------------------------------------------

                          > Critical mass

                          > Strong market presence

                          > Experienced management

                          > Strong cash flow

                          > Broad technology platform


4                                                         [LOGO] Thermo Electron
<PAGE>   6


THE PLAN
- ---------------------------------------------------------------------------

     >    Sell businesses totaling $1.2 billion in revenues

     >    Spin off equity of Thermo Fibertek and new Medical Products company

     >    Spin in instrument companies


5                                                         [LOGO] Thermo Electron
<PAGE>   7


MAJOR DIVESTITURES
- ---------------------------------------------------------------------------

                             > Thermo Cardiosystems

                             > Trex Medical

                             > Thermo TerraTech

                             > Thermo Coleman

                             > Peek


6                                                         [LOGO] Thermo Electron
<PAGE>   8


PLAN PROCEEDS
- ---------------------------------------------------------------------------

Proceeds from Divestitures        $ 1.0 BILLION

Cost of Spin Ins                  $(0.4 BILLION)
                                  -------------
Net Increase in Cash              $ 0.6 BILLION


                             Invest all proceeds in
                             new instrument company


7                                                         [LOGO] Thermo Electron
<PAGE>   9


SPIN OFFS
- ---------------------------------------------------------------------------

                        > Market leadership

                        > Experienced management

                        > Independent market identities

                        > Balanced product mix

                        > Strong growth prospects


8                                                         [LOGO] Thermo Electron
<PAGE>   10


MEDICAL PRODUCTS
- ---------------------------------------------------------------------------

                               Thermo Biomedical

                               Thermedics Medical



                          1999E Revenues: $335 million


9                                                         [LOGO] Thermo Electron
<PAGE>   11


MEDICAL PRODUCTS
- ---------------------------------------------------------------------------

[Collage of photos representing the various businesses within the new Medical
Products company, including neurodiagnostic testing, respiratory care, infant,
audiology products, wireless patient monitoring, and medical polymers.]


10                                                        [LOGO] Thermo Electron
<PAGE>   12


THERMO FIBERTEK
- ---------------------------------------------------------------------------

                                Thermo Fibertek

                                Thermo Fibergen



                          1999E Revenues: $225 million


11                                                        [LOGO] Thermo Electron
<PAGE>   13


THERMO FIBERTEK
- ---------------------------------------------------------------------------

[Collage of photos representing the various businesses within the new Thermo
Fibertek company, including papermaking and recycling equipment,
water-management systems, waste-recovery, and fiber-based consumer products and
composites.]


12                                                        [LOGO] Thermo Electron
<PAGE>   14


THERMO ECOTEK
- ---------------------------------------------------------------------------

                         > Non-core asset

                         > Maximize value

                         > Goal: spin off in 1-2 years


13                                                        [LOGO] Thermo Electron
<PAGE>   15


- ---------------------------------------------------------------------------

                            Thermo Electron will be

                              a completely focused

                           instrument company in 2001


14                                                        [LOGO] Thermo Electron
<PAGE>   16

THERMO INSTRUMENT REVENUES
- ---------------------------------------------------------------------------
(in millions)

[Bar chart (without actual revenue numbers) showing increasing revenues from the
Thermo Instrument business from 1986 to 1999 estimate, indicating in 1998 actual
revenues of $1.66 billion.]



15                                                        [LOGO] Thermo Electron
<PAGE>   17


THERMO INSTRUMENT EBITDA
- ---------------------------------------------------------------------------
(in thousands)

[Bar chart (without actual EBITDA numbers) showing increasing EBITDA for the
Thermo Instrument business from 1986 to 1999 estimate, indicating in 1998 actual
EBITDA of $294 million.]



16                                                        [LOGO] Thermo Electron
<PAGE>   18


THERMO INSTRUMENT STOCK PRICE
- ---------------------------------------------------------------------------
(adjusted for splits)

[Line graph generally illustrating range of Thermo Instrument stock price
(without providing specific stock prices) from 1986 to present ranging from
approximately $2.00 per share to approximately $36.00 per share during the time
period shown.]


17                                                        [LOGO] Thermo Electron
<PAGE>   19


GROWTH PLAN 2000
- ---------------------------------------------------------------------------

                      > Manage according to market served

                      > New incentives for managers

                      > Divest of slow-growth units

                      > Continue strategic acquisitions

                      > Initiate e-commerce


18                                                        [LOGO] Thermo Electron
<PAGE>   20


OLD ORGANIZATION
- ---------------------------------------------------------------------------

[Graphic of partial depiction of old organizational chart of Thermo Instrument
Systems.]


19                                                        [LOGO] Thermo Electron
<PAGE>   21


NEW ORGANIZATION
- ---------------------------------------------------------------------------

                          1999E Revenues: $2.3 billion

     Life                                                           Measurement
   Sciences                       Photonics                         and Control

1999E Revenues                 1999E Revenues                     1999E Revenues
 $800 million                   $800 million                       $700 million


20                                                        [LOGO] Thermo Electron
<PAGE>   22


LIFE SCIENCES - GOALS
- ---------------------------------------------------------------------------

                         > Internal revenue growth >10%

                         > R&D commitment 8-10%

                         > Technology acquisitions

                         > Maintain 16% ROS


21                                                        [LOGO] Thermo Electron
<PAGE>   23


PHOTONICS - GOALS
- ---------------------------------------------------------------------------

                         > Internal revenue growth 7-8%

                         > R&D commitment

                           - Telecom >10%

                           - Balance   7%

                         > Instrument acquisitions

                         > Maintain strong cash flow

                         > Improve ROS to 13%


22                                                        [LOGO] Thermo Electron
<PAGE>   24


MEASUREMENT AND CONTROL - GOALS
- ---------------------------------------------------------------------------

                         > Internal revenue growth 4-5%

                         > R&D commitment 4-5%

                         > Double ROS to 10%

                         > Focus on cash flow

                         > Divestitures


23                                                        [LOGO] Thermo Electron
<PAGE>   25


NEW INCENTIVES FOR MANAGERS
- ---------------------------------------------------------------------------

                          > New bonus plan

                            - Growth

                            - Cash

                            - Combination

                          > Increase cash compensation

                          > Continue options in parent


24                                                        [LOGO] Thermo Electron
<PAGE>   26


DIVEST SLOW-GROWTH UNITS
- ---------------------------------------------------------------------------

              > Detailed review of measurement and control sector

              > Sale of

                - Gould

                - NIS

                - Pharos Marine


25                                                        [LOGO] Thermo Electron
<PAGE>   27


RECENT ACQUISITIONS
- ---------------------------------------------------------------------------

Spectra Physics AB  Feb. 1999                 BioStar             Nov. 1998
- -----------------------------                 -----------------------------
Laser-based instruments                       Point-of-Care Diagnostics
                                              -----------------------------
Purchase Price          $351M
Current Market Value
     SPLI           $450-500M
     Other              $350M                 Interactiva         Oct. 1999
     FLIR               $ 70M                 -----------------------------
- -----------------------------                 Biochips - e-commerce
Total Value         $870-920M                 -----------------------------


26                                                       [LOGO] Thermo Electron
<PAGE>   28


EBUSINESS - WWW.INFORMATION2.NET
- ---------------------------------------------------------------------------

                             Competitive Advantages

                          > Leverage knowledge assets

                          > Breadth of "touch points"

                          > Mining: metals to genomes

                          > One-to-one marketing


27                                                        [LOGO] Thermo Electron
<PAGE>   29


WELL-POSITIONED VS. COMPETITORS
- ---------------------------------------------------------------------------

[Segmented bar chart showing how Thermo Instrument and its competitors compare
in terms of the industries they serve.]

Source McKinsey & Co.

    Thermo Instrument              Life Sciences         40%
                                   Communications         9%
                                   Environmental         17%
                                   Industrial            34%

    Agilent                        Life Sciences          7%
                                   Communications        50%
                                   Environmental          5%
                                   Non Instrument        38%

    Waters                         Life Sciences         60%
                                   Environmental         40%

    Varian                         Life Sciences         35%
                                   Environmental         35%
                                   Non Instrument        30%

    Perkin Elmer                   Life Sciences         22%
                                   Environmental         13%
                                   Industrial            26%
                                   Non Instrument        39%


28                                                        [LOGO] Thermo Electron
<PAGE>   30


VALUATION
- ---------------------------------------------------------------------------

                                   EV/EBITDA

[Bar chart showing how Thermo Instrument has been valued by industry analysts in
terms of EV/EBITDA compared to its competitors based on trailing 12 months
EBITDA.]


Source:  Industry Analysts


Chart reflects ratio of EV (Enterprise Value)/EBITDA as follows:

   THI                8.0
   Agilent           24.0
   Waters            19.3
   Varian            20.2
   Perkin Elmer      12.0
   Mean              18.9

29                                                        [LOGO] Thermo Electron
<PAGE>   31


INSTRUMENTS PROVIDE KNOWLEDGE
- ---------------------------------------------------------------------------


                                   You cannot

                              improve and control

                             unless you can measure

                                   and detect


30                                                        [LOGO] Thermo Electron
<PAGE>   32



OLD STRUCTURE
- ---------------------------------------------------------------------------

[Graphic showing the old corporate structure of Thermo Electron indicating
Thermo Electron subsidiaries with minority investors as follows:]


Thermo Electron
    Thermo Instrument
          Thermo Quest
          ONIX Systems
          Thermo Spectra
          Thermo Optek
          Thermo BioAnalysis
          Metrika Systems
          Thermo Vision

    Thermo Coleman
          Thermo Information Solutions

    Thermo Biomedical

    Thermo Ecotek
          Thermo Trilogy

    Thermedics
          Thermo Sentron
          Thermedics Detection
          Thermo Cardiosystems
          Thermo Voltek

    Thermo Trex
          Trex Medical
          Trex Communications
          ThermoLase

    Thermo Fibertek
          Thermo Fibergen

    Thermo Power
          Thermolyte

    Thermo Terra Tech
          The Randers Group
          Thermo EuroTech
          Thermo Retec

31                                                       [LOGO] Thermo Electron
<PAGE>   33


NEW STRUCTURE
- ---------------------------------------------------------------------------

The term Thermo Electron superimposed over image of man looking through a
telescope, representing new Thermo corporate structure.

32                                                        [LOGO] Thermo Electron
<PAGE>   34


THE NEW THERMO ELECTRON
- ---------------------------------------------------------------------------

                             > Market focus

                             > Simple structure

                             > Tightly managed

                             > Dedicated resources


33                                                        [LOGO] Thermo Electron


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