THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED (THE "ACT"). THESE SECURITIES HAVE BEEN ACQUIRED FOR
INVESTMENT, AND NOT WITH A VIEW TO DISTRIBUTION OR RESALE, AND MAY NOT BE SOLD,
PLEDGED, MORTGAGED, HYPOTHECATED OR OTHERWISE TRANSFERRED (1) WITHOUT AN
EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT COVERING THESE SECURITIES OR (2)
UNLESS AN EXEMPTION FROM REGISTRATION IS AVAILABLE.


                               THERMO SENTRON INC.
                        Promissory Note Due June 30, 1999
                             Minneapolis, Minnesota

                                                               December 15, 1998

        For value received, THERMO SENTRON INC., a Delaware corporation (the
("Company"), hereby promises to pay to Thermo Electron Corporation (hereinafter
referred to as the "Payee"), or registered assigns, on June 30, 1999, as
described below, the principal sum of nineteen million dollars ($19,000,000) or
such part thereof as then remains unpaid, to pay interest from the date hereof
on the whole amount of said principal sum remaining from time to time unpaid at
a rate per annum equal to the rate of the Commercial Paper Composite Rate for
90-day maturities as reported by Merrill Lynch Capital Markets, as an average of
the first five business days of the Company's current fiscal quarter, plus
twenty-five (25) basis points, which rate shall be adjusted on the sixth
business day of each fiscal quarter of the Company and shall be in effect for
the entirety of such fiscal quarter, such interest to be payable in arrears on
the first day of each fiscal quarter of the Company during the term set forth
herein, until the whole amount of the principal hereof remaining unpaid shall
become due and payable, and to pay interest on all overdue principal and
interest at a rate per annum equal to the rate of interest announced from time
to time by BankBoston Corporation at its head office in Boston, Massachusetts as
its "base rate" plus one percent (1%). Principal and all accrued but unpaid
interest shall be repaid on June 30, 1999. Principal and interest shall be
payable in lawful money of the United States of America, in immediately
available funds, at the principal office of the Payee or at such other place as
the legal holder may designate from time to time in writing to the Company.
Interest shall be computed on an actual 360-day basis.

        This Note may be prepaid at any time or from time to time, in whole or
in part, without any premium or penalty. All prepayments shall be applied first
to accrued interest and then to principal.

        The then unpaid principal amount of, and interest outstanding on, this
Note shall be and become immediately due and payable without notice or demand,
at the option of the holder hereof, upon the occurrence of any of the following
events:

               (a) the failure of the Company to pay any amount due hereunder
        within ten (10) days of the date when due;

               (b) any representation, warranty or statement made or furnished
        to the Payee by the Company in connection with this Note or the
        transaction from which it arises shall prove to have been false or
        misleading in any material respect as of the date when made or
        furnished;

               (c) the failure of the Company to pay its debts as they become
        due, the insolvency of the Company, the filing by or against the Company
        of any petition under the U.S. Bankruptcy Code (or the filing of any
        similar petition under the insolvency law of any jurisdiction), or the
        making by the Company of an assignment or trust mortgage for the benefit
        of creditors or the appointment of a receiver, custodian or similar
        agent with respect to, or the taking by any such person of possession
        of, any property of the Company;

               (d) the sale by the Company of all or substantially all of its 
                   assets;

               (e) the merger or consolidation of the Company with or into any
        other corporation in a transaction in which the Company is not the
        surviving entity;

               (f) the issuance of any writ of attachment, by trustee process or
        otherwise, or any restraining order or injunction not removed, repealed
        or dismissed within thirty (30) days of issuance, against or affecting
        the person or property of the Company or any liability or obligation of
        the Company to the holder hereof; and

               (g) the suspension of the transaction of the usual business of
the Company.

        Upon surrender of this Note for transfer or exchange, a new Note or new
Notes of the same tenor dated the date to which interest has been paid on the
surrendered Note and in an aggregate principal amount equal to the unpaid
principal amount of the Note so surrendered will be issued to, and registered in
the name of, the transferee or transferees. The Company may treat the person in
whose name this Note is registered as the owner hereof for the purpose of
receiving payment and for all other purposes.

        In case any payment herein provided for shall not be paid when due, the
Company further promises to pay all cost of collection, including all reasonable
attorneys' fees.

        No delay or omission on the part of the Payee in exercising any right
hereunder shall operate as a waiver of such right or of any other right of the
Payee, nor shall any delay, omission or waiver on any one occasion be deemed a
bar to or waiver of the same or any other right on any future occasion. The
Company hereby waives presentment, demand, notice of prepayment, protest and all
other demands and notices in connection with the delivery, acceptance,
performance, default or enforcement of this Note. The undersigned hereby assents
to any indulgence and any extension of time for payment of any indebtedness
evidenced hereby granted or permitted by the Payee.



        This Note shall be governed by and construed in accordance with, the
laws of the Commonwealth of Massachusetts and shall have the effect of a sealed
instrument.


                                                   THERMO SENTRON INC.


                                                   By: /s/ Lewis J. Ribich
                                                       Lewis J. Ribich
                                                       President

[Corporate Seal]

Attest:


/s/ Sandra L. Lambert
Sandra L. Lambert
Secretary