<PAGE>

                                                                     EXHIBIT 4.8

                               THIRD AMENDMENT TO
                                CREDIT AGREEMENT

      THIS THIRD AMENDMENT ("Amendment") dated as of August 23, 2004, by and
between Perceptron, Inc. ("Company") and Comerica Bank, a Michigan banking
corporation ("Bank").

                                    RECITALS:

      A.    Company and Bank entered into a Credit Agreement dated as of October
24, 2002, which was amended by two amendments ("Agreement").

      B.    Company and Bank desire to amend the Agreement as hereinafter set
forth.

      NOW, THEREFORE, the parties agree as follows:

      1.    Section 8.1 of the Agreement is amended to read in its entirety as
follows:

            "Purchase, acquire or redeem any of its stock or make any material
      change in its capital structure, except redemptions of Company's stock for
      an aggregate purchase price not to exceed Two Million Dollars ($2,000,000)
      provided that at the time of each such redemption and after giving effect
      thereto no Event of Default shall have occurred and be continuing."

      2.    Company hereby represent and warrant that, after giving effect to
the amendments contained herein, (a) execution, delivery and performance of this
Amendment and any other documents and instruments required under this Amendment
or the Agreement are within Company's corporate powers, have been duly
authorized, are not in contravention of law or the terms of Company's Articles
of Incorporation or Bylaws, and do not require the consent or approval of any
governmental body, agency, or authority; and this Amendment and any other
documents and instruments required under this Amendment or the Agreement, will
be valid and binding in accordance with their terms; (b) the continuing
representations and warranties of Company set forth in Sections 6.1 through 6.5
and 6.7 through 6.12 of the Agreement are true and correct on and as of the date
hereof with the same force and effect as made on and as of the date hereof; (c)
the continuing representations and warranties of Company set forth in Section
6.6 of the Agreement are true and correct as of the date hereof with respect to
the most recent financial statements furnished to the Bank by Company in
accordance with Section 7.1 of the Agreement; and (d) no Event of Default (as
defined in the Agreement) or condition or event which, with the giving of notice
or the running of time, or both, would constitute an Event of Default under the
Agreement, as hereby amended, has occurred and is continuing as of the date
hereof.

      3.    Except as expressly provided herein, all of the terms and conditions
of the Agreement remain unchanged and in full force and effect.

      4.    This Amendment shall be effective upon (a) execution of this
Agreement by Company and the Bank and (b) execution by the Guarantor of the
attached Acknowledgment of Guarantor.

<PAGE>
                                                                     EXHIBIT 4.8

      IN WITNESS the due execution hereof as of the day and year first above
written.

COMERICA BANK                                PERCEPTRON, INC.

By: /s/ Vladimir R. Slapak                  By: /s/ John Garber
    -------------------------                   -------------------------------

Its: Assistant Vice President               Its:  VP - CFO

                                        2
<PAGE>
                                                                     EXHIBIT 4.8

                           ACKNOWLEDGMENT OF GUARANTOR

      The undersigned guarantor acknowledges and agrees to the foregoing
Amendment and confirms that the Guaranty dated October 24, 2002, executed and
delivered by the undersigned to the Bank remains in full force and effect in
accordance with its terms.

                                                  PERCEPTRON GLOBAL, INC.

                                                  By:  /s/ John Garber
                                                     --------------------------
                                                  Its:  Vice President

                                        3