Measuring device for measuring the amount of change in thickness of the paint layer

Claim 1

A measuring device for measuring a change in time-dependent thickness of a paint layer, comprising: a light source for emitting a coherent light; a means for collimating the light emitted from said light source along an optical axis and removing noise components thereof; a first chamber having a support means therein for the support of a test piece painted on one surface thereof with a paint layer to be tested; a control means for controlling the atmosphere in said first chamber to cause the paint layer to dry under a predetermined condition; a reflective mirror supported in said first chamber; a semitransparent mirror disposed in said first chamber and inclined to the optical axis of said collimating means for splitting the collimated light into first and second light beams, the first light beam being directed perpendicularly to the paint layer and the second light beam being directed perpendicularly to said reflective mirror; a receiver for receiving the first and second light beams after having been reflected from the paint layer and said reflective mirror, respectively, and then having been joined together by said semitransparent mirror, said receiver upon receipt of the first and second light beams forming thereon interference fringes resulting from the interference between the first and second light beams; and a means for measuring the amount of movement of the interference fringes; whereby change in thickness of the paint layer with time is indicated by the amount of movement of the interference fringes measured.