Abstract
An optical method for a thickness measurement of a polyethylene foam sheet has been developed based on the light theory. The accuracy of the method depends mainlyon the heterogeneous light transmissivity through the foam sheet due to its internal cell structureand a displacement of the foam sheet along the optical path caused by the movement of the sheet which is common condition in its production in industries. A 40 times averaging smooth out the fluctuation of the transmitted light power within ±4% and then the error rate of the thickness measurement within 2% for the thickness of 2mm. The error rate due to the displace-ment has been found approximately same as the averaging method by means of a proper optical arrangement, and then the total error of this method within 4%.
