A Rapid Photoelectric Optical Distortion Tester for Plastic Windows

This note describes an instrument suitable for use in the factory or industrial test room for the `pass-reject' testing of the optical distortion of small moulded plastic windows. The instrument incorporates a `Schlieren' optical system by which faulty windows deflect light off a stop on to a photocell so that the photocell current is a measure of the optical distortion. By means of an electronic circuit incorporating a hard valve trigger (self-resetting) the photocell current is made to operate an indicator lamp. Standardization is effected by adjustment of the circuit just to reject a glass distorting standard. The instrument derives its supply from the a.c. mains and sufficient stabilization is incorporated so that only infrequent standardization is needed. A testing rate of twenty-four windows per minute is easily attained.