Importance

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Abstract

Apparatus for detecting whether a measured dimension deviates from a nominal value by a predetermined increment. It comprises a feeler for following the surface of a component and a variable area window controlled by said feeler. Two pairs of photoelectric receivers are located behind the window and the photoelectric receivers of each pair receive differential illumination through the window. An electronic circuit includes a first trigger circuit which receives as input signal the differential output signal of the first pair of photoreceivers and delivers a first detection signal when this input signal exceeds a predetermined positive value, a second trigger circuit which receives as input signal the differential output signal of the second pair of photoreceivers and delivers a second detection signal when this input signal exceeds a predetermined negative value and a gate connected to said first and second trigger circuits which delivers a third detection signal when the two trigger circuits are simultaneously inoperative.

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First Claim