Multiple copy and transparency detector with illumination control

摘要

A sheet detector having an emitter (lamp), detector (phototransistor), operational amplifier and an RC network. As contamination is deposited on the emitter or detector, a feedback loop provides more drive to the lamp providing sufficient drive to hold the emitter of the phototransistor at its desired stage. As a first copy paper is passed between the emitter and detector, the RC network of a common mode operational amplifier detects a change and generates an output. As a subsequent sheet enters the system, the transmissibility abruptly changes again causing the common mode operational amplifier to provide a subsequent pulse indicating the presence of a multiple feed.