| 摘要 |
<p>A detector system for signaling the interruption of an illuminated field (12) by a relatively opaque element (18). The apparatus includes an ambient compensation network AC which can be used with an optoelectric pair including an emitter CR0 and an associated phototransistor Q0, or with a plurality of emitter-phototransistor pairs, CR0-Q0, CR1-Q1, etc., disposed about the periphery of the illuminated field (12). The ambient compensation network comprises a current compensation source (500) for injecting a current dependent only upon the ambient output of a phototransistor Q0 at the collector of the phototransistor to offset the effect of ambient conditions. A microprocessor U2 can be employed to sequentially activate emitter-phototransistor pairs. Each phototransistor (Q0, etc.) of each pair is activated for a longer time than the associated emitter (CR0, etc.). The ambient compensation network includes a voltage source Vcc, a voltage divider (100), an integrator (200), a sample and hold circuit (300), a buffer (400) and a current injection source (500) attached to each phototransistor collector. </p> |
