| 摘要 |
An improved photosensitive motion detector which detects abrupt changes within a field of view while ignoring gradual changes in ambient lighting therein. In addition, sensitivity to such changes is maintained without regard to the intensity level of the ambient light, and is not sensitive to the "flickering" of fluorescent lamps. Light from said field of view, which can contain an abrupt discontinuity therein, is focussed upon two substantially identical photocells, each of which is in parallel with one of two substantially identical photoresistors, each of which is closely optically coupled to one of two LEDs connected in parallel but in reverse polarity from a common junction to a common potential. Any imbalance between said two photocells is amplified by an operational amplifier and applied to said common junction between said two LEDs in such a way that increased light is cast by one LED upon the photoresistor in parallel with the photocell which receives the least light, and reduced light is cast by the other LED upon the photoresistor which receives the most light, both from the field of view. This balances the parallel resistance of the two circuit halves, and maintains a constant potential at said common junction, which is connected through a low impedance amplifier to an output terminal. Surveillance and/or recording equipment focussed on the field of view are triggered by voltages which have been developed by rapid changes in ambient light, or in the balance of light, from said field of view.
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