| 摘要 |
PURPOSE:To detect an intruding object irrespective of whether a reflection factor of the intrud object is good or not, and also, even if the intrud object stands still, by outputting a detecting signal in case when one of differences between mutual storage quantities of infrared-ray reflection quantities from a background, and the background and the intruding object, respectively has exceeded a threshold value. CONSTITUTION:An infrared-ray reflection quantity from a background and an intruding object, and an infrared-ray reflection quantity from the background, respectively are stored in the first integration circuit 12 whose time constant is small and the second integration circuit 13 whose time constant is large through a photodetector 3. When a reflection factor of the intruding object is large, a difference value by a differential circuit 14 of the circuit 12 and 13 exceeds a threshold value and a detecting signal of an H level is outputted from a comparator 16. At the same time, by this detecting signal, a switch of the circuit 13 is turned off through an inverter 23, the average value of an infrared-ray reflection storage value from the background is added to the differential circuit 14, and even when the intruding object stands still, the detecting signal is outputted. When an absorption factor is large and an infrared-ray reflection factor of the intruding object is small, the detecting signal is outputted in the same way, based on a difference between the storage values of the circuits 13, 12, and the intruding object is detected exactly irrespective of the reflection factor of the intruding object, and also, even when the intruding object stands still.
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