| 摘要 |
PURPOSE:To preclude malfunction by performing integration type operation normally based on the difference between the quantity of reflected light from the background and the quantity of reflected light from an intruder, but performing differentiation type detection based upon variation in the quantity of reflected light when said state continues for a prescribed time. CONSTITUTION:The output of a photodetector 3 is amplified, 10, detected 11, and integrated 12 and 13. Signals D and E obtained by amplifying 14 and 15 the difference between the integration outputs B and C as to plus and minus are compared 16 and 17 and when they are larger than a threshold value, signals F and are outputted. the signal F energizes a relay 20 through an OR circuit 18. The specific number of an integration circuit 13 is made small and the integration circuit 13 switches a large and a small specific number. When a power source 24 is turned on to output a signal H, inversion is caused to open a SW21, and re-inversion and delay 27 are performed to energize an AND19, which is closed when the signal G is H to energize the relay 20. While the OR18 is L, inversion is caused to close a SW22. Even when the input signal decreases and a detection signal goes up to H, a timer 30 outputs H to close the SW22. Consequently, the states of various intruders are correctly detected. |
