| 摘要 |
PURPOSE:To reduce a false alarm caused by a change for the worse of weather conditions, and also to reduce a burden of a monitor man by inhibiting an invasion monitoring operation of a specified group, when the number of receivers whose arrival energy become below a prescribed value exceeds a prescribed number. CONSTITUTION:When incident optical beam L1A, L1B to photodetectors R1A, R1B of a specified group become below a prescribed value, an output of comparators 4a, 4b are inverted to a high level. Also, receivers R1A, R1B whose arrival energy become below a prescribed value become plural pieces such as two pieces, etc., an output of an AND gate 5 is inverted to a high level, an output of NOR gates 6a, 6b becomes a low level irrespective of existence of an invasion detection based on cutting off a light by the photodetectors R1A, R1B, and an invasion monitoring operation of a specified group is inhibited substantially. Accordingly, the number of times of generation of a false alarm caused by rain, snow, etc. in case weather conditions change for the worse is reduced, and also a burden of a monitor man can be reduced. |
