| 摘要 |
PURPOSE:To take precautions in the state where an opening part is opened by installing a light emitting element and a photodetector near the apearture part on the outside of a building to face each other in the left and the right and generating a horizontal beam and using the space from a point of a certain length higher than the ground to the upper end of the opening part as a detection area. CONSTITUTION:An optical pulses is radiated from a light source 21 by a light source driving pulse oscillating circuit 51. When a part of a human body enters into the detection area, the optical beam is intercepted, and the signal quantity of a photodetector 22 is reduced in comparison with the case where no object exists in the detection area. The output of the photodetector 22 is amplified by an amplifier 52 and passes a switch 53 which is controlled by the light emitting pulse circuit 51 and is integrated by an integrating circuit 54. When the integral value is lower than a preliminarily set operation value because of the interception of the optical beam due to the human body, a value discriminating switch circuit 55 is made conductive to operate an alarm device 56. |
