| 摘要 |
PURPOSE:To detect a body in a specific area securely by outputting an alarm signal when the distance measured by detecting the reflection of light or infrared ray is less than specific limit distance. CONSTITUTION:A nearly planar alarm area is set along the external surface of a window 2 with four detection areas E1-E4 having limit distances determined by window end surfaces. A radiation source 6 which radiates light or infrared ray emits pulse light by a driving circuit 7 and the light is collimated by a collimator lens 8 into a nearly parallel beam. If there is a reflecting body M present in the traveling direction of the radiation beam, part of the reflected light is converged by a condenser lens 9, and is made incident to a couple of photodetecting elements 10 a and 10b. The ratio of the quantities of incident light depends upon the distance between a sensor and the reflecting body. Amplification outputs of circuits 11a and 11b are supplied to a dividing circuit 12 to calculate their ratio, and a threshold decision switch circuit 13 operates according to the value to generates an alarm output. |
