| 摘要 |
PURPOSE:To surely detect an object to be detected by providing a modulator to a reflecting section and supplying the light being the result of modulating the incident light from a projecting part to a photodetection part when no object to be detected exists. CONSTITUTION:The reflecting section 13 consists of a normal reflecting plate 16 and a crystal plate 17 arranged to the front face of the reflecting plate 16 and acting like an optical modulator. When no object to be detected exists in either of the incident optical path and the reflected optical path, the reflected light in a form that the incident light (a) is interrupted at a period T of transparent-opaque property of the crystal plate 17 enters the photodetection section 15 and the photodetection section 15 generates an electric signal corresponding to the reflected light (c). On the other hand, if an object to be detected such as a human body enters the incident optical path or the reflected optical path and the reflected light reaching the photodetection section 15 is shielded, a signal smoothing section 23 generates a low level output signal. Thus, the passing of the object to be detected can be detected.
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