| 摘要 |
PURPOSE:To detect an illegal intruder with high precision by arranging plural couples of projectors and photodetectors longitudinally so that every other beam directions are opposite. CONSTITUTION:There are two signals S32 and S23 which are projected on and photodetected by a couple of adjacent cylindrical bodies. An inverter 6 inverts the output signal S32 of a photodetector R32 which generates a high-level signal in photodetection, and the inversion output is sent out to a monostable multivibrator 8. The monostable multivibrator 8 detects the rising of the output signal of the inverter 6 to output a one-shot pulse having an about 1 second pulse width. This monostable multivibrator 8 is provided because an intruder does not cut off upper and lower beams L23 and L32 at the same time all the time. An AND circuit 10a sends out a high-level output when the beam L32 is cut off firstly and the light beam L23 traveling in the opposite direction between the same cylindrical bodies within a specific time after said cutoff. |
