| 摘要 |
PURPOSE:To eliminate noises and attain assured working of an air cleaning device by securing the synchronism between the output of a photodetecting element and the light emitting cycle of a light emitting diode and converting said output into an extended pulse signal. CONSTITUTION:A smoke sensor 3 detects smoke particles, and an air cleaning device like a ventilating fan, etc. is actuated via an off-delay timer at a control part. The sensor 3 drives intermittently a light emitting diode through a light emitting drive part 8 to emit light. Thus the smoke particles disperse the emitted light, and these dispersed beams are received by a photodetecting element 2 and detected at a level deciding part 10. This detection signal is synchronized with the light emission of the diode 1 and at the same time delivered in the form of a pulse signal extended to the prescribed pulse width. For this purpose, a pulse extending part 12 is formed with a synchronizing pulse charging part 15 and an output pulse part 16. Thus an output pulse containing no noise component is obtained. |
