| 摘要 |
<p>PURPOSE:To perform accurate infrared detection by using an AGC circuit having a prescribed delay time to control the amplification factor of an amplifying circuit in accordance with the output level of a detecting circuit and automatically obtaining a light reception signal output in a prescribed level. CONSTITUTION:When infrared rays from a light throwing device 1 are reflected by a wall surface or the like to by-pass it and are received by a photodetector 2, the amplification factor of an amplifying circuit 23 is not reduced with respect to a light reception signal waveform W as the output of the amplifying circuit 23 because the response delay time of an AGC circuit 27 does not elapse. Then, a light reception signal waveform W2 where a reflected light component B is superposed on the resultant value of a direct light component A and a noise component C is obtained, and an infrared alarm fails in reporting. Since the AGC circuit 27 reduces the amplification factor of the circuit 23, the resultant value of a reflected light component B1 and a noise component C1 does not exceed a discrimination level K of a discriminating circuit 25 but that of a direct light component A1, the reflected light component B1, and the noise component C1 exceeds this level K after a delay time T. Thus, accurate infrared detection is possible.</p> |
