| 摘要 |
<p>PURPOSE:To prevent mis-detection due to an interference light by adjusting a light receiving sensitivity for each optical axis with simple and inexpensive configuration. CONSTITUTION:Each of light receiving sections 6a to 6e of a light receiving device 5 consists of a photo diode 7, a bias resistor 8 and a preamplifier circuit 9. A FET 10a varies a bias of the photodiode 7 in the light receiving section 6a. The FET 10a receives a gate bias from the integration circuit 11a. When a light receiving control circuit 17 receives a light receiving signal in excess of a voltage V2 of a 2nd comparator 20 while receiving a validated light receiving signal from the light receiving section 6a via a selection means 13, the circuit 17 gives a control pulse signal Sx to the integration circuit 11a to decrease the light receiving sensitivity. Thus, the light receiving sections 6a to 6e are automatically adjusted to obtain a required and sufficient level of the light receiving signal.</p> |
