| 摘要 |
<p>PURPOSE:To detect abnormality of a photosensor by a method wherein a current always flowing through a light-emitting means is detected by a power detecting means, the detected current is compared with a reference value by a comparing means and an abnormality output is delivered when a detected value is abnormal. CONSTITUTION:A current flowing through LED 1 flows to the ground through a resistor R and voltages being proportional with the current appear at the opposite ends of the resistor R. A comparator circuit 13a compares the voltages at the opposite ends of the resistor R with a reference voltage Vref, and when the voltages at the opposite ends of the resistor R are higher than the reference voltage Vref, if gives a drive signal to the base of a transistor 14a of an alarm circuit 14. In response to the drive signal, the transistor 14a short-circuits a collector and an emitter. Accordingly, a relay 16 and an alarm sound generator 15 are driven in response to the continuity of the transistor 14a and thereby a monitor board 17 can be informed of abnormality of a photosensor 3.</p> |
