| 摘要 |
<p>PURPOSE:To quickly detect abnormality in a light receiving unit or a signal line. CONSTITUTION:A light receiving unit 1 modulates the output of a detecting circuit 4 into a pulse train signal through a modulating circuit 6 and outputs it to a signal line 2. A controller 3 demodulates a modulation signal through a detection signal demodulating circuit 13, and judges whether the modulation signal involves a pulse train or not through a pulse train detecting circuit 14. When the light receiving unit 1 is out of order, and a self-diagnosis circuit 5 therefore stops the outputting of the modulation signal, or the signal line 2 is short-circuited or disconnected, the signal fixed to H or L level is inputted into the controller 3. The pulse train detecting circuit 14 judges to be abnormal from the nondetectable pulse train signal to stop its output and to turn on LED 17 for informing the occurrence of an abnormal state.</p> |
