| 摘要 |
<p>PURPOSE:To provide a photoelectric switch surely giving an alarm for abnormality, surely detecting a return to a stable state in response to a state, and clearing the alarm of the abnormal state. CONSTITUTION:When the level of a light-receiving signal is brought to an unstable state, in which the level of the light-receiving signal lowers from a stable incident-light level, and exceeds a stable light-shielding level Lc, a timer circuit 21 starts its time limit operation, and an abnormality alarm signal is output as a self-diagnostic output by the working of the timer circuit 21 when the state of time limit operation is continued for a fixed time T. A counter 26 adds or subtracts a certain value according to whether or not the level of the light-receiving signal lowers from the stable light-shielding level during a time when the level of the light-receiving signal lowers from an operation level. A counter 25 adds or subtracts a certain value according to whether or not the level of the light-receiving signal exceeds the stable incident-light level or exceeds a complete incident-light level during a time when the level of the light-receiving signal exceeds the operation level. When either one count value of the counters 25, 26 reaches a fixed value, the abnormality alarm signal is output.</p> |
