| 摘要 |
PURPOSE:To facilitate testing and to improve reliability by operating all of plural pieces of photocouplers forcibly and deciding a fault when the logical product of the output signals thereof is not obtained. CONSTITUTION:In a normal stage, contacts 1 for signals are closed to allow the light emitting elements of photocouplers 4 to emit light and photodetectors are driven to turn the low level side of resistors 8 on. In the stage of checking the photocouplers 4, on the otherhand, relay contacts 2 for checking are opened or closed. The checking is controlled by a microprocessor and is accomplished automatically. The outputs of the many photocouplers are applied to an AND circuit 11 and an OR circuit 12. In the stage of starting the checking, the conditions for AND are not established but when the checking signal is applied, an AND circuit 15 operates to close the contacts 2 and the outputs of the photocouplers appear. Timers 13, 19, 23 transmit signals which continue for a specified time, and as a result, the photocouplers are checked for a specified time. If there is any photocouple which fails to produce output, a fault is displayed. |
