| 摘要 |
PURPOSE:To improve the reliability of a process controller by constituting a selection circuit for output of a multiplexed controller with a majority circuit and a diagnosis circuit for said majority circuit and switching the majority circuit when the diagnosis circuit detects a fault. CONSTITUTION:The signals selected by the intermediate value selecting circuits 5A and 5B among output signals S1A-S1C of controllers 2A-2C are delivered to a process 1 to be controlled as an output signal S2 of a process controller 4. The outputs of circuits 5A and 5B are monitored by diagnosis circuits 6A and 6B for detection of faults. When a fault of the circuit 5A is detected by the circuit 6A of a selection circuit 3 set at the using side, the output S4A of the circuit 6A is equal to ''1'' and energizes a relay 7. Therefore the contacts 7B and 7A of the relay 7 are turned off and on respectively. Thus the circuit 3A is switched to a selection circuit 3B set at the waiting side. Then an output signal S3B of the circuit 5B put under a waiting mode is used as the output signal S2 of the controller 4. |
