| 摘要 |
PURPOSE:To cope with any fault of a controller of a using system without giving any disturbance to a plant to be controlled, by providing a tracking device and a fault diagnosing device and controlling the output level when the outputs of both devices are switched. CONSTITUTION:If a fault of a controller 1A of a using system is due to a sudden change, the deviation between a control signal Qa of a using system and a control signal Qb of a waiting system and the variation of a process quantity P are immediately produced. Thus a fault diagnosing device 3 works in a short time to detect the fault of the controller 1A. Then the device 3 gives a switch signal S to a control system switch 2 to start a controller 1B of a waiting system. In case the controller 1A has a fault owing to a slow change of its control signal, a deciding circuit 4B applies a decision signal V to a tracking signal output circuit 4C. Then a tracking signal setting circuit 4A applies a tracking signal T to the controller 1B. The signal T is stored previously when the deviation between signals Qa and Qb is small and equal to the normal value of the controller 1A. While the device 3 gives a signal S to the switch 2 to start the controller 1B. |
