| 摘要 |
PURPOSE:To soften the shock to a plant due to abnormality of a control device, by using an output, which is obtained by averaging analogue outputs of plural control devices by an averaging circuit, as a control signal. CONSTITUTION:Analogue outputs OA and OB of control devices 22A and 22B are inputted to an averaging part 40 through normally closed contacts 39A and 39B which are opened by abnormality detecting devices 38A and 38B respectively, and an average output e0 becomes the control input of a plant 50 to control a valve operating part 32. The output of a valve opening detector 33 becomes a feedback signal I and is inputted to control devices, and the difference between respective target signals RA and RB and the signal I becomes the input to control devices practically to constitute a closed loop. Since the averaged output e0 is (OA+OB)/2, the half of an abnormal value is inputted to the plant even if the abnormal value is outputted from the control device 22A, and the influence appears as fluctuation of the feedback signal I, and the abnormal value is compensated by the control device 22B and is returned to an original output e0 in an instant. Thus, the shock due to abnormality of control devices is softened. |
