When analyzing the temperature control instrument system failure, two points must be noticed first: The system instrument mostly adopts electric instrument to measure, indicate and control; the system instrument measurement often has a large lag.
(1) The indication value of the temperature instrument system suddenly changes to the maximum or minimum value, which is generally a malfunction of the instrument system. Because the temperature measurement system has a large measurement lag, no sudden change will occur. The faults at this time are mostly caused by broken thermocouples , thermal resistors , compensation wires or transmitter amplifiers.
(2) The temperature control instrument system indicates a rapid oscillation phenomenon, which is mostly caused by improper adjustment of the control parameter PID.
(3) The temperature control instrument system indicates that a large and slow fluctuation is likely to be caused by changes in the process operation. If the process operation does not change at that time, it is likely that the instrument control system itself is faulty.
(4) The failure analysis steps of the temperature control system itself: check whether the input signal of the control valve changes, the input signal does not change, the control valve operates, the control valve diaphragm leaks; check whether the input signal of the control valve positioner changes, input signal No change, the output signal changes, the positioner is faulty; check the input signal of the positioner, and then check whether the output of the regulator is changed. If the input of the regulator is not changed, the output is changed, and it is the fault of the regulator itself.