Steps to Analyze Temperature Control Instrument System Failure

Two points must be noted when analyzing the failure of temperature control instrument system: in most cases electric instruments are used for measurement, indication and control; the system instruments often lags behind during measurement.

(1) The indicated value of temperature instrument system suddenly changes to the maximum or minimum, which is generally a failure of the system. Because of the large measurement lag of the temperature instrument system, no sudden changes will occur. Then the fault are mostly caused by the failure of thermocouple, thermal resistance, compensating wire disconnection or transmitter amplifier.

(2) The temperature control instrument system indicates rapid oscillation, which is mostly caused by improper adjustment of the control parameter PID.

(3) The slow fluctuation in a large range of system indication is probably caused by the changes in the process operation. If no change in the process operation, the problem may relate to a malfunction of the system itself.

(4) Steps to analyze the failure of temperature control system:

Check whether the regulating valve shows changes in the input signal, if the input signal does not change, but the regulating valve operates, the regulating valve diaphragm may be leaked;

Check whether the regulating valve positioner shows changes in the input signal, if the input signal does not change, but the output signal changes, the positioner may be faulty;

Check the input signal of the positioner and then whether the output of the regulator changes. If the regulator shows no change in the input but in the output, it may the fault of the regulator itself.