Fault Analysis Of Field Control Instrument System With Different Parameters

- Oct 14, 2019-

1. Fault analysis of flow control instrument system


(1) When the flow control instrument system indicates that the value reaches the minimum, first check the on-site detection instrument. If it is normal, the fault is on the display instrument. When the on-site instrumentation indicator is also the smallest, check the valve opening degree. If the valve opening degree is zero, it is often a fault between the regulator valve and the regulator. When the on-site detection instrument indicates the minimum and the adjustment valve opening is normal, the cause of the failure may be caused by insufficient system pressure, blockage of the digital display controller system, no pumping, crystallization of the medium, improper operation, and the like. If it is a fault in the instrument, the reasons are: the orifice differential pressure flowmeter may be a positive pressure pilot conduit plug; the differential pressure transmitter positive pressure chamber leak; the mechanical flowmeter is a gear stuck or a filter plug.


(2) When the flow control instrument system indicates that the value reaches the maximum, the test instrument will often indicate the maximum. At this point, the manual remote control valve can be opened or closed. If the flow rate can be lowered, it is generally caused by the process operation. If the flow value does not fall, it is caused by the instrument system. Check whether the regulating valve of the flow control instrument system is operating; check whether the measuring system is normal; check whether the signal transmission system of the instrument is normal.


(3) The flow control instrument system indicates that the value fluctuates frequently, and the control can be changed to manual. If the fluctuation is reduced, the instrument is the cause or the instrument control parameter PID is not suitable. If the fluctuation is still frequent, it is the process operation. Caused by.


2. Fault analysis of liquid level control instrument system


(1) When the indication value of the liquid level control instrument system changes to the maximum or minimum, you can check whether the detection instrument is normal. If the indication is normal, change the liquid level control to the manual remote control liquid level to see the liquid level change. If the liquid level can be stabilized within a certain range, the fault is in the liquid level control system; if the liquid level is stable, it is generally the fault caused by the process system, and the cause should be found from the process.


(2) When the differential pressure type liquid level control instrument indication and the on-site direct reading type indicating instrument are not on, first check whether the on-site direct reading type indicating instrument is normal. If the indication is normal, check the negative pressure guiding of the differential pressure type liquid level meter. Whether there is leakage in the pressure tube sealing liquid; if there is leakage, refilling liquid, zero adjustment point; no leakage, it may be that the negative migration amount of the meter is wrong, and the migration quantity is re-adjusted so that the meter indication is normal.


(3) When the liquid level control instrument system indicates that the fluctuation of the indication value is frequent, firstly, the capacity of the liquid level control object should be analyzed to analyze the cause of the failure. The large capacity is generally caused by the instrument failure. When the capacity is small, it is necessary to analyze whether the process operation has changed. If there is a change, it is likely that the process causes frequent fluctuations. If there is no change, it may be caused by instrument failure.


3, temperature control instrument system failure analysis steps


When analyzing the temperature control instrument system failure, we must first pay attention to two points: the system instrument uses electric instrument measurement, indication and control; the measurement of the system instrument often lags behind.


(1) The indication value of the temperature meter system suddenly changes to the maximum or minimum, which is generally the fault of the instrument system. Because the temperature meter system measures a large lag, no sudden changes will occur. The cause of the fault at this time is mostly caused by thermocouple, thermal resistance, compensation wire breakage or transmitter amplifier failure.


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


(3) The temperature control instrument system indicates a large and slow fluctuation, which is probably caused by a change in process operation. If there is no change in the process operation at the time, it is likely to be a malfunction of the instrument control system itself.


(4) Failure analysis step of the temperature control system itself: check whether the input signal of the regulating valve changes, the input signal does not change, the regulating valve acts, the diaphragm of the diaphragm head is leaked; whether the input signal of the regulating valve positioner changes, the input signal No change, the output signal changes, the positioner is faulty; check the positioner input signal changes, then check the regulator output for change, if the regulator input does not change, the output changes, this is the regulator itself failure.


4. Failure analysis of pressure control instrument system


(1) When the pressure control system indicates that there is rapid oscillation fluctuation, first check whether the process operation has changed. This change is mostly caused by poor process setting and PID parameter tuning of the regulator.


(2) The pressure control system indicates that the dead line is present, the process operation changes the pressure indication or does not change, the general fault occurs in the pressure measurement system, first check whether the measurement of the pressure guiding conduit system is blocked, not blocked, check the pressure change The transmitter output system has no change, there is a change, and the fault is in the controller measurement indication system.


The above is only the on-site fault analysis of the four common parameters of the site to control the instrument. There are some complicated control loops in the actual site, such as cascade control, split control, program control, interlock control and so on. The analysis of these faults is more complicated and needs to be analyzed.


Solution: Exclusion method


1. When the system is controlled, the judgment should be the same. It is easy to find the problem by determining the fault after each part is independent.


2. It is only the instrument displayed on the spot. It is suspected that the display data is not normal. The data can be estimated according to the process environment. If it is too far away, it will only be checked and adjusted.


3. On-site controlled instrument, suspected that the display data is not normal, can be automatically disconnected, observed, fixed process conditions data, you can determine whether the collected data is normal. If the control result is unstable, it is first determined whether the data acquisition is normal. The method is the same as above. Because the data acquisition is not normal, the control result is definitely not good.


After the above questions are judged, the actuator is normally started when checking the soft manual output. Finally adjust the PID parameters.