Instrument measurement parameters are generally classified into temperature, pressure, flow, liquid level four parameters.
According to the different measurement parameters, and to analyze the different instrument failures.
1, first, in a field instrument failure, to a thorough understanding of the relevant instrument system of the production process, production process and conditions understand instrument system design, the design intent, instrument system architecture, features, performance and specifications.
2, in the analysis of inspection instrument before the system failure, to the site operators to understand the production of loading and material parameters, viewing fault recording curve of the instrument, a comprehensive analysis to determine instrument failure.
3, if the instrument recording the curve to a dead line (a change not lines dead line), or recording curve wave, now suddenly become a line fault is likely the dash system. Because most current recording instruments are DCS computer systems, high sensitivity, response parameters can be very sensitive. You can artificially change of process parameter, see curve changes. If you do not change, concluded that a system problem if normal variation, concluded that the system has no major problems.
4, changing process parameters, found mutations or jumps to the top or bottom curve for records, failure in instrument system at this time.
5, fault before the instrument record curve had been normal, record after the volatility curve became erratic, or make the system difficult to control even the manual nor can control, fault may be caused by processes operating system at this time.
6, when they discovered DCS instrument is not functioning correctly, to inspect the Visual instruments of the same value, if they are very different, and instrument systems is likely to be faulty.
In short, when analyzing instrument failure causes, pay special attention to the object to be measured and controlled the performance changes, which may be the reason for field instrument system malfunction. So, we go from instrument systems and processes two aspects considered, careful analysis of the operating system, check the cause.
Two or four parameters measured steps instrument control, system and fault analysis
Step 1 temperature control meter system fault analysis
Analysis of temperature-control instrument system failure, first of all to pay attention to two points: the system uses electric instrument measuring, indicating, controlling; measurement of the system tends to lag behind larger.
(1) temperature indicator instrument system suddenly to maximum or minimum, General instrument system malfunction. Measurement of temperature instrument system lag larger, no sudden changes. At this time the cause of the failure is the thermocouple, RTD, compensating wire disconnection or transmitter amplifier failure.
(2) indicates a rapid oscillation of temperature control instrument system, mostly caused by improper adjusting parameters PID control.
(3) fluctuations in temperature control meter system instructions to slow sharply, is likely to be caused by a process change, if the operation does not change, you will most likely be of instrument control system failure.
(4) temperature control system itself of fault analysis steps: check Regulation valve entered signal whether changes, entered signal not changes, Regulation valve action, Regulation valve film head diaphragm leak has; check Regulation valve positioning device entered signal whether changes, entered signal not changes, output signal changes, positioning device has fault; check positioning device entered signal has changes, again check regulator output has no changes, if regulator entered not changes, output changes, at is regulator itself of fault.
Fault analysis of system step 2, pressure control instrumentation
(1) when the meter indicates a rapidly oscillating fluctuations of pressure control system, first check whether the process changes, this change is mostly technological operation and caused bad regulator PID parameter tuning.
(2) the instrument indicates a dead line of pressure control system, operation changes the pressure indicator is not changed, the General failure appear in the pressure measurement system first checks the measuring pressure catheter system for blocking not blocking, check whether the pressure transmitter output systems change, there is a change, measurement indicates fault in the controller system.
3, flow control instrument system fault analysis steps
(1) indicating when the minimum value of flow control instrument system, first check the live instrumentation, if it works, then the fault indicator. When the measuring instrument indicates the minimum, check the valve opening, valve opening degree zero, usually between regulator and valve failure. When the measuring instrument indicates minimum, adjusting valve opening normal fault probable cause is insufficient system pressure, pipe plug, pump up volume, medium crystalline and cause improper operation. Instrument failure, reason: orifice plate differential pressure flowmeter may be positive pressure catheter blocking; differential pressure transmitter with plenum leak; gear is jammed or mechanical flow meter filter plugging.
(2) indication of flow control instrument system when the maximum is reached, the instrumentation is also often indicates the maximum. Manual remote control valve up or down, if the flow can be lowered to the process causes. If flow does not fall, is the cause of instrument systems, check whether the valve flow control instrument system; check meter pressure is normal the system checking instrument signal system is normal.
(3) flow control instrument system indicates that the values fluctuate frequently, to manual control can be modified, if volatility decreases is the cause of instrument or instrument control parameters of PID is not appropriate, if fluctuations are still frequent, the operation is causing.
4, liquid-level control system failure analysis procedure
(1) liquid level control instruments when the system indicates that the value to a maximum or minimum, you can first check whether the instruments properly, if the instructions correctly, liquid level control to manual remote control level, look at liquid level changes. As the liquid level will stabilize at a certain range, then the fault in liquid level control system if unable to steady level, General technology systems caused by the failure, from processes find out why.
(2) poor pressure type liquid bit control instrument indicates and site straight read type indicates instrument indicates on not Shang Shi, first check site straight read type indicates instrument whether normal, as indicates normal, check poor pressure type liquid bit instrument of negative pressure guide pressure tube seal liquid whether has leakage; if has leakage, again irrigation seal liquid, adjustable zero points; no leakage, may is instrument of negative migration volume not has, again adjustment migration volume makes instrument indicates normal.
(3) liquid-level control system indicates that the values fluctuate frequently, first liquid level controls the size of the object you want to analyze, to analyze the cause of the failure, large capacity is usually the instrument malfunction. First analysis of the capacity of small operation if there is any change in the production, if there is any change is likely to be technology caused frequent fluctuations. If a no change possible instrument failure.
Is just four parameters control instrument on site field failure analysis, actual there are also complex control circuits, such as cascade control, control, control, interlocking control and so on. Failure analysis of these more complex and detailed analysis.