At present, with the continuous improvement in the automation level of petrochemical, steel, paper, food, and pharmaceutical companies, higher requirements are placed on the technical level of field instrument maintenance personnel. In order to shorten the processing time of the instrument and ensure safe production and improve economic efficiency, this paper publishes a little on-site maintenance experience for instrument maintenance personnel. First, the basic analysis steps of field instrument system failure Field instrument measurement parameters are generally divided into four parameters: temperature, pressure, flow, and liquid level. Two, four major measurement parameters instrument control system failure analysis steps 1. Temperature Control Instrument System Failure Analysis Steps
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According to the different measurement parameters, different field instrument faults are analyzed.
1. First of all, before analyzing the failure of the field instrument, it is necessary to thoroughly understand the production process, production process conditions and conditions of the relevant instrument system, understand the design scheme, design intent of the instrument system, the structure, characteristics, performance and parameter requirements of the instrument system.
2. Before the analysis and inspection of the failure of the on-site instrument system, the operator should be informed of the production load and the changes in the parameters of the raw materials, view the recording curve of the fault meter, and perform comprehensive analysis to determine the cause of the instrument failure.
3. If the meter records a dead line (a line that does not change at all is called a dead line), or if the record curve originally fluctuates, it suddenly becomes a straight line; the fault is likely to be in the instrument system. Because the current recording instruments are mostly DCS computer systems, the sensitivity is very high, and the change of parameters can be very sensitive to the reaction. At this point can artificially change the process parameters to see the curve changes. If it does not change, the basic conclusion is that the instrument system has a problem; if there is a normal change, it is basically determined that the instrument system has no major problems.
4. When changing the process parameters, it is found that the recorded curve has abruptly changed or jumped to the maximum or minimum. At this time, the fault is often in the instrument system.
5. Before the fault appeared, the instrument record curve had been performing normally. After the fluctuation, the recording curve became irregular or the system was difficult to control. Even the manual operation could not be controlled. At this time, the fault may be caused by the process operating system.
6. When it is found that the DCS display instrument is not normal, you can go to the scene to check the indicator value of the same intuitive instrument. If they are very different, it is likely that the instrument system has failed.
In short, when analyzing the causes of field instrument failures, special attention must be paid to the changes in the characteristics of the measured control object and the control valve, which may be the cause of the failure of the field instrument system. Therefore, we must comprehensively consider and carefully analyze the field instrument system and the process operating system to check the reason.
When analyzing the temperature control instrument system failure, we must first pay attention to two points: The system instrument uses electrical instrumentation to measure, indicate, and control; the measurement of the system instrument often lags behind.
(1) The indicator value of the temperature meter system suddenly changes to the maximum or minimum, which is generally a failure of the instrument system. Because the temperature meter system measures large lags, sudden changes do not occur. Most of the faults at this time are due to the thermocouple, thermal resistance, wire breakage in the compensation lead, or malfunction of the transmitter amplifier.
(2) Temperature control instrumentation system indicates rapid oscillation, which is mostly caused by improper adjustment of control parameter PID.
(3) The temperature control instrumentation system indicates the occurrence of large and slow fluctuations, which may be due to changes in process operations. If the process operation does not change at that time, it is likely that the instrument control system itself has failed.
(4) Failure analysis procedure 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 is actuated, and the diaphragm of the valve diaphragm is leaked; check whether the input signal of the regulating valve positioner changes, and the input signal No change, the output signal changes, the positioner has a fault; check the positioner input signal changes, and then check the regulator output if there is no change, if the regulator input does not change, the output changes, this time is the fault of the regulator itself.