On-site Instrumentation System Common Fault Analysis Steps

- Nov 08, 2017 -

At present, with the continuous improvement of the automation level of petrochemical, steel, papermaking, foodstuff and pharmaceutical enterprises, higher requirements are put forward on the technical level of on-site instrumentation maintenance personnel. In order to shorten the processing instrument failure time and ensure the safety of production and improve economic efficiency, this article published a little on-site maintenance experience instrumentation, instrumentation maintenance personnel for reference.

First, the basic analysis of field instrumentation system failure

    Field instrument measurement parameters generally divided into temperature, pressure, flow, liquid level four parameters.

    Now based on the different measurement parameters to analyze the different field instrument failure.

    1. First of all, before analyzing the failure of on-site instruments, it is necessary to have a thorough understanding of the production process, conditions and conditions of the relevant instrumentation systems, understand the design plan, design intent, structure, characteristics, performance and parameter requirements of the instrumentation system.

    2. Before analyzing and checking the failure of on-site instrumentation system, it is necessary to know the load of production and the parameters of raw materials on site, check the record curve of faulty instruments, and carry out comprehensive analysis to determine the cause of instrument malfunction.

    3. If the meter records a dead line (a line that does not change at all is called a dead line) or if the recording curve was originally fluctuating, it suddenly becomes a straight line; the fault is most likely in the instrumentation system. Because most of the current recording instruments are DCS computer systems, the sensitivity is very high, the parameters of the changes can be very sensitive to the reaction. At this point can be artificially changed the process parameters to see the curve changes. If not change, the basic conclusion is that the instrumentation system is a problem; if the normal changes, the basic conclusion that the instrumentation system has no big problem.

    4. Changes in process parameters, found that the record curve mutation or jump to the maximum or minimum, this time the fault is often in the instrumentation system.


    5. Instrument failure occurred before the record curve has been normal, after the record curve fluctuations become irregular or make the system difficult to control, and even manual operation can not control, then 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 same visual instrument indication value, if they are very different, it is likely that the instrument system failure.

    In short, the analysis of field instrument failure reasons, pay special attention to the measured changes in the characteristics of the control object and the control valve, which may be caused by the field instrumentation system failure. Therefore, we have to consider from both the field instrumentation system and process operating system, careful analysis, check the reason.

Second, the four measurement parameters Instrumentation control system failure analysis steps

    1. Temperature control instrumentation system failure analysis steps

    Analysis of temperature control instrumentation system failure, we must first pay attention to two points: the use of multi-system instrumentation to measure, indicate, control; measurement of the system often lag large.

    (1) temperature instrumentation system suddenly changes to the maximum or minimum indication, the general instrument system failure. Because of the large temperature gauge system measurement lag, will not happen suddenly change. At this point of failure are mostly thermocouple, RTD, compensation wire breakage or transmitter amplifier failure.

    (2) temperature control instrumentation system indicates a rapid oscillation phenomenon, mostly due to improper control of PID parameters.

    (3) The temperature control instrumentation system indicates a significant slow fluctuation, most likely due to changes in process operation, such as no change in process operation at that time, it is likely to be the failure of the instrumentation control system itself.

    (4) temperature control system fault analysis steps: check the control valve input signal is changed, the input signal does not change, the control valve action, the diaphragm diaphragm valve leak; check the valve positioner input signal changes, the input signal No change, the output signal changes, the locator is faulty; check the locator input signal changes, and then check the regulator output changes, if the regulator input does not change, the output changes, this is the regulator itself fault.

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