On-site measuring instruments are generally divided into four categories: temperature, pressure, flow, and liquid level.
(1): Sudden increase in temperature: This fault is mostly caused by thermal resistance (thermocouple) open circuit, loose terminal, (compensation) wire breakage, temperature failure, etc. At this time, it is necessary to know the location and wiring layout of the temperature. Using the multimeter's resistance (millivolt) file to measure several sets of data at different locations can quickly identify the cause.
(3): The temperature fluctuates greatly or oscillates rapidly: At this time, the process operation should be mainly checked (inspection adjustment system participating in the adjustment).
(1): The pressure suddenly becomes smaller, becomes larger or there is no change in the indication curve: at this time, the transmitter pressure system should be checked to check whether the root valve is blocked, whether the pressure pipe is unblocked, whether there is abnormal medium inside the pressure pipe, and sewage discharge. Whether the wire plug and the drain valve leak. Winter media freezing is also a common phenomenon. The transmitter itself is unlikely to malfunction.
c): Common faults and analysis of flow meter systems
(2): Flow indication: The main reason is that the negative pressure chamber pressure system is blocked or leaking. It may not be possible for the transmitter to be calibrated.
4): Common faults and analysis of liquid level instrumentation system
(2): The liquid level suddenly becomes smaller: mainly check whether the positive pressure chamber pressure system is blocked, leaked, gas collected, liquid-deficient, and the balance valve is closed. The specific method for checking whether the pressure guiding system is unblocked is to stop the transmitter, open the drain valve, and check the sewage discharge (except for the medium that cannot be leaked).
4): The liquid level fluctuates frequently: firstly, it is combined with the process personnel to check the feeding and discharging conditions, and after determining the normal state of the process, it can be stabilized by adjusting the PID parameters. The specific method is: adjust the valve to the manual state, first adjust the set value and the measured value to make the liquid level fluctuation smooth, and then slowly adjust the opening of the regulating valve, so that the liquid level slowly rises or falls, meets the process requirements, and then adjusts The set value is consistent with the measured value, and the regulating valve is automatically applied after the parameter is stabilized.
In short, once the instrument parameters are found to be abnormal, first of all, combined with the process personnel, starting from the two aspects of the process operating system and the field instrument system, comprehensive consideration, careful analysis, especially considering the relationship between the measured parameters and the control valve, the fault will be divided Step segmentation judgment, it is easy to find out the problem, solve the problem with the right medicine.
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