Zibo Yiyuan Engineering Technology reminds you that if there is a problem with the instrument, the cause is more complicated, and it is difficult to find the crux. Detection, intermediate transmission, and terminal display; at the same time, seasonal reasons should also be considered, such as anti-high temperature in summer and anti-freezing in winter; when the parameters involved in the adjustment are abnormal, firstly switch the regulator to the manual state, observe and analyze the reasons for adjusting the system, Then check the other factors one by one.

No matter what kind of instrument fails, we must first understand the production process conditions and conditions of the installation location of the instrument, and understand the structural characteristics and performance of the instrument itself; before maintenance, we must combine with the technicians to analyze and determine the real cause of the instrument failure. ;At the same time, it is also necessary to know whether the instrument is accompanied by adjustment and interlocking functions. After comprehensive consideration and careful analysis, the process should be kept as stable as possible during the maintenance process.

1. On-site measuring instruments

Generally divided into four categories: temperature, pressure, flow, liquid level

(1) Common fault analysis of temperature instrument system

(1): Sudden increase in temperature: This fault is mostly caused by thermal resistance (thermocouple) open circuit, loose terminals, (compensation) wire break, temperature failure, etc. At this time, it is necessary to know the location of the temperature and the wiring layout , you can quickly find out the reason by measuring several sets of data at different positions with the resistance (millivolt) file of the multimeter.

(2): The temperature suddenly decreases: this fault is mostly caused by short circuit of thermocouple or thermal resistance, short circuit of wire and temperature failure. It is necessary to start from the weak points that are prone to failure, such as wiring ports and wire bends, and check them one by one. The on-site temperature rises, but the master control indication remains unchanged, which is mostly caused by the presence of a liquid (water) with a lower boiling point at the measuring element.

(3): The temperature fluctuates greatly or rapidly: at this time, the process operation should be mainly checked (the inspection and adjustment system that participates in the adjustment).

(2) Common faults and analysis of pressure instrumentation system

(1): The pressure suddenly decreases or increases or the indication curve does not change: At this time, the pressure induction system of the transmitter should be checked to check whether the root valve is blocked, whether the pressure induction pipe is unblocked, whether there is abnormal medium inside the pressure induction pipe, and sewage Whether the plug and the drain valve are leaking, etc. Winter medium freezing is also a common phenomenon. The transmitter itself is less likely to fail.

(2): The pressure fluctuates greatly: This situation must first be combined with the craftsman, which is generally caused by improper operation. The parameters involved in the adjustment should mainly check the adjustment system.

(3) Common faults and analysis of flow instrumentation system

(1): The minimum flow indication value: generally caused by the following reasons: the detection element is damaged (the zero point is too low.; there is a problem with the display; the line is short-circuited or open; the positive pressure chamber is blocked or leaked; the system pressure is low; the parameters involved in the adjustment are also required. Check regulator, regulating valve and solenoid valve.

(2): The flow indication is the largest: the main reason is that the pressure system of the negative pressure chamber is blocked or leaked. It is unlikely that the transmitter will need adjustment.

(3): The flow fluctuates greatly: if the flow parameters are not involved in the adjustment, it is generally due to process reasons; if the flow parameters are involved in the adjustment, you can check the PID parameters of the regulator; for parameters with an isolation tank, check whether there are air bubbles in the pressure induction pipe, and the positive and negative pressure leads to Whether the liquid in the pressure pipe is the same height.

(4) Common faults and analysis of liquid level instrumentation system

(1): The liquid level suddenly increases: mainly check whether the pressure system of the negative pressure chamber of the transmitter is blocked, leaked, gas collected, lack of liquid, etc. The specific method of filling liquid is: stop the meter first in the order of stopping the meter; close the positive and negative pressure root valve; open the positive and negative pressure sewage valve to relieve pressure; open the double-chamber balance container filling plug; open the positive and negative pressure chamber sewage plug; At this time, the liquid level indication is maximum. Close the blowdown valve; close the blowdown plug in the positive and negative pressure chambers; slowly pour the same medium into the double-chamber balance container, and open the blowdown plug slightly to exhaust at this time; The transmitter indicates that it should return to zero. Then put the transmitter into use in the order of metering.

(2): The liquid level suddenly decreases: mainly check whether the positive pressure chamber pressure system is blocked, leaking, gas gathering, lack of liquid, and whether the balance valve is closed, etc. The specific method to check whether the pressure induction system is smooth is to stop the transmitter, open the blowdown valve, and check the blowdown condition (except for the medium that cannot be leaked).

(3): The indication of the master control room does not match the on-site liquid level: first determine whether the on-site liquid level gauge is faulty. At this time, the liquid level can be artificially increased or decreased, and the cause of the problem can be analyzed according to the on-site and master control instructions (the on-site liquid level Closed, blocked, and external leakage of the root valve may cause inaccurate on-site instructions). The liquid level can be restored to normal by checking the zero point, span, and filling. If it is still not normal, you can notify the technical personnel to monitor the site and remove the transmitter for pressure adjustment.

4): The liquid level fluctuates frequently: first, check the feeding and discharging conditions with the technicians, and after confirming that the process conditions are normal, it can be stabilized by adjusting the PID parameters. The specific method is: the regulating valve is put into the manual state, first adjust the set value to be consistent with the measured value, so that the fluctuation of the liquid level is stable, and then slowly adjust the opening of the regulating valve, so that the liquid level rises or falls slowly to meet the process requirements, and then adjust The set value is the same as the measured value. After the parameters are stable, the valve is automatically adjusted.

Zibo Yiyuan Engineering Technology reminds you that once you find that the instrument parameters are abnormal, you should first combine with the process personnel, start from the process operating system and the field instrument system, comprehensively consider and analyze carefully, especially the relationship between the measured parameters and the control valve. It is easy to find out the problem and solve the problem by applying the right medicine.