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How to do electromagnetic flowmeter zero instability

See the unstable process of the zero point electromagnetic flowmeter. First, follow the process to think about the initial steps and discriminate, and then exhaustively review and try to clean up the shortcomings. The sequence of the order of the items listed in the process can be observed or interrogated to understand that there is no need for a large operation, that is, it is difficult to follow the on-site inspection experience, and the frequency of occurrence is higher and the probability of occurrence may be higher in the future. Look at the required pleadings before you. If the first step is recognized by the first step, it can be reviewed in advance.

The pipe is not filled with liquid or the liquid contains bubbles. Objectively, there is no activity in the flow sensor and there is a slight amount of activity in practice. The main reason for this type of shortcoming is that the tightness of the shut-off valve of the pipeline is poor, and the small leak amount detected by the electromagnetic flowmeter is misinterpreted as zero change or zero instability.
Cases where the valve is used for a long time or the liquid is dirty to make the valve tightly closed are often encountered, especially for large valves. Another common reason is that the flow surface has a number of branches in addition to the main pipe, forgetting or neglecting the closing of the valves of these branches. Sometimes it is difficult to recognize that the management system is inactive at the scene. At this point, you can observe whether there is leakage.

The conductivity of the liquid changes or is uneven, and the zero point changes when it is stopped, and the output is shaken when it is active. Therefore, the flowmeter should be located away from the injection point or the chemical section of the pipeline. The flow sensor should be installed upstream of these places. If the liquid contains a solid phase, or the impurities accumulate on the inner wall of the flow metering tube, or the scale on the inner wall of the flow metering tube, or the electrode is contaminated by grease, etc., a zero point change may occur.

Because the fouling of the inner wall surface and the level of electrode contamination are not exactly the same and symmetrical, the equilibrium of the initial zero setting is destroyed. The active method is to eliminate the pollution and accumulation of scale; if the zero is not changed, the test can be zeroed from the beginning.

A change in the condition of the power device near the flow sensor (such as the addition of leakage current) constitutes a change in the ground potential, which also causes a zero change in the electromagnetic flowmeter. The influence of external disturbances such as stray current of the pipeline depends on the outstanding grounding protection of the electromagnetic flowmeter. Generally, the grounding resistance is less than 10, and it should not be grounded with other electrical appliances. Sometimes the environmental conditions are good, and the electromagnetic flowmeter can work normally without grounding. However, once the outstanding environment does not exist, there will be shortcomings on the surface, and then viewing it will bring a lot of trouble.

View the flowchart. A drop in the insulation of the signal loop can constitute a zero point instability. The main reason for the drop of the signal loop insulation is caused by the insulation of the electrode part, but it is also impossible to clean the signal cable and its terminal insulation or reduce the damage, because sometimes the site environment is very harsh, and the surface cover and the wire joint are not sealed. Be careful, with moisture mist or dusty dust invading the surface junction box or cable cover to reduce insulation.

The signal loop insulation resistance is checked by the two sides of the cable side and the flow sensor, and the meter is tested. Because the signal cable is easy to detect, it can be done first. Filled with liquid electromagnetic flowmeter electrode surface touch resistance and empty tube after flow metering electrode insulation resistance

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