Solving the Unstable Zero - Point Problem of Electromagnetic Flowmeters: A Comprehensive Guide

In industrial flow measurement scenarios, the unstable zero - point of electromagnetic flowmeters is a common issue that can significantly affect measurement accuracy. Here, I'll share some in - depth insights into its causes and solutions. 

1. Incompletely Filled Pipes or Presence of Bubbles: When the pipeline is not fully filled with liquid or contains bubbles, a peculiar situation occurs. Objectively, the flow sensor may seem to have no liquid flow, but in fact, there is a trace amount of liquid movement. The main cause of this type of problem is usually the poor tightness of the pipeline's shut - off valve. The tiny leakage detected by the electromagnetic flowmeter is easily misinterpreted as zero - point variation or instability.

2. Valve Tightness Issues: Over time, valves may experience wear and tear, or be affected by dirt in the liquid, resulting in incomplete sealing. This is particularly common in large - sized valves. Additionally, flowmeter systems often have several branch pipes in addition to the main pipeline. Forgetting or neglecting to close the valves of these branch pipes can also lead to similar problems. Sometimes, it's difficult to confirm whether there is liquid flow in the pipeline on - site. In such cases, you can check for leakage.

3. Liquid Conductivity Problems: Changes or non - uniformity in liquid conductivity can cause zero - point fluctuations when the liquid is stationary and make the output fluctuate when the liquid is flowing. Therefore, when installing the flowmeter, it should be located away from the liquid injection point or the downstream of the pipeline chemical reaction section. Installing the flow sensor upstream of these areas is a better choice. Moreover, if the liquid contains solid phases, impurities accumulate on the inner wall of the flow measurement tube, the inner wall of the flow measurement tube becomes scaled, or the electrodes are contaminated by grease, etc., it is likely to cause zero - point changes.

4. Inner Wall Scaling and Electrode Contamination: The degree of inner - wall scaling and electrode contamination in the flow measurement tube is unlikely to be completely uniform and symmetrical, which disrupts the balance set during the initial zero - point adjustment. An effective solution is to remove dirt and accumulated scale. If the zero - point variation is not significant, you can also try re - adjusting the zero - point.

5. Power Equipment and Grounding Problems: Changes in the status of power equipment near the flow sensor, such as an increase in leakage current, can cause changes in the grounding potential, thereby leading to zero - point changes in the electromagnetic flowmeter. External interferences like pipeline stray currents are mainly resisted through proper grounding of the electromagnetic flowmeter. Generally, the grounding resistance is required to be less than 10Ω, and it should not share the ground with other electrical equipment. In some well - conditioned environments, the electromagnetic flowmeter may work properly without grounding for a while. However, once the environment deteriorates, problems may arise. Checking and repairing at this time will be more troublesome.

6. Signal Circuit Insulation Problems: A decrease in the insulation performance of the signal circuit can lead to unstable zero - points of the electromagnetic flowmeter. The main cause of the decrease in signal - circuit insulation is usually the reduced insulation performance of the electrode part, but the possibility of a decrease in insulation or damage of the signal cable and its connection terminals cannot be ignored. In harsh on - site environments, if there is a slight oversight, such as poor sealing of the instrument cover and wire connections, moisture, acid mist, or dust may penetrate the instrument junction box or cable protective layer, reducing the insulation performance. When checking the insulation resistance of the signal circuit, it is necessary to test the cable side and the flow sensor separately using a megohmmeter. Since the signal cable is relatively easy to test, it can be tested first. At the same time, it is also necessary to detect the contact resistance of the micro - electromagnetic flow measurement electrodes when the tube is filled with liquid and the insulation resistance of the flow measurement electrodes when the tube is empty. 

If you've encountered similar issues or have any questions, feel free to leave a comment below! Let's discuss and find better solutions together. 

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