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In industrial production, it is common to encounter instability in the zeroing of electromagnetic flowmeters. There are various reasons for this issue; based on the many years of experience of equipment technicians, the main factors are as follows: 1. The pipeline is not filled with liquid or the liquid contains bubbles, which seemingly results in no movement inside the flow sensor, but in reality, there is still some minor movement. 2. Prolonged use of the valve or contamination by liquids, which leads to imperfect sealing of the valve, can also cause instability in the zero point. 3. Variations or unevenness in liquid conductivity can cause shifts in the zero point when at rest, and fluctuations in the output when in motion. 4. Since the scaling on the inner and outer walls as well as the degree of electrode contamination cannot be exactly the same and symmetrical, it disrupts the equilibrium condition of the initial zero-setting. 5. Changes in the condition of the electrical equipment located near the flow sensor (such as an increase in leakage current) can cause changes in the grounding potential, which in turn can lead to variations in the zero point of the intelligent electromagnetic flow meter. By analyzing the problems, we can identify appropriate solutions based on the corresponding phenomena. Control of zero drift in electromagnetic flowmeters I. Initial troubleshooting checks: Follow the procedure to examine the reasons for instability in the zero point of intelligent electromagnetic flowmeters. First, conduct a comprehensive preliminary investigation and assessment according to the established procedure, and then carry out detailed checks one by one to identify and eliminate faults. The order of the inspection items listed in the procedure follows this principle: (1) Those that can be determined through observation or inquiry without requiring complex operations should be checked first, that is, start with the easier tasks before moving on to the more difficult ones. (2) Based on past on-site maintenance experience, those with a high occurrence frequency and a high probability of occurring in the future are listed first. (3) The sequential requirements necessary for the inspection itself. If a preliminary investigation confirms the existence of several possible causes of the fault, a detailed inspection can also be carried out in advance. II. Improper grounding of the sensors in intelligent electromagnetic flowmeters leads to interference from external factors such as stray currents: External interferences like stray currents in the pipes can affect the proper grounding protection of electromagnetic flowmeters; it is generally required that the grounding resistance be less than 1000, and the same grounding should not be shared with other motors and electrical devices. In some cases, when environmental conditions are favorable, intelligent electromagnetic flowmeters can function properly even without being grounded. However, once such favorable conditions are no longer present, the instrument will malfunction. Conducting inspections at that time can lead to many complications. Changes in the condition of electrical equipment near the flow sensor (such as an increase in leakage current) can cause changes in the grounding potential, which in turn can result in variations in the zero point of the intelligent electromagnetic flowmeter. III. Causes related to the liquid side of intelligent electromagnetic flowmeters (such as issues like uniformity of liquid conductivity and electrode contamination). Changes or unevenness in liquid conductivity can cause the zero point to shift when the liquid is at rest, and it can cause fluctuations in the output when the liquid is flowing. Therefore, the flowmeter should be placed far away from the point where the liquid is injected or downstream of any sections of the pipeline where chemical reactions occur; it is best to install the flow sensor upstream of these areas. If the liquid contains solid particles, impurities that deposit on the inner walls of the measurement tube, scale formation on those inner walls, or if the electrodes become contaminated by grease or other substances, this can all lead to changes in the zero point. Since the degree of scaling on the inner wall surfaces and the level of contamination of the electrodes cannot be exactly the same or symmetrical, this disrupts the balance established during the initial zero calibration. Effective measures include removing contaminants and scale deposits; if the changes in the zero point are not significant, attempting to recalibrate it may also be an option. IV. Decrease in insulation of the signal circuit of electromagnetic flowmeters: A decrease in insulation of the signal circuit can lead to unstable zero points. The main cause of such a decrease is insulation degradation at the terminal connections; however, it is also possible that the insulation of the signal cable and its connection terminals has degraded or been damaged. In some cases, the field conditions are extremely harsh, and even minor carelessness – such as inadequate sealing at the instrument cover or wire connections – can allow moisture, acidic fumes, or dust particles to enter the instrument’s wiring box or cable shielding, thereby reducing insulation levels. The insulation resistance of the signal circuit should be checked separately on the cable side and the flow sensor side, using a megohmmeter. Since the signal cable can be checked first, the flow sensor should be tested in two steps: first by measuring the surface contact resistance of the electrodes when the sensor is filled with liquid, and then by measuring the insulation resistance of the U pole. V. Checking the electrode contact resistance and electrode insulation resistance is carried out in 2 steps: (1) Fill the liquid and measure the contact resistance between the liquid on the electrode surface and the electrode. Disconnect the signal cable of the electromagnetic flowmeter sensor, and use a multimeter to measure the resistance between each electrode and the ground point; the difference in the resistance values between the two electrodes relative to the ground should be within 10%–20%. Further details are provided in Section 9, ‘Measurement of Electrode Contact Resistance’. (2) Insulation check of the control electrode: Empty the measurement tube, wipe its inner surface with a dry cloth, and once it is completely dry, use an H500VDC megohmmeter to measure the resistance between each electrode and ground; this resistance value should be above 100 MΩ. Under normal circumstances, by following these five steps for inspection and operation, the issue of unstable zero point can be resolved. For more information, please visit the company’s official website at http://www.yb1518.com/. Please retain this link when reproducing the content! http://www.yb1518.com/UploadFiles/2012717174126829.jpg