Troubleshooting common malfunctions of electromagnetic flow meters

　　Common malfunctions in electromagnetic flow meters may be caused by improper instrument component selection, installation, environmental conditions, fluid characteristics, etc., resulting in fluctuating readings, reduced accuracy, or even instrument damage. These malfunctions are generally classified into two categories: malfunctions that occur during installation and commissioning (debugging malfunctions) and malfunctions that occur during normal operation (operational malfunctions).

　　(1) Debugging Malfunctions Debugging malfunctions usually occur during the installation and commissioning stages of the instrument and, once eliminated, usually do not reappear under the same conditions. Common debugging malfunctions are usually caused by improper installation, environmental interference, and the influence of fluid characteristics.

　　1) Installation Issues Malfunctions are usually caused by incorrect installation of the electromagnetic flow sensor, such as installing the sensor at the highest point of a pipeline system where gas may accumulate; or installing it vertically on a vertical pipe from top to bottom, which may lead to air expulsion; or lack of back pressure after the sensor, with the fluid directly discharging into the atmosphere, causing the pipe in the measuring tube to be unfilled.

　　2) Environmental Issues These mainly involve stray current interference in the pipeline, strong electromagnetic wave interference in space, and interference from the magnetic fields of large motors. Stray current interference in the pipeline can usually be solved by good separate grounding protection, but if strong stray currents are encountered (for example, in electroplating workshops, the peak-to-peak AC voltage Vpp induced on the two electrodes can reach 1V), additional measures need to be taken and insulation between the flow sensor and the pipeline is required. Electromagnetic wave interference is usually introduced through signal cables and is usually protected using single-layer or multi-layer shielding.

　　3) Fluid Issues Uniformly distributed tiny bubbles in the measured liquid usually do not affect the normal operation of the electromagnetic flow meter, but as the bubble size increases, the instrument's output signal will fluctuate. If the bubbles are large enough to cover the entire electrode surface, the passage of bubbles through the electrodes will cause an instantaneous break in the electrode circuit, resulting in a large fluctuation in the output signal. Low-frequency square wave excitation electromagnetic flow meters measuring slurries with high solid content will also produce slurry noise, causing output signal fluctuations. When measuring mixed media, if the measurement is taken before the mixture is uniform, the output signal will also fluctuate. Mismatches between the electrode material and the measured medium will also affect normal measurement due to chemical reactions or polarization phenomena. Electrode materials should be correctly matched according to instrument selection or relevant manuals.

　　(2) Operational Malfunctions Operational malfunctions refer to malfunctions that occur in the electromagnetic flow meter after commissioning and normal operation for a period of time. Common operational malfunctions are usually caused by deposits on the inner wall of the flow sensor, lightning strikes, and changes in environmental conditions.

　　1) Sensor Inner Wall Deposits Because electromagnetic flow meters are usually used to measure dirty fluids, deposits usually accumulate on the inner wall of the sensor after a period of operation, causing malfunctions. These malfunctions are usually caused by the conductivity of the deposits being too high or too low. If the deposit is an insulating layer, the electrode circuit will be disconnected, and the instrument will not work properly; if the conductivity of the deposit is significantly higher than the conductivity of the fluid, the electrode circuit will short-circuit, and the instrument will not work properly. Therefore, the deposits and dirt layers in the measuring tube of the electromagnetic flow meter should be cleaned regularly.

　　2) Lightning Strikes Lightning strikes can easily induce high voltage and surge currents in the instrument circuit, damaging the instrument. This is mainly introduced through the power lines, excitation coils, or flow signal lines between the sensor and the converter, most of which are introduced from the control room power lines.

　　3) Changes in Environmental Conditions During commissioning, the environmental conditions are good (e.g., no interference sources), and the flow meter works normally. In this case, installation conditions (e.g., poor grounding) are often overlooked. In this case, once the environmental conditions change, and new interference sources appear during operation (e.g., welding on nearby pipes, installing large transformers nearby), the normal operation of the instrument will be affected, and the input and output signals of the flow meter will fluctuate. V. Precautions and Safety Measures for the Use of Electromagnetic Flow Meters The following points should be noted during the installation and maintenance of electromagnetic flow meters: 1. In order to avoid the illusion of a non-zero indication when there is no liquid in the pipe, it is usually required that the electromagnetic flow meter be installed vertically to prevent the formation of bubbles when the liquid flows past the electrodes, leading to measurement errors. 2. The dirt layer deposited on the inner wall of the converter tube should be cleaned regularly to prevent electrode short circuits and the inability to measure flow. 3. Since the signal of the flow meter is relatively weak, especially when the flow is very small, special attention should be paid to the influence of external interference on its measurement accuracy. Therefore, the housing of the converter, the shielding wire, the measuring wire, and the pipes at both ends of the converter should be connected to a separately set grounding point to avoid introducing additional interference due to uneven ground potential. 4. The converter should be installed away from all magnetic sources and should not be subjected to vibration.