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Common faults of electromagnetic flowmeters

by:Sure     2021-08-05
Common faults in the use of electromagnetic flowmeters, some are caused by the damage of the instrument itself, and some are caused by improper selection, improper installation, environmental conditions, fluid characteristics and other factors, such as display fluctuations, decreased accuracy, or even instrument damage, etc. . It can generally be divided into two types: faults during installation and debugging (faults during debugging) and common faults in the use of electromagnetic flowmeters in normal operation. Some are caused by the damage of the instrument itself, and some are caused by improper selection and improper installation. Failure caused by factors such as proper temperature, environmental conditions, fluid characteristics, etc., such as display fluctuations, decreased accuracy, or even instrument damage. It can generally be divided into two types: faults during installation and debugging (faults during debugging) and faults during normal operation (faults during runtime). (1) Fault debugging during the debugging period Expected faults generally appear in the installation and debugging stage of the instrument. Once eliminated, they will generally not reappear under the same conditions in the future. Common faults during the commissioning period are generally caused by improper installation, environmental interference, and fluid characteristics. 1) In terms of installation, the fault is usually caused by the incorrect installation position of the electromagnetic flow sensor, such as installing the sensor on the highest point of the piping system that is easy to accumulate gas; or installing it on a vertical pipe from top to bottom, which may cause emptying; Or there is no back pressure behind the sensor, and the fluid is directly discharged into the atmosphere to form a non-full tube in the measuring tube. 2) The environment is usually mainly caused by pipeline stray current interference, strong electromagnetic wave interference in space, and magnetic field interference of large electric motors. Pipeline stray current interference usually takes good separate grounding protection to get satisfactory results, but if it encounters strong stray current (such as electrolytic workshop pipes, sometimes the peak value of the AC potential Vpp induced on the two electrodes can be as high as 1V), it is still Additional measures and insulation between the flow sensor and the pipeline are required. Space electromagnetic wave interference is generally introduced through signal cables, and is usually protected by single-layer or multi-layer shielding. 3) In terms of fluid, the evenly distributed microbubbles in the measured liquid usually do not affect the normal operation of the electromagnetic flowmeter, but as the bubbles increase, the output signal of the meter will fluctuate. If the bubbles are large enough to cover the entire electrode surface, As the bubbles flow through the electrode, the electrode circuit will be cut off instantaneously and the output signal will have greater fluctuations. When the electromagnetic flowmeter with low frequency square wave excitation measures the slurry with too much solid content, it will also produce slurry noise, which will cause the output signal to fluctuate. When measuring mixed media, if the flow sensor is used for measurement before the mixing is not uniform, the output signal will also fluctuate. Improper selection of the electrode material and the measured medium will also affect the normal measurement due to chemical effects or polarization phenomena. The electrode material should be correctly selected according to the instrument selection or relevant manuals. (2) Operation faults Operation faults are faults that occur after the electromagnetic flowmeter has been debugged and operated normally for a period of time. Common operating faults are generally caused by factors such as the adhesion layer on the inner wall of the flow sensor, lightning strikes, and changes in environmental conditions. 1) The adhesion layer on the inner wall of the sensor is often used to measure dirty fluids with electromagnetic flowmeters. After a period of operation, the adhesion layer on the inner wall of the sensor often accumulates and malfunctions. These failures are often caused by too much or too little conductivity of the adhesion layer. If the attachment is an insulating layer, the electrode circuit will be open and the meter will not work normally; if the conductivity of the attachment layer is significantly higher than that of the fluid, the electrode circuit will be short-circuited and the meter will not work properly. Therefore, the adhesion fouling layer in the measuring tube of the electromagnetic flowmeter should be removed in time. 2) Lightning strikes Lightning strikes can easily induce high voltage and surge current in the meter circuit, which will damage the meter. It is mainly introduced through the power line or excitation coil or the flow signal line between the sensor and the converter, etc., especially from the control room power line. 3) Changes in environmental conditions During the commissioning period, due to the good environmental conditions (for example, no interference source), the flowmeter is working normally. At this time, it is easy to neglect the installation conditions (for example, the grounding is not very good). In this case, once the environmental conditions change, a new source of interference appears during operation (such as electric welding on the pipeline near the flowmeter, installation of a large transformer nearby, etc.), which will interfere with the normal operation of the meter and the output of the flowmeter. The signal will fluctuate.
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