Common faults in the use of electromagnetic flowmeters
Common faults in the use of electromagnetic flowmeters, some are faults caused by damage to the components of the instrument itself, and some are faults caused by improper selection, improper installation, environmental conditions, fluid characteristics, etc., such as display fluctuations, reduced accuracy, and even instrument damage. . It can generally be divided into two types: failures during installation and commissioning (debug during commissioning) and failures during normal operation (running faults). (1) Debugging period Fault debugging It is expected that the fault generally occurs in the stage of installation and debugging of the instrument. Once it is excluded, it will not appear again under the same conditions in the future. Common commissioning failures are generally caused by improper installation, environmental disturbances, and fluid characteristics. 1) The installation aspect is usually the fault caused by the incorrect installation position of the electromagnetic flow sensor. Commonly, if the sensor is installed at the high point of the duct system which is easy to accumulate gas, or installed on the vertical tube from top to bottom, the emptying may occur. Or no back pressure after the sensor, the fluid is directly discharged into the atmosphere to form a non-full tube inside the measuring tube. 2) The environmental aspects are usually mainly caused by stray current interference in the pipeline, strong electromagnetic wave interference in space, and magnetic field interference of large motors. Pipe stray current interference usually takes good single grounding protection to get satisfactory results, but if you encounter strong stray current (such as electrolysis shop piping, sometimes the peak potential Vpp induced on the two electrodes can be as high as 1V), still Additional measures and insulation of the flow sensor and piping are required. Space electromagnetic interference is typically introduced via a signal cable and is typically protected by a single or multiple layers of shielding. 3) The fluid contains a uniform distribution of tiny bubbles in the liquid to be measured, which usually does not affect the normal operation of the electromagnetic flowmeter. However, as the bubble increases, the output signal of the instrument fluctuates. If the bubble is large enough to cover the entire electrode surface, As the bubble flows through the electrode, the electrode loop is momentarily broken and the output signal appears more fluctuating. When the low-frequency square-wave excited electromagnetic flowmeter measures the solid content of too much slurry, it will also generate slurry noise, which will cause the output signal to fluctuate. When measuring mixed media, if the flow sensor is measured before the mixing is not uniform, the output signal will also fluctuate. Improper matching of the electrode material and the measured medium will also affect normal measurement due to chemical action or polarization. The electrode material should be properly selected according to the instrument selection or related manual. (2) Operation period failure The operation period failure is a fault that occurs after the electromagnetic flowmeter has been debugged and operated normally for a period of time. The common operation period failure is generally caused by factors such as the adhesion layer on the inner wall of the flow sensor, lightning strike and environmental conditions. 1) The inner wall of the sensor is used to measure the dirty fluid due to the electromagnetic flowmeter. After running for a period of time, the adhesive layer often accumulates on the inner wall of the sensor and causes a malfunction. These failures are often caused by the electrical conductivity of the adhesion layer being too large or too small. If the attachment is an insulating layer, the electrode circuit will be broken and the meter will not work normally; if the conductivity of the adhesion layer is significantly higher than the fluid conductivity, the electrode circuit will be short-circuited and the meter will not work properly. Therefore, the fouling layer in the measuring tube of the electromagnetic flowmeter should be removed in time. 2) Lightning strikes lightning strikes easily induce high voltage and surge currents in the instrument line, causing damage to the instrument. It is mainly introduced through the power line or the excitation coil or the flow signal line between the sensor and the converter, especially from the control room power line. 3) Changes in environmental conditions During the commissioning period, due to good environmental conditions (for example, no interference source), the flowmeter works normally, and it is often easy to neglect the installation conditions (for example, the grounding is not so good). In this case, once the environmental conditions change, a new source of interference occurs during operation (such as welding on the pipeline near the flowmeter, installing 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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