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Common faults in the use of electromagnetic flowmeters

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, and 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 operation).

(1) During the debugging period, the debugging expects that the fault usually appears in the instrument installation and debugging stage. Once removed, it will generally not appear again 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 high point of the piping system that is easy to accumulate gas; or installing it on the 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 obtain satisfactory results, but if it encounters strong stray currents (such as electrolytic workshop pipelines, sometimes the peak value of the AC potential Vpp induced on the two electrodes can be as high as 1V). 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 instantly and the output signal will fluctuate more. 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 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 the 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. After a period of operation, the adhesion layer on the inner wall of the sensor often accumulates and causes 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 the fluid conductivity, the electrode circuit will be short-circuited and the meter will not work normally. Therefore, the adhesion fouling layer in the measuring tube of the electromagnetic flowmeter should be removed in time.

2) Lightning strikes Lightning strikes are likely to 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 good environmental conditions (for example, no interference source), the flowmeter is working normally, and 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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