Installation and failure of electromagnetic flowmeter

1. Introduction

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​Pipeline stray current interference usually takes good single grounding protection to obtain satisfactory results, but if encountering strong stray current (such as electrolysis workshop pipeline, sometimes the AC potential peak Vpp induced on the two electrodes can be as high as 1V), additional measures and flow sensor and pipeline insulation are required. Space electromagnetic wave interference is generally introduced through the signal cable, and is usually protected by single or multi-layer shielding.

3) Fluid aspect
The measured liquid contains uniformly distributed tiny bubbles, which usually do not affect the normal operation of the electromagnetic flowmeter, but as the bubbles increase, the output signal of the instrument will fluctuate. If the bubble is large enough to cover the entire electrode surface, the electrode circuit will be instantly disconnected as the bubble flows through the electrode, causing greater fluctuations in the output signal. When
the electromagnetic flowmeter with low-frequency square wave excitation measures slurry with excessive solid content, slurry noise will also be generated, causing the output signal to fluctuate.
When measuring mixed media, if the flow sensor is entered for measurement before the mixture is evenly mixed, the output signal will also fluctuate.
Improper matching of electrode materials and measured media will also affect normal measurement due to chemical reactions or polarization phenomena. The electrode material should be correctly selected according to the instrument selection or relevant manual.

3. Operational failures

Operational failures are failures that occur after the electromagnetic flowmeter has been debugged and operated normally for a period of time. Common operational failures 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) Adhesion layer on the inner wall of the sensor
Since electromagnetic flowmeters are often used to measure dirty fluids, after running for a period of time, an adhesion layer often accumulates on the inner wall of the sensor and causes failures. These failures are often caused by the conductivity of the adhesion layer being too large or too small. If the attachment is an insulating layer, the electrode circuit will be open-circuited and the instrument will not work properly; if the conductivity of the attachment layer is significantly higher than the conductivity of the fluid, the electrode circuit will be short-circuited and the instrument will not work properly. Therefore, the adhesion scaling 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 instrument circuit, causing damage to the instrument. It is mainly introduced through power lines, excitation coils, or flow signal lines between sensors and converters, especially from the power lines in the control room, which account for the vast majority.

3) Changes in environmental conditions
During the debugging period, the flowmeter works normally because the environmental conditions are good (for example, there is no interference source). 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, new interference sources appear 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 instrument and the output signal of the flowmeter will fluctuate.