1. The liquid in the tube is not full due to insufficient back pressure or poor installation position of the flow sensor, which causes the liquid in the measuring tube to be not full. The fault phenomenon has different performance due to the degree of insufficiency and flow condition.If a small amount of gas is layered flow or wavy flow in the water pipe, the fault phenomenon is manifested as increased error, that is, the measured flow value is not consistent with the actual value;If the flow is bubble flow or plug flow, the fault phenomenon is not only discrepant between the measured value and the actual value, but also the output sloshing will occur because the gas phase instantly covers the electrical surface.If the gas phase part of the cross-sectional area of the horizontal pipeline increases in the layered flow, that is, the degree of the liquid under the pipe increases, the output sloshing will also occur. If the liquid under the pipe is more serious, so that the liquid level is below the current level, the output overfull degree phenomenon will occur.

2 liquid contains solid phase liquid contains powdery particles or fibers and other solid, may produce in the fault;

(1) Slurry noise (2) Electrical surface contamination;(3) conductive deposit layer or insulating deposit layer to cover the electric or lining;(4) The lining is worn or covered by sediment, and the flow cross-sectional area is reduced.

3. The possible crystallization liquid, electromagnetic flowmeter should be used carefully Some easy crystallization chemical material, in normal under the condition of normal temperature measurement because of the transmission fluid pipe has good thermal insulation, insulation in normal when not crystallization, but difficult to implement electromagnetic flow sensor measurement of tube, thermal insulation, therefore, when the fluid flows through the measuring tube is caused by cooling wall in case, can be used to measure tube length is very short of "ring" electromagnetic flow sensor, and the flow meter of strengthened upstream pipe thermal insulation.In the pipeline connection method, considering that the flow sensor is easy to disassemble and install, once the crystallization occurs, it can be easily disassembled and maintained.

4. Problems caused by improper selection of electrical and grounding ring material due to the mismatch between the material and the measured medium caused by the failure of electromagnetic flowmeter and medium contact parts have electrical and grounding ring.In addition to corrosion resistance, the main cause of mismatching is electrical surface effect.Surface effects include :(1) passivation film formed on the surface of chemical reaction; (2) electric potential generated by electrochemical and chemical phenomena; (3) gas mist generated on the surface of catalyst.Ground rings also have these effects, but to a lesser extent.

5. Problems caused by the liquid conductivity exceeding the allowable range. If the liquid conductivity is close to the lower limit, there may be shaking phenomenon.Because the lower limit stipulated by the manufacturer's instrument specification is the low value that can be measured under all kinds of good use conditions, and the actual conditions can not be very ideal, so many times encountered the measurement of low distilled water or deionized water, its conductivity is close to the lower limit of 5S/cm stipulated by the electromagnetic flowmeter specification, but the output wobble appears when using.The lower limit of conductivity that can be measured stably is generally considered to be one or two quantities higher.

The liquid conductivity can be referred to the relevant manual, the lack of readily available data can be sampled with conductivity meter measurement, but sometimes there are samples from the pipeline to the laboratory measurement that is available, and the actual electromagnetic flowmeter can not work.This is due to the difference between the liquid and the liquid in the pipeline when the conductivity is measured. For example, the liquid has absorbed CO2 or NOx in the atmosphere and generated sulfuric acid carbonate, and the conductivity has increased.

For the noise slurry containing particles or fibers, the method of increasing the excitation frequency can effectively improve the output sloshing.

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