Analysis of the causes of errors in LDG-300S electromagnetic flowmeter

LDG-300S electromagnetic flowmeter has many advantages. When measuring the volumetric flow rate of a liquid, it is not affected by the temperature, pressure, density, viscosity, etc. of the liquid. Therefore, it has been favored by customers. However, if it is used improperly, there will be consequences. Errors occur and affect the measurement results. The following technicians summarized many years of work experience and concluded that the reasons for the error of the split electromagnetic flowmeter are mainly caused by the following aspects. The liquid in the LDG-300S electromagnetic flowmeter tube is not filled due to insufficient back pressure or poor installation position of the flow sensor, resulting in the liquid in the measuring tube not being filled. The fault phenomenon has different manifestations depending on the degree of underfill and the flow condition. If a small amount of gas flows in a stratified flow or a wavy flow in a water pipe, the fault phenomenon will be an increase in error, that is, the flow measurement value does not match the actual value; if the flow is bubble flow or plug flow, the fault phenomenon will be except that the measured value does not match the actual value. In addition, output sloshing will also occur due to the instantaneous covering of the electrode surface by the gas phase; if the flow cross-sectional area of ​​the gas part increases in the stratified flow of the horizontal pipe, that is, the degree of the liquid not filling the pipe increases, output sloshing will also occur. If the liquid does not fill the pipe If the situation is serious enough that the liquid level is below the electrode, the output will be over full. The cause of this kind of failure is often encountered in the after-sales service cases of manufacturers, and it is undoubtedly an engineering design error.

LDG-300S electromagnetic flowmeter The liquid contains solids. The liquid contains solids such as powder, particles or fibers. Possible faults include: ① slurry noise; ② contamination of the electrode surface; ③ conductive deposition layer or insulation The sediment layer covers the electrode or lining; ④ The lining is worn or covered by sediment, and the flow cross-sectional area is reduced. If conductive material is deposited on the insulating lining of the measuring tube of the split electromagnetic flowmeter sensor, the flow signal will be short-circuited and the instrument will fail. Since conductive substances are gradually deposited, this type of fault usually does not appear during the commissioning period, but will appear after a period of operation. LDG-300S electromagnetic flowmeter There are crystals in the liquid. The split type electromagnetic flowmeter should be used with caution. Some chemical materials that are easy to crystallize can be measured normally under normal temperatures. Since the conduits conveying the fluid have good heat tracing and insulation, during insulation work It will not crystallize, but the measuring tube of the electromagnetic flow sensor is difficult to implement heat tracing and insulation. Therefore, when the fluid flows through the measuring tube, it is easy to cause a layer of solid to form on the inner wall due to cooling. Since flowmeter measurement using other principles also has crystallization problems, if there is no other better method, a "ring-shaped" electromagnetic flow sensor with a very short measuring tube length can be used, and the upstream pipe of the flowmeter can be Heat tracing and insulation are enhanced. In terms of the pipeline connection method, consider that the flow sensor is easy to disassemble and assemble, so that it can be easily removed and maintained once it crystallizes. Problems caused by improper selection of materials for the electrodes and grounding rings of the LDG-300S electromagnetic flowmeter. Failures caused by the mismatch between the material and the measured medium. The parts of the electromagnetic flowmeter in contact with the medium include the electrodes and the grounding ring. In addition to corrosion resistance problems, improper matching , as long as it is the electrode surface effect. The surface effect should be: ① chemical reaction (formation of passive film on the surface, etc.); ② electrochemical and polarization phenomena (generation of electric potential); ③ Catalyst effect (generating aerosol on the electrode surface, etc.). Ground rings also have these effects, but to a lesser extent. Problems caused by the liquid conductivity of the LDG-300S electromagnetic flowmeter exceeding the allowable range. If the liquid conductivity is close to the lower limit, sloshing may occur. Because the lower limit value stipulated in the manufacturer's instrument specifications is the lowest value that can be measured under various good conditions of use, and the actual conditions cannot be ideal, so low-strength distilled water or deionized water has been encountered many times. , its conductivity is close to the lower limit value 5 specified in the electromagnetic flowmeter specification, but the output oscillates when used. It is generally believed that the lower limit of conductivity that can be stably measured is 1 to 2 orders of magnitude higher. The conductivity of liquids can be found in relevant manuals. If there is no ready data, samples can be taken and measured with a conductivity meter. But sometimes there are cases where samples are taken from the pipeline and taken to the laboratory for testing and are considered usable, but the actual split electromagnetic flowmeter cannot work. This is because the liquid when measuring conductivity is different from the liquid in the pipeline. For example, the liquid has absorbed CO2 or NO in the atmosphere, generating carbonic acid or nitric acid, and the conductivity increases. For noisy slurries produced by liquids containing particles or fibers, increasing the excitation frequency can effectively improve output sloshing.