Analysis of the causes of errors in LDG-100S electromagnetic flowmeter

LDG-100S electromagnetic flowmeter is not affected by the temperature, pressure, density, viscosity, etc. of the liquid when measuring the volumetric flow rate of the liquid, so it is favored by customers. However, if it is used irregularly, errors will occur. 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. 1. The liquid in the split electromagnetic flowmeter tube is not full. Due to insufficient back pressure or poor installation position of the flow sensor, the liquid in the measuring tube is not full. 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. 2. The liquid of LDG-100S electromagnetic flowmeter 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 insulating deposition layer covering the electrode or Lining; ④ The lining is worn or covered with 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. 3. There are crystals in the liquid. The split electromagnetic flowmeter should be used with caution. Some chemical materials that are easy to crystallize can be measured normally under normal temperature conditions. Since the conduits transporting fluids have good heat tracing and insulation, they will not crystallize during insulation work. However, it is difficult to implement heat tracing and insulation for the measuring tube of the electromagnetic flow sensor. 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.

4. Problems caused by improper selection of materials for electrodes and grounding rings. The components of electromagnetic flowmeters that are in contact with the medium and are in contact with the medium include electrodes and grounding rings. Improper matching will lead to malfunctions. In addition to corrosion problems, as long as it is the electrode surface effect. Surface effects should include: ① chemical reaction (formation of passive film on the surface, etc.); ② electrochemical and polarization phenomena (generation of electric potential); ③ catalytic action (generation of aerosol on the electrode surface, etc.). Ground rings also have these effects, but the impact is smaller. 5. Problems caused by liquid conductivity 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.