Considerations for the selection of electromagnetic flowmeters

Abstract: The main points of consideration for the selection of electromagnetic flowmeter meters are provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. Seven major elements of electromagnetic flowmeter selection 1. Application overview Large-diameter meters are mostly used in water supply and drainage projects. Small and medium calibers are often used in solid-liquid dual phase fluids that are difficult to measure or in places with high requirements, such as measuring pulp and black liquor in the paper industry, ore pulp in the non-ferrous metallurgy industry, and coal preparation. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the key points to consider in the selection of electromagnetic flowmeters. Seven major elements of electromagnetic flowmeter selection 1. Application overview Large-diameter meters are mostly used in water supply and drainage projects. Small and medium calibers are often used in places where solid-liquid dual phase is difficult to measure or in places with high requirements, such as measuring pulp and black liquor in the paper industry, ore pulp in non-ferrous metallurgy, coal slurry in coal preparation plants, strong corrosive liquid in chemical industry, and blast furnace tuyere in iron and steel industry. Cooling water control and leakage monitoring, flow measurement and control of long-distance pipeline coal hydraulic transportation. Small-caliber and micro-caliber are often used in places with hygienic requirements such as the pharmaceutical industry, food industry, and bioengineering. 2. Accuracy level and function The performance of general-purpose EMFs on the market is quite different. Some have high precision and multiple functions, and some have low precision and simple functions. The basic error of the instrument with high precision is (±0.5%～±1%)R, the instrument with low accuracy is (±1.5%～±2.5%) FS, the price difference between the two is 1 to 2 times. Therefore, it is not economical to use high-precision instruments in places where measurement accuracy is not very high (for example, non-trade accounting is only for control purposes, and only requires high reliability and excellent repeatability). Some models of meters claim higher accuracy, with a fundamental error of only (±0.2%～±0.3%) R, but there are strict installation requirements and reference conditions, such as ambient temperature 20 ~ 22 ℃, the length of the front and rear straight pipe sections is required to be greater than 10D, 3D (usually 5D, 2D). The straight pipe is integrated to perform real flow calibration on the flow standard device to reduce the influence of poor clamping. Therefore, when comparing multiple models, don't just look at the high indicators, but read the manufacturer's samples or instructions in detail for a comprehensive analysis. The functions of EMFs on the market are also very different. The simple one is to measure one-way flow, and only output analog signals to drive the rear instrument; , small signal removal, flow display and total calculation, automatic check and fault self-diagnosis, communication with the host computer and motion configuration, etc. The serial digital communication function of some models of instruments can choose a variety of communication interfaces and special-purpose chips (ASIC) to connect HART protocol systems, PROFTBUS, Modbus, CONFIG, FF fieldbus, etc. 3. The flow rate, full-scale flow rate, range degree and diameter of the selected instrument are not necessarily the same as the pipe diameter, and should be determined according to the flow rate. The process industry transports liquids with different viscosities such as water, and the pipeline flow rate is generally an economical flow rate of 1.5 to 3m/s. EMF is used on such pipes, and the sensor diameter is the same as the pipe diameter. When the EMF flow rate is full, the liquid flow rate can be selected in the range of 1 ~ 10m/s, and the range is relatively wide. The upper limit flow velocity is not limited in principle, however, it is generally recommended not to exceed 5m/s, unless the lining material can withstand the flow of liquid, and practical applications rarely exceed 7m/s, and more rarely exceed 10m/s. The lower limit of the full-scale flow rate is generally 1m/s, and some models of instruments are 0.5m/s. Some new construction projects have low flow rate or low flow rate in the early stage of operation. From the perspective of measurement accuracy, the diameter of the instrument should be changed to be smaller than the diameter of the pipe, and connected with a reducer. For fluids that are prone to adhesion, deposition, scaling, etc., the flow rate should not be lower than 2m/s, and increase to 3-4m/s or above, which plays the role of self-cleaning and preventing adhesion and deposition. It is used for highly abrasive fluids such as pulp, and the usual flow rate should be lower than 2-3m/s to reduce the wear on the lining and electrodes. When measuring low-conductivity liquids close to the threshold, select a lower flow rate (less than 0.5 to 1m/s) as much as possible. As the flow rate increases, the flow noise will increase, resulting in output sloshing. The range of EMF is relatively large, usually not less than 20, and the instrument with automatic range switching function can exceed 50 to 100. The diameter of the stereotyped products that can be provided in China ranges from 10mm to 3000mm. However, the actual application is still mostly small and medium-sized, but it is different from most other principle flow meters (such as volume type, turbine type, vortex type or Coriolis mass type, etc. ), large-diameter instruments occupy a larger proportion. 4. The premise of using EMF for liquid conductivity is that the liquid to be tested must be conductive and cannot be lower than the threshold (ie the lower limit). If the conductivity is lower than the threshold, it will cause measurement error until it can not be used. If it exceeds the threshold, it can be measured even if it changes. The indication error does not change much.× 10-6) between S/cm, depending on the model.
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