Electromagnetic flowmeter (EMF) is a new type of flow measuring instrument developed rapidly with the development of electronic technology in the 1950s and 1960s. Electromagnetic flowmeters are based on Faraday's law of electromagnetic induction and are used to measure the volume flow of conductive liquids. Due to its unique advantages, it has been widely applied to the flow measurement of various conductive liquids in industrial processes, such as various corrosive media such as acids, alkalis, and salts; various slurry flow measurements have formed a unique application field. Range confirmation: The flow rate of the measured medium for general industrial electromagnetic flowmeters is preferably 2 to 4 m/s. In special cases, the minimum flow rate should not be less than 0.2 m/s, and the maximum should not exceed 8 m/s. If the medium contains solid particles, the common flow rate should be less than 3m/s to prevent excessive rubbing of the lining and the electrode; for viscous fluids, the flow rate can be selected to be greater than 2m/s, and the larger flow rate helps to automatically eliminate sticking on the electrode. The role of stagnation will help improve the measurement accuracy.

In structure, electromagnetic flowmeter consists of electromagnetic flow sensor and converter. The sensor is installed in the industrial process pipeline. Its role is to linearly convert the volume flow rate of liquid flowing into the pipeline into an induced potential signal and send this signal to the converter through the transmission line. The converter is installed not too far from the sensor. It amplifies the flow signal from the sensor and converts it into a standard electrical signal output proportional to the flow signal for display, accumulation, and adjustment control.

The main advantages of electromagnetic flowmeters are as follows:

1) The sensor structure of the electromagnetic flowmeter is simple, there are no moving parts in the measuring tube, and there are no throttling parts that hinder the fluid flow. Therefore, when the fluid passes through the flow meter, it will not cause any additional pressure loss, and is one of the lowest energy consumption flow meters in the flow meter.

2) The flow rate of fouling medium, corrosive medium and suspension liquid-solid two-phase flow can be measured. This is due to the unobstructed flow components inside the instrument measuring tube. The only contact with the measured fluid is the measuring tube lining and the electrode. The material can be selected according to the nature of the measured fluid. For example, polytetrafluoroethylene or Teflon liners can be used to measure a variety of corrosive media such as acids, alkalis, and salts; wear-resistant rubber liners are particularly suitable for measuring wear with solid particles. Larger slurry, cement slurry, etc. Liquid-solid two-phase flow, and various suspended liquids with fiber liquids and pulps.

3) The electromagnetic flowmeter is a kind of volume flow measuring instrument. In the measurement process, it is not affected by the measured temperature, viscosity, density of the medium (in a certain range). Therefore, after the electromagnetic flowmeter is calibrated by water, it can be used to measure the flow of other conductive liquids.

4) The output of the electromagnetic flow meter is only proportional to the average flow velocity of the medium being measured, and is independent of the flow state (laminar flow or turbulent flow) under a symmetrical distribution. Therefore, the range of the electromagnetic flowmeter is very wide, with a measuring range of up to 100:1, and some even reach a flowable range of 1000:1.

5) The electromagnetic flowmeter has no mechanical inertia and reacts sensitively. It can measure instantaneous pulsating flow, and can also measure the flow in both positive and negative directions.

6) The scope of the industrial electromagnetic flowmeter is very wide, from a few millimeters up to a few meters. Moreover, the real-time flow calibration equipment with a caliber of up to 3m in China has laid a foundation for the application and development of electromagnetic flowmeters.

The main drawbacks of electromagnetic flowmeters are still as follows:

1) It cannot be used to measure gases, steam, and liquids containing large amounts of gas.

2) It cannot be used to measure liquid media with very low electrical conductivity. For media such as petroleum products or organic solvents, electromagnetic flowmeters are still powerless.

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