Correctly understand the advantages and disadvantages of electromagnetic flowmeter

Electromagnetic flowmeter is a new type of flow measurement instrument that has developed rapidly with the development of electronic technology in the 1950s and 1960s. Electromagnetic flowmeter is made according to Faraday's law of electromagnetic induction and is used to measure the volume flow of conductive liquids. Due to its unique advantages, it has been widely used in the flow measurement of various conductive liquids in industrial processes, such as various corrosive media such as acids, alkalis, salts, etc.; various slurry flow measurement, forming a unique application field.

Structurally, the electromagnetic flowmeter consists of two parts: an electromagnetic flow sensor and a converter. The sensor is installed on the industrial process pipeline. Its function is to linearly convert the volume flow value of the 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 far from the sensor. It amplifies the flow signal sent by 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 the electromagnetic flowmeter 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 flow of the fluid. Therefore, when the fluid passes through the flowmeter, it will not cause any additional pressure loss. It is one of the flowmeters with the lowest operating energy consumption.

2) It can measure the flow of dirty media, corrosive media and suspended liquid-solid two-phase flow. This is because there are no obstructive flow parts inside the measuring tube of the instrument. Only the measuring tube lining and electrodes are in contact with the measured fluid. The material can be selected according to the properties of the measured fluid. For example, using polytrifluoroethylene or polytetrafluoroethylene as the lining can measure various corrosive media such as acids, alkalis, and salts; using wear-resistant rubber as the lining is particularly suitable for measuring liquid-solid two-phase flows such as ore slurry and cement slurry with solid particles and large wear, as well as various suspended liquids such as fiber-containing liquids and pulp.

3) The electromagnetic flowmeter is a volume flow measurement instrument. During the measurement process, it is not affected by the temperature, viscosity, density and conductivity (within a certain range) of the measured medium. Therefore, the electromagnetic flowmeter only needs to be calibrated with water before it can be used to measure the flow of other conductive liquids.

4) The output of the electromagnetic flowmeter is only proportional to the average flow velocity of the measured medium, and has nothing to do with the flow state (laminar or turbulent) under symmetrical distribution. Therefore, the range of the electromagnetic flowmeter is extremely wide, and its measurement range can reach 100:1, and some even reach 1000:1 of the operable flow range.

5) The electromagnetic flowmeter has no mechanical inertia and is sensitive to reaction. It can measure instantaneous pulsating flow, and can also measure flow in both positive and negative directions.

6) The caliber range of industrial electromagnetic flowmeters is extremely wide, ranging from a few millimeters to a few meters, and there are actual flow calibration equipment with a caliber of 3m in China, which has laid the foundation for the application and development of electromagnetic flowmeters.

The main shortcomings of electromagnetic flowmeters are as follows.

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

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

3) Ordinary industrial electromagnetic flowmeters cannot be used to measure high-temperature media due to the limitations of the measuring tube lining materials and electrical insulation materials; they cannot be used to measure low-temperature media without special treatment to prevent condensation (frost) on the outside of the measuring tube from damaging the insulation.

4) Electromagnetic flowmeters are susceptible to external electromagnetic interference. (end)