Working principle of electromagnetic flowmeter

                                     Working principle of electromagnetic flowmeter

Electromagnetic Flowmeters (EMF for short) is a new type of flow measurement instrument developed rapidly with the development of electronic technology from 1950s to 1960s. Electromagnetic flowmeter is an instrument that measures the flow of conductive fluid according to the electromotive force generated when the conductive fluid passes through the external magnetic field by applying the principle of electromagnetic induction.

Electromagnetic flowmeter is a flowmeter for flow measurement according to Faraday's electromagnetic induction law. The advantage of electromagnetic flowmeter is that the pressure loss is very small and the flow range can be measured is large. The ratio of maximum flow to minimum flow is generally more than 20:1. The applicable industrial pipe diameter range is wide, up to 3m. The output signal and measured flow are linear, with high accuracy, and the measured conductivity is ≥ 5 μ S/cm of the fluid flow of acid, alkali, salt solution, water, sewage, corrosive liquid, slurry, pulp, etc. But it cannot measure the flow of gas, steam and purified water.

When the conductor moves to cut the magnetic line of force in the magnetic field, the induced potential will be generated in the conductor. The magnitude of the induced potential is in direct proportion to the effective length of the conductor in the magnetic field and the speed at which the conductor moves perpendicular to the magnetic field in the magnetic field. Similarly, when conducting fluid flows in a vertical direction in a magnetic field and cuts the magnetic induction force line, it will also generate an induced potential on the electrodes on both sides of the pipe. The direction of the induced potential is determined by the right-hand rule, and the magnitude of the induced potential is determined by the following formula:

Ex=BDv －－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－ Formula (1)

Where Ex - induced potential, V;

B - magnetic induction, T

D - pipe inner diameter, m

V - average velocity of liquid, m/s

However, the volume flow qv is equal to the flow velocity v of the fluid and the cross-sectional area of the pipe (π D ²）/ 4. Substitute equation (1) into this equation to get:

Qv=(π D/4B) * Ex －－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－ Formula (2)