Bidirectional Electromagnetic Flowmeters

The bidirectional electromagnetic flowmeter is a flowmeter for flow measurement according to Faraday's electromagnetic induction law, and it can measure both forward and reverse directions. The advantage of a bidirectional electromagnetic flowmeter is that the pressure loss is very small and the flow range can be measured as 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)

It can be seen from the above formula that when the pipe diameter D is fixed and the magnetic induction intensity B is kept constant, the measured volume flow is in a linear relationship with the induced potential. If an electrode is inserted on both sides of the pipe, the induced potential Ex can be introduced. The volume flow can be obtained by measuring the magnitude of this potential.

According to Faraday's electromagnetic induction principle, a pair of detection electrodes are installed on the pipe wall perpendicular to the axis of the measuring pipe and the magnetic line of force. When the conductive liquid moves along the axis of the measuring pipe, the conductive liquid cuts the magnetic line of force to generate an induction potential, which is detected by two detection electrodes. The value is in direct proportion to the flow rate, and its value is:

E=B·V·D·K

Where: E - induced potential;

K - coefficient related to magnetic field distribution and axial length;

B - magnetic induction intensity;

V - average flow rate of conductive liquid;

D - electrode spacing; (Measure the inner diameter of the pipe)

That's the same. The principle of the response flow of the two-way electromagnetic flowmeter is the same, but when we calculate it through the meter formula, all the values become negative. In most of our field conditions, the application of a bidirectional electromagnetic flowmeter is very extensive. Supmea bidirectional electromagnetic flowmeter is also famous at home and abroad. You can refer to its parameters for selection. For more details, please contact Supmea Professional Engineer.