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8. Principle of Operation
The operating principle of the electromagnetic flowmeter is based on Faraday's Law of electromagnetic induction and it is designed to measure the volumetric flow rate of fluid. An insulated pipe of diameter D is placed vertically to the direction of a magnetic field with flux density B (see Figure 8.1). When an electrically conductive fluid flows in the pipe, an electrode voltage E is induced between a pair of electrodes placed at right angles to the direction of magnetic field. The electrode voltage E is directly proportional to the average fluid velocity V.
The following expression is applicable to the voltage.
E = K × B × D × V [V] | (Eq. 8.1) |
Volumetric flow rate Q [m3/s] is:
Q = | π × D² | × V ................(Eq. 8.2) | |||||
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Using the Equation 14.1 and 14.2 | |||||||
E = K × B × D × | 4 | × Q | |||||
| π × D² | ||||||
E = |
| 4 × K × B |
| × Q ............(Eq. 8.3) | |||
| π × D |
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E = induced electrode voltage [V] K = constant
B = magnetic flux density [T] D = meter pipe diameter [m] V = fluid velocity [m/s]
Therefore, volumetric flow rate is directly proportional to the induced voltage.
Square-Wave Excitation
Figure 8.1 Principle of Operation
The LF414/LF600F, LF414/LF610F, LF414/LF620F and LF414 uses the