Principle Of Operation - Toshiba LF414 Instruction Manual

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 14.1). 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. 14.1)
Volumetric flow rate Q [m
Q =
Using the Equation 14.1 and 14.2
E = K × B × D ×
E =
Therefore, volumetric flow rate is directly proportional to the induced voltage.
The LF414/LF600F, LF414/LF610F and LF414 uses the square-wave excitation method, which provides
long-term stable operation. With square-wave excitation, the LF414/LF600F, LF414/LF610F and LF414 offers
reliable measurement without being affected by electrostatic or electromagnetic interference, or electrochemical
polarization between the electrodes and the fluid to be measured.
3
/s] is:
π × D²
× V ................(Eq. 14.2)
4
4
× Q
π × D²
4 × K × B
× Q ............(Eq. 14.3)
π × D
Figure 8.1 Principle of Operation
E = induced electrode voltage [V]
K = constant
B = magnetic flux density [T]
D = meter pipe diameter [m]
V = fluid velocity [m/s]
Square-Wave Excitation
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