Toshiba LF600F - Manual (Page 150)

TOSHIBA
i6,F,8,A0,8,6,9
14. 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 x B x D x V [ V ] ......(Eq. 14.1)
Volumetric flow rate Q [fnVs] is:
7C xD^
E = induced electrode voltage [V]
K = constant
B = magnetic flux density [T]
D = meter pipe diameter [m]
V = fluid velocity [m/s]
Q =
X
V.................(Eq. 14.2)
Using the Equation 14.1 and 14.2
4
xQ E = K x B x D x
7r XD^
4
X
K
X
B
E=--------- 7 —...................... (Eq. 14.3)
7 C X jj
Therefore, volumetric flow rate is directly proportional to the induced voltage.
Square-Wave Excitation
Figure 14.1 Principle of Operation
The LF60*F electromagnetic flowmeter uses the square-wave excitation method, which provides
long-term stable operation. With square-wave excitation, the LF60*F offers reliable
measurement without being affected by electrostatic or electromagnetic interference, or
electrochemical polarization between the electrodes and the fluid to be measured.
-
149
-