Toshiba LF434 - Manual (Page 144)

TOSHIBA
6 F 8 A 0 7 . 7 0
14. Principle of Operation
The operating principle of ihe electromagnetic flowmeter is based on I’araday'ii Law of
eleciroitiagnelic induction and it is designed to measure the volumetric How rate of fluid. An
insulated pipe of diameter D is placed verticaily to the direction of a magnetic field with
flux density B (see Figure 14.1)* When an clecirically conductive fluid flows in the pipe, an
electrode voltage F. is induced between a pair of electrodes placed at right angles to the
directionofmagneticfield. The elect rode voltage E is directly proportional to the average
fluid velocity V.
The following expression is applicable to the voltage.
E = Kx B x D x V [VJ.......... (Ec]. U.l)
Volumetric flow rale 0 [m^'s] is:
7T X
0= ------- 7-^ XV..................... (Fq. M2)
F. = induced electrode voltage [V]
K = constaiu
B = magnetic flux density [TJ
D = meter pipe diameter [ m ]
V = fluid velocity [m/s]
Using the Equation 14.1 and 14.2
4
--------- - X Q
TT X
E = K x B x D x
4 x K x B
E = —------ ........................... (Eq.l42)
X
D
Therefore, volumetric flow rate is directly proportional to the Induced voltage.
Figure 14,1 Principle of Operation
The J.F434,TF404 electromagnetic flowmeter uses the square-wave excitation method,
which provides long-term stable operation. With square-wave excitation, the LF434/1.F404
offers reliable measurement without being atfccicd by cJectrostalic or electromagnetic
interference, or electrochemical polarization between the electrodes and the fluid to be
measured.
- 1 -Н 3 -