－ ４３ －
６Ｆ８Ａ０８７０
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
3
/s] is:
Q = × V ................(Eq. 14.2)
Using the Equation 14.1 and 14.2
E = K × B × D × × Q
E = × Q ............(Eq. 14.3)
Therefore, volumetric flow rate is directly proportional to the induced voltage.
Figure 8.1 Principle of Operation
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.
E = induced electrode voltage [V]
K = constant
B = magnetic flux density [T]
D = meter pipe diameter [m]
V = fluid velocity [m/s]
π
× D²
4
4
π
× D²
4 × K × B
π
× D
Square-Wave Excitation
