ELECTRONET
UM-ELMAG 200-R3
PAGE 04 OF 34
4. OPERATING PRINCIPLE
The flow meter is designed for electrically conductive fluids. Measurement is based on Faraday’s
law of induction, according to which a voltage is induced in an electrically conductive body, which
passes through a magnetic field.
The following expression is applicable to the voltage:
U = K x B x v x D
Where:
U = induced voltage
K = an instrument constant
B = magnetic field strength
v = mean velocity
D = pipe diameter
Thus the induced voltage is proportional to the mean flow velocity, when the field strength is
constant. Inside the electromagnetic flow meter, the fluid passes through a magnetic field applied
perpendicular to the direction of flow. An electric voltage is induced by the movement of the fluid
(which must have a minimum electrical conductivity). This is proportional to the mean flow
velocity and thus to the volume of flow. The induced voltage signal is picked up by two electrodes,
Which are in contact with conductive fluid and transmitted to the signal converter.This method of
measurement offers the following advantages:
1) No pressure loss through pipe.
2) Since the magnetic field passes through the entire flow area, the signal represents a mean
value over the pipe cross-section; therefore, only relatively short straight inlet pipes x DN from
the electrode axis are required upstream of the primary head.
3) Only the tube liner and the electrodes are in contact with the fluid.
4) The signal produced is an electrical voltage, which is an exact linear function of the mean flow
velocity.
Fig.1
