KROHNE BATCHCONTROL 5014 C - Manual (Page 28)

Installation and operating instructions 28 BATCHCONTROL
8 Measuring principle
Flowmeter for electrically conductive
liquids.
Measurement is based on Faraday’s law
of induction, according to which a voltage
is induced in an electrically conductive
body passing through a magnetic field.
The following expression applies:
U = K × B × v × D
K
an instrument constant
B magnetic field strength
v mean velocity
D tube diameter
Thus, the induced voltage is proportional to the
mean flow velocity, when the field strength is
constant. Inside the electromagnetic flowmeter,
the liquid passes through a magnetic field
applied perpendicular to the direction of flow.
An electric voltage is induced by the movement
of the liquid (which must have a minimum
electrical conductivity), which is proportional to
the mean flow velocity and thus to the volume
of flow.
The induced voltage signal is picked up by two
electrodes that are in conductive contact with
the liquid, and transmitted to a signal converter
for a standardized output signal.
B
U
U
D
v
8