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Design and function
2
Design and function
2.1
Measuring principle
Measurements performed by the electromagnetic flowmeter are based on Faraday's law of
induction. A voltage is generated in a conductor when it moves through a magnetic field.
This principle is applied to a conductive fluid in the measuring tube through which a magnetic
field is generated perpendicular to the flow direction (see schematic).
The voltage induced in the fluid is measured by two electrodes located diametrically opposite
each other. This signal voltage U
spacing D and the average flow velocity v.
Considering that the magnetic induction B and the electrode spacing D are constant values, a
proportionality exists between the signal voltage U
equation for calculating the volume flowrate, it follows that the signal voltage is linearly
proportional to the volume flowrate: U
The induced voltage is converted by the transmitter to standardized, analog and digital signals.
Fig. 6: Electromagnetic flowmeter schematic
1 Magnet coil
2 Measuring tube in electrode plane
3 Signal electrode
U
Signal voltage
E
B Magnetic induction
D Electrode spacing
v Average flow velocity
q
Volume flow
v
16
is proportional to the magnetic induction B, the electrode
E
E
~ q
.
E
v
1
2
3
FSM4000
and the average flow velocity v. From the
B
D
v
U
~
E
2
D
v
qv =
4
U
~ q
E
v
G00005
D184B140U02
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