ABB COPA-XE, Instruction Bulletin

Page: 8 / 64

2
Electromagnetic Flowmeter
COPA-XE / MAG-XE
1.2 Principle of Operation
The electromagnetic flowmeters (EMF) from ABB Automation
Products are the ideal flowmeters for metering the flow of all liq-
uids, slurries and sludges which have a specific minimum elec-
trical conductivity. These flowmeters measure accurately,
create no additional pressure drop, contain no moving or pro-
truding parts, are wear free and corrosion resistant. Installa-
tions are possible in all existing piping systems
The ABB AUtomation Products “EMF” has proven itself over
many years and is the preferred flowmeter in the chemical in-
dustry, the pharmaceutical and cosmetic industries, municipal
water and waste water treatment facilities and in the food and
paper industries
1.3 Measurement Principle
Faraday’s Laws of Induction form the basis for the electromag-
netic flowmeter. A voltage is generated in a conductor when it
moves through a magnetic field.
This principle is applied to a conductive fluid which flows
through the metering tube perpendicular to the direction of the
magnetic field (see schematic).
U
E
~ B · D ·F
The voltage induced in the fluid is measured by two electrodes
located diametrically opposite to each other. This signal voltage
U
E
is proportional to the magnetic induction B, the electrode
spacing D and the average flow velocity v. Noting that the
magnetic induction B and the electrode spacing D are constant
values indicates that a proportionality exists between the signal
voltage U
E
and the average flow velocity v. The equation for cal-
culating the volume flow rate *) is: U
E
~ q
v
. The signal voltage
U
E
is linear and proportional to the volumetric flow rate.
1.4 Design
An electromagnetic flowmetering system consists of a
flowmeter primary and a converter. The flowmeter primary is
installed in the pipeline while the converter can be mounted
locally or at a central location. In the Compact Design the
flowmeter primary and converter constitute a single entity.
U
E
= Signal Voltage
B = Magnetic Induction
D = Electrode Spacing
v = Average Flow Velocity
q
v
= Volume Flowrate
Magnet Coil
Meter Tube in
Electrode Plane
Signal Electrode
Signal Voltage
U
E
*) q
v
=
B
∼
D v
⋅ ⋅
D
2
π
4
----------
v
⋅
U
E
q
v
∼
Fig. 1 Schematic of an Electromagnetic Flowmeter