2
Electromagnetic Flowmeter COPA-XT
2.
Principles of Operation
The ABB Automation Products electromagnetic flowmeters are
the ideal instruments for metering the flowrate of liquids, slur-
ries and sludges with a specific minimum electrical conductivity.
These flowmeters measure accurately, produce no additional
pressure drop, contain no moving or protruding parts, are wear
and corrosion resistant. They can be installed in any existing in-
stallation without difficulty.
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.
2.1
Measurement Principle
Faraday’s Laws of Induction form the basis for the
electromagnetic 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 ·v
The voltage induced in the fluid is measured by two electrodes
located diametrically opposite to each other. This flow 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 flow signal voltage U
E
and the average flow velocity v. From
the equation for calculating the volume flow rate *) it follows that
U
E
~ qv, that is, the flow signal voltage U
E
is linear and
proportional to the volumetric flow rate.
2.2
Design
An electromagnetic flowmeter system always consists of a
flowmeter primary and a converter. In the Compact Design the
flowmeter primary and the converter constitute a single entity.
This feature coupled with the 2-Wire technology in which the
supply power and the outputs are carried on the same cable
results in appreciably lower installation expenses than for the
conventional instruments.
Magnet Coil
Metering Tube in
Electrode Plane
Electrode
Flow Signal
U
E
= Flow signal voltage
B
= Magnetic induction
D
= Electrode spacing
v
= Average flow velocity
q
v
= Volume flowrate
*)
U
E
~
q
v
=
U
E
~ q
v
B D v
⋅ ⋅
D
2
π
---------- v
⋅
Electromagnetic Flowmeter Schematic