Electromagnetic Flow meters work on the principal
of Faraday's law of electromagnetic induction. It states that,
"If an electric conductor, in this
case the fluid to be measured, is moved through a magnetic
field, an electric voltage is induced in the conductor. This
voltage is directly proportional to the velocity of the conductor,
which is mean /average flow rate of the fluid flowing through the flow meter.
The flow meter consists of: a detector/sensor
and an amplifier.
The detector consists of a stainless steel pipe
with electrical insulating liner, a pair of coils on either
side of the flow tube and a pair of electrodes mounted at
right angles to the coil axis.
The coils are excited by a constant pulsed dc
current, which keeps the magnetic field strength constant.
The distance between the two electrodes is also constant.
So the induced voltage is only a function of (dependent on)
fluid flow velocity.
The induced voltage is detected by a pair of
electrodes and is processed by a high input impedance transmitter,
which gives the standardized output signal.
The induced voltage is unaffected by the physical
properties of the fluid such as viscosity, pressure, density,
temperature, etc. as long as the conductivity of the fluid
remains above the minimum threshold level.
- The principle of the flow meter is virtually
independent of pressure, density, temperature and viscosity
- Even fluids with entrained solids can be
metered (e.g. ore slurry, cellulose pulp)
- Large nominal-diameter range available ¼"
- 120"NB (5-3030mm)
- No obstruction to flow, absolute free pipe
- No moving parts
- Minimum or no maintenance requirement
- No pressure losses
- Very high turndown up to 1000:1
- High degree of measuring dependability and
repeatability, good long-term stability
- Automatic measurement of average velocity
throughout the cross-section of pipeline