Xylem Magflux Electromagnetic Flow Meter - Manual (Page 11)

11
Electromagnetic Flow Meter
FW: 842018/842009
The MagFlux ® Flow Meter
Measurement
Electromagnetic flow meters may have either direct current (DC) or alter-
nating current (AC) excitation.
When systems are AC excited, electrostatic and/or electromagnetic noise
may influence the measurements. A DC excited system however, is less
sensitive to noise produced by electromagnetic induction, simply be-
cause the voltage induced over the electrodes will be a DC voltage. The
drawbacks are measurement errors due to electro-chemical polarization
between the electrodes and the fluid.
The MagFlux
® electromagnetic flow meters are excited by a 2.5 Hz
square wave and thereby eliminate the drawbacks of both DC and AC
systems.
A microprocessor receives and measures the amplitude of the pulse with a
16-bit resolution, and converts and displays the result on the display unit.
Electrode Cleaning
Electrode cleaning is always in service to maintain clean and accurate
electrodes. The operating principle is a 55 Hz AC voltage superimposed
on the normal 2.5 Hz square wave. This step effectively reduces the risk
of a dirt layer build-up on the electrodes that eventually will deteriorate and
finally isolate electrical contact to the flow media.