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The ADMAG AXF magnetic flowmeter features electrode coating
diagnostics to ensure the accuracy of the meter isn't impeded by
build-up of material on the electrode, a situation that requires
periodic maintenance. With conventional magmeters, the maintenance
schedule is arrived at based on simple experience and observation.
With the new coating diagnostic function of the ADMAG AXF it is
possible to monitor the status of the electrodes in real time.
The coating level can be judged by measuring the resistance between
the electrodes and the earth rings. A small, rectangular current
pulse is fed from the electrode to the earth ring in order to measure
the resistance using Ohm's law. The pulse frequency is synchronized
with even multiples of the flow signals' frequencies. When the
flow signals are operated, the pulse frequency is cancelled out
and thus does not influence the operated computation outputs.
Conversely, when the coating diagnosis signals are operated,
the flow signals are cancelled out with no influence on the diagnosis
results. This kind of signal processing makes electrode coating
diagnosis possible even during flow measurement. The severity
of the coating is judged in four levels based on pre-defined values.
Level 3 corresponds to a warning and a status output signal can
be generated. When the coating level is judged to be level 4,
an alarm output can also be set. Although the coating criterion
levels are preset to reference values at the factory, they can be
changed by users depending on their application.
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