Answer Posted / carl_ellis

A magmeter cleaning unit can be used for applications where
deposits accumulate on the liner material and electrodes.
Non-conductive deposits will reduce the electrode signal,
while conductive deposits will partially shortcircuit the
electrode signal, in both cases deteriorating the accuracy
of the meter (depending on the character and thickness of
the deposits).

The cleaning unit is used for electrochemical cleaning of
the sensor (electrodes) by applying voltage for approx. 60
seconds. Metering is resumed after another 60 seconds when
cleaning is complete.
During cleaning (120 seconds) the transmitter/converter
typically maintains the last flow reading in the display and
in the signal outputs until metering is resumed.

AC cleaning is used to remove fatty deposits from the
electrodes. These fatty deposits are seen in waste water
applications, in abattoirs and water applications with oil
residuals. During the cleaning process, the surface of the
electrodes get warmer, which tends to soften grease
particles and the gas bubbles generated mechanically lift
deposits away from the surface of the electrodes.

DC cleaning is used to eliminate electrically conductive
deposits in the measuring pipe influencing the
measuring accuracy. Particularly in district heating
applications an electrically conductive deposit (magnetite)
may occur and short-circuit the electrode signal. In this
case the accuracy of the meter decreases and the
signal/noise conditions of the meter become inferior. The
problem only arises if the conductivity of the water is less
than approx. 250 μS/cm. During DC cleaning electrolysis
takes place where the flow of electrons removes the particle
deposits from the electrode area.

Setup parameters determine the frequency of a cleaning process.

It is mandatory that liquid fills the pipe during the
cleaning process. The “empty pipe detection” should be used
to detect when the cleaning process should be interlocked.

Carl Ellis
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