Cleaning Unit - Siemens MAG 1100 F Operating Instructions Manual

SITRANS F M
3.4

Cleaning unit

Mode of operation
AC-cleaning
DC-cleaning
3. Project guidance
The Siemens Flow Instruments cleaning unit can be used with MAG 5000 or 6000 in 19" insert non-
CT version.
The cleaning unit can be used in applications where the liner material and subsequently the
electrodes may be coated with deposits. If the coating is electrically insulating, the electrode signal
will be reduced. If the coating is electrically conductive, the electrode signal will be partly short-
circuited and in both cases the accuracy of the meter will decrease (dependent on the type and
thickness of the coating).
Note
Not to be used with sensors with Hastelloy or Tantalum electrodes.
The cleaning unit cleans the electrodes electro-chemically by applying a voltage to the electrodes
for approx. 60 sec. While cleaning, the transmitter stores and holds the latest measured flow reading
on the display and also the signal outputs. After an additional pausing period of 60 sec. the flowmeter
resumes normal measurement and the cleaning is now completed.
The relay in the transmitter activates the cleaning cycle. In the relay output menu (under cleaning)
the cleaning interval can be set between 1 hour and 24 hours.
Cleaning should only take place with liquid in the pipe. This can be detected via the empty pipe
detection function. It is therefore recommended to select "empty pipe detection" ON when using the
cleaning unit.
The cleaning sequence can also be controlled manually through the electrical input of the
transmitter. Before this is done, ensure that the measuring pipe is full.
AC-cleaning is used to remove fatty deposits on the electrodes. These fatty deposits are seen in
wastewater applications, in abbatoirs 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.
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