Endress+Hauser Mycom S CPM 153 Operating Instructions Manual page 18

4 Electrical connection
18
Symmetrical (with PML)
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Caution!
With a symmetrical connection, the line
to the potential matching pin (PML) must
be connected to the potential matching
terminal of the instrument. The PML must
always be in contact with the medium,
i.e. immersed in the buffer solution
during calibration.
Benefit of symmetrical connection
Measurement is easier under difficult
ambient conditions (e.g. strongly flowing
or high-impedance media or partially
soiled diaphragm).
Mycom S CPM 153
Unsymmetrical (without PML)
If the instrument input is unsymmetrical,
pH measuring chains connected to
assemblies can be connected without
an additional potential matching pin.
If necessary, connect the available
potential matching pin to terminal PE.
Disadvantage of unsymmetrical
connection
The measuring chain reference system
has a heavier load, meaning that measu-
ring errors in limiting operating conditi-
ons are possible (see symmetrically
high-resistance instrument input).
Monitoring of the reference electrode by
the SC system (s. page 52) is not pos-
sible with unsymmetrical measurement.
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Note!
Do not connect the PML, otherwise there
can be shunt excitations.
Endress+Hauser