Endress+Hauser promag 31, Operating Manual

Page: 20 / 60

2.7 Potential equalisation
The sensor and the medium must have
roughly the same electrical potential to
ensure that measurement is accurate
and no galvanic corrosion takes place
at the electrodes. Normally the refer-
ence electrode in the sensor or the met-
al pipe ensures that the potentials are
equalized. With an existing reference
electrode and for media carried in ear-
thed metal piping it is therefore suffi-
cient to connect the earthing terminal of
the Promag 31 transmitter housing to
the potential equalizing line.
With the remote-mounted version this
connection is made at the earth terminal of the connection housing (transmitter).
Fig. 24 shows the reference electrode in the sensor Promag F.
Potential equalisation for some special cases is described below:
Potential equalisation for lined
pipes with cathodic protection
When the medium cannot be earthed
for operational reasons, the measuring
unit must be installed that it is potential-
free (Fig. 25).
Please pay attention to national regula-
tions regarding potential-free installation
(e.g. VDE 0100).
It is also important to ensure that the
mounting material used does not result
in a conductive bond with the measur-
ing unit and that the material can
withstand the tightening torque used.
Plastic or lined piping
This arrangement (Fig. 26) is needed if
there is no reference electrode present
or the medium has to be earthed on
account of equalizing currents.
Caution!
Make sure the earthing discs are
corrosion-resistant.
Measuring electrodes
Reference electrode
b
a02
8y
2
2
Measuring pipe
Fig. 24
6 mm
2
Cu
Electrically
insulated Electrically
insulated
Isolating transformer
Supply
b
a
028y
23
Fig. 25
Earthing discs: appr. 3 mm thick
b
a
028y
24
6 mm
2
Cu
Fig. 26
2. Mounting and Installation Promag 31
20 Hauser