3.7 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
reference electrode in the sensor or the
metal pipe ensures that the potentials
are equalized. With an existing
reference electrode and for media
carried in earthed metal piping it is
therefore sufficient to connect the
earthing terminal of the Promag 30
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). Sensors Promag A and D are always fitted with a
reference electrode, in Promag F it is depending on the electrode material optional.
There is no reference electrode with Promag H as there is always a metallic
connection to the product. Fig. 25 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. 26).
Please pay attention to national
regulations 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
measuring unit and that the material can
withstand the tightening torque used.
Plastic or lined piping
This arrangement (Fig. 27) 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
Measuring pipe
Reference electrode
ba008y22
Fig. 25
Isolating transformer
Electrically
insulated
Electrically
insulated
ba008y23
6 mm
2
Cu
Supply
Fig. 26
Earthing discs: appr. 3 mm thick
ba008y24
6 mm
2
Cu
Fig. 27
Promag 30 3. Mounting and Installation
Endress+Hauser 25
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