4 Wiring Promag 53 PROFIBUS-DP/-PA
60 Endress+Hauser
Plastic pipes or pipes lined with insulating material
Normally the potential equalisation is accomplished via the reference electrodes in the
measuring tube. However, it is still possible that in some cases due to a plant's ground-
ing design that a large equalisation current will flow over the reference electrodes. This
can cause the destruction of the sensor, e.g. through the electrochemical erosion of the
electrodes. In such cases, e.g. with fiberglass or PVC pipes, we recommend that you
use ground disks to improve the potential equalisation (Fig. 38).
Mounting of ground disks
→ Page 26, 32.
Caution:
Risk of damage by electrochemical corrosion. Note the electrochemical series of met-
als, if the ground disks and measuring electrodes are made of different materials.
Fig. 38: Potential equalisation / ground disks with plastic pipes or lined pipes
Lined pipes (cathodic protection)
In such cases, the sensor should be installed in the pipes in a potential-free manner:
• When installing the measuring device, make sure that there is an electrical connection
between the two piping runs (copper wire, 6 mm
2
).
• Make sure that the installation materials do not establish a conductive connection to
the measuring device and that the installation materials withstand the tightening tor-
ques applied when the threaded fasteners are tightened.
• Also comply with the regulations applicable to potential-free installation.
Fig. 39: Potential equalisation and cathode protection
a = power supply isolating transformator, b = electrically isolated
F06-5xxxxxxx-04-xx-xx-xx-004F06-5xxxxxxx-04-xx-xx-xx-005
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