Installation of VMM
i
ndu
Q
®
- Series VMM
- 12 -
© SIKA
•
Ba_VMM_us
•
09/2018
4.2
Instructions on potential equalization and cathode protection
4.2.1
Potential equalization
The signal outputs (process outputs and the mains supply of the VMM are galvanic isolated
from each other. The housing and the interference filter of the mains supply are connected to
PE.
The electrodes and measuring electronics are related to the potential of the function ground
FE of the sensor. FE is not connected to PE, but may be connected with each other in the
sensor junction box. If the sensor is grounded by using ground disk
s (grounding rings), these
must in connected with the function ground FE.
At a separate assembly of sensor and display electronics the outer screen of the connecting
cable is connected to the housing of the display electronics and has PE potential. The inner
screens of the electrode line are connected to FE inside the junction box of the sensor and to
the mass (GND) of the display electronics.
Details of all wirings, terminals and drawing can be found in § 5 "Electrical connection".
IMPORTANT!
The display electronics can only process the measuring signal interference-free if this
voltage is referenced to a fixed potential (ground).
Potential equalization on electrically conductive
pipes:
The sensor is electrically connected to the pipe-
line in the sense of a potential equalization.
Thus, the pipeline is grounded, and the media and
therefore the signal voltage have a solid signal
common.
Potential equalization on electrically insulated pipes:
When using pipes lined with electrical insulation,
plastic tubing or concrete conduits, a separate
grounding washer is used to ground the measur-
ing media. The grounding washer is installed be-
tween the pipeline connection and the sensor’s
flange and the ring’s inside contacts the media.
Contrary to the diagram shown below, one
grounding washer on the inflow side is sufficient.
If bidirectional measurements are to be taken,
one grounding washer must be installed on either
side.
Protection washers or protection rings can also be used as grounding component; or special
grounding electrodes, incorporated in the sensor, may be installed.
Grounding electrodes are more economical than grounding washers. However, it must be
ensured that noticeable differences in potential within the equipment are eliminated, other-
wise the grounding electrodes will electrolyze and be destroyed.
