Loop-powered display unit
Wiring
23
The best results with regard to EMC are achieved in most cases with one-sided
shielding on the feed side (without capacitance termination at the field device).
Operation in the event of disturbance variables as per NAMUR NE21 is thus
guaranteed.
NOTICE
If the shielding of the cable is grounded at more than one point in systems without
potential matching, power supply frequency equalizing currents can occur that
damage the signal cable or have a serious effect on signal transmission.
‣
In such cases the shielding of the signal cable is to be grounded on one side only, i.e.
it must not be connected to the ground terminal of the housing. The shield that is
not connected should be insulated!
5.6
Connecting to functional grounding
5.6.1
Panel-mounted device
For EMC reasons the functional grounding should always be connected. When the
device is used in explosion hazardous environment (with optional Ex approval) the
connection is obligatory.
1
A0018894
8
Functional grounding terminal on panel-mounted device
5.6.2
Field device
For EMC reasons the functional grounding should always be connected. When the
device is used in explosion hazardous environment (with optional Ex approval) the
connection is obligatory and the field housing must additionally be grounded via a
grounding screw fitted on the outside of the housing.
