VEGA VEGAPULS 67 (≥ 2.0.0 - ≤ 3.8) 4 … 20 mA_HART four-wire - Manual (Page 24)

I
f screened cable is necessary, connect the cable screen on both ends
to ground potential. In the sensor, the screen must be connected
directly to the internal ground terminal. The ground terminal on the
outside of the housing must be connected to the potential equalisation
(
low impedance).
I f potential equalisation currents are expected, the connection on the
processing side must be made via a ceramic capacitor (e. g. 1 nF,
1500 V). T
he low frequency potential equalisation currents are thus
suppressed, but the protective effect against high frequency interfer-
ence signals remains.
T ake note of the corresponding installation regulations for Ex
applications. In particular, make sure that no potential equalisation
currents flow over the cable screen. In case of grounding on both sides
this can be achieved by the use of a capacitor or a separate potential
equalisation.
W ith the Exd version, the minus side of the signal output is galvanically
connected to ground via protective diodes. When connecting the
instrument to a grounded PLC, equalising currents can flow in case of
potential differences which can cause malfunctions. Make sure that
there is sufficient potential equalisation from the system side or realise
the connection via switching amplifier.
5 .2 Connection procedure
P roceed as follows:
1 U nscrew the housing cover
2 L oosen compression nut of the cable entry
3 R
emove approx. 10 cm (4 in) of the cable mantle (current output),
strip approx. 1 cm (0.4 in) insulation from the ends of the individual
wires
4 I nsert the cable into the sensor through the cable entry
5 L ift the opening levers of the terminals with a screwdriver
6 I
nsert the wire ends into the open terminals according to the wiring
plan
7 P ress down the opening levers of the terminals, you will hear the
terminal spring closing
8 C heck the hold of the wires in the terminals by lightly pulling on
them
9 C onnect the screen to the internal ground terminal, connect the
outer ground terminal to potential equalisation
10 T ighten the compression nut of the cable entry. The seal ring must
completely encircle the cable
11 C onnect the lead cable for power supply in the same way
according to the wiring plan, in addition connect the ground
conductor to the inner ground terminal.
Cable screening and
grounding
Installation with
Ex applications
24 VEGAPULS 67 • 4 … 20 mA/HART four-wire
5 C onnecting to power supply
32939
-EN
-100514