VEGA VEGAFLEX 66 (-110…+400°C) 4 … 20 mA_HART - Manual (Page 19)

W e generally recommend the use of screened cable for HART
multidrop mode.
O n the instrument with cable entry ½ NPT and plastic housing
there is a metallic ½" threaded insert moulded into the plastic
housing.
Caution:
N
o grease should be used when screwing the NPT cable
gland or steel tube into the threaded insert. Standard grease
can contain additives that corrode the connection between
threaded insert and housing. This would influence the stability
of the connection and the tightness of the housing.
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). The low frequency potential equalisation
currents are thus suppressed, but the protective effect against
high frequency interference signals remains.
T ake note of the corresponding installation regulations for Ex
applications. In particular, make sure that no potential equal-
isation 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.
5.2 Connection steps - Instrument housing
P roceed as follows:
1 U nscrew the housing cover
2 I f an indicating and adjustment module is installed, remove
it by turning it slightly to the left.
3 L oosen compression nut of the cable entry
4 R emove approx. 10 cm (4 in) of the cable mantle, strip
approx. 1 cm (0.4 in) insulation from the ends of the
individual wires
5 I nsert the cable through the cable gland into the sensor
Cable gland ½ NPT
Cable screening and
grounding
Select connec-
tion cable for Ex
applications
VEGAFLEX 66 • 4 … 20 mA/HART 19
5 C onnecting to power supply
32762
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EN
-080716