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2 connection steps – instrument housing – VEGA VEGAFLEX 66 (-110…+400°C) 4 … 20 mA_HART User Manual

Page 19

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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

-

EN

-080716