VEGA VEGAFLEX 65 4 … 20 mA_HART two-wire - Manual (Page 15)

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). T
he low frequency potential equalisation currents are thus
suppressed, but the protective effect against high frequency interfer-
ence signals remains.
Warning:
W
ithin galvanic plants as well as vessels with cathodic corrosion
protection there are considerable potential differences. Considerably
equalisation currents can be caused via the cable scrren when the
screen is earthed on both ends. To avoid this, the cable screen must
only connected to ground potential on one side of the switching
cabinet in such applications. The cable screen must not be connected
to the internal ground terminal in the sensor and the outer ground
terminal on the housing not to the potential equalisation!
Information:
T
he metallic parts of the instrument (transmitter, process fitting, etc.)
are conductively connected with the inner and outer ground terminal
on the housing. This connection exists either as a direct metallic
contact or via the shielding of the special connection cable on
instruments with external electronics. You can find specifications on
the potential connections within the instrument in chapter "Technical
data".
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.
5 .2 Connection procedure
P roceed as follows:
1 U nscrew the housing cover
Cable screening and
grounding
VEGAFLEX 65 • 4 … 20 mA/HART - two-wire 15
5 C onnecting to power supply
31845
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EN
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