VEGA VEGAFLEX 67 (-20…+250°C) 4 … 20 mA_HART four-wire - Manual (Page 16)

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.
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
Installation with
Ex applications
16 VEGAFLEX 67 • 4 … 20 mA/HART - four-wire
5 C onnecting to power supply
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-EN
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