VEGA VEGASON 61 4 … 20 mA_HART - four-wire - Manual (Page 18)

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5 Connecting to power supply
VEGASON 61 • 4 … 20 mA/HART - four-wire
28778-EN-130417
suppressed, but the protective effect against high frequency interfer-
ence signals remains.
Warning:
Considerable potential differences exist inside galvanic plants as well
as vessels with cathodic corrosion protection. Very large equalisa-
tion currents can flow through the cable screen when the screen
is grounded on both ends. To avoid this, the cable screen must be
connected to ground potential only on one end (inside the switch-
ing 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 potential equalisation!
Information:
The 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 instru-
ments with external electronics. You can find specifications on the po-
tential connections within the instrument in chapter "Technical data".
Take note of the corresponding installation regulations for Ex applica-
tions. 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.
With the Exd version, the minus side of the signal output is galvani-
cally 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
Proceed as follows:
1. Unscrew the housing cover
2. Loosen compression nut of the cable entry
3. Remove approx. 10 cm (4 in) of the cable mantle (current output),
strip approx. 1 cm (0.4 in) insulation from the ends of the indi-
vidual wires
4. Insert the cable into the sensor through the cable entry
5. Lift the opening levers of the terminals with a screwdriver
6. Insert the wire ends into the open terminals according to the wir-
ing plan
7. Press down the opening levers of the terminals, you will hear the
terminal spring closing
8. Check the hold of the wires in the terminals by lightly pulling on
them
9. Connect the screen to the internal ground terminal, connect the
outer ground terminal to potential equalisation
Installation with Ex
applications