Vega POINTRAC 31 Operating Instructions Manual page 17

Cable screening and
grounding
Connection technology
Connection procedure
POINTRAC 31 • 8/16 mA/HART - four-wire
If 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).
If 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 interfer-
ence signals remains.
Warning:
Within galvanic plants as well as vessels with cathodic corrosion
protection there are considerable potential differences. Considerable
equalisation currents can be caused via the cable screen when the
screen is earthed on both ends.
To avoid this, the cable screen must only be 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:
The metal parts of the instrument are conductive connected with the
inner and outer ground terminal on the housing. This connection exists
either directly metallic or with instruments with external electronics via
the screen of the special connection cable.
You can find specifications to the potential connections within the
instrument in chapter "Technical data".
The connection of the voltage supply and the signal output is carried
out via the spring-loaded terminals in the housing.
The connection to the indicating and adjustment module or to the
interface adapter is carried out via contact pins in the housing.
Proceed as follows:
The procedure applies to instruments without explosion protection.
1
Unscrew the big housing cover
2
Loosen compression nut of the cable entry
3 Remove approx. 10 cm (4 in) of the cable mantle, strip approx.
1 cm (0.4 in) of insulation from the ends of the individual wires
5 Connecting to power supply
17