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5 Connecting to power supply
VEGAMET 861 • 4 … 20 mA/HART
58866-EN-200401
5 Connecting to power supply
5.1 Preparing the connection
Always keep in mind the following safety instructions:
•
The electrical connection must only be carried out by trained,
qualified personnel authorised by the plant operator.
•
If overvoltage surges are expected, overvoltage arresters should
be installed.
Warning:
Only connect or disconnect in de-energized state.
The data for power supply are specified in chapter "
Technical data
".
The instrument belongs to protection class I, hence connection of an
earth conductor is required.
Use cable with round cross section. The cable diameter must be
suitable for the cable gland used to ensure the seal effect of the cable
gland (IP protection).
The voltage supply is connected with standard cable according to the
national installation standards.
Standard two-wire cable can be used for connecting the sensors. The
screening is absolutely necessary to ensure interference-free opera-
tion with HART sensors.
Note:
If the temperatures are too high, the cable insulation can be dam-
aged. Hence keep apart from the ambient temperature also the self-
heating of the instrument for the temperature resistance of the cable
in the connection compartment in mind
1)
.
When connecting HART sensors, the supplied ground terminal must
be attached to the outside of the housing. To do this, carefully remove
the pre-embossed opening (ø 6 mm) on the lower side of the device
with a suitable tool and screw in the ground terminal.
Connect the cable screening on both ends to ground potential. In the
sensor/VEGAMET 861, the shielding must be connected directly to
the internal ground terminal. The ground terminal on the outside of the
sensor housing/VEGAMET 861 must be connected to the potential
equalisation (low impedance).
If potential equalisation currents are expected, the screen connection
on the side of VEGAMET 861 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.
Safety instructions
Voltage supply
Connection cable
Cable screening and
grounding
1)
With an ambient temperature ≥ 50 °C (122 °F) the connection cable should
be suitable for an ambient temperature which is at least 20 °C (36 °F) higher.
