VEGA VEGAMET 391 4 … 20 mA_HART - Manual (Page 13)

13
5 Connecting to power supply
VEGAMET 391 • 4 … 20 mA/HART
36032-EN-130701
5 Connecting to power supply
5.1 Preparing the connection
Always keep in mind the following safety instructions:
•
Connect only in the complete absence of line voltage
•
If overvoltage surges are expected, overvoltage arresters should
be installed
In hazardous areas you must take note of the respective regulations,
conformity and type approval certificates of the sensors and power
supply units.
The voltage supply can be 20 … 253 V AC/DC, 50/60 Hz.
The operating voltage of VEGAMET 391 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.
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 sensor housing
must be connected to the potential equalisation (low impedance).
If potential equalisation currents are expected, the screen connection
on the side of VEGAMET 391 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.
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.
5.2 Connection procedure
Move on to electrical connection and proceed as follows:
1. Mount the instrument as described in the previous chapter
2. Remove terminal strip 1 on the upper side of the instrument
3. Connect sensor cable to terminal 1/2 (active input) or 5/6 (passive
input)
4. If necessary, connect digital inputs to 8 … 12
5. Plug terminal strip 1 to the upper side of the instrument
6. Remove terminal strip 2 on the lower side of the instrument
7. Connect power supply (switched off) to terminal 13/14
8. If necessary, connect relays or other outputs
9. Plug in terminal strip 2 on the lower side of the instrument
Note safety instructions
Take note of safety
instructions for Ex
applications
Select power supply
Select connection cable
Cable screening and
grounding
Select connection
cable for Ex applica-
tions