Connecting To Power Supply And Bus System; Preparing The Connection - Vega VEGABAR 81 Operating Instructions Manual

Safety instructions
Voltage supply
Connection cable
Cable screening and
grounding
Cable glands
VEGABAR 81 • Modbus and Levelmaster protocol
5 Connecting to power supply and bus
system
5.1

Preparing the connection

Always keep in mind the following safety instructions:
•
Carry out electrical connection 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 operating voltage and the digital bus signal are routed via sepa-
rate two-wire connection cables.
The data for power supply are specified in chapter "Technical data".
Note:
Power the instrument via an energy-limited circuit (power max. 100 W)
acc. to IEC 61010-1, e.g.
•
Class 2 power supply unit (acc. to UL1310)
•
SELV power supply unit (safety extra-low voltage) with suitable
internal or external limitation of the output current
The instrument is connected with standard two-wire, twisted cable
suitable for RS 485. If electromagnetic interference is expected which
is above the test values of EN 61326 for industrial areas, shielded
cable should be used.
Use cable with round cross section for instruments with housing and
cable gland. Use a cable gland suitable for the cable diameter to
ensure the seal effect of the cable gland (IP protection rating).
Make sure that the entire installation is carried out according to the
Fieldbus specification. In particular, make sure that the bus is termi-
nated with suitable terminating resistors.
Make sure that the cable screen and grounding are carried out ac-
cording to Fieldbus specification. We recommend to connect the
cable screening to ground potential on both ends.
In systems with potential equalisation, connect the cable screening
directly to ground potential at the power supply unit and the sensor.
The cable screening in the sensor must be connected directly to the
internal ground terminal. The ground terminal outside on the housing
must be connected to the potential equalisation (low impedance).
Metric threads
In the case of instrument housings with metric thread, the cable
glands are screwed in at the factory. They are sealed with plastic
plugs as transport protection.

5 Connecting to power supply and bus system

19