VEGA VEGABAR 87 Profibus PA - Operating Instructions - Manual (Page 18)

18
5 Connecting to power supply
VEGABAR 87 • Profibus PA
45047-EN-131107
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
The voltage supply is provided by a Profibus DP /PA segment coupler.
The voltage supply range can differ depending on the instrument
version. You can find the data for voltage supply in chapter "Technical
data".
Connection is made with screened cable according to the Profibus
specification. Power supply and digital bus signal are carried over the
same two-wire connection cable.
Use cable with round cross-section. A cable outer diameter of
5 … 9 mm (0.2 … 0.35 in) ensures the seal effect of the cable gland.
If you are using cable with a different diameter or cross-section,
exchange the seal or use a suitable cable gland.
Please make sure that your installation is carried out according to the
Profibus specification. In particular, make sure that the termination of
the bus is done with appropriate terminating resistors.
You can find detailed information of the cable specification, installa-
tion and topology in the "Profibus PA - User and Installation Guide-
line" on www.profibus.com.
With plastic housing, the NPT cable gland or the Conduit steel tube
must be screwed without grease into the threaded insert.
Max. torque for all housings see chapter "Technical data".
Make sure that the cable screening and ground is executed accord-
ing to the Fielbus specification. If electromagnetic interference is
expected which is above the test values of EN 61326-1 for industrial
areas, we recommend to connect the cable screen on both ends to
ground potential.
With systems with potential equalisation, connect the cable screen
directly to ground potential at the power supply unit, in the connection
box and at the sensor. The screen 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).
In systems without potential equalisation with cable screening on
both sides, connect the cable screen directly to ground potential at
the power supply unit and at the sensor. In the connection box or
T-distributor, the screen of the short stub to the sensor must not be
connected to ground potential or to another cable screen. The cable
screens to the power supply unit and to the next distributor must be
connected to each other and also connected to ground potential via a
Safety instructions
Voltage supply
Connection cable
Cable gland ½ NPT
Cable screening and
grounding