5 connecting to power supply, 1 preparing the connection – VEGA WEIGHTRAC 31 Profibus PA User Manual
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5 Connecting to power supply
WEIGHTRAC 31 • Profibus PA
43837-EN-131119
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 .
Replace all unused cable entries with suitable blind plugs. The thin
foam rubber washers in the cable glands only serve as a dust cover
during transport.
In the case of instrument housings with self-sealing NPT threads, it
is generally not possible to have the cable glands screwed in at the
factory. The openings for the cable glands are therefore covered with
red protective caps as transport protection.
Before setup you have to replace these protective caps with approved
cable glands or close the openings with suitable blind plugs. Unused
cable glands do not provide sufficient protection against moisture and
must be replaced with blind plugs.
The suitable cable glands and blind plugs come with the instrument.
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.
In 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
Safety instructions
Voltage supply
Connection cable
Cable entry
Cable gland ½ NPT
Cable screening and
grounding