VEGA MINITRAC 31 Foundation Fieldbus - Manual (Page 20)

20
5 Connecting to power supply
MINITRAC 31 • Foundation Fieldbus
41782-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
Power supply and digital bus cable via separate two-wire connection
cables. Power is supplied via the H1 voltage supply.
Connection is carried out with screened cable according to Fieldbus
specification.
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.
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.
Generally provide 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
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
Safety instructions
Voltage supply
Connection cable
Cable entry
Cable gland ½ NPT
Cable screening and
grounding