VEGA VEGAPULS SR 68 Foundation Fieldbus - Manual (Page 30)

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5 Connecting to power supply
VEGAPULS SR 68 • Foundation Fieldbus
38297-EN-130624
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 instrument requires a operating voltage of 9 … 32 V DC. Operat-
ing voltage and the digital bus signal are carried on the same two-wire
connection cable. Power is supplied via the H1 power 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.
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
ceramic capacitor (e.g. 1 nF, 1500 V). Low-frequency potential equali-
sation currents are thus suppressed, but the protective effect against
high frequency interference signals remains.
Safety instructions
Voltage supply
Connection cable
Cable gland ½ NPT
Cable screening and
grounding