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Connecting
8.9 PROFIBUS DP
Use RS 485 repeaters to connect segments or extend cable lengths.
Segments
A segment is a bus line between two terminating resistors. A segment may contain up to 32
nodes. In addition, a segment is limited by the permissible cable length, which varies according
to the transmission rate.
Terminating resistor
A cable must be terminated with its own surge impedance to prevent line disturbances caused
by reflections. Activate the terminating resistor at the first and last node on a subnet or segment.
The NCU must be either the first or the last node on the subnet.
Make sure that the stations to which the terminating resistor is connected are always supplied
with voltage during power-up and operation.
8.9.4
Rules for the laying of PROFIBUS cables
Laying of bus cables
During laying of the PROFIBUS cable, you must avoid:
• twisting
• stretching and
• squeezing
Supplementary conditions
During laying of the indoor bus cable, you must also consider the following supplementary
conditions (d
Table 8-17
Characteristics
Bending radius for a single bend
Bending radius (multiple times)
Permissible temperature range for cable routing
Temperature range for storage and stationary operation
78
= outer diameter of the cable):
O
Supplementary conditions for the laying of PROFIBUS cables
Supplementary conditions
80 mm (10xd
)
O
160 mm (20xd
)
O
-5° C to +50° C
-30° C to +65° C
Equipment Manual, 01/2022, A5E45627807B AE
NCU 1750
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