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 reections. Activate the terminating resistor at the rst and last node on a subnet or segment.
The NCU must be either the rst 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
O
= outer diameter of the cable):
Table 8-17 Supplementary conditions for the laying of PROFIBUS cables
Characteristics Supplementary conditions
Bending radius for a single bend 80 mm (10xd
O
)
Bending radius (multiple times) 160 mm (20xd
O
)
Permissible temperature range for cable routing -5° C to +50° C
Temperature range for storage and stationary operation -30° C to +65° C
Connecting
8.9PROFIBUS DP
NCU 1750
80 Equipment Manual, 10/2023, A5E45627807B AH
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