Connecting
7.8 PROFIBUS / MPI
NCU 7x0.2
Manual, 02/2011, 6FC5397-0AP20-0BA0
67
7.8.2 PROFIBUS cables and connectors
Cable specifications
The PROFIBUS cable is 2-wire, twisted, and shielded with defined technical data.
Table 7- 18 Cable specifications for X126 and X136
Characteristics Version
Connector type 9-pin SUB-D socket
Cable type PROFIBUS cable
Max. cable length 100 m for 12 Mbits
Table 7- 19 Technical data for PROFIBUS cables
Characteristics Values
Wave impedance Approximately 135 to 160 Ω (f = 3 to 20 MHz)
Loop resistance ≤ 115 Ω/km
Effective capacitance 30 nF/km
Damping 0.9 dB/100 m (f = 200 kHz)
Permissible conductor cross section 0.3 mm
2
to 0.5 mm
2
Permissible cable diameter 8 mm + 0.5 mm
Cable lengths and baud rate
The baud rate determines the cable length of a subnet segment.
Table 7- 20 Permitted cable length of a subnet segment for specific baud rates
Baud rate Max. cable length of a segment (in m)
19.6 to 187.5 kbit/s 1000
1)
500 kbit/s 400
1.5 Mbit/s 200
3 to 12 Mbit/s 100
1)
With isolated interface
Longer cable lengths:
If you must realize greater cable lengths than permitted in one segment, you must use
RS 485 repeaters. The maximum possible cable lengths between two RS 485 repeaters
correspond to the cable length of a segment. You can connect up to 9 RS 485 repeaters in
series.
Note that an RS 485 repeater must be counted as a subnet node when determining the total
number of nodes to be connected. This is true even if the RS 485 repeater is not assigned its
own PROFIBUS address.
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