Profibus Cable Lengths - Siemens SINUMERIK 840D sl Manual

Cable features
Table 9-3
Features
Wave impedance
Loop resistance
Effective capacitance
Damping
Permissible conductor cross section
Permissible cable diameter
Connector features
The bus connector is used to connect the PROFIBUS cable to the PROFIBUS DP interfaces
(X126, X136), thus establishing a connection to additional nodes.
Use of bus connectors with a 35° cable outlet is recommended so that the front cover of the
control unit can be closed.
9.7.3

PROFIBUS cable lengths

Cable lengths and baud rate
The baud rate determines the cable length of a subnet segment.
Table 9-4
Baud rate
19.6 to 187.5 Kbits/s
500 Kbits/s
1.5 Mbits/s
3 to 12 Mbits/s
With isolated interface
1)
Greater cable lengths
If the cables lengths you require exceed the permitted length for a segment, you must use
RS485 repeaters. The maximum possible cable length between two RS 485 repeaters
corresponds to the cable length of a segment. With these maximum cable lengths, however,
note that additional stations between the two RS 485 repeaters are not permitted. You can
connect up to nine RS 485 repeaters in series.
Note that an RS 485 repeater must be counted as a subnet station when determining the
total number of stations to be connected. This is true even if the RS 485 repeater is not
assigned its own PROFIBUS address.
NCU
Manual, 07/2007, 6FC5397-0AP10-2BA0
Properties of PROFIBUS cables
Permitted cable lengths of a subnet segment for specific baud rates
Values
Approx. 135 to 160 Ω (f = 3 to 20 MHz)
≤115 Ω/km
30 nF/km
0.9 dB/100 m (f = 200 kHz)
0.3 mm to 0.5 mm
2 2
8 mm + 0.5 mm
Max. segment cable length (in m)
1000
1)
400
200
100
Connections
9.7 PROFIBUS / MPI
83