Siemens SINUMERIK 840D sl Manual page 75

Table 9-11
Characteristics
Wave impedance
Loop resistance
Effective capacitance
Damping
Permissible conductor cross section
Permissible cable diameter
Cable lengths and baud rate
The baud rate determines the cable length of a subnet segment.
Table 9-12
Baud rate
19.6 to 187.5 kbit/s
500 kbit/s
1.5 Mbit/s
3 to 12 Mbit/s
With isolated interface
1)
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.
Connector features
The bus connector is used to connect the PROFIBUS cables to the PROFIBUS DP
interfaces (X126, X136), thus establishing a connection to additional nodes.
Only bus connectors with a 35° cable outlet should be used in order to ensure that the front
cover can be closed.
NCU
Manual, 03/2010, 6FC5397-0AP10-3BA0
Technical data for PROFIBUS cables
Permitted cable length of a subnet segment for specific baud rates
Values
Approximately 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. cable length of a segment (in m)
1000
1)
400
200
100
Connecting
9.8 PROFIBUS / MPI
75