Connection Components In Profibus - Siemens NCU 7x0.3 PN Series Manual

Connecting
7.8 PROFIBUS DP
Cable lengths and baud rate
The baud rate determines the cable length of a subnet segment.
Table 7- 22
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.
7.8.3

Connection components in PROFIBUS

Connection components
Individual nodes are connected by means of bus connectors and PROFIBUS cables.
Remember to provide a bus connector with a programming port at either end of the subnet.
This will give you the option of expanding the subnet if required, for example, for a
programming device.
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.
64
Permitted cable length of a subnet segment for specific baud rates
Max. cable length of a segment (in m)
1000
1)
400
200
100
Manual, 09/2011, 6FC5397-1EP40-0BA0
NCU 7x0.3 PN