Connection Components In Profibus - Siemens SINUMERIK 840D sl Equipment Manual

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.
Note
Increased cabling space using PROFIBUS adapter connectors
The adapter connector is required if the bus cable is to be looped through at the left-hand
PROFIBUS interface (X126) of the NCU (2 PROFIBUS cables are connected at the connector) and
at the same time the Ethernet interface X120 is connected to a FastConnect connector. When
using the adapter plug, the PROFIBUS connector is higher, which creates extra wiring space.
7.9.3

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.
Terminating resistor
A cable must be terminated with its own surge impedance to prevent line disturbances caused
by reflections. Activate the terminating resistor at the first and last node on a subnet or segment.
The NCU must be either the first 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.
NCU 7x0.3B PN
Equipment Manual, 10/2020, 6FC5397-1EP40-6BA1
Connecting
7.9 PROFIBUS DP
69