Profibus Connection - Beckhoff EL6731 Documentation

Mounting and wiring
Termination resistors
In systems with more than two stations all devices are wired in parallel. The PROFIBUS cable must
be terminated with resistances at both ends, in order to avoid reflections and associated transfer
problems.
Distances
The bus cable is specified in EN 50170. This yields the following lengths for a bus segment.
Baud rate in kbits/sec
Cable length in m
Stubs up to 1500 kbaud <6.6 m; at 12 Mbaud stub segments should not be used.
Bus segments
A bus segment consists of at most 32 devices. 126 devices are permitted in a PROFIBUS network.
Repeaters are required to refresh the signal in order to achieve this number. Each repeater is counted as
one device.
IP-Link is the subsidiary bus system for Fieldbus Boxes, whose topology is a ring structure. There is an IP
master in the coupler modules (IP230x-Bxxx or IP230x-Cxxx) to which up to 120 extension modules (IExxxx)
may be connected. The distance between two modules may not exceed 5 m. When planning and installing
the modules, remember that because of the ring structure the IP-Link master must be connected again to the
last module.
Installation guidelines
When assembling the modules and laying the cables, observe the technical guidelines provided by the
PROFIBUS User Organization (PROFIBUS Nutzerorganisation e.V.) for PROFIBUS DP/FMS (see
www.profibus.de).
Checking the PROFIBUS wiring
A PROFIBUS cable (or a cable segment when using repeaters) can be checked with a few simple resistance
measurements. The cable should meanwhile be removed from all stations:
1. Resistance between A and B at the start of the lead: approx. 110 Ohm
2. Resistance between A and B at the end of the lead: approx. 110 Ohm
3. Resistance between A at the start and A at the end of the lead: approx. 0 Ohm
4. Resistance between B at the start and B at the end of the lead: approx. 0 Ohm
5. Resistance between screen at the start and screen at the end of the lead: approx. 0 Ohm
If these measurements are successful, the cable is okay. If, in spite of this, bus malfunctions still occur, this
is usually a result of EMC interference. Observe the installation notes from the PROFIBUS User
Organization (www.profibus.com).
3.8

PROFIBUS Connection

M12 round connector
The M12 socket is inverse-coded and has five pins. Pin 1 transfers 5 V
termination resistor. These must never be misused for other functions, as this can lead to destruction of the
device.
Pins 2 and 4 transfer the PROFIBUS signals. These must never be swapped over, as this will prevent
communication. Pin 5 transfers the shield, which is capacitively connected to the base of the Fieldbus Box.
24
9,6 19,2 93,75
1200 1200 1200
Version: 2.8
187,5 500 1500
1000 400 200
pin 3 transfers GND for the active
DC,
12000
100
EL6731