Mounting and wiring
EK3100
19
Version: 1.5
Fig. 10: PROFIBUS cabling
Termination resistors
In systems with more than two stations all devices are wired in parallel. It is essential that the bus
cables are terminated with resistances at the conductor ends in order to avoid reflections and asso-
ciated transmission problems.
Distances
The bus line is specified in EN 50170. This yields the following lengths for a bus segment.
Bit rate in
kbits/sec
9.6
19.2
93.75
187.5
500
1500
12000
Cable
length in m
1200
1200
1200
1000
400
200
100
Stubs up to 1500 kbit/s <6.6 m; at 12 Mbit/s stub segments should not be used.
Bus segments
A bus segment consists of at most 32 devices. 125 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-
Link 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 Nutzerorganization e.V.) for PROFIBUS DP/FMS (see:
Check the PROFIBUS cable
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 line: approx. 110 Ohm
2. Resistance between A and B at the end of the line: approx. 110 Ohm
3. Resistance between A at the start and A at the end of the line: approx. 0 Ohm
4. Resistance between B at the start and B at the end of the line: approx. 0 Ohm
5. Resistance between shield at the start and shield at the end of the line: approx. 0 Ohm
