Printed in the Federal Republic of Germany
TR-Electronic GmbH 2005, All Rights Reserved
11/06/2018
TR - ECE - BA - DGB - 0045 - 06
Page 79 of 132
4.2 PROFIBUS – interface
4.2.1 RS485 Data transmission technology
All devices are connected in a bus structure (line). Up to 32 subscribers (master or
slaves) can be connected together in a segment.
The bus is terminated with an active bus termination at the beginning and end of each
segment. For stable operation, it must be ensured that both bus terminations are
always supplied with voltage. The bus termination can be switched in the measuring
system connector hood.
Repeaters (signal amplifiers) have to be used with more than 32 subscribers or to
expand the network scope in order to connect the various bus segments.
All cables used must conform with the PROFIBUS specification for the following
copper data wire parameters:
Parameter
Cable type A
Wave impedance in
Ω
135...165 at a frequency of 3...20 MHz
Operating capacitance (pF/m)
30
Loop resistance (
Ω
/km)
≤
110
Wire diameter (mm)
> 0.64
Wire cross-section (mm²)
> 0.34
The PROFIBUS transmission speed may be set between 9.6 kbit/s and 12 Mbit/s and
is automatically recognized by the measuring system. It is selected for all devices on
the bus at the time of commissioning the system.
The range is dependent on the transmission speed for cable type A:
Baud rate (kbits/s)
9.6
19.2
93.75
187.5
500
1500
12000
Range / Segment
1200 m
1200 m
1200 m
1000 m
400 m
200 m
100 m
A shielded data cable must be used to achieve high electromagnetic interference
stability. The shielding should be connected with low resistance to protective ground
using large shield clips at both ends. It is also important that the data line is routed
separate from power current carrying cables if at all possible. At data speed
≥
1.5 Mbit/s, drop lines should be avoided under all circumstances.
The measuring system connector hood offers the possibility of connecting the inward
and outward data cables directly to the removable connector hood. This avoids drop
lines and the bus connector can be connected to and disconnected from the bus at
any time without interruption of data traffic.
The PROFIBUS guidelines and other applicable standards and guidelines are to be
observed to insure safe and stable operation!
In particular, the applicable EMC directive and the shielding and grounding guidelines
must be observed!
