Download Profibus Actuator Control Profibus DP Option Card Installation Manual

Single and Dual Data Highway Configurations
4
SINGLE AND DUAL DATA HIGHWAY CONFIGURATIONS
4.1 Profibus Data Highway
The rules governing the installation and connection of a Profibus DP highway should be observed at
all times to produce a successful installation. The highway does not allow power to be transferred and
the Profibus module is powered from the actuator itself. The module can only report data when the
actuator is powered up.
PLC
+5V
+5V
T
T Terminator
0V
Profibus DP highway
0V
Screened cable
Fig 7: Typical Profibus DP Data Highway
The data highway must be terminated with a proper active termination network at each end of a
segment. To ensure successful operation the highway itself should not use tapped spur or stub
connections. The connection should be made in and out of each actuator in a daisy chain
arrangement on separate terminals to eliminate any internal stubs cabling inside the actuator. The
length of the highway and number of devices connected will vary from project to project. The standard
permits up to 32 devices to be connected on a section, though one of these will be the PLC. If more
devices are needed (up to the maximum addressable of 126) then repeaters may be added as
required. Up to 9 repeaters can be used on a single highway provided no more than 4 are between
any two devices.
Data Rate (Baud)
9600
19200
45.45k
93.75k
187.5k
500k
1.5M
Maximum Segment Length
1.2 km
1.2 km
1.2 km
1.2 km
1000m
400m
200m
Maximum Highway Length
10 km
10 km
10 km
10 km
10 km
4 km
2 km
Max number of
311
311
311
311
311
311
311
actuators/segment
Note: 1 – The PLC or Repeater module will be one device. Max 32 devices/segment
Since the data passes over a single 2 wire cable there are periods between messages when no
devices are actively driving the lines. In order to ensure that data continues to flow correctly after
these periods it is advisable to ensure the lines are biased to suitable voltage levels during the time
the line is idle. The PFU contains active termination circuits that ensure suitable levels are maintained
on the line even with no device transmitting. To select these termination components the appropriate
internal links must be fitted. A simple termination resistor is also included and can be connected by
linking the appropriate terminals (refer to the actuator wiring diagram).
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Publication S420E V3.0 Issue 01/05