Description
3.9 PROFIBUS
SITRANS P DS III with PROFIBUS PA
Operating Instructions, 06/2013, A5E00053276-07
37
● Automatic management of installation documentation
● Installation optimization on the fly during operation
In an automation system, there are generally multiple PROFIBUS PA lines connected to fast
PROFIBUS DP via coupler units. This is also connected to the process control system.
Both bus systems use the same protocol layer. This makes PROFIBUS PA a
"communications-compatible" extension of the PROFIBUS DP into the field.
Figure 3-14 Functional principle of the PROFIBUS automation system
The figure shows a section of a typical PROFIBUS automation system. The control system
consists of two masters with distributed tasks.
The class-1 master recognizes the control and regulation tasks. The class-2 master enables
the operating and monitoring functions. Between the class-1 master and the field devices
there is a periodic exchange of measurement and settings data. The status information from
the field devices is transmitted parallel to this data, and evaluated in the class-1 master.
Assignment of parameters for the field devices or the reading of additional device information
is not performed during periodic operation.
Besides periodic operation, one or more class-2 masters can access the field devices
asynchronously. Using this type of communication, additional information can be retrieved
from the devices or settings sent to them.
PROFIBUS PA allows bidirectional communication between a bus master and field devices.
At the same time, the shielded two-strand wiring provides auxiliary power to the two-wire
field devices.
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