Technical data

Active components
4.4 Active components for interfacing to PROFIBUS PA
PROFIBUS Network Manual
System Manual, Edition 04/2009, C79000-G8976-C124-03
95
● The PA master and PA slaves form a separate, underlying bus system.
● Increasing the number of DP/PA couplers simply serves to increase availability. All
DP/PA couplers along with the attached PA field devices form one common
PROFIBUS PA bus system.
DP/PA coupler
(max. 5)
S7 backplane bus
IM 153
DP/PA-Link
PA-Master
PA PA
DP
PA PA
DP-Slave
Figure 4-20 How the DP/PA Link works with DP/PA couplers
Rules
The following rules apply when configuring PROFIBUS PA:
● There can be a maximum of 31 PA field devices in a PROFIBUS PA system
● Only one device supplying power (=DP/PA coupler) may be connected in a physical
PROFIBUS PA segment.
● A maximum of 31 PA field devices can be attached to a DP/PA Link. The maximum
number of attachable PA field devices per physical PROFIBUS PA segment or per
DP/PA coupler is limited by the maximum output current of the DP/PA coupler and the I/O
data to be transferred.
Further information
Operating instructions DP/PA Coupler, DP/PA Link and Y Link (Bus couplers
(
http://support.automation.siemens.com/WW/view/en/1142696))