way a parameterizing tool can operate all devices which conform to profile no matter what their
type and manufacturer.
The system must be implemented with one or more PROFIBUS PA lines depending on the
automation job and thus the number of field devices. A PROFIBUS PA line consists of the
components illustrated below.
PLS / PC
Responsible for the control
DP/PA coupler / DP/PA link
Signal conversion DP-PA, bus feeding and bus termination are uni‐
fied in the "coupler" device.
T
Terminating resistor. Must be fitted at the far end of the bus for
transmission-technical reasons
Power supply
Power supply unit with safety extra-low voltage (SELV). The power
supply must have adequate reserves for bridging brief power failures.
FD
Field Device. The individual field devices can be connected almost
anywhere in the bus system
Figure 3-5
PROFIBUS PA architecture
Line length and maximum number of devices
The central process control system PLS or, in the case of low requirements, a PC, is responsible
for the control. As a rule the functions signal conversion DP-PA, bus feeding and bus termination
are unified in the "coupler" device. A DP/PA coupler or, in the case of higher requirements, a more
powerful DP/PA link is used depending on the number of PROFIBUS PA field devices to be
operated in the automation system. An additional terminating resistor must be fitted at the far
end of the bus for transmission-technical reasons. The theoretically possible line length (total of
all line sections) is a maximum 1900 m when using the recommended bus cable. However, the
current requirements of the individual users and voltage drop at the cable must be taken into
account in the planning. The individual field devices FD can be connected almost anywhere in
the bus system.
See the "PNO Guide PROFIBUS PA (
http://intranet.siemens.no/docs/ind/Anl_losn/Aut_pls/
Tekn_beskr/Profibuss/syspa_e.pdf
)" for further information.
The DP/PA coupler or DP/PA Link is supplied by a power supply unit with safety extra-low voltage
(SELV). This power supply must have adequate reserves for bridging brief power failures.
Description
3.5 PROFIBUS communication
SITRANS FUS060 with PROFIBUS PA
Operating Instructions, 09/2021, A5E02225054-AD
23