SIEMENS
3/72
Siemens IK PI · 2015
■
Design
(continued)
PROFIBUS
Electrical networks (PROFIBUS PA)
Introduction
3
Ring architecture with coupler and media redundancy
With the redundant DP/PA coupler pair (2 x FDC 157-0) of a
PA router, a ring segment with automatic bus termination can
also be implemented instead of a line segment with AFS.
Apart from the ring segment, only line segments with individual
couplers can be configured on this PA router. The PA router can
be connected to a single or a redundant PROFIBUS DP.
Integration of the PA field devices into the ring segment is
carried out via active field distributors AFD4, AFD8 or AFDiS,
the number of which is limited as with the line architectures
(up to 8 AFD4/AFD8, up to 5 AFDiS or up to 5 AFDiS and
AFD4/AFD8 in any combination). These field distributors have
electrically decoupled, short-circuit-proof spur line connections
for connecting the PA devices.
At the device level, flexible modular redundancy is possible by
grouping individual devices on different field distributors.
Special advantages of the ring architecture:
•
High availability
•
Transparent redundancy management of the intelligent DP/PA
couplers FDC 157-0 for the host system
•
Active bus terminators for automatic bus termination in the
DP/PA couplers FDC 157-0 and the active field distributors
AFD4, AFD8 and AFDiS enable:
- Automatic, smooth isolation of faulty subsegments in the
event of a short-circuit or open-circuit
- Modification of the ring configuration or instrumentation
during operation, including the addition or removal of ring
segments
•
Safety-related and fault-tolerant applications with low device
and cabling requirements
Cable lengths of bus segments and spur lines
The PROFIBUS PA is based on electrical transmission compo-
nents. A shielded two-wire cable is used for digital data trans-
mission and for the power supply of the field devices.
With line, tree and ring topologies, bus segments up to approx.
1.9 km can be configured. If AFD4/AFD8 active field distributors
are used, the length of the spur lines for connecting devices and
the quality of the cable used must also be considered when
calculating the total length of the bus segment. Spur lines on the
AFDiS are not relevant to the total length of the bus segment.
For bus segments with active field distributors, the spur lines can
have the following maximum lengths:
•
Up to 120 m in accordance with IEC 61158-2
•
Up to 60 m in accordance with IEC 60079-27 (FISCO)
With AFD4/AFD8 active field distributors, these maximum values
may be reduced depending on the number of spur lines of the
bus segment (for details, see section "Technical specification").
With the active field distributor AFDiS, this reduction is canceled
by the integrated repeater function.
The
SIMATIC Fieldbus Calculator
provides help in calculating
and designing fieldbus segments:
Intrinsically-safe PA devices in hazardous areas are preferably
integrated into a bus segment by means of active field distribu-
tors AFDiS. For PA devices in Ex zone 1/21, the connection via a
line segment on the PA router with DP/PA coupler Ex [i] is a
possible alternative. In such a configuration the max. possible
length per spur line is reduced to 30 m and per bus segment to
1 km.
Bus segments are terminated either automatically (with architec-
tures with active field distributors AFD4, AFD8, AFDiS) or with
the passive terminating element for PROFIBUS PA (SpliTCon-
nect terminator).
■
Technical specifications
PROFIBUS PA
Data transmission
MBP
Transmission rate
31.25 Kbps
Cable
2-wire shielded
Type of protection
EEx(ia/ib)
Topology
Line, tree, ring
Active field distributors per segment/
coupler
• AFD4/AFD8
8
• AFDiS or combinations of
AFDiS and AFD4/AFD8
5
PA devices per segment/coupler
31
PA devices per PA link
64
Max. current for all PA field devices
of a segment (for PA gateways with
FDC 157-0 coupler)
1 A
Cable length per segment,
dependent on transmission rate
1 900 m: standard
1 900 m: EEx(ib)
1 000 m: EEx(ia)
Bus segments with AFD4/AFD8
Max. spur line length related to the
total number of spur lines
Number of spur lines
(1 device per spur line)
• 1 to 12 spur lines
120 m
• 13 to 14 spur lines
90 m
• 15 to 18 spur lines
60 m
• 19 to 24 spur lines
30 m
• 25 to 31 spur lines
1 m
Bus segments with AFDiS
Max. spur line length independent of
total number of spur lines
Number of spur lines
(1 device per spur line)
• 1 to 31 spur lines
-
Not intrinsically-safe
120 m
-
Intrinsically-safe acc. to FISCO
60 m
© Siemens AG 2014