For plant areas up to hazardous Zone 2, a redundant DP/PA coupler together with a PROFIBUS PA ring topology permits cheaper safety-related and fault-tolerant applications than the previous standard architectures.

The PROFIBUS PA ring topology is connected to two redundant PROFIBUS DP segments of an S7-400FH controller via the redundant DP/PA coupler. Each of the maximum 8 Active Field Distributors (AFD) in this PROFIBUS PA ring with automatic bus termination has 4 short-circuit-proof spur lines for connection to devices.

As shown in the figure below, safety-related and fault-tolerant applications can be implemented with relatively low device and cable requirements. The configuration of the ring can also be changed during runtime. Even brief opening-up of the ring in order to integrate a further AFD is possible without production failures. The diagnostic integrated in the redundant couplers and the AFDs expand the existing possibilities for communication and cable diagnostics, and makes fault locating easier in the event of an open-circuit.
The concept of Flexible Modular Redundancy is thus implemented down to the field level.

The diagnosis: More reliability with the new SITRANS P DS III

The SITRANS P Series DSIII is a precision digital transmitter for pressure, absolute pressure, differential pressure, flow and level and has extensive diagnostics and simulation functions. The standard unit already delivers excellent, TÜV-approved reliability through its evaluation abilities.

The basic features are:
	Extensive diagnostics and simulation functions
	Accuracy <= 0,075%
	Long-Term Stability <= 0,25% / 60 months
	Wetted parts in stainless steel 1.4571, Hastelloy, Monel, Tantal, Gold
	Measuring range 1mbar to 400bar
	Wide range of certification and approval e.g. ATEX EEx ia, EEx ib, Dust protection, FM, CS