Siemens SIMATIC S7 System Manual page 103

Example: Four Redundant Sensors Connected via Two Channels to Two F-AIs (High Availability;
SIL3/Category 4)
The following figure presents the wiring diagram for two SM 336, AI 6 ☓ 13 bit modules with
4 mA to 20 mA current measurement range and 2-wire transducer output. The sensor is
supplied by the F-I/O. This wiring enables SIL2/Category 4 and high availability to be
achieved.
Figure 5-11
Safety Engineering in SIMATIC S7
System Manual, 04/2006, A5E00109529-05
5.2 Safety Functions for Achieving Safety Classes for F-I/O with Inputs
Example: Wiring Diagram for Four Redundant Sensors Connected via Two Channels to
Two F-AIs (1oo2, High Availability)
Achievable Safety Classes with F-I/O
5-11