Siemens SIMATIC S7 System Manual page 96

Achievable Safety Classes with F-I/O
5.2 Safety Functions for Achieving Safety Classes for F-I/O with Inputs
1oo1 Evaluation with High Availability (for S7 FH Systems only)
To achieve high availability, one sensor can be connected to two redundant F-DI or two
sensors can be connected redundantly to two F-DI in S7 FH Systems.
Example: One Sensor Connected via One Channel to Two F-DIs (High Availability; SIL2/Category 3)
The following figure presents the wiring diagram for 1oo1 sensor evaluation of a sensor
connected to two SM 326, DI 24 ☓ 24 VDC modules. The sensor is supplied externally. This
wiring enables SIL2/Category 3 and high availability to be achieved. SIL2/Category 3 can
only be achieved if a suitably-qualified sensor is used.
Figure 5-2
5-4
Example: Wiring Diagram for One Sensor Connected via One Channel to Two F-DIs
(1oo1, High Availability)
Safety Engineering in SIMATIC S7
System Manual, 04/2006, A5E00109529-05