Siemens SIMATIC S7-400H System Manual page 196

Using I/Os in S7–400H
13.4 Connecting redundant I/O to the PROFIBUS DP interface
You will find connection examples in Appendix Connection examples for redundant I/Os
(Page 461).
Note
Remember that the proximity switches (Beros) must provide the current for the channels of
both digital input modules. The technical data of the respective modules, however, specify
only the required current per input.
Using redundant digital input modules with redundant encoders
With redundant encoders you use digital input modules in a 1-out-of-2 configuration:
Figure 13-8
The use of redundant encoders also increases their availability. A discrepancy analysis
detects all errors, except for the failure of a non-redundant load voltage supply. You can
enhance availability by installing redundant load power supplies.
You will find connection examples in Appendix Connection examples for redundant I/Os
(Page 461).
196
Fault-tolerant digital input modules in 1-out-of-2 configuration with two encoders
System Manual, 03/2012, A5E00267695-11
S7-400H