Siemens SIMATIC S7-400H System Manual page 140

Using I/Os in S7-400H
10.5 Connecting redundant I/Os
Using redundant digital input modules with redundant encoders
With redundant encoders you use digital input modules in a 1-out-of-2 configuration:
Figure 10-7
The use of redundant encoders also increases their availability. 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.
When connecting an encoder to several digital input modules, the redundant modules must
operate at the same reference potential.
You will find connection examples in Appendix F.
Redundant digital output modules
Redundant control of an actuator can be achieved by connecting two outputs of two digital
output modules or fail-safe digital output modules in parallel (1-out-of-2 configuration)
Figure 10-8
The digital output modules must be connected to a common load voltage supply.
You will find connection examples in Appendix F.
140
Fault-tolerant digital input modules in 1-out-of-2 configuration with two encoders
Fault-tolerant digital output modules in 1-out-of-2 configuration
System Manual, 09/2007, A5E00267695-03
S7-400H