Siemens SIMATIC PCS 7 CPU 410-5H

I/O configuration variants
4.3 Fault-tolerant automation systems (redundancy operation)
CPU 410-5H Process Automation
60 System Manual, 09/2014, A5E31622160-AB
Redundancy nodes
Redundant nodes represent the fail safety of systems with redundant components. A
redundant node can be considered as independent when the failure of a component within
the node does not result in reliability constraints in other nodes or in the overall system.
The availability of the overall system can be illustrated simply in a block diagram. With a 1-
out-of-2 system,
one
component of the redundant node may fail without impairing the
operability of the overall system. The weakest link in the chain of redundant nodes
determines the availability of the overall system
No error/fault
Figure 4-6 Example of redundancy in a network without error