Siemens Simatic PCS 7 Function Manual page 44

High availability solutions in PCS 7
4.1 Solutions for the I/O
Availability
The block diagram shows the availability of the configuration illustrated above. When both
systems are operating without fault, the block diagram appears as follows:
The following figure shows how one component may fail without this affecting the operation of
the complete system.
The system remains available even when one component in part of a line of the redundancy
node fails. There is only one I/O module and therefore no corresponding redundancy node. It
is the weakest link in the complete system's chain.
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High Availability Process Control Systems (V9.0)
Function Manual, 05/2017, A5E39221836-AA