Redundancy Nodes - Siemens SIMATIC PCS 7 Function Manual

Basics of Fault Tolerance

2.10 Redundancy nodes

2.10 Redundancy nodes
Functionality
Redundancy nodes provided protection from failure of systems with redundant components.
A redundancy node is independent when the failure of one component within the node does
not affect the reliability in other nodes or in the entire system.
The availability of a complete system is illustrated in block diagrams. In a redundant system,
a component in the redundancy node can fail without affecting the operation of the complete
system. In the chain of redundancy nodes, the weakest link determines the availability of the
entire system.
The block diagrams below present examples to illustrated this point.
Redundancy nodes without fault
The following is a block diagram showing individual redundancy nodes operating without a
fault.
Availability of a redundancy node despite faults
If a component in a redundancy node fails, the overall system continues to operate.
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Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA