Logix SIS
Logix SIS redundancy is designed for safety applications that require high availability. Logix SIS uses redundant safety controllers to provide continuous operation after a single- channel fault. You can also use redundant safety controllers to execute standard tasks with no safety function. Redundancy operation for standard tasks within a safety controller is the same as
ControlLogix®
redundancy.In Logix SIS, redundant safety controllers execute tasks as follows:
- Both controllers simultaneously execute the safety task to maintain operation
- Only the primary controller executes standard tasks
For more information, see the Logix SIS Safety Reference Manual, publication 1756-RM015.
Logix SIS Redundancy
SIL 2 and SIL 3 Safety Functions
Logix SIS can achieve SIL 2/3 safety ratings. To support a SIL 3 safety function, redundant SIL 2 controllers must operate together. If one controller fails, the system must be repaired within your mean repair time (MRT).
If redundant operation is interrupted, the primary safety controller operates as a SIL 2, single-channel controller, and the secondary safety controller no longer participates in the safety function. Standard tasks continue to operate.
System Qualification and Synchronization
When the redundant system is first started, the redundancy modules run checks on the chassis. They check if both chassis have the correction modules and firmware. Additionally, they confirm that a safety application exists in the primary safety controller in a safety-protected state.
This stage of checks is referred to as qualification. During qualification, the primary safety controller transfers the safety application and safety signature, if one exists, to the secondary safety controller. After the redundancy modules complete qualification, synchronization takes place between the primary and secondary safety controllers.
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