Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual - Manual (Page 19)

Rockwell Automation Publication 1756-UM535D-EN-P - November 2012 19
About Enhanced Redundancy Systems Chapter 1
Enhanced Redundancy
System Operations
Once the redundancy modules in the redundant chassis pair are connected and
powered, they determine which chassis is the primary chassis and which is the
secondary chassis.
The redundancy modules in both the primary and secondary chassis monitor
events that occur in each of the redundant chassis. If certain faults occur in the
primary chassis, the redundancy modules execute a switchover to the unfaulted,
secondary chassis.
System Qualification and Synchronization
When the enhanced redundant system is first started, the redundancy modules
run checks on the redundant chassis to determine if the chassis contain the
appropriate modules and firmware to establish a redundant system. This stage of
checks is referred to as qualification.
After the redundancy modules complete qualification, synchronization can take
place. Synchronization is a state in which the redundancy modules execute these
tasks:
• Verify that the connection between redundancy modules is ready to
facilitate a switchover
• Verify that the redundant chassis continue to meet qualification
requirements
• Synchronize the data between the redundant controllers, also called
crossloading
This data is crossloaded:
– Updated tag values
– Force values
– Online edits
– Other project information
Synchronization always takes place immediately following qualification. Also,
depending on your system configuration, synchronization can take place at the
end of each program run within the controller project, or at other intervals that
you specify.