Switchover Behavior during Application Mismatch
Original instructions
Modifying the Application Variables
If a switchover occurs during application mismatch, the new Primary CPU executes its own, different application program with the data received from the other controller.
Depending on the modification, different behaviors occur:
Modification
Effect
Only code changed (same variables)
All the variables exchanged between the controllers are equal.
Variables added to the initial Primary CPU
Variables are not used by the new Primary CPU.
Variables deleted from the initial Primary CPU
New Primary CPU executes application program using the latest values for these variables.
Variables added to the initial Standby CPU
New Primary CPU executes application program using initial values for these variables.
Variables deleted from the initial Standby CPU
New Primary CPU does not use these variables
Modifying an SFC Section with Control Expert
Schneider Electric recommends not using the SFC programming language in a Hot Standby application.
NOTE: The SFC programming language is not available for 140 CPU 671 60S Hot Standby applications.
NOTE: Modification of existing SFC actions and transitions have no impact on the SFC execution. A Switchover does not reset the SFC to its initial step.
If SFC is used in a Hot Standby application, system reaction to online modifications depends on the setting of %SW60.3, the logic mismatch bit:
WARNING
UNINTENDED EQUIPMENT OPERATION
Ensure that the controllers contain the same application program during a Switchover.
Failure to follow these instructions can result in death, serious injury, or equipment damage.
If a Switchover occurs in the Run mode and there is an application mismatch between the two controllers, the Standby CPU assumes Primary CPU responsibilities and starts executing a different application program from the previous Primary CPU.
Remove any application mismatch by performing an Application Program Transfer as soon as possible after completing modifications.