Switchover Detection

The redundant controllers continuously monitor themselves

and each other for conditions that require a switchover. Each

controller runs continuous self-test routines to determine their

ability to function. A hard failure of the active controller will trigger

an immediate switchover to the standby controller. The standby

controller also monitors the I/O bus traffic to detect if the active

controller stops functioning and failed to issue a switchover

command. This switchover requires a verification cycle, during

which time all output signals hold their values until the new active

controller begins executing control strategies.

Replacing an existing standby controller is as simple as removing

the existing unit and installing a new controller. The active

controller will detect the standby and the system will automatically

commission and download the new hardware. A redundancy

license is required in addition to the redundant hardware. The

redundant controller appears in the Explorer window as a single

node, indicated by a redundant controller icon.