Schneider Electric 840 USE 106 0 manual Synchronizing Time of Day Clocks

Using a Quantum IEC Hot Standby System

Synchronizing Time of Day Clocks

Primary and	In a Hot Standby system, although the Primary and Secondary controllers have their
Secondary	own time-of-day clocks, they are not implicitly synchronized. At switchover, the time
controller time-	of day changes by the difference between the two clocks. This could cause
of-day clocks	problems if you are controlling a time-critical application.
	Assign the time-of-day clock eight 4x registers in the Specials dialog of the
	configurator. Be sure that none of these 4x registers resides in the nontransfer area,
	all of them need to be transferred to the Standby controller after each scan. Then
	use somewhere in the IEC logic the ‘SET_TOD’ EFB, which resides in the system
	library under the HSBY group.

Elementary	While the full IEC Hot Standby system is running, meaning the Standby controller is
Function Block	also online, your application logic should trigger (rising edge of the S_PULSE input)
(EFB) to set the	the EFB. This would then not only set the time-of-day clock in the Primary, but the
PLC’s time-of-	one in the Standby as well, at the same time. The trigger on the clocks might again
day clock	run at slightly different speeds, this time-set process should be repeated
	periodically, for example within a period of 1 minute.

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