Schneider Electric 840 USE 106 0 manual Constant Internal, Monitoring, Regular Data, Transfers

Using a Quantum IEC Hot Standby System

While Your System Is Running

Constant Internal	After your Hot Standby system has been started and is running normally, it
Monitoring	continues to function automatically. It constantly tests itself for faults and is always
	ready to transfer control from the Primary to the Standby if it detects a fault.
Regular Data
	While the system is running, the module automatically transfers all state RAM to the
Transfers	Standby unit at the end of each scan. This ensures that the Standby is aware of the
	latest conditions and is ready to take control if needed.
	If one or both of the links between the Hot Standby modules is not functioning, the
	Primary controller functions as though no backup is available.
	If the Primary controller fails, the Standby automatically assumes control of the
	remote I/O network. If the Primary controller recovers from failure, and a power cycle
	is completed, then it assumes Standby responsibilities. If it cannot recover, it
	remains offline.
	If the Standby controller fails, it goes offline. The Primary controller functions as a
	standalone and continues to manage the I/O networks.

146 840 USE 106 00 January 2003