Schneider Electric 840 USE 106 0 manual Primary and Standby Control, Description, Role of the CHS

Overview of Quantum Hot Standby

Primary and Standby Control

Description	The Quantum Hot Standby system is designed for use where downtime cannot be
	tolerated. The system delivers high availability through redundancy. Two
	backplanes are configured with identical hardware and software.
	One of the PLCs acts as the Primary controller. It runs the application by scanning
	user logic and operating remote I/O.
	The other PLC acts as the Standby controller. The Primary controller updates the
	Standby controller after each scan. The Standby is ready to assume control within
	one scan if the Primary fails.
	Primary and Standby states are switchable. Either controller can be put into the
	Primary state, but to do this, the other must be in the Standby state. The remote I/O
	network is always operated by the Primary controller.
	Note: A Quantum Hot Standby system supports only remote I/O. It does not
	support local I/O or distributed I/O (DIO).
Role of the CHS
	Each controller is paired with a 140 CHS 110 00 Hot Standby module. The module
110 Hot Standby	monitors its own controller and communicates with the other Hot Standby module.
Module	The system monitors itself continuously. If the Primary controller fails, the Hot
	Standby module switches control to the Standby, which then becomes the Primary
	controller.
	If the Standby controller fails, the Primary continues to operate without a backup.

16 840 USE 106 00 January 2003