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Overview of Quantum Hot Standby
16
840 USE 106 00 January 2003
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.
Role of the CHS
110 Hot Standby
Module
Each controller is paired with a 140 CHS 110 00 Hot Standby module. The module
monitors its own controller and communicates with the other Hot Standby 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.
Note: A Quantum Hot Standby system supports only remote I/O. It does not
support local I/O or distributed I/O (DIO).