A Hot Standby (HSBY) system is based on two identically configured programmable logic controllers linked to each other and to the same remote I/O network. If one controller stops, the other assumes control of the I/O system.
Primary and Standby Controller
The Quantum Hot Standby system is designed for use where downtime cannot be tolerated. The system delivers high availability through redundancy. Two racks 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 stops. 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 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).
