Rockwell-automation 5720 DriveLogix System Manuale Utente Scaricare il pdf (Pagina 226)

Publication 20D-UM002C-EN-P - November 2003

12-2 DriveLogix Back-Up on DeviceNet

How the Back-up Works

Figure 11.2 shows an example back-up system. In the back-up system, the

following occurs:

• Both controllers/scanners simultaneously receive all inputs.

• Both controllers execute in parallel but are NOT synchronized.

• Only the primary controllers sends output data to the I/O devices. A

virtual switch in the 1788-DNBO cards is used to switch outputs

between primary and secondary controllers.

• After failure or forced switchover, outputs are automatically switched by

the 1788-DNBO card from the primary controller to secondary. When

the switch occurs, the secondary controller becomes the primary

controller.

The switchover occurs so quickly that the I/O devices do not timeout;

these devices are unaware that redundant controllers/scanners exist and

are unaware of the switchover.

Figure 11.2

PanelView 300

DeviceNet

Primary controller

Secondary controller

All backed up devices must

operate on DeviceNet

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Rockwell-automation 5720 DriveLogix System Manuale Utente Pagina 226