Rockwell-automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual de usuario descargar pdf (Pagina 19)

Publication 1785-UM024B-EN-P - January 2003

Backup Concepts for the ControlNet PLC-5 Backup System 1-5

Switchover

Switchover is what occurs when the secondary programmable

controller assumes control of the process, thus becoming the primary

programmable controller. Several conditions can cause this to happen:

• critical failures in the primary programmable controller (e.g.,

hardware faults)

• internal conditions within the primary programmable controller

(e.g., a major fault), causing it to relinquish control of the

process to the secondary programmable controller

• external conditions recognized by the secondary programmable

controller (e.g., loss of communications with the primary

programmable controller), causing it to assume control of the

process

• a manual switchover (i.e., a forced switchover, where you cause

the secondary programmable controller to become primary, and

vice versa; you may choose to do this when testing your system

for backup performance and integrity, or as part of a system

maintenance program).

The ideal switchover time from the primary programmable controller

to the secondary programmable controller would be instantaneous.

The ControlNet PLC-5 hot backup system typically provides a

switchover time of 30-50 ms. This time is adequate to avoid a bump in

most systems, but you should determine the maximum allowable

switchover time for your applications.

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Rockwell-automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual de usuario Pagina 19