Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 15)

1 Publication 1785-UM024B-EN-P - January 2003
Chapter
1
Backup Concepts for the ControlNet PLC-5
Hot Backup System
Chapter Objectives This chapter describes why and how to use the ControlNet PLC-5
backup system and its basic system architecture.
Why Use a Backup System? The objective of any redundant system (i.e., backup system) is to
improve the amount of up-time of a machine or process by ensuring
consistent availability of that machine. This also reduces costs
associated with equipment failure. By using the ControlNet PLC-5 hot
backup system, you can help guard your application against
shutdowns caused by the programmable controller.
The backup option is used where you must transfer the control of the
process to a secondary system without interrupting the
machine/process operation.
To guard against system shutdown, a backup system must provide:
• equipment with exceptional reliability
• automatic fault isolation
• minimal disturbance of the process when switching from the
primary to the secondary system
ATTENTION
!
When using identical programs in both PLC-5
programmable controllers, using a backup system
does not necessarily protect you from faults
caused by programming errors or system timeouts.
Such errors or timeouts can also occur in the
secondary programmable controller. Be certain to
carefully check your programming, and to
thoroughly check redundant operations before
implementing the backup system.