Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 8)

Chapter
1
1-1
Choosing a Backup Configuration
The information in this chapter can help you:
understand backup concepts
evaluate different backup configurations
choose a switchover method
A backup system consists of two processors configured in such a way that
the backup processor will take control of outputs if the primary processor
faults. Figure 1.1 shows the basic concept of a backup system.
Figure 1.1
Basic Backup System
PRIMARY
PROCESSOR
BACKUP
PROCESSOR
TO/FROM I/O
I/O I/O
BACKUP
COMMUNICATION
10971ĆI
A second processor, which is identical to the first, is connected to the main
processor. During normal operation, the backup processor operates in a
listen-only mode. If the primary processor encounters a major fault, the
backup processor takes control of the outputs. This transfer of control also
can occur due to a loss of power to the primary processor or a broken
cable.
Chapter Objectives
Backup Concepts