Allen-Bradley ControlNet PLC-5 User Manual page 54

B-12 Backup States
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Reasons for Qualification Major Fault
While qualification should complete without any problems, there are
several checks performed during qualification that can cause it to fail.
When the qualification procedure fails, a major fault is declared.
Qualification could fail under any of the following circumstances or
conditions:
• Failure of the Qualification Data Table crossload
• Failure of the Qualification State Data Table crossload
• Failure of the Equivalence Check
• The occurrence of an unrelated major fault in the PLC-5 system
during qualification
• Movement of the keyswitch to Program mode during
qualification
• Inability to retrieve the Edit Resource at the beginning of
qualification
• Presence of one or more invalid backup configuration parameters
• A change in the primary status of the partner PLC-5 processor
(i.e., either the partner PLC-5 processor became primary during
qualification, or the partner PLC-5 went from primary to
non-primary during qualification).
• The ControlNet backup state was Invalid backup state.
Refer to Chapter 4 (Troubleshooting) for information on fixing a
Qualification major fault.
Switchover
Switchover occurs when one of the processors of the PLC-5
ControlNet backup system transitions from the Secondary backup
state to the Primary backup state. The new primary processor gains
control of the system outputs on the ControlNet channel; the old
primary processor loses control. There are two categories for
switchovers:
• Qualified Switchovers
• Unqualified Switchovers
Qualified Switchovers
Qualified Switchovers are switchovers that transition the primary
processor to the Secondary backup state and the secondary processor
to the Primary backup state. Thus after a Qualified Switchover, there
is still a qualified backup system. There are 2 Qualified Switchover
cases:
• Designated Primary
When you configure the PLC-5 ControlNet backup system and
enable the Designated Primary feature, the odd ControlNet node
of the odd-even ControlNet pair is always the primary processor
if the odd node has passed qualification. This feature is useful
when you want a particular processor to always be the primary,
whenever that processor is available.
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