Application planning
6.5 Failure scenarios
S7-1500R/H redundant system
214 System Manual, 01/2024, A5E41814787-AF
4. The redundant system does not switch to the backup CPU, but switches to the STOP system
state. The role of the backup CPU remains unchanged.
The backup CPU cannot distinguish between the following scenarios:
It can no longer access the primary CPU because the latter has failed.
The other redundancy connection has also been interrupted and the primary CPU may
still be running.
That is why the backup CPU does not become the primary CPU. This prevents an
undefined system state.
5. System redundancy has failed. The process is no longer controlled by the redundant system.
Diagnostics
System state and operating states after the failure of the redundancy connection and primary
CPU:
• Redundant system → STOP system state
• Primary CPU → failed
• Backup CPU → STOP operating state
– MAINT LED → yellow light: The H-system is not in the RUN-Redundant system state. No
partner CPU has been found in the H-system.
To get detailed diagnostics information, evaluate the diagnostics buffer.
Solution
Replace the defective redundancy connection and the primary CPU. You can find additional
information on the procedure in the sections Replacing defective redundancy connections
(Page 447) and Replacing defective R/H CPUs (Page 446).
6.5.4.3 Failure of the two PROFINET cables in the PROFINET ring at the primary CPU
Introduction
The following failure scenario describes the effects in case of a defect of both PROFINET lines
in the PROFINET ring at the primary CPU.
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