Getting Started
4.4 Examples of the response of the fault-tolerant system to faults
S7-400H
44 System Manual, 03/2012, A5E00267695-11
4.4 Examples of the response of the fault-tolerant system to faults
Example 1: Failure of a CPU or power supply module
Initial situation: The S7-400H is in redundant system mode.
1. Simulate a CPU0 failure by turning off the power supply.
Result: The LEDs REDF, IFM1F and IFM2F light up on CPU1. CPU1 goes into single
mode and continues to process the user program.
2. Turn the power supply back on.
Result:
– CPU0 performs an automatic LINK-UP and UPDATE.
– CPU0 changes to RUN, and now operates as reserve CPU.
– The S7-400H is now in redundant system mode.
Example 2: Failure of a fiber-optic cable
Initial situation: The S7-400H is in redundant system mode. The mode selector switch of
each CPU is set to RUN.
1. Disconnect one of the fiber-optic cables.
Result: The LEDs REDF and IFM1F or IFM2F (depending on which fiber-optic cable was
disconnected) now light up on both CPUs. The reserve CPU changes to ERROR-
SEARCH mode. The other CPU remains master and continues operation in single mode.
2. Reconnect the fiber-optic cable.
Result: The reserve CPU performs starts a LINK-UP and UPDATE. The S7–400H
resumes redundant system mode.
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