Influences On The Cycle Time When A Cpu Fails - Siemens Simatic S7-1500 Function Manual

5.3.4

Influences on the cycle time when a CPU fails

If one of the two CPUs fails during redundant operation, the other CPU controls the process
alone. If a CPU fails, the system state switches from RUN-Redundant to RUN-Solo. The
CPU continues executing the user program in RUN operating state.
Note
Dead time in case of a CPU failure
On the failure of a CPU, the cycle time also contains a dead time of up to 300 ms for
R-CPUs and up to 50 ms for the H-CPU. You must schedule this time as cycle time reserve
for a CPU failure.
To avoid excessive cycle times after a CPU failure, further increase the maximum cycle time
by this value.
Note
Change of the system state from RUN-Redundant to Run-Solo by the user
If you deliberately trigger a change of the system state, e.g. by switching the backup CPU to
STOP via the display, this will also extend the cycle time. However, the cycle time will not
increase to the same extent as with switchover of the CPUs in the event of an error (failure
of one of the CPUs).
Information on the causes for the failure of a CPU is available in the S7-1500R/H redundant
system (https://support.industry.siemens.com/cs/ww/en/view/109754833) system manual.
Cycle and response times
Function Manual, 10/2018, A5E03461504-AD
Cycle and response times of the S7-1500R/H redundant system
5.3 Influences on the cycle time of the S7-1500R/H redundant system
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