Siemens SIMATIC S7-1500 System Manual page 228

Basics of program execution
9.4 Special instructions for S7-1500R/H redundant systems
continues to ensure the control of the baggage handling system, but no second redundant
CPU is available.
Replace the failed CPU with a replacement CPU. The procedure for replacing the CPU is
described in the section Replacing defective R/H-CPUs (Page 321).
As soon as you set the exchanged CPU to RUN, the R/H-System responds as follows:
• The replaced CPU (Backup CPU) switches to SYNCUP operating state and sends a
corresponding status message to the primary CPU.
• The primary CPU then switches from the RUN operating state to RUN-Syncup.
• The S7‑1500R/H redundant system then does a SYNCUP.
During SYNCUP, the user program of the primary CPU runs through a cycle with an extended
cycle time. In this cycle, there is a delay before the redundant system responds to input signal
changes.
If a piece of baggage passes the scanner during the SYNCUP, the redundant system only
responds to the scanner after the extended cycle described above. In the worst case scenario,
the piece of baggage has already passed the deflector before the system responds. The piece
of baggage is then moved to baggage claim rather than to the connecting flight.
Feature
You need the "RH_CTRL" instruction, which allows you to disable and enable the execution of
the SYNCUP as required.
Solution
You use the "RH_CTRL" instruction to disable the execution of the SYNCUP system state for
the S7‑1500RH redundant system. If the disable is no longer required, you enable the
execution of the SYNCUP again with the "RH_CTRL" instruction.
Disable the execution of the SYNCUP to avoid a long program cycle when the baggage
handling system is operating at or near capacity. To do so, call the "RH_CTRL" instruction with
block parameter MODE = 3 in the user program.
Replace the failed CPU with a replacement CPU.
As soon as you set the exchanged CPU with disabled SYNCUP to RUN, the R/H-System
responds as follows:
• The exchanged CPU (Backup CPU) shows the SYNCUP state.
• The Primary CPU then displays the RUN‑Syncup state.
• The redundant system switches to the SYNCUP system state. The redundant system is not
yet running a SYNCUP.
As soon as the baggage handling system is operating at low capacity, for example at night,
enable the SYNCUP system state. To do so, call the "RH_CTRL" instruction with block
parameter MODE = 4 in the user program.
The redundant system runs a SYNCUP. The redundant system then switches to the RUN-
Redundant system state. Now disable SYNCUP again by calling the "RH_CTRL" instruction in
the user program with the block parameter MODE = 3.
Reference
You can find additional information on the "RH_CTRL" instruction in the STEP 7 online help.
You can find more information on SYNCUP in the section SYNCUP system state (Page 270).
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S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD