Honeywell Experion PKS User Manual page 220

9 PROFIBUS I/O MODULE (PIOMB) FUNCTION BLOCK
Scenario
C300 Switchover
(with connection between the
C300 and the PGM not re-
established within specified
period of time)
PGM Switchover
Loss of C300 power or Ram
Retention Restart
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Cause of loss/prerequisites
• PIOMB and CM1 are active.
• CEE is in the Run state.
• C300 and PGM are communicating.
• PIOMB and CM1 are active.
• CEE is in the Run state.
• C300 and PGM are communicating.
When a C300 loses power, the DSB must put the devices in the configured safe-state.
When the C300 recovers, if a battery is not present or if the C300 module failed and was
replaced, the configuration (C300, PIOMB, and CM) must be reloaded.
If a battery is present, the connection to the PGM is restored. Depending on the CEE
Restart option of the CM, the CM may need to be activated after recovery.
Effect of communication loss
The DSB sets the devices into their fail-
safe states.
Input type PIOMB
• PIOMB receives communication
failure status.
• Channel data is set to fail-safe values.
• Strategies react to the fail-safe values.
Output type PIOMB
• PIOMB receives communication
failure status.
• Channel blocks request upstream
blocks to go into initialization.
• Device output values will be set to
configured fail-safe values by the DSB.
Input/output type PIOMB
• Output values are held.
• Input values and control loops maintain
their current values.
• Switchover does not cause strategies to
set to fail-safe values.
However, if the PGM does not reestablish
the connection with the C300, the devices
put themselves in a safe-state, if such an
option is supported by the device.