Honeywell Experion PKS User Manual page 219

Scenario
Loss of communication
between C300 and PGM
Loss of communication
between PGM and the device
Loss of PGM power
C300 Switchover
(with connection between the
C300 and the PGM re-
established within the specified
period of time)
Cause of loss/prerequisites
Loss of communication between the C300
and the PGM can occur if both FTE cables
are disconnected. In such a case, a
notification that the PGM went OFFNET
is reported. The PDA sets the appropriate
status of the data passed to the PIOMBs.
Loss of communication between the PGM
and the device can occur under the
following scenarios.
• Cable on the PROFIBUS network
breaks.
• Device fails.
• Device power is disconnected.
When a PGM loses power such that the
secondary cannot take over, the devices
must put themselves in a safe state, if such
an operation is supported by the device.
• PIOMB and CM1 are active.
• CEE is in the Run state.
• C300 and PGM are communicating.
9 PROFIBUS I/O MODULE (PIOMB) FUNCTION BLOCK
Effect of communication loss
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 is set to
configured fail-safe values by the DSB.
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 are set to
configured fail-safe values by the DSB.
A Device OFFNET notification is also
reported.
If the devices do not go into a safe state,
the following changes occur.
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.
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.
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