User Manual

Control concept
Superposed plant controls
5
CM110664en_07 77 | 353
Stage Function Action
1 Safety function Check AllLifeSafety plant operating modes.
2 Preview Checks if the aggregates in question can be switched.
3 Abort sequence Incomplete sequences are interrupted.
4 Reset sequence Switch off unneeded aggregates.
5 Step-up sequence Switch on the newly needed aggregates.
6 Monitor switch-on states Start monitoring of countdown of delay period.
Step 1: Safety function AllLifeSafety
If all switch commands for a given plant operating mode have the priority Life
safety, it is referred to as the AllLifeSafety plant operating mode.
A pending AllLifeSafety plant operating mode in the [ValPgm] is executed
immediately in all cases and maintained regardless of previously existing and
newly occurring faults in the plant – human life takes precedence over plant
safety.
If the AllLifeSafety mode includes switch-on commands, then the preset delay
times (Delay and Timeout) will be observed. However, in the case of the
Timeout setting, the switching sequence will continue even in the absence of
any feedback signal. Interlocks cannot therefore be guaranteed, with the
exception of local interlocks implemented via Priority 1 (life safety, manual).
Priority 1 (life safety, manual) cannot be overwritten in the AllLifeSafety.
Step 2: Preview Look Ahead
Before changing to a different plant operating mode, in which referenced blocks
are to be enabled, block CMD_CTL checks to ensure that all the aggregates can
actually be enabled. For this purpose, the entries in the priority array [PrioArr]
for the switching sequence blocks are checked in advance. If switch commands
of a higher priority are found to be active (e.g., a minimum switch-off time or
the OFF-command of a repair switch), then CMD_CTL waits to implement the
new plant operating mode until the full switching sequence can be
implemented. Only referenced blocks, for which a switch-on command exists in
the new plant operating mode, are checked, and only if the operating-state
monitoring feature has been enabled.
The following priorities are checked:
● Priority 1 [EnSfty/ValSfty], life safety, manual.
● Priority 7 [EnSwi/ValSwi], manual operation, e.g., manual switch.
● Priority 8 [EnOp/ValOp], manual operation, operating unit.
● Priority 6 [TiMinOff], minimum switch off time.
Priority 6 is checked only for a switch on command to determine whether the
aggregate is still within the minimum switch off time. In this case, it waits until
the switch off time expires and only then switches on.
There is no Look Ahead for Desigo 7.
Priority 4 (plant safety, manual [EnCrit/ValCrit]) is not considered during the
check, since local mutual locking via data flow interconnection, such as
depicted in the figure
Cross-aggregate interlocking of damper/fan , would
change this value during the switch-on process.
The present operating mode remains until it is certain that all impacted
aggregates with active operating state supervision can be switched to the new
set state. A process alarm is triggered in CMD_CTL of a monitored block is not
switched on. The exception value [EcptVal] is active as the new plant operating
mode in this case. The online diagnostics for the Plant Control Editors
determines which element is the cause of the fault.