User Manual

Control concept
Superposed plant controls
5
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Switched on, a process alarm is generated and the plant operating mode
changes to exception value [EcptVal].
The momentary alarm state is visible from the state flag [StaFlg].
Monitoring is active from the point when the corresponding sequence
successfully completes the switch on process, that is, the process value for
block [PrVal] is not equal to Off and the transient state is completed [TraSta] =
No.
The [PrVal] of the block will be monitored. Hence, only those events which
affect [PrVal] can be detected, that is:
● Local fault shut down using interconnection of fault [Dstb] to enable safety,
manual [EnSfty].
● Local shut down of the block in a higher priority application program.
● Switch-off by manual operation of the output module if the I/O module
returns the manual setting value.
● Block switched off via HMI operation or manual switch in control panel
Command control is only in a position to recognize fault-related deviations and
act accordingly when the interconnection of all relevant faults [Dstb] occur
locally on a monitored output of value block to [EnSfty]. Its default value
[DefVal] becomes the process value [PrVal], if a referenced output or value
block is out of service [OoServ]. The state monitoring of the plant cannot
operate correctly, since [PrVal] no longer reflects the actual state of the
aggregate.
To reduce the frequency with which aggregates are switched on and off, it is
possible to define a minimum switch-off time [TiOffMin] in the aggregates. The
look-ahead mechanism in the CMD_CTL block prevents the switching of the
whole sequence if the minimum off-time in one aggregate with active state-
monitoring has not yet expired. The output [TraSta] shows the transitional state
and [PrVal] remains unchanged, at the last value. The new plant operating
mode will be implemented only when all the aggregates to be enabled in the
switching sequence can actually be enabled.
A minimum off-time should always be set for aggregates incorporating a
rotating mass (e.g., fans).
Operating mode changeover
The following figure shows a changeover from operating mode Stage Y to Night
cooling.
All objects were switched on in Stage Y. During the changeover to Night
Cooling, the system initially checks whether the new plant operating mode is an
AllLifeSafety mode. The Look Ahead check takes place in the second step;
followed by the check and abort of on-going sequences.
In the next step, the switch off series is conducted where the sequence
elements of switch off sequence 1 are switched off in parallel. It transitions to
the second sequence after the delay time expires. Object 5 is commanded to
Off with plant safety, priority 5. For plant safety or life safety (priority 2), the
delay times or timeouts have no effect. The transition to switch-off sequence is
immediately since object 4 is already switched on.
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1 2 3 4 5 6 7 8
Object nr.
State monitoring
Switch-on mode
Switch-on delay
Switch-off mode
Operating states
Stage X
Priority
None None None
None
Delayed
Delayed
Delayed
Delayed
On On On
Not cmd
On On
Spec. cmd
Spec. cmd
Spec. cmd
Spec. cmd
Spec. cmd
Spec. cmd
Spec. cmd
Spec. cmd
Sequence 1
Sequence 2
Sequence 3
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