User Manual

Control concept
Superposed plant controls
5
CM110664en_07 83 | 351
A process alarm occurs, when:
● One of the monitored aggregates is not switched on.
● One of the referenced aggregates cannot be switched on.
The exception value [EcptVal] becomes the present plant operating mode as a reaction to a process alarm.
In addition, an alarm is sent.
A system alarm occurs for the following configuration efforts:
● A referenced aggregate is not available.
● A referenced aggregate is not a commandable object.
● Impermissible priorities are used (priorities 2, 5, 14, 16 are allowed).
● [ValPgm] or [EcptVal] are outside the permissible range.
● The referenced aggregates have a different number of operating modes.
The command control attempts for a system alarm to enable all referenced blocks for local control. The
four commandable priorities are commanded – in other words enabled to Not commanded: Life safety (2),
plant safety (4), specific command control (14) and system control (16).
The response of the block to an alarm can be defined. The following mechanisms have been incorporated
to prevent hunting in the plant.
● Basic and standard: When the block goes into alarm, the exception value [EcptVal] is switched. When
all the aggregates are ready for switching again, CMD_CTL automatically tries to implement the present
plant operating mode [PrVal]. If all the aggregates are ready for direct switching immediately after
implementation of the exception value [EcptVal], hunting is likely to occur. In this case, CMD_CTL
prevents any further switch-on attempt, and the required plant operating mode [PrVal] must be
changed.
● Extended: When the block goes into alarm, the exception value [EcptVal] is switched. The alarm has to
be reset by the user, and there is therefore no risk of hunting.
The block is not alarmable for Desigo 7.
Out of service
The block can be taken out of commissioning using [OoServ]. The following occurs when switching
[OoServ] to On:
● Immediately abort of switch on and off sequences and monitoring.
● All objects are commanded with a release of the priorities: Life safety (2), plant safety (4), specific
command control (14) and system control (16)
Superposed power control PWR_CTL
The power control function block PWR_CTL is used for control and monitoring of the performance of a
number of energy producers (multiple boiler systems, refrigeration machines, etc.). As is the case for
command control CMD_CTL, the data is exchanged bilaterally between power control and the individual
energy producers (boiler, refrigeration aggregate, among others), via referencing. Since the energy
producers are generally implemented in the form of logical aggregates, and contain local logic, the
PWR_CTR block communicates only with MVAL blocks.
The control strategy is based on the use of tables and is designed for multi-stage energy producers.
Additional energy-producer stages are connected or disconnected in accordance with the actual power
demand. For modulating energy producers, a stepped output is converted into a proportional output within
the aggregate. This makes it possible to handle the full power range (0…100%) in one stage, or to divide
the power range into several stages (e.g., Stage 1: 0…20%; Stage 2: 20…40%; etc.).