User Manual

Control
concept
Superposed plant controls
5
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The operating state [OpSta] for both aggregates are formed within the compounds as illustrated in the
previous example from the AND link for [PrVal] and [TraSta].
5.3 Superposed plant controls
Two blocks are available in Desigo for superposed plant control:
● CMD_CTL command control for sequence control
● PWR_CTL power control for stepped control
Both blocks are based on the standard BACnet Command Object. They have both tables that define the
operating modes and switching response of the underlying aggregates. The commandable blocks in the
aggregates must have a BACnet [PrioArr] to use the following output and value blocks: AO, BO, MO, AVAL,
BVAL und MVAL.
PWR_CTL may only be communicated using the MVAL blocks based on the specialized task – controlling
steps.
Referencing
Referencing is used exclusively for communications by the superposed control blocks with the output and
value blocks in the aggregates to be commanded. The references are derived from the Technical
Designation (TD) of the block. The reference is defined relative to the control block to the command block.
The aggregate does not have to be in the same hierarchy; cross-plant communications is possible.
Example for a reference: B = \...\...\PreHcl’CmdVal
Where CmdVal is the designation for a BVAL object in the PreHcl aggregate. More than one block can be
referenced for each aggregate.
As the project-specific root is not part of the address, the references do not need to be modified if the root
changes. This simplifies project-specific name changes and the copying of library solutions into a project.
The references, that is, the technical designations with relative addresses are resolved in the controller at
runtime. Any addressing errors will therefore only be apparent during runtime. The cause of the error can
largely be eliminated, however, when parameterizing the controls blocks with the help of the Plant Control
Editors.
The figure shows that the [PrioArr] can communicate directly with the referenced blocks. You can
command switch and positioning values and enable them. A commanded command remains valid until the
priority entry is enabled again. The control blocks automatically enables all commanded priorities, when the
block commands the aggregates to the new plant operating mode. The entries for the [PrioArr] are deleted
in the commanded blocks when restarting the PX controller, with the exception of local, manual
interventions to priority 8.
Determining plant operating mode
A superposed plant control generally has different sources such as plant switch, scheduler program or
important fault messages, from which the resulting plant operating mode must be determined.
The ENSEL_MS (Enable Selector Multistate) and ENSEL_BO (Enable Selector Boolean) blocks are
available for evaluating the resulting plant operating mode in the firmware library of Desigo. As a rule, the
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