User Manual

Control
concept
Control concept and control blocks
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control hierarchy is subject to certain rules. A distinction is drawn between
higher-level plant control and local control of the functional units.
Superposed control
Within the hierarchical structure, higher-level control functions are typically
assigned to the partial plant level. All the variables which are influencing
factors on the overall plant are weighted and combined to give the effecting
plant operating mode. In respect of each of the possible plant operating modes,
a control strategy can be defined for each underlying functional element. This
makes it possible to develop specific plant scenarios, such as fire control,
smoke extraction, frost control, on/off-switch control.
Local control
Within the hierarchical structure, local control of the function elements is
typically assigned to the partial plant level. The main function of local control is
to respond to faults. The functional unit itself determines how the outputs are
to be controlled in the event of a fault. Interlocks between functional units (e.g.,
damper/fan) must be implemented locally. Local control prevents the risk of
damage to plant, in the event that the command control parameters are set
incorrectly.
The control hierarchy in the following figure considers only the example
application for ventilation.