User Manual

Control concept
Control concept and control blocks
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Control hierarchy
Control hierarchy is the map of the functional assignment and linking of those function blocks included in
the control concept for a plant. The structure of the 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.