| control structure with several control levels placed one over the other, in which the control equipment assigned to a higher level coordinates the work of the control equipment assigned to the next lower level, providing for instance pre-determining control tasks, command variables, reference variables or final controlled variables SEE: Figures 24 and 25. Note 1 to entry: Depending upon application, different control level models are used (see Figure 28). Nowadays standardization is not possible. The control level models shown in Figure 28 should serve as examples for possible hierarchical structures. Note 2 to entry: This entry was numbered 351-31-11 in IEC 60050-351:2006. 
Figure 24 – Examples of different control structures 
Figure 25 – Hierarchical control structure of the control equipment of a power station X Figure 28a – Example of a control level model in power station technology X Figure 28b – Example of a control level model in a chemical company Figure 28 – Examples of control level models
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