Devices and functions involved in controlling with the task of performing the spatial coordination and synchronisation of the individual sub-functions in a process. The sequence of all sub-functions is to be stored, the workflows are to be ensured in the correct order and at the correct time and a check is to be performed that the function has been performed. This process takes place in an open action flow, without considering the influence of disturbance variables on the actual state (Figure S 89).
In contrast to feedback control, control can be used as a collective term in regard to the functional workflow of a complex process. Logically, a workflow is also called a "control" if individual elements of the open loop control system are operated under control. This is often the case, for example, with numeric controls.
Distinguishing features of controls include the representation of information (analogue, digital), the method of signal processing (workflow control, logic control) or control structure (programmed control, functional control) (Figure S 90).
The control chain remains intact if the time sequence runs the process step by step as a function of the achieved states of the controlled arrangement (process-dependent workflow control).
In practical applications, the term control can have multiple meanings: It is not only used for the process of controlling, but also for all of the devices necessary for controlling.
The term control still comprises the processes and devices in signalling (signal flow) and in terms of power (power flow). As both have very different structures according to their function and devices, this distinction must be observed in all cases (Figure S 91).
Figure S 89: Block diagram of a velocity controller
Figure S 90: Characteristics to differentiate between controls
Figure S 91: Signal flow and power flow in a process cycle