Often, the entire is labelled as the controller. In a more narrow sense, this is only understood as the computing element (device, program) within the which continuously compares the control variable with the reference variable and forms the correcting variable from the difference (control deviation) (Figure R 21).
In order to achieve a stable feedback control, the properties of the controller must be coordinated with the controlled subsystem,. There are various controller types and controller concepts available for this. These are divided into three main groups:
- Linear controllers have a linear connection between the control deviation and correcting variable.
- Non-linear controllers do not have dynamic performance, i.e. they work without delay and are characterised by a non-linear characteristic curve.
- Sampling controllers sample a constant variable, form the corrective signal and keep it constant until the next sampling time.
Figure R 21: Classification of controller types