3. Controllers and controller types


3.5 Other controller types

While in the past switching controllers had a mechanical or electromechanical construction (for example bimetallic thermostats), electronic digital controllers are dominant these days. Here, it is possible to combine a continuous controller (P, PI, PID) with a switching output.

Switching outputs are particularly advantageous when used for slow control processes. They save costs thanks to the easy actuation of refrigeration systems, solenoid valves and heaters.

The continuous controller output variable y is converted into an appropriate pulse sequence for the control signal (pulse width modulation). To ensure that the permitted switching frequency of the actuator is not exceeded, a minimum period T can be specified.


Conversion of continuous controller output variable – switching control signal

There are also combinations of continuous and switching outputs. In the original application area of three-point controllers, these are used as so-called split-range controllers. For example, in temperature control the heating can be provided by a continuous controller output variable y, while the cooling is controlled by a switching control signal.