ON-OFF-controller - how it works
On-Off controllers, also known as Two-Point-Controllers or Binary Controllers are used for slow control systems. Here, the actual value changes only slowly. Examples for this: temperature control, level control, compressed air control, etc.
The following animation illustrates the function of a two-point controller at the example of a compressed air control. The air tank represents a PT1-controlled system.
The control behavior of a two-point controller in combination with a PTn- system looks quite different due to the overshoot of the controlled variable. As an example, a zinc bath is used. The heating resistors represent the first energy storage, the zinc the second energy storage. Therefor the zinc bath can be classified as a PT2 system.
The parameter of a ON-OFF controller is the setpoint and the switching hysteresis. The sensor signal is an input signal but not a parameter.
The switching and control behavior of a 2-point controller is further clarified by the static y(x) characteristic curve. By the way, this results in the symbol of this controller.
Since the time axis t is the common axis, both diagrams y(t) and x(t) can be combined to form the static y(x) characteristic diagram.