Onoffstyrning

On/offstyrning, or on/off control, is a basic control strategy in which the actuator operates in only two states: on and off. The method compares a measured process variable to a setpoint and switches the actuator when the variable crosses a threshold. It is often described as bang-bang or hysteresis control, because the output toggles between extremes and a hysteresis band is used to prevent rapid switching.

The core idea is simplicity: a controller delivers a binary signal to the process. A deadband or hysteresis region (two thresholds) is typically defined to avoid chattering. When the process variable falls to the lower threshold, the output turns on; when it rises to the upper threshold, the output turns off. This creates a predictable oscillation around the desired value.

Common implementations include mechanical devices such as bi-metal thermostats and electronic comparators. The approach is widely used where precise regulation is unnecessary or impractical, and where robustness, low cost, and fast response are valued. Typical applications include household thermostats for heating and cooling, lighting controls, refrigeration and ovens, basic motor starters, and irrigation systems.

Advantages of on/offstyrning are its simplicity, low cost, reliability, and insensitivity to measurement noise. Disadvantages include large oscillations around the setpoint, potential energy waste due to frequent switching, faster wear on actuators, and poor regulation accuracy. It is most suitable for slow-changing processes or where a binary action is sufficient, and often serves as a fallback or initial control method before implementing more advanced strategies.