OnoffRegler

OnOffRegler, commonly referred to as an on-off controller, is a simple control strategy used to regulate a process by switching the actuator completely on or completely off. The goal is to keep a process variable near a desired setpoint without continuous adjustment.

Operation: The controller monitors the process variable (PV) and compares it to a setpoint (SP). A hysteresis band or deadband is defined around the setpoint. When PV falls to or below the lower threshold (SP minus half the band), the controller turns the actuator on. When PV rises to or above the upper threshold (SP plus half the band), it turns the actuator off. This creates oscillations within the band that help maintain PV within specified limits.

Characteristics: Advantages include simplicity, low cost, robustness, and fast response for systems with slow dynamics. Drawbacks include coarse regulation, potential oscillation around the setpoint, and energy inefficiency if the band is too narrow. Proper design requires selecting the band width to balance comfort, energy use, and equipment longevity.

Applications and implementation: OnOffRegler is widely used in household thermostats, space heating and cooling, water heaters, ovens, and industrial processes with large time constants. Implementations can be analog (relay with hysteresis) or digital (microcontroller) with provisions to prevent rapid cycling, such as a minimum-off or minimum-on time.

Relation to other controls: On-off control is the simplest form of feedback control and is often contrasted with proportional, integral, and derivative (PID) control, which provide finer regulation at the cost of added complexity.