A two-position controller compares conditions to a set point and:

A two-position controller operates by comparing the current conditions of a system to a predetermined set point. When the current condition reaches the set point, the controller can either activate or deactivate the process, thus starting or stopping it as necessary. This binary function is characteristic of a two-position controller, which is designed for situations where a simple on/off operation suffices to maintain the desired conditions.

For example, in a heating system, when the temperature drops below the set point, the controller will activate the heating element. Conversely, when the temperature exceeds the set point, it will stop the heating element. This straightforward control mechanism is effective for many applications where precision modulation is not required.

Other options involve more complex operations that are not within the scope of a two-position controller. Modulating the final control element suggests continuous control, which is not a function of a two-position device. Automatically readjusting the set point implies a self-adjusting mechanism, which does not apply to basic two-position control. Lastly, maintaining the final control element position at 50% suggests a constant modulation that is typical of proportional control, rather than the binary action of a two-position controller.