What type of controller provides a proportional output based on the process variable and set-point?

The type of controller that provides a proportional output based on the process variable and set-point is one that utilizes the concept of feedback control. Specifically, a proportional controller adjusts the output in relation to the difference (or error) between the desired set-point and the actual process variable.

When the process variable deviates from the set-point, the controller calculates the error and produces an output that is directly proportional to this error. This means that larger errors result in larger output adjustments, allowing the system to respond dynamically to changes and bring the process variable back to the desired level. This proportional relationship is essential in maintaining a controlled process efficiently.

In contrast, other types of controllers mentioned do not operate on this principle. Controllers that provide on-off control simply switch the output on or off based on whether the process variable is above or below the set-point, lacking the capability for proportional adjustments. Multi-position controllers can have set points but do not necessarily provide continuous proportional output; they often operate in a fixed manner with discrete positions. Lastly, controllers that maintain the process variable at the set-point could encompass various types, including those that employ integral or derivative actions, rather than strictly proportional action.