What characteristic defines a proportional controller?

A proportional controller is defined by its ability to generate an output that is directly proportional to the difference between the process variable and the set-point. This characteristic means that the greater the deviation (error), the larger the output response from the controller. Therefore, when the process variable moves away from the desired set-point, the controller adjusts its output in proportion to that error, allowing for more fine-tuned control compared to on-off control or multi-position controllers.

This proportional response enables the system to be more stable and minimizes oscillations that can occur with less sophisticated control methods. It is particularly useful in maintaining a steady state without significant overshoot or undershoot, making it an effective choice in many applications where precise control is required.

In contrast, other options describe different types of control methods. For instance, on-off control does not provide a proportional output and merely switches the control element fully on or off based on the set-point. Multi-position control involves controlling devices with specific set positions rather than a continuous output adjustment based on error correction. Thus, understanding the unique characteristic of proportional output is essential in grasping the principles of control systems in refrigeration applications.