Closed-Loop, Two-State and Proportional Feedback

Closed-Loop Feedback System

A closed-loop system is a control mechanism that uses feedback to control its state or output.
It continuously monitors the output and adjusts itself in response to changes, thus reducing any errors.
The controller regulates the input based on the actual and desired system outputs. If the real output deviates from the intended output, the controller takes corrective action.
Closed-loop systems can anticipate future behaviour because it uses a predictive controller.
The stability of a closed-loop system can be improved through the use of proper system design and control methods.

A two-state control system is a type of control system that operates in one of two states, usually on or off.
These systems are relatively simple and cost-effective because they only need to respond to whether the process variable is above or below the setpoint.
An example of two-state control is a thermostat in a heating system. When the room temperature drops below a set threshold, the heating turns on (state 1); once the temperature reaches the desired level, it turns off (state 2).
Two-state control is effective for simpler systems where precision is not critical, but it can lead to a constant “hunting” around the setpoint known as cycling.

Proportional control, also known as P-control, is a type of linear feedback control system where the controller’s action is proportional to the error.
Instead of swinging between fully on or off states like two-state control, the proportional control adjusts the magnitude of its response in proportion to the size of the error.
The proportionality constant or gain determines the controller’s response to a given error. A higher gain leads to a larger response.
Proportional control alone is often insufficient for complex systems as it may leave a steady-state error. To eliminate this, it is often used in conjunction with integral and derivative control actions in a PID controller.

Understanding various feedback control methods is crucial for designing, comparing and maintaining control systems.
The right control method depends on the requirements of the system, such as its complexity, precision, cost-effectiveness, and stability. Hence, an engineer should be capable of selecting and implementing the most suitable control method for each application.