20.3:
Open and closed-loop control systems
Control systems are primarily classified as open-loop and closed-loop or feedback control systems.
The elements of an open-loop system are the controller and the controlled process. An input signal is applied to the controller, which controls the process so that the controlled variable performs according to prescribed standards.
Open-loop systems operate independently of the output. A practical example is a washing machine that operates on a time basis without measuring the clothes' cleanliness.
They are advantageous when the output is difficult to quantify or precise measurement is not economically feasible.
Closed-loop systems include one or more feedback links from the output to the input for more accurate control.
In a closed-loop idle-speed control system, any difference between the desired idling speed and the actual speed is sensed and corrected by adjusting the throttle angle. So, due to the use of feedback, the system quickly recovers after a disturbance to the preset value.
However, they are more complex to build and are generally higher in cost and power due to the use of more components.
20.3:
Open and closed-loop control systems
Control systems are foundational elements in automation and engineering. They are broadly categorized into open-loop and closed-loop systems. These classifications hinge on the presence or absence of feedback mechanisms, significantly influencing the system's performance, complexity, and application.
An open-loop control system operates without feedback from the output. It consists of two primary elements: the controller and the controlled process. The controller receives an input signal and manipulates the process to achieve the desired outcome. Importantly, open-loop systems function independently of the output, meaning there is no automatic correction based on the performance of the system. A common example of an open-loop system is a washing machine that runs on a predefined time cycle. It does not adjust its operation based on the cleanliness of the clothes, highlighting the absence of feedback. Open-loop systems are advantageous in scenarios where precise measurement of the output is either impractical or economically unfeasible. They are typically simpler and less costly to design and maintain due to their straightforward architecture.
In contrast, closed-loop or feedback control systems incorporate one or more feedback loops that continuously monitor the output and adjust the input accordingly to maintain the desired performance. This configuration significantly enhances accuracy and responsiveness. For instance, in a closed-loop idle-speed control system used in automotive engines, the system constantly monitors the idling speed and compares it to the desired speed. If a discrepancy is detected, the system adjusts the throttle angle to correct the speed. This feedback mechanism allows the system to quickly recover from disturbances and maintain the preset value, ensuring consistent performance.
Despite their superior accuracy and ability to handle disturbances, closed-loop systems are inherently more complex. They require additional components for monitoring and feedback, which increases the design complexity, cost, and power consumption. The choice between open-loop and closed-loop systems depends on the specific requirements of the application, including the need for precision, the feasibility of output measurement, and economic considerations.