closedloop

Closed-loop, or closed-loop control, refers to systems in which the output is measured and fed back to influence the input in order to achieve a desired behavior. The loop aims to reduce the difference between a target setpoint and the actual output, improving accuracy, stability, and robustness. In contrast, open-loop systems operate without feedback and cannot compensate for disturbances.

A typical closed-loop system includes an actuator, a sensor, a controller, and a reference signal. The controller computes an input based on the error signal (the difference between the reference and measured output). Common control strategies include proportional-integral-derivative (PID) control, which combines immediate response, accumulated error, and rate of change. The performance depends on loop gain, time delays, sensor noise, and nonlinearity.

Applications span engineering and beyond. In engineering and automation, closed-loop control is used for temperature regulation, flow and pressure control, robotics, and flight or automotive cruise control. In electronics, feedback in amplifiers can improve linearity and stability. Biological systems employ closed-loop processes for homeostasis, where signals regulate variables such as temperature or glucose levels. In practice, real-world closed-loop implementations must manage delays and nonidealities to avoid instability or oscillations.

Beyond technical systems, the term is used in business and product design. Closed-loop supply chains emphasize reclaiming products for reuse or remanufacture, while closed-loop marketing seeks to link customer data and outcomes back into product or service improvements. In all cases, the defining feature is a feedback pathway from output to input that continually shapes system behavior.