Feedback Loop
A control arrangement where a system's output is measured and fed back to adjust its input.
Definition
A feedback loop routes a measurement of a system's output back to its input so that the controller can correct deviations from the target. Negative feedback opposes the deviation, stabilizing the system; positive feedback reinforces it.
Delay is feedback's great enemy: a lag between action and measurement can turn a stabilizing loop into an oscillating one. This is why fast sensing and actuation, and explicit accounting for delay, are central to any high-performance control system.
Feedback's power to stabilize uncertain systems comes with a hazard: delay and excessive gain can turn a corrective loop into an oscillating or divergent one. This is why loop speed, sensor accuracy, and explicit accounting for time lag are central to high-performance control. The same negative-feedback principle that regulates a thermostat governs biological homeostasis and economic stabilization, making it one of the most broadly applicable ideas in engineering.
Open vs closed loop
- Open loop: acts without measuring the result.
- Closed loop: uses measured output to self-correct.
- Closed loop handles disturbances and uncertainty far better.
Why it matters
Feedback is the central idea of control, letting imperfect systems track targets despite noise and disturbances. The same principle governs biological regulation, economics, and machine learning training. Excessive gain or delay in the loop can cause instability.
Fusion connection
Magnetic confinement depends on fast feedback loops that sense the plasma's position and shape and adjust coil currents in real time to keep it centered and stable.