Feedback

Feedback is a process in which a system's output influences its subsequent activity. It can amplify or counteract changes in the system.

Feedback loop: A sequence of causal links in which a system's output returns to affect its input or later state. This loop is the basic structure through which feedback changes subsequent activity.
Homeostasis: The maintenance of relatively stable internal conditions in a living organism despite external change. Physiological feedback loops keep variables such as temperature and blood glucose within ranges.
System: A set of interacting elements considered together for a particular purpose or analysis. Feedback is defined by interactions among a system's output, state, and later activity.
Open-loop control: Control that acts without using measurements of the system's resulting output to adjust its action. Unlike feedback control, it does not revise action based on results.
Negative feedback: Feedback that opposes a change in a system, tending to reduce deviations from a reference state. It counteracts deviations and can stabilize the system.
Thermostat: A device that regulates temperature by switching heating or cooling in response to measured conditions. It is a familiar example of feedback correcting a difference from a target temperature.
Input–output model: A representation of a system in terms of signals entering it and results emerging from it. It makes the returning influence of an output easier to identify.
Feedforward control: Control that responds to anticipated disturbances before they affect a system's output. It acts on predicted changes rather than relying on the output's return signal.
Positive feedback: Feedback that reinforces a change in a system, tending to drive further change in the same direction. It amplifies deviations instead of correcting them.
Automatic control: The regulation of a process by a system that measures conditions and adjusts its operation without continuous human action. Feedback lets machines adjust their outputs in response to measured results.

Linked from 51 pages