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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
feedback (1) signal or data that is sent back to a commanding unit from a control process output for use as input in subsequent operations. In a closed-loop system, it is the part of the system that brings back information on the process condition under control. (2) the provision of a path from the output to the input of a system, such that the output may be made a function of both the input and the previous outputs of the system. (3) the technique of sampling the output of an amplifier and using that information to modify the amplifier input signal. A portion of the output is "fed back" to the input. Positive feedback occurs when the output is added to the input; negative feedback occurs when the output is subtracted from the input. Negative feedback, invented by communications engineer Harold Black in 1928, usually results in a gain-bandwidth tradeoff: decreasing and stabilizing the amplifier gain, while increasing the bandwidth. According to Norbert Wiener, feedback is a method of controlling a system by reinserting into it the results of its past performance. feedback amplifier a circuit configuration of amplifiers that has a feedback path. A negative
Reliability and Human Error in Systems
Published in Robert W. Proctor, Van Zandt Trisha, Human Factors in Simple and Complex Systems, 2018
Robert W. Proctor, Van Zandt Trisha
An important characteristic of a system has to do with feedback. Feedback refers to input or information flow traveling backward in the system. Different systems may have different kinds of feedback mechanisms, and often more than one. Feedback usually provides information about the difference between the actual and the desired state of the system. Positive feedback is added to the system input and keeps the state of the system changing in its present direction. Such systems are usually unstable, because positive information flow can amplify error instead of correcting it. The alternative to positive feedback is negative feedback, which is subtracted from the system input. It is often beneficial for a system to include negative feedback mechanisms.
Global Climate Change
Published in John C. Ayers, Sustainability, 2017
In contrast to negative feedback, positive feedback amplifies change. As noted by Brand (2009), “The word ‘positive’ in the phrase positive feedback does not mean ‘good.’ It usually means trouble, because a small perturbation can result in big changes…The climate system is nonlinear, which means its output is not always proportional to its input; occasionally, unexpectedly, tiny changes in initial conditions provoke huge responses.” One example of a positive feedback is ice-albedo feedback: Warming temperatures cause sea ice to melt, so that dark seawater that absorbs sunlight (low albedo) replaces ice that reflects sunlight back into space (high albedo), leading to even more rapid warming (Brand 2009). In a positive feedback loop subsequent changes reinforce the initial change, so the phenomenon is sometimes referred to as reinforcing feedback. Another example of positive feedback in the global climate system is the release of the greenhouse gas methane during melting of Arctic permafrost.
On the use of Youla–Kucera parametrisation in adaptive active noise and vibration control – a review
Published in International Journal of Control, 2020
When a correlated measurement with the disturbance is available, adaptive feedforward compensation of broadband vibrations or noise can be considered Elliott and Nelson (1994), Kuo and Morgan (1996), Jacobson, Johnson, McCormick, and Sethares (2001), Zeng and de Callafon (2006). However in many AVC (Active Vibration Control) or ANC (Active Noise Control) systems there is a ‘positive’ feedback coupling between the compensator system and the correlated measurement of the disturbance which serves as reference Jacobson et al. (2001), Zeng and de Callafon (2006), Hu and Linn (2000). The positive feedback may destabilise the system.
Identifying leverage points to transition dysfunctional irrigation schemes towards complex adaptive systems
Published in International Journal of Water Resources Development, 2020
André F. van Rooyen, Martin Moyo, Henning Bjornlund, Thabani Dube, Karen Parry, Richard Stirzaker
Positive feedback is self-reinforcing and a strong leverage point, so it is usually more effective than increasing negative feedback. In irrigation, this includes improving input supply and market access to increase yields and income, and stimulating reinvestment of profit in production.