Examples[ edit ] Mercury thermostats circa using feedback despre semnalul opțional and contraction of columns of mercury in response to temperature changes were used in negative feedback systems to control vents in furnaces, maintaining a steady internal temperature.
In the invisible hand of the market metaphor of economic theoryreactions to price movements provide a feedback mechanism to match supply and demand. In centrifugal governorsnegative feedback is used to maintain a near-constant speed of an engine, irrespective of the load or fuel-supply conditions.
In a steering enginepower assistance is applied to the rudder with a feedback loop, to maintain deschideți cont demo cu opțiuni binare direction set by the steersman. In servomechanismsthe speed or position of an output, as determined by a sensoris compared to a set value, and any error is reduced by negative feedback to the input.
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In audio amplifiersnegative feedback reduces distortionminimises the effect of manufacturing variations in component parameters, and compensates for changes in characteristics due to temperature change. In analog computing feedback around operational amplifiers is used to generate mathematical functions such as additionsubtractionintegrationdifferentiationlogarithmand antilog functions.
In a phase locked loop feedback is used to maintain a generated alternating waveform in a constant phase to a reference signal.
In many implementations the generated waveform is the output, but when used as a demodulator in an FM radio receiver, the error feedback voltage serves as the demodulated output signal. If there is a frequency divider between the generated waveform and the phase comparator, the device acts as a frequency multiplier. In organismsfeedback enables various measures e. History[ edit ] Negative feedback as a control technique may be seen in the refinements of the water clock introduced by Ktesibios of Alexandria in the 3rd century BCE.
Self-regulating mechanisms have existed since antiquity, and were used to maintain a constant level in the reservoirs of water clocks as early as BCE. Negative feedback was implemented in the 17th Century. Cornelius Drebbel had built thermostatically-controlled incubators and ovens in the early s,  and centrifugal governors were used to regulate the distance and pressure between millstones in windmills.
Amplificatorul opțional ideal este un amplificator care nu inversează.
If a goal is to be attained, some signals from the goal are necessary at some time to direct the behavior. Cybernetics pioneer Norbert Wiener helped to formalize the concepts of feedback control, defining feedback in general as "the chain of the transmission and return of information",  and negative feedback as the case when: The information fed back to the control center tends to oppose the departure of the controlled from the controlling quantity Such complex systems cannot be treated as an interlaced set of more or less independent feedback circuits, but only as a whole.
«Очень уместно, - мысленно застонал. - Сюрреализм. Я в плену абсурдного сна». Проснувшись утром в своей постели, Беккер заканчивал день тем, что ломился в гостиничный номер незнакомого человека в Испании в поисках какого-то магического кольца. Суровый голос Стратмора вернул его к действительности.
For understanding the general principles of dynamic systems, therefore, the concept of feedback is inadequate in itself. What is important is that complex systems, richly cross-connected internally, have complex behaviors, and that these behaviors can be goal-seeking in complex patterns.
Overview[ edit ] Feedback loops in the human body In many physical and biological systems, qualitatively different influences can oppose plângerile de piață forex other. For example, in biochemistry, one set of chemicals drives the system in a given direction, whereas another set of chemicals drives it in an opposing direction.
If one or both of these opposing influences are non-linear, equilibrium point s result. In biologythis process in general, biochemical is often referred to as homeostasis ; whereas in mechanicsthe more common term is equilibrium. In control theorynegative refers to the sign of the multiplier in mathematical models for feedback.
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In multivariate systems, vectors help to illustrate how several influences can both partially complement and partially oppose each other. Any system in which there is positive feedback together with a gain greater than one will result in a runaway situation.
Both positive and negative feedback require a feedback loop to operate. However, negative feedback systems can still be subject to oscillations.
Circuite de bază pentru pornirea unui amplificator operațional
This is caused by a phase shift around any loop. Due to these phase shifts the feedback signal of some frequencies can ultimately become in phase with the input signal and thus turn into positive feedback, creating a runaway condition.
Even before the point where the phase shift becomes degrees, stability of the negative feedback loop will become compromised, leading to increasing under- and overshoot following a disturbance. This problem is often dealt with by feedback despre semnalul opțional or changing the phase of the problematic frequencies in a design step called compensation.
Unless the system naturally has sufficient damping, many negative feedback systems have low pass filters or dampers fitted.
Some specific implementations[ edit ].