iPedia Free Information Center

Information about Negative Feedback

For auction-related negative feedback, see eBay




Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated. Many real-world systems have one or several points around which the system gravitates. In response to a perturbation, a negative feedback system with such point(s) will tend to re-establish equilibrium.

In many physical and biological systems, qualitatively different influences can oppose each 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, an equilibrium point(s) results.

In Biology, this process (generally biochemical) is often referred to as Homeostasis; whereas in Mechanics, the more common term is equilibrium.

In Engineering, Mathematics and the Physical and Biological Sciences, common terms for the points around which the system gravitates include: attractors, stable states, eigenstates/eigenfunctions, equilibrium points, and setpoints.

'Negative' refers to the sign of the multiplier in mathematical models for feedback. In delta notation, -output is added to or mixed into the input. In multivariate systems, vectors help to illustrate how several influences can both partially compliment and partially oppose each other.

In contrast, positive feedback is a feedback in which the system responds in the same direction as the perturbation, resulting in amplification of the original signal instead of stabilizing the signal. Both positive and negative feedback require a feedback loop to operate, as opposed to feedforward, which does not rely on a feedback loop for its control of the system.

Examples

Examples of the use of negative feedback to control its system are: thermostat control, phase-locked loop, hormonal regulation, and temperature regulation in animals.

A simple and practical example is a thermostat. When the temperature in a heated room reaches a certain upper limit the room heating is switched off so that the temperature begins to fall. When the temperature drops to a lower limit, the heating is switched on again. Provided the limits are close to each other, a steady room temperature is maintained. The same applies to a cooling system, such as an air conditioner, a refrigerator, or a freezer.

Some biological systems exhibit negative feedback such as the baroreflex in blood pressure regulation and erythropoiesis. Many biological process (e.g., in the human anatomy) use negative feedback. Examples of this are numerous, from the regulating of body temperature, to the regulating of blood glucose levels. The disruption of negative feedback can lead to undesirable results: in the case of blood glucose levels, if negative feedback fails, the glucose levels in the blood may begin to rise dramatically, thus resulting in Diabetes.

Electronic amplifiers

Main article: negative feedback amplifier


The negative feedback amplifier was invented by Harold Stephen Black at Bell Laboratories in 1927. Fundamentally, all electronic devices (e.g. vacuum tubes, bipolar transistors, MOS transistors) are nonlinear devices. Negative feedback corrects this by trading unused gain for higher linearity (lower distortion). Though much more accurate, amplifiers with negative feedback can become unstable if not designed correctly, causing them to oscillate. Harry Nyquist of Bell Laboratories managed to work out a theory regarding how to make it stable.

Negative feedback is used in this way in many types of amplification systems to stabilize and improve their operating characteristics (see e.g., operational amplifiers).

See also

External links

eBay Inc.

Public (NASDAQ:  EBAY )
Founded San Jose, California, USA (September 3, 1995)
Headquarters San Jose, California, USA

Key people Meg Whitman, CEO & President
Pierre Omidyar, Founder and Chairman
John Donahoe, Chief of eBay Marketplace
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
System (from Latin systēma, in turn from Greek σύστημα systēma) is a set of entities, real or abstract, where each entity interacts with, or is related to, at least one other
..... Click the link for more information.
A perturbation of a biological system is an alteration of function, induced by external or internal mechanisms. Biological systems can be perturbed through a number of means.
..... Click the link for more information.
mechanical equilibrium is:
A system is in mechanical equilibrium when the sum of the forces, and torque, on each particle of the system is zero,



..... Click the link for more information.
Biochemistry is the study of the chemical processes in living organisms.[1] The word "biochemistry" comes from the Greek word βιοχημεία biochēmeia, which means "the chemistry of life.
..... Click the link for more information.
Homeostasis is the property of either an open system or a closed system, especially a living organism, to regulate the state of its internal environment so as to maintain a stable, constant condition.
..... Click the link for more information.
For other uses, see Mechanic (disambiguation).


Mechanics (Greek Μηχανική
..... Click the link for more information.
mechanical equilibrium is:
A system is in mechanical equilibrium when the sum of the forces, and torque, on each particle of the system is zero,



..... Click the link for more information.
Stability can refer to:
  • Aircraft flight Stability (aircraft)
  • Atmospheric stability, a measure of the turbulence in the ambient atmosphere
  • BIBO stability (Bounded Input, Bounded Output stability), in signal processing and control theory, part of electrical

..... Click the link for more information.
Setpoint may refer to:
  • SetPoint (software), the driver suite for Logitech mice
  • Setpoint (control system), the desired value specified for controlling a system

..... Click the link for more information.
This article or section may contain original research or unverified claims.
Please help Wikipedia by adding references. See the for details.
This article has been tagged since September 2007.

..... Click the link for more information.
Feed-forward is a term describing a kind of system which reacts to changes in its environment, usually to maintain some desired state of the system. A system which exhibits feed-forward behavior responds to a measured disturbance in a pre-defined way — contrast with a
..... Click the link for more information.
A thermostat is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by controlling the flow of heat energy into or out of the system.
..... Click the link for more information.
A phase-locked loop or phase lock loop (PLL) is an electronic control system that generates a signal that has a fixed relation to the phase of a "reference" signal. A phase-locked loop circuit responds to both the frequency and the phase of the input signals, automatically
..... Click the link for more information.
hormone (from Greek όρμή - "to set in motion") is a chemical messenger that carries a signal from one cell (or group of cells) to another. All multicellular organisms produce hormones (including plants - see phytohormone).
..... Click the link for more information.
A thermostat is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by controlling the flow of heat energy into or out of the system.
..... Click the link for more information.
trillion fold).]]

Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
..... Click the link for more information.
Note: Air conditioning is a broad topic which would make an excessively long article if details of appliances called air conditioners were included in it.

..... Click the link for more information.
refrigerator (often called a "fridge" for short) is a cooling appliance comprising a thermally insulated compartment and a mechanism to transfer heat from it to the external environment, cooling the contents to a temperature below ambient.
..... Click the link for more information.
refrigerator (often called a "fridge" for short) is a cooling appliance comprising a thermally insulated compartment and a mechanism to transfer heat from it to the external environment, cooling the contents to a temperature below ambient.
..... Click the link for more information.
In cardiovascular physiology, the baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms for maintaining blood pressure. It provides a negative feedback loop in which an elevated blood pressure reflexively causes blood pressure to decrease; similarly,
..... Click the link for more information.
Blood pressure (strictly speaking: vascular pressure) refers to the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs.
..... Click the link for more information.
Erythropoiesis is the process by which red blood cells (erythrocytes) are produced. In human adults, this usually occurs within the bone marrow. In the early fetus, erythropoiesis takes place in the mesodermal cells of the yolk sac.
..... Click the link for more information.
Human anatomy is primarily the scientific study of the morphology of the adult human body.[1] It is subdivided into gross anatomy and microscopic anatomy.[1]
..... Click the link for more information.
Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
..... Click the link for more information.
Diabetes mellitus
Classification & external resources

ICD-10 E 10. –E 14.
ICD-9 250

MedlinePlus 001214
eMedicine med/546   emerg/134

MeSH C18.452.394.
..... Click the link for more information.
A negative feedback amplifier, or more commonly simply a feedback amplifier, is an amplifier which uses a negative feedback network, generally for improving performance (gain stability, linearity, frequency response etc.).
..... Click the link for more information.
Harold Stephen Black (1898-1983) was an American electrical engineer, who revolutionized the field of applied electronics by inventing the negative feedback amplifier in 1927.
..... Click the link for more information.
Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is part of the research and development organization of Alcatel-Lucent and previously the United States Bell System.
..... Click the link for more information.


This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus


page counter