Editing Hysteresis (section)

==In engineering==

===Control systems===

In control systems, hysteresis can be used to filter signals  so that the output reacts less rapidly than it otherwise would by taking recent system history into account. For example, a [[thermostat]] controlling a heater may switch the heater on when the temperature drops below A, but not turn it off until the temperature rises above B. (For instance, if one wishes to maintain a temperature of 20&nbsp;°C then one might set the thermostat to turn the heater on when the temperature drops to below 18&nbsp;°C and off when the temperature exceeds 22&nbsp;°C).

Similarly, a pressure switch can be designed to exhibit hysteresis, with pressure set-points substituted for temperature thresholds.

===Electronic circuits===

[[Image:Hysteresis sharp curve.svg|thumb|Sharp hysteresis loop of a [[Schmitt trigger]]]]
Often, some amount of hysteresis is intentionally added to an electronic circuit to prevent unwanted rapid switching. This and similar techniques are used to compensate for [[Switch#Contact bounce|contact bounce]] in switches, or [[Noise (electronic)|noise]] in an electrical signal.

A [[Schmitt trigger]] is a simple electronic circuit that exhibits this property.

A [[Relay#Latching relay|latching relay]] uses a [[solenoid]] to actuate a ratcheting mechanism that keeps the relay closed even if power to the relay is terminated.

Some positive feedback from the output to one input of a comparator can increase the natural hysteresis (a function of its gain) it exhibits.

Hysteresis is essential to the workings of some [[memristor]]s (circuit components which "remember" changes in the current passing through them by changing their resistance).<ref>{{cite news |url=http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=207403521&pgno=1 |title='Missing link' memristor created: Rewrite the textbooks? |last1=Johnson |first1=R. Colin |newspaper=EE Times April 30, 2008 |access-date=27 September 2011 |archive-url=https://web.archive.org/web/20120930074814/http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=207403521&pgno=1 |archive-date=30 September 2012 |url-status=dead }}</ref>

Hysteresis can be used when connecting arrays of elements such as [[nanoelectronic]]s, [[electrochrome cell]]s and [[memory effect]] devices using [[passive matrix addressing]]. Shortcuts are made between adjacent components (see [[crosstalk]]) and the hysteresis helps to keep the components in a particular state while the other components change states. Thus, all rows can be addressed at the same time instead of individually.

In the field of audio electronics, a [[noise gate]] often implements hysteresis intentionally to prevent the gate from "chattering" when signals close to its threshold are applied.

===User interface design===

A hysteresis is sometimes intentionally added to [[computer algorithm]]s. The field of [[user interface design]] has borrowed the term hysteresis to refer to times when the state of the user interface intentionally lags behind the apparent user input. For example, a menu that was drawn in response to a mouse-over event may remain on-screen for a brief moment after the mouse has moved out of the trigger region and the menu region. This allows the user to move the mouse directly to an item on the menu, even if part of that direct mouse path is outside of both the trigger region and the menu region. For instance, right-clicking on the desktop in most Windows interfaces will create a menu that exhibits this behavior.

===Aerodynamics===

In [[aerodynamic]]s, hysteresis can be observed when decreasing the angle of attack of a wing after stall, regarding the lift and drag coefficients. The angle of attack at which the flow on top of the wing reattaches is generally lower than the angle of attack at which the flow separates during the increase of the angle of attack.<ref>{{cite conference |url=http://www.public.iastate.edu/~huhui/paper/2008/AIAA-2008-0315.pdf |title=An Experimental Investigation on Aerodynamic Hysteresis of a Low-Reynolds Number Airfoil |author=Zifeng Yang |author2=Hirofumi Igarashi |author3=Mathew Martin |author4=Hui Hu |date=Jan 7–10, 2008 |publisher=American Institute of Aeronautics and Astronautics |conference=46th AIAA Aerospace Sciences Meeting and Exhibit |location=Reno, Nevada |id=AIAA-2008-0315 |access-date=2012-04-25 |archive-date=2017-08-10 |archive-url=https://web.archive.org/web/20170810081953/http://www.public.iastate.edu/~huhui/paper/2008/AIAA-2008-0315.pdf |url-status=dead }}</ref>

===Hydraulics===
Hysteresis can be observed in the stage-flow relationship of a river during rapidly changing conditions such as passing of a flood wave. It is most pronounced in low gradient streams with steep leading edge hydrographs.<ref>{{Cite conference |last=Holmes |first=Robert R. Jr. |date=February 2018 |title=River rating complexity |url=https://pubs.usgs.gov/ja/70193968/70193968.pdf |conference=Proceedings of the International Conference on Fluvial Hydraulics (River flow 2016)}}</ref>

===Backlash===

Moving parts within machines, such as the components of a [[gear train]], normally have a small gap between them, to allow  movement and lubrication. As a consequence of this gap, any reversal in direction of a drive part will not be passed on immediately to the driven part.<ref>{{cite journal |last1=Warnecke |first1=Martin |last2=Jouaneh |first2=Musa |title=Backlash Compensation in Gear Trains by Means of Open-Loop Modification of the Input Trajectory |journal=Journal of Mechanical Design |date=1 September 2003 |volume=125 |issue=3 |pages=620–624 |doi=10.1115/1.1596241}}</ref> This unwanted delay is normally kept as small as practicable, and is usually called [[backlash (engineering)|backlash]]. The amount of backlash will increase with time as the surfaces of moving parts wear.