Editing Reed switch (section)

{{short description|Electrical switch operated by an applied magnetic field}}
{{use dmy dates|date=June 2020|cs1-dates=y}}
[[Image:Reedrelay.jpg|thumb|right|258px|(from top) Single-pole reed switch, four-pole reed switch and single-pole reed relay. Scale in centimeters.]]
[[Image:Reed switch (aka).jpg|thumb|258px|Reed switch, contact detail.]]
[[Image:Reed switch symbol.svg|thumb|258px|Commonly-used circuit symbol]]
[[File:Reed switch.ogv|thumb|258px|Operation of the reed switch]]

The '''reed switch'''{{efn-lr|name="NB_Herkon"}} is an [[Electromechanics|electromechanical]] [[switch]] operated by an applied [[magnetic field]]. It was invented in 1922 by professor Valentin Kovalenkov at the [[Peter the Great St. Petersburg Polytechnic University#Soviet era|Petrograd Electrotechnical University]],<ref name="IEEE_Reed_relay_history"/> and later evolved at [[Bell Labs|Bell Telephone Laboratories]] in 1936 by Walter B. Ellwood into the reed relay. In its simplest and most common form, it consists of a pair of [[Ferromagnetism|ferromagnetic]] flexible metal [[Electrical contacts|contacts]] in a [[hermetic seal|hermetically sealed]] [[glass]] envelope. The contacts are usually [[normally open]], closing when a magnetic field is present, or they may be normally closed and open when a magnetic field is applied. The switch may be actuated by an [[electromagnetic coil]], making a [[reed relay]],<ref name="Graf_1975"/> or by bringing a permanent [[magnet]] near it. When the magnetic field is removed, the contacts in the reed switch return to their original position. The "reed" is the metal part inside the reed switch envelope that is relatively thin and wide to make it flexible, resembling the [[Reed (mouthpiece)|reed]] of a [[Musical instruments|musical instrument]]. The term "reed" may also include the external wire lead as well as the internal part.{{efn-lr|name="NB_Herkon"}}

A common example of a reed switch application is to detect the opening of a door or windows, for a [[security alarm]].<ref>{{Cite book|last=Platt|first=Charles|url=https://www.worldcat.org/oclc/855977865|title=Encyclopedia of electronic components|date=26 October 2012 |isbn=978-1-4493-3389-8|location=Sebastopol, CA|pages=17|oclc=855977865}}</ref>