Editing Galvanometer (section)

==History==
===Hans Christian Ørsted===
The deflection of a [[magnetic compass]] needle by the current in a wire was first described by [[Hans Christian Ørsted]] in 1820. The phenomenon was studied both for its own sake and as a means of measuring electric current.

===Schweigger and Ampère===
The earliest galvanometer was reported by [[Johann Salomo Christoph Schweigger|Johann Schweigger]] at the [[University of Halle]] on 16 September 1820. [[André-Marie Ampère]] also contributed to its development. Early designs increased the effect of the magnetic field generated by the current by using multiple turns of wire. The instruments were at first called "multipliers" due to this common design feature.<ref>{{cite web|title=Schweigger Multiplier – 1820|url=https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/museum/schweigger-multiplier|website=Maglab|publisher=National High Magnetic Field Laboratory|access-date=17 October 2017}}</ref> The term "galvanometer," in common use by 1836, was derived from the surname of Italian electricity researcher [[Luigi Galvani]], who in 1791 discovered that electric current would make a [[frog galvanoscope|dead frog's leg jerk]].

===Poggendorff and Thomson===
[[File:Thomsons mirror galvanometer, 1858. (9663806048).jpg|thumb|320px|Thomson mirror galvanometer, patented in 1858.]]

Originally, the instruments relied on the Earth's magnetic field to provide the restoring force for the compass needle. These were called [[#Tangent galvanometer|"tangent" galvanometer]]s and had to be oriented before use. Later instruments of the "[[#Astatic galvanometer|astatic]]" type used opposing magnets to become independent of the Earth's field and would operate in any orientation.

An early [[mirror galvanometer]] was invented in 1826 by [[Johann Christian Poggendorff]].<ref>{{Cite web |title=Museum of Technology, The History of Gadgets and Gizmos |url=https://museumoftechnology.org.uk/stories/galvos.php |access-date=2025-03-10 |website=museumoftechnology.org.uk}}</ref> An astatic galvanometer was invented by [[Hermann von Helmholtz]] in 1849; a more sensitive version of that device, the Thomson ''mirror galvanometer'', was patented in 1858 by [[William Thomson, 1st Baron Kelvin|William Thomson]] (Lord Kelvin).<ref>Lindley, David, ''Degrees Kelvin: A Tale of Genius, Invention, and Tragedy'', pp. 132–133, Joseph Henry Press, 2004 {{ISBN|0309167825}}</ref> Thomson's design was able to detect very rapid current changes by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents. Alternatively, the deflection of the suspended magnets could be observed directly through a microscope.

===Georg Ohm===
The ability to measure voltage and current quantitatively allowed [[Georg Ohm]], in 1827, to formulate [[Ohm's law]] – that the voltage across a conductor is directly proportional to the current through it.

===D'Arsonval and Deprez===
[[File:A moving coil galvanometer. Wellcome M0016397.jpg|thumb|An early d'Arsonval moving coil galvanometer]]

The early moving-magnet form of galvanometer had the disadvantage that it was affected by any magnets or iron masses near it, and its deflection was not linearly proportional to the current. In 1882 [[Jacques-Arsène d'Arsonval]] and [[Marcel Deprez]] developed a form with a stationary permanent magnet and a moving coil of wire, suspended by fine wires which provided both an electrical connection to the coil and the restoring torque to return to the zero position. An iron tube between the magnet's pole pieces defined a circular gap through which the coil rotated. This gap produced a consistent, radial magnetic field across the coil, giving a linear response throughout the instrument's range. A mirror attached to the coil deflected a beam of light to indicate the coil position. The concentrated magnetic field and delicate suspension made these instruments sensitive; d'Arsonval's initial instrument could detect ten [[Ampere|microamperes]].<ref>{{cite book |last=Keithley |first=Joseph F. |year=1999 |title=The story of electrical and magnetic measurements: from 500 B.C. to the 1940s |publisher=John Wiley and Sons |isbn=0-7803-1193-0 |pages=196–198}}</ref>

===Edward Weston===
[[File:D'Arsonval ammeter movement.jpg|thumb|320px|D'Arsonval/Weston galvanometer (ca. 1900). Part of the magnet's left [[pole piece]] is broken out to show the coil.]]
[[File:Weston galvanometer 6h440s49d 4j03cz922 dl full size.jpg|thumb|right|Weston galvanometer in portable case]]
[[Edward Weston (chemist)|Edward Weston]] extensively improved the design of the galvanometer. He substituted the fine wire suspension with a pivot and provided restoring torque and electrical connections{{Explanation needed|reason=electrical connections provided by springs??|date=September 2021}} through spiral springs rather than through the traditional wristwatch [[balance wheel]] hairspring. He developed a method of stabilizing the magnetic field of the permanent magnet, so the instrument would have consistent accuracy over time. He replaced the light beam and mirror with a knife-edge pointer that could be read directly. A mirror under the pointer, in the same plane as the scale, eliminated [[parallax]] observation error. To maintain the field strength, Weston's design used a very narrow circumferential slot through which the coil moved, with a minimal air-gap. This improved linearity of pointer deflection with respect to coil current. Finally, the coil was wound on a light-weight form made of conductive metal, which acted as a damper. By 1888, Edward Weston had patented and brought out a commercial form of this instrument, which became a standard electrical equipment component. It was known as a "portable" instrument because it was affected very little by mounting position or by transporting it from place to place. This design is almost universally used in moving-coil meters today.{{Citation needed|date=September 2021}}

Initially, laboratory instruments relying on the Earth's own magnetic field to provide restoring force for the pointer, galvanometers were developed into compact, rugged, sensitive portable instruments essential to the development of electro-technology.

===Taut-band movement===
The taut-band movement is a modern development of the D'Arsonval-Weston movement.  The jewel pivots and hairsprings are replaced by tiny strips of metal under tension. Such a meter is more rugged for field use.<ref>{{cite web |url=https://www.weschler.com/blog/the-taut-band-analog-meter/|title=The taut-band analog meter|date=20 February 2020|last=Weschler Instruments|access-date=25 April 2020}}</ref><ref>{{Cite web |url=http://www.dictionarycentral.com/definition/taut-band-meter.html |title=Dictionary Central |access-date=18 June 2018 |archive-date=18 June 2018 |archive-url=https://web.archive.org/web/20180618175954/http://www.dictionarycentral.com/definition/taut-band-meter.html |url-status=dead }}</ref>