Editing Multimeter (section)

== History ==
[[File:1920s multimeter 3738-6b.jpg|thumb|upright|left|1920s pocket multimeter]]
The first attested usage of the word "multimeter" listed by the [[Oxford English Dictionary]] is from 1907.<ref>{{cite OED|multimeter|access-date=14 March 2021}}</ref>

=== Precursors ===
The first moving-pointer current-detecting device was the [[galvanometer]] in 1820. These were used to measure resistance and voltage by using a [[Wheatstone bridge]], and comparing the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow and impractical in the field. These galvanometers were bulky and delicate.

The [[D'Arsonval galvanometer|D'Arsonval–Weston]] meter movement uses a moving coil which carries a pointer and rotates on pivots or a taut band ligament. The coil rotates in a permanent magnetic field and is restrained by fine spiral springs which also serve to carry current into the moving coil. It gives proportional measurement rather than just detection, and deflection is independent of the orientation of the meter. Instead of balancing a bridge, values could be directly read off the instrument's scale, which made measurement quick and easy.

The basic moving coil meter is suitable only for direct current measurements, usually in the range of 10&nbsp;μA to 100&nbsp;mA. It is easily adapted to read heavier currents by using shunts (resistances in parallel with the basic movement) or to read voltage using series resistances known as multipliers. To read alternating currents or voltages, a rectifier is needed. One of the earliest suitable rectifiers was the copper oxide rectifier developed and manufactured by Union Switch & Signal Company, Swissvale, Pennsylvania, later part of Westinghouse Brake and Signal Company, from 1927.<ref>"A New Electronic Rectifier", L.O Grondahl & P.H. Geiger, Transactions, American Institution of Electrical Engineers, February 1927 pp. 358–366</ref>

=== Avometer ===
[[File:AVO Model 8 Mk7 P4 by Megger.jpg|thumb|upright|[[Avometer]] Model 8]]
The invention of the first multimeter is attributed to British Post Office engineer, Donald Macadie, who became dissatisfied with the need to carry many separate instruments required for maintenance of [[telecommunication circuit]]s.<ref>{{cite web|url=http://www.glias.org.uk/news/237news.html |title=Greater London Industrial Archaeology Society |access-date=2010-11-02 |work=glias.org.uk}}</ref><!--(The statement that Mr MaCadie became dissatisfied with having to carry many separate instruments is questionable. At the time when the Original Avometer patent (GB200977, 1923) was granted, he was manager of the Post Office factory in Holloway, London and 50 years old. If he still had occasion to use meters in his work, he would very likely have had an assistant to carry them for him; he may have been very considerate towards his assistants.]<ref>Obituary Wireless World, April 1955</ref>--> Macadie invented an instrument which could measure [[amperes]] (amps), volts and [[ohm]]s, so the multifunctional meter was then named [[Avometer]].<ref name="Grace_AVO">{{cite web |url=https://www.gracesguide.co.uk/Avo |format=[[MediaWiki]] |website=gracesguide.co.uk |title=AVO |access-date=2010-11-02}}</ref> The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range.

The first Avometer had a [[Sensitivity (electronics)|sensitivity]] of 60&nbsp;Ω/V, three direct current ranges (12&nbsp;mA, 1.2&nbsp;A, and 12&nbsp;A), three direct voltage ranges (12, 120, and 600&nbsp;V or optionally 1,200&nbsp;V), and a 10,000&nbsp;Ω resistance range. An improved version of 1927 increased this to 13 ranges and 166.6&nbsp;Ω/V (6&nbsp;mA) movement. A "Universal" version having additional alternating current and alternating voltage ranges was offered from 1933 and in 1936 the dual-sensitivity Avometer Model 7 offered 500 and 100&nbsp;Ω/V.<ref>Advertisement – The Electrician, 1 June 1934</ref> Between the mid-1930s until the 1950s, 1,000&nbsp;Ω/V became a de facto standard of sensitivity for radio work and this figure was often quoted on service sheets. However, some manufacturers such as Simpson, Triplett and Weston, all in the US, produced 20,000&nbsp;Ω/V VOMs before the Second World War and some of these were exported. After 1945–46, 20,000&nbsp;Ω/V became the expected standard for electronics, but some makers offered even more sensitive instruments. For industrial and other "heavy-current" use low sensitivity multimeters continued to be produced and these were considered more robust than the more sensitive types.

The Automatic Coil Winder and Electrical Equipment Company (ACWEECO), founded in 1923,  was set up to manufacture the Avometer and a coil winding machine also designed and patented by MacAdie. Although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933. His son, Hugh S. MacAdie, joined ACWEECO in 1927 and became Technical Director.<ref>Imperial College Library Archives – Papers of Donald Macadie 1871–1956 MS2015/21</ref><ref>The Electrician 15 June 1923, p. 666</ref><ref name="Grace_AVO" /> The first AVO was put on sale in 1923, and many of its features remained almost unaltered through to the last Model 8.

=== Pocket watch meters ===
[[File:Pifco Universal-Prüfer.jpg|thumb|A pocket-watch-style meter made in the 1930s. It can measure voltage, current, continuity and the heating element of vacuum tubes]]

Pocket-watch-style meters were in widespread use in the 1920s. The metal case was typically connected to the negative connection, an arrangement that caused numerous electric shocks. The technical specifications of these devices were often crude, for example the one illustrated has a [[Electrical resistance|resistance]] of just 25&nbsp;Ω/V, a [[non-linear]] scale and no zero adjustment on both ranges.

=== Vacuum tube voltmeters ===
Vacuum tube voltmeters or valve [[voltmeters]] (VTVM, VVM) were used for voltage measurements in electronic circuits where high [[Electrical impedance|input impedance]] was necessary. The VTVM had a fixed input impedance of typically 1&nbsp;MΩ or more, usually through use of a [[Electronic amplifier#Common terminal|cathode follower]] input circuit, and thus did not significantly load the circuit being tested. VTVMs were used before the introduction of electronic high-impedance analog [[transistor]] and [[field effect transistor]] voltmeters (FETVOMs). Modern digital meters (DVMs) and some modern analog meters also use electronic input circuitry to achieve high input impedance—their voltage ranges are functionally equivalent to VTVMs. The input impedance of some poorly designed DVMs (especially some early designs) would vary over the course of a [[sample-and-hold]] internal measurement cycle, causing disturbances to some sensitive circuits under test.

=== Introduction of digital meters ===

The first digital multimeter was manufactured in 1955 by Non Linear Systems.<ref>{{cite web|url=http://www.eetimes.com/anniversary/designclassics/gauging.html|access-date=2008-01-26|title=Gauging the impact of DVMs|publisher=EETimes.com}}</ref><ref>{{cite book|page=286|year=2001|title=Survey of Instrumentation and Measurement|last=Dyer|first=Stephen|publisher=Wiley |isbn=0-471-39484-X}}</ref>

It is claimed that the first handheld digital multimeter was developed by Frank Bishop of Intron Electronics in 1977,<ref>{{cite web |title=The Handheld Digital Multimeter |url=https://www.frankbishopinventor.com/the-handheld-digital-multimeter-dmm-10/ |access-date=2024-09-02 |website=www.frankbishopinventor.com/}}</ref> which at the time presented a major breakthrough for servicing and fault finding in the field.