91:
483:. In this application, the charging of the battery deflects the needle to one side of the scale (commonly, the right side) and the discharging of the battery deflects the needle to the other side. A special type of zero-center ammeter for testing high currents in cars and trucks has a pivoted bar magnet that moves the pointer, and a fixed bar magnet to keep the pointer centered with no current. The magnetic field around the wire carrying current to be measured deflects the moving magnet.
301:
464:, which does not require a make-before-break switch. It also avoids any inaccuracy because of contact resistance. In the figure, assuming for example, a movement with a full-scale voltage of 50 mV and desired current ranges of 10 mA, 100 mA, and 1 A, the resistance values would be: R1 = 4.5 ohms, R2 = 0.45 ohm, R3 = 0.05 ohm. And if the movement resistance is 1000 ohms, for example, R1 must be adjusted to 4.525 ohms.
408:
run heavy circuit conductors up to the point of observation. In the case of alternating current, the use of a current transformer also isolates the meter from the high voltage of the primary circuit. A shunt provides no such isolation for a direct-current ammeter, but where high voltages are used it may be possible to place the ammeter in the "return" side of the circuit which may be at low potential with respect to earth.
164:
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provided by fine helical springs. The deflection of a moving iron meter is proportional to the square of the current. Consequently, such meters would normally have a nonlinear scale, but the iron parts are usually modified in shape to make the scale fairly linear over most of its range. Moving iron instruments indicate the
199:, and uses two spiral springs to provide the restoring force. The uniform air gap between the iron core and the permanent magnet poles make the deflection of the meter linearly proportional to current. These meters have linear scales. Basic meter movements can have full-scale deflection for currents from about 25
407:
may be used to provide a convenient small current to drive an instrument, such as 1 or 5 amperes, while the primary current to be measured is much larger (up to thousands of amperes). The use of a shunt or current transformer also allows convenient location of the indicating meter without the need to
117:
was used to measure currents using this effect, where the restoring force returning the pointer to the zero position was provided by the Earth's magnetic field. This made these instruments usable only when aligned with the Earth's field. Sensitivity of the instrument was increased by using additional
432:
with the meter. The resistances of shunts is in the integer to fractional milliohm range. Nearly all of the current flows through the shunt, and only a small fraction flows through the meter. This allows the meter to measure large currents. Traditionally, the meter used with a shunt has a full-scale
349:
There is also a range of devices referred to as integrating ammeters. In these ammeters the current is summed over time, giving as a result the product of current and time; which is proportional to the electrical charge transferred with that current. These can be used for metering energy (the charge
402:
Ammeters must be connected in series with the circuit to be measured. For relatively small currents (up to a few amperes), an ammeter may pass the whole of the circuit current. For larger direct currents, a shunt resistor carries most of the circuit current and a small, accurately-known fraction of
230:
Moving magnet ammeters operate on essentially the same principle as moving coil, except that the coil is mounted in the meter case, and a permanent magnet moves the needle. Moving magnet
Ammeters are able to carry larger currents than moving coil instruments, often several tens of amperes, because
210:
Because the magnetic field is polarised, the meter needle acts in opposite directions for each direction of current. A DC ammeter is thus sensitive to which polarity it is connected in; most are marked with a positive terminal, but some have centre-zero mechanisms and can display currents in
287:
only). The iron element consists of a moving vane attached to a pointer, and a fixed vane, surrounded by a coil. As alternating or direct current flows through the coil and induces a magnetic field in both vanes, the vanes repel each other and the moving vane deflects against the restoring force
366:
A picoammeter, or pico ammeter, measures very low electric current, usually from the picoampere range at the lower end to the milliampere range at the upper end. Picoammeters are used where the current being measured is below the limits of sensitivity of other devices, such as
521:
is a common tool for maintenance of industrial and commercial electrical equipment, which is temporarily clipped over a wire to measure current. Some recent types have a parallel pair of magnetically soft probes that are placed on either side of the conductor.
308:
In a hot-wire ammeter, a current passes through a wire which expands as it heats. Although these instruments have slow response time and low accuracy, they were sometimes used in measuring radio-frequency current. These also measure true RMS for an applied AC.
175:
This illustration is conceptual; in a practical meter, the iron core is stationary, and front and rear spiral springs carry current to the coil, which is supported on a rectangular bobbin. Furthermore, the poles of the permanent magnet are arcs of a
317:
In much the same way as the analogue ammeter formed the basis for a wide variety of derived meters, including voltmeters, the basic mechanism for a digital meter is a digital voltmeter mechanism, and other types of meter are built around this.
70:. Early ammeters were laboratory instruments that relied on the Earth's magnetic field for operation. By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in
329:(ADC); the digital display is calibrated to display the current through the shunt. Such instruments are often calibrated to indicate the RMS value for a sine wave only, but many designs will indicate true RMS within limitations of the wave
231:
the coil can be made of thicker wire and the current does not have to be carried by the hairsprings. Indeed, some
Ammeters of this type do not have hairsprings at all, instead using a fixed permanent magnet to provide the restoring force.
452:
To make a multi-range ammeter, a selector switch can be used to connect one of a number of shunts across the meter. It must be a make-before-break switch to avoid damaging current surges through the meter movement when switching ranges.
997:
478:
Zero-center ammeters are used for applications requiring current to be measured with both polarities, common in scientific and industrial equipment. Zero-center ammeters are also commonly placed in series with a
211:
either direction. A moving coil meter indicates the average (mean) of a varying current through it, which is zero for AC. For this reason, moving-coil meters are only usable directly for DC, not AC.
135:(also coined by Wheatstone) which was a device used to adjust the current in a circuit. Rheostat is a historical term for a variable resistance, though unlike rheoscope may still be encountered.
239:
An electrodynamic ammeter uses an electromagnet instead of the permanent magnet of the d'Arsonval movement. This instrument can respond to both alternating and direct current and also indicates
501:
can be used to convert the large current in the main circuit into a smaller current more suited to a meter. Some designs of transformer are able to directly convert the magnetic field around a
990:
983:
418:
Ordinary Weston-type meter movements can measure only milliamperes at most, because the springs and practical coils can carry only limited currents. To measure larger currents, a
1006:
801:
411:
Ammeters must not be connected directly across a voltage source since their internal resistance is very low and excess current would flow. Ammeters are designed for a low
23:
Demonstration model of a moving iron ammeter. As the current through the coil increases, the plunger is drawn further into the coil and the pointer deflects to the right.
90:
51:(A), hence the name. For direct measurement, the ammeter is connected in series with the circuit in which the current is to be measured. An ammeter usually has low
537:
259:
Face of an older moving iron ammeter with its characteristic non-linear scale. The moving iron ammeter symbol is in the lower-left corner of the meter face.
386:. Special design and usage considerations must be observed in order to reduce leakage current which may swamp measurements such as special insulators and
415:
across their terminals, much less than one volt; the extra circuit losses produced by the ammeter are called its "burden" on the measured circuit(I).
374:
Most picoammeters use a "virtual short" technique and have several different measurement ranges that must be switched between to cover multiple
513:
at full rated current, that can be easily read by a meter. In a similar way, accurate AC/DC non-contact ammeters have been constructed using
325:
to produce a calibrated voltage proportional to the current flowing. This voltage is then measured by a digital voltmeter, through use of an
52:
676:
1253:
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781:
696:
77:
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value of any AC waveform applied. Moving iron ammeters are commonly used to measure current in industrial frequency AC circuits.
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The needle's resting position is in the centre of the scale and the restoring spring can act equally well in either direction.
1156:
729:
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which moves when acted upon by the electromagnetic force of a fixed coil of wire. The moving-iron meter was invented by
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This type of meter movement is extremely common for both ammeters and other meters derived from them, such as
106:
547:
196:
129:
about 1840 but is no longer used to describe electrical instruments. The word makeup is similar to that of
636:
Geddes, L.A. (Feb–Mar 1996). "Looking back: How measuring electric current has improved through the ages".
494:, at best blowing a fuse, possibly damaging the instrument and wiring, and exposing an observer to injury.
1227:
680:
800:[Questionnaire from the Friedrich Drexler personal folder] (in German). Technisches Museum Wien.
62:
Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as
1055:
490:
has a very low resistance, mistakenly wiring the ammeter in parallel with a voltage source will cause a
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of a permanent magnet causes the coil to move. The modern form of this instrument was developed by
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It shows an average provided that the current's frequency is faster than the meter can respond to.
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The relation between electric current, magnetic fields and physical forces was first noted by
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Permanent magnet radiation hardness tests at the 100 MeV Linac: Preliminary results
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needs to be multiplied by the voltage to give energy) or for estimating the charge of a
113:
needle was deflected from pointing North when a current flowed in an adjacent wire. The
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the current passes through the meter movement. For alternating current circuits, a
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56:
855:
Lee, Mike Tien-Chen; Tiwari, Vivek; Malik, Sharad; Fujita, Masahiro (March 1997).
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turns of wire to multiply the effect – the instruments were called "multipliers".
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and a "current sink" method that eliminates range switching and associated
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857:"Power analysis and minimization techniques for embedded DSP software"
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151:. Of these, the flat, horizontal or vertical type is often called an
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An integrating current meter calibrated in ampere-hours or charge
864:
IEEE Transactions on Very Large Scale
Integration (VLSI) Systems
798:"Fragebogen aus der Personenmappe Friedrich Drexler (1858–1945)"
437:, so shunts are typically designed to produce a voltage drop of
264:
979:
467:
Switched shunts are rarely used for currents above 10 amperes.
776:. New York, NY: Holt, Rinehart, and Winston. chapter 11.
730:
720:
74:. It is generally represented by letter 'A' in a circuit.
81:
Ammeter from the
University of Dundee Physics Department
283:(as opposed to the moving-coil ammeter, which works on
125:
as a detector of electrical currents was coined by Sir
191:, where current passing through a coil placed in the
1195:
1139:
1013:
675:. IEE History of Technology Series. London, UK:
1007:Electrical and electronic measuring equipment
991:
517:magnetic field sensors. A portable hand-held
275:in 1884. This type of meter responds to both
8:
538:Class of accuracy in electrical measurements
247:for an alternative use for this instrument.
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765:
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761:
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984:
976:
505:into a small AC current, typically either
944:. Vol. 1: DC (free e‑book ed.).
904:"PocketPico ammeter theory of operation"
441:when carrying their full rated current.
55:so that it does not cause a significant
772:Spitzer, Frank; Howarth, Barry (1972).
628:
600:
957:
947:
936:"Chapter 8: DC metering circuits"
147:, meant to be mounted on some sort of
673:Sir Charles Wheatstone FRS: 1802–1875
394:is often used for probe connections.
168:Wire carrying current to be measured.
16:Device that measures electric current
7:
774:Principles of Modern Instrumentation
263:Moving iron ammeters use a piece of
47:. Electric currents are measured in
677:Institution of Electrical Engineers
184:is a moving coil ammeter. It uses
14:
460:or universal shunt, invented by
448:Ayrton shunt switching principle
378:. Other modern picoammeters use
172:Spring providing restoring force
934:Kuphaldt, Tony R. (2000–2023).
804:from the original on 2013-10-29
59:in the circuit being measured.
553:Electrical current#Measurement
321:Digital ammeter designs use a
1:
1203:Arbitrary waveform generator
1106:Transformer ratio arm bridge
969:Lessons in Electric Circuits
941:Lessons in Electric Circuits
456:A better arrangement is the
327:analog-to-digital converter
1277:
731:
721:
563:List of electronics topics
98:terminal service plant in
1254:Electronic test equipment
1208:Digital pattern generator
1101:Time-to-digital converter
1096:Time-domain reflectometer
109:in 1820, who observed a
749:A Greek–English Lexicon
671:Bowers, Brian (2001) .
548:Electrical measurements
182:D'Arsonval galvanometer
1228:Video-signal generator
650:10.1109/MP.1996.481376
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376:decades of measurement
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72:electric power systems
24:
1056:Microwave power meter
740:Liddell, Henry George
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143:Some instruments are
107:Hans Christian Ørsted
96:New York Penn Station
94:Ammeter from the old
93:
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22:
1081:Peak programme meter
683:. pp. 104–105.
568:Measurement category
433:deflection (FSD) of
281:alternating currents
115:tangent galvanometer
39:used to measure the
834:Stanford University
499:current transformer
474:Zero-center ammeter
405:current transformer
1213:Function generator
836:. 1 September 1992
497:In AC circuits, a
486:Since the ammeter
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450:
347:
306:
304:A hot-wire ammeter
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127:Charles Wheatstone
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25:
1249:Electrical meters
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1111:Transistor tester
1041:Frequency counter
1036:Electricity meter
1026:Capacitance meter
876:10.1109/92.555992
462:William E. Ayrton
273:Friedrich Drexler
31:(abbreviation of
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1223:Signal generator
1177:Waveform monitor
1157:Network analyzer
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1162:Oscilloscope
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915:. Retrieved
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887:. Retrieved
880:the original
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838:. Retrieved
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806:. Retrieved
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57:voltage drop
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1196:Generation
1187:Videoscope
1076:Peak meter
1061:Multimeter
917:2014-07-11
889:2009-12-02
840:11 October
832:(Report).
808:2013-07-10
624:References
573:Multimeter
216:voltmeters
189:deflection
53:resistance
37:instrument
1126:Voltmeter
1121:Wattmeter
1051:LCR meter
960:ignored (
950:cite book
644:: 40–42.
588:Voltmeter
583:Rheoscope
503:conductor
422:called a
356:capacitor
271:engineer
245:wattmeter
220:ohmmeters
123:rheoscope
121:The word
1140:Analysis
1131:VU meter
1071:Ohmmeter
1014:Metering
802:Archived
707:48111113
658:11392090
578:Ohmmeter
526:See also
430:parallel
420:resistor
296:Hot-wire
269:Austrian
241:true RMS
186:magnetic
132:rheostat
35:) is an
1091:Q meter
1021:Ammeter
966:— from
752:at the
733:ἱστάναι
481:battery
352:battery
313:Digital
176:circle.
111:compass
86:History
49:amperes
45:circuit
41:current
29:ammeter
780:
705:
695:
656:
277:direct
907:(PDF)
883:(PDF)
860:(PDF)
826:(PDF)
654:S2CID
595:Notes
488:shunt
439:50 mV
435:50 mV
425:shunt
139:Types
43:in a
962:help
842:2022
830:SLAC
778:ISBN
723:ῥέος
703:OCLC
693:ISBN
279:and
265:iron
218:and
180:The
872:doi
685:doi
646:doi
511:5 A
509:or
507:1 A
354:or
290:RMS
66:or
27:An
1245::
954::
952:}}
948:{{
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909:.
866:.
862:.
828:.
760:^
746:;
742:;
738:.
728:,
701:.
691:.
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652:.
642:15
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333:.
222:.
207:.
155:.
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874::
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687::
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648::
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