441:
power is low, rather than high). The difficulty is largely due to difficulty in accurate measurement of the alternating current, rather than voltage, and the relatively little need for low-power measurements. The specification for the meter should specify the reading error for different situations. For a typical plug-in meter the error in wattage is stated as ±5% of measured value ±10 W (e.g. a measured value of 100 W may be wrong by 5% of 100 W plus 10 W, i.e., ±15 W, or 85–115 W); and the error in kW·h is stated as ±5% of measured value ±0.1 kW·h. If a laptop computer in sleep mode consumes 5 W, the meter may read anything from 0 to 15.25 W, without taking into account errors due to non-sinusoidal waveform. In practice accuracy can be improved by connecting a fixed load such as an incandescent light bulb, adding the device in standby, and using the difference in power consumption. This moves the measurement out of the problematic low-power zone.
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412:(VA) is the power factor. A computer circuit uses the sampled values to calculate RMS voltage, RMS current, VA, power (watts), power factor, and kilowatt-hours. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted to other equipment for further use. Wattmeters vary considerably in correctly calculating energy consumption, especially when real power is much lower than VA (highly
135:
440:
There are limitations to measuring power with inexpensive wattmeters, or indeed with any meters not designed for low-power measurements. This particularly affects low power (e.g. under 10 watts), as used in standby; readings may be so inaccurate as to be useless (although they do confirm that standby
477:
power sensor converts incident radio frequency power to heat. The sensor element is maintained at a constant temperature by a small direct current. The reduction in current required to maintain temperature is related to the incident RF power. Instruments of this type are used throughout the RF
407:
A modern digital wattmeter samples the voltage and current thousands of times a second. For each sample, the voltage is multiplied by the current at the same instant; the average over at least one cycle is the real power. The real power divided by the apparent
229:
In 1974 Maghar S. Chana, Ramond L. Kraley, Eric A. Hauptmann Barry, and M. Pressman patented an early electronic wattmeter. This device is made up of power, current and voltage transformers, which measure the average power.
514:
is essentially a wattmeter which integrates the power over time (essentially multiplies the power by elapsed time). Digital electronic instruments measure many parameters and can be used where a wattmeter is needed:
640:
Data listed in text from manual for inexpensive plug-in electricity meter
Brennenstuhl PM230. The lowest measurable current is given as 0.02 A, which corresponds to about 5 W at 230 VAC
788:
598:
781:
399:
Electronic wattmeters are used for direct, small power measurements or for power measurements at frequencies beyond the range of electrodynamometer-type instruments.
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around the coil. The strength of this field is proportional to the line current and in phase with it. The potential coil has, as a general rule, a high-value
797:
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wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. A current flowing through the current coil generates an
465:
detectors are either directly connected to the source, or used with a sampling system that diverts only a portion of the RF power through the detector.
387:
Siemens electrodynamometer, circa 1910, F = Fixed coil, D = Movable coil, S = Spiral spring, T = Torsion head, M = Mercury cups, I = Index needle
691:
473:
are used to measure heat produced by RF power and can be calibrated either directly or by comparison with a known reference source of power. A
432:
may be very far from sinusoidal, leading to unknown and possibly large errors at any power. This may not be specified in the meter's manual.
740:
745:
523:, apparent instantaneous power, actual power, power factor, energy in W·h over a period of time, and cost of electricity consumed.
662:
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Instruments with moving coils can be calibrated for direct current or power frequency currents up to a few hundred hertz. At
100:
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Prodigit Model 2000MU (UK version), shown in use and displaying a reading of 10 watts being consumed by the appliance
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which shows that the power transmitted may be less than the apparent power obtained by multiplying the readings of a
119:
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circuit the deflection is proportional to the average instantaneous product of voltage and current, thus measuring
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with positive reference polarity at the ± terminal with respect to the other terminal of the potential coil, and
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is the current with reference direction flowing into the ± terminal of the current coil. The wattmeter reads
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and audio frequency power; other types are required for radio frequency measurements.
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spectrum and can even measure visible light power. For high-power measurements, a
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OpenWay wattmeter with two-way communications for remote reading, in use by
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Early wattmeter on display at the
Historic Archive and Museum of Mining in
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connected in series with it to reduce the current that flows through it.
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420:). Simple meters may be calibrated to meet specified accuracy only for
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616:"US Lawrence Livermore laboratory, Standby Power, Measuring Standby"
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This article incorporates text from a publication now in the
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296:(DC) circuit, the deflection of the needle is proportional to
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749:. Vol. 28 (11th ed.). Cambridge University Press.
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with the circuit, while the potential coil is connected in
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and φ is the angle by which the current lags the voltage.
568:
Close, Charles M. (1966). "Chapter 8: Power and Energy".
162:. Electromagnetic wattmeters are used for measurement of
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254:instrument. The device consists of a pair of fixed
169:A wattmeter reads the average value of the product
60:. Unsourced material may be challenged and removed.
510:An instrument which measures electrical energy in
643:
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682:Rebuldela, Gregorio; Jargon, Jeffery A. (1992).
681:
692:National Institute of Standards and Technology
193:, which in sinusoidal steady-state reduces to
798:Electrical and electronic measuring equipment
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684:"High Power CW Wattmeter Calibration at NIST"
482:directly measures heat produced by RF power.
457:circuit arranged to respond to current in a
292:The result of this arrangement is that on a
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120:Learn how and when to remove this message
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250:The traditional analog wattmeter is an
150:(or the average of the rate of flow of
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58:adding citations to reliable sources
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316:), thus conforming to the equation
269:The current coils are connected in
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27:Device that measures electric power
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570:The Analysis of Linear Circuits
45:needs additional citations for
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688:J Res Natl Inst Stand Technol
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994:Arbitrary waveform generator
897:Transformer ratio arm bridge
761:Lessons in Electric Circuits
657:. Newnes. pp. 351–370.
596:, "Electronic Wattmeter"
426:switched-mode power supplies
7:
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226:patented his AC wattmeter.
10:
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655:RF Components and Circuits
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453:(RF) a common method is a
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1050:Electronic test equipment
999:Digital pattern generator
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892:Time-to-digital converter
887:Time-domain reflectometer
804:
424:waveforms. Waveforms for
653:Carr, Joseph J. (2002).
746:Encyclopædia Britannica
1019:Video-signal generator
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436:Precision and accuracy
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847:Microwave power meter
549:Microwave power meter
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375:in the same circuit.
283:electromagnetic field
241:
148:electric active power
137:
872:Peak programme meter
756:DC Metering Circuits
701:10.6028/jres.097.031
430:electronic equipment
54:improve this article
622:on 22 December 2017
1045:Electricity meters
1004:Function generator
541:Electronics portal
508:
397:
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18:Electrodynamometer
1040:Electrical meters
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963:Spectrum analyzer
902:Transistor tester
832:Frequency counter
827:Electricity meter
817:Capacitance meter
664:978-0-7506-4844-8
492:Electricity meter
459:transmission line
451:radio frequencies
428:as used for much
210:is the period of
164:utility frequency
152:electrical energy
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16:(Redirected from
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676:Further reading
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110:December 2016
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65:Find sources:
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43:This article
41:
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32:
31:
19:
953:Oscilloscope
938:Bus analyzer
911:
837:Galvanometer
760:
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694:): 673–686.
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626:21 September
624:. Retrieved
620:the original
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416:loads, e.g.
410:volt-amperes
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365:power factor
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359:. Here, cos
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52:Please help
47:verification
44:
973:Vectorscope
907:Tube tester
877:Psophometer
857:Megohmmeter
594:US 3959724A
480:calorimeter
467:Thermistors
337:capacitance
277:. Also, on
258:, known as
224:Ottó Bláthy
191:v(t)i(t) dt
187:P = (1/T) ∫
69:"Wattmeter"
1034:Categories
987:Generation
978:Videoscope
867:Peak meter
852:Multimeter
555:References
512:watt hours
505:DTE Energy
422:sinusoidal
379:Electronic
333:inductance
80:newspapers
917:Voltmeter
912:Wattmeter
842:LCR meter
741:Wattmeter
475:bolometer
455:rectifier
369:voltmeter
144:wattmeter
138:Wattmeter
931:Analysis
922:VU meter
862:Ohmmeter
805:Metering
710:28053451
527:See also
414:reactive
339:. On an
329:AC power
287:resistor
275:parallel
246:, Mexico
173:, where
882:Q meter
812:Ammeter
734::
521:amperes
403:Digital
373:ammeter
302:current
244:Pachuca
218:History
179:voltage
177:is the
160:circuit
94:scholar
763:series
728:
708:
661:
600:
576:
279:analog
271:series
96:
89:
82:
75:
67:
517:volts
501:Itron
463:Diode
256:coils
156:watts
154:) in
101:JSTOR
87:books
706:PMID
659:ISBN
628:2011
574:ISBN
469:and
371:and
355:cos
327:For
300:the
298:both
212:p(t)
183:i(t)
175:v(t)
142:The
73:news
743:".
696:doi
335:or
310:and
204:rms
198:rms
56:by
1036::
704:.
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645:^
607:^
353:VI
347:,
341:AC
324:.
322:VI
308:)
266:.
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783:t
776:v
712:.
698::
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667:.
630:.
582:.
361:φ
357:φ
351:=
349:P
320:=
318:P
314:V
306:I
304:(
208:T
201:I
195:V
189:0
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117:(
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108:(
98:·
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