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instrument can be used, since its sensitivity need not be high, and the input resistance can be made high, reducing the current drawn from the circuit under test. Amplified voltmeters often have an input resistance of 1, 10, or 20 megohms which is independent of the range selected. A once-popular form of this instrument used a vacuum tube in the amplifier circuit and so was called the vacuum tube voltmeter (VTVM). These were almost always powered by the local AC line current and so were not particularly portable. Today these circuits use a solid-state amplifier using
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multiplying by a constant factor. Early "true RMS" circuits used a thermal converter that responded only to the RMS value of the waveform. Modern instruments calculate the RMS value by electronically calculating the square of the input value, taking the average, and then calculating the square root of the value. This allows accurate RMS measurements for a variety of waveforms.
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DVM measurement accuracy is affected by many factors, including temperature, input impedance, and DVM power supply voltage variations. Less expensive DVMs often have input resistance on the order of 10 MΩ. Precision DVMs can have input resistances of 1 GΩ or higher for the lower voltage ranges (e.g.
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with the instrument. The galvanometer has a coil of fine wire suspended in a strong magnetic field. When an electric current is applied, the interaction of the magnetic field of the coil and of the stationary magnet creates a torque, tending to make the coil rotate. The torque is proportional to the
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General-purpose analog voltmeters may have an accuracy of a few percent of full scale and are used with voltages from a fraction of a volt to several thousand volts. Digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies,
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Most VTVMs and FET-VMs handle DC voltage, AC voltage, and resistance measurements; modern FET-VMs add current measurements and often other functions as well. A specialized form of the VTVM or FET-VM is the AC voltmeter. These instruments are optimized for measuring AC voltage. They have much wider
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The sensitivity of such a meter can be expressed as "ohms per volt", the number of ohms resistance in the meter circuit divided by the full scale measured value. For example, a meter with a sensitivity of 1000 ohms per volt would draw 1 milliampere at full scale voltage; if the full scale was 200
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value of the waveform, assuming a fixed relation between the average value of the rectified waveform and the RMS value. If the waveform departs significantly from the sinewave assumed in the calibration, the meter will be inaccurate, though for simple wave shapes the reading can be corrected by
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The sensitivity and input resistance of a voltmeter can be increased if the current required to deflect the meter pointer is supplied by an amplifier and power supply instead of by the circuit under test. The electronic amplifier between input and meter gives two benefits; a rugged moving coil
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Voltmeters are made in a wide range of styles, some separately powered (e.g. by battery), and others powered by the measured voltage source itself. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus. Portable instruments, usually equipped to also
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One of the design objectives of the instrument is to disturb the circuit as little as possible and so the instrument should draw a minimum of current to operate. This is achieved by using a sensitive galvanometer in series with a high resistance, and then the entire instrument is connected in
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are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant.
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current through the coil. The coil rotates, compressing a spring that opposes the rotation. The deflection of the coil is thus proportional to the current, which in turn is proportional to the applied voltage, which is indicated by a pointer on a scale.
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use the mutual repulsion between two charged plates to deflect a pointer attached to a spring. Meters of this type draw negligible current but are sensitive to voltages over about 100 volts and work with either alternating or direct current.
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in the circuit so that the coil deflects in only one direction. Some moving-coil instruments are also made with the zero position in the middle of the scale instead of at one end; these are useful if the voltage reverses its polarity.
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with laboratory instruments capable of measuring to accuracies of a few parts per million. Part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. In laboratories, the
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ohms and at full scale, the meter would draw 1 milliampere from the circuit under test. For multi-range instruments, the input resistance varies as the instrument is switched to different ranges.
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502:(DVM) measures an unknown input voltage by converting the voltage to a digital value and then displays the voltage in numeric form. DVMs are usually designed around a special type of
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Simple AC voltmeters use a rectifier connected to a DC measurement circuit, which responds to the average value of the waveform. The meter can be calibrated to display the
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less than 20 V). To ensure that a DVM's accuracy is within the manufacturer's specified tolerances, it must be periodically calibrated against a
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as well as in bench and laboratory instruments. These largely replaced non-amplified multimeters except in the least expensive price ranges.
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Moving-coil instruments with a permanent-magnet field respond only to direct current. Measurement of AC voltage requires a
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is used as a standard voltage for precision work. Precision voltage references are available based on electronic circuits.
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can measure tiny voltages of microvolts or less. Digital voltmeters give a numerical display of voltage by use of an
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Analog voltmeters move a pointer across a scale in proportion to the voltage measured and can be built from a
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in a circle, with two emerging lines representing the two points of measurement.
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Two digital voltmeters. Note the 40 microvolt difference between the two
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bandwidth and better sensitivity than a typical multifunction device.
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In circuit diagrams, a voltmeter is represented by the letter
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volts, the resistance at the instrument's terminals would be
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The first digital voltmeter was invented and produced by
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so that it takes negligible current from the circuit.
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N and S are the north and south poles of the magnet.
202:. Unsourced material may be challenged and removed.
97:. Unsourced material may be challenged and removed.
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400:The red wire carries the current to be measured.
343:measure current and resistance in the form of a
182:An editor has performed a search and found that
627:"Andrew Kay, Pioneer in Computing, Dies at 95"
732:Electrical and electronic measuring equipment
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556:Class of accuracy in electrical measurements
529:of Non-Linear Systems (and later founder of
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417:can be used as a voltmeter by inserting a
280:Learn how and when to remove this message
262:Learn how and when to remove this message
157:Learn how and when to remove this message
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688:Lessons In Electric Circuits Vol 1 DC
16:Instrument used for measuring voltage
591:Potentiometer (measuring instrument)
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430:parallel with the circuit examined.
308:difference between two points in an
304:is an instrument used for measuring
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296:Demonstration analog voltmeter
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928:Arbitrary waveform generator
831:Transformer ratio arm bridge
694:Lessons In Electric Circuits
625:Markoff, John (5 Sep 2014).
452:Voltmeters operating on the
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504:analog-to-digital converter
337:analog-to-digital converter
188:to establish the subject's
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984:Electronic test equipment
933:Digital pattern generator
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826:Time-to-digital converter
821:Time-domain reflectometer
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571:Electronic test equipment
468:field-effect transistors
316:. It usually has a high
185:sufficient sources exist
19:Not to be confused with
561:Electrical measurements
454:electrostatic principle
953:Video-signal generator
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312:. It is connected in
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979:Measuring instruments
781:Microwave power meter
653:"What is RMS Voltage"
508:integrating converter
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806:Peak programme meter
682:DC Metering Circuits
606:Measurement category
196:improve this article
91:improve this article
472:digital multimeters
461:Amplified voltmeter
938:Function generator
596:Solenoid voltmeter
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306:electric potential
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974:Electrical meters
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897:Spectrum analyzer
836:Transistor tester
766:Frequency counter
761:Electricity meter
751:Capacitance meter
500:digital voltmeter
482:Digital voltmeter
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360:Schematic symbol
310:electric circuit
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887:Oscilloscope
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661:. Retrieved
659:. 2021-06-21
657:Electrical4U
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635:. Retrieved
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518:such as the
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84:verification
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907:Vectorscope
841:Tube tester
811:Psophometer
791:Megohmmeter
637:7 September
533:) in 1954.
520:Weston cell
354:Weston cell
327:and series
211:"Voltmeter"
106:"Voltmeter"
989:Voltmeters
968:Categories
921:Generation
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801:Peak meter
786:Multimeter
663:2023-04-23
612:References
581:Multimeter
527:Andrew Kay
506:called an
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318:resistance
222:newspapers
190:notability
147:April 2009
117:newspapers
46:improve it
21:Voltameter
851:Voltmeter
846:Wattmeter
776:LCR meter
576:Metrology
446:rectifier
302:voltmeter
52:talk page
865:Analysis
856:VU meter
796:Ohmmeter
739:Metering
631:Obituary
586:Ohmmeter
545:See also
419:resistor
329:resistor
314:parallel
816:Q meter
746:Ammeter
697:series.
551:Ammeter
392:of the
236:scholar
131:scholar
531:Kaypro
423:series
396:type.
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215:news
110:news
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