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Home / What Is a Normal Reading on a Multimeter for a 12 Volt Battery

What Is a Normal Reading on a Multimeter for a 12 Volt Battery

Electronic measuring instrument that combines several measurement functions in one unit

An analog multimeter, the Sanwa YX360TRF

A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter tin can mensurate voltage, resistance, and current, in which case it is besides known as a volt-ohm-milliammeter (VOM), as the unit is equipped with voltmeter, ammeter, and ohmmeter functionality. Some feature the measurement of additional properties such equally temperature and book.

Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters (DMM, DVOM) have numeric displays and have made analog multimeters virtually obsolete as they are cheaper, more precise, and more than physically robust than analog multimeters.

Multimeters vary in size, features, and price. They can be portable handheld devices or highly-precise bench instruments. Inexpensive multimeters tin can cost nether US$ten, while laboratory-form models with certified calibration can toll over Us$5,000.

History [edit]

The starting time moving-pointer current-detecting device was the galvanometer in 1820. These were used to measure resistance and voltage past using a Wheatstone bridge, and comparison the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very wearisome and impractical in the field. These galvanometers were beefy and delicate.

The D'Arsonval–Weston meter movement uses a moving coil which carries a pointer and rotates on pivots or a taut band ligament. The roll rotates in a permanent magnetic field and is restrained by fine spiral springs which as well 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 bones moving coil meter is suitable only for direct current measurements, usually in the range of x μA to 100 mA. It is hands adapted to read heavier currents past using shunts (resistances in parallel with the basic move) or to read voltage using series resistances known as multipliers. To read alternate currents or voltages, a rectifier is needed. One of the earliest suitable rectifiers was the copper oxide rectifier adult and manufactured by Union Switch & Point Visitor, Swissvale, Pennsylvania, afterward function of Westinghouse Brake and Signal Company, from 1927.[1]

The start attested usage of the word "multimeter" listed past the Oxford English language Dictionary is from 1907.[2]

The invention of the first multimeter is attributed to British Post Role engineer, Donald Macadie, who became dissatisfied with the need to carry many dissever instruments required for maintenance of telecommunications circuits.[3] Macadie invented an instrument which could measure amperes (amps), volts and ohms, and so the multifunctional meter was and then named Avometer.[4] The meter comprised a moving ringlet meter, voltage and precision resistors, and switches and sockets to select the range.

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 past MacAdie. Although a shareholder of ACWEECO, Mr MacAdie connected to work for the Post Office until his retirement in 1933. His son, Hugh S. MacAdie, joined ACWEECO in 1927 and became Technical Managing director.[five] [6] [iv] The commencement AVO was put on sale in 1923, and many of its features remained almost unaltered through to the final Model viii.

General properties of multimeters [edit]

Any meter will load the circuit nether examination to some extent. For instance, a multimeter using a moving roll motility with full-scale deflection current of 50 microamps (μA), the highest sensitivity commonly available, must draw at least fifty μA from the circuit nether test for the meter to attain the top end of its calibration. This may load a high-impedance circuit so much as to affect the excursion, thereby giving a depression reading. The full-scale deflection current may also be expressed in terms of "ohms per volt" (Ω/5). The ohms per volt figure is often called the "sensitivity" of the musical instrument. Thus a meter with a 50 μA motion will take a "sensitivity" of twenty,000 Ω/Five. "Per volt" refers to the fact that the impedance the meter presents to the circuit nether test volition be twenty,000 Ω multiplied by the full-scale voltage to which the meter is set. For example, if the meter is set to a range of 300 V full scale, the meter's impedance will be six MΩ. 20,000 Ω/V is the all-time (highest) sensitivity available for typical analog multimeters that lack internal amplifiers. For meters that practise have internal amplifiers (VTVMs, FETVMs, etc.), the input impedance is stock-still by the amplifier circuit.

Avometer [edit]

The first Avometer had a sensitivity of 60 Ω/Five, 3 direct current ranges (12 mA, 1.ii A, and 12 A), three directly voltage ranges (12, 120, and 600 V or optionally 1,200 V), and a ten,000 Ω resistance range. An improved version of 1927 increased this to 13 ranges and 166.6 Ω/V (6 mA) movement. A "Universal" version having additional alternate current and alternating voltage ranges was offered from 1933 and in 1936 the dual-sensitivity Avometer Model 7 offered 500 and 100 Ω/V.[7] Between the mid 1930s until the 1950s, i,000 Ω/5 became a de facto standard of sensitivity for radio work and this effigy was oftentimes quoted on service sheets. However, some manufacturers such as Simpson, Triplett and Weston, all in the USA, produced 20,000 Ω/5 VOMs before the Second Globe War and some of these were exported. Later 1945–46, 20,000 Ω/V became the expected standard for electronics, but some makers offered even more sensitive instruments. For industrial and other "heavy-current" use depression sensitivity multimeters continued to exist produced and these were considered more than robust than the more sensitive types.

High-quality analog (analogue) multimeters go along to be made by several manufacturers, including Chauvin Arnoux (France), Gossen Metrawatt (Federal republic of germany), and Simpson and Triplett (USA).

Pocket lookout meters [edit]

Pocket-spotter-fashion meters were in widespread use in the 1920s. The metal case was typically continued to the negative connection, an arrangement that caused numerous electric shocks. The technical specifications of these devices were often crude, for example the i illustrated has a resistance of just 33 Ω/V, a not-linear scale and no zero adjustment.

Vacuum tube voltmeters [edit]

Vacuum tube voltmeters or valve voltmeters (VTVM, VVM) were used for voltage measurements in electronic circuits where high input impedance was necessary. The VTVM had a fixed input impedance of typically 1 MΩ or more, ordinarily through use of a cathode follower input excursion, and thus did non significantly load the excursion existence tested. VTVMs were used earlier the introduction of electronic loftier-impedance analog transistor and field effect transistor voltmeters (FETVOMs). Modern digital meters (DVMs) and some modern analog meters likewise utilise electronic input circuitry to reach high input impedance—their voltage ranges are functionally equivalent to VTVMs. The input impedance of some poorly designed DVMs (peculiarly some early designs) would vary over the course of a sample-and-hold internal measurement bike, causing disturbances to some sensitive circuits under test.

Additional scales [edit]

Additional scales such equally decibels, and measurement functions such as capacitance, transistor gain, frequency, duty cycle, display hold, and continuity which sounds a buzzer when the measured resistance is modest accept been included on many multimeters. While multimeters may exist supplemented by more specialized equipment in a technician'due south toolkit, some multimeters include additional functions for specialized applications (temperature with a thermocouple probe, inductance, connectivity to a computer, speaking measured value, etc.).

Operation [edit]

A 4+ 1⁄2 -digit digital multimeter, the Fluke 87V

A multimeter is the combination of a DC voltmeter, Ac voltmeter, ammeter, and ohmmeter. An un-amplified analog multimeter combines a meter motion, range resistors and switches; VTVMs are amplified analog meters and contain active circuitry.

For an analog meter movement, DC voltage is measured with a serial resistor connected between the meter movement and the circuit nether test. A switch (usually rotary) allows greater resistance to be inserted in series with the meter movement to read higher voltages. The product of the basic full-calibration deflection electric current of the motility, and the sum of the series resistance and the movement'southward own resistance, gives the total-calibration voltage of the range. As an instance, a meter movement that required 1 mA for full-calibration deflection, with an internal resistance of 500 Ω, would, on a 10 5 range of the multimeter, have ix,500 Ω of series resistance.[8]

For analog current ranges, matched low-resistance shunts are connected in parallel with the meter movement to divert most of the current effectually the coil. Again for the example of a hypothetical 1 mA, 500 Ω movement on a i A range, the shunt resistance would exist just over 0.v Ω.

Moving curlicue instruments tin respond only to the average value of the electric current through them. To measure alternating current, which changes up and down repeatedly, a rectifier is inserted in the circuit so that each negative half bicycle is inverted; the result is a varying and nonzero DC voltage whose maximum value will be half the AC peak to peak voltage, assuming a symmetrical waveform. Since the rectified average value and the root mean square (RMS) value of a waveform are merely the same for a foursquare wave, unproblematic rectifier-blazon circuits tin only be calibrated for sinusoidal waveforms. Other moving ridge shapes require a dissimilar calibration factor to relate RMS and boilerplate value. This type of excursion normally has adequately limited frequency range. Since practical rectifiers take non-zippo voltage drop, accuracy and sensitivity is poor at low AC voltage values.[nine]

To measure out resistance, switches arrange for a pocket-size battery within the instrument to pass a electric current through the device under test and the meter roll. Since the current available depends on the state of charge of the bombardment which changes over fourth dimension, a multimeter normally has an adjustment for the ohm calibration to zero it. In the usual circuits institute in analog multimeters, the meter deflection is inversely proportional to the resistance, and then full-calibration will be 0 Ω, and higher resistance will correspond to smaller deflections. The ohms scale is compressed, and then resolution is improve at lower resistance values.

Amplified instruments simplify the pattern of the series and shunt resistor networks. The internal resistance of the gyre is decoupled from the selection of the series and shunt range resistors; the series network thus becomes a voltage divider. Where Ac measurements are required, the rectifier can exist placed later on the amplifier phase, improving precision at low range.

Digital instruments, which necessarily comprise amplifiers, use the same principles every bit analog instruments for resistance readings. For resistance measurements, commonly a modest abiding current is passed through the device under exam and the digital multimeter reads the resultant voltage drib; this eliminates the calibration compression found in analog meters, merely requires a source of precise electric current. An autoranging digital multimeter can automatically adjust the scaling network so the measurement circuits use the full precision of the A/D converter.

In all types of multimeters, the quality of the switching elements is critical to stable and accurate measurements. The best DMMs apply gold plated contacts in their switches; less expensive meters use nickel plating or none at all, relying on printed excursion board solder traces for the contacts. Accuracy and stability (e.g., temperature variation, or aging, or voltage/current history) of a meter's internal resistors (and other components) is a limiting cistron in long-term accuracy and precision of the instrument.

Measured values [edit]

Contemporary multimeters can measure many values. The most common are:

  • Voltage, alternating and direct, in volts.
  • Electric current, alternating and direct, in amperes.
The frequency range for which Ac measurements are accurate is important, depends on the circuitry design and construction, and should exist specified, so users tin can evaluate the readings they take. Some meters mensurate currents as low as milliamps or even microamps. All meters take a burden voltage (caused by the combination of the shunt used and the meter's circuit design), and some (even expensive ones) have sufficiently high burden voltages that low current readings are seriously impaired. Meter specifications should include the burden voltage of the meter.
  • Resistance in ohms.

Additionally, some multimeters also measure:

  • Capacitance in farads, merely unremarkably the limitations of the range are between a few hundred or thousand micro farads and a few pico farads. Very few general purpose multimeters can measure other important aspects of capacitor status such every bit ESR, dissipation factor, or leakage.
  • Conductance in siemens, which is the inverse of the resistance measured.
  • Decibels in circuitry, rarely in sound.
  • Duty bicycle as a per centum.
  • Frequency in hertz.
  • Inductance in henries. Like capacitance measurement, this is commonly better handled by a purpose designed inductance / capacitance meter.
  • Temperature in degrees Celsius or Fahrenheit, with an appropriate temperature test probe, often a thermocouple.

Digital multimeters may also include circuits for:

  • Continuity tester; a cablegram sounds when a circuit's resistance is low enough (just how low is enough varies from meter to meter), so the test must exist treated as inexact.
  • Diodes (measuring forward driblet of diode junctions).
  • Transistors (measuring current gain and other parameters in some kinds of transistors)
  • Bombardment checking for simple one.5 V and ix V batteries. This is a current-loaded measurement, which simulates in-use bombardment loads; normal voltage ranges draw very trivial current from the battery.

Various sensors can be attached to (or included in) multimeters to have measurements such every bit:

  • calorie-free level
  • sound pressure level level
  • acidity/alkalinity(pH)
  • relative humidity
  • very small electric current flow (downwards to nanoamps with some adapters)
  • very small resistances (downward to micro ohms for some adapters)
  • large currents – adapters are available which use inductance (AC current but) or Hall outcome sensors (both AC and DC electric current), usually through insulated clench jaws to avoid direct contact with high electric current capacity circuits which tin exist unsafe, to the meter and to the operator
  • very high voltages – adapters are available which grade a voltage divider with the meter's internal resistance, allowing measurement into the thousands of volts. Notwithstanding, very loftier voltages oft have surprising beliefs, aside from effects on the operator (perhaps fatal); high voltages which actually reach a meter'due south internal circuitry may internal harm parts, perhaps destroying the meter or permanently ruining its performance.

Resolution [edit]

Resolution and accuracy [edit]

The resolution of a multimeter is the smallest function of the scale which can be shown, which is scale dependent. On some digital multimeters it can be configured, with college resolution measurements taking longer to complete. For example, a multimeter that has a one mV resolution on a 10 5 scale can show changes in measurements in i mV increments.

Absolute accuracy is the error of the measurement compared to a perfect measurement. Relative accuracy is the error of the measurement compared to the device used to calibrate the multimeter. Most multimeter datasheets provide relative accuracy. To compute the absolute accurateness from the relative accuracy of a multimeter add together the accented accuracy of the device used to calibrate the multimeter to the relative accuracy of the multimeter.[10]

Digital [edit]

The resolution of a multimeter is often specified in the number of decimal digits resolved and displayed. If the most significant digit cannot take all values from 0 to nine information technology is generally, and confusingly, termed a fractional digit. For case, a multimeter which tin read upward to 19999 (plus an embedded decimal point) is said to read 4+ 1⁄ii digits.

By convention, if the most significant digit tin be either 0 or 1, it is termed a half-digit; if it can take higher values without reaching 9 (frequently three or v), it may be chosen three-quarters of a digit. A 5+ 1⁄ii -digit multimeter would brandish ane "half digit" that could but display 0 or ane, followed by five digits taking all values from 0 to nine.[eleven] Such a meter could show positive or negative values from 0 to 199999. A 3+ three⁄4 -digit meter can display a quantity from 0 to 3999 or 5999, depending on the manufacturer.

While a digital display can easily be extended in resolution, the extra digits are of no value if not accompanied past care in the design and scale of the analog portions of the multimeter. Meaningful (i.due east., high-accuracy) measurements crave a good agreement of the instrument specifications, adept command of the measurement conditions, and traceability of the calibration of the instrument. However, even if its resolution exceeds the accuracy, a meter can be useful for comparison measurements. For example, a meter reading 5+ ane⁄2 stable digits may indicate that one nominally 100 kΩ resistor is nearly vii Ω greater than another, although the fault of each measurement is 0.2% of reading plus 0.05% of total-calibration value.

Specifying "display counts" is some other mode to specify the resolution. Display counts requite the largest number, or the largest number plus 1 (to include the brandish of all zeros) the multimeter'south display tin show, ignoring the decimal separator. For instance, a 5+ 1⁄2 -digit multimeter tin can also be specified as a 199999 brandish count or 200000 display count multimeter. Frequently the display count is just called the 'count' in multimeter specifications.

The accuracy of a digital multimeter may exist stated in a two-term grade, such as "±1% of reading +2 counts", reflecting the unlike sources of error in the musical instrument.[12]

Analog [edit]

Display face of an analog multimeter

Analog meters are older designs, just despite being technically surpassed by digital meters with bargraphs, may still exist preferred[ according to whom? ] by engineers[ which? ] and troubleshooters.[ original research? ] Ane reason given is that analog meters are more than sensitive (or responsive) to changes in the circuit that is being measured.[ citation needed ] A digital multimeter samples the quantity being measured over time, and and then displays information technology. Analog multimeters continuously read the test value. If in that location are slight changes in readings, the needle of an analog multimeter will effort to track it, as opposed to the digital meter having to await until the next sample, giving delays betwixt each discontinuous reading (plus the digital meter may additionally require settling time to converge on the value). The digital brandish value as opposed to an analog display is subjectively more than difficult to read. This continuous tracking feature becomes important when testing capacitors or coils, for example. A properly operation capacitor should permit current to flow when voltage is applied, then the electric current slowly decreases to zero and this "signature" is easy to see on an analog multimeter merely not on a digital multimeter. This is similar when testing a coil, except the current starts depression and increases.

Resistance measurements on an analog meter, in particular, can exist of depression precision due to the typical resistance measurement circuit which compresses the calibration heavily at the higher resistance values. Inexpensive analog meters may take just a single resistance scale, seriously restricting the range of precise measurements. Typically, an analog meter will have a panel aligning to set the zero-ohms calibration of the meter, to compensate for the varying voltage of the meter battery, and the resistance of the meter'southward test leads.

Accurateness [edit]

Digital multimeters generally take measurements with accuracy superior to their analog counterparts. Standard analog multimeters mensurate with typically ±3% accurateness,[thirteen] though instruments of higher accuracy are made. Standard portable digital multimeters are specified to have an accurateness of typically ±0.five% on the DC voltage ranges. Mainstream demote-top multimeters are available with specified accuracy of better than ±0.01%. Laboratory grade instruments can have accuracies of a few parts per 1000000.[14]

Accuracy figures need to be interpreted with care. The accuracy of an analog instrument usually refers to full-scale deflection; a measurement of 30 V on the 100 Five scale of a iii% meter is subject to an mistake of 3 Five, 10% of the reading. Digital meters usually specify accuracy as a percentage of reading plus a percentage of total-scale value, sometimes expressed in counts rather than percent terms.

Quoted accuracy is specified as being that of the lower millivolt (mV) DC range, and is known as the "basic DC volts accurateness" figure. Higher DC voltage ranges, current, resistance, Air conditioning and other ranges will ordinarily have a lower accuracy than the bones DC volts figure. Air conditioning measurements only meet specified accuracy within a specified range of frequencies.

Manufacturers tin can provide calibration services so that new meters may exist purchased with a certificate of calibration indicating the meter has been adjusted to standards traceable to, for example, the US National Institute of Standards and Technology (NIST), or other national standards organisation.

Exam equipment tends to drift out of calibration over time, and the specified accuracy cannot be relied upon indefinitely. For more expensive equipment, manufacturers and tertiary parties provide calibration services so that older equipment may be recalibrated and recertified. The cost of such services is asymmetric for cheap equipment; however extreme accuracy is not required for most routine testing. Multimeters used for critical measurements may be role of a metrology plan to clinch calibration.

A multimeter can be causeless to be "boilerplate responding" to AC waveforms unless stated every bit existence a "truthful RMS" blazon. An average responding multimeter will just run across its specified accuracy on AC volts and amps for purely sinusoidal waveforms. A Truthful RMS responding multimeter on the other paw volition meet its specified accurateness on AC volts and electric current with any waveform blazon up to a specified crest factor; RMS operation is sometimes claimed for meters which report accurate RMS readings merely at certain frequencies (commonly low) and with certain waveforms (essentially always sine waves).

A meter's AC voltage and current accurateness may have unlike specifications at different frequencies.

Sensitivity and input impedance [edit]

When used for measuring voltage, the input impedance of the multimeter must be very loftier compared to the impedance of the circuit being measured; otherwise circuit operation may be affected and the reading volition be inaccurate.

Meters with electronic amplifiers (all digital multimeters and some analog meters) have a fixed input impedance that is high plenty not to disturb almost circuits. This is frequently either one or x megohms; the standardization of the input resistance allows the use of external high-resistance probes which course a voltage divider with the input resistance to extend voltage range up to tens of thousands of volts. Loftier-end multimeters generally provide an input impedance greater than x GΩ for ranges less than or equal to 10 V. Some loftier-end multimeters provide >x Gigaohms of impedance to ranges greater than 10 V.[10]

Near analog multimeters of the moving-pointer blazon are unbuffered, and depict electric current from the circuit under test to deflect the meter pointer. The impedance of the meter varies depending on the basic sensitivity of the meter motility and the range which is selected. For case, a meter with a typical 20,000 Ω/Five sensitivity will have an input resistance of 2 MΩ on the 100 V range (100 Five × 20,000 Ω/V = 2,000,000 Ω). On every range, at total-scale voltage of the range, the full electric current required to deflect the meter movement is taken from the excursion under test. Lower sensitivity meter movements are acceptable for testing in circuits where source impedances are low compared to the meter impedance, for instance, power circuits; these meters are more rugged mechanically. Some measurements in indicate circuits crave higher sensitivity movements so as not to load the excursion under examination with the meter impedance.[15] [16]

Sensitivity should not be confused with resolution of a meter, which is divers equally the lowest signal change (voltage, current, resistance and so on) that can change the observed reading.[xvi]

For general-purpose digital multimeters, the everyman voltage range is typically several hundred millivolts AC or DC, but the lowest current range may be several hundred microamperes, although instruments with greater current sensitivity are available. Multimeters designed for (mains) "electrical" use instead of general electronics engineering use volition typically forego the microamps current ranges.

Measurement of low resistance requires lead resistance (measured by touching the test probes together) to exist subtracted for all-time accuracy. This can exist washed with the "delta", "aught", or "null" feature of many digital multimeters. Contact pressure to the device nether exam and cleanliness of the surfaces tin affect measurements of very low resistances. Some meters offering a four wire test where two probes supply the source voltage and the others take measurement. Using a very high impedance allows for very depression voltage drop in the probes and resistance of the source probes is ignored resulting in very accurate results.

The upper end of multimeter measurement ranges varies considerably; measurements over mayhap 600 volts, x amperes, or 100 megohms may require a specialized test musical instrument.

Burden voltage [edit]

Every inline serial-continued ammeter, including a multimeter in a current range, has a certain resistance. Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it. The voltage drib is known as the burden voltage, specified in volts per ampere. The value tin can change depending on the range the meter sets, since different ranges usually use different shunt resistors.[17]

The brunt voltage can be pregnant in very low-voltage circuit areas. To bank check for its consequence on accuracy and on external circuit functioning the meter can be switched to unlike ranges; the current reading should be the same and excursion operation should not be affected if brunt voltage is not a problem. If this voltage is pregnant it tin can be reduced (likewise reducing the inherent accuracy and precision of the measurement) by using a higher current range.

Alternate current sensing [edit]

Since the basic indicator arrangement in either an analog or digital meter responds to DC only, a multimeter includes an AC to DC conversion circuit for making alternate current measurements. Basic meters utilize a rectifier circuit to measure the average or peak absolute value of the voltage, but are calibrated to testify the calculated root mean foursquare (RMS) value for a sinusoidal waveform; this volition give correct readings for alternating current as used in power distribution. User guides for some such meters requite correction factors for some simple non-sinusoidal waveforms, to permit the correct root hateful square (RMS) equivalent value to be calculated. More expensive multimeters include an Air conditioning to DC converter that measures the truthful RMS value of the waveform within sure limits; the user manual for the meter may indicate the limits of the crest factor and frequency for which the meter calibration is valid. RMS sensing is necessary for measurements on not-sinusoidal periodic waveforms, such as found in audio signals and variable-frequency drives.

Digital multimeters (DMM or DVOM) [edit]

Mod multimeters are often digital due to their accuracy, durability and extra features. In a digital multimeter the indicate nether examination is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal. A digital multimeter displays the quantity measured as a number, which eliminates parallax errors.

Mod digital multimeters may take an embedded reckoner, which provides a wealth of convenience features. Measurement enhancements available include:

  • Auto-ranging, which selects the correct range for the quantity nether test and then that the most pregnant digits are shown. For case, a four-digit multimeter would automatically select an appropriate range to brandish 12.34 mV instead of 0.012 V, or overloading. Automobile-ranging meters usually include a facility to hold the meter to a particular range, considering a measurement that causes frequent range changes can exist distracting to the user.
  • Automobile-polarity for direct-current readings, shows if the applied voltage is positive (agrees with meter lead labels) or negative (opposite polarity to meter leads).
  • Sample and hold, which volition latch the about recent reading for examination after the instrument is removed from the excursion nether test.
  • Electric current-express tests for voltage drop across semi conductor junctions. While not a replacement for a proper transistor tester, and most certainly not for a swept curve tracer type, this facilitates testing diodes and a variety of transistor types.[xviii]
  • A graphic representation of the quantity under examination, as a bar graph. This makes get/no-go testing piece of cake, and also allows spotting of fast-moving trends.
  • A low-bandwidth oscilloscope.[xix]
  • Automotive excursion testers, including tests for automotive timing and dwell signals (dwell and engine rpm testing is usually available as an option and is not included in the bones automotive DMMs).
  • Uncomplicated information acquisition features to record maximum and minimum readings over a given period, or to take a number of samples at fixed intervals.[20]
  • Integration with tweezers for surface-mountain technology.[21] [ better source needed ]
  • A combined LCR meter for small-size SMD and through-pigsty components.[22]

Modern meters may be interfaced with a personal estimator by IrDA links, RS-232 connections, USB, or an instrument bus such equally IEEE-488. The interface allows the computer to tape measurements as they are fabricated. Some DMMs tin store measurements and upload them to a computer.[23]

The outset digital multimeter was manufactured in 1955 by Not Linear Systems.[24] [25] It is claimed that the first handheld digital multimeter was adult by Frank Bishop of Intron Electronics in 1977,[26] which at the time presented a major quantum for servicing and error finding in the field.

Analog multimeters [edit]

Cheap analog multimeter with a galvanometer needle display

A multimeter may exist implemented with a galvanometer meter movement, or less often with a bargraph or simulated pointer such equally an liquid-crystal display (LCD) or vacuum fluorescent brandish.[ citation needed ] Analog multimeters were common; a quality analog instrument would cost about the same every bit a DMM. Analog multimeters had the precision and reading accuracy limitations described higher up, and so were not built to provide the aforementioned accurateness every bit digital instruments.

Analog meters were intuitive where the tendency of a measurement was more important than an exact value obtained at a detail moment. A alter in angle or in a proportion was easier to interpret than a modify in the value of a digital readout. For this reason, some digital multimeters additionally take a bargraph as a second display, typically with a more rapid sampling rate than used for the primary readout. These fast sampling rate bargraphs accept a superior response than the physical pointer of analog meters, obsoleting the older technology. With quickly fluctuating DC, Ac or a combination of both, advanced digital meters were able to track and display fluctuations better than analog meters whilst also having the ability to split and simultaneously brandish DC and AC components.[27]

Analog meter movements are inherently more than fragile physically and electrically than digital meters. Many analog multimeters feature a range switch position marked "off" to protect the meter motion during transportation which places a low resistance across the meter motion, resulting in dynamic braking. Meter movements equally separate components may be protected in the same style by connecting a shorting or jumper wire between the terminals when non in utilise. Meters which feature a shunt across the winding such as an ammeter may non require further resistance to arrest uncontrolled movements of the meter needle because of the low resistance of the shunt.

The meter movement in a moving pointer analog multimeter is practically always a moving-coil galvanometer of the d'Arsonval type, using either jeweled pivots or taut bands to support the moving coil. In a bones analog multimeter the current to deflect the curlicue and arrow is drawn from the circuit being measured; it is usually an advantage to minimize the current drawn from the circuit, which implies delicate mechanisms. The sensitivity of an analog multimeter is given in units of ohms per volt. For example, a very depression-cost multimeter with a sensitivity of 1,000 Ω/Five would draw i mA from a circuit at total-scale deflection.[28] More expensive, (and mechanically more frail) multimeters typically have sensitivities of 20,000 ohms per volt and sometimes higher, with 50,000 ohms per volt (drawing twenty microamperes at full scale) being about the upper limit for a portable, general purpose, non-amplified analog multimeter.

To avoid the loading of the measured circuit by the current fatigued past the meter move, some analog multimeters utilise an amplifier inserted between the measured circuit and the meter motion. While this increases the expense and complexity of the meter, by use of vacuum tubes or field effect transistors the input resistance can exist made very high and independent of the current required to operate the meter movement coil. Such amplified multimeters are chosen VTVMs (vacuum tube voltmeters),[29] TVMs (transistor volt meters), FET-VOMs, and like names.

Because of the absence of amplification, ordinary analog multimeter are typically less susceptible to radio frequency interference, then continue to have a prominent place in some fields even in a world of more authentic and flexible electronic multimeters.[30]

Probes [edit]

A multimeter tin can apply many dissimilar examination probes to connect to the excursion or device nether examination. Crocodile clips, retractable hook clips, and pointed probes are the three nearly common types. Tweezer probes are used for closely spaced test points, equally for instance surface-mount devices. The connectors are attached to flexible, well insulated leads terminated with connectors appropriate for the meter. Probes are connected to portable meters typically by shrouded or recessed banana jacks, while benchtop meters may use assistant jacks or BNC connectors. ii mm plugs and binding posts accept also been used at times, merely are less unremarkably used today. Indeed, safety ratings now crave shrouded banana jacks.

The banana jacks are typically placed with a standardized center-to-center distance of iii⁄4  in (xix mm), to permit standard adapters or devices such as voltage multiplier or thermocouple probes to be plugged in.

Clamp meters clamp around a conductor carrying a electric current to measure without the need to connect the meter in serial with the circuit, or make metallic contact at all. Those for AC measurement use the transformer principle; clamp-on meters to measure small electric current or directly current require more exotic sensors similar for example hall event based systems that measure the nonchanging magnetic field to determine the electric current.

Safety features [edit]

An instance of input protection on the Cat-4 rated Fluke 28 Series II Multimeter

Most multimeters include a fuse, or two fuses, which will sometimes preclude impairment to the multimeter from a current overload on the highest electric current range. (For added rubber, test leads with fuses built in are bachelor.) A mutual error when operating a multimeter is to ready the meter to measure resistance or current, and so connect information technology direct to a low-impedance voltage source. Unfused meters are often quickly destroyed by such errors; fused meters often survive. Fuses used in meters must carry the maximum measuring electric current of the instrument, but are intended to disconnect if operator error exposes the meter to a depression-impedance mistake. Meters with inadequate or unsafe fusing were not uncommon; this situation has led to the creation of the IEC61010 categories to charge per unit the prophylactic and robustness of meters.

Digital meters are rated into four categories based on their intended awarding, every bit set forth by IEC 61010-i[31] and echoed by country and regional standards groups such as the CEN EN61010 standard.[32]

  • Category I: used where equipment is not direct connected to the mains
  • Category II: used on single phase mains final subcircuits
  • Category Three: used on permanently installed loads such as distribution panels, motors, and three-phase appliance outlets
  • Category IV: used on locations where fault current levels can be very high, such as supply service entrances, main panels, supply meters, and master over-voltage protection equipment

Each Category rating besides specifies maximum prophylactic transient voltages for selected measuring ranges in the meter.[33] [34] Category-rated meters also characteristic protections from over-current faults.[35] On meters that allow interfacing with computers, optical isolation may exist used to protect attached equipment against loftier voltage in the measured circuit.

Good quality multimeters designed to run into Category II and above standards include high rupture capacity (HRC) ceramic fuses typically rated at more than 20 kA capacity; these are much less likely to fail explosively than more mutual glass fuses. They will also include high free energy overvoltage MOV (Metallic Oxide Varistor) protection, and circuit over-current protection in the form of a Polyswitch.[ citation needed ]

Meters intended for testing in hazardous locations or for use on blasting circuits may require employ of a manufacturer-specified battery to maintain their safety rating.[ citation needed ]

DMM alternatives [edit]

A quality full general-purpose electronics DMM is generally considered acceptable for measurements at signal levels greater than i mV or 1 μA, or below almost 100 MΩ; these values are far from the theoretical limits of sensitivity, and are of considerable interest in some excursion design situations. Other instruments—essentially similar, just with higher sensitivity—are used for authentic measurements of very pocket-size or very large quantities. These include nanovoltmeters, electrometers (for very low currents, and voltages with very high source resistance, such as 1 TΩ) and picoammeters. Accessories for more typical multimeters permit some of these measurements, as well. Such measurements are limited past available engineering science, and ultimately past inherent thermal dissonance.

Power supply [edit]

Analog meters tin mensurate voltage and current by using power from the test circuit, but require a supplementary internal voltage source for resistance testing, while electronic meters always crave an internal power supply to run their internal circuitry. Hand-held meters use batteries, while bench meters usually use mains ability; either organisation allows the meter to test devices. Testing often requires that the component nether test be isolated from the circuit in which they are mounted, as otherwise devious or leakage current paths may distort measurements. In some cases, the voltage from the multimeter may turn active devices on, distorting a measurement, or in extreme cases even damage an chemical element in the circuit being investigated.

See besides [edit]

  • Electronic test equipment
  • Electricity meter

References [edit]

  1. ^ "A New Electronic Rectifier", L.O Grondahl & P.H. Geiger, Transactions, American Institution of Electrical Engineers, February 1927 pp. 358–366
  2. ^ "multimeter". Oxford English Dictionary (Online ed.). Oxford Academy Press. Retrieved 14 March 2021. (Subscription or participating institution membership required.)
  3. ^ "Greater London Industrial Archaeology Society". glias.org.uk . Retrieved 2 Nov 2010.
  4. ^ a b "AVO" (MediaWiki). gracesguide.co.great britain . Retrieved 2 November 2010.
  5. ^ Imperial College Library Archives – Papers of Donald Macadie 1871–1956 MS2015/21
  6. ^ The Electrician 15 June 1923, p. 666
  7. ^ Advertisement – The Electrician, 1 June 1934
  8. ^ Frank Spitzer, Barry Howarth Principles of modern instrumentation, Holt, Rinehart and Winston, 1972 ISBN 0-03-080208-3 pp. 32–40
  9. ^ Stephen A. Dyer, Wiley Survey of Instrumentation and Measurement, John Wiley & Sons, 2004 ISBN 0471221651, pp. 277–281
  10. ^ a b "Model 2002 Multimeter Specifications". Keithley Instruments.
  11. ^ "Digital Multimeter Measurement Fundamentals". National Instruments. Retrieved 26 January 2008.
  12. ^ Stephen A. Dyer, Wiley Survey of Instrumentation and Measurement, John Wiley & Sons, 2004 ISBN 0471221651, p. 290
  13. ^ Milton Kaufman. Handbook of electronics calculations for engineers and technicians. McGraw-Loma.
  14. ^ Keysight Technologies. "Keysight 3458A Digital Multimeter Data Canvas" (PDF). Keysight Technologies . Retrieved 31 July 2014.
  15. ^ Horn, Delton (1993). How to Test Near Everything Electronic. McGraw-Colina/TAB Electronics. pp. 4–six. ISBN0-8306-4127-0.
  16. ^ a b Siskind, Charles S. (1956). Electrical circuits.
  17. ^ "Explanation of burden voltage by multimeter manufacturer Fluke". Fluke. Retrieved 2 November 2010.
  18. ^ Goldwasser, Samuel. "Basic Testing of Semiconductor Devices". Retrieved 28 Jan 2007.
  19. ^ Extech Instruments. "Extech five MHz Dual Channel Multiscope". Retrieved 28 January 2007.
  20. ^ "Extech Dual Channel, Datalogging multimeter". Extech Instruments. Archived from the original on 3 April 2007. Retrieved 28 January 2007.
  21. ^ Siborg Systems Inc. "Digital Multimeter Smart Tweezers from Siborg". Retrieved 23 April 2008.
  22. ^ Advance Devices Inc. "Smart Tweezers Digital Multimeter/LCR Meter" (PDF). Archived from the original (PDF) on 9 January 2007. Retrieved twenty Jan 2009.
  23. ^ Fluke Manufacturing. "Logging and analyzing events with FlukeView Forms Software" (PDF) . Retrieved 28 Jan 2007.
  24. ^ "Gauging the touch of DVMs". EETimes.com. Retrieved 26 January 2008.
  25. ^ Dyer, Stephen (2001). Survey of Instrumentation and Measurement. p. 286. ISBN0-471-39484-X.
  26. ^ "Intron Electronics | About". www.intronelectronics.com.au . Retrieved 17 July 2016.
  27. ^ Smith, Joe (24 August 2014). ""Brymen BM869s vs Fluke"". YouTube. Archived from the original on 17 November 2021. Retrieved 17 March 2020.
  28. ^ Frank Spitzer and Barry Horwath Principles of Mod Instrumentation, Holt, Rinehart and Winston Inc., New York 1972, no ISBN, Library of Congress 72-77731, p. 39
  29. ^ "The Incomplete Idiot's Guide to VTVMs". tone-lizard.com. Archived from the original on half-dozen Oct 2003. Retrieved 28 January 2007.
  30. ^ Wilson, Mark (2008). The ARRL Handbook for Radio Communications. ISBN978-0-87259-101-1.
  31. ^ "Rubber Standard IEC 61010-1 since 1.ane.2004". Archived from the original on ii December 2006.
  32. ^ Safety requirements for electrical equipment for measurement, command and laboratory use. General requirements. 1993. ISBN0-580-22433-3.
  33. ^ Dyer, Stephen (2001). Survey of Instrumentation and Measurement. p. 285. ISBN0-471-39484-10.
  34. ^ "Beefcake of a high-quality meter". Archived from the original on 18 October 2006. Retrieved v November 2015.
  35. ^ Mullin, Ray (2005). Electrical Wiring: Residential. Thompson Delmar Learning. p. 6. ISBNane-4018-5020-0.

External links [edit]

  • How to utilize a multimeter, sparkfun
  • How to select a Multimeter – Discusses the key considerations to select the right multimeter.
  • Multimeter Tutorial – Lots of useful information on Digital multimeter usage.
  • Beginners' Guide to the 830B Multimeter – Discusses the many uses of a cheap digital multimeter in the domicile.
  • How to Decide Digital Multimeter Accurateness
  • ABCs of Multimeter safety – (PDF)
  • Digital Multimeter – From theory to use
  • Multimeters and How to Utilize Them
  • DC Metering Circuits chapter from Lessons In Electric Circuits Vol ane DC free ebook and Lessons In Electric Circuits serial.

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Source: https://en.wikipedia.org/wiki/Multimeter