A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several functions in one unit. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical In the Physical sciences Quality assurance, and Engineering, Measurement is the activity of obtaining and comparing physical quantities A standard multimeter may include features such as the ability to measure voltage, current and resistance. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is There are two categories of multimeters, analog multimeters (or analogue multimeters in British English) and digital multimeters (often abbreviated DMM. British English or UK English ( BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the )

A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as batteries, motor controls, appliances, power supplies, and wiring systems. In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy Power supply is a reference to a source of Electrical power. A device or system that supplies Electrical or other types of Energy to an output load

Multimeters are available in a wide ranges of features and prices. Cheap multimeters can cost less than US$10, while the top of the line multimeters can cost more than US$5000. The United States dollar ( sign: $; code: USD) is the unit of Currency of the United States; it has also been

Contents 1 Quantities measured 2 Resolution 2.1 Digital 2.2 Analogue 3 Accuracy 4 Sensitivity and input impedance 5 Alternating current sensing 6 Digital Multimeters (DMM) 7 Analog Multimeters 8 Probes 9 Safety 10 History 11 See also 12 References 13 External links

Quantities measured

Contemporary multimeters can measure many quantities. The common ones are:

• Voltage in volts. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force.
• Current in amperes. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second
• Resistance in ohms. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance,

Additionally, multimeters may also measure:

• Capacitance in farads. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors This is about the capacitance unit of measure For the charge unit see Faraday (unit.
• Frequency in hertz
• Duty cycle as a percentage. Frequency is a measure of the number of occurrences of a repeating event per unit Time. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. In Telecommunications and Electronics, the term duty cycle is used to describe the fraction of time that a system is in an "active" state In Mathematics, a percentage is a way of expressing a number as a Fraction of 100 ( per cent meaning "per hundred"
• Temperature in degrees Celsius or Fahrenheit. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724
• Conductance in siemens. Electrical conductance is a measure of how easily Electricity flows along a certain path through an Electrical element. The siemens (symbol S is the SI derived unit of Electric conductance.
• Inductance in henrys
• Audio signal levels in decibels. An inductor is a passive electrical component designed to provide Inductance in a circuit The henry (symbol H is the SI unit of Inductance. It is named after Joseph Henry (1797-1878 the American scientist who discovered electromagnetic The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to

Digital multimeters may also include circuits for:

• Continuity that beeps when a circuit conducts. A continuity tester is an item of electrical test equipment used to determine if an electrical path can be established between two points that is if an Electrical circuit Electrical conduction is the movement of electrically charged particles through a Transmission medium ( Electrical conductor)
• Diodes and Transistors

Various sensors can be attached to multimeters to take measurements such as:

• light level
• Acidity/Alkalinity(pH)
• Wind speed
• Relative humidity

Resolution

Digital

The resolution of a multimeter is often specified in "digits" of resolution. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals Luminance is a photometric measure of the density of Luminous intensity in a given direction pH is the measure of the acidity or alkalinity of a Solution. Wind speed is the Speed of Wind, the movement of air or other gases in an atmosphere Relative humidity is a measurement of the amount of Water vapor that exists in a gaseous mixture of air and water For example, the term 5½ digits refers to the number of digits displayed on the readout of a multimeter.

By convention, a half digit can display either a zero or a one, while a three-quarters digit can display a numeral higher than a one but not nine. Commonly, a three-quarters digit refers to a maximum count of 3 or 5. The fractional digit is always the most significant digit in the displayed value. A 5½ digit multimeter would have five full digits that display values from 0 to 9 and one half digit that could only display 0 or 1. ^[1] Such a meter could show positive or negative values from 0 to 199,999. A 3¾ digit meter can display a quantity from 0 to 3,999 or 5,999, depending on the manufacturer.

While a digital display can easily be extended in precision, the extra digits are of no value if not accompanied by care in the design and calibration of the analog portions of the multimeter. Meaningful high-resolution measurements require a good understanding of the instrument specifications, good control of the measurement conditions, and traceability of the calibration of the instrument.

Analogue

Resolution of analog multimeters is limited by the width of the scale pointer, vibration of the pointer, the accuracy of printing of scales, zero calibration, number of ranges, and errors due to non-horizontal use of the mechanical display. Accuracy of readings obtained are also often compromised by miscounting division markings, errors in mental arithmetic, parallax observation errors, and less than perfect eyesight. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between

Resistance measurements, in particular, are of low precision due to the typical resistance measurement circuit which compresses the scale heavily at the higher resistance values. Mirrored scales and larger meter movements are used to improve resolution; two and a half to three digits equivalent resolution is usual (and may be adequate for the limited precision actually necessary for most measurements).

Accuracy

Digital multimeters generally take measurements with accuracy superior to their analog counterparts. Analog multimeters typically measure with three to five percent accuracy. Standard portable digital multimeters claim to be capable of taking measurements with an accuracy of 0. 5% on DC voltage and current scales. Mainstream bench-top multimeters make claims to have as great accuracy as ±0. 01%. Laboratory grade instruments can have accuracies in the parts per million figures. "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly ^[2]

Manufacturers can provide calibration services so that new meters may be purchased with a certificate of calibration indicating the meter has been adjusted to standards traceable to the National Institute of Standards and Technology. Such manufacturers usually provide calibration services after sales, as well, so that older equipment may be recertified. Multimeters used for critical measurements may be part of a metrology program to assure calibration. Metrology (from Ancient Greek metron (measure and logos (study of is the Science of Measurement.

Sensitivity and input impedance

The current load, or how much current is drawn from the circuit being tested may affect a multimeter's accuracy. A small current draw usually will result in more precise measurements. With improper usage or too much current load, a multimeter may be damaged therefore rendering its measurements unreliable and substandard.

Meters with electronic amplifiers in them, such as all digital multimeters and analog meters using a transistor for amplification, have an input impedance that is usually considered high enough not to disturb the circuit tested. This is often one million ohms, or ten million ohms. The standard input impedance allows use of external probes to extend the direct-current measuring range up to tens of thousands of volts.

Most analog multimeters of the moving pointer type are unbuffered, and draw 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 movement and the range which is selected. Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal Alternating current (AC For example, a meter with a typical 20,000 ohms/volt sensitivity will have an input resistance of two million ohms on the 100 volt range (100 V * 20,000 ohms/volt = 2,000,000 ohms). Lower sensitivity meters are useful for general purpose testing especially in power circuits, where source impedances are low compared to the meter impedance. Some measurements in signal circuits require higher sensitivity so as not to load down the circuit under test with the meter impedance. ^[3]

The sensitivity of a meter is also a measure of the lowest voltage, current or resistance that can be measured with it. For general-purpose digital multimeters, a full-scale range of several hundred millivolts AC or DC is common, but the minimum full-scale current range may be several hundred milliamps. Since general-purpose mulitmeters have only two-wire resistance measurements, which do not compensate for the effect of the lead wire resistance, measurements below a few tens of ohms will be of low accuracy. The upper end of multimeter measurement ranges varies considerably by manufacturer; generally measurements over 1000 volts, over 10 amperes, or over 100 megohms would require a specialized test instrument, as would accurate measurement of currents on the order of 1 microamp or less. The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance,

Alternating current sensing

Since the basic indicator system in either an analog or digital meter responds to DC only, a multimeter includes an AC to DC conversion circuit for making alternating current measurements. Basic multimeters may utilize a rectifier circuit, calibrated to evaluate the average value of a rectified sine wave. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. User guides for such meters will give correction factors for some simple waveforms, to allow the correct root mean square (RMS) equivalent value to be calculated for the average-responding meter. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the More expensive multimeters will include an AC to DC converter that responds to the RMS value of the waveform for a wide range of possible waveforms; the user manual for the meter will indicate the limits of the crest factor and frequency for which the meter calibration is valid. The crest factor or peak-to-average ratio ( PAR) or peak-to-average power ratio ( PAPR) is a measurement of a Waveform, calculated from RMS sensing is necessary for measurement s of non-sinusoidal quantities, such as found in audio signals, or in variable-frequency drives. A variable-frequency drive (VFD is a system for controlling the rotational speed of an Alternating current (AC Electric motor by controlling the frequency of the

Digital Multimeters (DMM)

Modern multimeters are often digital due their accuracy, durability and extra features.

In a DMM the signal under test is converted to a voltage and an amplifier with an electronically controlled gain preconditions the signal.

A DMM displays the quantity measured as a number, which prevents parallax errors. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between

The inclusion of solid state electronics, from a control circuit to small embedded computers, has provided a wealth of convenience features in modern digital meters. Commonly available measurement enhancements include:

• Auto-ranging, which selects the correct range for the quantity under test so that the most significant digits are shown. The significant figures (also called significant digits and abbreviated sig figs) of a number are those digits that carry meaning contributing to its accuracy For example, a four-digit multimeter would automatically select an appropriate range to display 1. 234 instead of 0. 012, or overloading. Auto-ranging meters usually include a facility to 'freeze' the meter to a particular range, because a measurement that causes frequent range changes is distracting to the user.
• Auto-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 will latch the most recent reading for examination after the instrument is removed from the circuit under test. In Electronics, a sample and hold circuit is used to interface real-world signals by changing analogue signals to a subsequent system such as an Analog-to-digital
• Current-limited tests for voltage drop across semiconductor junctions. Voltage drop is the reduction in Voltage in an Electrical circuit between the source and load A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact While not a replacement for a transistor tester, this facilitates testing diodes and a variety of transistor types. Transistor testers are instruments for testing the electrical behavior of Transistors and solid-state Diodes Types of tester There are three types Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes ^[4][5]
• A graphic representation of the quantity under test, as a bar graph. See CategoryBar chart templates for Wikipedia templates to make bar charts This makes go/no-go testing easy, and also allows spotting of fast-moving trends.
• A low-bandwidth oscilloscope. An oscilloscope (commonly abbreviated to scope or O-scope) is a type of Electronic test equipment that allows signal Voltages to be viewed ^[6]
• Automotive circuit testers, including tests for automotive timing and dwell signals. ^[7]
• Simple data acquisition features to record maximum and minimum readings over a given period, or to take a number of samples at fixed intervals. Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer ^[8]
• A miniature digital multimeter integrated with tweezers for Surface-mount technology. Surface-mount technology ( SMT) is a method for constructing electronic circuits in which the components (SMC or Surface Mounted Components are mounted directly onto ^[9]

Modern meters may be interfaced with a personal computer by IrDA links, RS-232 connections, USB, or an instrument bus such as IEEE-488. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated The Infrared Data Association ( IrDA) defines physical specifications Communications protocol standards for the short-range exchange of Data In Telecommunications, RS-232 (Recommended Standard 232 is a standard for serial binary data signals connecting between a DTE ( Data Terminal Equipment IEEE-488 is a short-range digital communications bus specification that has been in use for over 30 years The interface allows the computer to record measurements as they are made. Some DMM's can store measurements and upload them to a computer. ^[10]

The first digital multimeter was manufactured in 1955 by Non Linear Systems. ^[11][12]

Analog Multimeters

A multimeter may be implemented with an analog meter deflected by an electromagnet, as a classic galvanometer, or with a digital display such as an LCD or vacuum fluorescent display. A galvanometer is a type of Ammeter; an instrument for detecting and measuring Electric current. A vacuum fluorescent display (VFD is a Display device used commonly on consumer-electronics equipment such as Video cassette recorders Car radios

Analog multimeters are not hard to find (though less common and often more expensive than low-end digital units), but are not considered as accurate as digital because of errors introduced in zeroing and reading the analog meter face.

Analog meters may be implemented with vacuum tubes to precondition and amplify the input signal. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. Such meters are known as vacuum tube volt meters (VTVM) or vacuum tube multimeters (VTMM). ^[13]

Analog meters are sometimes considered better for detecting the rate of change of a reading; the ARRL handbook suggests that analog multimeters are often less susceptible to radio frequency interference. The American Radio Relay League (ARRL is the largest membership association of Amateur radio enthusiasts in the USA. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz ^[14]

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. A galvanometer is a type of Ammeter; an instrument for detecting and measuring Electric current. In a basic analog multimeter the current to deflect the coil and pointer is drawn from the circuit being measured; it is usually an advantage to minimize the current drawn from the circuit. The sensitivity of an analog multimeter is given in units of ohms per volt. For example, an inexpensive multimeter would have a sensitivity of 1000 ohms per volt and would draw 1 milliampere from a circuit at the full scale measured voltage. ^[15] More expensive, (and more delicate) multimeters would have sensitivities of 20,000 ohms per volt or higher, with a 50,000 ohms per volt meter (drawing 20 microamperes at full scale) being about the upper limit for a portable general purpose analog multimeter.

To avoid the loading of the measured circuit by the current drawn by the meter movement, later analog multimeters use an amplifier inserted between the measured circuit and the meter movement. While this increased the expense and complexity of the meter and required a power supply to operate the amplifier, by use of vacuum tubes or field effect transistors the input resistance can be made very high and independent of the current required to operate the meter movement coil. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. The field-effect transistor (FET is a type of Transistor that relies on an Electric field to control the shape and hence the conductivity of a 'channel' Such amplified multimeters are called VTVM (vacuum tube voltmeters) or TVM (transistor volt meter), and similar names.

Probes

A multimeter can utilise a variety of test probes to connect to the circuit or device under test. Crocodile clips, retractable hook clips, and pointed probes are the three most common attachments. A crocodile clip (or spring clip is a temporary Electrical connector, named for its resemblance to a Crocodile 's jaws The connectors are attached to flexible, thickly-insulated leads that are terminated with connectors appropriate for the meter. Handheld meters typically use shrouded or recessed banana jacks, while benchtop meters may use banana jacks or BNC connectors. A banana connector (commonly banana plug for the male, banana jack for the female) is a single- Wire (one conductor The BNC ( Bayonet Neill Concelman) connector is a very common type of RF connector used for terminating Coaxial cable. 2mm plugs and binding posts have also been used at times, but are not so common today.

Meters which measure high voltages or current may use non-contact attachment mechanism to trade accuracy for safety. Clamp meters provide a coil that clamps around a conductor in order to measure the current flowing through it.

Safety

Some multimeters include a fuse, which will sometimes prevent damage to the multimeter if it is overloaded. However the fuse often only protects the highest current range on the multimeter. A common error when operating a multimeter is to set the meter to measure resistance or current and then connect it directly to a low-impedance voltage source; meters without protection are quickly damaged by such errors, and can sometimes explode causing injury to the operator.

Digital meters are category rated based on their intended application, as set forth by the CEN EN61010 standard. European Committee for Standardization or Comité Européen de Normalisation ( CEN) is a private non-profit organisation whose mission is to foster the European economy ^[16] There are four categories:

• Category I: used where current levels are low.
• Category II: used on residential branch circuits.
• Category III: used on permanently installed loads such as distribution panels, motors, and appliance outlets.
• Category IV: used on locations where current levels are high, such as service entrances, main panels, and house meters.

Each category also specifies maximum transient voltages for selected measuring ranges in the meter. ^[17][18] Category-rated meters also feature protections from over-current faults. ^[19]

History

Multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. As modern systems become more complicated, the multimeter is becoming more complex or may be supplemented by more specialized equipment in a technician's toolkit. For example, where a general-purpose multimeter might only test for short-circuits, conductor resistance and some coarse measure of insulation quality, a modern technician may use a hand-held analyzer to test several parameters in order to validate the performance of a network cable. ^[20]

See also

• Ammeter
• Avometer
• Electronic test equipment
• Meter (electronics)
• Ohmmeter
• Voltmeter
• Wattmeter

References

External links

• Operating a multimeter
• How to use a multimeter with other pages on using multimeters and test equipment
• The Basics of Digital Multimeters from EC&M Magazine

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