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A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. The most basic instruments include an ammeter, voltmeter, and ohmmeter. Analog multimeters are sometimes referred to as "volt-ohm-meters", abbreviated VOM. Digital multimeters are usually referred to as "digital-multi-meters", abbreviated DMM.

A multimeter can be a handheld device useful for basic fault finding and field service work or a bench instrument which can measure to seven or eight and a half digits of accuracy. Such an instrument will commonly be found in a calibration lab and can be used to characterise resistance and voltage standards or adjust and verify the performance of multi-function calibrators.

Current, voltage, and resistance measurements are considered standard features for multimeter. AVO multimeters, a manufacturer of early multimeters, derived their name from amperes, volts, and ohms, the units used for the measurement of current, voltage, and resistance.

Newer equipment can measure many other quantities. Some common additional measured quantities and the units in which they are measured:
Capacitance in farads.
Frequency in hertz.
Duty cycle as a percentage.
Temperature in degrees Celsius or Fahrenheit.
Conductance in siemens.
Inductance in henrys.

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.

Analog multimeters are not hard to find in the used market, but are not very accurate 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. Such meters are known as vacuum tube volt meters (VTVM) or vacuum tube multimeters (VTMM).

The resolution of a multimeter is often specified in "digits" of resolution. The term "digits" dates back to the 1970's when multimeter vendors were very proud of how many digits their products could display (this was important, because readout displays were costly). The vendors started to specify the maximum resolution of the multimeter based on the digital display. For example, the term 5½ digits refers to the number of digits displayed on the readout of a multimeter. 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. This digital multimeter could show positive or negative values from 0 to 199,999. For a modern DMM, such as a PC-based multimeter, the term "digits" actually maps to the noise performance of the device.

Modern multimeters are exclusively digital, and identified by the term DMM or digital multimeter. In such an instrument, the signal under test is converted to a digital voltage and an amplifier with an electronically controlled gain preconditions the signal. Since the digital display directly indicates a quantity as a number, there is no risk of parallax causing an error when viewing a reading.

Similarly, better circuitry and electronics have improved meter accuracy. Older analog meters might have basic accuracies of five to ten percent. Modern portable DMMs may have accuracies as good as ±0.025%, and bench-top instruments have accuracies in the single-digit parts per million figures.

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:
Autoranging, which selects the correct range for the quantity under test so that the most significant digits are shown. For example, a four-digit multimeter would display 1.234 instead of 0.012.
Sample and hold, which will latch the most recent reading for examination after the instrument is removed from the circuit under test.
Current-limited tests for voltage drop across semiconductor junctions. While not a replacement for a transistor tester, this facilitates testing diodes and a variety of transistor types.
A graphic representation of the quantity under test, as a bar graph. This makes go/no-go testing easy, and also allows spotting of fast-moving trends.
A continuity tester that beeps when a circuit conducts.
A low-bandwidth oscilloscope.
A telephone test set.
Automotive circuit testers, including tests for automotive timing and dwell signals.
Simple data acquisition features to record maximum and minimum readings over a given period, or to take a number of samples at fixed intervals.

Digital meters often feature circuitry or software to accurately measure the AC voltage at any frequency. These meters integrate the input signal using the root mean square method, and will correctly read the true voltage of an input signal even if it isn't a perfect sine wave.

Modern meters may be interfaced with a personal computer by IrDA links, RS-232 connections, USB, or an instrument bus such as IEEE-488. The interface allows the computer to record measurements as they are made or for the instrument to upload a series of results to the computer.

As modern appliances and systems become more complicated, the multimeter is becoming less common in the technician's toolkit. More complicated and specialized equipment replaces it. Where a service man might have used an ohmmeter to measure resistance while testing an antenna, a modern technician may use a hand-held analyzer to test several parameters in order to determine the integrity of a network cable.


Flow Meters (932 companies) Flow meters (flowmeters) and flow sensors are devices used for measuring the flow rate or quantity of a moving fluid or gas. Learn more about Flow Meters
Digital Multimeters (349 companies) Digital multimeters (or multi-meters) are used to measure electrical quantities such as voltage, current, resistance, frequency, temperature, capacitance, and time period measurements. Learn more about Digital Multimeters
Electrical and Electronic Test Equipment (501 companies) Electrical and electronic test equipment includes large systems specifically designed for testing electrical and electronic components or equipment.
Liquid Flow Meters (344 companies) Liquid flow meters are used for measuring the flow or quantity of a moving fluid. Learn more about Liquid Flow Meters
Analog Voltmeters (107 companies) Analog voltmeters are instruments that measure voltage or voltage drop in a circuit. They display values on a dial, usually with a needle or moving pointer. Learn more about Analog Voltmeters
Gas Flow Meters (238 companies) Gas flow meters are used for measuring the flow or quantity of a moving gas in an enclosed pipe or passage. Learn more about Gas Flow Meters
Digital Voltmeters (201 companies) Digital voltmeters are instruments that measure voltage or voltage drop in a circuit. They use solid-state components and display values digitally. Learn more about Digital Voltmeters
Positive Displacement Flow Meters (94 companies) Positive displacement flow meters measure the volume or flow rate of a moving fluid or gas by dividing the media into fixed, metered volumes. These devices consist of a chamber that obstructs the media flow and a rotating or reciprocating mechanism that allows the passage of fixed-volume amounts. Learn more about Positive Displacement Flow Meters
Analog Multimeters (146 companies) Analog multimeters are instruments that are used to measure electrical quantities such as voltage, current, resistance, frequency and signal power. Learn more about Analog Multimeters
Digital Panel Meters (377 companies) Digital panel meters measure and display processes and electrical variables via an alphanumeric digital readout. Learn more about Digital Panel Meters
Utility Meters (41 companies) Utility meters are used to monitor the consumption of water, gas or electricity by businesses or residences.
Lux Meters (Light Meters) (81 companies) Lux meters or light meters measure illumination in terms of luxes (lx) or foot candles (fc). Learn more about Lux Meters (Light Meters)
Paddlewheel Flow Meters (39 companies) Paddlewheel flow meters have a paddle wheel that is perpendicular to the flow path, not parallel as in traditional turbine-type flow meter. The rotor axis is positioned to limit contact between the paddles and the flowing media. Learn more about Paddlewheel Flow Meters
Vortex Flow Meters (45 companies) Vortex flow meters are flow sensors that detect the frequency of vortices shed by a bluff body placed in a flow stream. The frequency of the vortices is proportional to the flow velocity. Learn more about Vortex Flow Meters
Fiber Optic Power Meters (78 companies) Fiber optic power meters are instruments that measure the average power of a continuous light beam. They are used to test signal power in fiber optic networks. Learn more about Fiber Optic Power Meters

2007-01-15 17:56:29

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