A Multimeter
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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. A standard multimeter may include features such as the ability to measure voltage, current and resistance. There are two categories of multimeters, analog multimeters (or analogue multimeters in British English) and digital multimeters (often abbreviated DMM.)
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.
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.
Quantities measured
Contemporary multimeters can measure many quantities. The common ones are:
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Voltage in volts.
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Current in amperes.
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Resistance in ohms.
Additionally, multimeters may also measure:
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Capacitance in farads.
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Frequency in hertz
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Duty cycle as a percentage.
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Temperature in degrees Celsius or Fahrenheit.
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Conductance in siemens.
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Inductance in henrys
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Audio signal levels in decibels.
Digital multimeters may also include circuits for:
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Continuity that beeps when a circuit conducts.
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Diodes and Transistors
Various sensors can be attached to multimeters to take measurements such as:
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light level
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Acidity/Alkalinity(pH)
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Wind speed
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Relative humidity
Resolution
Digital
The resolution of a multimeter is often specified in “digits” of resolution. For example, the term 5ÐÐ 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 5ÐÐ… digit multimeter