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Concept
Multimeter
Summary
A multimeter (also known as a volt-ohm-milliammeter, volt-ohmmeter or VOM) is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case can be used as a voltmeter, ammeter, and ohmmeter. Some feature the measurement of additional properties such as temperature and capacitance.
The first attested usage of the word "multimeter" listed by the Oxford English Dictionary is from 1907.
Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters (DMMs) have numeric displays and have made analog multimeters virtually obsolete as they are cheaper, more precise, and more physically robust than analog multimeters.
Multimeters vary in size, features, and price. They can be portable handheld devices or highly-precise bench instruments. Cheap multimeters can cost under , while laboratory-grade models with certified calibration can cost over .
The first moving-pointer current-detecting device was the galvanometer in 1820. These were used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow and impractical in the field. These galvanometers were bulky 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 coil rotates in a permanent magnetic field and is restrained by fine spiral springs which also 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 basic moving coil meter is suitable only for direct current measurements, usually in the range of 10 μA to 100 mA.
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Multimeter
A multimeter (also known as a volt-ohm-milliammeter, volt-ohmmeter or VOM) is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case can be used as a voltmeter, ammeter, and ohmmeter. Some feature the measurement of additional properties such as temperature and capacitance. The first attested usage of the word "multimeter" listed by the Oxford English Dictionary is from 1907.
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A shunt is a device that is designed to provide a low-resistance path for an electrical current in a circuit. It is typically used to divert current away from a system or component in order to prevent overcurrent. Electrical shunts are commonly used in a variety of applications including power distribution systems, electrical measurement systems, automotive and marine applications. One example is in miniature Christmas lights which are wired in series.
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An ohmmeter is an electrical instrument that measures electrical resistance (the opposition offered by a circuit or component to the flow of electric current). Multimeters also function as ohmmeters when in resistance-measuring mode. An ohmmeter applies current to the circuit or component whose resistance is to be measured. It then measures the resulting voltage and calculates the resistance using Ohm’s law . An ohmmeter should not be connected to a circuit or component that is carrying a current or is connected to a power source.
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