# Multimeter

A digital multimeter

A multimeter or a multitester is an electronic measuring tool that is a combination of several tools in one unit. It usually includes an ammeter, voltmeter, and ohmmeter. Digital multimeters are sometimes called DMM too.

Modern multimeters can be used to measure electrical quantities other than current, resistance and voltage. For example, they can be used to measure frequency, capacitance, transistors Hfe and temperature.

The multimeter can make many tests, so it is often called "multitester". When measuring resistance it acts as an ohmmeter, showing ohms. For volts it would be a Voltmeter. Sometimes it is called a mixture of things like Volt/ohm meter or VOM. Most meters can measure volts, amps, and resistance.[1]

## How it can be measured

The multimeter can be used to measure the voltage of a battery. It can also be used for measuring the voltage across two points in a circuit. The Voltmeter is placed in parallel between the positive and negative terminals of the battery. It can also be used to measure resistance and amps hence the name of some meters "Voltmeter, Ohmmeter, and Amperage".[2]

## History of multimeter

In 1820, the galvanometer was the first device with a moving pointer that could measure current. The Wheatstone bridge was used to measure resistance and voltage by comparing the unknown voltage or resistance to a known voltage or resistance. Even though the devices worked well in the lab, they were too slow to be useful in the field. These galvanometers were hard to use and big.

The D'Arsonval–Weston meter movement has a moving coil that holds a pointer and turns on pivots or a tight band ligament. The coil spins in a permanent magnetic field and is held in place by small spiral springs that also carry electricity into the moving coil. It gives a proportional measurement instead of just a detection, and the deflection is the same no matter how the meter is turned. Instead of balancing a bridge, values could be read directly from the instrument's scale, which made measurement quick and easy.

The basic moving coil meter can only be used to measure direct current, which is usually between 10 A and 100 mA. It can be easily changed to measure higher currents by adding shunts, which are parallel resistances or to measure voltage by adding multipliers, which are series resistances. A rectifier is needed to measure voltages or currents that change direction. In 1927, the copper oxide rectifier made by the Union Switch & Signal Company in Swissvale, Pennsylvania, which later became part of the Westinghouse Brake and Signal Company, was one of the first rectifiers that worked well.[3]

## References

1. "multimeter". Archived from the original on 3 May 2013. Retrieved 29 May 2012.
2. "multimeters" (PDF). Archived from the original (PDF) on 2010-06-05. Retrieved 29 May 2012.
3. Ahmed, Ali. "what is multimeter". Rawlix.`{{cite web}}`: CS1 maint: url-status (link)