Digital Multimeter (DMM) is an electronic measurement device measuring more than one electrical parameter. Digital Multimeters show measured values in numbers, usually on a liquid crystal display. This is in contrast to Analog Multimeters displaying measured values via a dial, typically a moving pointer or needle moving along a scale.
Historically current, voltage, and resistance measurements were standard features for early Digital Multimeters and they were reffered to as AVO meters, that was derived from Amperes, Volts, and Ohms, the units used for the measurement of current, voltage, and resistance.
Modern Digital Multimeters in addition to current, voltage, and resistance can measure also measure Capacitance, Inductance, Quality and Dissipation Factors, Frequency, Temperature, pH Factor, Humidity, etc. Currently one the most popular combinations is an LCR Digital Multimeters, the name derived from standard symbols used for Inductance (L), Capacitance (C) and Resistance (R).
Prices for Digital Multimeters vary from US$20 to US$500 depending on the accuracy and available features.
Earlier Analog Multimeters had basic accuracies of five to ten percent. For modern Digital Multimeters typical accuracy is a bout 1-3% but may may have accuracies as good as ±0.025%, and high-end bench-top instruments can have even higher accuracies better than 0.01%.
For a Digital Multimeter, resolution is the smallest change in an input signal that produces a change in the output signal.
Sometimes the resolution of a Digital Multimeter is specified in the number of digits Digital Multimeter could display. 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.
Digital Multimeters can be used to troubleshoot electrical problems in a wide array of household devices such as possibly dead batteries, washing and drying machines, kitchen appliances, and even automobile electronics and electrical systems.
Calibration Certificates for Digital Multimeters
Professional quality Digital Multimeters are normally sold with a certificate of calibration indicating the meter has been adjusted to standards traceable to the Institute for National Measurement Standards in Canada or National Institute of Standards and Technology in the USA. Such manufacturers usually provide calibration services after sales, as well, so that older equipment may be recertified.
Digital Multimeter Probes
Typically Digital Multimeters may utilize Crocodile clips, retractable hook clips, or pointed probes as the three most common attachments. 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 bench-top meters may use banana jacks or BNC connectors. Some Digital Multimeters are equipped with a tweezers that allow a one-hand operation when doing measurements.
Tweezers is an example of the ultimate integration of the tweezers and
the Digital Multimeter making it an indispensable tool for Surface
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.
Precision of Digital Multimeters
Precision is a measure of the stability of the Digital Multimeter and its capability of resulting in the same measurement when repeating measurements for the same input signal or component.
Precision is especially important when a Digital Multimeter is used to calibrate a device or to perform relative measurements.