Digital multi meters are instruments that are used to measure electrical quantities such as voltage, current, resistance, frequency, temperature, capacitance, and time period measurements. Basic functionality includes measurement of potential in volts, resistance in ohms, and current in amps. Multimeters are used to find electronic and electrical problems. Advanced units come with more features such as capacitor, diode and IC testing modes.
Digital multimeters are generally bench top or handheld. Bench top models can also be portable by use of handles and wheels. Handheld multimeters are specifically designed to be used while holding, i.e. can be operated with one hand. Digital multimeters display information on a digital screen. Commonly they have between 3 and 6 digits, but some units come with larger screens that can display 7 or more digits. The fastest sampling rate is also important to consider.
Specific measurements made by digital multimeters include DC voltage, AC voltage, DC current, AC current, resistance, capacitance, frequency range, time period, and special measurements. Special measurements include continuity check, audible continuity, diode test, maximum or minimum or peak spike measurement, RTD temperature measurement, thermocouple temperature, and transistor test. Continuity checks will give an indication to the user that a closed loop exists due to the probes touching each other. Digital multimeters with audible continuity will beep when probes are touching each other. Diode test will check to see if a diode is good or bad. Digital multimeters with maximum or minimum or peak spike measurement can measure and display when these events occur. Some multimeters are capable of measuring temperature with either an RTD or thermocouple probe. Multimeters with transistor test is capable of examining a transistor and telling the using where the emitter, collector, and base is located. When searching for digital multimeters it is important to consider the measurement range for whichever value is being measured.
Common features for digital multimeters include battery power, analog bar graph, dB readings, auto-ranging, adjustable sampling rate, programmable, data acquisition, data storage and logging, removable data storage, and triggering. Devices with battery power can be operated without plug in power. Output options for digital multimeters include GPIB, research 488, RS232, BCD, and D/A. An important environmental parameter to consider when searching for analog multimeters is the operating temperature.