multimeters

Multimeters are handheld electrical test instruments used to measure basic electrical quantities, typically including voltage, current, and resistance. They combine the functions of a voltmeter, an ammeter, and an ohmmeter into one device, simplifying electronics troubleshooting and measurement tasks. Multimeters come in analog form, with a moving-needle display, and digital forms. Digital multimeters (DMMs) are by far the most common today and often offer auto-ranging, true RMS sensing, and data-hold features.

Common measurement modes include DC and AC voltage, DC and AC current, resistance, continuity testing (an audible tone when a circuit is complete), diode testing, capacitance, and frequency. Some models add temperature, inductance, or noncontact voltage detection. Basic construction features a handheld case, a rotary selector for the function, and input jacks such as COM, V/Ω, and mA/µA or 10A for higher current. Many DMMs provide additional features like MIN/MAX, relative mode, and measurement memory.

Operating principles and safety: to read voltage, the meter is connected across the component; to measure current, it is inserted in series; resistance is measured with the circuit powered off. In voltage mode, input impedance is typically around 10 megaohms. Accuracy ranges commonly from about 0.5% to 1%, depending on range and device class. True RMS meters provide more accurate readings for non-sinusoidal signals. Users should observe proper safety ratings (CAT I–IV) and use appropriate probes and fuses.

Some multimeters include a separate current clamp for noncontact or clamp-on current measurements, forming a clamp meter when used with the same unit. Multimeters are widely used in electronics repair, automotive diagnostics, and electrical installations.