Glossary of Terms

A, ampere or amp: The basic unit of electric current.
AC, alternating current: An electric signal in which the current and voltage vary in a repeating pattern over time; the most common type of voltage.
analog meter: A mechanical measuring device using a needle moving across a graduated scale or dial.
auto ranging: A DMM that automatically selects the range with the best resolution and accuracy in response to the application.
calibration: Zeroing of an instrument to a known standard.
capacitance: Ability of a component to hold an electrical charge, usually stated in microfarads.
capacitor: Electronic component which stores energy and then discharges it; blocks DC and allows AC to pass through.
clamp-on: DMM with jaws that allow it to fit around a conductor to measure AC or DC current without breaking the circuit.
contact: A connection between two conductors that allows a flow of current.
continuity: The continuous path for current flow in a closed circuit.
current: The flow of an electrical charge through a conductor; measured in amperes or amps.
DC, direct current: an indirectional, steady voltage; typically produced through electromagnetism, chemicals (batteries), light, heat or pressure.
data hold: Feature of DMM that allows continued display of last reading taken after probes have been removed.
diode: Electronic device in circuits that allows current to flow easily in only one direction and blocks flow in the opposite direction.
DMM, digital multimeter: An instrument that uses an LCD typically capable of measuring voltage, current and resistance.
F, farad: The basic unit of capacitance.
frequency: The number of cycles per second that a wave form repeats; measured in hertz. (Line voltage in U.S. is 60 Hz.)
ground: A large conducting body (earth) used as a common return for current in a circuit.
H, hertz: One cycle per second; the unit of frequency.
harmonics: A signal with a frequency which is a multiple of the fundamental frequency (60Hz); may damage or degrade the performance of electrical devices.
harmonic distortion: Diminishes power quality; caused by non-linear loads such as variable speed motor drives, electronic lighting ballasts and computers.
impedance: Total opposition to current flow; includes resistance, capacitance and reactance.
load: Any device which consumes power in a circuit.
manual ranging: DMM that requires the user to manually select the range using the meter’s dial.
min/max: Feature that allows a meter to capture and store the highest and lowest readings during a specific measurement.
ohm: The basic unit of resistance, specified as equal to that of a conductor in which one amp of current is produced by one volt of potential across its terminals.
OL, overload: Signal amplitudes or frequencies above the specified limits of the instrument; typically displayed as “OL” on the display of a DMM.
peak hold: Feature of DMM that allows retention of highest reading in a series of measurements.
polarity: The positive or negative direction of DC voltage or current.
resolution: Increments in value that can be displayed by a DMM; the greater the resolution the more precise the readout.
resistance: Opposition to current; measured in ohms.
sleep mode: Automatically shuts down unit not in use to preserve battery life.
short: Any connection that has relatively low resistance or any resistance between two points below a preselected threshold.
true RMS meter: DMM that has the True RMS feature, allowing for accurate measurement of AC voltage in environments with harmonics (see harmonics).
V, volt: The unit of electrical pressure; one volt is the potential difference needed to cause one amp of current to pass through one amp of resistance.