Multimeter : Terms and Definitions

                                    Fig : 1 Manual (left) and Auto (right) Ranging in Multimeters

Published By : Yousuf Ibrahim Khan
Date : 9-9-2012

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.

APO- Auto-Power — Off  Automatically shuts down unit after a certain amount of time to preserve battery life. Most meters with APO may be disabled or set to a certain amount of time before shutting off.

auto ranging — A DMM that automatically selects the range with the best resolution and accuracy in response to the sensed values.

calibration — To adjust the meter measured value to a recognized artifact or 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 rapidly; 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 — A 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 — a direct, steady voltage; typically produced through electromagnetism, chemicals (batteries), light, heat or pressure.

data hold — Feature of a DMM that allows continued display of the 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 display 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 the U.S. is 60 Hz.)

ground — A large conducting body (earth) used as a common return for fault current in a circuit.

H, hertz — One cycle per second; the unit of frequency.

harmonics — A signal with a frequency which is  an integer 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. Typically, this is unintended.

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 Ohm of resistance.