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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.
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