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RMS (Root MeanSquare) is a term used to describe the effective or equivalent DC
value of an AC signal. True RMS is the term which identifies a DMM that responds
accurately to the effective RMS value regardless of the waveforms such as: square,
sawtooth, triangle, pulse trains, spikes, as well as distorted waveforms with the
presence of harmonics. Harmonics may cause :
1)Overheated transformers, generators and motors to burn out faster than normal
2)Circuit breakers to trip prematurely
3)Fuses to blow
4)Neutrals to overheat due to the triplen harmonics present on the neutral
5)Bus bars and electrical panels to vibrate
Crest Factor is the ratio of the Crest (instantaneous peak) value to the True RMS
value, and is commonly used to define the dynamic range of a True RMS DMM. A pure
sinusoidal waveform has a Crest Factor of 1.414. A badly distorted sinusoidal
waveform normally has a much higher Crest Factor.
Before and after hazardous voltage measurements, test the voltage function on a
known source such as line voltage to determine proper meter functioning.
