“KUSAM-MECO”
AN ISO 9001:2015 COMPANY
“KUSAM-MECO”
AN ISO 9001:2015 COMPANY
RMS (Root-Mean-Square) is the term used to describe the
effective or equivalent DC value of an AC signal. Most digital
multimeters use average sensing RMS calibrated technique to
measure RMS values of AC signals. This technique is to obtain
the average value by rectifying and filtering the AC signal. The
average value is then scaled upward (calibrated) to read the RMS
value of a sine wave. In measuring pure sinusoidal waveform, this
technique is fast, accurate and cost effective. In measuring non-
sinusoidal waveforms, however, significant errors can be
introduced because of different scaling factors relating average to
RMS values.
Average sensing RMS calibrated
True RMS
3) Fuses to blow
5) Bus bars and electrical panels to vibrate
True RMS is a 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
4) Neutrals to overheat due to the triplen harmonics present on
the neutral
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Crest Factor
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 1.4. A badly distorted sinusoidal waveform
normally has a much higher Crest Factor.
NMRR (Normal Mode Rejection Ratio)
NMRR is the DMM's ability to reject unwanted AC noise effect that
can cause inaccurate DC measurements. NMRR is typically
specified in terms of dB (decibel). This series has a NMRR
specification of >60dB at 50 and 60Hz, which means a good ability
to reject the effect of AC noise in DC measurements.
Common mode voltage is voltage present on both the COM and
VOLTAGE input terminals of a DMM, with respect to ground.
CMRR is the DMM's ability to reject common mode voltage effect
that can cause digit rolling or offset in voltage measurements. This
series has a CMRR specifications of >60dB at DC to 60Hz in ACV
function; and >120dB at DC, 50 and 60Hz in DCV function. If
neither NMRR nor CMRR specification is specified, a DMM's
performance will be uncertain.
CMRR (Common Mode Rejection Ratio)
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