Amprobe AM91RS Digital-Multimeter - Manual (Page 6)

5
Analog bar-graph
The analog bar graph provides a visual indication of measurement like a traditional analog
meter needle. It is excellent in detecting faulty contacts, identifying potentiometer clicks,
and indicating signal spikes during adjustments.
DC+AC True RMS
DC+AC True RMS is a term which identifies a DMM that responds accurately to the
total 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 and DC components. Harmonics and DC components 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
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 which can cause
inaccurate DC measurements. NMRR is typically specified in terms of dB (decibel). This
product 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.
CMRR (Common Mode Rejection Ratio)
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 which can cause digit rattle 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.