Extech Instruments MultiMaster MM560 User Manual page 11

Meter Description (MM570 Shown)
1. Liquid Crystal display
2. Function push-keys
3. Rotary function switch
4. 10A/-T2 input jack
5. V/Hz/Ω/Cap/+T1 input jack
6. COM input jack/-T1 input
7. mA-uA current/+T2 input jack
NOTE: RS-232 Optical interface is located
on the top rear of the meter.
Considerations & Features
Average sensing RMS calibrated
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.
AC True RMS
AC True RMS, normally referred to as True RMS, identifies a DMM
function that is AC coupled, and responds accurately only to the
effective RMS AC component value regardless of the waveforms.
However, DC component plays an important role in the distorted non-
symmetrical waveforms, and will also be of interest sometimes. A full
wave rectified sine waveform is a good example, and the AC true RMS
function will only give the AC component reading which is at 43.6% of
the total effective RMS reading.
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