RIGOL DM3068 - Manual (Page 145)

Chapter 5 Measurement Tutorial RIGOL
User’s Guide for DM3068 5-5
Crest Factor Errors (non-sinusoidal inputs)
A common misconception is that "since a multimeter can measure the true RMS of
signal, its sine wave accuracy specifications apply to all waveforms." Actually, the
waveform shape of the input signal can affect the measurement accuracy. A
common way to describe the signal wave shape is “crest factor”. Crest factor is the
ratio of the peak value to RMS value of a waveform.
In general, the greater the crest factor is, the greater the energy contained in high
frequency harmonics will be. All multimeters have errors that are relevant to the
crest factor. Crest factor errors of DM3068 are listed in “AC Characteristics” in
chapter 6.
You can estimate the measurement error due to signal crest factor according to
the equation below.
Total Error＝Error (Sine wave) + Error (Crest factor) + Error (Bandwidth)
Error (Sine wave): sine wave error as shown in chapter 6.
Error (Crest factor): additional crest factor error as shown in chapter 6.
Error (Bandwidth): bandwidth error can be estimated according to the formula
below.
Bandwidth Error
100%
BW 4
π
F C.F. -
2
Ч
Ч
Ч
= (% reading)
. .F C
: signal crest factor
F
: pulse fundamental wave frequency
BW
: multimeter’s effective bandwidth
Example:
Calculate the approximate measurement error for a pulse train with a crest factor
of 2 and a fundamental frequency of 20 kHz. Assume that the multimeter’s 1-year
accuracy is ± (0.05%× reading + 0.03%×range).
Total Error = (0.05%×reading + 0.03%×range) + (0.05%×range) +
(0.8%×reading) =0.85%×reading + 0.08%×range