RIGOL DM3058 - Manual (Page 121)

RIGOL
User’s Guide for DM3058/DM3058E 5-3
Crest Factor Errors (non-sinusoidal inputs)
A common misconception is that "since an ac multimeter is true RMS, its sine wave
accuracy specifications apply to all waveforms." Actually, the shape of the input
signal can dramatically affect measurement accuracy. A common way to describe
signal wave shapes is “crest factor”. Crest factor is the ratio of the peak value to
RMS value of a waveform.
Generally speaking, the greater the crest factor, the greater the energy contained
in high frequency harmonics. All multimeters have errors that are crest factor
dependent. Crest factor errors for DM3058/DM3058E are listed in the AC
Characteristics section in chapter 6. Please note that the crest factor errors do
not apply for input signals below 100Hz.
You can estimate the measurement error due to signal crest factor as shown
below:
Total Error＝Error (Sine wave) + Error (Crest factor) + Error (Bandwidth)
Error (Sine wave): error for sine wave as shown in chapter 6.
Error (Crest factor): crest factor additional error as shown in chapter 6.
Error (Bandwidth): estimated bandwidth error as shown below:
Bandwidth Error
100%
BW 4
π
F C.F. - 2
Ч
Ч
Ч
= (% reading)
. .F C
: signal crest factor
F
: fundamental frequency of pulse
BW
: effective bandwidth of the multimeter
Example:
Calculate the approximate measurement error for a pulse train input with a crest
factor of 2 and a fundamental frequency of 20kHz. For this example, assume the
multimeter’s 1-year accuracy specifications: ± (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