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SIGLENT
94 SDM3055 Digital Multimeter
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 of SDM3055 are listed in the AC
Characteristics section of chapter 6. (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%（% reading）
C.F.: 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 20 kHz. For this example,
assume 1-year accuracy specifications of the Multimeter: ± (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
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