SDM3055 Series Digital Multimeter User Manual
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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:
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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