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User's Manual
UT8806E Desktop Digital Multimeter
Crest Factor Error (non-sine wave input)
It is a common misconception that "Since the multimeter can measure the true effective
value of the signal, its sine wave accuracy index can naturally be applied to other waveform
input signals." In fact, the waveform of the input signal affects the accuracy of the
measurement. The signal waveform is generally described by the Peak Factor, which is the
ratio of the peak value of the waveform to its RMS value. In general, the larger the peak factor,
the more energy is contained in the high-frequency harmonics. All multimeter have an error
associated with crest factor. Note that crest factor error does not apply to input signals below
100Hz.
The measurement error due to signal crest factor can be estimated as follows.
Total Error = Error (Sine) + Error (Crest Factor) + Error (Bandwidth)
Error (Sine wave): Sine wave error
Error (Crest factor): Peak factor plus error
Error (Bandwidth): The bandwidth error can be estimated according to the following formula.
Bandwidth error
(% reading)
C.F.: signal crest factor
F: pulse fundamental frequency
BW: effective bandwidth of multimeter
Example
Calculate the approximate measurement error for a pulse train input with a peak factor of 2
and a fundamental frequency of 20 kHz. Assume that the one-year accuracy of the multimeter
is: ± (0.05% of reading + 0.03% of range).
Total Sum = (0.05% reading+ 0.03% range)+(0.05% range)+(0.8% reading)
= 0.85% reading+0.08% range
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