Rigol DM3068 Podręcznik Użytkownika Pobierz pdf (Strona 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%

BW4π

FC.F.-

(% reading)

..FC

: signal crest factor

: pulse fundamental wave frequency

: 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

1 2 ... 140 141 142 143 144 145 146 147 148 149 150 ... 170 171

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Rigol DM3068 Podręcznik Użytkownika Strona 145