User Manual, Firmware rev. 3.0 or LATER Owner's manual

Publication 1404-UM001F-EN-P - November 2009 167
Advanced Features Chapter 8
The standard IEC definition of harmonic distortion is the Distortion
Index (DIN) and is computed for each channel as follows:
Crest Factor
This is another quantity that is sometimes used to describe the amount
of distortion present in a waveform. It can also be used to express the
dynamic range of a measurement device. Crest Factor is the ratio of
the peak to the RMS.
A pure sinusoid Crest Factor equals .
DIN
∞
Σ
n 2=
H
n
()
2
∞
Σ
n 1=
H
n
()
2
---------------------
=
Where:
• H
n
= magnitude of the n
th
harmonic
(n ≤ 41 or 63)
• DIN is equivalent to IEC THD
Crest Factor Peak Value RMS Value⁄=
2