A
19
FFT Definitions
■
Averaging
With the FFT function, averaging is performed according to the following analytical expressions. Averaging
in the time domain produces meaningless data if performed with inconsistent trigger criteria.
(1)
Simple Averaging (Time and Frequency Domains)
Sequences of acquired data are summed and divided by the number of acquisitions.
𝐴𝐴
𝑛𝑛
=
(𝑛𝑛 − 1)𝐴𝐴
𝑛𝑛−1
+ 𝑍𝑍
𝑛𝑛
𝑛𝑛
............................................................... (11)
n
: count of measurements to average
An
: averaging results of n counts
Zn
: measurement data of n counts
(2)
Exponential Averaging (Time and Frequency Domains)
Before averaging, newer data is given exponentially greater significance than older data.
𝐴𝐴
𝑛𝑛
=
(𝑁𝑁 − 1)𝐴𝐴
𝑛𝑛−1
+ 𝑍𝑍
𝑛𝑛
𝑁𝑁
.............................................................. (12)
N
: Specified number of counts to average
n
: count of measurements to average
An
: averaging results of n counts
Zn
: measurement data of n counts
■
Overall Value
The overall value is the sum of the power spectrum at each frequency. This value is nearly equal to the
positive sum of the squares of the (RMS) input signals, except when frequency averaging is performed.
The FFT function of the instrument calculates and displays the RMS values for stored waveforms and the
overall value from the sum of the power spectrum for the frequency domain.
(𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂 𝑎𝑎𝑎𝑎𝑎𝑎) = ∑ 𝑃𝑃
𝑖𝑖
𝑖𝑖=0
...................................................................... (13)
P
i
: power spectrum of value i
■ Total Harmonic Distortion (THD)
Total harmonic distortion (THD) indicates the proportion of the higher harmonics to the fundamental
harmonic
This means that the larger the value, the more distorted the waveform.
THD
=
( )
( )
×
∑
V
V
n
2
0
100
[%] ........................................................ (14)
V
0
= fundamental wave
V
n
= next higher harmonic
Appx.
Содержание MR8827
Страница 19: ...14 Operation Precautions ...
Страница 81: ...76 Start and Stop Measurement ...
Страница 111: ...106 Manage Files ...
Страница 125: ...120 Miscellaneous Printing Functions ...
Страница 143: ...138 View Block Waveforms ...
Страница 191: ...186 Setting Output Waveform Parameters ...
Страница 291: ...286 FFT Analysis Modes Measurable Ranges With Octave Analysis 1 1 OCT 1 3 OCT ...
Страница 292: ...287 FFT Analysis Modes 1 1 OCT 1 3 OCT 13 FFT Function ...
Страница 293: ...288 FFT Analysis Modes 1 1 OCT 1 3 OCT ...
Страница 295: ...290 FFT Analysis Modes ...
Страница 309: ...304 Editor Command Details ...
Страница 387: ...382 Module Specifications ...
Страница 405: ...400 Dispose of the Instrument Lithium Battery Removal ...
Страница 431: ...A26 FFT Definitions ...
Страница 436: ......