Baumuller b maXX BM5800, Руководство по параметрам

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Description of the Software Modules and Parameters
Parameter manual b maXX BM5800
Document No.: 5.16029.03
699
of 814
3
104.9
FFT length
This parameter can be used to enter the length of the time window for FFT evaluation.
Entries are only possible with the FFT command Stop. The length applies to the two chan-
nels and may only be as Radix 2 (power of 2).
The length is decisive for the frequency resolution.
Example:
Sampling frequency 4 kHz (0.35 ms cycle), which means the maximum frequency is
2000 Hz. With an FFT length of 4096, the FFT has results in 2048 discrete value
pairs (real, imaginary) plus DC share. The frequency resolution is
2000 Hz / 2048 = 0.9765 Hz.
104.10
FFT windowing
This parameter can be used to switch FFT windowing on.

Since the FFT always works with a time frame (finite time record), the use of a window
function usually makes sense. The Window function serves to reduce the "Bin Leakage"
or "Side Lobe". The price for that is a certain reduction of frequency resolution. The
change of the Window type does not take effect until the FFT Command is (re) started.
104.11
Average number setup
This parameter is used to enter the number of mean values. Average determination can
improve the quality of the analysis.
104.12
Signal out amplitude
Here, the amplitude of the signal output of the signal generator (such as noise) can be
entered in the accordant units of the selected "Signal output target parameter" (
Z
104.6
–
).
FFT windowing Meaning
0 Without Window
1 Window Hann (used most often)
2 Window Hamming
3 Window Blackman-Harris
4 Window Flat Top