Description of the Software Modules and Parameters
Parameter manual b maXX BM3000
Document no.: 5.12001.07
711
of 820
4
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
The amplitude for the signal output (e.g. hissing noise) can be entered here.
104.13 Signal Output offset
The offset for the signal output (e.g. hissing noise) can be entered here.
FFT windowing Meaning
0 Without Window
1 Window Hann (used most often)
2 Window Hamming
3 Window Blackman-Harris
4 Window Flat Top
To Next Page
Loading...
Need help?
General