I have a set of data points taken every 15ms. There are 32506 data points. I do an FFT on tem using the VI in spectral measurements. I need help interpreting the out put. When I read about FFTs in Labview, it says that to get the amplitude, you use the formula:
Amplitude spectrum in quantity peak = |FFT(X)|/N; where N is the number of sample.
My question is: Has this already been done in the VI? Do I need to divide the output of the FFT by N after I get the data out?
Thanks.
Magreen
Question on LabView FFT vis
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Eugen Graf
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Re: Question on LabView FFT vis
Hello Magreen,
I use folowing VI and have no problems with amplitude. The Amplitude should be right if you use it so.
I use folowing VI and have no problems with amplitude. The Amplitude should be right if you use it so.
- Вложения
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- FFT.PNG (6.15 КБ) 5438 просмотров
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- FFT_help.PNG (11.4 КБ) 5437 просмотров
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- beginner
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Re: Question on LabView FFT vis
Thanks for the vi. Here is the one I tried.
I get the same output with the 2 FFTs.
My question is to get the peak FFT, do I
divide the data by N, the number of samples
or this has already been done in Labview?
The other question I have is on the
frequency axis. The express vi gives a
delta f which is different from the
df I calculate with the second FFT.
Thanks,
Magreen.
I get the same output with the 2 FFTs.
My question is to get the peak FFT, do I
divide the data by N, the number of samples
or this has already been done in Labview?
The other question I have is on the
frequency axis. The express vi gives a
delta f which is different from the
df I calculate with the second FFT.
Thanks,
Magreen.
- Вложения
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- peak-amplitude-FFT.vi
- (292.42 КБ) 433 скачивания
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