Question on LabView FFT vis

Signal acquisition, processing and output
Ответить
magreent
beginner
beginner
Сообщения: 14
Зарегистрирован: 19 мар 2008, 01:57
Версия LabVIEW: 7.1
Откуда: United States
Контактная информация:

Question on LabView FFT vis

Сообщение magreent »

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
Аватара пользователя
Eugen Graf

Activity Professionalism Silver Black
guru
guru
Сообщения: 6502
Зарегистрирован: 13 ноя 2007, 02:20
Награды: 4
Версия LabVIEW: 2009
Откуда: Saarbrücken
Контактная информация:

Re: Question on LabView FFT vis

Сообщение Eugen Graf »

Hello Magreen,

I use folowing VI and have no problems with amplitude. The Amplitude should be right if you use it so.
Вложения
FFT.PNG
FFT.PNG (6.15 КБ) 5387 просмотров
FFT_help.PNG
FFT_help.PNG (11.4 КБ) 5386 просмотров
magreent
beginner
beginner
Сообщения: 14
Зарегистрирован: 19 мар 2008, 01:57
Версия LabVIEW: 7.1
Откуда: United States
Контактная информация:

Re: Question on LabView FFT vis

Сообщение magreent »

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.
Вложения
peak-amplitude-FFT.vi
(292.42 КБ) 432 скачивания
Ответить
  • Похожие темы
    Ответы
    Просмотры
    Последнее сообщение

Вернуться в «Signal processing»