# LabVIEW

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## Using FFT PT BY PT

Hi guys,

I have attached a VI using FFT Pt by Pt with a known signal, a Sine Wave. How come my Waveform Graph on the FFT Pt by Pt dosen't work and it remains at 0 but the one using the normal FFT works? Can someone help me with it. Thanks. I attached my VI too.

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## Re: Using FFT PT BY PT

We're not all over to LV19... Posting an earlier version will get more response. Or, a screenshot\code snippet accompanying the VI.

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## Re: Using FFT PT BY PT

LV 2012 Version VI, WIEBE any ideas for advise

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## Re: Using FFT PT BY PT

You're creating an array of points, in sine shape.

Than, you pass one of those points to the FFT PtByPt. It never gets to see the sine, only the first point of it!

So, put the FFT PtByPt in a for loop, and pass all sine wave points to it, one by one (or, point by point).

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Solution
Accepted by topic author cyongjed

Like this:

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## Re: Using FFT PT BY PT

Hi Wiebe,

Thanks for the help given, just to clarify for the sample length in the fft pt by pt is it equal to the no of samples in the normal fft? I am quite confused by it...

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## Re: Using FFT PT BY PT

@cyongjed wrote:

Hi Wiebe,

Thanks for the help given, just to clarify for the sample length in the fft pt by pt is it equal to the no of samples in the normal fft? I am quite confused by it...

Well, as you work PtByPt, you can be feeding points for infinity. You could convert that to an FFT, but it would require infinite memory. So it needs a limit.

I think it compares to the normal FFT sample size. But the PtByPt will 'move' the samples.

If you're just interested in the amplitude of a simple frequency, there are more efficient options, btw.

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