Not getting real time FFT for a signal.

[Zikra_Furqan]

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I wanted to obtain the real time fft for a pulse signal and tried using the "fft by pt" sub vi with a window size of 100. I have used myrio for acquiring the signal and sampled it at 200hz. The fft shows a peak at 0 and goes to 0 level at 1. I am not able to figure out. Can anyone please help me out?

[JÞB]

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@Zikra_Furqan wrote:

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I wanted to obtain the real time fft for a pulse signal and tried using the "fft by pt" sub vi with a window size of 100. I have used myrio for acquiring the signal and sampled it at 200hz. The fft shows a peak at 0 and goes to 0 level at 1. I am not able to figure out. Can anyone please help me out?

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Going only by your limited information (you have not shown a vi, sample data or described the pulse width or repetition rate) I would have to conclude that the record indicates a large component of between 0hz and 2hz.  This does not surprise me in the least! It's a PULSE!

[altenbach]

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@Zikra_Furqan wrote:

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I wanted to obtain the real time fft for a pulse signal and tried using the "fft by pt" sub vi with a window size of 100. I have used myrio for acquiring the signal and sampled it at 200hz. The fft shows a peak at 0 and goes to 0 level at 1. I am not able to figure out. Can anyone please help me out?

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• How wide is the pulse (in # points compared to the 100 point history size).
• is it a square DC pulse or a pulsed high frequency signal?
• An FFT output is complex. Are you looking at the correct phase (or magnitude)?
• if your ptbypt size is 100 points, you'll only seem something for less that half a second at 200Hz).

As a first step, generate a static array containing your expected pulse and do a plain FFT. Work if out until you see what you expect to see. Then go back to the ptbypt, but use a simulated signal. Only once everything is worked out, go back to the real signal.

[Zikra_Furqan]

Will try it out and get back to you if there is any doubt. Thanks a lot for the inputs.

[Zikra_Furqan]

Thanks a lot for the inputs. Will definitely try to include more info next time.