How to create FFT from XY Envlope

[johnsold]

The reference time point for a timestamp is January 1, 1904.   3.4E9 is the number of seconds since then. You could get the current time just before starting the loop and then subtract that from the t0 inside the loop.  This will make your times a few seconds.

What do you expect the FFT of the envelope to look like?  The images you show do not have any periodic signals so the FFT is mostly random.  The FFT works best if you have 5 cycles of the epriodic signal or more in the data set you are transforming.  With sets containing less than one complete cycle, the FFT tends to treat everything as though it was almost all in the minimum frequency bin.

Your filtered signal (in the image) looks like the bandpass filter may have a significant amount of ringing. The enevlope may be more about the filter transfer function than about the frequency content of the signal.  Your LV program does not include any filtering.  What are the specifcations of the filter?

Lynn

[prakashsurya]

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@johnsold wrote:

The reference time point for a timestamp is January 1, 1904.   3.4E9 is the number of seconds since then. You could get the current time just before starting the loop and then subtract that from the t0 inside the loop.  This will make your times a few seconds.

What do you expect the FFT of the envelope to look like?  The images you show do not have any periodic signals so the FFT is mostly random.  The FFT works best if you have 5 cycles of the epriodic signal or more in the data set you are transforming.  With sets containing less than one complete cycle, the FFT tends to treat everything as though it was almost all in the minimum frequency bin.

Your filtered signal (in the image) looks like the bandpass filter may have a significant amount of ringing. The enevlope may be more about the filter transfer function than about the frequency content of the signal.  Your LV program does not include any filtering.  What are the specifcations of the filter?

Lynn

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Hi i want the fft analysis of the pressure data which is attached  here in csv file. i have done some work which is also attached here but the results i m getting is not right. I have just started to work on labview so i have very basic idea about the programming in this.

[johnsold]

Prakashsurya,

You did not attach anything.  This thread has been inactive for almost a year. You should probably start a new thread for your question.

Please specify what is not right about your results.  What did you expect to get?

Lynn