update FFT based on range of waveform chart

[subz]

I am working with seismic data that I recorded from explosive events.  The signatures that I'm recording could include the ignition of the explosion, the pressure wave hitting a barrier or debris hitting the ground.  The objective is to analyze the waveform and see if I can see any consistancy or trends.  I am loading in the seismic data into a LabVIEW program and displaying the waveform on a chart and then on an FFT.  I'm noticing with most of my data there are two or three distinct frequencies, so I would like to see where these occur on the waveform chart (each event has 2-13 seconds worth of data).  On the waveform chart I can zoom in on the x-axis and change the time range to look at areas of interest and count cycles, however that gets tedius.  Is there a way to update the FFT to show only the data that is in the time range on the waveform chart?

Thanks
Michael

[gwd]

Certainly you can extract a data subset and do an FFT on that. It sounds like a relatively involved user interface programming task to do this in a convenient way.

You might want to look at STFT Spectrogram.vi which I think does what you want.

[DavidJCrawford]

I don't have enough experience when working with the frequency domain but here is my attempt by following my nose.

There seems to be an error in the frequency detected but I don't know why.  Hopefully somebody else with more knowledge will step in with an explaination.

Here it is in LV7.1

David

Edit: Ah there you perhaps gwd can help

Message Edited by David Crawford on 11-21-2006 01:53 PM

Message Edited by David Crawford on 11-21-2006 01:53 PM

[IanW]

Hi Michael

I use cursors to do a similar task. Have a look at the example.

Hope this helps

Ian

[subz]

Thanks guys, I'll take a look at all the examples given and see if I can figure it out.  I was playing around with an event structure and based upon the event change in the waveform chart would cause the FFT to change.  Hopefully by seeing the examples given I can fully implement it.