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natural frequencies detection with peak detection.vi

Hi,

 

I'm trying to detect natural frequencies for a cantilivered plate in free vibration. I generate a swept signal with labview and NI USB 6221card. The response of the cantilevered plate is recorded by a vibrometer laser. Then I use the FFT-peak vi express to get the spectrum of the plate. I would like labview to detect each peak in the spectrum and then to give me the frequency corresponding with the maximums. I tried with the peak detection.vi but the results seems strange: I know that the firsts natural frequencies of the plate are 24 hz and 86 Hz. Labview find them at 1660 and 3880...whereas the spectrum graph looks correct with the right values... 

Any idea of the problem? I think it is due to the index of the array...

 

Thank you very much for your help!

 

Francis

 

PS: attached is the vi...

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Hello francisrct,

 

I saw that nobody answered your question.

So do you have any updates?

 

best regards

Richard

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Hi,

 

someone explain me that there is an equation to re-index the results. There is an exemple here: https://decibel.ni.com/content/docs/DOC-4475

My quest is now resolved 🙂

 

Francis

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