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##### FFT (with one time signal) with NI 9232 data

02-13-2018 10:57 AM

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I want to do FFT analysis on data gathered with Daqmx hardware - a cDAQ NI 9174 with a NI 9232 Sound and Vibration module. The goal being to find a resonant frequency and graph of the frequency domain data using Diadem. I gathered the data using the sample program IEPE - Continuous Input in LabVIEW and saved it as a TDMS file.

When I go to do the FFT analysis, I select the accelerometer data for the given access and leave all the default options. Is this the correct procedure? Do I need a Time signal, and if so, how do I generate one for any given TDMS data? Data saved in TDMS format should be of 'waveform' type, so I was thinking it shouldn't require it. However, the FFT generated does not match the analysis done by our vibration software running in parallel, and I'm trying to find the source of error.

02-14-2018 04:50 PM

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Hello,

Yes that is correct, you should not need a time channel because the data is of Waveform type. Can you include a picture of what you expect the FFT output to look like and what the one in DIAdem looks like?

Regards,

Conrad

Applications Engineer

National Instruments

02-15-2018 08:28 AM

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02-16-2018 11:54 AM

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Thanks for confirming that I can use waveform type that way. I've attached outputs of the DIAdem FFT and vibration software FFT for comparison. It seems the peaks are at similar frequencies (minus some DC component), but the magnitudes are all off. I've also attached FFT settings for Time Interval. Is it typical that:

# of intervals: 1

interval length: # of samples

02-16-2018 01:52 PM

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02-19-2018 10:51 AM

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