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Detecting FFT Frequency

Hi All,

I am using NI cDAQ-9171 to acquire accelerometer signal. I am trying to see if the FFT functions, DDT Power Spectrum and PSD.vi; FFT Spectrum (Mag-Phase).vi; and Spectral Measurements) can detect the frequency accurately by oscillating the accelerometer approximately 1Hz by hand. However, none of the FFT graphs show this result. Is there something wrong in my block diagram?  See attached pictures and VI (Version 17). (Yet, the Spectral Measurements function does work when I connect it to the sine wave simulator vi.)

 

Any advise will be appreciated.

 

Drake

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Hello,

 

Can you explain why are you converting your waveform into a 1D array? You should be able to plug in the waveform you are reading into the spectral VIs. The coercion dots may be causing the issue.

Marina B.
Technical Support Engineer
National Instruments
www.ni.com/support
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Thank you Marina for the reply. I tried to get rid of the coercion dots, see attached. But, it's still not working. Any suggestion?

 

Thank you,

Drake

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