help with natural frecuencies

Other Hardware Sensors
1

Hi, I am doing a research study at university using Arduino Uno, LabVIEW and an accelerometer 352C33.
The idea is to attach the accelerometer to a structure and with a hammer make the structure vibrate and then make that signal analysis with a power spectrum in order to know the natural frequencies. I have some questions:

  • The accelerometer needs at least 18V but with 5V the signal measuring is good for what I need but the spectral analysis is not. Does this have something to do or even with 5 Volts is should show some values?
  • I have 2 options for measuring and both don’t show correct values for the spectral analysis (with the Fourier Transform). 1 Use a point by point filter and the Fourier for point by point. 2 Use a for loop to keep some values and create an array and then use a normal filter and Fourier to evaluate the signal.
    I upload 2 Vi and some captures to show you that none of those solution works and I am stuck at this point. I am happy with the signal measuring cause is sufficiently precise but I can’t get the natural frequencies.
    Any suggestion will help. Thanks in advance

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2

What is the structure that you are hitting with a hammer? Do you have any idea what its natural frequencies are?

I guess your waveform is showing the acceleration of the structure due to the hammer blow not the subsequent resonant vibrations which are likely to be quite high audio frequencies. It may help if you start taking samples for Fourier analysis only some time after the initial impact.

As the resonant vibrations will be relatively low amplitude you need to consider the resolution of your analogue-to-digital conversion. Perhaps use a 16-bit analogue-to-digital converter and/or include amplification of your accelerometer signal, allowing clipping of the signal during the hammer impact (and excluding the period of clipping from Fourier analysis).

3

To get useful data from a sensor, ALWAYS follow the recommendations in the sensor data sheet.