sound and vibration

[osmosis]

Good day all,

Is there anyway I can obtain the natural frequency of a body which I have attached an accelerometer on.

I can as of now acquire the signal using labview, but need to know the natural frequency of the the body if possible.

I came across the hammer example, but its totally not what I want because I cannot attached a sensor to my source of force the shaker tabel so no way to use transfer function. I can like I said just collect the response of my body when I pushed it. Can I get the natural frequency from this? Thanks.

[Thoric]

Is the object (body) under forced vibration, or free oscillation? If the body is being driven by an external force, then the measurements from the accelerometer are unlikely to provide you with information regarding the objects natural frequency. If however the object is oscillating/vibrating freely then the fundamental frequency of the measured signal should be the natural frequency of the object. An FFT analysis should allow you to determine the fundamental frequency and it's subharmonics.

Search for Basic Harmonic Analyzer in the LabVIEW Example finder.

[osmosis]

Thanks for the detailed response.

Actually the object is under excitation from a shaker Table. Can I surmise from your explanation that I cannot get the natural frequency in this form?

If yes, is there any other way that I can get this. After I posted this. I return to labview for solution and I noticed that NI Sound and Vibration Toolkit can acquire the signal and give their FFT. Please do you know if this can work for what I want or not?

Thanks for your quick response once again.

[Thoric]

From my limited memory, if an object is under a forced vibration, it will vibrate at the frequency and not it's natural frequency. I presume you have control of the excitation table frequency? I suspect when vibrating at the objects fundamental frequency you will see the 'loudest' response (because the object is vibrating at the frequency at which is wants to naturally vibrate), therefore you could use an FFT to visually monitor the fundamental frequency of the measured signal and alter the excitation frequency until you see the greatest response from the object. Hopefully someone with a more experience at these measurement techniques can pitch in with some further ideas?

[osmosis]

Thanks once again.

Maybe this can solve my problem. Is there anyway I can introduce a RANGE of excitation frequency into Frequency Response VI. Because in Matlab, doing this will show those frequency where the body goes into resonance and thus I could pick their natural frequencies easily. But I try doing this into FFT but with no success, I mean exciting my body with a range of frequency  and seeing how it behaves at this different frequencies?

Thanks