Natural Frequency from impact testing question

[andyglidewell]

Hi all:

I'm trying to obtain natural frequencies of some mounts that my company designs and was wondering if there was a simple way of obtaining this from the example impact test vi's and outputting it? Currently I've been working with SVXMPL_Impact Test.vi and SVXMPL_Advanced Impact Test.vi  and I'm running Labview 2010 with the sound and vib add on.  

Andy

[Zachmx · Accepted solution]

Hi andy,

It looks like those example programs find the frequency of the stimulus signal. You could use the same SVFA FFT Spectrum (Mag-Phase).vi used in finding the hammer frequency to find the frequency of the response signal. Once you have this signal, you can use the SVFA Spectrum Peak Search to read the natural frequency from the frequency data.

[andyglidewell]

Thanks for the help.  It appears to be working for me.  

[Zachmx]

Hi Andy,

Great to hear! Let us know if you have any more questions.

[andyglidewell]

I was wondering if anyone knew of a good way to verify my results.  I was thinking something along the lines of attaching the accelerometer to a tuning fork but if there's a better way I'd love to know. 

[Luke_B]

Hi Andy,

I'm sorry to say I can't think of a better method off hand. I'd also warn that if you strap an accelerometer onto a tuning fork, you'll be changing its frequency somewhat depending on the size of the accelerometer relative to the size of the tuning fork. You'll still probably get a ballpark figure, but it might not be quite what you're looking for.

Regards,

[andyglidewell]

Well I've tried what I described with the tuning forks and I'm getting an incorrect reading.  On a 256 hz tuning fork I'm getting 4398 hz and for a 512 hz tuning fork I'm getting 3133 hz.  Again I'm new to this so it might be a unit conversion I missed.  Again thanks in advance.

Andy

[KatieC]

Andy, 

As Luke mentioned, you won't get great results using an accelerometer on tuning forks like that. I am surprised they are so far off, but not surprised they are inaccurate. You want your surface area much greater than the accelerometer in order to get accurate measurements. 

Katie