Interpreting Vibration Measurement Results

[fmerwick]

Hi all,
I am having trouble with an experiment I am conducting at the minute. I am designing a device to be mounted on a vibrating structure and am trying to determine a damping mechanism to eliminate the vibration on the imposed product. I have measured the vibration on the structure it is to be mounted on with the output measured in volts. I want to convert this to dB and am using the formula 20*Log(Vout/Vref) however what am I supposed to take as the Vref, is it 10^-3, as the charge amplification on the charge amplifier was at 10mV, or could anybody help me on this. Also how do I modify the dB reading to a displacement, velocity etc. in order to determine damping factor value?

Cheers P.

 

[GregLocock]

Vref was 10^-2 in this case, as 10 mV is 10^-2 V, although you need to make it very clear that you are quoting dB re whatever engineering unit was involved. The official dB reference for acceleration varies by application.

To convert to displacement etc you need to use integration, which is very easy in the frequency domain.






Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[fmerwick]

Thanks for the reply, yes I understand that the reference was 10^-2, but for this application is there a standard formula in order to convert it to an acceleration?

I have read that once it is in dB that all my results are referred back to the reference level once it is stated however I need to convert these results to a fixed unit of measurement in order to determine a sufficient damping mechanism for my device.

P

 

[GregLocock]

I don't know. Your questions don't make much sense to me, the choice of unit is up to the engineer. Did you mean 10^-3 or 10^-2 in your first post?

Personally if I am just looking at vibration I default to m/s/s, it is rare to need so much dynamic range that dB are necessary and people just get confused.

If it is less than 0.1 m/s/s don't worry about it, if it is more than 50 things will break.




Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight