curve conversion

[midsidenode]

I've been given the enclosed vibration curve. I'm not accustomed to seeing double amplitude vs frequency. Is there a way to convert this to PSD vs frequency?
thanks,
msn

 

[BrianE22]

I was trying to remember the conversion from years ago but got hung up on the /hz part you see on the PSDs. I believe it's a normalizing factor that takes into account the filter bandwidth (for old type analog spectrum analyzers) or the frequency resolution (for Fourier calculations). Anyways, I ran across this:

http://vibrationresearch.com/wp-content/uploads/2018/04/RandomRMSCalculation.pdf

It's backwards (acceleration to displacement) but I would think you could go in reverse.

 

[GregLocock]

A PSD of what?


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Tom Irvine]

The double amplitude vs. frequency plot is for a sine sweep where there is a single excitation frequency at anytime. That frequency itself varies with time, usually with a linear or logarithmic sweep rate.

PSD tests are for random vibration where a broadband of excitation frequencies occur simultaneously.

There is no method to directly convert from sine sweep to PSD or vice versa. This can be done indirectly, however, using vibration or fatigue damage spectrum methods. These methods assume that the base input is applied to a single-degree-of-freedom (SDOF) system. Each method determines the response of the system to the given base input.

 

[midsidenode]

Thank alot Tom.
and thank you Brian for that info as well.

 

[Tom Irvine]

Please visit the following web page if you want to learn more about sine sweeps & PSDs:

https://vibrationdata.wordpress.com/2017/01/19/webinar-index/

The materials on this blog are free to download and were informally sponsored by NASA.

Best wishes,
Tom