Sine sweep vs Random
Sine sweep vs Random
(OP)
If I do a sine sweep from, say from 20-500 Hz, and measure or analyze acce at one point, will I see the same frequncy peaks with a PSD test measuring or analyzing at the same point?
Just to clearify a discussion point with collegaues.
Thanks.
Just to clearify a discussion point with collegaues.
Thanks.





RE: Sine sweep vs Random
In other words, a 2-g rms random has its energy statistically distributed across the entire spectrum, so the amount energy available for exciting any mode is statistically low. Contrast with even a 0.1-g sine sweep where the entire 0.1-g acceleration is applied directly into a mode.
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RE: Sine sweep vs Random
Cheers
Greg Locock
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RE: Sine sweep vs Random
Fe
RE: Sine sweep vs Random
Thanks
RE: Sine sweep vs Random
- Steve
RE: Sine sweep vs Random
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RE: Sine sweep vs Random
"Random" implies measuring autospectrum and hence averaging, so given enough time, the random excited response should look like the sine excited response in terms of where the peaks are and their relative heights.
M
--
Dr Michael F Platten
RE: Sine sweep vs Random
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RE: Sine sweep vs Random
However, your comment about dwell times does make me think of a reason why you might get a difference between the position of the apparent peaks in a swept sine and the peaks in a random test. If the sweep rate is too fast and the damping very light, then you could get a situation where the resonance doesn't have enough time to build up to it's maximum response. In that case, the peaks in the swept sine test could appear in slightly the wrong frequency. The peaks in the random test will always be in the right place. Of course all this assumes linearity as others have already said.
M
--
Dr Michael F Platten
RE: Sine sweep vs Random
I guess we'll just have to do a test next time we're at the shaker table and see.
Thanks all for your input.
RE: Sine sweep vs Random
However, this can give very poor coherence at the peaks because there are so many non linearities (both deliberate and accidental) in a whole vehicle.
So on problematic systems I would use sine sweeps, sometimes with amplitude feedback, and sometimes not.
This has the advantage of giving great coherence, but can disguise problems with test setup. It also only tests each non linearity at one amplitude for each frequency, which is not necessarily representative.
Well that hasn't made life any simpler has it?
Cheers
Greg Locock
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RE: Sine sweep vs Random
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