PSD interpretation
PSD interpretation
(OP)
Hi,
I'm newbie in vibration field. How can you interpete PSD data? In other words, I have data of a PSD (g^2/Hz vs Hz)curve for a truck, how can I know or calculate the objet that I want to put in is safe (not damage by the truck's vibration)?
Thanks,
Mica
I'm newbie in vibration field. How can you interpete PSD data? In other words, I have data of a PSD (g^2/Hz vs Hz)curve for a truck, how can I know or calculate the objet that I want to put in is safe (not damage by the truck's vibration)?
Thanks,
Mica





RE: PSD interpretation
Hope this helps
Regards
Dave
RE: PSD interpretation
Thanks again,
Mica
RE: PSD interpretation
TTFN
RE: PSD interpretation
Also, you've not indicated what external environment the truck is seeing. If all it's doing is primary roads, there's no much that would affect most devices. On the other hand, a military truck going over railroad tie test track is wholely different matter.
TTFN
RE: PSD interpretation
Thanks,
Mica
RE: PSD interpretation
Regards
Dave
RE: PSD interpretation
Mica
RE: PSD interpretation
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Tobalcane
"If you avoid failure, you also avoid success."
RE: PSD interpretation
The PSD is a tool for looking at time/distance based data in the frequency domain. In your case (if I am interpreting correctly), you have a road profile. The road profile was likely created by measuring acceleration/force on a wheel as it rolled down the road.
That said, the PSDs you have are the INPUT into your system. The reccomendation by CESSNA is spot on; put your equipment on the shaker table and give the PSD to the operator. They will convert this frequency data back into time domain and give your equipment a ride.
These are the basics... you still need to look at acceleration factors (how much time), what vehicle it will be on (remember you have road profiles, there is a suspension and tire between you and the road), and other factors.
Hope I didn't muddle that up too much...
RE: PSD interpretation
Also, does the shaker table test will be able to provide the naturel frequency of my equipment?
Thanks,
Mica
RE: PSD interpretation
It is likely your equipment will have some transmissibility greater than one, and some less than one. All depends on stiffness, accel location, etc.
In essence, you will have to see what conclusions you can draw based on the data after the test is complete.
RE: PSD interpretation
I suggest that you get a copy of MIL-STD-810 and do some reading or get another engineer to help you.
TTFN
RE: PSD interpretation
Also, does the shaker table test will be able to provide the naturel frequency of my equipment?”
When you put your unit under test (uut) on the shaker, you have to put an accelerometer (response) on the part that you have the most concern. Now two things can happen. If your control plot (truck curve) matches your response curve (uut) you can not get any better than that. This means that the uut is basically moving with the truck. If your uut survives with out incident, you’re golden. If you see that the response plot has a spike anywhere along the control plot, you may have an issue. One, this is the natural frequency of spot you have the response accelerometer on, and second depending the calculated Q (transmisibility) you can calculate Gout. Once you do that, you have to go back into your design and calculate the stress and strain due to the Gout load. If your stress due to the Gout is less by a factor of safety your golden, if not, you may have to redesign.
Tobalcane
"If you avoid failure, you also avoid success."
RE: PSD interpretation
As third step, would be to know if the equipment has been designed for support shock or not. If yes, it is possible to compute the responses multiplied by the "realistic" random profile, and compute the resultant grms, and see if it is less than the shock to support.
If the equipment has not been designed to support shock, the way will be to select the appropriate transportation package.
MIL-STD-810 gives quite a lot about how to proceed.
RE: PSD interpretation
Thanks,
Mica
RE: PSD interpretation
Also, generally, you should be running your UUT against the truck profile.
TTFN
RE: PSD interpretation
Thanks again,
Mica
RE: PSD interpretation
yes
TTFN
RE: PSD interpretation
Mica