Meaning of Amplitude Change and Frequency Shift after Random Vib
Meaning of Amplitude Change and Frequency Shift after Random Vib
(OP)
We ran a random vib. on our component. After the vib test the lab discover that their slip table had some lubrication issues and fixed it, and we ran the post-sweep, and compared it to the pre-test sweep. Everything matched line to line, except one peak (@ ~60Hz)now is lower. we ran another post-sweep, and the 2 post-sweep looked exactly the same. Now we are left to explain the discrepancy to our customers. I want to eliminate and be ready for a few possibilities before blaming it on the unlubed table.
So, I understand that a frequency change of the peaks is indicative of growing of cracks/damage. What about the amplitude change? What does that usually indicate? slippage? or are the amplitude and frequency change usually linked?
Thanks for any insight.
So, I understand that a frequency change of the peaks is indicative of growing of cracks/damage. What about the amplitude change? What does that usually indicate? slippage? or are the amplitude and frequency change usually linked?
Thanks for any insight.





RE: Meaning of Amplitude Change and Frequency Shift after Random Vib
Cheers
Greg Locock
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RE: Meaning of Amplitude Change and Frequency Shift after Random Vib
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Meaning of Amplitude Change and Frequency Shift after Random Vib
1. Tighten all the screws holding the unit in place hand tight.
2. Once all the screws were in, back each off 1/8 turn.
3. Torque screws while holding the unit to what I judged was the most settled position (i.e. with gravity) to make sure that the turning of the screws did not reposition the unit.
After all of this we got better results than before but still had one or two signatures that went out of spec. This tells me that we were somewhere in the ballpark with our initial conclusion.
Anyway, I am not exactly sure what purpose the amplitude shift spec serves. Maybe someone else can enlighten me on that.
RE: Meaning of Amplitude Change and Frequency Shift after Random Vib
What frequency is your local electricity supply?
M
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Dr Michael F Platten