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Vibration Fixture Orientation

Vibration Fixture Orientation

(OP)
If I am designing a vibration fixture for testing in the vertical axis, does it matter if the test item is mounted upside down?
Some opinions say yes, since gravity is adding a 1g downward acceleration.
My opinion is that the feedback loop in the vibration controller will neutralise this and give an even acceleration in the up and downward directions.

RE: Vibration Fixture Orientation

Your shaker can only correct for what it can measure, which is typically the frequency dependent motion, not the static load. Moreover, the control accel is typically attached to the table or the fixture, not the UUT. Additionally, the inversion potentially alters the resonant frequencies within the UUT, and possibly adds new ones.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Vibration Fixture Orientation

(OP)
Thanks for the response, but if the shaker table is being controlled such that the positive and negative accelerations are identical does it matter which way up the UUT is mounted? I would have thought that the modes and frequencies of the UUT would be the same either way.

RE: Vibration Fixture Orientation

"I would have thought that the modes and frequencies of the UUT would be the same either way."

Sure, if it's a solid block of tungsten. Since you've provided zero information about the UUT, no one can give anything but a generalized answer. If there's anything that can decouple under test, then it might make a difference which way it's oriented, since you have no ability to invertgravity.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

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