laser vibrometers
laser vibrometers
(OP)
2 questions:
Does anyone have positive or negative comments about using laser vibrometers like http://www.bksv.com/1067.asp?
If i were to redirect the beam though a fiber optic cable, is the signal still usable? How would one correct for the change?
Does anyone have positive or negative comments about using laser vibrometers like http://www.bksv.com/1067.asp?
If i were to redirect the beam though a fiber optic cable, is the signal still usable? How would one correct for the change?





RE: laser vibrometers
Jim
Kennedy Space Center, FL
RE: laser vibrometers
The frequency response was only 400 Hz, and there are amplitude related limits as well.
The fibre optic idea is interesting, the blurb says you can measure through glass, ask B&K
One of the big problems is that it is not an inertial reference, so you measure the vibration of the instrument as well as the target.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: laser vibrometers
We're investigating the use of Polytec's scanning laser vibrometer, and I am curious as to whether anyone here has experience with it?
Our intended application would be in determining the vibrational modes of a cabin backwall as relate to a severe boom problem. The panel is roughly 8 feet by 8 feet, and we're interested in modes around 60 Hz, so we're predicting that a few hundred points will give us usable results.
The Polytec unit can scan this in broadband (white noise) mode in under 10 minutes, followed by a narrowband "fastscan" in about a minute at 10 x the original number of points.
The output will be an animation superimposed over a digital image of the panel, as well as FRF data on all 200 points.
RE: laser vibrometers
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: laser vibrometers
Which, given our current engineering budget, looks like what I'll be doing, starting this morning...
RE: laser vibrometers
One technique we did use that was fun was to use a mic as a roving pickup, as the local sound pressure is largely a function of the local surface velocity.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: laser vibrometers
I've used that microphone thing too, when doing a study of door skin "ring" - door slam noise. Found it gave essentially the same results as an accelerometer in measuring the effectiveness of damping sheet materials.
The weather's been too nice for me to try this yet though.
(When it's clear out, I do on-road testing...)
Regards,
R
RE: laser vibrometers
RE: laser vibrometers
Could you correlate torsional vibration level at an rpm to measured strains at the same conditions?
Then you'd have a guide to future torque levels based on torsional vibration?
Oh, wait: you're interested in overall torque, not torque variation, right?
Sorry.
RE: laser vibrometers
RE: laser vibrometers
bye
RE: laser vibrometers
Did you use a single-point or a scanning laser?
What did you use to drive the door panels?
What was your point density?
Thanks,
- R
RE: laser vibrometers
Cheers.
RE: laser vibrometers
RE: laser vibrometers
Speaking of your arm falling off:
We gridded just a part of the cab panel yesterday, and studied 49 points (a 7x7 grid) and it took 4 hours just to get the data - I don't even want to think about the time required to analyze that much data.
Ah, no: we don't have any modal software. We're working on the old graphical modal analysis model.