Checking for Shaft Eccentricity with a Strobe
Checking for Shaft Eccentricity with a Strobe
(OP)
I have a shaft that I suspect may have an eccentricity problem, and I am wondering if there is a procedure for checking for eccentricity with a strobe light. It is a three piece shaft through a screw pump. We could use a dial indicator on the straight stubs at the ends, but the centre section with the screw can't be measured that way. Have you ever checked for eccentricity using a strobe? How did you go about it and were the results helpful? Thanks!
rstock





RE: Checking for Shaft Eccentricity with a Strobe
yes, I have used a strobe for that sort of thing, main problem is that the deflections have to be quite large to be visible, so they only really work at low speeds.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Checking for Shaft Eccentricity with a Strobe
RE: Checking for Shaft Eccentricity with a Strobe
RE: Checking for Shaft Eccentricity with a Strobe
If you are looking at less than 0.100inch eccentricity, then, you might want to consider using a proximity probe: look at the display on a scope to determine the value you are looking for with a good degree of accuracy - if you have more than one probe you can get a measure of rotor deflection shape.
RE: Checking for Shaft Eccentricity with a Strobe
RE: Checking for Shaft Eccentricity with a Strobe
1 - you need the right geometry to be able to do it.
2 - you would presumably need a strobe resembling a point source. A wide source like our handheld strobe would create a blurry edge of the shadow (draw the lines from each side of the light past the edge of object to see width of shadow edge).
I would definitely endorse slight detuning from 1x to obtain slowly moving image... rather than trying to strobe at twice per rev. I have looked at things strobed at 2x before and I see two images but my brain has a hard time separating them. Difficult to tell what you are really looking at (try it).
rob - strobing at half speed (once per two revolutions) - makes even less sense to me. You would see the same image as strobing at 1x speed, except the image is not refreshed as often. Maybe you are thinking of strobing at twice speed (twice per revolution).
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RE: Checking for Shaft Eccentricity with a Strobe
Interfacing an LED to the strobe's trigger circuit shouldn't be too hard, otherwise build a delta F trigger using an F to V and V to F chip (I think that's the cheapest).
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Checking for Shaft Eccentricity with a Strobe
RE: Checking for Shaft Eccentricity with a Strobe
RE: Checking for Shaft Eccentricity with a Strobe
Mike Halloran
Pembroke Pines, FL, USA
RE: Checking for Shaft Eccentricity with a Strobe
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.