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George D

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Reply with quote  #16 
Thanks for setting this up Pete. It clearly took thought and creativity to set it up the way that made us think. I probably should have recused myself, as we have such a similar pair with similar issues.

I feel your pain when you re-counted your experience of having the vibration jump up unexpectedly with one reading. Having suffered through similar experiences, I’ve tried to make sense of it? In our case, I believe it starts with a flimsy lightly damped garage-built looking support frame with cheap fasteners. Over time as the structure may loosen, or with maintenance as fasteners are removed and reinstalled; structural lightly-damped natural frequencies may move close to the running speed... creating confusion and causing us to write blog entries about our observations.

Appreciate that you took the time to set this up Pete. Normal people do crosswords and sudoku puzzles. We do vibration case histories...
electricpete

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Reply with quote  #17 

Thanks for the kind words George.  Whenever I have an “WTF” moment followed by an “Aha” moment it suggests to me that it might be a good quiz (just start by trying to get everyone else as confused as I was).  Unfortunately the Aha moments seem to be decreasing lately even as the WTF moments are trending up [confused] .  But I do get benefit out of writing quizzes and cases since it helps me keep track of the details that otherwise tend to fade away. And often I learn something I didn’t expect from the forum. Speaking of which… 

Quote:
I feel your pain when you re-counted your experience of having the vibration jump up unexpectedly with one reading. Having suffered through similar experiences, I’ve tried to make sense of it? In our case, I believe it starts with a flimsy lightly damped garage-built looking support frame with cheap fasteners. Over time as the structure may loosen, or with maintenance as fasteners are removed and reinstalled; structural lightly-damped natural frequencies may move close to the running speed... creating confusion and causing us to write blog entries about our observations. 

Great point. I’ll add that to the top of our list of things to look at closer.

ivibr8

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Reply with quote  #18 

LOL     When I responded earlier this morning.....I didn't see the previous post re: transmitted energy (perhaps I didn't refresh?)
That's why I wrote up the bent shaft possibility since I thought you were still seeking the answer   [wink]  

To echo others, I love these quizzes as it keeps us thinking.
Over the years, I have (as well as anyone who does this for a living) seen this before (cooling towers, coolant pumps on same discharge structure, etc.)

Also, thanks for the link. It is now in my "Links" folder under Electrical

Regards
Jim 
electricpete

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Reply with quote  #19 
Quote:
LOL     When I responded earlier this morning.....I didn't see the previous post re: transmitted energy (perhaps I didn't refresh?)
That's why I wrote up the bent shaft possibility since I thought you were still seeking the answer 

Lol, that makes sense. I know very well that you're familiar with the ins and outs of slip, and I wasn't quite sure what you were getting at.  Now I can understand where you were coming from in a spirit of brainstorming / questioning an unsolved case. 
Quote:
Also, thanks for the link. It is now in my "Links" folder under Electrical

Glad you liked that one.  Since it is peripherally related to this thread (at least the title) and the attachments in that other forum don't work unless you are a member, I'll attach it here.

Attached - Low Speed And High Current Due To Misconnection




 
Attached Files
pdf LowSpeedHiCurrentDueToMisconnection.pdf (344.57 KB, 14 views)

fburgos

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Posts: 670
Reply with quote  #20 
Get single channels for input D (ods/modal and 2 plane balancing) I don't like to carry arround the 4channel thing or splitter.

Wonder if there is a single channel volts input it could be handy
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