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Noknroll

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Can anyone interperet this data?
Its a coast down of a shearing machine at home, I'm just practising before I need to do a one shot only job next week 
Are there 2 phase shifts or something wrong with my data collection. I did 3 coast downs and this is the only one with the 2 shifts? coast down.JPG

Noknroll

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Reply with quote  #2 
My mistake, there is another one with 2 shifts, but it looks a lot different to the first one, but it was exact same set up?
coast down 2.JPG

Travler

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Where the amplitude goes through zero with a phase shift is a response often seen of a bent or kinked shaft.
James.

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Hey mate, in the software you can just display the nyquist plot to interrogate. This is one I did on a vertical mounted motor.

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jpeg WP_20170409_06_41_11_Pro.jpg (444.21 KB, 22 views)

James.

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Reply with quote  #5 
And this is the bode plot of the same data, beauty ain't she.

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OLi

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Reply with quote  #6 
I have one like that from the driveshaft of a truck [smile] OEM forgot to check such details after changing gear ratio in the wheels for energy saving.
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Noknroll

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Reply with quote  #7 
Thanks fellas
So does mine look like valid data?
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Reply with quote  #8 
Quote:
Originally Posted by Noknroll
Thanks fellas
So does mine look like valid data?


Hey Noknroll,
Yep looks like you captured the peak and phase spot on. On your job have you only got one coast up / down or when on site can you start and stop as you need?
Noknroll

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Reply with quote  #9 
Hey James, its a FD fan in power station, may not even get to stop it, but need to be ready just in case.
James.

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Reply with quote  #10 
You got any history, or are you just going to gather data from all bearing locations and structure then at the highest point set up for coast down, obviously with it running at max running speed?
Ralph Stewart

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Reply with quote  #11 
Nokroll,

Just wondering, what you will be looking for on the fan? A specific problem? Or just some history data?

As far as your trial coastdown plots go, they look good to me.

There is a lot of information showing in both plots, even though they were over 30 minutes apart, and something could have been altered that was not readily or easily noticeable, which might account for the differences referenced in your quote. "looks a lot different to the first one, but it was exact same set up".


Thanks and Have a Great Day,
Ralph

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Noknroll

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Reply with quote  #12 
James, Ralph
Got elevated turning speed vibration after an impellor rebuild, most likely imbalance but client to wants to run a few tests before hand so I'll be doing standard vibe readings,+ peak and phase at various damper settings then finally a coast down........there call
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