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SNORMAN

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Reply with quote  #1 
I have a vane compressor here and the motor has a rising 1 x ts in the axial reading. I thought it was being caused by misalignment so i checked and the cross phase # is low (20) in the axial plane. the motor however seems to have an imbalance. from end to end on the motor itself the cross phase is around 180. I did check some other motors in the plant and they all seemed to be out of phase from end to end. Is this normal ? and are there any ideas as to what would cause this in the compressor motor. I do suspect the base a bit. But at the base bolts the channel phase is good but on top of the motor frame it is way off.

OLi

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Reply with quote  #2 
It may be that a specific unbalance distribution will excite a unwanted resonance at some speed and are therefor avoided at all cost. A bit far out but it does exist and may be good to know when balancing and would in that case the restrictions will be enforced by the OEM to every length if asked. Not that any instant disaster will occur as I naturally broke the rule as fast as I could not knowing why they had such stupid rules but only at a short term test scenario not in the long term final solution in that the OEM rules were kept to the dot (as we actually worked for the OEM). In our case it was the other way around than what you have. They were to be kept to have static residual unbalance and no dynamic weight installation in the field was accepted for any reason. I did a quick trim run with only weights in one end and that can be argued to be on the limit to not being a pure static weight but it worked and the test was performed.
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fburgos

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Reply with quote  #3 
all motors have 180 difference, are you correcting sensor position?
SNORMAN

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Reply with quote  #4 
"are you correcting sensor position? " sorry im not sure what you mean. i have them in the same plane 
fburgos

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Reply with quote  #5 

sorry sometimes i don't elaborate my replies as I should.

I mean they are pointing in the same direction?

For example 180° is when sensors are facing each other, then you apply a correction of -180° sensor direction, then your phase is 0° as it should.

SNORMAN

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Reply with quote  #6 
Ok, yes i had them facing the same direction that is how i was taught, but your tip will be handy because sometimes it is hard to orient them facing the same direction.
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