4 Run Balance Method
4 Run Balance Method
(OP)
Hi guys,
Have been performing the 4 run method for a while now. Works well enough with a vibration meter. The balance weight location works fantastic. However I find that the weight required according to the method is often incorrect (typically lower than required). What am I doing wrong?
Is there a way to improve on this?
thanks
Dynaman
Have been performing the 4 run method for a while now. Works well enough with a vibration meter. The balance weight location works fantastic. However I find that the weight required according to the method is often incorrect (typically lower than required). What am I doing wrong?
Is there a way to improve on this?
thanks
Dynaman





RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
cheers
M.
RE: 4 Run Balance Method
Walt
RE: 4 Run Balance Method
Use one of the on line calculators to check your working, it is much easier to see what is going on graphically.
I agree 60% is a huge error.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
RE: 4 Run Balance Method
RE: 4 Run Balance Method
I'd do some "bump" test with the sensor radially on the shaft out by the fan wheel, impacting out by the wheel, and some impacting other locations.
The running 1st bending resonance is possibly ( I first wrote likely, then changed my mind) to be somewhat higher than a static test if the fan wheel back plate is stiff enuff to provides some gyroscopic stiffening.
Is the fan isolation mounted?
Do you take vibration measurements elsewhere on the fan, structure and foundation?
RE: 4 Run Balance Method
Is the correction weight attached at same radius as the trial weights were?
Is it possible you have a weighing error for the trial weight or correction weight... that would give correct angle but wrong magnitude.
Sorry to suggest such simple things... just mentioned in the unlikely event you haven't looked at these already.
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(2B)+(2B)' ?
RE: 4 Run Balance Method
For those who asked, I'm using frequency analysis (FFT) to measure the peak amplitude at RPM. That way I can concentrate on the imbalance signal only. There were some other noise elements at higher frequencies but their magnitude was quite low relative to the imbalance. I also thought about coupling effects at RPM because its an overhung rotor........maybe.
So I think the 4 point method is fine its just how I measured the data.
RE: 4 Run Balance Method
1) use a triggered method instead unless you love puzzles
If we call the 4 runs U, T1 T2 and T3, where T1 is the trial weight at position 0 degrees, T2 is at 120 degrees, T3 at 240 degrees:
2) one or two of the runs T1-3 needs to be less than U. if not, use a smaller trial mass
3) one or two of the runs T1-3 needs to be greater than U, if not then it is physically impossible (with 120 spacing) so you must have a noisy measurement. Use a bigger trial mass.
4) if any of the T runs is zero then that run is the solution
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
What on earth are you talking about?
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(2B)+(2B)' ?
RE: 4 Run Balance Method
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(2B)+(2B)' ?
RE: 4 Run Balance Method
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(2B)+(2B)' ?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
I haven't heard of that and don't understand how it would work. Perhaps you or someone can explain how that would work?
I'd also be interested to understand what you meant by items 2 and 3 posted above?
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(2B)+(2B)' ?
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
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(2B)+(2B)' ?
RE: 4 Run Balance Method
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(2B)+(2B)' ?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
OK then, maybe I'm just slow. Please explain the comment "you are wrong" in more detail.
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(2B)+(2B)' ?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
If you don't have a trigger looking at shaft, neither 1 channel nor 2 channel works for 1-trial run balance calc.
2 channel adds the ability to calculate phase as difference between two vibration channels, but that's not what you need for balancing. (You need phase from a triger looking at the shaft.)
dynaman asked "How do you use a 2 channel FFT to calculate phase shift?". My response tried to explain there is nothing special about 2 channel that gives ability to calculate phase for balancing (the phase we gain by 2 channel has nothing to do with balancing). Apparently that was misinterpreted along the lines of "balancing cannot be done with 2 channel analyser."
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(2B)+(2B)' ?
RE: 4 Run Balance Method
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(2B)+(2B)' ?
RE: 4 Run Balance Method
Walt
RE: 4 Run Balance Method
Can you paste a link to the software you use to perform the transfer function? I would like to try this out.
thanks.
RE: 4 Run Balance Method
DASYLab® Software
Need Pro version for Transfer Function
Pasted from <http://www.mccdaq.com/products/dasylab.htm>
I have seen other programs advertised on Web. starting at about $100.00 that do TF analysis.
Walt
RE: 4 Run Balance Method
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method
RE: 4 Run Balance Method
Steve
RE: 4 Run Balance Method
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: 4 Run Balance Method