4 Run Balance Method

[dynaman]

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

 

[dynaman]

Okey dokey, but how can I use it to measure phase shift? I'm missing something here.

 

[electricpete]

So, if I understand correctly, you're saying we can do standard single plane 1-run balance using a 2-channel vibration analyser without any optical/laser sensor looking at the shaft?

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)' ?

 

[GregLocock]

No, of course you need a trigger see 5 Mar 13 19:01 and 5 Mar 13 16:51



Cheers

Greg Locock


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[electricpete]

For dynaman - do you have access to tunable strobe to freeze the shaft? If so, you can use that to determine phase for balancing.

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(2B)+(2B)' ?

 

[electricpete]

Sorry, NOT tunable - scratch that. The strobe would have to be triggerable... triggered from the measured vibration.

http://www.eng-tips.com/viewthread.cfm?qid=340252

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(2B)+(2B)' ?

 

[dynaman]

I can determine phase shift using a IR sensor on a dual trace scope BUT how can I used a 2 channel FFT to measure phase? Is there a better way to measure phase?

 

[electricpete]

How do you use a 2 channel FFT to calculate phase shift?

Two channel analyser can tell you relative phase of different points on the machine at a given time. I don't think it would be much use for balancing since the things we want to compare occur at different times. You need something some kind of pickup that is going to look at something on the rotating shaft and give you a once per revolution pulse can be used as reference for phase measurement.

ep - you are wrong. A 2 channel FFT analyser makes a great balancing analyser.

So, if I understand correctly, you're saying we can do standard single plane 1-run balance using a 2-channel vibration analyser without any optical/laser sensor looking at the shaft?

I haven't heard of that and don't understand how it would work. Perhaps you or someone can explain how that would work?

No, of course you need a trigger see 5 Mar 13 19:01 and 5 Mar 13 16:51

OK then, maybe I'm just slow. Please explain the comment "you are wrong" in more detail.


=====================================
(2B)+(2B)' ?

 

[dynaman]

Doh!

 

[GregLocock]

ep - just try it. it works. I have very rarely had the luxury of using a dedicated balance machine, and have used a 2 channel FFT analyser to do it for 30 years. trigger goes into chan 1, vibration into chan 2, transfer function 2/1 gives you phase.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[dynaman]

Ahh I see now.... geez thanks guys.

 

[electricpete]

If you have a trigger looking at shaft, either 1 channel or 2 channel works for 1-trial run balance calc.
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)' ?

 

[electricpete]

There may be a difference in types of equipment we're discussing. The single channel vibration analysers I have seen all have one analog vibration input plus a trigger input (for example TTL) and provide phase based on these inputs. That is the framework for my discussion. Greg is probably talking about vib analysers that don't have a separate trigger input, so 2-channel would be required to accommodate phase measurement using a trigger.

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(2B)+(2B)' ?

 

[Strong]

I have done balancing with a 2-channel (PC with external sound card)analyzer. Channel-1 was tachometer (1xSS) and channel-2 was vibration sensor (accelerometer). The phase was measured from the Transfer Function and vibration amplitude directly from the acceleration spectrum. In this case the "2-channel analyzer" did not have a separate Trigger input.

Walt

 

[dynaman]

Hi Walt,

Can you paste a link to the software you use to perform the transfer function? I would like to try this out.

thanks.

 

[Strong]

Here is one that I use on occasion:
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

 

[dynaman]

wow its really pricy software. I like how you can develop your own apps. Wondering if there is cheaper software for development?

 

[GregLocock]

Sure, Octave. It is free.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[GregLocock]

You may even find the Abravibe add on does what you want directly, I haven't installed it yet as I am in install hell with octave.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dynaman]

thanx

 

[spciesla]

If you are using the FFT to measure the peak amplitude, what kind of windowing are you using? Is it possible that the windowing is knocking your peak amplitude down such that the calculated correction weight is low.

Steve