PolyReference/PolyMAX and Agilent 35670A

[onemilimeter]

I have an Agilent 35670A. I carried out impact hammer tests and tried to find out the resonance frequencies of a simple structure (

http://www.eng-tips.com/viewthread.cfm?qid=253310&page=1).

Someone replied that "...no-one uses curve fits to the Nyquist plot any more for modal analysis (because it doesn't work very well when you have modes close together). These days it is all done using advanced multi-degree of freedom algorithms like Polyreference and PolyMAX." I have zero knowledge in Polyreference or PolyMAX. I wonder whether I could use the data measured by Agilent 35670A to obtain plots derived using Polyreference/PolyMAX algorithms. Could I? If yes, what are the measured data that I need for Polyreference or PolyMAX analysis?

Thank you very much

 

[GregLocock]

Manual circle fitting works well enough, but I must admit I'm glad I don't have to do it any more. The FRFs you have recorded are sufficient for polymax, the thing is you need to take more response and excitation points. Your next difficulty is finding polymax or polyref algortihms that you can use.

However I suspect the real problem is that with such light symmetrical structure the mode shapes will rotate around and follow your accelerometer.

Your circle fit looks like a good start, but you need to increase the frequency resolution by at least a factor of 2.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[onemilimeter]

Hi GregLocock,

Thanks for your reply.

You mentioned that "... with such light symmetrical structure the mode shapes will rotate around and follow your accelerometer". I do not fully understand the underlined part. Would you please kindly advise?

I will try to increase the frequency resolution. However, if I'm not mistaken, I already used the highest allowable frequency resolution for Agilent 35670A, i.e. 1600-line, for those measurements. I will check again.

 

[GregLocock]

I suggest you investigate and find out whether it applies in your case.
You have all the tools.


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.