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Signature acquisition lms test.lab

Hi, 
I have certain question that I'd like have a response.
These are the questions:

1- For the stability diagram how can I choose the model size. because If we change the size, the model of our system change which has influence on the identification result.
2- In the following picture, we have a stabilisation diagram, the size of the model here is 96.
For each pic, I chose the 's' in the same rank "95".
So I want to know ,if I choose 's ' in different rank, is there a difference than if they are in the same rank?

3-Finnaly, is there a tool that let me know if this pole is a structural pole or not.

Thank you 
Kind regards.
Asia 

1 REPLY

Re: Signature acquisition lms test.lab

Hi,

 

Here are some of my thoughts on the stabilization diagram (which is part of Modal Analysis not Signature):

 

1.  There is not set rule for model size. At the end of the day, one wants to get the proper modes of the structure.

 

2.  When you hold your mouse over a "s" in the stabilization diagram, it shows the frequency, damping and scatter in big yellow text (see picture) at the bottom of the screen. If these numbers are almost the same, there is no difference between selecting from row 95 or row 96.  In fact, the "s" indicates that between two consectutive rows that the the frequency is within 1% repeatability, the damping is within 5%, etc.  These tolerances are user defined by clicking on tolerances buttons in lower left corner.  Changing these numbers will change the letters in the diagram.

 

modal_repeat.png

 

3.  The picture of the stabilization diagram you included looks very busy.  It looks like maybe Time MDOF was used and not the Polymax curvefitter.  The Polymax curvefitter (Tools -> Add-ins -> Polymax) does a much better job of indicating if this is a true mode of the structure (see picture) for the same data. The Polymax stabilization at the bottom indicates the presence of modes much better than Time MDOF.

polymax.png

 

Hope that helps!