Least Squares Complex Exponential - VI

[bk.]

Hello all,

At the moment I am running a multi-input multi-output (MIMO) test on a bridge model I have developed in another program.  I am running the input and response signals through the FRF (MIMO) VI in labview.  The output from this test (based on two input signals) is 2 columns of the FRF matrix, these being 2-D Arrays. 

I am then trying to take the FRF matrix and run it through the Least Squares Complex Exponential (LSCE) VI to extract modal parameters. 

The problem is this:

The LSCE VI only takes 1-D Arrays.  So what I can do from the 2-D array outputs from the MIMO FRF is extract the individual 1-D arrays (corresponding to individual columns of the FRF matrix).  I can run these individually into the LSCE VI and compare the output modal parameters. This way though finds separate sets of modal parameters for each of the 1-D array inputs.

What I would like to do is be able to input the entire FRF Matrix due to multiple-inputs multiple-outputs into the LSCE VI in order to find one set of modal parameters for the set of inputs and outputs.

It seems like the LSCE works off of a single-input single-output (SIMO) test though, only accepting 1-D arrays. 

What I would like to know is if the LSCE VI can be used with a MIMO test output, by adding a full FRF matrix, (m_responses x n_inputs)???

Thank you for any information you can provide to help!

[mikeporter]

There are a host of array manipulation functions in LV. For example, if you take an array indexer and wire a 2D array to it you will see that it provides indices for specifying a row and column. However if you only wire one of them the output is a 1D array consisting of the specified row or column. Likewise, run a 2D array into a FOR loop, it will automaticaly index rows from the array and inside the loop present the rows one at a time. Transpose the array before it goes to the loop and it will index through the columns.

Mike...

[bk.]

"So what I can do from the 2-D array outputs from the MIMO FRF is extract the individual 1-D arrays (corresponding to individual columns of the FRF matrix).  I can run these individually into the LSCE VI and compare the output modal parameters"

i can get 1-D arrays.  i need more information on the LSCE VI

[1024channels]

Hi; You are exactly right - LSCE is SIMO and you need MISO or MIMO such as  LSCF is a freq domain or PTD is a time domain curve fit algorithms that do allow multiple references or additional rows and columns of the transfer function matrix to be handled.

Let me know if you need more help.  tim.copeland@mpina.com