Non Linear Curve Fitting - BET Calculation

[ManuelElze]

Hello, I am new to the LabVIEW community.

I am trying to do BET Fitting in LabVIEW.

Until now it was done in Excel using the Solver add, but I want to include this Fit-Model (and several others GAB,...) in my LabVIEW program. I am using the Nonlinear Curve Fit.vi but I am getting different results than with the Excel Solver add. 

Any Help would be much appreciated.

I attached my Vi and the Excel File.  

[altenbach]

You use a formula

m*c*a/((1-a)*(a+(c-1)*a))

While it should be 

m*c*a/((1-a)*(1+(c-1)*a))

See if that helps.

(Also note that the first element is index zero, so if you take a five elements subset starting at 1 for the Y values, you probably should also start at 1 for the x-values, else the x and y don't match up).

[altenbach · Accepted solution]

See if this helps.

[ManuelElze]

It seems to work just fine with the right formula.

Thank you so much. I was so focused on the wireing that I totaly missed this. Stupid me.