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birgit_s
Austria
2 Posts |
 Posted - 03/22/2018 : 09:20:52 AM
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Hello,
I am trying to fit my impedance sprecta (Z and tan(phi) vs. angular frequency with these 2 equations simultaneously, but it doesn't work:
Z=Rs+(Rp/(1+(w*Cp*Rp)^2))-((w*Cp*Rp*Rp)/(1+(w*Cp*Rp)^2));
tan(phi)=-((w*Cp*Rp*Rp)/(Rs*(1+(w*Cp*Rp)^2)+Rp));
Cp, Rp, and Rs should be found at the same time and should have the SAME value!
Each equation alone works quite well, but my paramters don't have the same values, as they should have. and if I try to fit it simultaneously it doesn't work anymore.
Do you have an idea, how it works?
Thanks,
Birgit
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arstern
USA
237 Posts |
Posted - 03/22/2018 : 12:34:54 PM
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Hi Birgit,
When creating the nonlinear fit equation did you first select Equations under Function Type -> Select Next
Then setup the parameters, variables, and equations as seen in the pictures below? If not, you may want to try this.
OriginLab
If the above is not helpful, please send your project file and .fdf files (user defined nonlinear fit files) to tech@originlab.com. You can find your .fdf files at \Documents\Documents\OriginLab\User Files\fitfunc
Thanks,
Aviel
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birgit_s
Austria
2 Posts |
Posted - 03/23/2018 : 09:31:58 AM
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Hi,
thank you for the fast reply :)
Now I have a new problem with the data selection:
Why is there an imaginary part in field 1, which is obviously the real part and vice versa? Or have I made a big mistake???
Thanks,
Birgit
BS |
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arstern
USA
237 Posts |
Posted - 03/23/2018 : 10:18:23 AM
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Hi,
With the dropdown menu you can select the correct dataset with the corresponding variables. The dialog automatically chooses the corresponding dataset by how your worksheet is organized. i.e. I am guessing that Real is listed before Imaginary in the worksheet.
Aviel
OriginLab |
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fitting 2 different curves