Skip to main content
C
Cornel19-Tanzanite
19-Tanzanite
August 20, 2024
Solved

Curve fitting problem - DC Magnetization Curves

  • August 20, 2024
  • 2 replies
  • 2561 views

Hello,

Using this fit formula from below, how to determine a, b, c, d, e, and x coefficients in such a way to fit the below plot Flux Density vs Magnetizing Force:

Cornel_2-1724156296194.png

Cornel_1-1724156201189.png

Cornel_0-1724156484547.png

Cornel_0-1724156172912.png


I think (but I do not know how to do) to read all the data points of each line (60uH, 40uH, 26uH) and then to make the curve fitting by using genfit Mathcad function, minerr or something like that.

Best answer by Werner_E

Do you really want a separate fit for each of the three curves?

Or is one of the 6 parameters a,b,c,d,e,x dependent of the inductivity value (60 µH, 40 µH, 26 µH) and if yes, in which way. You could then do the very same as I have shown in your other current curve fit question.

But comparing the results for all three inductivities shows that all six parameters are completely different and so may all be dependent in some way of the inductivity value.

Furthermore you get quite different results for the same data set with different guess values.

Werner_E_0-1724198793637.png

 

All seem to provide a fairly good fit (B4 fails for lower H values, though).

Werner_E_1-1724198822577.png

 

 

2 replies

C
Cornel19-TanzaniteAuthor
19-Tanzanite
August 20, 2024

 

For example below are the data points for the 3 lines: 60uH, 40uH, and 26uH lines from above graph.

Cornel_0-1724166443143.png

 

Cornel_1-1724166481918.png

 

MCP10 file attached.


Only x axis is log scale.

Now we need to find the values of a, b, c, d, e, and x coefficients in such a way to be able to generate these lines also with the above formula by fitting these curve with that given formula, by using genfit/mineer or something similar mathcad functions.

N
NickKemaev12-Amethyst
12-Amethyst
August 20, 2024

This option is for one of the branches.

Screenshot_1.jpg

C
Cornel19-TanzaniteAuthor
19-Tanzanite
August 20, 2024

Hi, it is not ok because you changed and used other fit formula. The fit formula that needs to be used was already given in the first post. 

W
Werner_E25-Diamond IAnswer
25-Diamond I
August 20, 2024

Do you really want a separate fit for each of the three curves?

Or is one of the 6 parameters a,b,c,d,e,x dependent of the inductivity value (60 µH, 40 µH, 26 µH) and if yes, in which way. You could then do the very same as I have shown in your other current curve fit question.

But comparing the results for all three inductivities shows that all six parameters are completely different and so may all be dependent in some way of the inductivity value.

Furthermore you get quite different results for the same data set with different guess values.

Werner_E_0-1724198793637.png

 

All seem to provide a fairly good fit (B4 fails for lower H values, though).

Werner_E_1-1724198822577.png

 

 

C
Cornel19-TanzaniteAuthor
19-Tanzanite
August 21, 2024

I am not aware of any relationship between any of a,b,c,d,e,x parameters and inductivity values. So, we need to go with no dependency between any of parameters. But I understand that if no dependency is assumed between one of a, b, c, d, e or x parameters and inductivity values then we need to make 3 genfit/Minerr fit curve separately for each inductivity values  (60 µH, 40 µH, 26 µH), right?

This below variant is with Minerr, fit curve for 26uH inductivity value.

Cornel_0-1724224828721.png

Cornel_0-1724225120748.png

 

 

 

fit curve for 60uH inductivity value.

 

Cornel_2-1724224921029.png

 

Cornel_1-1724225146381.png


And also for the last fit curve of 40uH, as above.

 

Is better Minerr than genfit?

W
Werner_E25-Diamond I
25-Diamond I
August 21, 2024
But I understand that if no dependency is assumed between one of a, b, c, d, e or x parameters and inductivity values then we need to make 3 genfit/Minerr fit curve separately for each inductivity values  (60 µH, 40 µH, 26 µH), right?

Right. If the equation does not contain a variable for these values, you can't expect one single equation (dependent on that variable) to cover all possible inductivity values like we could do in your other question with the frequency f.

 

 

Is better Minerr than genfit?

Don't think so. Usually the result are the same. Minerr may have advantages if you intend to apply additional constraints like a>5 or the like. You can't do so with genfit.

But as I had shown above, there seem to be a lot of possible functions of the type you provide with much different parameter values which all yield more or less suitable fits. The results depend heavily on he guess values provided. This is because the function type you had chosen depends on a lot (six) independent parameters.

Why must it be this specific function type?

 

In a non-log plot the correlation looks almost linear!?

Werner_E_0-1724233356981.png

 

Terms & ConditionsCookie settingsAccessibility statement