NON LINEAR CURVE FITTING

[John96Dee]

I need to plot the R(T) curve of the ntc probe (which is exponential decreasing). I calculated the temperature and resistance arrays, how do I use the "non linear curve fitting" block? can you give me an example?

[GerdW · Accepted solution]

Hi John,

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@John96Dee wrote:

how do I use the "non linear curve fitting" block? can you give me an example?

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Read the help for that function, scroll down til the end and open one of the listed example VIs…

[altenbach]

There is already an exponential fit built-in, just make sure that IF there is a vertical offset to adjust the bounds accordingly.

For more complicated models have a look here.

[John96Dee]

Hello, I made a VI that at the end of the process creates two vectors. One is a vector of 10 temperatures and the other is a vector of 10 resistances; for each temperature value, I have a corresponding resistance value (so I basically have 10 coordinates). The final goal of the VI is to create the R(T) characteristic of an NTC sensor and plot it graphically (so theoretically, the curve I should obtain is a decreasing exponential). I know I need to do the "fitting". Can someone help me use the "non-linear curve fit" block or if it possible " exp fit" im not able to use them? Thanks, I hope I was clear.

[GerdW]

Hi John,

please don't create new threads for the same topic…

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@John96Dee wrote:

Hello, I made a VI that at the end of the process creates two vectors. One is a vector of 10 temperatures and the other is a vector of 10 resistances; for each temperature value, I have a corresponding resistance value (so I basically have 10 coordinates). The final goal of the VI is to create the R(T) characteristic of an NTC sensor and plot it graphically (so theoretically, the curve I should obtain is a decreasing exponential).

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• Why don't you attach your VI with typical data for R and T included? (When using recent LabVIEW versions you should consider attaching a downconverted version of your VI (File->Save for previous). Most say LV2021 or older, I prefer LV2019.)
• What have you tried so far in using the fitting functions?
• Have you tried the exponential fit as suggested by Christian?

[John96Dee]

i'm sorry for the same question. yes i try to use the block but i'm not able to use it. if someone can upload some examples VI, it is better. thanks    

[GerdW · Accepted solution]

Hi John,

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@John96Dee wrote:

if someone can upload some examples VI, it is better.

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You already accepted a solution that told you how to find examples…

I asked for your example VI with your measurement data included: mind to share it?

I also have a tool to calculate interpolations:

There's a (German) user interface and the subVI to calculate the exponential fit…