caractéristique courant-tension

[altenbach]

I thought you can sample the signal already. And according to your other post, the sampling period is 100ms.

You need to be much more specific if this does not answer the question.

[arhemza]

I made a current and voltage value acquisition, for the purpose  to trace the current-voltage curve.
so, the current following'Y' and the voltage following 'X'.
because the voltage values are not separated regularly, I want to sample the curve

how can i calculate the voltage échatillonnage to sépérate the voltage value regularly?

[WenR]

Hello arhemza

I understand you have a Current-Voltage curve, if you want to obtain dV/di or di/dV, there is no need for a dt value, since there is no time in your curve. If you need one of the mentioned derivatives, you could implement the same solution posted before (adjust your data to a fitting curve, and derivate the curve). If not, could you explain the reason why you need the dt value?

Thanks

WenR

[arhemza]

hi,

in the solution posted before (attached file), we must determine the sampling interval in the derivative fucntion.

is that the value of the interval is determined arbitrarily? because i change the value ( 0.1 or 0.125 or 0.2...) the values of the derivatives will change, if not how can make the right sampling interval.

thank you.

[altenbach]

To display unevenly spaced data, simply use an xy graph. You can also resample each trace with a constant dt using interpolation.

Please show us your data and tell us what you want to do with it. All this is pretty basic stuff. The dt in the derivative function is simply a scale factor.

[altenbach]

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arhemza wrote:

in the solution posted before (attached file), we must determine the sampling interval in the derivative fucntion.

is that the value of the interval is determined arbitrarily? because i change the value ( 0.1 or 0.125 or 0.2...) the values of the derivatives will change, if not how can make the right sampling interval.

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OK, so you have some data and do a polynomial fit. Have you mentioned that before? Once you have a polynomial fit, you can recalculate the curve using an equally spaced ramp and the "evaluate polynomial" function. No loops needed.

You can also calculate the derivative of a polynomial analytically from the polynomial coefficients. That's what I would do. Try it!

[arhemza]

so, i want to ask about the polynomial fit, 

is the polynomial order related to the value of sampling interval?  

[altenbach]

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arhemza wrote:

is the polynomial order related to the value of sampling interval?  

---

You keep asking question that make no sense at all.

You seem to have absolutely no idea what the meaning of polynomial order or the sampling interval is.

Who wrote the program that you have attached earlier?

[arhemza]

i am askin before in the forum, that how can i make the derivative of curve in labview, 

so i saw the function derivative in labview but i dont understand how can i use it,  

so, someone posted me about the polynomial curve, and i am trying to make the right program

that's all.

[altenbach]

As I said, if the polynomial fit is sufficient to describe the data, you can calculate the derivative of that same polynomial using the nth derivative of a polynomial VI.

The derivative of a polynomal is just another polynomial. Given it's coefficients from the above tool, you can then calculate the derivative for any x using polynomial evaluation.

This seems trivial. Where do you have problems?