Non lineair calibration of signal

[ThijsBoeree]

Hi,

I have a rather complex question... at least i think it is. I've solved this once way back in LabVIEW 7. But when i look at my old vi's i can't recall what i did.

The problem: I have a large set of data let's say 4000 samples, my data should go from 10Volts to -10Volts but my recorded data goes from 12,8Volts to --6,4Volts, i can use a lineair calibration, with a calculated gain and offset:

Offset = (12,8 + -6,4) / 2 = 3,2
gain = (10 - -10) / (12,8 - -6,4) = 1,041

applied for max value: 12,8 - 3,2(offset) * 1,041 (gain) = 10
applied for min value: -6,4 -3,2 (offset) * 1,041(gain) = -10

See example:

But now i know there is a way to do a non-lineair calibration with more data points let's say 5, i thought it was something with a polynomal fit, but i can't rember...

Does anyone know how to do that?

Best regards,

Thijs

[GerdW]

Hi Thijs,

you could use a LUT (look-up table) from your 5 samples and Array-Interpolation functions to "scale" your measurement values.

Or you use the polynomial fit function on your 5 samples to calculate polynomial coefficients and apply them on your measurement data. The GeneralPolynomialFit function comes with an example in the example finder…

[ThijsBoeree]

Okay, but where do i place the polynomial function in my given "lineair calibration" example?

I have 4000 samples and only 3 to 5 fitting points...

Best regards,

Thijs

[GerdW]

Hi Thijs,

please convert your VI to LV2011 to get an answer…

[ThijsBoeree]

Here is a version 2011

Thanks for your help!

[GerdW · Accepted solution]

Hi Thijs,

this way:

[ThijsBoeree]

Do you mean with the XY values, the one that it should be and the raw one...?

[ThijsBoeree]

And what is the name of the VI you are using...?

[ThijsBoeree]

Thank you so much, i figured it out!

Best regards!

Thijs