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## Linearity - Potentiometer standard deviation

I am testing this 2 potentiometers and I want to determine whether or not the pot is linear.
The data collected on a good graphs look like this.

Where the RED line is the measured value and the GREEN line is the tolerance.
If the RED line is out of the GREEN line than these POT fails.
Attached below is a curve for linearity that I think will work with what I am doing?
If somehow we can make the GREEN LINES as wide at the end would fit into the model below.

The current program is not acturate and would always fail good units. It will pass today but fails tomorrow. The consistently of passing is not there. I think I need to open up the limits or find another way to determine pass or fail.

Do you think you can help?

Best regards,
Krispiekream
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Accepted by topic author krispiekream

## Re: Linearity - Potentiometer standard deviation

Hi kream,

I want to determine whether or not the pot is linear.

How do you define "linearity" with your pots?

I would define this as function of R_pot/R_full vs. slider position…

If somehow we can make the GREEN LINES as wide at the end would fit into the model below.

That's easy: either increase your LinTol value - or even set the tolerance to MAX(LinTol*value; FixedMinValue)…

I did change your core routine to:

Why do you need loops for polymorphic functions?

Best regards,
GerdW
CLAD expired, using LV2011SP1 + LV2017 (+LV2019 sometimes) on Win7+cRIO
Kudos are welcome

Message 2 of 7
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## Re: Linearity - Potentiometer standard deviation

I would define this as function of R_pot/R_full vs. slider position…

How would I do something like that? Do you have an example?

I increased the tolerance to 0.25 and its seems to be okay but I don't know if its accurate or not.

How would I implement something like this

vs what it is currently is.

Best regards,
Krispiekream
Message 3 of 7
(1,043 Views)

## Re: Linearity - Potentiometer standard deviation

Hi kream,

I don't know if its accurate or not.

According to your images you need to expect ±0.2% of non-linearity (type 3500), with respect to resistance range. For a 100kOhm resistor you need to expect ±200Ohm non-linearity…

How would I do something like that?

You need to know the slider position to know the expected resistance value. Only then you can compare with real/measured resistance and calculate the non-linearity…

Best regards,
GerdW
CLAD expired, using LV2011SP1 + LV2017 (+LV2019 sometimes) on Win7+cRIO
Kudos are welcome

Message 4 of 7
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## Learning to understand LINEARITY FIT functions.

Hi

I have these data I have collected from the tests.

I am not familiar with linear fit.vi

or its function.

The current code is what I see. But I don't understand how the code works.

It is currently in use for production now but I think its not accurate and doesn't meet the criteria.

LINEARITY of a 10K pot should be 20 ohms or 0.20% error.

Can someone help me look at my code and see where it can improve?

Thanks

Best regards,
Krispiekream
Message 5 of 7
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## Re: Learning to understand LINEARITY FIT functions.

Hi krispiekream,

is there a reason you need to put your measurement data into an array of cluster?

You use an arbitrary X axis for your fit, but I told you once you should use the current position of your pot(s) instead…

Best regards,
GerdW
CLAD expired, using LV2011SP1 + LV2017 (+LV2019 sometimes) on Win7+cRIO
Kudos are welcome

Message 6 of 7
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