# LabVIEW

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## Re: Keithley 6517B Current vs. Voltage Plot

Hi

I use your code and that works well.

But there is difference between measurement result and text file result.

As you see at picture, the result shows 1.74000E-10 But at text file the result shows 0.000000.

How can I fix this difference?

I will be so thank you if you give solutions.

Thank you.

Message 11 of 15
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## Re: Keithley 6517B Current vs. Voltage Plot

Hello JinyongKim,

When looking in the VI given by cstorey there is a Number to fractional String conversion with nothing wired to the precision input between the result output and the write to text file function.

As your result is 1.74000E-10 is it is converted as 0.000000.

There is now two possibilities :

- change that conversion to Number to Exponential String

- change the precision of the Number to fractional String to 10 or more

Here a small example for you to test what could be the most appropriate for your use.

Message 12 of 15
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## Re: Keithley 6517B Current vs. Voltage Plot

Thank you.

I change number to franctional string to exponential.

Then problem solved.

Message 13 of 15
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## Re: Keithley 6517B Current vs. Voltage Plot

Hello.

I want to ask one more thing.

There are measurement mode (voltage, current, charge, resistance). When I measure current and resistivity of resistance, there are right results.

I measure capacitance of 20 pF capacitor however the result I get 50 pF.

Even considering the error, there is too much difference.

Do I need charge measure code? Or I can resolve it in this code?

Message 14 of 15
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## Re: Keithley 6517B Current vs. Voltage Plot

Off the shelf capacitors have a lot of variability. (+-20%)  Also if you exceed the voltage limit on them you can heat them up and the measured value drift even further.  See - https://www.vishay.com/docs/40192/typperfmoldchipcaps.pdf

I doubt your measurement error is a software issue.  Most accurate capactirance measurement are not done using the quassi-static method but with a bridge instrument at a specific frequency.  The quassi-static method has many sources of potential errors; issues with grounding,  issues with cables and connectors, noise sources, etc..   Consider all these things since you are measuring very, very small capacitances (really very small currents - fA?) and any source of leakage or noise will have a big effect.

I should also point out that most capacitors are speced at a certain bias and frequency and you may not achieve this value in quassi-static measurement mode.

I'd look at the specs for your capacitor, measure within the tolerance limits, verify your experimental setup and cables are suitable for the 20pF capacitance range.

Best of luck.

Craig

Message 15 of 15
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