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2502, 6485, 6487 - Support
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Joined: January 11th, 2022, 1:43 am
Country: Poland


Post by voitec » January 11th, 2022, 3:27 am

Hi All,
As the 6487 specs does not contain information I am looking for, I've decided asking for help in the following matter.
What's relation between Voltage Source output voltages and Ohms ranges. Not any manual define that straight .
To be more precise , I want to measure resistances around 10 TOhm with voltage of 50V . Is it possible with high accuracy?
I am missing specifications which define each resistance range and correspondig minimal source voltage.
Here is example of such data from another manufacturer.
Capture3.PNG (29.6 KiB) Viewed 49 times
Is it possible to obtain such data for 6487 ?


Andrea C
Keithley Applications
Keithley Applications
Posts: 1662
Joined: October 15th, 2010, 10:35 am
Country: United States

Re: 6487

Post by Andrea C » January 13th, 2022, 10:52 am


Really depends on error budget.

For the 10T-Ohm at 50V, you'd expect only 5pA of current.

You may need to consider electrometer such as 6517B instead of 6487 for improved current measure range and lower error.
With the 6487, most sensitive range is 2nA range.
With the 6517B, most sensitive range is 20pA range.

To estimate overall measure error in the reported ohms: compute the voltage sourcing error and add the current measure error.
With 6487, using 50V source range and 2nA measure range, your errors will be in excess of 8% using 6487.
Most of the error comes from the current measure.

With 6517B, using 100V source range (to source 50v) and 20pA measure range, the total ohms errors will be a little more than 1%.

For such small currents, having a shield test fixture is imperative.
Also use of guarding to eliminate leakage paths from contributing to the measured current is important.
Here is video illustrating the low side guarding: https://www.tek.com/en/video/how-to/gua ... icoammeter

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