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Step-like behaviour of 6221 DC sweep for high ranges

6220, 6221 Current Sources
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Joined: January 11th, 2019, 7:48 am
Country: Russian Federation

Step-like behaviour of 6221 DC sweep for high ranges

Post by vskhromov » January 11th, 2019, 8:03 am

Dear colleagues,

I use 6221 to perform DC current (I) sweep through 2kOhm resistor. Voltage drop (U) across
resistor is measured with 2182a nanovoltmeter. Since it is expected to get linear (I,U) curve,
to control the accuracy of the experiment I consider quantity "U - Ufit_line", where "Ufit_line"
is linear approximation of experimental data.

For ranges 2e-9, 2e-8, 2e-7 of 6221 it works great and I get randomly placed points near
zero (Fig.1a) as expected. But for higher ranges these points are no more random, but
shaped like a ramp, for both small (Fig.1b) and large (Fig.1c) current steps.
Similar result (Fig.1d) is observed using data from topic on this forum: viewtopic.php?t=1721

It means that for range 2e-6 and higher experimental (I,U) curve is not linear, but splits into
series of steps that cross straight line (I,"Ufit_line").

My question is how to avoid this step-like behaviour, or where does it come from.

Regards, Vyacheslav.

P.S. My 6221 setup is:
Inner Shield = Guard;
Output low = Floating;
Current filter ON;
Output response SLOW;
Graph1.jpg (550.33 KiB) Viewed 16 times

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