Thank you for your time in testing.
For the sake of our readers who may not understand, the "SMU" you refer to is your Keithley 2410 which is defined as a high-impedance multimeter that has a built-in low-noise Power Supply. (In comparison, the Fluke 8845A used in my test is high-impedance but lacks a built-in Power Supply.) The documentation for the 2410 shows it can, in theory, measure from 50pA to 1.05A, whereas my Fluke 8845A can, in theory, measure only as low as 100pA when using the 100uA range setting.
In your test, rather than using resistors, you set your meter to generate a 10nA reference current, then used that same meter to measure it, and you repeated for 20nA, and so on, up to 200nA. You then said your meter gives you an error of only 1%+200pA. You then tested the uCurrent and found its error to be up to 11%.
I myself have no means to generate a stable and trustworthy "reference current" and so in my test I used resistance values (see my earlier post). And you can see that I am getting huge errors in the nA range, but small errors in the uA range. I am therefore curious if this is some problem with my Fluke 8845A, or a problem with using resistances in the test? To know the latter, I would be curious to know what kind of current measurements you get using the same resistance values I did.
Without being forced to buy a new meter (my Fluke works fine otherwise), I am seeking to know how to get the most accurate nA measurements possible. Do I really need a uCurrent, or is there something I need to do to adjust my Fluke meter?
Thank you.