Electronics > Metrology

Measuring nanoamps and below like a Ninja

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VintageNut:
This thread is a place to post your techniques, results, tips and tricks for forcing and measuring low current.

In my opinion the definition of low current starts somewhere between 1nA and 10nA. That is about the noise floor of unshielded wires in open air. You can test this waving your hand near some unshielded wire that is connected to an instrument that has a noise floor well below 1nA.

VintageNut:
I will begin with an example of how to characterize the noise floor of a measurement instrument.

The attached plot has current on the Y axis and "time" on the X axis for a KE6430.

Since this plot is pictorial only with no spreadsheet, I will use pk-pk amplitude to define and quantify the noise of the current measurement.

The technique is to place a metal triax cap over the trax jack of the instrument, force 0V and measure current.

In this case, the pk-pk noise is 3.78 x 10^-16.

There is an offset which is defined as the midpoint of the Y axis on the graph. Removing this offset leaves the user with just the p-p noise as the uncertainty of the measurement.

tggzzz:
Ah. An easy question to answer.

To measure current like a ninja, you just do nothing whatsoever.

OTOH, to measure current like a cowboy, you stick the two electrodes on your tongue.

HighVoltage:
I am using my trusted Keithley 410 PicoAmMeter

3roomlab:

--- Quote from: VintageNut on November 20, 2016, 05:14:17 pm ---
The technique is to place a metal triax cap over the trax jack of the instrument, force 0V and measure current.

--- End quote ---

i am curious about the measurement cables. i got some PTFE 2 core shielded, i applied 1000v 2 any 2 of the conductors, and measured the leakage (0.04uA/m or 26Gohm/m). so im not sure, how does this compare to a good PTFE insulated cable suitable for "low low loss" ?