uCurrent - minimum measurable current

[SilverSolder]

I tested a uCurrent Gold with a 400Hz AC signal, to get to grips with the lowest current I can measure with it.  I used an AC measurement to be able to filter out noise.


Setup:  Signal generator output 50mV RMS AC at 400Hz driving a precision isolation transformer 1:4 ratio, in turn driving a 7 digit Ratio Transformer at 200mV RMS.  Star ground point at the uCurrent negative output terminal to reduce noise.

uCurrent set to highest sensitivity, 1mV / nA.  Measurement taken with Agilent 54622D oscilloscope set to 512 averages, to reduce noise.





Results -

Lowest visible current with decent measurement accuracy (3%): 600pA at 400Hz




Calculating the current:  Ratio Transformer Drive Signal (200mV RMS) * Transformer Ratio (Dial) / Shunt Resistance of uCurrent

                               0.2VRMS  *  3.0E-5    /  10Kohm  =  600pA





Lowest visible current - but with poor measurement accuracy:  60pA  at 400Hz