[volt-nuts] nA advice

[Andrea Baldoni]

On Fri, Nov 13, 2015 at 12:27:28PM -0500, Todd Micallef wrote:

> Do you have a high Z input dmm on the 10V range? Perhaps you can characterize
> its impedance  with another high value resistor of known value and then
> connect the UUT to the meter and measure its drop across the input with a
> test voltage.

Good idea. Yes, I can use a 34401A, whose input could be set for >10GR on
100mV, 1V and 10V ranges.
However I can let it be 10MR that need not to be characterized and just measure
the voltage from the divider DUT/10M. With 50V and 5GR will be just about
100mV.

I can think that the 100mV range is already in effect a 10nA range.
It's a high impedance ammeter, but taking in accunt that the source will be
50V the error fall under the precision of the 10MR input impedance, that's
only 1%.
Or, set the multimeter to >10GR and use a shunt resistor of, say, 1MR .1%
(still cheap). Taking in account the multimeter (6.5 digits) in this case will
measure only to 10% of the 100mV range, the fact that the >10GR input is not
better characterized, the overall accuracy should be anyway the one of my
resistor.

Thank you!

Best regards,
Andrea Baldoni