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ADC-20 Input Impedance

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ADC-20 Input Impedance

Postby marko » Wed Jun 10, 2009 2:30 pm

I would like to use the ADC-20 to make low-level current measurements (nA...uA) by measuring the voltage drop across a shunt resistor. The shunt is likely to have such a large value that the input impedance of ADC-20 may affect the measurement.

The input impedance of ADC-20 is specified to be 1 Mohm. How accurate is this? Can the excact value be checked by a multimeter?

As I am measuring a current into earth, could one use the input impedance directly as a shunt? With 1 Mohm one would get a scale of 1V/1uA. Is this realistic?
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Postby PeterF » Fri Jun 12, 2009 12:48 pm

The input impedance of the ADC-20 is 1Meg ohm in single ended mode and is stable. I do not have a figure for the absolute accuracy but it would be easy to measure it. If you have an accurate 1uA current source you could inject it into the input and measure the resulting voltage. Any errors could be compensated for and the correct units displayed by using the "Scaling" option in channel set-up.
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