Quote:
Originally Posted by WaveyDipole
I have been trying to get my head around that since you posted it, but can't seem to figure out how one might go about passing a current across a resistor in both directions simultaneously? You could not have common ground on both sides of the resistor simultaneously? On the other hand if the grounds were not common (i.e. they were separate floating flows), then there would be no common reference voltage? Is there a practical circuit to demonstrate this?
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If your balance current source is floating it doesn't matter how the current you want to balance is ground referenced (or not). When the unknown and balance currents are equal and opposite there will be no voltage across the sense resistor. All you need is a null detector on the sense resistor and an accurate ammeter in the balance current loop. Both floating, of course as are battery powered DMMs and analog multimeters.
The whole arrangement is effectively the current dual of a potentiometer arrangement for infinite load resistance voltage measurement.
Ever wondered why a potentiometer is so called?