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Automated Guarded Bridge for Calibration of Multimegohm Standard Resistors

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tswan

New Member
I've trying to understand this paper:

https://ts.nist.gov/MeasurementServices/Calibrations/upload/Automated-guarded-bridge.pdf

The Wheatstone bridge is no problem, but I just don't understand how the author's bridge using 2 supplies works. In the paper he says that the detector measures the difference of the the currents flowing through Rx and Rs, but it sure looks like the detector would measure the sum of these two currents.

I know I'm not understanding something fundamental and I'm hoping someone here might be able to explain to me why adjusting the voltages will null out the current.

Thanks.
 

JimB

Super Moderator
Most Helpful Member
I agree with you, as fig 2 in the paper is drawn, the current through the detector will be the sum of the currents in the two resistors.
If the polarity of one of the voltage souces is reversed then the current through the detector will be the difference of the two resistor currents.

JimB
 
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