Christopher Brown wrote:
Who knows what this is?
<http://www.ebay.com/itm/Leeds-Northrup-Vintage-North-American-Aviation-Potentiometer-Wooden-Box-/380451657104?pt=US_Amplifier_Parts_Components&hash=item5894af9590>
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Its a potentiometer used to measure dc voltage.
A standard cell was used to set the total voltage across a series string
of resistors and a slide wire.
The dc voltage to be measured was balanced against the voltage developed
across a selected substring of resistors and the tap on a slide wire.
Lead acid batteries and similar cells were used as a source for the
slide wire and series resistor string current.
A galvanometer was used a s a null detector to determine when the
v0oltage across the slide wire and series resistor string were equal.
The resistors were typically immersed in mineral oil contained within a
copper tank below the ebonite (or similar ) faceplate.
Bruce
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