[volt-nuts] Ran across a interesting piece of old gear on ebay

[Robert Atkinson]

Hi Bruce,
You are correct in you description, but I think this unit had a particular application - measuring temperature using thermocouples. Note the "Reference Junction" control. I've actually used similar devices to calibrate the turbine temperature systems on aircraft (about 30 years ago and they were old then)
 
Robert G8RPI. 


________________________________
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
To: Discussion of precise voltage measurement <volt-nuts at febo.com> 
Sent: Friday, 24 August 2012, 8:28
Subject: Re: [volt-nuts] Ran across a interesting piece of old gear on ebay

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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