[volt-nuts] HP3450A Reference Peltier Chambers

Dave M dgminala at mediacombb.net
Fri Nov 27 13:55:26 EST 2015

I've been looking at the various voltage reference schemes used in HP's 345x 
line of DMMs.  I was intrigued by the use of a Peltier chamber to control 
the temperature of the reference element in the HP 3450A DMM.
I looked in the service manual for that unit, but I couldn't find a good 
picture of the reference assembly.  Would anyone having a 3450A be 
adventurous enough to pull it apart enough to take a few good pictures of 
the innards?  I found a Sales Amplifier paper from HP that roughly describes 
the reference assembly, but no good pictures.
I'm wondering if the diode under test and a thermistor should be mounted 
directly to the surface of the Peltier device or to a copper or aluminum 
interface between the Peltier and the thermistor & diode.  Any thoughts? 
How did HP do it in the 3450A chamber?
I have a number of 1N825 and 1N827 diodes that I'd like to toy with.  In 
particular, I'd like to build such a Peltier controlled chamber to ease the 
task of finding the zero tempco spot on the zeners.

Dave M 

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