Andreas: yes, I was hoping for the simplicity of USB data logging, at least for temperature.
iainwhite: I'm just a noob myself -- I think Conrad's circuit with a 2DW232 would be an ideal place to start!
Conrad: Indeed, cabling is critical, as I am discovering this evening!
My "mailer" cardboard boxes arrived today, so I thought I'd take some measurements with my Keithley 196 to decide which cables I should include with the reference, but my results were disappointingly inconsistent.
I've tried a bunch of cabling variations and am getting different readings. More importantly, the readings wander around by as much as 150uV, seemingly just from getting up and walking around the room.
I think I have an idea of what the problem is: I stuck a temperature probe directly into the Ohms sense jack and it read over 105F. Can you say "thermal gradient"?
Across all the various setups I tried, the overall span of readings went from around 10.00104 V to around 10.00150 V.
Setups I tried included:
I filed down one of the "logico" jacks and surprise! They do not appear to be copper (the body definitely isn't -- it shines like steel after filing off the plating. the springs miiiiight be some sort of really light looking copper alloy).
The Cinch banana plugs I salvaged from from a defunct banana DMM breakout project I worked on a while ago. They are brass with nickel-silver springs:
http://www.belfuse.com/resources/Johnson/productinformation/pi-108-0753-001.pdfI'm definitely open to advice here, but I suspect I'm fighting an uphill battle here -- a 105F to 75F gradient across my cables is just asking for trouble.
I think I'll go ahead and mail out the reference with some solid CAT5, the pomona mini-grabbers, and the screw-banana plugs.
(I really, really need to get GPIB up and running. Trying to describe the behavior of a DMM using sentences just doesn't cut it.)