[time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[Bruce Griffiths]

Randy Leifer wrote:
> Bigger Volt-nut here.
> ...albeit, less knowledgeable than most of you.
> I have been in the chase for the perfect volt.
> I have 2 JRL SCO-105 saturated cell references running 24/7.
> But checking it's accuracy....I must rely on my cal'd HP3457 meter.
> Although, those cells (6 total, 3 in each cabinet) are pretty stable, and good for determining drift of the Vrefs I build.
> I have a Geller 5v, and I've built a few of my own refs using some 
> National LM399AH-50 along with a chopper buffer. 
> (these LM399's come with a 1000 hr burn-in and a drift plot)
> I am getting a 10uV drift with these circuits, but that is over a +/- 15* F ambient temp range (as is the voltmeter)...and they're only in plastic cases in open air--not shielded yet.
> http://i5.photobucket.com/albums/y177/Midiot/my_lm399_ref.gif
>
> I am currently building/testing/tweaking a temp stable insulated enclosure,
> using a Peltier, a 5 watt controller, and 0.1% glass thermistors.....to house my Vrefs and some standard resistors. 
> I am shooting for 25* C, but the outside air still has an slight effect on the internal air (+/- 0.5* C on the inside).....not bad but I think I can do better. I put a low-ohm thermistor outside the box, in series with the main sensing thermistor inside, and this helps. But this may be a whole new topic.
> I'm up for a Vref project. How about you?
>
> =Randy=
>
>   
An LTZ1000 or LTZ1000A based reference will have better long term stability.
One can even build in a thermal conditioning cycle to "anneal" out
voltage shifts that occur when starting up after the reference loses power.

Bruce