[volt-nuts] Sub PPM 10V transfer standard

[WarrenS]

OH yea lots of things to be careful about and go wrong at 0.1PPM
Don't want to understate  that problem.
But the point is that it is doable.
Best thing I've found to reduce the effect of thermocouple problems and heat 
is to NOT have ANY heating or COOLING going on near by.
The way I do it here is to place a paper towel over the Bread board to 
eliminate air currents, and move the 5 volt regulator away from the rest of 
the parts.
(Like outside the controlled volume)
I'm always looking for ways to do things simpler AND get better performance 
at the same time.

With lots of care, the reference becomes the limiting factor.
What you do after that, just takes lots of careful good low level stuff.
Attached is a 5 hr plot of the 6.2 volt zener voltage.
It shows a low bandwidth noise level including the tester of about 0.01PPM 
RMS.

ws

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[volt-nuts] Sub PPM 10V transfer standard
Poul-Henning Kamp phk at phk.freebsd.dk

>But for 0.1ppm you need to address opamp heating and unintended
>thermocouples everywhere.

Actually, if you go that far anyway, adding a peltier and ntc to
hold the temperature constant is not a big deal.

Build the PCB (both Vref & Tctl) as surface-mount with no through-hole
and attach it directly to the Peltier with a thermal pad

The Peltier needs very little power if the temperature difference
is on the order of a few degrees and the power dissipation in the
controlled volume is low.

When I ran the MAX6350 experiment, the 12V Peltier was running
at slightly less than 1V most of the time.

I would let the Tctl output an analog control voltage and put the
Peltier power-driver outside the controlled volume.

I would recommend preregulating the input power with a linear
regulator (also outside the controlled volume) so that the power
dissipation in the controlled volume is as constant as possible. 
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