[volt-nuts] Sub PPM 10V transfer standard

[WarrenS]

Want a stable 10V ref?
Best thing to do is get a fluke 732A/B and  have it calibrated regularly for a few years.
BUT 
For the Extreme (or cheap) Volt Nut, There is another choice.
Attached is the circuit of a 0.1 PPM, 10 volt transfer standard. 

It has ONLY ONE critical part that limits its accuracy and stability.  
Everything else can be made to have so little effect as to be insignificant or else can be trimmed and calibrated out without using a precision voltage source using  a method similar to what the daily auto cal in the HP3458 does. It measures it's own internal 6+V reference.

Every year or more, best to record the value of the nominal 6.2 volts, to measurement the ageing rate, by using a known external 10 volt standard. 
To do that, an accurate external way is needed to find the exact ratio of the 6.2 volts to the external 10 volt standard.
This can be done by using a high resolution Linear DMM (aka HP3458A) OR a Kelvin-Varley divider (aka fluke 720 ) and null meter (aka Fluke 845). 
Lets assume if one wants to do 0.1 PPM things, then they have the equipment and skill needed to measure a 10v to 6v  ratio to 0.1 PPM.
After that ratio is known and recorded the units internal 10 volts can then be set to that same ratio without further need of the external 10V standard.

The main advantage of all this extra trouble is low cost accuracy and stability. 
There are no critical or expensive resistor needed or anything else critical, because all the TC and long term drift are canceled out whenever  a manual trim is done using an external ratio device to check its own 10 V against it's own 6.2 volts.

Nothing very special is needed to build this beside care and time.  
To get the best performance, It  does take a lot of Nut-time to match and select things.
Total parts cost with a well supplied analog junk box (or EBay) can be under $10. 

Any good 6V type reference device could be used. 
I'm using a well aged and selected 1n825 because I have a lot of history with them and they work good without an oven. 
I have not done any mailing test on these parts but they can be Zero TCed so that they do not change 0.1PPM over normal room temperature
and they show no change when powered down for short periods of time and tend to return to their original value when hit with a heat gun and cold stray, so it makes a good part to start experimenting with.

ws

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