[volt-nuts] Traveling Standards

[Bob Smither]

Charles P. Steinmetz wrote:

<snip>

> My understanding of Bob's original proposal was that he wants to build a 
> stable reference of uncertain voltage, and send that to someone (or 
> several someones) who will render an opinion on its actual voltage and 
> send it back.

Correct.

<snip>

> Bob did mention having the recipient power the traveling reference up -- 
> if possible, it should be shipped "hot" under battery power so there is 
> no power cycle/retrace to worry about.

I can see the advantage of this, but as an example the lm199ah draws 
about 15 mA at 25C.  If exposed to low temperatures during shipment it 
will draw more.  Perhaps this could be reduced if the part is put in a 
thermally insulated box.  A one week shipment (out and back), at 15 mA,
would require a 2600 mA-hr battery.  Certain not impossible, but 
somewhat heavy.

With the goal of 10ppm overall uncertainty, will the thermal hysteresis 
be a limiting factor if the unit is shipped un-powered?  How long should 
it be powered at the remote lab before a measurement is made?

Best regards,
-- 
Bob Smither, Ph.D.                                 Smither at C-C-I.com
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