[volt-nuts] Is there a "standard" much better than a LTZ1000, but much cheaper than a Josephson Junction Array?

[Attila Kinali]

Hoi David,

On Wed, 19 Oct 2016 22:10:15 +0100
"Dr. David Kirkby (Kirkby Microwave Ltd)" <drkirkby at kirkbymicrowave.co.uk> wrote:

> The question about the Josephson Junction Array got me thinking. I wonder
> if there are any sort of technologies that can produce a voltage with much
> better stability than the LTZ1000, but without the cost of a Josephson
> Junction Array. A sort of half-way house.

As far as I am aware of, no. Beside the standard cells, the only other
way I am aware of that was used were voltage balances. Ie measure
the size of the electromagnetic force of a capacitor vs a calibrated
weight. Of course the capacitor would need to measured precisely as well,
which would require a capacitance standard (aka calculable capacitor). 

To exert any measurable force, you'd need a couple of kV of potential,
which is not exactly nice to handle and to keep stable. And because
everything is very sensitive to the slightest disturbance, you'll have
to put everything into a vacuum chamber. Even though it does not need
to be high vacuum as for atomic clocks, it's still not something you'll
do on a kitchen table.

Maybe one way would be, if you could make use of the quadratic
relation of power dissipated over a impedance and the voltage over
the impedance, then you could work with a group of calculable capacitors
vs a watt balance and build a voltage standard like that...

Sorry it's late on this side of the globe and I'm not sure whether
this makes sense... much less whether the idea even works.

> 
> BTW, I see some rather battered up LTZ1000A's on eBay,
> 
> http://www.ebay.com/itm/1x-LTZ1000ACH-Ultra-Precision-Reference-LTZ1000A-/111325506311
> 
> that have dents in them. They are more expensive than buying the chip new
> from the Linear Technology website.
> 
> http://www.linear.com/purchase/LTZ1000
> 
> Yet people seem to buy them. Now I know the stability of those improve with
> age, but when they have dents in them, its clear they have not been exactly
> cared for. Maybe I will buy some new LTZ1000As and stick them on eBay for
> $100 and see how many I sell !!

Because people have no clue. A lot of people think that ebay = cheap, 
and if it's expensive on ebay, how much more expensive is it from the
manufacturer!

> It seems the real cost of an LTZ1000A standard is not the chip, but the
> resistors you need.

Well, you need to calibrate them. Which you can do using a null-volt
detector and a Kelvin-Varley divider, not something very cheap either,
but at least not difficult to build yourself. I think, with todays technology
it should be possible to build a self-calibrating Kelvin-Varley divider,
even if it would be very tedious. I am not so sure whether a null-volt
detector is easy to build. I have not figured out yet, how to compare to
voltages to nV levels precision.


			Attila Kinali
-- 
Malek's Law:
        Any simple idea will be worded in the most complicated way.