[volt-nuts] Traveling Standards

[Bob Smither]

Charles P. Steinmetz wrote:

<snip>

> When one is trying to achieve repeatability in the single-digit ppm 
> range, I would not leave anything to chance -- and retrace (hysteresis) 
> is always a matter of chance, particularly if the device has been 
> powered off for a long time (several days) and may have been exposed to 
> significant temperature shifts during that time.  In my view, the best 
> approach in this instance is to use something like a 5Ah gel cell (to 
> ensure relatively little voltage droop during the transit time), with at 
> least one stage of preregulation.  The total package should be under 2 
> kg and should easily fit into a USPS medium-size flat-rate box that 
> ships for $11 (this assumes that you and the recipient are both in the 
> US).  UPS should be similar.  (If $22 for a round trip is a 
> deal-breaker, we might conclude that one wasn't very serious about the 
> project.)

I agree with all of this - but my first objective is to obtain 10 ppm 
overall uncertainty.  At that level I am hoping that there will be 
several folks on the list willing to accept a unit, measure it, and ship 
it back to me.  Two have already stepped up - thanks!

At 1 ppm I suspect the population of those willing to measure will be 
reduced.  I know that I certainly could not play in that playground! 
Even the well regarded HP3458A only provides that sort of uncertainty 
for 24 hours.

> You also might include a charger, so that the recipient can top off the 
> battery before measurement (if necessary) and before return shipment.

Ouch - more weight and more to go wrong.

> All measurements would be made with the charger disconnected.

This brings up a good point.  I will look for a 24 V DC wall wart to 
power the LM7815A.  That will remove the transformer from the vicinity 
of the reference and should greatly reduce the effect of the line 
regulation of the LM7815A.  Use of a better 8K resistor would then 
eliminate the two largest sources of error (except for the lm199a 
itself, of course).

Thanks!
-- 
Bob Smither, PhD                                   Circuit Concepts, Inc.
=========================================================================
Firearms stand next in importance to the Constitution itself.  They are
the American people's liberty teeth and keystone under independence.  The
very atmosphere of firearms everywhere restrains evil interference.
   -- George Washington
=========================================================================
Smither at C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)  -4616(fax)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smither.vcf
Type: text/x-vcard
Size: 140 bytes
Desc: not available
URL: <http://www.febo.com/pipermail/volt-nuts/attachments/20110826/7baaee94/attachment.vcf>