[volt-nuts] Low-cost voltage reference questions

[Russ Ramirez]

Excellent points, especially the consideration of shipment effects
year-round and across major temperature variations. Thank-you Charles.

Russ

On Mon, Nov 23, 2015 at 4:26 PM, Charles Steinmetz <csteinmetz at yandex.com>
wrote:

> Russ wrote:
>
> What is considered the break-over point of precision with low uncertainty
>> versus cost to a group like this? Is there a rule-of-thumb for the cost of
>> each additional digit of precision after N digits?
>>
>
> One person's opinion:
>
> To a group like this, I'd be inclined to say that interest begins at a
> room-temperature (say, 20C +/- 3C) accuracy of 3ppm (i.e., guaranteed to
> remain within 3ppm from 18-22C for at least one year after purchase).  3
> ppm is 0.0003%.  There is at least one 10v reference with specifications in
> this ballpark available at an asking price under $130 (I'm told the seller
> has accepted offers significantly lower than this).
>
> If I sell someone a reference
>> that I've ascertained is 2.50163v @70.3 F with a calculated uncertainty,
>> is
>> it valuable as a 0.1% reference even though the error may be much less,
>> like +/- 0.08%?
>>
>
> I, for one, do not consider 0.08% to be "much less" than 0.1%.  One sneeze
> and it's out of spec.  Indeed, I would consider a claim of 0.1% accuracy to
> be bordering on fraudulent based on a calibrated measurement at 0.08%,
> unless the spec was qualified as "within 0.1% at [temperature within 0.1C]
> as is, where is -- no claim as to accuracy after it has been shipped to the
> buyer."
>
> Speaking as someone with substantial commercial design experience, I would
> never offer a voltage reference for sale as a claimed "0.1% standard" that
> I did not have excellent justification for believing would stay below 0.05%
> for a year over a several-degree range of temperature and multiple trips
> across the country via commercial carriers.  I wouldn't expect to be able
> to charge more than $10-15 for the product just described, and then only if
> the nominal output voltage were 10v (I think you will find that there is a
> very strong preference for 10v references over 5v, 2.5v, or other voltages).
>
> Best regards,
>
> Charles
>
>
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