Re: Low-cost voltage reference questions
>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 <at> 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%