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 <[email protected]> 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 > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
