Hi They were not cheap beasts to keep running. The cal process was an “HP only” thing and when you looked at what came back each year, any data you took over the last few months needed to be re-evaluated. After a while, people started poke into this and that. They would do a wonderful job sitting in a constant temperature bath. Like any crystal, they aged and this created some level of drift (well beyond 0.0001C per year). The more troublesome problem was hysteresis. If you cycled the probe between temperatures, it might take a day to get back “close” to the original temperature (but still not quite to 0.0001C). The final gotcha was mechanical shock bumps in normal use. Apparently this also created some offsets as well.
All of that added up to a frequency vs temperature curve that “moved around” at a level well past 0.0001C. Each time you sent it back, the coefficients got re-modeled. Use if for a while and the numbers don’t match the probe so much anymore. Just as with a SPRT, a triple point cell really needed to be part of the setup. For whatever reason, HP backed out of the business rather than get more complex. Fluke took a different approach (they bought Hart) and stayed in the business. There are certainly a number of other outfits making fancy temperature gear. Bob > On Mar 11, 2016, at 12:41 PM, Alan Ambrose <[email protected]> wrote: > > Hi, > > I hope this is still relevant and not too off-topic...but since it involves > crystals and tempco... > > Quartz thermometers (e.g. the HP 2804A) with their 'linear cut' crystals and > '0.0001C resolution' seem to have been a thing from the mid-60's to the > mid-80's: > > http://www.hparchive.com/Journals/HPJ-1965-03.pdf > > There still appear to be some manufacturers making the crystals: > > http://www.statek.com/products/pdf/Temp%20Sensor%2010162%20Rev%20B.pdf > > Anyone know why they died out? Did a better technology replace them? > > TIA, Alan > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
