Hi Bob, see my answer to Attila, which I have sent a minute ago.
Bernd DK1AG -----Ursprüngliche Nachricht----- Von: [email protected] [mailto:[email protected]] Im Auftrag von Bob Camp Gesendet: Samstag, 19. Juli 2014 15:00 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] temperature sensor Hi A temperature sensor crystal is very much the same thing as a normal crystal (except for angle of cut). The mounting is pretty much the same as the crystals you have seen before. The only thing you do to improve the thermal coupling is to do a backfill with something like helium. Backfill levels are low and they vary depending on the application and the cut of crystal. The thermal resistance isnt great, but its good enough. You only have micro watts going into the resonator. Increasing the backfill would increase the damping and thus the resistance. That would increase the power dissipated in the resonator. This would defeat any gain you got from the increased backfill. For direct contact sensing, you use SAW devices rather than BAWs. If you do things right you can put the SAW directly in contact with the stuff you are sensing. The thermal resistance in that case is essentially zero. Bob On Jul 19, 2014, at 7:45 AM, Attila Kinali <[email protected]> wrote: > On Wed, 25 Jun 2014 14:21:49 +0200 > "Bernd Neubig" <[email protected]> wrote: > >> the time-nut approach for temperature measurement would be to use a >> temperature sensor crystal - like the good old Hewlett-Packard guys >> did many years ago. If you do not look for ultra-linearity of the >> frequency vs. temp response, there are several possible types of >> crystal cuts possible. The simplest one is the Y-cut or the slightly >> rotated Y+5° cut, which has a slope of about 90 to 95 ppm/K @ room temperature. >> Smaller sensor crystals are tuning-fork type crystals, which come in >> the same small cylindrical package as normal watch crystals. >> For further reading I have attached an application note for such a >> crystal from AXTAL. > > Do you have any data on the temperature resistance from case to crystal? > The PT100 and NTC sensors have the nice property of having a very good > thermal coupling between the sensor element and the case. But i > suspect that temperature sensor crystals have a very small area that > couples the crystal to the case (in order to get a high enough Q for > the oscillator to work), which in turn limits the speed at which the > sensor reacts to temperature changes. > > Attila Kinali > > -- > I pity people who can't find laughter or at least some bit of > amusement in the little doings of the day. I believe I could find > something ridiculous even in the saddest moment, if necessary. It has > nothing to do with being superficial. It's a matter of joy in life. > -- Sophie Scholl > _______________________________________________ > 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. _______________________________________________ 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.
