Hi There are indeed published works on the physics behind thermistors. The ones I’ve read (many decades ago …) didn’t say a lot about aging mechanisms beyond the usual stuff you could guess at. Things like humidity can contaminate the material, glass sealing is a good idea ( not a big surprise … ).
The bottom line is still that they get used at fairly high temperatures and do indeed hold quite good drift specs. Conditioning of the parts prior to use is non-existant in an OCXO application. Mitsubishi makes some pretty good parts as do others ….. Bob > On Sep 27, 2020, at 8:37 AM, John Ponsonby <[email protected]> wrote: > > Bruce Griffith points to the note put out by Littelfuse. It is very meagre. > It says that '...thermistors can be produced with typical drift of only > 0.001˚C to 0.002˚C per Year." It doesn't say that they are produced and still > less that Littelfuse produces them. Bruce also refers to thermistors being > 'Suitably conditioned at 25˚C' What is this conditioning process and what if > the intended working temperature is not 25˚C?. Surely more must be known > about this matter. > Jeremy Nichols' questions are very apposite. > I see that the Steinhart Hart Equation seems to be entirely empirical without > any underlying semiconductor theoretical foundation. > John Ponsonby > > > Do we know what this ?Long Term Aging Process? is or is it proprietary? > > > > On Sat, Sep 26, 2020 at 5:03 PM Bruce Griffiths <[email protected] > <mailto:[email protected]>> > wrote: > >> Drift ~1-2mK per year for suitably conditioned thermistors at 25C: >> >> >> https://www.littelfuse.com/technical-resources/technical-centers/temperature-sensors/thermistor-info/thermistor-terminology/stability.aspx >> >> <https://www.littelfuse.com/technical-resources/technical-centers/temperature-sensors/thermistor-info/thermistor-terminology/stability.aspx> >> >> >> >> Bruce >> >>> On 27 September 2020 at 11:15 Bob kb8tq <[email protected] >>> <mailto:[email protected]>> wrote: >> >>> >> >>> >> >>> Hi >> >>> >> >>> Roughly speaking 99.99999% of all OCXO?s use thermistors as temperature >> sensors. >> >>> The normal evaluation process on a new one *probably* would catch >> something < 0.01C >> >>> over a few months. You may do it a couple different ways depending on >> the target >> >>> OCXO. The net result is still in the ?golly gee wiz low? sort of range. >> If you can detect a >> >>> drift / shift, you disqualify that part and move on to another one. Very >> few glass bead >> >>> parts seem to get tossed out ?.. >> >>> >> >>> Bob >> >>> >> >>> >> >>> >> >>>> On Sep 26, 2020, at 4:23 PM, John Ponsonby <[email protected] >>>> <mailto:[email protected]>> >> wrote: >> >>>> >> >>>> Have any time-nuts got any data on the long term stability or drift >> rates/ageing characteristics of thermistors? I am concerned with ability >> of holding temperature constant at the milliK level for years. I reckon >> that if one can measure it one can control it. Conversely if one can't >> measure it, because of the instability of the sensor, one can't control it. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
