[time-nuts] What do people use for meassuring temperature?

[Bob kb8tq]

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 <jebponsonby at gmail.com> 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 <bruce.griffiths at xtra.co.nz <mailto:bruce.griffiths at xtra.co.nz>>
> 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 <kb8tq at n1k.org <mailto:kb8tq at n1k.org>> 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 <jebponsonby at gmail.com <mailto:jebponsonby at gmail.com>>
>> 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.
>> 
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