[time-nuts] temperature sensor

Bob Camp kb8tq at n1k.org
Mon Jul 21 21:44:18 EDT 2014


If you want to hit 1 mK with your home made triple point cell, you will need a source of very clean water and some luck with materials and cleaning processes. If you want to go below that level, you will need an isotope readout on your water source. Rain water, and mid-continent well water are a bit different in their composition …. If I remember correctly, you want the mid-continent deep well stuff, but only from the “right” sort of well. 

Yes I’d bet there is a water isotope nuts mailing list somewhere ….


On Jul 21, 2014, at 8:10 PM, Attila Kinali <attila at kinali.ch> wrote:

>> To satisfy my curiosity and get actual data I'd like to place 6 or more
>> tiny analog high-resolution temperature sensors all around the OCXO of a
>> Trimble Thunderbolt. That's high-resolution both in temperature and in time.
>> In other words, no fake accuracy "averaging" allowed. The goal is to observe
>> thermal gradients in real-time and see how good, or how bad, the correlation
>> is among crystal temperature, case temperature, and DS1620 temperature
>> sensor (which is mounted a considerable distance from the OCXO). The same
>> technique, and maybe even the same conclusions, might apply to Rb.
> Ok... a couple hours of reading later.... ;-)
> My excursion into temperature measurement has brought some results:
> 1) PT sensors can be secondary standards for temperature calibration.
>   But standard industrial sensors do not have the stability or linearity
>   of the standard grade sensors. But at least they do not break when you
>   glare at them. Those in ceramic housing are supperior to those in glass
>   or metal housing. Thin film are inferior to wire wound. (in terms of
>   stability and accuracy, thermal coupling is a different matter)
>   (the price for a commercial standard grade PT sensor seems to be in
>   the order of 3kusd)
> 2) The uncertainty of the calibration of the standards grade PTR seems
>   to be in the order of 100uK to 10uK.
> 2) Making a triple point of water cell for calibration with an accuracy
>   better than 10mK seems to be quite simple and doable at home, most
>   likely something around 1mK is achievable. Also judging the quality
>   of the cell is quite simple: make multiple of them, the one with the
>   highest temperature is the most accurate one.
> 3) A well done ice bath gets you into the ballpark of 10mK accuracy.
>   Most of the error is due to impurities and gas in the water.
>   The air pressure effect is much smaller (and thus inconsequential)
>   unless living on a high mountain. Also an ice bath is easier to
>   do than using an triple point cell.
> 4) There are people on ebay who sell very pure Gallium and Indium that
>   could be used for (not so accurate) melting/freezing cells for
>   ~29.7°C and 156°C.
>   (if anyone knows what the non-nut would use those for, please tell me)
> 5) The book "Traceable Temperatures" by Nicholas and White is a very good
>   reading on temperature measurement and calibration. It explains the
>   procedures with what can go wrong and what accuracies are achievable.
>   It also contains a list of references for further reading. I did not
>   have a look at those yet, but from the titles they look very reasonable.
> 				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
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