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

[Bob kb8tq]

Hi

Indeed the most stable (long term) standard is a very high end RTD. These devices have a lot of voodoo 
in their design. Even with all that, they still arrive with a note on the box that reads “ for applications requiring
< 10 mk, re-calibrate before use”. More or less, you *also* need a triple point cell to use one. Triple point cells
do not bounce when they hit the floor …. I have empirical data on this :(

In terms of *resolution*, even the high end gear goes over to thermistors. You can get about an order of magnitude
increase in relative performance running a fancy thermistor rather than a fancy RTD. The Fluke / Hart web
site is a wonderful thing to drool at in this regard. Be sure to lock the credit card safely away before going 
anywhere near it.

https://us.flukecal.com/about/fluke-calibration-brands/hart-scientific <https://us.flukecal.com/about/fluke-calibration-brands/hart-scientific>

https://us.flukecal.com/products/temperature-calibration/probes-sensors <https://us.flukecal.com/products/temperature-calibration/probes-sensors>

Keep in mind that those probes are done with a specified accuracy. The real world numbers likely are better
than spec by some factor …..

=======

Getting back to TimeNuts stuff. If you want to make a practical controller for a fixed set point, the thermistor
still wins. You get more voltage / lower noise (in miliK) with the thermistor. The fact that you can get a good one
(= very low aging) for $2 rather than $200 also helps ….. :)

Bob

> On Sep 28, 2020, at 2:48 PM, John Moran, Scawby Design <john at scawbydesign.co.uk> wrote:
> 
> Thanks for going easy on me Bob ... a case of more haste, less speed! I focussed on low long-term drift specs without realising I had turned up a voltage reference, sorry.
> 
> However, I have found some YSI glass encased thermistors that have long-term drift specs of <10mK at 25C and 75C over a period of 100 months. They are in the YSI 46000 series - data sheet attached.
> 
> http://www.farnell.com/datasheets/169207.pdf
> 
> There is an interesting paper by NIST on achieving the International Temperature scale - link attached (it is 196 pages and 10MB) that seems to indicate platinum sensors are the most stable at less than 1mK and, of course, to be able to measure these resistors accurately, you need an equally low-drift voltage/current source. :-)
> 
> https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote1265.pdf
> 
> This reference appeared from an EEVblog where I think some Volt-nuts were discussing temperature. One of them confirmed that the most economical way was to have a group of lower-cost sensors and characterise them.
> 
> https://www.eevblog.com/forum/metrology/long-term-stability-of-temperature-sensors/
> 
> John 
> 
> 
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