Nanokelvin-resolution thermometry at room temperature
nature.com
nature.com
I can tell you, I spent probably a month just learning how difficult it is to measure temperature and what are all different ways you can screw up the measurement. You can't just stick a thermocouple anywhere you want. Everything has thermal mass, everything is thermal impedance, everywhere there is a thermal gradient. If you have ANY rate of change of temperature, your measurement method will always greatly impact the result regardless of how precise thermocouple and electronics you use.
If they really can get nanokelvin resolution I would be more interested in understanding their measurement method, because resolution is pretty much worthless if you stick it in the wrong place.
But for this project the price was not an issue and the real challenge and bulk of work was in building a model and control algorithm.
There is couple of gotchas. For example if you use very low current through the RTD (PT100 in my case) you get a lot of noise so you need to use relatively high current. But this causes it to heat up. Rather than try to eliminate this effect I decided to make sure this heating up is as constant as possible. This is one of the reasons it had poor absolute precision but was good for measuring changes over time.
Would this be a 4 wire pt100?
Also did you use a specialised chip for converting to digital readings?
I vaguely recall looking at some fancy reference RTD thermometers with glass housings (just found them, they seem to be called SPRTs - https://isotech.co.uk/products/isotech-model-670/)
It was definitely 4 wire (you don't want to measure wire resistance change and 4 wire is only way to get rid of it).
As to housing and type of RTD, a lot of the cost here is spent on making sure the measurements are stable over long time (so for example to prevent humidity and other gasses from putting it out of calibration).
In my case I did not care a lot about it because I wasn't after absolute precision, for me the important part was rate of change. If you are after absolute precision you might want one of the fancy RTDs.
But I cared that it is small and that it has very low thermal impedance interface with the measured object. Smaller means less thermal mass means faster response.
For the chip I used a general purpose ADC. You also need a very good voltage reference, otherwise even best ADC isn't worth much.
A good voltage reference (or current source) is important, but even more important is building up a reliable bridge topology.
PT100 is 0,4 Ohm/K. Or 0.0000000004Ohm/nK. This means, at 100Ohm, you are measuring 4 parts per (american) trillion for that nK.
Good Luck and please, report how many of those digits were pure noise!
Near linear but usually even for industrial use there is a three term polynomial correction applied.
There's a whole standard devoted to the subject, DIN/IEC 60751.
Useful reference from TI : https://www.google.com/url?sa=t&source=web&rct=j&url=https:/...
Is a bandwidth of 0.1 Hz good in this context? Does it imply that the temperatures they're measuring are very stable on a time scale of a second or so? Or are higher-frequency variations ignored?
The thing that is really good/interesting is the 60 nK/rtHz sensitivity at those frequencies. Off the top of my head, I believe that the best thermistor-based systems I've built have been in the 10-100 uK/rtHz realm.
It is interesting to ponder whether such extreme sensitivity for a small object might open up some new avenues in fundamental physics. Things related to temperature are generally hard, but every time a new technique emerges, it is worth looking around to see if any new doors have opened.
My previous understanding of the word calorimetry was "indirect vs. direct calorimetry" - which (I think) are two techniques for measuring the energy used by some person either at rest or during. It's useful to understand how much energy someone is burning for obvious reasons related to health, nutrition, energy balance, etc. It seems like calorimetry has a much more general usage though, and it's pretty much the science of measuring heat transfers. Cool :}
There is so-much extremely-high-context science out there, and it would would be so fun and thought-provoking to keep up with some it it. It feels like my only options are a) spending a ton of time trying to parse extremely high-context articles (and probably misinterpreting them, like I do above), or relying on pop-science communication. The latter, to me, seems to miss most of the time - it usually simplifies things to just conclusions like "new X does Y," which feels like it misses most of the scientific processes while also misunderstanding the scientific spirit of this sort of knowledge...
A quick search lead me to this conference, where you can see a wider range of uses of calorimetry in biological sciences.