[HN Gopher] Nanokelvin-resolution thermometry at room temperature
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Nanokelvin-resolution thermometry at room temperature
Author : pcrh
Score : 44 points
Date : 2022-06-17 16:11 UTC (6 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| AdamH12113 wrote:
| > Specifically, using a suspended asymmetric Fabry-Perot
| resonator and a wavelength-stabilized probe laser we demonstrate
| a thermoreflectance coefficient of >30/K, enabling measurements
| with a thermometry noise floor of ~60 [nK/root Hz] and a
| temperature resolution of <100 nK in a bandwidth of 0.1 Hz.
|
| 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?
| ISL wrote:
| It is a reasonable bet that the thermalization time of their
| sensor is in the neighborhood of 100ms or so (which is very
| fast).
|
| 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.
| twawaaay wrote:
| I have built a thermometer for an automation project with the
| requirement to be able to measure rate of temperature change 50
| times a second with resolution of 0.001K/s (between 50 and 140C).
|
| 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.
| semi-extrinsic wrote:
| Wow, 0.001K is impressive for something you've built yourself.
| Care to share what approach you used?
| twawaaay wrote:
| It wasn't anything special. I am an amateur EE and not
| especially talented. I did some cursory search on the
| Internet, found a circuit that was looking promising and
| brute forced it by using best components I could find and
| then ovenized it for great stability and removed any sources
| of noise I could imagine (for example using linear power
| supply, etc.) I think just the measurement circuit with the
| oven was about $500 which is just saying I did poor at
| optimising for the cost.
|
| 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.
| anfractuosity wrote:
| Out of interest what pt100 probe did you use?
|
| 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/)
| twawaaay wrote:
| I don't remember the exact PT100 I used but it wasn't very
| expensive (still probably one of the more expensive things I
| ever bought per unit of mass -- they are probably more
| expensive that diamonds).
|
| 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.
| ISL wrote:
| If you're primarily chasing sensitivity, one can generally
| be much more sensitive with a non-platinum thermistor.
| They're less stable but exhibit a _much_ greater change in
| resistance with temperature.
|
| A good voltage reference (or current source) is important,
| but even more important is building up a reliable bridge
| topology.
| [deleted]
| [deleted]
| narush wrote:
| Sounds like a bunch of very cool gobbledy-gook to me. My
| (extremely) layman's understanding is that this this is
| effectively better thermometers that could be useful for (among
| other things) bio-calorimetry.
|
| 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...
| pcrh wrote:
| Bio-calorimetry can be used to detect interactions between
| biological molecules, such as between proteins, drugs binding
| to proteins, etc,
|
| A quick search lead me to this conference, where you can see a
| wider range of uses of calorimetry in biological sciences.
|
| https://www.biocalorimetry.org/program/
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