The most accurate temperature measurements ever made. Probably.
It is now 25 years since the establishment of the International Temperature Scale of 1990. The scale has been extremely successful in enabling accurate and consistent temperature measurement around the world. However, it has become clear that the thermodynamic temperature estimates on which ITS-90 is based were in error, even at temperatures close to the triple point of water. The discovery and elucidation of this error is largely due to the development of acoustic thermometry.
Over the last decade, the development of combined microwave and acoustic resonators for the measurement of the Boltzmann constant has improved the state-of-the-art significantly and resulted in advances in theory, fabrication, and experimental techniques.
After reviewing some of these advances, we present new data on T - T90 at twenty temperatures in the range from 118 K to 303 K. The differences agree well with other recent estimates, but our low uncertainty reveals previously unseen detail. These measurements probably constitute the most accurate measurements of temperature ever achieved.
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