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Accurate measurements of temperature underpin a wide variety of fields, science, energy industry, environment, health, and life quality, just to name a few. Traditional temperature standards rely on properties of substances. The new definition of the kelvin, which links temperature to the Boltzmann constant, therefore brought a fundamental change to thermometry.

Two independent methods for measuring the Boltzmann constant were developed by NIM in the past decade: the cylindrical acoustic gas thermometer (c-AGT) and the Johnson noise thermometer (JNT). NIM determination of the Boltzmann constant by two primary thermometers have both contributed to the CODATA 2014 and 2017 adjustments of the constant. The CODATA 2017 recommended value of the Boltzmann constant has been used for the revision of the kelvin. NIM was an NMI that contributed to this revision with two primary methods of independent principle. As a result, the project “Key Technologies for the Redefinition of the Unit of Temperature” won NIM a first prize of the 2018 National Science and Technology Progress Award.

Besides, the technologies derived from this project provide a new solution for the direct thermodynamic temperature measurement in the Fourth-Generation Nuclear Reactor of China. It also bears great significance as it may help to realize temperature and other thermophysical quantities with multi-technological, zero-traceability chain, and in-situ approaches.