Thermal Metrology and Temperature Measurement Techniques

Thermal metrology underpins a vast array of scientific, industrial and societal applications by providing reliable and traceable temperature measurements across scales from cryogenic to high‐temperature environments. Primary thermometry techniques, which realise thermodynamic temperature directly from fundamental physical principles, include acoustic gas thermometry, dielectric‐constant gas thermometry, refractive‐index gas thermometry and Johnson noise thermometry. Secondary methods such as resistance thermometry, thermocouple measurements and semiconductor sensors rely on calibration against these primary standards. Central to modern practice is the International Temperature Scale of 1990 (ITS-90), which defines fixed points and interpolation instruments to ensure uniformity of measurements worldwide. The 2019 redefinition of the kelvin in terms of the Boltzmann constant has stimulated refinements in primary thermometry, driving improvements in uncertainty budgets to the sub‐millikelvin level. Contemporary research focuses on enhancing precision under non-ideal conditions, reducing systematic errors in optical and microwave resonators, and exploiting ab initio calculations of gas properties to support next-generation temperature standards. Such advances enable robust traceability for applications ranging from semiconductor manufacturing to climate monitoring and fundamental physics.

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Thermal Metrology and Temperature Measurement Techniques publication trend

The graph below shows the total number of articles in thermal metrology and temperature measurement techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Thermodynamic temperature: Fundamental measure of thermal energy of a system based on the mean kinetic energy of its particles.

International Temperature Scale of 1990 (ITS-90): Empirical temperature scale realised by defining a series of fixed points and interpolation instruments to ensure consistency across laboratories.

Standard Platinum Resistance Thermometer (SPRT): High-accuracy thermometer whose electrical resistance varies predictably with temperature, serving as a calibration reference.

Gas modulation refractometry (GAMOR): Technique alternating the filling and evacuation of a measurement cavity relative to a reference cavity to determine gas refractivity and infer thermodynamic parameters.

Fabry–Pérot cavity: Optical resonator formed by two parallel, highly reflective mirrors, whose resonant frequencies shift with changes in refractive index of the enclosed medium.

Triple point: Unique thermodynamic condition at which a substance’s solid, liquid and gas phases coexist in equilibrium at a defined temperature and pressure.

References

1. Investigations of Type 3 non-uniqueness in standard platinum resistance thermometers between 83 K and 353 K. Measurement (2023).
2. 2022 Update for the Differences Between Thermodynamic Temperature and ITS-90 Below 335 K. Journal of Physical and Chemical Reference Data (2022).
3. Thermodynamic effects in a gas modulated Invar-based dual Fabry–Pérot cavity refractometer. Metrologia (2022).
4. Ab Initio Calculation of Fluid Properties for Precision Metrology. Journal of Physical and Chemical Reference Data (2023).