Published: April 18, 2019


Patrick Rourke, Christof Gaiser, Roberto M. Gavioso, Michael R. Moldover, Laurent Pitre, Robin Underwood


The principles and techniques of primary refractive-index gas thermometry (RIGT) are reviewed. Absolute primary RIGT using microwave measurements of helium-filled quasi-spherical resonators has been implemented at the temperatures of the triple points of neon, oxygen, argon and water, with relative standard uncertainties ranging from 9.1 x 10-6 to 3.5 x 10-5, and a sample uncertainty budget for this approach is provided. Researchers are now adapting cylindrical microwave resonators for RIGT at high temperatures and conducting relative RIGT measurements on isobars at low temperatures. RIGT at optical frequencies is progressing.
Citation: Metrologia
Volume: 56
Pub Type: Journals


thermometry, thermodynamic temperature, refractive index, microwave resonators, polarizability, virial coefficients
Created April 18, 2019, Updated April 23, 2019