Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Progress in Primary Acoustic Thermometry at NIST: 273 K to 505 K



Gregory F. Strouse, Dana R. Defibaugh, Michael R. Moldover, Dean C. Ripple


The NIST Acoustic Thermometer determines the thermodynamic temperature by measuring the speed of sound of argon in a spherical cavity. We obtained the thermodynamic temperature of three fixed points on the Interna-tionalTemperature Scale of 1990: the melting point of gallium [T(Ga) = 302.9146 K] and the freezing points of indium [T(In) = 429.7485 K] and tin [T(Sn) = 505.078 K]. The deviations of thermodynamic temperature from the ITS-90 de-finedtemperatures are T -T90 = (4.7 0.6) mK at T(Ga) , T -T90 = (8.8 1.5) mK at T(In) , and T -T90 = (10.7 3.0) mK at T(Sn) , where the uncertainties are for a coverage factor of k = 1. Our results at T(In) and T(Sn) reduce the uncer-taintyof T -T90 by a factor of two in this range. The measured thermal expansion of the resonator between the triple point of water and T(Ga), and T -T90 at T(Ga) are both in excellent agreement with the 1992 determination at NIST. Thedominant uncertainties in the present data come from frequency-dependent and time-dependent crosstalk between the electroacoustic transducers. We plan to reduce these uncertainties and extend this work to 800 K.
Proceedings Title
Temperature, International Symposium | Eighth | Temperature: Its Measurement and Control in Science and Industry; Volume Seven | AIP
Conference Dates
October 21-24, 2002
Conference Title
AIP Conference Proceedings


acoustic, argon, ITS-90, speed of sound, temperature, thermodynamic
Created September 1, 2003, Updated February 17, 2017