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.
Temperature, International Symposium | Eighth | Temperature: Its Measurement and Control in Science and Industry; Volume Seven | AIP