Techniques for Primary Acoustic Thermometry to 800 K

Published

September 1, 2003

Author(s)

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

Abstract

The NIST Primary Acoustic Thermometer will measure the difference between the International TemperatureScale of 1990 and the Kelvin Thermodynamic Scale throughout the range 273 K to 800 K with uncertainties of only afew millikelvins. The acoustic thermometer determines the frequencies of the acoustic resonances of pure argon gascontained within a spherical cavity with uncertainties approaching one part in 10 6 . To achieve this small uncertainty atthese elevated temperatures we developed new acoustic transducers and new techniques for the maintenance of gaspurity and for temperature control. The new electro-acoustic transducers are based on the capacitance between a flexiblesilicon wafer and a rigid backing plate. Without the damping usually provided by polymers, mechanical vibrationscaused unstable, spurious acoustic signals. We describe our techniques for suppression of these vibrations. Our acousticthermometer allows the argon to be continuously flushed through the resonator, thereby preventing the build up ofhydrogen that evolves from the stainless-steel resonator. We describe how the argon pressure is stabilized whileflushing. The argon exiting from the resonator is analyzed directly with a customized gas chromatograph. Because theacoustic resonator was so large it has an outer diameter of 20 cm a sophisticated furnace, based on surrounding theresonator with three concentric aluminum shells, was designed to maintain thermal uniformity and stability of theresonator at a level of 1 mK. We describe the design, modeling, and operational characteristics of the furnace.

Proceedings Title

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

Volume

684

Conference Dates

October 21-24, 2002

Conference Title

AIP Conference Proceedings

Pub Type

Conferences

Keywords

acoustic, argon, ITS-90, speed of sound, temperature, thermodynamic

Citation

Ripple, D. , Defibaugh, D. , Moldover, M. and Strouse, G. (2003), Techniques for Primary Acoustic Thermometry to 800 K, Temperature, International Symposium | Eighth | Temperature: Its Measurement and Control in Science and Industry; Volume Seven | AIP (Accessed December 2, 2024)