Unit Of Thermodynamic Temperature Research Articles

The kelvin redefinition and its mise en pratique.

In 2018, it is expected that there will be a major revision of the International System of Units (SI) which will result in all of the seven base units being defined by fixing the values of certain atomic or fundamental constants. As part of this revision, the kelvin, unit of thermodynamic temperature, will be redefined by assigning a value to the Boltzmann constant k. This explicit-constant definition will define the kelvin in terms of the SI derived unit of energy, the joule. It is sufficiently wide to encompass any form of thermometry. The planned redefinition has motivated the creation of an extended mise en pratique ('practical realization') of the definition of the kelvin (MeP-K), which describes how the new definition can be put into practice. The MeP-K incorporates both of the defined International Temperature Scales (ITS-90 and PLTS-2000) in current use and approved primary-thermometry methods for determining thermodynamic temperature values. The MeP-K is a guide that provides or makes reference to the information needed to perform measurements of temperature in accord with the SI at the highest level. In this article, the background and the content of the extended second version of the MeP-K are presented.

Improved electronic measurement of the Boltzmann constant by Johnson noise thermometry

The unit of thermodynamic temperature, the kelvin, will be redefined in 2018 by fixing the value of the Boltzmann constant, k. The present CODATA recommended value of k is determined predominantly by acoustic gas-thermometry results. To provide a value of k based on different physical principles, purely electronic measurements of k were performed by using a Johnson noise thermometer to compare the thermal noise power of a 200 Ω sensing resistor immersed in a triple-point-of-water cell to the noise power of a quantum-accurate pseudo-random noise waveform of nominally equal noise power. Measurements integrated over a bandwidth of 575 kHz and a total integration time of about 33 d gave a measured value of k = 1.3806513(53) × 10−23 J K−1, for which the relative standard uncertainty is 3.9 × 10−6 and the relative offset from the CODATA 2010 value is +1.8 × 10−6.

G123 温度の単位ケルビンの再定義と音響気体温度計の開発

A decision at the 24th General Conference on Weights and Measures (CGPM) has been made to adopt a dramatic change of the International System of the Units (SI). The unit of thermodynamic temperature, kelvin, is likely to be redefined based upon the fundamental constant k_B, the Boltzmann constant. To this concern, leading national metrology institutes are developing thermodynamic thermometry systems to acquire reliable data for the Boltzmann constant to ensure this redefinition to take place smoothly. Another issue following the redefinition of kelvin is the deviation between the thermodynamic temperature and the temperature scale. This paper describes the background, the aim and the progress of the development of acoustic gas thermometry (AGT) at the National Institute of Advanced Industrial Science and Technology (AIST).

Current state of work on the redefinition of the unit of thermodynamic temperature

The current state of experimental work on the redefinition of the unit of thermodynamic temperature, the kelvin, is analyzed. Data on the main experimental devices for determination of the Boltzmann constant are examined. It is concluded that the prerequisites for a transition to a new definition of the kelvin at the 24th General Conference on Weights and Measures do not yet exist.

Final Report on CCT-K7: Key comparison of water triple point cells

The triple point of water serves to define the kelvin, the unit of thermodynamic temperature, in the International System of Units (SI). Furthermore, it is the most important fixed point of the International Temperature Scale of 1990 (ITS-90). Any uncertainty in the realization of the triple point of water contributes directly to the measurement uncertainty over the wide temperature range from 13.8033 K to 1234.93 K.The Consultative Committee for Thermometry (CCT) decided at its 21st meeting in 2001 to carry out a comparison of water triple point cells and charged the BIPM with its organization.Water triple point cells from 20 national metrology institutes were carried to the BIPM and were compared with highest accuracy with two reference cells. The small day-to-day changes of the reference cells were determined by a least-squares technique. Prior to the measurements at the BIPM, the transfer cells were compared with the corresponding national references and therefore also allow comparison of the national references of the water triple point.This report presents the results of this comparison and gives detailed information about the measurements made at the BIPM and in the participating laboratories. It was found that the transfer cells show a standard deviation of 50 µK; the difference between the extremes is 160 µK. The same spread is observed between the national references.The most important result of this work is that a correlation between the isotopic composition of the cell water and the triple point temperature was observed. To reduce the spread between different realizations, it is therefore proposed that the definition of the kelvin should refer to water of a specified isotopic composition.The CCT recommended to the International Committee of Weights and Measures (CIPM) to clarify the definition of the kelvin in the SI brochure by explicitly referring to water with the isotopic composition of Vienna Standard Mean Ocean Water (VSMOW). The CIPM accepted this recommendation and the next edition of the SI brochure will include this specification.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).