The kelvin redefinition and the MeP-K
Dr Bernd Fellmuth, Physikalisch-Technische Bundesanstalt, Germany
Abstract
Historically, the best guide for the realisation of the kelvin has been the text of the International Temperature Scales and accompanying documents. Recent developments and its redefinition have motivated the creation of a more flexible document: the Mise-en-Pratique of the definition of the kelvin (MeP-K). The MeP-K provides the information needed to perform a practical measurement of temperature.
In this contribution, the background and the content of the second version of the MeP-K is presented. This version is based on the planned redefinition of SI base unit kelvin via an explicit-constant definition. The kelvin will be defined in terms of the SI derived unit of energy, the joule, by fixing the value of the Boltzmann constant. The explicit-constant definition is sufficiently wide to encompass any form of thermometry and leaves the MeP-K to spell out the practical details.
The second version of the MeP-K consists of four parts:
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Introduction, stating the redefinition of the kelvin, the rationale for the change, and the effect on its realisation.
- Nomenclature, defining fundamental terms of thermometry to support an unambiguous taxonomy of methods.
- Primary thermometry, describing the realisation based on fundamental laws of statistical thermodynamics. Two primary methods, namely acoustic gas thermometry and radiometric thermometry, are shortly described. Details are given in appendices.
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Defined temperature scales, providing information for the ITS 90 and PLTS 2000. Further important information is given in appendices and guides.
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Dr Bernd Fellmuth, Physikalisch-Technische Bundesanstalt, Germany
Dr Bernd Fellmuth, Physikalisch-Technische Bundesanstalt, Germany
Bernd Fellmuth was born in Berlin, Germany, on June 25, 1953. He received his Dipl.-Phys. and Dr. rer. nat. degrees at the Humboldt-University zu Berlin, Germany, in 1977 and 1980, respectively, in the field of solid-state physics. Furthermore, he received the degree Dr. sc. nat. from the Technical University Dresden, Germany, in 1990 in the field of measurement of low temperatures. From 1980 to 1990 he was with the metrological institute of East Germany, and since 1991 he has been with the Physikalisch-Technische Bundesanstalt (PTB), Institute Berlin, Germany, where he is now head of the working group Fundamentals of Thermometry. His work has been concerned with precision temperature measurements, especially fixed-point realisation and vapour-pressure and gas thermometry.
Low uncertainty Boltzmann constant determinations and the kelvin redefinition
Dr Joachim Fischer, Physikalisch-Technische Bundesanstalt, Germany
Abstract
The General Conference on Weights and Measures agreed at its 24th meeting in October 2011 on new definitions for four of the seven base units of the International System of Units (SI). Kilogram, ampere, kelvin, and mole will be defined in terms of fixed numerical values of the Planck constant, elementary charge, Boltzmann constant and Avogadro constant, respectively.
The effect of the new definition of the kelvin referenced to the value of the Boltzmann constant is that the kelvin is equal to the change of thermodynamic temperature that results in a change of thermal energy kT by 1.380 650 x 10−23 J. The new definition would be in line with modern science where nature is characterised by statistical thermodynamics, which implies the equivalence of energy E and temperature T as expressed by the Maxwell-Boltzmann equation E = kT.
A refined value of the Boltzmann constant suitable for defining the kelvin is presently determined by fundamentally different primary methods like acoustic gas thermometry, dielectric constant gas thermometry, noise thermometry, and the Doppler broadening technique. Details of the measurements, progress to date, and further perspectives will be reported.
Necessary conditions to be met before proceeding with changing the definition are given. The consequences of the new definition of the kelvin on temperature measurement will be outlined.
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Dr Joachim Fischer, Physikalisch-Technische Bundesanstalt, Germany
Dr Joachim Fischer, Physikalisch-Technische Bundesanstalt, Germany
Joachim Fischer holds a PhD in physics from the Technical University of Berlin, Germany. Since 1982 he has been with the Physikalisch-Technische Bundesanstalt (PTB) in Berlin, first at the electron storage ring BESSY. In 1986 he joined the section temperature radiation. Since 2001 he has been head of the temperature department where the international temperature scale is developed and disseminated to the user by contact thermometry. He is involved in the improvement of temperature measurement and in research on a new definition of the SI-base unit kelvin by fixing the value of the Boltzmann constant.
He represents PTB in the Consultative Committee for Thermometry, chairs the working group for contact thermometry and the task group for the new SI. Other international work includes membership in the CODATA task group on fundamental constants and in standardisation bodies, and he is the German contact for the EURAMET Technical Committee of Thermometry.
On the meaning of temperature
Professor Peter Hänggi, University of Augsburg, Germany
Abstract
Most importantly, temperature is a derived quantity. It is given as the thermodynamic force of the thermodynamic state function, known as the entropy S. The absolute temperature T then obeys: 1/T = ∂S/∂E, wherein E denotes the internal thermodynamic energy state function. The inverse absolute temperature provides the integrating factor for the Second Law of thermodynamics, dS = δQrev/T, where δQrev refers to the reversible, quasi-static heat exchange.
JW Gibbs introduced two thermodynamic entropy expressions. A first one (i) known as volume entropy, termed here the `Gibbs entropy’ SG, reading: SG(E, λ) = kB ln Ω(E, λ), with λ denoting the set of external control parameters, such as the available volume, magnetic field, etc. Ω(E, λ) is the integrated, non-negative valued density of states. Gibbs also discussed a second entropy expression (ii) that is referred to as surface entropy SB (nowadays, commonly known also as the Boltzmann entropy), reading SB(E, λ) = kB ln [ε ω(E, λ)], with ε being some small energy constant so that the argument of the logarithm becomes dimensionless.
As recently shown with Ref. [1], for the consistency of an entropy function S with thermodynamics, that is to say with S obeying the celebrated 0th, 1st and 2nd thermodynamic laws singles out the Gibbs-entropy [1]. I point out shortcomings for the thermodynamics of systems of finite size and/or with an upper bound in energy if using (Boltzmann) entropy. The two corresponding thermodynamic temperatures TG and TB are then not equivalent and can considerably differ.
[1] S. Hilbert, P. Hänggi, and J. Dunkel, Thermodynamic Laws in Isolated Systems, Phys. Rev. E 90, 062116 (2014).
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Professor Peter Hänggi, University of Augsburg, Germany
Professor Peter Hänggi, University of Augsburg, Germany
Peter Hänggi is distinguished for his many seminal contributions in the area of statistical physics and driven quantum mechanics, which he achieved at the Polytechnic Institute of New York and the University of Augsburg. He is known worldwide for his key contributions to reaction rate theory, driven quantum mechanics, quantum dissipation, foundations of statistical mechanics, the phenomenon of Stochastic Resonance, his discovery of coherent destruction of tunnelling, and his initiation of the field of Brownian motors.
The new SI: progress and prospects
Professor Marc E. Himbert, LNE-Cnam, France
Abstract
Most national metrology laboratories and some major physics laboratories have been working for decades to improve the determination of several fundamental physical constants. As the uncertainty in the measurements tends to the accuracy of the materialisations of the relevant SI units, time has come for a major change in the SI definitions, where the so-called based units will be scaled relative to fixed values of a set of fundamental constants or constants of nature.
The frame of this new SI was proposed 10 years ago. Major resolutions were adopted by the CIPM and the CGPM to fix which conditions should be fulfilled before a final decision for the change. Such a decision is expected to be taken in 2018. The new SI will highly improve the accuracy and the sustainability of the set of references. It will also open the way to an easier traceability at the nano- and quantum scales.
The new kelvin will be linked to a fixed value of the Boltzmann constant k. Consequently the triple point of water will remain as a practical reference, to be calibrated. A draft of the future SI brochure, with the new definition of the kelvin, is on the way. New techniques, new concepts and new technologies are investigated to link new ways of measurements to the International temperature scale. The aim is to make profit of this new definition for absolute and relative determinations of temperatures.
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Professor Marc E. Himbert, LNE-Cnam, France
Professor Marc E. Himbert, LNE-Cnam, France
Professor Marc E. Himbert is 57. He graduated in 1980 from the Ecole normale supérieure in atomic and laser physics, under supervision of C.Cohen-Tannoudji, and was appointed as CNRS full time researcher in Kastler Brossel laboratory in Paris until 1989. He was made full professor of metrology at the National institute for arts and trade in France (CNAM) in 1992, and is at present the scientific head of the LNE-CNAM Joint metrology laboratory. He has participated in the Consultative committee for units (CCU) since 2003 as personal member. He was elected in 2009 as member of the National academy of technology of France (NATF). He also chairs the laboratory section of the French accreditation body (COFRAC). His scientific activities are mainly devoted to thermal and optical metrology, and quantum physics. In particular he participates in the measurements of k (acoustic way) and h (watt balance) presently performed in France.
Chair
Professor Martin Trusler, Imperial College London, UK
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Professor Martin Trusler, Imperial College London, UK
Professor Martin Trusler, Imperial College London, UK
J P Martin Trusler is Professor of Thermophysics in the Department of Chemical Engineering at Imperial College London. He obtained his BSc and PhD degrees in chemistry from University College London, and was both a Lindermann Trust Fellow and a Ramsay Memorial Fellow prior to joining Imperial as a lecturer in 1988. In 1984-5, he participated in the NBS (now NIST) project to re-determine the gas constant by means of sound-speed measurements with a spherical resonator. Spherical resonators were also the tool of choice in other early-career research, including the measurement of acoustic virial coefficients at low temperatures and determination of the thermodynamic properties of gas mixtures at high pressures. His current research is focused on studies of the thermophysical properties and phase behaviour of industrial fluids at high pressures, with applications in carbon capture, transportation and storage, and oil/gas exploration and production.