P. Bloembergen

Progress report for the CCT-WG5 high temperature fixed point research plan

An overview of the progress in High Temperature Fixed Point (HTFP) research conducted under the auspices of the CCT-WG5 research plan is reported. In brief highlights are: Provisional long term stability of HTFPs has been demonstrated. Optimum construction methods for HTFPs have been established and high quality HTFPs of Co-C, Pt-C and Re-C have been constructed for thermodynamic temperature assignment. The major sources of uncertainty in the assignment of thermodynamic temperature have been identified and quantified. The status of absolute radiometric temperature measurement has been quantified through the circulation of a set of HTFPs. The measurement campaign to assign low uncertainty thermodynamic temperatures to a selected set of HTFPs will begin in mid-2012. It is envisaged that this will be complete by 2015 leading to HTFPs becoming routine reference standards for radiometry and high temperature metrology.

Analytical representations of the size-of-source effect

In this paper it is shown that the size-of-source effect (SSE) of a radiation thermometer measured for a range of source diameters Di, can be fitted by means of empirical analytical approximations F(D), selected on the basis of quite general arguments. This is necessary to analytically process SSE data and to rigorously quantify the uncertainties associated with the correction for the SSE. To test the proposed fitting scheme 35 size-of-source curves, measured by five institutes for different radiation thermometers, have been analysed. In a companion paper the uncertainty in the correction for the SSE will be elaborated in detail for two examples.

Construction of high-temperature fixed-point cells for thermodynamic temperature assignment

A multi-partner project is currently being conducted within Working Group 5 (Radiation thermometry) of the CIPM Consultative Committee for Thermometry (CCT), which aims at assigning thermodynamic temperatures to a selected set of high-temperature fixed-points (HTFPs) based on metal-carbon eutectics. A work package of this project (WP2) consists in producing sets of HTFP cells to serve the final phase of the project, assignment of definitive thermodynamic temperatures (WP5). The four fixed-point types are the metal-carbon eutectic points, Re-C (2474 °C), Pt-C (1739 °C), and Co-C (1324 °C), and the Cu point (1084.62 °C). The first phase of the WP2 work treats the construction of HTFP cells, which were carried out by eight National Metrology Institutes (NMIs). The cells were constructed in accordance to instructions laid out in the WP protocol, based on years of experience of WG5 member NMIs. Cells constructed in this way should, in principle, have the required performance in terms of the realized temperature, reproducibility, and long term stability. The constructed cells were then evaluated for their performance in the second phase of the WP. The WP aims at identifying at least four cells of each of the four fixed-point types to be supplied to WP5 of the CCT-WG5 research plan for final thermodynamic temperature assignment. This paper describes the first phase of the WP2. Details of the cell construction conditions and procedures are presented.

On the uncertainty in the correction for the size-of-source effect

In the first part of this paper a procedure is described for calculating the standard uncertainty u[F(D)] in the approximation F(D) to the size-of-source effect σ(Di), measured for a range of source diameters Di, for two examples out of a total of 35 considered in an accompanying paper. The overall uncertainty includes the uncertainty sfit of the approximation F(D) to the experimental data and other components such as the repeatability of the measurements, the effect of interreflections and the in-focus/out-of-focus shift. In the main part of the paper this procedure is tailored to the calculation of the uncertainty uSSE[S(Dref)]/S(Dref) in the correction for the size-of-source effect as a function of the reference diameter Dref, a relationship characteristic for a given thermometer–source combination. The source considered here is a eutectic fixed-point radiator, Re–C, radiating at the eutectic temperature of 2747 K. The correction is carried out by transformation of the directly obtained results, in terms of the signals S measured under the local prevailing measurement conditions, to univocal results associated with a specified reference condition. The utility of the formalism is demonstrated by some practical applications given in an appendix to the paper.

A new approach to the determination of the liquidus and solidus points associated with the melting curve of the eutectic Co?C, taking into account the thermal inertia of the furnace

In the case of metal–carbon eutectics, with transition temperatures above 1000 °C, the liquidus-point temperature, associated with melting, serves as a prime reference temperature. Factors influencing the shape of the melting curve and how to deal with them when specifying the liquidus temperature are the main subject of this paper. Influence factors investigated are the impurity factor, the furnace-temperature gradient, and a factor not considered before: the thermal inertia of the furnace and the associated transient in furnace temperature during melting. These investigations resulted in an improved method for determining the liquidus point, demonstrated for Co–C, which implicitly corrects for the post-melting effect, if any. In addition, a new method, the step-shift method, is proposed for the determination of the solidus point by direct observation. As shown, there is a clear justification for establishing reference methods to determining the solidus and liquidus points of M–C eutectics along the lines set out in this paper.