High-temperature fixed-points with specified temperature values for phase transition temperatures and their uncertainties can be used to establish a temperature scale above the silver point as part of the SI. Current assigned temperatures had uncertainties increased to make the data consistent; seemingly with under-reported uncertainties which may have been due to variation in furnace thermal environment not being taken fully into account. As part of another round of temperature assignments to extend the available temperature options, the effect of changing furnace temperature gradients on the realization of different high-temperature fixed-point cells was investigated. The resulting uncertainty components are reported, and these should be included in any uncertainty budget. In this work, we present data for four phase transitions: iron-carbon (Fe-C), palladium-carbon (Pd-C), ruthenium-carbon (Ru-C) and tungsten carbide-carbon (WC-C).

Main text This report outlines the equipment, measurement method, results and uncertainties associated with the participant measurements for the Consultative Committee of Thermometry Key Comparison K10 (CCT-K10), "ITS-90 realisations above the silver point using two transfer radiation thermometers and a set of high temperature fixed-point blackbody cells", over the period from around summer 2014 to the final measurements made during January 2020. The report presents differences of the participant data from the KCRV values for both the radiation thermometer and HTFP measurements. Note: this interim report excludes the measurement data of VNIIM, Russia - see explanation at the end of Section 6. 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 https://www.bipm.org/kcdb/ . The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The Mise-en-Pratique for the recent redefinition of the kelvin has opened the possibility to directly disseminate the thermodynamic temperature by the mean of high-temperature fixed points whose thermodynamic temperature was assigned once and for all. These newly characterised fixed points offer to NMIs and DIs the possibility to perform a temperature scale directly linked to a thermodynamic temperature, without the complexity of an absolute measurement and without the need for extensive characterisation of the pyrometer performing the extrapolation. This article describes the various stages of the European project “Realising the redefined kelvin”, aimed at opening up these new possibilities to European laboratories.

The Mise-en-Pratique for the definition of the kelvin at high temperatures has opened the possibility of disseminating thermodynamic temperature through relative primary radiometry mediated by high- temperature fixed points (HTFPs). The thermodynamic temperatures of Co-C, Pt-C and Re-C were assigned in 2016. Here, we report on the assignment of thermodynamic temperatures of the phase transitions of four more HTFPs, namely, Fe-C similar to 1427 K, Pd-C similar to 1765 K, Ru-C similar to 2227 K and WC-C similar to 3021 K, with expanded uncertainties ranging from 0.15 K to 0.27 K.

Abstract This paper presents the utilization of Fe-C and Pd-C high-temperature fixed points (HTFPs) for the dissemination of thermodynamic temperature and the International Temperature Scale of 1990 (ITS-90). Initially, the HTFPs were manufactured and evaluated to determine the thermodynamic temperature during the melt of these materials. Subsequently, the cells were employed to compare the local realization of the International Temperature Scale of 1990 (ITS-90) in an ISO 17025 accredited industrial laboratory and two National Metrology Institutes (NMIs) with limited experience in operating HTFPs. The HTFPs were installed in Alumina tube furnaces, which have a maximum operating temperature of approximately 1600 °C. The investigation focused on the Fe-C (1153 °C) and Pd-C (1492 °C) fixed-point materials due to their suitability for realizing the temperature scale through interpolation schemes in this type of furnace. The findings of this comparative study contribute to enhancing the understanding and application of HTFPs for thermodynamic temperature dissemination.

Report "CHARACTERISATION OF FURNACE THERMAL EFFECTS ON THE REPRODUCIBILITY OF HIGH-TEMPERATURE FIXED-POINT CELLS" was written as part of WP1 of Real-K 18SIB02 and can be found at 10.5281/zenodo.7896128 A summary was presented at the 10th International Temperature Symposium DOI10.6028/NIST.SP.2100-05 and a paper to be submitted to the proceedings Data files contain individual melt curves provided by participants, together with the results from fitting 3-rd order polynomial curves as described in the report. The output from each melting curve has: The point-of-inflection, with type-1 uncertainty An extrapolated upper limit to the liquidus, with type-1 uncertainty The melting range The liquidus and its uncertainty are derived from the above

LNE-Cnam has changed its traceability chain for measuring the spectral irradiance of a light source. This facility allows calibration of spectral irradiance of a standard lamp based on a comparison with a high temperature blackbody (HTBB). The reference spectral irradiance is determined by measuring the temperature of the HTBB with a filter radiometer calibrated against our radiant flux reference. This traceability scheme differs from the one used in our former setup, which was mainly based on the International Temperature Scale, ITS-90. Both principles are used in National Measurement Institutes. Our facility uses well known methods adapted to our best capabilities as well as a particular development in optical arrangement and filter radiometer calibration. Thanks to this new measurement setup, our spectral irradiance reference is now traceable to radiometric reference, i.e. our cryogenic radiometer. We have extended our measurement capability to cover the spectral range from 250 nm to 2500 nm. We have simplified the process by reducing the number of benches (three in one) and the number of operations, and we have designed a compact measuring setup through the use of a rotating integrative sphere. This allows us to reduce by at least a factor two our measurement uncertainties over almost the entire spectral range. With this new measurement facility, France participates in the ongoing CCPR k1.a key comparison. This is a key comparison of the Consultative Committee of Photometry and Radiometry for Spectral irradiance from 250 nm to 2500 nm of tungsten halogen lamps. This communication shows the method used, and its validation.

We report new developments in instrumentation and techniques for both acoustic (speed of sound) and radiometric primary thermometry methods. These include both new cylindrical resonators for extending acoustic gas thermometry to higher temperatures and absolute radiation thermometers incorporating InGaAs detectors to extend primary radiometry to lower temperatures than can be achieved using Si-detector based instruments. These new approaches have been established in order to determine the difference between thermodynamic temperature, T, and the International Temperature Scale of 1990 (the ITS-90), T 90, over the temperature range from 430 K to 1358 K as part of the three-year EMPIR project ‘Implementing the new kelvin 2' (InK2). This paper describes the facilities and measurement methodologies for measuring T—T 90 at each of the different institutes, along with an assessment of the target uncertainties. The work is ongoing, but we anticipate that the results of these measurements will ultimately be pooled to provide consensus values of T—T 90 with associated estimated uncertainties. These consensus values will initially feed into the technical annex of the mise en pratique for the definition of the kelvin (MeP-K-19) and, if required, will be used to help to provide a foundation for any future temperature scale.

At LNE-Cnam, the international temperature scale of 1990 (ITS-90) and thermodynamic temperature measurements above the silver point, are carried out with a radiance comparator. This instrument is, more generally, devoted to any radiance comparison in temperature range from the ambient to 3000 °C. The instrument developed in the early 1990s at LNE-Cnam has the advantage of being completely adjustable. Compared to compact radiation thermometers based on lenses and a narrow-band interference filter, the radiance comparator is only made of gold coated mirrors and a Czerny–Turner monochromator to select the spectral bandwidth. The instrument offers the possibility to tune the geometric extent and the slit scattering function. In return, the radiance comparator is a complex instrument that requires a complete and a regular characterisation at the highest level of accuracy. In the first part, this paper describes the instrument and its operating principle. In a second part, a complete study of the wavelength calibration, the slit scattering function, size of source effect, out-of-band transmittance, linearity and other main sources of uncertainty are presented and discussed. Their associated uncertainties are estimated separately and are grouped together to give an example of propagation of uncertainties when realising the ITS-90.

This paper describes a new relative technique developed at LNE-Cnam, for the determination of the thermodynamic temperature of blackbodies without recourse to a radiometric reference. This technique is referred to as the ‘synthetic double wavelength technique’ (SDWT) as it is considered to be a particular case of the ‘double wavelength technique’ (DWT). It offers a new experimental technique for the determination of the thermodynamic temperature at high temperature and as such a new means for the mise-en-pratique of the new definition of the kelvin achievable by any national metrology institute provided a multi-wavelength radiation thermometer combining large and narrow bandwidths is available. In this work, a first experimental implementation of this technique based on a wavelength-tuneable spectroradiometer providing both narrowband and broadband signals with the particularity of the broadband signal being virtually synthesised from the spectral distribution of the narrowband signals sampled over a wide spectral range. SDWT determination of the thermodynamic temperature of a blackbody at 2760 K was performed with a level of uncertainty that confirms the promising capabilities of this technique.

In the frame of the EMPIR-funded joint research project 15SIB02 “Implementing the new kelvin – 2” (InK2) the determination of T-T90 over the temperature range between 430 K and 1358 K with a target uncertainty around the 10 mK level is under preparation in several NMIs, among which LNE-Cnam and CEM. The two laboratories have joined their efforts for the thermal characterisation of a set of three aluminium fixed-point pyrometric cells. The cells were constructed using the hybrid design based crucibles and the piston filling method both developed by LNE-Cnam over the past decade. To study the effect of the temperature gradients on the freezing temperatures of the cells, two three-zone furnaces were used for the implementations of the cells with different temperature distributions. Finally, a first determination of the thermodynamic temperature of the freezing plateau was determined by extrapolation from the thermodynamic temperature of the copper point of LNE-Cnam. The results of the characterisations and the temperature determination are presented.

Within the frame of a European project called Eura-Thermal, the general objective was to upgrade the regional metrological infrastructure (Bosnia & Herzegovina, Croatia, Ireland, Serbia...) with new capabilities, especially in the field of thermal measurements. This paper highlights the strategy used for improving in the short term, scientific knowledge transfer and the capabilities of different emerging institutes. Furthermore, as a main output, the impacts and benefit for Industry and for the end-users are also presented as examples.

The eutectic alloys rhenium-carbon, platinum-carbon and cobalt-carbon have been proposed as reference standards for thermometry, with temperature and uncertainty values specified within the mise en pratique of the definition of the kelvin. These alloys have been investigated in a collaboration of eleven national measurement institutes and laboratories. Published results reported the point-of-inflection in the melting curve with extremely low uncertainties. However, to be considered as standards it is necessary to stipulate what phenomenon a temperature value has been ascribed to; specifically, this should be a thermodynamic state. Therefore, the data have been further evaluated and the equilibrium liquidus temperatures determined based on a consideration of limits and assuming a rectangular probability distribution. The values are: for rhenium-carbon 2747.91 +/- 0.44 K, for platinum-carbon 2011.50 +/- 0.22 K and for cobalt-carbon 1597.48 +/- 0.14 K, with uncertainties at approximately a 95% coverage probability. It is proposed that these values could be used as the basis of thermodynamic temperature measurement at high temperatures (above 1300 K).

Les recherches consacrees aux points fixes a haute temperature (PFHT) ont ete intensifiees depuis 1996, suite a une recommandation du Comite Consultatif de Thermometrie de developper des references au-dela de 2000 °C. Les Laboratoires Nationaux de Metrologie se sont alors engages dans le developpement de PFHT construits a partir d'alliages de metal et de carbone. Ces points fixes ont montre des transitions de phase a des temperatures reproductibles independamment de la proportion de carbone dans le metal. Les projets internationaux qui ont suivis les premiers developpements ont permis d'accroitre la robustesse et la stabilite a long terme des points fixes et ont mis en evidence l'importance des conditions thermiques de mise en œuvre. Aujourd'hui ces points fixes montrent une reproductibilite de l'ordre de 0.1 °C et sont en voie de renforcer l'exactitude des mesures pyrometriques aux plus hautes temperatures, jusqu'ici limitee par l'incertitude d'extrapolation dans l'Echelle Internationale de Temperature (EIT-90). Un projet de mesure par voie radiometrique de la temperature thermodynamique des PFHT les plus etudies a ete recemment mene. Les resulats de ces mesures absolues permettent aujourd'hui d'aborder la future mise-en-pratique du kelvin a haute temperature, par des methodes de dissemination directe de la temperature thermodynamique sans recours a l'EIT-90. Ce document decrit les principales etapes depuis la conception de ces nouvelles references, jusqu'a la mesure de leur temperature thermodynamique.

This paper presents the work carried out to evaluate the radiometric performance of a radiance-meter system which has been built at the LNE-Cnam to determine the thermodynamic temperature of high-temperature fixed points. The work comes as an integral part of the 'implementing the new Kelvin' (INK) project in which nine National Metrology Institutes (NMIs) strive to assign the thermodynamic temperatures to the melting curve of high-temperature fixed points with the lowest possible uncertainty. The method used in this research is based on the radiance approach. It exploits a system based on a laser-illuminated integrating sphere source whose radiance is absolutely measured by a trap detector through a well-defined geometry. The trap detector is calibrated traceable to the LNE-Cnam's cryogenic radiometer. Once the radiance of the sphere is defined, a single grating-based spectroradiometer is used to measure the radiance of the fixed point source at the laser wavelength through direct comparison with the sphere radiance. This allows the thermodynamic temperature of the fixed point to be determined using Planck's radiation law. The work provides a thorough evaluation of the system along with a detailed study of all related systematic effects and their corresponding uncertainties.

The mise-en-pratique for the definition of the kelvin at high temperatures will formally allow dissemination of thermodynamic temperature either directly or mediated through high-temperature fixed points (HTFPs). In this paper, these two distinct dissemination methods are evaluated, namely source-based and detector-based. This was achieved by performing two distinct dissemination trials: one based on HTFPs, the other based on absolutely calibrated radiation thermometers or filter radiometers. These trials involved six national metrology institutes in Europe in the frame of the European Metrology Research Programme joint project ‘Implementing the new kelvin’ (InK). The results have shown that both dissemination routes are possible, with similar standard uncertainties of 1–2 K, over the range 1273–2773 K, showing that, depending on the facilities available in the laboratory , it will soon be possible to disseminate thermodynamic temperatures above 1273 K to users by either of the two methods with uncertainties comparable to the current temperature scale.

The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature.

Calibration of the industrial pyrometers in the temperature range between 1 000 ◦C and 3 000 ◦C requires a blackbody cavity source which temperature is measured using a reference pyrometer. The use of such blackbody cavity source is imposed by the characteristics of the pyrometers to be calibrated, because of the large field-of-view (usually of the order of 10 mm to 30 mm), which is not compatible with the dimensions of the fixed points used to calibrate reference pyrometers. The reference pyrometer and the pyrometer under the calibration can also have very different spectral characteristics. The filter’s transmission bandwidth of the reference pyrometer filter is generally of the order of 20 nm, but it can reach several hundred nanometers for the pyrometer under calibration. An unbiased comparison of the two instruments can be only obtained with a transfer blackbody cavity with emissivity equal to 1. The different spectral and spatial characteristics of the compared pyrometers require a determination of the effective emissivity of the cavity and a determination of the radial profile of surfaces intercepted by the field-of-view of pyrometers. The high temperature furnace Thermogauge HT-9500 LNE-Cnam has been characterized for use as a transfer cavity. For this, the longitudinal and radial gradients in the cavity have been measured by various methods. The effective emissivity of the cavity was calculated. An estimate of the corrections and uncertainties associated with non-unit emissivity are presented in this article.