The homogeneity variation along thermo elements has been investigated, using a new technique based on the Curie-point of ferromagnetic materials. This method provides a simple solution for determination of thermocouple inhomogeneity, which is one of the pressing problems associated with high level practical temperature metrology. These achievements in the measurement of temperatures lead to improved stability in processes where temperature is a critical factor. This work is performed within the framework of the European Metrology Program for Innovation and Research (EMPIR) project 18RPT03 MetForTC [1]. Received: April 25, 2023Accepted: May 29, 2023

This report present the results of the EURAMET inter-comparison carried out to compare the calibration of thermocouples from 419,527 °C (freezing point of Zn) up to 1492 °C (melting point of the Pd-C eutectic). This inter-comparison is intended to be used to support the calibration and measurement capabilities (CMCs) of the participants in the calibration of thermocouples. The comparison was organized in three loops with nineteen participating laboratories and it allowed the performance of the measurement either in fixed points and/or by comparison. The method used to analyse the results of the comparison was the generalized weighted mean that takes into account the full covariance matrix that includes correlations between the participants which have similar traceability sources and between measurements performed by the same laboratory (i.e. the pilots that performed measurements at the beginning and at the end of each loop and the measurements performed by the same laboratory in fixed points and by comparison at the same calibration point). 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 (CIPM MRA).

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.

An alternative calibration procedure has been applied using apparatus built in-house, created to optimize thermal conductivity measurements. The new approach compared to those of usual measurement procedures of thermal conductivity by guarded hot plate (GHP) consists of modified design of the apparatus, modified position of the temperature sensors and new conception in the calculation method, applying the temperature at the inlet section of the specimen instead of the temperature difference across the specimen. This alternative technique is suitable for eliminating the effect of thermal contact resistance arising between a rigid specimen and the heated plate, as well as accurate determination of the specimen temperature and of the heat loss at the lateral edge of the specimen. This paper presents an overview of the specific characteristics of the newly developed "high-temperature thermal conductivity measurement apparatus" based on the GHP method, as well as how the major difficulties are handled in the case of this apparatus, as compared to the common GHP method that conforms to current international standards.

Some of the national metrology institutes (NMIs) have developed devices which generate a standard surface temperature under conditions which resemble, as closely as possible, those encountered during the routine use of surface sensors. Several comparisons of measurements among European NMIs, coordinated by MKEH, were undertaken in order to validate the methods used and the reference conditions. The characteristics of the reference surface significantly influence the measurement error, as its temperature, inclination and thermophysical properties. This paper presents a method of determining a correction function, containing the effects of these factors. The measurements have been taken in the temperature range from \(100\,^{\circ }\hbox {C}\) to \(500\,^{\circ }\hbox {C}\), with a specific sensor having an inflexible head. The technique developed of MKEH is suitable for quantifying the effect of the above parameters, optimizing the surface temperature measurements in this regard.

The development of thermal conductivity reference materials for high-temperature insulation consists of three stages: provisional assessment of candidate reference materials, detailed assessment of candidate reference material(s) and corresponding inter-laboratory comparisons. This paper describes the detailed characterization of a candidate high-temperature thermal conductivity reference material, a high-density calcium silicate (HDCaSi-N). The selection criteria, assessments of uniformity and stability, the thermal expansion behavior and their effects on the thermal conductivity reference specimens are presented in the paper. The uniformity assessments include the thermal expansion variation in orthogonal orientations and different locations and from different boards, as well as thermal conductivity variation within the batch of the specimens. The dimensional stability assessment in terms of thermal expansion and the short-term stability in terms of thermal conductivity are also presented.

The selection of a material for making the hot and cold plates of high-temperature guarded hot plates (HTGHPs) working up to \(800\,{^\circ }\hbox {C}\) is still an issue. The material must be machinable, have a high mechanical stability to keep the high level of flatness of the plates and have a high thermal conductivity and a high resistance to oxidation when used in air. Nickel 201 alloy has been used in several instruments, but has shown, sometimes, problems of mechanical stability. The total hemispherical emissivity of the plates must be higher than 0.8 as recommended by the standards. Three ceramic materials, a silicon infiltrated silicon carbide (SiSiC), a machinable aluminum nitride and a sintered aluminum nitride (AlN) with high thermal conductivity claimed at ambient temperature, were selected for tests in thermal conductivity and opacity to thermal radiation. Three paints withstanding high temperatures were tested in total hemispherical emissivity and durability at high temperature. Above \(600\,{^\circ }\hbox {C}\), Nickel 201 alloy has a higher thermal conductivity than the three ceramics. Below \(600\, \,{^\circ }\hbox {C}\), the SiSiC and the sintered AlN have a thermal conductivity significantly higher than Nickel 201, but the sintered AlN shows a wide transparency spectral band at short wavelengths (below \(6.5\,\upmu \hbox {m}\)). Above \(300\,{^\circ }\hbox {C}\), the three paints have a total hemispherical emissivity above 0.8. One of the paints has polluted the specimens of an insulation material tested in thermal conductivity up to \(650\,{^\circ }\hbox {C}\). The other two can be recommended to coat the hot and cold plates of HTGHPs used up to \(800\,{^\circ }\hbox {C}\).

A new advanced technique was developed at the Hungarian Metrological Institute (MKEH), devoted to optimizing the realization of the International Temperature Scale ITS-90. The work was performed within the framework of the European project “Novel techniques for traceable temperature dissemination.” The paper is devoted to describing this new measurement technique and its setup. The time evolution of the solid fraction and melt fraction along the phase transformation has been followed, using a technique based on the difference of the electrical conductivity between the solid and liquid phases of the metal. The measurement technique provides electrical signals, which are suitable for improving the quality of the freezing plateaus realized in the case of different fixed-point realizations, covering the temperature range from \(-39\,^{\circ }\mathrm{C}\) to \(962\,^{\circ }\mathrm{C}\). The ideal section of the freezing plateau can be maintained by ensuring a continuous flow of mass and energy of the fixed-point substance in the axial direction. The intervention is achieved by modifying the temperatures of the different zones of the furnace controller with more degrees, with the aid of developed intervening devices. Recent developments permit the selection of the ideal section of a freezing plateau and, what is more, the increase of this plateau section to practically unlimited for all metal fixed points.

European national metrology institutes use calibration systems of various types for calibrating thermometers in air. These were compared to each other for the first time in a project organized by the European Association of National Metrology Institutes (EURAMET). This EURAMET P1061 comparison project had two main objectives: (1) to study the equivalence of calibrations performed by different laboratories and (2) to investigate correlations between calibration methods and achievable uncertainties. The comparison was realized using a pair of 100 \(\Omega \) platinum resistance thermometer probes connected to a digital thermometer bridge as the transfer standard. The probes had different dimensions and surface properties. The measurements covered the temperature range between \(-40\,^{\circ }\mathrm{{C}}\) and \(+150\,^{\circ }\mathrm{{C}}\), but each laboratory chose a subrange most relevant to its scope and performed measurements at five nominal temperature points covering the subrange. To enable comparison between the laboratories, comparison reference functions were determined using weighted least-squares fitting. Various effects related to variations in heat transfer conditions were demonstrated but clear correlations to specific characteristics of calibration system were not identified. Calibrations in air and liquid agreed typically within \(\pm 0.05\,^{\circ }\mathrm{{C}}\) at \(+10\,^{\circ }\mathrm{{C}}\) and \(+80\,^{\circ }\mathrm{{C}}\). Expanded uncertainties determined by the participants ranged from \(0.02\,^{\circ }\mathrm{{C}}\) to \(0.4\,^{\circ }\mathrm{{C}}\) and they were shown to be realistic in most cases.

In the framework of the European Metrology Research Program, NOTED is a multi-institute project focused on the development of new advanced techniques for providing improved traceability to the kelvin to support its wider and simpler dissemination to science, industry and, in general, every user of temperature measurements. The main objectives of the project are to develop simpler and cheaper primary thermometers, new robust high performance sensors, optimisation of calibration procedures and reduced uncertainties in temperature measurement. This paper gives an overview of the project and the different activities that are being developed.

The first intercomparison on the density of heat flow-rate measurements has been organized by MKEH (Hungarian Trade Licensing Office, Metrology Division) within the framework of EUROMET (Project No. 426). This round-robin test gives evidence about the measurement capabilities of the local realizations of a density of a heat flow-rate scale up to 100 W · m−2. Two types of heat flux plate sensors differing in their size were circulated among partner laboratories. Each one of the six partners calibrated the sensors using its own calibration system, a guarded hot plate or a heat flow meter apparatus. This article compares all the results of the round-robin test and gives the mutual differences among the partners. The participants could benefit from the measurement results by improving, in case of need, their calibration methods and procedures and by reducing their uncertainties. The impact of this comparison will go directly to the users in industry.

The results of a EURAMET key comparison of water triple-point cells (EURAMET.T-K7) are reported. The equipment used, the measuring conditions applied, and the procedures adopted for the water triple-point measurement at the participating laboratories are synthetically presented. The definitions of the national reference for the water triple-point temperature adopted by each laboratory are disclosed. The multiplicity of degrees of equivalence arising for the linking laboratories with respect to the “mother” comparison CCT-K7 is discussed in detail.

The comparison EUROMET.T-K4 is the regional extension of CCT-K4: an intercomparison of the realisations of the freezing points of Al (660.323 degrees C) and Ag (961.78 degrees C). The intercomparison was organized in four loops with long stem standard platinum resistance thermometers (SPRTs) as travelling standards: One 25 Omega thermometer to be used only at the Al freezing point and two high temperature SPRTs to be used only at the Ag freezing point in each loop. Parallel to the measurements with thermometers the pilot and sub-pilots organized an internal intercomparison using an Ag fixed point cell.Most HTSPRTs showed a strong drift which is mainly due to mechanical stress and poisoning of the sensor by impurities. This drift can partly be compensated by a correction applying Matthiessen's rule. An evaluation of the data taking into account both HTSPRTs in each loop, the linkage of the sub-pilots by measurements at the Ag freezing point and a possible compensation according to Matthiessens's rule allows to calculate the results of the participants also for the measurements at the Ag freezing point. European reference values (ERV) were calculated for measurements at the Al and Ag freezing points. The difference between these ERVs and the corresponding KCRVs of CCT-K4 is also given, which allows the linking of the different comparisons.

The EUROMET.T-K3 comparison is the regional extension of CCT-K3. The comparison involved the six European national metrology institutes (NMIs) previously involved in CCT-K3 (LNE-INM/CNAM, SMU, INRiM, NMi-VSL, NPL, PTB) and 18 additional European national laboratories. The comparison was divided into five different loops, each coordinated by a co-pilot chosen from the laboratories having participated in the CCT-K3 comparison. LNE-INM/CNAM played the role of pilot in linking the five loops. In each loop, an artifact in the form of a standard platinum resistance thermometer (SPRT, 25 Ω) was circulated among the participating laboratories. To have sufficient information about the possible drift of the SPRTs, the co-pilots performed a calibration over the full temperature range at the beginning and at the end of the loop. A EUROMET reference value (ERV), taking into account the whole comparison, was defined, and the differences (T Lab − T ERV) were calculated with the associated uncertainties. The method for establishing the link between the participants in CCT-K3 and in EUROMET.T-K3 is described.

The EUROMET.T-K4 comparison is the regional extension of CCT-K4, an intercomparison of the realizations of the freezing points of Al (660.323°C) and Ag (961.78°C). The intercomparison was organized in four loops. Long-stem standard platinum resistance thermometers (SPRTs) were used as traveling standards: 25 Ω thermometers to be used only at the Al freezing point and two high-temperature standard platinum resistance thermometers (HTSPRTs) to be used only at the Ag freezing point in each loop. Parallel to the measurements with thermometers, the pilots and sub-pilots organized an internal intercomparison using an Ag fixed-point cell. Most HTSPRTs showed a strong drift which is mainly due to mechanical stress and poisoning of the sensor by impurities. This drift can be partially compensated by a correction based on Matthiessen’s rule. An evaluation of the data taking into account both HTSPRTs in each loop, the linkage of the sub-pilots by measurements at the Ag freezing point, and a possible compensation according to Matthiessens’s rule, allows calculation of the results of the participants’ measurements at the Ag freezing point. The results of the participating laboratories are summarized, and proposals for key comparison reference values and linking of the results to CCT-K3 and CCT-K4 are presented.