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).

This paper describes the collaborative project between National Research Council of Canada (NRC) and Centro Español de Metrología (CEM) for the construction and comparison of high temperature fixed points (HTFPs). A hybrid-type crucible that uses the piston method for filling has been jointly developed. A series of 12 high temperature fixed point blackbodies (HTFPBBs) have been constructed, including Cu, Ru-C, Ir-C, Re-C and WC-C covering the temperature range from 1084°C to 2750°C. All these cells were filled in NRC facilities by CEM and NRC staff. Two cells of each type of fixed point were constructed (except for the WC-C cells), using crucibles from two different suppliers in order to study the influence of the density and emissivity of the crucible in the HTFPs’ performance. Moreover, four WC-C cells were made using tungsten powder from two different suppliers, covering all the possible combinations of tungsten powder and crucibles acquired for this project. All cells, and additionally a Pt-C HTFPBB belonging to NRC, have been measured firstly at NRC and, afterwards, at CEM. Both laboratories have calculated the ITS-90 temperatures from their respective measurements and the results have been compared. Differences on the ITS-90 temperatures of the HTFPBBs measured at each lab are within uncertainties of the comparison. After the comparison, CEM kept one Cu cell, one Ru-C cell, one Re-C cell and two WC-C cells. The rest of the fixed points involved in the comparison were sent back to NRC.

Silicon photonic thermometers are candidates for next generation secondary and working thermometry standards. We report on recent progress at NRC on Si ring resonator thermometers. The thermometer module uses non-contact stress free assembly, and free space optical coupling to the ring from a multi-fiber block. A temperature measurement reproducibility of better than ±5 mK over hundreds of hours has been achieved by using improved ring design, SiO2 cladding materials, and low optical power to avoid self-heating. These results represent an order of magnitude improvement over previous work.

In July 2016 the Consultative Committee for Thermometry’s Non-Contact Thermometry Working Group formed a task group to compile a complete list of uncertainties for high-temperature fixed points, categorize them as well specified or not, and recommend areas of future research. We describe herein two paths to realizing T by indirect primary radiometry using high-temperature fixed-point blackbody cells: one in which published values for the metal–carbon eutectic material transition temperatures are used and the other where a set of cells has their transition temperatures determined directly. The uncertainty components that need to be considered for each path are given together with typically achievable values and how well those values are known. This work concentrates on Co–C, Pt–C and Re–C.

Uncooled thermal imaging sensors in the LWIR (7.5 μm to 14 μm) have recently been developed for use with small RPAS. This study derives a new thermal imaging validation methodology via the use of a blackbody source (indoors) and real-world field conditions (outdoors). We have demonstrated this method with three popular LWIR cameras by DJI (Zenmuse XT-R, Zenmuse XT2 and, the M2EA) operated by three different popular DJI RPAS platforms (Matrice 600 Pro, M300 RTK and, the Mavic 2 Enterprise Advanced). Results from the blackbody work show that each camera has a highly linearized response (R2 > 0.99) in the temperature range 5–40 °C as well as a small (<2 °C) temperature bias that is less than the stated accuracy of the cameras. Field validation was accomplished by imaging vegetation and concrete targets (outdoors and at night), that were instrumented with surface temperature sensors. Environmental parameters (air temperature, humidity, pressure and, wind and gusting) were measured for several hours prior to imaging data collection and found to either not be a factor, or were constant, during the ~30 min data collection period. In-field results from imagery at five heights between 10 m and 50 m show absolute temperature retrievals of the concrete and two vegetation sites were within the specifications of the cameras. The methodology has been developed with consideration of active RPAS operational requirements.

Fiber Bragg gratings (FBG) are extensively used to perform high-temperature measurements in harsh environments, however the drift of the characteristic Bragg wavelength affects their long-term stability resulting in an erroneous temperature measurement. Herein we report the most precise and accurate measurements of wavelength drifts available up to date on high-temperature FBGs. The measurements were performed with a set of packaged π-phase-shifted FBGs for high wavelength resolution, in caesium and sodium pressure-controlled heat pipes for stable temperature environment and with a tunable laser for stable wavelength measurements with a 0.1 pm resolution. Using this dataset we outline the experimental caveats that can lead to inconsistent results and confusion in measuring wavelength drifts, namely: influence of packaging; interchangeability of FBGs produced under identical conditions; birefringence of π-phase-shifted FBGs; initial transient behaviour of FBGs at constant temperature and dependence on the previous thermal history of FBGs. In addition, we observe that the wavelength stability of π-phase-shifted gratings at lower temperature is significantly improved upon by annealing at higher temperature. The lowest value of the wavelength drift we obtain is +0.014 pm·h−1 at 600 °C (corresponding to +0.001 °C·h−1) after annealing for 400 h at 1000 °C, the longest annealing time we have tried. The annealing time required to achieve the small drift rate is FBG-specific.

Temperature measurement plays a primary role in numerous aspects of the world we live in, such as in industrial process control, scientific investigations, and sustainability of our living environment. TEMPMEKO provides a meeting place for the exchange of information and views in the field of temperature and thermal measurements among the members of the international scientific community, professional metrologists, manufacturers of measurement equipment, and engineers and students working in this field. TEMPMEKO & TEMPBEJING 2019 and MMC 2019 was held from June 10 to 14, 2019 in Chengdu, China. This was the first meeting in this field after the redefinition of the SI base unit kelvin that took place in May 2019, and therefore presentations were made on the various technological achievements that contributed to this redefinition, and served to address the new challenges in view of the future opportunities afforded by the change. This special section of Measurement Science and Technology includes 16 selected papers from TEMPMEKO TEMPBEJING 2019 and MMC 2019, highlighting temperature measurement science and technology, humidity and moisture, applications of thermometry, and thermometric traceability and in sensors and measurement systems are found in this special section. In an attempt to develop a primary

Slow dissolution of the borosilicate container of triple-point-of-water (TPW) cell is widely recognized as the main cause of long-term drift in observed triple point temperature. We add to the available experimental data a comparison of two large batches of TPW cells (67 cells in total) of various ages (from 1 year to 64 years), manufacturers (NRC, VSL, Fluke, Isotech, etc), and materials (borosilicate glass and fused-silica) which was undertaken in 2018. After measuring the TPW temperatures realized by all 67 cells, 12 borosilicate cells were opened and their water was analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in order to correlate their impurity content with their respective age and their realized TPW temperature. No direct correlation was observed between the TPW cells age/impurity content and their measured triple-point temperature for neither borosilicate cells nor fused silica cells (Pearson's correlation coefficient r(xy) is within the range -0.60 <= r(xy)<= +0.40 for all the pairs considered). For fused-silica cells, the results indicate that after the isotopic variation in the water source is taken into account, the long-term drift due to the dissolution of glass envelope, if any, is negligibly small: (+0.4(+/- 0.6) mu K center dot yr(-1) reported herein). Given that all the fused-silica cells realize the TPW temperature within 100 mu K of NRC and VSL national reference cells and since the analyzed time period of 15 years is equal to the average lifespan of a TPW cell, we conclude that fused-silica TPW cells are superior to those made from borosilicate glass.

In recent years photonic thermometers—temperature sensors based on optical frequency measurement which exploit the thermo-optic effect to translate thermal changes into frequency shifts—are gaining popularity as a possible alternative to their electrical counterparts: platinum resistance thermometers and thermocouples. In this work, we report our results of testing photonic thermometers based on silica fiber-Bragg-grating technology supplied by a commercial company, as well as preliminary testing results of a silicon ring-resonator thermometer developed at the National Research Council of Canada. The main purpose of showing these two examples is to highlight some of the challenges that need to be addressed if photonic thermometers are to replace thermocouples or platinum resistance thermometers in metrology laboratories and other environments where high accuracy and stability are required, namely the influence of packaging on the sensor’s performance and the need for rigorous testing to be done in a temperature metrology lab.

Spectral pattern recognition is used to measure temperature and generate calibrated wavelength/frequency combs using a single silicon waveguide ring resonator. The ring generates two incommensurate interleaving TE and TM spectral combs that shift independently with temperature to create a spectral pattern that is unique at every temperature. Following an initial calibration, the ring temperature can be determined by recognizing the spectral resonance pattern, and as a consequence, the wavelength of every resonance is also known. Two methods of pattern-based temperature retrieval are presented. In the first method, the ring is locked to a previously determined temperature set-point defined by the coincidence of only two specific TE and TM cavity modes. Based on a prior calibration at the set-point, the ring temperature and hence all resonance wavelengths are then known and the resulting comb can be used as a wavelength calibration reference. In this configuration, all reference comb wavelengths have been reproduced within a 5 pm accuracy across an 80 nm range by using an on-chip micro-heater to tune the ring. For more general photonic thermometry, a spectral correlation algorithm is developed to recognize a resonance pattern across a 30 nm wide spectral window and thereby determine ring temperature continuously to 50 mK accuracy. The correlation method is extended to simultaneously determine temperature and to identify and correct for wavelength calibration errors in the interrogating light source. The temperature and comb wavelength accuracy is limited primarily by the linewidth of the ring resonances, with accuracy and resolution scaling with the ring quality factor.

We present the design and experimental results for a silicon photonic thermometer module for secondary and working thermometry standards. The chip is mechanically robust and insensitive to contamination. Using surface coupling gratings the chip temperature can be monitored remotely using free space beams, thereby eliminating temperature hysteresis effects arising from conventional optical assembly methods and materials.

The National Research Council (NRC) of Canada has established a next generation facility for the primary realization of optical radiant power. The main feature of this facility is a new cryogenic electrical substitution radiometer with a closed-cycle helium cryocooler. A monochromator-based approach allows for detector calibrations at any desired wavelength. A custom-designed motion apparatus includes two transfer standard radiometer mounting ports which has increased our measurement capability by allowing the calibration of two photodetectors in one measurement cycle. Measurement uncertainties have been improved through several upgrades, including newly designed and constructed transimpedance amplifiers for the transfer standard radiometers, and a higher power broadband light source. The most significant improvements in uncertainty arise from the enhanced characteristics of the new cryogenic radiometer including its higher cavity absorptance and reduced non-equivalence effects.

The properties of six large area semiconductor photodetectors were investigated in the near infrared wavelength range. For potential use as transfer standard detectors in absolute spectral responsivity calibrations, the spatial uniformity and spectral responsivity of four InGaAs and two Ge photodiodes were characterized. Spatial uniformity measurements carried out at 1000 nm, 1550 nm, and 1650 nm show that photodiode spatial non-uniformity changes with wavelength for both InGaAs and Ge detectors. The photodiode characterization apparatus, results, and analysis are presented.

Two Au fixed points filled using metal of different nominal purities in carbon crucibles have been developed at the National Research Council Canada (NRC). The primary motivation behind this project was to provide the means for direct thermocouple calibrations at the Au freezing point (\(1064.18~^\circ \hbox {C}\)). Using a Au fixed point filled with the metal of maximum available purity [99.9997 % pure according to glow discharge mass spectroscopy (GDMS)], multiple freezing plateaus were measured in a commercial high-temperature furnace. Four Pt/Pd thermocouples constructed and calibrated in-house were used to measure the freezing plateaus. From the calibration at Sn, Zn, Al and Ag fixed points, the linear deviation function from the NIST-IMGC reference function (IEC 62460:2008 Standard) was determined and extrapolated to the freezing temperature of Au. For all the Pt/Pd thermocouples used in this study, the measured EMF values agree with the extrapolated values within expanded uncertainty, thus substantiating the use of 99.9997 % pure Au fixed point cell for thermocouple calibrations at NRC. Using the Au fixed point filled with metal of lower purity (99.99 % pure according to GDMS), the effect of impurities on the Au freezing temperature measured with Pt/Pd thermocouple was further investigated.

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).

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.

A multi-partner project to determine the thermodynamic temperatures of a selected set of high-temperature fixed points based on metal-carbon eutectics is underway as a working group activity within the Comité International des Poids et Mesures. The investigation focuses on four fixed-point types, namely, the three metal-carbon eutectic points of Re-C \((2474\,^{\circ }\hbox {C})\), Pt-C \((1738\,^{\circ }\hbox {C})\), and Co-C \((1324\,^{\circ }\hbox {C})\), and the Cu point \((1084.62\,^{\circ }\hbox {C})\). This paper describes the construction, pre-evaluation, and screening stage of the cells prior to their thermodynamic temperature determinations. The construction of the HTFP cells was undertaken by nine national metrology institutes (NMIs) according to instructions laid out in a pre-agreed protocol that ensures production of best quality cells. Four NMIs conducted the evaluation, each for a certain fixed-point type, and screened out cells that did not meet pre-determined selection criteria while assuring sufficient variety in the sources of the cells in the final selected sets. In autumn 2012, the selected cells were successfully passed on to the final stage of the project, the thermodynamic temperature measurement, and assignment.

A robust fixed point using pure nickel contained in an alumina crucible has been developed for thermocouple calibrations. It was observed that a deep supercool often caused the freezing plateau to be short and have a large slope. A procedure for realizing the pure nickel fixed points was developed that reserved a small amount of nickel in the solid state to act as a seed for nucleation of the freeze. This procedure was found to allow freezing plateaus that were suitably long and flat to make them useful for calibrating thermocouples. Using a calibrated Pt/Pd thermocouple, the freezing temperature of nickel was determined to be \(1455.22\,^{\circ }\hbox {C}\) with a \((k = 2)\) uncertainty of \(0.8\,^{\circ }\hbox {C}\).