Fixed-point Blackbody Research Articles

The experiment on the ISS with low-temperature fixed points – a stage in developing high-stable on-board fixed-point blackbodies for in-flight calibrating the Earth observation IR instruments

The experiment on the ISS with low-temperature fixed points – a stage in developing high-stable on-board fixed-point blackbodies for in-flight calibrating the Earth observation IR instruments

Direct observation of plateau progression in fixed-point blackbodies via X-ray imaging

In this study, we address the challenge of calibrating radiation thermometers using blackbody furnaces that employ a metal melting/freezing plateau. Here, we first present the observation results utilizing X-rays, enabling us to monitor the entire temperature cycle, from heating to cooling, during the calibration process. Through this approach, we directly observe the emergence of voids within deteriorating metal cells, which may give insights into the underlying mechanisms occurring within enclosed graphite cells.

Gallium Fixed-point Blackbody Radiation Source for Calibration of Sea Surface Temperature Radiometer

Gallium Fixed-point Blackbody Radiation Source for Calibration of Sea Surface Temperature Radiometer

Final report for CCT comparison of ITS-90 realisations above the silver point using two transfer radiation thermometers and a set of high temperature fixed-point blackbody cells

Main textThis 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).

A novel radiometric calibration of an infrared thermometer

A new temperature calibration scheme was proposed and implemented on the National Physical Laboratory infrared radiometer Absolute Measurements of Blackbody Emitted Radiance (AMBER) operating in the wavelength range from 9 µm to 11 µm and equipped with a cryogenically cooled mercury cadmium telluride detector. The scheme involves measurements of the relative spectral responsivity of the filter radiometer including the spectral transmittance of the window and lens. It requires calibration at two reference temperatures, but does not involve measurement of the zero-radiance signal. The scheme uses a Ga-point blackbody as one reference point, and a variable temperature blackbody source at close to −30 °C with its temperature measured with a standard platinum resistance thermometer as the other. The measured temperature was compared using the variable temperature blackbody as the source against the temperature measured by the standard platinum resistance thermometer and agreement within the uncertainties was confirmed at intermediate temperatures. The scheme has the advantage that it makes full use of the small uncertainty realised by the fixed-point blackbody. The scheme was successfully implemented in an international comparison of sea surface temperature measuring radiometers where AMBER served to provide the reference.

Thermodynamic temperature measurements of Al–Cu, Al, Ag, Cu and Co–C fixed points by radiometry hybrid method

The radiometry hybrid method, by introducing a lens to the irradiance method with a 900 nm filter radiometer, was adopted to measure the thermodynamic temperature of the aluminum-copper (Al–Cu) eutectic point, aluminum (Al) freezing point, silver (Ag) freezing point, copper (Cu) freezing point and cobalt carbon (Co–C) eutectic point at the National Institute of Metrology, China. By scanning the uniformity of fixed-point blackbodies, the effective diameters were accurately estimated according to the size of the source effect (SSE). The lens transmittance measurement with the closest diameter aperture was adjusted to reduce the uncertainty of SSE. The discrepancy between the thermodynamic temperature and ITS-90 values (T-T 90) of Al–Cu, Al, Ag, Cu and Co–C fixed point blackbodies were concluded as 0.022 °C, 0.014 °C, 0.097 °C, 0.137 °C and 0.317 °C, respectively. The standard uncertainty of the fixed point thermodynamic temperature was estimated to be (0.1 to 0.3) °C (k = 2).

A triple point of water cell-based fixed-point blackbody for radiation thermometry

The radiation temperature metrology above 150 °C relies heavily on the use of physical interpolation equations and known reference temperature (provided by solid–liquid phase transition of high-purity metals and metal-carbon eutectic alloys) fixed-point blackbodies. Recent achievements in thermal infrared detector technologies triggered the extension of the scale interpolation below this temperature down to 0 °C by using the reference temperatures provided by Sn, In, Ga fixed-points and ice-point, where the reference temperature of the later is dependent on external parameters. In this work, we demonstrate that the triple-point of water (TPW) based fixed-point blackbody is the metrologically grounded alternative to the ice-point. For this purpose, a fixed-point blackbody, incorporating only a cavity and large area TPW (LATPW) cell was designed, constructed, and validated for the precise calibration of radiation thermometers (RTs) and thermal cameras at the thermodynamic temperature of TPW. The conceptual design of the LATPW cells is similar to the ones used in contact thermometry, where a thermometer well of the cell is employed as a borehole for a cavity, where the cavity is easily detachable. Four different cavities (two different designs with aperture sizes of 40 mm and 50 mm) and three LATPW cells with two distinct well geometries were comparatively studied in several combinations. The largest absolute temperature difference observed between the primary level reference TPW cell (used in contact thermometry) and the LATPW cells is measured to be only 0.37 mK. Radiometric measurements demonstrate that all radiators maximally reflect the blackbody condition including emissivity close to unity, high uniformity across the aperture and high temporal stability. The simplicity of maintenance and easy in-field usage (only distilled water and dry ice are required) make the TPW blackbodies very versatile for the in-situ calibrations of RTs and thermal cameras, allowing its application in many areas including clinical environments.

Spectral irradiance scale realization and uncertainty analysis based on a 14 mm diameter WC–C fixed point blackbody from 250 nm to 2500 nm

Spectral irradiance scale in the wavelength range from 250 nm to 2500 nm was realized at National Institute of Metrology on the basis of a large area tungsten carbide–carbon (WC–C) high temperature fixed point blackbody, which is composed of a 14 mm diameter WC–C fixed point cell and a variable temperature blackbody BB3500MP as a furnace. A series of 1000 W FEL tungsten halogen lamps were used as transfer standards. The new spectral irradiance scale was compared with the scale based on a variable-temperature blackbody BB3500M, and the divergence between these two methods varied from −0.66% to 0.79% from 280 nm to 2100 nm. The measurement uncertainty of spectral irradiance scale based on fixed-point blackbody was analyzed, and the expanded uncertainty was estimated as 3.9% at 250 nm, 1.4% at 280 nm, 0.43% at 400 nm, 0.27% at 800 nm, 0.25% at 1000 nm, 0.62% at 1500 nm, 0.76% at 2000 nm, and 2.4% at 2500 nm respectively. In the range from 300 nm to 1000 nm the fixed-point scale was improved obviously: the uncertainty decreased by more than 25% compared to the uncertainty based on the variable temperature blackbody. Below 300 nm, the uncertainty became higher because the signal to noise ratio was poor. Above 1100 nm, the contribution of temperature measurement to the uncertainty of spectral irradiance decreases, therefore the uncertainties of two methods are almost at the same level. The fixed-point blackbody was also used to realize the correlated colour temperature and distribution temperature of a tungsten filament lamp, the deviation from the variable temperature blackbody method was −0.5 K and −2.9 K, respectively.

On the uncertainties in the realization of the kelvin based on thermodynamic temperatures of high-temperature fixed-point cells

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.

Approximation of a melting plateau of large area HTFP cells used for spectral irradiance realization.

This paper adopted an approximation of a melting plateau to solve the problem that temperature data cannot be monitored continuously when measuring the spectral irradiance of a large area tungsten carbide-carbon high-temperature fixed-point blackbody at each measured wavelength. Tests with fully measured curves showed that the method has a rather small deviation from the measured data of 0.017 K maximum, which corresponds to the spectral irradiance deviation of 0.005% at 500 nm. The maximum relative deviation between the Akima fitting method and the measured temperature in terms of spectral irradiance was 0.002%, which was better than -0.067% of a single temperature of 3020.11 K method and 0.026% of a linear interpolation method.

New fixed point of on-orbit calibration scale based on the In-Bi eutectic alloy for application in novel high-stable space-borne standard sources

The problem of ensuring stability of Earth observation space-borne instruments undertaking long-term temperature measurements within thermal IR spectral range is described. For in-flight reliable control of the space-borne IR instruments characteristics the stability of onboard reference sources should be improved. The function of these high-stable sources will be executed by novel onboard blackbodies, incorporating the melt↔freeze phase transition phenomenon, currently being developed. As a part of these works the task of realizing an on-orbit calibration scale within the dynamic temperature range of Earth observation systems 210−350 K based on fixed-point phase transition temperatures of a number of potentially suitable substances is advanced. The corresponding series of the onboard reference blackbodies will be set up on the basis of the on-orbit calibration scale fixed points. It is shown that the achievement of the target lies in carrying out a number of in-flight experiments with the selected fixed points and the prospective onboard fixed-point blackbodies prototypes. The new In-Bi eutectic alloy melt temperature fixed point (~345 K) is proposed as the significant fixed points of the future on-orbit calibration scale. The results of the new fixed point preliminary laboratory studies have been analyzed. The results allowed to start preparation of the in-flight experiments investigating the In-Bi alloy for the purpose of its application in the novel onboard reference sources.

A selective multiple fit method of the point of inflection for the large-area HTFP melting plateau curve

National Institute of Metrology (NIM) has set up a new large-area tungsten carbide–carbon (WC-C) high-temperature fixed-point (HTFP) blackbody system as the direct radiation source for measuring spectral irradiance. The point of inflection (POI) of the HTFP melting plateau curve was important to determine the liquidus point and applied as the reference point in temperature calibration. This paper presented a selective multiple fit method. The maximum discrepancy of different factors for the new method and traditional methods were 0.001 K and 0.633 K which led to 0.0003% and 0.20% spectral irradiance errors at 500 nm. In addition, when used to calculate POIs of WC-C and Re-C small-area HTFPs, the maximum deviation between the new method and the average value of traditional methods were −0.004 K and −0.03 K. This method was verified to be insensitive to the influencing factors and more effective for large-area HTFPs applications.

Research on the Temperature Transfer Relationship Between Miniature Fixed-Point and Blackbody for On-Orbit Infrared Remote Sensor Calibration

Miniature fixed-point blackbody (MFPB) can realize the on-orbit calibration of temperatures by tracing the miniature fixed-point. This ability can effectively improve the precision and life span of earth observation systems. Researchers have verified the feasibility of the MFPB in engineering through experiments. However, the temperature relationship between the miniature fixed-point and the blackbody is unclear at present, which means that the transfer relationship between radiation temperature of space infrared radiation standard source and international temperature scale cannot be established accurately. In this article, a temperature transfer relationship between miniature fixed-point and blackbody in MFPB is established, and the temperature transfer equation (TTE) is proposed to obtain the run-off point temperature of blackbody (RPTB). The effects of heating power and ambient temperature on the temperature transfer relationship between miniature fixed-point and blackbody are investigated numerically. Retrieval results show that a linear relationship exists between the RPTB and the heating power and ambient temperature in a single fixed-point temperature range. The TTE is obtained and explained theoretically. All experimental results of the gallium fixed-point are in good agreement with this equation. Furthermore, the RPTBs are accurately predicted at gallium-stannum and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O fixed-points by TTE. The average and maximum errors are 0.0044 and 0.0063 K, respectively. The current study is of considerable importance to the development of MFPB technology and improvement of the on-orbit infrared remote sensor calibration.

Accurate numerical model for characteristic temperature acquisition of miniature fixed-point blackbodies

Miniature fixed-point blackbodies (MFPBs) can realize the on-orbit multipoint temperature calibration through the known characteristic temperature. This ability is important for improving the precision and life span of earth observation systems. For acquisition of characteristic temperature, numerical simulation has lower cost and test condition requirements. However, ordinary numerical models can’t meet the accuracy requirements of MFPB. The purpose of this paper is established an accurate numerical model for characteristic temperature acquisition of miniature fixed-point blackbodies. A novel thermal resistance equivalent corrected method (TRECM) is proposed in accordance with the difference between the numerical model and actual experiment. The equivalent correction of the total thermal resistance between two temperature points is achieved by correcting a certain term of thermal resistance in the heat flow transfer path. The TRECM can effectively replace the detailed structure, complex surface radiation and unknown parameters. Characteristic temperatures of blackbody are obtained during Ga, Ga-In, and H2O phase transitions at different heating powers by using proposed model. Meanwhile, an experimental system is established to validate the model. The results showed that the average model error of characteristic temperature between the calculated results and the experimental results decreased from 77.2 m K to 6.2 m K by the TRECM.

A method for spectral irradiance measurement based on a large area WC-C fixed point blackbody.

We have proposed a novel method for the spectral irradiance measurement of the standard lamp. The measurement has been realized by using national primary scale based on a large area WC-C fixed point blackbody for the first time. The wavelength range is from 450 nm to 1000 nm. The spectral irradiance of the standard lamp has been measured based on the traditional variable temperature blackbody and large area WC-C fixed point blackbody. The results of the two methods agree within the uncertainties. Compared with the traditional measurement method, the fixed point method can reduce the major component of the spectral irradiance measurement uncertainty related to the temperature measurement.

Development and Realization of Fe–C and Co–C Eutectic Fixed-Point Blackbodies for Radiation Thermometry at CSIR-NPL

A series of metal–carbon (M–C) eutectics with robust reproducible melting phase transitions are evolving as the reference high-temperature fixed-points up to 3000 °C for radiation thermometry. The mise-en-pratique prepared for the realization and dissemination of new kelvin allows the use of set of M-C blackbody fixed-points or a combination of M-C fixed-points along with silver (Ag), gold (Au) or copper (Cu) blackbodies for the direct measurement of thermodynamic temperatures at high-temperature range. The iron–carbon (Fe–C) [1153 °C] and cobalt–carbon (Co–C) [1324 °C] fixed-point cells are the doorway to high temperature above a copper fixed-point. This paper describes the in-house development of Fe–C and Co–C eutectic graphite crucible blackbodies and their realizations by linear spectral pyrometer (LP4, 650 nm) at CSIR-NPL, National Metrology Institute (NMI) of India. The novel design and assembly approaches were employed to fabricate the blackbody crucibles with 120o inner-well cone, 100 mm ingot length and 8 mm aperture diameter with 0.9997 emissivity and robust thermo-mechanical stability. The eutectic ingots were prepared by multiple fillings of the homogeneously ground and mixed powders with 4.2 and 2.6 weight percentage of carbon in Fe and Co, respectively. Repeatability of measured melting plateau and uncertainty of the temperature measurement for both Fe–C and Co–C cells are presented. The ITS-90 temperatures (T90) to these M-C fixed-points were assigned by a spectral radiance ratio measurement (Planck’s Law) relative to the freezing point of Ag [961.78 °C]. The T90 temperatures thus determined for Fe–C and Co–C blackbody fixed-point cells are 1154.05 °C and 1323.93 °C with the expanded uncertainty of 0.37 °C and 0.50 °C, respectively.

真空低背景红外高光谱亮温计量标准装置研制

The Vacuum Infrared Hyperspectral Radiance Temperature Standard Facility for Infrared Hyperspectral radiance calibration was established at National Institute of Metrology for calibrating the radiance temperature of infrared remote sensing payloads. The state-of-the art of the system was introduced, such as, the structure, the new designed standard blackbody, the calibration method and the traceability. The vacuum reduced background chamber was built for the customer blackbodies. The standard blackbodies, including the variable temperature blackbodies and the fixed-point blackbodies, were designed. The radiance temperature of the customer blackbodies were calibrated by the standard blackbodies through a Fourier transform infrared spectrometer. The temperature range of the new designed standard blackbody was from 125 K to 500 K with a 30 mm in diameter and 0.999 7 emissivity of the cavity. The radiance temperature standard uncertainty of the blackbody was better than 0.026 K@300 K/10 m. The fixed point blackbodies included a mercury blackbody, a gallium blackbody and an Indium blackbody. The cavities diameter were all 25 mm, and the uncertainty of the fixed blackbodies was better than 0.020 K@300 K. The system could support the requirements of lots of infrared remote sensing payloads. This facility can provide the radiance temperature tracebility for most infrared remote sounders with low uncertanty, high sprectral resolution and strong extensibility.

Development of large-area high-temperature fixed-point blackbodies for photometry and radiometry

Large-area high-temperature fixed-point (HTFP) blackbodies with working temperatures of approximately 2748 K and 3021 K, based on an Re–C eutectic and a WC–C peritectic respectively, have been developed and investigated. The blackbodies have an emissivity of 0.9997, show high-quality phase-transition plateaus and have high repeatability of the melting temperatures, but demonstrate temperature differences (from 0.2 K to 0.6 K) compared with small-cell blackbodies of the same HTFP. We associate these temperature differences with the temperature drop effect, which may differ from cell to cell. The large radiating cavity diameter of 14 mm allows developed HTFP blackbodies to be used for photometric and radiometric applications in irradiance mode with uncertainties as small as 0.12% (k = 1) in the visible. A photometer and an irradiance-mode filter radiometer (visible range), previously calibrated at VNIIOFI, were used to measure illuminance and irradiance of the HTFP blackbodies equipped with a precise outer aperture. The values measured by the detectors agreed with those based on the blackbody calculation to within 0.2%. The large-area HTFP blackbodies will be used in a joint PTB–VNIIOFI experiment on measuring thermodynamic temperature.

Comparative Study of Two InGaAs-Based Reference Radiation Thermometers

More than one decade ago, an InGaAs detector-based transfer standard infrared radiation thermometer working in the temperature range from \(150\,{^{\circ }}\hbox {C}\) to \(1100\,{^{\circ }}\hbox {C}\) was built at TUBITAK UME in the scope of collaboration with IMGC (INRIM since 2006). During this timescale, the radiation thermometer was used for the dissemination of the radiation temperature scale below the silver fixed-point temperature. Recently, a new radiation thermometer with the same design but with different spectral responsivity was constructed and employed in the laboratory. In this work, we present the comparative study of these thermometers. Furthermore, the paper describes the measurement results of the thermometer’s main characteristics such as the size-of-source effect, spectral responsivity, gain ratio, and linearity. Besides, both thermometers were calibrated at the freezing temperatures of indium, tin, zinc, aluminum, and copper reference fixed-point blackbodies. The main study is focused on the impact of the spectral responsivity of thermometers on the interpolation parameters of the Sakuma–Hattori equation. Furthermore, the calibration results and the uncertainty sources are discussed in this paper.

Bilateral Comparison of Spectral Irradiance Between NIM and VNIIOFI from 250 to 2500 nm

With the new spectral irradiance measurement facility based on blackbody BB3500M of National Institute of Metrology (NIM), a bilateral spectral irradiance comparison was carried out between NIM and VNIIOFI (All Russian Research Institute for Optical and Physical Measurements) in the spectral wavelength from 250 to 2500 nm for the period of January 2015 to June 2016. The temperature measurement of the high temperature blackbodies were traced to the Pt–C and Re–C fixed point blackbodies and checked against the WC–C fixed-point blackbody for the two institutes respectively. The consistency of the temperature at 3021 K is better than 70 mK. The comparison result shows that the average relative deviation of spectral irradiance at 44 designated wavelengths is 0.45%. The consistency is better than 0.9% except the maximum deviation 1.1% at the wavelength of 2000 nm. The spectral irradiance units measured by NIM and VNIIOFI in this comparison are in agreement within the combined standard uncertainties of the laboratories over the wavelength range compared.