A Simple Quasi-2D Numerical Model of a Thermogage Furnace

A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically 99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients. In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement was obtained.     

Investigating Temperature Distribution of Two Different Types of Blackbody Sources Using Infrared Pyrometry Techniques

A comparison between two different types of thermal radiation sources maintaining near blackbody conditions has been carried out in the range from 50 to 500 °C. An infrared total radiation pyrometer was used as a transfer standard to measure the temperature of blackbodies. A thorough study of temperature distribution has been carried out for the large surface source in order to characterize the best location over the surface blackbody for temperature determination precisely of the order of better than 0.1 °C. The expanded uncertainty in the estimation of temperature of the radiating source in the above range of measurement was evaluated to be within ±0.24 °C at 50 °C and ±0.88 °C at 500 °C. The blackbody temperature sources found to be suitable for calibration of infrared total radiation pyrometers and thermal imaging devices in the operational range as mentioned above for laboratory use or other industrial and medical applications.     

T 90 Measurement of Co-C, Pt-C, and Re-C High-Temperature Fixed Points at the NIM

The blackbodies of high-temperature fixed points (HTFPs), namely, Co-C, Pt-C, and Re-C eutectic points, were gradually established at the National Institute of Metrology (NIM) of China after 2007, and their characteristics were studied. Recently, the primary standard pyrometer was improved with the lower size-of-source effect, distance effect, and partial temperature controls. The pyrometer was characterized at the new facility for the calibration of the spectral responsivity. The measurement of its nonlinearity extended to a primary standard pyrometer (PSP) reading of approximately 2680 °C for the HTFP measurements. The International Temperature Scale of 1990 above the silver point was realized at the NIM by an improved scheme, the fixed-point blackbody pyrometer assembly. Two cells each for Co-C, Pt-C, and Re-C points were assigned associated uncertainties (k = 2) of 0.22 °C, 0.37 °C, and 0.75 °C, respectively, in accordance with the NIM scale. These HTFP blackbodies are being adopted for the study and calibration of radiation thermometers at the NIM.     

Low-Temperature Blackbodies for Temperature Range from ?60?��C to 90?��C

Low-temperature cavity-type blackbodies (BB), VTBB and BB100K1, are developed at VNIIOFI for operation as IR radiation sources of the Middle Background Calibration Facility in the temperature range from ?60 °C to 90 °C, which is being constructed by KRISS for calibration of multi-spectral cameras for space applications. The VTBB model, featured by a 30 mm output aperture and hermetic housing and flange for mounting to a vacuum chamber, covers the complete temperature range under a vacuum environment (up to 10^?2 Pa), and the temperature range from 20 °C to 90 °C under open air conditions. BB100K1 has a wide aperture of 100 mm diameter, which shows stable operation in the temperature range from ?60 °C to 90 °C inside a vacuum chamber, and in the temperature range from ?40 °C to 90 °C in a dry-air or inert-gas environment with the usage of an extra hood with an aperture. The effective emissivity of the radiating cavities of both BB, covered with Lord Aeroglaze Z306 black paint, was calculated with the usage of STEEP3 Monte-Carlo simulation software, taking the measured temperature gradients into account. The numerical calculations yield an emissivity of at least 0.9997 for the VTBB cavity, and 0.997 for the BB100K1 cavity. The radiating cavity temperature of VTBB and BB100K1 is stabilized at the level of ±0.01 °C by means of an external precise closed-loop liquid thermostat (Huber Unistat 705 model). The temperature distribution along the radiating cavities and across the BB bottoms is monitored by five precision PRT thermometers and a digital multimeter equipped with a scanner card. Experimental tests using a thermal camera at KRISS demonstrated high-temperature uniformity of both radiation sources not exceeding ±50 mK over the entire temperature range, in vacuum as in a dry-air environment. The combined standard uncertainty of VTBB and BB100K1 temperature measurements accounts for about 40 mK within the range of their working temperatures.     

Measurement and Analysis of the Temperature Gradient of Blackbody Cavities,for Use in Radiation Thermometry

Blackbody cavities are the standard radiation sources widely used in the fields of radiometry and radiation thermometry. Its effective emissivity and uncertainty depend to a large extent on the temperature gradient. An experimental procedure based on the radiometric method for measuring the gradient is followed. Results are applied to particular blackbody configurations where gradients can be thermometrically estimated by contact thermometers and where the relationship between both basic methods can be established. The proposed procedure may be applied to commercial blackbodies if they are modified allowing secondary contact temperature measurement. In addition, the established systematic may be incorporated as part of the actions for quality assurance in routine calibrations of radiation thermometers, by using the secondary contact temperature measurement for detecting departures from the real radiometrically obtained gradient and the effect on the uncertainty. On the other hand, a theoretical model is proposed to evaluate the effect of temperature variations on effective emissivity and associated uncertainty. This model is based on a gradient sample chosen following plausible criteria. The model is consistent with the Monte Carlo method for calculating the uncertainty of effective emissivity and complements others published in the literature where uncertainty is calculated taking into account only geometrical variables and intrinsic emissivity. The mathematical model and experimental procedure are applied and validated using a commercial type three-zone furnace, with a blackbody cavity modified to enable a secondary contact temperature measurement, in the range between 400 °C and 1000 °C.     

Metrological Investigation of Pyrographite High-Temperature Blackbodies

The results are reported from experimental investigations of the spectral radiance and irradiance distributions, the temperature gradient, and the effective emissivity of the radiating cavity of high-temperature pyrographite blackbodies designed at VNIIOFI (Scientific-Research Institute of Optophysical Measurements). An experimental method of determining the effective high-temperature emissivity of a blackbody is described.     

Research on H500-Type High-Precision Vacuum Blackbody as a Calibration Standard for Infrared Remote Sensing

Based on the calibration requirements of vacuum low background aerospace infrared remote sensing radiance temperature, a high-precision vacuum blackbody (H500 type) is developed for the temperature range from ??93 °C to +?220 °C at the National Institute of Metrology, China. In this paper, the structure and the temperature control system of H500 are introduced, and its performance, such as heating rate and stabilization of temperature control, is tested under the vacuum and low-background condition (liquid-nitrogen-cooled shroud). At room temperature and atmospheric environment, the major technical parameters of this blackbody, such as emissivity and uniformity, are measured. The measurement principle of blackbody emissivity is based on the control of surrounding radiation. Temperature uniformity at the cavity bottom is measured using a standard infrared radiation thermometer. When the heating rate is 1 °C min^?1, the time required for the temperature to stabilize is less than 50 min, and within 10 min, the variation in temperature is less than 0.01 °C. The emissivity value of the blackbody is higher than 0.996. Temperature uniformity at the bottom of the blackbody cavity is less than 0.03 °C. The uncertainty is less than 0.1 °C (k?=?2) over the temperature range from ??93 °C to +?67 °C.     

Comparison Measurements of Infrared Ear Thermometers Against Three Types of Blackbody Sources

Body temperature is a basic vital sign of the human body, and the use of infrared ear thermometers for medical diagnosis and health management on human bodies has been widespread nowadays. To gain credibility and confidence in the usage of IR ear thermometers, a standard blackbody source (BBS) with a calibration traceable to ITS-90 is necessitated. Three types of cavity-shaped blackbodies (designated BBC-A, BBC-E, and BBC-J) vertically immersed in a temperature-controlled stirred water bath were developed at the Center for Measurement Standards (CMS) as standard BBSs to calibrate and verify 14 commercial IR ear thermometers produced by six manufacturers. The basic structure of each cavity was designed based on the informative examples recommended in ASTM E-1965, EN 12470-5, and JIS T 4207 standards. The temperature of the blackbody cavity shall be represented by the water temperature near the bottom of the cavity that is measured using an immersed platinum resistance thermometer (PRT) for which the calibration is traceable to our national standard and with an uncertainty no greater than 0.03 °C (k = 2). The water bath was evaluated using the PRT to be stable within ±3.5 mK over 1 h and uniform within ±1.1 mK. Three types of BBSs were compared and analyzed utilizing two IR ear thermometers of 0.01 °C resolution as well as the statistical technique of analysis of variance (ANOVA). On the contrary, IR ear thermometers were tested and verified against three BBSs at three blackbody temperatures of 35.5 °C, 37 °C, and 41 °C. The analysis results of ANOVA showed that there is no significant temperature difference among three different structured blackbodies, and the average measured radiance temperature of three BBSs at 35.5 °C, 37 °C, and 41 °C were within 0.026 °C, 0.024 °C, and 0.027 °C of each other. Three among fourteen IR ear thermometers tested were outside of the 0.2 °C MPE (maximum permissible error) recommended by ASTM E-1965, EN 12470-5, or JIS T 4207 standards while BBC-A and BBC-E were used; however, four were outside of MPE requirement when BBC-J was used.     

Thermodynamic Temperature Measurements Traceable to Photometric Standards

The replacement of ITS-90 temperature measurements by direct thermodynamic temperature measurements based on radiometric techniques in the temperature range above 1000 °C has been proposed by many national measurement laboratories. This article reports on work at NMIA to develop a simple and robust traceability scheme for thermodynamic temperature, based on the use of photometers and a Thermogage furnace with a graphite tube element modified to improve its temperature uniformity and emissivity. A simple luminance meter was constructed using a commercial photometer and pairs of precision apertures to view the rear of the blackbody cavity. This photometer was calibrated against NMIA reference illuminance lamps, and relative spectral responsivity measurements were used to determine the color-temperature correction between the lamps and the Thermogage blackbody. Thermodynamic temperature determinations made using various combinations of apertures and photometers showed a range of less than 0.2 °C at 1700 °C, consistent with the calculated uncertainty of 0.29 °C (k = 2). ITS-90 measurements made by NMIA??s LP5 and HTSP primary radiation thermometers with an uncertainty of 0.16 °C (k = 2), are consistent with the thermodynamic measurements. It is suggested that routine thermodynamic temperature determinations can now be made with an effort comparable to that required to realize the ITS-90 above 1000 °C.     

Use of a High-Temperature Integrating Sphere Reflectometer for Surface-Temperature Measurements

The National Institute of Standards and Technology (NIST) has developed a new facility for the characterization of the infrared spectral emissivity of samples between 150 and 1,000°C. For accurate measurement of the sample surface temperatures above 150°C, the system employs a high-temperature reflectometer to obtain the surface temperature of the sample. This technique is especially useful for samples that have significant temperature gradients due to the thermal conductivity of the sample and the heating mechanism used. The sample temperature is obtained through two measurements: (a) an indirect sample emissivity measurement with an integrating sphere reflectometer and (b) a relative radiance measurement (at the same wavelengths as in (a)) of the sample as compared to a blackbody source. The results are combined with a knowledge of the blackbody temperature and Planck’s law to obtain the sample temperature. The reflectometer’s integrating sphere is a custom design that accommodates the sample and heater to allow reflectance measurements at temperature. The sphere measures the hemispherical-near- normal (8°) reflectance factor of the sample compared relative to a previously calibrated room-temperature reference sample. The reflectometer technique of sample temperature measurement is evaluated with several samples of varying reflectance. Temperature results are compared with values simultaneously obtained from embedded thermocouples and temperature-drop calculations using a knowledge of the sample’s thermal conductivity.     

The NPL InSb-based Radiation Thermometer for the Medium Temperature Range ( < 962°C)

Over the temperature range from 156 to 962°C, the NPL maintains a series of heatpipe blackbody sources for the calibration of customer sources, radiation thermometers, and thermal imagers. The temperature of each of the sources is determined using a calibrated platinum resistance thermometer or gold-platinum thermocouple placed close to the radiating surface at the back of the cavity. The integrity of such a blackbody source relies on it having good temperature uniformity, a high and well-known effective emissivity, and having the sensor in good thermal contact with the cavity. To verify the performance of the blackbody sources, it is necessary to use an infrared thermometer that has been independently calibrated to compare the radiance temperature of the source with the temperature measured by the contact sensor. Such verification of the NPL blackbodies has been carried out at short wavelengths: from 500 to 1,000°C using the NPL LP2 calibrated using the NPL gold point, and at 1.6 μm using an InGaAs-based radiation thermometer calibrated at a series of fixed-points from indium (156°C) to silver (962°C). Thermal imaging systems traditionally operate over the 3–5 μm waveband and are calibrated using NPL sources. Up until now, it has not been possible to verify the performance of the sources in this waveband except indirectly by cross-comparison of the sources where they overlap in temperature. A mid-infrared (nominally 3–5 μm) radiation thermometer has, therefore, been designed, constructed, and validated at NPL. The instrument was validated and calibrated using the fixed-point blackbody sources and then used to validate the heatpipe blackbodies over their temperature range of operation. The results of the instrument validation and blackbody measurements are given.     

Design and Evaluation of Large-Aperture Gallium Fixed-Point Blackbody

To complement existing water bath blackbodies that now serve as NIST primary standard sources in the temperature range from 15 °C to 75 °C, a gallium fixed-point blackbody has been recently built. The main objectives of the project included creating an extended-area radiation source with a target emissivity of 0.9999 capable of operating either inside a cryo-vacuum chamber or in a standard laboratory environment. A minimum aperture diameter of 45 mm is necessary for the calibration of radiometers with a collimated input geometry or large spot size. This article describes the design and performance evaluation of the gallium fixed-point blackbody, including the calculation and measurements of directional effective emissivity, estimates of uncertainty due to the temperature drop across the interface between the pure metal and radiating surfaces, as well as the radiometrically obtained spatial uniformity of the radiance temperature and the melting plateau stability. Another important test is the measurement of the cavity reflectance, which was achieved by using total integrated scatter measurements at a laser wavelength of 10.6 μm. The result allows one to predict the performance under the low-background conditions of a cryo-chamber. Finally, results of the spectral radiance comparison with the NIST water-bath blackbody are provided. The experimental results are in good agreement with predicted values and demonstrate the potential of our approach. It is anticipated that, after completion of the characterization, a similar source operating at the water triple point will be constructed. Certain commercial equipment, instruments, or material are identified in this paper to specify the experimental procedures and result adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that material or equipment identified are necessarily the best available for the purpose.     

Calibration of Radiation Thermometers and Blackbodies in the Temperature Range from 160 ��C to 420 ��C

The NMIJ has established a new calibration facility consisting of a 1.6??m radiation thermometer and three fixed-point blackbodies of indium (156.5985 °C), tin (231.928 °C), and zinc (419.527 °C) in the temperature range from 160 °C to 420 °C. The expanded uncertainties (k = 2) of the fixed-point blackbodies are estimated to be 28 mK for the In point, 22 mK for the Sn point, and 32 mK for the Zn point. The expanded uncertainties in the temperature scale of the 1.6??m radiation thermometer are estimated to be 40 mK to 77 mK. When this standard is used to calibrate devices under test to be used in industry, uncertainties (k = 2) of 61 mK for the In point, 67 mK for the Sn point, and 99 mK for the Zn point, 91 mK to 136 mK for a 1.6??m radiation thermometer, and 73 mK to 116 mK for a variable-temperature blackbody can be achieved.     

Construction and Characterization of a Large Aperture Blackbody for Infrared Radiometer Calibration

A large aperture blackbody (LABB) with a diameter of 1 m has been successfully constructed for calibrating radiation thermometers and infrared radiometers with a wide field of view in the temperature range between 10 °C and 90 °C. The blackbody is a 1 m long cylindro-conical cavity with a diameter of 1.1 m. Its conical bottom has an apex angle of 120°. To achieve good temperature stability and uniformity, the cavity is integrated to a water-bath to which the pressurized water is supplied from a reservoir. To reduce the convection heat loss from the cavity to the ambient, the cavity is purged of the dried air that passes through a coiled tube immersed in the reservoir. For an uncertainty evaluation of the LABB, its temperature stability was measured by using a reference radiation thermometer (RRT) and a platinum resistance thermometer (PRT), and its radiance temperature distributions on the aperture plane were measured by using a thermal camera. Measuring the spectral emissivity of the coating material, the effective emissivity of the blackbody was calculated to be 0.9955 from 1 ??m to 15 ??m. The expanded uncertainty of the radiance temperature scale was evaluated based on the PRT readings, which vary from 0.3 °C to 0.5 °C (k = 2) in the temperature range. The temperature scale is validated by comparing with the RRT of which the temperature scale is realized by a multiple fixed-point calibration.     

Radiation Thermometry and Emissivity Measurements Under Vacuum at the PTB

A new experimental facility was realized at the PTB for reduced-background radiation thermometry under vacuum. This facility serves three purposes: (i) providing traceable calibration of space-based infrared remote-sensing experiments in terms of radiation temperature from  −173 °C to 430 °C and spectral radiance; (ii) meeting the demand of industry to perform radiation thermometric measurements under vacuum conditions; and (iii) performing spectral emissivity measurements in the range from 0 °C to 430 °C without atmospheric interferences. The general concept of the reduced background calibration facility is to connect a source chamber with a detector chamber via a liquid nitrogen-cooled beamline. Translation and alignment units in the source and detector chambers enable the facility to compare and calibrate different sources and detectors under vacuum. In addition to the source chamber, a liquid nitrogen-cooled reference blackbody and an indium fixed-point blackbody radiator are connected to the cooled beamline on the radiation side. The radiation from the various sources is measured with a vacuum infrared standard radiation thermometer (VIRST) and is also imaged on a vacuum Fourier-transform infrared spectrometer (FTIR) to allow for spectrally resolved measurements of blackbodies and emissivity samples. Determination of the directional spectral emissivity will be performed in the temperature range from 0 °C to 430 °C for angles from 0° to ±70° with respect to normal incidence in the wavelength range from 1 μm to 1,000 μm. References to commercial products are provided for identification purposes only and constitute neither endorsement nor representation that the item identified is the best available for the stated purpose.     

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.     

Apparatus for Measuring Spectral Emissivity of Solid Materials at Elevated Temperatures

Spectral emissivity measurements at high temperature are of great importance for both scientific research and industrial applications. A method to perform spectral emissivity measurements is presented based on two sample heating methods, the flat plate and tubular furnace. An apparatus is developed to measure the normal spectral emissivity of solid material at elevated temperatures from 1073 K to 1873 K and wavelengths from \(2\,\upmu \hbox {m}\) to \(25\,\upmu \hbox {m}\). Sample heating is accomplished by a torch flame or a high temperature furnace. Two different variable temperature blackbody sources are used as standard references and the radiance is measured by a FTIR spectrometer. Following calibration of the spectral response and background radiance of the spectrometer, the effect of the blackbody temperature interval on calibration results is discussed. Measurements are performed of the normal spectral emissivity of SiC and graphite over the prescribed temperature and wavelength range. The emissivity of SiC at high temperatures is compared with the emissivity at room temperature, and the influence of an oxide layer formed at the surface of SiC on the emissivity is studied. The effect of temperature on the emissivity of graphite is also investigated. Furthermore, a thorough analysis of the uncertainty components of the emissivity measurement is performed.     

A High-Emissivity Blackbody with Large Aperture for Radiometric Calibration at Low-Temperature

A newly designed high-emissivity cylindrical blackbody source with a large diameter aperture (54 mm), an internal triangular-grooved surface, and concentric grooves on the bottom surface was immersed in a temperature-controlled, stirred-liquid bath. The stirred-liquid bath can be stabilized to better than 0.05°C at temperatures between 30 °C and 70 °C, with traceability to the ITS-90 through a platinum resistance thermometer (PRT) calibrated at the fixed points of indium, gallium, and the water triple point. The temperature uniformity of the blackbody from the bottom to the front of the cavity is better than 0.05 % of the operating temperature (in °C). The heat loss of the cavity is less than 0.03 % of the operating temperature as determined with a radiation thermometer by removing an insulating lid without the gas purge operating. Optical ray tracing with a Monte Carlo method (STEEP 3) indicated that the effective emissivity of this blackbody cavity is very close to unity. The size-of-source effect (SSE) of the radiation thermometer and the effective emissivity of the blackbody were considered in evaluating the uncertainty of the blackbody. The blackbody uncertainty budget and performance are described in this paper.     

关于换热器的低温黑体辐射源

介绍一种工作在-80℃～+100℃的基于换热器的新型低温标准黑体辐射源的设计和其发射率的计算.这种黑体辐射源采用液体恒温槽均温致冷和采用气帘隔离法消除低温凝露和结霜,黑体空腔形状为圆锥圆柱型,锥角为120°,空腔内径50mm,腔长为300mm,控温稳定性优于±0.05℃/30min.理论计算的黑体空腔有效发射率为0.998(保留小数点后三位),比对实验测量得到的有效发射率为0.997(保留小数点后三位),二者接近一致.