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.     

Absolute Radiation Thermometry in the NIR

A near infrared (NIR) radiation thermometer (RT) for temperature measurements in the range from 773 K up to 1235 K was characterized and calibrated in terms of the “Mise en Pratique for the definition of the Kelvin” (MeP-K) by measuring its absolute spectral radiance responsivity. Using Planck’s law of thermal radiation allows the direct measurement of the thermodynamic temperature independently of any ITS-90 fixed-point. To determine the absolute spectral radiance responsivity of the radiation thermometer in the NIR spectral region, an existing PTB monochromator-based calibration setup was upgraded with a supercontinuum laser system (0.45 \(\upmu \hbox {m}\) to 2.4 \(\upmu \hbox {m}\)) resulting in a significantly improved signal-to-noise ratio. The RT was characterized with respect to its nonlinearity, size-of-source effect, distance effect, and the consistency of its individual temperature measuring ranges. To further improve the calibration setup, a new tool for the aperture alignment and distance measurement was developed. Furthermore, the diffraction correction as well as the impedance correction of the current-to-voltage converter is considered. The calibration scheme and the corresponding uncertainty budget of the absolute spectral responsivity are presented. A relative standard uncertainty of 0.1 % \((k=1)\) for the absolute spectral radiance responsivity was achieved. The absolute radiometric calibration was validated at four temperature values with respect to the ITS-90 via a variable temperature heatpipe blackbody (773 K ...1235 K) and at a gold fixed-point blackbody radiator (1337.33 K).     

NIST Radiance Temperature and Infrared Spectral Radiance Scales at Near-Ambient Temperatures

The realization and the dissemination of spectral radiance and radiance temperature scales in the temperature range of −50 to 250°C and spectral range of 3–13 μm at the National Institute of Standards and Technology are described. The scale is source-based and is established using a suite of blackbody radiation sources, the emissivity and temperature of which have been thoroughly investigated. The blackbody emissivity was measured using the complementary approaches of modeling, reflectometry, and the intercomparison of the spectral radiance of sources with different cavity geometries and coatings. Temperature measurements are based on platinum resistance thermometers and on the direct use of the phase transitions of pure metals. Secondary sources are calibrated using reference blackbody sources, a spectral comparator, a controlled-background plate, and a motion control system. Included experimental data on the performance of transfer standard blackbodies indicate the need for development of a recommended practice for their specification and evaluation. Introduced services help to establish a nationwide uniformity in metrology of near-ambient thermal emission sources, providing traceability in spatially and spectrally resolved radiance temperature, spectral radiance, and background-corrected effective emissivity.     

可见光与热像融合的三维温度模型重建

热像仪因其能够通过检测物体表面热辐射而产生温度图像,近年来被广泛应用于多种工业场合.然而,由于热像图缺少直观的几何信息,当物体表面温度相近时,难以通过人眼分辨物体特征差异.为了解决这个问题,提出了一种结合可见光几何信息与热像图温度信息的三维模型重建方法.首先使用自制标定板进行可见光相机与热像仪的校正;随后,通过运动恢复...     

Simultaneous Measurements of Temperature and Iron–Slag Ratio at Taphole of Blast Furnace

As the initial process in an integrated steel-making plant, molten iron is produced in a blast furnace. The molten iron has a temperature between 1700 K and 1900 K. The outflow stream discharged from a taphole comprises the molten iron and slag (which is a mixture of molten oxides). Monitoring of the stream temperature is important because it has information on the thermal condition inside the blast furnace. A newly developed simultaneous measurement technique for temperature and iron–slag ratio is reported. A monochromatic CCD camera with a short exposure time is used to obtain a thermal image of the rapidly moving stream. The thermal image has a marble-like pattern caused by the physical separation of the iron and slag and their different optical properties. Iron thermometry is realized by automatically detecting the peak of the iron gray-level distribution on a histogram. Meanwhile, the thermal radiance of the semitransparent slag varies as a function of the thickness. The slag temperature is calculated from the maximum gray level, presuming that the emissivity of the slag is constant at a thick slag part. The slag ratio is measured by counting the number of pixels on the histogram. A field test was carried out at an operating blast furnace. The iron temperature, slag temperature, and slag ratio were successfully measured. This multiple image measurement is expected to be the new information source for stable blast furnace operation.     

面向非稳态传热的热像仪相对测温性能评估

提出了一种热像仪相对测温的性能评价方法。将薄片热电偶的热节点固定在温度场均匀的加热单元表面,作为标准辐射温度发生单元,被待评价的热像仪观测和测温,对比热像仪观测的热电偶热节点表面温度场数据和热电偶自身测得的温度数据的相似度,对热像仪相对测温性能进行评价。基于国内外4个品牌的7款不同规格热像仪进行测试,结果表明热像仪的相对测温误差和绝对测温误差相差较大,相对测温误差通常介于噪声等效温差和绝对测温误差之间,同时发现6号热像仪性能较差,温漂严重,通过装置中的A、B两靶标同时测试热像仪性能,评价结果的标准差均在8%以内,这表明该方法具有较高的可靠性,对热像仪相对测温性能评价研究有一定的参考意义。     

火灾损伤混凝土结构红外热像检测与评估

根据红外检测原理，采用红外热像技术对混凝土结构火灾损伤进行实验研究，给出了火灾损伤混凝土红外热像平均温或随时间的变化曲线，建立了混凝土红外热像平均温升与其受火温度及强度损失的回归方程，并运用上述检测模型对火灾损伤的混凝土建筑物进行了检测和评估。     

Facility for Measuring the Spatial Uniformity of the Radiation Power of the Surface of the Large-Area Blackbody

The new stage of the development of space-borne information systems is the creation of the Global Earth Observation System. For the full functioning of such a system, it is necessary to provide the uniformity of measurements of all national systems as members of the global system, with high-quality measurement data. This requires the implementation of a high level of ground (prelaunch) calibration of Earth remote sensing instruments. To solve these problems, there were created calibration facilities on the basis of large vacuum chambers with vacuum reference radiation sources, including sources on the basis of black bodies with a wide aperture of 500 mm in the spectral range from \(3~{\upmu }\hbox {m}\) to \(14~{\upmu }\hbox {m}\). Such a facility was created by FGUP “VNIIOFI” in cooperation with FGUP “TsNIIMash”. The ground calibration of Earth remote sensing instruments is being carried out by using blackbody models as radiation sources with known spectral radiance. Facility for ground calibration of remote sensing devices on spectral radiance is based on the usage of a large-aperture blackbody (LABB) with 500 mm diameter and working temperature range from 213 K to 423 K, as a radiation source. This calibration setup comprises a set of reference blackbodies, such as a blackbody on the phase transition of Gallium, a variable-temperature blackbody with temperature range from 213 K to 423 K, a reference blackbody cooled with liquid nitrogen, and IR Fourier spectrometer utilized as a comparator to perform LABB calibration on spectral radiance. The second important characteristic of LABB is the uniformity of spectral radiance across the radiating aperture of this blackbody. The paper describes the device for measuring the spatial homogeneity of the radiation power of the LABB’s radiating surface. This device is based on the use of two-color InSb-CdHgTe detector equipped with modulator and IR lens, which are mounted on a two-axis translation stage suitable for operation in vacuum and installed in the vacuum chamber against LABB. During the measurement of the radiation uniformity, the modulator sequentially sends probing radiation spot either from the LABB’s surface or from the thermostatic radiation source to the detector input. The principle of operation of the device is described. The results of measurements of the radiation power homogeneity across the LABB’s radiating aperture are presented in wide-temperature range.     

Effects of Environmental Conditions on the Performance of Thermal Imagers

An experimental setup for characterization of thermal imagers has been designed and constructed. The setup comprises a climatic chamber and a temperature-controlled flat blackbody target that allow testing of thermal imagers in the ambient temperature range from ?13 °C to + 23  °C and at target temperatures from ?15 °C to + 120 °C. The setup has been tested with a high quality thermal imager for scientific use and a mid-range thermal imager for industrial applications. The test results indicate that the setup allows monitoring the changes in indication of thermal imagers within the standard uncertainty limits of 0.5 °C.     

Comparison of a Detector-Based Near-IR Radiance Scale to an ITS-90 Calibrated Radiation Thermometer

Integrating-sphere-input InGaAs radiometers (ISIR) have been developed at the National Institute of Standards and Technology (NIST) to extend the detector-based calibration of radiation thermometers from the Si range to the near-infrared (NIR). These near-infrared radiometers are used to determine the reference spectral irradiance responsivity scale based on the primary-standard cryogenic radiometer. The irradiance responsivity scale is then propagated to spectral radiance at the exit port of an integrating sphere. The near-infrared radiation thermometer (NIRT) is calibrated using this detector-based radiance scale. The first phase of this research work is reported here where the relative spectral radiance responsivity of the NIRT has been determined using a monochromator-based system. Thereafter, the relative spectral responsivity of the NIRT is converted into an absolute responsivity using the radiances from the Zn fixed point blackbody. Then, the NIRT is used to extend these calibrations for temperature measurements between 157 °C and 1000 °C. The NIRT has also been calibrated in this temperature range using the five, fixed point blackbodies of the ITS-90. The two different calibration approaches for temperature measurements are compared.     

Radiation Thermometry Based on Photonic Crystal Fiber

Fiber-coupled radiometry allows for the radiometric measurement of high temperatures in environments where there is no line of sight to the target. However, transmission through conventional silica optical fibers degrades rapidly at elevated temperatures, and exotic fibers??such as sapphire fibers??typically cannot be bent. As part of a project to investigate the performance of solid oxide fuel cells, the feasibility of using an alternative fiber, solid-core silica photonic crystal fiber (PCF), was tested. The test system used an Inconel blackbody as a source, and a detection system based on an InGaAs array spectrometer with a wavelength range of 907 nm to 1681 nm. The temperature was determined from the spectrometer signal at particular wavelengths using the Planck relationship. Two tests were performed: (1) long-term high temperature soak tests to measure the drift and noise in thermal radiation levels, in which spectra are sequentially recorded over a long period of time with the blackbody cavity at a constant temperature and (2) temperature dependence tests, whereby thermal radiation spectra are recorded with the blackbody cavity at several temperatures. At 934 °C, the transmission of the PCF decreased at a rate of 0.078 % per hour corresponding to a temperature error of ?0.12 °C per hour. The transmission of conventional silica fiber decreased at a rate of 0.5 % per hour corresponding to a temperature error of ?0.8 °C per hour. While the PCF represents a significant improvement over conventional fiber, it is still not good enough for most practical purposes. At 600 °C there was no observable decline in transmission and there may be applications for PCF in that regime.     

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.     

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.     

Partial Collimation of Diffuse Light from a Diffusely Reflective Source

Abstract

A general purpose collimator capable of collimation of radiation from an arbitrary thermal source of diffuse light is incompatible with the second law of thermodynamics. It is known, however, that diffusion of coherent light from a particular ground glass can be reversed holographically. A new collimator is presented which produces a partially collimated beam of increased radiance when placed close to a white (diffusely reflective) source.     

基于红外热成像技术的复合式温场测温方法

针对测量目标发射率和吸收率估计不准确将造成红外热像仪测量温场误差较大的问题,提出了用热电偶作为标准建立红外热像仪修正模型的方法.建立热电偶所在位置的修正模型后,用其修正热像仪在其它位置的测量结果,从而提高了热像仪测量温场的准确度.30～200℃的实验证明其修正值具有较好的重复性和复现性.     

Feasibility of a New Moving Collimator for Industrial Backscatter Imaging

Conventional direct radiography may fail to successfully produce images of corrosion in large pipes containing liquid and in tanks because the attenuation can be very high. It also fails when either side of the object is not accessible. These limitations do not exist in backscatter imaging because it is a one-sided imaging technique. However, backscatter imaging can be slow. In this study, the feasibility of a new backscatter imaging system based on a moving collimator that can produce images quickly is studied. Backscattered radiation from a broad-beam industrial X-ray machine is collimated by a special collimator to allow only parallel scattered radiation to pass and reach the image plate. Because part of the backscattered radiation can be stopped by the collimator septa, the collimator is put into motion; this allows a complete image to be revealed. An electro-mechanical system is designed to move the collimator either in steps or continuously. The distance, speed and direction of the movement are controlled by a smart motor using LabVIEW. Images of Polyvinylchloride (PVC) and aluminum objects are shown. Moving collimators can be added to existing radiographic systems to make them useful for both direct and backscatter imaging.     

Comparison of Transfer Standard Industrial Lamps against PTB-assigned Radiance Temperature of Vacuum and Gas Filled Tungsten Strip Lamps

Accurate determination of temperature is one of the prime requirements in almost all the areas of physical metrology as it affects the process of any of the industrial manufacturing products. Planck’s equation serves the best approximation for determining temperature of a thermal radiating source. The ratio of pyrometric output signal due to intensities of two radiating sources can be utilized to measure temperature of an unknown source in terms of the temperature of reference metal freezing point source or a high stability tungsten strip lamp. The present paper provides an assessment of a set of tungsten lamps having strip or ribbon filament when compared against the emission of high stability standard lamps. The temperature measured in terms of electrical current across the lamp terminals has been estimated with an uncertainty reasonably acceptable for accurate determination of radiance temperature by these lamps. The uncertainty of temperature at each comparison point for lamps under assessment has been evaluated and reported. The best uncertainty of temperature was estimated to be ±1.7 K at 1073 K, ±1.5 K at 1273 K and ±3.7 K at 2473 K. The uncertainty at 1,073 K is higher as compared to at 1,273 K, is because of very low value of photocurrent signal produced due to low intensity observed at this temperature. The industrial strip lamps, compared against reference standard lamps serve as accurate sources of radiance temperature for comparing the disappearing filament Opto-spectral pyrometers used as direct temperature measuring instruments in the laboratories and in industries in the range above 1,073 K to as high as 2,500 K.     

Nondestructive Testing of Thermal Shock Resistance of Cordierite/Silicon Carbide Composite Materials after Cyclic Thermal Shock

Two different types cordierite/silicon carbide composite ceramic materials (KS 50 and KZ 50) were used for this investigation. Both materials were exposed to the water quench test from 950°C, applying various numbers of thermal cycles. When refractory samples are subjected to the rapid temperature changes crack nucleation and propagation occurs resulting in loss of strength and materials degradation. The formation of cracks decreases the density and elastic properties of material. Therefore, measuring these properties can directly monitor the development of thermal shock damage level. Dynamic Young modulus of elasticity and strength degradation were calculated using measured values of ultrasonic velocities obtained by ultrasonic measurements. Level of degradation of the samples was monitored before and during testing using Image Pro Plus program for image analysis. The capability of ultrasonic velocity technique and image analysis for simple and reliable nondestructive methods of characterization was presented in this investigation. It was found that both composite materials exhibit good thermal shock resistance.     

Sapphire-fiber thermometer ranging from 20 to 1800 degrees C

A novel, to our knowledge, sapphire-fiber thermometer ranging from 20 degrees to 1800 degrees C is presented that combines the radiance detection and the fluorescent lifetime detection schemes into one system. The thermal probe is a sapphire fiber grown from the laser-heated pedestal growth method. Its end part is doped with Cr(3+) ion and coated with some radiance material to constitute a minifiber cavity. The sapphire fiber is coupled with a Y-shaped silica fiber bundle for signal transmission. Radiance and fluorescence signal processing schemes are also set up within one thermometer system. A sandwich two-band p-i-n detector is used that may respond to both the radiation and the fluorescence. Preliminary experimental results show that the thermometer is suitable for practical application with potential long-term stability and a high-temperature resolution.     

Normal Spectral Emissivity Measurement of Molten Cu–Co Alloy Using an Electromagnetic Levitator Superimposed with a Static Magnetic Field

The normal spectral emissivity of molten Cu–Co alloy with different compositions was measured in the wavelength range of 780 nm to 920 nm and in the temperature range of 1430 K to 1770 K including the undercooled condition by an electromagnetic levitator superimposed with a static magnetic field. The emissivity was determined as the ratio of the radiance from a levitated molten Cu–Co droplet measured by a spectrometer to the radiance from a blackbody calculated by Planck’s law at a given temperature, where a static magnetic field of 2.5 T to 4.5 T was applied to the levitated droplet to suppress the surface oscillation and translational motion of the sample. We found little temperature dependence of the normal spectral emissivity of molten Cu–Co alloy. Concerning the composition dependence, the emissivity decreased markedly above 80 at%Cu and reached that of pure Cu, although its dependence was low between 20 at%Cu and 80 at%Cu. In addition, this composition dependence of the emissivity of molten Cu–Co alloy can be explained well by the Drude free-electron model.