多光谱测温法的实验研究——发射率模型的自动判别

在多光谱辐射温度计的数据处理中需要假设发射率与波长的数学模型,本文提出一种自动判别发射率与波长数学模型的新方法,并通过实验证明了此方法的确是一种解决目标真温及光谱发射率等测量问题行之有效的方法。     

Fast fiber-optic multi-wavelength pyrometer

A fast fiber-optic multi-wavelength pyrometer was developed for the ultraviolet-visible-near infrared spectra from 200 nm to 1700 nm using a CCD detector and an InGaAs detector. The pyrometer system conveniently and quickly provides the sufficient choices of multiple measurement wavelengths using optical diffraction, which avoids the use of narrow-band filters. Flexible optical fibers are used to transmit the radiation so the pyrometer can be used for temperature measurements in harsh environments. The setup and calibrations (wavelength calibration, nonlinearity calibration, and radiation response calibration) of this pyrometer system were described. Development of the multi-wavelength pyrometer involved optimization of the bandwidth and temperature discrimination of the multiple spectra data. The analysis results showed that the wavelength intervals, Δλ(CCD) = 30 nm and Δλ(InGaAs) = 50 nm, are the suitable choices as a tradeoff between the simple emissivity model assumption and the multiple signal discrimination. The temperature discrimination was also quantificationally evaluated for various wavelengths and temperatures. The measurement performance of the fiber-optic multi-wavelength pyrometer was partially verified through measurements with a high-temperature blackbody and actual hot metals. This multi-wavelength pyrometer can be used for remote high-temperature measurements.     

An emissivity-corrected method for the accurate radiometric measurement of transient surface temperatures during braking

The main difficulty encountered in brake disc infrared temperature measurements is the lack of knowledge of the disc surface emissivity, which is nonuniform and varies during braking. To provide information on the nonuniformity and variations of emissivity, brake disc surface temperatures were investigated by an original two-colour fibre optic pyrometer and an infrared camera. The first result is the measurements of the accurate surface temperature. Besides, it is shown that the local emissivity varies with friction due to modifications of surface properties. Thermal phenomena observed on the disc track are correlated with temporal changes of normal and tangential frictional forces.     

A universal pyrometer for molecular-beam epitaxy setups

A universal fiber-optic pyrometer for the molecular-beam-epitaxy growth module developed in collaboration with JSC Semiconductor Technologies and Equipment is described. This instrument is designed for controlling the technological process of growing semiconductor heterostructures on substrates of various types (GaAs, InP, Si, and sapphire). The pyrometer allows measurements of the temperature of semiconductor substrates to be performed in the range 450–1200°C with an accuracy no worse than ±0.5% under the conditions when such characteristics as the emissivity of the material, the transparency of the optical medium, and the dimensions of the studied surface are unknown. These feasibilities can be realized owing to the use of a procedure of periodic calibration of the pyrometer against an actual object directly during the technological cycle with the use of additional information on the object temperature.     

Single wavelength and ratio pyrometry reflection errors in temperature measurement of gas turbine blade

Radiation thermometers are the instruments most opted for when measuring surface temperatures of high speed rotating parts non-intrusively in many industrial applications. However, reflection of ambient radiation from the measured target goes against the operating principles of most of these thermometers thus introducing errors to the temperature measurements. Reflection errors introduced into single wavelength and ratio pyrometer temperature measurements of a rotating cooled gas turbine blade were investigated in this work through simulation. Errors for the two pyrometers based on varied target surface emissivity, view factor and ambient temperature were calculated. At high ambient temperatures, high view factors and low surface emissivity, errors exceeding 70% and 30% were realized for single wavelength and ratio pyrometers respectively. Thus temperature measured on reflective targets surrounded by surfaces at much higher temperature should be corrected for reflection errors if its reliability is to be guaranteed.     

Emissivity estimation for high temperature radiation pyrometry on Ti–6Al–4V

The paper demonstrates a versatile procedure suitable for industrial implementation of temperature measurement on a hot titanium alloy. The driving force has been the need for an accurate temperature measurement during additive manufacturing using laser welding technology where Ti–6Al–4V-wire is melted. The challenges consider both industrial constraints and the varying emissivity of the surface. Measurements makes use of a narrow bandwidth spot radiation pyrometer and a calibration procedure for estimation of the surface temperature through spectral emissivity estimation. The theoretical results are validated through experiments. A number of difficulties in radiation temperature measurements for metals with varying surface properties are discussed; especially the case of surface oxidation. The uncertainty in temperature reading due to the uncertainty in the emissivity estimate is established along with a model that qualitatively describes surface oxidation. The procedure is expected to be useful for several manufacturing applications where it is important to control high temperatures.     

Error analysis on measurement temperature by means dual-color thermography technique

Dual color thermography is a non-contact measurement temperature technique used mainly when the emissivity of surface is unknown; it is based on ratio of monochromatic emissive power calculated by means Planck’s radiation equation and allows measuring the temperature of gray body surface objects without being assigned their emissivity and without approximations.For real surfaces, the emissivity varies with the temperature of surface as well as the wavelength and the direction of radiation. In this case, the dual color thermometry is executed by equipping the IR camera of two narrow band pass filters, so as to consider the surface emissivity of a quite constant value. This allows calculating the ratio between the radiative fluxes of the two different emission wavelengths that is almost independent to the surface emissivity.One of the crucial factor in this technique is the choice of the two narrow filter wavelengths. In fact the measurement errors depends directly on the two wavelengths and the variation of spectral emissivity related to the wavelength chosen and it also depends inversely on distance between central value of filters.In this paper, the authors have developed and validated a mathematical model of experimental setup to measure object surface temperature by means IR thermo-camera. This mathematical model was used to quantify the temperature measurement error in the dual-color technique. A novel correlation to estimate temperature measurement error was provided.     

红外热像仪精确测温技术

为实现红外热像仪对温度的精确测量,根据热辐射理论和红外热像仪的测温原理,推导了计算被测物体表面真实温度的通用计算公式;讨论了发射率对测温精度的影响,分析了用红外热像仪进行精确测温的条件,探讨了环境、大气和热像仪本身对测量精度的影响,并绘制了各种因素对测温精度影响的理论曲线。结果表明:发射率为0.7时,真实温度为50℃,发射率偏离0.1时,对于3~5 μm热像仪来说,测温结果偏离真实温度0.76~0.89 ℃; 对于8~14 μm热像仪来说,测温结果偏离真实温度1.56~1.87℃。本研究结果对提高热像仪测量温度和表面发射率的准确性,减小不必要的测量误差具有实际意义。     

基于面阵CCD图像的温度场测量研究

推导出具有实物面的高温辐射体温度和CCD像素点亮度之间的关系。结合比色测温法，给出一种基于彩色CCD图像的温度场测量方法。用一套经黑体炉标定过的测温系统，分别在黑体炉和普通煤炉上进行测温试验，取得较好结果。通过比较计算温度值和热电偶测量值，分析了本测温方法的误差来源。     

低温状态下的材料法向发射率测量

研究了在-60~50℃条件下准确测量材料法向发射率的方法。基于发射率定义建立了材料法向发射率测量模型。为屏蔽环境杂散辐射与大气吸收的影响,利用真空液氮背景通道搭建了低温状态下材料发射率测量装置。测量了氧化铜与高发射率陶瓷两种样品的法向发射率随温度、波长的变化情况。结果表明:两种样品的法向光谱发射率均随波长增加而降低;随温度的升高,氧化铜样品法向积分发射率稳定为0.850±0.012,陶瓷样品的法向积分发射率降低了0.124。最后,实现了低温状态下红外光谱辐射的高精度采集,对低温状态下材料法向光谱发射率测量结果的不确定度进行了评定,得到的结果显示其相对扩展不确定度小于6.0%。     

Total emissivity of CO2 near earth atmospheric condition

The purpose of this paper is to predict total emissivity of CO₂ near earth atmospheric conditions. Due to lack of total emissivity information in this temperature range, it was predicted from line data or spectral emissivity data. The results have been compared with several methods in this paper. The models compared are by Bliss [2], Hottel [4], Atwater and Ball [5, 7], wide band model by Edwards [6], Yamamoto and Sasamori [7, 8], and using HITRAN data base [12]. For spectral emissivity, the results by Yamamoto and Sasamori match well with predictions using HITRAN data base. For total emissivity, the deviations between models are rather large and sometimes more than about 0.05 at the upper bound value around 0.2. In general, for a given condition, the upper bound of total emissivity is given by Hottel, and lower bound is given by HITRAN. The predictions by Edwards are in between but near to those of Hottel.     

Aeroacoustic simulations of a blunt trailing-edge wind turbine airfoil

We demonstrate the effectiveness of semi-empirical Brooks, Pope and Marcolini model and hybrid large eddy simulations in calculating the blunt trailing edge wind turbine noise at higher Reynolds number conditions. The 4 million element meshes of sharp and blunt trailing edge airfoils were tested at a Reynolds number of 3.2 million and an angle of attack of 4 degrees. The predicted airfoil self-noise by the modified semi-empirical formula with a low frequency directivity function and an additional term for large thickness ratio was compared to the experiments. The sound pressure level spectra from the hybrid large eddy simulation show that the predictions agree well with experimental measurements at the same observer location in the peak frequencies of the blunt trailing edge noise and sound pressure level rates of change at lower frequencies are also similar to experiments. The modified semi-empirical formula and the hybrid large eddy simulation can be considered as promising tools for high vorticity flow problems, especially for flatback airfoils for use on large wind turbines.     

Design, construction, and analysis of a continuous-temperature infrared calibrator for temperature measurement using an infrared scanner

A continuous-temperature infrared calibrator is designed and constructed for providing reference video signals in temperature measurement using an infrared scanner. The calibrator can be controlled for a wide range of temperature settings and to present a continuous span of reference signals for calibration purposes. Both analytical and experimental methods are used to evaluate the performance of the calibrator. Results show that the calibrator has a normal total emissivity of at least 0.984, which is about 1% lower than the predicted value. Methods to improve the emissivity of the calibrator are also discussed. The paper provides for analytical equations useful for parameters estimation in the future design of the calibrator.     

Enhancing radiative cooling performance using metal-dielectric-metal metamaterials

Thermal energy management, especially cooling, is becoming increasingly important in today’s high energy consumption world. Passive cooling, which does not require additional energy consumption, could be an effective approach to thermal energy management. We analyzed spectral selective thermal emitters by investigating the performance of a type of passive cooling known as radiative cooling. Our results can be used to improve radiative cooling. As we can control the radiation characteristics of Metal-dielectric-metal (MDM) structures, we developed an MDM-based spectral selective emitter. We measured the spectral emissivity of the fabricated MDM structure in the direction of the zenith and at an incline. We also simulated structures of different sizes to determine the effect of varying the size of the structure on the emissivity. Finally, we calculated the radiative cooling performance of the selectively emissive surface. In these calculations, we considered temperature changes caused by atmospheric and surface radiation. The radiative cooling performance of our MDM-based spectral selective emitter was better than the cooling performance of a non-selective emitter. The surface temperature of the best MDM spectral selective emitter was 38 °C below the ambient temperature.     

Infrared thermometers for small wires drawing

This work describes the design of two contactless thermometers based respectively on a total radiance and two-color pyrometry scheme, developed to measure the temperature of a small brass coated steel wire during wire drawing. In this critical condition, wire oscillation and relevant insertion errors do not allow using commercial contact or contactless sensors. Thus, ad hoc pyrometers optical layouts have been designed in order to minimize sensitivity to the wire oscillations and emissivity changes. Moreover, performances associated to different infrared detectors have been compared using as figure of merit the achieved measurement uncertainty simulating typical disturbances, i.e. the background temperature variation, the slope of the wire’s emissivity and the effect of the atmosphere transmittance. Finally, the uncertainty budgets were drawn, evidencing the limitations of the proposed methods and identifying the best configuration for both developed instruments.     

大型空间反射镜发射率测量及误差分析

为了准确测定空间相机主镜毛坯件的表面发射率以便定量分析相机热控效果,本文在分析热像仪测温原理的基础上,利用现有测量条件,提出一种利用两种已知发射率材料作为参考的发射率测量方法.根据测量试验,得到主镜表面发射率为0.565.为定量反映各因素对测量精度的影响,对测量公式进行了误差分析.分析结果表明,与被测件表面发射率接近的材料的热像仪测温误差及发射率标称误差对测量精度有较大影响,同时得到本次试验因热像仪测温误差及参考材料发射率标称误差带来的测量误差为±0.028.最后,结合相机热平衡试验的数据对测量结果进行了验证,结果表明测量得到的主反射镜的发射率基本反映了热平衡试验的主镜表面状态,证明本文的方法对主反射镜发射率的测量是适用有效的.     

An Infrared Pyrometer for Monitoring the Temperature of Materials in Vacuum Systems

A pyrometer of IR radiation for monitoring the melting and strengthening temperatures of metals in vacuum systems is described. A diaphragmed optical system is used, which ensures the required spatial resolution and protects the pyrometer from the vaporizing metal. The measured temperature range is 20–1200°C, and the measurement accuracy is 2% at a time constant of 1 s.     

红外高光谱干涉仪辐射定标误差敏感性因子的仿真分析

鉴于对高精度高时空分辨率大气探测资料日益增长的科研和业务需求,我国正大力发展星载红外高光谱探测系统。星载红外高光谱干涉仪光机结构复杂,仪器状态会显著影响其定标精度。本文通过理论分析和仿真实验,分别讨论了内黑体发射率、低温黑体发射率、内黑体与环境温度差、非线性系数以及直流电压演算等误差敏感性因子影响辐射定标精度的特征。分析表明定标辐射偏差的绝对值与内黑体/低温黑体发射率呈线性关系,且与内黑体与环境温度差、非线性系数、直流电压呈正相关;提高内黑体发射率和低温黑体发射率到0.985以上、控制内黑体与环境温度差在0.6 K左右、控制干涉仪的非线性效应系数低于0.04,这些方案均是实现0.1 K辐射定标精度的必要条件;辐射定标参数对定标辐射的影响特征结合地面真空实验的定标参数估计,可以迭代得到已测得和未知的定标参数的最优估计,从而提高定标精度。本文的研究结果对于红外高光谱干涉仪的参数设计以及辐射定标误差来源的识别和订正有着十分重要的意义。     

发射率在线测试仪的研制

为了长时在线测量物体表面发射率,设计了一种基于反射率法的发射率在线测试仪,由探测器、硬件电路、上位机和电源4个部分组成。基于反射率法的测量原理,考虑到现场发热和振动等恶劣环境,对测试仪的探测器、硬件电路进行了特殊的设计,并推导了消除热敏电阻红外传感器非线性误差后的发射率求解公式。最后通过试验表明:该测试仪能满足发射率长时在线测量的要求,测量精度达到±0.03。