基于径向基函数网络多光谱辐射测温技术理论研究

在多光谱辐射测温技术中常需要假设光谱发射率及波长之间的数学模型。文中介绍了一种基于神经网络的多光谱辐射测温数据处理方法,代替了假设发射率模型的方法。利用径向基函数网络,可由网络的输出直接得到目标的真温和光谱发射率,并分析了各种测试情形对测结果的影响。计算机仿真结构表明此方法是一种比较好的获知真温与发射率的方法．     

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.     

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%。     

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。     

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.     

基于彩色CCD的比色测温校正方法

基于彩色CCD的比色测温技术是当前高温测量领域中的研究热点之一.被测物体的发射率随辐射波长变化以及CCD光谱响应特性非理想是该方法的主要误差来源.通过对比色测温原理和CCD成像原理的分析,提出了含有发射率校正系数和CCD响应带宽校正系数的比色测温公式,以减少CCD光谱响应特性非理想和被测辐射体发射率变化带来的测量误差.提出利用黑体炉实验标定CCD响应带宽校正系数a、b,利用现场实验标定发射率校正系数c.实验表明,本方法能有效地减小测温误差,具有较强的实用性.     

Methodology for spectral emissivity measurement by means of single color pyrometer

The application of non-intrusive optical devices, such as infrared pyrometers able to measure the temperature of surfaces, makes possible the evaluation of emissivity curve of the tested materials at different temperature values. In this paper the authors propose a methodology for the spectral emissivity measurement by means of a single color pyrometer providing a semi-empirical formula, obtained experimentally at CIRA’s laboratory. The semi-empirical formula allows to know the actual emissivity value of the sample’s surface for whatever emissivity value set up on the pyrometer. The agreement between the experimental emissivity and the emissivity predicted by semi-empirical formula was verified.     

Dual-band pyrometry for emissivity and temperature measurements of gray surfaces at ambient temperature: The effect of pyrometer and background temperature uncertainties

A dual-band pyrometry model for target temperature (240–360 K) and emissivity measurement was developed, in which two pyrometers with different spectral bands are surrounded by an enclosure at a given background temperature. Nine equal-power spectral bands were selected for the pyrometers from wavelengths between 8 and 14 μm. The Monte Carlo method was used to compute the dual-band measurement uncertainties of temperature and emissivity caused by the propagation of the uncertainties associated with the temperatures of the two pyrometers and the temperature of the background. It was found that the rate of decrease of dual-band measurement uncertainties with increasing difference between target and background temperatures decreases with increasing target temperature. Considering the uncertainty of the background temperature, it was found that dual-band measurement uncertainties are virtually not affected by the background temperature uncertainty when the background temperature is lower than the target temperature, and dual-band measurement uncertainties increase significantly with increasing background temperature uncertainty when the background temperature is higher than the target temperature.     

复杂背景下三维弯曲表面红外测温修正

航空发动机涡轮叶片的断裂脱落与叶片温度密切相关,准确测量涡轮叶片温度对航空发动机的安全运行具有重要意义。针对涡轮叶片材料发射率不均匀、周围高温物体反射严重以及探测角度变化等因素导致传统红外辐射测温方法精度难以保证的问题,基于辐射传输理论与红外热成像测温原理,分析了对红外测温结果影响的主要因素,提出了复杂背景下三维弯曲表面红外辐射测温的修正模型。通过设计实验测量获得弯曲表面的发射率、双向反射分布函数、角系数等重要参数,根据提出的温度修正模型,得到弯曲表面红外修正温度。通过与典型位置上热电偶的测温结果对比,测温误差由修正前的4%左右下降到1%以内,证明了所提的修正模型具有较高的精度和适应性,可为涡轮叶片气动传热试验技术的提升和航空发动机等重大装备的研制提供支撑。     

Simultaneous measurement of temperature and emissivity of lunar regolith simulant using dual-channel millimeter-wave radiometry

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments (high temperature, pressure, and corrosive environments). The state-of-the-art dual channel MMW passive radiometer with active interferometric capabilities at 137 GHz described here allows for radiometric measurements of sample temperature and emissivity up to at least 1600?°C with simultaneous measurement of sample surface dynamics. These capabilities have been used to demonstrate dynamic measurement of melting of powders of simulated lunar regolith and static measurement of emissivity of solid samples. The paper presents the theoretical background and basis for the dual-receiver system, describes the hardware in detail, and demonstrates the data analysis. Post-experiment analysis of emissivity versus temperature allows further extraction from the radiometric data of millimeter wave viewing beam coupling factors, which provide corroboratory evidence to the interferometric data of the process dynamics observed. These results show the promise of the MMW system for extracting quantitative and qualitative process parameters for industrial processes and access to real-time dynamics of materials behavior in extreme environments.     

Adaptive spectral band identification method in noncontact temperature measurement based on dynamic programming

An adaptive method based on dynamic programming is proposed to identify the spectral band for noncontact measurement of surface temperature of heatshield materials when Fourier transform infrared (FTIR) spectrometer is used to collect the radiation spectrum in the dynamic heating environment of a high-frequency plasma wind tunnel. First, the radiation spectrum is converted to a time series. Then, high-frequency parts of the measurement spectral signal are obtained by multi-resolution analysis of one-dimensional discrete wavelet and then the suitable spectral band required by a noncontact temperature measurement is adaptively identified based on dynamic programming. Eventually, surface temperature and its corresponding emissivity can be determined. Results of the experiment conducted on a benchmark material (graphite) in the dynamic heating environment of high frequency plasma wind tunnel show the proposed method to be practical.     

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.     

Measurement technology for material emissivity under high temperature dynamic heating conditions

The thermal dissipation of radiation is main heat shield mechanism for non-ablative thermal protection materials on hypersonic vehicles withstanding high temperature dynamic heating cycle during endo-atmospheric ascent, cruise and reentry. Therefore, it is necessary to know the thermal radiative properties of the material under the simulated high temperature dynamic heating conditions on the ground. The emissivity depends on the surface state and its temperature. A new simultaneous measurement technology of emissivity and varying surface temperature is proposed under high temperature dynamic heating conditions. This new technology solved synchronous measurement problems by utilizing spectral signal of Fourier transform infrared (FTIR) spectroscopy. The calibration of different temperature ranges, the background disturbances, the influences on temperature measurement by wavelength range and its corresponding fluctuations of measurement signal, were thoroughly investigated. The measured results of steel and graphite as reference materials proved the effectiveness of this simultaneous measurement technology and showed great potential in engineering applications under high temperature dynamic heating conditions.     

Investigation on grinding temperature in ultrasonic vibration-assisted grinding of zirconia ceramics

The feasibility of ultrasonic vibration-assisted grinding (UVAG) in machining brittle materials, such as zirconia ceramics, has been preliminarily proved. The high temperature generated in grinding processes is a main factor responsible for thermal and surface/subsurface damage. However, there are few reports about grinding temperature for zirconia ceramics by UVAG. In this study, a grinding force model is used for the analysis of grinding temperature in UVAG based on kinematic principle of ultrasonic vibration and brittle material fracture removal mechanism. Then, the heat fluxes equation during grinding process is analyzed. And the grinding temperature model is developed based on theoretical grinding force model and heat fluxes. Finally, pilot experiments are carried out to analyze influence of vibration parameters and process parameters on UVAG temperature and verify the mathematical model. The comparison results show that ultrasonic vibration has an important influence on grinding temperature with the reduction of 10.6%. In addition, there is a good consistency between mathematical model and the experimental results. The average relative error is within 10%. Therefore, the mathematical model could be used to predict the UVAG temperature.     

Multiple pulse-heating experiments with different current to determine total emissivity, heat capacity, and electrical resistivity of electrically conductive materials at high temperatures

A modified pulse-heating method is proposed to improve the accuracy of measurement of the hemispherical total emissivity, specific heat capacity, and electrical resistivity of electrically conductive materials at high temperatures. The proposed method is based on the analysis of a series of rapid resistive self-heating experiments on a sample heated at different temperature rates. The method is used to measure the three properties of the IG-110 grade of isotropic graphite at temperatures from 850 to 1800 K. The problem of the extrinsic heating-rate effect, which reduces the accuracy of the measurements, is successfully mitigated by compensating for the generally neglected experimental error associated with the electrical measurands (current and voltage). The results obtained by the proposed method can be validated by the linearity of measured quantities used in the property determinations. The results are in reasonably good agreement with previously published data, which demonstrate the suitability of the proposed method, in particular, to the resistivity and total emissivity measurements. An interesting result is the existence of a minimum in the emissivity of the isotropic graphite at around 1120 K, consistent with the electrical resistivity results.     

分析法的瞬态高温外推实验研究

为了拓展蓝宝石光纤黑体腔温度传感器的测温范围和提高其测温精度,提出了一种瞬态高温测试的拓展方法。用磁控溅射法在蓝宝石光纤一端镀制一层氧化锆陶瓷材料形成黑体腔,分析了黑体腔的传热规律,并建立了黑体腔的传热数学模型,用分析法求解了黑体腔传热数学模型,设计了实验验证方法,对黑体腔传热数学模型和分析求解法进行了实验验证。实验结果表明,利用分析法得出的外推结果与红外测温仪测到的结果在变化趋势和最高值处表面出了较好的一致性,证明了黑体腔传热数学模型与分析求解法是正确的。     

光谱吸收型光纤多气体传感系统

基于气体的近红外吸收机理，研究了一种可以检测多种气体的全光纤传感方法，采用光纤光栅波分复用技术．通过光纤光栅和压电陶瓷（PZT）对宽带光源LED进行波长调制，获得与相应气体吸收峰相对应的窄带反射出射光，检测二次谐波，实现对多种气体的较高灵敏度测量。利用二次谐波与光纤光栅透射光强的比值来消除光路干扰。建立了谐波检测的数学模型，进行了光纤C2H2和CO气体测量系统的实验研究。     

端面滑动摩擦副接触界面波段发射率研究

为研究滑动摩擦过程中接触界面波段发射率的变化规律,设计并开展了一系列实验。以端面滑动摩擦副的接触界面为研究对象,在含二硫化钼的脂润滑条件下,开展定载荷、定转速实验,利用热像仪和自制装置测量了不同摩擦时间后的波段发射率,并根据发射率变化规律对红外测温仪测得的接触界面辐射亮温进行了修正。结果表明：测量装置能够较准确地实现摩擦接触界面波段发射率的测量;含有润滑脂和磨屑的接触界面发射率总体上在一定范围内波动,在摩擦过程中,具有先下降后上升的趋势;在稳定摩擦阶段,对辐射亮温的修正精度较高。     

Application of multispectral radiation thermometry in temperature measurement of thermal barrier coated surfaces

Ceramics coatings are materials widely used in gas turbines to provide thermal shielding of superalloy materials against excessive turbine temperatures. However, measurement of their surface temperatures using conventional radiation thermometers, more so in the presence of high ambient radiation and low emissivity is quite challenging. A multispectral method employing curve fitting technique to measure the temperature of such targets in the range of 800–1200 K and ambient temperature of 1273 K is implemented in this paper through simulation. Several simulated experiments were carried out to identify emissivity models best suited for multispectral radiation thermometry applicable to ceramic coatings. The best emissivity model applicable to yttria-stabilized zirconia of coating thickness of 330 μm in the wavelength range of 3.5–3.9 μm was found to predict temperature with an error of less than 1.5% in the presence and absence of background noise.     

空间光谱成像仪热设计参数的灵敏度

针对空间光学遥感器在轨运行期间其热物理属性的实际参数与热设计参数之间存在一定的偏差,从而影响整机热设计的问题,本文基于系统灵敏度理论,对空间光学遥感器的热设计进行了分析,并建立了在轨条件下的热平衡方程组.通过分析热平衡方程组的设计变量,总结出影响整机温度分布的热设计参数.以某空间光谱成像仪热设计为例,分析了上述影响整机温度分布的设计参数的灵敏度.灵敏度分析结果表明:整机平均温度对太阳吸收系数的灵敏度几乎为零;对红外半球发射率的灵敏度为2.2～14.55℃;对内部热源的灵敏度为1.8～2℃/W;对导热率的灵敏度为2.25×10-3～4.39×10-2 m℃2/W:对接触导热系数的灵敏度为0～1.1×10-3 m2℃2/W.试验验证结果表明,基于灵敏度分析结果的热控设计方案有效且可行.