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。     

基于多光谱辐射的高速轴承温度测量方法

针对轴承升温过程很难在可变动态载荷下进行高精度实时监测的问题,文中提出了一种高速轴承多光谱温度测量方法。首先,根据Palmgren方法建立高速轴承热力学模型;然后,利用辐射传热原理分别分析轴承热辐射源和背景热辐射源的影响机理,建立轴承的多光谱温度测量模型。为了验证文中方法的有效性,利用800～1 700 nm波段的光谱对深沟球轴承进行温度测量实验。实验结果表明,轴承材料的发射率近似为常数,其背景辐射源的发射率近似为线性。与传统的有限元方法相比,多光谱测温法的平均绝对误差范围为-0. 160～0. 285℃,标准差范围为0. 484～0. 639℃。文中方法能够有效地测量高速轴承的动态温度。     

辐射温度计的等效波长及其应用

经典的有效波长和亮度温度理论仅适用于高温测量等可忽略环境辐射影响的场合.考虑了环境辐射影响,基于中值定理推导并定义等效波长,用于简化测温数学模型.用有效辐射和等效波长概念定义单色和带通辐射温度计的测量结果--亮度温度.阐述了等效波长的计算方法.利用矩形带通光谱响应近似模型,解决了难以测定光谱响应度的宽带辐射温度计的等效波长计算问题.针对(8～14)μm宽带辐射温度计计算了等效波长,可简化计算和不确定度评定.在应用实例中分析了黑体辐射源发射率对宽带辐射温度计校准的影响和用黑体辐射源直接校准发射率设定值为0.95的宽带辐射温度计的方法误差.     

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%。     

材料光谱发射率精密测量装置

采用光栅单色仪方案研究了光谱发射率的测量装置,以加热方式将材料样品温度控制在473～1 000 K,可在2～15 μm测量样品的定向光谱发射率.应用锁相放大技术和统计测量方法提高样品与黑体的辐射亮度比较测量的信噪比.对测量装置性能进行了评价实验,并提出一种双黑体法评价光谱辐射测量系统的线性度.测量了氧化不锈钢样品和高发射率涂料的光谱发射率并进行了不确定度评定,合成标准不确定度小于0.04.     

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.     

基于多光谱显微成像的颗粒表面温度分布测量

分别采用彩色相机和多光谱相机构建辐射测温系统,利用黑体炉进行温度模型标定实验,并基于BP神经网络对标定数据进行训练得到测温模型。通过蜡烛火焰的温度测量实验,验证了测温模型的可靠性,且结果显示多光谱成像测温系统的测温精度高于彩色相机测温系统。针对常规辐射成像测温系统空间分辨率不足的问题,采用多光谱相机结合显微镜搭建了显微测温平台,对高温热台内的单石油焦颗粒燃烧过程进行记录,得到了石油焦颗粒表面的温度分布以及随时间的温度变化过程。     

辐射光谱测温法测量误差实验研究

针对辐射光谱测温法测量误差问题,利用黑体炉搭建了标准辐射测温实验平台,选用200~1 100nm波段光谱仪对标准高温源进行辐射光谱测量。讨论了高温源辐射光谱特征,并基于辐射光谱测温法获得了温度测量值,该值与标准参考值的相对偏差小于4%,同时分析了测量重复性引起的标准不确定度分量,为辐射测温法应用提供参考。     

基于彩色CCD的高温场辐射测温方法

针对基于彩色CCD的高温场辐射测温问题,提出利用红、绿基色值进行比色测温来获取单一光圈快门组合内的最大测温范围,并进一步利用变换光圈快门组合来使得测温范围能够覆盖高温生产的常用温度范围;通过标定减少CCD光谱响应带宽和被测对象光谱发射率对测温精度的影响,提高测温精度.在此基础上,开发了CCD高温场测量仪.计量校准结果表明,测温仪具有较高的测温精度和实用性,能够满足常见高温生产过程对于温度测量的应用要求.     

基于双波段比能量法的非接触测温系统的研究

为实现表面发射率未知但稳定的材料的中高温(300～550℃)温度的精确测量,提出了一种双波段比能量测温法,并基于该方法设计了一套非接触测温系统。非接触测温系统选用工作波段为0.9～1.65μm和5.5～14.5μm的红外辐射传感器,传感器将2个波段的能量信号转化为电压信号,并将电压信号做比值,得到和温度相关的K因子,使用面源黑体炉和金属样板对系统进行标定及测试。实验结果表明:使用双波段比能量测温法的非接触测温系统不需要知道目标发射率,也能较为精确地得到中高温物体的真实温度,且温度误差在10℃以内。基于该方法的非接触测温系统对中高温物体真实温度的精确测量具有重要的研究意义。     

Experimental mathematical model as a generalization of sensitivity analysis of high temperature spectral emissivity measurement method

The development of an experimental mathematical model describing temperature state of the sample during high temperature spectral emissivity measurement is introduced. Dimensional analysis of the measurement process gives the physical dimensionless quantities and sensitivity analysis of the measurement process provides the large set of performed model experiments. Evaluated experimental mathematical models are presented including their accordance with model experiments. Established equations are generalization of sensitivity analysis of high temperature spectral emissivity measurement method and can be used for computation of spectral emissivity total uncertainty.     

Measurement of temperature distributions across laser heated samples by multispectral imaging radiometry

Two-dimensional temperature mapping of laser heated diamond anvil cell samples is performed by processing a set of four simultaneous images of the sample, each obtained at a narrow spectral range in the visible to near infrared. The images are correlated spatially, and each set of four points is fitted to the Planck radiation function to determine the temperature and the emissivity of the sample, using the gray body approximation. The method is tested by measuring the melting point of Pt at 1 bar and measuring laser heated Fe at 20 GPa in the diamond anvil cell. The accuracy and precision are shown to compare well to standard spectroradiometry, and the effect of imaging resolution on the measured distribution is evaluated. The principal advantages of the method are (1) the temperature and emissivity of the sample are mapped in two dimensions; (2) chromatic aberrations are practically eliminated by independent focusing of each spectral band; and (3) all of the spectral images are obtained simultaneously, allowing temporal variations to be studied. This method of measuring temperature distributions can be generalized to other hot objects besides laser heated spots.     

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.     

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.     

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.     

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.     

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.     

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.     

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.