固定发射率辐射温度计校准中的温度修正分析

在当前的辐射温度计的检定中,温度修正分析有着十分重要的作用。但是从辐射温度计实际使用的过程可以看到,辐射温度计的温度修正还存在若干问题,很多用户都要求校准后需要使用不同发射率下的辐射温度计修正值。基于这个背景,在本次课题的研究中,主要分析了固定发射率下的辐射温度计校准中的温度修正。     

基于VBA实现黑体辐射源发射率偏离1引起有效亮度温度修正

按照最新的工作用辐射温度计检定规程和辐射测温用-10～200℃黑体辐射源校准规范要求,需要根据有效亮度温度概念,通过对黑体辐射源进行发射率影响修正和环境辐射误差修正,文章对有效亮度温度发射率影响数学模型,使用VBA语言,研究二分算法,高效实现有效亮度温度与实际温度的修正计算,从而为日常检定、校准工作提供了有力的技术保障。     

黑体辐射源发射率对辐射测温准确度的影响及修正方法

随着辐射温度计的广泛应用,对准确测量、校准或检定的要求越来越高.尽管黑体辐射源的性能不断提高,但黑体辐射源发射率偏离1仍然是影响辐射温度计校准/检定或相关应用准确度的关键问题.可是目前对辐射温度计的校准常常忽略黑体辐射源发射率偏离1的影响或在分析中采用不适当的计算.针对常见的辐射温度计,阐述了对黑体辐射源发射率的影响进行修正与不确定度评定的一般方法,对复杂的宽带辐射温度计提出可行的近似计算方法,并对最常见的8～14μm宽带辐射温度计给出了计算结果.分析结果表明,对于较长波长的辐射温度计,在中高温区的校准或检定中所经常使用黑体辐射源发射率值所引起的亮度温度误差是显著的,应予以修正.     

发射率0.95的单波段辐射温度计的校准方法探讨

目前发射率0.95的辐射温度计应用十分广泛,对于这类辐射温度计还没有统一的校准规范。文章对发射率为0.95、光谱范围为8~14μm单波段辐射温度计的校准方法进行了探讨,主要首先讨论了辐射源的选用,其次针对选用黑体辐射源作为标准时辐射温度计理论示值的修正算法,对斯忒藩—玻尔兹曼全辐射定律、极限有效波长法和积分法得到的结果进行了比较,最后对校准过程中环境辐射的影响、校准距离的确定和对辐射源腔口直径的要求给出了相关建议。     

有效亮度温度测量中发射率影响的修正

经典的短波高温修正模型不适用于中长波红外温度计的发射率修正和不确定度评定。采用有效亮度温度概念,得到了对于温度范围和测温波长具有广泛适用性的发射率影响模型以及具有简明物理含义的微差近似形式,包含了经典亮度温度理论中的发射率影响修正和环境辐射误差修正。定量分析了经典的短波高温修正模型的误差。针对黑体辐射源的不同溯源方法,讨论了辐射温度计校准中的发射率影响修正方法,并给出修正实例。所用方法可用于辐射测温应用、辐射温度计校准和黑体辐射源校准中的发射率和环境影响修正以及辐射源发射率不确定度对校准结果不确定度贡献的计算。     

固定发射率工作用辐射温度计校准方法研究

讨论分析了用于校准固定发射率工作用辐射温度计的原理。在校准中,应用辐射面源是必要的,其发射率应与温度计的固定发射率一致,以保证温度量值传递的准确性,并分析了由于两个发射率的不一致而带来的温度误差,给出了在不同温度下由发射率偏离而引起的温度误差计算式。在发射率为0.95、温度为700 K的情况下,最大误差可以达到15 K。如果实际测量对象的发射率与温度计的固定发射率相同,则可以直接测量出被测对象的真实温度。     

500℃以下工作用辐射温度计校准结果示值修正方法探讨

我国对工作用辐射温度计的校准使用《500℃以下工作用辐射温度计检定规程》和《工作用辐射温度计检定规程》,两本规程分别适用于温度范围在500℃以下和300～2200℃的工作用辐射温度计的检定。两本规程都规定,在检定过程中,对于温度计有发射率修正和调节功能的,应将发射率设置为1或将发射率设置为与辐射源靶面的有效发射率相同的数值。在实际工作中,很多工作用辐射温度计的发射率没有调节功能,恒为0．95,有的甚至没有标明发射率是多少,而一般计量部门的标准辐射源的发射率都为1．00。     

环境温度对固定发射率辐射温度计校准示值修正的影响

介绍环境温度变化对固定发射率(ε=0.95)辐射温度计校准时示值修正的影响,通过计算给出具体的数据,结果表明在中低温范围内环境温度的变化对校准示值修正的影响较大。     

发射率影响修正近似公式及其适用性分析

黑体辐射源的有效发射率影响是辐射测温计量标准中的重要影响因素.本文利用有效亮度温度概念,对辐射温度计或黑体辐射源检定校准中的发射率影响修正模型的多种简化形式进行了分析比较.定量分析了Wien近似、忽略环境辐射近似和微差近似等几种近似模型的温度与波长适用性.其中微差模型具有简明的物理含义,经典的短波高温修正模型不宜用于常见的8～14μm辐射温度计的测量结果修正.在有效亮度温度测量与校准的发射率修正和不确定度传播计算中,本文分析结果为在不同波长和温度范围合理选择简化公式提供了参考依据.     

发射率设定值不为1的辐射温度计的校准

分析了用黑体辐射源校准发射率设定值小于1的辐射温度计时,对温度计示值的影响,介绍了近似修正方法及典型计算结果.     

Influence of Non-ideal Blackbody Radiator Emissivity and a Method for its Correction

Demands for accurate temperature measurement and calibration are increasing along with the wider use of radiation thermometry in industry. However, the deviation of a ‘blackbody’ radiator emissivity from the emissivity of an ideal blackbody remains one of the main uncertainty contributions in the calibration of radiation thermometers, although the performance of blackbody radiators has been continually improving. Nevertheless, the influence of this deviation was often ignored due to the complexity of the correction. In this paper, general methods to evaluate the influence of the emissivity deviation of a blackbody radiator from unity for typical radiation thermometer models are described. An approximate practical method for wide-band radiation thermometers is proposed. Moreover, the concept of equivalent wavelength and the corresponding calculation method are introduced to simplify the mathematical model. The calculation result and a mathematical expression for the equivalent wavelength applicable to most popular radiation thermometers with a spectral range of 8–14 μm are given. The analysis and calculation show that the influence of blackbody radiator emissivity on longer working-wavelength radiation thermometer calibrations at mid or high temperatures cannot be ignored.     

大口径高发射率面型黑体辐射源的研制

黑体辐射源作为定标标准器,在红外测量设备的辐射定标中具有重要作用。为应对大口径红外测量设备的辐射定标工作需求,设计了1台辐射面积为400mm×400mm的面型黑体辐射源。采用多路控温和连接固定冷源的方式对黑体进行温度控制;通过热仿真确定合适的传热模型,同时结合高发射率涂层工艺与辐射面的结构设计使黑体具备高发射率,辐射面有效发射率可达到0.992;在真空环境下,利用标准铂电阻温度计测量得到黑体辐射面源的温度均匀性偏差最大为0.101K,稳定性平均值为0.018K/10min,该黑体辐射光源能够满足现阶段大口径红外测量设备的使用需求。     

红外耳温计分度方法及数据分析

研制了一种专门用于红外耳温计分度的双孔黑体空腔,并用研制的黑体空腔对红外耳温计在37℃和41℃进行了分度实验.实验结果表明,此黑体空腔的空腔发射率已达到0.999,完全能作为红外耳温计分度的标准辐射源.最后对实验结果进行了不确定度的评定.     

Automation of reading liquid-in-glass thermometers

In this paper, the automation of calibration of liquid-in-glass thermometers (LiGTs) is discussed. Temperature readings are taken automatically with the use of a measuring system that consists of a standard calibration setup, a video camera and illumination, an image acquisition module and a computer that executes the algorithm for image processing and analysis. Once the reading of the temperature is extracted from the acquired image, this value can be passed to any other data processing program, which includes the comparison with the values from the reference thermometer and determination of correction and combined uncertainty. Data achieved in this way can be directly used to prepare the calibration certificate     

Propagation of Uncertainty Due to Non-linearity in Radiation Thermometers

The measurement of the non-linearity of radiation thermometers is important in the realization of ITS-90 above the silver point and in the calibration of primary or secondary radiation thermometers using multiple fixed points both above and below the silver point. A non-linearity function is usually derived, enabling correction of the measured signals. Uncertainties in this non-linearity function propagate to the uncertainty in the determination of an unknown temperature. Since the same non-linearity function is used both during calibration and in subsequent use of the thermometer, there is a high degree of correlation between the uncertainties in the corrected calibration signals and the corrected in-use signals. While these correlations obviously lead to zero uncertainty at the calibration points, it is difficult to determine the correlation coefficients for temperatures away from these points. This article sets out a mathematical framework, based on interpolation theory, for propagating the uncertainty due to non-linearity in which correlation is easily included. The method is illustrated for a thermometer realizing ITS-90 up to 3,000°C based on one fixed point (silver, gold, or copper), and also for alternative realization schemes based on two or more fixed points. The total non-linearity uncertainty for the multipoint schemes is considerably lower than for the ITS-90 method. The mathematical framework can also be applied to secondary calibrations below the silver point, where non-linearity is typically more problematic for the detectors used in this temperature range.     

辐射源尺寸效应实验方案设计

在进行辐射温度计的校准时,辐射源尺寸效应会给校准结果带来影响,需设计一套实验方案,完成辐射源尺寸效应实验,以便在辐射温度计的校准中减小源尺寸效应的影响。本文重点讨论了适合本实验室的实验方案设计、实验过程及结果分析。同时对辐射温度计的校准给出了指导意见。     

红外测温系统在航空发动机轮盘试验中的应用

该文论述了红外测温基本理论和红外测温仪工作原理,设计开发了适用于航空发动机轮盘试验的非接触红外测温系统,分析影响红外测温系统测量准确度的主要因素,研究发射率的确定方法,在轮盘静止和旋转状态下进行了试验验证。其结果表明:影响红外测温系统测量准确度最重要的因素是发射率;用热电偶对发射率进行确定的方法是可行的;轮盘在静止和旋转状态下的发射率相同,静止状态下确定的发射率可用于旋转状态下的温度测量。     

黑体辐射源的多波长有效亮度温度校准和不同溯源方式特点分析

介绍了中国计量科学研究院建立的标准变温黑体辐射源和有效亮度温度比较装置;阐述了黑体辐射源多波长有效亮度温度校准的2种方法,给出典型校准结果并分析了辐射源特性。比较分析了3种溯源方式的性能特点及其应用的影响因素。提出控温复现性的概念,它是以往未被重视的辐射源关键性能参数。多波长有效亮度温度校准是可减小或消除有效发射率和接触测温测点温差影响的溯源方案,与传统溯源方式特性互补,可用于评价辐射源的有效发射率和测点温差,对控温复现性好的辐射源效果最优。     

Spectral Emissivity of Surface Blackbody Calibrators

The normal spectral emissivity of commercial infrared calibrators is compared with measurements of anodized aluminum samples and grooved aluminum surfaces coated with Pyromark. Measurements performed by FTIR spectroscopy in the wavelength interval from 2 to 20 μm and at temperatures between 5 and 550°C are presented with absolute uncertainties from 0.25% to 1% in spectral regions with sufficient signal and no significant atmospheric gas absorption. A large variation in emissivity with wavelength is observed for some surfaces, i.e., from 1% to 3% to more than 10%. The variation in emissivity using similar materials can be reduced to 0.5–1% by optimizing the coating process and the surface geometry. Results are discussed and an equation for calculation of the equivalent blackbody surface temperature from FTIR spectra is presented, including reflected ambient radiation. It is in most cases necessary to correct temperature calibration results for calibrators calibrated at 8–14 μm to obtain absolute accuracies of 0.1–1°C in other spectral regions depending on the temperature. Uncertainties are discussed and equations are given for the correction of measured radiation temperatures.     

Radiative Properties of Blackbody Calibration Sources:Recent Advances in Computer Modeling

The radiative characteristics (spectral effective emissivity, spectral radiance, and radiance temperature) of blackbody calibration sources widely used in radiation thermometry are an important subject for advanced computer modeling by the Monte Carlo method. An algorithm and code for stochastic modeling of the radiant heat transfer inside cavities has been developed on the basis of the reciprocity principle and backward ray tracing. The importance sampling technique has been applied to generate the reflected rays according to the surface reflection model that can be a linear combination of the following primary models: Lambertian, Specular, and TETRA (a microfacet model of random tetrahedral pits that mimics reflections from a rough surface). A wide range of axisymmetrical cavities, cylindrical cavities with an inclined flat bottom, and a rectilinear grooved radiator of polygonal profile have been implemented. Various conditions of observation can be modeled to compute appropriate radiation characteristics. A number of different temperature distributions can be assigned to the same node set on the cavity surface, so several related tasks can be modeled in a single run. The results obtained for the radiative properties of isothermal and non-isothermal non-diffuse blackbodies used for the calibration of infrared radiation thermometers are presented and discussed.