Calibration of an Absolute Radiation Thermometer for Accurate Determination of Fixed-Point Temperatures

For accurate determinations of thermodynamic temperature, NPL has developed its absolute radiation thermometer (ART), which is calibrated traceably against a cryogenic radiometer. This article reviews some of the potential sources of systematic uncertainty present in the calibration and use of ART. In particular, this article is concerned with the evaluation of the size-of-source effect and the lens transmittance, as well as potential differences in the responsivity of a transfer trap detector when calibrated in terms of radiant power and used in irradiance mode.     

双通道医用输液泵自动校准系统开发

针对医用输液泵人工校准过程中存在的工作效率低、检测精度低、温度偏差与数据无法批量处理等问题,提出了一个基于间接式流量法的输液泵自动校准方案。通过实验标定特定玻璃管段的体积获得累计流量体积,对输液泵进行自动校准时通过测量注满所标定体积的时间得到累计时间,两者的比值即输液泵的平均流量。由此设计了一套双通道医用输液泵自动校准系统,可以对测量结果进行误差和重复性分析及不确定度评定并给出校准报告。验证实验表明,自动校准系统的相对误差可达到2%以内,满足相关规范5%的要求。该系统可重复测量同一输液泵在不同流量时的准确度,也可利用双通道同时对多个输液泵进行流量校准测试,以及校准输液泵的阻塞报警情况。     

基于高温黑体炉的钨铼热电偶校准方法研究

基于中国计量科学研究院的高温黑体炉设计了一种适用于钨铼偶等高温热电偶的校准方法。优化设计的均温块测温孔轴向均匀性20mm范围内小于0.5℃,优选的测温孔与中心孔的辐射温度差异可达到小于0.5℃。经铂铑10-铂热电偶验证了基于高温黑体炉的校准方法,在800~1300℃与S型热电偶标准热电势间差异小于0.5℃,不确定度评估为0.8~1.5℃,k=2。在800~1900℃范围内,测试了多只不同来源的C型钨铼偶热电势并考核了偶丝校准前后的均匀性,实验结果表明,钨铼偶丝与国际标准钨铼偶热电势的差异基本保持在1%以内,校准不确定度为3.7~13.0℃,相对不确定度为0.7%t (t为温度),k=2。     

Solid laboratory calibration of a nonimaging spectroradiometer

Field-based nonimaging spectroradiometers are often used in vicarious calibration experiments for airborne or spaceborne imaging spectrometers. The calibration uncertainties associated with these ground measurements contribute substantially to the overall modeling error in radiance- or reflectance-based vicarious calibration experiments. Because of limitations in the radiometric stability of compact field spectroradiometers, vicarious calibration experiments are based primarily on reflectance measurements rather than on radiance measurements. To characterize the overall uncertainty of radiance-based approaches and assess the sources of uncertainty, we carried out a full laboratory calibration. This laboratory calibration of a nonimaging spectroradiometer is based on a measurement plan targeted at achieving a 相似文献   

基于波长函数的辐射温度计一点标定法及其精度的理论估计与实验验证

叙述了通过测量辐射温度计波长函数和一个温度点的输出信号,从而得到辐射温度计全量程标定方法估计了各项误差源对温度标定误差的影响,给出了重要结论。进一步以某多波长高温计为例,在黑体炉标定实验基础,进行了一点标定法的验证,结果证明该方法可以得到较高精度的标定。     

Modeling of laser scanning system to determine its associated uncertainty of measurement

In the fabrication of fine wires such as filaments of lamps and optical fibers, it is always necessary to measure the diameter in real-time and correct the extrusion process. For metrological purposes, laser beam scanning technique will produce similar results as comparative to diffraction-assisted methods. A computerized laser beam scanning measurement system (LSM) is designed and fabricated. The LSM consists of a low power helium-neon gas laser source, a specially designed collimating lens, a hysteresis synchronous motor, a photo detector and a protective replaceable window along with temperature sensor. The LSM is mathematically modeled to identify various error contributing sources. The LSM is calibrated using a set of national reference standard cylindrical pins and a set of national reference standard slots to determine its relative calibration factor. The uncertainty of measurement achieved in the range of (0–35) mm is ± (0.55 +39.2L/m) μm.     

X射线剂量当量仪校准因子不确定度评估

为了准确评估X射线剂量监测用防护仪表的校准因子的不确定度,依据有关技术规范,用标准电离室对参考点位置处的剂量当量率参考值进行测量;采用替代法获得待校仪表的显示值,从而确定校准因子结果的相关影响因素,并分别对影响量的不确定度进行评定;得出仪表校准因子的相对扩展不确定度为5.0％(k=2)。影响校准因子不确定度的主要来源包括校准用辐射场的均匀性、标准电离室本身的刻度因子及能量响应、剂量当量转换因子、待检仪表显示值的统计标准偏差等。在对该类仪表的校准过程中,通过提高标准参考值的不确定度水平可以改善校准因子的不确定度。     

自适应蒙特卡洛法评定全站仪测距不确定度

全站仪测距精度的校准需要在标准基线场上进行,由于野外环境不可控和气象条件波动剧烈,因此判断全站仪的测量结果的可靠程度具有重要意义。为了解决全站仪测距不确定度评定模型的非线性和输入量强相关等问题,本文首先采用了自适应蒙特卡洛法进行不确定度评定,然后与GUM的不确定度评定结果进行对比,当测距距离为1 176 m时,自适应蒙特卡洛法评定的不确定度结果为2.2 mm,GUM为2.6 mm,结果显示两种不确定度评定方法的测量结果均在合理预期之内,且自适应蒙特卡洛法评定的不确定度置信区间更窄。自适应蒙特卡洛法结合了大量数据样本和自适应优化仿真次数的优势,不仅对全站仪测距过程中的各项误差源引入的不确定度分量评估更为全面,而且在保证了全站仪测距不确定度评定结果准确的同时,相比于蒙特卡洛法节约了70%的样本数量。     

固体式密度天平校准系统的设计与实现

针对目前密度天平仅能在液体模式校准、无法在固体模式校准的情况,研制了一种挂钩式空腔玻璃砝码作为固体密度标准,对密度天平固体测量模式校准,并提出了一种称量式密度天平校准方法。对固体式密度天平的校准实验显示,校准结果的扩展不确定度为0.0016g/cm3(k=2)。     

Determination of PRT Hysteresis in the Temperature Range from −50 °C to 300 °C

This paper discusses the contribution of hysteresis to the measurement uncertainty of industrial platinum resistance thermometers (IPRTs). Hysteresis is one of the sources of uncertainty that has so far not been sufficiently researched and documented. The term hysteresis applies to any system that is path dependent; the output depends on the history of the input. In our case, thermal hysteresis results in different resistance values at the same temperature point, depending on whether the temperature was increasing or decreasing. The reason for such behavior is related to the construction of the thermometer (strain due to thermal expansion and contraction) and also to possible moisture inside the encapsulation. In the process of evaluation of the calibration and measurement capabilities (CMCs) of IPRTs within Working Group 8, the Consultative Committee for Thermometry (CCT WG8) concluded that the uncertainty due to hysteresis is not uniformly defined and not always added to the total uncertainty of the resistance thermometer under calibration. In order to estimate the uncertainty contribution due to the hysteresis and compare different procedures, resistance measurements were carried out on a number of IPRTs of different qualities and tolerance classes. The temperature span was between ?50 °C and 300 °C, which is the most frequent temperature range in the practical use of IPRTs. The hysteresis was then determined in different ways (change of resistance at the ice point and at the midpoint temperature according to the ASTM International Standard E644 and according to the new version of IEC Standard 60751), and a comparison of results was made.     

聚合酶链式反应分析仪温度校准系统

针对聚合酶链式反应(PCR)仪温度校准的需求,提出一种热敏电阻的封装方法,研制出基于热敏电阻传感阵列的PCR仪温度在线校准系统,并进行了实验验证。结果表明:研制的PCR仪温度校准系统的均匀度不大于0.15℃,示值误差绝对值不大于0.06℃,示值误差的扩展不确定度优于0.07℃ (k=2)。利用研制的温度校准系统对PCR仪进行了温度校准,获得了校准PCR仪的示值误差、均匀度和升、降温速率等参数。     

四种不同量程温度变送器0℃时的测量误差不确定度评定

参照JJF 1183-2007《温度变送器校准规范》,对四种不同量程温度变送器进行校准,本文仅选用了温度0℃时的校准状态,并对其测量误差的不确定度进行评定。温度变送器在其他温度下的校准状态和测量误差的不确定度评定与本文描述过程等同。     

Calibration of specific absorption rate (SAR) probes in waveguideat 900 MHz

The radiation safety tests for hand-held mobile phones require precise calibration of the small electric field probes used for the measurement of specific absorption rate (SAR) in phantoms simulating the human body. In this study, a calibration system based on a rectangular waveguide was developed for SAR calibrations at 900 MHz. The cross-sectional dimensions of the waveguide are a=190 mm and b=140 mm. The waveguide is loaded with a rectangular liquid slab where the dielectric parameters of the medium simulate human muscle and brain. The precise SAR reference is derived from the temperature rise during a short-term (10-15 s) microwave heating of the lossy slab by measuring with sensitive thermistor-type probes equipped with highly resistive lines. The thermistor probes are calibrated against a calibrated mercury thermometer. To improve the uniformity of the electric field at the calibration position, the thickness of the tissue equivalent slab was varied to adjust the standing wave pattern. This resulted in an almost threefold reduction in the positioning error of the E-field probe. The absolute uncertainty of the calibration is estimated to be ±5% (2σ) not including the uncertainty of the conductivity. The difference between the thermally measured SAR and a value computed with the FDTD method was well within this limit of uncertainty. This kind of closed waveguide system is more compact and requires less microwave power than open field calibration systems. Moreover, no radio-frequency interference is generated     

Calibration of a 7.6 cm x 7.6 cm (3 inch x 3 inch) sodium iodide gamma ray spectrometer for air kerma rate

An experimental procedure is described for converting a gamma ray spectral measurement from a 7.6 cm x 7.6 cm (3 inch x 3 inch) sodium iodide (NaI) detector to air kerma rate. The calibration procedure involves measuring the energy deposited in the detector using 10 radioactive sources of known activity covering an energy range from 60 keV to 1,836 keV. For each of the 10 sources, gamma ray spectra were measured with the source at different angles to the detector axis. The total energy deposited in the detector for the ten sources was confirmed by Monte Carlo calculations. The spectra measured at different angles were combined to produce a spectrum that would represent a homogeneous semi-infinite source of radiation. The resultant spectrum was then subdivided into 10 energy regions. Based on the known air kerma rates due to the sources, a calibration coefficient was calculated for each of the 10 energy regions. These calibration coefficients could then be used to convert the energy deposited in the 10 regions of an unknown spectrum to air kerma rate. The calibration procedure was confirmed by comparing the results from the detector with those from calibrated collimated beams of 137Cs and 60Co. A comparison of measurements using a calibrated pressurised ionisation chamber with those from a similar Nal spectrometer in Finland provided additional confirmation of the calibration procedure.     

Uncertainty Budgets for Calibration of Radiation Thermometers below the Silver Point

Below the freezing point of silver, radiation thermometers are generally calibrated by implementing the multi-point interpolation method using blackbody measurements at three or more calibration points, rather than the ITS-90 extrapolation technique. The interpolation method eliminates the need to measure the spectral responsivity and provides greater accuracy at the longer wavelengths required below the silver point. This article identifies all the sources of uncertainty associated with the interpolation method, in particular, those related to the reference blackbody temperatures (either variable-temperature or fixed-point blackbodies) and to the measured thermometer signals at these points. Estimates are given of the ‘normal’ and ‘best’ uncertainties currently achievable. A model of the thermometer response is used to propagate all the uncertainties at the reference points and provide a total uncertainty at any temperature within the calibration range. The multi-point method has the effect of constraining the total uncertainty over this range, unlike the ITS-90 technique for which the uncertainties propagate as T ². This article is a joint effort of the working group on radiation thermometry of the Consultative Committee for Thermometry (CCT), summarizing the knowledge and experience of all experts in this field.     

数据采集系统通道采集速率评价中的几个问题

介绍了一种简单实用的数据采集系统采集速率的方法，讨论了评价过程的误差来源，以及减小其评价误差的几种对策；同时，给出了评价过程的计算机仿真结果。     

紫外辐射计的波长定标及不确定度分析

限于常规汞灯谱线法波长定标的局限性,构建了紫外辐射计波长定标装置,研究了紫外辐射计波长定标的物理过程和测量链,并对紫外辐射计中臭氧十二个吸收波长进行了光谱定标,通过对定标影响量的分析和计算,得到定标影响量的测量不确定度和波长定标合成标准不确定度,其中波长定标合成标准不确定度为0.026nm,同时通过光学CAD分析和实验验证紫外辐射计的光谱带宽可以达到1.0nm.应用自行构建的紫外波长定标装置较好地完成了紫外辐射计臭氧吸收谱线的定标工作,满足了臭氧反演所需的波长精度要求和光谱带宽要求.     

Bayesian uncertainty analysis with applications to turbulence modeling

In this paper, we apply Bayesian uncertainty quantification techniques to the processes of calibrating complex mathematical models and predicting quantities of interest (QoI's) with such models. These techniques also enable the systematic comparison of competing model classes. The processes of calibration and comparison constitute the building blocks of a larger validation process, the goal of which is to accept or reject a given mathematical model for the prediction of a particular QoI for a particular scenario. In this work, we take the first step in this process by applying the methodology to the analysis of the Spalart-Allmaras turbulence model in the context of incompressible, boundary layer flows. Three competing model classes based on the Spalart-Allmaras model are formulated, calibrated against experimental data, and used to issue a prediction with quantified uncertainty. The model classes are compared in terms of their posterior probabilities and their prediction of QoI's. The model posterior probability represents the relative plausibility of a model class given the data. Thus, it incorporates the model's ability to fit experimental observations. Alternatively, comparing models using the predicted QoI connects the process to the needs of decision makers that use the results of the model. We show that by using both the model plausibility and predicted QoI, one has the opportunity to reject some model classes after calibration, before subjecting the remaining classes to additional validation challenges.     

工业CT探测尺寸误差的校准及误差分析

针对工业CT探测尺寸误差的校准需求,提出一套基于标准球的校准工业CT探测尺寸误差的方法,并对引起探测尺寸误差的各种因素进行了详细分析。首先使用中国计量科学研究院标准测长机对标准球的直径进行校准,再使用标定后的标准球校准工业CT探测尺寸误差。实验结果表明球标准器能够满足工业CT探测尺寸误差校准的需求,既能被精密校准,又可在工业CT中获得低伪像的高质量图像,从而实现对工业CT探测尺寸误差的校准。通过对影响工业CT探测尺寸误差因素的分析,讨论了工业CT成像过程中各环节的误差源,对于建立工业CT测量系统全面的校准方法和溯源具有重要意义。     

Calibration of Air Thermometers in a Climatic Chamber and Liquid Baths

The paper deals with calibration of digital indication thermometers designed for air temperature measurements. These were calibrated by comparison with a reference thermometer in two different calibration media: in the air when a climatic chamber was used and in a liquid when a calibration bath was used. The main difference between the media was thermal conductivity, which was more than ten times lower in the air. To compare both methods, we calibrated two sets of air thermometers twice. The first set comprised of small temperature loggers with an internal sensor, whereas the second set was a group of temperature probes connected to the measurement unit. The temperature ranges for the loggers were from 0 \(^{\circ }\)C to 40 \(^{\circ }\)C and for the probes from ?20 \(^{\circ }\)C to 60 \(^{\circ }\)C. The results showed that the measured temperature errors were smaller in the bath as well as less scattered. Furthermore, the assigned measurement uncertainty was lower, if calibration was performed in a calibration bath, mostly due to better thermal homogeneity of a liquid compared to the air in a climatic chamber. Calibration shall assure traceability of a measurement equipment in such a way that a calibration procedure simulates an actual use of equipment; otherwise, the corrections and associated measurement uncertainty could be misleading. Therefore, when air thermometers, which are designed to measure a gaseous medium, are calibrated, they should be calibrated under similar conditions as they are used. The paper presents the differences in results of calibration of air thermometers under different calibration conditions.