Uncertainty analysis of high frequency image-based vibration measurements

Image-based vibration measurement techniques allow to remotely measuring the displacement of multiple targets in the field of view, without the need to mount anything on the measurand. In this paper the uncertainty budget of vision systems has been performed in order to both optimize the measurement procedure and identify the potential application fields. Two different types of camera are used in this work, both of them equipped with a 1280 × 1024 px sensor but with two different maximum frame rates at full resolution: 25fps and 2000fps respectively. The uncertainty analysis proposed here is based on a careful identification of the uncertainty sources and on experimental tests on an electro-magnetic shaker, where the displacement measured with the cameras are calibrated by means of the reference measurements provided by state-of-the-art traditional techniques.     

Calibration and uncertainty evaluation of single pitch deviation by multiple-measurement technique

Gears are key elements of power transmission systems, and the inspection of their pitch deviation is one of the most important tests on gears. The specifications of gears are assessed using gear measuring instruments (GMIs) or coordinate measuring machines (CMMs), and the results of the measurements must be validated under an appropriate traceability system. In the traceability system, calibrated gauges whose measuring uncertainties are estimated are necessary. In the case of pitch deviation measurement, special artefacts or gears manufactured with high dimensional accuracy are used as reference gauges. In this paper, authors propose calibration and uncertainty evaluation methods for the single pitch deviation of gears measured using CMMs. First, the evaluation of single pitch deviation using a multiple-measurement technique and the estimation of its uncertainty based on the analysis of variance are formulated. Second, a technique for reducing the measurement trials based on the symmetry of the measurement is discussed. Finally, the proposed calibration method is validated through experiments.     

三坐标机测量齿轮齿廓的不确定度评价

介绍了坐标测量中几种常用的不确定度评价方法.指出传统的三坐标测量机的测量不确定度评价方法大都不适用于评价坐标测量中面向对象的测量不确定度,并对使用蒙特卡洛方法评价测量不确定度进行了研究.首先,根据三坐标测量机详细标定文件及补偿策略说明建立测量模型.然后,将测量中的采样点通过测量模型生成大量测量结果,并以此评价测量不确定度.在齿廓评价实验中,评定齿廓误差的测量不确定度为0.96 μm时,多次评价结果之间的最大差值不超过0.03 μm,具有可靠的理论依据和较稳定的评定结果.文章指出,目前商用三坐标测量机大都不能为特定的测量对象提供测量不确定度报告,使用蒙特卡洛方法有希望改变此现状.     

Validation of a method for composition measurement of a non-standard liquid fuel for Emission Factor evaluation

In this paper the theoretical and experimental aspects are described concerning the validation of a method for the measurement of the percentage composition of a generic liquid fuel, even though specific reference materials for instrumentation calibration are unavailable. This new method could be used for the evaluation of the Emission Factor (EF) of an unknown fuel for emission trading purposes, according to the requirements of both the juridical and technical standards. The validation of the procedure is based on the comparison of different techniques for the measurement of Gross Calorific Value (GCV), Net Calorific Value (NCV) which are quantities useful in EF evaluation; this new combination of actions established a complete and validated methodology for EF evaluation. The experimental results and uncertainty analysis show that this method is suitable for the estimation of the composition measurement and also that of GCV, NCV and EF also for non-standard liquid fuels; a comparable accuracy with respect to the methods for standard fuels has been estimated, making this method suitable for practical applications.     

电容耦合非接触电极及心电信号获取

电极与皮肤间接触所导致的不适感,是穿戴式心电信号测量系统实际应用中的常见问题。设计了一种非接触心电信号测量系统。采用印刷电路板制作的测量电极,借助电容耦合测量位移电流的方式获取心电信号。采用反接二极管提供测量所需的高阻值偏置电阻,结合高输入阻抗仪表放大器,制作了测量电极信号提取电路。测量系统由两个测量电极与一个直接与测量电路地相连的参考电极组成。选择金属铝板、导电纤维和导电橡胶作为参考电极,实验研究了共模干扰抑制性能与参考电极接触阻抗之间的量化关系。将主元分析与奇异谱分析相结合,提出了一种心电信号处理算法。实验结果表明,该系统可在棉质线衣外侧有效获得满意的心电信号。     

Uncertainty budgeting for range calibration

The Guide to the Expression of Uncertainty in Measurement (GUM) established a general procedure to evaluate measurement uncertainty. The Guide covers only the evaluation of a single result or a set of individual results. Modern measuring instruments and procedures operate over a wide range of values. Therefore in practice a calibration procedure is needed that is valid for this range. The procedure should include an evaluation of uncertainty associated with the calibration results and for the subsequent measurements performed with the calibrated instrument. Traditionally regression analysis is used for this purpose. In this paper we will discuss some weaknesses of the regression approach and suggest an alternative. We show that for instruments with a linear response function the regression can be replaced by 2-point calibration. We introduce a limit of the deviation from linearity to address observed deviations from a linear response function of the instrument. To improve an existing instrument with a non-linear response function a combination of the instrument and a correction function can be treated as a virtual linear measuring device and a 2-point calibration can be applied. As an example we use the calibration of a pressure sensor to illustrate the procedure. The approach can be used for instruments and measurement procedures with a linear or non-linear response function.     

寄生式时栅传感器测量不确定度的分析与评定

为了全面分析寄生式时栅误差和不确定度来源,提高寄生式时栅的测量精度,建立符合国际GUM规范检测结果的不确定度评定模型,以84对级的寄生式时栅为研究对象,根据其测量原理分析所测量角度的计算公式,进而将不确定度来源分为插补脉冲个数的误差、插补脉冲信号的量化误差、行波信号的周期误差和环境误差四大类,从理论上建立各不确定度分量之间的理论传递关系,应用现代不确定度理论,推导出合成测量不确定度计算公式。搭建实验平台,利用示波器等仪器的测量结果评定各不确定分量具体数值大小,计算被测角度的合成测量不确定度值。通过与寄生式时栅整圆周的实际测量误差相比较,可以看出利用该评定方法评定的传感器角度测量不确定度与实际误差相符,因此可以用于寄生式时栅传感器的实际评定。     

晶体硅光伏电池的标准测试

为了建立太阳电池的标准测试规范流程,对影响太阳电池标准测试不确定度的各类因素进行了评价和筛选。基于太阳光模拟器、分光感度仪、IV测试仪、标准太阳电池等二级太阳电池标准测试设备与器件,开展了多项标准测试技术的研究。对电池测量过程中太阳电池模拟光源的空间不均匀性、时间不稳定性、仪器测量重复性、扫描方向导致的不确定度、电池反射率和透射率、面积测量不确定度、量子效率等各类影响因素进行了测量,给出了高效晶体硅太阳电池测量不确定度的测量流程,最终导出在现有实验室测量条件下的扩展测量不确定度为±3.94%。基于对常规太阳电池测试数据的比较,对常规电池测量方法进行了改进,将测量不确定度降低了0.19%。最后,提出了双面电池的精确测试流程和方法,为其它双面光电池的标准化测量提供了借鉴。     

面向对象的大尺寸测量不确定度分析

测量结果必须说明不确定度。常规尺寸的解析法和标准比对法难以适用于评价大尺寸测量不确定度,尤其是特定拟合任务结果的不确定度。针对大尺寸测量的特殊性,研究基于蒙特卡罗的评价方法评价大尺寸特定测量对象的不确定度,并用计算机可视化直观表示离散点云。利用离线仿真评价测量不确定度,用于设计最优采样策略。以激光跟踪仪测量大型圆形截面工件分析为例,给出测点对称、均匀分布和半径约束等优化测量思想。最后应用于激光跟踪仪测量隧道构件的实例当中。仿真和实际实验表明,蒙特卡罗评价和离散点云表示法可准确、直观评价大尺寸测量特定测量对象的不确定度,制定的最优采样策略可提高测量精度。     

时空图像测速法的敏感性分析及不确定度评估

时空图像测速方法(STIV)是一种以测速线为分析区域、通过检测合成时空图像的纹理主方向估计一维时均流速测量方法。由于具有空间分辨率高、实时性强的优点,在河流水面流速、流量的实时监测中具有特别的应用潜力。但鉴于现场环境的复杂性和河道水流的变化性,现有研究在敏感性分析及不确定度评估方面尚存在不足,使得方法的实用性受限。对此设计了一种滚动画幅装置来模拟河流水面运动,并在此基础上全面开展了频域STIV方法的定量评估。相比数值模拟和现场比测的方法,该装置能够提供相对真实的测量环境和稳定的运动参数。实验结果表明:测速线长度和示踪条件是影响测量精度的主要敏感因素。通过合理的参数设置可以将方法的不确定度控制在±1%以内,能够满足水文测验的精度要求。     

HGT-1000型容重器容积测量结果的不确定度分析

系统地分析了容重器的容积测量结果标准不确定度的影响因素,并进行了较详细的评定。对容重器关于容积测量结果不确定度的建模、分量计算、合成评定标准不确定度的评定和数据处理方法为同类标准器具测量结果的不确定度评定方案的确定和后续处理提供了参考依据。     

Improvement and uncertainty evaluation of mercury sealed piston prover using laser interferometer

Many NMIs (National Measurement Institute) and calibration laboratories are using a mercury sealed piston prover as calibration system for gas flow meter. But it has problems in deciding measuring volume, traveling time of piston and generating low flow rate below 10 cc/min. In this study, a new structure of a piston prover is designed and its flow measurement uncertainty is evaluated according to ISO/IEC 17025. A laser interferometer, instead of optical sensors used in a typical piston prover, is employed to measure testing time and moving distance of the piston, accurately. A new material of the piston is used to eliminate contaminated particles from the material of the piston body. Uncertainty is calculated by evaluating various uncertainty factors which have influence on gas flow measurement. The expanded uncertainty of the piston prover is 0.11% at the confidence level of 95%. The uncertainty evaluation procedure of this study would be useful in flow measurement uncertainty determination of other types of gas flow measurement systems.     

新型高精度多通道测温系统的研究

提出一种基于NTC热敏电阻的新型高精度多通道测温方案。采用比较测量法,消除了恒流源的不确定性对测量精度的影响;采用高性能模拟开关进行切换,实现了多通道测温。设计了测量电路,通过采用电流倒向技术和恒流源与ADC共用基准源,提高了测温精度。测试结果表明,该测温系统在18℃-22℃范围内,温度测量精度可达±0.01℃,测量分辨率为0.001℃。     

The role of extrinsic factors in industrial task-specific uncertainty

The measurement of large components using portable measuring equipment is important to many industries, including ship-building and aerospace. Portable measuring instruments – such as laser trackers, laser radar, indoor GPS, and other systems – are used to obtain measurement data for process control, assembly alignment, or geometric conformance decisions. Traditional uncertainty estimations often focus on the measuring instrument and its performance as a primary contributor to the overall uncertainty for specific measurands. The research reported here focuses on the uncertainty contributors that are due to extrinsic effects such as part deformation due to gravitational loads and thermal distortion of the workpiece, where the uncertainty contribution from the instrument is considered insignificant in comparison.     

Integration of a laser interferometer and a CMM into a measurement system for measuring internal dimensions

In order to improve the existing comparative procedure for calibrating internal dimensions, we have developed a new measurement set-up for traceable absolute measurements. It consists of a co-ordinate measuring machine (CMM) and a laser interferometer (LI). The LI serves as a traceable measurement system, while the CMM is only used as a guiding system for the measuring probe. Extended research focused on defining probe parameters such as diameter, bending and indentation, as well as probing head repeatability and other error sources. The final goal of the research was to determine uncertainty of measurement under existing laboratory conditions. The main outcomes of the research and final uncertainty of measurement are presented in this article.     

冲击式气扳机噪声测量不确定度研究

该文主要研究冲击式气扳机空转噪声测量结果的不确定度评定,按照标准JB/T8411-2006《冲击式气扳机》和GB/T 5898-2008/ISO 15744:2002《手持式非电类动力工具噪声测量方法工程法(2级)》要求,在半消声室中对冲击式气扳机噪声的A计权声功率级测量结果进行不确定度评定,验证了噪声检测方法的合理性与设备检测精度,同时为冲击式气扳机噪声测量结果不确定度评定提供参考。     

On the effect of the electrode shape and contraction section on the right-angled electromagnetic flowmeter

Flow measurement is of great importance in many industries, such as the chemical industry, energy and urban drainage. Electromagnetic flowmeter is widely used due to its wide range, high response and suitability for multiphase flow detection. To meet the needs of small-caliber and low-flow applications and wider installation scenarios, this paper proposes a new insertion-type right-angled bent electromagnetic flowmeter. The measurement signal of the electromagnetic flowmeter is closely related to its internal fluid flow state, thus computational fluid dynamics (CFD) method is used to optimize the electrode shape and contraction section shape of the electromagnetic flowmeter. Through comparison experiments of flat electrodes and cone electrodes, a better model is obtained. Furthermore, three new models of the contraction section are proposed: the sharp contraction type, the gradual contraction type, and the Widosinski curve contraction section. The Widosinski curve contraction section is easier to stabilize the flow field inside the flowmeter. The experimental data are in good agreement with the results of the large eddy simulation, and the results show that the measurement performance of the cone electrode is better than that of the flat electrode. When measuring small flow rates, the error of the cone electrode is only 5%, much smaller than the error of the flat electrode. The findings of this study provide a new idea for the development and optimization of the measurement performance of the right-angled electromagnetic flowmeters.     

Uncertainty analysis of a laser calibration system for evaluating the positioning accuracy of a numerically controlled axis of coordinate measuring machines and machine tools

This paper presents an uncertainty analysis of a Positional Error Calibrator based on a laser interferometer system. This laser calibration system is capable of evaluating the positioning accuracy of a numerically controlled axis of machine tools and coordinate measuring machines (CMM) under dynamic conditions. In order to assess the measurement uncertainty of this calibrator, an analysis of the uncertainty components that make up the uncertainty budget of this calibrator has been carried out. These uncertainty components can be classified into three categories as follows: (1) uncertainties intrinsic to the laser system; (2) uncertainties due to environmental effects; (3) measuring uncertainties due to the installation. The procedure for evaluating the uncertainty of this calibrator follows GUM (“Guide to the Expression of Uncertainty in Measurement”). This uncertainty analysis was carried out when this calibrator was used to assess the positional errors of the “X” axis of a moving bridge type CMM.     

Water jet velocity uncertainty in laser Doppler velocimetry measurements

The present work deals with the uncertainty evaluation in water jet velocity measurements carried out by means of a laser Doppler dual-incident-beam velocimeter in reference-beam configuration developed at the WJLab (Water Jet Laboratory of Dipartimento di Meccanica of Politecnico di Milano). The applied experimental procedure makes it possible to calculate the measurement uncertainty through the determination of its various components. Once uncertainty is known, the laser Doppler system is suitable for objective and significant velocity evaluations but also for improvements allowed by the knowledge of the most effective uncertainty sources. Such a subject is typically not considered by the specific water jet literature, but is becoming more and more important due to the evolution of water jet machining towards high precision applications.     

分布光度计测量LED路灯光通量的不确定度评定

为了减少检测的误差,提高检测结果精确度,评定LED路灯光通量的不确定度,分析了用分布光度计法测量LED路灯光通量的影响因素,建立数学模型对测量不确定度进行评定,并计算出A类、B类不确定度,最终给出测试结果的不确定度报告。相对扩展不确定度评定结果为4.13%,置信概率P为99%。结果表明,光谱辐射计的测量误差和标准灯的不确定度所产生的测量不确定度影响因素最大。