Machine tool calibration: Geometric test uncertainty depends on machine tool performance

In order to show a sufficient geometric performance, every machine tool has to be calibrated geometrically before it may come into operation. The geometric machine errors have to be identified. They can afterwards be compensated either mechanically or numerically in the machine control.Machine tools are usually calibrated geometrically by performing a sequence of different measurements to identify single errors such as squareness errors between linear axes, straightness errors, positioning errors etc.The uncertainty of such measurements is of course affected by the uncertainty of the measuring device under the given environmental conditions. Methods to describe such influences are widely known and applied.Other effects having an impact on the error parameters to be determined (e.g. squareness errors) are dependent on the performance of the machine tool under test. Neglected geometric errors, hysteresis and thermal drift affect the measurement result. Such effects may be much more important contributors to the overall test uncertainty than the measurement uncertainty of the measuring device.In this paper the problem of error interdependencies leading to a worse test uncertainty is explained. The occurrence of such effects is shown with exemplary measuring results. A method for estimating the overall test uncertainty even for complex measurements is introduced. The dependence of the test uncertainty on the geometric machine performance is explained.     

Metrological evaluation of skin conductance measurements

Electrodermal activity is a frequently measured physiological response in various applications. It is also being increasingly used in clinical applications. Numerous published papers report results of skin conductance measurements in absolute values, but few are concerned with the quality of results. This paper describes a procedure for metrological evaluation of skin conductance measurement. Three commercial devices for measuring skin conductance were calibrated by comparison with a precision digital ohmmeter used as a reference. Combined measurement uncertainty of skin conductance meters was calculated by means of uncertainty of reference instrument and uncertainties due to measurement repeatability, reproducibility, resolution and environmental condition. Additionally, a procedure for evaluation of the effect of electrode displacement and electrode gel was shown. A model of finger skin conductance profile was build. Measurement uncertainty analysis showed that contributions due to resolution and sensitivity of the measuring device, usually obtained from specifications, are negligible when compared to uncertainty of measuring method. Our results indicate that measurement uncertainty does not meet target uncertainty requirements for certain applications.     

Uncertainty study of fiscal orifice meter used in a gas Algerian field

Uncertainty variation of a fiscal orifice measurement system used in an Algerian natural gas exportation station is studied using data from a natural gas production field known as Gas Tin Fouye Tabankort (GTFT) located in the south-east of Algeria. The expected results are uncertainty calculus over a range of temperature and pressure variation and to the customs authorities’ allocation.In fact, each quantity of measured fluid flow has certain uncertainty and then the fiscal measurement station is very important for gas exportation, which means the income. Therefore, the pursuit of flow metering device uncertainty and its influence on the measured quantities in the transmission networks is very important.For that, the uncertainty caused by flowmeter in the measurement station causing economical revenue fluctuations is studied. The work was done to justify why there is a production decrease of hydrocarbons without identifying reasons during summer. The difference between the mass flow rate quantity produced and the transmitted value was important that is why our work is done to clarify exactly from where the problem can come.The measurements setting with two operating conditions (gas temperature and pressure) show that the uncertainty is dominated by seasonal temperatures and pressures variations which induce fluctuation in gas and pipe temperatures and influence the metrological performance of the transmitters. Indeed, the metrological measurement chain performance is affected also by these two operating conditions.The present work is done according to the ONML (National Legal Metrological Office) instructions regarding differences between the measured and the seller values represented by the mass flow rate.In natural gas transmission network, the important problem in the management and control of the network is represented by the unaccounted for gas, a quantity of measuring error which is to be considered in the equation of network balancing. One of the unaccounted for gas sources are the environmental conditions and systematic measurement errors.In this work, the calculation of the combined uncertainty of the mass flow rate measured by an Orifice fiscal gas metering plant is done. From the results founded, the authors confirm that the uncertainty in the measurement system causing by the climatic conditions generates unaccounted for gas.     

Ancillary device for flow rate measurement using dye tracer technique

Dye tracer technique is a successful tool for measuring liquid flow in closed conduits and open channels. The technique is based on the continuous injection of a tracer into the flow and on the measurement of the dilution ratio. As one of the requirements, the tracer injection rate must be known and well controlled. A device was designed to obtain this control. Such device implements a volumetric flow measurement technique and provides accurate digital display readout. Experimental results indicate that the apparatus can be used to measure the injection flow rate in a range from 235 to 2000 ml min⁻¹ with a relative error smaller than 1.5% of the reading. Even with these low injection flow, the dilution method can be applied to determine the much higher flow rates typically found in domestic or industrial outfalls as well as in artificial or natural channels. This paper also presents an application of the dilution method to flow rate measurement of an industrial outfall and the uncertainty analysis associated with the obtained values. The results indicate that the main errors of discharge estimation can arise from non-steady state flow conditions, incomplete tracer mixing, uncertainty of tracer concentration and tracer injection rate measurements.     

基于指数法评估激光量热仪吸收测量不确定度

为了掌握熔石英样品在紫外波段的吸收特性,研究了精确评估激光量热仪测量不确定度的方法。介绍了激光量热仪的吸收测量原理,选用指数法对吸收测量数据进行了拟合;通过分析各吸收率测量结果的影响分量,建立了测量不确定度评估模型;对各输入量的估计值以及估计值的标准不确定度逐一进行计算,并对影响吸收率测量结果的拟合计算参数A、γ进行了修正。考虑背景温度漂移对被测样品温度测量的影响,利用Matlab编程分析了线性、非线性温度漂移对吸收计算结果的影响,获得其相对标准不确定度及相对扩展不确定度分别为2.6%和5.2%。最后,更换熔石英基底并进行多次吸收测量,计算了吸收率10次测量结果平均值的相对标准不确定度为2.3%,相对扩展不确定度为4.6%,与评估结果基本相同。     

基于激光位移传感器的面角度测量技术研究

针对面角度现场测试需求,利用激光位移传感器的漫反射测量特性,搭建了面角度非接触测量装置,提出了一种结合三坐标测量机和位置敏感探测器对激光位移传感器进行空间坐标化标定的方法,从而构建出精确的面角度测量模型;采用蒙特卡洛法对面角度非接触测量装置的不确定度进行评定,在±25°测量范围内其结果为U=0.044°~0.046°(k=2);通过性能验证试验、重复性试验和稳定性试验对装置的性能指标进行考核,在±25°测量范围内其绝对测量示值误差不超过0.036°,重复性不超过0.004°,稳定性不超过0.021°;实验结果表明该基于激光位移传感器的面角度非接触测量装置准确可靠,具备开展面角度现场测试应用的前景。     

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.     

An experimental method for assessing the contribution of the production process variations to the task-specific uncertainty of coordinate measurements

The present paper deals with an important source of variation often neglected in uncertainty estimates of coordinate measurements: the between-sample variation. This source of variation becomes relevant to the measurement uncertainty when significant interactions occur between variations in the production process and specific limitations in the measurement process. This paper discusses some particular types of interaction which usually lead to between-sample variation in coordinate measurements. For analysing the statistical significance of the between-sample variation and for assessing its contribution to the measurement uncertainty, an experimental method using multiple calibrated workpieces is described. A case study involving the uncertainty estimation of a roundness measurement process using a coordinate measuring machine is presented. The results show the importance of considering the between-sample variation in uncertainty evaluations of coordinate measurements.     

交变光场时空耦合型位移测量系统的研制

针对现有光栅精密刻划加工难度大制约测量精度的问题,设计了一种以交变光场为测量媒介的时空耦合线性位移测量系统。该测量系统利用四路正交的交变光场与四组正交的正弦透光面调制耦合形成电行波信号实现高精度位移测量。在对测量系统测量原理分析的基础上,建立了该系统的理论模型和误差模型,通过仿真详细分析了该系统在时间相位不正交、空间相位不正交以及结构安装不平行时的误差规律。开展实验验证了一次、二次和四次谐波的产生原因,根据误差来源改进了测量装置的结构,优化了相应的参数。实验结果表明:在180mm测量范围内,用栅距0.6mm的测量系统实现了±0.4μm的测量精度。该测量系统规避了现有光栅精密刻划的问题,结构简单、安装方便,为光学位移测量提供了新思路。     

一种永置式石油生产地面多井组单井轮巡 三相流监测装置及应用研究

为了解决传统石油开发集中计量方式难以获取单口油井油气水三相流相关参数的难题,采用流体体积和有限元分析等方法在建立该测量装置的数值仿真模型基础上对其结构参数、气液分离效果等进行了深入研究与优化,从而确定了该监测装置的最优结构参数,并研制了可以在现有集中计量环境中长期、稳定与可靠使用的一种永置式石油生产多井组单井轮巡三相流监测装置。另外,还在搭建的永置式石油生产地面多井组单井轮巡三相流多参数监测平台上开展了实验研究,实验结果表明,所研制的装置在气、液相流量5～70 m³/d,液相持水率50%～90%等混合流体下持水率、气量测量误差均小于10%,流量测量误差小于4%。仿真和实验均证明了永置式监测装置具有良好的多分相测量性能。     

多线砂轮复合自动修磨装置的设计与精度检验

多线砂轮复合自动修磨装置采用CNC数控系统,利用两个独立金刚石滚轮休整器,实现单支和多支砂轮的高精度修磨,极大地降低了人工操作带来的加工误差,提高了产品加工精度和效率。通过表面粗糙度检测数据可知,具有多线砂轮复合自动修磨装置的数控丝锥螺纹磨床完全符合加工精度要求。同时,采用多元回归方程建立基于砂轮修整参数的表面粗糙度预测模型,并设计单因素试验,得到砂轮修整参数与表面粗糙度之间的关系。由显著性分析结果得出,径向修整进给量是影响表面粗糙度的主要因素。     

Evaluating a task-specific measurement uncertainty for gear measuring instruments via Monte Carlo simulation

Evaluating the measurement uncertainty for gears with analytical or experimental methods is usually very time- and cost-consuming. In this paper we therefore present a Monte Carlo based method for evaluating the measurement uncertainty of gear measurements on gear measuring instruments, the VCMM-Gear, which is based on the method of the VCMM for coordinate measuring machines. Necessary extensions of the mathematical model of the measurement process in order to consider the significant uncertainty influences from rotary tables, workpiece clamping and scanning are described. Additionally the statistical reliability of the evaluated measurement uncertainty and the consideration of systematic error contributions to the measurement uncertainty are discussed. Finally the results of some first verification measurements are presented, giving a reliable impression of the capability and suitability of the VCMM-Gear.     

一种石油生产永置式地面井口持水率动静态测量装置研究

为满足采油地面井口多相流持水率测量的实际要求,本文结合电导动态测量与筒状电容静态测量技术,研制了一种永置式石油生产地面井口多相流持水率动静态测量装置(PDSWHMD＿SM)。具体地,文中采用有限元方法(FEM)构建了电导-电容一体式传感器(CCIS)数值模型,在此基础上对CCIS管道内流体处于流动及静止状态下分相介质的分布特性、CCIS结构参数、CCIS电学分布特性、不同多相流工况下的响应特性等进行了深入研究,最终确定了CCIS最优结构参数：H_e=90 mm、ID=30 mm、Ih_e=3 mm、H_c=375 mm、IR₁=26 mm、T_c=1 mm、H_m=56 mm,证明了其测量误差在5%以内。另外,本文以总流量5～70 m³/d,持水率50%～90%等多相流工况为例进行了实验研究,实验结果表明：研制的装置PDSWHMD＿SM持水率测量误差同样在5%以内。仿真和实验均证明了PDSWHMD＿SM具有良好的持水率测量性能。     

Volumetric wear assessment of retrieved metal-on-metal hip prostheses and the impact of measurement uncertainty

In hip replacement the use of hard bearing materials, which have been shown to have lower wear rates than traditional metal-UHMWPE couples, has been encouraged in an effort to extend component life-in-service. With a view to further extending this period of joint activity metal-on-metal hip resurfacings have been developed which allow for implantation into younger and more active patients. However, these bearings have recently been the subject of a MHRA device alert due to unexplained hip pain and reported soft tissue reactions and indeed are under investigation having been shown to exhibit high failure rates. This has highlighted the need for a traceable metrological approach to the quantification and characterization of in vivo wear as currently there is no standard dedicated to the measurement of such wear.This study is the first to develop a comprehensive method for measuring the wear geometry of retrieved bearings whilst also assessing and quantifying both the magnitude and effect of the three-dimensional measurement uncertainty on the measurement process as a whole.This study shows that the magnitude of the expanded measurement uncertainty is an important, and until now overlooked, factor and that a statement of uncertainty is vital in measuring retrieved components as a means of comparison between studies and as a measure of confidence in measurement data.Based on the results of this study, it is recommended that care be taken when performing wear measurements on retrieved bearings. Factors such as point pitch and scan line separation can have a great effect on the likely uncertainty of the obtained measurement result and indeed the uncertainty of the measurement can be of the same order as the wear being measured.     

Experimental evaluation of software estimates of task specific measurement uncertainty for CMMs

Estimation of the uncertainty of Coordinate Measuring Machine (CMM) measurements for real, imperfect parts is a very complex undertaking. Not only are there many contributors to the uncertainty that may interact in a non-linear fashion, making it difficult to mathematically determine an uncertainty estimate, but it is also difficult to predict the long-term variation of these parameters. Our work seeks to provide experimental validation of the uncertainties predicted by two different commercial software packages that purport to predict the task-specific measuring uncertainty of CMM measurement results. The validation procedure uses repeated measurements of calibrated artifacts to experimentally determine measurement uncertainties. These measurements can then be simulated in the commercial software packages. The comparison will allow the software to be tested to see if it appropriately accounts for the influences of the operator, environment, and part placement. This paper reports the results of actual part measurements and the predicted uncertainty provided by commercial simulation packages. Differences between experimental and simulated uncertainties are highlighted, and their causes examined.     

The effect of calibration equations on the uncertainty of UV–Vis spectrophotometric measurements

The effect of adequateness of the calibration equations on measurement uncertainty was not mentioned by EURACHEM. In this work, we investigate the sources of uncertainty when measuring glucose concentration with a UV–Vis spectrophotometer. The effect of two calibration equations on the uncertainty was compared. The sources of the glucose concentration measurement uncertainty include purity, volume of flasks, mass and the calibration equations. The effects of two calibration equations, linear and polynomial equation, on the uncertainty source were evaluated using the inverse calibration equation. The results indicated that the uncertainty components from purity were the smallest. The volumes of the volumetric flasks had only modest effect on the uncertainty, while the mass was an important source of the uncertainty. The contribution of the calibration equation to the total relative measurement uncertainty was 59.39% for the linear equation and 30.34% for the polynomial equation. With the selection of the adequate equation, the uncertainty source of the calibration equation could be reduced significantly.     

Bayesian degradation assessment of CNC machine tools considering unit non-homogeneity

Field reliability assessment and prediction is critical for the estimation, operation and health management of CNC machine tools. The classical methods for field reliability of CNC Machine Tools assessment and prediction are challenged with the issues of expensive reliability tests, small sample size and unit non-homogeneity. In order to solve these problems, this paper introduces a degradation analysis based reliability assessment method for CNC machine tools under performance testing. Since the degradation is an independent increment process, the gamma process is employed to characterize the degradation process of CNC machine tools. The random effects are introduced to accommodate performance degradation model with unit non-homogeneity. The parameters of model are updated by Bayesian estimation approach. As a case study, the CNC Machine Tools is studied to illustrate the approach. And the proposed method is demonstrated precise for practical use.     

Uncertainty analysis for measurement of measurand

For measuring the true value of a measurand, vague statistical concept of measurand results in inefficient uncertainty analysis of measurement. The vagueness is caused by the fact that true value of the measurand is an unknown parameter such as population mean or median and the measurement of this true value is a random variable. Generally a parameter may be estimated remarkably more efficiently than the prediction of the random variable. The classical uncertainty analysis in the literature has been developed based on the structure that a measurand is a random variable. This misspecification of statistical concept costs serious price of sacrificing efficiency in terms of length of the uncertainty interval. The purpose of present study is to formally formulate a statistical model for the true value of measurand and provide an uncertainty analysis for the measurement of this true value.     

悬臂式测量机测量不确定度分析与验证

针对在某五轴数控机床加工现场有限空间限制下,复杂结构工件的原位在线测量问题,设计了一种悬臂式坐标测量机.根据不确定度评定准则,分析了影响测量机测量不确定度的因素,提出了从理论上估计所设计结构形式测量机测量不确定度的方法,并从机构运动误差、机构变形以及温度等方面对测量机的测量不确定度进行了估计.实验结果显示,测量机的测量误差均小于测量指标所要求的测量不确定度.     

Modification of the equation for mass flow rate (mass) measurement of liquid with account of dynamic influencing factors

The paper introduces theoretical foundations for the method of transferring units of mass and volume of liquid in the flow, mass and volumetric liquid flow rates using the indirect measurement method. The equation for measuring the mass flow rate (mass) was modified in terms of assessing the dynamic influencing factors caused by transient processes: liquid flow rate fluctuations and turbulent pulsations, unevenness of the liquid velocity profile in the nozzle exit of the diverter. The modified equation was derived from the continuity equation in physical and mathematical modeling of hydrodynamic processes of liquid flow in the nozzle exit of the diverter using mathematical statistics methods. The main uncertainty sources of calibration units with weighing devices were identified. The results of the approbation of the method of transferring units of mass and volume of liquid in the flow, mass and volumetric liquid flow rates were obtained on calibration units with weighing devices in a wide range of geometric and operating parameters. A comparison of the expanded measurement uncertainty of the calibration unit with weighing devices when transferring units of mass and volume of liquid in the flow, mass and volumetric liquid flow rates, determined using the method of indirect measurements and comparison testing with a transfer standard, was performed.