Contribution To Measurement Uncertainty Research Articles

Validation of a laboratory method for the traceability of a rainfall weighing gauge

This study aims to develop a laboratory method for the traceability of a rainfall weighing gauge, including an evaluation of the measurement uncertainty. The adopted procedure is similar to the one used for the non-automatic weighing instruments. A static approach is followed to achieve the calibration deviation of the precipitation scale. The method used to evaluate the measurement uncertainty is based on a nonlinear mathematical model. The Monte Carlo method is used to calculate uncertainties and validate estimates following the conventional Guide to the Expression of Uncertainty in Measurement (GUM) approach. Measurement uncertainty contributions of input quantities to the mathematical model used to calculate rainfall also require specific calibration procedures. Results show the accuracy level achievable with rainfall weighing gauges commonly used as a reference for meteorological monitoring networks and data modelling.

International interlaboratory comparison of Raman spectroscopic analysis of CVD-grown graphene

There is a pressing need for reliable, reproducible and accurate measurements of graphene’s properties, through international standards, to facilitate industrial growth. However, trustworthy and verified standards require rigorous metrological studies, determining, quantifying and reducing the sources of measurement uncertainty. Towards this effort, we report the procedure and the results of an international interlaboratory comparison (ILC) study, conducted under Versailles Project on Advanced Materials and Standards. This ILC focusses on the comparability of Raman spectroscopy measurements of chemical vapour deposition (CVD) grown graphene using the same measurement protocol across different institutes and laboratories. With data gathered from 17 participants across academia, industry (including instrument manufacturers) and national metrology institutes, this study investigates the measurement uncertainty contributions from both Raman spectroscopy measurements and data analysis procedures, as well as provides solutions for improved accuracy and precision. While many of the reported Raman metrics were relatively consistent, significant and meaningful outliers occurred due to differences in the instruments and data analysis. These variations resulted in inconsistent reports of peak intensity ratios, peak widths and the coverage of graphene. Due to a lack of relative intensity calibration, the relative difference reported in the 2D- and G peak intensity ratios () was up to 200%. It was also shown that the standard deviation for values reported by different software packages, was 15× larger for Lorentzian fit functions than for pseudo-Voigt functions. This study has shown that by adopting a relative intensity calibration and consistent peak fitting and data analysis methodologies, these large, and previously unquantified, variations can be significantly reduced, allowing more reproducible and comparable measurements for the graphene community, supporting fundamental research through to the growing graphene industry worldwide. This project and its findings directly underpin the development of the ISO/IEC standard ‘DTS 21356-2—Nanotechnologies—Structural Characterisation of CVD-grown Graphene’.

Filtering Biomechanical Signals in Movement Analysis.

Biomechanical analysis of human movement is based on dynamic measurements of reference points on the subject’s body and orientation measurements of body segments. Collected data include positions’ measurement, in a three-dimensional space. Signal enhancement by proper filtering is often recommended. Velocity and acceleration signal must be obtained from position/angular measurement records, needing numerical processing effort. In this paper, we propose a comparative filtering method study procedure, based on measurement uncertainty related parameters’ set, based upon simulated and experimental signals. The final aim is to propose guidelines to optimize dynamic biomechanical measurement, considering the measurement uncertainty contribution due to the processing method. Performance of the considered methods are examined and compared with an analytical signal, considering both stationary and transient conditions. Finally, four experimental test cases are evaluated at best filtering conditions for measurement uncertainty contributions.

Uncertainty in Analytical Measurements: Approaches, Evaluation Methods and Their Comparison Based on a Case Study of Arsenic Determination in Rice

All measurements have uncertainty and they are not absolute. Therefore, identification, determination and evaluation of critical influencing factors based on recent approaches are important and necessary. Laboratories shall identify and evaluate all components and contributions to measurement uncertainty. In this article, two different approaches for evaluation of measurement uncertainty of arsenic in rice are studied and compared. These different approaches are GUM approach and Monte Carlo approach. The results clarified, evaluated uncertainty for the measurand was the same in the GUM and MCA, statistically and it is clarified that evaluated uncertainty by these approaches have no significant difference.

An Uncertainty-Driven and Observability-Based State Estimator for Nonholonomic Robots

The problem addressed in this article is the localization of a mobile robot using a combination of onboard sensors and ultrawideband (UWB) beacons. By using a discrete-time formulation of the system's kinematics, we identify the geometric conditions that make the system globally observable and cast the state estimation problem into the framework of least-squares optimization. The observability filter thus obtained is remarkably different from classic Bayesian filters, such as the Kalman Filter, since it does not need a priori stochastic models of process and measurement uncertainty contributions and thus proves to have better performance than the Kalman filters if such contributions are partly unknown or differ from the expected values. The second important outcome of this work is the analytical study of uncertainty propagation. The effectiveness of the designed filter, the validity of the theoretical analysis of estimation uncertainties, and the comparisons with a state-of-the-art extended Kalman filter (EKF) are corroborated by extensive simulations and validated experimentally.

Disregarded Measurement Uncertainty Contributions and Their Magnitude in Measuring Plasma Glucose.

Each measurement is subject to measurement uncertainty (MU). Consequently, each measurement of plasma glucose concentration used for diagnosis and monitoring of diabetes mellitus (DM) is affected. Although concepts and methods of MU are well established in many fields of science and technology, they are presently only incompletely implemented by medical laboratories, neglecting MU of target values of internal quality control (IQC) materials. An empirical and practical approach for the estimation of MU based on the analysis of routine IQC using control samples with assigned target values is presented. Its feasibility is demonstrated exemplarily by analyzing IQC data from one year obtained for glucose employing the hexokinase method with IQC of two different concentrations. Combined relative extended (k = 2) MU comprising bias, coefficient of variation (CV), and MU of the target values assigned to control materials were about 9% with a lower (~ 56 mg/dL; ~3.1 mmol/L) and 8% with a higher (~ 346 mg/dL; ~19.2 mmol/L) concentration sample, analyzing IQC of one year from three different devices. Estimation of MU in this study is quite reliable due to the large number of IQC data from one year. The MU of the target values of the commercial control material in this study was considerably larger than other MU contributions, ie, standard deviation and bias. In the future, the contribution of MU of commercial IQC should be addressed more carefully and technologies to measure glucose should be geared toward smaller MU possible, as needed, especially for glucose concentration measurements in diagnosis and management of DM.

Understanding the contribution of operator measurement variability within Flow Cytometry data analysis for Quality Control of Cell and Gene Therapy manufacturing

Flow Cytometry is a measurement technique used in Quality Control and in-process measurements of biomanufactured Cell and Gene Therapy products. However, it contains a number of sources of measurement variation at; sample preparation, instrument setup, analysis, and post-analytical data analysis stages. The latter sees variation introduced from operator subjectivity, which is investigated here to understand what effects the interpretation of diagrammatical protocols have on inter-operator analysis.36 operators from different sites were given a series of histograms to analyse, gating a shifting peak. This was repeated with diagrammatical protocols to apply gates which reduced inter-operator variation by up to 92%. Various control limits include and exclude different results and when adjusted with a log transform differences in outlier discrimination have been found. This research supports the use of Flow Cytometry diagrammatical protocols to reduce the contribution of inter-operator variation and measurement uncertainty associated within Cell and Gene Therapy manufacturing scenarios.

Laser light source limited uncertainty of speckle-based roughness measurements.

Surface microtopography measurement (e.g., form, waviness, roughness) is a precondition to assess the surface quality of technical components with regard to their applications. Laser speckle-based roughness measurement is an optical scattered light measuring technique that provides field of view dimensions of some square millimeters and measuring frequencies in the kilohertz domain enabling in-process roughness characterization of even moving part surfaces. However, camera exposure times of microseconds or less and a high detector pixel density mean less light energy per pixel. This affects the minimal achievable measurement uncertainty, which has not been clarified yet for almost plain sample shapes. For this reason, the measurement uncertainty limit of the surface roughness parameter Sa due to fundamental, inevitable noise sources such as laser shot noise and detector noise is analytically estimated and compared to experimental data. The results show a mainly shot-noise-limited measurement uncertainty contribution of less than 0.033 nm. In addition, a significant influence of laser beam profile variations on the achievable roughness measurement uncertainty is identified for the current experimental setup, which is generally below 0.3 nm and can be improved in future setups. The already achieved low measurement uncertainty offers ideal preconditions for in-process roughness measurements on samples with a similar surface structure in industrial environments.

Setup for the dynamic calibration of bridge amplifiers from DC up to 10 kHz

<p class="Abstract">Measurements of mechanical quantities are often carried out with transducers with a bridge output. The output signals are conditioned using bridge amplifiers. If dynamically changing quantities are going to be measured traceably, the bridge amplifier must be calibrated dynamically.</p>This paper describes a dynamic bridge amplifier calibration setup based on the new PTB dynamic bridge standard. The calibration is carried out by the synchronous sampling of the bridge amplifier output voltage and a reference signal provided by the calibrated dynamic bridge standard. The dynamic bridge standard enables calibrations in a frequency range from DC (static calibration) up to 10 kHz. An overview of the different measurement uncertainty contributions is given, and the first measurement results show good agreement with a previously established measurement setup.

Base-Case Model for Measurement Uncertainty in a Reverberation Chamber Including Frequency Stirring

We address the uncertainty of reverberation chamber (RC) measurements in presence of both mechanical and frequency stirring (FS). A base-case model is derived for reverberation fields affected by the measurement uncertainty due to the lack of a perfect statistical uniformity of fields in a RC. It is found that the measurement uncertainty associated with the FS depends on both the total uncorrelated samples and the local insertion loss (IL). The local IL depends on the frequency stirring bandwidth (FSB). The model allows us for obtaining separate measurement uncertainty contributions. Measurements support the achieved uncertainty model. In particular, results show that the dependence on the IL is normally rather weak also when very wide FSBs are used.

Calibration of automatic catchweighing instruments in dynamic mode of operation

The article presents a method developed for calibration of automatic catchweighing instruments, which operates in the dynamic mode. The specifics of the calibration of the automatic catchweighing instruments in the dynamic mode of operation are highlighted and basic information about the measurement method, error model and measurement uncertainty contributions are given. The use of harmonized and validated methods will enable a traceable calibration of the catchweighing instrument in the dynamic mode of operation.

Production of trace elements in coastal sea water certified reference material NMIA MX014.

A certified reference material (CRM) for trace elements in acidified sea water, NMIA MX014, has been produced by the National Measurement Institute Australia (NMIA). The CRM consists of natural coastal sea water with 12 elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se and V) fortified to levels relevant to environmental regulatory testing in Australia ranging from 0.4 to 22μg/kg. Certified values for these 12 elements were assigned using reference methods developed at NMIA, using either isotope dilution or standard addition with ICP-MS measurement. Specialised sample preparation (coprecipitation) and ICP-MS optimisation (online dilution, collision/reaction chemistry, high mass resolution) were used to negate the effect of the high level of dissolved solids. Multiple confirmatory experiments were performed in order to verify that ICP-MS spectral interferences were eliminated and to estimate the measurement uncertainty contribution from method precision and method trueness. Extensive homogeneity and stability testing was performed and the measurement uncertainty of certified values includes contributions from between-bottle homogeneity, short-term stability, medium-term stability and long-term stability. Special attention was paid to the stability of Hg due to well-known preservation problems. Acidified sea water matrix was satisfactory for stabilising Hg at 0.4μg/kg for at least 4years. Relative expanded uncertainties (k = 2) for the 12 certified values were between 1 and 11%. NMIA MX014 is intended for use as a reference material for analytical method validation and quality control for quantification of trace elements in saline water and other similar sample types.

Proficiency testing of wastewater sampling: What did we learn?

The proficiency testing of wastewater sampling is organized by the Laboratory for Environmental Sciences and Engineering at the National Institute of Chemistry, Slovenia (NIC). Preliminary tests started in 2010 at two candidate sites to choose for a trial the most convenient one. In 2012, we organized the first collaborative field trial on wastewater sampling and such trials continued in 2013 and 2014. Between 16 and 20 sampling teams were selected from those that (1) participate in the national wastewater monitoring program and (2) perform analytical activities in laboratories. The participants used a 6-h time proportional sampling approach. They used sampling equipment with different principles of sample collection which take a series of discrete samples at fixed time intervals. Subsequent analyses involved both field and laboratory measurements. The participants, with only one exception, exhibited required technical skills for measuring field parameters (temperature and pH value). All samples taken were also analyzed at NIC. The variability between reported values of participants in the trials, expressed as CV, was found to be 8.5 %, 11.1 % and 9.5 % for chemical oxygen demand. Of all parameters, the largest variability was found for total organic carbon concentration amounting to 23.7 % and 35.7 %. Particular attention was given to separate the measurement uncertainty contributions arising from sampling and chemical analyses.

Estimate of the inertial torque in rotating shafts - a metrological approach to signal processing

This article studies the setting of the method to model the inertial torque in the acceleration regimes of a rotating axis system. The angular speed measurement to obtain an estimated acceleration and the moment of inertia axis of the variables are used to calculate the inertial torque. The evaluated dynamic regimes are acceleration ramps between levels (intervals) of angular speed, which are implemented using variable speed drives that are coupled to AC motors. The article focuses on assessing the main parameters in signal processing, such as the derivation of the speed signal, application of digital filters and data- smoothing methods, and their effects on the main features of interest in the generated torque curves, such as the peak torque amplitude, ascending and downward slopes, stability and repeatability. A qualitative approach was performed to identify the measurement uncertainty contributions. Thus, the validation methodology of the processing methods and the proposed physical principle are feasible.

Uncertainty restrictions of transfer click-torque wrenches

For different types of click-torque wrenches, measurement uncertainty contributions of typical calibration conditions were investigated. Procedures which differ from those given in ISO 6789 were suggested for transfer measurements at calibration facilities for click-torque wrenches in order to improve their reproducibility. Examinations were carried out for influences like lever length, rise time, temperature and humidity.

Bismuth Film Anodic Stripping Voltammetry for the Determination of Lead in Kerosene: A Metrological Study

AbstractAnodic stripping voltammetry and bismuth film electrode (BFE) were used to develop a method for the determination of lead in a complex sample (kerosene) prepared as a stable microemulsion. The method allowed the sensitive determination of lead with a quantification limit, in the sample, of 1.4×10−7 mol L−1 employing a 240 s accumulation time. Fortified sample analysis enabled the average analyte recovery around 99% which was statistically similar to the one achieved using a reference method (atomic absorption spectrometry). A detailed metrological evaluation was made including the calculation of the uncertainty associated to the voltammetric measurement indicating that repeatability (variations in the formation of different films and in the behavior of the analyte in the prepared microemulsions) is the main contribution of measurement uncertainty.

Investigating out-of-specification test results of chemical composition based on metrological concepts

A metrological background for investigating out-of-specification (OOS) test results of chemical composition is discussed. When an OOS test result is identified, it is important to determine its root causes and to avoid reoccurrence of such results. An investigation of the root causes based on metrological concepts would be beneficial. It includes (1) assessment of validation data of the measurement process, (2) evaluation of the measurement uncertainty contributions, and (3) assessment of metrological traceability chains critical for measurement parameters and environmental conditions influencing the test results. The questions, how can the validation data be applied for this investigation, and how can measurement uncertainty contributions and/or metrological traceability chains change a probability of OOS test results, are analyzed.

Standardisation of data from real-time quantitative PCR methods – evaluation of outliers and comparison of calibration curves

BackgroundAs real-time quantitative PCR (RT-QPCR) is increasingly being relied upon for the enforcement of legislation and regulations dependent upon the trace detection of DNA, focus has increased on the quality issues related to the technique. Recent work has focused on the identification of factors that contribute towards significant measurement uncertainty in the real-time quantitative PCR technique, through investigation of the experimental design and operating procedure. However, measurement uncertainty contributions made during the data analysis procedure have not been studied in detail. This paper presents two additional approaches for standardising data analysis through the novel application of statistical methods to RT-QPCR, in order to minimise potential uncertainty in results.ResultsExperimental data was generated in order to develop the two aspects of data handling and analysis that can contribute towards measurement uncertainty in results. This paper describes preliminary aspects in standardising data through the application of statistical techniques to the area of RT-QPCR. The first aspect concerns the statistical identification and subsequent handling of outlying values arising from RT-QPCR, and discusses the implementation of ISO guidelines in relation to acceptance or rejection of outlying values. The second aspect relates to the development of an objective statistical test for the comparison of calibration curves.ConclusionThe preliminary statistical tests for outlying values and comparisons between calibration curves can be applied using basic functions found in standard spreadsheet software. These two aspects emphasise that the comparability of results arising from RT-QPCR needs further refinement and development at the data-handling phase. The implementation of standardised approaches to data analysis should further help minimise variation due to subjective judgements. The aspects described in this paper will help contribute towards the development of a set of best practice guidelines regarding standardising handling and interpretation of data arising from RT-QPCR experiments.

Influence of polycrystalline silicon as electrical shield on reliability and stability of piezoresistive sensors

In this paper, the influence of polycrystalline silicon as a protective field shield on the reliability and stability of piezoresistive silicon sensors is investigated. For this purpose, the behaviour of piezoresistive sensors with and without polycrystalline silicon shield is observed under changes of environmental condition, such as relative humidity and temperature. The obtained sensor-offset change under humidity stimulation is smaller than that observed by temperature excitation. The samples with polycrystalline silicon shield exhibit a lower humidity and temperature coefficients as compared to the samples without this shield. The values of uncertainties in measurement are evaluated according to the ISO “Guide to the Expression of Uncertainties in Measurement” (GUM). The uncertainty contribution caused by internal disturbing of the sensors can be neglected. Comparing two types of piezoresistive sensors investigated, the samples with polycrystalline silicon shield produce a considerably reduction of all measurement uncertainty contributions. The results show that an additional polycrystalline silicon shield between two insulating layers connected to the supply voltage, which provides a determined potential distribution inside the passivation layer stack, improves the device reliability and the accuracy of measurement.

Isotope dilution with ICP-MS—simplified uncertainty estimation using a robust procedure based on a higher target value of uncertainty

The objective of this paper is to bring forward a simple tool for uncertainty estimation in ID-MS (isotope dilution mass spectrometry) using a robust measurement procedure. This basic form does not allow the ultimate performance to be obtained regarding uncertainty, but will still produce results that have reliable uncertainties which can be more difficult to evaluate with other calibration strategies (such as external calibration, internal standard, standard addition). The paper describes an a priori simulation process of the uncertainty that will be achieved using a validated procedure for an analyte in a matrix. For this, a valid model equation is built, where the different influence quantities are allowed to vary within a wide, robust tolerance window. For these influence quantities an approximate measurement uncertainty contribution relative to the measurand (i.e., quantity to be measured) is calculated and only those that significantly affect the measurement uncertainty (expanded, k = 2, relative) at the target level are taken into account. A target value of uncertainty of 2% is used here as an example since it is deemed to be achievable by experienced laboratories that are not primarily concerned with measuring at a lower uncertainty level. The approach is demonstrated in the determination of nickel in low-alloy steel and copper in fresh water. However, this basic approach using target uncertainty and wide tolerance windows is general and can easily be adapted for other applications.