Major Contribution To Uncertainty Research Articles

Analysis of Major Benchmark Uncertainties for Fast Metal Assemblies in the ICSBEP Handbook

The International Handbook of Evaluated Criticality Safety Benchmark Experiments includes thousands of criticality safety benchmark configurations that have been collected since the early 1990s. Their quality and uncertainty analysis have greatly expanded over the years, as computer codes have also expanded and accelerated. Along with the increase in effort required for benchmarks today, the cost of performing experiments has also gone up. This paper evaluates plutonium fast metal and highly enriched uranium fast metal experiments for their major uncertainty contributions and identifies where to focus efforts in future experiment design.

Uncertainty analysis of the air velocity standard based on LDA and wind tunnel

This paper deals with uncertainty analysis an air velocity standard consisting of a wind tunnel and a laser Doppler anemometer (LDA) measuring system. The analysis is performed for air velocities between 0.3 m/s and 40 m/s, and a calibration procedure with the readings from the LDA and the device under test (DUT) taken simultaneously. The calculation of the reference air velocity includes a systematic correction of the velocity measured by the LDA to the position of the DUT. The study provides a complete and detailed methodology for estimating all major uncertainty contributions attributed to the LDA standard, position correction including velocity field uniformity, stability and uncorrected blockage effect. The contribution of the blockage effect was estimated for three different anemometers. For the Pitot static tube, the contribution of position correction predominates; however, for the other two larger anemometers, the contribution of the uncorrected blockage effect predominates at higher velocities.

UNCERTAINTY EVALUATION ON THE CALIBRATION OF DC & AC CURRENT GENERATED BY COMBINATION OF AC/DC CURRENT SOURCE AND CURRENT COIL USING SUBSTITUTION METHOD

Development of measurement method for calibrating current coil continues to be made to maintain measurement traceability for high DC and AC current scope which are generally used for clamp meter calibration services in Laboratory of National Measurement Standard for Electricity and Time (Lab NMS ET). This paper describes the uncertainty evaluation method developed in Lab NMS ET for calibrating high DC and AC current from 50 A up to 990 A generated by a single system consisted of a DC/AC current source and a 50-turn current coil. The uncertainty analysis was carried out based on the calibration principle using the substitution method combined with the principle of multiplication between output current of a DC/AC current source and a 50-turn current coil. It resulted in six source of uncertainty component derived from the current source, the current coil, and a meter. Their sensitivity coefficients were calculated as well to adapt the unit of each uncertainty budget to the final unit in Ampere (A). Using this uncertainty evaluation principle, at the measuring range of 50 A to 990 A, the expanded uncertainties for DC current were spanned from 0.69% to 1%. As for AC current, they were spanned from 0.8% to 1.4%. The major uncertainty contribution comes from the current coil which is representation of uncertainty due to various factors affecting the current coil performance. Validation had been carried out and the normalized error (EN number) values were in the range -0.48 to -0.16 for DC current measurements and in the range of -0.06 to 0.16 for AC current measurements.

An Innovative Approach to Express Uncertainty Introduced by Voltage Transformers

The importance of monitoring voltage harmonics in distribution grids has raised because of the increasing diffusion of power electronics-based nonlinear devices. In this respect, the role of voltage transformers (VTs) is vital since they represent the input stage in power quality monitoring systems, and they are responsible for one of the major uncertainty contributions. Nevertheless, their metrological performances are still quantified in terms of accuracy class, namely, rating maximum ratio error and phase displacement. The aim of this article is moving from the concept of maximum error to that of uncertainty, while proposing a new approach to evaluate and express the accuracy of VTs employed for harmonic measurements. The method is applied to the calibration of a conventional inductive VT by means of a proper setup that allows injecting complex multitone waveforms. Experimental results clearly show the advantages of the proposed approach, which permits a better description of the metrological behavior with respect to the usual ratio error and phase displacement.

Uncertainty analysis of adsorption measurements using commercial gravimetric sorption analyzers with simultaneous density measurement based on a magnetic-suspension balance

A commercial gravimetric sorption analyzer, which is based on a magnetic-suspension balance, was significantly improved to reduce the uncertainty in adsorption measurements. In a previous paper, we investigated the force-transmission error (FTE) of the instrument’s magnetic-suspension coupling, and we analysed the uncertainty of the density measurement. In the present paper, equations for the determination of the adsorption on porous and quasi non-porous materials are provided, where the FTE is taken into account, and a detailed uncertainty analysis is presented. The uncertainty analysis was applied to both the improved measurement system and a typical commercial gravimetric sorption analyzer. Adsorption test measurements were conducted with carbon dioxide along the T = 283 K isotherm at pressures up to the dew-point pressure using both a porous material (zeolite 13X) and a quasi non-porous material (solid metallic sinkers). The major uncertainty contributions for adsorption on the porous material were the mass and volume of the adsorbent sample and the assumption of the density of the adsorbed fluid; for the quasi non-porous material, the main contributions were the weighing values of the balance, the density of the investigated fluid in the gas phase, and the volume of the non-porous material. The influence of the FTE on the adsorption on the porous material was approximately 0.002 mmol⋅g−1, which was negligibly small; but the influence of the FTE was significant in the case of the quasi non-porous material, i.e., approximately 0.7 mmol⋅m−2 or about 22% of the adsorption capacity with the highest adsorption observed in this work (near the dew-point pressure). This indicates that the influence of the FTE increases significantly with decreasing adsorption capacity of the adsorbent sample.

A Boltzmann constant determination based on Johnson noise thermometry

A value for the Boltzmann constant was measured electronically using an improved version of the Johnson Noise Thermometry (JNT) system at the National Institute of Standards and Technology (NIST), USA. This system is different from prior ones, including those from the 2011 determination at NIST and both 2015 and 2017 determinations at the National Institute of Metrology (NIM), China. As in all three previous determinations, the main contribution to the combined uncertainty is the statistical uncertainty in the noise measurement, which is mitigated by accumulating and integrating many weeks of cross-correlated measured data. The second major uncertainty contribution also still results from variations in the frequency response of the ratio of the measured spectral noise of the two noise sources, the sense resistor at the triple-point of water and the superconducting quantum voltage noise source. In this paper, we briefly describe the major differences between our JNT system and previous systems, in particular the input circuit and approach we used to match the frequency responses of the two noise sources. After analyzing and integrating 50 d of accumulated data, we determined a value: J K−1 with a relative standard uncertainty of and relative offset from the CODATA 2014 recommended value.

The tracking analysis in the Q-weak experiment

The Q-weak experiment at Jefferson Laboratory measured the parity violating asymmetry (A P V ) in elastic electron-proton scattering at small momentum transfer squared (Q 2=0.025 (G e V/c)2), with the aim of extracting the proton’s weak charge ( ${Q^p_W}$ ) to an accuracy of 5 %. As one of the major uncertainty contribution sources to ${Q^p_W}$ , Q 2 needs to be determined to ∼1 % so as to reach the proposed experimental precision. For this purpose, two sets of high resolution tracking chambers were employed in the experiment, to measure tracks before and after the magnetic spectrometer. Data collected by the tracking system were then reconstructed with dedicated software into individual electron trajectories for experimental kinematics determination. The Q-weak kinematics and the analysis scheme for tracking data are briefly described here. The sources that contribute to the uncertainty of Q 2 are discussed, and the current analysis status is reported.

Estimation of the Measurement Uncertainty of a Gravimetric Analytical Procedure Applied in Fluvial Hydrosedimentology - A Didactic Example for Metrology in Chemistry Education in Technical and Undergraduate Courses

The measurement uncertainty is fundamental to assess the ‘quality’ of the results of any experiment. The measurement result with the corresponding uncertainty statement ensures its fitness for purpose by giving a measure of the confidence that can be placed on the results. This paper presents a detailed and didactic evaluation of the uncertainties for suspended sediment concentration determined by a gravimetric analytical method by filtration and for the river solid discharge using both the variance propagation law and its particular cases for sums (subtractions) and multiplications (divisions). The sources of uncertainties considered to estimate the uncertainty of the suspended sediment concentration were the weighing (resolution and calibration of the balances), the resolution of the conversion factor, the intermediate precision of the whole analytical procedure and the repeatability precision due to the direct measurements. The major uncertainty contributions for the suspended sediment concentration uncertainty were the intermediate precision and weighing of the samples. DOI: 10.5935/1984-6835.20160058

Final report on force key comparison EUROMET.M.F-K2: 50 kN and 100 kN (EURAMET Project No 518)

This report describes EURAMET Key Comparison EUROMET.M.F-K2, a comparison between the force standard machines of twelve national measurement institutes, at generated forces of 50 kN and 100 kN, in the period from 2007 to 2009. Two different measurement schemes were employed, one for machines capable of generating both 50 kN and 100 kN and the other using the single force of 50 kN, for machines of a lower maximum capacity than 100 kN. Multiple transducers were used and the force-time profile was strictly controlled, to minimise effects of creep. Analysis of the results took careful account of the drift of the transducers' sensitivities throughout the comparison period, as this was one of the major uncertainty contributions. The final results are linked to the KCRV determined in CIPM Key Comparison CCM.F-K2 through the use of two common deadweight force standard machines in the two comparison exercises.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Measurement uncertainty of isotopologue fractions in fluxomics determined via mass spectrometry

Metabolic flux analysis implies mass isotopomer distribution analysis and determination of mass isotopologue fractions (IFs) of proteinogenic amino acids of cell cultures. In this work, for the first time, this type of analysis is comprehensively investigated in terms of measurement uncertainty by calculating and comparing budgets for different mass spectrometric techniques. The calculations addressed amino acids of Pichia pastoris grown on 10% uniformly (13)C labeled glucose. Typically, such experiments revealed an enrichment of (13)C by at least one order of magnitude in all proteinogenic amino acids. Liquid chromatography-time-of-flight mass spectrometry (LC-TOFMS), liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry (GC-MS) analyses were performed. The samples were diluted to fit the linear dynamic range of the mass spectrometers used (10 μM amino acid concentration). The total combined uncertainties of IFs as well as the major uncertainty contributions affecting the IFs were determined for phenylalanine, which was selected as exemplary model compound. A bottom-up uncertainty propagation was performed according to Quantifying Uncertainty in Analytical Measurement and using the Monte Carlo method by considering all factors leading to an IF, i.e., the process of measurement and the addition of (13)C-glucose. Excellent relative expanded uncertainties (k = 1) of 0.32, 0.75, and 0.96% were obtained for an IF value of 0.7 by LC-MS/MS, GC-MS, and LC-TOFMS, respectively. The major source of uncertainty, with a relative contribution of 20-80% of the total uncertainty, was attributed to the signal intensity (absolute counts) uncertainty calculated according to Poisson counting statistics, regardless which of the mass spectrometry platforms was used. Uncertainty due to measurement repeatability was of importance in LC-MS/MS, showing a relative contribution up to 47% of the total uncertainty, whereas for GC-MS and LC-TOFMS the average contribution was lower (30 and 15%, respectively). Moreover, the IF actually present also depends on the isotopic purity of the carbon sources. Therefore, in the uncertainty calculation a carbon source purity factor was introduced and a minor contribution to the total uncertainty was observed. The results obtained by uncertainty calculation performed according to the Monte Carlo method were in agreement with the uncertainty value of the Kragten approach and showed a Gaussian distribution.

Determination of PAHs: A Practical Example of Validation and Uncertainty Assessment

The objective of this study was to present a reliable and practical example of method validation and uncertainty assessment with an analytical method for the determination of polycyclic aromatic hydrocarbons (PAHs) in urban dust. The method was gas chromatography-mass spectrometry in combination with isotope dilution principle to achieve better accuracy for the results. The method performance parameters for five PAHs were determined (phenanthrene, fluoranthene, benzo[a]anthracene, benzo[a]pyrene and benzo[ghi]perylene); this method was used in the key comparison of CCQM-K50b for PAHs in particulate matter. The limits of detection and quantification were lower than 0.075 and 0.250 µg/g, respectively. The linear correlation coefficients were greater than 0.99. The major uncertainty contributions resulted from the accuracy of each analyzed PAH and the repeatability of the process. Certified reference material (National Institute of Standards and Technology SRM 1649a, urban dust) was used to determine the accuracy and precision of the method. The obtained results were satisfactory and agreed with all evaluated performance parameters.

Experimental Characterization of Uncertainty Sources in a Software-Only Synchronization System

Over the past few decades, centralized computing systems have been replaced by decentralized systems, consisting of simple nodes interconnected by a communication network. The time reference of the distributed nodes must be synchronized in order to be able to coordinate the operation or compare the data collected by the different nodes. Several synchronization protocols have been developed to be used instead of global positioning system or dedicated synchronization systems. For example, the network time protocol (NTP) is a very popular synchronization protocol used to synchronize computers over wide area networks, like the Internet. In addition, IEEE 1588, a synchronization protocol dedicated to high-performance synchronization in local networks, was recently established. However, submicroseconds synchronization can be obtained only using dedicated hardware devices, thereby increasing the cost of each node. For these reasons, PTP software-only implementations are quite common in real systems, with a resulting synchronization uncertainty varying from a few to hundreds of microseconds and quite burdensome to estimate or measure. The work presented in this paper focuses on the analysis of the major uncertainty contributions in a software-only implementation. Particularly, a careful analysis of timestamp mechanism and time management in a PC platform is carried out. In addition, a method for the experimental evaluation of uncertainty contributions is proposed. A test case based on a software implementation of the IEEE 1588 (the so-called PTPd) is presented. The experimental tests presented in the paper highlight that the main uncertainty source of a software-only synchronization approach is the timestamp method. Timestamping accuracy can be affected by the computational load of the node itself: in normal conditions, the maximum uncertainty introduced by the timestamp mechanism is in the order of 10 , but in case of high computational load, it can raise up to 224 μs.

Final report on force key comparison CCM.F-K2.a and CCM.F-K2.b (50 kN and 100 kN)

This report describes CIPM key comparison CCM.F-K2, a comparison between the deadweight force standard machines of fourteen National Measurement Institutes, at generated forces of 50 kN and 100 kN, in the period from 2004 to 2007. Two different measurement schemes were employed, one for machines capable of generating both 50 kN and 100 kN and the other using the single force of 50 kN, for machines of a lower maximum capacity than 100 kN. Multiple transducers were used and the force–time profile was strictly controlled, to minimize effects of creep. Analysis of the results took careful account of the drift of the transducers' sensitivities throughout the comparison period, as this was one of the major uncertainty contributions. The final results suggest that the nominal 50 kN forces generated at four of the fourteen laboratories (and the 100 kN forces at two of them) may be statistically significantly different from the same nominal forces generated at the other laboratories.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Half-life measurement of 124Sb

The half-life of (124)Sb was determined experimentally by following the decay of a source from a radiopure solution with a Centronic IG12 ionisation chamber. Thousands of measurements were performed over a period of 358 days, i.e. about six half-life periods. However, the data analysis was restricted to the first 221 days, in order to limit the dominant uncertainty component associated with the hypothetical possibility of a systematic error on background subtraction. The resulting value for the (124)Sb half-life, 60.212 (11) days, is found to be in very good agreement with published values, but carries a lower uncertainty. Major uncertainty contributions pertain to possible systematic errors in background correction, long-term changes in source-detector geometry and medium- and long-term instability of the instrument. Additional measurements were performed with a high-purity germanium detector to confirm the above value.

Approach to accuracy assessment of the glass-electrode potentiometric determination of acid-base properties

Thermodynamic data are suitable subject for investigating strategies and concepts for the evaluation of complete measurement uncertainty budgets in situations where the measurand cannot be expressed in a mathematical formula. Some suitable approaches are the various forms of Monte Carlo simulations in combination with computer-intensive statistical methods that are directed to an evaluation of empirical distribution curves for the uncertainty budget. Basis of the analysis is a cause-and-effect diagram. Some experience is available with cause-and-effect analysis of thermodynamic data derived from spectrophotometric data. Another important technique for the evaluation of thermodynamic data is glass-electrode potentiometry. On basis of a newly derived cause-and-effect diagram, a complete measurement uncertainty budget for the determination of the acidity constants of phosphoric acid by glass-electrode potentiometry is derived. A combination of Monte Carlo and bootstrap methods is applied in conjunction with the commercially available code SUPERQUAD. The results suggest that glass-electrode potentiometry may achieve a high within-laboratory precision because major uncertainty contributions become evident via interlaboratory comparisons. This finding is further underscored by analysing available literature data.

Uncertainty contributions to single and double isotope dilution mass spectrometry with HPLC-CV-MC-ICP-MS for the determination of methylmercury in fish tissue

A full uncertainty budget has been used to compare the performance of species specific single and ‘approximate matching’ double isotope dilution mass spectrometry (IDMS). Two fish tissue reference materials were employed in this study, DORM-2 (NRC, Canada) and BCR464. Methylmercury was separated from inorganic mercury by HPLC, which was coupled to multicollector ICP-MS via a cold vapour generation system for the measurement of isotope amount ratios. For each CRM the mass fraction of methylmercury determined by the two IDMS methods was not statistically different, within the limits of uncertainty, from the certified values. Double IDMS was found to be more precise than single IDMS when a full uncertainty budget was estimated, the converse applied when the method precision was estimated only by the standard deviation of replicate analysis. For single IDMS the major uncertainty contribution was derived from the standard uncertainty of each analytical replicate, Uwithin. The between blend standard uncertainty, Ubetween, was the major contributor to the expanded uncertainty for approximate matching double IDMS.

Uncertainty contributions to species specific isotope dilution analysis. Part 2. Determination of methylmercury by HPLC coupled with quadrupole and multicollector ICP-MS

Species-specific isotope dilution analysis (IDA) has been used to determine the mass fraction of methylmercury in a fish muscle certified reference material, DORM-2. Two spike solutions were prepared and their mass fractions determined by coupling high-performance liquid chromatography (HPLC) with both quadrupole (Q) and multicollector (MC) inductively coupled plasma mass spectrometry (ICP-MS) and uncertainty budgets calculated. For the Q-ICP-MS determination the relative standard uncertainty of the spike was 4.1%. The major uncertainty contribution (62%) arose from the uncertainties associated with the relative isotopic abundances of Hg isotopes as given by IUPAC. The measured isotope amount ratios (200Hg∶199Hg and 205Tl∶203Tl) contributed 37% of the combined uncertainty. For the multicollector instrument the relative standard uncertainty of the spike solution mass fraction was 0.7%. In this case the uncertainty budget was dominated by the Hg isotopic uncertainties, with a contribution of 99%. The uncertainty contributions from the measured isotope amount ratios were reduced to 0.7% of the total when using MC-ICP-MS. The two spike solutions were separately used to determine the mass fraction of methylmercury in DORM-2 CRM by species-specific IDA, using HPLC coupled with quadrupole ICP-MS. The values found were 4.45 ± 0.90 µg g−1 and 4.25 ± 0.47 µg g−1 using spikes characterised by Q- and MC-ICP-MS, respectively (the uncertainties quoted are the expanded uncertainty, k = 2), compared with a certified value of 4.47 ± 0.32. The major uncertainty contribution for each determination was from the measured isotope amount ratios (70%) with lesser contributions from the uncertainties associated with the natural isotopic abundance of Hg and the spike mass fraction.

Calorimetric determination of the half-life of antimony-124

The half-life of 124Sb was determined experimentally by following the decay of a source from a radiopure solution with a Centronic IG12 ionisation chamber. Thousands of measurements were performed over a period of 358 days, i.e. about six half-life periods. However, the data analysis was restricted to the first 221 days, in order to limit the dominant uncertainty component associated with the hypothetical possibility of a systematic error on background subtraction. The resulting value for the 124Sb half-life, 60.212 (11) days, is found to be in very good agreement with published values, but carries a lower uncertainty. Major uncertainty contributions pertain to possible systematic errors in background correction, long-term changes in source-detector geometry and medium- and long-term instability of the instrument. Additional measurements were performed with a high-purity germanium detector to confirm the above value.