Small Measurement Uncertainties Research Articles

Experimental uncertainty evaluation by measuring a micro gear standard using focus variation

Abstract Micro gears play an increasingly important role in various industrial applications, and the minimization of their deviations is challenging for metrology and manufacturing. A promising method is the focus variation technology, which enables areal measurements of micro gears. Practice-related standards are used to determine measurement uncertainties by comparison with calibration values. In this work, the external micro gear standard of the Physikalisch-Technische Bundesanstalt (PTB) is used to evaluate experimental measurement uncertainties of a focus variation coordinate measurement system for the first time. The traceable standard with modules between 0.1 and 1 mm is calibrated using micro tactile coordinate measurements. Optical and tactile measurements are then compared. As a result, small expanded measurement uncertainties of less than 4 µm are achieved.

Optimal speckle size and signal processing for displacement measurements using a 4f optical setup

Fully developed laser speckle patterns are, due to their high contrast and statistical nature, well suited to measure strain and displacement via an appropriately designed measurement system. Laser speckle patterns are formed when a sufficiently coherent light source, such as a HeNe-laser, illuminates an optically rough surface. Therefore, methods based on laser speckle patterns can be applied to any surface scatterer with a minimum mean surface roughness of about a quarter of the laser’s wavelength. This includes also materials such as thin natural and technical fibres as well as foils, for which the presented measurement system, including the digital signal processing, was designed. In order to achieve the best possible resolution of a speckle-based measurement system, combined with a sufficiently small measurement uncertainty, all available design parameters must be optimised. One of these parameters is the speckle size, which is dependant on the properties of the imaging optics. In this paper a subjective laser speckle-based measurement system based on a so-called 4f-optical setup is presented. This setup allows the speckle size to be controlled in both axial and lateral dimensions separately, which is achieved with the help of an aperture in the Fourier plane of the optics. It is shown that the optimal speckle size for the presented measurement system, not only depends on the physical setup, but also on the signal processing applied. The signal processing routine estimates displacements of the speckle pattern, leading to an estimate for the strain. Additionally, it is demonstrated that the optimal speckle size can be lower than the commonly reported optimum between two and five pixel pitches, necessary to circumvent aliasing in the image data. While this is shown for a measurement setup using 4f-optics, the results are of general importance to speckle-based strain or displacement measurement systems and should thus be taken into account.

Final report of APMP.AUV.V-S2: supplementary comparison on calibration of laser tachometers using mechanical generators or optical simulators

Main textThis is the final report for APMP supplementary comparison APMP.AUV.V-S2 in the area of 'vibration' (quantity of rotational speed). The aim of this comparison was to compare primary measurements of rotational speed in the range from 30 r/min to 99 996 r/min. Six Metrology Institutes from two RMOs, APMP and AFRIMETS, have participated in the comparison with the National Institute of Metrology, P.R. China as the pilot lab. NIM, NMC and NIS used a mechanical generator for calibration, with expanded uncertainties in the order from 10-3 to 10-5. NML, NIMT and KEBS used an optical simulator for calibration, with expanded uncertainties in the order from 10-4 to 10-5. All the participating laboratories provided their calibration results, which were all consistent within their declared expanded uncertainties for the measurement results. Each participant contributed to the SCRVs calculated for five rotational speed comparison values of two laser tachometers, NLYZ-02 and 03, except that NIS's measurement results of NLYZ-03 are invalid. Smaller measurement uncertainties than the order of 10-5 for the calibration of laser tachometers are difficult to achieve for either mechanical generators or optical simulators with the current technology of rotational speed standard devices and laser tachometers.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 https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Development of a coulometry system at the Korea Research Institute of Standards and Science and evaluation of the measurement uncertainty originating from the system

Coulometry is used to realize the definition of the mole and enables the direct determination of the purity of high-purity substances that are used as standards for other relative measurements with very small measurement uncertainty. However, despite several studies reporting the development of accurate and precise coulometry systems, there is a lack of detailed description of the system and systematic evaluation of the measurement uncertainty arising from the system. In this study, coulometry systems constructed at the Korea Research Institute of Standards and Science (KRISS) are described in detail and the uncertainties associated with these systems are systematically evaluated using a bottom-up approach. The relative expanded uncertainty resulting from the measurement system for the amount-of-substance content of acid in high-purity potassium hydrogen phthalate is approximately 0.0005%. The performance of the KRISS coulometry systems has been verified through several international comparisons and comparative measurements using certified reference materials.

Evaluating potential of leaf reflectance spectra to monitor plant genetic variation

Remote sensing of vegetation by spectroscopy is increasingly used to characterize trait distributions in plant communities. How leaves interact with electromagnetic radiation is determined by their structure and contents of pigments, water, and abundant dry matter constituents like lignins, phenolics, and proteins. High-resolution (“hyperspectral”) spectroscopy can characterize trait variation at finer scales, and may help to reveal underlying genetic variation—information important for assessing the potential of populations to adapt to global change. Here, we use a set of 360 inbred genotypes of the wild coyote tobacco Nicotiana attenuata: wild accessions, recombinant inbred lines (RILs), and transgenic lines (TLs) with targeted changes to gene expression, to dissect genetic versus non-genetic influences on variation in leaf spectra across three experiments. We calculated leaf reflectance from hand-held field spectroradiometer measurements covering visible to short-wave infrared wavelengths of electromagnetic radiation (400–2500 nm) using a standard radiation source and backgrounds, resulting in a small and quantifiable measurement uncertainty. Plants were grown in more controlled (glasshouse) or more natural (field) environments, and leaves were measured both on- and off-plant with the measurement set-up thus also in more to less controlled environmental conditions. Entire spectra varied across genotypes and environments. We found that the greatest variance in leaf reflectance was explained by between-experiment and non-genetic between-sample differences, with subtler and more specific variation distinguishing groups of genotypes. The visible spectral region was most variable, distinguishing experimental settings as well as groups of genotypes within experiments, whereas parts of the short-wave infrared may vary more specifically with genotype. Overall, more genetically variable plant populations also showed more varied leaf spectra. We highlight key considerations for the application of field spectroscopy to assess genetic variation in plant populations.

Highly Sensitive Fiber Relative Humidity Sensor Based on Tip Michelson Interferometer With Agarose Gel Coating

A tip Michelson interferometer (MI) is proposed and experimentally demonstrated for relative humidity (RH) sensing. The device consists of a short capillary tube with a small inner diameter that is spliced to a single-mode fiber (SMF) and coated with agarose gel on its end face, and the solid capillary wall and gel act as the sensing arm of the MI. When the agarose gel absorbs water modules, its refractive index (RI) and volume vary, resulting in the shift of the reflection spectrum of the MI. The relationship between the structural parameters and the performance of the device is revealed after performing theoretical analysis and experimental verification, which provides guidance for optimizing the device. The maximum sensitivity of 0.752 nm/% RH with a linear correlation coefficient of (Adjusted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}) 0.9927$ </tex-math></inline-formula> within the range of 25%–90% RH is obtained. Moreover, the proposed sensor exhibits good performances of robustness, compact size, high repeatability, fast response (< 100 ms), and small measurement uncertainty (< 0.21% RH), which makes the sensor promising for accurately static or dynamic moisture measuring.

Tracer and observationally derived constraints on diapycnal diffusivities in an ocean state estimate

Abstract. Use of an ocean parameter and state estimation framework – such as the Estimating the Circulation and Climate of the Ocean (ECCO) framework – could provide an opportunity to learn about the spatial distribution of the diapycnal diffusivity parameter (κρ) that observations alone cannot due to gaps in coverage. However, we show that the inclusion of misfits to observed physical variables – such as in situ temperature, salinity, and pressure – currently accounted for in ECCO is not sufficient, as κρ from ECCO does not agree closely with any observationally derived product. These observationally derived κρ products were inferred from microstructure measurements, derived from Argo and conductivity–temperature–depth (CTD) data using a strain-based parameterization of fine-scale hydrographic structure, or calculated from climatological and seafloor data using a parameterization of tidal mixing. The κρ products are in close agreement with one another but have both measurement and structural uncertainties, whereas tracers can have relatively small measurement uncertainties. With the ultimate goal being to jointly improve the ECCO state estimate and representation of κρ in ECCO, we investigate whether adjustments in κρ due to inclusion of misfits to a tracer – dissolved oxygen concentrations from an annual climatology – would be similar to those due to inclusion of misfits to observationally derived κρ products. We do this by performing sensitivity analyses with ECCO. We compare multiple adjoint sensitivity calculations: one configuration uses misfits to observationally derived κρ, and the other uses misfits to observed dissolved oxygen concentrations. We show that adjoint sensitivities of dissolved oxygen concentration misfits to the state estimate's control space typically direct κρ to improve relative to the observationally derived values. These results suggest that the inclusion of oxygen in ECCO's misfits will improve κρ in ECCO, particularly in (sub)tropical regions.

Quantitative atomic force microscopy: A statistical treatment of high-speed AFM data for quality control applications

Prior to the recent developments of high-speed atomic force microscopy (HS-AFM), atomic force microscopy (AFM) was not favoured by industry because of its complexity and slow image acquisition speed which may lead to poor resolution and unreliable quantified results. HS-AFM, however, is capable of imaging several frames per second and thus capable of quick, accurate, and representative measurements – ideal for quality control applications. This study demonstrates HS-AFM as a useful quality control tool by assessing the roughness of silicon carbide (SiC) monofilament fibres as a challenging example of how large HS-AFM datasets in excess of 200 images can be collected and used for reliable quantification.A comparison of two roughness methods utilising either area or line roughness parameters has been conducted, where very little difference was noted apart from the lower statistical significance of line roughness. The roughness of ten SiC fibre samples was measured with Sa (the area equivalent to Ra) roughness results varying from 34 nm to 53 nm. The small measurement uncertainties, as a result of the large number of measurements, meant that the roughness results were distinguishable from one another even though all ten SiC fibres were very similar to each other, having been produced by the same manufacturer and process. The robustness of the methods have been tested by repeating the analysis for each fibre, and in the one instance where the repeated data did not agree, a further dataset proved which one was incorrect, illustrating how industry can use these methods for quality control. A methodology of identifying the minimum number of frames required to account for sample variability, as well as recommendations on how to use HS-AFM for quantitative measurements in quality control, are also included to enable easy reproduction and adaptation of this work for other samples and measurements.

Design of Electrostatic Feedback for an Experiment to Measure G

The torsion pendulum at the heart of the apparatus to measure the gravitational constant, G at the Bureau International des Poids et Mesures (BIPM) is used to measure the gravitational torque between source and test-mass assemblies with two methods. In the Cavendish method, the pendulum moves freely. In the electrostatic-servo method, the pendulum is maintained at a constant angle by applying an electrostatic torque equal and opposite to any gravitational torque on the pendulum. The electrostatic torque is generated by a servo. This article describes the design and implementation of this servo at the National Institute of Standards and Technology. We use a digital servo loop with a Kalman filter to achieve measurement performance comparable to the one in an open loop. We show that it is possible to achieve small measurement uncertainty with an experiment that uses three electrodes for feedback control.

Feasibility Study of Performance Assessment Gauge for Freeform Measurement

Recent product components have been designed as a combination of complex forms for advanced functionality. Such high degree-of-freedom forms are shaped by various manufacturing processes. In the industrial supply chain, the deviation of a manufactured form from its designed form must be verified to ensure product quality. Three-dimensional (3D) measuring systems are typically used for verification. To validate the product manufacturing performance accurately, a measurement procedure that can derive the measurands of forms with small measurement uncertainty is necessitated. For simple geometries such as flats, spheres, and cylinders, precise measurement and uncertainty evaluation methods have been established; however, those for complex forms are still being developed. In this study, measurement uncertainty is assessed by measuring a calibrated gauge and comparing the measured with calibrated values. Several gauges configured with basic geometric elements have been proposed as a reference for complex form measurements, and some issues remain. Some of the gauges do not sufficiently simulate the forms of actual product components, whereas other gauges are difficult to calibrate with small uncertainties. Herein, we discuss a possible approach for solving these problems in the metrology of complex forms using 3D measuring systems. First, a new gauge concept is proposed. The gauge is designed by extracting the complex features of the actual product form and segmenting the gauge’s form into various circular arc curvatures. The geometric parameters are well calibrated, and the measurable angular range of the curvature is not limited. A representative gauge based on this concept is described. Next, a robust and small-uncertainty calibration method for complex-form objects is described. The area encompassing the target cross-section is measured, and an envelope is generated on the probe tip mechanical surface from the probe tip centers to determine the measured surface. Finally, the calibration and measurement uncertainty evaluation for the geometric parameters of the new gauge are quantitatively presented. It is verified that the proposed calibration procedure is applicable to freeform measurements, and that both simple and complex forms can be measured within a 1.5 μm uncertainty.

Mass balance method for SI-traceable purity assignment of synthetic oxytocin

Oxytocin is not only a significant peptide drug for enhancing uterine contractions, but also an emerging biomarker and therapeutic target of mental disorders in clinical practice. There is a pressing need for the standardization of oxytocin assays because of its low pharmaceutical quality and large variations among measurement approaches. International System of Units (SI)-traceable analytical methods and well-characterized pure reference materials are urgently needed to set up standard reference measurement systems in laboratory medicine, ensuring the accuracy and comparability of test results. Herein, the purity assignment of a synthetic oxytocin containing a disulfide linkage was established based on a mass balance method, which had never been performed for a cross-linked peptide. An in-house validated liquid chromatography-high-resolution tandem mass spectrometry method was developed for the determination of structurally-related impurities in the study material. Twenty-one structurally-related impurities including deamidations, oxidations, and amino acid insertions, etc. ranging from 0.05 mg g-1 to 15.65 mg g-1 were identified and quantified by applying a hierarchy calibration concept. This study subsequently discusses a fit for purpose assessment for non-peptide related impurities including water, non-volatile counterions, inorganic elements, and volatile organic compounds that were determined using coulometric Karl Fischer titration, ion chromatography, inductively coupled plasma mass spectrometry, and headspace gas chromatography-mass spectrometry, respectively. The resulting assigned value (796.5 mg g-1) is determined to be traceable to SI associated with a small measurement uncertainty of 6.5 mg g-1 (k = 2). The method developed in this study has been verified through an international key comparison jointly coordinated by the Bureau International des Poids et Mesures and the National Institute of Metrology.

Mass Balance Method for Si-Traceable Purity Assignment of Synthetic Oxytocin

Oxytocin is not only a significant peptide drug for enhancing uterine contractions, but also an emerging biomarker and therapeutic target of mental disorders in clinical practice. There is a pressing need for the standardization of OXT assays because of its low pharmaceutical quality and large variations among measurement approaches. SI-traceable analytical methods and well-characterized pure reference materials are urgently needed to set up standard reference measurement systems in laboratory medicine, ensuring the accuracy and comparability of test results during the manufacture, clinical diagnosis and treatment. Herein, the purity assignment of a synthetic oxytocin containing a disulfide linkage was established based on a mass balance method, which had never been performed for a cross-linked peptide. An in-house validated liquid chromatography-high-resolution tandem mass spectrometry method was developed for the determination of structurally-related impurities in the study material. 21 structurally-related impurities including deamidations, oxidations, and amino acid insertions, etc. ranging from 0.05 mg g-1 to 15.65 mg g-1 were identified and quantified by applying a hierarchy calibration concept. This study subsequently discusses a fit for purpose assessment for non-peptide related impurities including water, non-volatile counterions, inorganic elements, and volatile organic compounds that were determined using coulometric Karl Fischer titration, ion chromatography, inductively coupled plasma mass spectrometry, and headspace gas chromatography-mass spectrometry, respectively. The resulting assigned value (796.5 mg g-1) is determined to be traceable to SI units associated with a small measurement uncertainty of 6.5 mg g-1 (k= 2). The method developed in this study has been verified through an international key comparison jointly coordinated by the Bureau International des Poids et Mesures and the National Institute of Metrology.

Discriminative sensing of temperature and acoustic impedance by using forward Brillouin scattering in large effective area fiber

We experimentally clarified the characteristics of forward Brillouin scattering induced by radial acoustic modes (R 0,m ) in large effective area fiber. The measured resonance frequencies of R 0,m modes were shown to have different sensitivities to acoustic impedance. Then we performed discriminative measurement of temperature and acoustic impedance by selecting a pair of different R 0,m modes that would achieve the minimum measurement error, where we had successfully achieved small measurement uncertainties of 0.4 °C and 0.03 kg·s–1 · mm–2, respectively.

Excitation Strategies for 3-D Electrical Capacitance Tomography Sensors

This article presents investigation of 3-D electrical capacitance tomography (ECT) sensors with different excitation strategies, including dual-electrode excitation in the same plane, in adjacent plane, in planes separated by one plane or two planes, and in the adjacent position or opposite position in the same or different planes. The results show that a 3-D ECT sensor with dual-electrode excitation in the opposite position provides higher mean capacitance and lower standard deviation than in the adjacent position. Dual-electrode excitation in different planes can increase the capacitance signal and decrease the dynamic range of capacitance measurements, and thus, decrease random errors and improve the quality of 3-D reconstructed images. A 3-D ECT sensor with dual-electrode excitation in planes separated by one plane and opposite position can provide small measurement uncertainty and high image quality.

Contributions of scanning metrology uncertainty to milling force prediction

This paper describes an uncertainty evaluation for axial location-dependent cutting edge radius and angle values extracted from structured light scans of a variable pitch endmill. Two cases are evaluated: 1) a single scan of the endmill is performed and that scan is manually fit five times to record the cutting edge geometry for all teeth on the endmill; and 2) five scans of the endmill are performed and each scan is manually fit a single time. Both cases therefore include five manual fits. The standard deviations in radius and angle values are used to represent the statistical uncertainty and the two cases are compared. The mean standard deviations in radius are 0.005 mm and 0.007 mm; the mean standard deviations in angle are 0.066 deg and 0.092 deg. As expected, the uncertainties are higher with additional scans. The scan results are then used in a time-domain simulation to predict the cutting force profiles for the variable pitch endmill. It is shown that the two cases provide similar agreement between prediction and measurement due to the small measurement uncertainties.

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.

Thermodynamic temperature of the triple point of xenon measured by refractive index gas thermometry

Measurements of the refractive indices of helium and argon using a quasi-spherical microwave resonator and upgraded experimental protocol are reported at the temperatures of the triple points of water and xenon. The results at the triple point of water are used to determine the compressibility of the resonating cavity, which is bounded by the copper shell of the resonator. This experimentally-determined compressibility is consistent with the literature value for copper, but with much smaller measurement uncertainty. The measured compressibility is extrapolated to the triple point of xenon, and combined with the refractive index results at that temperature to determine the thermodynamic accuracy of the International Temperature Scale of 1990 (ITS-90): mK at ITS-90 temperature K, corresponding to a xenon triple point thermodynamic temperature of K. The experimental compressibility is further extrapolated to the triple points of argon, oxygen and neon, and used to re-analyze earlier refractive index gas thermometry measurements made using the same resonator, yielding updated values with reduced uncertainties: mK at T90 = 83.8058 K, mK at T90 = 54.3584 K, and mK at T90 = 24.5561 K. The ITS-90 thermodynamic accuracy results of the present refractive index gas thermometry study agree with those previously reported by acoustic gas thermometry and dielectric constant gas thermometry.

Ensemble learning methodologies to improve core power distribution abnormal detectability

Several ensemble learning methodologies have been presented to improve the performance of the core power distribution reconstruction, such as boosting technology, bagging technology and stacking technology. Four commonly used core power reconstruction methods, including PEM, TPS, WCM and ANN are adopted as base learners or meta-learners. The power distribution of the control rod drop accident and quadrant power tilt accident, which combine with detectors measurement noise, is reconstructed. The numerical simulation shows that the results of the stacking methodology can be better than any single one of these base learners under large sample spatial variation of power distribution and large measurement uncertainty. Otherwise results that close to the best one of these base learner results could be generated in stacking methods. In bagging and boosting methodologies, for the unstable learner such as TPS and ANN methods with large measurement uncertainty, both methodologies will help to reduce the reconstruction errors. The boosting methodology could even get better results than bagging. While for the stable learner (such as PEM learner, WCM learner) or unstable learner (e.g. the TPS or ANN method) but under small spatial variation (or small measurement uncertainty) that is not sensitive to the change of sample data, the bagging or boosting method even will reduce the reconstruction performance. Generally, ensemble learning methodologies have capability to improve the core abnormal detectability in most operation scene. Usually stacking methodology performs much better than bagging and boosting methodologies.

Chemical Separation of Tungsten and Other Trace Elements for TIMS Isotope Ratio Measurements Using Organic Acids

One requirement for isotope ratio measurement results with small measurement uncertainties is that the element of interest is effectively separated from the sample matrix. Efficient chemical separation of W from matrix components, especially Ti, can be challenging, particularly for large test portion masses (&gt; 1 g). We present a new W separation procedure that takes advantage of the distinct complexation behaviour of Ti and W with citrate ligand in a moderately low pH, oxidising solution. This preparation procedure can reduce the Ti/W ratio of large (4–10 g) basaltic (i.e., high‐matrix) test portions by a factor of 105, relative to their original compositions, in a two‐step separation procedure. The procedure additionally provides a separate, well‐purified Mo fraction. We show that optimal separation requires precise selection of reagent concentrations and sample load. The procedure was employed to determine the μ182W composition of BHVO‐2 as −6.7 ± 4.2 (2 standard deviation, 2s). The principles derived from this method may prove useful for chemical separation of other elements used for geochemical and cosmochemical applications given an appropriate selection of organic acid. Future successful applications of this method may reveal that the use of organic acids as procedural reagents is a currently under‐utilised tool for efficient chemical separation protocols.

Lessons learned from inter-laboratory studies of carbon isotope analysis of honey

Forensic application of carbon isotope ratio measurements of honey and honey protein to investigate the degree of adulteration with high fructose corn syrup or other C4 plant sugars is well established. These measurements must use methods that exhibit suitable performance criteria, particularly with regard to measurement uncertainty and traceability – low levels of adulteration can only be detected by methods that result in suitably small measurement uncertainties such that differences of 1‰ or less can be reliably detected. Inter-laboratory exercises are invaluable to assess the state-of-the art of measurement capabilities of laboratories necessary to achieve such performance criteria. National and designated metrology institutes from a number of countries recently participated in an inter-laboratory assessment (CCQM-K140) of stable carbon isotope ratio determination of bulk honey. The same sample material was distributed to a number of forensic isotope analysis laboratories that could not participate directly in the metrological comparison. The results from these studies have demonstrated that the majority of participants provided isotope delta values with acceptable performance metrics; that all participants ensured traceability of their results; and that where measurement uncertainties were reported; these were fit-for-purpose. A number of the forensic laboratories only reported precision rather than full estimates of measurement uncertainty and this was the major cause of the few instances of questionable performance metrics. Reporting of standard deviations in place of measurement uncertainties is common practice outside metrology institutes and the implications for interpretations of small differences in isotopic compositions are discussed. The results have also highlighted a number of considerations that are useful for organisers of similar inter-laboratory studies in the future.