Measurement Uncertainty Budget Research Articles

Tool pose measurement using shadow imaging sensors

Due to the high positioning uncertainty and low stiffness of robots, significant geometrical deviations occur in robotic incremental sheet forming (ISF) which requires an optical in-process tool pose measurement. To achieve a measuring uncertainty of less than 50 μm for the position components and less than 0.05∘ for the orientation components in the machining volume, a multi-sensor system based on shadow imaging sensors is proposed. To calculate the six-degree-of-freedom tool pose, the sensor system measures the positions of three LEDs attached to the tool. The LEDs emit light with different colors, and the associated shadows are separately detected by using color filters. In addition, each sensor consists of a shadow-casting mask and a monochrome camera. Experimental results show that the systematic error dominates the measurement uncertainty budget and needs to be calibrated, while the random error is one order of magnitude smaller than the required measuring uncertainty. Furthermore, the color filters reduce the cross-sensitivities between the signals to an acceptable level. Final experiments on a robot demonstrate plausible pose measurements indicating the feasibility to apply the multi-sensor system in robotic ISF.

Development and international multicentre pilot testing of a postal dosimetry audit methodology for high dose rate brachytherapy

Background and PurposeDosimetry audits are essential for reducing errors in brachytherapy. A postal dosimetry audit methodology was developed and tested in an international multicentre pilot, to assess the accuracy of the Reference Air Kerma Rate of 192Ir and 60Co brachytherapy sources. Materials and MethodsA compact phantom made of polymethyl methacrylate was developed to accommodate two catheters, a radiophotoluminescence dosimeter (RPLD) for dose measurements and a Gafchromic (RTQA2) film strip for source position verification. Deviations of the audit setup from TG-43 conditions were quantified experimentally and compared to previous Monte Carlo (MC) simulations. A measurement uncertainty budget was estimated for the RPLD analysis. The methodology was tested in an international pilot study consisting of 59 dosimeter sets among 48 centres from 11 countries. ResultsThe experimental correction factors showed good agreement with previous MC simulations, and the total correction factor accounting for non-water equivalence, lack of scatter and beam quality was found to be 1.029 ± 0.009 for 192Ir and 1.059 ± 0.007 for 60Co sources, to be employed in audit measurement. The total uncertainty budget was estimated to be 2.24 % (k = 1). In the multicentre study, the ratio between measured and reported user dose ranged from 0.968 to 1.049, with all irradiated dosimeter sets within ± 5 %, and 54 out of 59 within ± 3 %. ConclusionsThe methodology was tested in an international multicentre pilot study and has shown good performance validating the uncertainty budget.

Fundamental representation of the amount of substance fraction of carbon dioxide in nitrogen according to the dynamic volumetric principle

Abstract The new Austrian primary standard for the amount of substance fraction of carbon dioxide in nitrogen is presented. The primary standard is working according to the dynamic volumetric principle and is a fundamental representation of the measurement quantity. The direct traceability to the basic SI units is thereby thermodynamically realized without an artefact. A complete measurement uncertainty budget is calculated and verified with a bilateral inter-laboratory comparison.

Experimental installation of a reference source of low currents for calibration of electrometers

Today, there is great scientific interest in the possibility of implementing reference sources of low currents based on single-electron pumps using the single-electron tunneling effect and the modern definition of the SI system. However, the practical use of this effect in everyday metrological practice has not yet reached the stage of widespread use. Typically, for routine calibration work in laboratories, either mass-produced instruments (low current sources and meters, electrometers) are used, which are calibrated against higher standards, or specially designed precision current sources. The article describes a reference installation developed on the basis of the VNIIFTRI, where in the mode of generating ultralow currents the principle of forming a linearly increasing voltage on a reference capacitor is used. A simplified block diagram of the reference setup is shown. Issues of practical adjustment of modern electrometers are considered. The generalized results of participation in international comparisons on low currents EURAMET.EM-S44 “Comparison of ultra-low DC current sources” conducted by national metrological institutes in 2018–2020 are presented. The results of a metrological study of the calibration factor Q and an example of calculating the uncertainty budget of measurements carried out at the VNIIFTRI as part of these international comparisons are presented. The research described in the article to increase the accuracy of measurements of small and ultra-low currents of this level has valuable practical significance in the field of electrical measurements, in aeroionometry and metrology of ionizing radiation.

Analytical performance specifications for combined uncertainty budget in the implementation of metrological traceability.

In addition to the correct implementation of calibration traceability, the definition and fulfillment of maximum allowable measurement uncertainty (MAU) are essential in assuring that laboratory measurements are clinically usable. Across the entire calibration hierarchy, three major contributors to the measurement uncertainty (MU) budget are identified, starting with the higher-order reference providers, extending through the in vitro diagnostic (IVD) manufacturers and their processes for assigning calibrator values, and ending with medical laboratories generating the random variability of results reported to clinicians. To understand if it is possible to achieve MAU and, consequently, to fix the possible drawbacks, the definition of combined MU budget limits across the entire calibration hierarchy has a central role. In particular, quality specifications for MU of reference and commercial calibrator materials should be defined according to the MAU on clinical samples. All involved stakeholders (i.e., higher-order reference providers, IVD manufacturers, medical laboratories) should be prepared to improve their performance whenever the clinical application of the test is made questionable by the failure to achieve MAU.

Gamma irradiation system's performance tests.

This study reviews the performance analysis of a 137Cs irradiation system that has recently been installed in the laboratory of Uzbek National Institute of Metrology. The laboratory is responsible for calibrating calibration facilities and for calibrating most protection level radiation monitoring instruments used in medical, nuclear, industrial and academic settings in Uzbekistan. This system employs the most advanced radiation safety standards, along with 21st century source automation methods. In this work, we review the system's performance according to ISO 4037 and present measurement uncertainty budget. Our analysis shows excellent results in terms of scattered radiation, beam uniformity and field size, change in source position, test for source impurities, chamber stability and source calibration, and all these parameters fully comply with the requirements of ISO 4037.

State primary standard of the unit of overpressure in the range of static pressure from 10 to 1600 MPa and in the range of impulse pressure

The necessity and relevance of precision pulse pressure measurements in industry (high-speed technological processes) and transport (existing and new types of engines) is shown. The device, the principle of operation and the result of metrological studies of the State Primary Standard of the unit of overpressure in the range of static pressure from 10 to 1600 MPa and in the range of pulse pressure from 1 to 1200 MPa and the effective area of piston pairs of piston pressure gauges in the range from 0.05 to 1 cm2 GET 43-2022 are presented. The GET 43-2022 includes hydraulic and pneumatic installations, as well as an ultra-high pressure valve designed to compare installations from the GET 43-2022 composition working with different standard fl uids in the range of 250-1200 MPa. The reproduction range of the pulse pressure unit GET 43-2022 is 1-1200 MPa. The method of reproducing the pulse pressure unit in liquid and gas media using hydraulic and pneumatic installations is described. The metrological characteristics of GET 43-2022 are investigated, the budget of measurement uncertainty is calculated when reproducing the pulse pressure unit. The results obtained make it possible to meet the needs of the development of a fl eet of working standards for pulse pressure measuring instruments traceable to GET 43-2022.

Towards Operational Fiducial Reference Measurement (FRM) Data for the Calibration and Validation of the Sentinel-3 Surface Topography Mission over Inland Waters, Sea Ice, and Land Ice

The Copernicus Sentinel-3 Surface Topography Mission (STM) Land Altimetry provides valuable surface elevation information over inland waters, sea ice, and land ice, thanks to its synthetic aperture radar (SAR) altimeter and its orbit that covers high-latitude polar regions. To ensure that these measurements are reliable and to maximise the return on investment, adequate validation of the geophysical retrieval methods, processing algorithms, and corrections must be performed using independent observations. The EU-ESA project St3TART (started July 2021) aims to generalise the concept of Fiducial Reference Measurements (FRMs) for the Copernicus Sentinel-3 STM. This work has gathered existing data, made new observations during field campaigns, and ensured that these observations meet the criteria of FRM standards so that they can be used to validate Sentinel-3 STM Land Altimetry products operationally. A roadmap for the operational provision of the FRM, including the definition, consolidation, and identification of the most relevant and cost-effective methods and protocols to be maintained, supported, or implemented, has been developed. The roadmap includes guidelines for SI traceability, definitions of FRM measurement procedures, processing methods, and uncertainty budget estimations.

IAEA/WHO postal dosimetry audit methodology for electron beams using radio photoluminescent dosimeters.

Independent dosimetry audits are an important intervention in radiotherapy for quality assurance. Electron beams, used for superficial radiotherapy treatments, must also be tested in dosimetry audits as part of a good quality assurance program to help prevent clinical errors. To establish a new service for IAEA/WHO postal dosimetry audits in electron beams using RPL dosimeters. A novel postal audit methodology employing a PMMA holder system for RPLDs was developed. The associated correction factors including holder dependence, energy dependence, dose response non-linearity, and fading were obtained and tested in a multi-center (n=12) pilot study. A measurement uncertainty budget was estimated and employed in analyzing the irradiated dosimeters. Holder and energy correction factors ranged from 1.004 to 1.010 and 1.019 to 1.059 respectively across the energy range. The non-linearity and fading correction models used for photon beams were tested in electron beams and did not significantly increase measurement uncertainty. The mean dose ratio±SD of the multi-center study was 1.001±0.011. The overall uncertainty budget was estimated as±1.42% (k=1). A methodology for IAEA/WHO postal dosimetry audits in electron beams was developed and validated in a multi-center study and is now made available to radiotherapy centers as a routine service.

National measurement standard of liquid density unit: structure, metrological characteristics, and operation principles

The article presents the structure, composition, operation principle, and metrological characteristics of the national primary measurement standard of liquid density unit. This measurement standard realizes the liquid density unit by reference procedure and is the basis for comparison and metrological traceability for other measurement standards of liquid density unit, that made it possible to give it the national primary standard status. Based on accuracy characteristics analysis of primary measurement standards from other countries (CMC-lines from the KCDB of the International Bureau of Weights and Measures based on key and supplementary comparisons), it is possible to prove its high metrological status and initiate international comparisons for establishing its metrological equivalence to the analogical measurement standards from other countries. Measurement standard operation algorithms (in weighting and comparing mode) and uncertainty sources contributing to the uncertainty budget of liquid density measurement, which make it possible to submit measurement results according to established international requirements, are analyzed in the publication.

Uncertainties in TDCR measurement revisited: Contribution of optical effects

In the Triple to Double Coincidence Ratio method in Liquid Scintillation Counting, the detection efficiency is calculated from the value of a free parameter describing the intrinsic light yield of the counting system. This model is generally based on a Poisson distribution of the number of photoelectrons detected and the detection efficiency is obtained from the complement of the non-detection efficiency. In the classical free parameter model, the mean of the Poisson distribution, m, is a constant but some variability of this mean could be expected from optical effects due to internal reflections inside the LS source or from non-homogeneity of the detection efficiency of the photomultiplier tubes. Then, m becomes a random variable and the distribution of the photoelectrons becomes a compound Poisson distribution, with a random variable as mean value.This paper explores the implications of the variance of m, which were, to our knowledge, never considered previously in the uncertainty budget of TDCR measurements.

A high precision VIS/NIR dynamic goniometer-spectrometer

We present a method for measuring the refractive index (RI) and spectral characteristics of transparent triangular prisms based on the minimum deviation technique. The proposed method has been developed to automatically measure RI simultaneously for three different wavelengths to determine the spectral dependence of RI. A high precision dynamic goniometer with a He-Ne ring laser and continuously rotating autocollimation mirror was used to implement the proposed method. A set of reference prisms made of optical glass were experimentally studied and the measurement uncertainty budget was estimated. The obtained values of the expanded measurement uncertainty did not exceed 4.6 × 10−6 for near-infrared and 1.2 × 10−5 for visible wavelength ranges with a coverage factor k = 2 (95% level of confidence). It is shown that this method can be used for high-precision measurements of the RI and determine the spectral characteristics.

Current observed global mean sea level rise and acceleration estimated from satellite altimetry and the associated measurement uncertainty

Abstract. We present the latest release of the global mean sea level (GMSL) record produced by the French space agency Centre National d’Etudes Spatiales (CNES) and distributed on the AVISO+ website. This dataset is based on reprocessed along-track data, so-called L2P 21, of the reference missions TOPEX/Poseidon (TP) and Jason-1, Jason-2 and Jason-3. The L2P 21 CNES/AVISO+ GMSL record covers the period January 1993 to December 2021 and is now delivered with an estimate of its measurement uncertainties following the method presented in Ablain et al. (2019). Based on the latest calibration (Cal) and validation (Val) knowledge, we updated the uncertainty budget of the reference altimetry mission measurements and demonstrate that the CNES/AVISO+ GMSL record now achieves stability of performances of ± 0.3 mm yr−1 at the 90 % confidence level (C.L.) for its trend and ±0.05 mm yr−2 (90 % C.L.) for its acceleration over the 29 years of the altimetry record. Thanks to an analysis of the relative contribution of each measurement uncertainty budget contributor, i.e. the altimeter, the radiometer, the orbit determination and the geophysical corrections, we identified the current limiting factors to the GMSL monitoring stability and accuracy. We find that the radiometer wet troposphere correction (WTC) and the high-frequency errors with timescales shorter than 1 year are the major contributors to the GMSL measurement uncertainty over periods of 10 years (30 %–70 %), for both the trend and acceleration estimations. For longer periods of 20 years, the TP data quality is still a limitation, but more interestingly, the International Terrestrial Reference Frame (ITRF) realization uncertainties becomes dominant over all the other sources of uncertainty. Such a finding challenges the altimetry observing system as it is designed today and highlights clear topics of research to be explored in the future to help the altimetry community to improve the GMSL measurement accuracy and stability.

Prospects for the Development of Reference Materials of the Wobbe Index

The thermophysical properties of gaseous fuel, including the calorific value and the Wobbe index, are one of its main properties for industrial use. The correctness of measurements of the volumetric energy of gas combustion is currently ensured by using sets of certified reference materials of the lowest volumetric energy of combustion based on pure gases: hydrogen, methane, ethane and propane GSO 11662–2020 / GSO 11665–2020 and gaseous mixtures GSO 11904–2022 / GSO 11907–2022 with metrological traceability to GET 16–2018. However, it becomes necessary to measure the gas relative density to air with established traceability to GET 18–2014 when determining the Wobbe index.The purpose of this research is to improve the accuracy of the pycnometer method for measuring the density of gases for further development and creation of metrological assurance in the field of measuring the Wobbe index.In the course of the research, an analysis of existing methods for determining the gas density was performed, as a result of which the pycnometer method set forth in GOST 17310–2002, GOST 34721–2021 was taken as the basis for the developed method. The uncertainty budget of gas density measurements was estimated using the pycnometer method. It has been established that the mass determination of the gas under study makes the greatest contribution to the total uncertainty. It was decided to increase the internal volume of the pycnometer and use a modified method for determining its volume to minimize the uncertainty.An imitator of a pycnometer with an increased volume was manufactured in an original design to solve the task of developing a modified pycnometer method for measuring the gas density. A gravimetrically produced gaseous mixture of the following composition was chosen for testing the developed method: CO2 – 40.22 mol. %, CH4 – rest.The theoretical significance of the results obtained lies in approbation of a modified pycnometer method to improve the measurement accuracy of such a gaseous fuel property as the Wobbe index. In the process of developing a modified pycnometer method, the measurement algorithm was tested, the density values of the studied gas were obtained, and the uncertainty budget of density measurements was estimated.The practical significance of the results of this research will expand the possibility of establishing metrological characteristics during the metrological assurance of Wobbe index analyzers, as well as apply the developed method in future accuracy control of the measurement results of the gas relative density to air.

Radiometric Traceability for Pyranometer Calibration Based on High Flux LEDs and Reference Detector

This article aims to establish a new system for pyranometer calibration traceable to the radiometric chain. Different spectrum high flux LEDs have been used as tunable irradiance sources. The calibration procedure, uncertainty budget, and traceability chain of the solar irradiance measurements are presented. Additionally, the results were evaluated using a reference pyranometer, calibrated traceable to radiometric traceability and World Radiometric Reference (WRR). The uncertainty values are also estimated to be around 1.19 % (k = 2) for LEDs-based pyranometer-pyranometer calibration (WRR traceability), and about 0.68 % ( k = 2 ) for reference standard radiometer based (Radiometric traceability). The deviation between the reference pyranometer and the pyranometer under test was about 0.8% using LED at 655nm for irradiance of 500 W/m2. The sensitivity results have been evaluated by reference standard pyranometer traceable to WRR using a xenon lamp as a solar source, with a deviation of about 1 %.

Derivation of uncertainty budgets for continuous above-water radiometric measurements along an Atlantic Meridional Transect.

Fiducial reference measurements are in-situ data traceable to metrology standards, with associated uncertainties. This paper presents the methodology used to derive the uncertainty budget for underway, above-water measurements from the Seabird Hyperspectral Surface Acquisition System deployed on an Atlantic Meridional Transect in 2018. The average uncertainty of remote sensing reflectance for clear sky days was ∼ 6% at wavelengths < 490 nm and ∼ 12% at wavelengths > 550 nm. The environmental variability such as sun position, wind speed and skylight distribution caused the greatest uncertainty. The different components of the uncertainty budget are critically assessed to indicate how the measurement procedure could be improved through reducing the principal uncertainty sources.

Uncertainty determination of a novel single flank rolling test facility for micro spur gears

Micro gears are particularly complex to manufacture in many respects, as their deviations are relatively high concerning their component size. In addition, tolerance specifications of common gear standards are currently not defined for small gear modules. To make a quantitative statement about the rolling behavior of a micro gear, the single flank rolling test is considered, since this method can provide information about the functional behavior of a gear. This novel approach investigates a single flank rolling test facility for micro spur gears specifically developed for this application and evaluates measurement uncertainties of single flank rolling deviation parameters. After a detailed description of the test facility, a task-specific measurement uncertainty budget is developed based on the experimental structure of the measuring instrument. Intensive experiments revealed expanded uncertainties of less than 1.5 µm. In addition, a process suitability analysis of the measurement system was carried out, which was proven for all investigated gear deviation parameters by extrapolated standard tolerances. This demonstrates that single flank rolling tests on micro gears with low measurement uncertainties are technically possible and forms a basis for further investigations in quantifying uncertainties of micro test facilities.

Measurement uncertainty analysis of a measurement flexure hinge in a torque standard machine

Abstract. An alternative method to using strain gauges to measure FT (please see Appendix A for a list of definitions) and TM under a static multi-component load by using a hinge flexure (also called measurement flexure or MF) is presented. Its usage in the 5 MN m torque standard machine (TSM) at the Physikalisch-Technische Bundesanstalt (PTB) to detect calibration torque moment shunts is described. The working principle consists of a displacement measurement by an interferometer and the determination of the MF stiffness in a special CSU. Essential measurement uncertainty influences, such as stiffness determination and measurement conditions, are discussed and quantified. The measurement uncertainty budget for this measurement principle is presented. A FE validation for the MF is discussed.

Errors-in-variables calibration with dark uncertainty

A model for errors-in-variables regression is described that can be used to overcome the challenge posed by mutually inconsistent calibration data. The model and its implementation are illustrated in applications to the measurement of the amount fraction of oxygen in nitrogen from key comparison CCQM-K53, and of carbon isotope delta values in steroids from human urine. These two examples clearly demonstrate that inconsistencies in measurement results can be addressed similarly to how laboratory effects are often invoked to deal with mutually inconsistent results from interlaboratory studies involving scalar measurands. Bayesian versions of errors-in-variables regression, fitted via Markov Chain Monte Carlo sampling, are employed, which yield estimates of the key comparison reference function in one example, and of the analysis function in the other. The fitting procedures also characterize the uncertainty associated with these functions, while quantifying and propagating the ‘excess’ dispersion that was unrecognized in the uncertainty budgets for the individual measurements, and that therefore is missing from the reported uncertainties. We regard this ‘excess’ dispersion as an expression of dark uncertainty, which we take into account in the context of calibrations that involve regression models. In one variant of the model the estimate of dark uncertainty is the same for all the participants in the comparison, while in another variant different amounts of dark uncertainty are assigned to different participants. We compare these models with the conventional errors-in-variables model underlying the procedure that ISO 6143 recommends for building analysis functions. Applications of this procedure are often preceded by the selection of a subset of the measurement results deemed to be mutually consistent, while the more discrepant ones are set aside. This new model is more inclusive than the conventional model, in that it easily accommodates measurement results that are mutually inconsistent. It produces results that take into account contributions from all apparent sources of uncertainty, regardless of whether these sources are already understood and their contributions have been included in the reported uncertainties, or still require investigation after they will have been detected and quantified.

The measurement uncertainty of air object spatial coordinates by rho-theta fixing

The features of measurement uncertainty evaluation of the coordinates of an air object by the rho-theta fixing are discussed. Measurement models are presented that link its coordinates in the local rectangular coordinate system with the spherical coordinates of air object, found using a rangefinder and a goniometer. The models include a correction for determining the location of the base station, a correction for determining the angle of elevation due to inaccuracies in the leveling of the station platform and azimuth, and a correction related to the inaccuracy of the station’s reference to the north. The measurement uncertainty budgets of rectangular coordinates which can be a basis for creation of software for automation of calculation of measurement uncertainties are resulted. Estimates of expanded uncertainties are found by the method of kurtosis. Expressions for the relative standard uncertainties of coordinate measurements are written and an example of their estimation for real data is given.