Calibration Chain Research Articles

Proof of concept and new developments on a Kibble extension

Abstract This article describes the proof of concept of a Kibble extension for vacuum mass comparators and its further development. A Kibble extension is a technical extension for vacuum mass comparators to connect to the new definition of the International System of Units (SI) of 2019. A commercially available high-vacuum prototype mass comparator from Sartorius serves as the basis. It is used to compare kilogram prototypes, such as the international prototype kilogram ( K ) $(\mathfrak{K})$ , directly with other kilogram mass standards in order to realize a calibration chain. According to the new definition of the SI in 2019, the kilogram is defined by the Planck constant (h), therefore the Kibble extension is designed to enable high-vacuum mass comparators to be converted by technical modifications to allow mass to be realized according to the new definition. The aim is to realize kilogram prototypes and mass standards in the range from 1 mg to 1 kg according to the E1 standard of OIML R111-1 (2004). Initial measurement results with a prototype of the Kibble extension are presented and evaluated. Based on the experience gained, a lightweight magnet system developed with the use of simulation methods is presented. This is intended to contribute to the further development of the Kibble extension.

Uncertainty-based determination of recalibration dates

Traceability is of vital importance in metrology and is achieved by an unbroken chain of calibrations that relate the measurement result to a reference. Less clear is the temporal aspect of traceability, namely the determination of recalibration dates. Relevant standards require the conduction of recalibrations in a planned manner, and thus in general there is a calibration history consisting of a number of past calibrations for measurands that are part of the traceability chain. Nevertheless, commonly only the results of the last calibration of the standards of the traceability chain are considered when determining a measurement result. Furthermore, recalibration dates are often determined in a rather unscientific manner. Within this paper, a method is proposed to predict the current value of a measurand along with its uncertainty, taking into account all past calibrations. Based on the predetermined target measurement uncertainty of the measurand, it is possible to recognize the need for and thus to date recalibrations. The applicability of the method is investigated by examining the metrological compatibility of the predicted results with the results of subsequent calibrations of the calibration histories of a number of different standards. There is an explainable limitation of the applicability of the method to calibration histories that exhibit a correlation of time and the chosen calibration laboratory. However, the paper leads the way of future research to remedy the currently unsatisfying state regarding the handling of calibration histories and the determination of recalibration dates.

Novel developments of refractive power measurement techniques in the automotive world

Refractive power measurements serve as the primary quality standard in the automotive glazing industry. In the light of autonomous driving new optical metrics are becoming more and more popular for specifying optical quality requirements for the windshield. Nevertheless, the link between those quantities and the refractive power needs to be established in order to ensure a holistic requirement profile for the windshield. As a consequence, traceable high-resolution refractive power measurements are still required for the glass quality assessment. Standard measurement systems using Moiré patterns for refractive power monitoring in the automotive industry are highly resolution limited, wherefore they are insufficient for evaluating the camera window area. Consequently, there is a need for more sophisticated refractive power measurement systems that provide a higher spatial resolution. In addition, a calibration procedure has to be developed in order to guarantee for the comparability of the measurement results. For increasing the resolution, a measurement setup based on an auto-correlation algorithm is tested in this paper. In order to benchmark the proposed high-resolution refractive power measurement technique, a novel laser-based setup has been realized in the Volkswagen Laser Laboratory as a reference method tuned for high-accuracy measurements. Furthermore, a calibration procedure is established by using a single reference lens with a nominal refractive power of . For the calibration of the entire measurement range of the system, the lens is tilted by an inclination angle orthogonal to the optical axis. The effective refractive power is then given by the Kerkhof model. By adopting the measurement and calibration procedure presented in this paper, glass suppliers in the automotive industry will be able to detect relevant manufacturing defects within the camera window area more accurately paving the way for a holistic quality assurance of the windshield for future advanced driver-assistance system (ADAS) functionalities. Concurrently, the traceability of the measurement results is ensured by establishing a calibration chain based on a single reference lens, which is traced back to international standards.

Improved Primary Reference Cell Calibrations for Higher Accuracy Photovoltaic Cell and Module Performance Measurements

The adoption of photovoltaic (PV) modules for clean electricity relies on accurate measurements of their performance, which are essential for estimating their energy production potential. Herein, the calibration chain of PV cells and modules, with particular emphasis on primary reference cell calibrations, is discussed. Also, herein, the direct sunlight method the group has developed for these calibrations is presented and critical improvements and upgrades that lead to calibration uncertainty as low as 0.45% are discussed. The ultimate motivation behind this work is to provide low‐uncertainty performance measurements of PV modules, and lowering the calibration uncertainty of primary reference cells is a key first step toward achieving this goal. As the use of solar electricity continues to grow, the demand for primary reference cell calibrations inevitably increases beyond what the small handful of primary calibration laboratories can provide today. Therefore, this work can serve as a useful guide for implementing primary PV reference cell calibrations using the outdoor method, as well as outlining the critical elements required to make these calibrations highly accurate.

SSRMP Recommendations No 9: Reference dosimetry in low and medium energy x-ray beams

The SSRMP recommendations on reference dosimetry in kilovolt beams as used in radiation therapy were revised to establish current practice in Switzerland.The recommendations specify the dosimetry formalism, reference class dosimeter systems and conditions used for the calibration of low and medium energy x-ray beams. Practical guidance is provided on the determination of the beam quality specifier and all corrections required for converting instrument readings to absorbed dose to water. Guidance is also provided on the determination of relative dose under non-reference conditions and on the cross calibration of instruments.The effect of lack of electron equilibrium and influence of contaminant electrons when using thin window plane parallel chambers at x-ray tube potentials higher than 50kV is elaborated in an appendix. In Switzerland the calibration of the reference system used for dosimetry is regulated by law. METAS and IRA are the authorities providing this calibration service to the radiotherapy departments. The last appendix of these recommendations summarise this calibration chain.

The site-specific primary calibration conditions for the Brewer spectrophotometer

Abstract. The Brewer ozone spectrophotometer (the Brewer) is one of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW)'s standard ozone-monitoring instruments since the 1980s. The entire global Brewer ozone-monitoring network is operated and maintained via a hierarchical calibration chain, which started from world reference instruments that are independently calibrated via the primary calibration method (PCM) at a premium site (National Oceanic and Atmospheric Administration's (NOAA) Mauna Loa Observatory, Hawaii). These world reference instruments have been maintained by Environment and Climate Change Canada (ECCC) in Toronto for the last 4 decades. Their calibration is transferred to the travelling standard instrument and then to network (field) Brewer instruments at their monitoring sites (all via the calibration transfer method; CTM). Thus, the measurement accuracy for the entire global network is dependent on the calibration of world reference instruments. In 2003, to coordinate regional calibration needs, the Regional Brewer Calibration Center for Europe (RBCC-E) was formed in Izaña, Spain. From that point, RBCC-E began calibrating regional references also via PCM instead of CTM. The equivalency and consistency of world and regional references are then assured during international calibration campaigns. In practice, these two calibration methods have different physical requirements, e.g., the PCM requires a stable ozone field in the short term (i.e., half-day), while the CTM would benefit from larger changes in slant ozone conditions for the calibration periods. This difference dictates that the PCM can only be implemented on Brewer instruments at certain sites and even in certain months of the year. This work is the first effort to use long-term observation records from 11 Brewer instruments at four sites to reveal the challenges in performing the PCM. By utilizing a new calibration simulation model and reanalysis ozone data, this work also quantifies uncertainties in the PCM due to short-term ozone variability. The results are validated by real-world observations and used to provide scientific advice on where and when the PCM can be performed and how many days of observations are needed to achieve the calibration goal (i.e., ensure the calibration uncertainty is within a determined criterion, i.e., ≤5 R6 units; R6 is a measurement-derived double ratio in the actual Brewer processing algorithm). This work also suggests that even if the PCM cannot be used to deliver final calibration results for mid- or high-latitude sites, the statistics of the long-term PCM fitting results can still provide key information for field Brewer instruments as stability indicators (which would provide performance monitoring and data quality assurance).

Coulometric method with titratable impurity analysis and mass balance method: convert acidimetric purity to chemical purity for SI-traceable highest standard of qNMR (potassium hydrogen phthalate), and verified by qNMR.

In this study, the coulometric method with titratable impurity analysis and the mass balance method were successfully applied in the quantification of the certified reference material of potassium hydrogen phthalate (KHP) with accurate metrological traceability of chemical purity value (99.983% with an expanded uncertainty of 0.024%, k = 2). In contrast to the general coulometric titration method, the coulometric method with titratable impurity analysis enables the conversion of acidimetric purity to chemical purity: The acidimetric purity was determined by coulometric titration method, and then the impurities that may be titrated as principal components were found as far as possible using various methods and the result of deducting these impurities from the acidimetric purity can be considered as chemical purity. The mass balance method also accounted for all possible types of impurities as much as possible to improve the accuracy of the determined result. The accuracy and reliability of the purity results were subsequently verified by a two-step quantitative nuclear magnetic resonance (qNMR) method. This KHP certified reference material was the first hydrophilic internal standard of qNMR (applied in polar solvents) with an expanded uncertainty lower than 0.03%, which will become a major reference standard in the organic chemistry traceable calibration chain, especially when evaluating hydrophilic organic compounds to obtain purity values with very low uncertainty.

The Kelvin Redefinition and Practical Primary Thermometry

In May 2019 four of the seven base units of the International System of Units (the SI) were redefined and are now founded on defined values of fundamental physical constants. One of these was the kelvin which is no longer defined by the triple point of water but instead through a fixed value of the Boltzmann constant. In this paper the kelvin redefinition is introduced and the implications for temperature traceability and practical temperature sensing discussed. This will include outlining new approaches for temperature traceability, as well as discussing the rise of in-process calibration through practical primary temperature sensing approaches (where, in principle, no sensor calibration is required). These forthcoming changes are likely to have significant impact on everyone in the temperature calibration chain, whilst the advent of in-process temperature calibration should lead to step change improvements in process control, energy efficiency and product quality consistency and will help facilitate autonomous production.

Generalized electrical substitution methods and detectors for absolute optical power measurements

We have developed generalized methods for electrical substitution optical measurements, as well as cryogenic detectors which can be used to implement them. The new methods detailed here enable measurement of arbitrary periodic waveforms by an electrical substitution radiometer (ESR), which means that spectral and dynamic optical power can be absolutely calibrated directly by a primary standard detector. Cryogenic ESRs are not often used directly by researchers for optical calibrations due to their slow response times and cumbersome operation. We describe two types of ESRs with fast response times, including newly developed cryogenic bolometers with carbon nanotube absorbers, which are manufacturable by standard microfabrication techniques. These detectors have response times near 10 ms, spectral coverage from the ultraviolet to far-infrared, and are ideal for use with generalized electrical substitution. In our first tests of the generalized electrical substitution method with FTS, we have achieved uncertainty in detector response of 0.13% (k = 1) and total measurement uncertainty of 1.1% (k = 1) in the mid-infrared for spectral detector responsivity calibrations. The generalized method and fast detectors greatly expand the range of optical power calibrations which can be made using a wideband primary standard detector, which can shorten calibration chains and improve uncertainties.

Wide-Range Calibration of Magnetic Moments for Vibrating Sample Magnetometers

Vibrating sample magnetometers (VSMs) have been widely used in the characterization of industrial magnetic materials, and their reliability is dependent on proper calibration. To improve the precision and range of calibration for VSMs, current-carrying microcoils were used to produce a tunable magnetic moment over a wide range. Based on comprehensive designing, we built a detection coil set of 0.3% uniformity in 8 mm along vibration direction. The calibration chain via moment coils of 2.5 mm diameter and height has been linked up between Ni spheres and the quantum benchmark. The differential magnetic moment due to a change in the applied current was used for calibration without dependence on the magnetic field. Magnetic moments with ranges across four orders of magnitude were calibrated and compared to those of the nickel standard and slope method. In situ calibration of a wide range of magnetic moments for VSMs without dependence on the field and materials was established, and the typical relative standard error did not exceed 0.3% within the range of 2.5~3.7 memu.

Ionizing radiation metrology at the service of health: quality control of radiopharmaceutical dose calibrators in nuclear medicine unit -accurarcy, reproducibility and linearity tests-

Ensuring the effective use of a dose calibrator used for the practice of nuclear medicine, and the injection of the correct dose to the patient is the subject of a long traceable calibration chain, which serves to establish the relationship between the values of the activity indicated by the dose calibrator and the activity corresponding to ISO 2919 certified sealed sources whose activity is known with an uncertainty of less than 1 %. Our calibration program consists in carrying out various quality control on the CRC 55TR activimeter, namely the daily control which is carried out in the absence of any radioactive source, then the fidelity control carried out by a source of 37Cs and a source of 60Co, then the reproducibility check performed with a 137Cs source, and finally the linearity check performed with a 99mTc source. In our case the results obtained from the specific tests used to verify the proper functioning of the Capintec CRC 55tR activimeter in a nuclear medicine service in Morocco, shows an agreement with international standards so that the measurement of activities is done with significant results, in addition, to guarantee the metrological quality of the measurements delivered, Our laboratory registers in an accreditation process according to ISO 17025.

Application of systems thinking to the establishment of metrological traceability chains

International agreements in the field of metrology and accreditation of calibration laboratories are the basis for establishing global metrological traceability. Important elements of metrological traceability are calibration of measurement standards and measuring instruments, assessment of measurement uncertainty. The International Laboratory Accreditation Cooperation has a specific policy regarding on traceability of measurement results and estimation of measurement uncertainty in calibration.
 The partial concept diagram around metrological traceability in accordance with the International Vocabulary of Metrology is proposed. This diagram contains a total of nine metrological concepts, which have most of the associative relations. There are associative relations between the concept of metrological traceability chain and concepts of metrological traceability, measurement standard, calibration and calibration hierarchy, and through the concept of measurement standard with the concept of measurement uncertainty.
 Systems thinking to the analysis of state of proposed terminological system around metrological traceability was applied. For construction of generalized metrological traceability chain, all the established properties of the system elements around the terminology system of metrological traceability were taken into account.
 Generalized metrological traceability chain for different levels of the calibration hierarchy was proposed. The proposed chain can be used to develop appropriate chains for specific areas of measurement. To achieve this, it is necessary to determine the specific measured value, the required measurement uncertainty for different levels of the calibration hierarchy and select the necessary measurement standards. Such schemes should be used in national metrology institutes and calibration laboratories.

Ensemble transfer learning for cutting energy consumption prediction of aviation parts towards green manufacturing

Cutting energy consumption prediction gives decision supports for the energy-saving operation to realise green manufacturing. However, there are challenges when predicting aviation parts due to the machining features causing tool wear and expensive data labelling. Consequently, this paper builds a prediction model and emphasises training with limited experimental data by proposing an ensemble transfer learning approach. The approach incorporates transfer learning, i.e., TrAdaBoost-R2 (TR) algorithm, and calibration, i.e., Bayesian and Markov chain Monte Carlo calibration (MCMC). Firstly, a cutting energy consumption prediction model considering tool wear is formulated with cutting and tool parameters as the inputs. Secondly, a dataset including experiment and simulation data for training is constructed, where TR is used to identify the valuable data from the simulation model calibrated by MCMC. Then random forest regression (RFR) is introduced as a base learner to train the prediction model on the hybrid dataset. Finally, a case study of the aluminium alloy 7075 parts milling process shows that the proposed method is accurate in cutting energy consumption prediction. Compared with RFR and TR-RFR, the proposed method's coefficient of determination (R2) increases by 11.60% and 3.55%, indicating high goodness of fit under the same small samples of the experiment. Therefore, the proposed method could help determine the most efficient process plan without excessive time, materials and energy, significantly contributing to green manufacturing.

Verification of an in situ calibrated optomechanical accelerometer for use as a strong ground motion seismic reference

Optomechanical accelerometers offer in situ traceability to the international system of units through laser interferometry, providing an alternative to a calibration chain using instrumented shakers. Here, we examine the ‘self-calibrating’ property of a prototype optomechanical accelerometer for use as a seismic reference. We report the optomechanically derived sensitivity of the accelerometer and compare this in situ calibrated output to input accelerations from an instrumented shaker, finding agreement to be within ±1%. The comparison spanned frequencies between 3 Hz and 30 Hz, and for sinusoidal accelerations with amplitudes ranging from 0.01 m s−2 to 0.6 m s−2. These results are evidence that optomechanically derived sensitivity calibration can be equivalent to established international methods for primary calibration.

Calibration of the underground muon detector of the Pierre Auger Observatory

To obtain direct measurements of the muon content of extensive air showers with energy above 1016.5 eV, the Pierre Auger Observatory is currently being equipped with an underground muon detector (UMD), consisting of 219 10 m2-modules, each segmented into 64 scintillators coupled to silicon photomultipliers (SiPMs). Direct access to the shower muon content allows for the study of both of the composition of primary cosmic rays and of high-energy hadronic interactions in the forward direction. As the muon density can vary between tens of muons per m2 close to the intersection of the shower axis with the ground to much less than one per m2 when far away, the necessary broad dynamic range is achieved by the simultaneous implementation of two acquisition modes in the read-out electronics: the binary mode, tuned to count single muons, and the ADC mode, suited to measure a high number of them. In this work, we present the end-to-end calibration of the muon detector modules: first, the SiPMs are calibrated by means of the binary channel, and then, the ADC channel is calibrated using atmospheric muons, detected in parallel to the shower data acquisition. The laboratory and field measurements performed to develop the implementation of the full calibration chain of both binary and ADC channels are presented and discussed. The calibration procedure is reliable to work with the high amount of channels in the UMD, which will be operated continuously, in changing environmental conditions, for several years.

Analytical solution of uncertainty with the GUM method for a dynamic stereo vision measurement system.

Directed at the strong correlation among the input parameters and long measurement chain, which are difficult for uncertainty analysis with the guide of the expression of uncertainty in the measurement (GUM) method, a novel dynamic stereo vision measurement system based on the quaternion theory is presented to reduce the orthogonality restrictions of shafting manufacturing and application. According to the quaternion theory in the kinematic model of the cameras and the analytical solution of uncertainty with the GUM method, the complete, detailed, and continuous uncertainty results of the full-scale measurement space can be obtained. Firstly, one-dimensional turntables and rigid connections are utilized to form the motion cores and the automatic control carriers in the system. Secondly, the novel measurement model is used in the measurement process to shorten the calibration and measurement chains. Once the system based on the novel measurement model is set up, the analytical solution of uncertainty is utilized in the accuracy process. During the analysis process, the strong correlation among the extrinsic parameters is decoupled by introducing virtual circles and the measurement strategy with the GUM method. Through analyzing the relationship among the attitude angles, the major factors which influence the uncertainties in each axis and the final uncertainty are clarified. Moreover, the analytical continuous uncertainty maps for the uncertainties along each axis, combined standard uncertainty, and the expanded uncertainty are illustrated and the uncertainty variation tendency is declared. Finally, the analytical solution of uncertainty with the GUM method proposed in this paper predicts the uncertainty in the full-scale space and provides a new idea of the uncertainty analysis for the complicated combined measurement system.

Calibration chain transformation improves the comparability of organic hydrogen and oxygen stable isotope data

Abstract Stable hydrogen and oxygen isotopic compositions (δ2H and δ18O, respectively) of animal tissues have been used to infer geographical origin or mobility based on the premise that the isotopic composition of tissue is systematically related to that of local water sources. Isotopic data for known‐origin samples are required to quantify these tissue–environment relationships. Although many of such data have been published and could be reused by researchers, differences in the standards used for calibration and analytical procedures for different datasets limit the comparability of these data. We develop an algorithm that uses results from comparative analysis of secondary standards to transform data among reference scales and estimate the uncertainty inherent in these transformations. We apply the algorithm to a compilation of known‐origin keratin data published over the past ~20 years. We show that transformation improves the comparability of data from different laboratories, and that the transformed data suggest ecophysiologically meaningful differences in keratin–water relationships among different animal groups and taxa. The compiled data and algorithms are freely available in the ASSIGNR r‐package to support geographical provenance research, and more generally offer a methodology overcoming several challenges in geochemical data integration and reuse.

Metrological traceability of reference measurement procedures

Metrological traceability is a key concept of measurement uniformity assurance, characterizing the property of a measurement result, according to which it can be correlated with a reference for comparison through a documented continuous chain of calibrations, each of which contributes to measurement uncertainty. A unit of measurement through its practical implementation, or a measurement technique that includes a unit of measurement for quantities other than ordinal, or a standard can serve as a basis for comparison. However, for many objects in biotechnology and medicine a system for confirming the correctness and required accuracy of the measurement result cannot be implemented. The paper discusses methods and schemes for the implementation of the principle of metrological traceability in the absence of a chain of metrological traceability of the measurement result to a measurement standard. A calibration hierarchy scheme is proposed that combines measurements based on reference measurement procedure and reference materials certified with their help, carried out in the chemical industry and medicine.

MEASUREMENT UNCERTAINTY OF THE OPTICAL WAVELENGTH CALIBRATION 633 nm BY BEAT FREQUENCY MEASUREMENT METHODS

Measurement traceability is one of the critical aspects in metrology area. The measurement uncertainty had been evaluated to assure reliability of the optical wavelength calibration system for stabilized He-Ne laser 633 nm in SNSU-BSN. Beat frequency measurement was applied as a calibration method by utilizing KIM-1 as a reference standard that traceable to SI unit through CCL-K11 key comparison. Best measurement capability declares with a relative uncertainty of ±1.3×10 -10 by excluding UUC effect. The calibration replica was performed as a validation process, dual mode laser head Agilent 5519B took a role as UUC. As calibration result, beat frequency of KIM-1 and UUC is (122.931±0.060) MHz. Among all of the uncertainty sources, KIM-1 uncertainty most significant influence to the beat frequency uncertainty and the optical wavelength of the UUC laser in vacuum condition. Based on the evaluation result, the calibration system of stabilized He-Ne laser can be validated and trace back with documented unbroken calibration chain to the primary standard of length, KIM-1 where established in SNSU-BSN.

Status of the Phase-2 Tracker Upgrade of the CMS experiment at the HL-LHC

The Phase-2 Upgrade of the CMS experiment is designed to prepare its detectors for operations at the High Luminosity Large Hadron Collider (HL-LHC). The upgraded collider, scheduled to start operations in 2027, will lead to challenging conditions in terms of data throughput, pile-up and radiation. For these reasons the tracker detector will be entirely replaced by a new detector, the Phase-2 tracker. We present the status of the design, test and validation of the components of the Phase-2 tracker, and its read-out, calibration, control, and data processing chains.