Metrological Performance Research Articles

The Usage of High Voltage Amplifiers to Set up Reference Calibrators for Combined and Impulse Voltages up to 1 kV

An approach to set up reference calibrators to generate combined voltages, using voltage amplifiers, has been demonstrated. Four high voltage amplifiers were tested and studied. Measurements and experiments have shown that this approach could be used to set up calibrators for combined voltages, at least up to 1 kV. The advantage is the flexibility to generate separate or combined wave shapes (combination of AC, DC, distorted shapes, double exponential impulses such as lightening and switching impulses). This method could be beneficial to the fields where impulses, combined or not with DC or AC voltages, need a reference calibrator to calibrate digitizers. This method, relatively cheaper and simple to develop, reaches high metrological performance. For example, for lightning impulses up to 900 V, the uncertainties are lower than 0.2 % for the peak voltage, 1 % for the front time and 0.5 % for the time to half value . The traceability to the international system of units can be ensured by characterizing the gain using a step response, followed by the convolution technique.

Improvement in metrological performances of phthalocyanine-based QCM sensors for BTX detection in air through substituent’s effect

Molecular engineering in macrocyclic materials like metallophthalocyanines (MPc) is a powerful strategy to tune the thin film properties that can be relevant to develop high performance gas sensors. In this context, the present work reports the enhancement in BTX sensing properties of MPc-based quartz crystal microbalance (QCM) sensors through exploiting the large surface area of tertiary-butyl (ttb) substituent grafted at the periphery of CuPc. Thin films of CuPc and ttb-CuPc reveal distinct morphologies and microstructures, in which the former presents a locally organized columnar structure, while the latter has an amorphous structure, containing agglomeration of molecular clusters. Such structural variation of the MPc films has huge implications on benzene, toluene and xylenes (BTX) sensing properties of the QCM sensors, utilizing these materials as sensing layers. Responses of ttb-CuPc-based QCM sensor are amplified by ca. 4-times and response time is reduced, compared to CuPc-based sensor. Moreover, ttb-CuPc-based QCM sensor displays high repeatability, resolution better than 20 ppm, negligible hysteresis and high sensitivity with limit of detection to 2 ppm, 1 ppm and 0.7 ppm for benzene, toluene and xylenes, respectively. Such favorable metrological characteristics combined with negligible interference from other gases make this microsensors suitable for BTX detection in real environment at concentrations below the recommended guidelines.

Designing Patterns for DIC with Poisson Image Editing

BackgroundThe pattern used in DIC directly influences the quality of the measurement obtained with this technique, so it is of prime importance to optimize the geometry of the features characterizing the pattern to achieve the best metrological performance.ObjectiveThe primary objective of this study is to quantify the influence of the collinearity between the actual displacement and the pattern image gradient on the systematic and random errors affecting displacement fields measured by DIC.MethodsPoisson Image Editing (PIE), a technique borrowed from the image processing community where it was introduced to perform seamless cloning of images, has been employed here to render various patterns whose gradient is globally collinear to the displacement field. Directly integrating the displacement field considered as the image gradient does not lead to a sufficiently contrasted pattern. A texture is therefore superposed to the displacement field before integration.ResultsDifferent patterns obtained or not by PIE are compared, and it is shown with suitable simulations performed with synthetic images that rendering a pattern where the image gradient is globally collinear to the displacement significantly reduces the total error affecting the measurements. The value of this improvement depends on the texture added to the displacement field before applying PIE.ConclusionThis study demonstrates that the collinearity between the speckle image gradient and the displacement field reduces the error affecting the displacement fields measured by DIC. It also proposes a route to account for this displacement in the design of an optimized pattern when a priori knowledge on the direction of the displacement is available. If not, it is shown that a small checkerboard inlayed in a larger one leads to a metrological performance much better than that obtained with a classic random pattern, and close to that achieved with an optimized pattern for which the displacement field is accounted for.

Easy-to-implement measurement method for the energy dissipated on board train with uncertainty estimation

In the near future, the railway is seen as the most important solution for reducing greenhouse gas emissions due to transportation. Investment in this sectors are ongoing, in order to increase both the level of service and energy efficiency. The adoption of recent technological solutions, as storage systems or reversible substations, could foster the efficiency, increasing the capability of recovering braking energy. The braking energy is very difficult to measure, it requires installing expensive measurement systems on board trains. In a previous paper the authors already faced this issue developing an accurate technique usable off-line. In the present paper a simplified method, easy to be implemented on train control unit, based only on already available data, is proposed. The paper describes the phenomena of interest and related measurement issues. The analytical model for the power measurement together with a deep analysis on the input quantities are presented. The uncertainty analysis of the proposed method is presented and the uncertainty budget is performed on a real test case. The metrological performances of the method show suitable accuracy level for train energy management.

3D DIGITIZATION OF TRANSPARENT AND GLASS SURFACES: STATE OF THE ART AND ANALYSIS OF SOME METHODS

Abstract. In the field of industrial metrology, there is a rising need for 3D information at a very high resolution for micro-measurements and quality control of transparent objects such as glass bottles (beer, wine, cola, cosmetics, etc.). However, such objects are particularly challenging for optical-based 3D reconstruction methods and systems such as photogrammetry, photometric stereo, structured light scanning, laser scanning, typically resulting in poor metrological performances. Indeed, these methods require the surface of the object to diffusely reflect the incoming light, which is not the case with the glass material where refraction and absorption phenomena do not permit their use. Over the years, various methods have been investigated and developed to avoid the coating (or powdering) treatment often used to make transparent objects opaque and diffusely reflecting. Most of the approaches require either some a priori knowledge of the transparent object or assumptions about how light interacts with the surface. This paper provides a general overview of state-of-the-art 3D digitization methods for optically non-cooperative surfaces featuring absorption, scattering, and refraction. The paper reviews research works summarizing them into four categories including shape-from-X, direct ray measurements, hybrid, and learning-based approaches. Moreover, we provided some 3D results to better highlight the advantages and disadvantages of each method in practice when dealing with transparent objects.

SU(2) hyper-clocks: Quantum engineering of spinor interferences for time and frequency metrology

In 1949, Ramsey's method of separated oscillating fields was elaborated boosting over many decades metrological performances of atomic clocks and becoming the standard technique for very high precision spectroscopic measurements. A generalization of this interferometric method is presented replacing the two single coherent excitations by arbitrary composite laser pulses. The rotation of the state vector of a two-level system under the effect of a single pulse is described using the Pauli matrices basis of the SU(2) group. It is then generalized to multiple excitation pulses by a recursive Euler-Rodrigues-Gibbs algorithm describing a composition of rotations with different rotation axes. A general analytical formula for the phase-shift associated with the clock's interferometric signal is derived. As illustrations, hyper-clocks based on three-pulse and five-pulse interrogation protocols are studied and shown to exhibit nonlinear cubic and quintic sensitivities to residual probe-induced light-shifts. The presented formalism is well suited to optimize composite phase-shifts produced by tailored quantum algorithms in order to design a new generation of optical frequency standards and robust engineering control of atomic interferences in AMO physics with cold matter and anti-matter.

Pupil apodization in digital holographic microscopy for reduction of coherent imaging effects

A dark-field Digital Holographic Microscope with a single lens for imaging is a potential candidate for future overlay metrology on semiconductor wafers. Aberrations caused by this single lens are computationally corrected allowing high-resolution imaging over a large wavelength range. However, the spatially-coherent imaging conditions in our microscope introduce coherent imaging artifacts that can limit the metrology performance. We present computational apodization of the optical field in the exit pupil of the lens as a potentially effective solution to mitigate these coherent imaging effects. A comparison of experimental data and simulations is presented that demonstrates the importance of this apodization in metrology applications. Moreover, our data also shows that exploiting the full potential of DHM requires an imaging lens with low optical scattering levels.

Improving the dimensional accuracy of 3D x-ray microscopy data

X-ray microscopy instruments have the unique ability to achieve nondestructive imaging with higher spatial resolutions than traditional x-ray computed tomography (CT) systems. This unique ability is of interest to industrial quality control entities, as they deal with small features in precision manufactured parts (with tolerances in the order of ±25 µm or better). Since many of today’s technology and manufacturing companies demand increasingly higher levels of precision, accuracy, and reliability for dimensional measurements on feature sizes that are much smaller than 5 mm, it would be ideal to further expand the imaging capabilities of x-ray microscopy to the field of precision metrology. To address such demand, this paper describes the development of a measurement workflow, through a package consisting of hardware and software, to improve the accuracy of dimensional data obtained with 3D x-ray microscopes (XRMs)—also known as sub-micrometer CT systems. The measurement workflow, called Metrology Extension (MTX), was designed to adjust and configure the XRM instrument work-zone to perform dimensional measurement tasks. The main adjustments of an XRM instrument through the MTX workflow, which must be implemented before scanning parts of interest for dimensional evaluation, include applying a distortion map correction on the image projections produced by the x-ray detector and a voxel scale correction. The main purpose of this article is to present, evaluate, and analyze the experimental results of various measurement tests to verify the metrological performance of several XRM systems operating with the MTX workflow. The main results show that these systems can produce repeatable and reproducible measurements, with repeatability standard deviations of the order of 0.1 μm and reproducibility standard deviations of less than 0.5 μm. In addition, coordinate-based 3D XRM measurements produce dimensional accuracies comparable to those offered by high-precision tactile coordinate measurement machines (with deviations within the range of ±0.95 µm). Therefore, once the MTX workflow is executed, XRM instruments can be used to measure small volumes, in the order of (5 mm)3 or less, with improved dimensional accuracy.

Effects of counter-rotating-wave terms on the noisy frequency estimation

We investigate the problem of estimating the tunneling frequency of a two-level atomic system embedded in a dissipative environment by employing a numerically rigorous hierarchical equations of motion method. The effect of counter-rotating-wave terms on the attainable precision of the noisy quantum metrology is systematically studied beyond the usual framework of perturbative treatments. We find the counter-rotating-wave terms are able to boost the noisy quantum metrological performance in the intermediate and strong coupling regimes, whether the dissipative environment is composed of bosons or fermions. The result presented in this paper may pave a guideline to design a high-precision quantum estimation scenario under practical decoherence.

Optical diffraction tomography meets metrology — Measurement accuracy on cellular and subcellular level

Three-dimensional quantitative phase imaging (3D QPI) delivers volumetric information about the refractive index distribution within microobjects. Such imaging and measurement capabilities are of great interest for technical and biomedical applications, yet there are no standardized methods for testing and reporting metrological performance. Proper metrology is crucial for further developments in QPI and for cross-referencing a range of physical properties with other laboratories and techniques. In this paper we present methodology for metrological evaluation of the 3D QPI instruments for single-cell and subcellular structures. The methodology entails suitable phantom, its digital twin, quality assessment metric and easily reproducible protocol that is attainable for both numerical and experimental analysis. We demonstrate its applicability by comparing simulated reconstructions with measurement results from 3 optical diffraction tomography systems. The results will serve as a reference point for past and future research, encourage to benchmark the new systems in a similar manner and further the efforts towards the standardization in 3D QPI metrology.

Distributed phase estimation and networked quantum sensors with W -type quantum probes

Quantum sensors, offering novel sensing and imaging technologies beyond the capabilities of any classical device, enable harnessing new technologies from atomic clocks and nanoscale microscopy to gravitational wave detection and delicate biological measurements. We consider the performance of $W$-type quantum states as the probe for the networked quantum sensors. Providing an analytic result on the metrological performance of networked quantum sensors, we attain a criterion for the enhancement of the distributed phase estimations in networked quantum sensors. This insight enables us to compare the metrological power of certain quantum states. We also consider schemes that enable the generation and utility of such entangled quantum probes in practical settings.

Traceable determination of non-static XCT machine geometry: New developments and case studies

It is fundamental to determine the machine geometry accurately for dimensional X-ray computed tomography (XCT) measurements. When performing high-accuracy scans, compensation of a non-static geometry, e.g. due to rotary axis errors or drift, might become necessary. Here we provide an overview of methods to determine and account for such deviations on a per projection basis. They include characterisation of stage error motions, in situ geometry measurements, numerical simulations, and reconstruction-based optimization relying on image quality metrics and will be discussed in terms of their metrological performance. Since a radiographic calibration is always required to provide an initial absolute geometry, this method will be presented as well. The improvements of the XCT geometry correction methods are presented by means of case studies. The methods can be applied individually or in combination and are intended to provide a toolbox for XCT geometry compensation.

Advances in the metrological traceability and performance of X-ray computed tomography

X-ray computed tomography (XCT) is increasingly being used for evaluating quality and conformance of complex products, including assemblies and additively manufactured parts. The metrological performance and traceability of XCT nevertheless remains an important research area that is reviewed in this paper. The error sources influencing XCT measurement results are discussed, along with related qualification, calibration and optimization procedures. Moreover, progress on performance verification testing and on the determination of task-specific measurement uncertainty is covered. Results of interlaboratory comparisons are summarized and performance in various dimensional measurement fields is illustrated. Conclusions and an outlook for future research activities are also provided.

Influence of Concept Drift on Metrological Performance of Low-Cost NO2 Sensors

Low-Cost Air Quality Monitoring Systems (LCAQMS) and Machine Learning techniques are enabling a new paradigm in Air Quality Monitoring Networks. Nevertheless, compliance with Data Quality Objective (DQO) is still an open point. The assessment of various calibration models proposed in literature has ever neglected the Concept Drift, i.e. the differences in data distributions associated with input and target variables of the streaming data coming from dynamic nonstationary environments. The influence of the concept drift is investigated on the maintenance of the (calibrated) low-cost instrumentation. The data from mid-term co-location campaigns are firstly used to train a Multiple Linear Regression as calibration model. Then, an original methodology based on the Two-Sample Kolmogorov-Smirnov Test is proposed for automatically detecting the presence of the concept drift. The time evolution of the Relative Expanded Uncertainty is considered as well, to highlight the negative influence of the concept shift on the metrological performance of the LCAQMS, proving the need for the estimation of a new calibration model during the maintenance of the instrumentation in order to match the DQOs. A quantitative analysis is carried out on the distances among the training and test distributions about the input and outputs of the calibration model by correlating them with the time evolution of uncertainty. The scheme of an add-on block based on the proposed approach is designed for the continuous monitoring of the metrological performance exhibited by the calibration model. This management of the concept drift is expected to allow the long-awaited achievement of DQOs.

Conoscopic Holography feasibility for form error in-situ monitoring in Additive Manufacturing

The lack of standardization and the low quality of parts produced by Additive Manufacturing requires in certain cases the use of in-situ monitoring techniques based on the use of different types of sensors, each of which has advantages and disadvantages depending on the type and nature of the signatures to be analyzed. Therefore, in this work the feasibility of Conoscopic Holography (CH) technology is analyzed for in-situ monitoring of form errors that take place during the creation of each layer in an AM process. The results obtained using this sensor are compared to those of a Coordinate Measuring Machine used as ground truth. The CH sensor is also compared to a Contact Image Sensor in terms of metrological performance, proving the former to be more suitable and versatile for monitoring this type of errors.

Предпосылки для применения метода предиктивной аналитики для оценки метрологических характеристик турбинных преобразователей расхода

Предпосылки для применения метода предиктивной аналитики для оценки метрологических характеристик турбинных преобразователей расхода

A New Approach to Measure the Energy On-Board Train During Braking

Measuring energy wasted during braking by trains is a nontrivial task because it is performed by power semiconductor devices that switch high current levels at a few hundred hertz. The chopped signals produced are difficult to analyze, not only for the high switching frequency but also for the high slew rate that produces even higher harmonic content. In this harsh scenario, it is challenging to guarantee an adequate level of accuracy and it could be very expensive for railway operators, who often completely renounce measuring these quantities of interest, estimating it from mechanical quantities. In a previous article, we have already faced this issue by developing an accurate technique usable offline. Here, two simplified methods with suitable accuracy levels for train energy management and easy to be implemented on train control unit are proposed. This article describes the phenomena of interest and related measurement issues. A numerical solution together with a deep analysis on the input quantities needed is presented. The methods are applied to experimental data from a measurement campaign, conducted on-board train in the northern part of Italy. Furthermore, the metrological performances of the methods are assessed by adopting as a reference the offline technique.

Evaluation and Metrological Performance of a Novel Ionisation Vacuum Gauge Suitable as Reference Standard

Evaluation and Metrological Performance of a Novel Ionisation Vacuum Gauge Suitable as Reference Standard

Optimized Design and Characterization of a Non-Linear 3D Misalignment Measurement System

This work proposes a framework for the optimization of the metrological performances of a system that measures the relative position and orientation between two rigid bodies using the International Organization for Standardization (ISO) guide to the expression of uncertainty in measurement as a reference for the analysis. The developed method identifies a nonlinear measurement model of the instrument. The procedure uses the Monte Carlo method (MCM) and the design of experiments (DOE) techniques for determining the instrument uncertainty and the uncertainty sensitivity versus the geometrical and metrological instrument’s characteristics. The innovative result of the proposed approach lies in the derivation of nonlinear numerical models of the measurement uncertainty and the bias error components. A case study related to a misalignment measurement system based on a universal joint is presented. The measurement uncertainty computed with the proposed method is compared with the one obtained in fit-to-purpose experiments performed with a robotic manipulator. An optimal calibration procedure is then developed to identify the parameters of the system by minimizing the overall uncertainty. Results evidenced that the uncertainty of the misalignment, in the tested configuration, mainly depends on the uncertainty of the rotational measurements. The model has also been used to improve the design of the system by increasing the mounting and manufacturing tolerances of the most critical components.

Occupancy grid mapping for rover navigation based on semantic segmentation

Obstacle mapping is a fundamental building block of the autonomous navigation pipeline of many robotic platforms such as planetary rovers. Nowadays, occupancy grid mapping is a widely used tool for obstacle perception. It foreseen the representation of the environment in evenly spaced cells, whose posterior probability of being occupied is updated based on range sensors measurement. In more classic approaches, the cells are updated to occupied at the point where the ray emitted by the range sensor encounters an obstacle, such as a wall. The main limitation of this kind of methods is that they are not able to identify planar obstacles, such as slippery, sandy, or rocky soils. In this work, we use the measurements of a stereo camera combined with a pixel labeling technique based on Convolution Neural Networks to identify the presence of rocky obstacles in planetary environment. Once identified, the obstacles are converted into a scan-like model. The estimation of the relative pose between successive frames is carried out using ORB-SLAM algorithm. The final step consists of updating the occupancy grid map using the Bayes’ update Rule. To evaluate the metrological performances of the proposed method images from the Martian analogous dataset, the ESA Katwijk Beach Planetary Rover Dataset have been used. The evaluation has been performed by comparing the generated occupancy map with a manually segmented ortomosaic map, obtained by drones’ survey of the area used as reference.