Metrological Performance Research Articles

Improvement of Hall Effect Current Transducer Metrological Performances in the Presence of Harmonic Distortion

The performance of Hall effect current transducers (HECTs), under distorted waveform conditions, is usually characterized by means of a frequency response test. In this paper, it was investigated if frequency response is able to correctly evaluate the ratio and the phase errors under distorted conditions. Two HECTs, with the accuracy class level of 1% and 0.5%, respectively, were experimentally characterized under two conditions: 1) sinusoidal excitation with frequencies ranging from 50 to 750 Hz, which is the well-known frequency response test, and 2) nonsinusoidal excitation using fundamental frequency and one harmonic with adjusted amplitude and phase shift. It was found that ratio and phase errors are weakly affected by the harmonic amplitude and phase shift, with respect to the fundamental in the accuracy level of 0.1% and 0.05°. They have, instead, a strong dependence from conductor location in the HECT window. These results suggest that the frequency response approach for the evaluation of HECT performance, under distorted waveform conditions, can be used for an error compensation method only if the position of the primary conductor is known. An error compensation method, based on the frequency response, was implemented and tested with a distorted waveform composed of fundamental and many harmonics. For each of the harmonic components, the errors were reduced to one tenth of the measured ones.

Computer aided design of Langasite resonant cantilevers: analytical models and simulations

Analytical models for the piezoelectric excitation and for the wet micromachining of resonant cantilevers are proposed. Firstly, computations of metrological performances of micro-resonators allow us to select special cuts and special alignment of the cantilevers. Secondly the self-elaborated simulator TENSOSIM based on the kinematic and tensorial model furnishes etching shapes of cantilevers. As the result the number of selected cuts is reduced. Finally the simulator COMSOL ® is used to evaluate the influence of final etching shape on metrological performances and especially on the resonance frequency. Changes in frequency are evaluated and deviating behaviours of structures with less favourable built-ins are tested showing that the X cut is the best cut for LGS resonant cantilevers vibrating in flexural modes (type 1 and type 2) or in torsion mode.

The use of ultrasonic treatment for improvement of metrological performance of sorption atomic absorption determination of lead(II) and cadmium(II) traces

Abstract The optimal parameters for ultrasonic treatment (frequency 200–300 kHz, intensity 2–4 W cm−2) were obtained to intensify Pb(II) and Cd(II) sorption concentration by carbon sorbent from apricot pit. The combined action of ultrasonic frequency of 18 kHz and 1 MHz on concentrate slurry increases its sedimentation stability from 3 to 180 minutes and decreases Sr value up to 7% at Pb(II), Cd(II) hybrid sorption atomic absorption determination in natural waters, brines, common salt.

Metrological performance of optical coordinate measuring machines under industrial conditions

An increasing number of manufactured parts are measured in industry using non-contact measuring systems. The paper describes an industrial comparison of coordinate measuring machines (CMMs) equipped with optical sensors, performed in Europe from August 2007 to January 2009 involving 21 optical CMMs. Participants, mainly small–medium size industrial companies, were asked to measure a set of calibrated artefacts with measurement tasks of different complexity. They include both 1D/2D standards (glass scale and optomechanical hole plate) and 3D injection moulded workpieces of different colours (four plastic Lego bricks). In addition to the evaluation of actual metrological performances of optical CMMs in industry, an important aim of the comparison was to investigate the validity of measurement uncertainty statements provided by participants. The focus of this investigation was on the additional error sources that emerge when using optical CMMs. Results demonstrate that: (i) the interactions of optical sensors with material and surface of parts are among the most important error sources; (ii) the users of optical CMMs in most cases are not aware of the magnitude of these effects; (iii) specific uncertainty evaluation procedures, suitable for industrial users of optical coordinate measurements, are needed.

Methodology for metrological analysis of periodic coding images: measurement resolution and spatial resolution

Optical full-field techniques have a great importance in modern experimental mechanics. Even if they are reasonably spread among the university laboratories, their diffusion in industrial companies remains very weak for several reasons, especially a lack of metrological performance assessment. A full-field measurement can be characterized by its resolution, bias, measuring range, and by a specific quantity, the spatial resolution. The present communication proposes an original procedure for the estimation in one single step of the resolution, bias and spatial resolution for a given operator (decoding algorithm, such as image correlation, low-pass filters, derivation tools, ...). This procedure is based on the construction of a particular multi-frequential field, and a Bode diagram representation of the results. This analysis is applied to various phase demodulating algorithms for the estimation of in-plane displacements.

An empirical regressive model to improve the metrological performance of mobile spatial coordinate measuring systems

The mobile spatial coordinate measuring system (MScMS) is a system to perform dimensional measurements of large-scale objects. It consists of a wireless measuring probe with ultrasonic (US) transceivers, the position of which is determined using a distributed constellation of analogous transceivers arranged around the measuring area. The principle is to measure the time-of-flight (TOF) of the US signals exchanged between pairs of transceivers and, consequently, to obtain an estimate of their distances. The accuracy of TOF measurements can be attributed to many factors; the most influential are those associated with US signal attenuation. The purpose of this paper is to build an experimental correction model to reduce the MScMS’ error in TOF measurements. First, a two-way block design, which is based on exploratory experiments, is created to show that transmitter—receiver distance and relative orientation between US transceivers have significant effects on TOF measurement error. Next, an empirical regressive model is constructed on the basis of additional detailed experiments. After performing an extensive experimental validation, the model is automatically implemented by MScMS, with an iterative procedure. The most important benefit of such a model is an important reduction in the dispersion and an improved accuracy associated with TOF measurements.

Optimising calibration and measurement capabilities in terms of economics in conformity assessment

Calibration measurement capabilities (CMC) are key factors in declaring the metrological performance of national metrology institutes (NMIs). Different countries have different CMC capabilities, reflecting both the existing measurement science competence as well as the perceived national needs for traceable calibration. This paper deals with increasing interest in decision-making in conformity assessment in terms of effective costs associated with measurement, testing and incorrect decision-making. The work examines the CMCs of calibration laboratories and NMIs with economic decision theory, in particular, in terms of customer satisfaction and with respect to conformity assessment issues. Optimal strategies for calibration costs, maintenance of national measurement standards, testing and production costs are illustrated in practical examples. CMCs are an essential instrument to enable conformity assessment both for product safety, legal metrology, quality requirements as well as scientific research. The newly defined term “target measurement uncertainty”, introduced in the latest international metrology vocabulary (VIM), should be therefore always related to appropriate CMCs and related dissemination paths in the whole conformity assessment procedure. These requirements are clear and transparent justification for the development of required national metrological infrastructures, in order to fulfil the requirements of target measurement uncertainty for intended use or application in the particular conformity assessment procedure.

Dielectric Spectroscopy of Liquids Through a Combined Approach: Evaluation of the Metrological Performance and Feasibility Study on Vegetable Oils

In this work, a time domain-based approach for the estimation of the dielectric parameters of liquids is presented. The proposed approach combines traditional time-domain reflectometry measurements with a specific data processing and modeling that leads to the evaluation of the Cole-Cole parameters. The pivotal step of the procedure is the implementation of an accurate transmission line model of the used measurement cell. In this way, the error contributions due to undesired parasitic effects are minimized; hence, the overall accuracy is significantly enhanced. The proposed approach is tested through repeated measurements on well-referenced materials; this also allowed performing the related metrological analysis. Successively, the proposed procedure is applied for the evaluation of the Cole-Cole parameters of vegetable oils. In fact, at the state-of-the-art, only limited data are available for the dielectric characteristics of vegetable oils. In particular, ten different types of vegetable oils are considered. Results show that the proposed approach has strong potential also for possible practical applications in the area of anti-adulteration and quality control.

Characterization of analogue-to-digital converters of a commercial digital voltmeter in the 20 Hz to 400 Hz frequency range

This paper describes the result of work performed at the Laboratoire National de Métrologie et d'Essais (LNE) aiming at characterizing the metrological performance of analogue-to-digital converters of a commercial digital voltmeter in the 20 Hz to 400 Hz frequency range. In order to reach uncertainties at the 10−6 level, ac–dc thermal transfer techniques have been used to determine the most suitable sampling parameters for these digitizers with respect to the measured signal frequency. Under such conditions, the agreement between the sampling technique and thermal ac–dc transfer is of the order of 2 µV V−1.

Metrological Performance of Traffic Detection Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> All of the more advanced traffic management techniques base their efficiency on reliable traffic detection systems. In a very important and emerging field, where the technical solutions proposed to measure and collect traffic primary data are not few, a unique methodology to evaluate and compare their performance still misses. In this paper, the problem of the metrological characterization of traffic detection systems is widely treated, founding inspiration on the ISO Guide to Uncertainty in Measurement. Experimental results are reported to demonstrate the applicability of the suggested procedure to some commercial instruments. </para>

Investigation of the grid method for accurate in-plane strain measurement

This paper deals with the accurate measurement of the in-plane strain components on a deformed specimen using the grid method. A crossed grid transferred on the specimen surface is used for this purpose. Images of this grid are captured with a CCD camera before and after deformation. The complete strain state is deduced by processing these images with a suitable procedure described in the paper. The originality of this procedure is twofold. The first one is to determine the phase derivatives directly from the images. The second one is to compensate local variations of the grid pitch as well as local rotations of the grid, because these two phenomena may corrupt the final strain maps if they are not taken into account. The metrological performance of this procedure is assessed and discussed in terms of accuracy, measurement noise and spatial resolution. Two types of tests are used for this purpose: a translation and a rotation. These tests simulate the effect of rigid-body motion in a strain field that is rigorously equal to zero. One example finally illustrates the procedure: a tensile test performed on an open-hole specimen.

A procedure for measuring the metrological performance of a dissolved oxygen sensor

A procedure for measuring the linearity of a dissolved oxygen sensor is proposed and substantiated mathematically. The application of the proposed procedure is illustrated by the results from an experimental study of a serially produced analyzer of dissolved oxygen.

Surface-Response-Based Modeling of Digitizers: A Case Study on a Fast Digital Integrator at CERN

A statistical approach to simulation in behavioral modeling for assessing dynamic metrological performance during the concept design of accurate digitizers is proposed. A surface-response approach based on a statistical experimental design allows operating conditions to be systematically and comprehensively explored, simulation to be optimized, and identification and validation uncertainty to be verified. An actual case study on the dynamic metrological characterization of a fast digital integrator for high-performance magnetic measurements at the European Organization for Nuclear Research (CERN) is presented.

Mobile Spatial coordinate Measuring System (MScMS) – introduction to the system

In many industrial fields (for example, automotive and aerospace) dimensional measurements of large size objects should be easily and rapidly taken. Nowadays, the problem can be handled using many metrological systems, based on different technologies (optical, mechanical, electromagnetic, etc.). Each of these systems is more or less adequate, depending on measuring conditions, a user's experience and skill, or other factors like time, cost, dimensions, accurateness, portability, etc. In general for measuring medium-large size objects, portable systems can be preferred to fixed systems. Transferring the measuring system to the measured object place is often more practical than vice-versa. The purpose of this paper is to introduce a new system called Mobile Spatial coordinate Measuring System (MScMS). The system has been designed to perform dimensional measurements of medium-large size objects. MScMS is made up of three basic parts: a ‘constellation’ of wireless devices, liberally distributed around the working area; a mobile probe to register the coordinate points of the measured object; and a PC to store data sent by the mobile probe – via Bluetooth – and to process them by means of ad hoc application software. MScMS is easily adaptable to different measuring environments and does not require complex procedures for installation, start-up or calibration. This document presents the system hardware/software/firmware architecture and functionalities and describes the peculiarities and metrological performances of MScMS first prototype, which has been developed at the industrial metrology and quality laboratory of DISPEA – Politecnico di Torino. Finally, the most critical aspects of MScMS are illustrated and the research perspectives for future improvements are given.

Configuration control of carbon nanotube probe in atomic force microscopy

To precisely control the nanotube probe’s length and orientation, focused ion beam (FIB) milling and irradiation processes are utilized in the study. The carbon nanotube (CNT) probes’ length is optimized by FIB milling and the end of the CNT probe after FIB processing is found to be a round end with a fullerenelike cap. Using ion beam irradiations method, the carbon nanotube probes are bended and aligned to the desired orientation due to the strain introduced by the ion beam and CNT’s excellent plastic ability as well. The evaluation of carbon nanotube probe’s metrology performance is also made by correlating CNT probe structures with the probe’s atomic force microscopy (AFM) images resolution. It is found that the CNT probe can well overcome the bending response effect on the image resolution if its lateral force constant is larger than 0.086 N/m and CNT probe’s angle is less than 30°. The nanotube probe after FIB alignment shows high image resolution, and it can detect an edge with vertical angle of 88.374°, which a common pyramid-shaped AFM probe is not capable of doing. It is also confirmed that the probes with fullerenelike cap end show higher imaging resolution than those with an open end.

A metrological large range atomic force microscope with improved performance

A metrological large range atomic force microscope (Met. LR-AFM) has been set up and improved over the past years at Physikalisch-Technische Bundesanstalt (PTB). Being designed as a scanning sample type instrument, the sample is moved in three dimensions by a mechanical ball bearing stage in combination with a compact z-piezostage. Its topography is detected by a position-stationary AFM head. The sample displacement is measured by three embedded miniature homodyne interferometers in the x, y, and z directions. The AFM head is aligned in such a way that its cantilever tip is positioned on the sample surface at the intersection point of the three interferometer measurement beams for satisfying the Abbe measurement principle. In this paper, further improvements of the Met. LR-AFM are reported. A new AFM head using the beam deflection principle has been developed to reduce the influence of parasitic optical interference phenomena. Furthermore, an off-line Heydemann correction method has been applied to reduce the inherent interferometer nonlinearities to less than 0.3 nm (p-v). Versatile scanning functions, for example, radial scanning or local AFM measurement functions, have been implemented to optimize the measurement process. The measurement software is also improved and allows comfortable operations of the instrument via graphical user interface or script-based command sets. The improved Met. LR-AFM is capable of measuring, for instance, the step height, lateral pitch, line width, nanoroughness, and other geometrical parameters of nanostructures. Calibration results of a one-dimensional grating and a set of film thickness standards are demonstrated, showing the excellent metrological performance of the instrument.

Challenges and Opportunities for Optical CD Metrology in Future Lithography Process

As the IC industry is progressing towards 32 nm technology, Optical CD metrology will play an important role to help address many challenges in process control. OCD has the unique capability to characterize many critical dimensions in-line for complicated device structures nondestructively. Future process integration requires frequent W2W monitoring and feed forward / feedback control for critical layers. This makes integrated metrology (IM) a key option in process tools, and currently OCD is the only viable option for CD IM. In order to seize these opportunities, many improvements for OCD are need. Optical tools may need to be further optimized for better CD metrology performance. OCD modeling software should be able to model complicated structures and greatly boost ease of use. Furthermore, a well developed IM-SA OCD common platform is needed as the foundation for advanced process and equipment control.

Optimal pitch map generation for scanning pitch design in selective sampling

The reverse engineering process represents one of the best known methodologies for creating three-dimensional (3D) virtual models starting from physical ones. Even if in the last few years its usage has significantly increased, the remarkable involvement of the operator has until now represented a significant constraint for its growth. Having regard to the fact that this process, and in particular its first step (that is the acquisition phase), strongly depends on the operator’s ability and expertise, this paper aims at proposing a strategy for automatically supporting an “optimal” acquisition phase. Moreover, the acquisition phase represents the only moment in which there is a direct contact between the virtual model and the physical model. For this reason, designing an “optimal” acquisition phase will provide as output an efficient set of morphological data, which will turn out to be extremely useful for the following reverse engineering passages (pre-processing, segmentation, fitting, …). This scenario drives the researcher to use a selective sampling plan, whose grid dimensions are correlated with the complexity of the local surface region analyzed, instead of a constant one. As a consequence, this work proposes a complete operative strategy which, starting from a first raw preliminary acquisition, will provide a new selective sampling plan during the acquisition phase, in order to allow a deeper and more efficient new scansion. The proposed solution does not require the creation of any intermediate model and relies exclusively on the analysis of the metrological performances of the 3D scanner device and of the morphological behaviour of the surface acquired.

Integration of metrological principles and performance evaluation in a proficiency testing scheme in support of the Council Directive 98/83/EC

Proficiency testing as a means of external quality assessment plays the role of independent evidence of laboratories’ performance. To enable laboratories to fulfil the requirements stated in legislation, methodology for evaluation of laboratories’ performance in proficiency testing schemes should incorporate principles of measurement results which are fit for intended use and incorporate evaluation of laboratories’ performances based on independent reference value. A proficiency testing scheme was designed to support Drinking Water Directive (98/83/EC) specifically. The methodology for performance evaluation, which takes into account a “fitness for purpose”-based standard deviation for proficiency assessment, is proposed and discussed in terms of requirements of the Drinking Water Directive. A ζ′-score, modified by application of target uncertainty was developed in a way that fulfils requirements defined in the legislation. As an illustration, results are reported for nitrate concentration in water. The approach presented can also be applied to other fields of measurements.

Multi-system measurement of aerodynamic loads

The basic features of projection and manufacture of multicomponent system of measurement of aerodynamic loads of beam type are observed. The previous estimation of metrology performances of the gained system is conducted.