1,721,114 research outputs found
Metodi e strumenti di misura per l’esecuzione di test non distruttivi su materiali conduttori
No full textOptimized complex signals for Eddy Current Testing
No full textThe choice of optimized excitation devices and strategies is now interesting recent studies about Non Destructive Eddy Current Testing (ND-ECT). Recently, the attention has been paid to the use of complex excitation signals, meant as signals different from the sinusoidal ones and with wide frequency content. In particular, some studies have highlighted their suitability, respect to the sinusoidal one, in supporting the measurement, detection and quantification stages when 'difficult cases' are explored (i.e. very short or annealed cracks). Generally, two class of signal have been proposed in literature. They concern with signals that have to be analysed in the time domain and signals analysed in transformed domains. The former class is represented by signal as the pulsed or pseudo-noise, while the latter contains signal as the chirp or multi-frequency as the best candidate. The author have placed their attention to this second class of signal and in this paper they propose an experimental comparison among different realization of these excitation signals suitably designed to improve the quality of experimental data when difficult cases are experienced
Calibration and adjustment of an eddy current based multi-sensor probe for non-destructive testing
No full textIn this paper an easy way to calibrate and adjust the output response of a multi-sensor probe for non-destructive testing on conductive material is proposed in order to perform the calibration, a simple coil is used, considered as a reference magnetic field generator thanking to a preliminary characterization carried out by using a simulation software. An FFT based algorithm was then used for probe adjustment. The calibration and adjustment apparatus can be easily integrated in the realized multi-sensor probe, so realizing a self-calibrating NDT instrument. The realized probe has then been tested on specimen with known cracks and the experimental results have been compared with the theoretical ones showing a very good agreement
A measurement-driven approach to assess power line telecommunication (PLT) network quality of service (QoS) performance parameters
No full textPower line telecommunication (PLT) technology offers cheap and fast ways for providing in-home broadband services and local area networking. Its main advantage is due to the possibility of using the pre-existing electrical grid as a communication channel. Nevertheless, technical challenges arise from the difficulty of operating on a hostile medium, not designed for communication purposes, characterized by complex channel modeling and by varying time response. These aspects put practical problems for designers and testers in the assessment of network quality of service performance parameters such as the throughput, the latency, the jitter, and the reliability. The measurement of these parameters has not yet been standardized so that there do not exist reference test set-ups and measurement methodologies (i.e. the type of isolation from the ac main, the observation time and the number of experiments, the measurement uncertainty and so on). Consequently, experiments executed by adopting different methods may lead to incompatible measurement results, thus making it also impossible to have reliable comparisons of different PLT modems. Really, the development of standard procedures is a very difficult task because the scenarios in which the PLT modems can work are very wide and then the application of an exhaustive approach (in which all the parameters influencing the PLT performance should be considered) would be very complex and time consuming, thus making the modem characterization very expensive. In this paper, the authors propose a methodological approach to develop an efficient measurement procedure able to reliably assess the performance of PLT modems (in terms of network quality of service parameters) with a minimum number of experiments. It is based on both creating a reconfigurable grid to which real disturbing loads are connected and implementing an original design of the experiment technique based on the effects of the uncertainty of the measurement results. Methods are also provided to analyze measurement results and to estimate the measurement uncertainty
An uncertainty analysis for the calibration of GNSS-based vehicle speed meters
No full textIn the field of traffic speed measurement, thanks to the accuracy claimed by the manufacturer of Global Navigation Satellite System (GNSS) receivers (about 0.1 km/h) they are increasingly used as reference equipment for calibration of speed measurement instruments. In order to assure the traceability of the measurement results also the GNSS should be calibrated according to the rules of ISO/IEC 17025 standard and complying with the ILAC (International Laboratory Accreditation Cooperation) policy on the traceability of measurement results. Unfortunately, in this context, worldwide there is a strong limitation about the compliance to the ILAC policy. In this paper, an analysis about the suitability of an experimental calibration method for GNSS speed measurement systems has been carried out. Considering all the measurement uncertainty contribution a sensitive analysis has been made in order to understand which are the limits and/or the applicability of this calibration methodology in a speed range from 30 to 250 km/h, in compliance with the ISO/IEC 17025 and ILAC policy
Performance comparison in Ultra Wide Band positioning in sensor networks: least square minimization versus grid search approach
No full textThe localization task in sensor networks is partic-ularly critical whenever the sensor measurements are position-related, as in case of thermal and electromagnetic quantities. The deployment of a sensor network often requires the usage of low-cost devices able to achieve acceptable measurement accuracy and having the need to retrieve fast and accurate positioning information. In such networks, the localization task is generally performed by a special node coordinating the network. Nevertheless, its computing power is often limited. To this aim, in this paper we compare two different positioning techniques (least square minimization, grid search), to be applied in Ultra- Wide-Band positioning scheme, from the accuracy point of view and computing time required for accomplishing the task. They differ in working principle, needed a priori information, localization resolution and time to completion parameter. According to the available resources, the adoption of one of them should be prefer-able to the other one. Obtained results prove the goodness of both methods, specifically ranking them by application purposes. The paper is intended to give the designers an extensive analysis to evaluate pros and cons to adopt a completely blind positioning technique, namely the least square minimization, versus a more informed and constrained system, as the grid search case
Valutazione dell’applicabilità di filtri digitali per il monitoraggio della Power Quality in accordo con la Norma IEC 61000-4-7 su piattaforma FPGA
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Modelling, parametric analysis, and optimization of an experimental set-up for acoustic antenna calibration
No full textThe growing interest in the use of acoustic antennas in different fields justifies the increasing attention on calibration problems related to them. This paper focuses on the calibration problems of acoustic antennas proposing a dedicated strategy with the aim of assessing an optimized experimental setup guaranteeing the maximum accuracy. The effect of the location of sound sources and reference microphone was investigated first following a parametric approach: a dedicated numerical model, based on spherical wave equation solution, was used to theoretically predict signal produced by each microphone. After achieving precious information on the influence on the accuracy of the mentioned experimental setup parameters, a dedicated optimization process was adopted to identify layout configuration guaranteeing time delay satisfaction for the largest number of array microphones, compatibly with room available space constrain
A novel TMR based triaxial eddy current test probe for any orientation crack detection
No full textThe paper proposes the development, the analysis, and the experimental validation of a novel probe for Eddy Current (EC) Non-Destructive Testing especially thought to warrant good signal to noise ratios in the detection of thin defects when low excitation currents are adopted and whatever the orientation of the probe respect to the orientation of the defect. The probe is based on a simple double coil excitation, that generate a single direction EC flow, and adopts three magnetic sensors that form a triaxial magnetic sensor. Other main contributions of this paper are: i) performance analysis of an EC triaxial probe carried out in simulation environment that considers the measurement uncertainty of the magnetic sensors; ii) an experimental campaign that allow evaluating the performance of the realized probe; iii) a comparison between simulated and experimental results that prove the goodness of the proposed approach
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