1,721,097 research outputs found
Design of an efficient mobile measurement system for urban pollution monitoring
Full text linkIn recent years, the pollution monitoring in urban areas has become one of the most critical issues for local public authorities, which wish (or must) verify that pollution levels not exceed limits considered unsafe or that are regulated by local laws. Generally, the pollution monitoring is performed by using measurement stations located in few points of the region of interest since these stations are generally characterized by high costs, weights, and dimensions. Then, the pollution levels over the remaining area are predicted by means of suitable interpolation models. Due to the great variety of urban scenarios, it becomes very difficult to obtain reliable pollution levels in area in which the measurements has not been directly taken but only predicted. Consequently, the pollution monitoring can suffer of a lack of reliable information indispensable for the actuation of proper environmental management policies. In this framework, this paper proposes a mobile measurement system for the real time monitoring of environmental pollutions over urban areas. The proposed approach is based on the use of a set of vehicles, typically employed for public transportation inside the urban area, equipped with the proposed mobile measurement system allowing it to measure, store, and transmit the acquired data to a remote supervisor unit somewhere on the path followed by the vehicles. Particular attention has been paid on the definition of the metrological characteristics of the measurement devices with the aims of complying with the applicable European Directives accuracy requirements and of selecting a suitable trade-off between accuracy and cost. The experimental measurement campaign performed on a suitable urban scenario has confirmed the goodness of the proposed system
A method to design open loop current transducers for Busbar applications
No full textNon-contact current measurements are largely required in the context of smart grid applications, in which the flexibility, reduced size and low cost play a fundamental role. In this field, the current transducers based on magnetic field sensors has attracted the attention of many research activities. Several methods were proposed in literature to overcome the skin effect impact on the accuracy of this type of current transducers and to increase the immunity from the external magnetic fields, especially for rectangular conductors (e.g. flat busbars), characterized by a non-uniform distribution of the magnetic field with the frequency. In this context, this paper suggests a methodology to design a current transducer based on magnetic field sensors that identifies the best positioning of the magnetic sensors to achieve the required accuracy. The method is able to guarantee the accuracy in the full required frequency bandwidth and it can release the usage of the current transducer from the conductor geometry. The main idea of this methodology consists of calculating a linear combination of the magnetic sensors measurements, ensuring the linearity of the current transducer. The linear coefficients of this linear combination are optimized in the methodology to minimize the current measurement error related to the frequenc
A Novel multi-excitation ECT probe for deep defects with any orientation
No full textThe paper proposes a novel 4-quarter probe for Eddy Current (EC) nondestructive testing on conductive materials. The innovative aspect consists of the possibility to detect small superficial and buried defects with arbitrary orientation. The EC induced in the conductive plate is rotated by means of an amplitude modulation of two currents that generate two orthogonal magnetic fields in order to obtain a suitable detection of arbitrary oriented cracks. The probe performance is evaluated by means of Finite Element Analysis in the simulation environment of the software COMSOL Multiphysics. The goodness of the proposed probe was analyzed considering a defect with a length of 5 mm, height of 1 mm and thickness of 0.1 mm, positioned at different depths in an aluminum plate, showing good detection capabilities
Improving Defect Detection in Eddy Current Testing using Multi-Frequency Rotating Eddy Current Strategy
No full textThe detection capability of small defects, such as cracks, with arbitrary orientations, using eddy current testing techniques, is affected by both the direction of the eddy current path respect to the main defect orientation and the depth of the defect to be detected. To give an answer to this problems Rotating Eddy Current (REC) techniques and multi-frequency excitation have been proposed by the scientific community. In this paper, these two solutions have been applyed together in order to improve the detection performance for buried and superficial defects with any orientation. The developed probe together with the novel REC multi-frequency excitation strategy are detailed described and experimentally characterized in various scenarios, including surface and buried cracks, demonstrating the effectiveness of the proposed solution
Automated Eddy Current non-destructive testing through low definition lissajous figures
No full textIn the framework of Eddy Current Testing (ECT), this work presents an automated non-destructive testing method based on Eddy Currents which uses few geometric features of low definition Lissajous figures. A features vector representing the shape of the ECT magnetic field response represented in the complex plane is used as signature to recognize specific defects of aerospace structures. In order to evaluate the proposed method, the accuracy, specificity, sensitivity, precision, F-Measure, AUC, and Matthews correlation coefficient are used to rate the following classifiers: J48, multi-layer neural network and Naive Bayes. The used data set is carried out by lab experiments performed on an aircraft test-piece with several well-known defects. The results show the usefulness of the proposed approach to be used as an aided tool for ECT data analysis. It allows both an easier and shorten data interpretation by the qualified inspectors, and an increase in the diagnosis quality
A Non-invasive technique for long-term monitoring of gastroesophageal reflux-a pilot study
Full text linkMany people suffer from gastric or gastroesophageal reflux disorder (GERD) due to a malfunction of the cardia, the valve between the esophagus and the stomach. GERD is a syndrome caused by the ascent of gastric juices and bile from the stomach. This article proposes a non-invasive impedance measurement method and demonstrates the correlation between GERD and impedance variation between appropriately chosen points on the patient's chest. This method is presented as an alternative to the most widely accepted diagnostic techniques for reflux, such as pH-metry, pH-impedance measurement, and esophageal manometry, which are invasive because they use a probe that is inserted through a nostril and reaches down to the esophagus
GMR-based instrument for ECT on conductive planar specimens
No full textThe paper proposes a novel instrument for the eddy current non-destructive testing on conductive materials. The instrument is composed by a smart eddy current probe, based on a Giant Magneto Resistance sensor, and a suitable processing unit. Key features of the proposed instrument are the capability to detect, locate and characterize thin defects as superficial and sub-superficial cracks. The cost effective of the proposal, and the metrological performances of the realized instrument make it suited in several applications fields such as aerospace and maritime. In the paper the steps followed toward the instrument realization are described together with a preliminary experimental characterizatio
An AMR-Based Three-Phase Current Sensor for Smart Grid Applications
No full textIn a smart grid (SG) scenario, accurate and realtime information about key grid parameters (such as voltage and current in each node of the net) are strategic requirements. In order to grant the best tradeoff between the measurement accuracy and the economic sustainability of SG distributed measurements, the design and the development of suitable lowcost current/voltage sensors are required. To this aim, this paper proposes a three-phase contactless current sensor based on anisotropic magnetoresistance effect. A suitable sensors placement strategy is used to compensate the uncertainty due to the interfering magnetic fields (i.e., magnetic fields generated from other electrical apparatus near to the sensors or from the other wires of the three-phase system). After a preliminary characterization of the proposed solution in a simulated environment, an experimental validation is carried out and reported in this paper
Multisensor Acoustical Systems: Calibration and Related Problems
No full textNowadays, acoustic antennas are used in different application fields with the primary aim of detecting the presence and the position of acoustic sources. The uncertainty in the evaluation of the acoustic source position is related to the knowledge of right acoustic locations of the microphones in the array, which is different from the geometric ones and needs a suitable calibration procedure to be evaluated. This paper, after an analysis of the problems related to the calibration of acoustic antennas, proposes a dedicated strategy with the aim of assessing an optimized experimental setup guaranteeing the best uncertainty in the acoustic source location
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