Marco Laracca

Crack Shape Reconstruction in Eddy Current Testing Using Machine Learning Systems for Regression

Nondestructive testing techniques for the diagnosis of defects in solid materials can follow three steps, i.e., detection, location, and characterization. The solutions currently on the market allow for good detection and location of defects, but their characterization in terms of the exact determination of defect shape and dimensions is still an open question. This paper proposes a method for the reliable estimation of crack shape and dimensions in conductive materials using a suitable nondestructive instrument based on the eddy current principle and machine learning system postprocessing. After the design and tuning stages, a performance comparison between the two machine learning systems [artificial neural network (ANN) and support vector machine (SVM)] was carried out. An experimental validation carried out on a number of specimens with different known cracks confirmed the suitability of the proposed approach for defect characterization.

Crack Depth Estimation by Using a Multi-Frequency ECT Method

In many industrial application fields as manufacturing, quality control, and so on, it is very important to highlight, to locate, and to characterize the presence of thin defects (cracks) in conductive materials. The characterization phase tries to determine the geometrical characteristics of the thin defect namely the length, the width, the height, and the depth. The analysis of these characteristics allows the user in accepting or discarding realized components and in tuning and improving the production chain. The authors have engaged this line of research with particular reference to non-destructive testing applied to the conductive material through the use of eddy currents. They realized methods and instruments able to detect, locate, and characterize thin defects. In this paper, a novel measurement method able to improve the characterization of the crack depth is proposed. It is based on the use of a suitable multi-frequency excitation signals and of digital signal processing algorithms. Tests carried out in an emulation environment have shown the applicability of the method and have allowed the tuning of the measurement algorithm. Tests carried out in a real environment confirm the goodness of the proposal.

GMR-Based ECT Instrument for Detection and Characterization of Crack on a Planar Specimen: A Hand-Held Solution

This paper proposes a novel instrument for eddy-current (EC) nondestructive testing on conductive materials. The instrument is composed by a smart EC probe, based on a GMR sensor, and a suitable processing unit. The key features of the proposed instrument are the capability of detecting, locating, and characterizing thin defects as superficial and subsuperficial cracks. The main goal of the proposal is the realization of a very low cost instrument that is able to reach performance comparable with instrumentation available on the market and especially suited for application fields such as aerospace and maritime. In this paper, the steps followed for the instrument realization, together with its experimental characterization, are described in detail.

Improving GMR Magnetometer Sensor Uncertainty by Implementing an Automatic Procedure for Calibration and Adjustment

Giant Magnetoresistance (GMR) sensors have taken an important role in magnetic field sensing applications thanks to their small size, high sensitivity, large frequency response, low power and relatively low cost. A metrological characterization of a GMR magnetometer has highlighted the contributes to the measurement uncertainty due to hysteresis, non linearity and dependence from temperature. Starting from these knowledge, an automatic procedure for calibration and adjustment of GMR magnetometer has been set up. This procedure, based on a mixed hardware-software solution, allows a deep reduction of the measurement uncertainty for both AC and DC magnetic field strength measurements using GMR.

Multifrequency Excitation and Support Vector Machine Regressor for ECT Defect Characterization

Eddy current testing (ECT) has three main tasks: detection, location, and characterization of defects. The characterization task, which means the ability to find the geometrical characteristics of the defect, is still in the research domain, although in many industrial applications this task has to be carried out with good accuracy to allow reliable acceptance or rejection decision indispensable to save costs and even human lives. This paper proposes an ECT measurement method that allows the reliable estimation of the geometrical characteristics of thin defects (i.e., length, height, and depth) by using a combination of a multifrequency excitation and an optimized support vector machine for regression. The proposed solution is tested on real specimens with known cracks by using a suitable measurement setup comprising a giant magnetoresistance-based biaxial ECT probe.

Cost-Effective FPGA Instrument for Harmonic and Interharmonic Monitoring

The need of large-scale monitoring of power quality (PQ) in electrical power systems require the design of reliable and cost-effective measurement instruments. In this framework, Field Programmable Gate Array (FPGA) architectures seem to offer valid solutions since they allow powerful measurement algorithms to be implemented on low-cost hardware with reconfigurable firmware. This paper proposes a FPGA-based measurement instrument for harmonic and interharmonic monitoring in compliance with the most important PQ standards. Key feature of the proposed instrument is the very low requirements of hardware and firmware FPGA resources, thus making it suitable for applications that require cost-effective measurements. The proposed instrument shows performance comparable with one of the powerful and more expensive measurement solutions available on the market. In particular, despite the absence of a sampling frequency synchronization system, the proposed instrument proves to be compliant with IEC 61000-4-30, even in the presence of huge frequency deviations. After a description of the proposed hardware and firmware solutions, the experimental characterization of the proposed instrument in emulated and real environments is reported.

Multi-frequency Eddy Current Testing using a GMR based instrument

The paper proposes the use of a suitable multi-frequency approach applied to a novel instrument for 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 by a suitable processing unit. Key features of the proposed instrument are the capability of detecting, locating, and characterizing thin defects such as superficial and sub-superficial cracks. The proposed multi-frequency solution, together with a suitable data processing, allow both the sensitivity in the defect detection to be increased and the ability to evaluate the defect characteristics in terms of shape and dimension to be improved.

A measurement-driven approach to assess power line telecommunication (PLT) network quality of service (QoS) performance parameters

Power 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.

Calibration and adjustment of an eddy current based multi-sensor probe for non- destructive testing

In 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.

An FPGA-Based Instrument for the Estimation of

It is well known that most of todays electric and electronic devices frequently work with nonsinusoidal waveforms; then, all the passive R, L, and C components sited in these circuits are involved with nonsinusoidal stimuli. Because of their intrinsic nonlinearity, real resistors, inductors, capacitors, and so on show behaviors that are very different from those expected in a sinusoidal environment. Consequently, a problem of reliable assessment of these components in the presence of nonsinusoidal environments arises. This problem is even more critical in applications such as the creation of hybrid filters, control circuits based on patterns of sensing elements, and circuits of digital protection in power systems, where the design and control of electrical and electronic circuits depend on the correct modeling of the R, L, and C components. In previous research works, the authors proposed a suitable measurement method for the estimation of R, L, and C parameters of passive components in nonsinusoidal conditions. This paper deals with the realization of a measurement instrument, based on a Field Gate Programmable Array, that is able to continuously update the estimated values of the considered components. The instrument realization passes through an optimized implementation of the previously proposed measurement method aimed at minimizing the hardware resources and the computational burden and increasing the measurement rate. After a preliminary tuning of the measurement method, carried out in a simulation environment, the hardware and the software architectures of the realized measurement instrument, together with the measurement strategy, are described and experimentally characterized.