Marcantonio Catelani

SBT soft fault diagnosis in analog electronic circuits: a sensitivity-based approach by randomized algorithms

This paper addresses the fault diagnosis issue based on a simulation before test philosophy in analog electronic circuits. Diagnosis, obtained by comparing signatures measured at the test nodes with those contained in a fault dictionary, allows for sub-systems testing and fault isolation within the circuit. A novel method for constructing the fault dictionary under the single faulty component/unit hypothesis is proposed. The method, based on a harmonic analysis, allows for selecting the most suitable test input stimuli and nodes by means of a global sensitivity approach efficiently carried out by randomized algorithms. Applicability of the method to a wide class of circuits and its integration in diagnosis tools are granted since randomized algorithms assure that the selection problem can be effectively carried out with a poly-time algorithm independently from the fault space, structure, and complexity of the circuit.

Fault diagnosis of electronic analog circuits using a radial basis function network classifier

Abstract In this paper a fault diagnosis technique, which employs neural networks to analyze signatures of analog circuits, is proposed. Radial basis functions networks (RBFN) are used to process circuit input–output measurements, and to perform soft fault location. Both noise and effect of parameter variations in the tolerance ranges of non-faulty components are taken into account. The network is trained with circuit signatures, obtained by measuring and coding both circuit input and output signals, which are contained in a ‘fault dictionary’. In this context RBFN architecture is selected, because it is able to cope with ‘new fault’ conditions not well represented in the fault dictionary used for network training. The RBFN classifier was applied to linear and non-linear sample circuits, considering faults both at sub-system level and at component level. Simulations and experimental results show that the developed nets succeeded in classifying faults. The nets trained with single faults has in many cases detected also multiple faults.

Analog network testability measurement: a symbolic formulation approach

A symbolic formulation approach is applied to the problem of computing testability features of analog linear networks. The program, SAPTES, obtained by following this approach is presented. The program can be a very useful tool for designers and researchers in the field of linear analog circuits. SAPTES, which is written in LISP and runs on MS-DOS personal computers, is able to compute the testability of linear circuits of rather high complexity (composed of tens of components and nodes). Computational times range from a few tens of seconds to some tens of minutes on medium speed computers. The program is easily transportable to workstations or a mainframe, and, for the mainframe, program performance will considerably increase. >

On the application of neural networks to fault diagnosis of electronic analog circuits

This paper presents a new method for fault diagnosis in linear and non-linear analog circuits that is based on artificial neural networks. A fault dictionary in the frequency domain, previously constructed, represents the set of supervised data for learning. Feedforward networks acting as autoassociators with one hidden layer, trained by backpropagation, are used in order to identify the most likely faulty element causing the failure of the electronic circuit under test.

FMECA technique on photovoltaic module

The solar photovoltaic industry has seen rapid expansion in the past decade with an ever-increasing share of the electricity-generating capacity for the world. For the emerging photovoltaic (PV) industry the assessment of the quality and reliability of its products is becoming more and more important. To this aim and to ensure an optimal design and material choice, a failure modes, effects and criticality analysis methodology (FMECA) to classify the occurrence, the severity and the impact of all possible failure mechanisms on the PV system has been introduced. This helps to eliminate or reduce the impact of potential failure modes before the completion of the design and before failures occur in the field. By means of this analysis it can be noticed that a crucial aspect in PV systems is the cleaning status of the panel surface. In this paper this problem has been analyzed by means of an experimental activity. Finally a method for the assessment of the PV panel condition has been proposed.

A fuzzy approach for soft fault detection in analog circuits

Abstract An automatic fault diagnosis technique based on a fuzzy approach is presented and its performance is analyzed by means of two examples. The proposed technique is applied to the detection and the isolation of single soft faults in analog electronic circuits. Both faults at component and sub-system level are considered. A ‘simulation before test’ approach is followed: a fault dictionary is a priori generated by collecting signatures of different fault conditions simulated in the frequency domain. A fuzzy classifier is trained by data contained in the fault dictionary and used to process the circuit under test response during test phase. The effects of noise and of non-faulty parameter tolerance are taken into account.

Improvements to numerical testability evaluation

In this paper, some recent theoretical developments are reviewed and associated algorithms are proposed to determine the numerical testability for large multiinput multioutput systems. In our approach, the modified nodal analysis and the usual techniques for the sensitivity computation in the frequency domain are employed. According to the theoretical basis provided by Sen and Saeks [1] the testability evaluation is related to the computation of the number of linearly independent columns in a convenient form of the sensitivity matrix with rational entries having a common denominator. Then, by extending some results already obtained in [3], it is shown that the above-mentioned number can be determined by computing the numerical rank of a matrix comprised of the coefficients obtained by expanding the numerators of the sensitivities in a suitable orthogonal polynomial series. The numerical rank computation is simplified, particularly for large systems, through an algorithm based on the estimation of the polynomial degrees, which is performed by the iterative comparison between the Chebycheff and the corresponding Stirling coefficients.

A simplified procedure for the analysis of Safety Instrumented Systems in the process industry application

Abstract International Standards and Guidelines propose qualitative and quantitative methodologies for the safety assessment of the Safety Instrumented System (SIS). However, some of these methodologies are often complex and not very easy to apply. In fact, some criticalities are found by technicians voted to the functional safety such as the study of SIS for complex architectures, calculation of safety parameters, difficulties in the identification of the SIS subsystem during the design review to guarantee the safety requirements, and so on. The aim of this paper is to propose a simplified and more efficient methodology for safety assessment of electromechanical SIS in compliance with the Standards IEC 61508 and IEC 61511. The proposed technique is based on an alternative implementation of the Reliability Block Diagram (RBD) approach for the performance analysis of the Safety Instrumented System. In order to demonstrate the advantages of the proposal, a case study of some of the safety functions is considered. With respect to other methodologies normally used for safety analysis, the results proved the proposed approach both easier in the application and time-saving. In addition, such results are comparatively close to those obtained by using the Standard methods.

The FMEDA approach to improve the safety assessment according to the IEC61508

According to the Standard IEC61508, the paper presents a case study concerning the evaluation of both the safe failure fraction (SFF) and the probability of failure on demand (PFD) for a complex system. After a preliminary presentation of the criteria for the safety integrity level (SIL) verification, the work focuses the attention on the method to achieve the PFD. In particular, an approach based on failure modes, effects and diagnostic analysis (FMEDA) is proposed and then a comparison with the approach described in the Standard. The paper aims to clarify both the knowledge and the application of the IEC61508 and proposes a technique to satisfy the hardware safety integrity requirements.

Recursive random-sampling strategy for a digital wattmeter

A recursive random-sampling strategy is proposed for the implementation of a digital broadband wattmeter. In this strategy each sampling instant is obtained by adding to the preceding one a predetermined constant lag plus a random increment. In order to correlate the measurement uncertainty to the bandwidth, the asymptotic mean-square error arising from the sampling strategy and the filtering algorithm is evaluated and analyzed; it has been shown that the proposed sampling strategy does not limit the bandwidth of the instrument if an appropriate statistical distribution of the random increments is selected. The theoretical results are compared with those obtained by simulating the measurement process. >