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Science, Measurement and Technology, IEE Proceedings -

Issue 4 • Date Jul 1995

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Displaying Results 1 - 10 of 10
  • Modelling and analysis of electrically conducting vessels and pipelines in electrical resistance process tomography

    Page(s): 313 - 322
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    Analyses of a novel boundary excitation strategy are given by employing both analytical and finite element method models to image the resistivity distribution of materials inside a process vessel having an electrically conducting boundary. A grouped-node technique is developed to model the conducting wall of the vessel and/or the consequent large electrode surfaces. The theoretical principle of the sensitivity density algorithm is derived and a sequence of unprocessed images depicting relative resistivity changes inside the test vessel are reconstructed using the sensitivity density coefficient reconstruction algorithm to demonstrate the effect of different insulated boundary electrode geometries. The significance of the data reported demonstrates the viability of using electrical resistance tomography in metal-walled process vessels and pipelines: applications which would greatly benefit from such low-cost robust sensing principles View full abstract»

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  • Signal processing of the contingent negative variation in schizophrenia using multilayer perceptrons and predictive statistical diagnosis

    Page(s): 269 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    An event related potential known as the contingent negative variation (CNV) was recorded from two sites from the brains of 20 medicated schizophrenics and 20 normal control subjects. The aim was to apply signal processing, artificial neural networks and statistical techniques to the CNV waveform to improve the understanding of schizophrenia and to develop a neurophysiological technique for its identification and monitoring. CNV recording sites were the vertex and from a point midline approximately 30 mm anterior to the vertex (frontal). Three-layer multilayer perceptrons (MLPs) were used to discriminate between the CNV waveforms of the schizophrenics and normal subjects. Although the MLP technique was successful in discrimination, it did not provide a quantitative measure for the analysis. Furthermore, during the test phase it always classified the subjects into one of the two categories and did not provide an output for either type (unknown type). To improve the clinical diagnosis a discrimination technique based on predictive statistical diagnosis (PSD) was developed. The input parameters to the PSD were a time domain feature and three features obtained from the energy spectrum of the CNV waveform. The PSD output indicated the probability and the atypicality index of each subject belonging to one of the two groups. Discrimination accuracy of the PSD was 100% for normal subjects. Three schizophrenics could not be classified into either type, but the rest were identified correctly. T-tests carried out on the recorded CNV waveforms showed that the CNV waveform recorded from the vertex site in normal subjects is significantly different from that recorded from the frontal site; however this was not the case for schizophrenics View full abstract»

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  • Effect of barriers on tree growth in solid insulation

    Page(s): 283 - 287
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The effect of the inclusion of particulate barriers in point-plane samples of polyester resin is investigated. The increase in lifetime as the particle size was increased is found to be only indirectly related to the particle size. The increase in lifetime is found to be due to a layer of compressive strain at the resin/barrier interface. This strain can be reduced by annealing or by destroying the adhesive bond between particle and resin. A similar discovery had been made with the inclusion of woven fibre barriers having a range of mesh size and thread diameter. When aluminium oxide particles are added to the fabric barriers, the resistance of the fabric to treeing is greatly enhanced. In addition to the improved treeing resistance, the addition of aluminium oxide also increases the thermal conductivity of the insulation, allowing higher equipment ratings to be achieved View full abstract»

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  • Finite-element variational formulation of the impedance boundary condition for solving eddy current problems

    Page(s): 293 - 298
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The impedance boundary condition (IBC), cast in magnetic vector potential (MVP) form as a general Neumann boundary condition, is imposed through the two-dimensional finite-element variational formulation to solve eddy current problems, especially at high frequencies. The proposed work introduces for the first time a boundary matrix (IBC matrix) which can be added to the original finite-element matrix. The results obtained from two test examples show that the formulation is valid for solving such problems View full abstract»

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  • Electromagnetic analysis of a two-wire transmission line of parallel cylinders of unequal radii with dielectric coating

    Page(s): 288 - 292
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The paper presents a method for the evaluation of capacitance, characteristic impedance and velocity of propagation of a dielectric-coated two-wire transmission line of parallel cylinders of unequal radii under TEM mode approximation. A conformal transformation is used to transform the conductor and dielectric boundaries to appropriate contours extending over a fixed region along the imaginary axis in the transformed plane. Approximating the continuous curve obtained through transformation of dielectric boundaries by a very large number of discrete steps, the expression for the capacitance is derived in the form of a definite integral. Numerical data on capacitance, characteristic impedance, velocity of propagation in the absence and presence of a perfectly conducting ground plane are presented View full abstract»

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  • Balloon model of biological cell electropermeabilisation in relation to the radius dependence of membrane dielectric breakdown

    Page(s): 277 - 282
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    A previously developed biological cell model, based on liquid-filled dielectric spheroid membranes, is used to investigate characteristics of electrofusion and electroporation. In particular, the radius dependence of dielectric breakdown is manipulated so as to reduce that dependence. This is accomplished by varying the decay time of a DC capacitive discharge impulse and by varying the resistivity of the model suspension medium. A slight adaption to the model shows that it is possible to cause dielectric breakdown of a balloon within a balloon at the same threshold levels. This is indicative of an organelle such as a nucleus inside a cell View full abstract»

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  • General approach to prove the existence and uniqueness of the solution in vector potential formulations of 3-D eddy current problems

    Page(s): 299 - 306
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    Gauging of vector potential formulations of 3-D eddy current problems is considered from a new viewpoint. Assuming that the formulation in terms of E and B of the eddy current problem under consideration has a unique solution, gauging can be regarded as setting conditions on potentials, say A, V and ψ, that ensure a one-to-one correspondence between pairs (E,B) and triples (A,V,ψ). This approach decouples two different issues which are usually mixed: gauging properly said and well-posedness of the field problem. Once the above one-to-one correspondence is proved, the existence and uniqueness of (A,V,ψ) will then automatically follow from that of (E,B) whenever the field problem is well-posed. Proving that the correspondence between (E,B) and (A,V,ψ) is one-to-one is a definitely easier task than proving the existence and uniqueness of (A,V,ψ) directly. The approach presented applies to both A,V, and T,ψ formulations and to problems ranging from magnetostatics to high frequency electromagnetics; no additional complexity comes out when dealing with nonlinear materials. Practical impact of the proposed method is discussed View full abstract»

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  • Phenomenon of sympathetic interaction between transformers caused by inrush transients

    Page(s): 323 - 329
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    In power systems with appreciable resistance, the transformers already connected to the supply system can experience unexpected saturation during the inrush transient of an incoming transformer. This saturation, which is established by the asymmetrical voltage drop across the system resistance caused by the inrush current, demands offset magnetising currents of high magnitude in the already connected transformers. This generates a transient interaction between the transformers, a `sympathetic interaction', that affects the magnitude and duration of the inrush current. As a consequence, problems in the operation of the system, such as false operation of transformer differential relays and prolonged temporary harmonic overvoltages, can occur. The sympathetic interaction between the transformers is analysed in the paper. System configurations with transformers in parallel and in series are investigated. The transformers and system models have been validated using small transformers View full abstract»

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  • Shape classification of flaw indications in three-dimensional ultrasonic images

    Page(s): 307 - 312
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    The rapid evolution of computing hardware technology now allows sophisticated software techniques to be employed which will aid the NDT data interpreter in the process of defect detection and classification. The paper describes an investigation into the area of three-dimensional ultrasonic image evaluation and, more specifically, the problem of characterising the shape of suspect flaw regions. A backpropagation neural network is used as the classifier for a series of four three-dimensional feature extraction methods which are individually assessed on two particular recognition problems. The optimum technique was determined for inclusion in an evaluation environment called the NDT Workbench, which has been designed for the processing of real data. Two acquired ultrasonic data sets are assessed using the best-performing classification method View full abstract»

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  • Expert system for the optimum design of measurement systems

    Page(s): 330 - 336
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    An expert system for the automatic design of measurement systems has been developed. The expert system furnishes an unskilled user with specific information about system architecture, its devices and components, and practical indications for their use, optimising both consultation time and number of questions. In the paper, the knowledge base entities and the problem solving strategy are described in detail. An implementation pertaining to electrical power measurements is reported to highlight the main features of the proposed system View full abstract»

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