Online ISSN
1751-8830
Print ISSN
1751-8822
IET Science, Measurement & Technology
Volume 2, Issue 5, September 2008
Volumes & issues:
Volume 2, Issue 5
September 2008
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- Author(s): M. Paulvanna Nayaki and A.P. Kabilan
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 269 –274
- DOI: 10.1049/iet-smt:20070080
- Type: Article
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p.
269
–274
(6)
The application of an optoelectronic-sensor-based virtual instrument designed by the authors, for visualising and estimating the degree of corrosion of steel surfaces exposed to different concentrations of sulphuric acid, is reported. The optoelectronic sensor consisting of a light-emitting diode (LED) and a pair of photo detectors was fixed very close to the sample placed on a stepper motor-driven moving platform so that the sample surface may be scanned by a thin light beam from the LED. The reflected and scattered light signals from each point in the scanned area were acquired separately by the two detectors in the sensor module. A parameter incorporating the relative value of these signals proved to be a fairly reliable measure of the degree of corrosion. The corrosion factor values were computed by a personal computer and presented in the form of a three-dimensional graph. The average values of the corrosion factor for different steel samples were plotted against the concentration levels of the corroding agent. The variation of the corrosion factor was found to obey a bilogarithmic law, which was in conformity with the previous results. - Author(s): P.M. Nirgude ; D. Ashokraju ; A.D. Rajkumar ; B.P. Singh
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 275 –285
- DOI: 10.1049/iet-smt:20070072
- Type: Article
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p.
275
–285
(11)
Frequency response analysis (FRA) is an emerging, powerful non-intrusive condition monitoring and diagnostic tool for verifying the mechanical integrity of power transformers. FRA results are graphical in nature and require trained experts to interpret test results. The work reported discusses numerical-criteria-based evaluation techniques. Persons not familiar with interpreting the FRA results can apply the evaluation criteria. The various criteria help in deriving proper conclusions. By evaluating correlation coefficient (CC), standard deviation and absolute sum of logarithmic error (ASLE) techniques, it is possible to discriminate between defective and non-defective windings. Experimental studies were conducted on two test transformers for axial and radial displacements, and additionally two sets of identical substation transformers. The techniques mentioned above are useful for interpreting frequency responses even in situations when a reference fingerprint was not available. However, it was concluded that if original fingerprints are available, the method gives very reliable indication for diagnosing the faulty winding. In addition, the severity of displacement/deformation can also be concluded from the amount of variation of the parameters from the suggested critical values. - Author(s): P. Raumonen ; S. Suuriniemi ; L. Kettunen
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 286 –294
- DOI: 10.1049/iet-smt:20070101
- Type: Article
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p.
286
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(9)
Manifolds offer a generalisation to the modelling procedure, where the domain of an electromagnetic boundary value problem is a subset of a particular coordinate system. First of all, instead of identifying the points of the domain with coordinates, manifolds implement the principle that coordinates are not canonical. Second, in manifolds the coordinates are deliberately not bound by the distances between the points of the domain they represent. Finally, a manifold does not need to be coverable by a single coordinate system, but by several. These basic properties of manifolds make it possible to choose a coordinate system or systems that alleviate mesh generation problems caused by limited accuracy of floating point numbers. The authors propose three practical mesh generation-friendly problem representations. - Author(s): G. Antonini and F. Ferranti
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 295 –303
- DOI: 10.1049/iet-smt:20070110
- Type: Article
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p.
295
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(9)
A method for analysing tapered lossy transmission lines is presented. The Telegrapher's equations are solved by using the closed-form Green's function of the corresponding uniform transmission line. The space-dependent characteristic impedance is handled as a forcing term of the Telegrapher's equations whose effect is incorporated into the Fredholm integral equation of the second kind describing the space voltage distribution. The method allows to avoid the segmentation technique which is prone to inaccuracies because of spurious reflections at the boundaries of each section. Several tests are carried out and excellent results are obtained confirming the superior accuracy of the proposed method with respect to the standard segmentation technique. - Author(s): M. Birkett ; J. Brooker ; R. Penlington ; A. Wilson ; K. Tan
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 304 –309
- DOI: 10.1049/iet-smt:20070076
- Type: Article
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p.
304
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(6)
Thin film resistors have been manufactured to evaluate the electrical performance characteristics of AlCuMo thin films. The films were prepared on Al2O3 substrates at room temperature as a function of Mo concentration by DC magnetron sputtering and were then annealed at various temperatures in air and N2 atmospheres. The effect of annealing temperature on the electrical properties of the films was systematically investigated. Increase in Mo content produced a decrease in temperature coefficient of resistance (TCR), an increase in resistivity (ρ) and an improvement in long term stability (ΔΩ/Ω) of the films. TCR varied from negative to positive and further improvements in resistance stability of the films were also achieved through increasing annealing temperature in both air and N2 atmospheres. A temperature region is proposed where ‘near zero’ TCR (ppm/°C) and long term stability of better than 0.2% can be realised. - Author(s): G. De Cicco and B. Morten
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 310 –316
- DOI: 10.1049/iet-smt:20080007
- Type: Article
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p.
310
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A method of simple implementation is presented for the measurement of the specific heat of thick film layers. It has to do with a system, operating at room temperature in accordance with a dynamic non-adiabatic technique, whose function regards the transient phase of a heating process between two steady states. It consists of a compact ensemble of three elements: a small plate thermistor serving as a heater, an alumina disk as a sample support and a tiny calibrated thermistor as a temperature sensor. The voltage across the heater and temperature from the sensor are monitored. An accurate evaluation of the dissipated energy allows the absorbed energy, responsible for the temperature variation, to be brought out. That makes possible the determination of thermal capacity of a small mass material deposited on a substrate. The achievement of the result simply involves the recording of a voltage and temperature during the transient phase, a fitting procedure with given analytical functions and a mathematical elaboration. The measuring system, its calibration procedure together with the transient operation are described. An application concerning screen-printed ferroelectric thick films on alumina substrate is presented and the results discussed. - Author(s): B.K. Li ; H.T. Hui ; C.H. Yang ; S. Crozier
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 317 –325
- DOI: 10.1049/iet-smt:20080033
- Type: Article
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p.
317
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A new decoupling method for magnetic resonance imaging (MRI) phased arrays is studied by experimental measurements. A laboratory measurement setup is built to characterise the signal coupling paths and their coupling strengths. A new concept, the receiving mutual impedance, is introduced to measure the coupled signals between the phased array elements. Measured values of the receiving mutual impedances for a typical two-element surface-coil array are obtained and used in other experiments to find the uncoupled voltages from the received voltages. Results show that the new decoupling method is both accurate and robust over a wide frequency range. Comparison of the uncoupled voltages with the actual ideal uncoupled voltages confirms that if the position of the signal source is known, almost error-free uncoupled voltages can be obtained. The errors resulted from a change of the position of the signal source are also measured and it is found that they generally increase with the deviation of the signal source from its position where the receiving mutual impedances are measured. The maximum % error of the uncoupled voltages is found to be below 10% when the signal source changes its position over a distance of half the length of a surface coil. Over this distance change, the signal isolation between the two surface coils is found to be at least 20 dB, whereas the maximum is more than 300 dB. The results demonstrate the effectiveness and the feasibility of the new decoupling method for use in MRI phased arrays. - Author(s): J. Lei ; S. Liu ; Z.H. Li ; M. Sun
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 326 –336
- DOI: 10.1049/iet-smt:20080029
- Type: Article
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p.
326
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Electrical capacitance tomography (ECT) is a non-invasive imaging technology that aims at the visualisation of the cross-sectional permittivity distribution of a dielectric object based on the measured capacitance data. Successful applications of ECT depend greatly on the precision and speed of the image reconstruction algorithms. ECT image reconstruction is a typical ill-posed problem, and its solution is unstable, that is, the solution is sensitive to noises in the input data. Methods that ensure the stability of a solution while enhancing the quality of the reconstructed images should be used to obtain a meaningful reconstruction result. An image reconstruction algorithm based on the regularised total least squares (TLS) method that considers the errors in both the sensitivity field matrix and the capacitance data for ECT is presented. The regularised TLS method is extended using a combination robust estimation technique and an extended stabilising functional according to the ill-posed characteristics of ECT, which transforms the image reconstruction problem into an optimisation problem. In addition, the Newton algorithm is employed to solve the objective functional. Numerical simulations indicate that the algorithm is feasible and overcomes the numerical instability of ECT image reconstruction; for the cases of the reconstructed objects considered here, the spatial resolution of the reconstructed images obtained using the algorithm is enhanced; as a result, an efficient method for ECT image reconstruction is introduced. - Author(s): V. Thiagarajan
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 337 –348
- DOI: 10.1049/iet-smt:20070092
- Type: Article
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p.
337
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When a pulsed electric potential is applied to the terminals of a sliding electrical contact system, the armature translates under the influence of Lorentz forces caused by diffusing currents. The inductance gradient is conventionally used as a parameter to quantify the total Lorentz force acting on the armature and size the systems. The determination of the variation of the inductance gradient with system parameters such as the dimensions of the rails and armature, and the ramp rate of the applied potential is of interest in the design of sliding electrical contact systems with specified objectives. It is also useful in scaling results from laboratory to fieldable systems. The inductance gradient can be calculated with finite-element analyses using codes such as EMAP3D; this will be a time-consuming process. Semi-analytical formulations are possible for systems with simple and regular geometries such as rectangular sections. Solutions of the field diffusion equation can be expressed as a weighted sum of eigen functions characteristic of the geometry with imposed boundary conditions. A semi-analytical formulation based on eigen functions is presented here for computing and scaling inductance gradients of a sliding electrical contact system with rectangular rails and armatures. The effects of the dimensions of the rails and armatures, and the effect of the external ramp rate of the applied current on the inductance gradients are studied. The results are compared with available computational and experimental data. - Author(s): D. Thrimawithana and U.K. Madawala
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 349 –358
- DOI: 10.1049/iet-smt:20070064
- Type: Article
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p.
349
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(10)
Mathematical modelling of electric fence structures for high-voltage (HV) pulse propagation is complex in nature and, as such, electric fence energisers are currently manufactured using empirical rules together with a trial-and-error design approach. With no insight into the behaviour of HV pulse propagation along the fence line, the trend has merely been to develop electric fence energisers that could generate pulses with the highest voltage and the longest pulse duration allowed by the safety standards. Consequently, most current electric fence energisers are over rated and not optimally designed to produce an effective electric shock. An accurate insight into HV pulse propagation is an essential requirement for electric fence design and a semi-analytical technique is proposed to predict the propagation characteristics of HV transient pulses along multi-wire electric fences. The technique models the multi-line fence in frequency-domain to facilitate an analytical solution for the propagation of HV pulses along the fence. A modal transformation is used to decouple the frequency-domain solution, which is then transformed into time domain through a numerical Laplace inversion algorithm to determine the propagation characteristics of the fence at a given location and time. For various line conditions, the propagation of HV pulses is investigated, and the results are presented with comparisons to simulations by power systems computer-aided design to show the validity of theoretical analysis. The technique provides an insight into the propagation characteristics of HV pulses along multi-wire fence lines and thus serves as a tool at the design phase of electric fence energisers. - Author(s): S.L. Dvorak and B.K. Sternberg
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 359 –366
- DOI: 10.1049/iet-smt:20070117
- Type: Article
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p.
359
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The authors demonstrate how a transmitter (Tx), a reciprocal transmitter/receiver (Tx/Rx) signal path and two unidirectional receiver (Rx) paths can be used together with short, open, and load standards for the absolute vector error correction (AVEC) of a Tx/Rx module. Once calibrated, this Tx/Rx module can then provide accurate vector measurements of the signals that are flowing into and/or out of the test port. This novel AVEC technique is one of the key concepts in the design of a wideband absolute vector signal measurement system, which overcomes the limitations of traditional measurement instruments by combining the features of vector signal analysers, spectrum analysers, and vector network analysers. The AVEC method is validated using numerical simulation data for a simplified baseband test circuit. The AVEC technique is then extended to the calibration of wideband, high-frequency Tx/Rx modules that involve frequency up/down conversion mixers in a follow-on paper. - Author(s): V. Thiagarajan
- Source: IET Science, Measurement & Technology, Volume 2, Issue 5, p. 367 –375
- DOI: 10.1049/iet-smt:20080013
- Type: Article
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p.
367
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Electromagnetic launch involves diffusing fields and currents and finite-element analyses are usually employed to compute the transients in launch systems. The simulation times of interest in launch components such as sliding electrical contact systems and pulsed power systems vary from a few microseconds to a few milliseconds. Numerical solutions in such short time scales require very fine meshes to avoid instabilities. Benchmarking and validation of codes with finite-element analyses of coupled electromagnetic equations require checks on errors and instabilities. For this purpose, analytical series solutions have been derived here to describe the diffusing field transients in a few milliseconds in a ring conductor with rectangular cross section. A linearly ramped or step voltage is imposed on one axial end of the ring conductor, whereas the other axial end is grounded and maintained at zero potential. The coupled transient, one-dimensional diffusion equations have been solved using classical methods in applied mathematics. The distributions of currents and fields inside the conductor and the stored magnetic energy with time have been computed. The method presented here can be applied to any general excitation encountered in electromagnetic launch.
Real-time corrosion mapping of steel surfaces using an optoelectronic instrument based on lightwave scattering
Application of numerical evaluation techniques for interpreting frequency response measurements in power transformers
Applications of manifolds: mesh generation
Integral equation-based approach for the analysis of tapered transmission lines
Electrical characterisation of AlCuMo thin films prepared by DC magnetron sputtering
Method for specific heat measurement of thick film layers
A new decoupling method for phased arrays in magnetic resonance imaging: an experimental approach
Image reconstruction algorithm based on the extended regularised total least squares method for electrical capacitance tomography
Computation and scaling of inductance gradients in electromagnetic launch systems
Pulse propagation along multi wire electric fences
New absolute vector error correction technique for a transmitter/receiver module
Analytical solution for transient, diffusing fields inside a ring conductor with rectangular cross section
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