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Online ISSN 1751-8830 Print ISSN 1751-8822

IET Science, Measurement & Technology

Volume 4, Issue 2, March 2010

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Volume 4, Issue 2

March 2010

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    • Dynamic link performance analysis of a rescue worker's off-body communication system using integrated textile antennas
      • Author(s): P. Van Torre ; L. Vallozzi ; C. Hertleer ; H. Rogier ; M. Moeneclaey ; J. Verhaevert
      • Source: IET Science, Measurement & Technology, Volume 4, Issue 2, p. 41 –52
      • DOI:  10.1049/iet-smt.2009.0018
      • Type: Article
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      • p. 41 –52 (12)
        The performance of wireless data communication for fully equipped firemen walking indoors and communicating through textile patch antennas integrated into their clothing is evaluated. The small-scale fading experienced in the building is characterised, then a measurement with a walking test person is performed in different real-life situations. The channel estimations, level crossing rate and bit error rate for the signals of the multi-antenna receiver are studied and compared in different circumstances. The performance of diversity techniques is evaluated and the advantage of applying diversity is validated under different conditions.
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      Lightning impulse behaviour of short rod–plane gaps with a dielectric-covered rod
      • Author(s): P.N. Mavroidis ; P.N. Mikropoulos ; C.A. Stassinopoulos
      • Source: IET Science, Measurement & Technology, Volume 4, Issue 2, p. 53 –62
      • DOI:  10.1049/iet-smt.2008.0137
      • Type: Article
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      • p. 53 –62 (10)
        The breakdown mechanism of dielectric–covered rod/plane air gaps under positive lightning impulse voltages is investigated. Several gap lengths, varying between 2.5 and 15 cm, were employed and the simple air gaps were regarded as reference. The basic characteristics of coronas, namely inception time and voltage, were measured at applied voltages just sufficient for their inception up to voltages causing breakdown. Multiple level tests were conducted; thus, corona inception and breakdown probability distributions were obtained and time to breakdown was measured at several voltage levels. Interpretation of the results was made based on oscillograms of the electric field strength at the earthed plane, which was monitored through a capacitive probe, geometric field calculations and still photographs of the discharge at breakdown. In the dielectric-covered rod/plane gaps, breakdown occurs at higher applied voltages as a result of increase in both corona inception voltages and discharge path. The development of the discharge depends on the electric field distribution as modified by both space and surface charges associated with coronas preceding breakdown. Surface charge accumulation may affect the discharge path at breakdown.
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      Positive lightning impulse discharges along cylindrical insulating surfaces bridging a short rod-plane gap
      • Author(s): L.A. Lazaridis  and  P.N. Mikropoulos
      • Source: IET Science, Measurement & Technology, Volume 4, Issue 2, p. 63 –75
      • DOI:  10.1049/iet-smt.2009.0082
      • Type: Article
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      • p. 63 –75 (13)
        The salient characteristics of the predischarge phenomena and flashover along cylindrical insulating surfaces bridging a short rod-plane gap under positive lightning impulse voltages were measured in a wide range of applied peak voltages. Materials used in the investigation were polytetrafluoroethylene (PTFE), silicone-rubber, nylon and glazed porcelain; the case of air alone was regarded as reference. Corona inception is favoured by the presence of an insulating surface, this being more evident for materials of high permittivity and for initial than secondary corona. At relatively high applied voltages, the initial corona characteristics are directly related to the field enhancement at the tip of the stressed electrode. However, near threshold inception conditions there is a marked reduction of the inception field with material permittivity; an assisting mechanism of initiatory electron production was put forward to explain this behaviour. Initial corona streamers require higher applied voltages to arrive at the earthed plane when propagating along an insulating surface than in air alone. Flashover, closely related to secondary corona characteristics, is always preceded by continuous corona growth, occurring mainly in free air away from the insulating surface because of possible positive surface charge deposition by the initial corona; the latter is characteristic for polymeric insulating surfaces. There is a reduction of the dielectric strength of the gap in the presence of an insulating surface, more pronounced for higher material permittivity, related to the facilitating action of the field enhancement close to the rod tip on continuous corona growth preceding flashover.
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      Wavelet energy-based testing using supply current measurements
      • Author(s): M.G. Dimopoulos ; A.D. Spyronasios ; D.K. Papakostas ; A.A. Hatzopoulos
      • Source: IET Science, Measurement & Technology, Volume 4, Issue 2, p. 76 –85
      • DOI:  10.1049/iet-smt.2009.0037
      • Type: Article
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      • p. 76 –85 (10)
        In this study a test method based on wavelet energy of the supply current measurements is presented. The method has been utilised by a microcontroller-based versatile test system which is used for the production line testing of emergency luminaire products. The presented method is simple, offers a single–point test measurement solution and may easily be adapted to test various other analogue and mixed-signal systems. Fault detectability comparative experimental results between the wavelet energy and the root mean square (RMS) plus spectrum component values of the supply current measurements are presented showing the effectiveness of the proposed test method.
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      Parameters' optimisation for surge arrester circuit models
      • Author(s): C.A. Christodoulou ; L. Ekonomou ; G.P. Fotis ; P. Karampelas ; I.A. Stathopulos
      • Source: IET Science, Measurement & Technology, Volume 4, Issue 2, p. 86 –92
      • DOI:  10.1049/iet-smt.2009.0048
      • Type: Article
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      • p. 86 –92 (7)
        The appropriate modelling of metal–oxide (MO) surge arresters and the determination of the equivalent circuit parameters are significant issues, since the efficient representation of the arresters dynamic behaviour by the models improves the quality and reliability of the lightning performance studies. In the current work, an optimisation algorithm for the evaluation of the surge arrester models parameters is developed. Optimum arrester model equivalent circuit parameter values are selected, minimising the error between the simulated peak residual voltage value and this given by the manufacturer. The proposed methodology is applied on a 120 kV MO arrester, presenting its effectiveness, reducing the relative error between the simulated and manufacturer's peak residual voltage value around 50% with the use of the obtained optimum parameter values.
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      Adaptive complex unscented Kalman filter for frequency estimation of time-varying signals
      • Author(s): P.K. Dash ; S. Hasan ; B.K. Panigrahi
      • Source: IET Science, Measurement & Technology, Volume 4, Issue 2, p. 93 –103
      • DOI:  10.1049/iet-smt.2009.0003
      • Type: Article
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      • p. 93 –103 (11)
        A simple and robust non-linear filter algorithm has been proposed in this study for estimating the frequency of a time-varying sinusoidal signal under high noise conditions. The real signal is first converted to an analytical signal and its complex state-space model is derived. An unscented complex Kalman filter (CUKF) is then obtained using the complex signal model and the error covariances along with the Kalman gain are updated iteratively. Also, the stability and the convergence characteristics of the proposed filter are presented for a single sinusoid embedded in noise. It has been shown that the proposed algorithm works efficiently for the estimation of abrupt changes in signal frequency under high noise conditions. To evaluate the performance of the proposed algorithm several computer simulation results of real-time and synthetic signals are presented. Further to improve the performance of the proposed filter in the presence of significant noise and distortions, the covariance matrices are tuned iteratively.
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