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Electrical Engineers, Proceedings of the Institution of

Issue 9 • Date September 1973

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Displaying Results 1 - 25 of 26
  • Active RC lowpass filters for f.d.m. and p.c.m. systems

    Page(s): 945 - 953
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1018 KB)  

    Various techniques of active RC realisation of lowpass filters are discussed, and two methods which are considered to have engineering relevance are investigated in detail. The design of lowpass filters suitable for use in f.d.m. and p.c.m. systems is presented. The results of tests carried out on microelectronics models of these filters show that they meet the requirements for use in practical systems. View full abstract»

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  • THISS voter-switch analysis

    Page(s): 954 - 958
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    THISS is a hybrid combination of majority voting (originated by Von Neumann) and classical standby redundancy. The acronym THISS stands for `t.m.r./hybrid/single/single¿, where t.m.r. is an abbreviation of triple modular redundancy, or 2-out-of-3 majority voting of three parallel channels or convertors. The last two letter of THISS describe the terminal old age of the THISS system, which employs each of two surviving single channels, instead of the `2-out-of-3¿ majority voting used in the system's youth. Exact formulas for system reliability and unreliability are given, as well as good approximations for short missions and long missions. Both the effect of the redundancy itself and the effect of imperfect coverage can be described by formulas given for the mission-time-improvement factor. Any approach to the architecture of ultrareliable systems is very sensitive to uncoverage, or the discrepancy between the actual value of coverage and the ideal of unity. For the THISS system the simple formulas given for unreliability clearly indicate the quantitative effect of uncoverage and its importance. View full abstract»

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  • Double-stream flow in the smooth-bore magnetron

    Page(s): 959 - 961
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (426 KB)  

    The smooth-bore magnetron exhibits anomalous behaviour when the magnetic field is large enough to `cut-off¿ the device. Although it appears certain that instabilities are responsible for this, a knowledge of the possible types of flow taking no account of instabilities is necessary for a fuller understanding. This paper studies the double-stream flow and reports complete solutions where previously only certain special cases have been analysed. The solutions show that, for some cloud radii, a number of solutions exist, and suggest a possible instability mechanism which may contribute to the anomalous effects. View full abstract»

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  • Optimised slot reradiation to modify foreground reflection into an array

    Page(s): 962 - 964
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (539 KB)  

    The reduction of foreground reflection into a vertically polarised 1000 MHz u.h.f. low delta aerial using a half-wave resonant slot in a one-quarter-wavelength-wide conducting flange is examined. The impedance, radiation efficiency and polar-diagram characteristics of a slot in limited conducting planes are presented. Procedures to optimise a slot to complement the Yagi-type array of vertical monopoles are described, and the application of such a slot to a 21.840 MHz h.f. aerial in Townsville, Australia, is discussed. View full abstract»

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  • Eigenvalues of spherical hybrid modes in corrugated conical horns

    Page(s): 965 - 967
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    An iterative algorithm for computing the eigenvalues of spherical hybrid modes in corrugated conical horns with arbitrary corrugation depth is presented. The eigenvalue equation is expressed in terms of definite integrals and the eigenvalues appear as constants associated with the integrands. The Newton-Raphson iteration technique is used for evaluating the eigenvalues. Starting values needed for the iteration are supplied through an asymptotic solution for eigenvalues, available in closed form and valid over a wide range of semiflare angle (0 < ¿0 ¿ 90°) of the horn. A computer program is available for calculating eigenvalues of the HE11 mode in horns with arbitrary corrugation depth (0.25 ¿ h/¿ ¿ 0.50). View full abstract»

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  • Quasi-sine-wave fully regenerative invertor

    Page(s): 969 - 976
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1068 KB)  

    The paper shows that, if a cage induction motor is fed with a quasi-square-wave current, the motor terminal voltage is approximately sinusoidal under normal operating conditions. A simple analytical approach, based on the assumption that the motor resistances and inductances do not change with frequency, is shown to describe adequately the motor-terminal voltage. The quasi-square-wave-current supply is derived by modification of a known variable d.c.-link-voltage invertor. These modifications result in numerous advantages. The modified invertor is capable of regeneration back into the mains supply, has only 12 noninvertor-grade thyristors, and is undamaged by short-circuiting of the output terminals or by misfire of the output thyristors. Overall, the invertor lends itself to a simpler electrical and mechanical arrangement. View full abstract»

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  • Self-commutated rectifier to improve line conditions

    Page(s): 977 - 981
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (711 KB)  

    When thyristor rectifiers are used for electrical drives, reactive power is produced with fundamental and harmonic frequencies. Especially in single-phase traction lines, with their low short-circuit power, a technical solution of this problem, applicable mainly to thyristor-driven rail cars and locomotives, had to be found. In this paper, the sector-control system of a self-commutated unsymmetrical bridge is described. In the unsymmetrical half-controlled bridge connection, the two thyristors can be quenched by adding a self-commutating device. This attachment (supplement) can be applied to the single bridge or to two bridges in series (sector control). By using this self-commutating attachment, it is possible to shift the fundamental of the current to a leading angle with respect to the voltage. The resultant cos ÿ can be brought to unity or even to leading values. View full abstract»

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  • Pull-in criterion for reluctance motors

    Page(s): 982 - 986
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    The behaviour of reluctance machines during synchronisation and attempted synchronisation is carefully examined. Critical modes of synchronisation are identified, and, based on these, a pull-in criterion is developed. This enables the possible combinations of inertia and load torque that any given motor can synchronise to be simply and reliably predicted. Evaluation of the criterion can be carried out manually, making it entirely suitable for routine design purposes. The accuracy of the criterion is established by comparison with a wide range of transient solutions. View full abstract»

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  • Analysis of high-rupturing-capacity fuselink prearcing phenomena by a finite-difference method

    Page(s): 987 - 993
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (915 KB)  

    The complex nature of heat flow within a modern current-limiting fuselink precludes direct analysis using classical techniques. This paper describes a method which has been developed for determining the prearcing and steady-state behaviour of such devices. It uses a finite difference technique and is numerical, the calculations being performed by a digital computer. Examples of current and temperature distributions found for some fuse-links are given, and comparisons of calculated and test results for fuselink-clearance times are shown. View full abstract»

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  • Transient recovery voltage and thermal performance of an airblast circuit breaker

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (834 KB)  

    This paper examines the way in which the current-interrupting ability of a gas-blast circuit breaker is influenced by the initial transient recovery voltage (t.r.v.). Theoretical relationships are explored between t.r.v. waveshape, circuit-breaker are parameters and performance. Limitations which may result from the presence of high-frequency oscillations of the recovery voltage in the first few microseconds after current zero are also calculated. Encouraging agreement is obtained between calculations and the results of systematic experiments on an air-blast interrupter in a synthetic test plant. Possible applications of the work to the rating and testing of circuit breakers are discussed. View full abstract»

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  • Prediction of the parameters of an impulse generator for transformer testing

    Page(s): 1001 - 1005
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (515 KB)  

    Simple expressions have been developed by which it is possible to predict the parameters of an impulse generator required to produce the standard lightning-impulse waveshape for the testing of transformers. The formulas also help to determine the limiting testing capability of a given generator. A simple method of extending the testing capability of a given resistance-front-control generator is also proposed. View full abstract»

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  • Interactive design of electricity-distribution networks

    Page(s): 1006 - 1011
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1242 KB)  

    This paper describes a computer-display method for interactive design of electricity-distribution networks. The display facility consists of a hardware character generator and storage tube, linked to an 8 K IBM 1130 computer. Thus the designer has an up-to-date network diagram to help him decide on the most suitable reinforcement plan. The designer can also call for information, such as substation data, relating to the network, and the results of both d.c. and a.c. analysis methods may be displayed in tabular form. A design study commences with the existing network, although authorised reinforcements which have not currently been installed may be included. Any proposed network is very easily studied for a wide range of operating conditions. Circuit outages may be considered, and bus loads can be increased for the purpose of load-flow studies in order to simulate load growth. The method is illustrated by a 22-node network which has been taken as an example from the MANWEB distribution system. Computation times for this network are short enough to suggest that the method can be applied to much larger networks. The designer's range of ideas is increased as a result of using this system, and he is therefore likely to obtain significantly improved designs over what present methods will afford. View full abstract»

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  • Laser Doppler instrument for measurement of vibration of moving turbine blades

    Page(s): 1017 - 1023
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (963 KB)  

    A laser Doppler instrument using a 1 mW laser has been developed for the measurement of the vibration of moving objects. Particular interest has been taken in rotating turbine blades. The design and optimisation of the instrument are described, and details given of its performance and resolution. It is shown that resolution is limited by signal/noise ratio and by Doppler broadening, both of which can be predicted. A coherence loss factor is established which enables the expected signal/noise ratio to be estimated from simple `noncoherent¿ measurements of light scattered from a target. Experiments are described which compare the performance of photomultipliers and avalanche photodiodes. The instrument has been used successfully on a turbine having blade-tip velocities up to 300 m/s, equivalent to Doppler shifts up to 1000 MHz. At the lower frequencies, photomultipliers and avalanche photodiodes are comparable in performance, but at the top end of the range only the latter is satisfactory. Resolution in velocity of about one part in 104 is achieved with an output bandwidth of 1 kHz. View full abstract»

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  • Signal/noise ratio in laser Doppler systems

    Page(s): 1024 - 1029
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    A comprehensive analysis is presented of the signal/noise ratio of laser Doppler systems. Three parameters have been introduced:an easily measurable generalised system parameter is used to account for the noise performance of the system. The signal is determined by the coherent-reflectivity loss factor of the target, and the overall signal/noise ratio is specified by a noise figure. As defined, the noise figure is almost independent of signal strength and can be used as a unique specification of the optical receiver. It is shown that the system can easily be optimised using these parameters and its performance predicted. Three types of photodetector (photomultipliers, p-i-n photodiodes and avalanche phqtodiodes) have been considered and it is shown that a confident choice can be made for a specified set of operating conditions. View full abstract»

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  • Numerical analysis of the electromagnetic flowmeter

    Page(s): 1039 - 1043
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (497 KB)  

    The paper exploits the numerical solution of the flowmeter equation as an alternative to Bevir's analytical method. The behaviour of flowmeters with point electrodes having short magnetic-field and insulating-liner lengths may be analysed for nonaxisymmetric rectlinear flow profiles. The numerical method can be more easily extended to situations which are complicated by flow profile, fluid properties and boundary conditions, but is less accurate than Bevir's method because of the limitation of computer storage. The results obtained are compared with various exact solutions and are within about 1% of the exact values. View full abstract»

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  • New method for determining the electron swarm parameters in attaching gases

    Page(s): 1044 - 1047
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (447 KB)  

    This method requires the generation of electrons from a point source at a cathode and the measurement of both the amplification and radial distribution of the electrons arriving at an anode, after drifting and diffusing through the gas in a uniform electric field. At each value of E/p0 (ratio of electric field to gas pressure) the experimental results are summarised on two curves expressed as a function of p0d (product of gas pressure and gap separation). The first curve represents the mean-square radial displacement, from an axis drawn through the point source perpendicular to the cathode, and the second represents the current amplification. These curves are easily analysed to give simultaneously the values of the ratio of the radial diffusion coefficient to mobility, Dr/¿, and attachment coefficient ¿, and the primary ionisation coefficient ¿. The method has been used to evaluate Dr/¿, ¿/p0 and ¿/p0 in CF4, and measurements have been made for 375 ¿ E/p0 ¿ 52.5 Vm¿1 Pa¿1 at 0°C. View full abstract»

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  • Boundary compensation in the mapping of Laplace fields using a computer

    Page(s): 1048 - 1054
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (649 KB)  

    The paper describes the application of the concept of the matching field to compensate for the finite boundary in the mapping of Laplacian-type fields. The idea has been adopted for the solution of problems using a computer, and the procedure is very convenient in 2-dimensional and axially rotational 3-dimensional cases. Examples are given and some further interesting developments are suggested. View full abstract»

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Aims & Scope

The Proceedings of the Institution of Electrical Engineers was published by the IET between 1963 and 1979.

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