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Electrical Engineers, Proceedings of the Institution of

Issue 2 • Date February 1975

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Displaying Results 1 - 25 of 40
  • Data transmission with variable-redundancy error control over a high-frequency channel

    Publication Year: 1975 , Page(s): 113 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (618 KB)  

    Results of computations and field tests on a binary-data-transmission system, operating at 1 kbaud over an h.f. channel, are presented. Error correction is effected by means of error detection and automatic request for repeat, via a feedback channel (a Post Office private line). A set of short, fixed-block-length cyclic codes is available, a code of appropriate redundancy being automatically selected to match the varying channel conditions. The decision about which code to use is made at the receiver, and the transmitter is informed via the feedback channel. The results show that relatively simple, reliable, and efficient data communication can be realised by this means. View full abstract»

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  • Zero-crossing preservation in the low-bit-rate pseudorandomly dithered quantisation of speech signals

    Publication Year: 1975 , Page(s): 119 - 123
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (730 KB)  

    In earlier investigations, it has been found that, at low bit rates, the dithered quantisation of speech samples in pulse-code modulation (p.c.m.) is perceptually pleasing but is less intelligible than normal fixed-level quantised p.c.m. Also, it has been suggested that a possible cause of the reduced intelligibility of the dithered p.c.m. is the effect that the dithering has on the zero crossings of the speech signal. This paper reports on an investigation into this suggestion. A number of methods of dithered quantisation are considered in which the zero crossings of the speech signal are preserved, and the results of intelligibility tests carried out to compare the various methods of dithering are presented. The statistical analysis of the results shows that, for 3, 4 and 5 bits per sample quantisation, two of the methods of dithered quantisation are significantly more intelligible than normal, correspondingly low-bit-rate p.c.m., and the advantage is better than 1 bit per sample. View full abstract»

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  • Two-dimensional computer analysis of a dielectric surface-loaded GaAs bulk element

    Publication Year: 1975 , Page(s): 124 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    It is well established by experiment and theory that a travelling high-field domain in a GaAs bulk element is suppressed by surface loading of a dielectric material on the GaAs. To investigate this effect in more detail, a computer analysis based on a 2-dimensional model is performed. For the simulation, the full surface of a GaAs element of n = 5 × 1015cm¿3, L = 8.7 ¿m and d = 4.2 ¿m is loaded with dielectric materials of various permittivities and 0.9 ¿m thick. The cathode and anode are extended to infinity, where a linear potential distribution is assumed. The results are summarised as follows: (a) Space charges in GaAs are accumulated near the boundary between GaAs and the dielectric material, and consequently the electric field from the space charges leaks into the dielectric material. (b) As a result, the growth of a high-field domain is suppressed, and no cyclic generation of the domain occurs, if the relative permittivity of the dielectric material is 500 or more. (c) A static voltage/current characteristic of the GaAs bulk element, loaded with a dielectric material of relative permittivity 10 000, shows a current saturation. (d) All results of the present computer simulation show a qualitative agreement with the reported experiments. View full abstract»

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  • Geostationary-satellite earth coverage

    Publication Year: 1975 , Page(s): 131 - 134
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (542 KB)  

    The basic problem considered is the relation of the shape of the beam of a geostationary satellite antenna to the area that it covers on the surface of the earth. It is envisaged that circular or elliptical beams may be used, but the beam is defined in general terms by a beam contour on a beam plane perpendicular to the beam axis by two angular co-ordinates ¿ and¿, while the earth contour in which the beam cuts the surface of the earth is defined by the latitude ¿ and the longitude ¿. Corresponding points on the two contours are linked by the direction cosines of the line from the satellite passing though them, leading to equations for finding ¿ and ¿ from ¿ and and ¿ and vice-versa. The process of finding the shape of a beam to serve a specified area on the earth with as little excess coverage as possible is discussed, with the limited possibility of compensating for the difference in clear-air attenuation in different directions from the satellite. The major problem of absorption, for example, by rain or clouds, is regarded as outside the scope of the paper. View full abstract»

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  • Modified butterworth functions with low Q factor

    Publication Year: 1975 , Page(s): 135 - 136
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (281 KB)  

    A method is given to determine the coefficients of a modified lowpass maximally flat (at the origin) Butterworth polynomial, with a reduced dominant-pole-pair Q factor at the expense of increasing order of the transfer function with multiplicity of the dominant pole pair greater than one. View full abstract»

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  • Hardware implementation of a recursive digital filter for m.t.i. radar

    Publication Year: 1975 , Page(s): 137 - 141
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (591 KB)  

    The important features of the hardware implementation of a recursive digital filter for use with m.t.i. radar are described.The filter can operate with pulse widths of 0.8¿6 ¿s, over a wide range of pulse-repetition frequencies, and can handle up to 512 range bins in multiples of 8. It is programmable to realise a 1st-, 2nd- or 3rd-order Butterworth or Cheb¿shev frequency response, by simply entering three appropriate binary coefficients into the system. Experimental results are included to verify the performance of the system. View full abstract»

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  • Effect of numerical integration on the poles and zeros of a transfer function

    Publication Year: 1975 , Page(s): 142 - 144
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (395 KB)  

    An expression for the transfer function of a numerical integrator is derived, and is illustrated by a mapping in the complex plane. Analysing a complete system using numerical integration is shown to be equivalent to displacing the poles and zeros of its transfer function. A simple graphical method for determining this displacement is described. The implicit Euler, trapezoidal and Shichman integration formulas are considered in detail. It is shown that these are special cases of a general formula, which possesses A stability. The trapezoidal formula is the most accurate A -stable equation, although it requires a reliable method of step-length adjustment. The implicit Euler and Shichman formulas sacrifice accuracy for better stability properties, when using large step lengths. View full abstract»

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  • Unified theory of cascade synthesis

    Publication Year: 1975
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  • Part symmetrisation of 3-phase windings

    Publication Year: 1975 , Page(s): 145 - 148
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    Polyphase symmetrisation has become a valuable technique in the design of pole-amplitude-modulated (p.a.m.) windings. Electrical unbalance in asymmetrical windings has been almost completely eliminated by its application. Difficulties have remained only in a few, but very important, special cases, such as in p.a.m. machines with very small numbers of slots per pole per phase. Part symmetrisation is an extension of the basic symmetrising principle. It permits either the negative-sequence winding component, or the zero-sequence winding component, but not both, to be eliminated from a 3-phase winding. It has found application mainly for the elimination of the negative sequence winding component, since the zero sequence has little or no adverse effect in a winding connected in star. Many p.a.m. windings with a high zero-sequence content for one or other of the main pole numbers have been designed and are currently in use. One such winding, for 4/6 poles in 24 slots, is discussed in detail. View full abstract»

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  • Axial magnetic forces in induction motors with skewed slots

    Publication Year: 1975 , Page(s): 149 - 153
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (566 KB)  

    A comprehensive analysis of the axial force experienced by the rotor of an induction motor, as a function of slip, is presented. It is shown that the varying saturation along the stack of a skewed induction motor considerably affects the axial force due to skew. The calculated values obtained for the force are found to compare quite favourably with experimental results. It is also established that the force decreases with increase in the airgap length. View full abstract»

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  • Pole-change windings for linear induction motors

    Publication Year: 1975 , Page(s): 154 - 160
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (791 KB)  

    Pole-change techniques are potentially valuable for the speed control of linear induction motors. However, they are more difficult to apply in the linear case because of the nonuniform nature of the airgap flux. This precludes the use of parallel paths which are normally employed to reduce the complexity of the switching. The paper describes a new winding connection technique, and shows how it can reduce the number of switch contacts required. The method requires the series connection of alternate coils to form one winding; the remaining coils form a second. Parallel connections are then made between these two windings. An analysis is presented that gives the currents in any general set of serially connected coil groups connected to independent voltage sources. From this, the complete electrical and mechanical performance of the machine can be calculated. The technique can deal with any asymmetric windings having parallel paths, and, while it is ideally suited to the machines under consideration, it has other potential applications. The work is supported by a selection of experimental results that were taken from a pole-change linear motor driving a disc secondary. View full abstract»

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  • IEE Conference Publication 99. Electricity distribution: CIRED 1973. Part 2: Discussion

    Publication Year: 1975
    Save to Project icon | PDF file iconPDF (125 KB)  
    Freely Available from IEEE
  • Transfer functions for variable-frequency induction motors with high-inertia loads

    Publication Year: 1975 , Page(s): 161 - 162
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (199 KB)  

    A variable-speed induction motor is a nonlinear system, but, for small perturbations about an equilibrium point, it is approximately linear. For the case of ¿high¿-inertia loads a simplified approximate transfer function is proposed that relates speed variations to input-frequency variations. A method of determining the ¿high¿ criterion is suggested and computed. Predicted and measured results are compared. View full abstract»

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  • D.C. dynamic braking of induction motors with secondary capacitors

    Publication Year: 1975 , Page(s): 163 - 164
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    The presence of secondary-circuit capacitance permits large torque to be developed in induction motors at high speeds, with d.c. dynamic braking. Variation of braking torque at fixed speed can be achieved by variation of excitation current or capacitance, or by the inclusion of resistance in series or parallel with the capacitor. Test results are given for an experimental drive with a 3-phase wound-rotor machine. Computed performance curves, taking saturation of the machine into account, give acceptable agreement with the experimental results. View full abstract»

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  • Induction-run performance of single-phase motors

    Publication Year: 1975 , Page(s): 165 - 167
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (406 KB)  

    On a basis of the ¿exact¿ equivalent circuit of a single-phase induction motor operating on its main winding only, accurate solutions are obtained for (a) speed and torque at pullout,(b) speed and torque-gradient at zero torque, and (c) torque, current, power factor and efficiency at any speed. These are derived for a gap m.m.f. sinusoidally distributed and modified in a simple manner for the presence of space harmonics. View full abstract»

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  • Discussion on ¿Distance-protection comparator with signal-dependent phase-angle criterion¿

    Publication Year: 1975 , Page(s): 167 - 168
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  • Some concepts involved in the analysis of the magnetic field in cage induction machines

    Publication Year: 1975 , Page(s): 169 - 175
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (919 KB)  

    The precise meaning of terms widely used in the analysis of harmonic fields in the airgaps of rotating machines is examined. The available methods of analysis of induction-motor fields are compared, and a simplified approach to field harmonics involving the concept of modulation is outlined. The flux components observed at stator and rotor in a cage-rotor machine are classified, and their relative significance in producing loss is examined by experiment. An unusual method of displaying the total flux spectrum is demonstrated, and this clearly shows that considerable simplification is possible by neglecting certain harmonics that, in the case of loss, are relatively unimportant. View full abstract»

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  • IEE North Midland Centre: Chairman's address. The engineer in electricity distribution

    Publication Year: 1975 , Page(s): 175 - 176
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (319 KB)  

    First Page of the Article
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  • Solution of the transmission-line equations for lossy conductors and imperfect earth

    Publication Year: 1975 , Page(s): 177 - 182
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    A numerically stable and efficient method of diagonalising the product of the per-unit-length impedance and admittance matrices for multiconductor transmission lines with lossy conductors or lossy earth return is presented. Cases are discussed where, by an approximation, the product of these matrices, which is complex and frequency-dependent, can be diagonalised using a real, frequency-independent modal-decomposition matrix. Frequency dependence is included in the calculation of the modal-propagation constants. View full abstract»

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  • IEE Conference Publication 123. Power electronics: semiconductors and their applications

    Publication Year: 1975
    Save to Project icon | PDF file iconPDF (148 KB)  
    Freely Available from IEEE
  • Optimal profiles of disc-type spacers for gas insulation

    Publication Year: 1975 , Page(s): 183 - 188
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (835 KB)  

    By adopting the suitable contact angle of a disc-type spacer, the surface flashover may be effectively suppressed on account of the decrease of the maximum field strength at the spacer surface. The calculation has clarified that the optimal contact angle of the spacer is 60¿70° according to the relative permittivity of the spacer for R2/R1 (ratio of inner and outer electrode radii) = 1/3, and that 20¿30% decrease in the maximum strength can be brought about in various spacer-electrode arrangements. The effect on the field-relaxation of R2R1, the relative permittivity of the spacer, and the spacer shape have been studied. Experiments in air at atmospheric pressure and in compressed SF6 have verified that very few flashovers take place at the surface of the field-relaxing spacers. View full abstract»

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  • Speed and torque control of a single-phase linear induction motor

    Publication Year: 1975 , Page(s): 188 - 189
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  • New technique for quadrilateral distance relay

    Publication Year: 1975 , Page(s): 189 - 190
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  • New superconducting switch: field-circuit version

    Publication Year: 1975 , Page(s): 191 - 192
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  • Sufficient conditions for the nonoscillation of nonlinear pulse-controlled systems

    Publication Year: 1975 , Page(s): 193 - 196
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (521 KB)  

    In this paper, the sufficient conditions for the absence of periodic modes for unforced nonlinear pulse-controlled feedback systems are given. These criteria relate to the behaviour of discrete nonlinear feedback systems within the Popov-Hurwitz sector, and the structurally similar in form to the well known circle and Popov criteria of the frequency domain, with the same simple graphical interpretation. The pulse controllers under consideration are of the pulsewidth or pulse-amplitude type, and a general classification of pulse controllers is given. Illustrative examples of systems that fail the Aizerman and Kalman conjectures are investigated with the techniques developed in the paper to evaluate the largest nonlinearity sector that guarantees the absence of certain periodic modes. 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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