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Electrical Engineers, Proceedings of the Institution of

Issue 6 • Date June 1963

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Displaying Results 1 - 17 of 17
  • Parallel binary adders using the crossed-film cryotron

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1167 KB)  

    The speed of operation of a parallel adder tends to be limited by the time taken to propagate a `carry¿ from one end to the other. Three methods have been used to reduce this limitation: special circuits, improved logic, in which carries are not propagated entirely serially, and detection of the end of carry propagation instead of waiting the maximum time. The existing literature is based either on particular transistor logic units, or on units with somewhat artificial properties. The paper considers some existing designs and some new refinements, and gives circuits for constructing them with crossed-film cryotrons. Comparisons are then made of the speed and cost of the various designs. A design of cryotron adder which is often described consists of a long ladder network. The propagation of carries in this network is found to be extremely slow. This result may be useful in guiding the design of other cryotron applications, such as special stores. The experimental analogue described in the paper and used to obtain exact speeds for a complicated network may have other applications in cryotron circuit design. View full abstract»

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  • Rectangular-waveguide attenuation at millimetre wavelengths

    Page(s): 1008 - 1014
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (979 KB)  

    Measurements of the attenuations produced by air-filled rectangular waveguides of various materials have been made at frequencies of 35, 70 and 140Gc/s. Some effects of corrosion, annealing waveguides in a hydrogen atmosphere, acid etching of internal surfaces and electroplating have been determined. Internal surface finishes of many waveguide samples have been observed and d.c. resistivities of the materials have been measured. Measured losses are all well in excess of the theoretical values as predicted by formulae for perfectly smooth walls (e.g. up to 2.5 times in the case of copper at frequencies of 70 and 140 Gc/s). The discrepancies between calculated and experimental values increase with frequency and cannot be wholly accounted for at millimetre wavelengths by surface roughness. Attenuations can be reduced considerably by annealing or etching waveguide surfaces. Losses in waveguides increase after exposure to the atmosphere, and the corrosion characteristics of tellurium-copper, which has been recommended13 for millimetre wavelengths, appear to be no better than those of pure copper or standard silver. Electroplating of certain waveguide components for millimetre wavelengths may be worth while. View full abstract»

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  • Statistical model with relation to radio-link circuits in two sections

    Page(s): 1015 - 1020
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (618 KB)  

    The purpose of the paper is to deduce the overall statistical distribution of signal/noise ratio over a 2-hop line-of-sight radio link when the fading statistics for the individual hops are assumed to be known. A theoretical model is proposed that reproduces the essential features of the situation. The results deduced from the model are intended to have particular reference to double over-water hops. The model is also adapted to allow ideal diversity reception to be assumed on both sections of the link. The general results are applied to the Rayleigh fading distribution, and in this case the overall distributions are obtained in closed form together with much simpler asymptotic forms which are adequate for most system planning applications. It is seen that, if the asymptotic expression is used instead of the full expression to determine the median signal/noise ratio for the 2-hop link (without diversity), a maximum error of 1. 5 dB can occur. A parameter k appears in the distributions that can be adjusted to allow for inequalities in path loss, feeder losses, aerial gains and receiver temperatures. View full abstract»

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  • Fresnel gain of aperture aerials

    Page(s): 1021 - 1027
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (619 KB)  

    When a transmitting aperture A0 and a receiving aperture B0 are coupled in the Fraunhofer region, the ratio of received to transmitted power is given by the Friis formula. It is well known that the Fraunhofer gains Ga0 and Gb0 of A0 and B0 are constant and are determined independently. In the paper, the product of the gains GaGb in the Fresnel region is determined as an integral over both apertures, assuming the gains Ga and Gb for A0 and B0. It is pointed out that GaGb cannot generally be separated into the individual factors, but a formula similar to that of Friis still holds in the Fresnel region. The author proposes to define the `gain-product reduction factor¿, ¿a¿b, as the ratio GaGbGa0Gb0. The individual gain Ga or Gb may be determined only when A0 and B0 are identical and the illuminations of both apertures are the same. Then the `gain reduction factor¿, ¿, is defined as the ratio Ga/Ga0. Assuming uniform amplitude and phase of illumination over A0 and B0, ¿a¿b and ¿ are determined for circular and rectangular apertures. For circular apertures, the same factors are determined for a set of illuminations which approximate to commonly used tapers, and the effect of defocusing the primary feed in lenses and dishes is also discussed. View full abstract»

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  • Networks with amplitude response falling 10dB per decade

    Page(s): 1028 - 1034
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (870 KB)  

    Distributed networks are described briefly, and their limitations discussed. Suitable locations of poles and zeros of lumped networks are proposed, giving a frequency response approximating to an equal-ripple characteristic. The design of several networks covering three decades of frequency, and with deviations from the ideal of approximately 0.25 dB, is described in detail. View full abstract»

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  • Linear sodium lighting with intensity control applied to airport visual landing aids

    Page(s): 1037 - 1043
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1158 KB)  

    Early use of sodium light for the crossbars of the Calvert runway approach lighting system and experiments at the Royal Air Force station at Gutersloh during the Berlin Airlift gave rise to a strong preference among pilots for this type of light. However, controlled dimming is not practicable with the 140W lamp and its use was limited. When the linear-type lamp became available in 1959, the Air Ministry raised the question of its suitability, and as a result a special form of the lamp was developed in which a lamp oven was used instead of the vacuum jacket to maintain the arc-tube temperature. After experiments with other methods, a system of thyratron brightness control was chosen, and equipment was made up for trial at Stansted Airport, Essex, in 1961. The projectors each gave 20kcd intensity over ±4° vertically on their direction of aim, with a wide fan horizontally. Six stages of dimming were provided, each reducing the intensity to one-third that of the previous stage. It was possible to flash any or all of the lamps at any desired rate from 30 to 240 per minute. The trials confirmed the eminent suitability of the linear sodium lamp for approach lighting on all-weather runways, providing as it does a non-dazzling, distinctive, high- and low-intensity all-purpose light, with brilliancy control adjustable within an acceptable time response to suit the prevailing meteorological visibility. Two aerodromes are now to be equipped in Scotland. The technical and economic advantages of the development are of great interest to airport authorities throughout the world, not only in latitudes subject to fog and mist but also wherever dust storms and other disturbances impair a pilot's vision. View full abstract»

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  • An improved solution for the field near bundle conductors

    Page(s): 1044 - 1050
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (705 KB)  

    The electric field near bundle conductors can be determined by replacing each conductor of the bundle by two filament conductors suitably displaced from each other and symmetrically placed with respect to the centre of the conductor they represent. The equipotential surface taking the place of the conductor will approach more closely a true circle than the corresponding surface arising from replacing each conductor by a single filament as described in a previous paper by the author. When the ratio r/R of the radius r of each conductor to the radius R of the bundle circle is small, say equal to 0.1 for a bundle of two conductors, the single-filament representation will be sufficiently accurate in calculating the electric field. For higher ratios of r/R, however, the twin-filament representation will yield better results. The position of the twin filaments relative to the original conductor is so arranged that, at the point of maximum surface gradient, the equipotential surface representing the conductor exactly coincides with the conductor. The paper deals first with the evaluation of the electric field outside the bundle conductors as well as the field at various points on the conductor surface. It is followed by applying the field outside the bundle conductors to the case of a triode and also to a 3-core belted-type cable. In the triode, the amplification factor as calculated by the method given in the paper is checked against that by Ollendorff for different values of screening fraction S. The field inside a 3-core cable leads to the determination of the thermal resistance of the cable, and the result compares favourably with that given by Simons. View full abstract»

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  • Multi-generator transient-stability performance under fault conditions

    Page(s): 1051 - 1064
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1443 KB)  

    The paper describes the results of field tests, carried out on a section of the Central Electricity Generating Board's system during the summer of 1961, to measure the behaviour of interconnected generating sets, including a 200 MW unit, under the influence of transient faults and to compare with predicted performance by different methods of analysis. The results stressed that a rapid clearance of close-up 3-phase faults is essential with modern generators to prevent transient instability, but the dynamic severity of the fault attenuates rapidly away from the point of its application. They also confirmed previous findings, namely that the conventional method of analysis by network analyser or digital computer predicts the amplitude of generator-rotor first swing with good accuracy, and thereafter gives a pessimistic indication of system-recovery. Micro-models and analogue computers give a greatly improved prediction of system post-fault recovery. View full abstract»

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  • Silicon controlled rectifier static alternators

    Page(s): 1065 - 1071
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (827 KB)  

    The paper gives a general introduction to a new technique of using silicon controlled rectifiers in ring counters for polyphase sine-wave generation based on the experimental observation that such waveforms occur across diametrically opposite output terminals of a multistage ring counter having an optimum network geometry. A specific application of this-principle in the form of a d.c. to 3-phase a.c. sinusoidal inverter is then described in detail, the design and evaluation data of a prototype 30 V d.c. to 240 V, 60 VA per phase unit operating at 400c/s being presented as an example of practical design. View full abstract»

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  • Factors affecting the results of 50 c/s wet flashover tests

    Page(s): 1072 - 1076
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    The wet flashover voltage of an insulator depends partly on the angle at which the water-drops fall but mainly on the quantity of water striking the insulator. A visual estimate of the angle and a measurement of the vertical rate of fall does not give a satisfactory indication of the quantity striking the insulator if spiral nozzles are used. A suggestion is made to improve the consistency of wet-test results by using plain nozzles and by making two simple measurements of spray intensity. View full abstract»

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  • Effect of humidity on flashover of air-gaps and insulators under alternating (50 c/s) and impulse (1/50 μs) voltages

    Page(s): 1077 - 1081
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (527 KB)  

    The effects of humidity, for alternating voltages up to about 700 kV r.m.s. and impulse voltages up to about 1500kV, on gaps between 1m spheres, on rod-gaps, on suspension insulators and on pedestal-post insulators are described. Data are given on cylindrical-post insulators with alternating current and on point-plane gaps with impulse voltages. The data are limited but appear to be sufficient to justify conclusions which could affect practice, in particular, it appears that the a.c. flashover voltage of some gaps and insulators falls at high humidities, so that the negative correction in use at present should be replaced by a positive correction. The data for positive impulses, except for the sphere-gap, show that flashover voltages increase continuously with humidity. The effect with negative impulses is in some cases negligible. View full abstract»

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  • Impulse flashover of air-gaps and insulators in the voltage range 1¿2.5 MV

    Page(s): 1082 - 1088
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (879 KB)  

    Impulse flashover voltages are given for air-gaps, string insulators and post insulators which might be used in transmission systems at voltages from 132 to 400 kV. For a given length of air-gap, the flashover voltage with 1/50 ¿s impulses is least between a positive point and an earthed plane, and for this arrangement the 50% flashover voltage for gaps above lm is about 525 kV/m. For a negative point the voltage is considerably higher, the proportionate difference decreasing as the gap length increases. For point-point gaps and for suspension-insulator strings, on which flashover takes place clear of the intermediate metal fittings between insulator units, there is less polarity effect, and the voltage/length characteristics are intermediate between the positive and negative characteristics for point-plane gaps. For air-gaps and such insulator strings the voltage range over which the flashover probability is fractional is small. For long post insulators, over which flashover takes place via the intermediate metal fittings, the fractional-flashover-probability voltage range may be larger and the increase of flashover voltage with length may be smaller than for suspension strings. The polarity effect decreases with length of gap or insulator. View full abstract»

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  • The magnetohydrodynamics of the coreless induction furnace

    Page(s): 1089 - 1095
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (603 KB)  

    An idealized induction furnace, in which the motion is due to thermal buoyancy, is analysed by the simultaneous solutions of the Maxwell, Navier¿Stokes and energy equations commonly used in magnetohydro-dynamics. Temperature and velocity profiles are obtained, and an understanding of the coupling between electromagnetic, thermal and mechanical phenomena is gained. It is shown that, for a given applied magnetic field produced by the exciting coil and a given furnace width, there is an optimum frequency of exciting current which produces maximum motion of the molten charge. View full abstract»

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  • Divergent oscillations and their excitation in control systems with two saturation-type non-linear elements

    Page(s): 1096 - 1106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1023 KB)  

    Control systems are considered which have two saturation non-linearities separated by a linear phase-advance network. Because of the high-pass-filter characteristic of the linear element, distortion produced by the first saturation element is amplified and changes the gain given, to the fundamental component, by the second saturating element. It is shown that the change so caused produces a phase shift through the saturating elements. A joint describing function for the two elements is derived and used to predict sustained oscillations. These oscillations are found to be unstable, and once disturbed, diverge to infinite amplitude. Methods of excitation are examined, and the amplitudes of step functions and sine waves which just excite divergent oscillations are determined. However, the power level of a noise signal which also excites a divergent transient, when applied to the input of the system, is not determined. Analysis of the system when noise is injected into the second saturating element indicates that, in this case, noise has a stabilizing influence. View full abstract»

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  • Textures and properties developed in grain-oriented 0.004 in 3% silicon-iron strip

    Page(s): 1107 - 1114
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    Either the Goss (110) [011] texture or the cube (100) [001] texture may be developed in 0-004 in 3% silicon-iron strip. The texture that develops on secondary recrystallization is dependent on the purity of the furnace atmosphere and the temperature at which the final heat treatment is carried out. A simple theoretical treatment of the energy-balance equation of a growing grain in a primary recrystallization matrix shows how the experimental results can be explained on the basis of surface-energy differences between grains of different orientations, and the dependence of these differences on the heat-treatment conditions. It is predicted that a grain with six or more sides can undergo unlimited growth, provided that the difference in surface energy (¿m ¿ ¿g) between the growing grain (¿g) and the matrix grains (¿m) is greater than about 70 ergs/cm2. Power-loss measurements on both cube-texture and Goss-textured materials are presented, and a comparison is made with commercial grain-oriented material. Experimental results from measurements on single-crystal picture frames are used to predict how far it should be possible to lower this loss. Magnetostrictive measurements on Goss- and cube-textured strip show no appreciable difference in the magnetostrictive behaviour of the two materials, and a general discussion on magnetostriction in terms of domain-wall movements is given. It is concluded that an increase in the degree of grain orientation will bring about a reduction in power loss and magnetostriction. 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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