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1887

Proceedings of the Institution of Electrical Engineers

Volume 115, Issue 10, October 1968

Volumes & issues:

Volume 115, Issue 10

October 1968

Multiconsole-computer display system utilising television techniques
  • Author(s): J. Standeven ; S. Mihailovic ; D.B.G. Edwards
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1375 –1379
  • DOI:  10.1049/piee.1968.0244
  • Type: Article
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  • p. 1375 –1379 (5)
    Standard television-raster techniques can provide good-quality digitally generated alpha-numeric and graphical displays at low cost. The regeneration of displayed information for a multiconsole system can be conveniently and economically achieved using a magnetic-drum buffer store whose parallel-access ability and synchronous nature are particularly attractive features. A system for 30 or more independent consoles online to a computer is considered, each console comprising a television display and silent keyboard. The relative merits of the 405- and 625-line standards are discussed and schemes using software and hardware character generation are outlined. The computer must organise the data for display and handle the keyboard inputs. In large systems a small satellite computer can fulfil these functions without the efficient utilisation of the main computer being significantly impaired.
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Crystal filters with extended bandwidths
  • Author(s): G.C. Bown  and  E. Birkinshaw
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1380 –1384
  • DOI:  10.1049/piee.1968.0245
  • Type: Article
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  • p. 1380 –1384 (5)
    The properties of a lowpass prototype filter of degree 4, exhibiting equal-ripple behaviour in the passband, are discussed. Explicit solutions are given for the element values of the corresponding crystal bandpass filter, and, from these, it is seen that the attainable bandwidth depends on one parameter only of the lowpass prototype. For the case where a deliberate mismatch is introduced into the lowpass prototype design, there are two possible solutions, one of which is found to lead to designs permitting bandwidths in excess of those obtained from the conventional matched design.
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Ternary arithmetic unit
Analysis of the accuracy of p.c.m. cascade coders
  • Author(s): P. Bylanski
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1389 –1394
  • DOI:  10.1049/piee.1968.0247
  • Type: Article
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  • p. 1389 –1394 (6)
    The cascade type of p.c.m. coder appears at the present time to provide the most suitable means of high-speed p.c.m. encoding. The paper describes the sources of inaccuracy in such a coder and the nature and relative gravity of the resulting errors. Criteria for error-free operation are developed in the course of an analysis based on both worst-case and statistical approaches. It emerges that the cascade coding process can be regarded as a random-walk problem, facilitating a ready method of attack. The treatment brings to light certain characteristics peculiar to the cascade coder.
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Synthesis of multimode waveguide transition sections
  • Author(s): E. Bahar  and  G. Crain
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1395 –1397
  • DOI:  10.1049/piee.1968.0248
  • Type: Article
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  • p. 1395 –1397 (3)
    Two different analytical solutions are employed to synthetise waveguide transition sections. The first is derived from the generalised telegraphist's equations attributed to Schelkunoff, and the second is based on a generalised quasioptical approach. Both solutions are expressed in terms of an infinite set of simultaneous differential equations which are solved numerically through an iterative process. The relative merits of these solutions, which depend strongly on the coupling between the simultaneous differential equations, are compared with experiment.
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Determination of the aperture field of an antenna by a beam-displacement measurement
  • Author(s): S. Cornbleet
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1398 –1402
  • DOI:  10.1049/piee.1968.0249
  • Type: Article
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  • p. 1398 –1402 (5)
    A method is given for obtaining the scalar amplitude distribution in the aperture of an antenna through the single precise measurement of the aberration of the direction of the peak of the radiated beam caused by partially obscuring the aperture by a refiectionless dielectric sheet of known small phase-insertion delay. Analysis is presented whereby the distribution obtained can be presented as the sum of presumed modes in the aperture, although the scalar treatment does not allow the phases of such modes to be assumed. Agreement with experiment is shown to be quite good for a linear aperture in the form of an Eplane sectoral horn, and extremely good for a circular antenna with a monopulse feed giving precise measurements of the angular beam displacement.
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Antenna noise temperature
  • Author(s): J. Dijk ; M. Jeuken ; E.J. Maanders
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1403 –1410
  • DOI:  10.1049/piee.1968.0250
  • Type: Article
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  • p. 1403 –1410 (8)
    Expressions for calculating the noise temperature of an antenna are deduced. The influence of the atmosphere and the environment of the antenna are discussed. It appears that analytical expressions for the sky temperature T(θ, φ) are available. So, if the antenna gain function G(θ, φ) is also known analytically, it is possible to calculate the noise temperature of the antenna. If G(θ, φ) is unknown, it is still possible to predict the noise temperature by finding the power lost through several causes, such as blocking and diffraction. This power does not contribute to the main lobe and is mostly scattered in all directions. In some cases, however, it is also possible to predict into what solid angles this lost power is radiated.
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Impedance properties of capacitively loaded dipoles
Fields in the image space of symmetrical focusing reflectors
  • Author(s): H.C. Minnett  and  B.MacA. Thomas
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1419 –1430
  • DOI:  10.1049/piee.1968.0252
  • Type: Article
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  • p. 1419 –1430 (12)
    The fields scattered by circular symmetric reflector illuminated by a linearly polarised wave incident normally on the aperture are calculated from the induced surface currents. It is shown that the fields in the axial region can be represented by a spectrum of near-spherical hybrid waves propagating along the axis. For large microwave focusing reflectors, the wavefronts are effectively plane in the significant part of the image space. The axial wave fields are linear combinations of the TEln and TMln fields appropriate for circular metal pipes, but can be bounded only by anisotropic-reactance surfaces. Axial-wave theory is used to investigate the characteristics of the fields in the focal region of a paraboloidal reflector, when the incident wave is uniform and plane. For radiotelescope focal ratios, the image structure differs significantly from the classical Airy pattern, deduced by scalar analysis, of optical focusing systems. Energy vortexes circulating about the dark rings influence the efficiency obtainable from aperture-type feeds in the focal plane. Application of axial-wave analysis to spherical reflectors, and the synthesis of high-efficiency low-noise feeds, using hybrid-waves in corrugated guides, are described briefly.
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Measurements of the propagation component of radar tracking noise at a wavelength of 3cm
  • Author(s): G.C. Evans  and  A.H. Shaw
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1431 –1438
  • DOI:  10.1049/piee.1968.0253
  • Type: Article
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  • p. 1431 –1438 (8)
    Measurements have been made of the angular propagation noise and amplitude scintillations on a 15km overland path at 1° elevation in northern England. They indicate r.m.s. deviations in angle of arrival ranging between 1" and 10" (4.8–48μrad) for aerials of 2m aperture during one year's observations. The propagation noise (short-term angle-of-arrival fluctuation) spectrum falls rapidly with increasing frequency and is negligible at frequencies above 1 Hz for this aerial aperture. Little correlation is apparent between the magnitude of the effects and changes in atmospheric humidity, but the r.m.s. level is approximately proportional to mean air temperature (in degC). Autocorrelation analysis on a single path, and crosscorrelation analysis on two adjacent paths, indicate a mean scale of turbulence of about 15m for an inclined path extending from 5 to 300m above the surface. Amplitude scintillations of the received signal give a similar power spectrum to that of angular propagation noise, and a general level of power change of the order of 0.1 dB is observed. The results are similar to those obtained by workers in the USA, and are in fair agreement with theory, although the scarcity of information on atmospheric-turbulence parameters at heights below 300m, and the use of an inclined path, make accurate comparison with theory difficult.
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Correlation of signal fluctuations at two frequencies in propagation through an irregular medium
Modal expansions for electromagnetic scattering from perfectly conducting cylinders of arbitrary cross-section
  • Author(s): R.H.T. Bates
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1443 –1445
  • DOI:  10.1049/piee.1968.0255
  • Type: Article
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  • p. 1443 –1445 (3)
    The scattering of plane waves from perfectly conducting cylinders is studied, using the condition that the total field inside the cylinders must be zero. It is shown that the surface current density can always be expressed as a sum of proper modes. In general, fewer modes are required for calculating the scattered far field than are required for calculating the surface current density to the same accuracy. Two new approximate methods are introduced. These methods complement the method of physical optics, and the more accurate of them is suitable for calculating the scattering over a wide range of bistatic angles.
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Wave scattering from a circular cylinder coated with an inhomogeneous plasma at oblique incidence
  • Author(s): William C. Wong  and  David K. Cheng
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1446 –1450
  • DOI:  10.1049/piee.1968.0256
  • Type: Article
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  • p. 1446 –1450 (5)
    The scattered fields of a plane wave incident obliquely upon an infinite conducting cylinder enveloped in a radially inhomogeneous plasma sheath are determined by the stratification technique. A transmission-coefficient matrix is introduced for each layer, so that the tangential field components at any interface can be related to those at any other interface by a composite matrix through chain multiplication. It is then not necessary to deal either with summations of the solutions of mathematically untractable coupled second-order differential equations with variable coefficients or with the simultaneous solution of many equations representing the boundary conditions at the interfaces. The computation procedure is much simplified, despite the fact that, at oblique incidence, the axial components of the electric and magnetic fields are coupled. Numerical results are obtained for the back-scattering cross-section as a function of the plasma electron-density profile, the plasma thickness, the direction of incident-wave polarisation, and the angle of incidence.
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Corrigendum: Threshold extension of an f.m. demodulator using a dynamic tracking filter
Techniques for load prediction in the electricity-supply industry
  • Author(s): P.D. Matthewman  and  H. Nicholson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1451 –1457
  • DOI:  10.1049/piee.1968.0258
  • Type: Article
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  • p. 1451 –1457 (7)
    Considerable work has been carried out in recent years on problems concerned with load-flow analysis, economic generation scheduling and system-security checking in electrical power systems. An aspect of the overall problem which has not received much attention is that of forecasting electrical load demand. It is, however, important from the practical point of view of economic generation scheduling and security checking to be able to predict accurately load demand several hours in advance. Methods of prediction fall into two basic categories: those which use weather forecasts and meteorological information, and those which use past load data only. In the paper, the various methods which are commonly used for short-term prediction are described and their relative merits are discussed.
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Discussion on “Loading of power transformers”
Investigation of the load-flow problem
  • Author(s): L.L. Freris  and  A.M. Sasson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1459 –1470
  • DOI:  10.1049/piee.1968.0260
  • Type: Article
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  • p. 1459 –1470 (12)
    A mesh approach is developed for the formulation of the network equations in load-flow analysis. It is shown to converge at least as fast as the usual methods using the nodal-impedance matrix. A hybrid approach is then developed, using a combination of an impedance-matrix method and a nodal-admittance-matrix method. The hybrid exhibits very fast convergence, and is the most powerful method encountered by the authors. It needs no optimum acceleration, and the number of iterations appear to be independent of system size and configuration. Finally, an investigation into the choice of an optimum swing/reference bus produced the only reliable criterion known to the authors.
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Starting performance of synchronous motors with solid salient poles
  • Author(s): G.F.T. Widger  and  B. Adkins
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1471 –1484
  • DOI:  10.1049/piee.1968.0261
  • Type: Article
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  • p. 1471 –1484 (14)
    The asynchronous performance of a synchronous motor, at a given slip, may be estimated from the 2-axis operational-admittance frequency functions Yd(jsω0), Yq(jsω0). The functions are commonly depicted as frequency-response loci. The frequency-response loci of a laminated-pole motor are shown to be analogous to the traditional induction-motor circle diagram. An accurate theoretical method is given to determine the asynchronous performance from the 2-axis loci, allowing for the effect of armature resistance. In addition, an approximate graphical method is given for the simplified condition when armature resistance is neglected.New equivalent circuits for the solid-pole motor are derived. The new circuits allow for the distribution of flux entering the rotor surface, and for the possibility of complete pole-tip saturation. Impedances, representing the parts of the magnetic circuit containing solid iron, are based on the rectangular magnetisation characteristic, and therefore have a magnitude, determined by the voltage across them, and a constant angle of 26.6°. The impedances are inserted into the equivalent circuits and the operational admittances are calculated by an iterative method. It is shown that the angle of the single effective ‘solid iron’ rotor impedance is found to lie between 26.6° and 45°, depending on the rotor frequency and flux. The method is also applicable to machines in which adjacent pole shoes are connected by end rings.Comparisons are shown between calculated and measured operational-admittance loci and between calculated and measured starting-performance characteristics for the solid-salient-pole micromachine at Imperial College, London, and for ten large solid-salient-pole machines of widely different dimensions and numbers of poles.A method of measuring, without attenuation, the component of oscillating starting torque of a synchronous motor, by measuring the total instantaneous input power, is demonstrated.
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Copper drag on commutators
  • Author(s): B.R.G. Swinnerton  and  M.J.B. Turner
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1485 –1492
  • DOI:  10.1049/piee.1968.0262
  • Type: Article
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  • p. 1485 –1492 (8)
    The paper includes a survey of the very sparse literature on copper drag and gives a general outline of the metallurgy of commutator bars and copper drag from various sources. Laboratory experiments are described which simulate the production of copper drag, and typical specimens obtained are shown to be very similar to practical examples. The basic cause of copper drag appears to be a vibration and hammering action of the brushes predominantly occurring under low-load conditions. This produces a flowed surface layer on the commutator of heavily cold-worked material. The effects of temperature, time, bar material and sparking or arcing are discussed. Several recommendations are given for reducing or preventing the occurrence of copper drag on bothnew and existing machines.
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New method of measuring 2-axis quantities
  • Author(s): J.D. Edwards
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1493 –1498
  • DOI:  10.1049/piee.1968.0263
  • Type: Article
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  • p. 1493 –1498 (6)
    The paper describes a new measuring technique in which synchro resolvers are used to generate the transformed 2-axis variables from the armature phase quantities. It is applicable to any a.c. machine under dynamic conditions, and the technique has particular significance in the analysis of synchronous machines, enabling much information to be obtained from a single starting test. Frequency-response loci of the axis impedances are readily obtained from an oscillogram of the 2-axis quantities, and in certain cases the loci may be extrapolated to yield the usual machine reactances. The technique also enables the instantaneous electromagnetic torque to be determined and analysed with the aid of the complex admittance loci into components associated with the direct and quadrature axes.
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Discussion on “Digital-computer methods in dynamic-response analyses of turbogenerator units”
Magnetic equivalent circuits
  • Author(s): C.J. Carpenter
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1503 –1511
  • DOI:  10.1049/piee.1968.0265
  • Type: Article
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  • p. 1503 –1511 (9)
    The possibilities of using magnetic, instead of electric, equivalent circuits for eddy-current devices, which have recently been pointed out by Laithwaite, are here explored further. Couplings between distributed flux paths and windings can be expressed in terms of a generalised linkage parameter N, which is associated with flux linkage in electric circuits, and with an analogous current linkage in the magnetic equivalent. The magnetic-circuit treatment extends to rotating, as well as to static, devices, and leads to a view of induction machines as nonpassive magnetic elements.The relationships between the energy flow through the terminals, the mechanical forces and the magnetic terminal parameters are examined, and an alternative equivalent circuit, in which the analogue of current is not the flux but its rate of change, is shown to be in many respects a more useful one. The force equations are applicable, in particular, to devices in which induced currents are important.
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Discussion on “New developments in high-pressure discharge lamps”
Thyristor-supplied tandem cold mill
  • Author(s): D.W. Draper  and  R.J. Goodridge
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1513 –1521
  • DOI:  10.1049/piee.1968.0267
  • Type: Article
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  • p. 1513 –1521 (9)
    A modern tandem mill has a high performance, which requires a complex, sophisticated control system. Antiparallel-connected thyristor convertors combine fast response with high efficiency for supplying the continuously controllable power to vary the speed of the d.c. motors. The changeover time from one antiparallel convertor to the other when a reversal in power is required (e.g. at the commencement of mill slowdown) is made very short to avoid tension disturbances in the strip. Although a thyristor supply presents problems of voltage dips to the a.c. supply, this can be alleviated by careful design. In order to accelerate quickly, the reel control incorporates a new control system, which utilises the full available power of the motor during speed changes. This involves a spillover scheme to weaken the motor field when the voltage approaches the rated value, and this is also used on the stand-speed control. Other features on the mill drive include digital position control for the thyristor-supplied screw motors, automatic gauge control, which incorporates direct control of interstand tension by means of stand-speed variation, comprehensive data logging and automatic slowdown provided by a digital process-control computer.
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Unbalanced magnetic push
Protection of structures against lightning
Fast-pulse breakdown of nonuniform-field pressurised-air spark gaps
  • Author(s): J.E. Gruber  and  T.E. James
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1530 –1534
  • DOI:  10.1049/piee.1968.0270
  • Type: Article
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  • p. 1530 –1534 (5)
    Pulse-breakdown data in the nanosecond range are given for 3–5 mm nonuniform-field air spark gaps at a pressure of 1–6atm. The 3-electrode gap has a central disc trigger electrode having an edge radius of 0.5 mm. A negative voltage pulse, whose rate of rise increases linearly from 10 to 100kV/ns, is applied to the trigger electrode with various voltages previously applied to the outer main electrodes. Breakdown is initiated with a very low jitter by field emission from the trigger electrode. Comparison with similar data for pressurised uniform-field gaps is made.
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Effect of domain-wall motion on power loss in grain-oriented silicon-iron sheet
  • Author(s): C.R. Boon  and  J.A. Robey
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1535 –1540
  • DOI:  10.1049/piee.1968.0271
  • Type: Article
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  • p. 1535 –1540 (6)
    Loss measurements and domain observations are presented for two types of grain-oriented 3%-silicon-iron sheet having widely differing domain sizes, in order to elucidate the origin of anomalous loss in magnetic materials. An alternative method is presented for separation of eddy current and hysteresis losses, which gives a more realistic representation of the processes of domain magnetisation than the conventional definitions. The large eddy-current and hysteresis losses, under alternating conditions at power frequencies, can be ascribed to the wide variation in domain-wall displacements. At high flux densities most of the anomalous loss is due to the large increase in effective a.c. hysteresis loss. By reducing the spread of wall displacements in commercial grain-oriented silicon iron, the losses at 50 Hz could be reduced by up to 30%, and by up to 50% by a reduction in domain width.
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Direct digital control—the state of the art in 1967
  • Author(s): A. Thompson
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1541 –1547
  • DOI:  10.1049/piee.1968.0272
  • Type: Article
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  • p. 1541 –1547 (7)
    The paper tries to point out the essentials of a direct digital control system. If the plant is to run 24 hours every day, those parts of the program which operate control valves can never be stopped. A clear distinction between what is fundamentally d.d.c. and what is really ‘supervisory’ is therefore necessary. A simple form of multiprogramming is described, in which it is possible to change ‘supervisory’ programs without losing control of the plant. The fundamental d.d.c. programs cannot be changed without stopping the machine, but, fortunately, this should rarely be necessary. Most of the complaints about systems being late in delivery and then suffering for months from ‘teething troubles’ have arisen from trying to write a complete d.d.c. and supervisory program before the machine went on line, and then spending a lot of time patching in machine code or recompiling from an ‘assembler’. The author's approach commissions the system in minimal form, and specifically allows for the supervisory programs to be built up steadily over several months. The system works as well with machine code and a small store as it does with a high-level language and a backing store. The second half of the paper deals with methods of valve operation, an area where there is still room for improvement. The importance of taking a measurement of actual valve position and using it in the control loop is stressed. Finally, there is a section on operator's panels, and in the Appendix is a typical software specification for a complete d.d.c. installation.
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Development of online load-prediction techniques with results from trials in the south-west region of the CEGB
Optical beam rider
  • Author(s): W.R.F. Gosling
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1559 –1567
  • DOI:  10.1049/piee.1968.0274
  • Type: Article
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  • p. 1559 –1567 (9)
    A new type of optical-beam-riding system is described in which the vehicle position is derived by scanning a spatial modulation pattern. The optical beam is produced by a transmitter which incorporates a conventional filament lamp as source and a motor-driven nutating lens or equivalent mechanism as scanner. Misalignment signals are obtained in vehicle axes, an important advantage if the vehicle is not roll-stabilised. In addition, these signals are, to a first approximation, independent of the distance from the transmitter out to maximum design range. Sources of error include transmitter noise due to imperfections of the scanning mechanism and receiver noise generated by photodetectors and amplifiers. In addition, there is some signal loss at extremes of range due to defocusing, because the equipment uses fixed-focus optics.
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Simple predictive controller for high-order systems
  • Author(s): J. Billingsley  and  J.F. Coales
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1568 –1576
  • DOI:  10.1049/piee.1968.0275
  • Type: Article
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  • p. 1568 –1576 (9)
    The paper describes a ‘universal controller’ having the following characteristics. It can be quite easily adjusted to give near-optimal control of almost any single-variable plant, whether of high order or nonlinear or including pure time-delays, for small errors. The performance is insensitive to changes of the plant characteristics, and in a sense the controller is ultrastable. Provided that the plant drives are adequate, it will control the plant for large errors, such as occur when the plant is started up or shut down. Finally, the performance for random changes of plant inputs and parameters over a limited range will be near optimal; however, the effect of measurement noise cannot as yet be predicted, and would have to be investigated for each particular application.
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Performance of a predictive automatic load-dispatching system
  • Author(s): C. Brewer ; G.F. Charles ; C.C.M. Parish ; J.N. Prewett ; D.C. Salthouse ; B.J. Terry
  • Source: Proceedings of the Institution of Electrical Engineers, Volume 115, Issue 10, p. 1577 –1586
  • DOI:  10.1049/piee.1968.0276
  • Type: Article
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  • p. 1577 –1586 (10)
    This paper describes the experimental use of a predictive automatic load-dispatching system, and discusses the experience gained. The objectives of control were the economic dispatch of active power only, while maintaining the security of the power system against loss of generation and transmission capacity. The control system used a digital computer, which allocated loads to individual generators for various times in the future, and transmitted instructions to the power stations, where they were automatically implemented by special machine controllers. The system was operational for about ten months.The aspects of control considered in the paper are prediction, the dynamic performance of the loading program, power-system security, frequency control, and operating economies. Other subjects treated in companion papers are the influence of machine-controller parameters on system stability, the performance of the machine controllers, and operator work load.Although it was only possible to examine the behaviour of a control system employing predictive techniques and regular instruction of generation, it was concluded that prediction of system conditions about 10min ahead was optimal for executive control of generation, but that regular instruction had serious drawbacks. Operating economies of a few tenths of one per cent seem feasible, but are markedly influenced by the way in which the constraints of the power system are quantified and handled.
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