摘要:

A technique for reducing the visibility of transmission errors in television signals which have been digitally encoded using differential pulse-code modulation(d.p.c.m.) is to weight the predicted value of the signal by a factor less than unity. This prediction ‘leak’ has the effect of reducing the extent of the propagation, and hence the visibility, of transmission errors, but it may also increase the quantising distortion. A closely controlled subjective investigation of this error visibility against quantising distortion trade-off is described. Details of both the equipment and procedure followed are given and a mathematical model is derived to allow the plotting of curves of constant impairment for varying leak factor and error rate. The investigation indicated that for moderate channel error rates, a leak factor of 15/16 is a good compromise between error visibility and quantisation distoration.

DOI:10.1049/piee.1977.0161

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper describes a general computer model for a power thyristor that will accurately simulate thyristorstatic and -dynamic characteristics. The state-space equations of the nonlinear model facilitate programmable and controllable gate characteristics, turn on and off time, reverse recovery characteristics, holding and latching current anddv/dttriggering effects. These properties, along with the model derivation, are presented and discussed in relation to a computer simulated impulsed-commutated d.c. chopper; the results of which are in excellent agreement with experimental results.

DOI:10.1049/piee.1977.0162

出版商:IEE    

年代:1977

数据来源: IET

DOI:10.1049/piee.1977.0163

出版商:IEE    

年代:1977

数据来源: IET

摘要:

Two- and three-port network analysis by scattering renormalisation, the principle of which was described in earlier papers, is extended to the 4-port case by derivation of the 4-port renormalisation transforms. The transforms are completely general and take into account complex normalising impedances that are different for all ports as well as passive and active nonreciprocal networks. As in previous associated papers, scattering parameter definitions are based on the voltage-wave concept with complex normalisation derived directly from classical transmission line theory in which the characteristic impedance and propagation constant are both complex. A few examples of 4-port circuit analysis are given including a rigorous solution of the 4-port directional coupler. The method employed in deriving the transforms is briefly described.

DOI:10.1049/piee.1977.0164

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A simple method for designing activeRCfilters with zero SQKsensitivity is proposed. The method requires a lower amplifier gain as compared to other zero-sensitivity realisations. A general activeRCconfiguration can be used to design any biquadratic filter requirement with zero sensitivity.

DOI:10.1049/piee.1977.0165

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper describes a sophisticated visually interactive computer-aided design(c.a.d.) system for electricity distribution networks. A version of this has been made available for the personal use of planning engineers at the Merseyside and North Wales Electricity Board (MANWEB). An original spare-capacity model and an automatic network reinforcement algorithm are presented. These have been incorporated in the c.a.d. system, thereby providing a comprehenisve network performance assessment of the simulation.

DOI:10.1049/piee.1977.0167

出版商:IEE    

年代:1977

数据来源: IET

摘要:

Development of the tungsten-halogen lamp has produced a wide range of light sources with a higher luminous efficacy and longer life than conventional incandescent lamps, but ultimate failure is still filament burnout caused by the formation of hot spots. Recent research has been directed towards reviewing other means of securing further improvements and has included alternative materials infrared reflecting coatings and the application of double quantum phosphors. However, the major area of progress has been in the development of tungsten-halogen lamps with a selfhealing regenerative cycle to delay the formation of hot spots. Experimental lamps have already been made that have double the life of established tungsten-halogen counterparts.

DOI:10.1049/piee.1977.0168

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A single-phase axial-flux travelling-wave machine is described, which has series connected windings on a doublesided linear stator block, and shunt connected capacitors. When driving an aluminium disc, the force/speed curve is similar to that of a conventional 3-phase linear induction motor. The maximum speed, however, can be changed by changing the shunt capacitance. With a fixed value of shunt capacitance, and when the machine is loaded, there is a contraction in wavelength, i.e. the travelling-wave machine is found to have no fixed synchronous speed. There is also attenuation that increases as the rotor speed falls. The paper includes an analysis based on a simplified model using the current-sheet method.

DOI:10.1049/piee.1977.0170

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A set of rational criteria are identified for assessing the merits of pole-changing windings for cage induction motors, in terms of capacity and performance of the two speed settings. It is shown that a change-pole setting is simply a nonstandard design that differs from the standard design essentially in respect of flux density and winding factor. In terms of these two quantities, relative performance indexes are derived that are pure numerics, with unity for the standard machine. Optimum coil spans are obtained for the familiar 1:2 pole, changing winding. Other criteria are the quality of the winding in terms of balance and m.m.f.harmonics, and the size of the controller. The uses of the main criteria are illustrated by application to some existing designs. Earlier criteria are surveyed and shown to be either incomplete or incorrect. The new criteria form a logical basis on which meaningful comparison can be made, not only between pole. changing machines and standard machines, but also between different designs of two-speed machine for a given pole combination.

DOI:10.1049/piee.1977.0171

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The steady state and transient operation of thyristor and diode controllers for variable voltage control of three-wire 3-phase induction motors is considered. Throughout the analysis the state-space form of system representation is used, which facilitates the application of switching constraints at the stator (primary) terminals. The steady state solution for constant speed was obtained in a closed form in terms of state transition matrices with the motor represented in stationaryd-q-axes. The results of experimental studies on a motor show good correlation with theoretical results. It was found that the losses in thyristor and diode controlled motors are mostly due to operation at high slips, and that time harmonic currents produce very little additional losses, especially at high speed. Compared with an inverse-parallel thyristor pair in each supply line the thyristor-diode or thyrode connection has an economic advantage but results in rather worse copper losses, mainly due to a predominant second harmonic component of current. The start-up transient currents, torques and speed of a 3-phase induction motor were obtained for sinusoidal, thyristor and thyrode control. A comprehensive computer-aided analysis gave good agreement between measured and calculated current transients. The thyrode controller resulted in larger peak currents and larger negative shaft torques than the corresponding thyristor controller.

DOI:10.1049/piee.1977.0172

出版商:IEE    

年代:1977

数据来源: IET