摘要:

The paper deals mainly with the development of the BBC 625-line u.h.f. television services and the introduction of colour, but reference is made, where appropriate, to other important developments, both at home and abroad. It also looks at the future and mentions some of the new techniques likely to be exploited to reduce engineering costs, increase reliability, improve performance and extend the range of production facilities. Reference is made to planning methods developed by the BBC, using a digital computer, which have resulted in greater precision over earlier methods. The problems of selecting, testing and acquiring transmitter sites are described, and the conclusion is reached that 98% of the population will be served on u.h.f. by 58 main and 450 relay stations. The paper outlines the equipment arrangements at the transmitting stations and the techniques employed to achieve reliability of service. Reference is also made to the use of a p.c.m. ‘sound-in-synch.’ system of programme distribution to the transmitters, developed by the BBC, which will dispense with separate sound circuits. Following an outline history of experimental colour television in the UK leading to the start of the BBC2 colour service using the Pal system, the paper outlines the problems of choosing colour studio apparatus to meet the production facilities and the impact on studio operations and training. The intercontinental exchange of ‘live’ television programmes in colour has, since 1962, become commonplace through communications satellites, which now cover most of the world. The paper describes how technical problems posed by standards-conversion requirements were overcome and points out that the output picture quality is now mainly determined by the input signal and not by the complexities of the latest standards convertors developed by the BBC. It is considered that there is unlikely to be any change in the basic characteristics of the television picture. In the studio, the increased use of integrated circuits and digital techniques should become economical. Automatic monitoring of programme distribution and transmission networks is expected, among other trends. The paper finally concludes that the 1970s are more likely to be a decade of consolidation, in which we shall see the u.h.f. services extended throughout the UK and the remaining monochrome facilities converted to colour working.

DOI:10.1049/piee.1970.0305

出版商:IEE    

年代:1970

数据来源: IET

摘要:

After an historical sketch of the development of the electron microscope, the main features of the various types of existing instruments are described. Attention is confined to those which are commercially available, and experimental models are discussed only when they embody significant new ideas. The emphasis is on design and operation. Applications are included only incidentally, and specimen preparation not at all. The transmission electron microscope is dealt with in greatest detail, followed in importance by the scanning electron microscope. Electron- and ion-emission microscopes are also described, and a brief account is given of mirror microscopes and the electron-probe microanalyser. To avoid repetition, certain features common to all or most of these instruments are discussed in an initial Section, in particular electron guns and magnetic lenses. The review concludes with an attempt to chart the further development of electron microscopes by extrapolation of some current trends in their design and uses.

DOI:10.1049/piee.1970.0306

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper reviews electrical safety in industry, excluding mining and public electricity supply. A discussion of the incidence and nature of electrical hazards and injuries is followed by a brief consideration of the regulations affecting premises under the Factories Acts*—which includes building and civil engineering, and cargo handling in docks—and also recent legislation relating to offices, shops and railways. The importance of standards and the certification of safe equipment is also discussed.In the Sections dealing with specific hazards, particular attention is paid to earthing, circuit protection, fire and explosion hazards, portable apparatus and building and civil engineering. The final Section outlines certain aspects of modern electrical control systems. High-voltage switch gear and substation equipment, and, in particular, protective systems and rupturing duty and capacity, have not been discussed, since it is expected that, at a later date, these will be dealt with in association with electricity supply.

DOI:10.1049/piee.1970.0307

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper presents a survey of miniature-circuit-breaker (m.c.b.) design and practice. After tracing the origins of m.c.b. technology in Europe and the USA, it examines their influence on the British concept, with particular reference to the degree of overload and short-circuit protection provided. To ensure the successful application of m.c.b.s, it is essential that they be properly integrated into distribution networks and not be merely regarded as one protective device replacing another: consequently, they must be correctly co-ordinated with the fuses or other circuit breakers with which they may be associated, and the various aspects of discrimination and backup protection are therefore studied in some detail; it is shown that the let-through energy (I2t) is the controlling quantity in this respect. Future trends may include the increasing use of the quick-acting-type m.c.b., which embodies a ‘cutoff’ feature and which therefore has an increased short-circuit capacity, but this design has also certain limitations. Universal application of m.c.b.s is likely to be further encouraged by the progress made in international standardisation and approval, particularly within Europe, since this will contribute towards the removal of technical trade barriers.

DOI:10.1049/piee.1970.0308

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The growing importance of portable and transportable power sources is emphasised. This is to some extent associated with the growth in the use of cordless appliances of all types, but the range of applications storage batteries, the reliability of which has been well established, is also steadily expanding. Claims have been made that there are now 95 distinct uses for secondary cells and batteries. The use of portable power sources would, however, be greatly extended by the development of systems with higher energy and power densities, particularly in the field of electric traction.The basic principles of these electrochemical power sources are outlined, and the manufacturing processes and performance of the main types briefly described. Some details are given of newcomers, capable of much higher outputs than conventional batteries; in particular, sodium-sulphur, lithium-chlorine and zinc-air cells. The commercial viability of these has yet to be determined. Fuel cells are described in some detail and indications given of outstanding problems.Finally, the characteristics of the various power sources are summarised, and the relationships between the power and energy densities are illustrated graphically. While significant advances have been made in the performance of conventional types during the past 20 years or so, these appear to be approaching the limits of their capabilities under present régimes of use. Outstanding problems make it unlikely any of the new systems described will come into large-scale commercial use within the next 10 years.

DOI:10.1049/piee.1970.0309

出版商:IEE    

年代:1970

数据来源: IET