摘要:

The paper opens with some information regarding conditions governing fatal injury due to electric shock.Then follows a discussion of the electrical characteristics of the low-voltage circuits found in X-ray plant, and of the problems of earthing and safety in respect of supply potentials.Reference is made to the presence of high-frequency currents in the primary circuit, and some suggestions are offered for the removal of their effects.Some advantages and disadvantages of signal lights are mentioned.The paper next deals with the secondary side of the X-ray equipment, and reviews the various voltages and typical circuits employed. A brief study is made of the possible shock effects due to three types of plant.Safety measures are then considered in some detail. Arrangements for partial and total enclosure of dangerous components of X-ray equipment are examined, and instances are cited from commercial and experimental apparatus.Examples of the use of high-voltage flexible cables in X-ray work are mentioned, and some characteristics of the cables are discussed. Particulars are given of methods of “making off” high-voltage cable ends.Finally, some foreign safety regulations are reviewed; while in the Appendix an extract on the subject of electrical safety is quoted from the International Recommendations for X-ray and Radium Protection.

DOI:10.1049/jiee-1.1934.0130

出版商:IEE    

年代:1934

数据来源: IET

摘要:

It is known that in mercury-vapour rectifier circuits certain important advantages may be obtained by the addition of a smoothing filter in which the first element is a choke. In this paper it is shown that the inductance of this choke has to be sufficiently great to ensure that at every instant at least one of the rectifying valves is passing current. A method of calculating the minimum value of inductance required, and some notes on the practical design of a choke, are given.

DOI:10.1049/jiee-1.1934.0132

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The results of early international comparisons of frequency are briefly discussed. In measurements carried out in 1925 the agreement obtained was 0.1 per cent, and in 1929 an agreement of 0.006 per cent was realized. At this time the frequencies of the standards at several laboratories could be determined absolutely with an accuracy greater than that with which the comparisons could be effected.The nature of the recent modulated emissions is described and the results of three of the emissions are given. In two of the comparisons, measurements made at three different laboratories are in agreement within 1 part in 107An experiment is described showing that the frequency of modulation of an aerial current can be controlled by a distant standard with an accuracy of at least 2 parts in 108; and that the frequency measurements can be effected with this order of accuracy.

DOI:10.1049/jiee-1.1934.0133

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper discusses problems encountered in the reception of wireless signals in naval ships. Certain features of apparatus which has been developed are described.The paper is divided into four principal sections:-(1) Aerials and cable systems, in which the problem of connecting the aerial to the receiver is examined.(2) General conditions to be fulfilled by naval receivers. This section contains a discussion of the problem of selectivity from the naval point of view.(3) Brief description of receivers.(4) Power supplies utilizing batteries and alternating current.

DOI:10.1049/jiee-1.1934.0134

出版商:IEE    

年代:1934

数据来源: IET

摘要:

Following a discussion of the acoustical load to which a telephone receiver is exposed when held to an ear, an account is given of measurements of the mechanical impedances of diaphragms. Since the measurements were made under circumstances for which the effects of the air on each side of the diaphragm were known, it has been possible to isolate the mechanical impedance of the diaphragm alone. Consequently modifications of the frequency characteristic of a receiver, resulting from known changes of the acoustical load, can be estimated. It is shown that the presence of the steady flux is responsible for most of the mechanical resistance of the diaphragm.The magnetic forces by which the diaphragm is actuated have been studied by measurements of both the direct and alternating flux leaving the pole-pieces, and of the pull on the diaphragm due to the direct flux. Different diaphragms, spacing distances, and receivers, were used for these tests. It appears that, with the very adequate magnet strength used in modern receivers and the resultant degree of magnetic saturation of the diaphragm, the sensitivity of the receiver is not critical to variations either of magnet strength or of air-gap.Typical examples of frequency characteristics of receivers, taken on an artificial ear, are shown, illustrating the effects of various simple modifications to the construction of the receiver. The sensitivity as recorded by the frequency characteristic of a receiver is in good agreement with that calculated from measurements of flux, pull, and mechanical impedance.Some measurements are recorded of both amplitude distortion and non-linear distortion introduced by telephone receivers; the magnitudes are such as would not ordinarily be perceived by the ear.

DOI:10.1049/jiee-1.1934.0136

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The quantitative limitations of wireless broadcasting have stimulated an interest in alternative methods of distributing programmes to listeners. Wire broadcasting has certain basic technical and economic advantages over wireless broadcasting. Wire-broadcasting technique has been extensively applied in Holland, where 50 per cent of the Dutch listeners have their programme service laid on to the house by a wire connection. Relatively slight developments of the same nature have taken place in Great Britain.ldquo;Audio-frequency rediffusion” is the most common form of “wire broadcasting” existing to-day. In “audio-frequency rediffusion,” programmes originally transmitted by “wireless” are picked up by a receiver located where reception conditions are favourable, and the output of this receiver is connected, usually by landline, to the input of an amplifier which raises the level of the receiver output to a value sufficient to energize at once a thousand or more loud-speakers connected to the amplifier by a conducting network.In common practice this network is supported on house chimneys, but sometimes it is carried on poles. The consumersapos; branch feeders are wired in lead-covered cable.The paper analyses the effects set up by the interaction of the reactances and resistances composing the network and the loud-speakers, and it shows that the received level, particularly towards the ends of the lines, varies enormously both with loading at certain audio frequencies and with audio frequency for a given loading.Certain generalized rules are laid down to indicate how the distortions incidental to this form of wire broadcasting may be partly minimized or wholly eradicated.The analysis of the network performance allows the preparation of a specification for the amplifier necessary to supply power to the network.

DOI:10.1049/jiee-1.1934.0137

出版商:IEE    

年代:1934

数据来源: IET

摘要:

This paper sets on record the steps which have recently been taken to analyse the various types of interference to which the wireless communications of the mercantile marine are subjected.It deals with the interference caused by broadcasting and the interference caused by transmissions from other ships, both from the point of view of telegraphic communications and from that of direction-finding.

DOI:10.1049/jiee-1.1934.0140

出版商:IEE    

年代:1934

数据来源: IET

摘要:

An exposition of the principles of straight-line diode detection is given with reference to the direct production of an undistorted audio-frequency output voltage from a modulated radio-frequency input voltage. The exposition is accompanied by experimental evidence, which establishes the validity of the theory.It is shown that by proper choice of circuit constants, almost perfect detection can be obtained, even with 100 per cent modulation. Both the theory and the experiments take account of the circuit coupling the detector to the next valve. The effect of positive bias is examined and is shown to be beneficial.

DOI:10.1049/jiee-1.1934.0142

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0143

出版商:IEE    

年代:1934

数据来源: IET