摘要:

The necessity for reduction in the cost and price of coal is considered, and the use of labour-saving machinery in the primary processes of winning coal is indicated as the most effective means by which the high labour cost can be substantially reduced.The evolution and early history of coal-cutters are outlined, the later developments of these machines a:e indicated, and the leading characteristics of the bar, chain and disc coalcutters are detailed.The nature of the service required of coal-cutters is explained, and the conditions under which the service is rendered are defined.Conveyors for underground use are described, and an outline is given of their place in the practice of intensive mining; first, in increasing the output per man at the coalface, and, second, as an aid to the reduction of the cost of transport of the coal from site to the mechanical haulage.An endeavour is made to indicate the respective spheres of electricity and compressed air for actuating coal-face machinery.

DOI:10.1049/jiee-1.1926.0109

出版商:IEE    

年代:1926

数据来源: IET

摘要:

This paper deals with the general considerations which affect the design of a battery locomotive for use in mines. The usefulness of such a piece of apparatus in a mine is briefly discussed and the general conditions to be met are described.Detail points in the design are dealt with on broad lines, and the results are given of certain tests designed to compare the coefficient of adhesion obtained with specially prepared wheels and standard wheels on rails prepared to represent conditions met with in practice.The various methods of obtaining flame-proof enclosure of the electrical apparatus are described.Finally a rough idea of the cost of running a battery locomotive is given.

DOI:10.1049/jiee-1.1926.0110

出版商:IEE    

年代:1926

数据来源: IET

摘要:

The paper provides a general review of the present position of electricity in mines, with particular reference to coal mines. Dealing with the safety aspect, it is claimed that the special requirements of colliery work have been amply met by manufacturers of electrical apparatus. It is further claimed that Great Britain has established a lead over other countries in respect of the design of mining electric plant. The question of public versus private supply is discussed, and the author states that, in his opinion, supply from an outside source is overwhelmingly the correct policy wherever two rival estimates show an equal, or nearly equal, financial result.Some general statistics are given and the conclusion is ultimately drawn that one-half the motive power of the mines of Great Britain still remains non-electric.Finally, some important directions in which the use of electricity in mines is likely to increase are mentioned.

DOI:10.1049/jiee-1.1926.0111

出版商:IEE    

年代:1926

数据来源: IET

摘要:

The value is demonstrated of the frequency/amplitude characteristics of telephone systems or apparatus in determining the transmission efficiency, including volume and articulation efficiency. The audio-frequency ranges of importance for speech and music are then considered.Methods are described for the direct and indirect production of constant acoustic output over the audio range, and the calibration of acoustic measuring instruments is dealt with.The next section of the paper deals with the production of electrical energy of constant value over the required frequency range, and a description is given of a special form of oscillator, together with associated apparatus for the direct recording of frequency characteristics.The concluding part of the paper gives frequency characteristics of each part of the apparatus used in a telephone connection, and also of audio-frequency amplifiers and loud-speakers. For the purely electrical portions of the circuit, current or voltage characteristics are given, whilst for apparatus such as transmitters and receivers the characteristics are given in terms of acoustic pressures on the diaphragm. The characteristics of some commercial types of granular transmitters are first given, then under the heading of receivers will be found the characteristics of both the Bell pattern and some typical loud-speakers of the horn and hornless types. Particulars are given of apparatus designed to measure diaphragm motion, some results obtained by an aural balancing method being included.In the section dealing with lines will be found characteristics for unloaded open wires and cables and for loaded cables. An impedance/frequency characteristic is also given and its application to fault location illustrated.Some notes on telephone line repeater characteristics are included, and the next section deals with exchange cord circuits and subscriber's instrument characteristics.Under audio-frequency amplifiers some typical intervalve transformers of the type used for broadcast reception are characterized, and an extension is given of the theory of this type of transformer covering the effects of resistance and capacity loads.

DOI:10.1049/jiee-1.1926.0114

出版商:IEE    

年代:1926

数据来源: IET

摘要:

The theoretical expression for the voltage amplification of a valve followed by a transformer is developed in its simplest possible terms, and various particular cases are considered. The importance of low leakage inductance for the uniform amplification of the higher frequencies is emphasized.A practical verification of the theory is provided by actual measurements of the vector amplification ratio and comparisons with the theoretical equations, and graphical methodsare given whereby the constants of a transformer can be deduced from these measurements and the amplification ratio extrapolated to frequencies beyond the range of convenient measurement.A practical design of transformer is described in which low leakage inductance and self-capacity are ensured by a sectionalized and spaced construction, and a curve of amplification of this transformer is given.Various questions relating to intervalve transformers are briefly considered, and circuits are described for increasing the amplification of low frequencies and the effective stepup ratio of the transformer.The use of low-frequency reaction for correcting distortion is described and is illustrated by measurements.

DOI:10.1049/jiee-1.1926.0116

出版商:IEE    

年代:1926

数据来源: IET

摘要:

Melsom and Booth have investigated experimentally the theory of overlapping joints, dividing the resistance of the joint into two parts: one representing the resistance due to the contact, and the other that due to the stream lines of the current at the joint. In the present paper the latter part is obtained theoretically in terms of elliptic functions. The result is expanded and leads to a very simple formula, with which the experimental results of Melsom and Booth are found to agree.

DOI:10.1049/jiee-1.1926.0118

出版商:IEE    

年代:1926

数据来源: IET

DOI:10.1049/jiee-1.1926.0119

出版商:IEE    

年代:1926

数据来源: IET