DOI:10.1049/ji-2.1948.0065

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper discusses the desirable features to be embodied in the design of apparatus for the detection and measurement of combustible gases and vapours in the atmosphere, and records some of the work carried out during the development of a portable gas detector which was manufactured for use by the Admiralty, Ministry of War Transport and the War Office.The paper describes tests carried out to determine the catalytic reaction of combustible vapours upon platinum and palladium filaments and relates the heat of combustion of a vapour or gas/air mixture to the heat given to electrically heated filaments.It is shown that the combustible properties of a gas can be studied by the use of a suitably designed apparatus employing heated catalytic filaments.The delaying effect of porous enclosures upon the reaction of combustible vapour/air mixtures on a platinum filament such as may be used in automatic methane detectors is studied, and it is shown that the pressure drop set up inside the container is extremely small and is dependent upon the catalytic properties of the filament and also upon the porosity of the enclosure.The difficulty of ensuring that the deposit of dust upon the enclosure will not affect the pressure drop, combined with the fact that the catalytic properties of the filament must be maintained at a constant value when taking comparative measurements, may lead to unreliable results.In the author's opinion the measurement of the catalytic reaction is to be preferred to that of measuring the fall in pressure, which is a secondary effect.Attention is drawn to the need of official adoption of standard methods for the testing and calibration of gas detectors, and the paper describes the methods adopted in the author's laboratory.It is stated that the practice of analysing small samples of gas taken from relatively large spaces is likely to give rise to inaccurate results, and it is claimed that, of known methods, continuously indicating instruments give the most reliable results, particularly when in the hands of unskilled personnel.The permissible inaccuracy of gas detectors is discussed and it is pointed out that detectors are often used for the measurement of concentrations which are below the inflammable range but are in the toxic range. In such cases it is considered desirable that there should be some official lead regarding the limits which are considered safe for normal working operations.Reference is made to research work which has been instituted as the result of the development of convenient methods of producing vapour in a readily measurable concentration

DOI:10.1049/ji-2.1948.0066

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper discusses the problems which confront the electrical engineer working under tropical conditions. It deals with the difficulties promoted by the scarcity of skilled labour, the effect of high temperature, strong sunlight and high humidity on materials and equipment, and the special problems introduced by the prevalence of salt-laden atmosphere, dust and animal pests. It cites typical examples of troubles encountered, and suggests methods of design and engineering practice to overcome them or minimize their effect.

DOI:10.1049/ji-2.1948.0069

出版商:IEE    

年代:1948

数据来源: IET

摘要:

In an age when measuring devices of the highest precision are being produced, the bulk of quantitative information necessary to economic life is still determined by the less spectacular methods.The paper deals, mainly in retrospect, with the performance of Grid metering and mentions modifications which have been made as the result of operating experience over the past fifteen years. After a brief recapitulation of the commercial functions, comparative limits of error are discussed.The chief difference between Grid metering and other forms is the wide use of automatic summation and demand recording. A critical survey follows, of the various systems adopted, with a review of the difficulties encountered and the steps taken to overcome them. An account is given of the principles and methods of testing and maintenance.Changes in practice and design are described, with some remarks on the arrangements for recording performance and for summarizing meter readings for commercial and operational desiderata. Finally, a forecast is made of future developments.

DOI:10.1049/ji-2.1948.0073

出版商:IEE    

年代:1948

数据来源: IET

摘要:

A calibration has been made of the direct and alternating breakdown voltages for the 2-cm diameter sphere-gap, at spacings up to 1 cm. The results show that some revision is required of the calibration Tables given in the present British Standard.

DOI:10.1049/ji-2.1948.0076

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Astbury's modification of the Carey-Foster bridge is briefly described, with an account of the experience gained of its use since its installation in 1938. A more detailed description is then given of the precision Schering bridge in use at the National Physical Laboratory, in which particular attention has been paid to the screening of the components. The substandard air and mica capacitors, covering the range 200 μμF to 1 μF, which are used in conjunction with the Schering bridge, are described, with the methods used for their calibration. The tendency in recent years has been to use the Schering bridge for measurements of capacitance and power factor, and to use the Astbury bridge chiefly for the verification of the substandards. Errors do not exceed ± 1 part in 10 000 on capacitance and ± 0.00002 on power factor when testing any but the smallest capacitors.The Appendix gives an account of the method used to determine the inductance of the internal connections of capacitors.

DOI:10.1049/ji-2.1948.0077

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Methods are proposed for determining the flux of a fluorescent lamp from illumination readings at a comparatively close distance without the aid of an integrator.A full mathematical analysis based on a previous paper of the authors is given and experimental checks are described.Of the methods described, one, the “three illumination-readings” method might be useful for type-tests; while another, the “single illumination-reading” method is applicable to routine tests on a particular lamp-type.

DOI:10.1049/ji-2.1948.0078

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The losses in the windings of a double squirrel-cage motor during starting, braking and reversing, differ in many respects from those in an ordinary squirrel-cage motor. Although the total rotor loss in both cases is the same, yet the distribution between the two cages of the double-cage motor is very unequal. The outer cage, in which the dimensions of the conductors are as a rule smaller, will take the greater part of the loss and will therefore be rather heavily loaded.The loss which will be produced in the stator winding in a double-cage motor is smaller than the corresponding loss in an ordinary squirrel-cage stator. Further, there is not a simple relationship between starting, braking and reversing losses.

DOI:10.1049/ji-2.1948.0079

出版商:IEE    

年代:1948

数据来源: IET

摘要:

It is suggested that the early stages of oil deterioration progress at a rate which has the characteristics of autocatalysis. This is followed by a prolonged period during which the rate is controlled by the partial pressure of oxygen in the atmosphere. It is shown that the period of autocatalytic acceleration can be shortened by slightly modifying the design of transformers, thus increasing the useful life of the oil. Tests are described which indicate the amount of improvement likely to be gained.Attention is also directed to the behaviour of oil vapour under electrical stress, and to the large quantities of acid and sludge sometimes produced as a result of stress from live conductors, terminals and insulators projecting above the oil surface.

DOI:10.1049/ji-2.1948.0080

出版商:IEE    

年代:1948

数据来源: IET

摘要:

This paper describes a d.c. resistance test which has been developed in connection with the maintenance of transformer and switch oils on the Central Electricity Board's system. Details of the testing technique are given, and the results of resistance measurements made on representative samples of oil in various stages of deterioration are discussed.It is shown that the d.c. resistance is related to the power factor sufficiently closely to enable either parameter to be used equally well as an indication of the characteristics of the oil. Data are given on the variation of resistance with temperature, and it is found that, for used oils of relatively low resistance, the logarithm of the resistance is proportional to the reciprocal of the absolute temperature.It is demonstrated that d.c. resistance measurements can be used as a criterion of oil condition if the following limits of resistivity at 20°C are adopted:—“Good”—Greater than 20 × 106megohm-cm.“Fair”—From 2 to 20 × 106megohm-cm.“Bad”—Less than 2 × 106megohm-cm.It is concluded that the resistance test gives more information about the condition of used oil than any other single test, and it is suggested that consideration should be given to its adoption as a standard test.

DOI:10.1049/ji-2.1948.0081

出版商:IEE    

年代:1948

数据来源: IET