摘要:

Explosions of ether-air or ether-oxygen mixtures have occurred from time to time in operating theatres, some of them with fatal results. Those having an electrical origin might oftenhave been prevented had the conditions of electrical ignition of such mixtures been known. The proportions of ether and oxygen and air within which ignition is possible vary with the type ofsource. With hot wires, such as cauteries, ignition can occur within limits as wide as 3 to 80 per cent of ether in oxygen. With sparks, in general the limits are much narrower. The work described determines these limits and the least currents that cause ignition when broken slowly or suddenly, or by fusing wires. Second only to hot wires as a possible risk are the fizzling sparks at a slower intermittent break of circuit between fine wires. When the current is kept below certain well-defined values it is found that ignition can always be prevented. It is then only necessary to specify that the. total resistance of the circuit for any given voltage shall besuch that these currents cannot under any circumstances flow in the circuit. A factor of safetyof 2 is ample for this purpose.

DOI:10.1049/jiee-1.1938.0125

出版商:IEE    

年代:1938

数据来源: IET

摘要:

Cases of ignition of anaesthetic vapours have occurred in hospitals which it has been difficult to account for except as a result of a spark due to unsuspected static electrification of the equipment used in operating theatres. Tests have been carried out in a number of hospitals, and it has been found that electrification of a frictional character, sufficient to produce a spark capable of igniting anaesthetic vapours, can often be generated in a simple manner. Measurements have been made in connection with methods suggested for the reduction of the risk to a negligible quantity. Phenomena are discussed which may lead to ignition due to the use of oxygen at high pressure.The recent development of electrically-conducting rubber promises to afford a valuable preventive of static electrification.A bibliography has been compiled which indicates the seriousness of the risks associated with electrification.

DOI:10.1049/jiee-1.1938.0126

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The paper establishes theoretical formulae for the predetermination of the mean d.c. voltage of a 6-phase gridcontrolled mercury-arc rectifier at large ignition angles. The formulae apply to all loads, from the highly inductive to the essentially non-inductive, and include all essential factors. An experimental investigation gives satisfactory evidence of their validity. This fuller theory proves that, strictly speaking, it is incorrect, in non-overlap cases, to allow for arc-drop by arithmetic subtraction. A selection of oscillograms is included which show smaller ignition angles than those generally accepted (a) for arc extinction, and (b) for the limiting angle between overlap and non-overlap on non-inductive loads.

DOI:10.1049/jiee-1.1938.0130

出版商:IEE    

年代:1938

数据来源: IET

摘要:

In the Introduction the authors discuss how the development of high-power valves is influenced by the standard of reliability demanded by such services as broadcasting.The principles governing the constructional design of each main part of the valve are outlined; differential expansion frequently appears as a controlling factor.The glass-work is of lead-potash-soda glass, the anodes of thick copper tubing; for glass-to-metalseals nickel-iron alloy is preferred, but copper is sometimes used.Insulating members have been eliminated from the active part of the valve. Grids are not cross-braced, grid seals include a large ring section let into the bulb, and there is an 8-lead multiple seal for pentodes.Cathode seals for 1 000 amperes are described; these support the whole cathode system, the evolution of which into a freehanging multiple construction is outlined. Heat transferbetween anode and cooling liquid is discussed, and also forcedair cooling.Modern evacuation technique proves to be governed by two effects; the lower readings of grid current in the “gas test” are shown to be due to photo-electric electron emission caused by X-rays from the anode and not directly to gas, and the clean-up capability of the valve is found to be very large.The method is described for determining the operating filament voltage for a standard emission by extrapolation to full emission from a reduced-emission test. Examination of the statistics of emission-test data shows that former variations are to be ascribed to variable thermal emissivity and not variable dimensions.Methods are given for extrapolating low-power spacecurrent readings into the operating region, with allowance for division between anode and grid, and the “tail” of the anodecurrent characteristic is discussed. The control of the secondary-emission component of the grid current and the effect of the magnetic field of the filament are described.An account is given of later experiments and of recent experience with flash-arc breakdowns (Rocky Point effect).Recommendations are made for switching-on filaments and anode potential in operation, and for purity of cooling water.Curves are shown of the distribution of evaporation wastage in various types of filament. Typical valve-life data from normal operation are illustrated by survivor curves for constant voltage and for constant emission during life, and Table is given showing the recent performance of the largest valves at three stations.A table of ratings for the various types of valve covered by the paper is also included.

DOI:10.1049/jiee-1.1938.0131

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The paper describes a method for the calibration of shortwave field-strength measuring sets by radiation using a loop transmitter in the horizontal plane. It is shown experimentally that in the case of vertically polarized waves the simple ray theory does not apply-unless the transmitter and receiver are both elevated to considerable heights above the ground. With horizontally polarized radiation, however, the simple ray theory holds on short waves for practically all heights of transmitter and receiver. This distinction between the propagation characteristics of the two types of radiation suggests the use of horizontally polarized waves for fieldstrength calibrations on short waves. The advantages ensuing from the use of horizontally polarized waves for this purpose may be summarized as follows:—(a) The heights of transmitter and receiver may be reduced practically to any extent, so that high masts are no longer required.(b) For low heights of transmitter and receiver the reflection coefficient of the ground is sensibly unity for all types of the earth's surface, so that little error can be introduced in the analysis due to wrong assumptions as to the electrical properties of the ground.The analysis of the results is considerably simplified when the reflection coefficient of the ground is approximately unity.(d) With no masts at the transmitter or receiver it is an easy matter to take an attenuation run, so that the calibration is not dependent on one observation.(e) It is particularly suitable for the calibration of receivers incorporating rectilinear antennae, as there is no error in calibration due to varying height of the aerial above ground.

DOI:10.1049/jiee-1.1938.0134

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The interconnection of generating stations through overhead networks has not only increased the number of short-circuits but has spread their disturbing effect over a much wider area. The disturbances are of major importance when they affect rotating machines, and the degree of stability of a system immediately after a short-circuit may be the determining factor which governs the amount of power transferable over a given line. Attempts to increase this power limit by controlling the excitation of the synchronous machines were only partially successful because they did not cater for certain short-circuit conditions. It is now recognized that the mostsuccessful way of dealing with such conditions is to disconnect rapidly the faulty section and sominimize the development of angular displacement between machines in interconnected stations.The paper reviews the various factors determining total system stability, the importance of quickly relieving the system of short-circuits, and the order of time delay which can be tolerated if system stability is to be maintained. The effect of short-circuits on load stability, and means for preventing the loss of machine load following faults, are also discussed.After outlining the essential requirements of high-speed protection generally, descriptions of various methods and systems now in use are given.The method of calculating the degree of stability (or instability) of a system following a fault condition is outlined in the appendices.

DOI:10.1049/jiee-1.1938.0139

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The present paper relates to an instrument of the microphone-amplifier-meter type, which has been adjusted for measuring the equivalent loudness of noise. Many noisemeters on these lines are available commercially, but the author has not met with any (other than those based on designs supplied to firms by, the National Physical Laboratory) which give results even approximately correct for a series of impulsive sounds. The essential feature of the work now described has been the adjustment of the circuits of the meter so that gives correct results for intermittent and impulsive noises, as well as for continuous tones. The paper describes the principles upon which an empirical adjustment was made, and produces evidence that the meter gives results in excellent agreement with average assessments, by the standard aural technique, of the equivalent loudness of a variety of moderate and loud noises. It is commented that meters which pass certain specification for sound-level meters which has been tentatively proposed recently may give results for impulsive sounds very much below the true values of their equivalent loudness.An important point revealed incidentally was that inconsistencies arise in aural measurements when the loudness of noise is compared. with that of a reference tone heard simultaneously. The difficulties are resolved by adopting technique in which the noise and the reference tone are heard alternately.

DOI:10.1049/jiee-1.1938.0141

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The circuit noise-meter (or psophometer) is an instrument which has been designed for measuring the disturbing effect of power induction on telephone conversation. Measurements have indicated that some form of frequency weighting in the instrument is desirable. The proposed C.C.I.F. specification for the instrument is quoted and discussed. Some useful applications of the psophometer are given. The limitations of present models as applied to other types of noise are reviewed.

DOI:10.1049/jiee-1.1938.0142

出版商:IEE    

年代:1938

数据来源: IET