摘要:

Measurement in impedance bridges by pulse excitation is discussed, and an application described in which the indications of ten resistance strain gauges are displayed on a single cathode-ray tube either in waveform or in amplitude.Frequencies of 0–3000 c/s are resolved, and at maximum sensitivity 1 mm on the screen corresponds to 0.001% strain.The performance of the method of pulse excitation is discussed with particular reference to strain gauges, but impedance gauges can be devised for the measurement of other physical effects.

DOI:10.1049/pi-2.1951.0048

出版商:IEE    

年代:1951

数据来源: IET

摘要:

In designing electrical installations for large chemical factories, the following four major factors have to be considered. The area of the factory is often very large and there may be many widely separated buildings, the processes are continuous and there are long runs between stoppages, the heavy power demand has a high load-factor, and there are frequent additions and alterations to buildings and electrical systems.It is shown that a high-voltage distribution system is required, and that the methods and materials of good practice in the supply industry are in general suitable. Experience shows that it is inadvisable to “tailor” an installation too closely to a body which is likely to have grown before the “suit” is much worn.The internal wiring and the electrical equipment of factory buildings having good clean conditions are discussed in some detail; it is claimed that the majority of the motors can be of the squirrel-cage type, directon-line started, and that contactor-type air-break starters are preferable to oil-immersed ones for their control.To combat corrosive and explosive hazards as much of the electrical equipment as practicable is installed outside the danger zone and the remainder is specially chosen for these conditions.A note is included on the effect of static charges on inflammable substances and inert powders, and mention is made of some methods of preventing the accumulation of a dangerous charge.The standardization of equipment and layout is briefly discussed.

DOI:10.1049/pi-2.1951.0051

出版商:IEE    

年代:1951

数据来源: IET

摘要:

In the measurement of frequency to a precision of 1 part in 108, or better, it is necessary to consider small variations that may exist in the unit of time. The determination of time is an astronomical process, and the paper reviews briefly the principles involved. Various factors affecting the uniformity of the observed time are described. Reference is made to the astronomical instruments employed or planned for use for the determination of time at the Royal Greenwich Observatory. The clocks and other equipment are next described, together with the methods currently employed in the operation of the time service.The standard of accuracy now attained is discussed in relation to both time and frequency, and it is shown that, for frequency, agreement between Greenwich and the U.S. Naval Observatory is normally within 1 part in 108.In practice, two time systems are now employed: Greenwich Mean Time, based directly on the astronomical observations and applicable to surveying and astronavigation, and a more uniform time system which is not yet precisely defined, suitable for accurate work in frequency measurement and in related scientific investigations.

DOI:10.1049/pi-2.1951.0054

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The precision of frequency standardization increased rapidly after the introduction of mechanical oscillators maintained in continuous operation.A tuning fork gave an accuracy of 1 part in 106in 1924, and about 10 years later quartz oscillations were being used with an accuracy approaching 1 part in 108. A critical analysis of the results obtained with quartz standards suggests that still higher frequency-stability could be obtained with improved mounting of the quartz and better control of the operating conditions. The N.P.L. ring oscillators appear to have given a very satisfactory performance in the important respect of long-term frequency stability, and a further development of these rings at the Post Office has yielded very promising results.The widespread distribution of the standard by means of radio transmissions has been extended and a detailed study made of the Doppler change of frequency caused by movements of the reflecting layers in the ionosphere.Early in the development of quartz oscillators it became clear that they were more reliable timekeepers than pendulum clocks and they are now used at the larger observatories as standards of time regulated to keep in phase with the earth's rotation. The accuracy of time prediction and the uniformity of time signals has in consequence shown a marked improvement. This in turn facilitates the calibration of frequency standards. Extended observations with these precision clocks have made it clear that the period of the earth's rotation is subject to variations, which will limit the precision of time and frequency measurements so long as they are based on the period of the earth's rotation.Suggestions have been made that the velocity of light could be used as a standard, but the experimental accuracies of such methods are at present two or three orders lower than that of relating frequency to the mean solar second.Methods have been developed for measuring frequencies up to 50,000 Mc/s in terms of quartz standards; and also for controlling the frequencies of oscillators in this region by means of high-Qcavity resonators. These techniques have made it possible to investigate and measure the microwave absorption spectra of various gases. A resonance at 23,870 Mc/s in ammonia gas has been used to control the frequency of a quartz oscillator in an equipment which has been described as the first atomic clock, and other methods of using molecular and atomic resonances are being explored. Although the accuracy so far achieved is less than that of existing quartz clocks the foundation is being laid for an entirely new type of standard, which would be unaffected by the irregularities in the earth's movement.

DOI:10.1049/pi-2.1951.0055

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The paper is a review of the operating mechanisms, special properties and constructional details of the particle and radiation detectors used in modern nuclear instruments. For the most part, the detectors described are those which are in use at the Atomic Energy Research Establishment, at Harwell, and the constructional techniques are those which have been found satisfactory under laboratory conditions there, or under production conditions in British industry. The emphasis in the paper is on the detectors themselves, but brief details are given of their use in complete instruments.The characteristics of the nuclear particles (α-particles, β-particles, protons, neutrons, fission fragments, etc.) and quanta (X-rays and γ-rays) to be detected are discussed, and classification of detectors is given, the principle of detection being explained in each case and attention being called to the two different methods of use, namely as counters responding to each individual ionizing event, and as integrating elements measuring the total energy dissipation over a given interval of time.The paper also gives a detailed description of the ion chamber, the theory of its operation and the practical details of its construction. Examples of its use in radiation monitoring apparatus and in assay instruments are given. Attention is called to the use of ion chambers in process-control instrumentation and in pile-control plants.It is proposed to give a full discussion of proportional counters, Geiger-Müller counters and scintillation counters in Part 2 of the paper, to which this part (Part 1) forms an introduction.

DOI:10.1049/pi-2.1951.0058

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The paper describes a counting-rate meter with which high accuracy and good linearity are obtained by virtue of the circuit design, which makes the reading very nearly independent of valve characteristics.The causes of errors are analysed, and it is concluded that no individual source is likely to contribute an error of more than 1%. Tests indicate that an overall stability better than ± 1% is obtained in practice.

DOI:10.1049/pi-2.1951.0059

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The paper describes an instrument whose output voltage is proportional to the logarithm of the rate at which the input pulses are received. This relationship can be made to hold, to a good approximation, over a range of pulse rates of from 1 to 105pulses per second without range switching.The causes of inaccuracy and instability are examined, and it is shown that errors may be expected to be less than 10% of the pulse rate throughout the range of a five-decade instrument; the errors are correspondingly smaller in an instrument covering a smaller range.The paper shows how the instrument may be used in the investigation of some problems in nuclear physics.

DOI:10.1049/pi-2.1951.0060

出版商:IEE    

年代:1951

数据来源: IET

摘要:

This is a continuation of a companion paper entitled “Nuclear Particle and Radiation Detectors: Part 1—Ion Chambers and Ion-chamber Instruments”, and it discusses counters and counting systems. Again the emphasis is on the detectors (i.e. the counters in this case), but some details are given of the auxiliary equipment required for a counting system, namely amplifiers, counting-rate meters, sealers and registers, and examples of a number of complete instruments are also given.Proportional, Geiger-Müller and scintillation counters are considered in detail, whilst crystal counters, secondary-emission particle detectors and thermal detectors receive only brief mention. As was the case in Part 1, the aim has been to provide sound theoretical and practical descriptions of those instruments which—in the opinion of the authors—are likely to find wide application in nuclear engineering. Illustrations of instruments and components are given, and applications are drawn wherever possible from present practice at the Atomic Energy Research Establishment.

DOI:10.1049/pi-2.1951.0063

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The paper gives an account of the various stages in the development of end-window self-quenching Geiger-Müller counter tubes for the detection of β-particles.Commencing as a tube using the feather-edge type of copper-to-glass seal, one inch in diameter, with a copper-foil end window, the design was later modified to one more suitable for production on a larger scale, employing a standard Kovar/glass eyelet seal, the assembly of all metallic joints being effected by means of soft solder.To permit the detection of slower β-particles, a similar tube was developed having a Duralumin window of thickness 1 mil, which was soldered to an electroplated copper layer. The assembly process was subsequently simplified by use of a thermosetting plastic adhesive wax called “Araldite”.For the detection of very slow β-particles it was necessary to use a mica window of about 0.25-mil thickness, and a suitable seal, using Araldite, was devised for windows of this material.It was found during the course of development that extreme purity of the filling gas and quenching vapour was unnecessary, and less rigorous pumping than that associated with most electronic tubes was also permissible, the most important factors in obtaining good tubes being cleanliness and freedom from loose particles and lint.

DOI:10.1049/pi-2.1951.0064

出版商:IEE    

年代:1951

数据来源: IET

摘要:

The paper describes a small portable equipment for use by the private prospector in the location and approximate assay of radioactive ores. Its features are cheapness in cost and maintenance, simplicity of operation, long battery-life (2000 hours), robustness, lightness of weight (6 lb) and smallness of size (8⅞ in × 8 in × 3½ in). A pair of headphones and a meter are supplied as indicators; one quarter of full-scale deflection of the meter denotes the presence of bed rock containing 0.03% uranium oxide, U3O8(0.003r/hfor γ-rays from radium), and full-scale deflection denotes that of 1% uranium oxide, U3O8(0.018r/h).Cold-cathode valves are used in the instrument, one acting as a constant-amplitude oscillator feeding a miniature Cockroft-Walton voltage-quadrupler producing a stabilized voltage output. The moulded plastic container is completely weatherproof.The Geiger-Müller counter tubes use bromine as the quenching agent, have thresholds of about 300–330 volts, and have very long lives. The range of temperature over which they will operate is from −50° C to +40° C, the temperature coefficient of threshold voltage being less than 0.2 volt/°C. Plateaux are 100 volts in length, with slopes from 0.03–0.1 %/volt. The counters may be operated at ±800 volts without damage. Their efficiency is not appreciably different from that of standard tubes.

DOI:10.1049/pi-2.1951.0065

出版商:IEE    

年代:1951

数据来源: IET