Showing papers in "Journal of the Institution of Electrical Engineers in 1930"
TL;DR: In this paper, it is shown that where heat at a comparatively low temperature is required, heating efficiencies of the order of from 300 to 500 per cent or even more may be obtained, the heating efficiency being defined as the ratio of the heat produced by the heat pump to the heat equivalent of the electrical energy consumed.
Abstract: The paper deals with a method—which so far has not received the attention of engineers—of converting electrical energy into heat energy. The method is based on the general principle that the efficiency of the heat engine working in the normal cycle is given by (T1 — T2)/T1, where T1 is the high temperature and T2 the low, and that the heating efficiency of a reversed-cycle heat engine is given by T1/(T1 — T2). The reversed-cycle heat engine (or heat pump) is described, and it is shown both from theoretical considerations and from practical tests on refrigerating plant that where heat at a comparatively low temperature is required, heating efficiencies of the order of from 300 to 500 per cent or even more may be obtained, the heating efficiency being defined as the ratio of the heat produced by the heat pump to the heat equivalent of the electrical energy consumed.The application of this principle to the heating of buildings and for such purposes as the heating of public baths is discussed, and estimated figures for a public-bath installation are given. The paper concludes with a description of experiments which the author has been carrying out during the past 2 years, and which have demonstrated the soundness of the general principles on which the heat pump is based.
15 citations
TL;DR: The earthing resistances of electrodes of inextensive area depend directly on the resistivity of the surrounding soil, and so relations were obtained showing the effect of moisture, temperature and salt on soil resistivity.
Abstract: The phenomena of polarization and endosmose which accompany the flow of direct current in soil were investigated in various laboratory experiments. Polarization was an effect of gas bubbles on the measured soil resistance—bubbles which formed owing to a small electrolytic decomposition of the soil moisture by the current and which accumulated at the electrodes. Endosmose was extensive and occurred even against an appreciable hydraulic back-pressure. The earthing resistances of electrodes of inextensive area depend directly on the resistivity of the surrounding soil, and so relations were obtained showing the effect of moisture, temperature and salt on soil resistivity. The resistivities of coal, coke, ashes, chalk and dried soil were also obtained.Various types of electrodes of inextensive area, viz. pipes, plates and strips, were installed in aplot of ground and tested over a period covering one year. The results are important as being typical of what may be obtained in practice, but not as criteria of comparative utility of the various electrode types on account of the soil resistivity being—there were reasons to presume— appreciably non-uniform. The earthing resistances of the various electrode types were, however, calculated theoretically, a soil of uniform resistivity being assumed, and the results obtained may be used as criteria. The seasonal variations in resistance were determined during the year, and the effect of moisture in this respect was greater than that of temperature.Some electrodes of extensive area, viz. water pipes, the lead sheath of a large size cable and the steel structures of buildings, that were in the vicinity of the other electrodes, were also tested. Their earthing resistances were much smaller than those of the other types, and the smallest resistance was that of a water pipe. The possible differences between alternating-current and direct-current measurements made on electrodes in the field were investigated. The greatest difference obtained was an increase in resistance of about 20 per cent with direct current and with the positive electrode one of inextensive area.The various types of electrodes of inextensive area are considered theoretically in an Appendix.
11 citations
TL;DR: All of the necessary relationships between field current, induction-motor torque and slip, which determine whether or not a given load of a definite flywheel effect can be brought into synchronism, are determined.
Abstract: The problem of the pulling into step of a synchronous motor has proved very difficult to solve, since it centres about a non-linear differential equation One solution of the equation is not enough All possible solutions with all combinations of the coefficients need to be made and classified into two groups, those that synchronize and those that do not Until recently this has been practically impossible because of the amount of time required to make the solutions by graphical or point-by-point methodsThe development of the integraph by Dr Bush and his associates at the Massachusetts Institute of Technology has made it possible to solve this problem by machine integration This integraph, which performs two successive integrations simultaneously, is particularly adapted to the solution of first- and second-order total differential equations The solutions described in this paper were obtained by using the integraph in this wayThis paper presents the complete solution of the problem for the case of a non-salient-pole synchronous motor The results are put in a simple form convenient for practical use By means of these results all of the necessary relationships between field current, induction-motor torque and slip, which determine whether or not a given load of a definite flywheel effect can be brought into synchronism, are determined An example of a practical application is given
9 citations
TL;DR: In this article, two methods of measuring peak voltage have been invetigated, and the accuracy of the methods is considered theoretically for different wave-froms, results arrived at by the two methods are compared, and agreement to about 2 parts in 1000 is obtained.
Abstract: Two methods of measuring peak voltage have been invetigated. In the one method a condenser divider is used, and the voltage on the low-voltage arm of the divider is rectified. In the other the current through a condenser connected across the voltage to be measured is rectified, and the mean current so obtained is a measure of the peak voltage across the condenser. The accuracy of the methods is considered theoretically for different wave-froms, results arrived at by the two methods are compared, and agreement to about 2 parts in 1000 is obtained.
7 citations
Abstract: If the heating curve of a coil or a machine were exponential the final temperature-rise could be calculated from the initial portion of the curve and the heating test thereby shortened. A large number of heating curves have been examined, and it is found that the final temperature, as calculated from the rate of increase of resistance, is always less than—often considerably less than—the actual value. The greater part of the paper is devoted to an analysis of the influence upon the shape of the curve, and thereby upon the ratio of the calculated to the actual rise, of such factors as the variation of (a) speed, (b)power generated in winding, (c)the temperature-rise per watt as affected by radiation and natural convection, (d)thermal conductivity, (e)specific heat, (f)point of maximum temperature and (g) heating time-constant.
6 citations
TL;DR: In this paper, the design and lay-out of distribution systems, the earthing of the neutral point and the application of arc-suppression coils are briefly discussed, more particularly in their relation to problems of protection.
Abstract: The problems associated with the protection of transmission lines and feeders have in recent years become of great moment, and much development of the art has resulted. Some of the difficulties which have arisen in practice are emphasized and some of the methods of overcoming them are described. The design and lay-out of distribution systems, the earthing of the neutral point and the application of arc-suppression coils are briefly discussed, more particularly in their relation to problems of protection. Factors which influence the choice of protective systems are considered and the requirements of schemes to meet the exacting conditions of modern transmission systems are surveyed. The several methods of obtaining discriminative protection are then reviewed. Commencing with modern design of time-discriminative overcurrent relays, emphasis is laid upon the importance of a definite minimum time characteristic and upon correct methods of obtaining directional features. The special requirements of such relays when applied to give sensitive earth-fault protection are indicated, and means of obtaining a suitable polarizing voltage are explained; a description of sensitive earth-fault relays of the wattmeter type is also given. The theory and application of impedance relays is discussed, with reference to definite-impedance and impedance-time relays. A method of compensation for voltage-drop across the arc resistance of a fault is indicated. The field of application of low-voltage release relays is defined and the method of their use illustrated. Attention is then directed to the advantages of pilot-wire feeder protection, and the limiting features of older forms are mentioned. Typical modern opposed-voltages and circulating-current methods which are giving satisfactory service on modern systems are described in some detail. The new field of direct-current pilot-wire protection is discussed; the main classifications of this type of gear are defined and examples are given. The paper concludes with a description of a novel and flexible method of protection for duplicate and multiple parallel feeders.
6 citations
TL;DR: In this article, the authors present a comprehensive investigation of a manufacturer of electrical plant on the noise emitted by machinery and other apparatus, a subject of great present and future importance, and the need for treating the subject in a thorough and quantitative manner for engineering purposes is pointed out.
Abstract: The paper deals with part of a comprehensive investigation which is being carried out by a manufacturer of electrical plant on the noise emitted by machinery and other apparatus, a subject of great present and future importance. The need for treating the subject in a thorough and quantitative manner for engineering purposes is pointed out. The physical magnitudes involved in the measurement of the sound set up by a vibrating body are discussed generally, together with the characteristics of the ear. The characteristics that should be possessed by a sound-measuring apparatus intended for use in engineering problems are pointed out and a brief survey is made of existing types of apparatus. The principle, development and final form of the apparatus, which enables a complete analysis of a complex sound to be made, are described, together with the methods employed to verify the accuracy of the apparatus. The influence of the conditions under which sound measurements on engineering apparatus are carried out is discussed, and a special laboratory which has been set up for acoustical work is described. Some sound-test results on engineering apparatus are given as examples.
6 citations
TL;DR: In this article, the effects of transposing the line conductors on the operation characteristics and power losses of three-phase power by high-voltage lines were investigated. But the authors did not make any general recommendation regarding transposition on short double circuit lines and each case must be judged on its merits.
Abstract: This report deals with two problems of primary importance in connection with the transmission of three-phase power by-high voltage lines, viz.:- (a) The effects of transposing the line conductors on the operation characteristics and power losses.† (b) The impedance of a line conductor and earth return when one phase is accidentally earthed. Item (a) affects the design and construction of the line and its normal operation, while item (b) is the principal factor in determining the magnitude of the "failure" current returning through the earth (under fault conditions) upon which the amount of interference with communication circuits is dependent. Transposition makes the power lines electrically balanced, equalizes the phase impedances and reduces the induction from normal operating currents and voltages. On single circuit lines transposition entails practically no additional cost and ought to be adopted as standard in all cases. On double circuit lines, however, special "transposition towers" (costing in the case of the "grid" lines several hundred pounds extra per tower) have to be employed at each transposition point (to prevent the conductors touching in the span), and this factor renders it desirable to avoid transposition whenever practicable. On long lines (fed entirely from one end) transposition appears essential both on account of inductive interference and to avoid large differences between the phase impedances. On short lines (say up to 50 miles long, which covers most practical cases in this country), the latter effect is negligible compared with the transformer impedances, and transposition is unnecessary when, in addition, interference with communication circuits arising from normal operating currents and voltages is unimportant. Thus on short double circuit lines no general recommendation regarding transposition can be made and each case must be judged on its merits. On all double circuit lines, whether
5 citations
TL;DR: In this paper, the voltage control of large alternators is considered, with special reference to large high-speed machines now being installed in capital stations, and the treatment is descriptive and is dealt with under the following headings:Exciter stability.Alternator response.
Abstract: The voltage control of large alternators is considered, with special reference to large high-speed machines now being installed in capital stations.With a view to stimulating discussion the treatment is descriptive and is dealt with under the following headings:—Exciter stability.Exciter response.Alternator stability.Alternator response.Combined response of alternator and exciter.
5 citations
TL;DR: In this paper, a voltage proportional to, and in phase with, a given alternating current was measured for the purposes of measurement, and the effects of a number of variables on the transformer performance were investigated.
Abstract: The paper describes apparatus for obtaining for purposes of measurement a voltage proportional to, and in phase with, a given alternating current. The Introduction outlines defects in the water-cooled tube resistors which have been in use at the National Physical Laboratory for this purpose; these defects have led to the construction of air-cooled resistors for moderate currents, and current transformers with nickel-iron cores for heavy currents. Section (1) deals with the requirements for the air-cooled resistors, and with theoretical and practical points in their design; tests showing very satisfactory performance are described. Section (2) outlines the construction of the special current transformers, and deals at some length with the method of calibrating them. Finally, the effects of a number of variables on the transformer performance are investigated: the characteristics are shown to be very good, and no sign of instability is found.
4 citations
TL;DR: In this article, a number of special cases are deduced from these general formulae, and a curves are given to facilitate computation, which are shown to facilitate the computation.
Abstract: Formuae are given for the distribution of radiation in different directions. The paper is divided into the following sections:- (1) Introduction. (2) Antenna elements. (3) Polarization. (4) Current distribution. (5) Effect of image in the ground. (6) A straight wire inclined at any angle. (7) A system of similar antennae spaced in any given manner. (8) A system of antennaeh uniformly distributed around the circumference of a circle. A number of special cases are deduced from these general formulae, a curves are given to facilitate computation.
TL;DR: In this paper, an historical account of the evolution of the a.c. potentiometer is given, followed by descriptions of the Drysdale-Tinsley, Larsen, Gall, Pedersen, Campbell and other types of the instrument.
Abstract: An historical account of the evolution of the a.c. potentiometer is given, followed by descriptions of the Drysdale-Tinsley, Larsen, Gall, Pedersen, Campbell and other types of the instrument. The theory and accuracy of such instruments are discussed, and examples are given of their application for various tests.
TL;DR: In this article, an experimental investigation of this phenomenon is given, and this is followed by a critical survey of existing data, leading to an explanation to account for this deposition of metal, and an investigation into the mechanism of the passage of current from the slip-ring or commutator to the brush.
Abstract: One of the troubles experienced in the collection of current is that of “copper picking”. A description is given of an experimental investigation of this phenomenon, and this is followed by a critical survey of existing data, leading to an explanation to account for this deposition of metal, and an investigation into the mechanism of the passage of current from the slip-ring or commutator to the brush.The variation of contact voltage-drop with speed, brush pressure and current is shown. Peripheral speeds higher than previously have been used and an investigation has been made at very low current densities.In order to show the variation of contact voltage-drop, oscillograms have been taken which show its fluctuating nature. These oscillograms show the effect of increased speed and brush pressure, and the change in nature of the contact as the latter is reduced. Intermittent contact is shown to account for rising voltage-drop with speed, but a speed is attained at which an air film is drawn between the brush and the ring.
TL;DR: In this article, the authors describe the principles and development of an ammeter which has been made for measuring current of very high frequencies, such as 30000 kilocycles per sec The ammeter is of the dynamometer type and has a geometrical form for which all the changes of current distribution can be calculated.
Abstract: This paper describes the principles and development of an ammeter which has been made for measuring current of very high frequencies, such as 30000 kilocycles per sec The instrument is of the dynamometer type and has a geometrical form for which all the changes of current distribution can be calculated The correcting factors approach a limiting value and do not increase continuously with frequency as they do in thermal instruments A special feature of the design is that an instrument can be made to carry unshunted a current of any magnitude This removes all uncertainty about shunting ratio and so the instrument should be more reliable than one in which the current is supposed to divide evenly among a number of resistance wires in parallel Methods are described for checking the calculated correction factors and there are also some calibrations at frequencies round about 1000 kilocycles per sec In addition, measurements are described of the high-frequency resistance and of the inductance and terminal capacity
TL;DR: In this paper, a quick and ready method of measuring the ratio and phase angle of highvoltage transformers is described in which the well-known high-voltage Schering bridge is employed.
Abstract: A quick and ready method of measuring the ratio and phase angle of high-voltage transformers is described in which the well-known high-voltage Schering bridge is employed. Formulae for the voltage ratio and phase angle are given, together with expresssions for the sensitivity of the bridge. The accuracy obtained by the method meets the requirements of all industrial tests as well as of research work.
TL;DR: The last phase of machine telegraphy will certainly be that in which intercommunication between centres will be automatically effected and intermediate manual transmission avoided, and the single-channel system will, in course of time, replace the multiplex system for inland telegraphs.
Abstract: The design and operation of machine telegraph systems has been very considerably affected in recent years by the production of high-speed communication links of the transoceanic order of length, and by new methods of operation on land lines enabling the line plant unit?the telephone pair?with its series loading and its repeater stations en route to be used for either the transmission of telegraph signals or speech, or both, simultaneously and independently. The regenerative repeater, by enabling several sections of cable and land line to be interlinked, has given rise to methods of operation far reaching in their effect both from the point of view of economy to the Administration and from that of reliability and speed to the user. While the possibility of connecting two remotely situated medium-traffic offices over a single channel of a main-line high-speed multiplex system has been known for a number of years, this has not led to any considerable developments in that direction. Conditions are, however, arising in which medium traffic offices will use start-stop single-channel systems to an increasing extent, and this is being influenced by the large number of channels rendered available by the dual use of the land telephone cable. Wherever the telephone network extends, the telegraph network is ready to hand, and the single-channel system will, in course of time, replace the multiplex system for inland telegraphy. The long-distance links with their regenerative repeaters require a precision in speed and phase control not necessary heretofore, and a study of this subject therefore forms a considerable portion of this paper. The sending and receiving apparatus of the start-stop single-channel system are the inverse of each other, and the paper endeavours to establish a general underlying principle for the different variants described. The last phase of machine telegraphy will certainly be that in which intercommunication between centres will be automatically effected and intermediate manual transmission avoided. This is possible by reason of the large number of channels available through the previously-mentioned dual use of the wire plant, and by the present-day standard of automatic switching technique.
TL;DR: In this article, the results obtained on two electrical machines, one with a rotating armature and the other with rotating field, which were tested with different load and field currents, different speeds, etc.
Abstract: The factors governing the temperature-rise of electrical machines are so interwoven that the only satisfactory method of separating them is to test actual machines with different distributions of losses, different speeds, etc.; conclusions derived form tests on models must be accepted with caution. In this paper are given the results obtained on two electrical machines, one with a rotating armature and the other with a rotating field, which were tested with different load and field currents, different speeds, etc. The machines were also tested when totally enclosed and when cooled by an induced draught. Temperature-rises were measured by thermometer, by thermo-junction and by the increase of resistance. In the case of the machine with the rotating armature it was found possible to follow the temperature variation of the latter by placing a thermo-junction a short distance away from the armature, and it si suggested that this method might be used for shortening the duration of heat-runs.
TL;DR: In this paper, the authors describe measurements of surge voltages made under actual working conditions on 33-kV transmission lines both overhead, underground and composite, and describe the specially designed auxiliary condensers required to subdivide the line voltage.
Abstract: The paper describes measurements of surge voltages made under actual working conditions on 33-kV transmission lines both overhead, underground and composite. The apparatus used for the measurements was the klydonograph, and the paper gives a description of this instrument in its final form and a discussion of its working principles. The specially designed auxiliary condensers required to subdivide the line voltage are also described. Measurements on three important transmission systems covering a year or more of continuous recording are detailed. Generally there is a large amount of oscillatory surging set up by brushing at insulators when such insulators are in a dirty condition, the over-voltage being of very high frequency and of the order of three times the normal line voltage. The atmospheric conditions under which salt is deposited on insulators are described and some of the records show the effect on the line voltage of a salt-laden insulator up to the time at which flash-over occurred and the line was put out of operation. The question of porcelain insulators to meet the prevailing foul conditions and to avoid surges due to brushing is discussed. It is shown that with proper attention to design the voltage at which brushing commences can be materially increased, and it is suggested that this factor is of even greater importance than a very high initial flash-over voltage.
TL;DR: In this paper, the authors describe the first twin transmitters, erected at Brookmans Park, Hertfordshire, to serve London and the Home Counties, and deal with the considerations underlying the choice of sites for broadcasting stations, the type of power supply adopted, and the factors contributing to reliability in operation, as well as with the wireless transmitters themselves.
Abstract: The B.B.C. Regional Scheme involves the construction of number of twin wireless transmitting stations, each capable of radiating simultaneously two programmes on different wavelengths, and each at a power of 50 kW in the aerial. This paper describes the first of these twin transmitters, erected at Brookmans Park, Hertfordshire, to serve London and the Home Counties. The paper deals with the considerations underlying the choice of sites for such broadcasting stations, the type of power supply adopted, and the factors contributing to reliability in operation, as well as with the wireless transmitters themselves. Detailed considerations underlying the design of such transmitters have been avoided in the anticipation that they will form the subject of a further paper; but, nevertheless, some information in regard to the essential and major points in their design is contained herein. The paper deals further with the general station lay-out, the building and the auxiliary services, as well as with lowfrequency apparatus for supplying modulation to the transmitter and apparatus for testing and monitoring purposes, etc. Of particular interest is the use of high-tension directcurrent machines at this station for the production of hightension voltage for anode supply to the main power valves. The type of generator developed especially for this work is considered in some detail.
TL;DR: The jet-wave rectifier as discussed by the authors is a purely mechanical rectifier which has been developed into a means for high-power rectification, and has been shown to have a high capacity rectifier, of a character quite distinct from that of the mercury-arc rectifier.
Abstract: The subject of this paper is the jet-wave rectifier, a purely mechanical device which, in the course of the last 15 years, has been developed into a means for high-power rectification. Prototypes of the constituent parts of the apparatus have been described elsewhere; in the present paper it is shown how the rectifier can be designed on the basis of these prototypes, and especially on the result of investigations with regard to the theoretical relations between their qualities. These relations are stated and are used in working out examples of typical designs. In addition, a review of the general properties of the jet-wave rectifier, and anticipations with regard to its future development, are given. It is concluded that a new high-capacity rectifier, of a character quite distinct from that of the mercury-arc rectifier, but likely to be used for similar duties, has been brought into existence.
TL;DR: The author outlines a simple method of testing current transformers that does not call for expensive apparatus or rely on the existence of a number of "standard" transformers.
Abstract: The author outlines a simple method of testing current transformers. The method is an absolute one and does not call for expensive apparatus or rely on the existence of a number of "standard" transformers.
TL;DR: In this paper, the authors describe how the testing of current transformers may be carried out with speed and accuracy by means of a potential-divider bridge, and show that, by taking a few simple precautions, an accuracy of 0.01 per cent for ration measurements, and of 1 minute for phase-angle measurements, is attainable if the transformer characteristics are stable to this limit.
Abstract: The paper describes in detail how the testing of current transformers may be carried out with speed and accuracy by means of a potential-divider bridge. The corrections to be made to the readings are deduced from the theory of the bridge; and it is shown that, by taking a few simple precautions, an accuracy of 0.01 per cent for ration measurements, and of 0.1 minute for phase-angle measurements, is attainable if the transformer characteristics are stable to this limit. A very sensitive and accurate bridge, which is not so convenient for general purposes as the potential-divider bridge, is than described. Results obtained with this bridge are compared with those obtained with the potential-divider bridge, and found to be in close agreement.
TL;DR: The author sums up the advantages of the method and describes some interesting applications of it in connection with the testing of power transformers etc.
Abstract: The paper describes some of the common methods and the author's new null method of testing instrument transformers. The technical points of the method are discussed and examples are given illustrating the simple derivation of ratio and phase-angle error of current and potential transformers. The accuracy of the method is dealt with, tests on a holetype current transformer are described, and the number of standard transformers required is discussed. In conclusion the author sums up the advantages of the method and describes some interesting applications of it in connection with the testing of power transformers etc. In the Appendix is given the proof of the method.
TL;DR: In this article, a four-aerial direction-finding system is described at a site near the Radio Research Station, Slough, and details of the tests carried out on this apparatus at wavelengths of 300 to 600 m. The system is based on the Adcock principle, but a modification has been introduced to correct for the asymmetry of the aerial system with respect to its upper and lower portions which is unavoidable if the operating hut is at ground level.
Abstract: Part (1) describes a four-aerial direction-finding system erected at a site near the Radio Research Station, Slough, and gives details of the tests carried out on this apparatus at wavelengths of 300 to 600 m. The system is based on the Adcock principle, but a modification has been introduced to correct for the asymmetry of the aerial system with respect to its upper and lower portions which is unavoidable if the operating hut is at ground-level. In the first test the performance of the new direction-finding system was compared with that of a rotating-loop direction-finder over a prolonged period which included conditions of most severe ?night effect.? In the second test a calibration of the system was made by means of a transmitter attached to a kite which provided a source of downcoming waves of known angle of incidence and polarization. The results of the tests show the new system to be considerably superior to the closed-loop system for conditions of ?night effect.? They indicate, however, a residual instrumental error of the system in the presence of down-coming waves. Finally, a further modification of the system by which it is hoped this will be eliminated is described. Part (2) describes two distinct types of portable short-wave direction-finding apparatus and gives details of the methods by which they were tested and compared under working conditions at wavelengths of 12 to 60 m. The first instrument is of the totally-screened closed-loop type. The second instrument is of the rotating Adcock type consisting of a single pair of spaced vertical aerials pivoted about a vertical axis. The tests described are divided into four sections:? (a) Testa for instrumental error with a local transmitter situated first on the ground and then elevated 40 ft. above the ground with its aerial at various angles to the vertical to give waves of varying polarization. (b) Tests on the effects of the immediate surroundings of the receiver. (c) Direction-finding observations on the ?ground ray? of a transmitter up to the maximum distance at which the ray is detectable. (d) Long-range tests at which only downcoming waves were being received. Test (a) showed the Adcock to be much superior to the loop in the presence of downcoming horizontally polarized waves, while, (b), (c) and (d) show that for observations on the ground ray both instruments are equally satisfactory and that with due precaution in the choice of a site their performance is much the same as that the of longer-wave apparatus. For observations just outside the range of the ground ray both systems are equally useless, while at greater ranges (beyond the ?skip distance?) the results again demonstrate the superiority of the Adcock to the loop. It is shown that the results generally confirm the conclusions with respect to the nature of the propagation of the waves arrived at by Eckersley from somewhat similar experiments.
TL;DR: In this article, the wave-form of rectified currents is computed by treating the rectifier characteristic as a continuous curve having an equation E=f(I) in every part of the circuit except the rectifiers, since the harmonics are independent.
Abstract: The classical mathematical method of calculating the wave-form of rectified currents is applicable to rectifiers whose volt-ampere characteristic consists of two interesting straight lines. It is based on the observed fact that there is for each rectifier a conducting phase and an insulating phase. If the characteristics for each are linear, the differential equations are linear and can be solved for each separetely. The discontinuities between the two conditions are bridged by transient terms in the integrated equations. To evaluate the harmonics, Fourier's theorem is necessary. Even for the simplest circuit the labour of calculation is very great, although the result is mathematicallly exact. A new method is proposed which treats the rectifier characteristic as a continuous curve having an equation E=f(I) In every part of the circuit except the rectifier the harmonics are independent, since the coefficients L.R.C are assumed constant. It is therefore an easy matter in any given circuit to calculate each harmonic of E in terms of the harmonics of I. The voltage and current must, however, at every instant of time satisfy the characteristic equation of the rectifier, and this leads to sufficient equations for a solution by successive approximation. The method is applicable to cases of biphase rectification, and, like the classical method, has its simplest application for ideally perfect rectifiers having a characteristic equation EI=0 The paper shows the method of reducing the equations to tractable form for solution by successive approximations, using the algebra of plane vectors, and it is shown by means of a numerical example how the approximations converge on the true value deduced by the classical method.
TL;DR: In this article, various ways are considered in which a 3-electrode valve should be used in a thermionic voltmeter, and the accumulated experience is described of several years' work by the author in making valve voltmeters for various purposes.
Abstract: In this paper the various ways are considered in which a 3-electrode valve should be used in a thermionic voltmeter, and the accumulated experience is described of several years' work by the author in making valve voltmeters for various purposes. No one arrangement can possess every desirable property, and it is shown how to produce a voltmeter to fulfil specified requirements. The effective input resistance of the various arrangements, and the harmonic currents produced by grid current, are the harmonic currents produced by grid current, are considered analytically and experimentally. The effect on range and sensitivity of providing additional batteries is also discussed, extra batteries being found to be an advantage only in very low-range instruments.The effect on the calibration of a change in the valve and in temperature is found to depend on the form of the rectifier used. In general, a thermionic voltmeter cannot read R.M.S. values. The wave-form error of various systems is investigated; with one arrangement the reading is proportional to the peak voltage and in another to the mean. The possibility of a frequency error is discussed; tests show that the error is negligible for frequencies up to 1 000 kilocycles per sec., whilst from indirect tests it would appear that the error is probably negligible for frequencies up to 30 times this value.
TL;DR: In this paper, an improved method of measuring the amplification of a radio receiver is described, together with the manner in which this method can be applied to practical cases, particularly at short wavelengths.
Abstract: The paper describes researches which have been carried out at the National Physical Laboratory for the Radio Research Board. An improved method of measuring the amplification of a radio receiver is described, together with the manner in which this method can be applied to practical cases, particularly at short wavelengths. The apparatus covers a wavelength range of from 15 to 30000 metres, and is capable of dealing with inputs of from 0.25 to 1000 mV over this range. After describing in detail the construction and operation of the apparatus in Section (1), the results of tests on four receivers of widely different types are given in Section (2), and some general deductions are obtained from the properties of these receivers. In conclusion, suggestions are made in Section (3) for a possible means of classifying receivers for different purposes.
TL;DR: In this paper, the free air pressures of a sound wave may be increased at the diaphragm of a microphone in a ratio greater than 2: 1 at certain frequencies, when there is concavity in the face of the microphone.
Abstract: It has been observed that the free air pressures of a sound wave may be increased at the diaphragm of a microphone in a ratio greater than 2: 1 at certain frequencies, when there is concavity in the face of the microphone. A method of calculating the magnitude of this increase is applied to a condenser transmitter of the Wente type, and close agreement is found with experimental results. The calculations involve certain simplifying approximations the validity of which is discussed.
TL;DR: In this paper, the authors investigated the effect of the number of air-gaps of the resonator on the frequency of oscillations in the plate circuit of a simple Pierce circuit.
Abstract: A quartz resonator connected between the grid of a valve and either of the other electrodes gives rise to oscillations in the plate circuit when the constants of that circuit satisfy certain conditions. The frequency of the oscillations depends mainly upon the natural frequency of the quartz, and is, therefore, fairly constant when the temperature is constant. In addition to temperature effects, which are not considered in the present paper, variations of frequency can be produced by (i) variations of the air-gaps of the resonator, i.e. the air-gaps between the quartz and the two electrodes of the resonator; (ii) variations of the constants of the plate circuit; and (iii) variations of the inter-electrode capacities and conductances. The object of the investigation is the study of these variations, both theoretically and experimentally. In the theoretical treatment, the quartz is replaced by a circuit made up of an inductance, a resistance and a capacity in series, the whole being in parallel with a second capacity. The validity of such a substitution has been studied experimentally by Dye. The combination of quartz resonator, valve and plate circuit is represented by a network of admittances, from which three circuit equations are obtained; to these is added the fundamental equation of the valve. These four equations yield a single linear differential equation of the fifth order, with constant coefficients. In the case under investigation, it is only required to find the frequency, and the amplitude of oscillations after the latter have reached a constant amplitude. This consideration affords a means of reducing the differential equation to one of the same type, but of the second order. From the latter equation, of which the general solution is known, formulae are developed for the changes of frequency resulting from variations in the resistance and capacity of the plate circuit, in the resistance of the grid leak, in the inter-electrode capacities, and in the air-gap. These formulae provide useful information as to the influence of each variable on the frequency, and can with advantage be applied to the choice of the best circuits and the best valve for a quartz oscillator. As the oscillations build up after switching on, the average plate conductance of the valve alters gradually. When the amplitude of oscillation has reached its final value, the value of the average plate conductance is such as to annul the damping term, i.e. the coefficient of dy/dt in the differential equation. From this condition the average plate conductance can be determined for any values of the circuit variables. The amplitude of oscillations in the plate circuit is a function of this average plate conductance. Formulae are developed which give the conditions for the maintenance of oscillations, and an investigation is made of the variations of amplitude with variations in (a) capacity in the plate circuit, (b) resistance in the plate circuit, and c) grid conductance. Points of importance in the choice of circuits and valves are deduced from the formulae and the theoretical curves Two types of quartz oscillator are investigated, namely, the cases in which the quartz resonator is connected between i) the grid and the plate of the valve, and (ii) the grid and the filament of the valve. A fairly complete experimental investigation is described. The admittances of the valve and of the circuits were measured, and the equivalent electrical network of the quartz was determined. The behaviour of the quartz oscillator was then investigated by altering in turn each variable in the circuits. The theoretical and experimental results are compared and discussed. The paper does not deal with circuits especially devised for obtaining large outputs from quartz crystals. Its object the study of the influence of the circuit variables on the frequency and on the power generated as regards the simple Pierce circuits.