摘要:

The paper deals with some of the technical considerations of the design and application of control gear to machine tools.The application of electrical control to machine tools is compared with other orthodox types of control gear, and the choice of electrical control gear is discussed with particular reference to the frequency of operation. Design of components (in particular, contactor design) is given due consideration, and the paper also shows how design may be based on results obtained from experimental work and past experience. After a note on complex schemes of control, the need for incorporating reliable interlocks is stressed, especially electrical interlocks involving auxiliary switches. Thesupply voltage is shown to have its importance, and low-voltage control circuits are compared withthose operating from line voltage.Speed control is next treated, with some regard to the application of electronics. The importance of motor protection is stressed, with particular reference to protection by h.r.c. fuses. Electricbraking, especially the d.c. injection method, is dealt with in some detail. Types of timing devices are described, and the electrical timer is compared with mechanical and thermal types. After discussing d.c. supply and its advantages over a.c. supply in connection with motor speed control, future developments in design of control gear and its application are reviewed.

DOI:10.1049/pi-2.1950.0130

出版商:IEE    

年代:1950

数据来源: IET

摘要:

It is well known that certain factors, notably flicker noise and zero drift, determine the smallest signal voltage that can be satisfactorily amplified by a thermionic d.c. amplifier. Better results can often be obtained by using a suitable modulator to convert the direct current to alternating current and following this by an a.c. amplifier and rectifier.The paper discusses the advantages of the second-harmonic type of magnetic modulator for this purpose, and presents a theoretical analysis of an idealized modulator of this type, with particular reference to the influence of various controllable parameters on the signal/noise ratio and zero error.The paper also describes experimental work, which, with allowance for the idealizations in the theoretical analysis, is considered to provide a satisfactory qualitative verification of the latter. Particular emphasis is placed on the need for great care in the design of the various circuits, toeliminate additional sources of noise and zero error, and it is believed that the noise output of the apparatus described is due mainly to Barkhausen effect in the modulator cores, and is equivalent to a signal input of about 10−19watt for a bandwidth of 1 c/s; the zero drift is, however, considerably greater than this, and is equivalent to a signal input of about 3 × 10−18watt over a two-hour period.

DOI:10.1049/pi-2.1950.0139

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The paper presents a completely new theory of the magnetic amplifier with a finite load resistance and a low-impedance signal circuit. The analysis assumes that theB/Hcurve for the core material has a constant initial slope, followed by abrupt transition to zero slope at the saturation level. From this basic assumption, flux waveforms are derived and equations are developed for the magnetomotive forces operating at every instant in the cycle for a transductor with any degree of self-excitation. Analytical expressions are thence derived for the output characteristics, and the particular conditions of zero self-excitation and full self-excitation are examined in detail. Further expressions, both in full and in simplified form, are obtained for the current amplification and time-constant of a transductor, since these quantities are of considerable importance in design work.Because of the idealized form assumed for theB/Hcurve, the theoretical characteristics are not completely realized in practice; but the theory provides a basis for improved methods of design, and explains certain important phenomena (such as the variation of the current amplification with change of the load resistance) which are not revealed by more elementary treatments of the subject.

DOI:10.1049/pi-2.1950.0140

出版商:IEE    

年代:1950

数据来源: IET

摘要:

Following a brief review of present-day ignition requirements, the elementary principles of magneto operation, including low-speed performance, are discussed, and arguments are given to explain the discrepancy which is found between theory and practice in the magnetic circuit.Development and progress in regard to the mechanical operation of contact-breakers is described, and a review of their electrical limitations leads to explanations why this component imposes a practical upper limit on the output voltages and sparking speeds of magnetos.Interesting phenomena associated with high-voltage distribution are included, particular referencebeing made to distributor operation at high altitudes.Some developments are discussed, including special circuit and transformer design, which aim at increasing the output beyond that possible with conventional design, and the paper concludes with a brief reference to capacitor-discharge ignition systems of the contactmake and high-frequency types.

DOI:10.1049/pi-2.1950.0144

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The methods used hitherto for the determination of synchronousmotor and alternatorload-characteristics are similar, and depend on the estimation of the m.m.f.'s and fluxes underload conditions. This is, however, difficult to do with accuracy, owing to saturation, leakage and the different reluctances of the magnetic paths.The paper shows that tests can be performed at low speeds to reproduce exactly the m.m.f. and flux conditions which occur in a synchronous motor at normal speeds and loads. The errors inherent in previous methods are thereby avoided, enabling the synchronousmotor characteristics to b predetermined with a high degree of accuracy.The method described is applicable to cylindrical-rotor and salientpole machines.

DOI:10.1049/pi-2.1950.0147

出版商:IEE    

年代:1950

数据来源: IET

摘要:

An a.c. supply of high stability is required for many purposes, particularly metercalibration, and can be obtained only from some type of stabilizer. Few stabilizers have been designed with stabilities he order of 0.1 to 0.01%. The paper deals with the advantages and disadvantages of various basic stabilizer arrangements, and then considers in detail a special type of “indicator” using a thermistor. The theory of two types of “controller” is then discussed.The design of a stabilizer of high accuracy using the above special indicator is then considered in detail. Such a stabilizer can be produced with a stability of 0.01% and with an output upto 2 kVA.

DOI:10.1049/pi-2.1950.0157

出版商:IEE    

年代:1950

数据来源: IET