摘要:

The paper reviews the present practice with regard to the type of lift installed in block dwellings by a large housing authority.Reference is made to the general planning aspects as they affect the engineer and the lift service required. Special reference is made to the siting and construction of the lift installation, and to the necessary fire precautions.The immediate post-war years made it necessary to save steel and to investigate suitable alternative materials where possible.While the original aim was to install a lift that would be least affected by misuse and give as little opportunity as possible for malicious damage, it became apparent from experience gained during the operation of these lifts that departures in design and control from normal practice, as recommended by the Building Industries National Council Code of Practice for Electric Lifts, would prove necessary. Results comparing the breakdown rate before and after the introduction of these modifications are put forward to support this view and to dispel any fears that the safety of the passenger is adversely affected.The introduction of a “mechanic control station” on the roof of the car is also suggested as a means of ensuring greater safety to the maintenance mechanic and of assisting the inspecting engineer in his task.

DOI:10.1049/pi-2.1954.0014

出版商:IEE    

年代:1954

数据来源: IET

摘要:

The use of the non-linearity of the magnetization curves of transformer cores appears to have first been used in this country by the author's father for testing large power transformers in 1907–08.*This and bridge methods employed more recently work on the change with magnetizing field of the incremental permeability of the magnetic core. The advent of high-permeability materials with a sharp knee in the magnetization curve has resulted in the development of the transductor, which essentially consists of two cores which are alternatively driven far into saturation in each half-cycle of the supply frequency. Transductors are essentially d.c. amplifiers, the magnetization of the cores being biased by input windings connected to the excitation windings in series opposition. The operation of a transductor is similar to that of a pair of grid-controlled rectifiers in that as soon as saturation of one core is reached the inductances of the windings on it decrease to a low value and the currents rapidly increase, driving the core far into saturation. The impedance of the windings must then remain small until the current through them has decreased to a very small value; since the impedance is small this can result only from the excitation voltage decreasing almost to zero.Another important principle in the operation of transductors is that the current through the load is only significant when one core is saturated and the other is not, in which case there is tight coupling between the input and excitation circuits, and ampere-turn balance must be maintained between them. Thus the current gain of a simple transductor is always equal to the ratio of the numbers of turns on the excitation and input windings, and the transductor is equivalent to a current amplifier of high gain with 100% negative feedback. This results in a highly linear relationship between input and output but a low power gain. As might be expected, the power gain can be increased by feeding the rectified load current back to the input in the positive sense. This is known as self-excitation and results in some reduction of the linear range and increased drift. There is, however, considerable improvement in transient response, since, independent of the amount of feedback employed, the time-constant of the transient response is almost directly proportional to the current gain, whereas the power gain is proportional to the square of the current gain. It has been shown that, provided 100% self-excitation is required, this can be more simply achieved in parallel-connected transductors by the use of rectifiers to suppress in each half-cycle the excitation current in the winding which will not be saturated.Self- or auto-excitation results in increased standing current, and, as might be expected, this results in reduction of stability. It is easily shown that the chief cause of drift is change of the rectifier characteristics, and with the best rectifiers available at present the smallest input signal that can be discriminated with this type of transductor is 10-7watt. The simple two-core transductor does not distinguish between positive and negative input currents; to do this, a push-pull arrangement results in some improvement of stability, and the smallest input power which can be discriminated is of the order of 10-9watt. By connecting the load to additional windings, magnetically similar to the input windings, and suppressing by means of a high impedance the even harmonics which would otherwise be induced in the input circuit, these harmonic currents can be forced into the load circuit. This circuit then has no standing current, but, since ampere-turn balance must be maintained, it has the same signal current as before. This results in a very great improvement in stability, and by the use of elaborate valve circuits a short-term stability of 10-18watt can be achieved. If, however, the magnetic modulator is to be followed by a magnetic amplifier, since the greatest gain that can be achieved in the modulator is about 103, the best stability that can at present be achieved with an all-magnetic system is of the order of 10-12watt.Developments by R.A. Ramey in the United States, using materials having almost rectangularB/Hloops with high remanence, have resulted in transductor circuits for which the time-constant of the transient response is never more than half a period of the a.c. excitation.

DOI:10.1049/pi-2.1954.0017

出版商:IEE    

年代:1954

数据来源: IET

摘要:

After a brief description of the Ince site and the station layout thereon, the paper sets out the major factors involved in considering the degree of enclosure of a semi-outdoor station—a technique first used in the United States—and describes that adopted at Ince. It discusses the structural design of the station and its effect upon site erection, and shows that, while the savings in capital cost resulting from the semi-outdoor design are difficult to evaluate, they may exceed £1 per kilowatt installed. It then considers the effect of partial exposure upon the boiler plant and describes the precautions adopted against corrosion and frost.

DOI:10.1049/pi-2.1954.0020

出版商:IEE    

年代:1954

数据来源: IET

摘要:

An account is given of the equipment used and the methods which have been developed at the National Physical Laboratory for calibrating alternating-current indicating instruments to an accuracy of 0.1%, or better, of full-scale deflection. The power required for carrying out these tests may range from a few watts for a low-range voltmeter or ammeter up to 60 kW for the equipment used in a turbo-alternator test at high voltage. When the power required is large and at a frequency below 600 c/s, rotating machinery is used, giving an output stable to 0.02% and of waveform with harmonic content not exceeding 2%. For smaller powers, oscillator-amplifier sets are used at all frequencies from 50 c/s up to lOOkc/s, giving an output stable to 0.01% and of waveform with harmonic content not exceeding 0.3%.Instruments are tested by comparison with a standard voltmeter or wattmeter which must itself be calibrated to a higher order of accuracy, say 0.01 or 0.02%. The auxiliary resistors used with these instruments for range changing must also maintain constant and known values under all loading conditions to about 0.01%. Finally, the instrument, a voltmeter, used as a d.c./a.c. transfer instrument must be calibrated on direct current against a Weston cell in association with a suitable voltage divider. The e.m.f. of the Weston cell is maintained constant to approximately 0.001% by maintaining the cell at a temperature constant to 1/4° C, while the error of the voltage divider is of the same order, so that no significant error is introduced into the calibration on account of the d.c. standard.

DOI:10.1049/pi-2.1954.0023

出版商:IEE    

年代:1954

数据来源: IET

摘要:

Simplifying assumptions regarding the nature of certain types of continuous processes lead to transfer functions which are amenable to analysis. Criteria for optimum control based on the transient responses of such systems when under proportional plus derivative plus integral control are given.The effects of integral control at low frequencies are studied, and it is shown how conditional stability can be avoided when the process contains an integration. A low-frequency damped oscillation which can occur with three-term control is investigated, and the condition for its elimination is derived.An analytical method is developed which, for any given integral control setting, makes it possible to determine the optimum values for the two remaining controller settings. It is shown that the introduction of integral control allows an increase in the proportional control factor for the same degree of damping of the first normal mode of oscillation.Experimental results are given showing how an electronic simulator for process control has been used to confirm the results of the analyses and to assist in determining the optimum settings for integral control.For completeness, a brief description of an automatic-process-control system with definitions of the terms used is included in the paper.

DOI:10.1049/pi-2.1954.0027

出版商:IEE    

年代:1954

数据来源: IET

摘要:

A simple second-order remote-position-control servo mechanism stabilized by velocity feedback or by a phase-advance network, and having an amplifier exhibiting saturation, is taken as the basis for experimental work. Additional non-linear elements purposely introduced to modify the system are discussed and step-function responses are considered by phase-plane analysis. Experimental systems are described and the performances are quoted.

DOI:10.1049/pi-2.1954.0028

出版商:IEE    

年代:1954

数据来源: IET

摘要:

An analysis of the step-function response of a particular r.p.c. system is given, account being taken of saturation in the amplifier or servo motor. The object of the paper is to show the variation of the effective degree of damping with the increase in input step magnitude and to give quantitative data in graphical form.A simple second-order system has been taken in which the output torque is proportional to the control signal within the linear regime, and which has derivative-of-output or velocity-feedback stabilization.

DOI:10.1049/pi-2.1954.0029

出版商:IEE    

年代:1954

数据来源: IET

摘要:

A well-known theoretical proposition in electrical-engineering science resolves a pulsating magnetic field into two fields rotating in opposite directions. The authors have used the inverse of this principle as the theoretical basis for certain prototype indicating or measuring devices. Two oppositely rotating fields which may (or may not) be of the same magnitude and frequency are combined to give a resultant field which can be used practically in many ways for indication, measurement or control. Various electrostatic and electromagnetic applications of this new principle, with test results, are discussed in the paper.

DOI:10.1049/pi-2.1954.0032

出版商:IEE    

年代:1954

数据来源: IET

摘要:

Some time ago a research programme on the electric strength of pure liquids was started and has led already to a number of publications dealing with the strength of simple organic liquids. In the paper are given the results of a systematic investigation of some of the extraneous effects associated with the method of measurement.The tests were made under carefully controlled conditions with the test cell incorporated in a closed distillation system. Among the factors influencing the electric strength of pure liquids, the effects of moisture and gas in the liquid, as well as of gas adsorbed on the electrode surface, were examined. It was found that, for pure liquids, the conditioning of electrodes, i.e. the gradual increase of the electric strength with successive voltage applications, appears to be due to a gradual degassing of the electrodes. No such effect was observed with artificially degassed electrodes.Experiments on the effect of the electrode geometry have shown the remarkable result that, using a test cell of sufficient diameter, the electric strength of pure liquids does not depend on the size of the electrodes and their spacing, except for very small spacings, where there appears to be a tendency for the electric strength to increase.

DOI:10.1049/pi-2.1954.0033

出版商:IEE    

年代:1954

数据来源: IET

DOI:10.1049/pi-2.1954.0038

出版商:IEE    

年代:1954

数据来源: IET