DOI:10.1049/ree.1969.0106

出版商:IERE    

年代:1969

数据来源: IET

摘要:

The examination of a suspect transistor to determine its mode of degradation or failure always includes, at an early stage, checks on its junction and transistor characteristics, usually with the aid of a visual display on a curve tracer. This paper discusses the diagnostic significance of some of the abnormalities which may be observed on such displays.

DOI:10.1049/ree.1969.0107

出版商:IERE    

年代:1969

数据来源: IET

摘要:

Optimum performance of a control system in terms of its time domain response can be achieved by the use of a bang-bang controller. The binary nature of the control signal together with the inherent complexity of a controller designed to achieve optimum bang-bang control high-order systems, immediately suggests the use of an on-line digital computer. Previous methods of attempting bang-bang control using an line digital computer have encountered two major difficulties, namely excessively long computation time and excessive ripple at the output to sampling. In such methods the amount of computation increases enormously as the order of the process to be controlled increases. This paper describes a new method which bypasses both of these major difficulties. The problem of long computation time is solved by trading computation time for computer storage. The information required for determination of switching times is determined once and for all at leisure an off-line calculation. The information is then permanently retained the store of the on-line computer. The problem of output ripple is solved by means of a dual-mode system. For large state errors the bang-bang algorithm is employed whilst for suitably small-state errors the computer changes the mode of control to a pseudo-linear mode in which process receives an input signal which is still binary in form but which pulse-duration modulated in such a way that the average value of the signal is that which it would receive from a tightly compensated linear controller.The paper includes details of tests of the new method applied to a third-order type-0 process. These are a series of step-response tests on firstly a purely digital simulation and secondly a real-time hybrid simulation in which a digital computer is used on-line to bang-bang control a process simulated on an analogue computer. The results of these tests are compared with those in which the same process is controlled by means a practical three-term controller. The comparison indicates the superiority of the new system.

DOI:10.1049/ree.1969.0109

出版商:IERE    

年代:1969

数据来源: IET

摘要:

It is shown that networks can be produced to correct accurately the effects of the non-linear transfer characteristics of a cathode-ray tube. The gamma correction required is related to the undesirable non-linearity in mathematical terms and the basic gamma equation evolved. A simple exponential equation can be converted into a gamma equation by the introduction of a linear function and the appropriate constants. A network with the required gamma characteristic is equivalent to an amplifying stage incorporating exponential negative feedback.Circuits employing semiconductors are presented and discussed and the operational equations and performances are found to compare favourably with the theoretical gamma equation, and to support the theory. Networks employing negative feedback intended for operation at video frequencies call for special design to counteract the effects of gain and phase shift variation at those frequencies and a gamma stage suitable for television applications is presented. Stabilization of the operating point of the gamma stages with respect to temperature and power supply variations is described. Testing a gamma stage involves measurement of phase shift, frequency response and faithfulness of gamma as well as checks for the presence of waveform distortion.Although the treatment deals in particular with the linearization of c.r.t. displays, the techniques are applicable to accurate logarithmic amplifiers, photographic-film contrast correction and in colour television camera tube applications.

DOI:10.1049/ree.1969.0110

出版商:IERE    

年代:1969

数据来源: IET

摘要:

After outlining some of the problems associated with the design of fluid flow networks a brief survey is made of the methods whereby such systems have been simulated. The use of analogue techniques for this purpose is discussed and an attempt has been made to compare the various methods proposed. As a result of this study certain improvements were considered to be worth seeking, and a new type of simulator is described based on the exponential family of pipe resistance laws. A novel feature is the independent control of simulated length and diameter.

DOI:10.1049/ree.1969.0116

出版商:IERE    

年代:1969

数据来源: IET

摘要:

This paper is concerned with the selection of optimum channels for communication through media of which the quality is varying from any cause, including changing levels of interference. In particular it demonstrates the advantage of adaptive frequency selection when a block of channels is shared by relatively large numbers of random intermittent users, as is now the case with many portions of the h.f. band. Various methods of channelling including the broad-band spread-spectrum approach are discussed, and it is shown that adaptive selection of narrow band channels could be compatible with existing non-adaptive usage. The argument is further extended to include a discussion of adaptive use of the v.h.f. and u.h.f. bands for satellite communication on the basis of noninterference with existing services.

DOI:10.1049/ree.1969.0117

出版商:IERE    

年代:1969

数据来源: IET