摘要:

In computer input-output systems contention occurs when two or more peripheral devices make interrupt requests simultaneously. The currently used methods for resolving this contention are outlined, and an improved method which avoids their drawbacks is presented. Synchronous and asynchronous implementations are described, and the effects of bus propagation time are discussed.

DOI:10.1049/piee.1976.0181

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The operation and performance of a new quartz multivibrator is presented. The multivibrator is based on a freerunning circuit using a complementary regenerative switch. Owing to the use of this complementary switch, the multivibrator has high regeneration, low output impedance and no integration effect. As a result, it has small transition times (40ns) and a possibility of high loading (100Ω). Owing to the use of the quartz crystal, the multivibrator frequency is very stable at changes of supply voltage and load impedance. The circuit temperature stability is mostly dependent on that of the quartz crystal. The multivibrator can be adjusted for the generation of symmetrical or asymmetrical waveforms.

DOI:10.1049/piee.1976.0182

出版商:IEE    

年代:1976

数据来源: IET

DOI:10.1049/piee.1976.0183

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Modern swept-frequency network analysers readily display complex reflection and transmission coefficients as functions of frequency. Methods, applicable to both 1- and 2-port cavities, are presented for the convenient extraction of cavityQ-factor information from the frequency variation of reflection coefficient amplitude and/or phase. The methods are extended to cases where the coupling circuit is lossy.

DOI:10.1049/piee.1976.0184

出版商:IEE    

年代:1976

数据来源: IET

摘要:

This paper surveys the most recently reported attenuation measurements at microwave and millimetric frequencies on terrestrial and satellite (slant) radio paths. Greatest attention is given to direct measurements of attenuation, but radar and radiometric techniques are also considered. Measurements relating fading to the various meteorological parameters are reviewed as well as those presenting statistical information for the system designer. From the summary of all available statistical measurements of greater than one year duration, the variation of fade depth (exceeded for 0.01% of the time) with path length is characterised for 11 and 18 GHz on terrestrial paths. The accuracy of radar and radiometric measurements on satellite paths is also discussed, and related where possible to direct measurements with satellite beacons.

DOI:10.1049/piee.1976.0185

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A theoretical analysis of perturbation methods leads to proposals for some new techniques of phase measurement. These techniques are inherently automatic, use only one radio-frequency processing channel, and can be applied to modulated and low-level signals. Some methods of implementation are suggested, factors that affect the accuracy are discussed, and some applications are described.

DOI:10.1049/piee.1976.0186

出版商:IEE    

年代:1976

数据来源: IET

摘要:

An investigation has been made of the movement of conducting particles, under the action of the applied electric field, on the surface of an insulating spacer immersed in SF6between 0.47 and 1.5 MPa. Spheres moved fairly readily but particles of an irregular geometry, such as filings, did not. Movement was more pronounced with the higher stresses obtainable from impulsive fields than a.c. There was no effect of pressure. The incorporation of a particle trap showed that while it was effective in keeping a spacer clean if contamination could be induced to enter it, the trap could not guarantee spacer cleanliness because of the lack of particle movement. However, a further investigation of the prebreakdown discharge behaviour of a short length of SF6insulated cable showed that the range of contamination which caused low impulse flashovers can be detected on the laboratory scale at least. Using a balanced discharge detection system, it was observed that, for a given degree of contamination, discharge inception and the maximum discharge magnitude before 50 Hz flashover were both functions of pressure. The largest discharges (2pC) occurred at 0.3–0.4 MPa, and there was a correlation coefficient of 0.93 between the negative-polarity standard impulse breakdown voltage at 1.1 MPa and the discharge inception voltage at 0.4 MPa.

DOI:10.1049/piee.1976.0187

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Comparisons have been made between measurements and calculations of magnetic-flux in turbogenerator end-regions. The results of measurements on two 500 MW generators are presented. Two methods of calculation are reviewed. A method is given for relating the results derived from measurements and calculations to the load conditions. It is concluded that the use of a nonmagnetic rotor end-bell on these large generators willreduce eddy-current heat of the core-end.

DOI:10.1049/piee.1976.0189

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A 2-dimensional section of a synchronous machine is modelled using 1st-order triangular finite elements. Equations are formulated by the use of Ampere's law. The transient performance of the machine is obtained by determination of the vector potential distribution at successive instants in time, the effect of closed circuits being taken into account in the formulation of the equations by the introduction of conductivity matrices. Variable permeability of steel and the effect of eddy currents are taken into account. The method is applied to calculate the performance during a field-decrement test.

DOI:10.1049/piee.1976.0190

出版商:IEE    

年代:1976

数据来源: IET

摘要:

It is shown how compensators for turboalternator excitation-control schemes may readily be designed to appropriate stability margins using multivariable frequency-response methods. The proposed design approach offers a great improvement over previous methods, and the ease of its application is demonstrated by the design of a speed compensator for a static excitation system.

DOI:10.1049/piee.1976.0192

出版商:IEE    

年代:1976

数据来源: IET