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Abstract

The availability of on-line digital computers for use as a building element of measurement and control systems necessitates a complete rethinking of the forms of instrumentation, Functions such as signal conditioning, compensation, linearisation, filtering, etc., hitherto carried out by dedicated, special purpose and sometimes not practical hardware, can now be efficiently realised by using a computer, At the same time, digital computers in measurement and control systems need to communicate with other subsystems of the overall system, In particular, they must be connected to sensors.

Up to the present, in spite of significant advances in computer technology, sensor subsystems for use in connection with computers have remained in the form in which they were before the advent of computers, as analogue devices connected to the computer by some form of interface, No systematic studies have been carried out to arrive at systems
specifically devised to fit in optimal way into a system centred round a computer.

The aim of the present report is to examine from the first principles the sensor-signal conditioning device-communication channel-interface-computer chain in computer-based measurement and control systems with a view to arriving at conclusions concerning desirable ways to design and analyse the elements of the aforementioned chain, The problem of the industrial process control computer was kept specially in mind.

The motivation to undertake the study arose on the one hand from industrial needs as seen by the membership and relevant Committee of the SIRA Institute and on the other hand from the interest in The City University in the systemic approaches to instrumentation design (E.R. Carson, A, Pirouzan, 1972). Recent events have confirmed that the study is justified : the IMEKO VI Symposium dealt with means and methods for the instrument-computer interface and a special round table, concerning the problem of interface between the process and the computer was organised, An excellent paper (B.P.Th, Veltman, 1972) analyses in great detail the various aspects of interface, The conclusions mainly reflect the need for a suitable interface (involving both hardware and software) if the capabilities of the digital computer have to be fully used, A conference organised by IEE in September 1973, has the aim of discussing the same topic. The works at IMEKO have shown that the methods and elements used for the interface between the process and the computer are still behind the advances in computer technology, A systemic approach for solving this problem is undertaken in this report, Each element of the chain between the process and the computer is considered and analysed.

The state of the art in data aquisition systems is considered in Chapter 2, The typical requirements imposed to data aquisition systems and possible ways of improving their performance are analysed, The concept of transmitting analogue signals over long and noisy communication channels is challenged and justification for a new approach of this matter is given.

Chapter 3 presents fundamental problems in connection with quasi-digital signals, The notion of quasi-digital signal is postulated. The general properties of quasi-digital signals are discussed, Possible structures generating quasi-digital signals are examined.

The problem of signal transmission over communication channels is discussed in Chapter 4 The analysis is carried out for channels affected by Gaussian, as well as non-Gaussian noise, A non-Gaussian multivariate probability distribution function is proposed, based on the knowledge of marginal probability distribution functions, The transmission of signals is analysed for the cases of Gaussian and non Gaussian noise, Also the detection of signals corrupted by noise is examined and possible detector structures are given.

As the cost of the cables connecting the data sources to the computer is unlikely to decrease in the future, Chapter 5 is devoted to the optimisation of the cost of communication system, The leading idea is to use multiplexers placed at suitable locations instead of using an individual cable for each data source, Two heuristic algorithms, which find the optimum position for multiplexers, are proposed, The computer programs implementing them have been tested and the results produced by them are similar, Then the queuing theory for single-server facility is applied for estimating the capacity of multiplexers.

Chapter 6 contains final conclusions and possible lines for future investigation.

The Appendices contain elements relevant to the work which has been done, mainly with reference to the study of an oscillator, using piece-wise linearisation and root locus method, and computational problems encountered during the various stages of the thesis.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science Q Science > QA Mathematics > QA75 Electronic computers. Computer science Q Science > QA Mathematics > QA76 Computer software
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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