OpenUCT :: Browsing by Subject "Electrical and Electronic Engineering"

Browsing by Subject "Electrical and Electronic Engineering"

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Open Access
Adaptive noise cancelling applied to machine condition monitoring
(1990) Bremer, Paul Graham; Jongens, A W D
The objective of this thesis is to determine whether Adaptive Noise Cancelling can be used successfully in determining the state of machine elements. In addition, this thesis was used to gain experience in real-time computing. This was done by designing and building a real-time machine monitoring package using an IBM PC and a TMS 320C25 digital signal-processing chip manufactured by Texas Instruments. To determine which adaptive algorithm should be used in the package, experiments were carried out on a computer with different types of adaptive noise cancelling algorithms, the two main ones being the Least-Mean-Squares (LMS) and Recursive-Least-Squares (RLS) algorithms.
Open Access
Analysis of symmetrical components of harmonics for three phase power systems
(1986) Shum, Kwan Leung; Enslin, NC de V; Hoffman, K P
Harmonic distortion of three phase power systems is caused by large amounts of electric power consumers using power electronic installations (e.g. drives and rectifiers). It has a number of undesirable consequences and has become an increasingly important problem with the rapid growth and ready availability of the power electronic devices and installations. A famous mathematical technique called "symmetrical components" was used to model the fundamental components of three phase systems. This method was extended to various harmonics. The aim of this thesis is to measure both the magnitude and phase angles of various harmonics which exist in three phase power systems, and to express them in symmetrical components. A digital electronics and microprocessor-based instrument was designed and constructed using the novel signal modulation technique called "+1 and -1" which was developed by the author of this thesis. This instrument was employed to achieve the above objectives.
Open Access
An automated monitoring system for the production and measurement of metal fatigue
(1988) Upton, David Mark; Bell, J F W
New equipment for producing and following the fatigue process, in metals, has been developed. The specimens, which must be in the shape of tuning forks, are resonated at high amplitudes. This is achieved by attaching small, powerful, samarium-cobalt magnets to the ends of the tynes, enabling them to be driven efficiently by a "U"-core electromagnet. A small, piezoceramic strain gauge provides a method of picking up the vibrations. To maintain resonance, the signal is used in a positive feedback loop, which incorporates an analogue multiplier to provide AGC. This also keeps the amplitude constant at any desired level, throughout the duration of an experiment.
Open Access
Broadband, low-noise and power microwave amplifiers
(1986) Hall, Andrew D; Downing, B J
The design of Broadband, Low-Noise and Power Microwave Amplifiers using microstrip softboard technology is investigated. The software program TOUCHSTONE (TM) by EEsof is used extensively as a basic design tool. The characterisation of the GaAs Field Effect Transistors, used for the amplifiers, is carried out. These characterisations are then used by the program in its circuit analysis. A determination of the validity of using the manufacturer's data, for the designs, is determined by comparing it to the measured data. Source-Pull and Load-Pull measurements were performed for the Power GaAs FET characterisation. The noise-parameter device characterisation is carried out in a similar way to that for Load-Pull data. Each amplifier required final tuning adjustments in order to peak the performances. The Broadband Maximum Gain Amplifier had a 10 ± 1.5dB gain over a bandwidth from 2- to 6-GHz. The Low-Noise amplifier achieved 5dB Noise-Figure and 5.4 ± 1. 4dB gain over the 2- to 6-GHz band. The Power amplifier Output Power was 390mW over the 3.7- to 4.2-GHz band. Techniques of broadband matching are investigated, with Double-Stub matching producing the widest bandwidth. A literature survey is presented on aspects of broadband microwave amplifiers, as well as a survey on Computer-aided-design at microwave frequencies and techniques of Large-Signal Transistor characterisation.
Open Access
Colour analysis and the classification of fruit
(1992) Kay, Gary R; De Jager, Gerhard
The increasing high standards of fruit quality expected by the agricultural export market of South Africa has reached a stage that fruit must be accurately graded in a short a time as possible. This thesis describes colour systems and methods to grade the fruit automatically via the clustering and classification methods. After investigating several approaches to automatically sort fruit based on colour, an image processing approach was taken. The colours on the fruit (specifically apples) were analyzed, by capturing a colour image of the fruit and analyzing the pixels in the image. Several colour representation systems were investigated and they are: colours represented by spectral power distributions and spectral reflectance curves; the CIE 1931 XYZ tristimulus values; the CIE 1931 x ,y ,z chromaticity coordinates; the CIE 1960 L, u, v uniform chromaticity scale (UCS); the Munsell colour wheel of hue, value and chroma (HVC); the L*u*v* system; the L *a*b* system; the Red, Green and Blue (RGB) system; and the hue, saturation and intensity (HSI) perceptual colour representations. In addition, several clustering and classification techniques were investigated and they are: the supervised methods of Parametric Bayesian classification and minimum Euclidean distance classification; and the unsupervised methods of the K-means algorithm and the ISODATA classification approach. The ICS Texicon computer spectrophotometer (ICS Texicon Spectraflash Manual (1991)) was used to check the performance of most of the colour systems described by analyzing apple sample colours
Open Access
Comparison and evaluation of South African poletop designs for 11kV and 22kV rural distribution lines
(1992) Scott, R A; Dingley, Charles
The ultimate purpose of this thesis is to compare and evaluate. South African poletop designs for 11kV and 22kV rural distribution lines. However, a frame of reference is first established from the literature and from construction practice before the analytical stage is tackled. In 1989, when the work for this thesis was started, it was quite apparent that there existed a proliferation of configuration designs for rural overhead lines at 11 kV and 22kV in South Africa. The electricity supply industry did not use a universal configuration. Eskom supplied over 97 of South Africa's electricity in 1990 (Eskom, 1990). It was also operating 160 280km of lines at 22kV and below in that year and was largely responsible for this situation. Local supply authorities or distributors S!JCh as municipalities either bought components from Eskom or used an Eskom design, or developed their own designs internally or via consultants. In any event, the designs they used are not considered to be a significant portion of the total. Historically, Eskom developed on a strongly regionalised basis, the separate Undertakings joining up (electrically) to form the national grid in 1973. Prior to 1985 there were six Regions distributing the electricity generated by the power stations. Each Region developed its own designs, independently or based on designs imported from Britain.
Open Access
A contribution to the magnetic field of a shaded pole motor
(1988) Voss, Egon; Neubauer, R E
Beginning with the developed version of a shaded pole motor a contour of the area concerned is defined which follows the boundary between rotor iron and rotor conducting medium, the pole gap, figure 1. In this case the analysis is restricted to a region which is given in y-direction as the distance between rotor –and stator iron over half a pole pitch in x-direction. Due to the shading ring it is not possible to define boundary conditions for the contour parts along the pole –and the pole-gap axis
Open Access
Controller design via H[infinity] optimal control, quantitative feedback theory and fuzzy logic control : an application to load frequency control
(2000) Boesak, C D; Braae, Martin
This thesis describes the application of robust controller design techniques namely H[infinity] optimal control, fuzzy logic control and quantitative feedback theory to the load frequency control problem of power systems. It thus forms a comparative study of these design methods. Load frequency control is the closed loop control of electrical generating units to regulate the system frequency at its nominal value in the presence of load disturbances. Load frequency control also includes the regulation of the tie-line interchange powers.
Open Access
Design and implementation of a parallel registration algorithm for SAR images
(2001) Fadiran, Oladipo O; Inggs, Michael; Wilkinson, Andrew John
Registration of two or more images of the same scene is an important step in image processing that seeks to extract information not obtainable from one of the images in question. This process is required in many Engineering, Scientific and Medical applications. The accuracy of this step is crucial to the reliability of subsequent image processing and or decisions made on its basis. The huge size of the date to be processed, the speed at which the processing is required and the accuracy requirements necessitates a quick, efficient, robust and in some respects automatic program which efficiently harnesses available computing resources. This is the object of this project - the design of an image registration algorithm with a bias for SAR/InSAR applications but also applicable for other registration purposes, implemented on a parallel cluster of computing nodes.
Open Access
Design of a low pressure system to determine the acoustic nonlinearity parameter B/A for small volumes of sample liquids
(2003) Prenzlow, Bjorn; Tapson, Jonathan; Davies, J
This thesis aimed to design a measurement system to obtain B/A readings for different liquids using the isentropic phase method. The resulting system uses a sinusoidal wave source that operates on less than 20kPa to pressurize a sample liquid of less than 0.2 ml. The advantage of the system is that it can obtain measurements using relatively few parameters of the liquid, requiring only density and sound speed, and that it can obtain a result in a relatively short amount of time (less than 15 minutes after system has reached thermal equilibrium).
Open Access
Design of a simulation for trellis coded modulation
(1992) Lindebaum, Theo; Braun, Robin
The last decade has shown a very rapid increase in the application of digital computers to virtually all walks of life. This has resulted in a demand for better and faster digital communication links, at reasonable prices. Trellis coded modulation is a fairly recent development in the technology of digital communications that has helped to meet an aspect of this demand. The Department of Electrical Engineering at the University of Cape Town had not undertaken any research in the field of trellis coded modulation at the time this thesis was started. From what was understood of the topic at the time, it was deemed important to develop a foundation of skills and tools for working with trellis coded modulation. It was hoped that such a foundation will give current and future members of the department sufficient background to spot potential applications for the principles of trellis coded modulation.
Open Access
Design of control systems based on Q(Youla)-parmetrization
(1992) Jacobs, F C; Braae, Martin
This thesis is concerned with the application of a method for control system design based on Youla(Q)-Parametrization. The fundamental concepts of the parametrization method have been used by Newton et al, Franklin and Raggazzini [Maciejewski, 1989] as early as 1957. The importance of its implications were not noticed during those years, but Youla and Kucera renewed it in the seventies [Maciejewski, 1989]. For the special case of an open loop stable plant, the implementation can be realized in the Internal Model Control(IMC)-Structure [Morari, 1987]. The IMC-Structure is essentially a open loop design method for closed loop controllers, thereby simplifying the design procedure. A Multivariable controller design method is proposed that unifies the advantages offered by three design approaches/techniques, namely, The Q-Parametrization, The IMC-Structure and The Characteristic Loci Technique. The proposed method is based on controller parametrization. In addition, it retains the engineering insight and simplicity of the IMC-Structure. This is particularly useful in solving complex multivariable problems. The design method was evaluated by its application to the design of a control law for a FLOTATION PROCESS SIMULATOR RIG(FLOTRIG) built by Mr Fisher[Fisher, 1988]. The design of the Multivariable controller was based on a Transfer Function Matrix, G(s), which is a Linear Time Invariant(LTI) model of the FLOTRIG.
Open Access
The design of decentralised controllers for large scale systems
(1988) Gear, A B J; Braae, Martin
Decentralised control schemes are becoming more common in industry as the advantages of decentralised control become more apparent. These advantages include fewer tuning parameters than centralised controllers, the simplification and cost reduction of hardware requirements and greater reliability. In addition the application of decentralised controller design to large scale systems allows established CAD methods to be implemented easily and efficiently. When the control engineer designs a distributed controller the system is divided up into a number of subsystems and a controller designed for each subsystem. The controllers are designed independently for each subsystem ignoring any interaction that may occur between the different subsystems. In terms of the input-output representation of the system this means that the matrix representing the controller will be in a block diagonal form. In general the interactions between the different subsystems will not be negligible. In some cases the interactions will be such that stabilising the individual subsystems will not be sufficient to stabilise the system as a whole. Stability theorems are required to enable the designer to check if the decentralised controller that he has designed will in fact stabilise the system as a whole. Such stability theorems have been devised although at present they are too conservative. However even with such theorems available the designer must still select the subsystems to be controlled in such a way as to satisfy the conditions laid down for stability. The stability theories usually are based on a particular matrix structure. If the matrix representing the system possesses a structure detailed by the stability theorem in question then, subject to various conditions, the system as a whole will be stable under decentralised control. In this thesis a number of different matrix structures are considered that give information as to the stability of the closed loop system. Methods are developed that allow the designer to rearrange the matrix in such a way as to obtain a particular structure, if this is possible.
Open Access
The design of hardware and signal processing for a stepped frequency continuous wave ground penetrating radar
(2002) Langman, Alan; Inggs, Michael
A Ground Penetrating Radar (GPR) sensor is required to provide information that will allow the user to detect, classify and identify the target. This is an extremely tough requirement, especially when one considers the limited amount of information provided by most GPRs to accomplish this task. One way of increasing this information is to capture the complete scattering matrix of the received radar waveform. The objective of this thesis is to develop a signal processing technique to extract polarimetric feature vectors from Stepped Frequency Continuous Wave (SFGWV) GPR data. This was achieved by first developing an algorithm to extract the parameters from single polarization SFCW GPR data and then extending this algorithm to extract target features from fully polarimetric data. A model is required to enable the extraction of target parameters from raw radar data. A single polarization SFCW GPR model is developed based on the radar geometry and linear approximations to the wavenumber in a lossy medium. Assuming high operating frequencies and/or low conductive losses, the model is shown to be equivalent to the exponential model found in signal processing theory. A number of algorithms exist to extract the required target parameters from the measured data in a least squared sense. In this thesis the Matrix Pencil-of-Function Method is used. Numerical simulations are presented to show the performance of this algorithm for increasing model error. Simulations are also provided to compare the standard Inverse Discrete Fourier Transform (IDFT) with the algorithm presented in this thesis. The processing is applied to two sets of measured radar data using the radar developed in the thesis. The technique was able to locate the position of the scatterers for both sets of data, thus demonstrating the success of the algorithm on practical measurements. The single polarization model is extended to a fully polarimetric SFCW GPR model. The model is shown to relate to the multi-dimensional exponential signal processing model, given certain assumptions about the target scattering damping factor. The multi-snapshot Matrix Pencil-of-Function Method is used to extract the scattering matrix parameters from the raw polarimetric stepped frequency data. Those Huynen target parameters that are independent of the properties of the medium, are extracted from the estimated scattering matrices. Simulations are performed to examine the performance of the algorithm for increasing conductive and dielectric losses. The algorithm is also applied to measured data for a number of targets buried a few centimeters below the ground surface, with promising results. Finally, the thesis describes the design and development of a low cost, compact and low power SFCW GPR system. It addresses both the philosophy as well as the technology that was used to develop a 200 - 1600 MHz and a 1 - 2 GHz system. The system is built around a dual synthesizer heterodyne architecture with a single intermediate frequency stage and a novel coherent demodulator system - with a single reference source. Comparison of the radar system with a commercial impulse system, shows that the results are of a similar quality. Further measurements demonstrate the radar performance for different field test cases, including the mapping of the bottom of an outdoor test site down to 1.6 m.
Open Access
Development and implementation of a finite element program for static electromagnetic field problems
(1990) Gopal, G
A program is presented for the solution of static electromagnetic fields in bounded and unbounded 2- dimensional domains. The program comprises of a mesh generator which descretises the domain into triangular finite elements or if applicable into special elements, called infinite elements which model the bounded and unbounded domains respectively. The potential function is solved for, using a special solution technique which enhances the speed of the program. The program outputs data in the form of potential or flux component distributions along lines of interest.
Open Access
Development of a real-time automatic network analyzer measurement system
(1989) Murray, James John; Braun, Robin
This thesis concerns itself with the development of a real-time automatic Network Analyzer measurement system based on Hewlett Packard's manual HP8410C. The major limitation in non real-time systems is the time required to perform a measurement. Real-time systems have greater measurement speed than their non real-time counterparts, but are also generally less accurate. The main objectives of the thesis are to survey literature on high frequency measurements, to develop hardware and software for a real-time Analyzer and to perform tests with the system.
Open Access
Development of a system to measure marine turbulence
(1989) Main, Ian Cameron; Jongens, A W D
Various transducers have been developed turbulent shear in the ocean. The airfoil probe with it's piezoceramic beam encapsulated in a rubber airfoil has the simplest electronic processing system. However, the beam is very fragile and displays unpredictable thermal effects. An airfoil probe with semiconductor strain gauges on an aluminium cantilever beam has been developed as an alternative to the piezoceramic beam. The probe was calibrated by exciting it with a known shear generated by the water flow from an oscillating nozzle. During the calibration the thermal sensitivity of the probe was established to be -1.7 % °C-1• The probe, along with it's high gain, low noise processing system, is fitted to a tethered free-fall vehicle. A solid state data logger situated in the vehicle is used to record the data generated by the turbulence probe and a pressure transducer. Field trials at St.Helena Bay and Hout Bay showed that the sensitivity of the system is 20 dB lower than that of similar systems using piezoceramic beams. The system is able to resolve turbulent dissipation levels above 10-8 W kg-1, making it useful in regions characterised by a typical mixed layer (dissipation level of 10-W kg-1); however, it's sensitivity is not adequate for deep sea measurements where dissipation levels may be as low as 10-10 W kg-1.
Open Access
Development of an automatic system to monitor the performance of a dense medium (mineral) separation process
(1989) Alberts, P A; Downing, B J
Dense Medium Separation (DMS) is a process used extensively in the minerals processing industry to separate dense from less dense material in a dense fluid. It may be considered to be a simple “sink-float” separation process. DMS is used on a large scale in South African coal, iron ore and diamond operations. There are, however, no commercially available systems that can determine the separation efficiency of a DMS process on-line. This presents severe problems to those operating DMS processes. The present study attempts to provide a measurement technique for on-line application.
Open Access
The development of an ultrasonic Doppler bed-load velocimeter
(1989) Lazarus, Mark Doron; Braun, Robin
A instrument has been developed for measuring the velocity of solid particles adjacent to the pipe wall in a solids-liquid pipeline. It has been based on the Doppler shift principle and employs ultrasonic methods for detecting the bed-load particle velocity. Its application is in the mining industry for measuring the bed-load velocity of high concentration slurries such as in tailings and backfill hydraulic pipelines. Analyses have been conducted to investigate methods for increasing the accuracy of detecting the bed-load particle velocity. These methods have been implemented in the design of the transducer and the electronic circuitry. The system was tested using a simulation test-rig, hydraulic test-loops and at two industrial mining locations.
Open Access
Electronically tuned 23 GHz Gunn oscillators for a microwave datalink
(1988) Kratzenstein, L; Downing, B J
A market has been identified for 23 GHz, short-haul, low-capacity, digital radio. The dissertation presents the development of the varactor controlled Gunn oscillators that constitute the crystal locked microwave sources of the radio. An accurate description of a design procedure for Gunn oscillators at 23 GHz is presented. With reference to advanced modulation methods which require constant modulation indices, a method of linearising the voltage/frequency characteristic of the varactor controlled Gunn oscillator is described, which allows direct modulation of the source at 23 GHz. Due to the wide operating temperature of the radio a technique to temperature compensate the oscillator is presented. The dissertation ends with an investigation how the semiconductor device's spread affects the oscillator characteristics and an evaluation of the noise performance of the Gunn oscillator.