Browsing by Author "Besseling, Johann L N"

Now showing 1 - 7 of 7
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    Assessing vibrating viscometers in slurries
    (1977) Rachman, Yichal Aryeh; Besseling, Johann L N
    A number of vibrating transducers for viscosity measurement described in the literature have been evaluated, with a view to developing an instrument for measuring gold-mine slurries. Appropriate electronic measuring methods are discussed, and related theory using a simple mathematical model is derived, and verified experimentally. A low frequency vibrating transducer is described which is capable of measuring apparent viscosities of slurries. Measurements made on Newtonian liquids at four different frequencies using the same transducer agree to ± 2%, and correlate closely with measurements made using a Redwood orifice viscometer. In order to determine the accuracy of the transducer for slurries, comparative measurements at four frequencies are used to obviate the need for a reference instrument. For a dilute (Newtonian) slurry, these measurements agree to ± 10%, but similar measurements on more concentrated (non-Newtonian) slurries show marked divergence of the curves at high frequencies. It is suspected that this behaviour is a property of the slurries, related in some way to their observed non-Newtonian behaviour. These results are of a qualitative nature, but point to the possible usefulness of the instrument for slurry measurement.
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    Continuous gauging of electric traction contact wire
    (1975) Timm, Anthony Rex; Besseling, Johann L N; Van Nierop, J H
    In this system the electric traction overhead contact wire wear is continuously measured. A GaAs LED and lens combination produces a collimated beam of light along the pantograph pan. The beam, through which the contact wire slides, is monitored by a vertical array of phototransistors spaced at equal intervals. The number of phototransistors in shadow at any instant is proportional to the contact wire thickness. A fibre-optic data link conveys the encoded information from the pan at high tension to the locomotive at ground potential.
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    Control and monitoring of an intra-aortic balloon pump for cardiac assist
    (1971) Holmes à Court, Robert Leonard; Besseling, Johann L N
    An anatomical and physiological background to the heart as a pump, followed by a description of the causes and results of cardiogenic shock is given. A survey of the achievements of other researchers in this field is included. The design of a system for controlling and monitoring the Intra-Aortic Balloon Pump is described. A narrow band-pass filter is used to reduce noise and limit the input to the detector to the spectrum within which the R-wave of an ECG signal lies. A safety circuit to prevent the heart pumping against an inflated balloon is incorporated. History of the 8 secs preceding any instant is available. A description of the medical tests carried out so far is given.
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    A direct A.C. to A.C. regenerative frequency and voltage converter
    (1980) Case, Michael James; Enslin, NC de V; Besseling, Johann L N
    The reliable variable speed operation of an a. c. machine over a wide speed range is a problem that has received attention for some time. In this thesis a system to permit such operation from a fixed frequency fixed voltage supply is proposed, under the name of the asynchronous modulation converter. This converter is of the cycloconverter family, but is force-commutated and is not synchronised with the supply frequency. The power switching element comprises a power transistor in a diode bridge, coupled to the control circuitry by opto-isolators. The output of the a-mod converter is produced by a "chopper" modulation process and this results in the harmonics present being at frequencies well removed from the fundamental. A feedback system to ensure smooth commutation of the output current from the power switches is described. This feedback system operates by sensing the rate of rise of the inductive voltage surge on the load when a switch is opened to operate a freewheel path switch.
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    The measurement of liquid height in flotation cells using microwave techniques
    (1980) Archer, Michael Raymond; Besseling, Johann L N
    The flotation process is used in extractive metallurgy to concentrate the mineral contents of ores by 'floating' the mineral particles out of an ore pulp with air bubbles. The pulp consists of finely ground ore, water and reagents, whose purpose is to make the mineral particles attach themselves to the air bubbles passing through the liquid. These bubbles reach the surface of the pulp and form a layer of froth, containing the ore concentrate, which is skimmed off for further processing. In order to optimise the process, it is necessary to have a reliable method o of monitoring liquid level in the flotation cell. The presence of the flotation froth complicates this measurement as it obscures the surface from visual observation and clogs conventional mechanical level measurement systems. The presence of air bubbles in the pulp and foam, makes acoustic systems equally unsuitable due to attenuation effects. The absence of a microwave system for level measurement in flotation cells led to the proposal of this thesis. It is therefore concerned with investigating the feasibility of using a microwave level measurement system for automatic liquid level control in flotation cells.
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    An optical communications link
    (1975) Moore, Michael Hamilton; Besseling, Johann L N
    The thesis describes the development of a specification for, and prototypes of, an opto-electric voice communications link. The introductory sections deal with the generalised optical communications channel, the available hardware, and some of the research that has been done in the field. The information presented is used to motivate the type of system to be developed. The emphasis is placed on cost, though not as an overriding consideration. Modulation systems are examined, and frequency modulation of an m.f. subcarrier is chosen. The development of the practical system is covered in detail, in particular the receiver frontend circuitry. Considerable discrepancies between the design figures and actual measured performance are analysed, and their causes located. A practical mechanical design is presented, with suggested modifications for production. In conclusion, future developments in the field are examined.
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    A quasi-real-time inertialess microwave holographic imaging system
    (1981) Nilsen, Christopher S; Besseling, Johann L N
    This thesis records the theoretical analysis and hardware development of a laboratory microwave imaging system which uses holographic principles. The application of an aperture synthesis technique and the electronic commutation of all antennae has resulted in a compact and economic assembly - which requires no moving parts and which, consequently, has a high field mapping speed potential. The relationship of this microwave holographic system to other established techniques is examined theoretically and the performance of the imaging system is demonstrated using conventional optically- and numerically-based reconstruction of the measured holograms. The high mapping speed potential of this system has allowed the exploitation of an imaging mode not usually associated with microwave holography. In particular, a certain antenna array specification leads to a versatile imaging system which corresponds closely in the laboratory scale to the widely used synthetic aperture radar principle. It is envisaged that the microwave holographic implementation of this latter principle be used as laboratory instrumentation in the elucidation of the interaction of hydrodynamic and electromagnetic waves. Some simple demonstrations of this application have been presented, and the concluding chapter also describes a suitable hardware specification. This thesis has also emphasised the hardware details of the imaging system since the development of the microwave and other electronic components represented a substantial part of this research and because the potential applications of the imaging principle have been found to be intimately linked to the tolerances of the various microwave components. Bibliography: pages 122-132.