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This report is an analysis of the Model RT-2 Microhmmeter which is a portable apparatus using a pulse current power source in the measurement of load resistances in the microhm range. The need for accurately measuring resistances in the microhm range is quite real for testing electrical power circuit breaker contact resistance. Both during acceptance checking within the manufacturing process and in the field for preventative maintenance, contact resistance must be accurately determined. Before the invention of the Model RT-2 Micrometer, no device existed which could accurately measure resistances in the microhm range that was readily transported by an unaided individual. The design of the Model RT-2 Microhmmeter is based on a specification set derived from user requirements, and ANSI C37.09. In addition, a weight limit of 25 pounds for the portable apparatus was imposed by the designer which included the weight of the self-contained power source. This paper suggests changes that will result in both weight and power consumption savings. A major change in the high current power supply circuit is suggested that will allow the microhmmeter to be a more versatile piece of test equipment. The Model RT-2 Microhmmeter is operational and has been successfully proven in the field. By using the portable microhmmeter, the reduction in the amount of time required to determine contact resistance can result in appreciable cost savings to the user.

The study of mixing processes in supersonic flow has a great interest for a number of applications including scramjet developments. However, the usual tools employed are very limited. Sampling probes generally have a poor frequency response, and that makes measurements of fluctuating concentration problematic. The goal of this study is to design, build and test a probe capable of measuring concentration fluctuations of at least 1 kHz. This study shows the design of such a probe and how a high frequency response was achieved. A prototype was built and tested. The tests consist of a calibration phase and experiments inside a hypersonic wind tunnel. These last tests served two purposes. The first one was to verify that the measurements made with the probe gave the correct value of the concentration. The second purpose was to assess the frequency response of the probe by putting it through a concentration step change. Tests were conducted with various known mixtures of Helium and air from 0% to 100% flowing at Mach 2.0 with T_t=300 °K and P_t=4.4 atm. The probe proved capable of measuring concentration fluctuations up to approximately 2.5 kHz while also giving the adequate accuracy for values of mean concentration. / Master of Science

Thesis (M.Eng.)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This study entailed the investigation and evaluation of a new methodology for measuring high discharges passing through bridges. Pressure differences generated around bridge piers have been measured and related to the discharges. These pressure differences are mainly functions of downstream flow conditions. The pressure differences have been converted into velocities by applying Newton's second law expressed in terms of the laws of conservation of energy; momentum; and of power. The energy principle was re-evaluated following a preVIOUSstudy (Retief, 1999) on a limited number of model pier combinations and flow conditions. Comparison of the energy approach with newly developed theories in terms of the momentum and power laws respectively led to the conclusion that the energy principle gave the best results. The question of applicability of the theory to practical pier/stream width and length ratios as well as its validity under flow conditions commonly found under flood conditions required that additional laboratory tests be done. The energy-based discharge equation was calibrated in terms of newly selected measuring points, different pier width and length ratios, as well as pier rotations for both super and sub-critical downstream conditions. According to the new tests performed at the Hydraulics Laboratory of the University of Stellenbosch on model piers, clear relationships were found between discharges and pressure differences measured against the pier. Calibration curves for practical flow measurement application were derived in terms of principle dimensionless parameters. Application of the energy approach at the prototype level needs further investigation. / AFRIKAANSE OPSOMMING: Hierdie studie het behels die ondersoek en evaluering van 'n nuwe metode om hoë vloeie verby brïïe te meet. Drukverskille wat rondom brug pylers opgewekword is gemeet en omgeskakel na vloeie. Hierdie drukverskille is hoofsaaklik funksies van die stroomaf vloei toestande. Die drukverskille is omgeskakel na vloeisnelhede deur die toepassing van Newton se tweede wet, uitgedruk in terme van die behoud van energie, momentum so wel as drywing. Die energie beginsel is weer geëvalueer sedert 'n vorige studie (Retief, 1999) gedoen is op 'n beperkte aantal model pylerkombinasies en vloeitoestande. Hierdie energie-benadering is met nuwe metodes vergelyk, naamlik die momentum en drywings wette. Die gevolgtrekking is gemaak dat die energie metode die beste resultate gee. Die vraag oor die toepaslikheid van die teorie met praktiese pyler/stroom wydte en lengte verhoudings so wel as die toepaslikheid hiervan onder die vloei toestande wat algemeen onder vloedtoestande voorkom het addisionele laboratoriumtoetse vereis. Die energie gebaseerde vloeivergelyking is gekalibreer in terme van nuut geselekteerde meetpunte, verskillende pyler wydte en lengte verhoudings, asook pyler rotasies vir beide super en sub-kritiese stroomaf toestande. Na aanleiding van die toetse gedoen in die Hidroulika Laboratorium van die Universiteit van Stellenbosch op brugpylers, is duidelike verbande gekry tussen die vloeie en die drukverskille soos gemeet teen die pyler. Kalibrasie-kurwes vir die toepassing van praktiese vloeimeting is ontwikkel in terme van die toepassing van dimensielose parameters. Die toepassing van die energiebenadering op prototipe vlak verg verdere ondersoek.