No description available.

No description available.

This thesis is focused on the improvement of the meter performance and power consumption of non-mechanical flowmeters such as the conventional electromagnetic flowmeter and the fluidic oscillator. Each flowmeter is studied using Finite Element Modelling for the magnetic field, the virtual current and the fluid dynamics in order to simulate flow signal. The meter design of the conventional electromagnetic flowmeter is modified to provide a better signal level by optimising the geometry of the flow channel and the magnetic field. The signal level increase can be used to reduce power consumption. This improvement provides a 1.96 times greater signal or 51% less power consumption for the conventional electromagnetic flowmeter. An alternative coil-less electromagnetic flowmeter is proposed to reduce the energy consumption. A laminated magnetostrictive material/PZT piezoelectric material is used to control the magnetic field from a permanent magnet. Modelling is carried out to optimise the meter and the magnetic field control device. The device can provide a further reduction of 54.7% of energy usage over the improved conventional electromagnetic flowmeter. The modelling of the fluidic oscillator is undertaken not only with the fluidic dynamics but also the flow signal by using the electromagnetic sensing technique. Using these approaches, recommendations for a better signal level are proposed.

This thesis presents the results of an investigation into the design parameters of an externally mounted ultrasonic cross correlation flowmeter. A set of operational requirements are presented for the acoustical system and from these requirements a theoretical design is formulated for the ultrasonic transducer. The selection of an operating frequency is shown to depend on the operational requirements and both the transducer design and operating frequency are shown to be interdependent. Construction of the transducer is shown to affect the mode of operation and the governing relationship is presented. Transducers built to the theoretical design are tested in practice and shown to meet the operational requirements. A study of transducer mountings to pipe sections is also presented and in the light of experimental evidence an improved method of transducer mounting is outlined. Efficient methods of coupling the electrical energy into the transducer and the acoustical energy into the pipe section are investigated. Also, two methods of assessing a given transducer's characteristics are explained and their shortcomings highlighted. Further, it is shown that the selection of a high operating frequency overcomes the problems of acoustical cross-talk between the two transmitted ultrasonic beams. The determination of a suitable method of demodulating the received signal is investigated, both theoretically and practically. The theoretical results show that in a closed conduit, amplitude modulation of an ultrasonic beam will predominate. Practical observations confirm this and the expected modulation levels are achieved. The practical results also show that an amplitude demodulated signal is less susceptible to interference by extraneous noise such as that produced by plant vibrations. These results are confirmed for all the flowmeter configurations tested. A closed loop control scheme using a phase locked loop system is developed, whereby the flowmeter will be able to compensate for environmental changes. Three combinations of this system are presented and their poor performance and inability to control the flowmeter, investigated and explained. The analysis used to explain the above is extended to develop a further control scheme using a phase shift network in one channel of the flowmeter. This system is shown to be more stable and controllable than previous systems and is less susceptible to extraneous noise. A closed loop control scheme incorporating a system of this type is presented. Suggestions are made to further investigate the selection of operating frequency, transducer mounting and to determine the most suitable strategy for implementing a phase shift type closed loop control scheme.

Ce mémoire traite de la mise au point et des applications d’un fluxmètre gazeux à pression constante, instrument de référence primaire pour la mesure de très faibles débits gazeux, couramment utilisé par les Laboratoires nationaux de métrologie. Il intervient dans la traçabilité des basses pressions absolues, via la méthode d’expansion continue, et celle des fuites d’hélium, liées aux applications dans le domaine du vide. De plus, nous avons montré que le fluxmètre à pression constante du Laboratoire commun de métrologie (LCM) permettait le raccordement des mesures de micro-débits, sous-domaine de la débitmétrie. Outre les points clés de la conception et la caractérisation métrologique, ce mémoire décrit l’étude de l’expansion continue ainsi que les travaux de comparaison du fluxmètre gazeux à pression constante avec les méthodes de référence employées au LCM, en particulier la méthode de gravimétrie dynamique. / This dissertation concerns the development and applications of a constant pressure gas flowmeter, the primary reference instrument used by National metrology laboratories to measure very low gas flows. It guarantees the traceability of low absolute pressures, via the continuous expansion method, and that of helium leaks, both related to applications in the field of vacuum. In addition, we have shown that the Laboratoire commun de métrologie (LCM) constant pressure flowmeter is well suited to micro-flow measurements, a sub-field of flow metering. Besides key points of the design and metrological characterization, this document describes the study of the continuous expansion method and work on comparisons of the constant pressure gas flowmeter with reference methods used at LCM, in particular the dynamic gravimetric method.