Al-Khoory, Hassan Fadi; (1992) The Design and Development of a Vibrating Reed Transducer for Process Monitoring and Particle Characterisation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes the design and development of a novel vibrating reed technique for the measurements of various process parameters such as fluid density and viscosity under adverse conditions. Briefly, the system consists of a stiff elastic reed which is securely clamped at an intermediate point along its length. One free span, the remote end, is exposed to the test environment while the other is sinusoidally vibrated at the primary resonant frequency of the reed using an electromagnet. Changes in the vibrational characteristics of the system reveal information about the properties of the test medium. Early in the study, the design conditions required for the successful transfer of the vibration from the drive to the remote span together with the monitoring of the vibrational characteristics of the system at the same drive end are described. Two mathematical models, one based on finite element analysis and the other using the receptance approach have also been developed. These successfully predict, as verified by experimental evidence, some of the optimal design criteria required for maximum sensitivity and stability in response. The main thrust of the thesis deals with the application of the same type of device for particle characterisation in terms of thermogravimetry, sizing and classification. A typical resolution in terms of mass measurement is ± 3 x 10-3g when the system is employed as a thermogravimetric analyser in the range 20 - 500 °C. Particle sizes are measured using a modified version of the remote drive which handles dry powders in a 'vibro-fluidised' state. Average particle sizes for different types and shapes of powders in the range 20 - 950 μm are reported with ca. ±10 μm resolution. Also, the response of the system in the particle sizing mode is successfully predicted using a viscoelastic model.

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