A tomographic imaging system for pneumatic conveyors using optical fibres.

This thesis presents an investigation into the application of optical fibre sensors to a tomographic imaging system.Several sensing mechanisms for measurement using non-intrusive techniques are discussed and there relevance to pneumatic conveying discussed. Optical systems are shown to be worthy of investigation. The optical sensor is modelled to predict the expected sensor output voltage profiles arising from different, artificially produced flow regimes. These artificial flow regimes are created by placing a shaped obstruction inside a gravity drop conveyor in the path of the flowing solids. It is shown that for two arrays, each consisting of sixteen transducers, approximately 30% of the measurement volume is sampled.An image reconstruction method for optical tomography is described, based on the back projection between view lines algorithm.The design of the optical tomography system is described, with emphasis on preparation of the ends of the optical fibre, beam collimation and design of the transmitter and receiver circuits.The optical sensors are evaluated singly and as a tomographic array. Results relating to concentration measurement are presented for solids flow using sand with a mean of 300 micron and plastic beads of 2 mm nominal diameter. Measurements were made with a single optical sensor using the gravity flow rig. The results demonstrate the suitability of the optical sensor for concentration measurement for lightly loaded flows (up to approximately 2% solids by volume in the test). The test is extended to all thirty-two sensors using a range of solids mass flow rates from 40 to 320 gm/s with both dry sand and plastic beads over a range of artificially created flow regimes. The results obtained by comparing the measured and predicted flowrates show good general agreement. The statistical parameters for the error of the sand flow measurement have been calculated as having a mean of 6.76% and standard deviation of 3.94% and for plastic beads is 5.43% and standard deviation of 0.21%. The results also demonstrates that the system is reasonably independent of flow regime and so the optical fibre system is suitable as a concentration meter.Back projection is used to generate tomographic images as an alternative representation of the data on concentration measurement. This provides a visual representation of optical density (concentration) information which is not obvious from the concentration measurements.Results from experiments on particles with different sizes are presented. The results are analysed using frequency spectrum techniques and shown to be dependent upon the particle size for approximately spherical particles with diameters between 600 |im and 5 mm.Suggestions for further work on optical fibre sensors and optical fibre tomographic measurements are made.