A charge coupled device based optical tomographic instrumentation system for particle sizing

• Main Author: Idroas, Mariani
• Other Authors: Green, Bob ; Dutton, Ken
• Published: Sheffield Hallam University 2004
• Subjects: 616.0757028
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404456

This research investigates the use of charge coupled device (abbreviated as CCD) linear image sensors in an optical tomographic instrumentation system used for sizing particles. Four CCD linear image sensors are configured around an octagonal shaped flow pipe for a four projections system. The measurement system is explained and uses four CCD linear image sensors consisting of 2048 pixels with a pixel size of 14 micron by 14 micron. Hence, a high-resolution system is produced. Three main mathematical models based on the effects due to particles, light sources and diffraction are discussed. The models simulate the actual process in order to understand the limitations of the designed system. Detailed design of the optical tomography system is described, starting from the fabrication of the 'raybox 'of the lighting system, the design of the driving circuit in the detection system, the timing and synchronisation in the triggering system based on the PIC microcontroller and the data acquisition system. Image reconstruction for a four-projection optical tomography system is also discussed, where a simple optical model is used to relate attenuation due to variations in optical density, [R], within the measurement section. Expressed in matrix form this represents the forward problem in tomography [S][R]=[M] In practice, measurements [M] are used to estimate the optical density distribution by solving the inverse problem [R]=[S]-1[M]. Direct inversion of the sensitivity matrix, [S], is not possible and two approximations are considered and compared - the transpose and the pseudo inverse sensitivity matrices. The designed instrumentation system is calibrated using known test pieces and tested for accuracy, repeatability and consistency among measurements from different projections. The accuracy of the particle size measurement using the system is within 1 pixel i.e. + 14 micron (the maximum absolute error of 8.5 micron), with the maximum percentage error of 1.46%. Moreover, the system has a good repeatability and consistency - within 1.25 pixel. The range of particle size that has been tested using the system is between 0.18 mm up to 11 mm diameter. A spherical shaped and an irregular shaped particle are tested on the designed system to complete analysis of the overall performance of the system. This thesis is concluded with achievements of objectives of the research, followed with suggestions for future work.