Optical sensor configurations for process tomography

Abstract

This paper describes an investigation into the optimum design of optical fibre sensing arrays to be incorporated in an optical tomographic measurement system for on-line monitoring of particles and droplets. Two approaches are considered to cover opaque and transparent materials; optical path length and optical attenuation. Four flow models are investigated: single-pixel flow representing a single particle or droplet, two-pixel flow as a simple check on aliasing in the reconstructed image, half flow representing half the sensing cross section filled with material and full flow, where the whole sensing cross section is full of material. Six projection geometries of the fibre sensors are considered. For tomographic imaging, the forward problem, which assumes particles are placed in specific places in the measurement cross section and calculates voltage outputs for the individual sensors, is modelled. The solutions from the forward problem are used to solve the inverse problem, which uses actual sensor voltage readings to estimate the spatial distribution of the material in the measurement cross section. The solution of the inverse problem is used to derive the linear back projection (LBP) and filtered LBP algorithms. In order to improve image quality, a hybrid reconstruction algorithm is implemented. This algorithm first checks if any sensors read zero and sets (locks for this estimation) all pixels associated with them to zero (no material). The algorithm then proceeds as for the LBP.

Chemical species tomography

“…Experimental (Terzija et al, 2008;Wright et al, 2010) and numerical (Daun, 2010;Verhoeven, 1993;Ibrahim et al, 1999) CST experiments have shown that reconstruction accuracy depends strongly on the arrangement of light sources and detectors. The cost and complexity of the laser and detection optics demand that these components be used to their maximum potential.…”

Research Progress of the Optical Fiber Sensors in Process Tomography

“…In the practical system, the various optical path projectors are required to reduce the Optical Fiber Sensors in Process Tomography aliasing. Various arrangements of the fiber sensors are considered for five types of projections [13,14] : two orthogonal projections (Figure 2a In order to ensure simple and intuitive design for Figure 2e, only a fan beam optical source was drawn. However, two other fan beam sources are needed maintain a certain emission angle with the current source on the 120 and 240 positions so that they form three fan-shaped projections together.…”

“…In 1999, Ibrahim et al [13] used LBP and FLBP algorithms to achieve image reconstruction. Although, to keep balance among the pixels of projections can reduce errors, it still cannot meet the accuracy.…”

Optical tomography sensor configuration using two orthogonal and two rectilinear projection arrays

“…The beam of light must diverge as little as possible to avoid overlapping of the received signals and loss of the beam intensity [3]. Three methods are used to collimate the light source.…”