Ken Dutton

Optical sensor configurations for process tomography

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.

Concentration measurements of bubbles in a water column using an optical tomography system

Optical tomography provides a means for the determination of the spatial distribution of materials with different optical density in a volume by non-intrusive means. This paper presents results of concentration measurements of gas bubbles in a water column using an optical tomography system. A hydraulic flow rig is used to generate vertical air-water two-phase flows with controllable bubble flow rate. Two approaches are investigated. The first aims to obtain an average gas concentration at the measurement section, the second aims to obtain a gas distribution profile by using tomographic imaging. A hybrid back-projection algorithm is used to calculate concentration profiles from measured sensor values to provide a tomographic image of the measurement cross-section. The algorithm combines the characteristic of an optical sensor as a hard field sensor and the linear back projection algorithm.

Self-tuning control of a cold mill automatic gauge control system

This paper describes the modelling and simulation of part of the hydraulic automatic gauge (thickness) control system (AGC) for a single stand, cold reversing mill. Identification studies to validate the model against real plant using correlation techniques are described. An adaptive controller is designed and tested in simulation. A simple pole-placement algorithm is used in the interests of short execution times. The use of U-D factorization in the parameter estimator, and of the Kucera algorithm in the control synthesis, are mentioned. The former is found to be necessary, and the latter unnecessary, in this application. Finally, some limiting of control action is discussed for practical application.

Lensed optical fiber sensors for on-line measurement of flow.

This paper describes a system using lensed optical fiber sensors that are arranged in the form of two orthogonal projections. The sensors are placed around a process vessel for upstream and downstream measurements. The purpose of the system is for on-line monitoring of particles and droplets being conveyed by a fluid. The lenses were constructed using a custom heating fixture. The fixture enables the lenses to be constructed with similar radii resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. By collimating radiation from two halogen bulbs, radiation can be obtained by the sensors with radiation intensity related to the nature of the media. Each sensor interrogates a finite section of the measurement section. Each sensor provides a view. Parallel sensors provide a projection. Signal processing is carried out on the measured data in the time and frequency domains to investigate the latent information present in the flow signals.

A tomography system using optical-fibre sensors for measuring concentration and velocity of bubbles

Figure 1: An isometric view of the arrangement of optical fibres around the flow pipe. two rectilinear projections (Figure I). The orthogonal projections consist of an 8x8 array of optical-fibre sensors, whereas the rectilinear projections consist of an 11 x 11 array (the number of sensors are chosen to give a balanced sensitivity). Thus 38 opticalfibre sensors are used for each plane; and for cross-correlation purposes, the total number is doubled to 76 as there are two planes placed axially along the flow pipe. The optical fibres are positioned adjacent to each other to provide a large number of views. Ideally the two orthogonal and two rectilinear projections system should be in the same plane. If they were, however, they would overlap and so two of the projections have to be placed in a separate plane. These planes are separated by only a few millimetres, with the two orthogonal projections system placed on top of the rectilinear projections. Each optical-fibre receiver is 22 cm in length from the flow pipe to the electronic circuit. The receiver circuit has been designed for signal conditioning using

An Integrated Optical Fibre and Lens System for Tomography

(I) in which: <X = the angle between the incident light and the horizontal axis; 0i = the incident angle; P= angle of transmitted light; 00 = divergent angle or angle between the incident light and the horizontal axis; no = refractive index of the medium at the front end of the optical fibre; nj = refractive index of the optical-fibre core; n2 = refractive index of the fibre cladding; nm = refractive index of the medium at the back end of the optical fibre; h = radius of the fibre-optic core = 0.5 mm; RJ = radius of the lens at acceptance and emission angles of the light energy transmitted by the fibre. In order to avoid overlapping of the received signals and loss of beam intensity, the light-beam must diverge as little as possible. This can be achieved by using an optical lens. In addition, it is important to design the lenses such that all fibres have smooth surfaces and similar radii, resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. The optical-fibre lens model with lenses at both ends is depicted in Figure 2. Each lens has a different value of radius. The model takes into account that a large divergent beam is undesirable because it decreases the energy centred in the beam and can cause overlapping of adjacent transmitted beams at the receivers. The optimum radius to provide a lens for a particular application is determined from the model. From the model it can be shown that: Modelling opticalfibre lenses

Design of a fuzzy logic hydraulic turbine governor

In this article a fuzzy logic turbine governor is designed and simulated for the control of a hydraulic turbine, together with its penstock, based on a nonlinear turbine model. The designed fuzzy logic governor can be used in hydropower plants, and may replace the commonly used classical PID turbine governors that are causing instability problems.

Optical tomography for concentration and velocity profiles in two component flows

Optical tomography involves the use of non-invasive optical sensors to obtain information in order to produce images of the dynamic internal characteristics of process systems. This paper presents an investigation using optical tomography suitable for determining concentration and velocity profiles in two component flows in a fluid conveying pipe. The system is capable of detecting and measuring the amount of undissolved gas in waster, or gas in oil, where the mixture is flowing in a pipe. The system employs four projections consisting of a combination of two orthogonal and two rectilinear projections. The light transmitters consists of four halogen bulbs. Each orthogonal receiver projection employs 8 sensors and each rectilinear receiver projection uses 11 sensors making a total of 38 receiver sensors. The voltage profile from the sensors gives spatial information of the flow regime. Signal processing provides time-averaged signals which will generate peripheral concentration profiles. To observe the velocity profile via cross- correlation, a second identical measurement system has been constructed. One array of sensors is positioned upstream and the other downstream in the process measurement. Cross-correlograms provide mean velocities of velocity profiles over the measurement section.

Optical fiber sensors for flow measurement

The overall aim of this project is to investigate the use of optical fiber sensors for on-line monitoring of particles and droplets having low concentration being conveyed by a fluid. In this project, the system employs lensed optical fiber sensors developed using a low cost approach. A general mathematical model for the lens constructed at each end of the fiber optic was derived which takes into consideration that a large divergent beam is undesirable because it reduces the energy centered in the beam and can cause overlapping of adjacent transmitted beams at the receivers. Initially, the optical fibers are polished. Then, the lenses are formed using a specially-made heating platform. The receiver fiber is coupled to a photodiode, enabling the received light level to be measured. Optical fiber sensors are suitable for monitoring flowing materials where the conveyed component ratio is less than 10% vol./vol. The use of optical fibers provides an opportunity to design sensors with a very wide bandwidth, thus enabling the measurement of high speed flowing particles or droplets. The light extinction method used in this project is suitable for measurement of particles or droplets equal and greater than 100 micrometers .