R. Abdul Rahim

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.

Further development of a tomographic imaging system using optical fibres for pneumatic conveyors

This paper describes the further development of optical sensor hardware for a process tomography system in which emitters and detectors are used to exploit the optical characteristics of multiphase flow regimes. The optical arrangement is described and the importance of fibre beam position discussed. The proportion of the measurement volume interrogated by the beams is derived. The response of a single fibre is shown followed by a reconstructed concentration profile.

Concentration profiles in a gravity chute conveyor by optical tomography measurement

This paper describes an investigation into the use of optical fibre sensors in a tomographic measurement system designed to measure the flow of dry solids in gravity drop and pneumatic conveyors. A simple model of the system is provided and used to predict the response of individual sensors and the full system. Results are provided which show the model is acceptable for use in a gravity conveyor. The system is used to provide tomographic images of solid concentration within a gravity chute.

Application of transmission-mode ultrasonic tomography to identify multiphase flow regime

This paper presents an application of ultrasonic tomography where the main objective is to identify the multiphase flow regime which is liquid, gas and solid at once. The system was designing non-invasively by using offline method. The transmission mode with fan shaped beam back projection had been implemented for sensing purposes where 8×8 projections were produced. Beside, the linear back projection (LBP) algorithm was implemented in the software system for the image reconstruction part. Experiments show that the multiphase flow regime for liquid, gas and solid at once can be identifying by using ultrasonic tomography. The results of experiments and possible future improvement were also discussed.

Improving gas component detection of an ultrasonic tomography system for monitoring liquid/gas flow

The development of an ultrasonic transmission tomography system is described. The system is intended for the imaging of two component flows (such as gas/water) inside pipes of industrial processes. Transmission-mode approach has been used for sensing the gas/liquid two-phase flow, which is a kind of strongly inhomogeneous medium. A prototype fixture of vertical column and a mobile prototype design of sensors jig for ultrasonic tomography imaging are used. The fixture of the vertical column is designed to hold the sensors jig that will have the 16-pairs of ultrasonic sensors attached to it. The investigations were based on the transmission and the reception of ultrasonic sensors that were mounted circularly on the surface of experimental vessel. This paper also explains the hardware and circuitry design for the Ultrasonic Tomography System. Detailed explanations are presented on relationship of the smallest resolution the system are able to detect with the characteristics of the installed ultrasonic sensor.

Non-invasive ultrasonic tomography: Liquid/gas flow visualization

This paper presents the non-invasive ultrasonic tomography system for imaging liquid and gas flow. Transmission-mode approach has been used for sensing the liquid/gas two-phase flow, which is a kind of strongly inhomogeneous medium. The algorithms used to reconstruct the concentration profile for two-phase flow using fan-shaped beam scanning geometry were presented. Experiments showed that the performance of the system is acceptable. Results of the experiments using LBPA, HRA and HBRA were discussed.

Optical-fibre sensor for process tomography

Abstract This paper describes an investigation into the use of optical-fibre sensors in a tomographic measurement system, designed to measure the flow of dry solids in gravity-drop and pneumatic conveyors. A simple model of the system is provided and used to predict the response of both individual sensors and the full system. Results are provided which show that the model is acceptable. The system is used to provide tomographic images of solid concentration within a gravity conveyor.

Evaluation of square type electromagnetic field screen implementation on interference effects in magnetic induction tomography modality

This paper discusses and evaluates the implementation of square type electromagnetic screen on the excitation coil of Magnetic induction tomography (MIT) through real experiment. By using electromagnetic screen, interference phenomena due to scattered primary field can be reduced, hence reducing the sources of errors in the measurement data. In this experiment, two types of screen with different thickness of 2 mm and 25 mm had been evaluated. The measurements have shown that relative to without screen, 2 mm thickness screen reduces the field at about 84.31% at the back area while increased the field strength up to 19.45% in the front region. Excitation screen with 25 mm thickness provides better reduction of 98.43% at the back, however there is also reduction at about 9.82% of the field strength at the front region. The result from this experiment provides valuable information on the specification needed when applying electromagnetic screen to the individual excitation coil in the MIT system.

Simulation on using cross-correlation technique for two-phase liquid/gas flow measurement for Ultrasonic Transmission Tomography

Combining Ultrasonic Transmission Tomography (UTT) with the cross-correlation flow measurement technique can provide more information on the flow than usual. A simulated dual-plane UTT system for use on laboratory and plant-scale process equipment has been developed on the basis of this idea. This paper focuses on the correlator used to cross-correlate the tomogram images between the downstream and upstream plane of the simulated dual-plane ultrasonic transmission tomography system. This paper proposed the use of 2D correlation coefficient for the correlator and the result of its use is discussed. The principle of measurement of the local gas velocity distribution in a bubbly gas/liquid pipe flow which is based on cross-correlation of two plane images is also described. Initial experimental results illustrate the feasibility of the method presented here.

Data acquisition process in optical tomography : Signal sample and hold circuit

This paper describes the application and construction of signal sample and hold (S/H) circuit to facilitate data acquisition process using the Keithley Metrabyte DAS 1802HC. A basic tomographic system consists of sensors, signal conditioning circuit, data acquisition system and the creation of suitable computer software to display the reconstructed image obtained from pipeline. The analogue signals, which are also the data needed for image reconstruction have to be managed properly, in terms of minimizing the data transfer time from the signal conditioning circuit to the data acquisition card. Besides having a “DC memory” characteristic which can easily be converted into digital format, the sample and hold circuit also has the ability of sampling a segment of waveform and holding it until the proper timing for conversion of the required control signal. In order to generate the relevant signals to control both the signal sample and hold circuit and the data acquisition card, the PIC microcontroller is being used. With the combination of signal sample and hold circuit and microcontroller, transition of analogue signals to the data acquisition system can be performed efficiently.