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ELECTRICAL CAPACITANCE AND RESISTANCE TOMOGRAPHY WITH VOLTAGE EXCITATION

Rodriguez Frias, Marco Antonio

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

Multi-phase flow measurement is a challenging task due to the involvement of differ-ent flow regimes, materials and a varying water-in-liquid ratio (WLR). One approachresearchers have taken to tackle this difficult task, is the development of dual-modalityimaging systems, fusing Electrical Capacitance Tomography (ECT) and Electrical Re-sistance Tomography (ERT) in a single measuring device. This is due to the abilityof each technique to take advantage of different phenomena, i.e. imaging conductivemedia is a demanding task for ECT, but ERT yields good quality results. On the otherhand, with an ERT system is not possible to get any information regarding the regionof interest if there is no conductive media to allow the current to flow, but in this caseECT can perform the imaging exploiting the materials’ dielectric properties. Becauseof those characteristics dual-modality tomography has been foreseen as a practical anda low cost solution to image a wide range of complex media.Through years, ERT has proven to be an effective and a low cost imaging technique,but in order to integrate it to a dual-modality imaging system in parallel with ECT,it is necessary to improve it and at the same time to make it more compatible to thecapacitive imaging technique, allowing in this way to exploit the best capabilities ofboth modalities. This requires a complete sensor and circuitry redesign.An ERT system has been developed featuring a voltage excitation and current mea-surement sensing scheme making use of an ECT sensor built with electrodes insidethe vessel and an available data acquisition system. This set up images successfullynon-conductive material over liquid solutions with low and high conductivities as abackground.A comparison between current excitation and voltage measurement ERT and voltageexcitation and current measurement ERT is performed showing that the latter not onlymakes ERT more suitable to integrate with a ECT system, but also improves its perfor-mance. The design of a sensor with internal electrodes and driven external guards canreduce notably the fringe effect and improve the images obtained by means of an ERTsystem.