Flow Measurement and Instrumentation 31 (2013) 61–68

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Flow Measurement and Instrumentation

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Visualization of recovered palm oil using portable ECT imager inextraction palm oil process

E.J. Mohamad a,n, R.A. Rahim b,1, P.L. Leow b,1, M.H.F. Rahiman c,2, O.M.F. Marwah d,3,N.M.N. Ayob b,1

a Department of Mechatronics and Robotics Engineering, Faculty of Electrical Electronics Engineering, Universiti Tun Hussein Onn Malaysia, Pt. Raja,

Bt. Pahat, 86400 Johor, Malaysiab Process Tomography & Instrumentation Research Group, Cybernetics Research Alliance, Faculty of Electrical Engineering, Universiti Teknologi Malaysia,

UTM Skudai, 81310 Johor, Malaysiac School of Mechatronic Engineering, Universtiti Malaysia Perlis, 02600 Arau, Perlis, Malaysiad Department of Manufacturing and Industrial Engineering, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussien Onn Malaysia,

Pt. Raja, Bt. Pahat, Johor, Malaysia

a r t i c l e i n f o

Available online 29 November 2012

Keywords:

Portable ECT imager

Non-invasive

Visualization

Crude palm oil

86/$ - see front matter & 2012 Elsevier Ltd. A

x.doi.org/10.1016/j.flowmeasinst.2012.10.004

esponding author. Tel.: þ60 745 37000; fax:

ail addresses: elmy@uthm.edu.my (E.J. Mohama

fke.utm.my (R.A. Rahim), leowpl@fke.utm.my

nimap.edu.my (M.H.F. Rahiman), mdfaizan@ut

akkir@mail.com (N.M.N. Ayob).

l.: þ60 755 35220; fax: þ60 755 66272.

l.: þ60 497 98289; fax: þ60 497 9801.

l.: þ60 7453 7000; fax: þ60 7453 6080.

a b s t r a c t

A portable Electrical Capacitance Tomography (ECT) imager for a palm oil process monitoring system is

developed and presented in this work. Intended as a support instrument, the system will enable local

and foreign palm oil mills to control efficiently the flow process monitoring of crude palm oil in

conveying pipelines during extraction. This monitoring system enables the visualization of the liquid

percentage inside the vessel, and the data obtained can then be used to design better mill process

equipment or control certain processes. Thus, the quality of crude palm oil can be maximized and the

process of palm oil mill effluent treatment improved. In previous studies, ECT was developed rapidly

and used successfully for multiphase flow measurements in many applications in the oil and gas

industry, gas/solids cyclones, milk flows, and fluidized beds. The present work experimentally

investigates the capability of portable ECT sensors with 16 electrodes to identify the concentration,

velocity profile, and phase concentration of crude palm oil in related multiphase systems (liquid

and gas).

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Tomography is a technique used to obtain cross-section imagesof an industrial process (for example, the multiphase flow in anoil pipeline) so that the internal behavior can be investigated [5].Process flow tomography refers to non-invasive methods of obtain-ing internal characteristics from a set of measurements on oroutside the domain of interest. Tomography provides several real-time methods for obtaining cross-section images of a process to gaininformation on the material distribution. Generally, this involvestaking numerous measurements via sensors placed around thesection of the process being investigated and processing the datato reconstruct an image [1–4].

ll rights reserved.

þ60 745 36060.

d),

(P.L. Leow),

hm.edu.my (O.M.F. Marwah),

The different sensing methods commonly used in tomographyinclude electrical, ultrasound, X-ray, nuclear magnetic resonance,and microwaves. Tomography techniques based on measuringelectrical properties have received significant attention in recentyears [6]. A novel tomographic sensing system for highly elec-trically conductive multiphase flow measurements was devel-oped using Electrical Resistance Tomography with a voltagesource and current sensing to overcome the current source limits.The amplitude of the current output reached more than 300 mA[27].

Using tomographic techniques, measurements such as that ofthe flow rate or the solid concentration of material flowingthrough a pipeline can be obtained. Sensors are used to acquireinformation and produce two- or three-dimensional images of thedynamic internal characteristics of the process system. Informa-tion on the flow regime, vector velocity, and concentrationdistribution may be determined from the images. The data canhelp advance process equipment design, the verification of exist-ing computational modeling and simulation techniques, or pro-cess control and monitoring [8].

Electrical Capacitance Tomography (ECT) has been widelystudied since the early 1990s. This technique is one of the most

Fig. 1. Overview of the system development.

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–6862

attractive and promising methods for the measurement of two-phase flow because of its non-invasion, reliability, simplicity, andhigh-speed capabilities [9]. ECT has been used to achieve the real-time visualization of industrial processes and void fraction mea-surements of two-phase flows. ECT can be used for the imaging ofmulti-component industrial processes involving non-conductingfluids and solids in pipelines [10].

In a previous study, ECT was created rapidly and utilizedsuccessfully in multiphase flow measurements for numerousapplications in the oil and gas industry, gas/solids cyclones, milkflows, and fluidized beds, as well as in the pharmaceuticalindustry [7]. A novel capacitive system has been developed forthe concentration measurements of gas–solid flow in pneumati-cally conveyed pulverized fuel at power stations. The capacitancesensor for measuring concentration uses source-grid sensingelectrodes. Active and dummy sensors are used to form adifferential configuration. A correlated double sample techniqueand a lock-in detector with a closed loop were used in theinterface circuit to eliminate baseline drift, build immunity tostray capacitance, and ensure accurate measurement under verylow solids/air mass flux ratios [28].

Aside from applications in the gas, petroleum, and pharma-ceutical industries, palm oil milling can also be considered apotential approach for implementation. The palm oil processingindustry has not been monitored previously with ECT. This isprobably because not every country is involved with palm oilproduction. In the present research, the monitoring of recoveredpalm oil concentrations was performed with ECT.

The liquid waste generated from palm oil extraction using thewet process comes mainly from the oil room after the separatoror decanter. This liquid waste, combined with the wastes from thesterilizer condensate and cooling water, is called palm oil milleffluent (POME). POME is a high-volume liquid waste. It is non-toxic and organic in nature but has an unpleasant odor and ishighly polluting. The palm oil industry is the source of the worstwater pollution. Water pollution can be minimized by reducingthe amount of POME. However, POME or wastes such as water,volatile matter, dirt, or sludge cannot be reliably monitored insidethe vessel before the separation process. No monitoring systemsare yet in place at local palm oil mills to determine the percentageof load waste inside the vessel.

This work presents a technique for visualizing the crude palmoil concentration during the separation process (i.e. collecting therecovered crude palm oil from the liquid waste before separation)to monitor the load waste percentage. A portable ECT Imager wasdeveloped to ensure reliable monitoring of the quality of crudepalm oil. The system is intended as a support instrument for local

and foreign palm oil mills in efficient quality monitoring of crudepalm oil flow through the conveying pipelines during extraction.This monitoring system provides a visual reconstruction of theload waste percentage inside the vessel. The data obtained can beused to design better mill process equipment or control certainprocesses to maximize the quality of crude palm oil and improvethe POME treatment process.

The new on-board sensing plate offers a new design and conceptfor a portable ECT system that can be assembled for differentpipeline diameters. The flexible application of such a system toany pipeline size eliminates the need for redesigning the sensingmodule, thereby allowing the sensor to work independently. In mostprevious studies on ECT, the signals from the sensor electrodes wereusually conveyed to the signal conditioning circuit by a coaxialcable. The coaxial cable can shield against disturbance or straycapacitance and thus introduce very low noise. However, it is theprimary source of stray capacitance. Therefore, this connecting cableshould be made as short as possible. In the present work, weproposed the elimination of the cables connecting the electrodeplates and signal conditioning circuit, which is thus termed as directmounting. The electrodes were connected to the signal conditioningcircuit directly without the cable to eliminate most of the straycapacitance noise successfully.

2. System development

This research aims to investigate the use of a portable sensorin an ECT Imager. As shown in Fig. 1, the project can be dividedinto three stages, namely, the portable sensor design, centralcontrol unit design, and software programming.

A typical ECT system consists of a sensor composed of 8, 12, or16 electrodes, a capacitance measurement circuit, central controlunit, and a control PC [12]. The electrode, which is normally madeof a conductive plate, acts as a sensing surface that connects tothe measuring area. The electrode provides excitation signals andconverts the capacitances into voltage signals, which are condi-tioned and digitized for data acquisition. The capacitance mea-suring circuit, better known as the signal conditioning circuit, isused to collect data and convert the measurement readings intodigital signals. The central control unit is designed to synchronizeall the operations and transfer the data to a control PC. Thecontrol PC receives the measurement readings, stores theacquired data, reconstructs images from the integral measure-ments, and sends action feedback to control the flow [13].

The signal conditioning system consists of several parts,namely, the capacitance measurement, amplifying, filter, andAC-to-DC converter circuits. In addition, a high frequency sinewave generator is also required as the excitation source for thesensor electrodes. The electronic devices output the data and sendit to the data acquisition system for analog-to-digital conversion(ADC) purposes. Finally, the digital data are sent to the computerfor analysis and image reconstruction.

3. ECT measurement principle

Any two adjacent conductors can be considered as capacitor,and different dielectric properties between the conductors willcreate different capacitor values as shown in Eq. (1). The sensorsusually consist of two electrode plates and the capacitor. Thecapacitance of which is determined as follows:

C ¼e0erA

dpð1Þ

Fig. 2. Cross-sectional view of ECT sensor with 16 segmented portable electrodes.

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–68 63

where C is the capacitance (F), e0 is the permittivity of free space,er is the permittivity of the dielectric, A is the area of the plate, anddp is the distance between those plates.

The e0 and er are the global averages of the fluid dielectricproperties over the entire sensing volume, or the permittivity, ofthe sensor [14]. If the area of the plates and the distance betweenthem are known, measuring the capacitance effectively measuresthe dielectric constant. In this case, the capacitance value isproportional to the permittivity between the electrodes. Thesignal-to-noise ratio of the measurement can be improved byincreasing the sensing area of the electrodes [15]. In tomographicimaging, the sensors must facilitate multiple and localized mea-surements throughout the region of investigation. Thus, multipleelectrodes should be arranged around the boundary of the region,and the capacitance between all the combination pairs of electro-des should be measured to perform a ‘‘body scan’’ of the imagingvolume.

A complete cycle of an ECT system measurement is initiatedwhen the first electrode (electrode 1) functions as the excitationor source electrode, in which the electrode is supplied with a sinewave. The other electrode then acts as a receiver of the capacitorvalue corresponding to the dielectric in between. For example, thecapacitances between electrodes 1 and 2, 1 and 3, 1 and 4, until1 and the last electrode are measured in parallel. During thismeasurement phase, the electrodes other than electrode 1 are atthe virtual earth potential imposed by the transducer and arecalled detecting electrodes.

Fig. 3. A 16 electrodes sensor array.

4. Portable ECT sensor design configuration

An ECT sensor consists of multiple measurement electrodesmounted equally around the cross section of a process to beimaged. An earthed screen is placed outside the measurementelectrodes [26] to eliminate the external electrical interferencesand protect electrodes from damage [16]. The inter-electrodecapacitances are typically fractions of a picofarad. An earthedscreen must be placed around the electrodes to eliminate theeffects of extraneous signals and variations in the stray capaci-tance to earth, which would otherwise predominate and corruptthe measurements. The space between the electrodes is filledwith either gas or other insulating materials. This phenomenonwould produce standing capacitance that will be measured forimage reconstruction.

In the present research, 16 portable electrodes were fabricatedonto a 110 mm diameter pipeline. Essentially, the pipeline mate-rial must be a pure insulator to ensure that it has no effect on thesignals measured. However, the thickness of the pipeline willinfluence the measured value of the standing capacitance. Ifeither e of the material or the pipe wall thickness increases, ahigher standing capacitance ensues. Thus, the thickness of thepipeline should be negligible to decrease field divergence. How-ever, other factors, such as corrosion, abrasion, temperatureresistance, and temperature stability, may limit the selection ofthe pipeline material [25]. Fig. 2 shows an arrangement of 16electrode sensors that were designed to cover acrylic pipes with adiameter of 11 cm, a wall thickness of 0.5 cm, an inner pipelineradius (R1) of 5 cm, an outer pipeline radius (R2) of 5.5 cm, and anelectrode stretch angle (y) of 22.51.

The placement of the electrodes on the outer surface is donecarefully to ensure that the electric field produced during excita-tion is evenly distributed among the detecting electrodes. There-fore, the circle (cross-section) of the pipeline was divided equallyinto 16 sectors, wherein each sector measured 22.51, as shown inFig. 3. The total width for one section was 21.6 mm.

4.1. Portable electrode sensor design

The ideal capacitance measuring system will have a very lownoise level, a wide dynamic measurement range, and high immunityto stray capacitance. Stray capacitance is a type of noise where theleakage capacitance is caused by the connection from the circuit andcable to the electrode [17,24]. A new technology, named as theintergraded electrode sensor, was introduced in this research tominimize the noises created by the cable. The signal conditioningcircuit was built on the electrode sensor to function as an ECT sensormodule. This module not only reduces noise but can also workindependently.

In most previous studies on ECT, the signals from the sensorelectrodes were usually conveyed to the signal conditioningcircuit by a coaxial cable. The coaxial cable can shield againstdisturbance or stray capacitance and thus introduce very lownoise. However, it is the primary source of stray capacitance.Therefore, this connecting cable should be made as short aspossible. In the present work, we eliminated the use of cablesconnecting the electrode plates and signal conditioning circuit,a technique which is thus termed as direct mounting.

Under ideal conditions, the pipeline thickness is zero. Thus, theradius–electrode ratio, r (where r¼R1/R2), is equal to 1. A highelectrode covering ratio produces high image fidelity [18].

Fig. 5. Electrode’s dimension.

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–6864

The smaller the r, the larger the effect of pipeline thickness willbe. Pipeline thickness significantly influences, not only capaci-tance, but also the final image. The maximum capacitance changein a previous study was at r¼0.85, which is favorable tocapacitance measurement and image reconstruction [15]. In thepresent research, r¼0.9 was used.

The electrode material must be highly conductive. Materialssuch as copper, aluminum, silver, brass, tungsten, or iron aresuitable. Copper was chosen for the present study because it canbe found on any bare Printed Circuit Board (PCB). In addition,copper is a highly conductive material, which is desirable in anECT system; it is cost-efficient and easy to fabricate as well. Basedon these concepts, the portable ECT was developed using aspecially designed PCB, as shown in Fig. 6. The sensor modulewas composed of a double-layer, copper-plated FR4 (eg¼4.6) PCBwith a thickness of 1.6 mm. The FR4 is a stiffener widely used forflexible PCBs and is a cost-efficient solution for high-end applica-tions involving impedance control and high frequencies. Com-pared with previous ECT system designs, the new electrodesensor does not flex or stick to the pipe wall.

The sensor was arranged symmetrically in a hexadecagonsurrounding the pipeline. Each electrode sensor was 19 mm wideand had a sensor area 100 mm long. The electrodes were madeof copper and driven as shown in Fig. 4. The specific length of thesensor was chosen because the axial length of electrodes is relatedto inter-electrode capacitance, signal bandwidth, and measurementuncertainty of the measured media. Longer electrodes produce anaverage signal over a greater axial length, which results in baddynamic performance. Shorter electrodes may result in a capaci-tance too small to be measured accurately [19,20].

In an ideal ECT sensor, the electric field lines will be normal tothe sensor axis. However, if the electrodes used are shorter thanthe sensor diameter, the electromagnetic field lines will spread outat the electrode termini. This situation will have two consequences.First, the capacitance measured between electrodes will bereduced, hence, reducing the measurement sensitivity. Second,the axial resolution of the sensor will be degraded because of theaxial spreading of the field lines at the electrode termini. Therefore,guard electrodes were used to maintain a parallel electric fieldpattern across the sensor in the measuring electrodes region,thereby preventing the electric field lines from spreading axiallyat the ends of the measuring electrodes. This improves both theaxial resolution and the sensitivity of the sensor. In addition,earthed guard electrode tracks may also be needed betweenadjacent measuring electrodes to reduce the standing capacitancebetween adjacent electrodes to a value low enough to avoidoverloading or saturating the capacitance measuring system.

The sensing plates were covered by an earth screen made of adouble-layer PCB. The earth screen covers the entire surface onthe top layer. The driven guard electrode was integrated onto the

Fig. 4. Electrode plate.

electrode sensor to prevent the electric field lines from spreadingat the ends of the measuring electrodes. These driven guardelectrodes surrounded the circumference of the pipeline once allthe 16 electrodes had been installed. The length of the guardelectrodes was 33 mm on the left and 43 mm on the right, asshown in Fig. 5.

4.2. Measurement and signal conditioning circuits

An important issue with instrumentation design is the circuitperformance in the presence of noise generated by externalinterference and thermal effects within components [21]. Inselecting and designing a capacitance measuring circuit, a stray-immune circuit must be used A stray-immune circuit measuresonly the capacitance between the selected pair of electrodes andis insensitive to the stray capacitance between the selected andredundant electrodes, as well as those between the selectedelectrodes and the earth.

Each signal conditioning circuit is unique and independent fromone another because all the measuring operations are controlled by asingle microcontroller on the circuit. In addition, each of the circuitsconsists of a signal switching, signal detection and amplifier, absolutevalue, low pass filter circuit, and ADC circuits, as well as a program-mable gain amplifier and a microcontroller control unit. The desiredsequence operation of an electrode signal selection, including themeasuring and conversion data, depends on the microcontrollerprogramming. The electrode sensor in this research was designedfor direct plugging onto the PCB sockets of the signal conditioningcircuit, becoming a single sensing module. Fig. 6(a) shows the blockdiagram of the measurement circuit. A measurement circuit modulewith pin connectors is shown in (b). Fig. 7 shows the completeportable sensing module.

Fig. 6. (a) Block diagram of measurement circuit and (b) measurement circuit

with pin connectors.

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–68 65

The 16 boards were interconnected by a 26-way insulation-displacement connector cable. This design eliminates the need forcables to connect the electrodes and signal conditioning circuits.Furthermore, this design reduces the maintenance costs of thesystem. In cases where only one sensing module is malfunction-ing, users can simply plug out the old board and replace it with anew one. Fig. 8 shows all 16 portable electrode sensors.

5. Image reconstruction

The overall concentration of the ECT sensor contents can becalculated either from the normalized pixel values in the recon-structed ECT image or from the normalized capacitance measure-ments directly. Calculating the overall concentration from imagepixels is done by summing up the values of the individual pixelsin the ECT images for the required image frame and dividing thisfigure by the sum of these pixel values when the sensor is filled

Fig. 7. Complete portable sensing module.

Fig. 8. Sixteen portable electrode sensor.

Table 1Digital data transfer to PC for image reconstruction.

Rx(1) Rx(2) Rx(3) Rx(4) Rx(5) Rx(6) Rx(7) Rx(8)

Tx(1) 220 164 93 70 58 52 39

Tx(2) 219 169 92 69 58 51

Tx(3) 217 165 91 61 56

Tx(4) 213 175 99 65

Tx(5) 222 163 91

Tx(6) 219 174

Tx(7) 216

Tx(8)

Tx(9)

Tx(10)

Tx(11)

Tx(12)

Tx(13)

Tx(14)

Tx(15)

Tx(16)

with the higher permittivity material. In mathematical terms,

VR¼1

MSUM

PðiÞ

Pkð2Þ

where VR is the concentration, M is the total number of pixels, P(i)is the value of the ith pixel, and Pk is the value of the ith pixelwhen the sensor is filled with the higher permittivity material(nominally, 1). In calculating from the normalized inter-electrodecapacitances, the concentration is obtained by summing up all ofthe normalized capacitance values for one image frame anddividing these by the sum of the normalized capacitances whenthe sensor is filled with the higher permittivity material. Inmathematical terms,

VR¼1

NSUM

Cn

Ckð3Þ

where N is the total number of electrode-pair measurements, Cn isthe individual electrode-pair normalized capacitances, and Ck isthe electrode-pair capacitances when the sensor is filled with thehigher permittivity material (nominally, 1).

5.1. Error measurement in the ECT system

A simple and effective method for evaluating the discre-pancy between the reconstructed concentration profile andthe real concentration profile was previously described in.

Rx(9) Rx(10) Rx(11) Rx(12) Rx(13) Rx(14) Rx(15) Rx(16)

37 46 53 54 67 93 165 215

43 35 47 45 57 64 89 163

50 42 34 50 49 56 71 87

51 53 41 33 45 47 54 66

67 52 48 40 35 43 49 53

87 65 56 47 45 38 44 53

163 95 67 57 52 42 35 40

215 172 96 61 57 54 40 36

217 169 87 62 55 46 37

223 163 94 60 57 45

225 177 97 63 58

227 168 92 68

215 170 98

219 172

222

Fig. 9. Complete ECT Imager System Development.

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–6866

The equation for the error measurement is

% Error ¼A�M��

��

A100% ð4Þ

where A is the actual concentration percentage of the pipeline, andM is the concentration percentage measured in the system. Thiserror percentage is the ratio between the measured concentrationand the actual concentration. The modulus ensures no negativevalues in the ratio.

Fig. 10. Reconstructed image obtained for different flow concentrations of palm oil and

oil; (c) 30% water, 70% palm oil; (d) 40% water, 60% palm oil; (e) 50% water, 50% palm oi

oil; (i) 90% water, 10% palm oil; and (j) 100% water, 0% palm oil.

5.2. Data transfer

The data transfer rate of the Universal Serial Bus (USB)communication depends on the data acquisition rate of thesystem. The data acquisition rate is counted based on the timewhen the system collects all the measurement data in one frame.The minimum data in one USB frame of data transferred to the PCwas pre-determined by the full frame data in the 16-electrodeECT system, which is 120. The data transferred to the PC was in

water. Two phase flow (a)–(j). (a) 10% water, 90% palm oil; (b) 20% water, 80% palm

l; (f) 60% water, 40% palm oil; (g) 70% water, 30% palm oil; (h) 80% water, 20% palm

Table 2Comparison between actual concentration and concentration obtained from measurement for water/palm oil flow.

Fig. 11. ECT image concentration measurement.

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–68 67

digital format, as shown in Table 1. The ADC module in the systemcan convert analog data to 10 bit digital information. However,the data obtained in this research was converted to 8 bit, or 1byte, which is more convenient for sending to computers. Thus,the data varied from 0 to 255.

5.3. Graphical User Interface

The Graphical User Interface (GUI) was developed to visualizethe image reconstructed. The GUI can perform online and offlineimage reconstruction, display tomograms, select different imagereconstruction algorithms, and display the material distributionin the pipeline, among others. The GUI was used to display the datacollected, tomograms, frame rate, distribution of low-permittivityand high-permittivity materials, image reconstruction, algorithmsperformed, and the current status of the GUI. Through the GUI,the analysis results can be displayed in tomographic, numeric, andbar graph forms. Fig. 9 shows the complete ECT Imager systemdeveloped.

6. Two-phase flow visualization analysis

This experiment was performed to measure the concentrationprofiles of the water-and-palm-oil mixture inside the pipeline, asshown in Fig. 10. A pipeline with a diameter of 110 mm and a wallthickness of 6 mm was used for the two-phase flow measurementexperiments on the palm oil/water flow. The concentration measure-ments based on pixel value provided a more accurate reading thanthe concentration measurements based on sensor value [22]. Thus,the concentration measurements based on pixel value were used for

further analysis. Fig. 10 shows the image reconstruction of the two-phase flow of palm oil/water.

In the first part of the experiment, the water concentrationvaried from 10% to 100% in a step size of 10% of the pipe diameter.The resulting images based on the linear back projection algorithmand operated in real time under the reconstruction program areshown in Fig. 10. As shown in the picture, color tone represents thewater concentration in the pipe. Water concentration varied fromlow (white) to high (black). For instance, 50% water and 50% airflow in the pipe produced a reconstructed image with a region halfin white and a region half in black.

The comparison between the actual concentration and theconcentration obtained from palm oil/water measurements isshown in Table 2. The concentration measurements show a max-imum error of approximately 12% for water concentrations less than50%. These errors may arise because some of the oil was mixed withthe water. The accuracy of the reconstructed image depends on twofactors: internal pipe temperature and calibration method. Whenhardware surrounding the pipe is turned on, the temperature in thepipe increases. In addition, errors may occur during normalizedvoltage calibration. Increases in temperature and calibration errorcause errors in the reconstructed image.

The repeatability of image concentration measurements for thetwo-phase flow measurement experiments on the palm oil/waterflow was evaluated using the Gage R&R method, a well-knownprocedure for evaluating measurement systems. In this study, 10parts with different percentages of image concentration settingswere analyzed. Four-time repeatability measurements were con-ducted for 40 runs based on the experimental design layout usingthe Minitab statistical randomization software.

The chart for the image concentration percentages in Fig. 11shows the individual readings of each part varied significantly inthe averages obtained. Thus, the image concentration percentagesdiffer significantly from one another. Meanwhile, the measurementreadings were taken very close to the part average, which clearlyshows the differentials between each concentration measured bythe ECT device. Based on the experimental verification, the repeat-ability of the concentration measurement analysis shows that thesystem is consistent in the concentration measurements and candetect part-to-part differences.

7. Conclusions

This paper presents the results obtained from a portable ECTImager, which provides visual reconstructions of the palm oil

E.J. Mohamad et al. / Flow Measurement and Instrumentation 31 (2013) 61–6868

concentration in a closed vessel. The overall performance of thesystem was evaluated through the tomograms reconstructed bythe system. The linear back projection algorithm was applied inproducing a good quality tomogram. A portable sensor electrodeoffers a new design and concept of a portable ECT system that canbe assembled on and easily removed from any pipeline of anydiameter. The flexible application of such system to any pipelinesize eliminates the need for redesigning the sensing module. Thesensing module also contains an integrated electrode sensingcircuit on each of the segmented sensor electrodes. A microcon-troller unit and a data acquisition system were integrated withthe electrode sensing circuit, while USB technology was applied inthe data acquisition system, thereby enabling the sensor to workindependently.

References

[1] Vizireanu DN. Morphological shape decomposition interframe interpolationmethod. Journal of Electronic Imaging 2008;013007:1–5.

[2] Vizireanu DN. Generalizations of binary morphological shape decomposition.Journal of Electronic Imaging 2009;16(1) 01302-1–01302-6.

[3] Vizireanu DN, Udrea RM. Visual-oriented morphological foreground contentgrayscale frames interpolation method. Journal of Electronic Imaging2009;18(2) 020502-1–020502-3.

[4] Vizireanu DN, Halunga S, Marghescu G. Morphological skeleton decomposi-tion interframe interpolation method. Journal of Electronic Imaging2010;19(2):1–3 023018-1–023018-3.

[5] Williams RA, Beck MS. Introduction to process tomography. In: Scott DavidM, editor. Frontiers in Industrial Process Tomography. Oxford: Butterworth-Heinemann Ltd.; 1995. p. 1–7.

[6] Teniou Samir, Meribout Mahmoud, Al-Hanaei Thuraya, Al-Zaabi Fatima,Banihashim Rehab, Al-Ghafri Sameya. A new constrained hierarchical recon-struction method for electrical capacitance tomography. Flow Measurementand Instrumentation 2012;23:66–75.

[7] Strazza Domenico, Demori Marco, Ferrari Vittorio, Poesio Pietro. Capacitancesensor for hold-up measurement in high-viscous-oil/conductive-water core-annular flows. Flow Measurement and Instrumentation 2011;22:360–369.

[8] Zheng Gui-Bo, Jin Ning-De, Jia Xiao-Hui, Lv Peng-Ju, Liu Xing-Bin. Gas–liquidtwo phase flow measurement method based on combination instrument ofturbine flowmeter and conductance sensor. International Journal of Multi-phase Flow 2008;34:1031–1047.

[9] Lin Z. Gas–liquid two-phase flow and boiling heat transfer. Xi’an, China: Xi’anJiaotong University Press; 2003.

[10] Abdul Rahim Ruzairi, Zhen Cong Tee, Fazalul Rahiman Mohd Hafiz, Pusppa-nathan Jayasuman. A low cost and high speed electrical capacitance tomo-graphy system design. Sensors and Transducers Journal 2010;114(3):83–101.

[12] Marashdeh Qussai, Warsito Warsito, Fan Liang-Shih, Teixeira Fernando L. Amultimodal tomography system based on ECT sensors. IEEE Sensors Journal2007;7(3):426–433.

[13] Zhaoa Tong, Takeia Masahiro, Masakia Kenta, Ogisob Ryoji, Nakaob Koji,Uchiurac Akira. Sensor design and image accuracy for application of capaci-tance CT to the petroleum refinery process. Flow Measurement and Instru-mentation 2007;18:268–276.

[14] Huang M, Liu C, Shen LC. Monitoring the contamination of soils by measuringtheir conductivity in the laboratory using a contactless probe. GeophysicalProspecting 1995;43:759–778.

[15] Martınez Olmos A, Carvajal MA, Morales DP, Garcıa A, Palma AJ. Developmentof an Electrical Capacitance Tomography system using four rotating electro-des. Sensors and Actuators A: Physical 2008;148:366–375.

[16] Chee Wei Tan. Measurement of two-phase imaging (Water/gas bubbles) byusing electrical capacitance tomography (ECT). BSc thesis. Universiti Tekno-logi, Malaysia; 2003.

[17] Byar Malcolm. Developments in electrical capacitance tomography. PTLapplication notes; 2001.

[18] Xie CG, Huang SM, Hoyle BS, Lenn C, Snowden D, Beck MS. Electricalcapacitance tomography for flow imaging: system model for developmentof image reconstruction algorithms and design of primary sensors. IEEProceedings G 1992;139:89–98.

[19] Daoye Yang, Bin Zhou, Chuanlong Xu, Guanghua Tang, Shimin Wang. Effect ofpipeline thickness on electrical capacitance tomography. Journal of Physics:Conference Series 2009;147:012030.

[20] Yang WQ, Peng Lihui. Image reconstruction algorithms for electrical capacitancetomography. Measurement Science and Technology 2003;14(1):R1–R13.

[21] Williams Philip, York Trevor. Evaluation of integrated electrodes for electricalcapacitance tomography. In: Proceedings of the 1st world congress onindustrial process tomography; 1999.

[22] Zhen Cong Tee, Abdul Rahim Ruzairi, Kok San Chan. An optical tomographysystem based on the universal serial bus. Jurnal Teknologi 2004;41:43–52.

[24] Byars Malcolm. Developments in electrical capacitance tomography.Cheshire, United Kingdom: Process Tomography Limited; 2001.

[25] Flores Norberto, Carlos GamioJ, Ortiz-Aleman Carlos, Damian Enrique. Sensormodeling for an electrical capacitance tomography system applied to oilindustry. In: Proceedings of the COMSOL multiphysics user’s conference.Boston; 2005.

[26] Yang WQ, Spink DM, Gamio JC, Beck MS. Sensitivity distributions ofcapacitance tomography sensors with parallel field excitation. MeasurementScience and Technology—IOP Science 1997;8:562–569.

[27] Jiabin Jia , Mi Wang, H. Inaki Schlaberg, Hua Li, A novel tomographic sensingsystem for high electrically conductive multiphase flow measurement, FlowMeasurement and Instrumentation, Vol 21, 2010, 184–190.

[28] H.L. Hua, T.M. Xu, S.E.Hui, Q.L. Zhou, A novel capacitive system for theconcentration measurement of pneumatically conveyed pulverized fuel atpower stations, Flow Measurement and Instrumentation, Vol 17, 2006, 87–92.