Modeling of a charge coupled device based optical tomographic instrumentation system for particle sizing M. Idroas a , R. Abdul Rahim b, ⁎, M.H. Fazalul Rahiman c , R.G. Green d , M.N. Ibrahim b a Faculty of Chemical & Natural Resources Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia b Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia c School of Mechatronic Engineering, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia d School of Engineering, Sheffield Hallam University, Sheffield, United Kingdom abstract article info Article history: Received 16 May 2010 Received in revised form 31 March 2011 Accepted 20 April 2011 Available online 6 May 2011 Keywords: Particle size CCD tomography Optical instrument This research investigates the use of charge coupled device (CCD) linear image sensors in an optical tomographic instrumentation system used for sizing particles. Four CCD linear image sensors are configured around an octagonal shaped flow pipe for a four projections system. The measurement system used four CCD linear image sensors consisting of 2048 pixels with a pixel size of 14 by 14 μm. Hence, a high-resolution system is produced. Three mathematical models based on the effects due to particles, light sources and diffraction are discussed. The models are used to simulate the actual process in order to understand the limitations of the designed system. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Industrial processes are often controlled using process measure- ments at one or more points. The amount of information contained in such measurements is often minimal, and in some cases (multiphase flow) there are no adequate sensors [1]. To better understand certain chemical processes, a more sophisticated approach is needed. Process tomography is a means of visualizing the internal behavior of industrial processes, where tomographic images provide valuable information about the process for the assessment of equipment design and on-line monitoring [2,3]. There are several modalities used in process tomography, such as electrical (impedance, capacitance, and inductance), radiation (opti- cal, X-ray, positron electromagnetic (PET), and magnetic resonance) and acoustic (ultrasonic) [4,5]. Electrical tomography has a relatively poor spatial resolution of about 10% of the diameter of the cross- section [6]. The X-ray computed tomography method is well known, but specific safety procedures need to be followed by the operator. PET needs operator intervention and radioactive particles. Ultrasonic tomography is complex to use due to spurious reflections and diffraction effects and may therefore require a high degree of engineering design [4]. Optical techniques are desirable because of their inherent safety (the transducer does not require direct physical contact with the measurand), high efficiency [8] and have the potential to improve manufacturing in the chemical industries [9]. For processes handling transparent fluids, and where optical access is possible, optical techniques can provide high-resolution images [2], i.e. 1% spatial resolution [7]. Particle sizing is very important for many industrial processes and has led to much research. Typical problems relate to pulverized coal for combustion and liquid fuels, spray characterizations, the analysis and control of particulate emissions, industrial process control, manufacture of metallic powders and the production of pharmaceu- ticals [10,12]. Fig. 1 summarizes the major techniques used in particle- size measurements [11]. The majority of the techniques are off-line, with the direct optical technique providing the only truly on-line measurement [10]. Existing on-line optical methods use Fraunhofer diffraction to determine the positions or angles of optical emission spectra, generally within a limited measurement volume, which sets a limit on the quality of the images produced by optical systems [13]. Morikita et al. [14] used the Fraunhofer response curve (size–intensity relationship) to measure the equivalent diameter of non-spherical particles ranging from 20 to 200 μm; both of these methods are inferential. Horbury et al. [15] investigated transparent slurries with particle sizing and flow profiles using optical fibers. An optical tomography system that uses optical fiber bundles has problems in ensuring that every fiber has similar optical characteristics [16]. Thus, a system based on CCD devices is proposed which may provide very high resolution (better than 1%) on-line measurement over the full measurement cross-section and with high speed data acquisition based on proprietary items [17]. Powder Technology 212 (2011) 25–37 ⁎ Corresponding author. Tel.: + 60 7 5537801; fax: + 60 7 5537811. E-mail addresses: mariani@fkkksa.utm.my (M. Idroas), ruzairi@fke.utm.my (R.A. Rahim), hafiz@unimap.edu.my (M.H.F. Rahiman), r.g.green@shu.ac.uk (R.G. Green). 0032-5910/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2011.04.017 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec