Determination of Hydrocarbon Level in Distilled Water ... - IEEE Xplore

IEEE SENSORS JOURNAL, VOL. 15, NO. 11, NOVEMBER 2015

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Determination of Hydrocarbon Level in Distilled Water via Fiber Optic Displacement Sensor Noriah Bidin, Daing Hanum Farhana Abdul Munap, Mundzir Abdullah, Faridah Mohd Marsin, Shumaila Islam, Nurul Hida Zainuddin, and Moh Yasin Abstract— Fiber optic displacement sensor offers a feasible way to detect hydrocarbon level in water. A reflective light intensity modulation technique is accomplished to detect hydrocarbon concentration in the ranges of 0%–20%. The reflective configuration technique enables the sensor to collect output voltage at a different displacement. The output voltage decreases linearly with hydrocarbon level at a corresponding optimized displacement of 1.5 mm. Linearity index close to one indicates that a high confident degree the sensor. Simple in design and low cost, makes this system as a promising sensor for determination of hydrocarbon level in water. Index Terms— Displacement, fiber intensity, level, reflective, sensor, water.

optic,

hydrocarbon,

I. I NTRODUCTION

T

HE measurement of hydrocarbon in water is important for both process control and reporting to regulatory authorities. The concentration of hydrocarbon in water is traditionally evaluated using reference methods based on Gas Chromatography and Flame Ionisation Detection (GC-FID), infrared (IR) absorption, and gravimetric analysis [1]. Freon or other solvents are normally used in most of the methods that are approved for determining the hydrocarbon concentration in water. The hydrocarbons from the water sample are extracted by these solvents prior to determine the concentration. The absorption band for hydrocarbon which normally comprised the molecule bonding between carbon and hydrogen C-H is Infrared 3.4 µm is used to determine the hydrocarbon concentration. However Freon subjected to the depletion of the ozone layer in the upper atmosphere.

Manuscript received January 1, 2015; revised June 25, 2015; accepted June 25, 2015. Date of publication June 30, 2015; date of current version August 26, 2015. This work was supported by the Ministry of Education through the Research University Grant within the Flagship Program under Grant vote 03G08. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani. (Corresponding author: Noriah Bidin.) N. Bidin, D. H. F. Abdul Munap, M. Abdullah, and N. H. Zainuddin are with the Advance Photonic Science Institute, Universiti Teknologi Malaysia, Johor Bahru 81310, Malaysia (e-mail: [email protected]; [email protected]; [email protected]; nurulhida90@ gmail.com). F. M. Marsin is with Jabatan Kebajikan Masyarakat, Skudai 81300, Malaysia (e-mail: [email protected]). S. Islam is with the Laser Center, Ibnu Sina Institute for Scientific and Indusrial Research, Universiti Teknologi Malaysia, Johor Bahru 81310, Malaysia (e-mail: [email protected]). M. Yasin is with the Department of Physics, Faculty of Science, Airlangga University, Surabaya 60231, Indonesia (e-mail: [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2015.2451176

Furthermore the cost of Freon has increased considerably due to the lack of availability. Clearly, there is a need for alternative methods of determining the hydrocarbon in water concentrations where solvents are not used. Laser and fiber optic based technology have provided a solution to the measurement of hydrocarbon in water. Furthermore this technology does not use any solvents and therefore provides a long-term solution. Some reports related to this work using laser induced breakdown spectroscopy (LIBS) technique to determine the hydrocarbon in water [2]. Laser induced breakdown spectroscopy (LIBS), is a well-established analytical technique. In principle laser photons are sent to the target and photons emitted by the plasma are detected, can allow direct and in situ measurements of numerous elements in complex liquids. It can briefly be described as an elemental analysis based on emission from plasma generated by focussing a laser beam on a sample. Other method to analyse hydrocarbon concentration in water is reported in other text [3] also using a Q-switched Nd:YAG laser but using different mechanism. In this manner an acoustic shock wave is used instead of plasma emission to determine the hydrocarbon concentration in water. Piezo-electric transducer is used to detect the sound which carried the information regarding the concentration of hydrocarbon. The system is referred as laser induced acoustic wave LIA. Either LIBS or LIA system involving high power laser normally which relatively high cost and need skillful personnel to handle. Due to the expensive equipment is necessary, this method is considered as not conducive in the real field. Thus more economical method is preferable. Alternatively, conventional sources are utilized depending on the degree of concentration, for low level hydrocarbon UV light was used while for high dense range radio-frequency microwave was used to determine the level of hydrocarbon [4]. Fluorescence sensor is also another common technique used to determine the hydrocarbon level in water. UV source normally used to excite and the re-emit fluorescence used to determine the hydrocarbon level [5]. However, there are organics such as bacteria and other suspended particles that will interfere during light transmission measurement and gives false reading on the hydrocarbon measurement. Hence an alternative method needs to be considered in order to determine the hydrocarbon level in water in more economic and faster way. Fiber optic sensor is one of the candidates. Such sensor has been widely used for other application [6]–[11]. Recently fiber optic sensor has been established for industrial application [12]. As an extension

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Fig. 1. Schematic experimental setup of fiber optic displacement sensor for detecting the hydrocarbon concentration.

of the work and further detail procedure are discussed in this present paper. The sensor operation is based on the intensity modulation technique using a plastic optical fiber-based bundle as a probe. The simplicity, reliability, and high confident level of the system are discussed in detail. II. E XPERIMENTAL S ET-U P Figure 1 shows a schematic diagram of the fiber optic displacement sensor for detection of hydrocarbon level. The sensor setup consists of a Helium-Neon laser as a light source, fiber optic probe, reflective flat mirror, a silicon photodetector, and a digital multimeter. A Helium-Neon laser with center wavelength of 635 nm is used as a light source. In this experiment, the Fiber optic probe is made up of 2 meter long polymethyl methacrylate which comprise of one transmitting core of 1mm in diameter and 16 receiving cores of 0.25 mm in diameter. It has numerical aperture of 0.5, core refractive index of 1.492 and cladding refractive index of 1.402. The Fiber Optic probe is connected to a Silicon detector. A Quartz cell contains sample solutions of diluted hydrocarbon in distilled water. The displacement is accomplished by mounting the fiber optic probe on a micrometer translation stage which is attached to a vibration free table. Light from the visible red He-Ne laser is directed through the transmitting fiber onto the receiving core. The signal is measured by moving the probe away from the zero point. In this case the reflective surface of flat mirror and the probe are assumed to be in close contact. The Silicon detector is used to measure light intensity from the fiber probe. The amount of light collected from fiber probe at Silicon detector is determined by converting the signal from the detector to voltage and measured by a digital Multimeter. The measurement of hydrocarbon level in distilled water was accomplished by moving the receiving fiber probe axially, thus changing the distance between the mirror and receiving fiber. At different displacement, the diverging source beam was refracted as it entered the different concentrations of distilled water containing hydrocarbon solutions. A portion of it was collected by the receiving fiber to transmit into the silicon detector where its intensity was measured. The intensity of the collected light is a function of the displacement of the fiber optic. Prior of experiment, the He-Ne laser was gently adjusted until a bright beam spot of 633 nm appear on an infrared card. While a silicon photodetector was aligned to maximize

collecting the lights from the receiving Fiber. Lube oil was deployed as hydrocarbon sample. It mixed up with distilled water via hydrochloric acid to produce hydrocarbon solution. Various hydrocarbon solution were prepared within 0 – 20%. In the preparation of hydrocarbon in distilled water with different percentage, a substantial amount of 2 ml hydrochloric acid (HCl) was added into 100 ml Distilled water to induce acidic water. The confirmation of acidic solution is accomplished by shaking the mixture till achieved of pH 2. After that, different volume (mL) of hydrocarbon (lube oil) is injected into the acidic distilled water depending on the required concentration (in percentage). An example of calculated concentration of hydrocarbon is expressed as: Per centage o f concentr ati on Lube oil (m L) × 100% = hydr ocar bon soluti on (m L) 20 m L o f Lube oil = × 100% 20 m L Lube oil + 80 m L o f di stilled water = 20% (1) The zero percent mean no lube oil is added into the acidic water solution. The rest in order to make 20% hydrocarbon concentration means 20 mL of lube oil was added into hydrocarbon solution which comprised of the mixture of 20 ml of lube oil diluted into 80 mL acidic distilled water (the total volume of the solution is 100 mL). The refractive index each of the solution has been reported in other text [3, 12]. A quartz cell with dimension 3 × 3 × 3 cm3 was used to fill the tested sample. Initially the fiber sensor was calibrated using acidic distilled water (0% of hydrocarbon concentration). The output voltage of the reflected light was directly recorded by a multimeter. The voltage was measured at variation of displacement by adjusting a micrometer of vertical linear translation stage. The displacement was adjusted within the ranges of 0 to 4 mm. The measurements were then carried out for different hydrocarbon concentration. In order to validate the performance of fiber optic displacement sensor with reflected technique a linearity index is identified. In attempt to achieve this goal two known hydrocarbon concentrations were selected. This known concentration is also referred as actual concentration. The two actual concentrations comprised of 2% to represent a lower part and 24% for higher one. In this particular study, ten samples for each set of hydrocarbon solution were prepared. The measurement of output voltage from the fiber sensor was performed on the individual sample. This means each set of tested concentrations (2 and 24%) will have ten measurements of output voltage. Each individual tested concentration was determined based on a calibration curve of fiber sensor. The linearity index is computed following this expression: T ested concentr ati on (2) Actual concentr ati on The fiber sensor performance was identified based on it responses to the received of light. The parameters involved the rise up and fall down response of the sensor with respect to the distance. The sensitivity of the initial response is determined base on the front slope m. Meanwhile the sensitivity for the fall Li neari t y i ndex =

BIDIN et al.: DETERMINATION OF HYDROCARBON LEVEL IN DISTILLED WATER VIA FIBER OPTIC DISPLACEMENT SENSOR

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TABLE I P ERFORMANCE OF F IBER O PTIC D ISPLACEMENT S ENSOR -F RONT S LOPE

TABLE II Fig. 2. Calibration curves of fiber optic displacement sensor at different Hydrocarbon level.

P ERFORMANCE OF F IBER O PTIC D ISPLACEMENT S ENSOR -BACK S LOPE

time is measured based on the back slope. The reproducibility of the measurement of output voltage with respect to the distance is referred to as its repeatability or coefficient correlation R 2 . All these measurements are limited in the linear region. The accuracy of the fiber sensor is based on the estimation of the standard deviation, whereas, the resolution of the fiber sensor is determined by its limit of detection LOD. This means the lowest concentration that the sensor can detect. It can be expressed by the following relation: 3S D (3) m where SD is a standard deviation, m is the slope of the linear curve. The standard deviation is expressed as: LOD =

SD =

i=N 2 1 Vi − V¯ N −1

(4)

i=1

where N is recurrence, Vi is the output voltage at any distance, and V¯ is the mean or average of output voltage. In this experiment the measurement of the output voltage at each individual distance was repeated for five times. The whole experiment was carried out in room temperature of 25 °C under normal atmospheric pressure. The error due to the temperature variation is negligible. III. R ESULT AND D ISCUSSION Figure 2 shows a graph of output voltage versus displacement for different Hydrocarbon concentration. The output voltage is measured the intensity signal from reflected light. Meanwhile the displacement is a measurement of distance of the reflecting mirror to the fiber optic probe. Each curve represents a fingerprint for each individual hydrocarbon concentration. In general the fingerprint exhibits a peak voltage with a steep front slope whereas the back slope follows almost an inverse square law function. At zero displacement, light cone does not receive by the probe, hence the output signal is zero. As the displacement is increased the probe started receiving signal and the voltage output also increased. Hence drastic change occurs in the output voltage with the displacement at the front slope of the graph. This is occurred when the reflected cone power falls

within the surface area of receiving fiber. Further overlapping volume of light cone leads to higher output signal until it reaches a maximum point or peak value. However, there is a limit, whereby an optimum displacement is achieved as indicates by the peak output voltage. The optimum voltage is achieved at a displacement of 1.5 mm, obviously it occurs for all tested hydrocarbon concentration. Further increment in displacement causes larger volume size of the reflected light to intersect with the receiving fiber probe. As a result, the output signal decreases due to the fact that the power density decreases with larger size of light cone and only a fraction of the reflected light is detected. Almost all curves of output signal following an inverse square law against displacement for the back slope of the graph as shown in Figure 2. The configuration of the curve based on displacement interpret that, drastic change occur within a displacement before peak value and drop gradually after the peak value. Such configuration explains that, the sensor is more sensitive and significant at the front slope as comparison to the back slope. The change of sensitivity of the front slope for different concentration is more pronounce, whereas the back slope is less significant because the sensitivity of the sensor is very close to each other. Furthermore the repeatability of the front slope is more prominent because close and consistence to 99% for all concentration. Thus the fiber optic sensor is more sensitive when the displacement is less than 1.5 mm. Beyond the optimum displacements, the fiber optic sensor is less sensitive. Overall the performance of the fiber optic sensor in this stage is depended on the displacement. The performance of the fiber optic displacement sensor is summarized in Table I and II. There are two parameters

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Fig. 5.

Testing the known hydrocarbon concentration. TABLE III

L INEARITY I NDEX OF 2% H YDROCARBON

Fig. 3.

Performance of fiber sensor. (a) Front slope. (b) Back slope.

Fig. 4. Calibration between peak voltage versus Hydrocarbon concentration.

were computed to describe the performance of sensor; the sensitivity and the repeatability. Both parameters are obtained from the linear part of the fingerprint curve for each individual hydrocarbon solution a shown in Fig 3. The figure illustrate the front slope (Fig 3(a)) and back slope (Fig 3(b)). The sensitivity of the sensor is high if the detection of intensity signal is high for every percent of concentration and the repeatability remain consistence and close to 100%. Then this classified as good sensor performance. This mean the response to detect the hydrocarbon concentration is high. The intensity of light is high at low concentration thus gives high amplitude of voltage. Good example when fiber sensor is used to detect distilled water without adds in hydrocarbon (lube oil). A graph of peak voltage versus hydrocarbon concentration is depicted in Fig 4. The peak voltage is obtained at the probe

distance of 1.5 mm. It is found that the peak voltage decreases linearly with the hydrocarbon concentration. The sensitivity of the sensor is obtained as 0.11 V for each percent of hydrocarbon concentration with repeatability up to 97%. As the concentration is high the intensity of light is reduced due to various factor including absorption, scattering, diffraction and refraction. The refraction beam getting bigger as the refractive index change in high concentration of hydrocarbon. The probe received less power density due to the enlargement of cone angle as well as the area of beam as the concentration increased. Thus the intensity of the light reduced before reaching to the probe. As a result less intensity signal was received as quantified by the low voltage. Hence the sensitivity of the sensor is low as the concentration of hydrocarbon is high. Fig 5 depicted the typical results for validating the performance of fiber optic displacement sensor. The graph is following the fingerprint of the fiber displacement sensor. The focused in this study is to get the frequency of the peak voltage in the same tested hydrocarbon concentration. Clearly shown that the peak voltage or the output of fiber sensor is remained constant at 1.5 mm. As a result all the rest of each individual tested hydrocarbon concentration (2 and 24%) were measured by fixing the distance at 1.5 mm. The collected data are presented in Table III and IV for the hydrocarbon solution of 2 and 24% respectively. The measured peak voltage for each individual tested hydrocarbon solution was used to determine the concentration based on

BIDIN et al.: DETERMINATION OF HYDROCARBON LEVEL IN DISTILLED WATER VIA FIBER OPTIC DISPLACEMENT SENSOR

TABLE IV L INEARITY I NDEX OF 24% H YDROCARBON

calibration curve of Fig 4. The linearity index for each individual hydrocarbon was estimated by using Equation (2). Table III and IV show calculation result of linearity index for 2 and 24% of hydrocarbon concentration respectively. It is clearly shown that both linearity indexes are approaching to 1 validating the measurement of fiber optic displacement sensor with respect to hydrocarbon concentration is almost consistence with high repeatability. The linearity index shows the level of confidence of the fiber sensor. The closer the linearity indexes to one the higher confidence level of the fiber sensor. This meant this sensor can be used to measure the hydrocarbon concentration in water with high reproducibility or repeatability. The linear relationship between peak voltage and hydrocarbon concentration and high linearity index of the sensor open opportunity for the fiber optic displacement sensor to be used as environmental device for detecting or monitoring the hydrocarbon level in water.

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[3] N. Bidin, S. Raheleh Hosseinian, W. Nugroho, F. M. Marsin, and J. Zainal, “Hydrocarbon level detection with nanosecond laser ablation,” Laser Phys., vol. 23, pp. 126003-1–126003-6, 2013. [4] D. H. F. Liu and B. G. Liptak, Eds., Groundwater and Surface Water Pollution. Boca Raton, FL, USA: CRC Press, 2000, p. 150. [5] V. Malkov and D. Sievert, “Oil-in-water fluorescence sensor in wastewater and other industrial applications,” Powerplant Chem., vol. 12, no. 3, pp. 144–154, 2010. [6] M. Yasin, S. W. Harun, H. Z. Yang, and H. Ahmad, “Fiber optic displacement sensor for measurement of glucose concentration in distilled water,” Optoelectron. Adv. Mater.-Rapid Commun., vol. 4, no. 8, pp. 1063–1065, 2010. [7] H. A. Rahman et al., “Detection of stain formation on teeth by oral antiseptic solution using fiber optic displacement sensor,” Opt. Lasers Technol., vol. 45, pp. 336–341, Feb. 2013. [8] N. Hida, N. Bidin, M. Abdullah, and M. Yasin, “Fiber optic displacement sensor for honey purity detection in distilled water,” Optoelectron. Adv. Mater.-Rapid Commun., vol. 7, nos. 7–8, pp. 565–568, 2013. [9] M. Abdullah, M. Yasin, and N. Bidin, “Performance of a new bundle fiber sensor of 1000 RF in comparison with 16 RF probe,” IEEE Sensors J., vol. 13, no. 11, pp. 4522–4526, Nov. 2013. [10] H. A. Rahman, S. W. Harun, N. Saidin, M. Yasin, and H. Ahmad, “Fiber optic displacement sensor for temperature measurement,” IEEE Sensors J., vol. 12, no. 5, pp. 1361–1364, May 2012. [11] M. Yasin, S. W. Harun, H. A. Abdul-Rashid, K. Kusminarto, and H. Ahmad, “The performance of a fiber optic displacement sensor for different types of probes and targets,” Laser Phys. Lett., vol. 5, no. 1, pp. 55–58, Jan. 2008. [12] D. H. A. Munap, N. Bidin, S. Islam, M. Abdullah, and F. M. Marsin, “Fiber optic displacement sensor for industrial applications,” IEEE Sensors J., vol. 15, no. 9, pp. 4882–4887, May 2015.

Noriah Bidin received the Ph.D. degree from Universiti Teknologi Malaysia, in 1995, where she is currently the Director and a Full Professor with the Laser Centre, Ibnu Sina Institute for Scientific and Industrial Research, Universiti Teknologi Malaysia. She has over 100 publications with 50 impact factors. Her research interests include laser physics and engineering, nanophotonic, biophotonic, and laser spectroscopy.

IV. C ONCLUSION Fiber optic displacement sensor has been used to determine the level of hydrocarbon in water. The higher concentration of hydrocarbon the lower intensity of light can be detected by the probe due to the optical losses and deviation in refractive index. The refraction beam induced a greater cone angle thus reduced the light to be received by the probe. The displacement sensor produced finger print for each hydrocarbon concentration. The peak voltage is achieved at constant displacement of 1.5 mm. A linear relationship is achieved between the peak voltage and concentration which reliable to stand as a calibration curve. The sensor also provides high degree of linearity index which indicates the high degree of confident level. It is a promising device for monitoring the level of water pollutant in the environmental or in industrial waste management sector. R EFERENCES [1] P. Polygerinos, L. D. Seneviratne, and K. Althoefer, “Modeling of light intensity-modulated fiber-optic displacement sensors,” IEEE Trans. Instrum. Meas., vol. 60, no. 4, pp. 1408–1415, Apr. 2011. [2] P. Fichet, P. Mauchien, J.-F. Wagner, and C. Moulin, “Quantitative elemental determination in water and oil by laser induced breakdown spectroscopy,” Anal. Chim. Acta, vol. 429, no. 2, pp. 269–278, Feb. 2001.

Daing Hanum Farhana Abdul Munap received the B.Sc. degree in pure physics and the M.Sc. degree in physics with a minor in photonic field from Universiti Teknologi Malaysia, in 2013 and 2015, respectively. She is currently pursuing the Ph.D. degree with the Laser Center. She is involved in bundle optical fiber displacement sensor for investigating the hydrocarbon concentration in water.

Mundzir Abdullah received the B.Sc. (Hons.) and Ph.D. degrees from Universiti Teknologi Malaysia, Johor Bahru, Malaysia, in 2013 and 2015, respectively. He is involved in laser matter interaction, including laser surface alloying, a bundle optical fiber displacement sensor, and laser induced breakdown spectroscopy. He has authored over 12 papers with accumulative impact factor more than 12.

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Faridah Mohd Marsin received the B.Sc. degree in industrial chemistry and the M.Sc. degree in chemistry from Universiti Teknologi Malaysia, in 2006 and 2008, respectively, where she is currently pursuing the Ph.D. degree. She is also a Chemist with the Malaysian Chemistry Department. She has experience in analyzing and reporting cases related to drinking water, wastewater, surface water, scheduled waste, and oil spill identification under Environment Quality Act in 1974, and Merchant Shipping Ordinance in 1975.

Nurul Hida Zainuddin received the B.Sc. and master’s degrees in physics from University Teknologi Malaysia, in 2012 and 2014, respectively. She is currently pursuing the Ph.D. degree with University Putra Malaysia, Selangor. Her project during master’s program is dealing with fiber optic displacement sensor to check purity of honey.

Shumaila Islam received the Ph.D. degree from Universiti Teknologi Malaysia, Johor Bahru, Malaysia, in 2015. She has many publications. Her research interests include nanomaterials, and their applications in optoelectronic devices.

Moh Yasin is currently a Senior Lecturer and an Associate Professor with Universitas Airlanggar Surabaya Indonesia. He is the Head of the Optic Laboratory with the Physics Department, Universitas Airlanggar Surabaya Indonesia. He has over 100 publications with 100 impact factors. His research interests include fiber optic displacement sensor.