Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 168 (2016) 359 – 362 30th Eurosensors Conference, EUROSENSORS 2016 NDIR Ethanol Gas Sensor with Two Elliptical Optical Structures JinHo Kima, KeunHeon Leeb, SeungHwan Yia* a KNUT(Korea National University of Transportation), 50 DaeHakRo, Chungjushi, Chungbuk 27469, Repulic of Korea b Humas Co.,59-6 Jang-Dong, YuSeong-Gu, DaeJeon 34113, Repulic of Korea Abstract A unique elliptical structure is designed and prototyped for a nondispersive infrared (NDIR) ethanol gas sensor A temperature compensation method is also derived for this structure, in this study The initial output voltages of the ethanol, reference IR, and temperature sensors show linear temperature dependencies, and the variations are less than േ mV, േ mV, and േ 2%, respectively The estimated ethanol concentrations show high accuracies, with less than േ5% error, in the temperature range from 253 K to 333 K © Published by Elsevier Ltd This ©2016 2016The TheAuthors Authors Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference Keywords: NDIR gas sensor; ethanol sensor; elliptical structure; blackbody IR source; temperature compensation Introduction Ethanol gas detection is very important for screening potential disasters in industries, and for preventing traffic accidents caused by intoxicated drivers Breathalyzers have been used in vehicles for the past three decades to prevent casualties from car crashes The breathalyzer used in automobiles for screening driving while intoxicated (DWI) consists of several main components such as the ethanol sensor, microcontroller, and memories for registering the conditions of the driver and the vehicle operation Currently, the concentration of exhaled ethanol is measured using an electrochemical sensor [1]; however, it requires frequent calibration and high power is required to heat up the sensor surface to activate the sensor Due to these disadvantages, and the lack of long-term stability and reliability, the National Highway Traffic Safety Administration (NHTSA) has requested a new and robust design for the breathalyzer Two alternatives have been under research for almost ten years A promising candidate for the ethanol sensor is the NDIR-type sensor for measuring the target gas L Lindberg et al [2] reported the first NDIR * Corresponding author Tel.: +82-43-841-5129; fax: +82-43-841-5120 E-mail address: isaac_yi@ut.ac.kr 1877-7058 © 2016 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference doi:10.1016/j.proeng.2016.11.122 360 JinHo Kim et al / Procedia Engineering 168 (2016) 359 – 362 ethanol sensor for screening DWI Another group revealed the concept and initial results of a unique NDIR ethanol sensor, which has two ellipses for optical waveguides [3, 4] The previous results of ethanol sensor show that the sensitivity and accuracy are slightly lower that the expected values due to the amplification of noise components [4] Therefore, in order to enhance the sensitivity and accuracy, a pre-amplified thermopile signal obtained from an application-specific integrated circuit (ASIC) chip packaged in the same housing has been used for further signal conditioning in this research This paper also describes the temperature dependencies of the ethanol sensor (which has two ellipses), and the temperature-compensation methods, in order to present the possibilities of the new breathalyzer applications Sensor fabrication and experimental setup Recent researches on the NDIR gas sensors have focused on their unique optical structures and on gases that have large absorption wavelengths, in order to increase the sensitivity and to make the sensor more compact [5, 6] However, the radiated energy at large wavelengths (for ethylene, ethanol, etc.,) is very small compared to the energy at the peak wavelength of the infrared (IR) source Therefore, high sensitivity can be achieved by implementing optical lenses or by designing circuitry to enhance the signal-to-noise ratio In addition, the unique optical structure can magnify the energy density of the IR light in the detector without any additional component Figure shows the results of a simulation based on the unique optical structure and the prototype sensor proposed in this study The IR lights from the common focal point (A) of the two ellipses were reflected once from the surface of the spheroid formed by the two ellipses They were finally focused on the detector areas (on the left sides of the ellipses: B, C) as shown in Fig (a) [3] The optical structure and the prototype ethanol sensor are shown in Fig (b), and they are based on the simulation results presented in Fig (a) In order to achieve reliable results from the ethanol sensor (as functions of temperature), the prototype sensor has two IR sensors—one is for ethanol detection and the other is for the measurement of the condition of optical structure They have an ASIC chip for amplifying the thermopile output and measuring the ambient temperature A blackbody IR source is placed at the common focal point (on the right side in Fig 1(b)) a b Fig Proposed optical structure and prototype sensor: (a) Simulation result of optical structure, (b) Photo of prototyped ethanol sensor After implementing the basic algorithm in the microcontroller unit (MCU), the sensor was installed in the gas measurement system as described in a previous article [4] Then, the temperature of the gas measurement system was changed from 253 K to 333 K in steps of 20 K After stabilizing the temperature and the initial ethanol concentration, the dry ethanol gas was injected into the gas chamber by manipulating the mass flow controller The prototype sensor downloaded the information over an RS485 link into the computer to analyze the outputs of the sensors—ethanol, reference IR (with a center wavelength of 3.91 um), and temperature Results and discussions Figure shows the output voltages of the prototype ethanol sensor at nearly 0-ppm ethanol gas concentration The output voltages of the three sensors show linear temperature dependencies with high coefficient of 361 JinHo Kim et al / Procedia Engineering 168 (2016) 359 – 362 determination, R2 > 0.983 Because the applied voltage remains almost constant, the energy radiated from the IR source, ܫ will decrease when the ambient temperature increases as described in equation (1) However, as can be seen in Fig 2, the output voltages of the ethanol and reference IR sensors increase linearly These results might be due to the shifts in the center wavelengths of the narrow bandpass filters used in the thermopile detectors [7], which cause an enhancement of the radiation energy density on the thermopile detectors as the ambient temperature increases ସ ସ െ ܶǤ ሻ (1) ܫ ൌ ߪ ή ሺܶ where ɐ is the Stefan–Boltzmann constant, ܶ is the blackbody temperature, and ܶǤ is the ambient temperature Fig Output voltages of ethanol, reference IR, and temperature sensors as a function of temperature @ ppm ethanol gas Fig Temperature dependency of output voltage of ethanol gas sensor as a function of ethanol concentration from to 1000 ppm The output voltages of the ethanol gas sensor in the temperature range from 253 K to 333 K are shown in Fig as functions of the ethanol concentration The output voltages of the ethanol sensor fit well in the following equation (2): (2) ܸ௨௧ ൌ ܸ ݔ݁ כሺെܾݔሻ where ܸ is the output voltage at ppm [V], is the gas absorption coefficient [1/ppm], and ݔis the ethanol concentration [ppm] Because the output voltage of the ethanol sensor increases with the temperature increment, the parameters that are affected by the temperature variations are analyzed based on the above results; the derived parameters are shown in Fig The initial output voltageܸ presented high linearity with the temperature variation, with R2 = 0.996 The gas absorption coefficients followed the second-order polynomial functions with R2 = 0.949 From equation (2) and the temperature-dependent parameters, the estimated concentrations of the prototype ethanol sensor can be calculated by the following equation: ݔሺ݉ሻ ൌ െ ೇ ቀ ೠ ቁ ೇబ ൌെ ሺሻ (3) The numerator in equation (3) can be described by the standard series given below in equation (4) [8], and finally, the estimated ethanol concentration can be calculated using equation (5) ݈ ݊ሺܽሻ ൌ ʹ ቀ ିଵ ାଵ ଵ ିଵ ଶ ଵ ିଵ ସ ଵ ିଵ ଷ ାଵ ଷ ାଵ ଷ ାଵ ቁ ή ͳ ቀ ଶ ିଵ ݔሺ݉ሻ ൌ െ ቀ ାଵ ቁ ቀ ቁ ቀ ቁ ڮ൨ ଵ ିଵ ଶ ଵ ିଵ ସ ଵ ିଵ ଷ ାଵ ଷ ାଵ ଷ ାଵ ቁ ή ͳ ቀ ቁ ቀ ቁ ቀ ቁ ڮ൨ (4) (5) Because the initial output voltages of the ethanol sensor at 0-ppm ethanol reveal a high linear dependency on the ambient temperature in this elliptical structure, ܸ can be easily predicted by the calculation of ambient temperature from the output voltage of the temperature sensor described in Fig Moreover, the ethanol absorption coefficients are given by the second-order polynomial as functions of ambient temperature; therefore, their relationships can be 362 JinHo Kim et al / Procedia Engineering 168 (2016) 359 – 362 also programmed in the MCU Therefore, the estimated ethanol concentration can be accurately predicted using equation (5) with precise measurement of the initial output voltage of the ethanol sensor and estimation of the temperature-dependent ethanol absorption coefficients as shown in Fig (b) The temperature variations are less than േ2% from the target temperatures, and the output voltages of the reference IR sensor are almost constant at the designated temperatures with less than േ2-mV variations The standard deviations of the output voltages of the ethanol sensor are calculated to be less than േ2 mV throughout the experiments in the temperature range from 253 K to 333 K a b Fig Temperature dependency of parameters: a) initial output voltage, b) gas absorption coefficient Fig Temperature dependency of parameters: a) initial output voltage, b) gas absorption coefficients From equation (5) and the temperature-dependent parameters, the ethanol concentrations are predicted with high accuracies and with less than േ5% error in the temperature range from 253 K to 333 K Conclusions A unique elliptical structure was modeled and prototyped for NDIR ethanol gas measurement, in this research By using temperature-dependent parameters and governing equations based on gas concentrations, the ethanol gas concentration was accurately estimated with less than േ5% error in the temperature range from 253 K to 333 K The prototyped sensor and temperature-compensation algorithm can be used in other gas-monitoring systems also Acknowledgements This research was supported by R&D Center for Green Patrol Technologies through the R&D for Global Top Environmental Technologies funded by Ministry of Environment, Republic of Korea (MOE) References [1] S Edna, S David, An analysis of ethanol breath tests results with portable and desktop breath testers as surrogates of blood ethanol levels, Accident Analysis and Prevention 43 (2011) 2188-2194 [2] L Lindberg, S Brauer, P Wollmer, L Goldberg, A.W.Jones, and S.G Olsson, Breath ethanol concentration determined with a new analyzer using free exhalation predicts almost precisely the arterial blood ethanol concentration, Forensic Science International 168 (2007) 200-207 [3] S.H Jang, S.H Chung, S.H Yi, Characteristics of an optical waveguide with two identical elliptical structures, Journal of Korean Institute of Gas 18 (2014) 48-54 [4] S.H Yi, J.H Kim, B.D Kang, J.M Ihn, Characteristics of NDIR ethanol sensor with elliptical optical structures, Journal of Auto-Vehicle Safety Association (2015), 39-43 [5] L Jun, T Qiulin, Z Wendong, X Chenyang, G Tao, X.Jijun, Miniature low-power IR monitor for methane detection, Measurement 44 (2011) 823-831 [6] A Sklorz, S Janben, W Lang, Detection limit improvement for NDIR ethylene gas detectors using passive approaches, Sensors and Actuators B: Chemical 175 (2012) 246-254 [7] S Kim and C K Hwangbo, Derivation of the center-wavelength shift of narrow-bandpass filter under temperature change, Optics Express 12 (2004) 5634-5639 [8] Jan J Tuma, Ronald A Walsh, Engineering Mathematics Handbook, fourth ed., McGraw-Hill, New York, 1998, pp.118 ... optical waveguide with two identical elliptical structures, Journal of Korean Institute of Gas 18 (2014) 48-54 [4] S.H Yi, J.H Kim, B.D Kang, J.M Ihn, Characteristics of NDIR ethanol sensor with. .. voltages of ethanol, reference IR, and temperature sensors as a function of temperature @ ppm ethanol gas Fig Temperature dependency of output voltage of ethanol gas sensor as a function of ethanol. .. 168 (2016) 359 – 362 ethanol sensor for screening DWI Another group revealed the concept and initial results of a unique NDIR ethanol sensor, which has two ellipses for optical waveguides [3,