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A Fiber-Optic Sensor Using an Aqueous Solution of Sodium Chloride to Measure Temperature and Water Level Simultaneously
Wook Jae Yoo, 1 Hyeok In Sim, 1 Sang Hun Shin 1 , Kyoung Won Jang, 1 Seunghyun Cho 2 , Joo Hyun Moon 3 , Bongsoo Lee 1
1  School of Biomedical Engineering, College of Biomedical & Health Science, BK21 Plus Research Institute of Biomedical Engineering, Konkuk University, 268 Chungwon-daero, Chungju-si, Chungcheongbuk-do 380-701, Korea; s:(W.J.Y.);(H.I.S.);(S.H.S.);(K.W.J.)
2  Department of Organic Materials & Fiber Engineering, College of Engineering, Soongsil University, 369 Sangdo-ro, Dongjak-gu, Seoul-si 156-743, Korea
3  Department of Nuclear & Energy System Engineering, College of Natural Science, Dongguk University-Gyeongju, 123 Dongdae-ro, Gyeongju-si, Gyeongsangbuk-do 780-714, Korea

Published: 10 October 2014 by MDPI in Sensors
MDPI, Volume 14; 10.3390/s141018823
Abstract: A fiber-optic sensor system using a multiplexed array of sensing probes based on an aqueous solution of sodium chloride (NaCl solution) and an optical time-domain reflectometer (OTDR) for simultaneous measurement of temperature and water level is proposed. By changing the temperature, the refractive index of the NaCl solution is varied and Fresnel reflection arising at the interface between the distal end of optical fiber and the NaCl solution is then also changed. We measured the modified optical power of the light reflected from the sensing probe using a portable OTDR device and also obtained the relationship between the temperature of water and the optical power. In this study, the water level was simply determined by measuring the signal difference of the optical power due to the temperature difference of individual sensing probes placed inside and outside of the water. In conclusion, we demonstrate that the temperature and water level can be obtained simultaneously by measuring optical powers of light reflected from sensing probes based on the NaCl solution. It is anticipated that the proposed fiber-optic sensor system makes it possible to remotely monitor the real-time change of temperature and water level of the spent fuel pool during a loss of power accident.
Keywords: temperature, OTDR, Water level, fiber-optic sensor, Nacl Solution
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