Refractometric Fiber Optic Sensor for Detecting Salinity of Water

Supriya S. Patil, Arvind D. Shaligram

Department of Electronic Science, Abasaheb Garware College, Pune, India.
Department of Electronic Science, University of Pune, Pune, India.

DOI: 10.4236/jst.2013.33012                

Abstract

Salinity is an important property of industrial and natural waters. It is defined as the measure of the mass of dissolved salts in a given mass of solution. High salinity has an impact on people and industries reliant on water. High levels of salt can reduce crop yields, limit the choice of crops that can be grown and, at higher concentrations over long periods, can kill trees and make the land unsuitable for agricultural purposes. Salinity increases the “hardness” of water, which can mean more soap and detergents have to be used or water softeners installed and maintained. This can also cause scaling in pipes and heaters. The experimental determination of the salt content by drying and weighing presents some difficulties due to the loss of some components. The only reliable way to determine the true or absolute salinity of natural water is to make a complete chemical analysis. However, the method is time consuming and cannot yield the precision necessity for accurate work. Thus to determine salinity, one normally used method involves the measurement of a physical property such as conductivity, density or refractive index. The paper reports the refractometric fiber optic sensor for detection of salinity of water. The mathematical model is developed for detection of the refractive index of liquid and simulated in MATLAB. The fiber optic sensor probe is developed to measure the refractive index of the solution containing different amount of salt dissolved in water i.e. different molar concentrations. Experiments are carried out using the developed probe for these solutions. Experimental results are showing good agreement with the simulated results.

Keywords

Fiber Optic Chemical Sensor; Hardness of Water; Refractometry; Retro-Reflective Type Fiber Optic Sensor; Salinity of Water

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Z. J. Min, J. P. Li and S. H. Jiang, “Measurement of Salt Salinity in Solar Pond by Supersonic Method,” Acta Eneglae Solaris Sinica, Vol. 16, No. 2, 1995, pp. 224-228.
[2]	F. B. Diniz, K. C. S. de Freitas and W. M. de Azevedo, “Salinity Measurements with Polyaniline Matrix Coated Wire Electrodes,” Electrochemistry Communications, Vol. 1, No. 7, 1999, pp. 271-273. doi:10.1016/S1388-2481(99)00057-0
[3]	H. Minato, Y. Kakui, A. Nishimoto and M. Nanjo, “Remote Refractive Index Difference Meter for Salinity Sensor,” IEEE Transactions on Instrumentation and Meas- urement, Vol. 38, No. 2, 1989, pp. 608-612. doi:10.1109/19.192359
[4]	Y. Zhao and Y. B. Liao, “Novel Optical Fiber Sensor for Simultaneous Measurement of Temperature and Salinity,” Sensors and Actuators B: Chemical, Vol. 86, No. 1, 2002, pp. 63-67. doi:10.1016/S0925-4005(02)00148-X
[5]	B. A. Brice and M. Hawler, “A Differential Refractometer,” Journal of the Optical Society of American, Vol. 41, No. 12, 1951, pp. 1033-1037. doi:10.1364/JOSA.41.001033
[6]	E. M. Stanley, “The Refractive Index of Seawater as a Function of Temperature, Pressure and Two Wavelengths,” Deep Sea Research and Oceanographic Abstracts, Vol. 18, No. 8, 1971, pp. 833-840.
[7]	O. Esteban, M. Cruz-Navarrete, A. González-Cano and E. Bernabeu, “Measurement of the Degree of Salinity of Water with a Fiber-Optic Sensor,” Applied Optics, Vol. 38, No. 25, 1999, pp. 5267-5271. doi:10.1364/AO.38.005267
[8]	J. Cong, X. M. Zhang, K. S. Chen and J. Xu, “Fiber Optic Bragg Grating Sensor Based on Hydrogels for Measuring Salinity,” Sensors and Actuators B: Chemical, Vol. 87, No. 3, 2002, pp. 487-490. doi:10.1016/S0925-4005(02)00289-7
[9]	A. L. Chaudhari and A. D. Shaligram, “Multi-Wavelength Optical Fiber Liquid Refractometry Based on Intensity Modulation,” Sensors and Actuators A: Physical, Vol. 100, No. 2-3, 2002, pp. 160-164.
[10]	S. S. Patil and A. D. Shaligram, “Modeling and Experimental Studies on Retro-Reflective Fiber Optic Micro-Displacement Sensor with Variable Geometrical Properties,” Sensors and Actuators A: Physical, Vol. 172, No. 2, 2011, pp. 428-433. doi:10.1016/j.sna.2011.10.006