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Proceedings Paper

Quasi-distributed pH sensor
Author(s): Nicholas J. Elliott; Peter A. Wallace; Mahesh Uttamlal; Sheila Smith; Michael Campbell
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Paper Abstract

A Quasi-distributed pH sensing system based on Optical Time Domain Reflectometry (OTDR) was developed to determine the spatial and intensity information from fluorescence signals coupled back into a single fiber. The evanescent wave due to a 488 nm light pulse from a N2 pumped dye laser was used to excite a pH sensitive fluorophore and the emission around 515 nm was detected. A 3dB Y-coupler was used to convey excitation light to the sensing sites and to deliver emission signals from these sites back to a filtered photomultiplier tube. Data collection was performed using a HP 54540A 500 MHz digital scope and analysis was carried out using a dedicated Pentium 166 MHz PC. A reproducible laboratory fabrication process was developed to produce sensing sites at discrete intervals along the length of the fiber. A polishing process carefully removed the cladding at each sensing site and photo- polymerization was then used to covalently bind the fluorophore fluorescein with a co-polymer directly onto the site. The results show the sensors performance over a range of pH4-pH10 with a pKa value of 6.3. The present system was chosen to have sites 10 m apart, however, based on the propagation rate of 5 ns m-1 for light in the fiber and 10 ns for the fluorescence lifetime, a resolution of approximately 1 m is possible.

Paper Details

Date Published: 9 December 1999
PDF: 7 pages
Proc. SPIE 3860, Fiber Optic Sensor Technology and Applications, (9 December 1999); doi: 10.1117/12.372992
Show Author Affiliations
Nicholas J. Elliott, Glasgow Caledonian Univ. (United Kingdom)
Peter A. Wallace, Glasgow Caledonian Univ. (United Kingdom)
Mahesh Uttamlal, Glasgow Caledonian Univ. (United Kingdom)
Sheila Smith, Glasgow Caledonian Univ. (United Kingdom)
Michael Campbell, Glasgow Caledonian Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 3860:
Fiber Optic Sensor Technology and Applications
Michael A. Marcus; Brian Culshaw, Editor(s)

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