19 October 2006 Exploiting cross sensitivity: achieving integrated temperature compensation via a dual-element optical oxygen sensor
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Abstract
Temperature compensation is a key issue that must be addressed in almost all sensors and is particularly relevant to chemical sensor systems. Although independent temperature measurement coupled with temperature calibration of the chemical sensor can be employed to address this issue, the difficulty of accurate temperature measurement of the sensor material remains a problem. We report here a novel solution to this issue and prove the principle in the context of optical oxygen sensing. The measurement technique involves the use of two temperature-calibrated, fluorescence based oxygen sensors that display different sensitivities to oxygen. The mathematical representation of this dual-element sensor results in a system of two equations that can be solved for both oxygen concentration and temperature. A numerical technique based on successive approximation has been developed that allows the use of non-linear calibration equations, which accurately describe the responses of the sensor membranes used and, therefore, yield accurate values for oxygen concentration and temperature. The oxygen sensitive membranes in question consist of the oxygen-sensitive, fluorescent ruthenium complex, [Ru(II)- tris(4,7-diphenyl-1,10-phenanthroline)]2+, (Ru(dpp)3 2+), immobilised in a porous sol-gel matrix. Sol-gel matrices that were derived from different precursors were used to yield membranes with different sensitivities. 3D calibration surfaces were generated for both sensor membranes using a temperature-controlled flow cell, yielding calibration equations with R2 values of > 0.9999 in both cases. This provides the system with a high degree of baseline accuracy. The principle of operation of the system has been verified experimentally. This has significant implications for the development of optical sensors, as the use of such a technique obviates the need for separate temperature measurement devices such as thermistors or thermocouples. While the technique has been demonstrated here using phase fluorometric oxygen sensors, it is applicable to a broad range of measurement situations,
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John P. Moore, Clare Higgins, Orla McGaughey, Brian G. Lawless, Brian D. MacCraith, "Exploiting cross sensitivity: achieving integrated temperature compensation via a dual-element optical oxygen sensor", Proc. SPIE 6377, Advanced Environmental, Chemical, and Biological Sensing Technologies IV, 63770I (19 October 2006); doi: 10.1117/12.718682; https://doi.org/10.1117/12.718682
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