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For the problems of light source fluctuation noises, zero drift and other problems of H 2 S gas concentration sensor in optic-fiber evanescent-wave absorption spectroscopy, double-light-path absorption system was designed to theoretically analyze the relationship between evanescent-wave power and gas concentration as well as detection sensitivity. Moreover, the relationship between evanescent-wave power and optical-fiber residual diameter in the optic fiber corrosion process was also studied. The sensing probes with different evanescent-wave power ratios were used to detect experiments of H2S gas concentration. The experimental results show that the sensitivity is up to 0.169 μw/ppm when the evanescent-wave power ratio of sensing probe is 10%, detected minimum H 2 S gas concentration is 5.1 ppm, the detection repeatability is good and the response time is only 2.03s. Due to low production cost, high sensitivity and short response time, the optic-fiber evanescent-wave sensor can be used for real-time on-line measurement of H 2 S gas in the area of the hydrocarbon exploration and development. [ABSTRACT FROM AUTHOR]

Abstract: An optical fiber gas sensor using hollow-core photonic bandgap fiber as a gas cell is proposed to detect H2S mixed with natural gas. This sensor is advantageous for eliminating instability of light source, impact of thermal zero drift, and zero shift of photoelectric device. The gas sensing probe of configuration is using two shorter pieces of hollow-core photonic bandgap fiber (HC-PBF) with the same overall length instead of one long piece of HC-PBF to improve the system response. The experimental dates indicate that a minimum detectivity of 10ppm for the system configuration was estimated. [Copyright &y& Elsevier]