Research On SF₆ Gas Humidity Sensor Based On Optic Fiber Micro-Bubble

Sulfur hexafluoride gas is now widely used as an important insulation and interrupting medium in high-voltage electrical equipment,and its relative humidity,as an important operating parameter,urgently needs a monitoring method that meets the requirements of continuous online monitoring and is safe and reliable.Therefore,there is important theoretical and practical significance to research and develop fiber optic gas humidity sensors that can be applied to the field of low humidity measurement with high sensitivity,good linearity and reusability.The main research of this thesis is as follows.（1）The establishment of the multi-beam interference mathematical model based on the Fabry-Pérot interference principle and the analysis of the sensing mechanism of humidity-sensitive membranes This thesis analyzes the basic principle of Fabry-Pérot interferometer;establishes the multi-beam interference mathematical model based on the structural parameters of fiber optic microcavity gas humidity sensor;describes the relevant properties of humidity sensitive materials and analyzes the humidity sensitive mechanism under the adsorption theory and compound refractive index theory of humidity-sensitive film.（2）Mathematical modeling and numerical simulation analysis of fiber optic micro-cavity gas humidity sensor.The paper establishes the equivalent mathematical model under the humidity environment by using the finite element method analysis,verifies the rationality of the mathematical model by simulation,and analyzes the effect of the variation of the structural parameters of the fiber micro-cavity gas humidity sensor on the interference spectrum,which provides theoretical guidance for the preparation of the humidity sensor prototype.（3）Fiber optic microcavity structure and preparation of the humidity-sensitive film.The structural design parameters were determined based on the simulation analysis results,and the preparation scheme with high controllability,good reproducibility,and relatively low fabrication cost was analyzed and selected through trial fabrication;the preparation of the humidity-sensitive film was completed by dipping and evaporation method,and the spectral differences before and after coating were compared based on the spectral analysis method and observed by optical microscopy.（4）Experiment and analysis.Firstly,a humidity environment simulation device was designed and a wavelength-modulated humidity sensing experimental system was built.Humidity and temperature response characteristics experiments were conducted respectively,and the experimental results showed that the humidity sensitivity of the sensor was 86pm/%RH when working under 0～30%RH,with high sensitivity performance at low humidity,good linearity at low humidity,good reusability and stability.The sensor also has a low and stable temperature sensitivity,which makes it possible to solve the temperature and humidity cross-sensitivity problem by temperature compensation.The sensor has a simple structure,small size,low cost,and good stability,especially in the low humidity range presents good sensitivity and linearity,which meets the demand for low humidity detection of SF₆ gas and has the potential to offer feasible solution support in online monitoring technology and fault warning of operating parameters of high-voltage electrical equipment,and providing certain methods and experience for the design of such sensors in the future.