Development And Application Research Of High Sensitivity Temperature And Pressure Sensing System

In recent years,optical fiber sensing systems have received more and more attention.Compared with traditional electrical sensing systems,optical fiber sensing systems have strong electromagnetic interference resistance,small size,light weight,good mechanical properties.Changes in external conditions such as temperature,pressure,refractive index and vibration are more sensitive.In this thesis,the Fabry-Perot temperature sensor,pressure sensor and the fiber grating humidity sensor are used to replace the original electrical sensor.The experimental results show that the optical sensor has better sensitivity,accuracy and faster response time than electrical sensors.The main contents of this thesis mainly include the following parts:The preparation and packaging methods of the fiber optic temperature and humidity sensor were demonstrated,and the characteristics of the sensor were measured experimentally.Based on femtosecond laser processing technique,a 50?m×70?m microcavity was etched on the fiber end face,and Fabry-Perot cavity is formed by arc discharge technology for temperature sensing,and then a high thermal coefficient epoxy resin is injected to the Fabry-Perot cavity by using a needle tube.The outermost part adopts metal tube to package,and the tail fiber adopts armored optical fiber to package.The influence of the microcavity size and the loss in the manufacturing process on the reflectance spectrum was analyzed theoretically.The sensitivity of the probe measured by the experiment could reach 390pm/?;the humidity sensing probe is coated with a polyvinyl alcohol(PVA)film in the Bragg fiber grating area through dip coating method.The outermost part adopts open-hole metal tube to package,and the tail fiber also adopts armored optical fiber to package.The packaged optic fiber temperature and humidity sensor is applied to the measurement of the flue gas,and the measurement result show that the optic fiber sensor has higher sensitivity and faster response time than the conventional electric sensor.The preparation of fiber-optic bubble sensor based on optical Vernier effect was fabricated,and the sensing characteristics of the sensor were measured experimentally.Using arc discharge technology,the single-mode optical fiber and silica capillary tube(SCT)are spliced together,and then the electrode is placed at a distance of 180?m from the fusion point,and a small bubble is formed at the end,adjusting the position of the electrode gradually to the end and make the bubbles bigger and bigger to form a Fabry-Perot air chamber,then a femtosecond laser is used to write a reflection surface directly in the single-mode optical fiber at a distance of 81 ?m from the left wall of the air cavity to realize the optical Vernier effect.The influence of the different cavity length ratios of the two Fabry-Perot chambers on the envelope period is theoretically analyzed.The experimental pressure sensitivity of the sensor with the Vernier effect by the could reach 3.97nm/Mpa,the temperature sensitivity is 109pm/°C.A portable fiber optic sensor analysis machine was designed and assembled.The temperature sensor,the humidity sensor and the pressure sensor are integrated with industrial microcomputer and fiber Bragg grating demodulator.The device enables in-situ monitoring of parameters in a variety of test environments.In terms of hardware,the 3D drawing software Solidworks is mainly used to design the outer shell of the microcomputer and the demodulator,and then the assembly parts are assembled and assembled using the 3D printer.In terms of software,use Labview for initialization of FBG demodulator and calculation of measurement parameters.Eight channels can be used simultaneously and the corresponding parameters of the current environment can be displayed in real time.