Research On Dual-parameter Emodulation Technology Of Temperature And Pressure In Compound Fabry-Perot Cavity

Fiber-optic Fabry-Perot(FP)cavity sensor is a new type sensor that emerged with the development of fiber-optic technologies,with high sensitivity,small size and good stability,so it is widely used in industrial production,mineral extraction,aerospace and other fields for temperature and pressure measurements.Conventional fiber-optic FP sensors can only achieve a single physical measurement of temperature or pressure.However,the pressure measurement in high-temperature environments can lead to obviously deviations because of the pressure-temperature cross-sensitivity.In order to achieve accurate pressure measurement in high-temperature environments,this thesis uses a composite FP cavity structure for the simultaneous measurement of temperature and pressure,and a composite FP cavity sensor demodulation technology for simultaneous temperature and pressure measurements was studied.The main research contents are as below.Firstly,from the interference principle of FP cavity,the interferometric mathematical models of fiber optic FP sensors with single and composite cavities,the relationship between the cavity length and the phase of the interference spectrum are derived.And the variation characteristics of the output interferometric spectra of single and composite cavity sensors with different end-face reflectance and different cavity lengths are studied.The principles of typical fiber-optic FP sensing demodulation schemes are introduced,and error analysis for each demodulation scheme is presented.Then,the composite FP cavity sensing demodulation system is designed and built,which mainly includes the optical path part,the circuit part and the software part.The optical path part mainly includes the use of a modular SLD to irradiate the sensor,and a miniature spectrometer module to collect the interference spectrum reflected from the sensor for demodulation.The circuit part mainly includes the constant current and constant temperature driving circuit of the SLD,the signal processing control circuit to complete the driving of the miniature spectrometer module,the A/D sampling processing of the spectral signal,and the demodulation circuit using FPGA as the control chip to complete the demodulation processing of the interferometric spectral signal to realize the cavity length measurement of the sensor.Finally,the circuit and software design of the demodulation system that completed the design development.were tested,mainly including the driver test of the spectrometer,the A/D sampling circuit driver test and the overall test of the system.The experimental validation platform was built,and the pressure and temperature validation tests were conducted for the demodulation system at 600? and 700KPa?and the pressure sensitivity of the air cavity of the sensor at 700KPa was obtained as-0.296nm/KPa,and the temperature sensitivity of the basal cavity was 0.28nm/?,and the relationship between the pressure value and the cavity lengths of the basal and air cavities after completing the temperature compensation correction was given.