The Research Of Optic Fiber Flow-sensor Based On The Michelson Interferometer

With the development of modern flow measurement, the increasing demandsrelated to many factors, such as measuring accuracy, reliability, dynamic range, andapplication environment, especially for high temperature, high pressure oil down-holeflow measurement. It is urgent to propose reliable measuring technology using onthese environment. The remarkable characteristics of fiber optic flow sensors are highaccuracy, high sensitivity, high temperature, high pressure, anti-electromagneticinterference, so fiber optic flow sensors arise widespread concern in the field oflogging.This thesis proposed a pressure-differential fiber flow sensing method for oildown-hole flow measurement, combining flow rate differential pressure with opticalinterferometry to achieve the accurate measurement of fluid flow. We studied the theoryof sensing method, optical structure, signal demodulation, and carried on experimentalstudies. Theoretical and experimental studies have shown that the method can achieveaccurate measurement of flow. Based on the sensor head package structure design, it is agood way to meet the environmental requirements of the oil down-hole flowmeasurement. The main work of the thesis is as follows:1.We proposed a optical flow sensing method that combining the flow ratedifferential pressure with Michelson interferometer structure, constructed a theoreticalmodel of the pressure differential interferometric fiber-optic flow sensor, and carried outa double optical path interference and interference signal demodulation simulationanalysis, the reliable conclusion laid the foundation for the system design.2. Using the control of the polarization of light with a Faraday rotator to control thepolarization random signal fading. By using polarization controller and inserting theFaraday rotator into the end of the Michelson interferometer, it can eliminate thepolarization fading effectively.3. We carried out experiments of phase demodulation method of interferometricfiber-optic flow sensors. On the one hand, by using the carrier generation phasemodulation (PGC) random phase signal fading to eliminate the random signal phase demodulation effectively. On the other hand, we adopt dual optical interferometerclosed-loop compensation to realize the DC signal phase demodulation.4. We took on the design and production of high-temperature, high-pressurepressure-sensitive sensor head. In order to realize the modulation on optical phase ofpressure, we combined the pressure sensitive diaphragm with light space coupling, andenforced sensing light path of the closed package, so the technology can be spread to thehigh-temperature, high-pressure test environment.5. We compiled the software modules of PGC based on the carrier phase, promotedexperiments of flow tests, verified the high-sensitivity measurement of the flow ratedifferential pressure combined with the light phase demodulation by theoretical analysisand experiments.