Research On The Demodulation Sytem Of Fiber Bragg Grating Used In The Measurement Of Viscosity

The project is supported by State Key Laboratory of Precision Measuring Technology and Instruments and CNOOC Energy Development Company Limited. The main aim of the research is combining the Fiber Bragg Grating sensor technology with solution viscosity measurement and studying the torsional solution viscosity measurement method based on FBG.Fiber Grating sensor is a new kind of optical passive component.It has many physical merits,such as small size/strong anti interference capability and so on. The paper advanced and accomplished a set of FBG demodulation system which can be used in viscosity testing. The feasibility of the system is approved by experiments.The main work of the project is as follows:1.The characteristics of Fiber Grating sensor/application situation and common demodulation technology is introduced. The sensing mechanism of FBG is derivied with the coupled mode theory and some solutions which can be used to eliminating the cross-sensitive phenomenon is summaried.2.The torsional vibration sensitive structure of FBG based on equal strengthbeam is designed and the cross sensitivity problems in the measurement process is solved by the method of reference Fiber Bragg Grating.3.Based on the edge filter demodulation technology and the long period grating, an experimental system is built up to achieve the signal of FBG which was used to detecting the viscosity. The system can achieve linear demodulation with a bandwith of 3.59nm, an demodulation sentivity of 0.097 nm -1, an wavelength resolution of 0.01nm and an demodulation error of 0.004nm.The system also can detect low frequency vibration signal.4.In order to reduce the effect of temperature on LPG, a scheme for the compen-sation of its drift is designed. With packaging technology, the diift coefficient decreasefrom 115pm/℃to 36pm/℃, so the stability of the system is improved.5.With the system, the signal which can achieve the torsional vibration amplitude of the head is demodulated. The experiments prove that the system is suitable for the viscosity detection based on FBG.