Research On The Key Technology Of All Optical Fiber Current Sensor With Large Dynamic Range And High Precision

The all-fiber optical current sensor(AFOCS)is a current detection device based on the Faraday effect,which eliminates magnetic saturation.It has wide frequency response range and fast response to faults.However,the application process is slow due to the small dynamic range and temperature-affecting effects.This thesis aims to study high-precision,large dynamic range AFOCS to improve its measuring range and reduce temperature sensitivity.Firstly,this thesis proposes an online reflection AFOCS scheme with dead zone compensation and establishes the light wave evolution model.The principle of dead-zone compensation by superimposing bias voltage before stepped wave formation is analyzed,which ensures the detection precision at low current.An asymmetric square wave modulation closedloop demodulation algorithm is proposed,which extends the dynamic range,eliminates the influence of the light source intensity and error coefficient,and ensures the stability of operation.Then,the influence of temperature on AFOCS is analyzed,and a temperature compensation method to change the initial phase delay angle of 1/4 wave plate is proposed.Theoretical and experimental results show that the effect is obvious when the delay angle is about 101°.The integrated temperature sensor compensation scheme and the polarization interference optical temperature sensor(PI-OTS)are proposed.The real-time temperature compensation based on the measured temperature can ensure the precision within the specified temperature range.Then,this thesis integrates PI-OTS and AFOCS,and designs a AFOCS system with large dynamic range and high precision.The system hardware circuit is analyzed and designed,including light source drive,control,monitoring and signal acquisition.The system software is analyzed and designed,including the signal acquisition and demodulation,temperature compensation,light source power closed-loop control,data access and display,etc.Finally,the prototype of PI-OTS has been developed and passed the performance test of Jiangsu Metrology Institute.The results show that the PI-OTS's resolution reaches 0.01?,and the precision reaches ±0.1?.The prototype of the AFOCS based on PI-OTS was developed.The precision,dynamic measurement range and temperature characteristics were tested and results show that the differential of AFOCS within the temperature range of-40? ~ 70? fluctuates within ±0.2%,and the prototype meets the requirements for accurate level limits of 0.2s for measurement and 5P30 for protection.