The Digital Closed-loop Detection Technology Of Sagnac Optic-fiber Interferometer

Sagnac optic-fiber interferometer has a wide range of applications in measuring angular velocity and current.It mainly has two signal processing schemes,one is open-loop detecting scheme and the other is closed-loop detecting scheme.In contrast to the open-loop detecting scheme,the closed-loop detecting scheme has a greater dynamic range and better linearity of the scaling factor.The closed-loop system structure is simpler and more conducive to the system miniaturization,engineering and mass production.This thesis is concentrate on the research of digital closed-loop detection technology of sagnac optic-fiber interferometer.The thesis first analyzes the basic principles of digital closed-loop detection technology.And then analyzes the system structure,optical structure,optical devices and optical noise of closed-loop system.Finally the thesis focuses on analyzing the circuit design of closed-loop scheme.The digital closed-loop scheme was based on square wave modulation and step wave feedback.The core signal processing unit is FPGA,and the main loop and second loop feedback circuits are all designed in FPGA.By changing the parameters of the parameterized modules designed in FPGA,the circuits are applicable to different ring length sagnac optic-fiber interferometers.The result data stored in FPGA can be transferred to computer by the communication controller designed in FPGA.As a result,no extra external communication circuit is needed.This can simplify the circuit board design.Using the designed digital closed-loop circuit to detect the number one and number two interferometric optic-fiber gyroscope.The difference between the number one gyroscope and the number two gyroscope is that the ring length of these two gyroscopes are different.The testing result of number one gyroscope is that in the range of±70°/s,the scaling factor of IFOG is 159.1 bit/°/s,the nonlinerity of scale factor is 593.54 ppm,the asymmetry of scale factor is 377.12 ppm,the zero drift of IFOG is 4.9089°/h.The testing result of number two IFOG is that the zero drift is 0.514°/h,the zero bias is-31.535°/h,the scaling factor is 251.415 bit/°/s. Using the lock-in amplifier instrument to detect the number two gyroscope,the testing result shows that the zero drift of IFOG is 0.818°/h,the zero bias is-29.455°/h, the scaling factor is 8.8 mv/°/s.The experiment result indicates that the designed digital closed-loop circuit is applicable to different ring length sagnac optic-fiber interferometers.The testing result by the designed circuit is closed to the testing result of lock-in amplifier instrument.