Research Of Basic Theory On The Innovative Marine Gravity Sensor

The measurement of high-precision marine gravity has great impact on exploration,exploitation and utilization of ocean.The technology of relatively gravity measurement has been mature in European and American which country has developed and commercialized high-precision and reliable gravimeter.In contrast,the domestic gravimeter lags behind relatively.The drawbacks of existing spring gravimeters will limit their performance such as bulky volume and vulnerability to horizontal acceleration.In light of this,this paper proposes an innovative gravimeter.The distinguishing feature of the structure is spatial cross-shape flexible supporting.The design ideas and working principles of the innovative gravimeter is introduced,and its advantage is also pointed out,and then set forth on the design of its cross-shape supporting and the torque structure.What is more,a model of static force is studied under equilibrium steady state based on Euler –Bernoulli beams theory and then a vibration pattern by dynamic equation is set up to calculate the characteristics such as inherent frequency,moment of inertia and pendulosity.Magnetic structure circuit is designed based on the principles of the magnetic.Finite element analysis(FEA)method is used to analyse and verify the above issues.The servo loop was proposed on the base of structural and kinetic equations of this gravity sensor.Mixed-signal circuit based on characteristics and function of the loop was designed to overcome the defeat of analog circuit.The loop implements on FPGA.The analog part is composed of capacitance-to-voltage converter,modulator circuit and amplifying circuit.The digital part is composed of reset circuit,carrier signal generation circuit and synchro-demodulation circuit with CORDIC algorithm,low-pass FIR filter circuit,PID correcting circuit and serial communication circuit.The digital part was realized by hardware description language and had been verified in ModelSim.The results of simulation and calculation on mechanical structure and the servo loop show that the theoretical resolution of the gravimeter reaches 3.7?Gal,which meets the need of gravitational acceleration measurement.