Design And Error Analysis Of Torsion Balance Gravity Gradiometer

Gravity of the second derivative can well describe the characteristics of the earth’s gravitational field,and be suitable for detecting the partial small geologic body with higher space resolution ratio compared with Gravity measurement.At present,the application prospect of gravity gradient measurement is very wide,having already made some success in the gravity resources exploration and improved the precision of inertial navigation,etc.Gravity gradiometer is an instrument for measuring gradient of gravity field.At present,there are many kinds of gravity gradiometer,such as torsion balance gravity gradiometer,electrostatic accelerometer gravity gradiometer,rotating accelerometer gravity gradiometer,superconducting gravity gradiometer,etc.Among them,the torsion balance gravity gradiometer having simple structure,low cost,high measure precision can be used as a gravity gradient measurement system of the gravity datum instruments system,and it’s high precision measure gravity gradient values can calibrate other gravity instrument.In this paper,the current typical torsion balance principle of gravity gradiometer in the world were summarized in detail.Considering the disadvantage of the traditional extraction method of gravity gradient,we studied the principle of the least squares method which provides a theoretical basis for the high precision extraction of gravity gradient by taking into account the error of the coefficient matrix and the observation vector.Then analyzed the torsion gradiometer structure,torsion structure and size selection.In order to achieve the design goal of 0.5E measurement precision of the gravity gradient,preliminary determined processing and positioning index,and measurement requirements of the attitude angle of the torsion balance system by anlaying the thermal noise limit,first order error and two order error of it.In addition,considering the stable time of torsion balance suspension system was too long,which had great impacted the efficiency of the gravity gradient measurement,we designed an amplitude attenuation system in combination with PID control technology in our laboratory.By plus two pairs of feedback on both sides of the torsion balance,the systemused electrostatic feedback mode to control it when the torsion balance deviating from the equilibrium position,so as to realize the rapid attenuation of amplitude.And by the simulink simulation,finding that 10000 urad amplitude decay time only need 7 minutes,so this system could greatly improve the work efficiency of torsion balance.