Research On Testing Scheme And Magnetic Effect Of Mass Calibration Field

The gravity and gravity gradient data,which can be obtained by gravimeter and gravity gradiometer,play an important part in research,as well as civil and military applications.These instruments need to be calibrated when they are developed.After being calibrated,the accuracy of these instruments can be improved by compensating the output.According to the requirements of the national Precision Gravity Measurement Facility(PGMF),a highprecision indoor mass calibration field needs to be built to meet the needs of various gravimeters and gravity gradiometers.The construction index of the mass calibration field is 50 ?Gal for gravity,accuracy of2 ?Gal,500 E for gravity gradient,accuracy of 1E.In order to meet the requirements of this indicator,three configurations of the mass calibration field were firstly introduced in detail.Configuration A is the scheme of fixed mass.Configuration B is the scheme of vertically moving mass.configuration C is the scheme of horizontally moving mass.These configurations can complement each other to calibrate various gravimeters and gravity gradiometers.Secondly,the corresponding testing schemes for each of these configurations were designed.Important parameters such as the initial and final positions of the test,positioning accuracy,and the theoretically predicted values of gravity/gravity gradient changes were given.Then the testing schemes applicable to various gravimeters and gravity gradiometers were categorized.Finally,the factors such as the dislocation of the device and the thermal expansion/contraction of the mass,which can affect the testing accuracy were analyzed.The construction index was proposed that the lateral dislocation of each layer of the mass in configuration A is less than 28 mm,the lateral dislocation of the device in configuration B is less than 20 mm,and the vertical dislocation of the device in configuration C is less than 41 mm.The temperature control index was proposed that the temperature fluctuation in configuration A is less than 7°C,the temperature fluctuation in configuration B is less than 26°C,and the temperature fluctuation in configuration C is less than 61°C.It's also important to solve the problem that the mass' magnetic field will affect the output of the gravity gradiometer instrument(GGI)during the calibration process.Firstly,the magnetic modulation experiment was carried out on the GGI accelerometers.Subsequent analysis revealed qualitatively how the magnetic field affects the accelerometer.Secondly,the governing equations in the process was theoretically derived to summarize the quantitative influence of magnetic field.Then,the model of circular current and the process of testing accelerometer magnetic coefficient were designed,and the influence of the mass' magnetic field on the GGI was given.Finally,according to the process of the magnetic field affecting the GGI,the corresponding magnetic shielding operations were carried out on the GGI,thus reducing the influence of the mass' magnetic field to within 10 E for the required accuracy of GGI.