Design of digital balance loop in gravity gradiometer based on AD5791

The scale factor balance loop is the key part in the rotating accelerometer gravity gradiometer. The digitization of the balance loop can provide lower noise and higher reliability, and also reduce the size and the weight. The design with the high performance 20-bit digital-to-analog converter AD5791 is introduced in this paper. A floating-point 32-bit digital signal controller TMS320F28335 is used as the controller of a daisy-chain with four AD5791 converters. The hardware module diagram and the operation sequence of the digital balance loop are also provided. Their key parameters of AD5791, integral nonlinearity error, differential nonlinearity error, and low frequency noise, are measured and evaluated particularly. According to the results of testing, this device has the ability of 20-bit resolution and 1ppm accurate. By this design of digital balance loop based on AD5791, the consistency of the scale factors of accelerometer pairs can be tuned for six magnitudes theoretically, that is, from the initial order of 10^-5 to the targeted order of 10^-11.