Implementation of the scale factor balance on two pairs of quartz-flexure capacitive accelerometers by trimming bias voltage.

Gravity gradient measurement makes use of the difference between the outputs of pairs of linear accelerometers, which results in cancelling out the common mode accelerations caused by mounting platform and external environment. One of the key technologies is to match the acceleration-to-voltage or acceleration-to-current transfer functions of the pairs of the accelerometers to an extremely high degree of accuracy. The differential signals then make the gravity gradients observable. By using two pairs of the quartz-flexure accelerometers with a capacitive sensing and electrostatic closed-loop control, the electrostatic control bias voltages were trimming remotely and automatically in real time. Each pair of accelerometers was matched individually and then all four accelerometers were finally re-balanced. The experimental results show that the consistency of five digits is achieved at a noise level of ~5×10(-8) g/√Hz (1 g ≈ 9.8 m/s(2)) and the scale factors ranging from 0.25 to 0.32 V/mg. Further improvement to the achieved level of matching is limited by the intrinsic noise of the accelerometers used.