Performance measurements of an inertial sensor with a two-stage controlled torsion pendulum

A novel two-stage electrostatically controlled torsion pendulum has been developed to simultaneously investigate the performance of a translational and a rotational degree of freedom of an electrostatic inertial sensor on ground. The motions of the proof mass (PM) relative to the electrode frame are monitored by a high-precision capacitance transducer, and are synchronously controlled by electrostatic actuators. The parasitic stiffness induced by capacitance transducers and the effect of the magnetic field are measured. Both translational and rotational motions of the PM succeed to be simultaneously controlled, and the cross-coupling effect between both controlled degrees of freedom is also preliminary measured. The experiments show that the scheme obviously suppresses the translational to rotational effect of the PM, and then effectively improves the torque resolution compared with the single-stage torsion pendulum. The noise floors of the controlled torsion pendulum come to 1.2 x 10-11 N Hz-1/2 along the translational degree of freedom, and 1.4 x 10-13 N m Hz-1/2 along the rotational degree of freedom, near 30 mHz, which are mainly limited by the back action of the capacitance transducer below 0.1 Hz and by the horizontal seismic noise disturbance above 0.1 Hz.