Six degree-of-freedom ground motion measurement method based on eight accelerometers

A new approach to measure rotational and true translational acceleration components of free field or structure under the action of earthquake, which means 6 degree-of-freedom (DOF) ground motion, was developed by using 8 force-balance accelerometers. Because of the usage of 8 accelerometers, rotational and true translational acceleration components of ground motion can be measured directly. The 8 accelerometers were mounted on a rigid base according to certain positions and directions and those were regarded as a rigid body. The differential equations that describing the relationship between 8 accelerometers outputs and 3 rotational and 3 translational acceleration components were established based on the rigid body motion theorem. To guarantee the computing accuracy, 4th-order Runge-Kutta algorithm was used to solve the differential equations. The real-time computing was implemented in TMS2407 digital signal processor. Additionally, the way to compensate the system errors was proposed too. The method presented in this paper is expecting to perfect the traditional strong motion observing system based on 3 force-balance accelerometers.