Low-frequency response of accelerometers for observer design in a gravity environment

Abstract

Analytical and experimental results demonstrate that the dynamic effect of gravity degrades low-frequency accelerometer measurements. The attitude of an accelerometer in motion in a constant uniform gravity field can cause the output signal to indicate an incorrect amplitude (magnitude and phase) relative to the actual acceleration of the point on the structure at which the sensor is mounted. The effect of gravity is to attenuate the accelerometer signals to the extent that a 180-deg phase shift between signals at different locations may occur in the lower modes of vibration. The positions on the structure where the phase shift occurs are called accelerometer nodal locations, because the output of accelerometers located at these positions are theoretically zero. The effect is demonstrated analytically and experimentally when results from a pendulum and a two-dimensional grid structure are used. An observer is designed for the grid structure in which accelerometer measurements are used as input. The observer performance, including the dynamic effect of gravity on the accelerometer, is compared to the performance of an observer using the output signal from the accelerometers without compensating for the signal errors induced by the gravity field. The results show that the dynamic effect of gravity must be included in the observer design for low-frequency response estimates in a gravity environment.