Primary laser vibration metrology: evaluation of the rocking motion impact in the accuracy of acceleration measurements

Abstract

Optical interferometry for the absolute calibration of standard accelerometers is based on displacement amplitude measurements considering a uniaxial sinusoidal excitation movement at a given frequency. In reality, the movement generated by a shaker also contains components perpendicular to the oscillation axis, introducing a rocking motion effect. In the primary calibration of vibrations by laser interferometry, the rocking motion is a critical issue to be considered for high accuracy measurements. The knowledge of the impact of this effect in the performances of acceleration amplitude measurement is fundamental for the definition of a robust calibration approach. Generally, this effect increases with the excitation frequency and, beyond a certain threshold, its influence in the final result may become quite relevant. In this work, we study the influence of the rocking motion in the calibration of one accelerometer with two shaker models. The study comprises a nominal acceleration of 100 m.s^-2 for frequencies between 1 kHz and 9 kHz, considering a sinusoidal excitement. An interferometric system based on heterodyne detection was used for the high frequency regime. Measurements were performed for 12 incidence points equally spaced along the border of the surface of a dummy mass attached to the standard accelerometer, and the corresponding average was estimated, allowing the characterisation of the rocking motion effect and the estimation of the corresponding component in the expanded uncertainty budget.