Dual-beam Laser Interferometer for the Ac- Curate Determination of Rocking Motion

Most primary accelerometer calibrations, or absolute calibrations, are currently performed using laser interferometry under the guideline of the international standard (ISO 16063-11, 1999). Due to rocking motion of vibration shakers, however, the measured accelerometer sensitivities at different laser incidence points can vary for up to a few percent. For the accurate determination of rocking motion on the effect of calibration results, a dual-beam laser interferometer was developed at National Research Council Canada. This paper describes the method and apparatus for simultaneous measurements of displacement amplitudes and its distribution along a straight line using a dual-beam laser interferometer. The interferometer directs two beams that are incident at distinct points on a moving surface. A separation distance between the two sensing spots on the moving surface is provided. In the present setup, the separation distance is adjustable along a straight line. This feature allows the interferometer to measure the displacement distribution along a line. To reduce the measurement uncertainty a model-based estimation is used to accurately determine the displacement amplitudes from the current outputs of photo diodes. This paper also presents the measurement results showing the difference of displacement amplitudes due to rocking motion. The system may also be used for direct quantitative study of moving surface deformation during vibration.