| Résumé | Most primary accelerometer calibrations, or absolute calibrations, are currently performed using laser interferometry under the guideline of the international standard (ISO 16063-11, 1999). The laser interferometric method measures the displacement amplitude of a moving surface with an accelerometer mounted. To achieve high accuracy in the measurement of acceleration it requires a poston-like and distortion-free vibration of the accelerometer at calibration frequencies and amplitudes. Unfortunately, vibration shakers usually present hgih levels of rocking motion. Rocking motions is an unwanted phenomenon exhibited by vibration shaker. It is usually manifested in oscillatory back and forth, side to side, or rotatory movements. It causes the measurements of accelerometer sensitivity deviating from each other for up to a few percent. To reduce the effect of rocking motion, measurements may be performed at multiple incidence points equally spaced along the border of the accelerometer on the mounting surface and the corresponding average is then estimated. Recently, mechanical filters have been used to decouple the rocking motion from vibration shaker to acceleromteter. to obtain the best results, the filter should be optimized for a specific type of reference accelerometer. For this purpose, a real-time rocking motion monitoring system was developed at the National Research Council Canada. This paper describes the improvements of the system since it was developed and reported and presents the measurement results of rocking motion for different conditions. |
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