EXPERIMENTAL INVESTIGATION INTO THE EFFECTS OF EXCITER MOTIONS ON THE PRIMARY CALIBRATION OF SINGLE-ENDED ACCELEROMETER

摘要

It is widely known that in the primary calibration of accelerometers by using a laser interferometer, a unit under test (UUT) and the laser interferometer should measure vibration at the same position. However, this is not applicable to single-ended accelerometers because of the limitation of their design. One way of overcoming this limitation is to measure the vibration at several positions on the plate which connects UUT to a vibration exciter. However this can present the effects of rocking motions of the exciter. Although the motions of vibration exciters are presented in several studied, the different model of exciters might have different characteristics. This paper aims to study the motions of an air-bearing exciter (model 2911) used at National Institute of Metrology (Thailand) in order to expose their characteristics, their effects on the calibration results and the measurement errors due to these effects. The motions of the exciter are shown in terms of magnitude and phase shift distributions of sensitivities. These can be obtained by measuring the magnitudes and phase shifts at several positions on the plate. The effects of exciter motions are measured in terms of how much the magnitudes and phase shifts at each measured positions deviate from the average values. To illustrate these effects, parametric studies were conducted. The influences of four parameters, i.e. the angular positions of the laser points, the distance of the laser positions from the centre of the plate, the number of measured positions to be averaged and the mass loading effect, were examined experimentally. The frequency of interest is between 10 Hz and 15 kHz.