Displacement measurement of a shaker in an accelerometer calibration system

The vibration displacement of a shaker in an accelerometer calibration system is detected by a Michelson type of a phase quadrature laser interferometer. The interferometric signals are stored in a digital storage scope and transferred to a computer for displacement calculation. Due to the high resolution, fast acquisition speed, and large memory capacity of the scope, this system demonstrates a measuring range from about 10 nm to 100 micrometers at the frequency range of DC to 20 kHz. A cyclical signal- preserving algorithm is developed to preserve the signal's phase and amplitude while reducing the drift and random noise level. The standard deviations of the measured displacements are 1.3% for 13 nm and rapidly lower to 0.04% for 500 nm or greater. The measured displacement in conjunction with the vibration frequency and the output voltage of the accelerometer then give its sensitivity. Preliminary results demonstrate that the sensitivities calibrated by both the direct displacement measuring method (our experiment) and the conventional fringe-disappearance method agree within 0.6%.