A SIMPLE MEASURING SYSTEM FOR VIBRATIONS AT LOW AMPLITUDES

A simple laser system for the measurement of low amplitudes of vibrati on is presented which can be used for calibration purposes in vibratio n pickups, It is based on the amplitude measurement of the fundamental frequency component in the photocurrent spectrum (the so-called J(1) Bessel method for the measurement of very small amplitudes of vibratio n) using a differential optical configuration. The dynamic range in th e upper region can be extended up to the micrometer region by judiciou s choice of the beam crossing angle and the wavelength of the laser us ed. In this way a region of low amplitudes normally excluded in the af orementioned method is covered. The stability of the system during the measurement is assisted by means of a digital controller. (C) 1997 El sevier Science Ltd.