Calibration of Vibration Pickups at Large Amplitudes

Abstract

Axial resonances of long rods and tubes were used to generate motion for accurate calibration of vibration pickups over the frequency range from below 1 to above 20 kc at acceleration levels up to 12 000g. The resonators were driven by an electromagnetic shaker at low frequencies and by a piezoelectric ceramic stack shaker at high frequencies. Vibration amplitude was measured optically by means of a microscope using stroboscopic light and by means of the interference fringe disappearance technique. Adequate overlap between the two methods was achieved by going up to the 60th disappearance of the fringes. A simple, direct measurement of the phase angle between the pickup signal and the motion is described. Construction details of a small, light pickup which is unaffected by the high acceleration levels are given.