Anti-vibration and Precise Vibration Measurement for Absolute Gravimetry

Abstract

An absolute gravimetry apparatus of Mizusawa is equipped with an anti-vibrating device in order to cancel the vertical displacements of the horizontal vacuum chamber. The method of anti-vibration is as follows: Signals from a long period vertical component seismometer (natural period is 30 seconds) on a concrete pier are reversed and given to the piezo elements which are attached to the foots of the horizontal vacuum chamber. On the other hand, the residual vibrations are monitored by another vertical component seismometer (natural period is 15 seconds) on the horizontal vacuum chamber. Experiments were achieved to investigate the characteristics of the anti-vibrating device and suitable electric circuits were developed for vibration measurering equipments. In the experiments it was found that the amplitude of vibration of the horizontal vacuum chamber were eliminated to about one-tenth by making use of the anti-vibrating device, but the rosonance of the horizontal vaccum chamber was seen at about 25 Hz. As a result of anti-vibration, high sensitive measurements of the residual vibration of the horizontal vacuum chamber were obtained and its resolution reached about a few nanometers. The precise calibration of seismometer and removal of the resonance of the horizontal vacuum chamber need further extended studies.