Automated resonance-bar damping measurement system

Abstract

This paper describes an automated internal friction measurement system which allows continuous resonant-frequency tracking and continuous recording of damping and resonant frequency during resonance-bar internal friction experiments. A phase-locked loop based on a phase detector maintains the system at resonant frequency although the frequency may change during the course of an experiment. A modified White cathode follower is used to overcome capacitive loading effects in coaxial cables between the damping system and electronic controlling–recording components. In this manner, monitoring and recording components may be located at distances of tens of meters from the drive-detector-specimen damping system, which may in turn be located in some hostile environment of interest. The automated system may be used with damping measurement systems which employ piezoelectric, electromagnetic, or electrostatic drive-detection transducers.