TORSIONAL VIBRATION DENSITOMETER

摘要

A direct measurement of density of a fluid is made by coupling the fluid to a rod under torsional oscillation. The frequency of torsional oscillation is maintained at the resonant frequency by sensing the phase difference between the stress in the rod and the current in a driving coil which produces the force to sustain torsional oscillation in the rod. The stress is measured by strain gauges which provide the electrical signal for phase comparison with the driving coil current. The frequency of the current is controlled by a voltage controlled oscillator whose input is derived from the phase comparison to provide a frequency which is at the resonant frequency of the oscillatory rod as modified by the density of the fluid to which it is coupled. The precise relationship between fluid density and resonant frequency is established by calibration.