Abstract
An improved design of the vertically oscillating buoy viscometer with real-time computer control, evaluation, and plotting is presented. In this method, the optically observed phase lag of the buoy relative to a sinusoidal driving force is a direct and absolute measure of viscosity. Construction features of the new version improve reassembly precision and give three-axis positioning of the sphere, as well as an 80-fold improvement in the signal-to-noise ratio for small amplitudes of the buoy motion. Design of the ‘‘crossed coil’’ system is discussed and the magnetic and mechanical faults which lead to various kinds of motional instability are considered. Boundary layer corrections are now computer corrected as are temperature variations. The evaluation of ‘‘intrinsic viscosity’’ as a measure of molecular ellipticity is discussed and one measurement set is presented.
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