A viscosity and density meter with a magnetically suspended rotor

A device for measuring the viscosity and density of liquids is presented. It is a Couette-type viscometer that uses a submerged rotor to measure the viscosity without errors originating in the contact of the rotor with the sample/air boundary. The inner cylinder is a glass rotor suspended in the liquid, and the outer cylinder is also made of glass. The rotor is stabilized on the axis of the outer cylinder by an electromagnetic force controlled by feedback from the rotor's vertical position. In the lower part of the rotor is an aluminum cylinder located in a magnetic field generated by rotating permanent magnets. The interaction of this rotating magnetic field with eddy currents generated in the aluminum cylinder causes rotation of the rotor. This rotation is optically detected, and viscosity is calculated from the measured angular velocity of rotor. The density of the liquid is calculated from the applied vertical equilibrating force. A computer controls the whole measurement. The device works at constant temperature or while scanning temperature. The sample volume is 1.6 ml, and the accuracy of measurement of both viscosity and density is similar to0.1%. The range of measured densities is (0.7-1.4) g/ml, and viscosity can be measured in the range (3x10(-4)-0.3) Pa s. The shear rate of the viscosity measurement varies in the range (20-300) s(-1). The accuracy of the temperature measurement is 0.02 K. (C) 2003 American Institute of Physics.