National Metal and Refining Company, Ltd.

Donald W Nelson

Frank J Matusik

J Vincent Fitzgerald

John L Schrag

A rheometer for determining the viscoelasticity of a liquid from the mechanical impedance which the liquid presents to an oscillating surface. The incremental power required to maintain a fixed amplitude of oscillation of the surface upon immersion in the liquid is determined. The differential shift in oscillation frequency due to immersion in the liquid is also determined. By relating (i) the incremental oscillation power to mechanical resistance presented by the liquid to the oscillating surface, and (ii) the differential shift in a oscillation frequency to the mechanical reactance presented by the liquid to the oscillating surface, the viscoelasticity of the liquid is determined. Applications include laboratory measurements and process control.

Apparatus and method for determining the viscoelasticity of liquids

A torsional mode rotational vibratory viscometer having an elastic hollow metal sheath extending below a support plate and secured to the plate by a weld. A rigid rod is disposed within the sheath and welded to the lower end of the sheath. An immersible tip is also secured to the lower end of the sheath. The free upper end of the rod extends above the support plate. A crossbar with ends of magnetically permeable material is secured to the free end of the rod and is caused to oscillate by a magnetic drive coil adjacent one end of the crossbar. Prior to mounting of the crossbar, the assembly is subjected to a specific heat treating schedule. A magnetic detector coil adjacent the other end of the crossbar detects the angular oscillation of the rod. Circuitry connected to the coils maintains the amplitude of oscillation of the rod constant. When the tip is immersed in a fluid, the power supplied to the drive coil is determined by the circuit and is a measure of the viscosity-density product of the fluid. The circuitry includes a sample-and-hold circuit having a clipping level which varies with the detector coil signal level, and a variable exponent amplifier to accurately correct for deviation of the drive coil current-power relationship from a square function.

Rotational vibratory viscometer transducer and circuit

A rotational vibratory viscometer-densitometer for in-line process control and similar applications, having an elastic hollow metal tube extending between two clamps, and a relatively rigid transverse yoke secured to the tube at a point midway between the clamps. The yoke has magnetically permeable ends and a magnetically permeable center portion. Electromagnets adjacent one end of the yoke and the center portion thereof interact with the yoke to cause the tube to oscillate simultaneously in torsion and in flexure at the natural frequency of the tube in combination with the fluid within it. The amplitude of torsional oscillation is maintained constant by a torsional detector and control circuit, and the power required to maintain said amplitude is determined, said power being a measure of the viscosity of the fluid flowing through the tube. The frequency of flexural oscillation of the tube is determined by a flexural detector and associated circuit, said frequency being a measure of the density of the fluid flowing through the tube.

In-line vibratory viscometer-densitometer

A rotary viscometer of the type which measures the viscous torque to which a rotating spindle is subjected, by measuring the current drawn by the electric motor driving the spindle. True viscosity, i.e. the slope of the torque-spindle rotation speed curve, is approximated by varying the spindle speed stepwise in sets of speed measurements having a fixed speed difference, and obtaining the difference between the corresponding torque values for each set. By repeating this process throughout the desired speed range, an approximate derivative of the torque-speed curve is obtained, corresponding to an approximation of the true viscosity of the fluid being characterized.

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Voorhees, NJ, United States of America

Donald W Nelson