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.
A guided torsional wave sensor has a cross-section with a strong interaction of torsional wave energy and the surrounding fluid, such that a wave propagates in the sensor with a functional dependence on a single fluid characteristic. In one embodiment, the sensor body is optimized for fluid density. Diamond, polyhedral and curved-sided embodiments are described. In another embodiment, the sensor body responds to fluid viscosity. This embodiment is preferably hollow, and may include threaded, fractal or roughened surface features to enhance viscous coupling. Different systems include further sensors, sensors with portions of differing profile, and special mounting or activation structures.
Electronic control circuitry for obtaining precise inline process control data as to viscosity of fluids over a wide viscosity range, with high tolerance of ambient noise and vibration. An electromechanical transducer with an oscillating sensor is immersed in a flowing liquid, with the power required to sustain predetermined oscillation parameters being a measure of viscosity-density product. The gain of a variable gain amplifier which provides positive feedback to sustain oscillation is controlled in response to the integrated error signal output of a comparator which compares a DC value corresponding to the RMS amplitude of mechanical oscillation with a DC reference value. The monitoring of RMS amplitude rather than peak amplitude (as is done by a phase-sensitive sample-and-hold arrangement in the prior art), coupled integration of the error signal, results in a great improvement in immunity to ambient noise and vibration. Other features includes automatic calibration and temperature compensation whereby viscosity at a desired temperature can be determined even though the measurement is made at different temperature.
A vibrating tube densimeter characterized by separate electrical conductors attached to and moving with the tube. By interaction with a constant magnetic field in which they move, and in cooperation with an electronic circuit outside the invention, one of the conductors vibrates the tube and the other senses the vibration. The novel design is simple and permits operation at high temperatures.
The viscometer provides a viscosity value (X.sub..eta.) which represents the viscosity of a fluid flowing in a pipe connected thereto. It comprises a vibratory transducer with at least one flow tube for conducting the fluid, which communicates with the pipe. Driven by an excitation assembly, the flow tube is vibrated so that friction forces are produced in the fluid. The viscometer further includes meter electronics which feed an excitation current (i.sub.exc) into the excitation assembly. By means of the meter electronics, a first internal intermediate value (X.sub.1) is formed, which corresponds with the excitation current (i.sub.exc) and thus represents the friction forces acting in the fluid. According to the invention, a second internal intermediate value (X.sub.2), representing inhomogeneities in the fluid, is generated in the meter electronics, which then determine the viscosity value (X.sub..eta.) using the two intermediate values (X.sub.1, X.sub.2). The first internal intermediate value (X.sub.1) is preferably normalized by means of an amplitude control signal (y.sub.AM) for the excitation current (i.sub.exc), the amplitude control signal corresponding with the vibrations of the flow tube. As a result, the viscosity value (X.sub..eta.) provided by the viscometer is highly accurate and robust, particularly independently of the position of installation of the flow tube.
The viscometer provides a viscosity value (X.sub..eta.) which represents the viscosity of a fluid flowing in a pipe connected thereto. It comprises a vibratory transducer with at least one flow tube for conducting the fluid, which communicates with the pipe. Driven by an excitation assembly, the flow tube is vibrated so that friction forces are produced in the fluid. The viscometer further includes meter electronics which feed an excitation current (i.sub.exc) into the excitation assembly. By means of the meter electronics, a first internal intermediate value (X.sub.1) is formed, which corresponds with the excitation current (i.sub.exc) and thus represents the friction forces acting in the fluid. According to the invention, a second internal intermediate value (X.sub.2), representing inhomogeneities in the fluid, is generated in the meter electronics, which then determine the viscosity value (X.sub..eta.) using the two intermediate values (X.sub.1, X.sub.2). The first internal intermediate value (X.sub.1) is preferably normalized by means of an amplitude control signal (y.sub.AM) for the excitation current (i.sub.exc), the amplitude control signal corresponding with the vibrations of the flow tube. As a result, the viscosity value (X.sub..eta.) provided by the viscometer is highly accurate and robust, particularly independently of the position of installation of the flow tube.
