Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1998-07-16
2001-05-15
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S047000, C073S861356, C073S861357
Reexamination Certificate
active
06233526
ABSTRACT:
BACKBROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to process parameter sensors and methods of operation therefor, and more particularly, to vibrating conduit parameter sensors and methods of operation therefor.
2. Statement of the Problem
Coriolis effect mass flowmeters are commonly used to measure mass flow and other information for materials flowing through a conduit. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. No. 4,109,524 of Aug. 29, 1978, U.S. Pat. No. 4,491,025 of Jan. 1, 1985, and Pat. No. Re. 31,450 of Feb. 11, 1982, all to J. E. Smith et al. These flowmeters typically include one or more conduits having a straight or a curved configuration. Each conduit may be viewed as having a set of vibration modes, including, for example, simple bending, torsional, radial and coupled modes. In a typical mass flow measurement application, each conduit is driven to oscillate at resonance in one of its natural modes as a material flows through the conduit. The vibration modes of the vibrating, material-filled system are effected by the combined mass and stiffness characteristics of the conduits and the characteristics of the material flowing within the conduits.
A typical component of a Coriolis flowmeter is the drive or excitation system. The drive system operates to apply a periodic physical force to the conduit that causes the conduit to oscillate. The drive system typically includes at least one actuator mounted to the conduit(s) of the flowmeter. The actuator typically comprises one of many well known electromechanical devices, such as a voice coil device having a magnet mounted to a first conduit and a wire coil mounted to a second conduit, in an opposing relationship to the magnet. A drive circuit continuously applies a periodic, e.g., a sinusoidal or square wave, drive signal to the actuator coil. The periodic drive signal causes the actuator to drive the two conduits in an opposing periodic pattern that is thereafter maintained.
When there is effectively “zero” flow through a driven flowmeter conduit, points along the conduit tend to oscillate with approximately the same phase or a “zero-flow” phase with respect to the driver, depending on the mode of the driven vibration. As material begins to flow from an inlet of the flowmeter, through the conduit and out of an outlet of the flowmeter, Coriolis forces arising from the material flow tend to induce phase shifts between spatially separate points along the conduit. Generally, as material flows through the conduit, the phase on the inlet side of the conduit lags the driver, while the phase on the outlet side of the conduit leads the driver. The phase shift induced between two locations on the conduit is approximately proportional to the mass flow rate of material through the conduit.
To measure mass flow rate, conventional Coriolis flowmeters typically measure phase at two transducers, e.g., coil-type velocity transducers, located near respective ends of the conduit, symmetrically placed with respect to a centrally positioned driver. However, manufacturing-induced errors in transducer placement as well as other structural variations and nonlinearities in the conduit structure may cause measurement inaccuracies.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide parameter sensors and methods of operation therefor which can provide more accurate techniques for measuring process parameters such as mass flow rate, totalized mass flow rate, viscosity and the like in a vibrating conduit parameter sensor.
This and other objects, features and advantages are provided according to the present invention by vibrating conduit parameter sensors and methods of operation therefor in which a spatially integrated estimate of a process parameter associated with a material in the conduit, e.g., mass flow rate, totalized mass flow, viscosity and the like, is determined. A plurality of forces associated with an excited sensor conduit is identified. Motion signals are received representing motion at a number of locations on the sensor conduit that exceeds the number of the identified forces such that the plurality of motion signals provide an overdetermined information source for resolution of conduit motion into motion attributable to the plurality of forces. A potentially more accurate estimate of a process parameter associated with the moving material may thereby be generated.
In particular, according to the present invention, a process parameter sensor for a material processing system includes a conduit configured to contain material from the material processing system. A plurality of motion transducers is operative to produce a plurality of motion signals representing motion at a number of locations on the conduit. An overdetermined process parameter estimator is responsive to the plurality of motion transducers and configured to receive the plurality of motion signals. The overdetermined process parameter estimator is operative to resolve the conduit motion into motion attributable to each of a predetermined number of forces and to estimate a process parameter associated with a material in the conduit according to the resolved motion, wherein the number of locations exceeds the number of forces such that the plurality of motion signals provides an overdetermined information set for resolution of the conduit motion into motion attributable to the predetermined number of forces. The overdetermined process parameter estimator may include means for generating an estimate of motion attributable to a Coriolis force, and means, responsive to the means for generating an estimate of motion, for generating an estimate of a process parameter such as mass flow from the estimate of motion.
According to an aspect of the present invention, a group of motion signals is combined to produce a spatially averaged motion signal. A process parameter is estimated from the spatially averaged motion signal using, for example, a conventional Coriolis measuring circuit.
According to another aspect of the present invention, a number of real modes are identified. A plurality of motion signals is produced, the plurality of motion signals representing motion at a number of locations exceeding the number of real modes such that the plurality of motion signals represent an overdetermined information source for resolution of motion of the conduit into motion in the plurality of real modes. An estimate of modal motion attributable to a Coriolis force may be generated from the plurality of motion signals, and an estimate of a process parameter may be estimated from the estimate of modal motion.
According to yet another aspect of the present invention, a complex mode is identified. A plurality of motion signals is produced, the plurality of motion signals representing motion at a number of locations exceeding two such that the plurality of motion signals provides an overdetermined information source for resolution of the conduit to motion in the complex mode. An estimate of a complex modal transformation may be generated from the plurality of motion signals, and an estimate of a process parameter may be generated from the estimate of the complex modal transformation. Improved estimates of process parameters such as mass flow rate may thereby be provided.
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Rieder, Drahm; “A New Type of Single Straight Tube Coriolis Mass Flowmeter”, Flomenko '96, presented at the 8thInternational Confer
Barbee Manuel L.
Chrisman Bynum & Johnson, P.C.
Hoff Marc S.
Micro Motion Inc.
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