Data processing: measuring – calibrating – or testing – Calibration or correction system – Fluid or fluid flow measurement
Reexamination Certificate
1998-07-16
2001-06-19
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Fluid or fluid flow measurement
C073S001310, C073S001340, C073S861351, C073S861356, C073S861352
Reexamination Certificate
active
06249752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to process parameter sensors, operating methods and computer program products, and more particularly, to vibrating conduit parameter sensors, operating methods and computer program products.
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 U.S. 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 may comprise 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 driver typically 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.
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, with the phase on the inlet side of the conduit generally lagging the actuator and the phase on the outlet side of the conduit generally leading the actuator. The phase shift induced between two locations on the conduit is approximately proportional to the mass flow rate of material through the conduit.
Unfortunately, the accuracy of measurements obtained using conventional phase shift or time delay methods can be compromised by nonlinearities and asymmetries in the flowmeter structure, as well as by vibration introduced into the flowmeter structure by external sources such as pumps. These effects may be reduced, for example, by using balanced mechanical designs that reduce the effects of external vibration and by using frequency domain filtering to remove frequency components associated with undesirable vibrations. However, mechanical design approaches may be constrained by geometric considerations, and frequency domain filtering may be ineffective at removing unwanted vibrational energy that occurs at or near resonant frequencies of interest, e.g., the drive frequency used to excite the conduit.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide vibrating conduit parameter sensors, operating methods and computer program products which can provide accurate estimates of process parameters in sensor conduits having structural nonlinearities and asymmetries and in the presence of external vibration.
This and other objects, features and advantages are provided by vibrating conduit process parameter sensors, operating methods and computer program products in which motion signals representing motion of a vibrating conduit are processed to resolve the conduit motion into a plurality of real normal modal components from which a process parameter such as mass flow may be estimated. In an embodiment of the present invention, a mode pass filter is applied to the motion signals to produce an output that preferentially represents a component of the conduit motion associated with one or more real normal modes, for example, one or more real normal modes that are preferentially correlated with Coriolis force associated with a material in the conduit. An estimate of a process parameter such as mass flow may then be generated from the output using, for example, conventional phase difference techniques. In another embodiment according to the present invention, real normal modal motion is estimated from the plurality of motion signals and a process parameter is estimated from a subset of the estimated real normal modal motion, e.g., from motion in real normal modes that are preferentially correlated with Coriolis force.
Because the conduit motion is resolved into real normal modal components, more accurate estimates of process parameters can be obtained. For example, a mode pass filter may pass components of the conduit motion corresponding to real normal modes that are closely correlated with Coriolis forces, while attenuating components of the conduit motion associated with external noise sources. The filtered output may be thus be less corrupted by noise and vibration, and can therefore be advantageously used to generate an accurate estimate of a process parameter such as mass flow. Similarly, estimated real normal modal motion of selected modes correlated with Coriolis force may be used to generate an accurate estimate of a process parameter while disregarding modal motion that is attributable to other sources.
In particular, according to the present invention, a process parameter sensor for determining a process parameter includes a conduit configured to contain material, and a plurality of motion transducers operative to produce a plurality of motion signals representing motion at a plurality of locations of the conduit. A real normal modal resolver is responsive to the plurality of motion transducers and operative to process the plurality of motion signals to resolve the motion represented by the plurality of motion signals into a plurality of real normal modal components. A process parameter estimator is responsive to the real normal modal resolver and operative to estimate a process parameter from a real normal modal component of the plurality of real normal modal components.
In an embodiment of the present invention, the real normal modal resolver comprises a mode pass filter operative to produce an output from the plurality of motion signals that preferentially represents a component of the motion associated with a real normal mode of the conduit, for example, a real normal mode that is preferentially correlated with Coriolis force. The process parameter estimator is responsive to the mode pass filter and operative to estimate a process parameter from the output.
In another embodiment of the present invention, the real normal modal resolver comprises a real normal modal motion estimator operative to estimate real normal modal motion from the received plurality of motion signals. The process parameter estimator is operative to estimate a process parameter from the estimated real normal modal motion, for example, from estimated motion for a set of real normal modes closely correlated with Coriolis force. The real normal modal motion estimator may comprise means for estimating motion in a first real normal mode and means for estimating motion in a second real normal mode that is preferentially correlated with a Coriolis force. The process parameter estimator may include means for normalizing the estimated motion in the second real normal mode with respect to the estimated motion in the f
Cunningham Timothy J.
Normen David F.
Pawlas Gary E.
Shelley Stuart J.
Chrisman Bynum & Johnson, P.C.
Micro Motion Inc.
Shah Kamini
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