Oblong Vibrating Member Frequency Separation
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Solution Overview
Problem
Existing vibrating densitometers face challenges in accurately measuring fluid density due to close frequency separation between vibration modes, caused by manufacturing imperfections, leading to errors in density determination.
Innovation Solution
A vibrating member with an oblong cross-sectional shape, featuring arcuate and non-arcuate portions, increases frequency separation between vibration modes by creating an offset span, allowing for easier discrimination between radial vibration modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a perfectly round and uniform cross-sectional shape is used for the vibrating member, then only one three-lobed frequency mode shape is produced in theory, but manufacturing tolerances and imperfections cause two vibration mode shapes to be very close together in frequency, making it practically impossible to distinguish between them and introducing error into density measurement
Solution Approach 1:
The patent applies asymmetry by intentionally designing the vibrating member with a non-circular cross-sectional shape (such as rectangular, oval, or other asymmetric geometries). This deliberate asymmetry creates a frequency separation between vibration modes that is large enough to be easily distinguished, thereby resolving the measurement accuracy problem caused by manufacturing tolerances in perfectly circular shapes.
2Measurement precision
If a non-circular cross-sectional shape is used to increase frequency separation between vibration modes, then measurement accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the geometric parameters of the vibrating member by using non-circular cross-sectional shapes with specific dimension ratios. By optimizing parameters such as the aspect ratio of rectangular or oval sections, the patent achieves sufficient frequency separation while maintaining manufacturing feasibility through standard fabrication processes.
3Manufacturing precision
If manufacturing tolerances are tightened to achieve a perfectly uniform cross-sectional shape, then only one vibration mode would be produced, but this increases manufacturing cost and complexity
Solution Approach 1:
Rather than tightening tolerances to achieve perfect symmetry, the patent deliberately introduces asymmetry through non-circular cross-sectional shapes. This approach achieves the desired single dominant vibration mode effect without requiring expensive and complex manufacturing processes, as the asymmetric shape can be easily fabricated with standard tolerances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The oblong cross-sectional shape enhances frequency separation, simplifies manufacturing, reduces costs, and improves the accuracy of density measurements by allowing for better separation of vibration modes, making the design less sensitive to manufacturing tolerances.
Implementation Method 1
The conduit can be vibrated and a resonant frequency can be measured. As is generally known in the art, the density of the fluid under test can be determined by measuring a resonant frequency of the conduit in the presence of a flow fluid. According to well-known principles, the resonant frequency of the conduit will vary inversely with the density of the fluid that is contacting the conduit.
Implementation Method 2
The driver receives a drive signal from a meter electronics and vibrates the vibrating member at or near a resonant frequency.
Data Source
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AI summary
A vibrating member (412) adapted for use in a vibrating densitometer (400) includes a base (407) and a vibrating tube portion (405) affixed to the base (407). The vibrating tube portion (405) includes a first arcuate portion (430a), a second arcuate portion (430b), a first non-arcuate portion (432a), and a second non-arcuate portion (432b). The first and second non-arcuate portions (432a, 432b) are located between the first and second arcuate portions (430a, 430b). The vibrating tube portion (405) is formed with an oblong cross-sectional shape having a major axis dimension that is greater than a minor axis dimension. The oblong cross-sectional shape increases a frequency separation between vibration modes in the vibrating tube portion (405).