Vibrating Tube Axial Offset for Mode Separation

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Solution Overview

Problem

Prior vibrating densitometers face challenges in accurately measuring fluid density due to close frequency separation of vibration modes caused by manufacturing imperfections, leading to errors in density determination, which is difficult to distinguish and requires tight tolerances and high manufacturing costs.

Innovation Solution

A vibrating member with an axially shifted inner and outer diameter, featuring a gradient of wall thickness, is designed to increase frequency separation between vibration modes, allowing for easier discrimination and reducing manufacturing complexities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a perfectly round and uniform vibrating member is used, then only one vibration mode shape is produced, but manufacturing tolerances cause asymmetries that result in two close frequency modes

Engineering Contradiction:

Improvecircularity and uniformity of vibrating memberVSAvoidfrequency separation between modes

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The patent applies asymmetry by intentionally introducing an axial offset between the inner and outer diameters of the vibrating member. This deliberate asymmetric geometry creates a controlled frequency separation between vibration modes, counteracting the unwanted mode splitting caused by manufacturing tolerances. The asymmetric design ensures that even with typical manufacturing variations, the vibration modes remain well-separated and distinguishable.

Inventive Principle:

Principle #4Asymmetry

2Measurement precision

If tight manufacturing tolerances are applied to achieve perfect roundness and uniform thickness, then vibration mode separation is improved, but manufacturing complexity and cost increase

Engineering Contradiction:

Improvevibration mode discriminationVSAvoidmanufacturing tolerances and processes

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Instead of requiring tight tolerances on a symmetric design, the patent uses an inherently asymmetric design with axial offset between inner and outer diameters. This approach achieves the desired frequency separation through geometry rather than precision manufacturing, significantly reducing manufacturing complexity and cost while maintaining excellent mode discrimination.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes the geometric parameters of the vibrating member by introducing an axial offset between the inner and outer diameters. This parameter modification fundamentally alters the vibration characteristics to achieve mode separation without requiring tight manufacturing tolerances, thereby simplifying the manufacturing process.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If radial vibration mode is used, then the vibrating member is self-balancing and mounting characteristics are less critical, but frequency separation between modes remains very small

Engineering Contradiction:

Improveself-balancing propertyVSAvoidfrequency separation

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent maintains the radial vibration mode's self-balancing property while introducing asymmetric geometry through axial offset. This combination preserves the stability benefits of radial modes while simultaneously achieving the needed frequency separation, as the asymmetric cross-section creates distinct vibrational characteristics that prevent mode merging.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent applies local quality by creating different wall thicknesses at different angular positions around the vibrating member's circumference. This localized variation in geometry (thinner wall in some regions, thicker in others due to the axial offset) creates the frequency separation while maintaining the overall self-balancing radial vibration mode.

Inventive Principle:

Principle #3Local quality

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 solution effectively increases frequency separation between vibration modes, enhancing the accuracy of density measurements and reducing manufacturing costs by simplifying the design and assembly process.

Implementation Method 1

The vibrating tube portion comprises an inner diameter and an outer diameter, wherein the inner diameter is axially shifted from the outer diameter such that the inner diameter is not concentric with the outer diameter, and wherein the axial shift increases a frequency separation between vibration modes in the vibrating tube portion

Methodology Applied

Scientific EffectVibration: Vibration

Implementation Method 2

The driver receives a drive signal from a meter electronics and vibrates the vibrating member at or near a resonant frequency

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS10571381B2Vibrating member for a vibrating densitometer

Publication Date: 2020.02.25 MICRO MOTION INC

AI summary

A vibrating member adapted for use in a vibrating densitometer is provided. The vibrating member comprises a base and a vibrating tube portion affixed to the base. The vibrating tube portion comprises an inner diameter and an outer diameter, wherein the inner diameter is axially shifted from the outer diameter such that the inner diameter is not concentric with the outer diameter, and wherein the axial shift increases a frequency separation between vibration modes in the vibrating tube portion.