Coriolis Flow Sensor Asymmetric Detection Elements
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Solution Overview
Problem
Conventional Coriolis flow sensors are not sensitive enough to measure low fluid flows, requiring calibration for each fluid and being unsuitable for measuring unknown fluids, whereas micromachined Coriolis flow sensors capable of low flow measurements do not exist commercially.
Innovation Solution
A Coriolis flow sensor design featuring a Coriolis tube with transverse extension and excitation means inducing twisting oscillations, combined with detection elements positioned on opposite sides of the tube to enhance sensitivity, reducing the distance between detection elements and the excitation axis, and optimizing the placement of read-out structures like combs to increase measured Coriolis displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detection elements are positioned closer to the tube to increase sensitivity, then measurement precision improves, but sensitivity to excitation oscillations increases causing noise
Solution Approach 1:
The patent positions the two detection elements asymmetrically with respect to the excitation axis. One detection element is offset at a first distance from the excitation axis, while the other is offset at a second distance, where the offsets are unequal. This asymmetric arrangement creates differential sensitivity to Coriolis forces while maintaining balanced sensitivity to excitation oscillations, allowing the sensor to distinguish between useful Coriolis displacement and harmful excitation noise.
Solution Approach 2:
Instead of positioning detection elements symmetrically on opposite sides of the tube (conventional approach), the patent inverts the approach by deliberately creating asymmetric offsets from the excitation axis. This inversion of the symmetric positioning principle allows the detection elements to be closer to the tube for higher sensitivity while the asymmetric arrangement naturally differentiates between excitation oscillations (which affect both elements equally) and Coriolis forces (which create differential displacement).
2Object-affected harmful factors
If detection elements are positioned farther from the excitation axis to reduce excitation sensitivity, then noise from actuation oscillation decreases, but sensitivity to Coriolis displacement also decreases
Solution Approach 1:
The patent transitions from considering only the radial distance from the tube center to a two-dimensional positioning approach, where detection elements are positioned at different angular positions and radial distances from the excitation axis. By utilizing both radial and angular dimensions, the asymmetric positioning optimizes the balance between excitation noise rejection and Coriolis signal sensitivity, achieving both goals simultaneously through spatial arrangement in multiple dimensions.
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 improved sensor can measure up to 50 μg/s with zero stability of 14 ng/s, a 40-fold improvement over prior art, increasing sensitivity and reducing noise levels by minimizing actuation oscillation sensitivity and enhancing Coriolis amplitude.
Implementation Method 1
excitation means (108, 108') designed to induce a twisting oscillation of the Coriolis tube (124) about an excitation axis (29)
Implementation Method 2
As a fluid flows in the vibrating tube, it induces Coriolis forces, proportional to the mass-flow, which affect the tube motion and change the mode shape
Implementation Method 3
The detection elements each comprise capacitive read-out structures defined by two comb like structures
Data Source
AI summary
The invention relates to a Coriolis flow sensor, comprising at least a Coriolis-tube, wherein the flow sensor comprises an excitation element for causing the tube to oscillate, as well as a detection element for detecting at least a measure of displacements of parts of the tube during operation. In some embodiments, the detection element comprises two detection elements that are positioned on both sides of the Coriolis tube, wherein the detection elements partly overlap each other.