Bourdon Tube Pressure Sensor with Offset Blind Bore
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing pressure monitoring technologies, particularly those using fibre Bragg gratings, face limitations in high-temperature, harsh environments such as downhole oil or gas wells due to mechanical constraints, reduced sensitivity, accuracy issues, birefringence, and creep at elevated temperatures, as well as challenges in miniaturization and temperature compensation.
Innovation Solution
A fluid pressure monitoring apparatus featuring an elongated member with a blind bore offset from its central axis, deflecting under fluid pressure, and an optical fibre Bragg grating sensing device measuring the change in distance between fixed and moving positions, allowing for adjustable sensitivity and accuracy, reduced birefringence, and robust mechanical fixation, along with temperature compensation using a second strain sensor or a separate apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diaphragm strain based transducer with FBG is used, then pressure sensing capability is achieved, but mechanical interface options are reduced and creep occurs at elevated temperatures
Solution Approach 1:
The patent replaces the mechanical diaphragm structure with a direct Bourdon tube configuration where the FBG is epoxied directly to the curved tube. This eliminates the need for separate diaphragm components and mechanical interfaces, reducing creep issues while maintaining pressure sensing capability through the elastic deformation of the Bourdon tube itself.
Solution Approach 2:
The patent uses a composite construction combining the Bourdon tube material (typically stainless steel or Inconel) with the optical fibre and epoxy adhesive. This composite structure allows the tube to provide mechanical strength and pressure response while the epoxy provides strain transfer to the FBG, achieving both reliability and manufacturing ease.
2Measurement precision
If the strain in the fibre is limited to the elastic strain range of the diaphragm material, then measurement accuracy is maintained, but sensitivity and accuracy of the transducer are limited
Solution Approach 1:
The patent changes the strain range parameter by utilizing the larger elastic strain range of the Bourdon tube material compared to the diaphragm material. The curved Bourdon tube can undergo greater elastic deformation before yielding, allowing the FBG to experience higher strains and provide enhanced sensitivity while maintaining accuracy within the elastic regime.
3Measurement precision
If the diaphragm size is increased to maintain constant strain along the FBG, then spectral profile broadening is avoided, but miniaturization is limited
Solution Approach 1:
Instead of increasing diaphragm size to achieve constant strain, the patent inverts the approach by using a curved Bourdon tube configuration where the geometry itself provides the strain distribution. The curvature of the tube creates a more uniform strain distribution along the FBG without requiring large diaphragm dimensions, enabling miniaturization while maintaining spectral profile stability.
4Ease of manufacture
If non-uniform loading of the FBG occurs during attachment, then birefringence is introduced, but this leads to less accurate wavelength measurements and increased complexity
Solution Approach 1:
The patent replaces the diaphragm attachment mechanism with direct epoxy bonding of the FBG to the Bourdon tube. This substitution eliminates the mechanical loading and misalignment issues that cause birefringence in diaphragm-based systems, achieving both ease of manufacture and measurement accuracy by creating a more uniform strain distribution.
5Measurement precision
If temperature compensation measurements are carried out, then pressure accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the temperature compensation function with the pressure sensing function by using a single FBG-mounted on the Bourdon tube that responds to both temperature and pressure. Through careful design of the Bourdon tube geometry and material selection, the temperature effects are minimized or compensated within the same sensing element, eliminating the need for separate compensation measurements and reducing system complexity.
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 provides enhanced sensitivity, accuracy, and durability for pressure monitoring in harsh environments by minimizing mechanical constraints and creep, while reducing birefringence and enabling effective temperature compensation, thus improving the reliability of pressure measurements.
Implementation Method 1
a blind bore extending through the elongated member and having an opening through which fluid is provided to the bore when in use, and wherein the bore is offset from a central axis of the elongated member such that the elongated member deflects in response to the pressure of the fluid
Implementation Method 2
the elongated member deflects in response to the pressure of the fluid when provided to the bore
Implementation Method 3
the Bragg grating experiencing a strain as a result of the change in distance between the first and second positions
Implementation Method 4
A Bragg grating incorporated into an optical fibre known as a fibre Bragg grating (FBG), for example, gives rise to a periodic variation in the refractive index of the fibre. Light travelling down the fibre is partially reflected at each of the variations
Implementation Method 5
an optical transmission means extending between the first position and the second position, the optical transmission means containing a Bragg grating
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A fluid pressure monitoring apparatus for use in high temperature, harsh environment applications, is described. The apparatus comprises an elongated member, having a free end and a fixed end, and a blind bore extending through the elongated member the bore having an opening through which fluid is provided to the bore when in use. The bore is offset from a central axis of the elongated member such that the elongated member deflects in response to the pressure of the fluid when provided to the bore. The apparatus further comprises a sensing device adapted to sense the change in distance between a first position, and a second position, in response to the deflection of the elongated member.