Fiber Optic Pressure Sensor Strain Decoupling
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Solution Overview
Problem
Existing fiber optic pressure sensors face issues with temperature grating susceptibility to induced strain and vibration, leading to cross-coupling with pressure measurements, and require additional fiber for improved temperature compensation, which increases sensor size and may not fit in well environments.
Innovation Solution
A pressure sensor assembly with a flexible wall and separate fiber optical cable sections, one bonded to the flexible wall for pressure measurement and the other to a thermal reference body with a strain-decoupled connection, allowing for precise temperature compensation using FBGs with nominally identical wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a single optical fiber is used with closely spaced pressure and temperature gratings, then the sensor structure is compact, but the temperature grating becomes susceptible to induced strain and vibration causing cross-coupling with pressure measurements
Solution Approach 1:
The patent divides the optical sensing function into two separate fiber optic cable sections: one dedicated to pressure measurement (first section bonded to flexible wall) and another to temperature measurement (second section bonded to thermal reference body). This segmentation isolates the temperature grating from mechanical strain and vibration, eliminating cross-coupling errors while maintaining compact sensor design through integrated housing.
2Measurement precision
If additional fiber is added for improved temperature compensation, then temperature sensitivity is enhanced, but sensor size increases and may not fit in well environments
Solution Approach 1:
The patent nests both fiber optical cable sections and their respective gratings within a single integrated sensor housing. The first fiber section with pressure grating and the second fiber section with temperature grating are accommodated together with the flexible wall and thermal reference body, allowing improved temperature compensation without increasing overall sensor dimensions beyond well environment constraints.
3Device complexity
If the temperature grating is bonded directly to the pressure sensing structure, then the sensor structure is simplified, but the temperature grating experiences induced strain from pressure changes
Solution Approach 1:
The patent introduces a thermal reference body as an intermediary between the temperature grating and the pressure sensing structure. The second fiber optical cable section is bonded to this thermal reference body, which is connected to the sensor housing by a strain-decoupled mechanism. This intermediary isolates the temperature grating from pressure-induced strain while maintaining thermal coupling for accurate temperature sensing.
4Measurement precision
If FBGs with nominally identical wavelengths are used for both pressure and temperature sensing, then measurement precision is improved through better differentiation, but the device complexity increases
Solution Approach 1:
The patent segments the optical sensing into two separate fiber sections with FBGs having nominally identical wavelengths. The first section measures pressure through flexible wall deformation, while the second section measures temperature through thermal reference body expansion. This segmentation enables precise differentiation of pressure and temperature effects using identical wavelength FBGs, with the separate physical paths eliminating cross-interference.
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
This design reduces measurement uncertainty, enhances temperature sensitivity, and allows for more precise pressure measurements by isolating temperature sensing from mechanical strains, while maintaining a compact sensor size suitable for well environments.
Implementation Method 1
Each of the first and second fiber optical cable sections comprises at least one Fiber Bragg Grating (FBG) of which the length varies in response to variation of the length of the cable section comprising the FBG
Implementation Method 2
a sensor housing having a flexible wall that is configured to deform in response to a pressure difference between the interior and exterior of the sensor housing
Implementation Method 3
a second fiber optical cable section which is bonded to a thermal reference body, which is connected to the sensor housing by a strain decoupled connection mechanism and is configured to deform substantially solely in response to thermal changes
Data Source
AI summary
A pressure sensor assembly comprises a sensor housing having a flexible wall that is configured to deform in response to a pressure difference between the interior and exterior of the sensor housing; -a first fiber optical cable section that is bonded to the flexible wall of the sensor housing such that the length of the first fiber optical cable section changes in response to deformation of the wall in response to the said pressure difference; a second fiber optical cable section which is bonded to a thermal reference body, which body is connected to the sensor housing by a strain decoupled connection mechanism, such as a tack weld or flexible glue, and is configured to deform substantially solely in response to thermal deformation, such that the length of the second fiber optical cable section solely changes in response to thermal deformation of the thermal reference body.