Fiber-optic strain gauge manometer
First Claim
1. A fiber-optic strain gauge manometer for measuring pressure of a fluid, to be respectively connected to a light source and a measurement apparatus, said manometer comprising:
- a cylindrical hollow body of predetermined length and acting as a pressure transducer, said hollow body having a central axis, cylindrical inner and outer surfaces, an end, and an opposite end provided with an inlet by which said fluid can get inside said hollow body, said ends being free to move longitudinally with respect to said central axis such that longitudinal and circumferential strains are generated in said hollow body when said pressure is applied on said inner surface, thereby producing a dilatation of said hollow body; and
a highly birefringent optical fiber which can maintain only some polarization states, said birefringent optical fiber having a sensing portion bonded with bonding means to said outer surface of said hollow body along a longitudinal path such that birefringence of said sensing portion changes when said sensing portion is subjected to said dilation of the hollow body, said sensing portion having a length smaller than said length of the hollow body, which is selected in function of a desired sensitivity;
wherein a polarized light beam is generated by said light source and transmitted in a form of two polarization eigenstates each parallel to one of two parallel principal birefringence axes of said birefringent optical fiber, the state of polarization of the input light beam being strain-modulated after a passage in said sensing portion, the stain-modulated output light beam being collected by said measurement apparatus for detecting and measuring change in said birefringence as a function of said dilatation, thereby giving indication of said pressure inside said hollow body.
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Abstract
A fiber-optic strain gauge manometer and a method thereof are for measuring pressure of a fluid, to be respectively connected to a light source and a measurement apparatus. The manometer comprises: a cylindrical hollow body, acting as a pressure transducer, having an inlet by which the fluid can get inside, free ends such that longitudinal and circumferential strains are generated in the hollow body by the pressure of the fluid, thereby producing a dilatation of the hollow body, and a highly birefringent optical fiber having a sensing portion bonded to the outer surface of the hollow body along a longitudinal path such that its birefringence changes when the sensing portion is subjected to the dilatation of the hollow body. A polarized light beam is generated by the light source and transmitted in a form of two polarization eigenstates each parallel to one of two parallel principal birefringence axes of the birefringent optical fiber. The state of polarization of the input light beam, being strain-modulated after a passage in the sensing portion of the birefringent optical fiber is collected by the measurement apparatus for detecting and measuring change in the birefringence as a function of the dilatation, thereby giving indication of the pressure inside the hollow body. This fiber-optic strain gauge manometer can be used for measuring pressure up to at least 100 MPa.
36 Citations
18 Claims
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1. A fiber-optic strain gauge manometer for measuring pressure of a fluid, to be respectively connected to a light source and a measurement apparatus, said manometer comprising:
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a cylindrical hollow body of predetermined length and acting as a pressure transducer, said hollow body having a central axis, cylindrical inner and outer surfaces, an end, and an opposite end provided with an inlet by which said fluid can get inside said hollow body, said ends being free to move longitudinally with respect to said central axis such that longitudinal and circumferential strains are generated in said hollow body when said pressure is applied on said inner surface, thereby producing a dilatation of said hollow body; and a highly birefringent optical fiber which can maintain only some polarization states, said birefringent optical fiber having a sensing portion bonded with bonding means to said outer surface of said hollow body along a longitudinal path such that birefringence of said sensing portion changes when said sensing portion is subjected to said dilation of the hollow body, said sensing portion having a length smaller than said length of the hollow body, which is selected in function of a desired sensitivity; wherein a polarized light beam is generated by said light source and transmitted in a form of two polarization eigenstates each parallel to one of two parallel principal birefringence axes of said birefringent optical fiber, the state of polarization of the input light beam being strain-modulated after a passage in said sensing portion, the stain-modulated output light beam being collected by said measurement apparatus for detecting and measuring change in said birefringence as a function of said dilatation, thereby giving indication of said pressure inside said hollow body. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for measuring pressure of a fluid inside a cylindrical hollow body of predetermined length and acting as a pressure transducer, said hollow body having a central axis, cylindrical inner and outer surfaces, an end, and an opposite end provided with an inlet by which said fluid can get inside said hollow body, said ends being free to move longitudinally with respect to said central axis such that longitudinal and circumferential strains are generated in said hollow body when said pressure is applied on said inner surface, thereby producing a dilatation of said hollow body, a portion of highly birefringent optical fiber which can maintain only some polarization states being bonded to said outer surface of the hollow body along a longitudinal path for subjecting said portion to said dilatation, said method comprising steps of:
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transmitting a polarized input light beam in a form of two polarization eigenstates each parallel to one of two parallel principal birefringence axes of said birefringent optical fiber, said input light beam being strain-modulated after a passage in said portion of the highly birefringent optical fiber due to change in birefringence of said birefringent optical fiber as a result of said dilatation; collecting the strain-modulated output light beam; measuring polarization change in the state of polarization between the input light beam and the strain-modulated output light beam; and determining a value indicative of said pressure as a function of the measured change in the state of polarization.
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Specification