WO1991013329A1 - Capteur de pression - Google Patents

Capteur de pression Download PDF

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Publication number
WO1991013329A1
WO1991013329A1 PCT/GB1991/000297 GB9100297W WO9113329A1 WO 1991013329 A1 WO1991013329 A1 WO 1991013329A1 GB 9100297 W GB9100297 W GB 9100297W WO 9113329 A1 WO9113329 A1 WO 9113329A1
Authority
WO
WIPO (PCT)
Prior art keywords
sensor
waveguide
fibre
pressure
length
Prior art date
Application number
PCT/GB1991/000297
Other languages
English (en)
Inventor
Mahmoud Farhadiroushan
Ian Peter Giles
Original Assignee
University College London
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University College London filed Critical University College London
Publication of WO1991013329A1 publication Critical patent/WO1991013329A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
    • G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
    • G01L11/025—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means using a pressure-sensitive optical fibre
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis

Definitions

  • This invention relates to a pressure sensor which uses an optical waveguide, preferably an optical fibre.
  • optical fibres have developed primarily for long distance communication systems, the inherent properties of optical fibres offer significant advantages in certain sensing application areas.
  • the advantages of optical fibres can be highlighted in applications where a sensitive measurement technique is required, such as in hazardous environment or in an environment where there is a high level of electromagnetic interference and where, as a consequence, electrical equipment is undesirable.
  • Optical fibres are remarkably strong, providing a compact tough passive low loss transmission medium which allows remote sensing in otherwise inaccessible measurement locations.
  • Optical fibre sensors have been originally classified into two basic categories, so called extrinsic and intrinsic sensors.
  • extrinsic sensors the optical fibre is used only to transmit/receive the optical signals from a measurement location whereas in intrinsic sensors the transmission of the light through the fibre can be affected by the measurand.
  • the extrinsic devices usually tend to require high precision optical arrangements to couple light in and out of the fibre and usually suffer from high losses in the bulk optics sensor head.
  • the sensor may be arranged so that either the intensity of the light varies directly with the measurand (intensity type of sensor) or the intensity of the detected light is dependent on the phase of the optical wave
  • interferometric type The intensity type of sensors are simpler to process but lead to mechanical design complexity and reduced measurement sensitivity.
  • the interferometric techniques are extremely sensitive, detecting variations of 1 part in
  • a pressure sensor using low birefringence fibre is described in Bertholds A and Dandliker R. , "High- resolution photoelastic pressure sensor using low- birefringence fibre". Applied optics. Vol. 25, No. 3, pp 340-343.
  • a substantial length of fibre is employed, and in the experimental arrangement described the fibre is bent into a loop with a 45mm radius of curvature.
  • the application of a pressure to the fibre produces a substantial number of interference fringes, and a phase measuring system is used to determine the change in birefringence induced by the pressure, and hence the value of the pressure itself.
  • differential compensation as in Dakin and Wade
  • complicated phase measurement techniques as in Berthold and Dandliker
  • a pressure sensor which comprises an optical waveguide which supports the two orthogonal fundamental guided modes and whose length is short compared to the beat length of the waveguide, polarizing means for linearly polarizing light supplied to and received from the said waveguide, and pressure means permitting the said waveguide to be subjected, by a pressure which the sensor is to be measured, at an acute angle to the axis of polarization to a force or to a force which differs from that to which it is subjected at other angles.
  • the waveguide is preferably an optical fibre,and most preferably a single mode optical fibre, though it could be some other form of solid waveguide, which would not necessarily have an outer cladding boundary of circular cross-section.
  • short length we mean short compared to the beat length of the fibre, preferably less than 10% ⁇ of the beat length, and more preferably less than 1% of the beat length.
  • Figure 1 shows how the polarization of light in an optical fibre depends on the application of an external force (Figure lb) and on an alteration in temperature (Figure lc) ;
  • FIG. 2 shows an embodiment of the invention
  • Figure 3 is a graph showing, the variation of intensity with the phase shift produced in the invention.
  • Figures 4 to 7 show various ways in which a force may be applied to an optical fibre in the invention
  • FIGS 8 to 10 show three alternative configurations to that shown in Figure 2.
  • Figure 11 shows a complete sensing arrangement
  • FIG. 1 shows a fibre having three regions, the first of which is unperturbed (i.e. subjected to no external influence) , the second of which is subjected to force and the third of which is subjected to a temperature change.
  • Diagrams (a), (b) and (c) show the polarization of light propagating in each of the three sections.
  • the fibre is a conventional single mode fibre of low birefringence.
  • a single mode optical fibre allows two orthogonal polarization modes to propagate at the same velocity without coupling energy, provided the fibre is isotropic and homogeneous. Any inho ogeneities in the fibre produce a birefringence (i.e. directionally dependent refractive index) which modifies the relative phase velocity of the polarization modes, consequently altering the state of the polarization of the light. This effect is unavoidable in commercially available optical fibre because of "frozen in" birefringence and environmentally induced birefringence. The sum total of these two sources of birefringence is referred to below as the natural birefringence of the fibre.
  • An optical fibre can be characterized by a beat length, that is to say, the length of fibre through which light must pass before, on average, the two above mentioned orthogonal modes will have shifted in phase relative to one another by 2 ⁇ r as a result of the natural birefringence. If the length of fibre is small compared to the beat length the relative phase shift will also be small. Since the beat length of- a typical commercial fibre is of the order of lm, the "short length" required by the present invention is typically less than 10cm and preferably less than 1cm.
  • any polarization state can then be described by a linear superposition of the above mentioned two modes.
  • a linear input polarization can be resolved into two orthogonal polarization modes with equal intensities ( Figure 1) .
  • Figure 1 When the two polarization modes are combined with a 45° polarizer, i.e. a polarizer in which the axis of polarization is at 45° to both the above mentioned orthogonal polarization modes, the output intensity is given by:
  • I E oj is the input intensity and ⁇ is the phase difference between the two polarization modes.
  • the output intensity is a periodic function of the phase difference.
  • Measurement of the phase variation gives a simple method to measure the level of the applied force. Although the refractive index of the fibre changes with temperature, the difference between the refractive indices of the two polarization modes does not change ( Figure lc) . Therefore the operation of the pressure sensor is not effected by the environmental temperature variations.
  • the sensor probe 10 is a single fibre interferometer. This is an intrinsic device which offers high sensitivity and yet has the simplicity of a single fibre device.
  • the sensor is constructed from a short length of standard single mode optical fibre 11 connected to a polarizer 12, preferably an all fibre polarizer, the polarization axis of which is at 45* to the direction in which force is to be applied.
  • the end of the fibre is mirrored, represented diagrammatically by mirror 13, to reflect the light back through the polarizer.
  • An input optical signal which is preferably of random polarization, though-it may have any polarization except plane polarization orthogonal to the polarization axis of the polarizer 12, is passed through the polarizer 12 to define a single polarization mode which can be resolved parallel and perpendicular to the direction of the applied force.
  • Applying a force produces a birefringence proportional to the force, which modifies the state of polarization, thus changing the sensor output intensity.
  • the "natural" birefringence of the optical fibre 11 is very low and the propagation length very small, and therefore any temperature variations produce negligible phase difference between orthogonal polarization modes.
  • the present invention makes it possible to use low coherence sources, such as LEDs and multimode semiconductor lasers, and therefore imposing less stringent requirements on the coherence properties of optical source than that of the Bertholds and Dandliker device.
  • induced birefringence, B for a circular cross-section fused silica fibre, can be expressed as: —
  • a is a constant, equal to 1.58 for round fibre
  • n is the index of refraction of the core
  • C is the elasto-optic coefficient for fused silica
  • f is the force per unit length of the fibre
  • D is the outside diameter of the fibre
  • ⁇ is the optical wavelength of the source.
  • a force of F 6.8 N is required. If a pressure, P, is exerted onto the fibre by a means of a plate squeezing the fibre, then the magnitude of the force can be adjusted depending on the size of the area of the plate, A, such that
  • the sensitivity of the sensor can be adjusted by controlling the effective interaction area over which the pressure is exerted on to the fibre.
  • the sensitivity of the sensor is adjusted such that the maximum range of the operation does not exceed its half cycle period as indicated in Figure 3.
  • Figure 3 is a plot of intensity on the ordi ⁇ ate against phase on the abc ⁇ i ⁇ sa.
  • the dynamic range R used is from O to TT .
  • the sensor can be considered as a simple intensity output sensor with a well known output characteristic as a function of applied pressure. Intensity signal processing techniques can therefore be employed to monitor the sensor output intensity.
  • Pressure can be applied to the fibre in a variety of ways.
  • One way is by using a plate above the fibre to squeeze it as shown schematically in Figure lb.
  • Another way, for use in an application where the sensor is to measure fluid pressure, is shown in Figure 4.
  • the optical fibre 11 is set in a recess 14 formed in a solid block 15, the recess being covered by a membrane 16 which is impermeable to the fluid concerned.
  • Fluid pressure is applied to the other side of the membrane through an aperture 17 formed in another solid bl ⁇ ck 18.
  • the fibre can be shape the fibre so that it is asymmetric in cross-section. This last technique allows the measurement of hydrostatic pressure by simply placing the probe into the measurement area.
  • the asymmetry can be introduced by polishing one side of the optical fibre 11 (or two opposite sides) so that at least one flat 20 is produced ( Figure 5) .
  • the fibre can be set in a rectangular aperture 21 formed in a block 22 (see Figure 6) so that pressure is applied asymmetrically on to the fibre. As can be seen in Figure 6, the top and bottom surfaces of the aperture 21 apply a force to the fibre, whereas the side walls do not.
  • the asymmetrical application of force can also be achieved by coating the fibre asymmetrically ( Figure 7) , and such a coating can also serve to protect the fibre. In this way a differential force is applied across the fibre resulting in birefringence.
  • the upper and lower surfaces of the fibre have coating strips 23 and 24 applied to them and the sides are uncoated.
  • a coating is applied completely around the fibre, but more thickly is two diametrically opposed regions than elsewhere. This enables the protection just mentioned to be provided.
  • the sensing element described above has the polarizer at the sensor head. This is not essential and an alternative approach is to make the polarizer remote from the sensor head, by using a polarization maintaining optical fibre 30, as shown in Figure 8.
  • the polarizer 12 is aligned to one axis of the polarization maintaining optical fibre 30 at one end thereof, and the other end of the fibre 30 is spliced by a splice 31 to the fibre 11 with the polarization axis, at an angle of 45" to the direction of applied pressure.
  • FIGS 9 and 10 Modifications of this, for use in transmission rather than reflection, are shown in Figures 9 and 10.
  • two polarizers 12a and 12b are located at opposite ends of the fibre.
  • two polarizers 12a and 12b are again used, but in this instance each is remote from the optical fibre 11 and is connected thereto via respective polarization maintaining fibres 30a and 30b and 45* splices 31a and 31b.
  • Figure 11 shows a complete sensing arrangement using the sensor probe 10 shown in Figure 2.
  • Light from an optical source 40 for example an LED, passes through a four-port coupler 41. This is connected to the sensor probe and to a pair of photodetectors 42 and 43.
  • the photodetector 42 monitors the intensity of the light returning from the probe 10, and the photodetectors 42 and 43.
  • the photodetector 42 monitors the intensity of the light returning from the probe 10, and the photodetector 43 provides a reference by monitoring the intensity of light being sent to the proble 10.

Abstract

On décrit un capteur de pression utilisant un guide d'onde optique à mode simple tel qu'une fibre optique à mode simple (11). On applique la lumière à la fibre à travers un polariseur (12) et ladite lumière est reçue de la fibre soit, après réflexion, à travers le même polariseur, soit par transmission à travers un deuxième polariseur. La pression à mesurer exerce une force sur la fibre uniquement suivant un angle aigu, de préférence 45°, par rapport à l'axe de polarisation. Alternativement, la pression crée à l'intérieur de la fibre une contrainte pour l'angle aigu, différente de ce qu'elle est pour d'autres angles.
PCT/GB1991/000297 1990-02-26 1991-02-26 Capteur de pression WO1991013329A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9004240.9 1990-02-26
GB909004240A GB9004240D0 (en) 1990-02-26 1990-02-26 Optical fibre pressure sensor

Publications (1)

Publication Number Publication Date
WO1991013329A1 true WO1991013329A1 (fr) 1991-09-05

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1991/000297 WO1991013329A1 (fr) 1990-02-26 1991-02-26 Capteur de pression

Country Status (3)

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AU (1) AU7312091A (fr)
GB (1) GB9004240D0 (fr)
WO (1) WO1991013329A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5336883A (en) * 1991-05-03 1994-08-09 Focas Limited Optical fiber sensor for producing a variable transverse strain in a localized portion of the fiber
EP0622622A2 (fr) * 1993-04-27 1994-11-02 Hitachi, Ltd. Appareil de détection d'une quantité physique et appareil de contrôle d'un moteur à combustion interne, chaqun utilisant une fibre optique
GB2277585A (en) * 1993-04-23 1994-11-02 Focas Ltd Fibre optic sensor
GB2414543A (en) * 2004-05-25 2005-11-30 Polarmetix Ltd Method and apparatus for detecting pressure distribution in fluids
US9347312B2 (en) 2009-04-22 2016-05-24 Weatherford Canada Partnership Pressure sensor arrangement using an optical fiber and methodologies for performing an analysis of a subterranean formation

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2123810A (en) * 1982-07-14 1984-02-08 Hitachi Cable Fabrication of single polarization optical fibres
EP0120999A2 (fr) * 1983-03-30 1984-10-10 Licentia Patent-Verwaltungs-GmbH Elément sensible à fibre optique pour mesurer des forces et des pressions, aussi applicable dans le domaine de surveillance et de protection
US4488040A (en) * 1982-11-19 1984-12-11 Gte Products Corporation Fiber optic sensor
EP0144509A2 (fr) * 1983-11-09 1985-06-19 Polaroid Corporation Transducteur d'interféromètre par fibre optique
US4920261A (en) * 1989-05-24 1990-04-24 Universite Du Quebec A Hull Birefringent optical fiber device for measuring of ambient pressure in a stabilized temperature environment

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2123810A (en) * 1982-07-14 1984-02-08 Hitachi Cable Fabrication of single polarization optical fibres
US4488040A (en) * 1982-11-19 1984-12-11 Gte Products Corporation Fiber optic sensor
EP0120999A2 (fr) * 1983-03-30 1984-10-10 Licentia Patent-Verwaltungs-GmbH Elément sensible à fibre optique pour mesurer des forces et des pressions, aussi applicable dans le domaine de surveillance et de protection
EP0144509A2 (fr) * 1983-11-09 1985-06-19 Polaroid Corporation Transducteur d'interféromètre par fibre optique
US4920261A (en) * 1989-05-24 1990-04-24 Universite Du Quebec A Hull Birefringent optical fiber device for measuring of ambient pressure in a stabilized temperature environment

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Applied Optics, volume 28, no. 15, 1 August 1989, (New York; US), T.H. Chua et al.: "Fiber polarimetric stress sensors" pages 3158-3165 *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5336883A (en) * 1991-05-03 1994-08-09 Focas Limited Optical fiber sensor for producing a variable transverse strain in a localized portion of the fiber
GB2277585A (en) * 1993-04-23 1994-11-02 Focas Ltd Fibre optic sensor
GB2277585B (en) * 1993-04-23 1997-04-16 Focas Ltd Fibre optic sensor
EP0622622A2 (fr) * 1993-04-27 1994-11-02 Hitachi, Ltd. Appareil de détection d'une quantité physique et appareil de contrôle d'un moteur à combustion interne, chaqun utilisant une fibre optique
EP0622622A3 (en) * 1993-04-27 1994-11-23 Hitachi Ltd Physical quantity detecting apparatus and internal combustion engine control apparatus each utilizing optical fiber.
US5693936A (en) * 1993-04-27 1997-12-02 Hitachi, Ltd. Physical quantity detecting apparatus and internal combustion engine control apparatus each utilizing optical fiber
GB2414543A (en) * 2004-05-25 2005-11-30 Polarmetix Ltd Method and apparatus for detecting pressure distribution in fluids
GB2414543B (en) * 2004-05-25 2009-06-03 Polarmetrix Ltd Method and apparatus for detecting pressure distribution in fluids
US7940389B2 (en) 2004-05-25 2011-05-10 Fotech Solutions Limited Method and apparatus for detecting pressure distribution in fluids
US9347312B2 (en) 2009-04-22 2016-05-24 Weatherford Canada Partnership Pressure sensor arrangement using an optical fiber and methodologies for performing an analysis of a subterranean formation
US10246989B2 (en) 2009-04-22 2019-04-02 Weatherford Technology Holdings, Llc Pressure sensor arrangement using an optical fiber and methodologies for performing an analysis of a subterranean formation
US10837274B2 (en) 2009-04-22 2020-11-17 Weatherford Canada Ltd. Pressure sensor arrangement using an optical fiber and methodologies for performing an analysis of a subterranean formation

Also Published As

Publication number Publication date
GB9004240D0 (en) 1990-04-18
AU7312091A (en) 1991-09-18

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