GB2252402A - Fibre optic sensor - Google Patents

Fibre optic sensor Download PDF

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Publication number
GB2252402A
GB2252402A GB9027175A GB9027175A GB2252402A GB 2252402 A GB2252402 A GB 2252402A GB 9027175 A GB9027175 A GB 9027175A GB 9027175 A GB9027175 A GB 9027175A GB 2252402 A GB2252402 A GB 2252402A
Authority
GB
United Kingdom
Prior art keywords
optical fibre
test medium
light
fibre
light source
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
GB9027175A
Other versions
GB9027175D0 (en
Inventor
Abdul Latif Khalaf Al-Mohanadi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AL MOHANADI ABDUL LATIF KHALAF
Original Assignee
AL MOHANADI ABDUL LATIF KHALAF
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 AL MOHANADI ABDUL LATIF KHALAF filed Critical AL MOHANADI ABDUL LATIF KHALAF
Priority to GB9027175A priority Critical patent/GB2252402A/en
Publication of GB9027175D0 publication Critical patent/GB9027175D0/en
Publication of GB2252402A publication Critical patent/GB2252402A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
    • 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

Abstract

A fibre optic sensor 10 comprises an optical source 1 connected to an optical fibre 2 which has a multiplicity of convoluted turns 3 in a zone 4 arranged to be immersed in a test medium; the convoluted turns can be replaced by other loops, or parts of loops, with at least one turn of at least 180 degrees. Variations in light attenuation due e.g. to temperature variations of the medium are measured at detector 5. <IMAGE>

Description

Fibre ODtic Sensors The present invention is concerned with fibre optic sensors.
A known type of fibre optic sensor falling within the broad category of intensity modulated sensors, is a fibre optic sensor, which comprises an optical fibre whose optical transmission characteristics vary with temperature. Optical fibres generally have a central core, entirely surrounded by a plastics or glass sheath (the cladding) of refractive index lower than that of the cor.e.
In use, light is passed from a light source to a light detector; comparison between the light intensity at the source with that at the detector enables the temperature of a test medium through which the sensor passes to be determined. If the temperature of the test medium is known, the measurement may be used to determine other parameters such as pressure or rate of flow.
According to the present invention, there is provided a fibre optic sensor, which comprises a light source; an optical fibre coupled to said light source; and a light detector for detecting light from said source passed along said optical fibre; characterised in that said optical fibre has a region arranged to be immersed in a test medium, which region comprises at least one turn in the optical fibre of at least 180 degrees. The turn may be in the nature of a loop (or part thereof) in which an axis of curvature is transverse to the elongate direction of the optical fibre, and/or in the nature of a torsional twist, in which an axis of curvature is in the above-mentioned elongate direction.
The present invention further comprises a method of measuring a parameter of a test medium, which comprises transmitting light along the optical fibre of a fibre optic sensor according to the invention with said region in said test medium, and monitoring attenuation of light along the optical fibre so as to provide a measurement depending on the value of the parameter of the test medium.
The basis of the present invention is as follows. All optical fibres undergo losses of transmitted light; these losses can be divided into two main categories, namely those which are inherent in the fibre itself, and those which result from distortion of the fibre. If bends, loops, twists or the like are present in the optical fibre, with a radius less than a critical value, then such losses increase dramatically. Tris is believed to be because that portion of a wavefront on the '1inside'1 of a bend has to travel more slowly than that on the "outsIde" in order to maintain a stable wavefront; this differential slowing on the "inside" is measured as a loss, the loss being greater, the smaller the radius of the bend.The magnitude of the loss has been found to be critically dependent on temperature at the zone of the bend, and hence the effect can be used to measure temperature of a test medium accurately.
The present invention further comprises test apparatus which comprises a sensor according to the invention, in which the light source (such as a laser) is optically coupled to an end of the optical fibre, and the light detector is arranged to generate a signal representative of the quantity of light transmitted from the light source via the optical fibre.
The apparatus according to the invention preferably further comprises a receptacle for receiving a quantity of the test medium, such that the above-mentioned region can be immersed therein. The receptacle may be, for example, a conduit in which a test medium (generally a gas or liquid) may be arranged to flow; alternatively, it may be a substantially closed receptacle for the test medium.
It is particularly preferred that the region arranged to be immersed in the test liquid should contain a plurality of turns of the optical fibre, which are preferably in the nature of loops, optionally with one or more twists in additIon.
The apparatus according to the invention may be used for measurement of parameters other than temperature, in which case, a preferred parameter for measurement is pressure. When pressure is measured in this way, the apparatus is typically calibrated for temperature and the test medium maintained at substantially a constant temperature; any variation in the test medium is attributable to changes in pressure, therefore.
A preferred embodiment of the present Invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic sectional view of an optical fibre used in a sensor according to the invention; and Figure 2 illustrates the way in which a sensor according to the invention can be used.
Referring to Figure 1, the sensor 10 comprises an optical source 1 connected to an optical fibre 2 which has a multiplicity of convoluted turns 3 in a zoce 4; the distal end of the optical fibre is connected to a detector 5.
Referring to Figure 2, a light source 22 (preferably a laser) emits light to a beam splitter 23, from which part of the beam is fed back through a loop comprising a photodetector compensator 24 and a line 25 to the light source 22 to stabilise and regulate the output thereof.
The remaining light from beam slttr 23 enters the sensor 10 and thence passes to a photodetector 15. An electrical signal from the latter is passed along line 26 to processing hardware 27, and hence to a display 28, which is calibrated to display the temperature of the medium in which sensor 10 is in contract.

Claims (6)

Claims:
1. A fibre optic sensor, which comprises a light source; an optical fibre coupled to said light source; and a light detector for detecting light from said source passed along said optical fibre; characterised in that said optical fibre has a region arranged to be immersed in a test medium, which region comprises at least one turn in the optical fibre of at least 180 degrees.
2. A sensor according to claim 1, wherein said turn is cf a loop, or part thereof, in which an axis of curvature is transverse to the elongate direction of the optical fibre, and/or in the nature of a torsional twist, in which an axis of curvature is in said elongate direction.
3. A method of measuring a parameter of a test medium, which comprises transmitting light along the optical fibre of a fibre optic sensor according to claim 1 or 2, with said region in said test medium, and monitoring attenuation of light along the optical fibre so as to provide a measured value depending on corresponding parameter of the test medium.
4. Test apparatus which comprises a sensor according to claim 1 or 2, in which the light source is optically coupled to an end of the optical fibre, and the light detector is arranged to' generate a signal representative of the quantity of light transmitted from the light source via the optical fibre.
5. Apparatus according to claim 4, which comprises a receptacle for receiving a quantity of the test medium, such that said region can be immersed therein.
6. Apparatus according to claim 5, wherein said receptacle comprises a conduit in which a test medium may be arranged to flow.
GB9027175A 1990-12-14 1990-12-14 Fibre optic sensor Withdrawn GB2252402A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9027175A GB2252402A (en) 1990-12-14 1990-12-14 Fibre optic sensor

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9027175A GB2252402A (en) 1990-12-14 1990-12-14 Fibre optic sensor

Publications (2)

Publication Number Publication Date
GB9027175D0 GB9027175D0 (en) 1991-02-06
GB2252402A true GB2252402A (en) 1992-08-05

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB9027175A Withdrawn GB2252402A (en) 1990-12-14 1990-12-14 Fibre optic sensor

Country Status (1)

Country Link
GB (1) GB2252402A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19738651A1 (en) * 1997-09-04 1999-03-11 Alsthom Cge Alcatel Device for determining the temperature of an object and method for producing such a device
EP0984254A1 (en) * 1998-09-04 2000-03-08 Talltec Technologies Holdings S.A. Fiber-optical temperature sensor

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986005273A1 (en) * 1985-03-07 1986-09-12 Sopha Praxis Optical device for strain detection, method for measuring the strain by means of said device and their application to scales
EP0208562A2 (en) * 1985-07-12 1987-01-14 Eldec Corporation Fiber optic sensor
EP0242894A1 (en) * 1986-03-04 1987-10-28 Coenecoop B.V. Pressure sensor using optical fibres
EP0247909A1 (en) * 1986-04-24 1987-12-02 Photonetics Fibre-optical sensor
GB2201511A (en) * 1987-02-26 1988-09-01 Bicc Plc Optical sensors
GB2208711A (en) * 1988-08-16 1989-04-12 Plessey Co Plc Fibre optic sensor
EP0387376A1 (en) * 1989-03-15 1990-09-19 GLÖTZL GESELLSCHAFT FÜR BAUMESSTECHNIK mbH Pressure sensor

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986005273A1 (en) * 1985-03-07 1986-09-12 Sopha Praxis Optical device for strain detection, method for measuring the strain by means of said device and their application to scales
EP0208562A2 (en) * 1985-07-12 1987-01-14 Eldec Corporation Fiber optic sensor
EP0242894A1 (en) * 1986-03-04 1987-10-28 Coenecoop B.V. Pressure sensor using optical fibres
EP0247909A1 (en) * 1986-04-24 1987-12-02 Photonetics Fibre-optical sensor
GB2201511A (en) * 1987-02-26 1988-09-01 Bicc Plc Optical sensors
GB2208711A (en) * 1988-08-16 1989-04-12 Plessey Co Plc Fibre optic sensor
EP0387376A1 (en) * 1989-03-15 1990-09-19 GLÖTZL GESELLSCHAFT FÜR BAUMESSTECHNIK mbH Pressure sensor

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19738651A1 (en) * 1997-09-04 1999-03-11 Alsthom Cge Alcatel Device for determining the temperature of an object and method for producing such a device
US6079875A (en) * 1997-09-04 2000-06-27 Alcatel Apparatus for measuring the temperature of an object with a temperature sensor and method of making the temperature sensor
EP0984254A1 (en) * 1998-09-04 2000-03-08 Talltec Technologies Holdings S.A. Fiber-optical temperature sensor
WO2000014498A1 (en) * 1998-09-04 2000-03-16 Talltec Technologies Holdings S.A. Temperature sensor with optical fibre
US6511222B1 (en) 1998-09-04 2003-01-28 Talltec Technologies Holdings S.A. Temperature sensor with optical fibre

Also Published As

Publication number Publication date
GB9027175D0 (en) 1991-02-06

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