Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-06-11
2003-07-01
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227140, C385S013000
Reexamination Certificate
active
06586723
ABSTRACT:
The present invention relates to a detection system for use in detecting the presence of a non-aqueous organic measurand, such as a hydrocarbon. One example is to detect the leaking of crude oil from a pipeline.
WO94/18536 describes a system for detecting the presence of an aqueous measurand. The system includes a fibre-optic probe assembly which incorporates an optical fibre, a thin film of a water swellable hydrogel and a rigid containment structure. The hydrogel is in contact with the optical fibre such that a volumetric change in the hydrogel causes a microbend of the optical fibre which is detected by a sensor assembly coupled to the probe assembly by means of optical time domain reflectometry (OTDR).
However, the system described in WO94/18536 is only for the detection of aqueous target measurands which serve to swell a responsive hydrogel material and as such are sensitive only to water-containing measurands. Moreover, the hydrogel block copolymers disclosed therein have a high degree of hydrogen bonding and can therefore be susceptible to the Marangoni effect (see below).
WO95/08838 discloses a method and apparatus for detecting the presence of a liquid or vapour hydrocarbon analyte. The apparatus employs discrete units of silicone rubber to absorb hydrocarbons and thus expand. However, to allow sufficient expansion of the absorber-expander material for detection, the material is typically in the range of 10 mm or more in diameter. Furthermore, calibration of the apparatus is necessary and since it is not possible to produce a continuous coating due to cost, the spatial sensitivity is dependent on the spacing of the discrete units of silicone rubber.
It is an object of the present invention to provide a detection system which is capable of detecting the presence of a wide variety of non-aqueous organic measurands.
According to the present invention, there is provided a detection system for use in detecting the presence of a non-aqueous organic measurand, said system comprising: a fibre-optic probe assembly incorporating an optical fibre which is susceptible to micro bending anywhere along its length, and a body of material contained within a rigid containment structure, wherein the body of material comprises a rubber, plastic or semi-crystalline/rubbery polymeric material which is subject to a volumetric change capable of inducing a microbend in said optical fibre in the presence of said non-aqueous organic measurand and wherein the body of material is a substantially continuous coating which has a thickness prior to contact with the non-aqueous measurand of less than 7.5 mm;
and a sensor assembly coupled to the probe assembly, the sensor assembly having optical signal transmitting and receiving means arranged to identify optical fibre microbend changes arising, in use, from forces imposed locally on the fibre by the interaction of the rigid containment structure and volumetric changes in the body of material.
Substantially continuous coating is understood to refer to a coating of material comprising a rubber, plastic or semi-crystalline/rubbery polymeric material which covers more than 50%, preferably more than 65%, and most preferably, more than 80% of the surface of a former or optical fibre.
The system may be used simply to detect the presence of a target measurand at an unspecified location along the length of the optical fibre, though it is preferred that said signal transmitting and receiving means is also capable of detecting the particular location on the optical fibre where the signal carrying property of the optical fibre has changed and thus also detecting the particular location of the affected portion of the body of material (which is preferably elongate).
In a modification, the system may have more than one probe assembly in which case the sensor assembly is provided with a logic function output circuit to decipher the effects of different target measurands on the different polymers of the different probe assemblies.
The body of material may be extended to form a continuous rod or may be deposited as a coating on a former or the optical fibre. The thickness of the rod or coating is less than 7.5 mm, such as less than 1 mm, for example less than 200 &mgr;m or even 50 &mgr;m. Preferably the rod or coating is continuous with the length of optical fibre, thereby enabling extremely accurate detection of a microbend of the optical fibre and positioning of the non-aqueous organic measurand ingress.
The body of material may expand on exposure to one target measurand, and may contract on exposure to another target measurand to be detected.
The exposure of the body of material to a target measurand may result in a permanent change in volume, or the material may return to its original configuration on removal of the target measurand.
Preferably also, the rubber, plastic or semi-crystalline/rubbery polymeric material has chemical characteristics tailored to provide responsiveness to the target measurand.
The body of material may comprise a second component, said component being tailored to provide responsiveness to the target measurand. The second component can either through interaction with the rubber, plastic or semi-crystalline/rubbery polymeric material, or alone, be subject to volumetric change on exposure to said target measurand.
Preferably also, the containment structure comprises a sheath which may be braided for externally protecting the optical fibre and the body of material from external disturbance, which sheath is porous to allow the body of material to be exposed to the target measurand. Alternatively, the sheath may be non-porous but sacrificially corrodible in the presence of the target measurand.
If the signal transmitting and receiving means produces pulses of optical energy into the optical fibre the backscattered energy resulting from such microbends may be measured as a function of time, or distance travelled along the fibre length. This technique is known as Optical Time Domain Reflectometry (OTDR), and an earlier application of OTDR is described, for example, in EPA 0 490 849.
The optical fibre is preferably bound to the body of material, which is preferably elongate, by an inelastic third member. Most preferably, the third member is thread-like in form. With this arrangement, expansion or contraction of a portion of the body of material causes the thread-like member to bite into, or relax its grip on the optical fibre at one or more distinct locations, thus increasing or decreasing the microbends formed in the optical fibre by the thread-like member and facilitating detection and location of the presence of the target measurand.
The sensor assembly may utilise a continuous coating of an organic measurand (eg. fluid or vapour swellable) rubber, plastic or semi-crystalline/rubbery polymeric material system along the entire length of an optical fibre. This is achieved by either coating the absorbent material directly onto the optical fibre or by attaching a separate, coated former or rod along the entire length of the optical fibre. As the coating or attached coated former/rod is continuous along the length of the optical fibre, the complete length of the sensing cable will be responsive to the presence of an organic measurand. The coating is not sensitive to and does not swell to any significant degree in water or other aqueous measurands. Thin responsive coatings (e.g. <50 or <200 microns) will give a rapid detecting response in the order of seconds or minutes. However, in some situations, thicker coatings (>200 microns) may be used where a larger microbending response is desired, in which case the time of the detection response will be in the order of minutes to hours. By carefully selecting the absorbent polymeric material, it is possible to detect almost any organic measurand.
As an example, polymeric materials in contact with chemically and thermodynamically compatible organic liquids, initially, absorb and swell with the molecules of the organic liquid to form a swollen gel. The swelling of the material is accompanied by a vol
Michie Walter Craig
Moran Christopher Raymond
Alston & Bird LLP
Pyo Kevin
University of Strathclyde
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