EP0334533A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Fibre optic discrete or continuous liquid level sensor
Assignee: IMO Industries Inc
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Filing: 1989-03-14
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Granted: —
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Expires: 2009-03-14
Abstract
Abstract A fibre optic sensor, particularly for ascertaining fluid levels, utilizes at least two optical fibres or waveguides (1,2) having at least a portion thereof embedded in a transparent substrate material (4) of similar refractive index. One of the fibres (1) is coupled to a light source (5), the other (2) to a light detector (6). The source fibre (1) illuminates the interior of the substrate (4) so that light exiting the source fibre (1) is coupled to the detector fibre (2) when total internal reflection at the substrate-fluid interface occurs in the presence of a first fluid. In the presence of a second fluid of higher refractive index than the first fluid, there will be no coupling, due to the loss of light into the fluid by refraction. One mechanism for coupling light into the detector fibre (2) is fluorescence within that fibre causing it to provide a light signal which varies with the level of the second fluid. Several different embodiments, to achieve discrete or continuous level sensing or the sensing of other parameters, are disclosed.
Inventors
- 👤 James W. Snow
- 👤 Paul D. Colbourne
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-31 09:05
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/28; G01F23/284; G01F23/292; G01F23/2921; G01F23/2922; G01F23/2925; G01F23/2927
Claims Analysis
Total Claims: 28
Claim 1
Independent Claim
148 words
An indicating device for showing the level of fluids in a container, comprising at least two optical fibres having at least a portion thereof embedded in a transparent substrate material of similar refractive index, one of said fibres being optically connected to a light source and being capable of emitting a particular wavelength or range of wavelengths of light along its length, the other fibre being optically connected to a light detector and being doped so as to fluoresce at the wavelength(s) emitted by said source fibre, the two optical fibres being oriented with respect to the substrate-fluid interface so that light exiting the source fibre is coupled into the detector fibre when total internal reflection occurs at the substrate-fluid interface in the presence of a first fluid, and coupling does not occur in the presence of a second fluid of higher refractive index than the first fluid.
Claim 2
Dependent Claim
148 words
An indicating device for showing the level of fluids in a container, comprising at least two optical fibres having at least a portion thereof embedded in a transparent substrate material of similar refractive index, one of said fibres being optically connected to a light source and being capable of emitting a particular wavelength or range of wavelengths of light along its length, the other fibre being optically connected to a light detector and being doped so as to fluoresce at the wavelength(s) emitted by said source fibre, the two optical fibres being oriented with respect to the substrate-fluid interface so that light exiting the source fibre is coupled into the detector fibre when total internal reflection occurs at the substrate-fluid interface in the presence of a first fluid, and coupling does not occur in the presence of a second fluid of higher refractive index than the first fluid.
Claim 3
Dependent Claim
24 words
The device according to Claim 1 wherein the source and detector optical fibres are essentially parallel to each other and to the substrate-fluid interface.
Claim 4
Dependent Claim
54 words
The device according to Claim 1 , characterized in that the source and detector optical fibres and the planar substrate - fluid interface are not parallel to each other, the deviation from the parallel being arranged such as to linearize the optical output in irregular-shaped tanks, thereby giving a direct measurement of liquid quantity.
Claim 5
Dependent Claim
39 words
The device according to Claim 1, characterized by the application of mirrors, reflective gratings, and/or lenses to maximize the radial optical coupling between the source optical fibre and the detector optical fibre under the condition of total internal reflection.
Claim 6
Dependent Claim
32 words
The device according to Claim 1, characterized in that a portion of the substrate's interface to the fluid is reflective such that some reflection always occurs thus providing a self checking feature.
Claim 7
Dependent Claim
32 words
The device according to Claim 4, characterized in that the lenses are convex or cylindrical positive if the lens material is of a higher refractive index than that of the substrate material.
Claim 8
Dependent Claim
32 words
The device according to Claim 4, characterized in that the lenses are concave or cylindrical negative if the lens material is of a lower refractive index than that of the substrate material.
Claim 9
Dependent Claim
50 words
The device according to Claim 1, characterized in that periodic opaque spacers segment the substrate to block shallow angle light rays exiting the source optical fibre and to prevent coupling of these light rays to the detector optical fibre by other than the primarily radial direction of total internal reflection.
Claim 10
Dependent Claim
41 words
The device according to Claim 1, characterized in that an opaque separator is provided longitudinally between the source optical fibre and the detector optical fibre to prevent any optical coupling between the two optical fibres by other than total internal reflection.
Claim 11
Dependent Claim
31 words
The device according to Claim 1 configured with a series of bundled source fibres of different lengths, the output signal from the fluorescent detector fibre varying stepwise with the fluid level.
Claim 12
Dependent Claim
36 words
The device according to Claim 1 wherein the detector fibre includes discrete fluorescent segments joined alternating with non-fluorescent segments, the output thereby varying stepwise with the fluid level, the source fibre being a single line fibre.
Claim 13
Independent Claim
88 words
A method for detection of movement or position, wherein there is optical coupling between two adjacent and parallel or nearly parallel optical fibres, one of which is modified to leak light along its length, the other of which has its core doped with a fluorescent material, the resulting fluorescence optical power being proportional to the coupling length, such optical coupling length being varied by an opaque shutter between the two optical fibres, the position of the shutter being subject to the external movement or displacement to be measured.
Claim 14
Independent Claim
88 words
A method for detection of movement or position, wherein there is optical coupling between two adjacent and parallel or nearly parallel optical fibres, one of which is modified to leak light along its length, the other of which has its core doped with a fluorescent material, the resulting fluorescence optical power being proportional to the coupling length, such optical coupling length being varied by an opaque shutter between the two optical fibres, the position of the shutter being subject to the external movement or displacement to be measured.
Claim 15
Dependent Claim
103 words
The device according to Claim 1, the fibres being arranged within the substrate such that light emitted from the source fibre illuminates the core of the substrate, which serves as a larger waveguide, and (a) is coupled into the detector fibre when total internal reflection occurs at the substrate-fluid interface, which is the case when the first fluid if relatively low refractive index is present, or (b) is not coupled into the detector fibre when refraction occurs at the substrate-fluid interface, which is the case when the second of higher refractive index, namely the fluid whose level is to be measured, is present.
Claim 16
Dependent Claim
42 words
The device of CLaim 13, wherein the source fibre is made to emit a particular wavelength or range of wavelengths of light so as to excite longer wavelength fluorescence in said detector fibre only when total internal reflection occurs within the substrate.
Claim 17
Dependent Claim
16 words
The device according to Claim 14, wherein the substrate or waveguide is circular in cross section.
Claim 18
Dependent Claim
33 words
The device according to Claim 15, wherein the fluorescent detector fibre extends longitudinally of the sensor's length and is positioned eccentrically of the central axis so as to intercept the predominant skew rays.
Claim 19
Dependent Claim
29 words
The device according to Claim 15, wherein the fluorescent detector fibre extends helically along and around the sensor over its length so as to intercept the predominant skew rays.
Claim 20
Dependent Claim
40 words
The device according to Claim 17, wherein the pitch of the detector fibre helix is decreased to compensate for attenuation of the light source along the sensor's length, or is varied to provide a linear response for irregular container shapes.
Claim 21
Dependent Claim
39 words
The device according to Claim 15, wherein the fluorescent detector fibre is shrouded from the source illumination near the top of the sensor in the region where the substrate or waveguide core is not yet fully and uniformly illuminated.
Claim 22
Dependent Claim
35 words
The device according to Claim 15, wherein the end of the substrate opposite the source is mirrored to provide an abrupt increase in fluorescence when the fluid level drops below the end of the substrate.
Claim 23
Dependent Claim
22 words
The device according to claim 15, wherein the end of the substrate opposite the source is made non-reflecting to simplify linearization requirements.
Claim 24
Dependent Claim
40 words
The device according to claim 14, wherein the source fibre is angled such that its numerical aperture or exit cone of light satisfies the principle of total internal reflection within the substrate unless the liquid to be sensed is present.
Claim 25
Dependent Claim
36 words
The device according to claim 15, wherein each source fibre of a bundle of source fibres is splayed radially to more uniformly illuminate the core of the substrate and increase light level for improved sensor performance.
Claim 26
Dependent Claim
25 words
The device according to claim 16, 17 or 23 wherein the detector fibre has segments of the fluorescent-doped material separated by segments of non-fluorescent fibre.
Claim 27
Dependent Claim
27 words
The device according to claim 23, wherein the fibres making up the source bundle are cut to different lengths and mounted at different distances along the substrate.
Claim 28
Dependent Claim
30 words
The device according to claim 13, wherein two source fibres and two detector fibres are used to provide insensitivity to variations in lead fibre attenuation, source intensity, and detector responsivity.
References Cited (Backward Citations)
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