EP0000319B2 - Dispositif pour élaborer un signal lumineux caractéristique de l'indice de réfraction d'un fluide et son utilisation - Google Patents

Dispositif pour élaborer un signal lumineux caractéristique de l'indice de réfraction d'un fluide et son utilisation Download PDF

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Publication number
EP0000319B2
EP0000319B2 EP78810001A EP78810001A EP0000319B2 EP 0000319 B2 EP0000319 B2 EP 0000319B2 EP 78810001 A EP78810001 A EP 78810001A EP 78810001 A EP78810001 A EP 78810001A EP 0000319 B2 EP0000319 B2 EP 0000319B2
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EP
European Patent Office
Prior art keywords
light
fluid
curvature
curved
refraction
Prior art date
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Expired
Application number
EP78810001A
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German (de)
English (en)
French (fr)
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EP0000319B1 (fr
EP0000319A1 (fr
Inventor
Alan Lewis Harmer
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Stanley Electric Co Ltd
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Battelle Memorial Institute Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/284—Electromagnetic waves
    • G01F23/292—Light, e.g. infrared or ultraviolet
    • G01F23/2921—Light, e.g. infrared or ultraviolet for discrete levels
    • G01F23/2922—Light, e.g. infrared or ultraviolet for discrete levels with light-conducting sensing elements, e.g. prisms
    • G01F23/2924—Light, e.g. infrared or ultraviolet for discrete levels with light-conducting sensing elements, e.g. prisms for several discrete levels, e.g. with more than one light-conducting sensing element
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G01N21/43—Refractivity; Phase-affecting properties, e.g. optical path length by measuring critical angle
    • G01N21/431—Dip refractometers, e.g. using optical fibres

Definitions

  • devices of the type already known by way of example comprising a transparent straight rod fitted respectively, at one of its ends, with an optomechanical system responsible for injecting into the rod a light brush at a well-defined angle of incidence, and at its other end, a photoelectric detector responsible for measuring the light intensity thus transmitted through the rod by multiple internal reflections of well-determined incidence: the rod being immersed in the fluid medium to be measured, the angle of incidence of the light brush injected into the rod is then continuously decreased while observing the transmitted light intensity, the sudden drop in intensity which occurs when the angle d the incidence of multiple reflections exceeds the limit angle with respect to the fluid considered, thus making it possible to determine this limit angle, and consequently the refractive index of the fluid.
  • devices of this type have the major drawback of being extremely complicated, since they require, among other things, the presence of a relatively sophisticated light injection system, since it must ensure both the parallelization of the incident light brush using optical means, and the continuous variation of the angle of incidence of this brush using mechanical means.
  • Such devices appear a priori to be particularly advantageous, given their great simplicity and low cost, as well as the fact that they seem in principle to be able to be used both for detecting discontinuous changes and for continuous changes in the characteristics of the device. liquid to be tested.
  • these devices have the major drawback of being endowed with a very low sensitivity, so that not only their use as refractometers proves to be most limited (due to their inability to be able to detect small variations in the refractive index of liquid to be tested), but that even their use as simple level indicators is far from satisfactory (due to low contrasts likely to be recorded).
  • the present invention specifically aims to overcome the aforementioned drawbacks, by proposing a simple device endowed with an excellent sensitivity, which can detect both discontinuous changes of state of a fluid as well as continuous variations of various characteristics of this fluid. related to its refractive index.
  • the subject of the present invention is a device for producing a light signal characteristic of the refractive index of a fluid, comprising a single elongated light-conducting body consisting of an inlet section and an outlet section connected to each other by a curved intermediate section, said inlet section being intended to receive light by its free end and at least said curved section being intended to be immersed in said fluid, the curvature of said curved section being moreover chosen to be sufficiently pronounced to give rise to a significant passage of light by refraction in said fluid, function of the refractive index of said fluid, the refractive index of the elongated body being greater than that of fluid, characterized by the fact that said curved intermediate section has a profile comprising at least two successive alternating curves which are sufficiently pronounced, alternative concave and convex.
  • the present invention also relates to the use of such a device for detecting the presence or absence of said fluid, or for measuring the refractive index of said fluid.
  • the expressions “elongated body which conducts light or” light guide • are intended to denote any elongated body capable of transporting light by multiple internal reflections. These expressions thus mean in particular encompass both light guides constituted by a simple rod made of a transparent material, as guides constituted by an optical fiber (this transparent rod or this optical fiber being moreover shaped so as to comprise an intermediate section curved with the desired profile).
  • the essential characteristic of the device according to the invention resides in the use of a light guide comprising a curved intermediate section consisting of a plurality of alternating curvatures (number of curvatures at least equal to 2).
  • a structure with alternating curvatures has the major advantage of giving the device of the invention a particularly high sensitivity (the degree of sensitivity of such a structure can be determined by the extent of the variation in the light intensity transmitted for a given variation in the refractive index of the fluid to be measured), and in any event significantly greater than that which can be obtained with a structure with a single curvature (whether it is a curvature in the form of U or a curvature of at least 360 °).
  • the intermediate section with alternating curvatures of the light guide constituting the device according to the present invention can take multiple forms, provided that the different curvatures of this intermediate section remain arranged one after the other so that any one of these curvatures is always turned in the opposite direction to the curvatures that are adjacent to it.
  • this intermediate section it is thus possible to envisage using structures with double curvature, in which the downstream curvature is turned in the opposite direction from the upstream curvature, or else structures with triple curvature, in which the median curvature is turned in the opposite direction of the upstream and downstream curvatures, or of structures having a higher number of curvatures.
  • the various curvatures can moreover be connected to each other by straight intermediate portions, or on the contrary be directly contiguous (that is to say directly connected to each other without being separated by portions straight).
  • these straight portions will moreover be advantageously chosen so that their length remains relatively small compared to that of the curvatures to which they are connected.
  • each of the curvatures can moreover take any form provided that it is sufficiently pronounced.
  • curvature it is thus possible to envisage designing curvatures having a constant radius of curvature taking the form of a circular arc, the extension of this circular arc can also be variable (semi-circle, quarter-circle, full turn, etc ...), or on the contrary curvatures having a variable radius of curvature, this radius can then vary in an increasing or decreasing manner.
  • the radius of curvature R of the various alternating curvatures will be chosen, for a given cylindrical light guide of radius r, so that the ratio R / r is between approximately 3 and 5.
  • this rod may be made of any suitable transparent material.
  • This material must however be chosen in the case where the device is used to determine continuous variations of index, so as to have a refractive index higher than that of the liquid to be detected, whereas it could very well have, in the case where the device is used as a level indicator, any refractive index, higher or lower than that of the liquid to be detected.
  • the size of the cross section of the light conducting rod with alternating curvatures according to the invention has little importance in itself, since it is the ratio R / r of the radius of curvature R of the different curvatures and of the radius r of the rod which is in fact decisive for obtaining the desired effect. It follows that it is possible in practice to use both rods with a very small cross section and rods with a relatively large cross section; it suffices simply to adapt in each case the magnitude of the curvature to the value of the cross section that has been chosen for the rod.
  • this cross section be circular, and one can very well consider using rods with a square, hexagonal, elliptical cross section (the radius of curvature R then, in such a case, be sufficient small compared to that of the dimensions of said cross section which is contained in the plane of curvature).
  • a light guide consisting of an optical fiber
  • these fibers could moreover be made of materials both based on glasses and based on plastics.
  • index hopping fibers it will be chosen to use more specifically so-called index hopping fibers.
  • the presence of a sheath around the light conducting core has the additional advantage of preventing, in the non-curved parts of the fiber, any risk of parasitic influence.
  • the curved portions of these fibers it is also possible to envisage either stripping them completely of their sheath, so as to allow direct contact of the central core with the fluid medium to be tested, or on the contrary leaving them as they are.
  • angle of incidence of a light ray on a surface will moreover be used according to its usual definition, namely“ angle which this light ray makes with respect to the normal to this surface of incidence ”. According to this definition, an increase in the obliquity of the light ray with respect to the incidence surface therefore amounts to a reduction in its angle of incidence.
  • the ratio I ta ll o of the light intensity I ta transmitted by the guide in the presence of air will be called “transmission coefficient in air” respectively: the light intensity 1 0 injected into the guide (this coefficient allowing somehow define the losses of light by refraction in the presence of air), and "contrast or" coefficient of contrast r the ratio I ta / I ti of the light intensity I ta transmitted in the presence of air to the intensity light I ti transmitted in the presence of liquid.
  • the “sensitivity of the device can therefore also be defined as being represented by the magnitude of the variation of contrast obtained for a variation of predetermined index (sensitivity corresponding to the slope of the curves of the diagram in FIG. 6 ).
  • FIGs 1a and 1b illustrate by way of example two devices known from the prior art. The purpose of these first two illustrations is to clearly highlight the essential differences which exist between these known devices and the different embodiments of the device according to the invention which will be described below.
  • the device shown in Figure 1a comprises a transparent rod 1 in the form of a U consisting of a curved section 2 of semi-circular shape extending at each of its ends by straight sections 3 and 4.
  • the free end 3a of one of the straight sections 3 is used to inject light into the rod 1, while the free end 4a of the other straight section 4 is used to detect the light transmitted through the rod 1 ( injection and light output shown schematically by arrows in the drawing).
  • the curved section 2 being immersed in a liquid 9 to be tested, it can be seen that the quantity of light emerging at the end 4a is a function of the refractive index of the liquid 9.
  • the device represented in FIG. 1 b is similar to that of FIG. 1a, apart from the fact that the curved section 2 of semi-circular shape is here replaced by a section 2 ′ curved at 360 °.
  • Figure 2 illustrates a first embodiment of the device according to the invention, according to which a light guide is used consisting of a simple transparent rod provided with two alternating curvatures.
  • the device shown in this figure comprises a rod 10 made of a transparent material, which is respectively composed of a curved intermediate section 11 in the shape of an S, and two straight sections 15 and 16 extending substantially vertically from each of the ends of this curved section 11.
  • the straight sections 15 and 16 are intended to serve respectively as an inlet section and as an outlet section for the rod 10.
  • the curved section 11 in the form of an S is respectively composed of two portions curved 12 and 13 in the form of an arc of a circle connected to each other by a straight intermediate portion 14, these two curved portions 12 and 13 being moreover arranged so as to be substantially symmetrical with respect to the 'other, while being turned in opposite directions to each other.
  • the transparent rod 10 has a circular cross section of radius r, while the curved portions 12 and 13 have a constant radius of curvature R.
  • a source of light radiation 5 responsible for injecting light into the transparent rod 10
  • a detection system 6 responsible for determining the light intensity transmitted by the rod 10.
  • this detection system 6 can be constituted by a photoelectric detector 7 electrically connected to a measurement and / or display device 8.
  • the curved section of this device is intended to be immersed in a liquid 9 of refractive index n, of which it is desired to determine one of the characteristics linked to this refractive index.
  • the transparent material constituting the rod 10 is finally chosen so as to have a refractive index n greater than the refractive index n of the liquid to be tested.
  • the geometry of the double curvature structure which has just been described is essentially controlled by three parameters: the radius of curvature R of each of the curved portions 12 and 13 (or the quotient R / r normalized to the radius r of the rod) , the distance D separating the centers of curvature of each of these curved portions and the horizontal displacement H.
  • R the radius of curvature R relatively small compared to r if one wishes to increase optimally the contrast and the sensitivity of the device.
  • this radius of curvature R will be chosen so that the quotient R / r is between approximately 3 and 5.
  • the curved section 11 of this device being immersed in the liquid 9 to be tested, light is injected into the transparent rod 10 by means of the source 5.
  • the beam of light delivered by this source 5 can a priori have any opening, since the amount of light actually trapped by the transparent rod 10 depends only, as is well known, on the "digital aperture" of this rod and not on the opening of the incident beam.
  • the light effectively trapped inside the transparent rod 10 is then transmitted by multiple internal reflections through the straight section 15, until it arrives in the curved section 11 immersed in the liquid 9 to be tested.
  • the first curvature 12 of this curved section 11 has the effect of modifying the incidence of the rays which strike its walls, in particular causing a reduction in the angle of incidence of those of the rays which strike its exterior surface (this angle of incidence reduction being also a function of the magnitude of the curvature), so that those of the incident rays whose angle becomes less than the limit angle relative to the surrounding liquid 9 are then forced to pass through refraction in this liquid (behavior illustrated by the radius P1 in the drawing).
  • this reduction in incidence is not moreover identical for all the rays which arrive with the same incidence in this curved portion 12, since it depends on the contrary on the depth to which these rays could penetrate into this curved portion before coming to strike its outer surface, so that only part of the rays which arrive under the same incidence is likely to pass out of the rod 10 by refraction in the surrounding liquid.
  • This more or less large part of rays which are likely to exit by refraction in the surrounding liquid is obviously a function of the refractive index of this liquid since the limit angle of total reflection depends on this index.
  • This major part of the rays forced to pass by refraction in the surrounding liquid is obviously also a function of the refractive index of this liquid, since the limit angle of total reflection here again depends on this index.
  • the light intensity thus emerging at the other end 16a of the rod which is substantially equal to the light intensity injected into the rod minus the refractive losses suffered when passing the curved portions 12 and 13 (aux losses by absorption in the rod), is therefore also a function of the refractive index of the medium surrounding the curved portion.
  • This transmitted light intensity therefore constitutes a light signal characteristic of the refractive index of the medium surrounding the curved section of the rod.
  • the light signal thus produced by the device which has just been described differs in a fundamental manner, however, from that produced by the known devices of FIGS. 1a and 1b (although it is in both cases characteristic of the refractive index of the fluid to be tested) by the fact that it has a much greater sensitivity here, this completely unexpected result being due to the presence of the second curvature 13 arranged in the opposite direction to the first curvature 12 which plays a sort of role of amplification of the effects already observable during the crossing of this first curvature.
  • This second curvature 13 disposed in the opposite direction makes it possible to multiply the effects obtained during the passage of the first curvature 12, due to the fact that the rays entering this second curvature have already seen their path sufficiently modified during their passage through the first curvature to have to be forced to strike the second curvature under a strong obliquity, which strong obliquity thus obliges the major part of these rays to come out by refraction of the rod at the level of this second curvature (strong obliquity moreover impossible to achieve during penetration into the first curvature, due to the “digital opening limited to the inlet section 15 of the transparent rod).
  • FIG 3 illustrates a first variant of the device according to the invention, according to which a structure is used consisting of a transparent rod 21 having three alternating curvatures.
  • the W-shaped rod 21 shown in this figure consists, respectively, of three curved portions 22, 23 and 24 in the form of a circular arc connected with each other by two intermediate portions 25 and 26 (the middle curved portion 23 being arranged in the opposite direction to the external curvatures 22 and 24), the free ends of the external curvatures 22 and 24 being further extended by the straight portions 27 and 28.
  • FIG. 4 illustrates a second embodiment of the device according to the invention, based on the use of a double curvature optical fiber.
  • This structure is similar to that of FIG. 2, except that the transparent rod 10 made of a single material is here replaced by an optical fiber 31, consisting of a central core 32 surrounded by a thin sheath 33, this optical fiber 31 also remaining undressed over its entire length.
  • the geometry of this structure also differs from that shown in FIG. 2 by the fact that the curvatures 12 and 13 are here directly contiguous (no intermediate portion between the curvatures) and of semi-circular shapes, the horizontal displacement H being also chosen. equal to zero.
  • FIG. 5 illustrates a variant of the device of FIG. 4, according to which the optical fiber 31 is provided with a curved section 35 comprising four alternating curvatures (instead of two as in FIG. 4), this curved section 35 also being completely stripped of its sheath 33 (core 32 exposed).
  • the above-mentioned structures can, for example, be produced by heating the fiber to a temperature of between approximately 100 and 200 ° C., and by shaping the fiber thus heated around cylindrical dies of appropriate dimensions (dies having in particular an external radius equal to 1.75 mm.
  • Light transmission measurements are then carried out through each of these structures by means of a source constituted by a quartz-iodine lamp of 150 W of power and a detector constituted by a silicon photodiode having a spectral response between 400 and 950 nm with a peak at 700 nm.
  • a whole series of measurements is carried out, by immersing these different structures in a succession of liquids with known indices. The results thus obtained are plotted on the diagram of FIG.
  • the purpose of this example is to illustrate how the light intensity transmitted by the device according to the invention varies as a function of the magnitude of the curvatures imparted to the light conducting rod of this device.
  • optical fibers (sold commercially under the name CROFON by the Company Dupont de Nemours) with an external diameter of 1 mm are used, consisting respectively of a central core made of a first plastic material of index equal to 1.49 (polymethyl methacrylate), and a sheath made of a second plastic material with an index equal to 1.39 (the thickness of the sheath being less than 50 microns).
  • Three optical fiber structures with double curvatures are produced, identical to those illustrated in FIG. 4 (ie structure having a distance D equal to (2 R + 2 r) and a distance H zero), these curvatures being different from one another. simply by the fact that the radius of curvature R is chosen to be different in each of the cases, namely 2 mm, 1.75 mm and 1.5 mm respectively (D then being respectively equal to 5 mm, 4.5 mm and 4 mm ).
  • Each of these structures is successively immersed in air and in a reference liquid with an index equal to 1.39 (essence), and the light transmitted through these structures is measured each time in the same way as previously. The measurements obtained make it possible to determine, for each of these structures, a contrast coefficient respectively equal to approximately 8, 18 and 75, as well as a coefficient of transmission in the air respectively equal to 55%, 50% and 43%.
  • the contrast increases strongly as a function of the magnitude of the curvatures, this strong growth with respect to the contrast being accompanied, moreover, by a relatively small reduction in the coefficient of transmission in the air.
  • the development by the device according to the invention of a light signal characteristic of the refractive index of the fluid in which it is immersed can be used both to detect discontinuous changes of state of this fluid and to determine different characteristics of this fluid linked to its refractive index (or continuous variations of these characteristics).
  • the device according to the invention may in a particularly advantageous manner be used to detect the presence or absence of a fluid at a determined location, and more particularly the height or the level of a fluid in a given container, the various curvatures constituting the curved section of the light conductor then being arranged at the level which it is desired to detect.
  • the device can be simplified to the extreme, since it must detect only two very different states: it is thus possible to completely remove the detection system of the transmitted light and replace it with a simple one.
  • the curvature of the curved portions being also advantageously chosen so as to cause minimal light losses in the absence of liquid, so that the detection end of the light conductor will appear dark if the liquid is at the desired level or on the contrary will become clear if he runs out of liquid.
  • a simple auxiliary light source for example a portable lamp such as a flashlight
  • this level detection it is also possible to envisage carrying out both discrete detection (measurement of a single level) and almost continuous detection (measurement of different possible levels inside the same container. , for example maximum and minimum levels mum), by installing a device at each of the levels to be detected.
  • FIG. 7 illustrates by way of example an installation for measuring three distinct levels inside a container 40 (maximum, medium and minimum levels).
  • This installation comprises three optical fibers according to the invention 41, 42 and 43 mounted inside a tubular conduit 44 immersed in the container 40, these three optical fibers having curved sections 41a, 42a and 43a in the form of W arranged up to each of the levels to be measured.
  • the injection of light into the fiber entry sections is carried out using a single light source 45, while the level indication is obtained by simple visual observation of the free end outlet sections of these fibers.
  • the container being by way of example three-quarters full in the drawing, only the outlet end of the fiber 41 appears clear in the drawing, the ends of the other two fibers 42 and 43 remaining dark.
  • the applications of the device according to the invention as a level indicator are multiple. We can first of all consider using it in the field of automotive (or even aeronautical) instrumentation, to detect levels such as the levels of the fuel tank, of the engine oil or of the transmission, brake fluid, battery electrolyte, fluid for washing the windshield, etc., the different control ends of the optical fibers used to detect all these levels being, for example, mounted on the vehicle dashboard . It is also possible to envisage using such a level indicator in many other fields, such as storage of liquefied gases (where level measurements are generally difficult to take into account given the risk of fire, reduced temperatures and the corrosive environment), chemical storage tank, etc.
  • the device according to the invention can also be used as a refractometer, with a view to measuring, either directly the refractive index of a fluid, or other characteristics of this fluid related to its refractive index, such as concentration of a solution, proportion of one of the constituents of a composite fluid, temperature of a liquefied fluid, etc.
  • the system for detecting transmitted light can be constituted by an electrical system comprising by example a phototransistor connected to a measurement device, (capable of being developed in such a way as to give the value of the characteristic to be measured directly) or on the contrary by a simple visual system based on the observation of an attenuation of brightness or d '' a color change (possibly susceptible to be compared with those of a control fiber).
  • the device according to the present invention has many advantages over known level gauges or refractometers: simplicity both in its construction and its use, low cost, high contrast making it particularly attractive for its use as a level indicator, excellent sensitivity to changes refractive indices allowing good use as a refractometer.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Fluid Mechanics (AREA)
  • Health & Medical Sciences (AREA)
  • Thermal Sciences (AREA)
  • Chemical & Material Sciences (AREA)
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EP78810001A 1977-07-01 1978-06-01 Dispositif pour élaborer un signal lumineux caractéristique de l'indice de réfraction d'un fluide et son utilisation Expired EP0000319B2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH8105/77 1977-07-01
CH810577 1977-07-01

Publications (3)

Publication Number Publication Date
EP0000319A1 EP0000319A1 (fr) 1979-01-10
EP0000319B1 EP0000319B1 (fr) 1981-09-02
EP0000319B2 true EP0000319B2 (fr) 1984-09-05

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EP78810001A Expired EP0000319B2 (fr) 1977-07-01 1978-06-01 Dispositif pour élaborer un signal lumineux caractéristique de l'indice de réfraction d'un fluide et son utilisation

Country Status (10)

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US (1) US4187025A (it)
EP (1) EP0000319B2 (it)
JP (1) JPS5918654B2 (it)
AU (1) AU521314B2 (it)
BR (1) BR7804186A (it)
CA (1) CA1102151A (it)
DE (1) DE2860995D1 (it)
ES (1) ES471327A1 (it)
IT (1) IT1096885B (it)
MX (1) MX143781A (it)

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IT7825155A0 (it) 1978-06-29
JPS5918654B2 (ja) 1984-04-28
DE2860995D1 (en) 1981-11-26
JPS5419794A (en) 1979-02-14
ES471327A1 (es) 1979-01-16
EP0000319B1 (fr) 1981-09-02
AU3765978A (en) 1980-01-03
MX143781A (es) 1981-07-13
BR7804186A (pt) 1979-04-03
IT1096885B (it) 1985-08-26
EP0000319A1 (fr) 1979-01-10
CA1102151A (en) 1981-06-02
AU521314B2 (en) 1982-03-25
US4187025A (en) 1980-02-05

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