WO1998043060A1

WO1998043060A1 - Volatile organic substance leak detector having water-proof mechanism

Info

Publication number: WO1998043060A1
Application number: PCT/EP1998/001634
Authority: WO
Inventors: Yusuke Takano; Hironobu Yamamoto; Akihiro Tagaya; Ashley Sabin; James Stamatoff
Original assignee: Aventis Research & Technologies Gmbh & Co Kg
Priority date: 1997-03-21
Filing date: 1998-03-20
Publication date: 1998-10-01
Also published as: JPH10267840A

Abstract

A volatile organic substance leak detector free from any influence of water and so on, and a leak monitoring system using the detector are provided. The volatile organic substance leak detector has a light source unit, and a sensor unit comprising a sensor element having a polymer thin film which exhibits a change in at least one of a thickness and a refractive index in response to a contact with a vaporized organic substance. Light from the light source unit is incident on the polymer thin film, and reflected light therefrom exits from a light transmitting/outputting unit. The sensor unit has a vapor inlet port in which a mechanism is provided for preventing water from immersing into the interior of the sensor unit.

Description

VOLATILE ORGANIC SUBSTANCE LEAK DETECTOR HAVING WATER-PROOF MECHANISM

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a volatile organic substance leak detector which can optically detect the existence and/or concentration of a vaporized volatile organic substance, such as, for example, gasoline, light oil, kerosine, jet combustible, heavy oil, and so on, and more particularly, to such a volatile organic substance leak detector which can detect a leaked volatile organic substance even in places where the organic substance is likely to be mixed with splashed water, mud, or so on or buried under water, mud, or the like, without influences thereof, particularly suitable for use in a fuel vapor detector and a fuel leak monitoring system for detecting leaked fuel in earliest possible stages.

Description of the Related Art

A float type sensor is well known for detecting a leaked fuel in a fuel tank or the like which may be installed underground in a gas station area. The float type sensor has a float which rises in response to a fuel leaking from the tank and activates a switch when the amount of the leaked fuel exceeds a preset value to determine a fuel leak. Other than the float type leak sensor, several methods for detecting a leaked fuel have been proposed as illustrated below.

Japanese Patent Laid-open No. 3-503674 discloses a computerized automatic system for detecting the volume of a leaked liquid from an underground storage container, including measurements of pressure, temperature, level (liquid surface) and temperature. A electro-mechanical level sensor is employed for measuring a liquid level. Japanese Patent Laid-open No. 2-233393 discloses a leaked oil detector intended to eliminate disadvantages encountered in the detection of a ked oil by a leaked oil display. The leaked oil detector comprises a water-floatable oil detecting means disposed in a gas detecting tube buried near an underground tank and electrically connected to an alarming means.

Japanese Patent Laid-open No. 6-201510 discloses a leaked oil measuring apparatus for accurately detecting leaked oil in a tank such as a gasoline tank which may experience high temperatures. This leaked oil measuring apparatus applies a pressure to the tank itself and employs a diaphragm type silicon pressure sensor for measuring a change in external pressure (applied pressure).

These known techniques commonly have a disadvantage in that an initial leak detection cannot be provided. In other words, the occurrence of fuel leak can be determined only after a certain amount of leaked fuel has been accumulated. As a result, the leak may be found too late, and consequently, because of its electrical measuring principles, the risk of explosion is potentially involved.

In tanks installed on the ground for storing fuel transported from tankers, the need of a detector which enables early detection of leaked fuel has been earnestly appealed for some time past since leaked fuel soaked into the underground is highly likely to cause environmental pollution. As to such a detector, several techniques have already been proposed as illustrated below.

U.S. Patent No. 5,349,181 discloses an apparatus for detecting chemical species dissolved in water or vaporized chemical species. This apparatus, however, requires electric power for driving an optical device in a probe, so that this apparatus potentially implies the risk of explosion when used in a dangerous zone.

To eliminate the risk of explosion due to electricity, an optical fuel vapor detector for optically detecting fuel vapor has already been proposed as illustrated in Fig. 1. In the illustrated fuel vapor detector, a light beam sent from a light source 200 through an optical fiber 202 is incident on a polymer film 208 formed on a substrate 206 in a sensor probe 204. The light beam reflected off the polymer film 208 is sent to and detected by a light detector 210 through the same optical fiber 202. The polymer film 208 reacts with a fuel vapor passing through the sensor probe 204, or adsorbs or absorbs the fuel vapor, so that, as a result of such interaction, the polymer film 208 exhibits a change in thickness and/or refractive index. Since the fuel vapor is optically detected utilizing the characteristics inherent to the high polymer film 208 as mentioned above, a fuel leak can be advantageously found in early stages. Also advantageously, the fuel vapor detector is intrinsically safe because the optical fiber 202 is used (because the detection is achieved without using electric power).

In a fuel vapor detector illustrated in Fig. 1 , a interference enhance reflection method (hereinafter referred to as the "IER method") is utilized. Specifically, light reflected off the surface of the polymer film 208 has a phase relationship with light reflected off the surface of the substrate 206 supporting the polymer film 208, and they interfere with each other. Thus, since the reflectivity of the high polymer film 208 or the intensity of the reflected light changes as the thickness and/or the refractive index of the polymer film 208 changes, the existence and/or the concentration of the fuel vapor can be detected as a function of the intensity of the reflected light.

In the fuel vapor detector illustrated in Fig. 1 , the amount of light reflected from the polymer film 208 increases to alarm a fuel leak when a fuel vapor exists. If water, mud, or the like is splashed onto the sensor probe 204 used in the air or if the sensor probe 204 itself is submerged in water to cause water, mud, or the like to flow into the sensor probe 204, the amount of reflected light on the polymer film 208 largely changes to generate an alarm indicative of a trouble. In such a case, the sensor probe 204 requires maintenance such as washing of the inside of the sensor probe 204, replacement of the polymer film 208, and so on, so that it is practically difficult to install the sensor probe 204 in a place where an inflow of underground water and so on frequently occur. SUMMARY OF THE INVENTION

The present invention has been made in view of the problems mentioned above, and its general object is to provide a volatile organic substance leak detector which comprises a water-proof mechanism for allowing for the installation of the detector even at a site where inflow of water, mud or the like is likely to occur, and which is capable of transmitting only a fuel vapor and blocking water when used in the air, and of selectively trapping fuel dissolved or separately existing in water as a vapor and blocking water when used in water.

More specifically, it is an object of the present invention to provide a fuel vapor detector which is intrinsically safe, simple in structure, easy in manufacturing, highly reliable, inexpensive, and susceptible of a reduction in size.

It is another object of the present invention to provide a volatile organic substance leak monitoring system which is capable of remotely monitoring a fuel leak utilizing the fuel vapor detector mentioned above.

To achieve the above objects, the present invention provides a volatile organic substance leak detector which comprises a water-proof mechanism to allow for the installation of the detector even in a place where an inflow of water, mud, or the like may occur. The water-proof mechanism can transmit only a vaporized volatile organic substance but block water when used in the air, and can selectively trap a volatile organic substance dissolved or separately existing in water as a vapor but block water when used in water. The detector is capable of detecting at least one of the existence and the concentration of a vaporized volatile organic substance. As illustrated in Fig. 2, the leak detector comprises: a light source unit having a light emitting element; a sensor unit including a sensor element formed of a polymer thin film deposited on a reflecting surface, wherein the polymer thin film exhibits a change in at least one of a thickness and a refractive index in response to a contact with the vaporized volatile organic substance, and the sensor unit is positioned such that light from the light source unit is incident normal to the sensor element, and also including a mechanism capable of blocking water and transmitting the vaporized volatile organic substance, when used in the air, and capable of trapping the volatile organic substance dissolved or separately existing in water as a vapor when used in water; a light transmitting/outputting unit positioned between the light source unit and the sensor unit for transmitting light from the light source unit so that the light is incident on the sensor unit and for outputting reflected light reflected off the sensor element; and a light detector unit coupled to receive the reflected light for producing a signal corresponding to the reflected light.

The volatile organic substance leak detector may be installed at a site likely to suffer from inflow of water such as an underground tank, thump, surroundings of an oil immersed pump, a ground tank, an oil refinery, an oil transporting line, an oil transporting tanker, and so on.

The present invention detects the existence or the concentration of a vaporized volatile organic substance by measuring a change in the reflection characteristic of the sensor unit, making use of the fact that the polymer thin film exhibits a change in at least one of the thickness and the refractive index in response to a contact with a vapor under detection. As a result of an interaction of the polymer thin film with the vaporized volatile organic substance, the polymer thin film experiences physical changes such as, for example, swelling. Also, such swelling causes the polymer thin film to change the thickness and the refractive index which are optical parameters inherent thereto. Since such changes result in a change in the optical property of the polymer thin film, a vaporized volatile organic substance can be detected by measuring the reflection characteristic of the polymer thin film.

To realize the detection of a vaporized volatile organic substance, in the present invention, light from the light source is incident normal to the sensor unit. The light is reflected off the sensor element to cause the light to propagate through the same path as when it was incident thereto. Then, the light is reflected off the light transmitting/outputting unit in a direction different from that of the propagation path to introduce the light into the light detector unit which produces an electric signal corresponding to the light reflected from the sensor element. It should be particularly noted in the present invention that by appropriately selecting a polymer material constituting the polymer thin film, it is possible to selectively or non-selectively detect the existence of a vaporized volatile organic substance such as, for example, fuel including gasoline, light oil, kerosine, jet combustible, heavy oil or the like. Moreover, since the polymer thin film has the reflection characteristic corresponding to the concentration of a fuel vapor, the volatile organic substance leak detector according to the present invention may serve as a concentration meter for a fuel vapor.

The present invention may employ, for example, the IER method for detecting a change in thickness and/or refractive index of the polymer thin film. As mentioned above, the IER method utilizes the optical interference characteristic of a thin film structure. Light reflected off the surface of the polymer thin film has a phase relationship with light reflected off the interface between reflecting surfaces of the polymer thin film and the substrate, and they interact with each other. The reflectivity of the sensor element largely depends on the thickness and/or the refractive index of the polymer thin film. In other words, as the thickness and/or the refractive index of the polymer thin film changes, the reflectivity of the polymer thin film or light reflected therefrom also changes. In this way, the existence and/or the concentration of a vaporized volatile organic substance can be detected as a function of the intensity of reflected light in accordance with the IER method.

As described above, while the IER method is sensitive to a change in thickness of the film, the present invention may attach more importance to the influence of the thickness of the polymer thin film than the refractive index, provided that a material having a refractive index not substantially different from the reflective index of a vaporized volatile organic substance is used as the polymer thin film used in the present invention. This is a unique advantage of the present invention over the prior art.

Another point to be emphasized for a comparison relates to the thickness of the polymer thin film. Fig. 3 illustrates a graph which plots the reflectivity of the polymer thin film having a refractive index equal to 1.5 formed on a silicon substrate, to which light is incident at an incident angle of 0° as a function of the thickness of the polymer thin film. It should be noted that polarized light and non-polarized light used herein have a wavelength of 633 nm, and the polymer thin film interacts with a fuel vapor.

It can be seen from the graph that the thickness of the polymer thin film suitable for the IER method is preferably adjusted depending on a particular concentration range of fuel vapor in the following manner. First, when a fuel vapor concentration is low, the reflectivity changes little, so that the polymer thin film adjusted to have a thickness corresponding to a minimum value or a maximum value of the IER curve would not provide a sufficient change in reflectivity. It is therefore understood that the thickness is preferably not a value near any multiple of λ/4ncosθ corresponding to the minimum value or the maximum value of the reflectivity, where λ is the wavelength of incident light, n is the refractive index of the polymer thin film, and θ is a light propagation angle within the polymer thin film. When the fuel vapor concentration is relatively high, on the other hand, the polymer thin film exhibits a larger change in reflectivity, so that the polymer thin film 4 preferably adjusted to have a thickness corresponding to the minimum value or the maximum value of the IER curve in order to take a large signal span. While the polymer thin film 4 may have a thickness in a range of 10 nm to 10 μm, a thickness less than 1 μm is preferable in view of a high speed response.

Materials for the polymer thin film 4 preferably include a homopolymer or a copolymer having a recurring unit represented by the following chemical formula (I):

I CH₂

I X-C-R¹ (I)

where X represents -H, -F, -Cl, -Br, -CH₃, -CF₃, -CN, or -CH₂-CH₃; R¹ represents -R² or -Z-R²;

Z represents -O-, -S-, -NH-, -NR²'-, -(C=Y)-, -(C=Y)-Y-, -Y-(C=Y)-, -(SO₂)-,

-Y'-(SO₂)-, -(SO₂)-V-, -Y'-(SO₂)-Y'-, -NH-(C=O)-, -(C=O)-NH- -(C=O)-NR²'-, -Y'-(C=Y)-Y-, or -O-(C=O)-(CH₂)n-(C=O)-O-; Y independently represents O or S; Y' independently represents O or NH; n represents an integer ranging from 0 to 20; and

R² and R²' independently represent hydrogen, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an unsaturated hydrocarbon group, an aryl group, a saturated or unsaturated hetero ring, or substitutes thereof. It should be noted that R¹ does not represent hydrogen, a linear alkyl group, or a branched alkyl group.

In the foregoing recurring unit (I):

X represents H or CH₃;

R¹ represents a substituted or non-substituted aryl group or -Z-R²;

Z represents -O-, -(C=O)-O-, or -O-(C=O)-; and

R² represents a linear alkyl group, a branched alkyl group, a cycloalkyl group, an unsaturated hydrocarbon group, an aryl group, a saturated or unsaturated hetero ring, or substitutes thereof.

A polymer used as the polymer thin film of the invention may be a polymer consisting of a single recurring unit (I), a copolymer consisting of another recurring unit and the above-mentioned recurring unit (I), or a copolymer consisting of two or more species of the recurring unit (I). The recurring units in the copolymer may be arranged in any order, and a random copolymer, an alternate copolymer, a block copolymer or a graft copolymer may be used by way of example. Particularly, the polymer thin film 4 is preferably made from polymethacrylic acid esters or polyacrylic acid esters. The side-chain group of the ester is preferably a linear or branched alkyl group, or a cycloalkyl group with the number of carbon molecules ranging preferably from 4 to 22.

Polymers particularly preferred for the polymer thin film of the present invention are listed as follows: poly(dodecyl methacrylate); poly(isodecyl methacrylate); poly(2-ethylhexyl methacrylate); poly(2-ethylhexyl methacrylate-co-methyl methacrylate); poly(2-ethylhexyl methacrylate-co-styrene); poly(methyl methacrylate-co-2-ethylhexyl acrylate); poly(methyl methacrylate-co-2-ethylhexyl methacrylate); poly(isobutyl methacrylate-co-glycidyl methacrylate); poly(cyclohexyl methacrylate); poly(octadecyl methacrylate); poly(octadecyl methacrylate-co-styrene); poly(vinyl propionate); poly(dodecyl methacrylate-co-styrene); poly(dodecyl methacrylate-co-glycidyl methacrylate); poly(butyl methacrylate); poly(butyl methacrylate-co-methyl methacrylate); poly(butyl methacrylate-co-glycidyl methacrylate); poly(2-ethylhexyl methacrylate-co-glycidyl methacrylate); poly(cyclohexyl methacrylate-co-glycidyl methacrylate); poly(cyclohexyl methacrylate-co-methyl methacrylate); poly(benzyl methacrylate-co-2-ethylhexyl methacrylate); poly(2-ethylhexyl methacrylate-co-diacetoneacrylamide); poly(2-ethylhexyl methacrylate-co-benzyl methacrylate-co-glycidyl methacrylate); poly(2-ethylhexyl methacrylate-co-methyl methacrylate-co-glycidyl methacrylate); poly(vinyl cinnamate) poly(butyl methacrylate-co-methacrylate); poly(vinyl cinnamate-co-dodecyl methacrylate); poly(tetrahydrofurfuryl methacrylate); poly(hexadecyl methacrylate); poly(2-ethylbutyl methacrylate); poly(2-hydroxyethyl methacrylate); poly(cyclohexyl methacrylate-co-isobutyl methacrylate); poly(cyclohexyl methacrylate-co-2-ethylhexyl methacrylate); poly(butyl methacrylate-co-2-ethylhexyl methacrylate); poly(butyl methacrylate-co-isobutyl methacrylate); poly(cyclohexyl methacrylate-co-butyl methacrylate); poly(cyclohexyl methacrylate-co-dodecyl methacrylate); poly(butyl methacrylate-co-ethyl methacrylate); poly(butyl methacrylate-co-octadecyl methacrylate); poly(butyl methacrylate-co-styrene); poly(4-methyl styrene); poly(cyclohexyl methacrylate-co-benzyl methacrylate); poly(dodecyl methacrylate-co-benzyl methacrylate); poly(octadecyl methacrylate-co-benzyl methacrylate); poly(benzyl methacrylate-co-benzyl methacrylate); poly(benzyl methacrylate-co-tetrahydrofurfuryl methacrylate); poly(benzyl methacrylate-co-hexadecyl methacrylate); poly(dodecyl methacrylate-co-methyl methacrylate); poly(dodecyl methacrylate-co-ethyl methacrylate); poly(2-ehtylhexyl methacrylate-co-dodecyl methacrylate); poly(2-ethylhexyl methacrylate-co-octadecyl methacrylate); poly(2-ethylbutyl methacrylate-co-benzyl methacrylate); poly(tetrahydrofurfuryl methacrylate-co-glycidyl methacrylate); poly(styrene-co-octadecyl acrylate); poly(octadecyl methacrylate-co-glycidyl methacrylate); poly(4-methoxystyrene); poly(2-ethylbutyl methacrylate-co-glycidyl methacrylate); poly(styrene-co-tetrahydrofurfuryl methacrylate); poly(2-ethylhexyl methacrylate-co-propyl methacrylate); poly(octadecyl methacrylate-co-isopropyl methacrylate); poly(3-methyl-4-hydroexystyrene-co-4-hydroxystyrene); poly(styrene-co-2-ethylhexyl methacrylate-co-glycidyl methacrylate).

It should be noted that in the methacrylate ester polymers or copolymers listed above, acrylate may be substituted for methacrylate. The polymers may be crosslinked on their own, or they may be crosslinked by introducing a compound that has corsslinking reactive groups. Such crosslinking reactive groups appropriate for the purpose include, for example, an amino group, a hydroxyl group, a carboxyl group, an epoxy group, a carbonyl group, a urethane group, and derivatives thereof. Other examples may include maleic acid, fumaric acid, sorbic acid, itaconic acid, cinnamic acid, and derivatives thereof. Materials having chemical structures capable of forming carbene or nitrene by irradiation of visible light, ultraviolet light, or high energy radiation may also be used as crosslinking agents. Since a film formed from crosslinking polymer is insoluble, the polymer forming the polymer thin film 4 may be crosslinked to increase the stability of an associated sensor. The crosslinking method is not particularly limited, and methods utilizing irradiation of light or radioactive rays may be used in addition to known crosslinking methods, for example, a heating method.

In the volatile organic substance leak detector according to the present invention, preferably, a substrate for supporting the polymer thin film is sufficiently flat such that a reflecting surface of the substrate reflects light, and the substrate itself preferably has a high reflectivity. The substrate may be a silicon wafer, by way of example. The polymer thin film may be formed on the surface of the substrate by a spin coat method or any other coating method commonly used in the art.

The light source unit may be implemented by a simple or a combination with a collimator or the like of any light emitting element such as a laser diode, a light emitting diode or the like. The light transmitting/outputting unit may be implemented by a glass plate, a beam splitter, a polarizing beam splitter, a non-polarizing beam splitter or a half mirror, and preferably by a beam splitter. The light detector unit may be formed of either a photodiode, a phototransistor or a photomultiplier tube, and preferably of a photodiode.

The light transmitting/outputting unit may be connected to a sensor unit through an optical fiber. A suitable light source unit in this case may be a laser diode or a light emitting diode. A light beam emitted from the light transmitting/outputting unit 12 is preferably introduced into the optical fiber through a collimator. The collimator used herein may be preferably a connector having a collimator lens, a SELFOC lens or the like available in the market. The optical fiber may be a single mode optical fiber, a multi-mode optical fiber, an optical fiber light waveguide formed of a single mode optical fiber, or an optical fiber light waveguide formed of a multi-mode optical fiber. Since light emanating from an optical fiber has a relatively wide angle, the light is preferably converged by a lens before it is incident on the sensor unit. A lens for this purpose may be preferably a glass spherical convex lens, a glass aspherical convex lens, a plastic spherical convex lens, a plastic aspherical convex lens, a quartz spherical convex lens, a quartz aspherical convex lens, a SELFOC lens, a ball lens or the like.

It goes without saying that any optical element need not be positioned between the light transmitting/outputting unit and the sensor unit. In this case, an increased degree of freedom may be provided. For example, light can be measured by the sensor unit spaced from the light transmitting/outputting unit by a desired distance. A light source unit for this case is preferably a laser diode. A collimator lens may be preferably used to collimate light from the light source unit. Such collimator lens may be a glass spherical convex lens, a glass aspherical convex lens, a plastic spherical convex lens, a plastic aspherical convex lens, a quartz spherical convex lens, a quartz aspherical convex lens, a SELFOC lens, a ball lens or the like, and a quartz aspherical convex lens may be preferably used.

In one embodiment of the present invention, the sensor unit comprises a housing having a chamber in which a sensor element having a polymer thin film formed on a reflecting surface of a substrate is positioned. The chamber is provided with a fuel vapor inlet port or a fuel vapor intake port for interacting a fuel vapor with the polymer thin film. A water-proof mechanism may be provided, if necessary, for transmitting only a fuel vapor and blocking water when used in the air and, for selectively trapping fuel dissolved or separately existing in water, i.e., trapping only fuel without water as a vapor while blocking water when used in water. Preferably, the water-proof mechanism may be formed, for example, of a polymer membrane, i.e., a membrane made of polyethylene, polypropylene, polystyrene, polycarbonate, polyphenylene oxide, polyphenylene ether, polyphenylene sulphide, polyether sulfone, polyether ether ketone, polyether imide, polysulphone, polyethylene naphthalete, polyacetal, polybutylene terphthalate, fluororesin, poly parabanic resin, all aromatic polyamides, polythiol, aminoalkyd resin, acrylic resin, poly cellulose, natural rubber, polyester, unsaturated polyester, epoxy resin, siiicone resin, and derivatives thereof, and a laminate of these polymers, or a membrane made of caramic, porous metal or the like, and a laminate thereof.

Among the materials listed above, a hydrophobic PTFE (polytetrafluorethylene) film, a hydrophobic PVDF (polyvinylidene fluoride) film, a hydrophobic polyethylene film, a hydrophobic polypropylene film, a hydrophobic polyethylene-PTFE laminate film, and a hydrophobic polypropylene-polyethylene-polypropylene laminate film.

A membrane having a pore diameter of 0.01 - 100 μm and a thickness of 50 - 2000 μm is preferably used, and a membrane having a pore diameter of 0.05 - 20 μm and a thickness of 70 - 300 μm is more preferably used. More specifically:

Hydrophobic PTFE film:

(0.1 - 70), (0.2 - 80), (0.5 - 75), (1 - 75), (3 - 75), (5 - 125), (10 - 125);

Hydrophobic polypropylene net support PTFE film:

(0.1 - 130), (0.2 - 130), (0.5 - 120), (0.2 - 175), (0.5 - 175), (1 - 145), (3 - 200);

Hydrophobic polyvinyliden fluoride film:

(0.1 - 125), (0.22 - 125), (0.45 - 125), (0.65 - 125), (5 - 125).

The numbers in parenthesis indicate a combination of a pore diameter and a thickness for each material in microns.

A window and a glass plate covering the window may be provided at a position of the housing of the sensor unit opposite to the sensor element as a light input/output unit for passing therethrough light from the light source unit and reflected light from the sensor element. However, when the light transmitting/outputting unit is connected to the sensor unit through an optical fiber, a leading end of the optical fiber may be extended to the chamber such that the leading end opposes the sensor element, instead of forming the window through the housing. In addition, a collimator lens may be provided at a position of the housing of the sensor unit opposite to the sensor element, if necessary, as a light input/output unit for passing therethrough light from the light source unit and reflected light from the sensor element.

In practice, the light source unit, the light transmitting/outputting unit, and the light detector unit may be integrated into a light emitting/light receiving unit, accommodated in a casing, and installed in an explosion-proof safe area. In this case, an integrated light emitting/light receiving laser having an additional hologram (see Japanese Patent Laid-open No. 6-52588) may be advantageously utilized. The sensor unit, in turn, may be installed at any site where it is highly likely to detect leaked fuel, for example, in a double-shell underground tank, an oil tube, an oil thump, a double-shell tank, and so on. In this event, the positional relationship between the casing containing the light source unit, the light transmitting/outputting unit and the light detector unit and the sensor unit is adjusted such that light emitted from the light source is incident normal to the sensor unit, and reflected light therefrom propagates back the same path.

In one embodiment, the light detector unit comprises electro-optical transducing means for producing an electric signal in accordance with the amount of reflected light, and means for comparing the electric signal with a predetermined value to notify at least one of the existence and the concentration of the vaporized volatile organic substance as the result of the comparison.

Furthermore, the present invention provides a volatile organic substance leak monitoring system comprising: at least one of so far described volatile organic substance leak detectors, wherein each volatile organic substance leak detector is arranged such that the sensor unit is positioned at a monitored site and the light emitting/light receiving unit is disposed in an alarm control unit; a determination circuit, associated with the alarm control unit, for determining whether or not a fault has occurred based on an electric signal outputted from the light emitting/light receiving unit, wherein the fault includes a trouble in the sensor unit and the existence of a vaporized volatile organic substance at a site where the sensor unit is positioned; bidirectional communicating means for coupling the alarm control unit to a remote location, such that the occurrence of the fault is monitored at the remote location.

In this volatile organic substance leak monitoring system, the alarm control unit further comprises: a memory for storing data indicative of a determination result by the determination circuit; and notifying means for transmitting data stored in the memory at predetermined time intervals when the determination result does not indicate the occurrence of a fault, and for immediately notifying the remote location of the determination result when the determination result indicates the occurrence of a fault.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram generally illustrating an exemplary structure of a conventional fuel vapor detector;

Fig. 2 is a block diagram generally illustrating a volatile organic substance leak detector according to the present invention, where the present invention is embodied as a fuel vapor detector;

Fig. 3 is a graph illustrating the reflectivity of a polymer thin film formed on a substrate of Fig. 1 ;

Fig. 4 is a schematic diagram generally illustrating the structure of a first embodiment of the volatile organic substance leak detector according to the present invention;

Figs. 5 and 6 are schematic diagrams each illustrating a structure for examining the characteristics of the fuel vapor detector of Fig. 4;

Fig. 7 is a schematic diagram generally illustrating the structure of a second embodiment of the volatile organic substance leak detector according to the present invention, where the present invention is embodied as a fuel vapor detector; Figs. 8 and 9 are schematic diagrams each illustrating a structure for examining the characteristics of the fuel vapor detector of Fig. 7;

Fig. 10 a schematic diagram generally illustrating the structure of a third embodiment of the volatile organic substance leak detector according to the present invention, where the present invention is embodied as a fuel vapor detector;

Figs. 11 A and 11 B are schematic diagrams each illustrating a structure for coupling a sensor unit of the fuel vapor detector of Fig. 10 to an end of an optical fiber;

Fig. 12 is a block diagram generally illustrating an analog circuit for processing an electric signal produced by a photodiode in each of the fuel vapor detectors illustrated in Figs. 4, 7 and 10;

Fig. 13 is a schematic diagram generally illustrating the structure of a sensor unit in a fourth embodiment of the volatile organic substance leak detector according to the present invention;

Fig. 14 is a graph illustrating a change, over time, in magnitude of a signal produced by a fuel vapor detector using the sensor unit of Fig. 13;

Fig. 15 is a schematic diagram generally illustrating the structure of a sensor unit in a fifth embodiment of the volatile organic substance leak detector according to the present invention;

Fig. 16 is a schematic diagram generally illustrating the structure of a light emitting/light receiving unit in a sixth embodiment of the volatile organic substance leak detector according to the present invention;

Fig. 17 is schematic diagram generally illustrating the structure of a sensor unit in a seventh embodiment of the volatile organic substance leak detector according to the present invention; Fig. 18 is a schematic diagram illustrating a fuel leak monitoring system using the volatile organic substance leak detectors according to the present invention;

Fig. 19 is a block diagram generally illustrating the structure of an alarm control unit in the fuel leak monitoring system illustrated in Fig. 18; and

Fig. 20 is a graph illustrating an output voltage of an analog determination circuit in the fuel leak monitoring system illustrated in Fig. 18 together with a gas alarm threshold and a trouble alarm threshold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereinafter be described with reference to several embodiments thereof in more specific manner, however, it should be understood that the present invention is not limited to such specific embodiments.

Fig. 4 schematically illustrates the structure of a first embodiment of a volatile organic substance leak detector according to the present invention, wherein the present invention is embodied as a fuel vapor detector. A laser diode 20, a beam splitter 22 and a sensor unit 10 are positioned such that light from the laser diode 20 passes through the beam splitter 22 and is incident normal to a sensor element 8 in the sensor unit 10. A light beam emitted from the laser diode 20 is split by the beam splitter 22 into two light beams, one of which is received by a first photodiode (reference channel photodiode) 24 as a reference signal. The other light beam is incident on the sensor element 8 and reflected off the surface of a polymer thin film 4 and an interface between the polymer thin film 4 and a substrate 6. The reflected light beams mutually interfere with each other to produce reflected light having an intensity corresponding to at least one of the thickness and the refractive index of the polymer thin film 4. The reflected light propagates back the same path as that passed by the light directing to the sensor element 8, and is incident on the beam splitter 22 which reflects the reflected light at a right angle so that a second photodiode (signal channel photodiode) 26 receives the reflected light as a sensed signal. The second photodiode 26 is used to monitor the thickness at the sensor element 8, while the first photodiode 24 is used to monitor fluctuations or the like in a light output of a light source unit 2 for correcting the output of the second photodiode 26. These photodiodes 24, 26 are connected to current-to-voltage converter circuits 24', 26', respectively, for producing voltage outputs.

The sensor unit 10 comprises a housing 30 having a chamber 28 formed therein for communicating a fuel vapor. The sensor element 8 comprises the polymer thin film 4 formed on a reflecting surface of the substrate 6, and positioned in place within the chamber 28 by any appropriate means such that light from the light source unit 2 is incident normal to the polymer thin film 4. A window 32 is formed through a side wall of the housing 30 opposite to the sensor element 8, and a glass plate 34 is fitted in the window 32 for transmitting light emitted from the light source unit 2 and light reflected from the sensor element 8. The window 32 and the glass plate 34 constitute a light input/output unit. The housing 30 of the sensor unit 10 is further provided with a fuel vapor inlet port (or a fuel vapor intake port) 36 for introducing a fuel vapor into the chamber 28 such that the fuel vapor interacts with the polymer thin film 4.

The fuel vapor inlet port 36 or the fuel vapor intake port is provided with a water-proof mechanism 38 which, when used in the air, is capable of blocking water but transmitting a fuel vapor, and when used in water, is capable of selectively trapping fuel dissolved or separately existing in water as a vapor but blocking water. The water-proof mechanism 38 is preferably formed, for example, of a teflon membrane, a polyethylene membrane, a polypropylene membrane or the like. Particularly, a hydrophobic film such as a teflon membrane is suitable.

For actually fabricating the sensor element 8, 8.5 grams of poly(benzyl methacrylate-co-2-ethylhexyl methacrylate) was dissolved in cyclohexanone to produce a solution having a total weight of 100 grams. The solution was spin-coated on a substrate made of silicon wafer at 2900 rpm to form a polymer thin film. The polymer thin film formed on the silicon wafer substrate was dried in a reduced pressure environment for one hour, and then the thickness of the polymer thin film, when measured using a three-wavelength automatic ellipsometer "Auto EL IV NIR III" manufactured by Rudolph Research Co, was approximately 330 nm. This silicon wafer substrate was diced into 10mm x 10mm squares to produce sensor elements 8.

For examining the performance of a fuel vapor sensor using the sensor element 8, the sensor element 8 was mounted in the chamber 28 opposite to and in parallel with the glass plate 34, as illustrated in Fig. 4. Then, a hydrophobic teflon membrane 38' with a pore diameter of 3 μm was fitted in the fuel vapor inlet port 36 as the aforementioned water-proof mechanism 38, and a laser diode capable of emitting light at wavelength of 670 nm was used as the laser diode 20. An experiment was made under these conditions. While the sensor unit 10 was left in air, the output of the second photodiode 26 after current-to-voltage conversion was approximately 890 mV. Then, the sensor unit 10 was accommodated in a vessel 40, a container containing gasoline was placed in the vessel 40, and the opening of the vessel 40 was covered with aluminum foil. Examining the output of the second photodiode 26 one hour after the vessel 40 was enclosed, a signal at 960 mV was produced from the second photodiode 26 as a current-to-voltage converted signal with a good reproductivity. Next, the container containing gasoline was removed from the vessel 40, and one hour later, a signal at 890 mV was produced from the second photodiode 26 as a current-to-voltage converted signal in the air with a good reproductivity.

Next, the vessel 40 was filled with water, and the sensor unit 10 was placed in the vessel 40 until the teflon membrane was submerged in water, as illustrated in Fig. 6. Then, the water was stirred, and the output of the second photodiode 26, when monitored after one hour, was 890 mV. At this time, the sensor unit 10 was extracted from the water for inspecting the interior. There was no evidence of water immersing into the sensor unit 10. Then, the sensor unit 10 was again submerged in water, and 10 cc of light oil was dripped into the water while the water was being stirred. After ten hours, the output of the second photodiode 26 indicated 905 mV. Thereafter, a mixture of water and light oil was completely removed from the vessel 40, and the vessel 40 was again filled with water. After three hours, the output of the second photodiode 26 was 890 mV.

It was revealed from the foregoing experiment that the sensor unit 10 of the structure illustrated in Fig. 4 can block water and transmit only a gasoline vapor when used in the air, and can selectively trap light oil dissolved or separately existing in water as a vapor but block water when used in water, and that the sensor unit 10 has a high sensitivity to gasoline and light oil.

Fig. 7 schematically illustrates the structure of a second embodiment of the volatile organic substance leak detector according to the present invention, wherein the present invention is embodied as a fuel vapor detector. The second embodiment differs from the first embodiment illustrated in Fig. 4 in that a light source unit 2 is composed of a combination of a laser diode 20 and a collimator lens 42, a glass plate 44 is used in place of the beam splitter 22, and a window 32 is provided with a glass plate 34 having an additional interference filter of the same wavelength as that of light emitted from the laser diode 20.

A light beam emitted from the laser diode 20 and passing through the collimator lens 42 is split by the glass plate 44, serving as a light splitting means, into two beams, one of which is incident on a first photodiode 24. The other light beam is incident normal to a sensor element 8 through the glass plate 34 with an interference filter. The light beam reflected off the sensor element 8 returns along the same path, and is reflected off the glass plate 44 in a direction different from the direction of the path, which the light beam has so far traced, and is received by a second photodiode 26.

In the second embodiment, the sensor unit 10 was fabricated using the laser diode 20 which emits light at wavelength of 830 nm, the glass plate 34 with an interference filter of 830 nm, the collimator lens 42 positioned at 10 mm from the glass plate 34, and the hydrophobic teflon membrane 38' fitted in a fuel vapor inlet port 36. When this sensor unit 10 was left in air, the output of the second photodiode 26 was approximately 300 mV after it was current-to-voltage converted. Then, the sensor unit 10 was accommodated in a vessel 40, a container containing jet combustible «vas placed in the vessel 40, and the opening of the vessel 40 was covered with aluminum foil, as illustrated in Fig. 8. Examining the output of the second photodiode 26 two hours after the vessel 40 was enclosed, a signal at 670 mV was produced from the second photodiode 26 as a current-to-voltage converted signal with a good reproductivity. Next, the container containing jet combustible was removed from the vessel 40, and three hours later, a signal at 300 mV was produced from the second photodiode 26 as a current-to-voltage converted signal with a good reproductivity.

Next, as illustrated in Fig. 9, the vessel 40 was filled with water, and the sensor unit 10 was placed in the vessel 40. Then, the water was stirred, and the output of the second photodiode 26, when monitored after one hour, was 300 mV. At this time, the sensor unit 10 was extracted from the water for inspecting the interior. There was no evidence of water immersing into the sensor unit 10. Then, the sensor unit 10 was again submerged in water, and 30 cc of heavy oil was dripped into the water, while the water was being stirred. After 15 hours, the output of the second photodiode 26 indicated 340 mV. Thereafter, a mixture of water and heavy oil was completely removed from the vessel 40, and the vessel 40 was again filled with water. After three hours, the output of the second photodiode 26 was 300 mV.

It was revealed from the foregoing experiment that the sensor unit 10 of the structure illustrated in Fig. 7 can block water and transmit only vaporized jet fuel when used in air, and can selectively trap heavy oil dissolved or separately existing in water as a vapor but block water when used in water, and that the sensor unit 10 has a high sensitivity to jet fuel and heavy oil.

Fig. 10 schematically illustrates the structure of a third embodiment of the volatile organic substance leak detector according to the present invention, wherein the present invention is embodied as a fuel vapor detector. The third embodiment differs from the first embodiment illustrated in Fig. 4 in that a highly directional light emitting diode 46 is used as a light source, an optical fiber 48 is used to couple between a beam splitter 22 and a sensor unit 10, and connectors 50, 52 with a collimator are connected to both ends of the optical fiber 48. Fig. 11 A illustrates a structure for coupling the optical fiber 48 to the sensor unit 10, where the connector 52 with a collimator is mounted to cover a window formed through a housing 30 of the sensor unit 10, and one end of the optical fiber 48 is connected to the connector 52. For example, the light emitting diode 46 emits light at wavelength of 660 nm, and the optical fiber 48 is a multi-mode optical fiber having a length of 50 meters.

In Figs. 10 and 11(A), one of optical beams emitted from the light emitting diode 46 and split by the beam splitter 22 is detected by a first photodiode 24 as a reference signal for compensating for fluctuations of the light emitting diode 46, while the other optical beam is guided by the connector 50 with a collimator to be incident on the optical fiber 48. Light from the optical fiber 48 is collimated by the connector 52 with a collimator, is incident normal to the sensor element 8, and reflected off the sensor element 8. Then, the reflected light passes back through the connector 52 with a collimator, propagates through the optical fiber 48, and is reflected off the beam splitter 22 toward a second photodiode 26 by which the light is finally received.

Alternatively, instead of the structure of Fig. 11 A, the leading end of the optical fiber 48 may be positioned in contact with a chamber 28 without forming a window through the housing 30, as illustrated in Fig. 11 B.

As illustrated in Figs. 11 A, 11 B, a hydrophobic teflon membrane 38' with a pore diameter of 3 μm is fitted in a fuel vapor inlet port 36. The membrane 38' blocks water and transmits only a gasoline vapor when used in air, and can selectively trap light oil dissolved or separately existing in water as a vapor but block water when used in water.

Here, an analog circuit for receiving electric signals from the first and second photodiodes 24, 26 illustrated in Figs. 4, 7 and 10 and outputting an electric signal indicative of the existence of a fuel vapor will be described with reference to Fig. 12. A reference signal Iref from the first photodiode 24 is converted to a reference signal Vref by a current-to-voltage convertor circuit 24', while a detected signal Idet from the second photodiode 26 is converted to a detected signal Vdet and amplified by a current-to-voltage convertor circuit 26'. The two signals Vref and Vdet are inputted to a compensating circuit 54. The compensating circuit 54 is provided for compensating the detected signal Vdet for possible fluctuations in the light emitting diode 46 using the reference signal Vref, and outputs a detected signal Vcom which is compensated for such fluctuations in the light emitting diode 46. The signal Vcom is guided to a difference circuit 56, which generates a value calculated by subtracting a signal V_base corresponding to a zero concentration from the signal Vcom, i.e., a voltage Vdif corresponding to a difference from a zero concentration. The voltage Vdif is compared with a comparison level V_th in a comparator circuit 58. The comparator circuit 58 outputs a voltage Vout at high level when Vdif exceeds V_th, and at low level when Vdif does not exceed V_th, so that the existence of a fuel vapor is sensed by this voltage Vout.

For example, the sensor unit 10 according to the third embodiment illustrated in Fig. 10 was placed in a hexane vapor atmosphere having a relative concentration of 0.4, and a sensing was attempted with the circuit of Fig. 11. At a room temperature (19°C), a signal at 5.95 V was produced as the detected signal Vdet. On the other hand, when the sensor unit 10 was placed in an atmosphere free of hexane vapor, the detected voltage Vdet was at 5.84 V. Between the two voltage, there is a voltage difference of 0.11 V, from which it is understood that the fuel vapor detector illustrated in Fig. 10 has sufficiently capabilities of sensing the existence of hexane vapor.

Fig. 13 schematically illustrates the structure of a fourth embodiment of the volatile organic substance leak detector according to the present invention, wherein the present invention is embodied as a sensor unit for a fuel vapor detector which is suitable for use in detection of diffused vapor. A sensor unit 10' illustrated in Fig. 13 is used in place of the sensor unit 10 in Fig. 7. A housing 30 of the sensor unit 10' is formed with fuel vapor intake ports 60 for trapping a diffused vapor into a chamber 28. Each fuel vapor intake port 60 is provided with a filter 62 made of teflon for preventing water, mud or the like from flowing into the chamber 28. One end of an optical fiber 48 is connected to a connector 52 with a collimator which covers a window 32 formed through the housing 30. The optical fiber 48 is, for example, a multi-mode optical fiber having a length of 50 meters which is positioned such that a light beam exiting from one end of the optical fiber 48 is converged by a glass spherical lens 64 to be incident normal to a sensor element 8.

Actually, a fuel vapor sensor using the sensor unit 10' of Fig. 13 was placed in the air of a diffusion bath having a volume of 200 liters, and changes in intensity of reflected light from the sensor element 8 were observed for a condition in which the diffusion bath was filled with air, and for a condition in which the diffusion bath was enclosed after 1 cc of kerosine in liquid state had been dripped onto the bottom of the diffusion bath. While the magnitude of the detected signal Vdet was 5.84 V when the diffusion bath was filled with air, the magnitude of the detected signal Vdet was 6.54 V when the diffusion bath was enclosed after kerosine had been dripped into the diffusion bath as mentioned above. Fig. 14 illustrates changes in magnitude of the detected signal Vdet in this case. When 1 cc of heavy oil in liquid state was poured into the diffusion bath in a similar manner, the magnitude of the detected signal was 5.90 V.

Next, after the heavy oil was extracted from the diffusion bath, the diffusion bath was filled with water until the fuel vapor intake port 60 of the sensor unit 10' was submerged, and the water was stirred. After one hour, the magnitude of the detected signal was 5.84 V. Thereafter, when the interior of the sensor unit 10' was inspected, no immersing water was found. Next, when 20 cc of heavy oil was dripped into the diffusion bath while the water was being stirred, the magnitude of the detected signal after 14 hours indicated 6.01 V. Thereafter, a mixture of water and heavy oil was completely removed from the diffusion bath, the diffusion bath was again filled with water, and the magnitude of the detected signal, when monitored after three hours, was 5.84 V.

It was found from the foregoing results that the sensor unit 10' having the structure illustrated in Fig. 13 can be used as a fuel vapor detector since it blocks water and transmits only a light oil vapor when used in air, while selectively traps heavy oil dissolved or separately existing in water as a vapor but blocks water when used in water. Fig. 15 schematically illustrates the structure of a fifth embodiment of the volatile organic substance leak detector according to the present invention, wherein the present invention is embodied as a fuel vapor detector which is suitable for use in detection of diffused vapor. A sensor unit 10" illustrated in Fig. 15 may be used in place of the sensor unit 10' in Fig. 12. A leading end of an optical fiber 48 passes through a side wall of a housing 30 of the sensor unit 10" and opposes a sensor element 8 through a SELFOC lens 66. This eliminates the need of the connector 52 with a collimator, so that the sensor unit 10" can be reduced in size. Similar to the sensor unit 10' of Fig. 13, the housing 30 is provided with fuel vapor intake ports 60, each of which has a teflon membrane 38' fitted therein, such that the sensor element 8 is in contact with external air.

Actually, the sensor unit 10" having the sensor element 8 of 3mm * 10mm in size positioned at 2 mm from the lower end of the SELFOC lens 66 was placed in the air of a diffusion bath having a volume of 200 liters, and changes in intensity of reflected light from the sensor element 8 were observed for a condition in which the diffusion bath was filled only with air, and for a condition in which the diffusion bath was enclosed after 1cc of gasoline had been dripped onto the bottom of the diffusion bath in a liquid state. While the magnitude of the detected signal Vdet was 6.95 V when the diffusion bath was filled with air, the magnitude of the detected signal Vdet was 7.78 V when the gasoline liquid existed on the bottom of the diffusion bath. It was found from the foregoing results that the volatile organic substance leak detector according to the fifth embodiment illustrated in Fig. 15 can be used as a fuel leak detector.

Fig. 16 schematically illustrates the structure of a light emitting/light receiving unit in a sixth embodiment of the volatile organic substance leak detector according to the present invention. The light emitting/light receiving unit in this embodiment is characterized by an integrated structure comprising an integrated light emitting/light receiving laser 70 having an additional hologram (see Japanese Patent Laid-open No. 6-52588), and a fiber receptacle FC connector 72 having a collimator lens, one end of which is connected to an optical fiber for propagating laser light between the integrated light emitting/light receiving laser 70 and a sensor unit 10. Referring specifically to Fig. 16, the integrated light emitting/light receiving laser 70 comprises, in an integrated form, a laser diode 74 having an oscillation wavelength of, for example, 780 nm; a photodiode (not shown) for monitoring laser light emitted from the laser diode 74; a light receiving photodiode 76 for detecting reflected light; and a hologram 78 for transmitting laser light emitted from the laser diode 74 and for deflecting reflected light from a sensor element 8 from a traveling direction so that the reflected light is incident on the light receiving photodiode 76. These elements are supported on an appropriate base.

The integrated light emitting/light receiving laser 70 is fixed to one end of a cylinder 80 made of aluminum, and a collimator lens 82 for collimating light transmitting the hologram 78 is fixed at an appropriate location in the cylinder 80 by an appropriate means. A lower end of the fiber receptacle FC connector 72 is secured to an upper end of the cylinder 80. The optical fiber 84, one end of which is linked to the sensor unit 10, has the other end drawn to the inside of the fiber receptacle FC connector 72. The other end of the optical fiber 84 is at a position at which laser light collimated by the collimator lens 82 is converged by a collimator lens 86.

When comparing the light emitting/light receiving unit illustrated in Fig. 16 with the structure illustrated in Fig. 2, the laser diode 74 corresponds to the light source unit 2; the hologram 78 to the light transmitting/outputting unit 12; and the light receiving photodiode 76 to the light detector unit 14, respectively.

Since the volatile organic substance leak detector of the sixth embodiment is configured as described above, laser light emitted from the laser diode 74 transmits the hologram 78, is collimated by the collimator lens 82 and converged at the lower end of the optical fiber 84 by the collimator lens 86, propagates through the optical fiber 84 to the sensor unit 10, and is reflected off the sensor element 8. The laser light reflected off the sensor element 8 propagates back the same path, passes through the collimator lens 82, and is incident on the hologram 78. The hologram 78 deflects the traveling direction of the incident light which is thereby incident on the light receiving photodiode 76. The existence of a fuel vapor can be detected by measuring the magnitude of an output signal from the light receiving photodiode 76. Actually, a diffusion type sensor unit (for example, as illustrated in Fig. 13) connected to the light emitting/light receiving unit of the structure illustrated in Fig. 16 through an optical fiber of 50 meters in length was placed in the air in a diffusion bath having a volume of 200 liters. 1 cc of gasoline in liquid state was dripped onto the bottom of the diffusion bath, and the diffusion bath was enclosed. Under this condition, the magnitude of a detected signal of the light receiving photodiode, when monitored for a gasoline vapor, was 2780 mV. The magnitude of the output signal of the light receiving photodiode was 1435 mV when the sensor unit was placed in the air. It was found from these results that the sixth embodiment can also be used as a volatile organic substance leak detector.

Fig. 17 schematically illustrates the structure of a sensor unit in a seventh embodiment of the volatile organic substance leak detector according to the present invention, wherein the present invention is embodied as a sensor unit for a fuel vapor detector which is suitable for sensing fuel components dissolved or separately existing in a diffused vapor or in water.

A sensor unit 10'" of Fig. 17 may be used in place of the aforementioned sensor unit, and an end of an optical fiber 48 is fixed to a receptacle 92 having a collimator lens through a FC connector 90. A sensor element 8 is positioned to oppose the collimator lens in the receptacle 92, and secured on the sensor element holder 94 with an adhesive or the like. The receptacle 92 and the sensor element holder 94 are fixed to a main body 96. An O-ring 100 fixed to an O-ring holder 98 is fitted into an open end of the main body in order to prevent water or the like from immersing from the outside. Further, a lid 104 having a PTFE filter 102 fitted therein is fixed on the other end of the main body 96. The lid 104 is formed with an opening 106 extending through a central portion thereof, such that the filter 102 is in contact with external air. Also, an O-ring 108 is arranged at one end of the lid 104 in contact with the holder 98 for holding the O-ring 100, so that the filter 102 is sandwiched between the O-ring 108 and a gasket and a support screen (either of which are not shown), and fixed to the lid 104. The FC connector 90, the receptacle 92 and the main body 96 have their outer peripheries covered with a cylinder 110 made of a material such as stainless steel to prevent water or the like from immersing into the inside.

Actually, a fuel vapor detector using the sensor unit 10'" of Fig. 17 was placed in the air in a diffusion bath having a volume of 200 liters, and changes in intensity of reflected light from the sensor element 8 were observed for a condition in which the diffusion bath was filled with air, and for a condition in which the diffusion bath was enclosed after 2cc of gasoline in liquid state had been dripped onto the bottom of the diffusion bath. The magnitude of the detected signal Vdet was 4.87 V when the diffusion bath was filled with air. On the other hand, the magnitude of Vdet was 6.54 V when the diffusion bath was enclosed after gasoline had been dripped into the diffusion bath. When 2 cc of light oil in liquid state was poured into the diffusion bath in a similar manner, Vdet was 5.2 V. Next, an empty diffusion bath was filled with water, and the water was stirred with the fuel vapor inlet port of the sensor unit bing submerged in water. After one hour, the detected signal Vdet was 4.87 V. Thereafter, when the interior of the sensor unit was inspected, there was no evidence of water immersing into the sensor unit. Next, 30 cc of heavy oil was dripped into the diffusion bath while water was being stirred. 13 hours after the heavy oil was dripped, the detected signal Vdet indicated 4.96 V. Subsequently, a mixture of water and heavy oil was completely removed from the diffusion bath, and the diffusion bath was again filled with water. The detected signal Vdet, when monitored three hours after the diffusion bath had been filled with water, was 4.87 V.

It was revealed from the foregoing observation that the sensor unit of this embodiment can be used as a fuel vapor detector since the sensor unit blocks water and transmits only a vaporized gasoline or light oil when used in air, and selectively extracts heavy oil dissolved or separately existing in water as a vapor but blocks water when used in water.

One important application of the volatile organic substance leak detectors so far described in detail is a system for remotely monitoring a leaked fuel vapor. Fig. 18 generally illustrates such a remote monitoring system for monitoring a leaked fuel vapor. Referring specifically to Fig. 18, sensor units 10.,, 10₂, 10₃, 10₄ according to the present invention are disposed at sites where a fuel vapor is likely to leak, and these sensor units are connected to an associated alarm controller 120 through optical fibers 48_{1 t} 48₂, 48₃, 48₄, respectively. The alarm controller 120 is installed at an appropriate site where a fuel vapor is likely to leak, for example, near a gas station, an oil supply station or the like, and are connected to a data processing apparatus 124 installed in a remote monitoring center 122 through arbitrary lines 126 such as a telephone line, a dedicated line, a wireless line, a satellite line or the like. A relay station 128 may be installed in the middle of each line 126 as required. It goes without saying that a plurality of the alarm controllers 120 may be connected to the monitoring center 122 such that a plurality of different sites can be collectively monitored at the same time.

Fig. 19 is a block diagram illustrating an exemplary structure of the alarm controller 120 which has three sensor units 10.,, 10₂, 10₃ each connected to one end of corresponding optical fiber 48^ 48₂ or 48₃. In Fig. 19, the alarm controller 120 comprises three alarm control units 130^ 130₂, 130₃ connected to the other ends of the optical fibers 48.,, 48₂, 48₃; a microprocessor 132 for generally controlling the operation of the alarm controller 120; a modem 134 connected to the telephone line 126; a memory 136 for storing monitored data; an external input terminal 138 through which external information is inputted to the alarm controller 120; and an alarm unit 140 for generating alarm.

The three alarm control units 130.,, 130₂, 130₃, which are in the same structure, each have a light emitting/light receiving unit, an analog determination circuit and a display unit. The light emitting/light receiving unit sends laser light to the optical fiber to irradiate the associated sensor unit with the laser light, and receives reflected light from the sensor unit and transduces the received light to an electric signal. The electric signal is compared with a gas alarm threshold value and a trouble alarm threshold value, respectively, in the analog determination circuit to determine whether or not leaked fuel is present, and whether or not the sensor units, the optical fibers, a light source or the like have failed. The analog determination circuit provides a determination result indicating either "Normal", "Fuel Leak Has Occurred" or "Trouble in Sensor Unit, Optical Fiber, Light Source or the Like". The microprocessor 132 always displays the determination result on the display unit to enable a field manager to know the situations at moriitored sites. The determination result may be printed out as required.

The microprocessor 132 temporarily stores the determination result in the analog determination circuit in the memory 136. If the determination result shows that the sensor units 101 , 102, 103 are normally operating, and no leaked fuel is found, the microprocessor 132 reads data indicative of the determination result from the memory 136 at predetermined time intervals, and sends the data to the monitoring center 122 together with a field identification code through the modem 104. In this event, the microprocessor 132 may send external data (for example, the amount of fuel stored in a tank, a power interruption occurring time, a power interruption recovery time, and so on) inputted from the external input terminal 138 to the data processing apparatus 124 in the monitoring center 122, through the modem 134 and the telephone line 126. The contents of data communicated to the monitoring center 122 may be set by sending instructions from the data processing apparatus 124 to the microprocessor 132 in the field using an appropriate input means. In addition, the values of the gas alarm threshold and the trouble alarm threshold may be set or changed similarly by inputting new values in the field, or by sending instructions from the data processing apparatus 124 to the microprocessor 132 through the telephone line 126.

On the other hand, if the determination result of the analog determination circuit shows that fuel is leaking or a trouble has occurred in any of sensor units, optical fibers, light source, and so on, the microprocessor 132 immediately activates the alarm unit 140 to generate alarm for prompting the field manager to take appropriate actions, and notifies the data processing apparatus 124 of the occurrence of the fault through the modem 134 and the telephone line 126. In this way, the data processing apparatus 124 displays a message for notifying the fault, and activates an alarm lamp or a buzzer to prompt the manager to take appropriate actions. It is therefore possible to find the occurrence of a fault at a remote location in its early stages. Fig. 20 is a graph illustrating an example of a change in output voltage from the analog determination circuit over time together with the gas alarm threshold at 2.5 V and the trouble alarm threshold at 0.5 V. When the output voltage of the analog determination circuit exceeds the gas alarm threshold or lowers below the trouble alarm threshold, the analog determination circuit determines the occurrence of leaked fuel or a fault such as a trouble in any of sensor units, optical fibers, light source, and so on.

As will be apparent from the foregoing detailed description of the present invention made with reference to several embodiments thereof, the volatile organic substance leak detector according to the present invention is particularly advantageous in that it can accurately detect a vaporized volatile organic substance or a volatile organic substance dissolved or separately existing in water, even in places where the organic substance is likely to be mixed with splashed water, mud or the like, or buried under water, mud or the like, without suffering from influences of such bad conditions. In addition, the volatile organic substance leak detector according to the present invention is simple in structure, can be manufactured at a low price, and is capable of detecting the existence and/or concentration of a volatile organic substance in an intrinsically safe state. Further, since the sensor units are disposed at sites where a leaked organic substance is more likely to occur and the sensor units are connected to light emitting/light receiving units through optical fibers such that the occurrence of a fault can be determined from the outputs of the light emitting/light receiving units, any fault can be safely detected in early stages.

Furthermore, since data produced by the sensor unit can be communicated to a remote location, monitored sites can be always kept monitored including even during the night when such monitored sites are unattended, thus making it possible to rapidly take appropriate actions when any fault occurs.

Claims

What is claimed is:

1. A volatile organic substance leak detector for detecting at least one of existence and concentration of a vaporized volatile organic substance comprising: a light source unit having a light emitting element; a sensor unit including a sensor element formed of a polymer thin film deposited on a reflecting surface, said polymer thin film exhibiting a change in at least one of a thickness and a refractive index in response to a contact with said vaporized volatile organic substance, said sensor unit being positioned such that light from said light source unit is incident normal to said sensor element; a light transmitting/outputting unit positioned between said light source unit and said sensor unit for transmitting light from said light source unit so that the light is incident on said sensor unit and for outputting reflected light reflected off said sensor element; a light detector unit coupled to receive said reflected light for producing a signal corresponding to said reflected light; a housing, forming part of said sensor unit, having a chamber formed therein for interacting said vaporized volatile organic substance introduced thereinto through a volatile organic substance inlet port with said polymer thin film; a light input/output unit positioned in said housing opposite to said sensor element; and a mechanism arranged in said inlet port, said mechanism for blocking water and transmitting said vaporized volatile organic substance, when used in the air, and for trapping said volatile organic substance dissolved or separately existing in water as a vapor when used in water.

2. A volatile organic substance leak detector according to claim 1 , wherein said light transmitting/outputting unit is connected to said sensor unit through an optical fiber.

3. A volatile organic substance leak detector according to claim 1 or 2, wherein said light source unit, said light transmitting/outputting unit, and said light detector unit constitute a light emitting/light receiving unit.

4. A volatile organic substance leak detector according to any of claims 1 - 3, wherein said light emitting/light receiving unit includes an integrated light emitting/light receiving laser having an additional hologram.

5. A volatile organic substance leak detector according to any of claims 1 - 4, wherein said light detector unit includes photoelectric transducing means for producing an electric signal in accordance with an intensity of said reflected light; and means for comparing said electric signal with a predetermined value to notify at least one of existence and concentration of said vaporized volatile organic substance as the result of the comparison.

6. A volatile organic substance leak monitoring system comprising: at least one volatile organic substance leak detector according to any of claims 1 - 5, each said volatile organic substance leak detector being arranged such that said sensor unit is positioned at a monitored site and said light emitting/light receiving unit is disposed in an alarm control unit; a determination circuit, associated with said alarm control unit, for determining whether or not a fault has occurred based on an electric signal outputted from said light emitting/light receiving unit, said fault including a trouble in said sensor unit and existence of a vaporized volatile organic substance at a site where said sensor unit is positioned; bidirectional communicating means for coupling said alarm control unit to a remote location, such that occurrence of said fault is monitored at said remote location.

7. A volatile organic substance leak monitoring system according to claim 6, wherein: said alarm control unit further comprises: a memory for storing data indicative of a determination result provided by said determination circuit; and notifying means for transmitting data stored in said memory at predetermined time intervals when said determination result does not indicate occurrence of a fault, and for immediately notifying said remote location of said determination result when said determination result indicates occurrence of a fault.