CA2239548A1

CA2239548A1 - Optical fuel vapor detector utilizing thin polymer film and fuel leak monitor system

Info

Publication number: CA2239548A1
Application number: CA002239548A
Authority: CA
Inventors: Tsunetoshi Sugiyama; Kenji Motosugi; Tetsu Yamamoto; Yusuke Takano
Original assignee: Individual
Current assignee: HOECHST RESEARCH AND TECHNOLOGY JAPAN Ltd
Priority date: 1995-12-05
Filing date: 1996-12-04
Publication date: 1997-06-12
Also published as: KR19990071930A; WO1997021098A1

Abstract

A fuel vapor detector system having a simple and low-cost structure, which is essentially safe, and a fuel leak monitor system using the detector. The fuel vapor detector includes a light source (2) having a light-emitting body; a detector (10) including a sensor (8) having a substrate (6) with a polymer coating (4) that changes its thickness and/or refractive index when coming into contact with a fuel vapor, the detector being disposed in such a manner that light from the light source is incident perpendicularly on it; a lighttransmitting output portion (12) for allowing light from the light source (2) to pass therethrough and to allow it to be incident on the detector (10), and receiving reflected light from the sensor (8), the output portion being placed between the light source and the detector; and a photodetector for receiving reflected light from the sensor (8) and generating a signal corresponding to reflected light.

Description

CA 02239~48 1998-06-04 SPECIFICATION

OPTICAL FUEL VAPOR DETECTOR AND FUEL LEAK MONITORING
SYSTEM UTILIZING POLYMER THIN FILM

TECHNICAL FIELD
5This invention relates to a fuel vapor detector for optically detecting the existence and/or the concentration of a vaporized fuel such as gasoline, light oil, kerosine, heavy oil and so on, which is particularly suitable for use in a fuel leak detector and fuel leak monitoring system for detecting a fuel leak as early as possible.
BACKGROUND ART
A float type sensor is well known for detecting a fuel leak in a fuel tank or the like which may be installed underground in a service station area or the like. 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 thereby determine a fuel leak. In addition, several methods for detecting a fuel leak have been proposed as illustrated below.
Published Japanese translation of PCT International publication for Patent Application No. 3-503674 discloses a computerized automatic system for detecting the volume of a leaked liquid including measurements of pressure and temperature as well as measurements of level (liquid surface) and temperature to detect a liquid leak from an underground storage container, wherein an electro-mechanical level sensor is employed for measuring a liquid level.

CA 02239~48 1998-06-04 Laid-open Japanese Patent Application No. 2-233393 discloses a leaked oil detector intended to eliminate disadvantages encountered in the detection of a leaked oil by a leaked oil display, wherein a water-floatable oil detecting means is disposed in a gas detecting tube buried near an underground tank, and the oil detecting means is electrically connected to an alarming means.
Laid-open Japanese Patent Application 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, wherein a pressure is applied to the tank itself, and a change in external pressure (applied pressure) is measured by means of a diaphragm type silicon pressure sensor.
These known methods have a disadvantage that an initial leak detection is impossible. In other words, the occurrence of fuel leak can be determined only after a leaked fuel has been accumulated to a certain amount. As a result, the methods are defective in that the leak may be found too late, and consequently, because of its electrical measuring principles, the risk of explosion is potentially involved.
To overcome the disadvantage of the prior art methods, a fuel vapor detector for optically sensing a fuel vapor has already been proposed as illustrated in Fig. 16. In this fuel vapor detector, a light beam sent from a light source 100 through an optical fiber 102 is incident on a polymer thin film 106 formed on a substrate 104. The light beam CA 02239~48 1998-06-04 reflected by the polymer thin film 106 is sent to and detected by a light detector 110 through another optical fiber 108. The polymer thin film 106 reacts with a fuel vapor passing through a passage 112, or adsorbs or absorbs the fuel vapor, so that, as a result of such interaction, the polymer thin film 106 exhibits a change in thickness and/or refractive index. Since the fuel vapor is optically detected utilizing the characteristics inherent to the polymer thin film 106 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 fibers 102, 108 are used (because free from electrical power).
In the fuel vapor detector illustrated in Fig. 16, an 16 interference enhanced reflection method (hereinafter referred to as the "IER method") is utilized. Specifically, light reflected on the surface of the polymer thin film 106 has a phase relationship with light reflected on the surface of the substrate 104 supporting the polymer thin film 106, and they interfere with each other. Thus, since the reflectivity of the polymer thin film 106 or the intensity of the reflected light changes as the thickness and/or the refractive index of the polymer thin film 106 changes, the existence and/or the concentration of a fuel vapor can be detected as a function of the intensity of the reflected light.
However, since the two optical fibers 102, 108 are used as illustrated in Fig. 16, a plurality of collimators CA 02239~48 1998-06-04 or connectors must be disposed between the light source 100 and the optical fiber 102, between the optical fiber 102 and the polymer thin film 106, and between the optical fiber 108 and the light detector 110, the fuel vapor detector has a problem of a complicated structure and an increased cost.
Another problem to be considered is a higher likelihood of fuel leak due to increasingly introduced oil-immersed pumps for purposes of reducing a cost in a service station. Conventionally, in a service station, each of oil supply machines is provided therein with a suction pump corresponding to an associated type of oil for sucking the oil. However, a system for feeding a fuel to respective oil supply machines by equipping a tank with a single oil-immersed pump has been employed in order to reduce a cost in a service station. However, when an oil-immersed pump is installed in a service station, the pressure of a fuel becomes higher than before so that once a leak occurs, a larger amount of fuel is likely to effuse in a shorter time period to result in serious environmental contamination.
Also, with any pump concerned, if a fuel leak occurs in an llnm~nned state such as at night, provision must have been made so that a service man can be immediately sent to the site. There is a strong need for the realization of a remote monitoring system which satisfies requirements as mentioned above.
DISCLOSURE OF THE INVENTION
This invention has been made in view of the problems mentioned above, and it is a general object of this CA 02239~48 1998-06-04 invention to provide a fuel vapor detector using no optical fiber or using one optical fiber for detecting the existence and/or the concentration of a fuel vapor, which is inexpensive and simple in structure. More specifically, it is an object of this invention to provide a fuel vapor detector which is intrinsically safe, simple in structure, easy to manufacture, highly reliable, inexpensive, and suitable for reduction in size. Further, it is another obJect of this invention to provide a fuel leak monitoring system which is capable of remotely monitoring a fuel leak utilizing a fuel vapor detector as mentioned above.
To achieve the above objects, this invention provides a fuel vapor detector for detecting at least one of the existence and concentration of a fuel vapor. The fuel vapor detector comprises, as illustrated in Fig. 1:
a light source unit 2 having a light emitting element;
a sensor unit 10 including a sensor element 8 made of a polymer thin film 4 formed on a substrate 6, where the polymer thin film 4 exhibits a change in at least one of a thickness and a refractive index due to a contact with the fuel vapor, and positioned such that light from the light source unit 2 is incident normal to the sensor element 8;
a light transmitting/outputting unit 12 disposed between the light source unit 2 and the sensor unit 10 for transmitting light from the light source unit 2 so that the light is incident on the sensor unit 10 and for outputting reflected light reflected by the sensor element 8; and CA 02239~48 1998-06-04 a light detector unit 14 for receiving the reflected light from the sensor element 8 to generate a signal corresponding to the reflected light.
The fuel vapor detector is preferably installed in an underground tank, a thump, surroundings of an oil immersed pump, a ground tank, an oil refinery, an oil transporting line, an oil transporting tanker, and so on.
This invention detects the existence or the concentration of a fuel vapor by measuring a change in the reflection characteristic of the sensor unit 10, making use of the characteristics of the polymer thin film 4 which exhibits a change in at least one of the thickness and the refractive index due to a contact with a vapor under detection. As a result of an interaction with a fuel vapor, the polymer thin film 4 experiences physical changes such as, for example, swelling. Also, such swelling causes the polymer thin film 4 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 4, a fuel vapor can be detected by measuring the reflection characteristic of the polymer thin film 4.
To realize this, in this invention, light from the light source 2 is incident normal to the sensor unit 10.
The light is reflected by the sensor element 8 to cause the light to propagate through the same path as when it was incident thereto. Then, the light is reflected by the light transmitting/outputting unit 12 in a direction different CA 02239~48 1998-06-04 from that of the propagation path to introduce the light into the light detector unit 14 which is forced to generate an electrical signal corresponding to the reflected light from the sensor element 8.
It should be particularly noted in this invention that by appropriately selecting a polymer material constituting the polymer thin film 4, it is possible to selectively or non-selectively detect the existence of a fuel vapor such as gasoline, light oil, kerosine, heavy oil or the like. Moreover, since the polymer thin film 4 has the reflection characteristic corresponding to the concentration of a fuel vapor, the fuel vapor detector of this invention may serve as a concentration meter for a fuel vapor.
In this invention, an IER method, for example, is employed for detecting a change in thickness and/or refractive index of the polymer thin film 4. As mentioned above, the IER method utilizes the optical interference characteristic of a thin film structure. Light reflected by the surface of the polymer thin film 4 has a phase relationship with light reflected from the interface between the polymer thin film 4 and a reflecting surface of the substrate 6, and they interact with each other. The reflectivity of the sensor element 8 largely depends on the thickness and/or the refractive index of the polymer thin film 4. In other words, as the thickness and/or the refractive index of the polymer thin film 4 changes, the reflectivity of the polymer thin film 4 or the intensity of CA 02239~48 1998-06-04 light reflected therefrom also changes. In this way, the existence and/or the concentration of a fuel vapor 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, this invention may attach more importance to the influence of the thickness of the polymer thin film 4 than the reflectivity of the same, provided that a material having a refractive index not substantially different from the reflective index of a fuel vapor is used as the polymer thin film 4 employed in this invention. This is a unique advantage of this invention over the prior art.
Another point to be emphasized for a comparison with the prior art relates to the thickness of the polymer thin film 4. Fig. 2 illustrates a graph which plots the reflectivity of the polymer thin film 4 having a refractive index equal to 1.5 formed on a substrate 6 made of silicon, to which light is incident at an incident angle of 0~, as a function of the thickness of the polymer thin film 4.
Polarized light and non-polarized light used herein have a wavelength of 633 nm.
According to this graph, the thickness of the polymer thin film 4 suitable for the IER method is preferably adjusted depending on a particular concentration range of a fuel vapor in the following manner. First, when a fuel vapor concentration is low, the reflectivity changes little, so that the polymer thin film 4 adjusted to have a thickness CA 02239~48 1998-06-04 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 ~/4ncos~
corresponding to the minimum value or the m~Ximum value of the reflectivity, where ~ is the wavelength of incident light, n is the refractive index of the polymer thin film 4, and H is a light propagation angle within the polymer thin film 4. When the fuel vapor concentration is relatively high, on the other hand, the reflectivity largely changes, so that the polymer thin film 4 is preferably adjusted to a thickness corresponding to the minimum value or the m~ximum 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 ~m, a thickness not more than 1 ~m 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

X-C-Rl (I) I

where X represents -H, -F, -Cl, -Br, -CH3, -CF3, -CN, or -CH2-CH3:
R1 represents _R2 or -Z-R2;

g CA 02239~48 1998-06-04 Z represents -O-, -S-, -NH-, -NR2'-, -(C=Y)-, -(C=Y)-Y-, -Y- ( C=Y ) -, - ( SO2 ) -, -Y - ( SO2 ) -, - ( SO2 ) -Y -, -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-;
6 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 straight-chain alkyl group, a branched-chain 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 straight-chain alkyl group, or a branched alkyl group.
Preferably, in the foregoing recurring unit (I):
X represents H or CH3;
Rl 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 straight-chain 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 4 may be a polymer consisting of a simple of the above-mentioned 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 CA 02239~48 1998-06-04 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 prepared from polymethacrylic acid esters or polyacrylic acid esters. The side-chain group of the ester is preferably a straight-chain 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 6 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);

CA 02239~48 1998-06-04 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 c;nn~m~te);
poly(vinyl c;nn~m~te-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);

CA 02239~48 1998-06-04 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).
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 into the polymer a compound that has crosslinking reactive groups. Such crosslinking reactive groups appropriate for the purpose include, for example, an amino group, a hydroxyl group, a carboxyl group, CA 02239~48 1998-06-04 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 the detector. There is no particular limits to the crosslinking method, 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 fuel vapor detector according to this invention, preferably, the reflecting surface of the substrate 6 for supporting the polymer thin film 4 is sufficiently flat such that a reflecting surface of the substrate 6 reflects light, and the substrate itself preferably has a high reflectivity. An example of the substrate 6 may be a silicon wafer. The polymer thin film 4 may be formed on the surface of the substrate 4 by a spin coat method or any other coating method used in common.
The light source unit 2 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 for emitting visible light or infrared rays. The light transmitting/outputting unit 12 CA 02239~48 1998-06-04 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 14 may be formed of either a photodiode, a phototransistor or a photomultiplier tube, and a photodiode is preferably used.
The light transmitting/outputting unit 12 may be connected to the sensor unit 10 through an optical fiber.
As the light source unit 2 for this case, a laser diode or a light emitting diode is suitable. 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 is preferably a connector having a collimator lens, a SELFOC lens or the like available in the market. The optical fiber is preferably 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 exiting from an optical fiber has a rather wide angle, the light is preferably converged by a lens before it is incident on the sensor unit 10. A lens for this purpose is 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 CA 02239~48 1998-06-04 unit 12 and the sensor unit 10. In this case, the degree of freedom is increased. For example, light can be measured by the sensor unit 10 spaced from the light transmitting/outputting unit 12 by a desired distance. A
light source unit 2 for this case is preferably a laser diode. A collimator lens may be preferably used to collimate light from the light source unit 2. While 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 may be used as such a collimator lens, a quartz aspherical convex lens is preferred.
In one embodiment of this invention, the sensor unit 10 comprises a housing having a chamber, and the sensor element 8 having the polymer thin film 4 formed on a reflecting surface of the substrate 6 is positioned in this chamber. 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 4, and provided with a fuel vapor exhaust port for exhausting a fuel vapor in the chamber to the outside, if necessary. A cover may be attached to the fuel vapor inlet port or the fuel vapor intake port for blocking stray light, dust, mist or the like from introducing and transmitting a fuel vapor. This cover is preferably formed, for example, of a sintered metal or a separating membrane of Teflon.
At a position of the housing of the sensor unit 10 CA 02239~48 1998-06-04 opposite to the sensor element 8, a window and a glass plate covering the window may be provided as a light input/output unit for passing therethrough light from the light source unit 2 and reflected light from the sensor element 8.
However, when the light transmitting/outputting unit 12 is connected to the sensor unit 10 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 8, 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 10 opposite to the sensor element 8, if necessary, as a light input/output unit for passing therethrough light from the light source unit 2 and reflected light from the sensor element 8.
In practice, the light source unit 2, the light transmitting/outputting unit 12 and the light detector 14 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 Laid-open Japanese Patent Application No. 6-52588) may be advantageously utilized. The sensor unit 10, in turn, may be installed at any site where fuel leak is highly likely to occur, 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 2, the light transmitting/outputting unit 12 and the light detector CA 02239~48 1998-06-04 unit 14 and the sensor unit 10 is adjusted such that light emitted from the light source unit 2 is incident normal to the sensor unit 10, and reflected light therefrom propagates back the same path.
In one embodiment, the light detector unit 14 comprises photoelectrical transducing means for generating an electrical signal in accordance with the amount of reflected light from the sensor element 8, and means for comparing the electrical signal with a predetermined value to notify the existence and/or the concentration of a fuel vapor as the result of the comparison.
Furthermore, this invention provides a fuel leak monitoring system characterized in that:
at least one of the so far described fuel vapor detectors is provided such that the sensor unit is installed at a monitored site and the light emitting/light receiving unit is disposed in an alarm controller;
the alarm controller has a determination circuit for determ,n'ng whether or not a fault has occurred based on an electrical signal output from the light emitting/light receiving unit, wherein the fault includes a trouble in the sensor unit and the existence of a fuel vapor at a site where the sensor unit is installed; and the alarm controller and the remote location are coupled by bi-directional communicating means, whereby the occurrence of a fault is monitored from the remote location.
In this fuel leak monitoring system, the alarm CA 02239~48 1998-06-04 controller further comprises:
a memory for storing data indicative of a determination result by the determination circuit; and communicating means for communicating data stored in the memory to the remote location at predetermined time intervals when the determination result does not indicate the occurrence of a fault, and for immediately communicating to the remote location when the determination result indicates the occurrence of a fault.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a diagram schematically illustrating the configuration of a fuel vapor detector according to this invention;
Fig. 2 is a graph illustrating the reflectivity of a polymer thin film formed on a substrate;
Fig. 3 is a diagram schematically illustrating the structure of a first embodiment of the fuel vapor detector according to this invention;
Fig. 4 is a diagram schematically illustrating the structure of a second embodiment of the fuel vapor detector according to this invention;
Fig. 5 is a graph illustrating changes over time of the magnitude of a signal generated by the fuel vapor detector of Fig. 4;
Fig. 6 is a diagram schematically illustrating the structure of a third embodiment of the fuel vapor detector according to this invention;
Figs. 7(A) and 7(B) are diagrams each schematically CA 02239~48 1998-06-04 illustrating a structure for coupling a sensor unit to an end of an optical fiber in the fuel vapor detector of Fig.
6;
Fig. 8 is a diagram schematically illustrating an analog circuit for processing electrical signals fetched from a photodiode in the fuel vapor detectors of Figs. 3, 4 and 6;
Fig. 9 is a diagram schematically illustrating the structure of a fourth embodiment of the fuel vapor detector according to this invention;
Fig. 10 is a graph illustrating changes over time of the magnitude of a signal generated by the fuel vapor detector of Fig. 9;
Fig. 11 is a diagram schematically illustrating the structure of a fifth embodiment of the fuel vapor detector according to this invention;
Fig. 12 is a diagram schematically illustrating the structure of a sixth embodiment of the fuel vapor detector according to this invention;
Fig. 13 is a schematic diagram of a fuel leak monitoring system using the fuel vapor detector according to this invention;
Fig. 14 is a block diagram schematically illustrating the configuration of an alarm controller in Fig. 13;
Fig. 15 is a graph illustrating an output voltage of an analog determination circuit in Fig. 14 together with a gas alarm threshold and a trouble alarm threshold; and Fig. 16 is a diagram schematically illustrating the CA 02239~48 1998-06-04 structure of an example of a conventional fuel vapor detector.
BEST MODE FOR CARRYING OUT THE INVENTION
This invention will hereinafter be described in connection with several embodiments thereof in specific forms, however, this invention is not limited to these embodiments.
Fig. 3 is a diagram schematically illustrating the structure of a first embodiment of a fuel vapor detector according to this invention. 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 16 diode 20 is split into two by the beam splitter 22, and one of the light beams 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 a surface of a polymer thin film 4 and off an interface between the polymer thin film 4 and a substrate 6. The reflected light mutually interferes 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. This reflected light propagates back the same path as the going path, enters the beam splitter 22, and is bent perpendicularly by the beam splitter 22 to be received by a second photodiode (signal channel photodiode) 26 as a detected signal.

CA 02239~48 1998-06-04 The second photodiode 26 is used to monitor the thickness of the sensor element 8, and the first photodiode 24 is used to monitor fluctuations in light output of the light source unit 2 or the like to compensate for the output of the second photodiode 26. The respective photodiodes 24, 26 are connected to current-to-voltage converter circuits 24', 26' for producing voltage outputs.
The sensor unit 10 comprises a housing 30 which is formed with a chamber 28 for communicating a fuel vapor to the inside. The sensor element 8 having the polymer thin film 4 formed on a reflecting surface of the substrate 6 is positioned in place within the chamber 28 by an appropriate means such that light from the light source unit 2 is incident normal to the polymer thin film 6. A window 32 is formed through a side of the housing 30 which faces the sensor element 8. A glass plate 34, transmitting light emitted from the light source unit 2 and light reflected by the sensor element 8, is fitted in the window 32 to constitute a light input/output unit. The housing 30 of the sensor unit 10 is further provided with a fuel vapor inlet port 36 for introducing a fuel vapor into the chamber 28 to promote interaction of the fuel vapor with the polymer thin film 4, and a fuel vapor exhaust port for exhausting the fuel vapor in the chamber 28 to the outside.
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 CA 02239~48 1998-06-04 was spin-coated on a substrate made of silicon wafer at 2900 rpm to form a polymer thin film. The polymer thin film was dried at 60~C in a reduced pressure environment for one hour, and then the thickness of the polymer thin film, when measured using a three-wavelength automatic ellipso-meter "Auto EL IV NIR III" manufactured by Rudolph Research Co.
was approximately 330 nm. This silicon wafer substrate was diced into 10 mm x 10 mm squares to produce sensor elements 8. To ex~m~ne the performance of a fuel vapor detector using this sensor element 8, the sensor element 8 is set in a chamber 28 in parallel to and opposite to the glass plate 34 as illustrated in Fig. 34. When a light source for emitting light at wavelength of 670 nm was used as the laser diode 20, the output of the second photodiode 26 after 16 current-to-voltage conversion was approximately 890 mV when nitrogen was introduced into the chamber 28. However, a signal of approximately 960 mV was generated from the second photodiode 26 after current-to-voltage conversion with good reproductivity when a gasoline vapor having a relative concentration of 0.4 was introduced into the chamber 28. It was revealed from this that the sensor element 8 using the polymer thin film 4 made of the aforementioned material has a larger sensitivity for a gasoline vapor than for nitrogen.
Fig. 4 is a diagra~m~ schematically illustrating the structure of a second embodiment of the fuel vapor detector according to this invention. This second embodiment differs from the first embodiment of Fig. 3 in that a light source is composed of a laser diode 20 and a collimator lens 40 in CA 02239~48 1998-06-04 combination, a glass plate 42 is used in place of the beam splitter 22, and a window 32 is provided with a glass plate 44 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 40 is split into two by the glass plate 42 as a light splitting means, and one of the light beams enters a first photodiode 24. The other light beam is incident normal to a sensor element 8 through the glass plate 44 having the interference filter. The light beam reflected by the sensor element 8 returns along the same path, and is reflected on the glass plate 42 in a direction different from the path, along which it has been travelling, and received by a second photodiode 26.
For example, a light source for emitting light at wavelength of 830 nm was used for the laser diode 20, a glass plate with an interference filter at 830 nm was used for the glass plate 44, and the collimator lens 40 was position at 10 meters from the glass plate 42. Then, a previously adjusted 1 vol% gasoline vapor was introduced into a chamber 28 through an inlet port 36 to observe changes in intensity of reflected light from the sensor element 8. The magnitude of an output signal from the second photodiode 26 was 300 mV after current-to-voltage conversion when air was introduced. When gasoline was introduced after exhausting the air from the chamber 28, an output signal having a magnitude of 670 mV was generated from the second photodiode 26 after current-to-voltage CA 02239~48 1998-06-04 conversion. Similarly, when lvol% light oil vapor was prepared and similar experiments were made, an output signal having a magnitude of 350 mV was generated from the second photodiode 26 after current-to-voltage conversion. Fig. 5 illustrates changes over time in magnitude of the output signal generated in the experiments. It was revealed from the foregoing that the fuel vapor detector of Fig. 4 could also be used as a fuel leak detector.
Fig. 6 is a diagram schematically illustrating the structure of a third embodiment of the fuel vapor detector according to this invention. The third embodiment differs from the first embodiment of Fig. 3 in that a highly directive light-emitting diode 46 is used as a light source, a beam splitter 22 and a sensor unit 10 are coupled by an optical fiber 48, and connectors 50, 52 having a collimator are connected to both ends of the optical fiber 48. Fig.
7(A) illustrates a structure for coupling the optical fiber 48 to the sensor unit 10, where a connector 52 with a collimator is mounted to cover a window 32 formed through a housing 30 of the sensor unit 10. One end of the optical fiber 48 is connected to this connector 52. For example, the light emitting diode 46 emits light at wavelength of 660 nm, and the optical fiber 8 is a multi-mode optical fiber having a length of 50 meters.
In Figs. 6 and 7(A), a light beam emitted from the light emitting diode 46 is split by the beam splitter 22 into two, one of which is detected by a first photodiode 24 as a reference signal for compensating for fluctuations of CA 02239~48 1998-06-04 the light emitting diode 46, and the other of which is introduced into the connector 50 with a collimator and incident on the optical fiber 48. The light from the optical fiber 48 is collimated by the connector 52 with a collimator, incident normal to a sensor element 8 and reflected there to again pass through the connector 52 with a collimator, and propagates through the optical fiber 48, and is reflected by the beam splitter 22 to be received by a second photodiode 26.
Instead of the structure of Fig. 7(A), an end of the optical fiber 48 may be positioned to be in contact with the chamber 28 without forming a window through the housing 30, as illustrated in Fig. 7(B).
Now, Fig. 8 is used to describe an analog circuit which receives electrical signals from the first and second photodiodes 24, 26 illustrated in Figs. 3, 4 and 6 to output an electrical signal indicative of the existence of a fuel vapor. A reference signal Iref from the first photodiode 24 is converted to a reference signal Vref and amplified by the current-to-voltage converter circuit 24', while a detected signal Idet from the second photodiode 26 is converted to a detecting signal Vdet and amplified by the current-to-voltage converter circuit 26'. Both the signals are input to a compensating circuit 54. The compensating circuit 54 uses the reference signal Vref to compensate for the detected signal Vdet with respect to fluctuations of the light emitting diode 46. The compensating circuit 54 outputs a detected signal Vcom which has been compensated CA 02239~48 1998-06-04 for fluctuations of the light emitting diode 46. This signal Vcom is lead to a differential circuit 56 which generates a value derived by subtracting a signal V_base corresponding to a zero concentration from the signal Vcom, 6 i.e., a voltage Vdif corresponding to a difference from the 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. This voltage Vout is utilized to sense the existence of a fuel vapor.
For example, a hexane vapor atmosphere having a relative concentration of 0.4 was introduced into the sensor unit 10 according to the third embodiment illustrated in Fig.
6, and sensing was attempted with the circuit of Fig. 8. At a room temperature (19~C), a signal at 5.95 V was generated as the detected signal Vdet. On the other hand, when the sensor unit 10 was free of hexane vapor, the detected voltage Vdet was at 5.84 V. Between the two voltages, there is a voltage difference or a span of 0.11 V, from which it is understood that the fuel vapor detector illustrated in Fig. 6 is sufficiently capable of sensing the existence of hexane vapor.
Fig. 9 schematically illustrates the structure of a sensor unit in a fourth embodiment of the fuel vapor detector according to this invention, which is an embodiment suitable for the sensing of diffused vapor. Fig. 9 illustrates the structure of a sensor unit 10' in this CA 02239~48 1998-06-04 embodiment, where the sensor unit 10' is used in place of the sensor unit 10 in Fig. 6. A housing 30 of the sensor unit 10' is provided with fuel vapor intake ports 60, 62 for taking a diffused vapor into a chamber 28, and a sintered metal filter is attached to each of the fuel vapor intake ports 60, 62 to prevent mist from intruding 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 of the housing 30. The optical fiber 48 is, for example, a multi-mode optical fiber having a length of 50 meters. 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 detector using the sensor unit 10' of Fig. 9 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 gasoline 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 at 6.54 V was generated when the diffusion bath was enclosed after the gasoline liquid had been dripped into the diffusion bath as mentioned above. Fig. 10 illustrates changes in magnitude of the detected signal Vdet in this case. When 1 cc of light oil in liquid state was poured CA 02239~48 1998-06-04 into the diffusion bath in a similar manner, the magnitude of the detected signal at 5.90 V was generated. It was revealed from the foregoing results that the fuel vapor detector of the fourth embodiment could also be used as a fuel leak detector.
Fig. 11 schematically illustrates the structure of a sensor unit in a fifth embodiment of the fuel vapor detector according to this invention, which is an embodiment suitable for the sensing of diffused vapor. A sensor unit 10"
illustrated in Fig. 11 may be used in place of the sensor unit 10' in Fig. 9. An end portion of an optical fiber 48 passes through a side wall of a housing 30 of the sensor unit 10", and its leading end opposes a sensor element 8 through a SELFOC lens 66. This results in elimination of the connector 52 with a collimator, so that the sensor unit 10" is reduced in size. Similar to the sensor unit 10' of Fig. 9, the housing 30 is provided with fuel vapor intake ports 60, 62, and a sintered metal filter is fitted in each of the fuel vapor intake ports 60, 62, such that the sensor element 8 is in contact with external air.
Actually, the sensor unit 10" having the sensor element 8 of 3 mm~ x 10 mm 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 1 cc of gasoline had been CA 02239~48 1998-06-04 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 detected signal Vdet of magnitude at 7.78 V was generated when the gasoline liquid existed on the bottom of the diffusion bath. It was revealed from the foregoing results that the fuel vapor detector according to the fifth embodiment illustrated could be used as a fuel leak detector.
Fig. 12 is a diagram schematically illustrating the structure of a light emitting/light receiving unit in a sixth embodiment of the fuel vapor detector according to this 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 Laid-open Japanese Patent Application 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.
In Fig. 12, 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 CA 02239~48 1998-06-04 8 from its 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 in place within 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 the light emitting/light receiving unit illustrated in Fig. 12 is compared with the structure illustrated in Fig. 1, 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 fuel vapor detector of the sixth embodiment is structured 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 other 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 by the sensor element 8. The laser light CA 02239~48 1998-06-04 reflected by the sensor element 8 propagates back along 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 so that it is forced to be 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 at this time.
Actually, a diffusion type sensor unit (for example, the one illustrated in Fig. 9) connected to the light emitting/light receiving unit of the structure illustrated in Fig. 12 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, and the magnitude of a detected signal of the light receiving photodiode was observed for a gasoline vapor, with a detected signal at 2780 mV being generated.
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 revealed from these results that the sixth embodiment can also be used as a fuel leak detector.
One important application of the fuel vapor detectors so far described in detail is a system for remotely monitoring leak of fuel vapor. Fig. 13 illustrates an outline of such a system for remotely monitoring leak of fuel vapor. In Fig. 13, sensor units 10l, 102, 103, 104 of a structure illustrated in any of Figs. 7, 9, 11 and 12 are CA 02239~48 1998-06-04 disposed at sites where a fuel vapor is likely to leak, and these sensor units are connected to an alarm controller 90 through optical fibers 481, 482, 483, 484, respectively. The alarm controller 90 is installed at an appropriate site where a fuel vapor is likely to leak, for example, near a service station, an oil supply station or the like, and are connected to a data processing apparatus 94 installed in a remote monitoring center 92 through arbitrary lines 96 such as telephone lines, dedicated lines, wireless lines, satellite lines or the like. The data processing apparatus 94 is for example an operation processing apparatus such as a personal computer or the like. Relay stations 98 may be installed in the middle of the line 96 as required. It goes without saying that a plurality of the alarm controllers 90 may be connected to the monitoring center 92 such that a plurality of different sites can be collectively monitored at the same time.
Fig. 14 is a block diagram illustrating an exemplary structure of the alarm controller 90 which has three sensor units 101, 102, 103 each connected to one end of an optical fiber 481, 482 or 483. In the figure, the alarm controller 90 comprises three alarm control units 1001, 1002, 1003 connected to the other ends of the optical fibers 481, 482, 483: a microprocessor 102 for generally controlling the operation of the alarm controller 90; a modem 104 connected to the telephone line 96; a memory 106 for storing monitored data; an external input terminal 108 through which external information is input; and an alarm unit 100 for generating CA 02239~48 1998-06-04 alarm.
The three alarm control units 100l, 1002, 1003, 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 sensor unit with the laser light, and receives reflected light from the sensor unit and transduces the received light to an electrical signal. The electrical signal is compared with a gas alarm threshold value and a trouble alarm threshold value, respectively, in the analog determination circuit for determining the presence or absence of a fuel leak and whether a trouble has occurred in the sensor unit, the optical fibers, the light source or the like. A
determination result in the analog determination circuit is either "Normal", "Fuel Leak Has Occurred" or "Trouble in Sensor Unit, Optical Fiber, Light Source or the Like". The microprocessor 102 always displays the determination result on the display unit to enable a field manager to know the situations at monitored sites. The determination result may be printed out as required.
The microprocessor 102 temporarily stores the determination result in the analog determination circuit in the memory 106. If the determination result shows that the sensor units 101, 102, 103 are normally operating, and no fuel leak has occurred, the microprocessor 102 reads data indicative of the determination result from the memory 106 at predetermined time intervals, and sends this data to the CA 02239~48 1998-06-04 monitoring center 92 together with a field identification code through the modem 104. In this event, the microprocessor 102 may also 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) input from the external input terminal 108 to the data processing apparatus 94 in the monitoring center 92, through the modem 104 and the telephone line 106. The contents of data thus communicated to the monitoring center 92 may be set by sending instructions from the data processing apparatus 94 to the microprocessor 102 using an appropriate input means in the field. 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 94 to the microprocessor 102 through the telephone line 96.
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 102 immediately activates the alarm unit 110 to generate alarm for prompting the field manager to take appropriate actions, and notifies the data processing apparatus 94 of the occurrence of the fault through the modem 104 and the telephone line 96. In this way, the data processing apparatus 94 displays a message for notifying the fault, activates an alarm lamp or a buzzer, and so on to prompt the manager to take CA 02239~48 1998-06-04 appropriate actions. It is therefore possible to find the occurrence of a fault at a remote location in early stages.
Fig. 15 is a graph illustrating an example of changes in the output voltage from the analog determination circuit over time together with the gas alarm threshold at 2.5 volts and the trouble alarm threshold at 0.5 volts. When the output voltage of the analog determination circuit exceeds the gas alarm threshold or lowers below the trouble alarm threshold, it is determined that leaked fuel or a fault such as a trouble in any of sensor units, optical fibers, light source and so on has occurred.
INDUSTRIAL USABILITY
As will be apparent from the foregoing detailed description of this invention made with reference to several embodiments thereof, the fuel vapor detector according to this invention is simple in construction and inexpensively manufacturable while highly reliable, and can intrinsically safely detect the existence and/or the concentration of a fuel vapor. Further, since the sensor units may be disposed at sites where a fuel is more likely to leak 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 utilizing the outputs of the light emitting/light receiving units, any fault can be safely detected in early stages.
Furthermore, since data generated by the sensor units can be communicated to a remote location, monitored sites can be always kept monitored, including even during the CA 02239~48 1998-06-04 night when monitored sites are unattended, thus making it possible to rapidly attend to any fault whenever it occurs.

Claims

1. A fuel vapor detector for detecting at least one of the existence and concentration of a fuel vapor.
comprising:
light source unit having a light emitting element;
a sensor unit including a sensor element made of a polymer thin film formed on a reflecting surface of a substrate, said polymer thin film exhibiting a change in at least one of a thickness and a refractive index due to a contact with said fuel vapor;
a light transmitting/outputting unit disposed 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 by said sensor element;
an optical fiber for bi-directionally transmitting light between said light transmitting/outputting unit and said detector unit, said optical fiber having one end attached to said detector unit such that light from said light source unit is incident normal to said sensor element;
and a light detector unit for receiving said reflected light from said sensor element to generate a signal corresponding to said reflected light.

2. (Deleted)

3. A fuel vapor detector according to claim 1, wherein said light source unit, said light transmitting/outputting unit and said light detector unit constitute a light emitting/light receiving unit.

4. A fuel vapor detector according to claim 3, wherein said light emitting/light receiving unit comprises an integrated light emitting/light receiving laser having an additional hologram.

5. A fuel vapor detector according to any of claims 1, 3, 4, wherein said detector unit comprises a housing which is formed with a fuel vapor inlet port, a fuel vapor exhaust port and a chamber for interacting said fuel vapor introduced from said fuel vapor inlet port with said polymer thin film, and said optical fiber is attached to a position opposite to said sensor element in said housing.

6. (Deleted)

7. A fuel vapor detector according to any of claims 1, 3, 4, 5, wherein said light detector unit comprises a photoelectrical transducing means for generating an electrical signal in accordance with said reflected light, and means for comparing said electrical signal with a predetermined value to notify at least one of the existence and the concentration of a fuel as a result of the comparison.

8. (Amended) A fuel leak monitoring system comprising at least one of said fuel vapor detector according to claim 1 connected to an alarm controller installed at a monitored site, said alarm controller being connected to a monitoring center at a remote location through a communication line, wherein;
said alarm controller comprises:

determining means for determining based on an electrical signal output from said detector unit whether or not a faulty state has occurred, said faulty state including a trouble in said detector unit itself and the existence of a fuel vapor at the monitored site where said detector unit is installed;
a memory for storing data indicative of a determination result by said determining means: and communicating means for sending data stored in said memory to said monitoring center through said communication line at a predetermined time without receiving instructions from said monitoring center when said determination result does not indicate the occurrence of a faulty state, and responsive to the result of said determination indicating the occurrence of a faulty state for communicating said faulty state to said monitoring center through said communication line, said fuel leak monitoring system enabling the occurrence of a faulty state at said monitored site to be monitored from said remote location.

9. (Deleted)

10. A fuel vapor detector according to claim 3 or 4, wherein said light emitting/light receiving unit and said detector unit are coupled by an optical fiber.

11. A fuel leak monitoring system according to claim 8, wherein said communicating means of said alarm controller sends an identification code indicative of said monitored site to said monitoring center together with the data stored in said memory.

12. A fuel leak monitoring system according to claim 8 or 11, wherein said determining means has a threshold value for determining whether or not said faulty state has occurred, and setting and change of said threshold value can be instructed from said monitoring center through said communication line.

13. A fuel leak monitoring system according to any of claims 8, 11, 12, wherein said light source unit, said light transmitting/outputting unit and said light detector unit constitute a light emitting/light receiving unit.

14. A fuel leak monitoring system according to claim 13, wherein said light emitting/light receiving unit comprises an integrated light emitting/light receiving laser having an additional hologram.

15. A fuel leak monitoring system according to claim 13 or 14, wherein said light emitting/light receiving unit and said sensor unit are coupled by an optical fiber.