WO1999042816A1

WO1999042816A1 - Organic material detector having function of calibrating indication and organic material monitor system using the same

Info

Publication number: WO1999042816A1
Application number: PCT/EP1999/000960
Authority: WO
Inventors: Yusuke Takano; James Stamatoff; Hironobu Yamamoto; Akihiro Tagaya
Original assignee: Axiva Gmbh
Priority date: 1998-02-20
Filing date: 1999-02-13
Publication date: 1999-08-26
Also published as: JP3086674B2; JPH11237336A

Abstract

An organic material detector (20) capable of adjusting a zero-point and calibrating an indication for an instrument in a monitor center is provided. The organic material detector comprises a sensing element (30) which exhibits a change an attribute when in contact with an organic material; a filter (38), an inlet tube (50) and a chamber (56) for bringing a medium into contact with the sensing element; an inlet tube (50) for bringing at least one of the medium not including the organic material and a medium including the organic material in a known concentration into contact with the sensing element; and a receptable (26) for outputting light for irradiating the sensing element therewith and for receiving light reflected off the sensing element. The organic material detector is connected to a monitor center which has a supply section for supplying either the medium not including the organic material and the medium including the organic material in a known concentration for a predetermined period.

Description

1

ORGANIC MATERIAL DETECTOR HAVING FUNCTION OF CALIBRATING INDICATION AND ORGANIC MATERIAL MONITOR SYSTEM USING THE SAME

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to a detector for detecting an organic material existing in a medium such as air, water or the like and a monitor system using the same, and more particularly to an organic material detector having functions of adjusting a zero point and calibrating an indication for an instrument in a monitor center, and a monitor system using the same.

Description of the Related Art

The applicant of the present application has been proposed a variety of detectors for detecting the type and/or concentration of an organic material dissolved in a vapor mixed in air or in water. Fig. 1 generally illustrates an example of such detectors. In Fig. 1 , the detector comprises a light source 2; a light detector 4; and a sensing element 8 made of a polymer thin film coated on a flat reflective holder 6, all of which are integrally held in a housing 10. Used as a sensing element 8 is a polymer material which has the properties of reacting with a particular organic material, or absorbing or adsorbing the organic material, if in contact therewith, to change at least one of the thickness and the refractive index.

A light beam emitted from a light emitting element such as a laser diode disposed in the light source 2 is incident on the sensing element 8, reflected off the sensing element 8, and detected by a light detecting element in the light detector 4. In this event, the light reflected off the surface of the sensing element 8 and light reflected off the surface of the holder 6 for supporting the sensing element 8 have a phase relationship to interfere with each other. Therefore, as the thickness and/or the refractive index of the sensing element 8 changes, this results in a change in the reflectivity of the sensing element 8 or the intensity of the reflected light. It is 2

therefore possible to detect the existence and/or concentration of a fuel vapor as a function of the intensity of the reflected light from the sensing element 8. The housing 10 is formed with an inlet port 12 for introducing air mixed with an organic material or water in which an organic material is dissolved; an outlet port 14 for discharging the air or the water; and a passage 16 for communicating the inlet port 12 with the outlet port 14 to bring the organic material into contact with the sensing element 8. When air mixed with a particular organic material or water having an organic material dissolved therein is introduced through the inlet port 12 into the housing 10, the organic material contacts with the sensing element 8 to cause a change in the thickness and the refractive index of the sensing element 8, thereby making it possible to determine that the particular organic material is mixed in the air or dissolved in the water as an output of the light detector 4.

Generally, a minimum detectable limit (MDL) of an organic material detector under a certain environment may be calculated by setting one to the ratio of a fluctuating width of a zero level to a signal strength of the organic material detector under that environment. However, when the signal strength exhibits temperature-humidity characteristics, MDL also exhibits the same temperature-humidity characteristics. Factors associated with fluctuations of the zero level of the organic material detector include the temperature-humidity characteristics of an employed sensing element, the temperature-humidity characteristics of the detector itself, electrical noise inherent to the detector, external noise (including electrical noise and oscillations), and so on.

It is possible to correct the temperature-humidity characteristics of a sensing element or an organic material detector itself using the temperature-humidity characteristics of the detector which have been measured after installation in order to improve MDL. However, measurements of the temperature-humidity characteristics for individual organic material detector would require a long time and cause a significant increase in manufacturing cost. Also, strictly speaking, the organic material detector may imply hysteresis characteristics which could not be completely corrected at any expense, and as an additional problem, such measurements would require that a probe for measuring the temperature-humidity characteristics be operated in a hazard area in which the organic material detector is installed. Furthermore, the conventional organic material detector as illustrated in Fig. 1 only processes optical signals and excludes electrical components in consideration of safety. However, it is substantially impossible to measure the temperature-humidity characteristics of the organic material detector as illustrated only through optical signals without adding any electrical component to the organic material detector.

In addition, the conventional organic material detector is defective in that when installed for a long term at a site including an organic material (for example, a place contaminated with an organic material), a sensing element contained therein suffers from inherent changes in characteristics to cause a drift in the output of the organic material detector.

OBJECTS AND SUMMARY OF THE INVENTION

This invention has been made in view of the problems mentioned above, and it is an object of this invention to provide an organic material detector which has a novel configuration that provides for zero point adjusting and index calibrating functions performed for an instrument in a monitor center, and is intrinsically safe, simple in structure, easy to manufacture, highly reliable, inexpensive, and capable of a reduction in size.

It is another object of this invention to provide a monitor system which is capable of adjusting a zero-point and calibrating an indication in a measurement section using the organic material detector.

To achieve the above objects, this invention provides an organic material detector comprising: a sensing element which exhibits a change in attribute when in contact with an organic material; first means for bringing a medium into contact with the sensing element; second means for bringing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into contact with the sensing element; and 4

optical means for outputting light for irradiating the sensing element therewith and for receiving light reflected off the sensing element.

The organic material detector may be installed in 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.

Preferably, the optical means includes an optical fiber for transmitting light for irradiating the sensing element therewith and reflected light from the sensing element, and a receptacle coupled to one end of the optical fiber and including a lens for converging the light from the optical fiber on the sensing element and for transmitting the light reflected from the sensing element to the optical fiber.

Depending on how the organic material detector is used, the first means preferably includes in some cases a holder for carrying the sensing element thereon to position the sensing element opposite to the receptacle, a vent hole formed through the holder, and a filter interposed between the holder and the medium for blocking the medium but passing an organic material contained in the medium therethrough, and in other cases a holder for carrying the sensing element thereon to position the sensing element opposite to the receptacle, and for transmitting the medium.

In one embodiment of this invention, the second means includes an inlet tube in communication with a space defined between the receptacle and the holder for introducing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into the space, and an outlet tube for evacuating the space.

Also, to achieve the above objects, this invention provides a monitor system having an organic material detector and a monitor center connected to the organic material detector, wherein: the organic material detector comprises: a sensing element which exhibits a change in attribute when in contact with an organic material; first means for bringing a medium into contact with the sensing element; 5

second means for bringing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into contact with the sensing element; and optical means for outputting light for irradiating the sensing element therewith and for receiving light reflected off the sensing element, the monitor center comprises: a supply section for supplying the second means with at least one of the medium not including the organic material and the medium including the organic material in a known concentration for a predetermined period; and a measurement section for supplying the optical means with light, and for processing reflected light transmitted through the optical means to output a signal indicative of either the existence or the concentration of the organic material, and the monitor system adjusts a zero-point for the measurement section when the supply section supplies the second means with the medium not including the organic material, and calibrates an indication for the measurement section when the supply section supplies the second means with the medium including the organic material in a known concentration.

Preferably, in the monitor system: the optical means includes an optical fiber for transmitting light for irradiating the sensing element therewith and reflected light from the sensing element, and a receptacle coupled to one end of the optical fiber and including a lens for converging the light from the optical fiber on the sensing element and for transmitting the light reflected from the sensing element to the optical fiber, and the measurement section includes a laser diode coupled to the other end of the optical fiber to emit laser light to the optical fiber, and a detector/transducer for detecting the laser light reflected from the sensing element to output an electrical signal corresponding to the intensity of the laser light.

Preferably, the supply section may include in some cases a first bottle for storing a dry inorganic gas, a second bottle for storing air including an organic material in a 6

known concentration, and valve means for coupling either the first bottle or the second bottle to the organic material detector, and in other cases a first bottle for storing water free of a dissolved organic materia, a second bottle for storing water having dissolved therein an organic material in a known concentration, and valve means for coupling either the first bottle or the second bottle to the organic material detector.

An attribute of the sensing element, for example, the thickness or the refractive index changes when the sensing element is in contact with an organic material. The existence or the concentration of the organic material is detected utilizing this phenomenon. Specifically, as a result of an interaction with the organic material, the sensing element experiences a physical change, for example, swelling or the like. Further, the swelling causes a change in the thickness and the refractive index of the sensing element which may serve as optical parameters. Since such a change results in a change in the optical properties of the sensing element, an organic material can be detected by measuring a reflection characteristic of the sensing element.

By properly selecting a polymer material constituting the sensing element, it is possible to selectively or non-selectively detect the existence of an organic material, for example, fuel such as gasoline, light oil, kerosine, jet combustible, heavy oil or the like. Moreover, since the sensing element has the reflection characteristics corresponding to the concentration of an organic material, the organic material detector according to this invention can serve as a concentration meter for an organic material.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram illustrating the structure of a conventional organic material detector;

Fig. 2 is a partially cross-sectional schematic diagram illustrating the structure of a first embodiment of an organic material detector according to this invention; Fig. 3 is a diagram generally illustrating the configuration of a first embodiment of a monitor center according to this invention, connected to the organic material detector of Fig. 2;

Figs. 4A and 4B show the operation timing for a switching valve in Fig. 3; Fig. 4C is a graph showing a period in which a zero-point adjustment and an indication calibration are performed for an instrument;

Fig. 5 is a block diagram generally illustrating the configuration of an apparatus which can be used instead of a first bottle illustrated in Fig. 3;

Fig. 6 is a partially cross-sectional schematic diagram illustrating the structure of a second embodiment of the organic material detector according to this invention; and

Fig. 7 is a diagram generally illustrating the configuration of a second embodiment of the monitor center according to this invention, connected to the organic material detector of Fig. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several embodiments of this invention will hereinafter be described with reference to the accompanying drawings. Fig. 2 illustrates the structure of a first embodiment of an organic material detector according to this invention, which is adapted to detect an organic material mixed in air.

In the organic material detector 20 of Fig. 2, an optical fiber 22 has one end connected to a measurement/control section 62 (Fig. 3) in a monitor center 60, and the other end fixed to a receptacle 26 with a collimator lens through an FC connector 24. A sensing element 30 secured to a sensing element holder 28 with an adhesive or the like is disposed opposite to the collimator lens in the receptacle 26. Light emitted from the measurement/control section 60 and transmitted through the optical fiber 22 is irradiated to the sensing element 30 through the collimator lens in the receptacle 26, reflected off the sensing element 30, and passes through the optical fiber 22 in the opposite direction back to the measurement/control section 62.

The receptacle 26 is fixed to one end of a cylindrical body 32, and the sensing element holder 28 is fixed inside the body 32. An O-ring 34 is provided along an o

opening at the other end of the body 32 for preventing water or the like from intruding into the housing 32 from the outside. The O-ring 34 is fixed to an O-ring holder 36.

A lid 40 having a filter 38 therein is fitted on the outer periphery near the other end of the body 32. The lid 40 is formed with an opening 42 extending therethrough, so that the filter 38 is in contact with external air through the opening 42. The filter 38 has the properties of blocking water but passing therethrough an organic material dissolved in water. Another O-ring 44 in contact with an O-ring holder 34 is also provided at one end of the lid 40, such that the filter 38 is sandwiched between the O-ring 44 and a gasket and a supporting screen (both not shown) and fixed to the lid

40. The sensing element holder 28 is formed with at least one vent hole 48 through which the sensing element 30 is in contact with external air passing through the filter 38.

The outer peripheries of the FC connector 24, the receptacle 26 and the body 32 are surrounded by a cylinder 46 made of stainless steel or the like to prevent water or the like from intruding.

The organic material detector 20 is further provided with an inlet tube 50 having one end selectively connected to one of bottles installed in the monitor center 60, and an outlet tube 52 having one end connected to an exhaust air processing unit. The two tubes 50, 52 extend through the cylinder 46 of the detector 20. The other end of the inlet tube 50 is air-tight coupled to one end of a lead-in path 54 formed through the body 32. The other end of the lead-in path 54 is open to a chamber 56 which is a space defined between the sensing element 30 and the receptacle 26. Similarly, the other end of the outlet tube 52 is air-tight coupled to one end of a discharge path 58 formed through the body 32, and the other end of the discharge path 58 is also open to the chamber 56. Alternatively, the inlet tube 50 and the outlet tube 52 may extend through the body 32 such that the other ends of the inlet tube 50 and the outlet tube 52 communicate with the chamber 56.

This invention utilizes the property of the sensing element 30 which changes its attributes, for example, the thickness and the refractive index when it is in contact with an organic material, and employs, for example, an IER (interference enhanced reflection) method for detecting the attributes of the sensing element 30. The IRE method utilizes the optically interfering characteristic of a thin film structure. Specifically, light reflected on the surface of the sensing element 30 has a phase relationship with light reflected off the interface between the sensing element of a reflective surface of the holder, and they interfere with each other. Thus, the reflectivity of the sensing element 30 largely depends on the thickness and/or the refractive index thereof. In other words, as the thickness and/or the refractive index of the sensing element 30 vary, the reflectivity of the sensing element 30 or the intensity of the reflected light therefrom changes. Consequently, the existence and/or the concentration of an organic material can be detected by the IER method as a function of the intensity of the reflected light.

While the IER method is sensitive to a change in thickness as mentioned above, this invention may attach more importance to the influence of the thickness of the sensing element 30 than the reflectivity of the same, provided that a material having a refractive index not substantially different from the reflective index of an organic material is used as the sensing element 30 employed in this invention. This is a unique advantage of this invention over the prior art.

It is known that the reflectivity of the sensing element 30 suitable for the IER method sinusoidally varies as the concentration of an organic material increases. Therefore, the sensing element 30 is preferably adjusted depending on a particular concentration range of the organic material in the following manner. First, when the concentration of the organic material is low, the reflectivity changes little, so that the sensing element 30 would not provide a sufficient change in reflectivity if it is adjusted to have a thickness corresponding to a minimum value or a maximum value of the 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 sensing element 30, and θ is a light propagation angle within the sensing element 30. When the concentration of the organic material is relatively high, on the other hand, the reflectivity largely changes, so that the sensing element 30 is preferably adjusted to a thickness corresponding to the minimum value or the maximum value of the reflectivity in order to take a large signal span. While the sensing element 30 may have a thickness in a range of 10 nm to 10 μm, a thickness not more than 1 μm is preferable for providing for a high speed response.

Materials for the sensing element 30 preferably include a homopolymer or a copolymer having a recurring unit represented by the following chemical formula (I):

CH,

( I )

X-C-R¹

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)-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-;

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 derivatives 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;

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 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 derivatives thereof. A polymer used as the sensing element 30 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 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 sensing element 30 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 suitable for use in the sensing element 30 are listed as follows: poly(dodecyl methacrylate); poly(isodecyl methacrylate); poly(2-ethylhexyl methacrylate); poly(2-ethylhexyl methacrylate-co-methyl methacrylate); poly (2-ethy Ihexyl 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(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(cyclohexyi methacrylate-co-butyl methacrylate); poly(cyclohexyl methacrylate-co-dodecyl methacrylate); poly(butyl methacrylate-co-ethyi 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-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-ethy Ibuty I 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-methy l-4-hyd roexystyrene-co-4-hyd roxystyrene) ; 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, 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 sensing element 30 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 organic material detector illustrated in Fig. 2, the surface of the sensing element holder 28 for supporting the sensing element 30 is preferably flat enough to reflect light. Alternatively, the sensing element holder 28 itself may have a high reflectivity. An example of the sensing element holder 28 may be a silicon wafer. The sensing element 30 may be formed on the surface of the sensing element holder 28 by a spin coat method or any other coating method used in common. For actually fabricating the sensing element 30, 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 was then dried at 60 °C in a reduced pressure environment for one hour. Afterward, 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, 14

was approximately 330 nm. This silicon wafer substrate was diced into 10mm x 10mm squares to produce the sensing elements 30.

The filter 38 in Fig. 2 preferably has the properties of transmitting only an organic material and blocking water when used in the air, and selectively trapping an organic material dissolved or separately existing in water, i.e., trapping only an organic material, excluding water, as a vapor while blocking water when used in water. For example, the filter 38 may be formed 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 poiyamide, polythiol, aminoalkyd resin, acrylic resin, poly cellulose, natural rubber, polyester, unsaturated polyester, epoxy resin, silicone resin, and derivatives thereof, and a laminate of these polymers, or a membrane made of ceramic, 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. Next, Fig. 3 illustrates an embodiment of a monitor center 60 according to this invention which is combined with the organic substance detector of Fig. 2 to constitute a monitor system. In Fig. 3, one end of an optical fiber 22 is connected to a measurement/control section 62; one end of an inlet tube 50 is connected to a switching valve 54; and one end of an outlet tube 52 is connected to an exhaust air processing section 66. A gas processed by the exhaust air processing section 66 is discharged to the atmosphere through a tube 68. Air filters 70, 72 may be interposed at appropriate positions in the inlet tube 50 and the outlet tube 52 if necessary. Also, the optical fiber 22, the inlet tube 50 and the outlet tube 52 are preferably armored by a pipe (indicated by broken lines), for example, made of Teflon or stainless steel for protection.

The measurement/control section 62 comprises a light source connected to one end of the optical fiber 22; a light detecting circuit for receiving reflected light reflected off the sensing element 30 and transmitted thereto through the optical fiber 22 to produce an electrical signal proportional to the intensity of the reflected light; an instrument for displaying the magnitude of the electrical signal; and a control circuit for controlling the switching valve 64 to operate at the timing shown in Figs. 4A - 4C. A laser diode or a light emitting diode is suitable for the light source.

The switching valve 64 is connected to a first bottle 74 which stores a compressed first gas, and a second bottle 76 which stores a compressed second gas different from the first gas. The switching valve 64 is switched to connect the inlet tube 50 to the first bottle 74 or to the second bottle 76 in response to a control signal 78 from the measurement/control section 62.

The first gas is used to perform a zero-point adjustment for the instrument in the measurement/control section 62, and is preferably such a gas as dry air, dry nitrogen and dry argon which do not include any organic material, and dry air is most preferable. During a period in which the inlet tube 50 is connected to the first bottle

74 through the switching valve 64, dry air, for example, is supplied from the first bottle 74 to the detector 20 through the inlet tube 50, and exhausted from the outlet tube 52, so that the instrument in the measurement/control section 62 can be 16

adjusted to indicate a zero point using the intensity of reflected light from the sensing element 30 during this period.

The second gas is used to calibrate indication of the instrument in the measurement/control section 62, and dry organic gas such as dry isobutane, dry propane or the like having a known concentration may be used. For example, when the detector 20 is installed in a service station to detect leaked petroleum, dry isobutane in concentration of 50 - 8,000 ppm, which is smaller than an explosion lower limit value of 8,500 ppm, preferably in concentration of 100 ppm, may be used as the second gas. When dry isobutane in concentration of 100 ppm is delivered into the chamber 56 through the inlet tube 50, the instrument in the measurement/control section 62 can be calibrated to indicate the existence of isobutane in concentration of 100 ppm, utilizing the intensity of reflected light from the sensing element 30 which has absorbed or adsorbed the isobutane.

Figs. 4A - 4C show the relationship between the timing at which the switching valve 64 connects the inlet tube 50 to the first bottle 74 or to the second bottle 76 and a calibration period for the measurement/control section 62 to calibrate the instrument. Specifically, Fig. 4A shows that the inlet tube 50 is connected to the first bottle 74 from time t1 to time t2, while Fig. 4B shows that the inlet tube 50 is connected to the second bottle 76 from time t2 to time t3. The measurement/control section 62 sends a control signal 78 to the switching valve 64 to control the switching valve 64 such that it periodically connects the inlet tube 50 alternately to the first bottle 74 and to the second bottle 76 one to ten times a day, and preferably eight times a day. While Figs. 4A - 4C show that the inlet tube 50 is connected to the first bottle 74 or to the second bottle 76 each time the control signal 78 is sent to the switching valve 64, the operations from time t1 to time t3 may be repeated several times each time the control signal 78 is sent.

The period in which the inlet tube 50 is connected to the first bottle 74 or to the second bottle 76 (in Figs. 4A - 4C, periods t1 - 12, t2 - 13, t3 - 14) may be set in accordance with the distance between the detector 20 and the monitor center 60, and generally ranges from 30 seconds to 60 minutes. An apparatus illustrated in Fig. 5 may be used instead of the first bottle 74. Specifically, in Fig. 5, air delivered from an air compressor 80 such as a reciprocal air compressor, a screw air compressor or the like is dried by an air drier (for example, a freeze air drier) 82, and temporarily stored in an air tank 84. Dry air from the air tank 84 passes through a first mist separator 86 and a second mist separator

88 to remove fine mist therefrom, and supplied to the switching valve 64 through an oil odor filter 90. If a compressed air source can be utilized, compressed air may be supplied to the switching valve 64 through the mist separators and the oil odor filter.

Next, the organic material detector and the monitor system using the same according to a second embodiment of this invention will be described with reference to Figs. 6 and 7. The organic material detector according to the second embodiment is intended to detect an organic material mixed in water. Components identical or similar to those in the first embodiment illustrated in Figs. 2 and 3 are designated the same reference numerals, and description thereon is omitted.

Fig. 6 illustrates the structure of the second embodiment of the organic material detector according to this invention. In the organic material detector 20' illustrated in Fig. 6, a receptacle 26 with a collimator lens is fixed on one side of a cylindrical body 32, and a sensing element 30 is disposed on the other side of the body 32 such that the sensing element 30 faces the collimator lens. The sensing element 30 may be secured to a sensing element holder 92 with an adhesive or the like. The sensing element holder 92 may be made of a water percolating material such as a sintered metal or the like, and is mounted to the body 32 in an air tight structure. A space defined between the sensing element 30 and the receptacle 26, i.e., a chamber 56 communicates with a inlet tube 50 and an outlet tube 52.

Fig. 7 illustrates the second embodiment of the monitor center according to this invention which is connected to the organic material detector 20' of Fig. 6. The monitor center 60' of Fig. 7 comprises a first tank 94 which stores a first fluid and a second tank 96 which stores a second fluid different from the first fluid. A switching valve 64 connected to one end of the inlet tube 50 is connected to the first tank 94 through a filter 98 and a pump 100, and to the second tank 96 through another filter 102 and another pump 104. As is the case of the first embodiment, the switching l o

valve 64 is switched by a control signal 78 from a measurement/control section 62 to connect the inlet tube 50 to the first tank 94 or to the second tank 96. One end of the outlet tube 52 is connected to a wasted liquid processing section 106, and water processed by the wasted liquid processing section 106 is discharged through a tube 108.

The first fluid is used to perform a zero-point adjustment for an instrument in the measurement/control section 62, and may be city water, well water, pure water or the like, and pure water is particularly preferred. The second fluid is used to calibrate indication of the instrument in the measurement/control section 62, and includes an organic material in a known concentration. Preferably, the second fluid may be water including an organic material in concentration of 1 - 200 ppm, for example, water including toluene in concentration of 10 ppm, or water including xylene in concentration of 10 ppm. For example, when water including 10 ppm toluene is supplied into the chamber 56 through the inlet tube 50, the instrument in the measurement/control section 62 can be calibrated to indicate the existence of the 10 ppm toluene utilizing the intensity of reflected light from the sensing element 30 which has absorbed or adsorbed the toluene.

Likewise in the monitor center 60' of Fig. 7, the measurement/control section 62 operates the switching valve 64 at the same timing as illustrated in Figs. 4A - 4C to connect the inlet tube 50 alternately to the first tank 94 or to the second tank 96.

The foregoing first and second embodiments are adapted to adjust a zero point and calibrate an indication for the instrument in the measurement/control section 62.

When either one of the zero-point adjustment and the indication calibration is sufficient, the switching valve 64 may be simply replaced with a valve which is controlled by the measurement/control section 62 to connect the inlet tube 50 at a predetermined timing to the first bottle 74 or the first tank 94 for adjusting the zero point, and to the second bottle 76 or the second tank 96 for adjusting the indication.

As will be apparent from the foregoing detailed description on the embodiments of this invention with reference to the accompanying drawings, this invention can adjust a zero point and calibrate an indication for an instrument without being affected by a variety of factors such as fluctuations in temperature at a site where the detector is installed, a shifting refractive index of a sensing element due to aging changes, and so on, thereby making it possible to highly accurately sense the existence and concentration of an organic material.

Claims

Patentclaims:

1. An organic material detector comprising: a sensing element which exhibits a change in attribute when in contact with an organic material; first means for bringing a medium into contact with said sensing element; second means for bringing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into contact with said sensing element; and optical means for outputting light for irradiating said sensing element therewith and for receiving light reflected off said sensing element.

2. An organic material detector according to claim 1 , wherein said optical means includes: an optical fiber for transmitting light for irradiating said sensing element therewith and reflected light from said sensing element; and a receptacle coupled to one end of said optical fiber and including a lens for converging the light from said optical fiber on said sensing element and for transmitting the light reflected from said sensing element to said optical fiber.

3. An organic material detector according to claim 1 or 2 wherein said first means includes: a holder for carrying said sensing element thereon to position said sensing element opposite to said receptacle; a vent hole formed through said holder; and a filter interposed between said holder and said medium for blocking said medium but passing an organic material contained in said medium therethrough.

4. An organic material detector according to claim 1 or 2, wherein said first means includes a holder for carrying said sensing element thereon to position said sensing element opposite to said receptacle, and for transmitting said medium.

5. An organic material detector according to any of claims 1 - 4, wherein said second means includes: an inlet tube in communication with a space defined between said receptacle and said holder for introducing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into said space; and an outlet tube for evacuating said space.

6. A monitor system having an organic material detector and a monitor center connected to said organic material detector, wherein: said organic material detector comprises: a sensing element which exhibits a change in attribute when in contact with an organic material; first means for bringing a medium into contact with said sensing element; second means for bringing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into contact with said sensing element; and optical means for outputting light for irradiating said sensing element therewith and for receiving light reflected off said sensing element, said monitor center comprises: a supply section for supplying said second means with at least one of the medium not including the organic material and the medium including the organic material in a known concentration for a predetermined period; and a measurement section for supplying said optical means with light, and for processing reflected light transmitted through said optical means to output a signal indicative of either the existence or the concentration of the organic material, and said monitor system adjusts a zero-point for said measurement section when said supply section supplies said second means with the medium not including the organic material, and calibrates an indication for said measurement section when said supply section supplies said second means with the medium including the organic material in a known concentration.

7. A monitor system according to claim 6, wherein: said optical means includes: an optical fiber for transmitting light for irradiating said sensing element therewith and reflected light from said sensing element; and a receptacle coupled to one end of said optical fiber and including a lens for converging the light from said optical fiber on said sensing element and for transmitting the light reflected from said sensing element to said optical fiber, and said measurement section includes: a laser diode coupled to the other end of said optical fiber to emit laser light to said optical fiber; and a detector/transducer for detecting the laser light reflected from said sensing element to output an electrical signal corresponding to the intensity of said laser light.

8. A monitor system according to claim 6 or 7, wherein: said second means includes: an inlet tube in communication with a space defined between said receptacle and said holder for introducing at least one of a medium not including the organic material and a medium including the organic material in a known concentration into said space; and an outlet tube for evacuating said space, and respective ends of said inlet tube and said outlet tube are connected to said supply section.

9. A monitor system according to any of claims 6 - 8, wherein said first means includes: a holder for carrying said sensing element thereon to position said sensing element opposite to said receptacle; a vent hole formed through said holder; and a filter interposed between said holder and said medium for blocking said medium but passing an organic material contained in said medium therethrough.

10. A monitor system according to any of claims 6 - 8, wherein said first means includes a holder for carrying said sensing element thereon to position said sensing element opposite to said receptacle, and for transmitting said medium.

11. A monitor system according to any of claims 6 - 10, wherein: said organic material detector is disposed in communication with external air, and said supply section includes: a first bottle for storing a dry inorganic gas; a second bottle for storing air including an organic material in a known concentration; and valve means for coupling either said first bottle or said second bottle to said organic material detector.

12. A monitor system according to any of claim 6 - 10, wherein: said organic material detector is disposed in water, and said supply section includes: a first bottle for storing water free of a dissolved organic material; a second bottle for storing water having dissolved therein an organic material in a known concentration; and valve means for coupling either said first bottle or said second bottle to said organic material detector.