JP2009053045A - Optical fiber hydrogen sensor and hydrogen detection system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical fiber hydrogen sensor, requiring no optical setting, having a high response speed and high sensitivity and being easy to be mass-produced, and to provide a hydrogen detection system that uses the sensor. <P>SOLUTION: A change in the bending loss produced in a partially thinned constricted part 12 by the volumetric expansion due to the hydrogen occulusion of a hydrogen-occuluding film 13 is detected by an optical fiber 11 equipped with the constricted part 12, the hydrogen-occuluding film 13 adhered to a part of the side surface of the constricted part 12 over the longitudinal direction that includes the constricted part 12, and the reflecting means 14 provided to the end surface near the constricted part 12 of the optical fiber 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an optical fiber hydrogen sensor that detects hydrogen using an optical fiber and a hydrogen detection system using the same, and more specifically, an optical fiber hydrogen sensor that detects hydrogen by detecting a bending loss of an optical fiber. And a hydrogen detection system using the same.

  Optical fiber sensors are expected to be used in a wide range of fields because of their excellent explosion-proof and electromagnetic noise resistance characteristics, and easy remote and multi-point monitoring. Optical fiber hydrogen sensors are also expected to be developed because of their advantages. It is rare.

Patent Documents 1, 2, 3, 4, and Non-Patent Document 1 describe sensors that detect hydrogen using an optical fiber or optical means.

Non-Patent Document 1 discloses a line-shaped hydrogen sensor that detects hydrogen by light absorption of an evanescent wave by using a light control glass material such as WO3 colored with hydrogen in the clad of an optical fiber.

Patent Document 1 discloses a hydrogen sensor that optically detects changes in light transmittance and reflectance associated with hydrogenation of a hydrogen-sensitive dimming mirror.

Patent Document 2 discloses a hydrogen sensor that optically detects changes in transmittance and reflectance of a catalytic metal film that adsorbs and dissociates hydrogen gas such as platinum and rhodium.

Patent Document 3 discloses a hydrogen sensor that detects hydrogenation of an Mg—Ni alloy thin film by a change in optical reflectance of the surface.

Patent Document 4 discloses a hydrogen sensor that detects distortion of a glass substrate caused by volume expansion of a hydrogen storage alloy film by an optical method.
JP 2005-265590 A Japanese Patent Laid-Open No. 5-19669 JP 2005-83832 A Japanese Patent No. 3866001 Okazaki et al., “Examination of line-shaped hydrogen sensor using optical fiber”, 23rd Lightwave Sensing Technology Study Group, LST23-22, pp.147-152 (1999)

However, the hydrogen sensor disclosed in Non-Patent Document 1 has problems in that the water resistance of tungsten oxide is poor, so that the sensor life is short, and the change in the reaction characteristics with respect to hydrogen is significant over time.

In sensors that detect changes in the transmittance and reflectance of hydrogen-sensitive materials, such as hydrogen-sensitive dimming mirrors disclosed in Patent Documents 1, 2, and 3, catalyst metals such as platinum and rhodium, and Mg-Ni alloy thins, Precise optical settings are required to detect changes in the transmittance and reflectance of the hydrogen-sensitive film formed on the substrate, and the problem is that the detected light intensity changes due to slight displacement of the optical components. there were.

In order to eliminate the complexity of such optical settings, a method of measuring the reflectance change by directly forming a hydrogen sensitive film on the end face of the optical fiber can be considered, but such a method is said to slow down the response speed. There was a problem. As disclosed in Patent Document 3, the transmittance measurement takes a long time to hydrogenate the entire film, so the response is slow, and the reflectance measurement that can immediately reflect changes in the film surface gives a faster response. It is done. However, when a hydrogen sensitive film is formed directly on the end face of an optical fiber, hydrogenation occurs from the surface of the film exposed to hydrogen, and it takes time to reach the end face of the optical fiber. There arises a problem that the response becomes slow.

In a hydrogen sensor that detects distortion of a glass substrate caused by volume expansion of a hydrogen storage alloy film disclosed in Patent Document 4 by an optical method, a complicated optical device such as an optical lever method is required to measure the distortion of the substrate. Therefore, precise optical setting is necessary, and there is a problem that the apparatus is complicated and expensive.

The present invention has been made in view of the above, and has as its purpose a hydrogen sensor that does not require complicated optical settings, has a high response speed, is highly sensitive, and is easily mass-produced, and a hydrogen detection system using the same. It is to provide.

Therefore, the present invention provides (1) a partially narrowed constricted portion, a hydrogen storage film attached to a part of the side surface in the longitudinal direction including the constricted portion, and a reflecting means on an end face close to the constricted portion. An optical fiber hydrogen sensor comprising: an optical fiber (11) comprising:

  (2) An optical fiber hydrogen sensor characterized in that the hydrogen storage film is Pd, Pd alloy, La—Ni alloy, rare earth metal-Ni alloy, or Mg—Ni alloy.

Further, (3) a thermal expansion counterbalance film made of a material having a thermal expansion coefficient similar to that of the hydrogen storage film and not causing a volume change by hydrogen is arranged symmetrically with the hydrogen storage film, thereby depending on the temperature. An optical fiber hydrogen sensor characterized by reducing the influence of a bending loss change is provided.

(4) The optical fiber hydrogen sensor is characterized in that the hydrogen storage film is made of Pd and the thermal expansion counterbalance film is carbon steel or pure iron.

  (5) an optical fiber hydrogen sensor, a transmission optical fiber that performs optical transmission between the optical fiber hydrogen sensor and the measurement unit, and a light emitting means that generates measurement light to be supplied to the optical fiber hydrogen sensor; Provided is a hydrogen detection system comprising: a light receiving unit that receives measurement light that has undergone a change in light quantity by the optical fiber hydrogen sensor; and an arithmetic processing unit that performs threshold processing or hydrogen concentration conversion on the output of the light receiving unit. .

(6) A temperature sensor, a temperature signal transmission path, and a temperature measurement unit are added to the hydrogen detection system, and the influence of the temperature of the arithmetic processing unit based on the temperature dependence data of the reflected light amount acquired in advance. The present invention provides a hydrogen detection system characterized in that the hydrogen is removed.

  Further, a plurality of light beams having specific wavelengths are demultiplexed to the specific optical fiber hydrogen sensor, and a plurality of the optical fibers for transmission are arranged in the transmission optical fiber via a multiplexing / demultiplexing filter that multiplexes the reflected light from the optical fiber hydrogen sensor. An optical fiber hydrogen sensor, a light emitting means for generating measurement light of a plurality of wavelengths to be supplied to the optical fiber hydrogen sensor, and measurement light consisting of a plurality of wavelengths subjected to a change in the amount of light by the optical fiber hydrogen sensor for each wavelength A wavelength branching filter for branching, a plurality of light receiving means for receiving the branched light of each wavelength, and a processing unit for performing threshold processing or hydrogen concentration conversion on outputs of the plurality of light receiving means. A multi-point hydrogen detection system is provided.

According to the present invention, it is possible to realize a hydrogen sensor that does not require complicated optical settings, has a high response speed, is highly sensitive, and is easily mass-produced. In addition, a hydrogen detection system that can detect hydrogen at a plurality of locations in real time can be realized with a simple configuration at low cost.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1A is a side view of the configuration of the optical fiber hydrogen sensor according to the first embodiment of the present invention, and FIG.

In the figure, reference numeral 1 denotes a hydrogen sensor unit. As shown in the configuration side view (a) and cut-away view (b), a constricted part 12, a hydrogen occlusion film 13 and a reflecting mirror 14 in which a part of the optical fiber 11 is thinned. It has.

The optical fiber 11 is preferably a single mode fiber in order to obtain a response with good linearity, and is preferably adapted to the optical communication wavelength band in terms of transmission distance and cost.

The constricted portion 12 serves to give the optical fiber 11 a bend with a large curvature with a small force and good reproducibility. The narrower the central diameter of the constricted portion 12, the higher the sensitivity. Hereinafter, the central diameter of the constricted portion 12 is referred to as a constricted diameter. However, if the constricted diameter is too thin, the light output tends to be non-linear, so an excessively constricted diameter is not desirable. For example, in the case of a normal single mode fiber having a cladding diameter of 125 μm and an MFD (mode field diameter) of about 10 μm (wavelength: 1.55 μm), the constriction diameter is desirably in the range of 50 to 90 μm. When the constricted diameter is 90 μm or more, light leakage due to bending hardly occurs. When the constricted diameter is 50 μm or less, light leakage is large even when there is no bending, and the light output tends to be nonlinear and unstable.

A hydrogen storage film 13 is formed on a part of the side surface of the fiber including the constricted portion 12 as shown in FIGS. 1 (a) and 1 (b). The width of the hydrogen storage film 13 in the longitudinal direction may be slightly wider than the width of the constricted portion 12. Further, the hydrogen storage film 13 is formed on a part of the side surface of the fiber so as to change the bending of the constricted portion 12 when volume expansion occurs due to storage of hydrogen. In order to cause bending most efficiently, it is preferable to form the hydrogen storage film 13 on the half of the side surface of the fiber. The material of the hydrogen storage film 13 is a material that absorbs hydrogen and causes volume expansion. For example, a rare earth metal alloy such as Pd, Pd alloy, La—Ni alloy, Mg—Ni alloy, or the like can be used. Naturally, a material having a larger volume expansion than hydrogen storage has a higher sensitivity. The hydrogen storage film 13 can be easily formed by a normal film forming apparatus such as a sputtering rig apparatus or an ion assist vapor deposition apparatus, and the film thickness is about 0.1 to 0.5 μm.

Reference numeral 14 denotes a reflection mirror, which should be light in weight so as not to hinder the bending operation of the constricted portion 12, and is preferably formed directly on the end face of the optical fiber 11 by film forming means such as sputtering or vapor deposition. The distance from the center of the constricted portion 12 to the reflecting mirror 14 is desirably shorter for weight reduction, and is usually 10 mm or less.

The operation of the optical fiber hydrogen sensor of this embodiment will be described with reference to FIG. FIG. 2 shows a change in bending of the hydrogen sensor unit 1. When forming the hydrogen storage film 13 on the side surface of the optical fiber 11 having the constricted portion 12, if the film forming temperature is set higher than room temperature, the sensor portion 1 is linearly formed during film formation as shown in FIG. Even so, since the hydrogen storage film has a larger coefficient of thermal expansion than that of the optical fiber (quartz), the hydrogen storage film 13 contracts more at room temperature, and the hydrogen sensor unit 1 bends appropriately as shown in FIG. It will be in the state which generates the leakage light. The intensity of this leakage light can be adjusted by the temperature at the time of film formation, and it is usually desirable to generate leakage light of about 5 to 10 dB from the viewpoint of linear response and dynamic range.

When the hydrogen sensor part 1 having an appropriate bend as shown in FIG. 5B is exposed to a hydrogen-containing gas, the hydrogen storage film 13 absorbs hydrogen and causes volume expansion, so that the bending curvature of the sensor part 1 is reduced. Since the leakage light is reduced and the reflected light intensity is increased, a hydrogen leakage detector can be obtained by detecting the change in the reflected light intensity.

  Although the hydrogen occlusion occurs from the surface of the hydrogen occlusion film 13 and penetrates into the back, the change in curvature of the hydrogen sensor unit 1 starts from the time when hydrogen is occluded on the surface of the hydrogen occlusion film 13, so that the response speed is fast. It becomes a hydrogen leak detector.

Further, since the curvature decreases as the hydrogen concentration increases, if the relationship between the hydrogen concentration and the reflected light intensity is acquired in advance, it can be used for measuring the hydrogen concentration.

  As described above, the components are integrated by configuring the hydrogen sensor unit 1 with the optical fiber 11 having the constricted portion 12, the hydrogen storage film 13 formed directly on the side surface of the optical fiber 11, and the reflecting mirror 14. Therefore, complicated optical component setting is not required, and it is easy to mass-produce because it can be manufactured by a thin film manufacturing process. Because it uses the bending loss of the constricted portion (12) that is extremely sensitive to bending, it is highly sensitive and simple. Since the structure is easy to manufacture, an inexpensive hydrogen sensor can be realized.

FIG. 3 shows a developed form of the first embodiment of the hydrogen sensor shown in FIGS. Reference numeral 15 denotes a thermal expansion counterbalance film, which is made of a material having a thermal expansion coefficient similar to that of the hydrogen storage film 13 and does not cause a volume change due to hydrogen. In FIG. 3, the side half of the optical fiber 11 is drawn as the thermal expansion counterbalance film 15 and the other side half is drawn as the hydrogen storage film 13 over the longitudinal direction including the constricted portion 12, but the two films are arranged symmetrically. They do not have to be arranged in half. The thicknesses of these two films are almost equal.

Specific examples of the material, a hydrogen storage layer 13 if the thermal expansion coefficient was Pd of 11.8 × ^{10 -6} / K, the thermal expansion coefficient of 11.7 × ^{10 -6} / K carbon steel or pure of Iron can be used as the thermal expansion coefficient canceling film 15.

  As described above, the thermal expansion canceling film 15 made of a material having a thermal expansion coefficient similar to that of the hydrogen storage film 13 and causing no volume change by hydrogen is arranged symmetrically with the hydrogen storage film 13, so that Since the bending change of the sensor unit 1 can be reduced, the hydrogen sensor is less susceptible to temperature changes.

  The operation of the hydrogen sensor provided with the thermal expansion counterbalance film 15 will be described.

  When the hydrogen storage film 13 and the thermal expansion canceling film 15 are formed at the same film forming temperature, the hydrogen sensor unit 1 is substantially linear even at room temperature, and the leaked light intensity at the constricted part 12 is substantially minimized.

When the hydrogen sensor unit 1 is exposed to a hydrogen-containing gas, the hydrogen storage film 13 absorbs hydrogen and expands in volume. Therefore, bending occurs in the constricted portion 12, leakage light increases, and reflected light intensity decreases. Therefore, hydrogen can be detected by measuring the reflected light intensity.

  FIG. 4 is a diagram showing a schematic configuration of a hydrogen detection system according to the third embodiment of the present invention.

In the figure, reference numeral 2 denotes a transmission optical fiber for guiding the signal light transmitted to the hydrogen sensor unit 1 and reflected signal light to the measuring unit 3. The main components of the measuring unit 3 are a light emitting element 4, an optical coupler 5, a light receiving element 6, an optical isolator 7, and an arithmetic processing circuit 8. The light emitting element 4 is a light source that can be incident on an optical fiber. In order to transmit a signal farther away, the wavelength band is preferably a communication wavelength band such as a 1.5 μm band or a 1.3 μm band. A semiconductor laser in the wavelength band can be used.

The measurement light emitted from the light emitting element 4 passes through the optical isolator 7 and the optical coupler 5, is sent to the optical transmission fiber 2, and enters the hydrogen sensor unit 1. After a part of light leaks at the constricted part 12, the measurement light is reflected by the reflecting mirror 14, leaks light again at the constricted part 12, reaches the optical coupler 5 through the transmission optical fiber 2, and receives the light receiving element 6. Is received. A part of the light returning to the light emitting element 4 side is blocked by the optical isolator 7. If the correlation between the reflected light intensity and the hydrogen concentration is input in advance to the arithmetic processing circuit 8 and the output of the light receiving element 6 is arithmetically processed, the system operates as a hydrogen concentration detection system.

Moreover, since all the main components of the measuring unit 3 can be purchased at low cost from commercial products used in optical communication, an inexpensive system can be configured.

  FIG. 5 shows a configuration in which the third embodiment of the hydrogen detection system shown in FIG. 4 is developed to improve temperature characteristics. In the figure, 31 is a temperature sensor, 32 is a temperature signal transmission path, and 33 is a temperature measurement unit. For the temperature sensor, in order to make the most of the characteristics of the optical fiber sensor system, for example, an optical fiber type temperature sensor as disclosed in Japanese Patent Application Laid-Open No. 2007-24527 by the present inventors is desirable. It is also possible to use a general sensor such as a body. The signal transmission path 32 differs depending on the type of the temperature sensor 32. For example, the optical fiber temperature sensor is an optical fiber, and the thermocouple is a compensating conductor. Similarly, the temperature measuring unit 33 is adapted to the temperature sensor.

  The temperature dependence of the output of the hydrogen sensor unit 1 measured in advance is input to the arithmetic processing circuit 8, and the temperature data is measured using the temperature sensor 21 to correct the influence of the temperature. It is an accurate hydrogen detection system that is not affected.

FIG. 6 is a diagram showing a schematic configuration of a multipoint hydrogen detection system according to the fifth embodiment of the present invention. Hereinafter, the operation of the system will be described. The light source 21 is a light source that emits a plurality of wavelengths, such as an ASE light source or a tunable laser, and the light emitted from the light source 21 passes through the optical isolator 7 and the two optical couplers 5 to the transmission optical fiber 2. Incident. A part of the light emitted from the optical isolator 7 is branched by the optical coupler 5 and incident on the power monitor light receiving element 24 for monitoring the light intensity change of the light source 21 and used as data for correcting the fluctuation of the light source.

When the measurement light reaches the demultiplexing filters 22-1, is branched into only the temperature sensor unit 11 side light of the wavelength lambda _1, the light of the remaining wavelength proceed the transmission optical fiber 2. The wavelength assigned to each hydrogen sensor unit 1- (1 to n) is branched, such as λ ₂ in the multiplexing / demultiplexing filter 22-2 and λ ₃ in the multiplexing / demultiplexing filter 22-3. The light of each wavelength reflected by each hydrogen sensor unit 1-(1 to n) is again incident on the transmission optical fiber 2 through the multiplexing / demultiplexing filter 22, and reaches the wavelength branching filter 23 through the optical coupler 5. The light is branched into each wavelength by the wavelength branching filter 23 and is incident on the assigned light receiving element 6.

If a threshold value of the light amount level is set in the arithmetic processing circuit 8 and an alarm is issued when the output of each light receiving element 6 reaches the threshold value, it operates as a multipoint hydrogen leak detection system.

If the relational expression between the hydrogen concentration and the reflected light intensity acquired in advance is inputted to the arithmetic processing circuit 8 and the output of each light receiving element 6 is arithmetically processed, each hydrogen sensor unit 1- (1 to n) It operates as a multipoint hydrogen concentration detection system that detects the hydrogen concentration.

By using light λ _{1 to} λ _n of different wavelengths for identification of each hydrogen sensor unit 1-(1 to n) and receiving light in parallel by a plurality of light receiving elements PD _{1 to} PD _n assigned to each wavelength, measurement time Becomes shorter and real-time measurement is possible.

The various components such as the transmission optical fiber 2, the optical coupler 5, the optical isolator 7, the multiplexing / demultiplexing filter 22, the wavelength branching filter 23, and the light receiving element 6 are inexpensive and reliable developed for optical communication. Therefore, it is possible to configure an inexpensive and highly reliable system.

  Although the invention has been described with reference to specific embodiments, various modifications may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. Such changes and modifications are also within the technical scope of the present invention.

It is a figure which shows the structure of the hydrogen sensor which is 1st Example of this invention. It is a side view explaining operation | movement of a sensor part. It is the side view and cutaway view of a sensor part which is 2nd Example of this invention. It is a figure which shows schematic structure of the hydrogen detection system which is 3rd Example of this invention. It is a figure which shows schematic structure of the hydrogen detection system which is 4th Example of this invention. It is a figure which shows schematic structure of the hydrogen detection system which is 5th Example of this invention.

Explanation of symbols

1: Hydrogen sensor unit 2: Transmission optical fiber 3: Measuring unit 4: Light emitting element 5: Optical coupler
6: light receiving element 7: optical isolator 8: arithmetic processing circuit 11: optical fiber 12: constricted part 13: hydrogen storage film 14: reflecting mirror 15: thermal expansion coefficient canceling film 20: multipoint measuring part 21: light source 22: (1 ˜n): multiplexing / demultiplexing filter 23: wavelength branching filter 24: light receiving element 31 for power monitoring: temperature sensor 32: temperature signal transmission path 33: temperature measuring unit

Claims (7)

A partially narrowed constriction (12), a hydrogen storage film (13) attached to a part of the side surface in the longitudinal direction including the constriction (12), and an end face close to the constriction (12) An optical fiber hydrogen sensor comprising an optical fiber (11) provided with a reflecting means (14).   The optical fiber hydrogen sensor according to claim 1, wherein the hydrogen storage film (13) is Pd, Pd alloy, La-Ni alloy, rare earth metal-Ni alloy, Mg-Ni alloy. The thermal expansion canceling film (15) made of a material having a thermal expansion coefficient similar to that of the hydrogen storage film (13) and not causing a volume change due to hydrogen is arranged symmetrically with the hydrogen storage film (13). The optical fiber hydrogen sensor according to claim 1. The optical fiber hydrogen sensor according to claim 3, wherein the material of the hydrogen storage film (13) is Pd, and the material of the thermal expansion counterbalance film (15) is carbon steel or pure iron. The optical fiber hydrogen sensor, a transmission optical fiber (2) for performing optical transmission between the optical fiber hydrogen sensor and the measurement unit (3), and a light emitting means for generating measurement light to be supplied to the optical fiber hydrogen sensor (4), a light receiving means (6) for receiving measurement light having undergone a change in light quantity by the optical fiber hydrogen sensor, and an arithmetic processing means (8) for converting the output of the light receiving means (6) into a hydrogen concentration. A hydrogen detection system characterized by comprising.   In addition to the optical fiber hydrogen sensor, a temperature sensor (31), a temperature signal transmission path (32), and a temperature measurement unit (33) are provided, and the calculation processing is performed based on the reflected light amount change data with respect to the temperature acquired in advance. 6. The hydrogen detection system according to claim 5, wherein temperature correction is performed by means (8).   The light of a specific wavelength is demultiplexed to a specific optical fiber hydrogen sensor, and is reflected to the transmission optical fiber (2) via a multiplexing / demultiplexing filter (22) that multiplexes the reflected light from the optical fiber hydrogen sensor. A plurality of the optical fiber hydrogen sensors arranged, a light emitting means (21) for generating measurement light of a plurality of wavelengths to be supplied to the optical fiber hydrogen sensor, and a plurality of light quantity changes received by the optical fiber hydrogen sensor A wavelength branching filter (23) for branching measurement light having wavelengths to each wavelength, a plurality of light receiving means (6) for receiving the branched light of each wavelength, and outputs of the plurality of light receiving means (6) A multipoint hydrogen detection system comprising the arithmetic processing means (8) for threshold processing or hydrogen concentration conversion.

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