JPH0339579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for detecting hydrogen gas or hydrogen-containing compound gas by optically detecting a change in the light absorption rate of a solid compound reduced by hydrogen atoms adsorbed and dissociated in a catalyst metal. related to gas sensors.

Conventionally, this type of gas sensor has been mainly catalytic combustion type or semiconductor type, but both are used after being heated with a heater etc.
There were problems in terms of safety, and since the sensing element was heated, it deteriorated quickly, and its characteristics were unstable, making it insufficiently reliable.

Therefore, the inventors of the present application developed a catalyst metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas, and a solid compound, such as tungsten trioxide, whose light absorption rate changes when reduced by the hydrogen atoms generated in the metal.
We developed a sensing element with a laminated structure with WO ₃ and proposed a gas sensor that can detect gas concentration by optically detecting changes in the light absorption rate of solid compounds (Japanese Patent Application No. 147749/1983). ).

By the way, after repeating various experiments, we found that the light absorption characteristics of an element with a layered structure of catalyst metal and solid compound are affected by changes in the element over time and by miscellaneous gases other than the gas to be detected, such as water vapor and alcohol. There was a risk that detection performance would deteriorate.

The present invention was made in view of these problems, and provides a highly stable and reliable gas sensor that can detect hydrogen gas or hydrogen-containing compound gas without being affected by changes over time or miscellaneous gases. The purpose is to provide.

To achieve this object, the present invention provides an element having a laminated structure of a metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas and a solid compound whose light absorption rate changes due to reduction by hydrogen atoms generated in the metal. The first detection unit detects light with a wavelength that causes a large change in optical absorption due to the reduction of the solid compound, and the second detection unit detects light with a wavelength that causes no or small change in optical absorption due to the reduction of the solid compound. The detection unit monitors the gas, and the presence or absence of hydrogen or hydrogen-containing compound gas is determined based on the detection signal of the first detection unit and the detection signal of the second detection unit.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

First, to explain the configuration, 1 is hydrogen gas or hydrogen-containing compound gas, such as ammonia gas NH ₃ ,
This is an element that causes a change in light absorption at a specific wavelength λs when hydrogen sulfide gas H ₂ S, silane gas SiH ₄ , etc. come into contact with each other. It has a layered structure with a solid compound 3 that is reduced by hydrogen atoms to cause a change in light absorption at a specific wavelength λs.

Here, palladium Pd is used as the catalyst metal 2 of the element 1, and 3 is used as the solid compound 3.
Tungsten oxide WO ₃ is used.

The device 1, which has a laminated structure of the catalyst metal 2 and the solid compound 3, is manufactured by placing the WO
It can be produced by vapor-depositing a solid compound 3 consisting of Pd to a predetermined thickness, and then vapor-depositing a catalyst metal 2 consisting of Pd on the solid compound 3 thinly enough to maintain transparency.

The element 1 used in the present invention shown in FIG.
It has a light absorption effect in the following way when it comes into contact with hydrogen gas or hydrogen-containing compound gas.

That is, for example, when hydrogen gas comes into contact, hydrogen is adsorbed and dissociated by the catalyst metal 2 to generate hydrogen atoms in the catalyst metal 2, and these hydrogen atoms are injected into the solid compound 3. The solid compound 3 into which protons H ⁺ have been injected by the catalyst metal 2 is reduced and its color center density changes, causing a change in light absorption at a specific light wavelength λs. Solid compound 3 as in the example above
When WO ₃ is used, solid compound 3 increases its light absorption upon contact with hydrogen gas, producing the changes shown in the second graph. In Figure 2, the solid line shows the transmittance for the wavelength when there is no contact with hydrogen gas, and the broken line shows the transmittance when there is contact with hydrogen gas, and when WO ₃ is used as the solid compound 3, λs = 1.4 The maximum light absorption change occurs near μm.

Referring again to FIG. 1, reference numerals 4 and 5 indicate light sources using light emitting diodes or the like, which are driven to emit light continuously or intermittently by a power source 30. The light source 4 has a light emitting characteristic that emits light having an energy spectrum centered at a wavelength λs at which a large optical change occurs upon contact with hydrogen gas or a hydrogen-containing compound gas, that is, λs = 1.4 μm as shown in the graph of FIG. Also, light source 5
Element 1 has the characteristic of emitting light with an energy spectrum centered at a wavelength λr that causes almost no change in optical absorption even when it comes into contact with hydrogen gas or hydrogen-containing compound gas, for example, λr = 1.0 μm in Figure 2. Motsu.

6 and 7 are light receiving sections using photodiodes or the like, and the light receiving section 6 receives light of wavelength λs given from the light source 4 via the element 1, and converts it into an electrical signal.
Further, the light receiving section 7 receives light of wavelength λr given from the light source 5 via the element 1, and converts it into an electrical signal.
Therefore, the light receiving section 6 has at least the wavelength λs.
In addition, the light receiving section 7 has light receiving characteristics including at least the wavelength λr.

In addition, when using light sources 4 and 5 that have emission characteristics in a wavelength band that includes wavelengths λs and λr, respectively, the light receiving sections 6 and 7 are provided with wavelengths λs that have a large light absorption change and wavelengths λs that have a small light absorption change. It is sufficient to use one having a characteristic of selectively receiving and outputting wavelength λr. Furthermore, the light sources 4, 5 and/or the light receiving sections 6, 7
In order to obtain wavelength characteristics of , a filter that passes the wavelength λs or λr may be used.

Reference numeral 8 denotes a discriminator, which inputs the light reception signals E1 and E2 from the light receivers 6 and 7. For example, if Es is the detection signal corresponding to the change in transmittance due to contact with hydrogen gas, then the ratio of E1 and E2 or The ratio of their difference, that is, Es=E1/E2 or Es=(E2-E1)/E2, is calculated. In the former case, when the detection signal Es becomes less than the threshold value that gives a predetermined gas concentration, the latter In this case, when Es exceeds a predetermined threshold value, a determination output indicating gas detection is generated.

In the embodiment shown in FIG. 1, the light sources 4 and 5, the element 1, and the light receiving sections 6 and 7 are provided in a sensor housing 9 that allows air to flow in from the outside.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, under normal conditions with no inflow of hydrogen gas, the received light signals of wavelength λs = 1.4 μm and wavelength λr = 1.0 μm passing through element 1 are E10, E20 as shown in the diagram of FIG. The detection signal Es in the discriminator 8 has an initial value of Eso=E10/
E20 or Eso = (E20-E10)/E20.

If hydrogen gas comes into contact with it in this state, a large light absorption change will occur in element 1 around λs = 1.4 μm, as shown by the broken line, but on the other hand, almost no light absorption change will occur at wavelength λr = 1.0 μm, so detection signal
Es changes from the initial value Eso to Es=E1/
Changes to E2 or Es = (E2 - E1) / E2. If this detection signal Es=E1/E2 is below a predetermined threshold level,
Alternatively, when Es=(E2-E1)/E2 becomes equal to or higher than a predetermined threshold level, the discrimination circuit 8 generates a discrimination output of gas detection.

FIG. 3 is a graph showing the transmittance of element 1 with respect to wavelength when air and miscellaneous gas come into contact in the embodiment shown in FIG. Indicates when.

That is, when miscellaneous gases such as water vapor and alcohol that are difficult to dissociate hydrogen atoms flow into the sensor housing 9, the transmittance of the element 1 changes uniformly over the entire element as shown by the broken line, and the miscellaneous gases Depending on the gas, no change in optical absorption occurs in a specific wavelength range. In response to such a change in transmittance due to the miscellaneous gas, the discriminator 8 detects the received light signals E10' and E at wavelengths λs and λr that have changed due to the miscellaneous gas.
Detection signal Eso′ (Eso′=E10′, /
E20′ or Eso′ = (E20′−E10′)/E20′), and this detection signal has wavelengths λs and λr in the air.
Detection signal Eso corresponding to the received light signals E10 and E20
(Eso=E10/E20) or Eso=(E20-E1
0)/E10). Therefore, element 1
Even if a miscellaneous gas such as water vapor or alcohol comes into contact with the gas, the discrimination section 8 will not produce an erroneous discrimination output of hydrogen gas or hydrogen-containing compound gas.

Similarly, even if the absolute value of transmittance changes due to aging of element 1, the transmission at wavelength λs that causes a large change in light absorption upon contact with hydrogen gas or hydrogen-containing compound gas, and at wavelength λr that causes almost no change in light absorption. Since the rate ratio does not change, the gas sensor according to the invention is hardly affected by aging.

In the example shown in FIG. 1, Pd,
Although WO ₃ was taken as an example as the solid compound 3, platinum Pt can also be used as the catalyst metal 2, and WO 3 is used as the solid compound 3.
Molybdenum oxide MO ₃ , titanium dioxide TiO ₂ , iridium hydroxide Ir(OH)n, vanadium pentoxide
V ₂ O ₅ can be used, and by detecting the transmittance at the wavelength λs where the change in light absorption is large due to contact with hydrogen gas or hydrogen-containing compound gas and the wavelength λr where the change in light absorption is small due to contact with hydrogen gas or hydrogen-containing compound gas, contact with miscellaneous gases and A gas sensor that is not affected by changes over time can be obtained. It has been experimentally confirmed that the change in light absorption of this element 1 shows a sufficient response to several hundred ppm of hydrogen gas at room temperature, and that the response speed after contact with hydrogen gas is also fast. This response speed can be further increased by heating the element 1 with a heater.

FIG. 4 is an explanatory diagram showing another embodiment of the present invention, and this embodiment is characterized in that light from a single light source is separated by a prism and passed through an element.

In FIG. 4, reference numeral 10 denotes a light source, in which an element 1 having a laminated structure of a catalyst metal 2 and a solid compound 3 emits a wavelength λs with a large change in light absorption and a wavelength λr with a small change in light absorption caused by contact with a gas to be detected. It emits light in the wavelength range that includes. The light from the light source 10 is separated by the prism 12 into light of wavelength λs and wavelength λr, and
The light passes through and enters the light receiving sections 6 and 7. Of course, the light-receiving outputs of the light-receiving sections 6 and 7 are inputted to a discriminating section 8 (not shown) as in the embodiment shown in FIG. 1, and the presence or absence of the gas to be detected is discriminated. According to this embodiment, the light source 10
Since only a single sensor is required, the sensor structure can be simplified, and errors due to non-uniformity of the light source can be eliminated.

FIG. 5 is an explanatory diagram showing another embodiment of the present invention, and this embodiment is characterized by having a single light source and a single light receiving section.

In FIG. 5, 10 emits light in a wavelength range that includes the light absorption wavelength λs of element 1 and the wavelength λr with a small change in light absorption, and the light transmitted through element 1 is vibrated at a constant period by a prism drive unit 14. The light is incident on the swing prism 13. Prism drive unit 14
It is used for buzzers, speakers, etc.
For example, a bimorph piezoelectric element is used. The swing prism 13 is vibrated by the prism drive unit 14 at the position indicated by the solid line and the position indicated by the broken line.
The transmitted light of the wavelength λr with a small change in light absorption is incident on the light receiving part 15 through the slit 16, and the transmitted light with a wavelength λr with a small change in light absorption is incident on the light receiving part 15 through the slit 16. . The light reception signal from the light receiving section 15 is sent to the swing prism 13.
By sampling in synchronization with the vibration drive of , the signal is input to a discriminator 8 (not shown), and the presence or absence of gas detection is discriminated from a detection signal corresponding to the ratio of transmitted light of wavelengths λs and λr.

FIG. 6 is an explanatory diagram showing another embodiment of the present invention, and this embodiment is characterized in that remote monitoring is performed using an optical fiber cable.

In FIG. 6, 17 is a receiver, which includes light sources 4 and 5 and light receiving sections 6 and 7, and the light source 4 emits light at a wavelength λs with a large change in light absorption at the element 1.
Further, the light source 5 emits light having a wavelength λr with a small change in light absorption. The light from the light sources 4 and 5 is connected to the remotely installed sensor housing 9 via the optical fibers 18a and 18b of the optical fiber cable 18, and the light from the optical fibers 18a and 18b is transmitted to the catalyst metal 2 and the solid compound 3. The light is transmitted through the element 1 having a laminated structure and returned to the light receiving sections 6 and 7 of the receiver 17 via optical fibers 18c and 18d.

According to this embodiment, since the sensor housing 9 is not provided with an electric circuit for remote monitoring of hydrogen gas or hydrogen-containing compound gas, explosive and combustible gases to be detected can be safely monitored. .

FIG. 7 is an explanatory diagram showing another embodiment of the present invention used for remote monitoring using the optical fiber cable of FIG. 6, and in this embodiment, the catalyst metal 2,
The element 1 made of the solid compound 3 is used as a reflector, and the wavelengths λs,
Inject light of λr into the solid compound 3 of the element 1,
The optical fiber 18 is reflected by the interface of the catalyst metal 2.
c and 18d, the signal is returned to the receiver side.

FIG. 8 is an explanatory view showing another embodiment of the present invention, and this embodiment is characterized in that the element structure used in the present invention is formed by vapor deposition on the end face of an optical fiber.

That is, the solid compound 3 and catalyst metal 2 constituting the element 1 are sequentially deposited on the end of the optical fiber 20 and housed in the sensor housing 9. A directional coupler 19 is provided on the receiver 17 side of the optical fiber cable 18, and transmits light in a wavelength range including the optical absorption wavelength λs and the wavelength λr with small optical absorption change from the light source 10 via the optical fiber 20. It is reflected by the element 1 formed on the end face of the optical fiber 20 and enters the swing prism 13 which is vibrated by the prism drive unit 14 through the directional coupler 19, and is transmitted through the slit 16 by the vibration of the swing prism 13 to the light receiving unit. Light having a wavelength λs with a large change in light absorption or a wavelength λr with a small change in light absorption is alternately incident on the light receiving section 15, and the light reception signal from the light receiving section 15 is synchronized with the vibration drive of the swing prism 13 as in the embodiment shown in FIG. The sampled gas is sampled by the determination unit, and the presence or absence of the gas to be detected is determined based on the difference between the received light signals of wavelengths λs and λr.

FIG. 9 is an explanatory diagram showing another embodiment of the present invention, and this embodiment is characterized in that an element structure made of a catalytic metal and a solid compound is formed in the clad structure of an optical fiber.

That is, a solid compound 3 such as WO ₃ is first vapor-deposited on the outer periphery of the optical fiber 20, which serves as a light propagation path, and then a catalyst metal 2 is further vapor-deposited to form a clad structure. A light source (not shown) propagates into the optical fiber 20 light corresponding to a wavelength λs at which light absorption is small and a wavelength λr at which light absorption change is small, which are generated when the solid compound 3 is reduced by hydrogen atoms.

The effect is that when there is no contact with the gas to be detected, the solid compound 3 and catalyst metal 2 that form the cladding of the optical fiber 20 have a small light absorption rate for both wavelengths λs and λr, so the light from the light source is The light is reflected within the optical fiber 20 and transmitted efficiently. On the other hand, when the gas to be detected comes into contact, the hydrogen atoms generated by the catalyst metal 2 reduce the solid compound 3, and when the solid compound is _WO3 , for example, a large optical absorption change occurs at the wavelength λs = 1.4 μm, and the optical fiber The amount of light of wavelength λs transmitted within 20 decreases,
On the other hand, the light amount of λr, which has a small change in light absorption, hardly decreases. Therefore, by dividing the light transmitted through the optical fiber 20 into wavelengths λs and λr and receiving the light, it is possible to determine the presence or absence of the gas to be detected.

FIG. 10 shows another embodiment of the present invention. For example, in the embodiment of FIG. 1, light of wavelengths λs and λr is transmitted in the stacking direction of the catalyst metal 2 and solid compound 3 in the element 1. However, this embodiment is characterized in that the transmitted light from the optical fiber is made to pass through the solid compound 3 forming the thin film optical waveguide.

That is, a solid compound 3 such as WO ₃ is placed on the substrate 21.
A device 1 is made by depositing a catalyst metal 2 such as Pd, a solid compound 3 forms a thin film optical waveguide between a substrate 21 and the catalyst metal 2, and optical fibers 20 are connected to both ends of the solid compound 3 to connect a light source. The guided light having a light absorption wavelength λs and a wavelength λr with a small change in light absorption are propagated into a thin film optical waveguide made of a solid compound 3.

FIG. 11 shows another embodiment of the present invention, and this embodiment is characterized in that a light source and a light receiving section are formed integrally with the element 1.
A cross section is shown.

That is, following the substrate 21, a solid compound 3 such as WO ₃ is vapor-deposited, and a catalyst metal 2 such as Pd is further vapor-deposited to realize the structure of the element 1. Each light having a wavelength λr with a small change in optical absorption compared to λs is propagated into an optical waveguide made of a solid compound 3, enters light receiving elements 6 and 7 formed integrally with the solid compound, and is converted into an electrical signal. This has the advantage that the element 1, the light sources 4 and 5, and the light receiving sections 6 and 7 can be integrated.

Next, to explain the effects of the present invention, an element having a layered structure of a metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas and a solid compound that is reduced by the hydrogen atoms generated in this metal, This element transmits or reflects light at a wavelength that causes a large change in optical absorption due to the reduction of the solid compound, and also transmits or reflects light at a wavelength that causes a small change in optical absorption, and detects the detected light at a wavelength that causes a large change in optical absorption. Since the presence or absence of hydrogen or hydrogen-containing compound gas is determined based on the detection signal of light with a wavelength that causes a small change in optical absorption, in the case of contact with miscellaneous gases such as water vapor or alcohol, light absorption is reduced due to reduction by hydrogen atoms. This makes it possible to reliably prevent false detection of the gas to be detected even if the overall light transmission or reflection characteristics of the element change.Furthermore, it is possible to prevent the transmission or reflectance characteristics from changing over time due to changes in the element's overall light transmission or reflection characteristics. Even if the gas changes over time, the presence or absence of the gas to be detected is determined based on the wavelength of light that causes a large change in optical absorption upon contact with the gas to be detected, and the light of a wavelength that causes a small change in optical absorption. has almost no effect on the detection characteristics,
A gas sensor with excellent stability and reliability can be obtained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the transmittance of the element in Fig. 1 at normal times and during gas detection with respect to light wavelengths, and Fig. 3
The figure is a graph showing the transmittance for light wavelength when it comes into contact with a miscellaneous gas, Figure 4 is an explanatory diagram showing another embodiment of the present invention using a single light source, and Figure 5 is a light source and light receiver. FIGS. 6 and 7 are explanatory diagrams showing another embodiment of the present invention with a single part; FIGS. 6 and 7 are explanatory diagrams showing an embodiment of remote monitoring using an optical fiber cable; FIG.
The figure is an explanatory diagram showing another embodiment of the present invention in which an element structure is formed on the end face of an optical fiber by vapor deposition, and FIG. 9 is an explanatory diagram of another embodiment of the present invention in which a sensor structure is provided on the cladding of the optical fiber. , FIG. 10 is an explanatory diagram showing another embodiment of the present invention using a thin film optical waveguide, and FIG. 11 is an explanatory diagram showing another embodiment of the present invention in which a light source, an element, and a light receiving section are integrated. 12 is a sectional view taken along the line AA in FIG. 11. 1: Element, 2: Catalyst metal, 3: Solid compound,
4, 5, 10: light source, 30: power supply, 6, 7, 1
5: Light receiving section, 8: Discrimination section, 9: Sensor housing, 1
2: Prism, 13: Swing prism, 14:
Prism drive unit, 16: slit, 17: receiver, 18: optical fiber cable, 18a to 18
d, 20: optical fiber, 19: directional coupler, 2
1: Substrate.

Claims (1)

[Scope of Claims] 1. An element having a layered structure of a metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas and a solid compound that is reduced by hydrogen atoms in the metal, and a device that absorbs light caused by the reduction of the solid compound. a first detection unit that monitors light with a wavelength that changes significantly; a second detection unit that monitors light with a small wavelength that does not cause a change in light absorption due to reduction of the compound; and the first detection unit A gas sensor comprising: a determination section that determines the presence or absence of the hydrogen or hydrogen-containing compound gas based on the detection signal of the second detection section and the detection signal of the second detection section.