JPH0339578B2 - - 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 repeated various experiments, it was found that the light absorption characteristics of an element having a layered structure of a catalytic metal and a solid compound are affected by changes in the temperature of the element, changes over time, etc., and the detection characteristics change.

The present invention has been made in view of these problems, and an object of the present invention is to provide a highly stable and reliable gas sensor whose detection characteristics do not change due to changes in temperature or changes over time.

To achieve this object, the present invention provides a first method 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. At the same time, light from a second element including a second solid compound made of the same material as the solid compound is detected as a reference value, and a light detection signal from the first element is detected. The presence or absence of hydrogen or hydrogen-containing gas is detected by comparison with the photodetection signal from the second element without being affected by temperature or changes over time.

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, reference numeral 1 is a sensor housing into which outside air can flow, and inside the sensor housing 1 there is a first
The element 2 and the second element 3 are arranged close to each other so as to receive the same environmental conditions, and the first element 2 and the second element 3 are provided with a light source such as a light emitting diode driven by a power source 4. The light from 5 is given as transmitted light so that the ratio is approximately the same.

Here, the first element 2 detects hydrogen gas, or ammonia gas _NH3 , hydrogen sulfide gas _H2S , silane gas _SiH4 , etc. known as hydrogen-containing compound gases, when they come into contact with each other. Catalytic metal 6 that adsorbs and dissociates molecules to generate hydrogen atoms
and a solid compound 7 whose light absorption rate changes due to the reduction action of hydrogen atoms generated in the catalyst metal 6. Here, palladium Pd is used as the catalyst metal 6, and tungsten trioxide _WO3 is used as the solid compound 7.

The first element 2, which has a laminated structure of the catalyst metal 6 and the solid compound 7, is manufactured on a transparent glass substrate.
A solid compound 7 made of WO ₃ is deposited to a predetermined thickness,
Next, a catalyst metal 6 made of Pd is placed on the solid compound 7.
It can be created by depositing it thinly enough to maintain transparency.

On the other hand, the second element 3 is made of the same material as the solid compound 7 of the first element 2, for example, tungsten trioxide.
It has a laminated structure of a second solid compound 8 using WO ₃ and a metal 9 deposited thinly on the solid compound 8 to maintain transparency. Metals that do not adsorb and dissociate, such as copper, aluminum
Al etc. are used.

A light-receiving element 10 as a first detection part and a light-reception element 11 as a second detection part are located at positions receiving the transmitted light of the first element 2 and the second element 3 installed in the sensor housing 1. is provided to convert the light transmitted through the first element 2 and the second element 3 into electrical signals. The detection signals of the light receiving elements 10 and 11 are given to the comparison detection circuit 12, and if the detection signal of the light receiving element 10 is E1 and the detection signal of the light receiving element 11 is E2, then, for example, (E2 - E1) /E2
=Es is performed, and when the detection output Es is greater than or equal to a predetermined threshold value, a gas detection output is generated.

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

First, when hydrogen gas comes into contact with the first element, the catalytic metal 6
adsorbs and dissociates hydrogen and converts hydrogen atoms into catalytic metal 6
This hydrogen atom is injected into the solid compound 7. The solid compound 7 into which protons H ⁺ have been injected by the catalyst metal 6 is reduced, its color center density changes, and its light absorption rate changes. In this example, tungsten trioxide is used as the solid compound 7.
Since WO ₃ is used, the solid compound 7 increases the light absorption rate, and the degree of increase becomes stronger as the gas concentration increases. Of course, when the hydrogen gas disappears, the protons H ⁺ injected into the solid compound 7 escape again, and the solid compound 7 decreases its light absorption rate.
Return to the original, more transparent state.

Such a light absorption phenomenon of the first element 2 is similar to contact with hydrogen-containing compound gases such as NH ₃ , H ₂ S, and SiH ₄ as described above in addition to hydrogen gas. In addition, the change in the light absorption rate of the first element 2 shows a sufficient response to several hundred ppm of hydrogen gas at room temperature.
It has been experimentally confirmed that the response speed after contact with hydrogen gas is also fast. This response speed can be further increased by heating the first element 2 with a heater.

On the other hand, in the second element 3 provided close to the first element 2 whose light absorption rate changes upon contact with hydrogen gas or hydrogen-containing compound gas, the metal 9 is made of Cu, Al, etc. that do not dissociate and adsorb hydrogen gas. Since it is a metal of
The same material as the solid compound 7 of the first element 2, e.g.
The light absorption of the second solid compound 8 using WO ₃ remains unchanged.

Due to the light absorption characteristics of the first element 2 and the second element 3 in response to contact with hydrogen gas or hydrogen-containing compound gas, in the steady monitoring state where there is no inflow of hydrogen gas, the first element 2 The light absorption rates of the solid compounds 7 and 8 made of the same material in the second element 3 are the same, and the same amount of light enters the elements 2 and 3 from the light source 5, so that the detection signals E1 and E2 are the same. .

On the other hand, when hydrogen gas flows in, hydrogen atoms generated by adsorption and dissociation by the catalyst metal 6 of the first element 2 are injected into the solid compound 7, and the solid compound 7
The light absorption rate changes due to the reduction of . For example, when tungsten trioxide WO ₃ is used as the solid compound 7, the light absorption rate increases due to reduction, and the amount of transmitted light to the light receiving element 10 decreases. On the other hand, in the second element 3, since the metal 9 does not have the function of adsorbing and dissociating hydrogen gas, the solid compound 8 is not reduced, and the light absorption rate of the solid compound 8 does not change even if hydrogen gas flows in. , the same transmitted light as in normal times reaches the light receiving element 1.
1.

Therefore, when hydrogen gas flows in, the detection signal E1 of the light receiving element 10 is detected by the reference light receiving element 1.
The signal level decreases from the detection signal E2 of 1 according to the gas concentration, and in the comparison detection circuit 12, Es=(E2−
A detection output corresponding to the gas concentration is obtained as E1)/E2, and a gas detection output is generated above a predetermined threshold.

Next, a compensation function for element temperature or changes over time will be explained.

If the light absorption characteristics of the first element 2 change due to the influence of the ambient temperature, the same will happen in the second element 3 using the solid compound 8 made of the same material as the solid compound 7 of the first element 2. This results in a change in the light absorption characteristics of the solid compound 8 in response to changes in ambient temperature. In this case, during normal times when there is no inflow of hydrogen gas,
Even if the amount of transmitted light of the first element 2 and the second element 3 changes due to temperature change, the relative amount of transmitted light between the first element 2 and the second element 3 does not change due to temperature, and the detection signal E1 and E2 are equal even when subjected to temperature changes, and gas detection is not performed by the comparison detection circuit 12.

On the other hand, when hydrogen gas flows in, there is no relative change in the amount of light transmitted through the first and second elements 2 and 3 due to temperature, and the first element adds the change in light absorption due to gas contact to the temperature change. The comparison detection circuit 12 always detects only the signal change due to the change in the light absorption rate of the first element 2 due to contact with the gas, based on the amount of transmitted light of the second element 3. do.

Such a compensation function is effective not only with respect to temperature but also with respect to changes over time, since the first and second elements 2 and 3 undergo approximately the same changes over time. By comparing and calculating the transmitted light detection signals of the element 2, a detection output that is not affected by changes over time can be obtained.

In the example shown in FIG. 1, palladium Pd is used as the catalyst metal 6 and WO ₃ is used as the solid compounds 7 and 8, but platinum Pt can also be used as the catalyst metal 6. , solid compounds 7 and 8 include molybdenum trioxide MO ₃ , titanium dioxide TiO ₂ , iridium hydroxide Ir(OH)n,
Solid compound 7 even with vanadium pentoxide V ₂ O ₅
It is possible to obtain the first element 2 which causes a change in optical absorption rate in the optical wavelength band determined by the above.

FIG. 2 is an explanatory diagram of the main structure of a sensor showing another embodiment of the present invention. In this embodiment, the second element 3 for obtaining the reference light is made of the same material as the solid compound 7 of the first element 2. For example, only the second solid compound 8 using WO ₃ is used, and the second element 3 contains Cu, Al.
It is characterized by not depositing metal 9 such as.

Also in the embodiment shown in FIG. 2, when hydrogen gas or hydrogen-containing gas compound gas flows in,
Although the transmitted light to the light receiving element 10 changes due to a change in the light absorption rate in the first element 2, the solid compound 8
The light absorption rate of the second element 3 made of only does not change,
By comparing and calculating the detection signals of the light receiving elements 10 and 11, a detection output that is not affected by temperature or changes over time can be obtained.

FIG. 3 is an explanatory view of the main part of a sensor showing another embodiment of the present invention, in which the same solid compound 7 contains a catalytic metal 6 and a non-catalytic metal 9.
are deposited adjacent to each other, and the first and second elements can be formed with a single element structure.

FIG. 4 is characterized in that the first and second elements 2 and 3 shown in the embodiment of FIG. 1 are provided in a sensor housing 4, and gas is detected remotely by transmission through an optical fiber.

That is, the light source 5 and the light receiving elements 10 and 11 are connected to the receiver 1.
3, and the first and second elements 2,
3 is installed, and light from a light source 5 is transmitted to the elements 2 and 3 of the sensor housing 1 through a pair of optical fiber cables 14. The passed light is similarly transmitted via a pair of optical fiber cables 14' to the receiver 1.
The light is made incident on the light receiving elements 10 and 11 of No. 3. Of course, the receiver 13 includes the light receiving element 1.
A comparison calculation circuit (not shown) for comparing and calculating the detection signals of 0 and 11 is provided.

FIG. 5 is an explanatory diagram showing another embodiment of the present invention. In this embodiment, the first and second elements 2,
3 is provided as a reflector for the light from the light source 5 that enters through a pair of optical fiber cables 14, and in the case of the first element 2, the light that has passed through the solid compound 7 and is reflected by the catalyst metal 6 is reflected by the optical fiber. The light is incident on the light receiving element 10 of the receiver 13 via the cable 14', and the second element 3 also receives the light that has passed through the solid compound 8 and was reflected by the metal 9 via the optical fiber cable 14'. It is characterized in that the light is made incident on the light receiving element 11 of the device 13.

The effect is that when the gas to be detected is not in contact with the first and second elements 2 and 3, the elements 2 and 3
The light absorption rate in each of element 2,
The amount of light reflected by the light receiving element 3 and incident on the light receiving elements 10 and 11 is large. On the other hand, if the gas to be detected flows in, the light absorption rate of element 2 increases, the amount of light reflected to the light receiving element 10 decreases, and the light absorption rate of element 3 does not change and the reflection is the same as normal. The amount of light is determined by the light receiving element 11
becomes incident on .

FIG. 6 shows another embodiment of the present invention, which is characterized in that the first and second element structures shown in FIG. 1 are deposited directly on the end face of an optical fiber.

That is, a solid compound 7 such as WO ₃ forming the first element 2 and a catalyst metal 6 such as Pd are deposited on the end face of one optical fiber cable 14, and a catalytic metal 6 such as Pd is deposited on the end face of the other optical fiber cable 14'. The first and second elements 2 are formed by vapor-depositing a solid compound 8 such as WO ₃ forming the second element 3 and a metal 9 such as Cu or Al that does not have a catalytic action, and forming the same on the end face of the fiber. 3 is provided inside the sensor housing 1.

On the other hand, the receiver 13 includes a light source 5 and a light receiving element 1.
0 and 11 are provided, the irradiated light from the light source 5 is applied to the elements 2 and 3 on the fiber end face via the optical fiber cables 14 and 14', and the reflected light from the elements 2 and 3 is applied to the directional couplers 15 and 15'. The light is separated and made incident on the light receiving elements 1 and 11, respectively.

The gas detection function in this embodiment is the same as that of the reflection method shown in FIG. An element structure that allows monitoring can be obtained.

FIG. 7 is an explanatory diagram showing an embodiment of the present invention, and this embodiment is characterized in that the element structure of the present invention shown in FIG. 1 is used for the cladding of an optical fiber.

That is, a pair of optical fibers 16 arranged in the center,
Solid compounds 7 and 8 of the same material are deposited on the outer periphery of the optical fiber 16', a catalyst metal 6 is deposited on the optical fiber 16 side, and a metal 9 having no catalytic action is deposited on the optical fiber 16' side. Forming a cladding layer of the optical fibers 16 and 16' respectively, allowing light from the light source 5 to pass through the optical fibers 16 and 16',
The light enters the light receiving elements 10 and 11, with the optical fiber 16 side serving as the first element and the optical fiber 16' side serving as the second element.

In the gas sensor structure shown in FIG. 7, the light absorption rate of the solid compound 7 and catalyst metal 6 that form the cladding of the optical fiber 16 is small in the absence of contact with the gas to be detected, and the cladding of the optical fiber 16' is small. The light absorption rate of the solid compound 8 and metal 9 formed is also small, and the light from the light source 5 that reflects and travels within the optical fibers 16, 16' is efficiently transmitted.
A sufficient amount of light reaches each of the light receiving elements 10 and 11. On the other hand, when the gas to be detected comes into contact, the hydrogen atoms generated in the catalyst metal 6 reduce the solid compound 7, and when the solid compound 7 is _WO3 , the light absorption rate increases and the transmittance of the clad decreases. The amount of light transmitted through the optical fiber 16 decreases, and the light receiving output of the light receiving element 10 decreases. On the other hand, in the case of the optical fiber 16', since the metal 9 does not have a catalytic effect even if it comes into contact with the gas to be detected, the solid compound 7
is not reduced and there is no change in light absorption rate, so the light receiving output of the light receiving element 11 is kept constant.

FIG. 8 is an explanatory diagram showing another embodiment of the present invention that employs a transmitted light method. In the embodiments shown in FIGS. 1, 2, and 3, light is transmitted in the stacking direction of elements 2 and 3. This embodiment is characterized in that the transmitted light from the optical fiber is made to pass through the solid compound forming the thin film optical waveguide.

That is, the light from the light source 5 is transmitted to the optical fiber cable 1.
4, 14' to the first element 2 and second element 3 which are arranged adjacent to each other, and solid compounds 7, 8 such as WO ₃ shown by broken lines are injected into the first and second elements 2, 3. A thin film optical waveguide is formed, and the light that has passed through the optical waveguide is made incident on the light receiving elements 10 and 11 via optical fiber cables 14 and 14'.

The details of this element structure are clear from FIGS. 9 and 10, which show cross sections along lines A-A and B-B in FIG. 8. First, in the case of the first element 2 shown in FIG. A solid compound 7 such as WO ₃ and a catalyst metal 6 such as Pd are deposited on a substrate 17 to form an element structure, and the solid compound 7 forms a thin film optical waveguide between the substrate 17 and the catalyst metal 6. Optical fiber cables 14 are connected to both ends of the optical fiber cable 14 so that light from a light source is propagated through a thin film optical waveguide made of a solid compound 7.

Also, in the case of the second element 3 shown in FIG.
Similarly, a solid compound 8 such as WO ₃ and a metal 9 such as Cu or Al having no catalytic action are deposited on the substrate 17,
The solid compound 8 is made to propagate within the thin film optical waveguide between the substrate 17 and the metal 9.

According to this structure, on the first element 2 side, the amount of transmitted light can be reduced according to the gas concentration by increasing the light absorption rate of the solid compound 7 due to the detected gas, while on the second element 3 side, the amount of transmitted light can be reduced according to the gas concentration. Since there is no change in the light absorption rate of the solid compound 8, a constant amount of transmitted light can always be obtained.

FIG. 11 shows another embodiment of the present invention, and FIG. 12 shows a cross section along the line CC.

This embodiment uses a light source 5 such as a light emitting diode and a light receiving element 1 such as a photodiode instead of the optical fiber cable used in the embodiment shown in FIG.
0 and 11 are provided directly on the elements 2 and 3, and the light from the light source 5 is separated by an optical distributor 18 of a thin film optical waveguide formed of solid compounds 7 and 8. The light is propagated into a thin film optical waveguide shown by a broken line in which a light beam 9 is vapor-deposited, and is made to enter the light receiving elements 10 and 11, which has the advantage that the element, the light source, and the light receiving element can be integrated.

Next, to explain the effects of the present invention, the laminated structure includes a catalyst metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas, and a solid compound whose light absorption rate changes due to reduction by the hydrogen atoms generated in the catalyst metal. Detecting the light from the first element having the same material as the solid compound of the first element, detecting the light from the second element using the same material as the solid compound of the first element,
Since the presence or absence of the detected gas is detected by comparing the light detection signals from the first and second elements, the effects of temperature and changes over time on the light absorption characteristics occur in both the first and second elements. Changes in the amount of light from the first element are detected based on the light from the second element, which has no change in light absorption rate even when gas comes into contact with it, so gas concentration can be detected based on temperature and changes over time. A gas sensor with excellent stability and reliability without fluctuation in output can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram showing an embodiment of another element structure of the present invention, and FIG. 3 is an explanatory diagram showing another embodiment of the element structure of the present invention. FIG. 4 is an explanatory diagram showing an example of remote monitoring using an optical fiber cable,
5 and 6 are explanatory diagrams showing another embodiment of remote monitoring using an optical fiber cable, FIG. 7 is an explanatory diagram of another embodiment of the present invention in which a sensor structure is provided in the cladding of the optical fiber, and FIG. The figure is an explanatory diagram showing another embodiment of the present invention having a thin film optical waveguide, FIG. 9 is a sectional view taken along the line AA in FIG. 8, and FIG. 10 is a sectional view taken along the line BB in FIG. 8.
A cross-sectional view, FIG. 11 is an explanatory view showing another embodiment of the present invention in which a light source, a sensor, and a light-receiving element are integrated, and FIG. 12 is a cross-sectional view taken along line CC in FIG. 1: Sensor housing, 2: First element, 3: Second element, 4: Power source, 5: Light source, 6: Catalyst metal, 7:
First solid compound, 8: Second solid compound, 9:
metal, 10: light receiving element (first detection section), 11:
Light receiving element (second detection section), 12: comparison detection circuit,
13: Receiver, 14, 14': Optical fiber cable, 15, 15': Directional coupler, 16, 16':
Optical fiber, 17: substrate, 18: optical distributor.

Claims (1)

[Claims] 1. A metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas, and a first metal that is reduced by hydrogen atoms in the metal.
a first element having a laminated structure with a solid compound; a second element having a second solid compound made of the same material as the first solid compound; and a second element comprising a second solid compound made of the same material as the first solid compound; A first detection section that detects the light, a second detection section that detects the light from the second element, and a comparison operation between the signal from the first detection section and the signal from the second detection section. A gas sensor comprising: a comparison detection circuit for detecting the presence or absence of the hydrogen or hydrogen-containing gas.