JP2017198604A - Gas sensor and gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor that reduces an influence of a non-detection target gas without reducing the sensitivity in detection of a detection target gas in the gas sensor.SOLUTION: There is provided a gas sensor 1 comprising: a case 20 that has an opening 21 formed therein through which gas circulates; a gas detection element 10 that is covered by the case and detects a detection target gas; and a filter body 40 that is provided between the opening and the gas detection element and adsorbs a non-detection target gas, wherein the filter body has a higher gas diffusibility on the opening side than that on the gas detection element side.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a gas sensor and a gas detection device.

  2. Description of the Related Art Conventionally, a gas sensor is known that is provided in a gas alarm device or the like and detects fuel gas or carbon monoxide gas generated by incomplete combustion of the fuel gas. The gas detection element used for such a gas sensor may react also with non-detection object gas, such as humidity (water | moisture) and environmental origin alcohol, for example.

  Therefore, a sensing element having a sensitive part, a silica gel filter that removes the non-detection target gas, and an inflow restriction plate that restricts the inflow of the non-detection target gas released from the silica gel filter due to a rise in ambient temperature to the sensitive part. It is known (see, for example, Patent Document 1).

JP-A-10-197470

  However, in the detection element according to Patent Document 1 described above, since the inflow restriction plate restricts the flow of the detection target gas to the sensitive part together with the non-detection target gas, the detection sensitivity of the detection target gas may be reduced. .

  The present invention has been made in view of the above, and an object thereof is to reduce the influence of a non-detection target gas without reducing the detection sensitivity of the detection target gas in a gas sensor.

  According to the gas sensor of one aspect of the present invention, a case in which an opening through which gas flows is formed, a gas detection element that is covered by the case and detects a detection target gas, and between the opening and the gas detection element And a filter body that adsorbs a non-detection target gas, and the filter body has higher gas diffusibility on the opening side than on the gas detection element side.

  According to the embodiment of the present invention, the influence of the non-detection target gas can be reduced without reducing the detection sensitivity of the detection target gas in the gas sensor.

It is a figure which illustrates schematic structure of the gas detection apparatus in embodiment. It is a section schematic diagram of a gas sensor in an embodiment. It is a section schematic diagram of a gas detection element in an embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

  FIG. 1 is a diagram illustrating a configuration of a gas detection device 100 according to the embodiment.

  As shown in FIG. 1, the gas detection device 100 includes a gas sensor 1, a drive unit 2, and a detection processing unit 3.

  The gas sensor 1 includes a gas detection element 10 and detects a detection target gas. The detection target gas is, for example, fuel gas (main components are methane, propane, and butane), carbon monoxide gas, hydrogen gas, and the like that are generated during incomplete combustion of the fuel gas. The drive unit 2 is connected to the gas detection element 10 of the gas sensor 1 and drives the gas detection element 10. The detection processing unit 3 is connected to the gas detection element 10 of the gas sensor 1 and performs detection processing of the detection target gas based on a detection signal obtained from the gas detection element 10. The functions of the drive unit 2 and the detection processing unit 3 are realized by, for example, a program that the CPU reads from the ROM and executes in cooperation with the RAM, a plurality of circuits, and the like.

  The gas detection device 100 may be provided with an operation input unit that performs operation input, a display unit that displays a detection result by the detection processing unit 3, a sound output unit that issues an alarm according to the detection result, and the like.

  FIG. 2 is a schematic cross-sectional view of the gas sensor 1 according to the embodiment.

  As shown in FIG. 2, the gas sensor 1 includes a gas detection element 10, a case 20, a filter body 40, and lead terminals 50. In the following description, the opening 21 side of the case 20 in the gas sensor 1 is on the upper side and the lead terminal 50 side is on the lower side.

  The gas detection element 10 is fixed to the upper surface of a stepped disk-shaped sensor base 11. The configuration of the gas detection element 10 will be described later. The lead terminal 50 projects downward from the sensor base 11 and connects the gas detection element 10 to the drive unit 2 and the detection processing unit 3 of the gas detection device 100.

  The case 20 is formed in a cylindrical shape, and the lower end side is fixed to the periphery of the sensor base 11 and covers the periphery of the gas detection element 10. An opening 21 through which a gas flows is formed on the upper end surface of the case 20 and has, for example, a circular shape. For example, the case 20 has a diameter of 8 mm and a height of 13 mm. Moreover, the diameter of the opening 21 is 5 mm, for example.

  The first mesh 31 is attached to the inside of the case 20 so as to cover the opening 21. The second mesh 32 is attached to the inside of the case 20 with a predetermined interval below the first mesh 31. The third mesh 33 is attached to the inside of the case 20 with a predetermined interval below the second mesh. The third mesh 33 is a double mesh for explosion protection.

  Each of the first mesh 31, the second mesh 32, and the third mesh 33 is a stainless steel net, and functions as a presser for the first filter 40a and the second filter 40b. The second mesh 32 functions as a partition between the first filter 40a and the second filter 40b.

  The filter body 40 is provided between the opening 21 of the case 20 and the gas detection element 10. The filter body 40 allows the detection target gas flowing from the opening 21 to pass therethrough and adsorbs the non-detection target gas. The filter body 40 includes a first filter 40a and a second filter 40b.

  The first filter 40 a is provided between the first mesh 31 and the second mesh 32, and allows the detection target gas flowing from the opening 21 to pass therethrough and adsorbs the non-detection target gas. The first filter 40a has a filter case (not shown) having an outer diameter equal to the inner diameter of the case 20 and innumerable ventilation holes, and granular (powder, spherical, crushed) filled in the filter case as an adsorbent. Activated carbon). The thickness of the first filter 40a is, for example, 1 mm to 3 mm.

  The second filter 40b is provided between the second mesh 32 and the third mesh 33 so as to be stacked below the first filter 40a. The second filter 40b passes the detection target gas flowing from the opening 21 and adsorbs the non-detection target gas that has passed through the first filter 40a. The second filter 40b includes a filter case (not shown) having an outer diameter equal to the inner diameter of the case 20 and innumerable vent holes, and granular (powder, spherical, crushed) filled in the filter case as an adsorbent. Activated carbon). The thickness of the second filter 40b is, for example, 1 mm to 3 mm.

  The activated carbon provided as an adsorbent in the first filter 40a and the second filter 40b performs physical adsorption by van der Waals force in the gas phase. Activated carbon adsorbs non-detection target gases such as alcohol vapor, siloxane compounds, SOx, NOx, VOCs, etc., and detection targets such as methane, propane, butane, carbon monoxide, and hydrogen, which are the main components of fuel gas Gas does not adsorb.

  For this reason, most of the non-detection target gas that has flowed into the case 20 from the opening 21 is adsorbed by the first filter 40 a and the second filter 40 b and reaches the gas detection element 10 in a very small amount. In addition, a very small amount of the detection target gas flowing into the case 20 from the opening 21 is adsorbed by the first filter 40a and the second filter 40b, but most of the gas passes through the first filter 40a and the second filter 40b. The gas detection element 10 is reached.

  As described above, in the gas sensor 1, the non-detection target gas is removed by the first filter 40a and the second filter 40b, so that the gas detection element 10 can detect the detection target gas with high accuracy. .

  Here, when the environment such as temperature and humidity around the gas sensor 1 changes, the non-detection target gas adsorbed on the first filter 40 a and the second filter 40 b may desorb and reach the gas detection element 10. If the concentration of the non-detection target gas increases around the gas detection element 10, the gas detection element 10 may react with the non-detection target gas and erroneously detect.

  Therefore, in the gas sensor 1 according to the present embodiment, the gas diffusibility of the first filter 40a is higher than the gas diffusivity of the second filter 40b. For this reason, the non-detection target gas desorbed from the second filter 40b is discharged from the opening 21 to the outside through the first filter 40a having high gas diffusibility. Further, the non-detection target gas desorbed from the first filter 40a is discharged outside through the opening 21 without going to the second filter 40b having low gas diffusibility.

  In this way, by making the gas diffusivity of the first filter 40a higher than that of the second filter 40b, the non-detection target gas desorbed from the first filter 40a and the second filter 40b is directed to the gas detection element 10 side. The discharge is suppressed and discharged from the opening 21 to the outside. For this reason, it can suppress that the detection accuracy of the gas detection element 10 falls by the non-detection object gas desorbed from the first filter 40a and the second filter 40b.

  The gas diffusibility of the first filter 40a and the second filter 40b can be adjusted by, for example, the particle size of activated carbon provided as an adsorbent.

  For example, the gas diffusivity of the first filter 40a can be made higher than that of the second filter 40b by making the average particle diameter of the activated carbon of the first filter 40a larger than the average particle diameter of the activated carbon of the second filter 40b. .

  Further, for example, by setting the minimum particle diameter of the activated carbon of the first filter 40a to be larger than the maximum particle diameter of the activated carbon of the second filter 40b, the gas diffusibility of the first filter 40a is made higher than that of the second filter 40b. Can do. For example, the particle size distribution of the activated carbon of the first filter 40a is 450 μm to 550 μm, and the particle size distribution of the activated carbon of the second filter 40b is 250 μm to 350 μm. By changing the particle size distribution in this way, the gas diffusibility of the first filter 40a can be made higher than that of the second filter 40b.

  As described above, by making the gas diffusibility of the first filter 40a higher than that of the second filter 40b, a non-detection target that is released from the first filter 40a and the second filter 40b and released to the gas detection element 10 side. Gas can be reduced and the detection accuracy of the gas detection element 10 can be maintained.

  Further, the diffusibility of the non-detection target gas in the first filter 40a and the second filter 40b can be adjusted by, for example, the porosity of the activated carbon filled in each filter.

  For example, the diffusivity of the first filter 40a can be made higher than that of the second filter 40b by making the porosity of the first filter 40a larger than the porosity of the second filter 40b. For example, the porosity can be arbitrarily adjusted by changing the pressing conditions by using the adsorbent as a molded body. Thus, by making the diffusivity of the first filter 40a higher than that of the second filter 40b, as described above, the non-detection is released from the first filter 40a and the second filter 40b and released to the gas detection element 10 side. The target gas can be reduced and the detection accuracy of the gas detection element 10 can be maintained.

  In addition, in the gas sensor 1 in this embodiment, the filter body 40 is comprised by two filters, the 1st filter 40a and the 2nd filter 40b, However, You may comprise by 3 or more filters. When the filter body 40 is composed of three or more filters, the particle size of the adsorbent of each filter and the porosity of each filter are adjusted so that the diffusibility becomes higher toward the opening 21 side of the case 20. The filter body 40 may be a single filter formed so that the gas diffusibility is higher on the opening 21 side of the case 20 than on the gas detection element 10 side. For example, the filter body 40 may be a single filter formed so that the gas diffusivity gradually increases from the gas detection element 10 side toward the opening 21 of the case 20.

  Further, the adsorbent for the first filter 40a and the second filter 40b is not limited to activated carbon, and may be silica gel, for example. Further, the first filter 40a and the second filter 40b may be formed of different adsorbents.

  FIG. 3 is a schematic cross-sectional view of the gas detection element 10 in the embodiment.

  As shown in FIG. 3, the gas detection element 10 includes a silicon substrate 101, a thermal insulation support layer 102, a heater layer 103, an electrical insulation layer 104, and a gas detection unit 105. Note that the size and thickness of each part of the gas detection element 10 shown in FIG. 3 are appropriately changed for the sake of explanation.

  The silicon substrate 101 has a through hole in a portion where the gas detection unit 105 is provided.

The heat insulating support layer 102 is formed on the upper surface of the silicon substrate 101 so as to cover the opening of the through hole of the silicon substrate 101 and have a diaphragm structure. The thermally insulating support layer 102 has a three-layer structure of a thermally oxidized SiO ₂ layer 102a, a CVD-Si ₃ N ₄ layer 102b, and a CVD-SiO ₂ layer 102c.

The thermally oxidized SiO ₂ layer 102 a is a heat insulating layer and makes it difficult to transfer heat generated in the heater layer 103 to the silicon substrate 101. Further, the thermally oxidized SiO ₂ layer 102a exhibits high resistance to plasma etching, and facilitates formation of a through hole of the silicon substrate 101 by plasma etching.

The CVD-Si ₃ N ₄ layer 102b is formed above the thermally oxidized SiO ₂ layer 102a. The CVD-SiO ₂ layer 102c is an electrically insulating layer and is formed on the upper side of the CVD-Si ₃ N ₄ layer 102b.

  The heater layer 103 is a Pt—W film, and is formed on the upper surface of the heat insulating support layer 102. The heater layer 103 is connected to the drive unit 2 of the gas detection device 100 through the lead terminal 50 and is supplied with power from the drive unit 2 to generate heat.

  The electrical insulating layer 104 is formed on the upper surface of the heat insulating support layer 102 so as to cover the heater layer 103. The electrically insulating layer 104 electrically insulates between the heater layer 103 and the sensing layer electrode 105b.

  The gas detection unit 105 includes a pair of bonding layers 105a, a pair of sensing layer electrodes 105b, a gas sensing layer 105c, and a gas selective combustion layer 105d.

  The bonding layer 105 a is, for example, a Ta film (tantalum film) or a Ti film (titanium film), and is formed on the upper surface of the electrical insulating layer 104. The bonding layer 105 a increases the bonding strength between the sensing layer electrode 105 b and the electrical insulating layer 104.

  The sensing layer electrode 105 b is, for example, a Pt film (platinum film) or an Au film (gold film), and is connected to the detection processing unit 3 of the gas detection device 100 through the lead terminal 50.

The gas sensing layer 105c is a SnO ₂ layer, and is formed on the upper surface of the electrical insulating layer 104 so as to cover at least a part of the pair of sensing layer electrodes 105b. Note that the gas sensing layer 105c may be formed using, for example, a metal oxide such as In ₂ O ₃ , WO ₃ , ZnO, or TiO ₂ as a main component.

The gas selective combustion layer 105d is a sintered body supporting at least one kind of catalyst such as palladium (Pd), platinum (Pt), or palladium oxide (PdO), and is a catalyst-supported Al ₂ O ₃ sintered material. The gas selective combustion layer 105d is formed on the upper surface of the electrical insulating layer 104 so as to cover the bonding layer 105a, the sensing layer electrode 105b, and the gas sensing layer 105c.

The gas selective combustion layer 105d can oxidize and remove the non-detection target gas by accelerating the combustion reaction of the reducing non-detection target gas having a stronger oxidation activity than the detection target gas. The gas selective combustion layer 105d increases the concentration of the detection target gas that reaches the gas sensing layer 105c, enabling detection with higher sensitivity. Note that the gas selective combustion layer 105d may be formed using, for example, a metal oxide such as Cr ₂ O ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , ZrO ₂ , SiO ₂ , or zeolite as a main component.

The gas sensing layer 105c is a SnO ₂ layer of an n-type metal oxide semiconductor and adsorbs oxygen on the surface. Oxygen has a strong electron-accepting property and adsorbs negative charges, so when oxygen is adsorbed on the surface of the gas sensing layer 105c, it takes in electrons from the gas sensing layer 105c. For this reason, when oxygen is adsorbed on the surface of the gas sensing layer 105c, the internal electron density decreases, the conductivity decreases, and the resistance increases.

When the gas sensing layer 105c on which oxygen is adsorbed is heated to about 300 ° C. to 500 ° C. by the heater layer 103, a combustion reaction such as CH ₄ , H ₂ , and CO of the detection target gas occurs. Oxygen (O ²⁻ ) adsorbed on the surface of the gas sensing layer 105c is consumed by the combustion reaction of these combustible gases, and the adsorbed oxygen electrons trapped in the adsorbed oxygen become free electrons in the gas sensing layer 105c. Returned to As a result, the gas sensing layer 105c has an increased internal electron density, an increased conductivity, and a low resistance.

The combustion reaction formula of the detection target gas (CH ₄ , H ₂ , CO) is as follows.

CH ₄ + 4O ²⁻ (ad) ⇒CO ₂ + 2H ₂ O + 8e
H ₂ + O ²⁻ (ad) ⇒H ₂ O + 2e
CO + O ²⁻ (ad) ⇒CO ₂ + 2e
The driving unit 2 of the gas detection device 100 intermittently supplies power to the heater layer 103 to heat the gas sensing layer 105c at a predetermined cycle. The detection processing unit 3 acquires an electric resistance value (hereinafter referred to as a sensor resistance value) of the gas sensing layer 105c through the sensing layer electrode 105b as a detection signal, and obtains the concentration of the detection target gas based on the sensor resistance value.

The gas selective combustion layer 105d covers the gas sensing layer 105c and is heated by the heater layer 103 to burn the non-detection target gas, thereby increasing the concentration of the detection target gas reaching the gas sensing layer 105c. For example, the gas selective combustion layer 105d selectively burns a high-boiling point hydrocarbon-based gas, a non-detection target gas such as ethanol or VOC, and allows a detection target gas such as CH _{4 to} pass therethrough.

  As described above, the gas sensor 1 adsorbs and removes the detection target gas in the first filter 40a and the second filter 40b. The non-detection target gas that has passed through the first filter 40a and the second filter 40b is burned in the gas selective combustion layer 105d. For this reason, in the gas sensor 1, the non-detection target gas that reaches the gas sensing layer 105c of the gas detection element 10 is reduced, and the detection target gas can be detected with high accuracy.

  As described above, in the gas sensor 1 according to the present embodiment, the non-detection target gas is adsorbed and removed by the filter body 40. Further, the filter body 40 has a gas diffusibility of the first filter 40a higher than that of the second filter 40b, and the gas diffusibility of the opening 20 side of the case 20 is higher than that of the gas detection element 10 side. For this reason, the non-detection target gas desorbed from the first filter 40a and the second filter 40b due to the temperature increase around the gas sensor 1 is suppressed from being released to the gas detection element 10 side and exhausted from the opening 21 of the case 20. The Therefore, the influence of the non-detection target gas due to the temperature change around the gas sensor 1 is reduced, and the gas detection element 10 can detect the detection target gas with high accuracy.

  Although the gas sensor and the gas detection device according to the embodiments have been described above, the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope of the present invention.

  For example, the gas detection element 10 provided in the gas sensor 1 may have a configuration different from the above-described embodiment as long as the detection target gas can be detected. Further, the gas sensor 1 may be provided with a gas detection element of a system different from the gas detection element 10 in the above-described embodiment.

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Drive part 3 Detection process part 10 Gas detection element 20 Case 21 Opening 40 Filter body 40a 1st filter 40b 2nd filter 100 Gas detection apparatus

Claims (7)

A case in which an opening through which gas flows is formed;
A gas detection element that is covered by the case and detects a detection target gas;
A filter body that is provided between the opening and the gas detection element and adsorbs a non-detection target gas;
The gas sensor according to claim 1, wherein the filter body has a higher gas diffusibility on the opening side than on the gas detection element side. The filter body includes a first filter that adsorbs the non-detection target gas, and a second filter that is stacked on the gas detection element side of the first filter and adsorbs the non-detection target gas,
The gas sensor according to claim 1, wherein the first filter has higher gas diffusibility than the second filter. The first filter includes a granular first adsorbent that adsorbs the non-detection target gas,
The second filter includes a granular second adsorbent that adsorbs the non-detection target gas,
The gas sensor according to claim 2, wherein an average particle diameter of the first adsorbent is larger than an average particle diameter of the second adsorbent. The first filter includes a granular first adsorbent that adsorbs the non-detection target gas,
The second filter includes a granular second adsorbent that adsorbs the non-detection target gas,
The gas sensor according to claim 2, wherein a minimum particle size of the first adsorbent is larger than a maximum particle size of the second adsorbent. The first filter includes a granular first adsorbent that adsorbs the non-detection target gas,
The second filter includes a granular second adsorbent that adsorbs the non-detection target gas,
The gas sensor according to claim 2, wherein the porosity of the first filter is larger than the porosity of the second filter.   The gas sensor according to any one of claims 3 to 5, wherein the first adsorbent and the second adsorbent are activated carbon. A gas sensor according to any one of claims 1 to 6;
A gas detection apparatus comprising: a detection processing unit that performs detection processing of the detection target gas based on a detection signal obtained from the gas sensor.

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