Gas concentration measuring device

Abstract

The gas concentration measuring device involved in the present invention is a gas concentration measuring device for measuring the concentration of aldehydes in an inspection object gas containing aldehydes and alcohols, and comprises: a first detection unit, which has a detected resistance value, which increases at a prescribed ratio as the concentration of the alcohol increases, and the detected resistance value does not increase even if the concentration of the aldehydes increases; and a second detection unit, which has a detected resistance value, which decreases at the same ratio as the change derived from the first alcohol as the concentration of the alcohol increases, and has a detected resistance value, which decreases at a prescribed ratio as the concentration of the aldehydes increases.

Description

Technical Field

[0001] The present invention relates to a gas concentration measuring device. Background Art

[0002] A gas concentration measuring device including a gas sensor for detecting a specific gas (chemical substance) contained in a gas to be detected (inspection target gas) is used in various applications in buildings, vehicles, and the like.

[0003] Examples of gases detected by the gas sensor include ethanol (C2H5OH), formaldehyde (HCHO), acetone (C3H6O), chloroform (CHCl3), and other volatile organic compounds (VOCs); methane (CH4), propane (C3H8), butane (C4H 10 ) and other flammable gases; toxic gases such as carbon monoxide (CO) and nitrogen oxides (NOx); and malodorous gases such as sulfur compounds (SOx). Among the above gases, VOCs contain highly toxic chemicals and are air pollutants that cause health damage such as headaches, dizziness, or nausea, and are also substances that cause sick home syndrome. In particular, formaldehyde, which is known as a type of aldehyde, is generated from homes and daily necessities and is considered to be a major cause of sick home syndrome and is considered a carcinogenic substance.

[0004] As one of the gas sensors for detecting the above-mentioned gases, there is a semiconductor sensor. Semiconductor sensors can react to a variety of gases with high sensitivity and are low in cost compared to other sensors such as electrochemical sensors. Therefore, the application of semiconductor sensors in VOC analysis and the like has been studied. At that time, semiconductor sensors reacted to a variety of VOCs with high sensitivity, and were prone to react to alcohols such as ethanol in addition to formaldehyde. Therefore, in order to measure formaldehyde separately from other VOCs such as alcohols, a gas concentration detection device that detects a variety of gases by having a plurality of gas sensors has been proposed.

[0005] As such a gas concentration measuring device, for example, a gas concentration measuring device has been proposed (see, for example, Patent Document 1), which includes: a first gas sensor for detecting a gas such as formaldehyde in a room, a second gas sensor for detecting an alcohol concentration in a room, and a control unit for calculating the gas concentration in the room by converting the concentration signals of the first gas sensor and the second gas sensor into electrical signals. In the gas concentration measuring device, the control unit measures the formaldehyde concentration based on the power difference between the concentration signal from the first gas sensor and the concentration signal from the second gas sensor.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-136291 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] However, in the gas concentration measuring device of Patent Document 1, when calculating the formaldehyde concentration, it is necessary to correct the concentration signal of the first gas sensor and perform calculation processing according to the case where the gas type is only formaldehyde, the case where the gas type is only ethanol, and the case where the gas type is a mixture of formaldehyde and ethanol. Therefore, the concentration of aldehydes such as formaldehyde cannot be simply measured.

[0011] An object of the gas concentration measuring device according to the present invention is to provide a gas concentration measuring device capable of simply and accurately measuring aldehydes.

[0012] Means used to solve problems

[0013] One form of the gas concentration measuring device involved in the present invention is a gas concentration measuring device for measuring the concentration of aldehydes in an inspection target gas containing aldehydes and alcohols, and comprises: a first detection unit, which has a detected resistance value, which increases at a prescribed ratio as the concentration of the alcohol increases, and the detected resistance value does not increase even if the concentration of the aldehydes increases; and a second detection unit, which has a detected resistance value, which decreases at the same ratio as the change derived from the first alcohol as the concentration of the alcohol increases, and has a detected resistance value, which decreases at a prescribed ratio as the concentration of the aldehydes increases.

[0014] Effects of the Invention

[0015] One aspect of the gas concentration measuring device according to the present invention can measure aldehydes simply and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a diagram showing an example of the configuration of a gas concentration measuring device according to an embodiment.

[0017] Figure 2 This is a diagram showing an example of the relationship between the gas concentration and the resistance value of the first detection unit.

[0018] Figure 3 This is a diagram showing another example of the relationship between the gas concentration and the resistance value in the first detection unit.

[0019] Figure 4 This is a conceptual cross-sectional view showing an example of the structure of a gas sensor.

[0020] Figure 5 This is a conceptual cross-sectional view showing an example of the structure of a gas sensor element constituting the gas sensor.

[0021] Figure 6 This is a diagram showing an example of the relationship between the gas concentration and the resistance value of the second detection unit.

[0022] Figure 7 This is a diagram for explaining an example of a control device.

[0023] Figure 8 It is an explanatory diagram showing an example of calculation of the synthetic resistance value of ethanol.

[0024] Fig. 9 It is an explanatory diagram showing an example of calculation of the synthetic resistance value of ethanol.

[0025] Fig.10 It is an explanatory diagram showing an example of calculation of the combined resistance value of formaldehyde.

[0026] Fig.11 It is an explanatory diagram showing an example of calculation of the combined resistance value of formaldehyde.

[0027] Fig.12 It is an explanatory diagram showing another example of calculation of the combined resistance value of formaldehyde.

[0028] Fig.13 It is an explanatory diagram showing another example of calculation of the combined resistance value of formaldehyde.

[0029] Fig.14 This is a diagram showing an example of another configuration of the gas concentration measuring device.

[0030] Fig.15 This is a graph showing the relationship between the ethanol concentration and the amount of change in resistance value of the gas sensor elements of Examples 1 to 5.

[0031] Fig.16 This is a graph showing the relationship between the formaldehyde concentration and the amount of change in resistance value of the gas sensor elements of Examples 1 to 5. DETAILED DESCRIPTION

[0032] The following is a detailed description of the embodiments of the present invention. In order to facilitate the understanding of the description, the same symbols are used for the same components in each drawing, and repeated descriptions are omitted. In addition, the scales of the components in the drawings are sometimes different from the actual ones. In addition, in this specification, the tilde "~" indicating a numerical range means that the numerical values ​​recorded before and after it are included as the lower limit and upper limit unless otherwise specified.

[0033] <Gas Concentration Measuring Device>

[0034] A gas concentration measuring device according to one embodiment is described. In this embodiment, as an example, the case of measuring the VOC contained in the air of the indoor space (space) of a building is described. Furthermore, the so-called VOC refers to aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, hexanal, heptanal, octanal, nonanal, glutaraldehyde, etc.; alcohols such as ethanol, methanol, n-butanol; acetone, toluene, xylene, ethyl acetate, chloroform, p-dichlorobenzene, etc. They are contained in, for example, chemicals, coatings, printing inks, adhesives, solvents, and combustion. In this embodiment, the case where the VOC measured by the gas concentration measuring device is formaldehyde and ethanol is described.

[0035] Figure 1 FIG. 1 is a diagram showing an example of the configuration of a gas concentration measuring device according to an embodiment. Figure 1 As shown, the gas concentration measuring device 1 includes a device body 10, a first detection unit 20, a second detection unit 30, a power supply unit 40, a resistance measuring unit 50, and a control device 60. The gas concentration measuring device 1 is installed in the same space S1 of a building or a vehicle. The first detection unit 20, the second detection unit 30, and the power supply unit 40 are connected in series via a conducting line L. The air in the space S1 contains formaldehyde and ethanol, which are VOCs, as the inspection target gas.

[0036] The device body 10 may be formed in a rectangular parallelepiped shape or the like and have a space inside. The device body 10 may be formed of, for example, synthetic resin or the like. Figure 1 As shown, the first detection unit 20 and the second detection unit 30 are arranged to be in contact with the space S1 on the surface of the device body 10. The device body 10 includes a power supply unit 40 and a resistance measuring unit 50 inside and a control device 60 outside.

[0037] The first detection unit 20 measures the concentration of ethanol (ethanol concentration) as the gas concentration in the inspection target gas, and functions as an ethanol concentration sensor. Figure 2 As shown in FIG. 1 , the first detection unit 20 has a change amount (a change amount derived from the first alcohol) ΔR11 derived from ethanol, in which the detected resistance value increases from resistance value R0 to resistance value R11 at a predetermined ratio as the ethanol concentration increases from zero concentration to concentration C1. Furthermore, in the first detection unit 20, if the ethanol concentration exceeds concentration C1, the detected resistance value decreases. In the first detection unit 20, the resistance value detected in the first detection unit 20 changes because the amount of oxygen around the first detection unit 20 changes with the ethanol concentration. Details of the change in the resistance value in the first detection unit 20 will be described later.

[0038] The resistance value detected by the first detection unit 20, that is, the resistance value R11 detected when the ethanol concentration is the concentration C1, may be maximized when the ethanol concentration is, for example, 0.1 ppm to 1.2 ppm.

[0039] like Figure 2 As shown, in the first detection unit 20, even if the concentration of formaldehyde as the gas concentration (formaldehyde concentration) increases from concentration zero to concentrations C1 and C2, the resistance value derived from formaldehyde detected does not increase. That is, in the first detection unit 20, when the formaldehyde concentration changes from concentration zero to concentration C2, the change in resistance derived from formaldehyde detected can be constant, preferably zero, regardless of the formaldehyde concentration.

[0040] In addition, if Figure 3 As shown in FIG. 1 , the first detection unit 20 may also have a change amount derived from formaldehyde (a change amount derived from the first aldehyde) ΔR12, in which the detected resistance value decreases at a predetermined ratio from the resistance value R0 to the resistance value R12 as the formaldehyde concentration increases from zero to the concentration C1. In addition, in the first detection unit 20, the resistance value detected when the formaldehyde concentration reaches a concentration higher than the concentration C1 (for example, the concentration C2) may decrease from the resistance value R12 at a ratio of the change amount ΔR12 derived from the first aldehyde.

[0041] A semiconductor sensor including a gas sensor element as a semiconductor element can be used as the first detection unit 20. An example of the configuration of the first detection unit 20 will be described. Figure 4 2 is a conceptual cross-sectional view showing an example of the structure of the first detection unit 20. Figure 4 As shown in FIG. 2 , the first detection unit 20 includes a housing 21, a sensor base 22, a gas sensor element 23, a metal mesh 24, and a terminal 25. The first detection unit 20 detects the inspection target gas G flowing from the space S1 into the housing 21. Figure 4 The arrow in represents the flow direction of the inspection object gas G. In addition, Figure 4 The configuration of the first detection unit 20 shown is an example configuration, and the configuration of the first detection unit 20 is not limited to this. Each configuration of the first detection unit 20 will be described.

[0042] The housing 21 is a substantially cylindrical body, and has an inlet 211 at one end thereof, the diameter of which is smaller than the diameter of the housing 21. The diameter of the inlet 211 is not limited to a specific size, and may be, for example, approximately several mm.

[0043] The sensor base 22 is formed in a disk shape and has a height difference at the end surface. The sensor base 22 includes: an insertion portion 221 whose outer diameter is substantially the same as the inner diameter of the housing 21; and a fixing portion 222 whose outer diameter is larger than the outer diameter of the housing 21. The insertion portion 221 is embedded in the other end of the housing 21. The fixing portion 222 is fixed to the other end of the housing 21 by welding or adhesive.

[0044] By fitting the insertion portion 221 of the sensor base 22 into the housing 21 , a detection space S2 is formed inside the housing 21 .

[0045] The gas sensor element 23 is arranged in the detection space S2 and fixed on the upper surface of the sensor base 22 ( Figure 4 The gas sensor element 23 is a thin film type semiconductor element. Figure 5 2 is a conceptual cross-sectional view showing an example of the structure of the gas sensor element 23. Figure 5 As shown, the gas sensor element 23 includes a substrate 231 , a heat insulating support layer 232 , a heating layer 233 , an insulating layer 234 , and a gas detection unit 235 .

[0046] The substrate 231 is a silicon substrate (Si substrate), but an alumina substrate, a sapphire substrate, a mica substrate, etc. may be used instead of the Si substrate. The substrate 231 has a through hole 231 a at a position where the gas detection unit 235 is formed in a plan view.

[0047] The heat insulating support layer 232 is disposed on the upper surface of the substrate 231 ( Figure 5 In the embodiment, the heat insulating support layer 232 is composed of a three-layer structure of a first SiO2 layer 232a, a Si3N4 layer 232b and a second SiO2 layer 232c.

[0048] The first SiO2 layer 232a can be formed by thermal oxidation at a thermal oxidation temperature of 800° C. to 1100° C. The first SiO2 layer 232a functions as a heat insulating layer and has a function of reducing heat capacity by preventing the heat generated by the heating layer 233 from being transferred to the Si substrate 11 side. In addition, the first SiO2 layer 232a shows high resistance to plasma etching, and a through hole can be easily formed on the substrate 231 by plasma etching.

[0049] The Si3N4 layer 232b can be formed on the upper surface of the first SiO2 layer 232a by chemical vapor deposition (CVD). Figure 5 in the upward direction).

[0050] The second SiO2 layer 232c can be formed by CVD method, and can improve the adhesion with the heating layer 233 while ensuring the insulation. The second SiO2 layer formed by CVD method can reduce the deformation in the insulating support layer 232 because of the small internal stress.

[0051] The heating layer 233 is disposed on the upper surface of the heat insulating support layer 232 ( Figure 5 The heating layer 233 is a thin film, for example, a Pt-W film containing Pt and W. The heating layer 233 is connected to the terminal 25 (refer to Figure 4 ) via terminal 25 (refer to Figure 4 ) is electrically connected to the power supply unit 40 and powered.

[0052] The insulating layer 234 is provided to cover the heat insulating support layer 232 and the heating layer 233. The insulating layer 234 may be formed of, for example, a SiO2 layer, etc. The insulating layer 234 can ensure electrical insulation between the heating layer 233 and the sensing layer electrode 235b, and can improve adhesion with the gas sensing layer 235c.

[0053] The gas detection unit 235 includes a pair of bonding layers 235a, a pair of sensing layer electrodes 235b, a gas sensing layer 235c, and an adsorption layer 235d.

[0054] The bonding layer 235a can be formed of, for example, a tantalum film (Ta film) or a titanium film (Ti film), and is provided on the insulating layer 234. The bonding layer 235a can improve the bonding strength between the sensor layer electrode 235b and the insulating layer 234.

[0055] The sensing layer electrode 235b can be formed of, for example, a platinum film (Pt film) or a gold film (Au film), etc. The sensing layer electrode 235b is provided on the pair of bonding layers 235a, and serves as a sensing electrode of the gas sensing layer 235c.

[0056] The gas sensing layer 235 c is formed on the insulating layer 234 in a manner connecting a pair of sensing layer electrodes 235 b .

[0057] The gas sensing layer 235c is as follows Figure 2 As shown in FIG. 1 , the gas sensing layer 235c can be formed of a material having a change amount ΔR11 derived from the first alcohol, in which the detected resistance value increases as the ethanol concentration increases, and in which formaldehyde is hardly detected, and the detected resistance value does not increase even when the concentration of aldehydes increases. Figure 2 As shown in FIG. 1 , the amount of resistance change due to formaldehyde is constant, or a material such as Figure 3As shown, the gas sensing layer 235c is formed of a material having a change amount ΔR12 due to the first aldehydes, which decreases as the formaldehyde concentration increases. As a material for forming the gas sensing layer 235c, for example, a metal oxide semiconductor containing SnO2 and a subsidiary component can be used.

[0058] The gas sensing layer 235c may contain, as a main component, a metal oxide such as In2O3, WO3, ZnO or TiO2 in addition to SnO2.

[0059] As the auxiliary component, Fe, Al, Si, Ag, etc. can be used. They can be used alone or in combination of two or more. Among them, from the viewpoint of easily adjusting the size of the change amount ΔR11 derived from the first alcohol, Fe, Al and Si are preferred, and Fe is more preferred.

[0060] The content of the auxiliary component is the size of the change ΔR11 derived from the first alcohol and can be appropriately designed, but in the gas sensing layer 235c, relative to SnO2, it is preferably 1.0 mol% to 10.0 mol% of the auxiliary component, more preferably 2.0 mol% to 8.0 mol% of the auxiliary component, and further preferably 4.0 mol% to 6.0 mol% of the auxiliary component.

[0061] The gas sensor layer 235c may also be formed into a porous structure or a columnar structure, thereby increasing the specific surface area of ​​the gas sensor layer 235c, thereby increasing the contact area with the inspection target gas and improving the sensitivity.

[0062] The adsorption layer 235 d is provided so as to cover the surfaces of the insulating layer 234 , the pair of bonding layers 235 a , the pair of sensing layer electrodes 235 b , and the gas sensing layer 235 c .

[0063] The adsorption layer 235d can be made of a sintered body in which at least one of the noble metal elements such as palladium (Pd) and platinum (Pt) is supported as a catalyst on a carrier having a porous structure. As a carrier, for example, metal oxides such as aluminum oxide (Al2O3), chromium oxide (Cr2O3), iron oxide (Fe2O3), nickel oxide (Ni2O3), zirconium oxide (ZrO2), silicon dioxide (SiO2), and zeolite can be used. They can be used alone or in combination of two or more. Carriers such as aluminum oxide can increase the area of ​​contact between the inspection object gas passing through the hole and the catalyst because they have a porous structure. In addition, when the atmosphere contains a reducing gas with a stronger oxidizing activity than the inspection object gas in addition to the inspection object gas, the combustion reaction of the reducing gas can be promoted, thereby improving the selectivity of the inspection object gas. As a result, the gas concentration of the inspection object gas reaching the gas sensing layer 235c can be increased, and the sensitivity of the gas sensor element 23 can be further improved.

[0064] The gas sensor element 23 has a diaphragm structure to provide high thermal insulation and low heat capacity. In addition, the gas sensor element 23 may not have a diaphragm structure.

[0065] like Figure 4 As shown, the metal mesh 24 is provided on the inlet 211. The outer diameter of the metal mesh 24 has a disk-like shape having a diameter substantially the same as the diameter of the inlet 211. The metal mesh 24 is a stainless steel mesh, and the mesh size of the metal mesh 24 is about several mm, and the opening ratio can be any size as long as the inspection target gas can flow in and out of the detection space S2.

[0066] like Figure 4 As shown in FIG. 1 , the terminal 25 is an electrode protruding from the sensor base 22 and connected to the sensor base 22 by a conducting wire L (see FIG. Figure 1 ) is connected to the second detection unit 30 (refer to Figure 1 ) and the power supply unit 40 (refer to Figure 1 ) Figure 4 As shown, the first detection unit 20 includes a plurality of ( Figure 4 The terminals 25a, 25b, 25c and 25d are used to connect the power supply unit 40 (see Figure 1 ) and the second detection unit 30 (refer to Figure 1 The terminals 25c and 25d are used to drive the heating layer 233 (see Figure 5 ) electrodes.

[0067] Terminals 25a, 25c and 25d are connected by electric wires L (see Figure 1 ) is connected to the power supply unit 40 (refer to Figure 1 ) on the terminal 25b through the electric wire L (refer to Figure 1 ) is connected to the second detection unit 30 (refer to Figure 1 )superior.

[0068] like Figure 4 As shown in FIG. 2 , the first detection unit 20 includes a gas sensor element 23 in a housing 21. In the first detection unit 20, the resistance value of the gas sensor element 23 changes with the amount of oxygen around the gas sensor element 23. Figure 5 As shown, the gas sensor element 23 has a gas sensing layer 235c. When oxygen adsorbed on the surface of the gas sensing layer 235c reacts with ethanol (surface reaction), oxygen is desorbed, but ethanol takes free electrons from the gas sensing layer 235c and converts them into ions (C2H5O - As a result, the free electrons on the surface of the gas sensing layer 235c are relatively reduced, and the resistance value of the gas sensor element 23 increases (see Figure 2). The concentration of ethanol in the air can be calculated from the increase in resistance. However, ethanol has a larger volume than oxygen and tends to be easily desorbed. Therefore, if ethanol is adsorbed in the form of ions to a certain concentration, the ethanol ions (C2H5O - ) is separated from the gas sensing layer 235c, and electrons are provided to the surface of the gas sensing layer 235c. Therefore, the free electrons existing on the surface of the gas sensing layer 235c are relatively increased, thereby reducing the resistance value of the gas sensor element 23 (refer to Figure 2 ).

[0069] The second detection unit 30 measures the formaldehyde concentration and the ethanol concentration in the air, respectively, and functions as a formaldehyde concentration sensor and an ethanol concentration sensor. Figure 6 As shown in FIG. 1 , as the ethanol concentration increases from zero to C1, the detected resistance value decreases at a predetermined ratio due to the change amount of ethanol (the change amount due to the second alcohol) ΔR21. The change amount due to the second alcohol ΔR21 is proportional to the change amount due to the first alcohol ΔR11 (refer to FIG. Figure 2 ) In the second detection unit 30, the resistance value detected from the ethanol concentration to a concentration higher than the concentration C1 (for example, the concentration C2) may also be reduced from the resistance value R21 in a ratio of the change amount ΔR21 derived from the second alcohol.

[0070] The second detection unit 30 has a change amount due to formaldehyde (a change amount due to the second aldehyde) ΔR22 in the detected resistance value that decreases at a predetermined ratio as the formaldehyde concentration increases from zero to C1. In addition, in the second detection unit 30, the resistance value detected when the formaldehyde concentration reaches a concentration higher than C1 (e.g., C2) may decrease from the resistance value R22 at a ratio of the change amount ΔR22 due to the second aldehyde.

[0071] The second detection unit 30 may be a semiconductor sensor including a gas sensor element as a semiconductor element. Figure 4 The gas sensing layer 235c (see Figure 5 ) has the same structure as the first detection unit 20 except that the material is changed. Figure 4 and Figure 5 , only the gas sensor layer 235c constituting the second detection unit 30 is described.

[0072] The second detection unit 30 is similar to the first detection unit 20. Figure 4 As shown, a gas sensor element 23 is provided in the housing 21. Figure 5 As shown, the gas sensor element 23 has a gas sensing layer 235c.

[0073] The gas sensing layer 235c of the second detection unit 30 is as follows Figure 6 As shown in FIG. 1 , the gas sensing layer 235c of the second detection unit 30 may be formed of a material having a change amount ΔR21 derived from the second alcohol and a change amount ΔR22 derived from the second aldehyde, which decreases the detected resistance value as the ethanol concentration and the formaldehyde concentration as the gas concentration increase from the concentration zero to the concentration C2. As the material forming the gas sensing layer 235c of the second detection unit 30, for example, a metal oxide semiconductor containing SnO2 may be used.

[0074] like Figure 4 As shown, the second detection unit 30 has a gas sensor element 23 in the housing 21. In the second detection unit 30, the resistance value of the gas sensor element 23 changes with the amount of oxygen around the gas sensor element 23. Figure 5 As shown in the figure, the gas sensor element 23 has a gas sensing layer 235c, and oxygen adsorbed on the surface of the gas sensing layer 235c reacts with formaldehyde or ethanol (surface reaction), and oxygen is desorbed. 2- ) is separated from the gas sensing layer 235c, free electrons are provided to the gas sensing layer 235c. Therefore, the amount of oxygen adsorbed on the surface of the gas sensing layer 235c is relatively reduced, and the amount of free electrons provided to the gas sensing layer 235c is increased, thereby reducing the resistance value of the gas sensor element 23. The concentration of formaldehyde and ethanol in the air can be calculated from the change in the resistance value.

[0075] The terminal 25a (see Figure 4 ) through the power line L (refer to Figure 1 ) is connected to the terminal 25b of the first detection unit 20 (refer to Figure 4 ) on the second detection unit 30, the terminals 25b, 25c and 25d (refer to Figure 4 ) through the power line L (refer to Figure 1 ) is connected to the power supply unit 40 (refer to Figure 1 )superior.

[0076] like Figure 1 As shown in FIG. 1 , the first detection unit 20 and the second detection unit 30 are connected in series via the conducting line L in the device body 10. That is, the terminal 25a (see FIG. 1 ) of the first detection unit 20 is connected to the second detection unit 30 in series. Figure 4 ) is connected to the power supply unit 40 through the power line L, and the terminal 25b of the first detection unit 20 (refer to Figure 4 ) is connected to the terminal 25a of the second detection unit 30 through the conducting wire L (refer to Figure 4 ) on the terminal 25b of the second detection unit 30 (refer to Figure 4 ) is connected to the power supply unit 40 (refer to Figure 4)superior.

[0077] The power supply unit 40 is as follows Figure 1 As shown in the figure, it is provided in the device body 10, and supplies power to the first detection part 20 and the second detection part 30. One electrode of the power supply part 40 is connected to the first detection part 20, and the other electrode is connected to the second detection part 30, and the power supply part 40 is connected to the first detection part 20 and the second detection part 30 in series.

[0078] like Figure 1 As shown in the figure, the resistance measuring unit 50 includes a first resistance measuring unit 50A for calculating the resistance value of the first detection unit 20 and a second resistance measuring unit 50B for calculating the resistance value of the second detection unit 30. The first resistance measuring unit 50A connects a pair of resistance units 50a to the conducting line L in a manner that sandwiches the first detection unit 20, and the second resistance measuring unit 50B connects a pair of resistance units 50a to the conducting line L in a manner that sandwiches the second detection unit 30. That is, the resistance measuring unit 50 calculates the gas sensing layer 235c (refer to Figure 5 ) is the same as the resistance value of the gas sensor layer 235c of the second detection unit 30 measured in the second resistance measurement unit 50B (refer to Figure 5 ) is the total resistance value obtained by adding up the resistance values ​​of the other resistance values.

[0079] The resistance measuring unit 50 and the control unit 61 (see Figure 7 ) is electrically connected and can be controlled by the control unit 61 (refer to Figure 7 ) reads the resistance value of the first detection portion 20 measured by the first resistance measurement portion 50A and the resistance value of the second detection portion 30 measured by the second resistance measurement portion 50B.

[0080] The gas concentration measuring device 1 may include a resistance measuring device such as an amplifier circuit and an analog-to-digital (AD) converter in addition to the power supply unit 40 and the resistance measuring unit 50 in the device body 10. In this case, the resistance measuring device may be provided in a manner connected in series with the first detection unit 20, the second detection unit 30, and the power supply unit 40.

[0081] like Figure 7 As shown, the control device 60 includes a control unit 61 , an operation unit 62 connected to the control unit 61 , and a display unit 63 .

[0082] The control unit 61 is connected to the power supply unit 40 and the display unit 63 so as to be able to control them.

[0083] The control unit 61 has a storage device for storing a control program and various storage information and a computing device that operates based on the control program. The storage device includes a RAM, a ROM, a memory, etc. The computing device includes a CPU, etc. The control unit 61 is implemented by the computing device reading and executing the control program stored in the storage device.

[0084] The storage means provided in the control unit 61 preferably stores information indicating the relationship between the ethanol concentration and the resistance value and the amount of change in the resistance value (the amount of change ΔR11 derived from the first alcohol and the amount of change ΔR21 derived from the second alcohol), and the relationship between the formaldehyde concentration and the resistance value and the amount of change in the resistance value (the amount of change ΔR12 derived from the first aldehyde and the amount of change ΔR22 derived from the second aldehyde). The control unit 61 can determine the formaldehyde concentration or the ethanol concentration by comparing the stored value stored in the storage means with the measured value measured by the resistance measuring unit 50.

[0085] The control unit 61 receives the measurement results of the resistance measuring unit 50 (the first resistance measuring unit 50A and the second resistance measuring unit 50B). In the present embodiment, the control unit 61 receives the signals of the measurement results of the ethanol concentration measured in the first resistance measuring unit 50A and the formaldehyde concentration and the ethanol concentration measured in the second resistance measuring unit 50B. The control unit 61 calculates the resistance value of the first detection unit 20 and the resistance value of the second detection unit 30 based on the signals received from the first resistance measuring unit 50A and the second resistance measuring unit 50B, and calculates the change amount of the resistance value of the first detection unit 20 detected in the first resistance measuring unit 50A and the change amount of the resistance value of the second detection unit 30 detected in the second resistance measuring unit 50B. Then, the control unit 61 adds up the resistance value of the first detection unit 20 and the resistance value of the second detection unit 30, and calculates the combined change amount obtained by adding up the change amount of the resistance value detected in the first detection unit 20 and the change amount of the resistance value detected in the second detection unit 30. The control unit 61 can determine the obtained combined change amount as the change amount of the resistance caused by formaldehyde and calculate the formaldehyde concentration.

[0086] The method of calculating the formaldehyde concentration from the synthetic change amount is described in detail. When calculating the synthetic change amount, the synthetic resistance of the total resistance derived from ethanol and the resistance derived from formaldehyde measured by the first detection unit 20 and the second detection unit 30 is obtained.

[0087] The total resistance of the resistance derived from ethanol measured by the first detection unit 20 and the second detection unit 30 will be described. Figure 8 As shown in FIG. 1 , if the change in resistance value due to ethanol, ΔR11, due to the first alcohol, and the change in resistance due to the second alcohol, ΔR21, due to ethanol concentration, are added together, the change in resistance due to ethanol is substantially zero up to the concentration C1. Fig. 9As shown in FIG. 1 , when the ethanol concentration is less than or equal to the concentration C1, the combined resistance R1 derived from the ethanol when the resistance value detected by the first detection unit 20 and the resistance value detected by the second detection unit 30 are added together is total is roughly constant.

[0088] The combined resistance of the resistance derived from formaldehyde measured by the first detection unit 20 and the second detection unit 30 will be described. Fig.10 As shown, the resistance value derived from formaldehyde in the first detection portion 20 is constant, and the amount of change in resistance value is zero, and the amount of change ΔR22 derived from the second aldehyde in the resistance value derived from formaldehyde in the second detection portion 30 decreases at a predetermined ratio. Fig.11 As shown in FIG. 1 , the combined resistance R2 derived from formaldehyde when the resistance value of the first detection unit 20 and the resistance value of the second detection unit 30 are added together is total From the concentration of zero to the concentration of C1, the resistance decreases in proportion to the change ΔR22 derived from the second aldehyde. total In the process from concentration C1 to concentration C2, the concentration also decreases in proportion to the change amount ΔR22 derived from the second aldehyde.

[0089] In addition, if Fig.12 As shown, the change amount ΔR12 of the resistance value derived from formaldehyde in the first detection portion 20 due to the first aldehyde is reduced at a predetermined ratio, and the change amount ΔR22 of the resistance value derived from formaldehyde in the second detection portion 30 due to the second aldehyde is reduced at a predetermined ratio. Fig.13 As shown in FIG. 1 , the combined resistance R2 derived from formaldehyde when the resistance value of the first detection unit 20 and the resistance value of the second detection unit 30 are added together is total From the concentration zero to the concentration C1, the resistance R2 decreases at a ratio equal to the sum of the changes ΔR12 and ΔR22 from the second aldehyde. total In the process from the concentration C1 to the concentration C2, the concentration decreases by a ratio ΔR22 obtained by summing the amounts of change ΔR12 and ΔR22 derived from the second aldehydes.

[0090] Therefore, when the combined change is calculated, the change in resistance due to ethanol calculated by adding the change ΔR11 due to the first alcohol and the change ΔR21 due to the second alcohol is substantially zero, and thus the combined change shows only the change in resistance due to formaldehyde.

[0091] The control unit 61 may use a relationship diagram showing the relationship between the ethanol concentration and the resistance value and the amount of change in the resistance value (the amount of change ΔR11 derived from the first alcohol and the amount of change ΔR21 derived from the second alcohol) and the relationship between the formaldehyde concentration and the resistance value and the amount of change in the resistance value (the amount of change ΔR12 derived from the first aldehyde and the amount of change ΔR22 derived from the second aldehyde) stored in advance in the storage device. The control unit 61 can obtain the formaldehyde concentration corresponding to the combined amount of change by comparing the measured value with the recorded value.

[0092] The control unit 61 can divide the resistance value derived from ethanol or formaldehyde stored in the storage means by the resistance values ​​R01 and R02 obtained when the ethanol concentration and the formaldehyde concentration are 0 ppm, respectively, as shown in the following equations (1) and (2), and store the obtained values ​​as ethanol sensitivity and formaldehyde sensitivity. The control unit 61 can obtain the ethanol concentration and formaldehyde concentration corresponding to the synthetic change amount by comparing the measured value with the recorded value using a relationship diagram showing the relationship between the ethanol concentration and the ethanol sensitivity and a relationship diagram showing the relationship between the formaldehyde concentration and the formaldehyde sensitivity.

[0093] Ethanol sensitivity (change in resistance) = resistance due to ethanol / resistance R01 (1) Formaldehyde sensitivity (change in resistance) = resistance due to formaldehyde / resistance R02 (2)

[0094] like Figure 7 As shown, the operation unit 62 is electrically connected to the control unit 61 and controls the control unit 61 .

[0095] The display unit 63 displays the calculated formaldehyde concentration, etc. As the display unit 63, a liquid crystal display or the like can be adopted.

[0096] Thus, the gas concentration measuring device 1 includes the first detection unit 20 and the second detection unit 30. In the gas concentration measuring device 1, if the synthetic variation is calculated by summing the variation of the resistance value of the first detection unit 20 and the variation of the resistance value of the second detection unit 30, the variation ΔR11 of the first detection unit 20 derived from the first alcohol and the variation ΔR21 of the second detection unit 30 derived from the second alcohol are summed. The variation of the resistance derived from ethanol calculated by summing them can be set to substantially zero. In the gas concentration measuring device 1, since the variation ΔR22 derived from the second aldehyde of the second detection unit 30 is detected, the synthetic variation shows only the variation of the resistance derived from formaldehyde. Therefore, the gas concentration measuring device 1 can stably obtain only the variation of the resistance derived from formaldehyde from the synthetic variation by using a relationship diagram indicating the relationship between the formaldehyde concentration and the synthetic variation obtained in advance. Therefore, the control device 60 can calculate only the formaldehyde concentration from the synthetic variation.

[0097] Therefore, even if the inspection target gas contains ethanol or the like, the gas concentration measuring device 1 can reduce the influence of ethanol, and thus can measure the formaldehyde concentration simply and with higher accuracy.

[0098] Since the gas concentration measuring device 1 has the above-mentioned characteristics, it can be effectively used for VOC analysis. Therefore, when analyzing VOC, even if the atmosphere contains ethanol in addition to formaldehyde, the gas concentration measuring device 1 can simply measure only formaldehyde, so it can be effectively used for VOC analysis in indoor environments and VOC analysis contained in human breath. Therefore, the gas concentration measuring device 1 can be effectively used for VOC analysis, and is therefore suitable for preventing sick house syndrome and managing health conditions.

[0099] The gas concentration measuring device 1 includes the control device 60, and can calculate the combined change amount by summing the change amount of the resistance value of the first detection unit 20 and the change amount of the resistance value of the second detection unit 30. Since the change amount of the resistance derived from ethanol calculated by summing the change amount ΔR11 derived from the first alcohol and the change amount ΔR21 derived from the second alcohol can be set to zero, the combined change amount can calculate only the change amount of the resistance derived from formaldehyde. Therefore, the control device 60 can calculate the change amount of the resistance derived from formaldehyde from the combined change amount by using a relationship diagram indicating the relationship between the formaldehyde concentration and the combined change amount obtained in advance, so that the formaldehyde concentration can be calculated from the combined change amount.

[0100] In the gas concentration measuring device 1, the first detection unit 20 can set the amount of change in resistance due to the concentration of aldehydes to zero. Therefore, when the gas concentration measuring device 1 calculates the combined amount of change by adding the amount of change in the resistance value of the first detection unit 20 and the amount of change in the resistance value of the second detection unit 30, it can detect only the amount of change ΔR22 due to the second aldehydes, so that only the amount of change in resistance due to formaldehyde can be accurately calculated from the combined amount of change. Therefore, the gas concentration measuring device 1 can more accurately calculate only the formaldehyde concentration from the combined amount of change.

[0101] The gas concentration measuring device 1 can maximize the resistance value detected by the first detection unit 20 when the ethanol concentration is 0.1 ppm to 1.2 ppm. Thus, even if ethanol is contained in the atmosphere at a low concentration range of 0.1 ppm to 1.2 ppm, the formaldehyde concentration can be stably measured.

[0102] The gas concentration measuring device 1 can be arranged in the device body 10 in a state where the first detection unit 20 and the second detection unit 30 are connected in series via the conducting line L. Thus, for example, it is sufficient to provide only one AD converter or the like in the device body 10 that converts the detection signals measured in the first detection unit 20 and the second detection unit 30 into a resistance value, so that the configuration of the gas concentration measuring device 1 can be simplified while reducing the manufacturing cost.

[0103] The gas concentration measuring device 1 can form the first detection part 20 by the gas sensing layer 235c containing SnO2 and any one or more of the accessory components of Fe, Al, Si and Ag, and form the second detection part 30 by the gas sensing layer 235c containing SnO2. Thus, only the concentration of ethanol can be measured by the first detection part 20, and the concentration of formaldehyde and ethanol can be measured by the second detection part 30, so the concentration of formaldehyde contained in the atmosphere can be measured more accurately.

[0104] The gas concentration measuring device 1 can use the gas sensor layer 235c containing 1.0 mol% to 10.0 mol% of the accessory component relative to SnO2 in the first detecting portion 20. As a result, the first detecting portion 20 can adjust the change amount ΔR11 of the first alcohol derived from ethanol detected in the first detecting portion 20 to an arbitrary size, and thus can compare the size with the change amount ΔR21 of the second alcohol derived from ethanol detected in the second detecting portion 30. Therefore, the change amount ΔR11 of the first alcohol detected in the first detecting portion 20 can be easily adjusted so that the difference with the change amount ΔR21 of the second alcohol detected in the second detecting portion 30 is zero. Therefore, the gas concentration measuring device 1 can calculate only the change amount of resistance derived from formaldehyde with high accuracy based on the combined change amount obtained by adding the change amount of resistance value of the first detecting portion 20 and the change amount of resistance value of the second detecting portion 30, and can more accurately measure the concentration of formaldehyde contained in the atmosphere.

[0105] As described above, the case where the gas concentration measuring device 1 measures the formaldehyde concentration in the atmosphere only in the space S of the building has been described, but the gas concentration measuring device 1 can also simply measure the formaldehyde concentration in the atmosphere only as described above. Therefore, the gas concentration measuring device 1 can be effectively used to measure the formaldehyde concentration in the air in spaces other than the indoor space of the building, such as the interior of a vehicle, the interior of a train, and the cabin of an airplane, by being installed in these spaces.

[0106] Furthermore, the gas concentration measuring device 1 can measure aldehydes such as acetaldehyde other than formaldehyde and alcohols such as methanol other than ethanol as inspection target gases, and can be effectively used for analysis of VOCs other than aldehydes and alcohols.

[0107] The gas concentration measuring device 1 can also be effectively used for methane (CH4), propane (C3H8) and butane (C4H 10 ) and other combustible gases, poisonous gases such as carbon monoxide (CO) and nitrogen oxides (NOx), malodorous gases such as sulfur compounds (SOx), etc. In this case, the gas concentration measuring device 1 can be used, for example, for the detection of gas leakage and incomplete combustion.

[0108] (Variation Example)

[0109] Furthermore, in the present embodiment, the amount of change ΔR22 derived from the second aldehydes detected in the second detection unit 30 may be increased at a predetermined ratio as the formaldehyde concentration increases.

[0110] In the present embodiment, the first detection unit 20 and the second detection unit 30 may be connected to the power supply unit 40 via the conducting line L in parallel.

[0111] In the present embodiment, the first detection unit 20 and the second detection unit 30 are provided in the device body 10 , but only one of them may be provided in the device body 10 and the other may be provided in the space S1 .

[0112] In this embodiment, the pair of resistors 50a of the resistance measuring unit 50 may be provided so as to be connected to the conducting line L across the first detecting unit 20 and the second detecting unit 30. Fig.14 As shown, the first detection unit 20 and the second detection unit 30 can be connected in series, and the pair of resistors 50a of the first resistance measuring unit 50A can be connected to the conducting line L in a manner that straddles the first detection unit 20 and the second detection unit 30. Thus, the gas concentration measuring device 1 can measure the change in the combined resistance of the first detection unit 20 and the second detection unit 30 as the change in resistance due to the concentration of formaldehyde by the control device 60, so that only the concentration of formaldehyde can be stably calculated.

[0113] In this embodiment, the control device 60 may be provided in the device body 10 , or at least one of the control unit 61 , the operation unit 62 , and the display unit 63 of the control device 60 may be provided in the device body 10 .

[0114] Example

[0115] Hereinafter, the embodiment will be described in more detail by showing examples, but the embodiment is not limited to these examples.

[0116] <Example 1>

[0117] [Production of semiconductor sensors]

[0118] A semiconductor-type gas sensor element formed of a tin oxide (SnO2) thin film is prepared.

[0119] [Determination of ethanol concentration and formaldehyde concentration]

[0120] The gas sensor element was placed in a container having a space formed therein, and the resistance value R0 (unit: Ω) when the gas sensor element was placed in the atmosphere (the concentration of ethanol gas and formaldehyde gas was 0 ppm) was determined.

[0121] Next, ethanol gas was supplied into the container as the detection target gas, and the gas sensor element measured resistance values ​​when the ethanol gas concentration was approximately 0.01 ppm, approximately 0.04 ppm, approximately 0.1 ppm, and approximately 1.0 ppm, respectively, to measure resistance value R1 (unit: Ω).

[0122] Next, formaldehyde gas was supplied into the container as the detection target gas, and the resistance value R2 (unit: Ω) was measured by the gas sensor element when the formaldehyde concentration in the container was 0.04 ppm, 0.1 ppm, and 1.0 ppm.

[0123] The resistance values ​​R1 and R2 were divided by the resistance value R0 obtained when the concentrations of the ethanol gas and the formaldehyde gas were 0 ppm, and the changes in the respective resistance values ​​were obtained as the ethanol sensitivity and the formaldehyde sensitivity. Fig.15 FIG. 2 shows the relationship between the ethanol concentration and the change in resistance value of a gas sensor element formed of SnO2. Fig.16 The relationship between formaldehyde concentration and resistance change is shown in FIG. The magnitude of the resistance change indicates the gas sensitivity. A larger resistance change indicates a higher gas sensitivity. A smaller resistance change indicates a lower gas sensitivity. In the case of no resistance change, it means that no gas is detected.

[0124] Ethanol sensitivity (change in resistance) = resistance R1 / resistance R0

[0125] Formaldehyde sensitivity (change in resistance) = resistance R2 / resistance R0

[0126] <Examples 2~6>

[0127] In Example 1, the same procedures as in Example 1 were followed except that tin oxide with added iron (Fe) (Fe: 1 mol%), tin oxide with added iron (Fe) (Fe addition: 2 mol%), tin oxide with added aluminum (Al) (Al addition: 2 mol%), tin oxide with added silicon (Si) (Si addition: 4 mol%), and tin oxide with added silicon (Si) (Si addition: 8 mol%) were used as materials for forming the gas sensor element. Fig.15The relationship between the ethanol concentration and the change in resistance value of the gas sensor element is shown in FIG. Fig.16 The relationship between the formaldehyde concentration and the amount of change in the resistance value is shown in FIG.

[0128] Example 1, Example 5 and Example 6 Fig.15 As shown in FIG. 1 , the resistance value tends to decrease as the ethanol concentration increases. Fig.16 As shown, the formaldehyde concentration hardly changes until the formaldehyde concentration reaches 0.04 ppm, and a decreasing tendency is confirmed when the formaldehyde concentration exceeds 0.04 ppm.

[0129] Example 2~Example 4 Fig.15 As shown in FIG. 1 , until the ethanol concentration reaches 0.1 ppm, the change in resistance value increases with the increase in ethanol concentration. Fig.16 As shown, until the formaldehyde concentration reaches 0.1 ppm, the formaldehyde concentration does not change or hardly changes, and it is confirmed that the resistance value is substantially constant.

[0130] From Examples 1, 5, and 6, it is confirmed that the sensitivity of ethanol can be adjusted by adjusting the amount of Si added. Therefore, as long as the person whose sensitivity of ethanol is adjusted and any one of Examples 2 to 4 is used as the first detection unit or the second detection unit, the change in the ethanol concentration obtained by the first detection unit 20 and the second detection unit 30 can be made substantially zero, so that only formaldehyde can be measured.

[0131] Therefore, it can be considered that the gas concentration measuring device according to one embodiment has a simple structure and can measure only the formaldehyde concentration with high accuracy even at a low ethanol concentration of about 0.1 ppm or less.

[0132] As described above, the embodiments are described, but the above embodiments are presented as examples, and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other ways, and various combinations, omissions, substitutions, changes, etc. can be made without departing from the scope of the main purpose of the invention. These embodiments and their variations are included in the scope and main purpose of the invention, and are also included in the invention described in the claims and their equivalents.

[0133] This application claims priority based on Japanese Patent Application No. 2019-188123 filed in the Japan Patent Office on October 11, 2019, and the entire contents of Japanese Patent Application No. 2019-188123 are cited in this application.

[0134] Explanation of symbols

[0135] 1-Gas concentration measuring device

[0136] 10-Device body

[0137] 20-1st Inspection Department

[0138] 235-Gas Detection Department

[0139] 235c-Gas sensing layer

[0140] 30-Second Detection Unit

[0141] 40-Power supply department

[0142] 50-Resistance measurement unit

[0143] 50A - 1st resistance measuring unit

[0144] 50B - Second resistance measuring unit

[0145] 60 - Control device

[0146] 61 - Control Department

[0147] G-Inspection target gas

[0148] S1 - Space

[0149] S2-Detection Space

[0150] ΔR11 - Change from the first alcohol

[0151] ΔR12 - Change from the first aldehyde

[0152] ΔR21 - Change from the second alcohol

[0153] ΔR22 - Change from the second aldehyde

Claims

1. A gas concentration measuring device for measuring the concentration of aldehydes in a test target gas containing aldehydes and alcohols, comprising: a first detection unit having a resistance value detected by a change amount derived from the first alcohol, which increases at a predetermined ratio as the concentration of the alcohol increases, and the resistance value detected does not increase even if the concentration of the aldehydes increases; and a second detection unit having a resistance value detected by a change amount derived from the second alcohol, which decreases at the same ratio as the change amount derived from the first alcohol as the concentration of the alcohol increases, and the resistance value detected by a change amount derived from the second alcohol, which decreases at a predetermined ratio as the concentration of the aldehyde increases. A low change originating from aldehydes; and a control unit, which adds up the change in resistance value detected by the first detection unit and the change in resistance value detected by the second detection unit, thereby setting the change in resistance originating from alcohols to zero, judging the obtained synthetic change as the change in resistance originating from the aldehydes, and calculating the concentration of the aldehydes from the synthetic change; the first detection unit contains SnO2 and one or more accessory components selected from Fe, Al, and Si, the concentration of the accessory components is 1.0 mol% to 10.0 mol% relative to SnO2, and the second detection unit contains SnO2.

2. The gas concentration measuring device according to claim 1, wherein: The first detection unit and the second detection unit are connected in series, and the gas concentration measuring device has a control unit that calculates the concentration of the aldehydes by taking the change in the combined resistance of the first detection unit and the second detection unit as the change in resistance derived from the concentration of the aldehydes.

3. The gas concentration measuring device according to claim 1 or 2, wherein: The amount of change in resistance of the first detection portion caused by the concentration of the aldehydes is zero.

4. The gas concentration measuring device according to claim 1 or 2, wherein: The resistance value detected by the first detection unit is maximum when the alcohol concentration is 0.1 ppm to 1.2 ppm.

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