JP2004150811A - Carbon monoxide sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly precisely detect a concentration of carbon monoxide in measurement object gas, improve workability in manufacturing and miniaturize the whole body. <P>SOLUTION: This carbon monoxide sensor is formed with an oxidation catalyst layer 27, an inside electrode 29, a solid electrolyte layer 28, an outside electrode 30, a hydrogen oxidation catalyst layer 31, a porous layer and a minute layer 33 in this order, on the external circumferential side of a heater part 22 formed into a narrow and long rod shape using a means such as curved surface printing. The whole body of a detecting element 21 of the concentration of the carbon monoxide is formed into a circular rod shape. The tip side of the heater 22 is provided with a heat radiating hole 26 to lower the heating temperature of the heater part 22 in the diametrically inside of the hydrogen oxidation catalyst layer 31 and efficiently oxidize the hydrogen in the measurement object gas by the hydrogen oxidation catalyst layer 31. An electromotive force corresponding to the concentration of the carbon monoxide in the measurement object gas is generated between the inside electrode 29 and the outside electrode 30 opposed to each other in the both sides of the solid electrolyte layer 28. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carbon monoxide sensor suitably used for detecting, for example, the concentration of carbon monoxide gas contained in a gas to be measured.
[0002]
[Prior art]
In general, carbon monoxide is a colorless, tasteless, and odorless gas (gas), and is lighter and more toxic than air. Therefore, when breathing at a low concentration of, for example, about 200 ppm (0.02%) over a period of two to three hours, the human body is not affected. Headaches. When the concentration of carbon monoxide in the air reaches 3000 to 6000 ppm (0.3 to 0.6%), breathing becomes difficult within a few minutes.
[0003]
Exhaust gas discharged from various heating appliances, combustion equipment such as a water heater, or an internal combustion engine contains such a carbon monoxide gas as a flammable gas. Among them, a carbon monoxide sensor capable of selectively detecting a carbon monoxide gas is also known (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-2002-5876
[0005]
This type of prior art carbon monoxide sensor has a first electrode and a second electrode provided on the surface side of a solid electrolyte heated by a heater, and one of these electrodes oxidizes carbon monoxide. And the concentration of carbon monoxide in the gas to be measured is detected from the potential difference generated between the electrodes.
[0006]
In addition, if hydrogen gas is contained in the gas to be measured in this case, the hydrogen gas at this time is oxidized by the oxidation catalyst, so that the detection accuracy for carbon monoxide gas is reduced. For this reason, the conventional carbon monoxide sensor has a configuration in which a hydrogen oxidizing unit for selectively oxidizing hydrogen is separately provided at a position away from the solid electrolyte and the oxidation catalyst.
[0007]
[Problems to be solved by the invention]
By the way, the carbon monoxide sensor according to the prior art described above is provided with a flat solid electrolyte layered on one side of a flat heater and a first and a second electrode on one side of the solid electrolyte. And the oxidation catalyst are stacked and provided, so that the heat generated by the heater cannot be efficiently transmitted to the solid electrolyte, and the electrode area cannot be increased with respect to the volume of the entire sensor. In order to obtain the detection accuracy, there is a problem that the entire sensor becomes large.
[0008]
Further, in order to prevent the detection accuracy of the carbon monoxide gas from being lowered by the hydrogen gas contained in the gas to be measured, the conventional carbon monoxide sensor is provided with a hydrogen oxidizing unit at a position away from the solid electrolyte and the oxidation catalyst. Is provided separately, which also causes a problem that the whole sensor is easily increased in size, the structure becomes complicated, the workability at the time of manufacturing is deteriorated, and the manufacturing cost is increased.
[0009]
Further, when a gas having a high molecular weight is contained in the gas to be measured, such as a sulfurous acid gas (SOx) or a silicon gas (an organic gas volatilized into the air from an adhesive or the like), these gases become poisonous substances. When the carbon monoxide sensor enters the sensor as described above, the carbon monoxide sensor is liable to be deteriorated early due to clogging or the like by a poisoning substance, which also causes a problem that the detection accuracy is reduced.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and an object of the present invention is to provide a method for stably detecting the concentration of carbon monoxide in a gas to be measured with high accuracy, and a work at the time of manufacturing. It is an object of the present invention to provide a carbon monoxide sensor capable of improving the performance and reducing the overall size.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a carbon monoxide sensor according to the invention of claim 1 is formed in a rod shape extending in an axial direction, and generates a heat by an externally supplied electric current, and one side of the heater in an axial direction. A heat radiating portion for providing a temperature distribution to the heat generation temperature of the heater portion such that the heat generation temperature of the heater portion is lower on one side in the axial direction than a portion in the axial direction, and on the outer peripheral side of the heater portion. An oxidation catalyst layer provided for oxidizing a combustible gas contained in the gas to be measured and diffusing oxygen therein; and an oxidation catalyst layer provided on an outer peripheral side of the heater section so as to cover the oxidation catalyst layer from outside, and the heater section An oxygen ion-conductive solid electrolyte layer activated by heat from a first electrode provided between the oxidation catalyst layer and the solid electrolyte layer and provided on an inner peripheral side of the solid electrolyte layer; , The solid electrolysis between the first electrode A second electrode provided on the outer peripheral side of the solid electrolyte layer so as to sandwich the layer, and a second electrode positioned closer to one side in the axial direction of the heater section than the second electrode, on the outer peripheral side of the solid electrolyte layer. A hydrogen oxidation catalyst layer that selectively oxidizes hydrogen among the combustible gases contained in the gas to be measured and diffuses the remaining combustible gas; A porous layer provided on the outer peripheral side of the solid electrolyte layer so as to cover the second electrode from the outside, and through which a combustible gas containing carbon monoxide and oxygen diffused from the hydrogen oxidation catalyst layer permeates; A dense layer provided on the outer peripheral side of the porous layer and the hydrogen oxidation catalyst layer, for suppressing poisons having a high molecular weight contained in the gas to be measured from entering the porous layer and the hydrogen oxidation catalyst layer. It consists of.
[0012]
With this configuration, the oxidation catalyst layer, the first electrode, the solid electrolyte layer, the second electrode, the hydrogen oxidation catalyst layer, A porous layer and a dense layer can be formed, and the entire carbon monoxide sensor can have a circular rod-like structure. As a result, the concentration of carbon monoxide in the gas to be measured can be detected stably and with high accuracy without being affected by the mounting direction of the carbon monoxide sensor, the flow direction of the gas to be measured, and the like. Further, since the oxidation catalyst layer is formed on the outer peripheral side of the heater section, the combustible gas contained in the gas to be measured can be oxidized by the oxidation catalyst layer, and oxygen diffused after the oxidation is reduced to a substantially constant partial pressure. It can be supplied to one electrode.
[0013]
Further, the heat radiating section provided in the heater section reduces the temperature of the hydrogen oxidation catalyst layer to, for example, 350 ° C. or lower by lowering the heat generation temperature of the heater section on one side in the axial direction which is the radially inner position of the hydrogen oxidation catalyst layer. The hydrogen in the gas to be measured can be efficiently oxidized by the hydrogen oxidation catalyst layer while suppressing the carbon monoxide gas and oxygen contained in the gas to be measured from the hydrogen oxidation catalyst layer side to the porous layer side. It can be selectively transmitted and diffused toward. At this time, carbon monoxide and oxygen permeating through the porous layer are adsorbed to the second electrode, thereby causing an electrode reaction to oxidize carbon monoxide to carbon dioxide on the second electrode side. be able to.
[0014]
As a result, an electromotive force or current corresponding to the concentration of carbon monoxide in the gas to be measured can be generated between the first and second electrodes facing each other with the solid electrolyte layer interposed therebetween. It can be used to detect the concentration of carbon monoxide in the gas to be measured. In addition, the dense layer provided on the outer peripheral side of the hydrogen oxidation catalyst layer and the porous layer includes a poisoning substance having a high molecular weight (for example, sulfurous acid gas, silicon gas, etc.) contained in the gas to be measured. It is possible to suppress the occurrence of clogging or the like due to intrusion into the layer, and it is possible to prevent deterioration of sensor characteristics due to poisons for a long time.
[0015]
Further, the heater portion is a mandrel portion, and an oxidation catalyst layer, a first electrode, a solid electrolyte layer, a second electrode, a hydrogen oxidation catalyst layer, a porous layer, and a dense layer are formed on the outer peripheral side over the entire circumference. Accordingly, even when the heater portion is formed to have a small diameter, the heat transfer area of the heater portion with respect to the solid electrolyte layer can be increased, and the heat from the heater portion can be efficiently transferred to the solid electrolyte layer and the like.
[0016]
And, by making the carbon monoxide sensor into a circular rod shape, the electrode area can be increased with respect to the volume of the entire sensor, and the internal resistance of the oxygen concentration cell can be reduced. As a result, a measurement error with respect to a temperature change in the detection unit such as the solid electrolyte layer can be reduced, and the detection accuracy of the concentration of carbon monoxide in the gas to be measured can be improved.
[0017]
In addition, since a heat radiating portion is provided on one side in the axial direction of the heater portion, which is a radially inner portion of the hydrogen oxidation catalyst layer, a temperature gradient is given to the heat generation temperature in the axial direction of the heater portion. The layer can be integrally formed on the outer peripheral side of the solid electrolyte layer using means such as curved surface printing, so that the structure of the entire sensor can be simplified and the number of manufacturing steps can be reduced. Cost reduction can be achieved.
[0018]
According to the second aspect of the present invention, between the first electrode and the second electrode, the electromotive force generated between the electrodes is detected as a signal corresponding to the concentration of carbon monoxide in the gas to be measured. And an electromotive force detecting means.
[0019]
In this case, the electromotive force generated between the first and second electrodes facing each other with the solid electrolyte layer interposed therebetween is detected by the electromotive force detection means as a signal corresponding to the concentration of carbon monoxide in the gas to be measured. Can be.
[0020]
According to the invention of claim 3, between the first electrode and the second electrode, a voltage applying means for applying an alternating voltage between the electrodes, and a current flowing between the electrodes is detected. And a current detecting means.
[0021]
In this case, by applying an alternating voltage between the first and second electrodes, for example, an electrode reaction such as repeated adsorption and dissociation of carbon monoxide on the second electrode side can be generated, and the electrode surface Carbon deposition (caulking) can be suppressed to prevent deterioration in durability, and processing such as heating cleaning can be eliminated. A current corresponding to the concentration of carbon monoxide in the gas to be measured flows between the first and second electrodes opposed to each other with the solid electrolyte layer interposed therebetween. Can be detected as the concentration of carbon monoxide in the gas to be measured.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a case where the carbon monoxide sensor according to the embodiment of the present invention is applied to a carbon monoxide concentration detecting device will be described as an example, and the details will be described with reference to FIGS. 1 to 11 of the accompanying drawings.
[0023]
Here, FIGS. 1 to 9 show a first embodiment of the present invention. In the figure, reference numeral 1 denotes a casing of a carbon monoxide concentration detecting device. The casing 1 has a stepped cylindrical holder 2 having an external thread portion 2A formed on one outer periphery in an axial direction, and the holder. A bottomed cylindrical cap 3 integrally fixed to the other side in the axial direction of 2, and a guide cylinder disposed coaxially within the cap 3 and positioned between a seal cap 10 and the holder 2 described below. 4.
[0024]
The holder 2, the cap 3, and the guide cylinder 4, which are components of the casing 1, are formed using a metal material such as stainless steel. The casing 1 is provided, for example, in a room in which a combustion device such as a heating appliance or a water heater is arranged, or in an underground parking lot (hereinafter, referred to as a detection target portion) of a vehicle or the like where exhaust gas is likely to be filled. The male thread 2A of the holder 2 is screwed to the detection target portion or the like in order to attach in a protruding state.
[0025]
Reference numeral 5 denotes an insulating support attached to the holder 2 of the casing 1 via a metal seal ring 6. The insulating support 5 is made of, for example, aluminum oxide (Al).₂O₃  ) Are formed in a cylindrical shape, and a detection element 21 is fixed to the inner peripheral side thereof using an inorganic adhesive or the like. The insulating support 5 positions the detecting element 21 in the casing 1 and holds the detecting element 21 electrically and thermally insulated from the casing 1.
[0026]
Reference numerals 7 and 8 denote insulating cylinders provided in the guide cylinder 4 of the casing 1. The insulating cylinders 7 and 8 are formed in a cylindrical shape from a ceramic material such as aluminum oxide (hereinafter, referred to as alumina). These contact plates 13 and 14 are held in an insulated state with respect to the casing 1.
[0027]
Reference numeral 9 denotes a spring as an elastic member provided in the casing 1 between the insulating support member 5 and the insulating cylinder 7, and the spring 9 is always attached to the insulating support member 5 toward the holder 2 side. This prevents vibrations, shocks and the like acting on the casing 1 from the outside from being directly transmitted to the detecting element 21.
[0028]
Reference numeral 10 denotes a seal cap that closes the other side of the cap 3 in the axial direction. The seal cap 10 is formed of a heat-resistant resin material such as polytetrafluoroethylene (PTFE) into a stepped cylindrical shape. Insulating cylinders 7, 8 and the like are positioned via springs 9 therein.
[0029]
Also, lead wires 11, 11,... For detection and lead wires 12, 12 (only one is shown) for heaters are inserted through the seal cap 10. These lead wires 11 and 12 are individually connected to the detection contact plates 13, 13,... And the heater contact plates 14, 14 in the insulating cylinder 8.
[0030]
Reference numeral 15 denotes a protector provided on the holder 2 of the casing 1, and the protector 15 is formed in a closed cylindrical shape using, for example, a metal plate having high heat resistance. The protector 15 has a base end attached to the holder 2 so as to cover one axial side portion of the detection element 21 described later from the outside, and a distal end (lid) side is provided to protrude from the holder 2 in the axial direction. .
[0031]
Further, a plurality of windows 15A, 15A,... Which allow the gas to be measured to flow are formed on the cylinder side of the protector 15. The windows 15A guide the gas to be measured flowing in the detection target toward one side (tip side) of the detection element 21, for example, in directions indicated by arrows A and B in FIG.
[0032]
Next, reference numeral 21 denotes a detection element constituting a carbon monoxide sensor provided on the casing 1 of the carbon monoxide concentration detecting device. The detection element 21 is mounted in the holder 2 of the casing 1 via the insulating support 5. The tip side protrudes from the holder 2 to one side in the axial direction. The detection element 21 includes a heater section 22, an oxidation catalyst layer 27, a solid electrolyte layer 28, a hydrogen oxidation catalyst layer 31, a porous layer 32, and a dense layer 33, which will be described later, as shown in FIGS. Things.
[0033]
Numeral 22 denotes a heater portion which becomes a mandrel portion formed in an elongated rod shape. As shown in FIGS. 2 to 4, the heater portion 22 is made of an alumina-based ceramic material containing, for example, magnesia (MgO) which is magnesium oxide. It comprises a heater core 23 formed in a small diameter solid rod shape extending in the axial direction, a heater pattern 24 and an insulating heater coating layer 25.
[0034]
Here, the heater core 23 is formed as a cylindrical rod having, for example, an outer dimension of about 3 to 4 mm and a length of about 40 to 60 mm by injection molding the alumina-based ceramic material. As shown in FIG. 3, a bottomed hole 23A and a heat radiating hole 26, which will be described later, are formed in the heater core 23 on both sides in the axial direction so as to be separated from each other.
[0035]
On the other hand, the heater pattern 24 is formed by printing a paste made of a heat-generating conductive material such as platinum (Pt) mixed with 10% by weight of α-alumina on the outer peripheral surface of the heater core 23 as shown in FIG. The film thickness is set to about 10 to 15 μm after firing.
[0036]
In addition, the heater pattern 24 has a pair of leads 24A, 24A extending from one side (distal side) in the axial direction of the heater core 23 to the other side (base end). Are connected to the respective contact plates 14 for the heater as shown in FIG.
[0037]
The heater pattern 24 is supplied with power from the outside via a heater power supply 35 to be described later through each of the heater lead wires 12, each of the contact plates 14, and each of the lead portions 24A, thereby activating the below-described solid electrolyte layer 28 and the like. The heater unit 22 is heated to a temperature suitable for the heating (for example, 350 to 500 ° C., preferably, a temperature before and after 400 ° C.).
[0038]
Further, the heater coating layer 25 is formed, for example, by adding a small amount of silicon oxide (Si 2 O 3) to α-alumina in order to protect the heater pattern 24 together with the lead portion 24A from the radial outside.₂  ) Is formed by printing a thick film on the outer peripheral side of the heater core 23 with the added ceramic material, and its film thickness is about 20 μm.
[0039]
Reference numeral 26 denotes a heat-dissipating hole as a heat-dissipating portion provided on one side in the axial direction of the heater core 23. The heat-dissipating hole 26 is formed as a bottomed hole extending in the axial direction from the end face on the front end side of the heater core 23. The distance L1 shown in FIG. 2 (for example, L1 = about 3.0 to 3.5 mm) is obtained.
[0040]
The heat radiation hole 26 is opened at the end face on the front end side of the heater core 23 to allow a gas (for example, an air flow) such as a gas to be measured to flow therein, and as shown by a characteristic line in FIG. A temperature distribution (temperature gradient) is given to the heat generation temperature.
[0041]
That is, the heat radiating hole 26 adjusts the heat generation temperature of the heater portion 22 at a position radially inward of the hydrogen oxidation catalyst layer 31 described later (a position from the tip of the heater portion 22 to a distance L1) to another portion (for example, a heater). (Position at a distance L2 from the tip of the portion 22), thereby having the function of suppressing the temperature of the hydrogen oxidation catalyst layer 31 to a temperature of 350 ° C. or lower, for example, as shown in FIG.
[0042]
On the other side of the heater core 23 in the axial direction, a bottomed hole 23A extending in the axial direction from the other end face is formed as shown in FIG. The heat radiation hole 26 has a substantially same axial length (hole depth) as the heat radiation hole 26.
[0043]
When the heater pattern 24 and the heater coating layer 25 are curved-printed on the outer peripheral side of the heater core 23 as shown in FIGS. , The solid electrolyte layer 28, the hydrogen oxidation catalyst layer 31, the porous layer 32, the dense layer 33, and the like are used as centering holes when performing curved printing. The bottomed hole 23 </ b> A and the heat dissipation hole 26 also function as heat capacity reduction holes that reduce the heat capacity of the heater core 23 by reducing the volume of the heater core 23.
[0044]
Reference numeral 27 denotes an oxidation catalyst layer formed on the outer peripheral side of the heater coating layer 25 of the heater section 22 by using a method such as curved surface printing. The oxidation catalyst layer 27 includes, for example, α-alumina and zirconia (Zr 2 O 3).₂  ), And about 0.5% by weight of each of platinum and palladium (Pd) powders.
[0045]
That is, the oxidation catalyst layer 27 is formed in a tubular shape by printing a paste-like material made of the porous oxidation catalyst material on the outer peripheral side of the heater coating layer 25 as shown in FIG. For example, the thickness is about 20 to 50 μm. It is not always necessary to use zirconia as a composite oxide used as a material of the porous oxidation catalyst material. For example, a composite oxide composed of α-alumina may be used.
[0046]
The oxidation catalyst layer 27 includes, for example, oxygen, hydrogen, carbon monoxide, and methane (CH) contained in the gas to be measured flowing in the direction of arrow A in FIG.₄) Has the function of oxidizing hydrogen, carbon monoxide, methane and the like, respectively, and diffusing only the remaining oxygen to the inner electrode 29 described later.
[0047]
Reference numeral 28 denotes an oxygen ion conductive solid electrolyte layer provided on the outer peripheral side of the heater section 22 so as to cover the oxidation catalyst layer 27 from the outside. The solid electrolyte layer 28 is, for example, 92% mol zirconia (Zr 2 O 3).₂  ), 8% mol of yttria (Y₂  O₃  ) Is mixed to prepare a paste made of so-called yttria-stabilized zirconia (YSZ), and this paste is printed on the outer peripheral side of the heater coating layer 25 by means such as curved printing as shown in FIG. It is formed in a substantially cylindrical shape by thick-film printing using
[0048]
The solid electrolyte layer 28 has a thickness of, for example, about 15 to 50 μm, and transports oxygen ions between electrodes 29 and 30 described below. As a result, the solid electrolyte layer 28 generates a detection signal of the concentration of carbon monoxide described later as an electromotive force (mV) shown in FIG.
[0049]
Reference numeral 29 denotes an inner electrode as a first electrode provided between the oxidation catalyst layer 27 and the solid electrolyte layer 28 and provided on the inner peripheral surface of the solid electrolyte layer 28. The inner electrode 29 is, for example, 90% by weight. 5% by weight of yttria-stabilized zirconia (YSZ) powder was mixed with the platinum (Pt) powder to prepare a paste-like material. The lead portion 29A extends toward the base end side of the heater portion 22 by forming a curved surface on the outer peripheral side of the layer 27.
[0050]
Here, the inner electrode 29 constitutes an anode electrode for performing a catalytic decomposition reaction (electrode reaction) according to the following chemical formula 1. The inner electrode 29 is formed as a cermet composed of the platinum and yttria-stabilized zirconia. Since there are many so-called three-phase interfaces (three-phase interfaces composed of platinum, cermet, and the atmosphere), the inner electrode 29 is formed by the electrode of the formula (1). The reaction is generated with small resistance.
[0051]
Numeral 30 denotes an outer electrode serving as a second electrode formed on the outer peripheral surface of the solid electrolyte layer 28. The outer electrode 30 is formed substantially in the same manner as the above-described inner electrode 29, and is expressed by the following formulas 1 and 2. The cathode electrode which performs the electrode reaction indicated by. The lead 30A of the outer electrode 30 also extends toward the base end of the heater 22.
[0052]
The outer electrode 30 is disposed so as to sandwich the solid electrolyte layer 28 from the inner electrode 29 from both sides in the radial direction. The axial positions of the electrodes 29 and 30 with respect to the solid electrolyte layer 28 are axial positions substantially corresponding to a distance L2 (for example, L2 = about 6 to 8 mm) from the tip of the heater section 22, as shown in FIG. ing.
[0053]
Then, the lead portion 30A of the outer electrode 30 is connected to the contact plate 13 and the lead wire 11 at the base end side of the detecting element 21 shown in FIG. Is connected to a later-described voltmeter 34 shown in FIG.
[0054]
Reference numeral 31 denotes a hydrogen oxidation catalyst layer which covers the solid electrolyte layer 28 from the outside together with a porous layer 32 described later. The hydrogen oxidation catalyst layer 31 is made of a material having high selectivity to hydrogen gas (for example, n-type oxide). As shown in FIG. 5, thick paste (curved surface printing) of a paste-like substance made of a semiconductor) is formed on the outer peripheral side of the solid electrolyte layer 28 so as to have a thickness of, for example, about 20 to 50 μm. is there.
[0055]
In this case, the n-type oxide semiconductor is, for example, iron oxide (Fe₂O₃), Selenium oxide (Ce 2 O)₂), Zinc oxide (ZnO)₂), Tin oxide (Sn 2 O 3)₂), Indium oxide (In)₂O₃), Titania (TiO 2)₂), Barium titanate (BaTiO 3)₃), Strontium titanate (SrTiO 3)₃), Strontium stannate (SrSnO)₃), Lanthanum-based oxides (La_0.6Sr_0.4CoO₃) Or other lanthanum-based oxides (La_0.6Sr_0.4MnO₃) And the like.
[0056]
Here, the hydrogen oxidation catalyst layer 31 is provided at a position on the outer peripheral surface of the solid electrolyte layer 28 that surrounds the heat radiating hole 26 of the heater section 22 from the outside (a position from the tip of the heater section 22 to a distance L1), Thereby, the temperature of the hydrogen oxidation catalyst layer 31 can be suppressed to a temperature of 350 ° C. or less as shown by a characteristic line in FIG. 9, for example.
[0057]
That is, the hydrogen oxidation catalyst layer 31 has a temperature at which the hydrogen gas can be selectively oxidized out of the gas to be measured flowing in the direction of arrow B in FIG. The temperature is maintained at a non-existent temperature (for example, a temperature of 350 ° C. or less) through the heat radiation holes 26 of the heater section 22 or the like.
[0058]
Thereby, the hydrogen oxidation catalyst layer 31 can efficiently oxidize hydrogen in the gas to be measured, and removes carbon monoxide gas, oxygen, and the like contained in the gas to be measured from the hydrogen oxidation catalyst layer 31 side in a porous manner. It selectively transmits and diffuses toward the layer 32 side.
[0059]
Reference numeral 32 denotes a porous layer provided on the outer peripheral side of the solid electrolyte layer 28 together with the hydrogen oxidation catalyst layer 31. The porous layer 32 covers the outer electrode 30 from the outside as shown in FIG. And is arranged at a position adjacent to and in contact with the hydrogen oxidation catalyst layer 31 in the axial direction.
[0060]
The porous layer 32 is made of, for example, α-alumina and zirconia (Zr 2 O 3).₂  To about 10 to 30% by weight of carbon powder as a pore-forming agent, to prepare a paste-like material. The paste-like material is mixed with a solid electrolyte layer as shown in FIG. 28 is formed by printing a thick film on the outer peripheral side by means such as curved surface printing, and the film thickness is, for example, about 20 to 50 μm.
[0061]
In this case, it is not always necessary to use zirconia as the material of the porous layer 32, and for example, a configuration in which carbon powder is added to a composite oxide powder made of α-alumina may be used. Then, these carbon powders are burned off as a pore-forming agent when the entire detection element 21 is fired as described below, whereby the porous layer 32 has a porous structure having open cells (open holes) therein. It is formed as a hollow cylindrical body.
[0062]
The porous layer 32 is formed of a gas other than the hydrogen oxidized in the hydrogen oxidation catalyst layer 31 among the gases to be measured flowing into the hydrogen oxidation catalyst layer 31 from the direction of arrow B in FIG. Gas, oxygen and the like permeate through the internal pores, and supply the carbon monoxide gas and oxygen at this time to the outer electrode 30.
[0063]
Reference numeral 33 denotes a dense layer provided on the outer peripheral side of the hydrogen oxidation catalyst layer 31 and the porous layer 32. The dense layer 33 is formed, for example, by adding α-alumina powder to silicon oxide (Si 2 O 3).₂) Is added to the powder to prepare a paste, and this paste is thick-film printed on the outer peripheral side of the hydrogen oxidation catalyst layer 31, the porous layer 32, and the solid electrolyte layer 28 by means such as curved surface printing. As shown in FIG. 2, it is formed in a stepped cylindrical shape, and its film thickness is, for example, about 20 to 50 μm.
[0064]
The dense layer 33 has a dense porous structure as compared with the hydrogen oxidation catalyst layer 31, the porous layer 32, and the like, so that the sulfur dioxide gas (SOx) and the silicon gas (adhesive) contained in the gas to be measured are included. Gases having a large molecular weight, such as organic gases volatilized into the air from the above, are prevented from becoming poisons and entering the hydrogen oxidation catalyst layer 31, the porous layer 32, and the solid electrolyte layer 28.
[0065]
Reference numeral 34 denotes a voltmeter provided as an electromotive force detecting means provided outside the casing 1, and the voltmeter 34 is connected between the inner electrode 29 and the outer electrode 30 via the lead wire 11 or the like as shown in FIG. The electromotive force generated between the electrodes 29 and 30 by the solid electrolyte layer 28 is output as a detection signal of the concentration of carbon monoxide as shown by a characteristic line in FIG.
[0066]
Reference numeral 35 denotes a heater power supply provided outside the casing 1. The heater power supply 35 is connected to the heater pattern 24 via the lead wires 12 and the like as shown in FIG. The heater power supply 35 maintains the temperature by applying a voltage to the heater pattern 24 of the heater section 22 to cause the heater section 22 to generate heat at a temperature before and after 400 ° C., for example.
[0067]
The apparatus for detecting the concentration of carbon monoxide according to the present embodiment has the above-described configuration. Next, a method for manufacturing the detection element 21 will be described with reference to FIGS.
[0068]
First, when the heater section 22 is manufactured, as shown in FIG. 3, in a core forming step, a heater core 23 is formed from an alumina-based ceramic material, and a cylindrical rod having bottomed holes 23A and heat radiation holes 26 on both axial sides. In this state, the heater core 23 is temporarily fired.
[0069]
Next, in the pattern printing step, a support shaft such as a chuck is engaged with both ends of the heater core 23 via the bottomed hole 23A and the heat radiation hole 26, and while rotating the heater core 23, for example, 10 wt% Is printed on the outer peripheral surface of the heater core 23 with a curved surface. Further, each lead portion 24A of the heater pattern 24 is integrally formed by printing means so as to extend toward the base end side of the heater core 23.
[0070]
Next, in the heater coating layer forming step, a paste-like material made of, for example, α-alumina is printed on the surface of the heater core 23 so as to cover the heater pattern 24 from the radial outside, or a ceramic green sheet of α-alumina or the like is formed on the heater core 23. The heater coating layer 25 is formed by being laminated on the outer peripheral side. As a result, the heater section 22 including the heater core 23, the heater pattern 24, and the heater coating layer 25 is formed as shown in FIG.
[0071]
Next, in the step of forming the oxidation catalyst layer 27 shown in FIG. 5, a paste made of a composite oxide such as, for example, α-alumina is printed on the outer surface of the heater coating layer 25 by performing curved printing. 27 is formed, and the heater section 22 is covered with the oxidation catalyst layer 27 from the outside.
[0072]
Then, following the step of forming the oxidation catalyst layer 27, the step of forming the inner electrode 29 is performed. In this case, the paste-like material made of platinum, yttria-stabilized zirconia, or the like described above is subjected to curved printing so as to be applied to the outer peripheral surface of the oxidation catalyst layer 27, thereby forming the inner electrode 29 as a cylindrical electrode. At this time, the lead portion 29A of the inner electrode 29 is formed by printing so as to extend to the base end side of the heater coating layer 25.
[0073]
In the subsequent step of forming the solid electrolyte layer 28, a paste-like substance made of, for example, zirconia and yttria is printed on the outer peripheral surfaces of the heater coating layer 25 and the oxidation catalyst layer 27 by performing a curved printing to apply oxygen ion conductivity. A solid electrolyte layer 28 is formed, and the oxidation catalyst layer 27 and the inner electrode 29 are covered with the solid electrolyte layer 28 from the outside.
[0074]
In the next outer electrode forming step, the same conductive paste as the inner electrode 29 is printed on the outer peripheral surface of the solid electrolyte layer 28 by a curved surface, so that the solid electrolyte layer 28 is sandwiched between the inner electrode 29 and the radial direction. The outer electrode 30 is formed as described above. Also, the lead portion 30A of the outer electrode 30 is formed by printing so as to extend to the base end side of the heater coating layer 25.
[0075]
Next, in the hydrogen oxidation catalyst layer forming step, a paste made of an n-type oxide semiconductor or the like is printed on the outer peripheral surface of the solid electrolyte layer 28 at a position closer to one side in the axial direction of the heater section 22 than the outer electrode 30. Thereby, the hydrogen oxidation catalyst layer 31 is formed.
[0076]
In the step of forming the porous layer 32, a paste made of, for example, α-alumina and carbon powder is printed on the outer periphery of the solid electrolyte layer 28 so as to cover the outer electrode 30 shown in FIG. Thereby, the porous layer 32 is formed.
[0077]
In the subsequent dense layer forming step, the hydrogen oxidation catalyst layer 31, the porous layer 32, and the like are covered so as to cover the hydrogen oxidation catalyst layer 31, the porous layer 32, and the solid electrolyte layer 28 shown in FIG. The dense layer 33 is formed on the outer peripheral side by, for example, performing a curved surface printing of a paste made of α-alumina and silicon oxide.
[0078]
Then, in the next firing step, the heater core 23, heater pattern 24, heater coating layer 25, oxidation catalyst layer 27, solid electrolyte layer 28, electrodes 29 and 30, hydrogen oxidation catalyst layer 31, and porous layer 32 formed as described above are formed. The molded product of the detection element 21 composed of the dense layer 33 is fired at a high temperature of, for example, about 1400 ° C. for about 2 hours, and these are integrally sintered.
[0079]
Thus, after the detection element 21 is manufactured by the above-described steps, the detection element 21 is housed in the casing 1 of the carbon monoxide concentration detection device as shown in FIG. 1 and the respective lead portions 24A, 29A, 30A are respectively provided. By contacting the contact plates 13 and 14 with spring characteristics and electrically connecting them, the carbon monoxide concentration detecting device (carbon monoxide sensor) is completed.
[0080]
Next, the operation of detecting the carbon monoxide concentration by the sensor will be described. First, the casing 1 of the carbon monoxide concentration detection device is connected to the detection target portion (for example, an underground parking lot) via the male screw 2A of the holder 2. ), And is fixed in a state where the tip side of the detection element 21 is projected into the detection target portion.
[0081]
Then, when the gas to be measured (including air) in the detection target portion is introduced around the detection element 21 via the protector 15, a part of the gas to be measured is guided in the direction of arrow A in FIG. As a result, the oxidation catalyst layer 27 forms oxygen, hydrogen, carbon monoxide, and methane (CH) contained in the gas to be measured.₄), Hydrogen, carbon monoxide, methane, etc. are oxidized, and only the remaining oxygen is supplied to the inner electrode 29.
[0082]
At this time, the gas to be measured is taken into the hydrogen oxidation catalyst layer 31 and the porous layer 32 in the direction of arrow B in FIG. Then, the hydrogen oxidation catalyst layer 31 oxidizes only the hydrogen in the gas to be measured, and the remaining gas to be measured (for example, carbon monoxide gas, oxygen, etc.) permeates toward the inside of the porous layer 32. For this reason, the porous layer 32 supplies the carbon monoxide gas and oxygen at this time to the surface of the outer electrode 30 while transmitting and diffusing the carbon monoxide gas and oxygen through the internal holes.
[0083]
In this state, when power is supplied from the heater power supply 35 to the heater pattern 24 and the entire detection element 21 is heated by the heater section 22, the solid electrolyte layer 28 is activated, and the position of the distance L 2 from the tip of the heater section 22 is activated. The inner electrode 29 and the outer electrode 30 are maintained at temperatures before and after 400 ° C. as shown by the characteristic lines in FIG.
[0084]
On the other hand, the hydrogen oxidation catalyst layer 31 disposed at a position up to the distance L1 from the tip of the heater section 22 is located at a position on the outer peripheral surface of the solid electrolyte layer 28 that surrounds the heat radiation hole 26 of the heater section 22 from the outside. The temperature of the hydrogen oxidation catalyst layer 31 is suppressed to a temperature of 350 ° C. or lower as shown by a characteristic line illustrated in FIG.
[0085]
For this reason, in the gas to be measured taken into the hydrogen oxidation catalyst layer 31 and the porous layer 32 in the direction indicated by the arrow B in FIG. 2, all the hydrogen is oxidized by the hydrogen oxidation catalyst layer 31 and the remaining carbon monoxide is removed. Gas, oxygen, and the like are selectively transmitted and diffused from the hydrogen oxidation catalyst layer 31 side to the porous layer 32 side.
[0086]
Thus, a reaction between the anode-side inner electrode 29 and the cathode-side outer electrode 30 based on the concentration of carbon monoxide in the gas to be measured is obtained by a reaction formula expressed by the following chemical formulas (1) and (2). Electric power is generated as shown in FIG.
[0087]
That is, on the inner electrode 29 side, an electrochemical catalytic decomposition reaction (electrode reaction) according to the following Chemical Formula 1 is performed, whereby oxygen in the gas to be measured is adsorbed on the surface of the inner electrode 29 and the adsorbed oxygen (Oad) is given an electron to generate oxygen ions.
[0088]
Embedded image
Oad + 2e → O^2-
However, Oad: adsorbed oxygen
e: Electronic
O^2-: Oxygen ion
[0089]
Then, the oxygen ions (O^2-) Are transported from the inner electrode 29 on the anode side to the outer electrode 30 on the cathode side via oxygen defects in the solid electrolyte layer 28.
[0090]
In addition, the outer electrode 30 on the cathode side adsorbs carbon monoxide (CO gas) and oxygen permeating the inside of the porous layer 32 on the surface, and for example, electrochemically represented by the following chemical formula (2) By performing a catalytic decomposition reaction (electrode reaction), carbon monoxide (CO) in the gas to be measured is converted into oxygen ions (O 2) at this time.^2-) And carbon dioxide (CO₂  ) And electrons (e).
[0091]
Embedded image
CO + O^2-→ CO₂  + 2e
[0092]
Further, the oxygen adsorbed on the outer electrode 30 undergoes a catalytic decomposition reaction according to Formula 1 substantially similar to that of the inner electrode 29 described above, and electrons are given to the adsorbed oxygen (Oad) at the outer electrode 30 as well. To generate oxygen ions. However, on the outer electrode 30 side, the oxygen partial pressure of the outer electrode 30 is reduced by the amount corresponding to the electrode reaction according to the formula (2), and the inner electrode 29 having a higher oxygen partial pressure and the outer electrode 29 having a lower oxygen partial pressure are used. An oxygen concentration cell is formed between the cell and the cell 30.
[0093]
Thereby, an electromotive force is generated between the inner electrode 29 and the outer electrode 30 of the detection element 21 by the reaction formulas 1 and 2, and the electromotive force at this time is detected using the voltmeter 34 or the like. Thus, the concentration of carbon monoxide in the gas to be measured can be detected as shown by the characteristic line in FIG.
[0094]
Also, as shown in the characteristic line of FIG. 8, an experiment was conducted in which the concentration of hydrogen gas was changed over a range of 0 to 1200 ppm under a condition of a carbon monoxide concentration of 500 ppm (a heater temperature of 400 ° C.). It was confirmed that the electromotive force from 21 became a substantially constant voltage value at about 8 mV (millivolt).
[0095]
Therefore, according to the present embodiment, even when a flammable gas such as hydrogen is present in the gas to be measured, the detection element 21 can selectively detect the carbon monoxide gas in the gas to be measured, The detection accuracy of the concentration can be improved, and the reliability as a carbon monoxide sensor can be surely improved.
[0096]
The inner electrode 29 and the outer electrode 30 diametrically opposed to each other with the solid electrolyte layer 28 interposed therebetween are formed as cylindrical electrodes having a small-diameter cylindrical shape. The electrode area can be increased, the internal resistance of the oxygen concentration cell can be reduced, and the measurement error of the concentration of carbon monoxide due to temperature fluctuation of the detection element 21 can be suppressed.
[0097]
Further, by covering the heater portion 22 with the solid electrolyte layer 28, the hydrogen oxidation catalyst layer 31, the porous layer 32, and the like from almost the entire outer periphery, the heater portion 22 is prevented from directly contacting the outside air, and is affected by the outside air temperature. Can be reduced, and the heat transfer area of the heater section 22 can be increased, and the heat from the heater section 22 can be efficiently transmitted to the solid electrolyte layer 28 and the like.
[0098]
As a result, a carbon monoxide sensor used as a final safety device in an underground parking lot where carbon monoxide gas is likely to be generated or in a space where ventilation is not sufficiently performed is reduced in energy consumption with low power consumption. In addition, the sensor can be provided as a compact sensor, and can be realized as a small-sized sensor. In addition, the responsiveness to carbon monoxide gas can be increased, the sensitivity can be increased, and the reliability can be improved.
[0099]
Next, FIGS. 10 and 11 show a second embodiment of the present invention. The feature of this embodiment is that an alternating voltage is provided between the first electrode and the second electrode and between the respective electrodes. And voltage detecting means for detecting a current flowing between the electrodes. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0100]
In the figure, reference numeral 41 denotes a detection element of the carbon monoxide sensor according to the present embodiment. The detection element 41 has substantially the same configuration as the detection element 21 described in the first embodiment. It has a layer 27, an inner electrode 29, a solid electrolyte layer 28, an outer electrode 30, a hydrogen oxidation catalyst layer 31, a porous layer 32 and a dense layer 33.
[0101]
However, the detection element 41 in this case is different from the first embodiment in that an alternating voltage is applied between the inner electrode 29 and the outer electrode 30 from a power supply unit 42 described later. .
[0102]
Reference numeral 42 denotes a power supply unit serving as voltage application means connected between the inner electrode 29 and the outer electrode 30 via the lead wire 11 or the like. The power supply unit 42 is connected in parallel between the inner electrode 29 and the outer electrode 30. It comprises first and second DC power supplies 43 and 44 arranged in a state, and a changeover switch 45 for selectively switching between the DC power supplies 43 and 44 and connecting between the electrodes 29 and 30.
[0103]
In this case, the DC power supplies 43 and 44 are arranged so that their polarities are opposite to each other. For example, while the DC power supply 43 applies a voltage from the inner electrode 29 to the outer electrode 30, the DC power supply 44 The configuration is such that a voltage is applied from the outer electrode 30 to the inner electrode 29.
[0104]
The changeover switch 45 switches the DC power supplies 43 and 44 between the electrodes 29 and 30 at a switching frequency of, for example, about 2 Hz (Hertz), and applies an alternating voltage between the inner electrode 29 and the outer electrode 30. It is.
[0105]
A current detector 46 is located between the inner electrode 29 and the power supply section 42 and is connected to the middle of the lead wire 11 as current detection means. The current detector 46 is connected to the inner electrode 29 and the power supply section 42. The current flowing between them is detected as a measurement current corresponding to the concentration of carbon monoxide, for example, as indicated by characteristic lines 47 and 48 in FIG.
[0106]
In this case, a characteristic line 48 indicated by a one-dot chain line in FIG. 11 shows the relationship between the applied voltage and the measured current when carbon monoxide does not exist in the gas to be measured (the concentration of carbon monoxide is 0 ppm). A characteristic line 47 indicated by a solid line in FIG. 11 indicates a relationship between the applied voltage and the measured current when carbon monoxide is present at a concentration of 1000 ppm in the gas to be measured.
[0107]
When the changeover switch 45 of the power supply unit 42 is switched to the DC power supply 43, for example, a positive (plus) voltage is applied to the electrode 29 side, and the current detector 46 is represented by the first quadrant in FIG. Detect the measurement current. When the changeover switch 45 of the power supply unit 42 is switched to the DC power supply 44, for example, a negative (minus) voltage is applied to the electrode 29 side, and the current detector 46 is represented by the third quadrant in FIG. It detects the measurement current.
[0108]
Thus, in the present embodiment configured as above, when the changeover switch 45 of the power supply unit 42 is switched to the DC power supply 43, for example, a constant voltage is applied from the inner electrode 29 to the outer electrode 30 (for example, in FIG. (0.5 V or 1.0 V shown in FIG. 1) promotes the electrode reaction on the outer electrode 30 side due to Chemical Formula 1.
[0109]
At this time, as the concentration of carbon monoxide increases, the amount of carbon monoxide adsorbed on the outer electrode 30 increases, so that the electrode reaction due to Chemical Formula 1 is suppressed. Thus, the measured current (mA) flowing through the current detector 46 decreases from the characteristic line 48 (0 ppm characteristic) to the characteristic line 47 (1000 ppm characteristic) in the first quadrant in FIG. Detected with negative correlation.
[0110]
When the changeover switch 45 of the power supply unit 42 is switched to the DC power supply 44 side, for example, a constant voltage (for example, −0.5 V or −1.0 V shown in FIG. 11) from the outer electrode 30 to the inner electrode 29. Is applied, the electrode reaction on the inner electrode 29 side is promoted by the chemical formula 1, and oxygen ions transported from the inner electrode 29 to the outer electrode 30 via oxygen defects in the solid electrolyte layer 28 are increased. .
[0111]
However, in this case, even if the concentration of carbon monoxide increases, there is no adsorption of carbon monoxide on the inner electrode 29 side, so that the electrode reaction due to Chemical Formula 1 is not suppressed, and the current detector 46 The measurement current (mA) determined by the temperature of the detection element 41 is detected as a current value represented by the third quadrant in FIG.
[0112]
Therefore, the detection element 41 according to the present embodiment allows the current corresponding to the concentration of carbon monoxide in the gas to be measured to flow between the inner electrode 29 and the outer electrode 30 opposed to each other with the solid electrolyte layer 28 interposed therebetween. In this case, the current measured at this time can be detected as the concentration of carbon monoxide in the gas to be measured by using the current detector 46, so that substantially the same operation and effect as those of the first embodiment can be obtained.
[0113]
However, in the present embodiment, an alternating voltage having a frequency of, for example, about 2 Hz is applied from the power supply section 42 to the inner electrode 29 and the outer electrode 30 so that the electrode on the outer electrode 30 side is applied. The reaction can be changed (promoted) intermittently, for example, to cause an electrode reaction such as repeated adsorption and dissociation of carbon monoxide.
[0114]
As a result, carbon deposition (caulking) on the surface of the outer electrode 30 can be satisfactorily suppressed even when the sensor is operated for a long time as a carbon monoxide sensor. In addition to this, it is possible to eliminate the need for a process such as heat cleaning, thereby improving the maintainability.
[0115]
In addition, by applying an alternating voltage from the power supply unit 42 and performing an arithmetic process for subtracting the absolute value of the amount of current flowing in the current detector 46 in both directions, a measurement error due to a temperature variation of the detection element 41 can be offset. And the concentration of carbon monoxide in the gas to be measured can be detected with higher accuracy.
[0116]
In each of the above embodiments, the heater core 23 serving as the mandrel of the heater 22 has been described as being formed by means such as injection molding. However, the present invention is not limited to this, and for example, the heater core 23 may be formed by means such as extrusion molding.
[0117]
Further, in each of the above embodiments, the case where the carbon monoxide sensor is provided in a detection target portion such as a room in which a combustion device such as a heating appliance or a water heater is arranged, or an underground parking lot has been described as an example. However, the present invention is not limited to this. For example, a configuration may be employed in which a carbon monoxide sensor is directly attached to a combustion device such as a heating device or a water heater, or an internal combustion engine.
[0118]
Next, technical ideas other than the claims that can be grasped from the above embodiments will be described below together with their effects.
[0119]
(1). 2. The carbon monoxide sensor according to claim 1, wherein the heat radiating portion is configured by a bottomed heat radiating hole extending with a predetermined length in an axial direction from one end surface of the heater portion, and the hydrogen oxidation catalyst layer includes: A carbon monoxide sensor formed by using means such as curved printing on the outer peripheral side of the solid electrolyte layer at a position radially outside the heat radiation hole.
[0120]
Thereby, the heat radiation hole provided in the heater portion allows the gas to be measured to flow therethrough, thereby increasing the heat generation temperature of the heater portion at a position on one axial side inside the hydrogen oxidation catalyst layer in the radial direction, and allowing hydrogen to flow therethrough. The temperature can be lowered to a temperature suitable for oxidation and to a temperature at which carbon monoxide has no oxidation activity, and hydrogen in the gas to be measured can be efficiently oxidized by the hydrogen oxidation catalyst layer.
[0121]
(2). 4. The carbon monoxide sensor according to claim 1, wherein the hydrogen oxidation catalyst layer is formed using an n-type oxide semiconductor material having high selectivity to hydrogen gas. 5.
[0122]
This allows the hydrogen oxidation catalyst layer to selectively oxidize the hydrogen gas contained in the gas to be measured, and to allow the remaining gas in the gas to be measured (for example, carbon monoxide gas excluding hydrogen, oxygen, etc.). ) Can be allowed to diffuse and permeate into the pores of the porous layer.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a carbon monoxide concentration detecting device to which a carbon monoxide sensor according to a first embodiment of the present invention is applied.
FIG. 2 is an enlarged longitudinal sectional view showing a detection element in FIG. 1;
FIG. 3 is a perspective view showing each step of forming a heater unit in FIG. 2;
FIG. 4 is a perspective view showing a state where a heater unit is formed.
5 is a perspective view showing each step of forming an oxidation catalyst layer, a solid electrolyte layer, an electrode, a hydrogen oxidation catalyst layer, a porous layer, and the like for the heater section in FIG.
FIG. 6 is a perspective view of the detection element showing a state where a solid electrolyte layer, a hydrogen oxidation catalyst layer, a porous layer, a dense layer, and the like are formed on the outer peripheral side of the heater section.
FIG. 7 is a characteristic diagram showing a relationship between a carbon monoxide concentration and a sensor electromotive force.
FIG. 8 is a characteristic diagram showing a relationship between a hydrogen concentration in a gas to be measured and a sensor electromotive force.
FIG. 9 is a characteristic diagram showing a heat generation temperature of a detection element by a heater section as a temperature distribution.
FIG. 10 is a longitudinal sectional view showing a carbon monoxide concentration detecting element according to a second embodiment.
FIG. 11 is a characteristic diagram showing a relationship between a voltage applied between electrodes and a measurement current.
[Explanation of symbols]
1 casing
11,12 Lead wire
13,14 Contact plate
21, 41 detecting element (carbon monoxide sensor)
22 heater section
23 heater core
24 Heater pattern
24A, 29A, 30A Lead
25 Heater coating layer
26 Heat dissipation hole (heat dissipation part)
27 Oxidation catalyst layer
28 Solid electrolyte layer
29 inner electrode (first electrode)
30 outer electrode (second electrode)
31 Hydrogen oxidation catalyst layer
32 porous layer
33 dense layer
34 voltmeter (electromotive force detection means)
35 Heater power supply
42 power supply section (voltage application means)
43,44 DC power supply
45 Changeover switch
46 Current detector

Claims (3)

A heater portion which is formed in a rod shape extending in the axial direction and generates heat when energized from the outside;
A heat radiating portion provided on one side in the axial direction of the heater portion and providing a temperature distribution to the heat generation temperature of the heater portion such that the heat generation temperature of the heater portion is lower on one side in the axial direction than a portion in the axial direction. ,
An oxidation catalyst layer provided on the outer peripheral side of the heater unit, for oxidizing a combustible gas contained in the gas to be measured and diffusing oxygen inside,
An oxygen ion-conductive solid electrolyte layer provided on the outer peripheral side of the heater section so as to cover the oxidation catalyst layer from the outside, and activated by heat from the heater section;
A first electrode provided between the oxidation catalyst layer and the solid electrolyte layer and provided on an inner peripheral side of the solid electrolyte layer;
A second electrode provided on the outer peripheral side of the solid electrolyte layer so as to sandwich the solid electrolyte layer between the first electrode and the first electrode;
It is provided on the outer peripheral side of the solid electrolyte layer at a position closer to one side in the axial direction of the heater section than the second electrode, and selectively oxidizes hydrogen of the combustible gas contained in the gas to be measured. A hydrogen oxidation catalyst layer that diffuses the remaining flammable gas,
The solid electrolyte layer is provided adjacent to the hydrogen oxidation catalyst layer in the axial direction so as to cover the second electrode from outside, and contains carbon monoxide and oxygen diffused from the hydrogen oxidation catalyst layer. A porous layer through which flammable gas permeates;
A dense layer provided on the outer peripheral side of the porous layer and the hydrogen oxidation catalyst layer, for suppressing a poisoning substance having a high molecular weight contained in the gas to be measured from entering the porous layer and the hydrogen oxidation catalyst layer. A carbon monoxide sensor configured. An electromotive force detection unit is provided between the first electrode and the second electrode to detect an electromotive force generated between the electrodes as a signal corresponding to the concentration of carbon monoxide in the gas to be measured. The carbon monoxide sensor according to claim 1. Between the first electrode and the second electrode, a voltage applying means for applying an alternating voltage between the electrodes and a current detecting means for detecting a current flowing between the electrodes are provided. The carbon monoxide sensor according to claim 1.

Images