JP2012042458A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor capable of stably measuring oxygen concentration of gas for measurement in which methane gas is contained.SOLUTION: The oxygen sensor includes: a cylindrical zirconia cell 50 with the bottom; a reference electrode 52 which is installed on the inner surface of a cell closed end 51 of the zirconia cell 50 and contacts reference gas; a measurement electrode 53 which is installed on the outer surface of the cell closed end 51 of the zirconia cell 50 and contacts the gas for measurement; and a cylindrical protective pipe 60 with the bottom which covers the zirconia cell 50. A protrusion 63 which contacts the measurement electrode 53 is provided on an inner surface 62 of the cell closed end 51 of the protective pipe 60. In addition, an introduction port 64 which introduces the gas for measurement to the measurement electrode 53 and becomes a state that the measurement electrode 53 is exposed is provided to the protective pipe 60. Thus, since the measurement electrode 53 is located at a position where the gas for measurement easily passes through and the gas for measurement is supplied to the measurement electrode 53 without remaining, the oxygen concentration of the gas for measurement can be stably measured.

Description

  The present invention relates to an oxygen sensor used for measuring the oxygen concentration inside a heat treatment furnace or the like.

  Conventionally, in a heat treatment furnace or the like, the oxygen concentration (oxygen partial pressure) in the furnace atmosphere is determined according to the principle of an oxygen concentration cell using an electrochemical reaction using a solid electrolyte body having oxygen ion conductivity at a high temperature such as zirconia. ) Is used (see, for example, Patent Document 1).

  In an oxygen sensor using a solid electrolyte body, a pair of platinum electrodes is generally provided on both the inner and outer surfaces of the closed end of a bottomed cylindrical solid electrolyte body. In this oxygen sensor, the inner platinum electrode is brought into contact with the atmosphere as a standard gas to serve as a reference electrode, and the outer platinum electrode is brought into contact with the atmosphere in the furnace as the measurement gas to serve as a measurement electrode. The oxygen sensor measures the oxygen concentration of the gas to be measured by detecting an electromotive force based on the difference in oxygen partial pressure between these electrodes.

  Moreover, in order to protect a solid electrolyte body, an electrode, a lead wire, etc., such an oxygen sensor includes a bottomed cylindrical outer tube formed of a metal material, a ceramic material, or the like that accommodates these. The measurement electrode of the oxygen sensor has a structure in which the pressure is narrowed between the tip of the fixed electrolyte body and the inner surface of the closed end of the outer tube.

JP 2004-294330 A

  By the way, in the oxygen sensor described in Patent Document 1, by placing a large amount of ceramic balls carrying barium carbonate in the vicinity of the electrode to be measured, a hydrocarbon gas contained in the gas to be measured by the catalytic action of platinum, For example, methane gas is decomposed to prevent the oxygen concentration from decreasing.

  However, in the above oxygen sensor, since the measurement electrode is covered with the ceramic ball, the gas to be measured passes through the gap between the ceramic balls and comes into contact with the measurement electrode. For this reason, the gas to be measured stays around the measurement electrode, and the methane gas may be decomposed to cause fine carbon deposition on the measurement electrode. When carbon deposition occurred on the measurement electrode, the electromotive force was not stable, and when carbon deposition occurred over time, the output from the measurement electrode drifted and the measurement result was not stable.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an oxygen sensor that can stably measure the oxygen concentration of a measurement gas containing methane gas.

In the following, means for achieving the above object and its operational effects will be described.
The invention described in claim 1 includes a bottomed cylindrical solid electrolyte body, a pair of electrodes opposed to the inner and outer surfaces of the closed end of the solid electrolyte body, and the gas to be measured. A bottomed cylindrical outer tube having an inlet for the gas flow, and an electrode on the inner surface of the closed end portion functions as a reference electrode in contact with a reference gas, and an electrode on the outer surface of the closed end portion is the gas to be measured In the oxygen sensor that functions as a measurement electrode that contacts the outer surface of the closed end and the inner surface of the closed end of the outer tube, the closed end of the solid electrolyte body and the measurement electrode The gist is that the introduction port is formed in the outer tube so as to be exposed.

  According to this configuration, the closed end portion that is the tip of the solid electrolyte body and the measurement electrode are exposed at the introduction port of the outer tube, in other words, the introduction port is formed in the outer tube so as to be visible. While being able to contact a measurement electrode easily, it can suppress staying around a measurement electrode. Therefore, carbon deposition due to decomposition of methane gas contained in the gas to be measured is suppressed, so that the measurement electrode is not deteriorated and the measurement result can be stabilized.

  According to a second aspect of the present invention, in the oxygen sensor according to the first aspect, a protrusion projecting toward the measurement electrode is provided on the inner surface of the closed end of the outer tube, and the protrusion and the closed end The gist of the invention is to narrow the pressure of the measurement electrode with the outer surface.

  According to this configuration, since the protrusion is provided on the inner surface of the closed end portion of the outer tube, the measurement electrode can be installed at a position away from the inner surface of the closed end portion. For this reason, since a measurement electrode leaves | separates from the inner surface of the closed end part of an outer cylinder pipe | tube with which measurement gas may retain, it can further suppress that measurement gas retains around a measurement electrode. Therefore, the measurement result can be further stabilized.

  According to a third aspect of the present invention, in the oxygen sensor according to the first or second aspect, the measurement electrode is disposed on the outer surface of the closed end portion and the outer surface of the main measurement electrode. The auxiliary measurement electrode is provided, and the auxiliary measurement electrode is formed larger than the main measurement electrode.

  According to this configuration, the auxiliary measurement electrode positioned outside the main measurement electrode and formed larger than the main measurement electrode serves as a catalyst member, and decomposes methane gas contained in the gas to be measured before reaching the main measurement electrode. Therefore, it is possible to further stabilize the measurement result.

  The invention according to claim 4 is the oxygen sensor according to any one of claims 1 to 3, wherein a through-hole penetrating from the outer surface to the inner surface is formed at the tip of the outer tube. It is said.

  According to this configuration, since the through hole is formed at the tip of the outer tube, it is possible to further increase the gas to be measured flowing into the outer tube. For this reason, the flow of the gas to be measured can be made in the outer tube, and the measurement gas can be further prevented from staying around the measurement electrode. Therefore, the measurement result can be further stabilized.

  The gist of the invention described in claim 5 is that, in the oxygen sensor according to any one of claims 1 to 4, a catalyst member is provided on at least one of the inner surface and the outer surface of the outer tube.

According to this configuration, when the gas to be measured enters the outer tube, the catalyst member decomposes the methane gas contained in the gas to be measured, so that the measurement result can be stabilized.
According to a sixth aspect of the present invention, in the oxygen sensor according to any one of the first to fifth aspects, the solid electrolyte body is attached to the sensor body via an airtight case having an airtight structure. It is a summary.

  According to this configuration, since the solid electrolyte body is attached to the main body of the oxygen sensor via an airtight case having an airtight structure, when a crack occurs in the solid electrolyte body, the oxygen sensor is installed in the furnace in which the oxygen sensor is installed. It is possible to suppress the inflowing reference gas to the volume fraction of the airtight case.

  According to the present invention, it is possible to stably measure the oxygen concentration of a measurement gas containing methane gas.

The whole oxygen sensor sectional view. The front end sectional view of an oxygen sensor. (A) Front end side view of oxygen sensor, (b) Front end front view of oxygen sensor. The front end sectional view of an oxygen sensor. The front end sectional view of an oxygen sensor. The front end sectional view of an oxygen sensor. The front end sectional view of an oxygen sensor. The front end sectional view of an oxygen sensor. The front end sectional view of an oxygen sensor.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the oxygen sensor 1 includes, in order from the base end side, a connector 10 for connecting to a measuring instrument (not shown) and a cylindrical case 20 connected to the connector 10. . The oxygen sensor 1 includes a cylindrical cell holding member 40 that is connected to the case 20 and holds the bottomed cylindrical zirconia cell 50, and a cylindrical protective tube 60 that covers the zirconia cell 50. ing. The case 20 and the cell holding member 40 function as an airtight case. The protective tube 60 corresponds to an outer tube.

  The connector 10 is provided on a connector flange 11 formed integrally with the flange. A plurality of connection terminals 13 are provided on the inner surface of the connector 10 via a hermetic seal 12 having an airtight structure. A lead wire 33 is connected to the case 20 side of the connection terminal 13. On the other hand, a case connection flange 21 connected to the connector flange 11 is fixed to the outer surface of the base end of the case 20 by welding. The connector flange 11 and the case connection flange 21 are fastened by bolts 22. Since the metal packing 14 is sandwiched between the connector flange 11 and the case connection flange 21, an airtight structure is formed between the connector flange 11 and the case connection flange 21. In addition, you may employ | adopt not only the metal packing 14 but an O-ring.

  On the side surface of the case 20, a cylindrical supply path 2 that supplies the atmosphere as a reference gas and a cylindrical discharge path 3 that discharges the atmosphere supplied into the sensor protrude perpendicularly to the side surface. It is firmly fixed by welding. At the base ends of the supply path 2 and the discharge path 3, an electromagnetic valve (not shown) is provided as means for stopping the gas flow.

  A case connection flange 23 for closely contacting the case 20 and the cell holding member 40 is fixed to the outer surface of the front end of the case 20 by welding. On the other hand, an airtight holding flange 25 connected to the case connection flange 23 is tightly fixed to the outer surface of the base end of the cell holding member 40 by welding. A ring groove 26 that holds the O-ring 24 is formed on the surface of the airtight holding flange 25 that faces the case connection flange 23. The case connection flange 23 and the airtight holding flange 25 are fastened by a bolt 27 and a nut 28 in a state where the O-ring 24 is installed in the ring groove 26. The case connection flange 23 and the airtight holding flange 25 have an airtight structure by an O-ring 24.

  A concave portion 41 is formed at the distal end of the cell holding member 40, and the proximal end outer surface of the protective tube 60 is tightly fixed to the inner surface of the concave portion 41 by welding. When the oxygen sensor 1 is attached to the heat treatment furnace, a furnace attachment flange 66 attached to the furnace wall of the heat treatment furnace is fixed to the outer surface of the protective tube 60 by welding.

  A distal end outer surface of a cylindrical adapter 30 extending inside the case 20 is connected and fixed to the inner surface of the base end of the cell holding member 40. The cell holding member 40 and the adapter 30 are made of a conductive metal material. Inside the adapter 30, a reference air pipe 31 is provided that extends from the supply path 2 to the inner surface of the closed end portion of the zirconia cell 50 and sends a reference gas to the inside of the tip of the zirconia cell 50. Here, the reference gas supplied into the tip end of the zirconia cell 50 by the reference air pipe 31 is discharged to the proximal end side through the zirconia cell 50, and then passes through the adapter 30 and the mounting bracket 34 to the case 20. And discharged from the discharge path 3 to the outside.

  An air tube connecting member 32 that connects and supports the reference air tube 31 is slidably fitted along the inner wall of the adapter 30 inside the adapter 30. A fitting 34 made of a conductive metal material to which the lead wire 33 connected to the connector 10 is attached is connected and fixed to the inner surface of the proximal end of the adapter 30. A biasing spring 35 that biases the reference air pipe 31 toward the zirconia cell 50 is installed between the mounting bracket 34 and the air pipe connecting member 32. Due to the biasing force of the biasing spring 35, the tip of the reference air tube 31 is in contact with the inner surface of the closed end portion of the zirconia cell 50. The zirconia cell 50 functions as a solid electrolyte body.

  A holding space 42 into which the zirconia cell 50 is fitted is formed inside the cell holding member 40. In the holding space 42, the base end side of the zirconia cell 50 is fitted, and three backup rings 43 and two O-rings 44 are alternately installed. The cell holding member 40 and the zirconia cell 50 have an airtight structure with a backup ring 43 and an O-ring 44. A cell restraining member 36 that urges the zirconia cell 50 toward the closed end portion 61 side of the protective tube 60 and slidably fits along the inner wall of the adapter 30 is fitted on the inner surface of the distal end of the adapter 30. A spring mounting projection 38 that supports a cell biasing spring 37 that biases the cell restraining member 36 toward the distal end is formed on the inner surface of the proximal end side of the adapter 30 over the entire circumference. A cell urging spring 37 that urges the zirconia cell 50 toward the closed end 61 of the protective tube 60 is installed between the spring mounting protrusion 38 and the cell holding member 36. The tip of the zirconia cell 50 is in contact with the inner surface of the closed end 61 of the protective tube 60 by the biasing force of the cell biasing spring 37.

  Here, a pair of opposing electrodes are provided on both the inner and outer surfaces of the cell closed end portion 51 on the tip side of the zirconia cell 50. That is, the reference electrode 52 made of platinum exposed to the reference gas is applied to the inner surface of the cell closed end portion 51. Connected to the reference electrode 52 is a lead wire 33 which is inserted into the reference air tube 31 and wired on the inner surface of the cell closed end portion 51 of the zirconia cell 50. On the other hand, a measurement electrode 53 made of platinum exposed to the gas to be measured is formed on the outer surface of the cell closed end portion 51. The measurement electrode 53 is energized through the mounting bracket 34 to which the lead wire 33 is attached, the adapter 30, the cell holding member 40, and the protective tube 60.

  As shown in FIG. 2, the reference electrode 52 installed on the inner surface of the cell closed end portion 51 of the zirconia cell 50 is made of a platinum paste 52 a in which a platinum paste is pasted on the order of μm. The measurement electrode 53 installed on the outer surface of the cell closed end portion 51 of the zirconia cell 50 includes a main measurement electrode 53a attached to the outer surface of the cell closed end portion 51 and an auxiliary measurement attached to the main measurement electrode 53a. And an electrode 53b. The main measurement electrode 53a measures the concentration of the gas to be measured. Further, the auxiliary measurement electrode 53b is provided for improving the contact stability between the protrusion 63 described later and the main measurement electrode 53a. The main measurement electrode 53a is a platinum paste in which a platinum paste is pasted on the order of μm. The auxiliary measurement electrode 53b is a platinum mesh in which mesh-like platinum is attached to the outer surface of the main measurement electrode 53a.

  The inner surface 62 of the closed end 61 of the protective tube 60 is provided with a hemispherical protrusion 63 that protrudes toward the proximal end of the protective tube 60, in other words, toward the zirconia cell 50. The tip of the zirconia cell 50 urged toward the projection 63 by the cell urging spring 37, in other words, the measurement electrode 53 is pressed against the projection 63. Therefore, the measurement electrode 53 and the protrusion 63 are in a state close to point contact, and the measurement electrode 53 is firmly narrowed by the outer surface of the cell closed end 51 of the zirconia cell 50 and the protrusion 63.

  As shown in FIG. 3A, two inlets 64 for introducing the gas to be measured into the protective tube 60 are provided on the side surface of the protective tube 60 on the closed end 61 side so as to face each other. ing. The base end side end surfaces 64 a of these introduction ports 64 are located on the base end side with respect to the position of the measurement electrode 53, and the closed end side end surfaces 64 b of these introduction ports 64 are on the closed end 61 side of the position of the measurement electrode 53. Is located. That is, when looking into the protective tube 60 through the introduction port 64, the measurement electrode 53 is sufficiently exposed. Further, the closed end side end face 64b of the closed end 51 of the introduction port 64 and the inner face 62 of the closed end 61 are set at the same position, so that the gas to be measured is difficult to stay.

  Further, as shown in FIG. 3B, the closed end portion 61 of the protective tube 60 is provided with four through holes 65 penetrating into the protective tube 60 from the tip. These through holes 65 are arranged around the protrusion 63 so as to surround the protrusion 63. Therefore, it can be suppressed that the measurement gas is sufficiently introduced into the measurement electrode 53 and the measurement gas stays around the measurement electrode 53.

Next, the operation of the oxygen sensor 1 configured as described above will be described.
In the oxygen sensor 1, the gas to be measured in the heat treatment furnace is introduced into the protective tube 60 through the introduction port 64 and the through-hole 65 provided in the protective tube 60, and the tip of the zirconia cell 50 and the protrusion 63 are connected. A measurement electrode 53 interposed therebetween contacts the gas to be measured. Further, the reference electrode 52 provided on the inner surface of the cell closed end portion 51 of the zirconia cell 50 comes into contact with the reference gas supplied by the reference air pipe 31. When the solenoid valves of the supply path 2 and the discharge path 3 are opened, the reference gas is supplied into the reference air pipe 31 and thus into the zirconia cell 50. Then, an electromotive force is generated based on a difference in oxygen partial pressure between the reference electrode 52 in contact with the reference gas and the measurement electrode 53 in contact with the measurement gas, thereby measuring the oxygen concentration of the measurement gas.

  Now, since the protective tube 60 of the oxygen sensor 1 of the present embodiment is provided with a protrusion 63 and the measurement electrode 53 is kept away from the inner surface 62 of the closed end portion 61, it is at a position where the gas to be measured can easily pass. A measurement electrode 53 is installed. Further, the protective tube 60 is provided with an introduction port 64 in a state where the measurement electrode 53 is exposed, and is provided with a through hole 65 penetrating from the tip of the closed end portion 61 to the inside, so that the gas to be measured is retained. And can be supplied to the measurement electrode 53. For this reason, the decomposition of the hydrocarbon gas caused by the residence of the gas to be measured around the measurement electrode 53, and hence the carbon deposition of the methane gas, is suppressed, and the electromotive force can be stabilized. Therefore, the oxygen concentration of the gas to be measured can be stably measured.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) Since the cell closed end portion 51 and the measurement electrode 53 of the zirconia cell 50 are exposed at the introduction port 64 of the protection tube 60, in other words, the introduction port 64 is formed in the protection tube 60 in a visible state, the gas to be measured is measured. While being able to contact the electrode 53 easily, staying around the measurement electrode 53 can be suppressed. Therefore, carbon deposition due to decomposition of methane gas contained in the gas to be measured is suppressed, so that the measurement electrode 53 is not deteriorated and the measurement result (electromotive force) can be stabilized.

  (2) Since the protrusion 63 is provided on the inner surface 62 of the closed end 61 of the protective tube 60, the measurement electrode 53 can be installed at a position away from the inner surface 62 of the closed end 61. For this reason, since the measurement electrode 53 is separated from the inner surface 62 of the closed end portion 61 in which the measurement gas may stay, the measurement gas can be further prevented from staying around the measurement electrode 53. Therefore, the measurement result can be further stabilized.

  (3) Since the through-hole 65 is formed at the tip of the protective tube 60, it is possible to further increase the gas to be measured flowing into the protective tube 60. For this reason, the flow of the gas to be measured can be made in the protective tube 60, and the measurement gas can be further prevented from staying around the measurement electrode 53. Therefore, the measurement result can be further stabilized.

  (4) Since the zirconia cell 50 is attached to the main body of the oxygen sensor 1 via the case 20 and the cell holding member 40 having an airtight structure, when a crack occurs in the zirconia cell 50, the inside of the furnace in which the oxygen sensor 1 is installed The reference gas flowing in from the oxygen sensor 1 can be suppressed to the volume of the case 20.

  (5) Since the projection 63 is hemispherical and the measurement electrode 53 is pinched by the tip of the projection 63, the measurement electrode 53 can be reliably pressed and the cell resistance can be stabilized. Moreover, since the protrusion 63 is hemispherical, stress breakage due to clamping pressure can be suppressed.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
In the above embodiment, the outer diameter of the auxiliary measuring electrode 53b is smaller than the circular shape of the main measuring electrode 53a. However, as shown in FIG. 4, the outer diameter of the auxiliary measuring electrode 53b is smaller than the circular shape of the main measuring electrode 53a. May be formed larger. According to this configuration, the auxiliary measurement electrode 53b formed larger than the main measurement electrode 53a serves as a catalyst member, and methane gas contained in the gas to be measured is decomposed before reaching the main measurement electrode, so that the measurement result is stabilized. Can do.

  -Moreover, as FIG. 5 shows, you may form the auxiliary | assistant measurement electrode 53b in a cap shape. That is, the outer diameter end portion of the auxiliary measurement electrode 53 b is formed so as to cover the cell closed end portion 51. According to this configuration, since the auxiliary measurement electrode 53b covers the cell closed end portion 51, the methane gas contained in the measurement gas can be further decomposed before reaching the main measurement electrode, and the measurement result can be stabilized.

  In the above configuration, as shown in FIGS. 6 and 7, a catalyst member 67 made of platinum mesh or the like may be provided on one of the inner surface and the outer surface of the protective tube 60 so as to cover the introduction port 64. That is, the catalyst member 67 is installed in front of the measurement electrode 53 in the gas path. According to this configuration, when the gas to be measured enters the protective tube 60 from the introduction port 64, the methane gas contained in the gas to be measured is decomposed before the catalyst member 67 reaches the main measurement electrode. Can be stabilized. Further, as shown in FIGS. 6 and 7, the catalyst member 67 made of platinum mesh or the like is provided on one of the inner surface and the outer surface of the protective tube 60 so as to cover the introduction port 64, but is provided on both the inner surface and the outer surface. May be. According to this configuration, methane gas is further decomposed, so that the measurement result can be further stabilized.

  -Moreover, as FIG. 8 shows, the catalyst member 67 may use the fiber body which apply | coated platinum etc. to the inner surface of the protective tube 60, and another support body. According to this configuration, since the gap between the fibrous bodies is narrower than the mesh, the contact with the gas to be measured can be further increased.

  6 and 8, when the through-hole 65 is provided in the closed end portion 61 of the protective tube 60, a fiber in which a platinum mesh, platinum, or the like is applied to the inner surface of the protective tube 60 so as to cover the through-hole 65 A catalyst member 67 made of a body or another carrier may be provided. According to this configuration, when the gas to be measured enters the protective tube 60 from the introduction port 64 or the through hole 65, the methane gas contained in the gas to be measured is decomposed before the catalyst member 67 reaches the main measurement electrode. Therefore, the measurement result can be further stabilized.

In the above configuration, the catalyst member 67 is formed over the entire circumference of the zirconia cell 50 and the protective tube 60, but may be provided in correspondence with the pair of introduction ports 64.
In the above configuration, a platinum alloy may be used instead of platinum.

  The hemispherical protrusion 63 that protrudes toward the base end side of the protective tube 60 is integrally provided on the inner surface 62 of the closed end portion 61 of the protective tube 60. However, the protrusion 63 is formed separately and protected. You may install so that it may protrude to the base end side of the pipe | tube 60. FIG.

  In the above embodiment, the protrusion 63 is hemispherical, but the protrusion 63 may be conical as shown in FIG. In other words, a columnar shape, a prismatic shape, a pyramid shape, or the like may be used as long as the measurement electrode can be held by point contact.

In the above embodiment, platinum is applied to the inner surface of the cell closed end portion 51 to form the reference electrode 52. However, a platinum mesh, a platinum plate, a platinum plate, or the like may be held under pressure to serve as the reference electrode.
In the above embodiment, the measurement electrode 53 is composed of the main measurement electrode 53a made of platinum paste and the auxiliary measurement electrode 53b made of platinum mesh. However, the main measurement electrode 53a made of platinum paste and the auxiliary electrode made of disc-shaped platinum disk are used. You may comprise from the measurement electrode 53b. The measurement electrode 53 is not limited to this as long as the cell resistance can be stabilized.

  In the above embodiment, the protective tube 60 is provided with a pair of introduction ports 64. However, if the measurement electrode 53 is exposed, only one introduction port 64 may be provided. Further, three or more introduction ports 64 may be provided in the protective tube 60.

In the above embodiment, the through hole 65 has a circular cross section, but may have an elliptical cross section.
In the above embodiment, the four through holes 65 are formed in the closed end portion 61 of the protective tube 60. However, 1, 2, 3 or 5 or more may be formed.

  In the above embodiment, the through hole 65 is formed in the closed end portion 61 of the protective tube 60. However, if the gas to be measured is sufficiently introduced into the protective tube 60 by the introduction port 64, the omitted configuration is adopted. Also good.

  In the above embodiment, the zirconia cell 50 is attached to the sensor body via the case 20 having the airtight structure and the cell holding member 40, but the reference gas leakage from the zirconia cell 50 is detected and the supply of the reference gas is stopped. If possible, the airtight structure may be omitted if the pressure difference between the atmosphere and the furnace is small and the leakage into the furnace is small, or if no airtight structure is required.

  In the above embodiment, an electromagnetic valve (not shown) is provided as a means for stopping the gas flow at the base ends of the supply path 2 and the discharge path 3, but any gas flow such as a check valve, an overflow prevention valve, or a manual valve is provided. It is sufficient that a means for stopping is provided.

  DESCRIPTION OF SYMBOLS 1 ... Oxygen sensor, 20 ... Airtight case, 21, 23 ... Case connection flange, 24 ... O-ring, 25 ... Airtight holding flange, 26 ... Ring groove, 30 ... Adapter, 31 ... Reference air pipe, 32 ... Air pipe connecting member 33 ... Lead wire, 34 ... Mounting bracket, 35 ... Biasing spring, 36 ... Cell restraining member, 37 ... Cell biasing spring, 38 ... Spring mounting projection, 40 ... Cell holding member, 41 ... Recess, 42 ... Holding Space, 43 ... Backup ring, 44 ... O-ring, 50 ... Zirconia cell, 51 ... Cell closed end, 52 ... Reference electrode, 53 ... Measurement electrode, 53a ... Main measurement electrode, 53b ... Auxiliary measurement electrode, 60 ... Protection tube , 61 ... closed end, 62 ... inner surface, 63 ... projection, 64 ... introduction port, 64a ... proximal end side end face, 64b ... closed end side end face, 65 ... through hole, 66 ... furnace mounting flange.

Claims (6)

A bottomed cylindrical solid electrolyte body, a pair of electrodes facing both inner and outer surfaces of the closed end portion of the solid electrolyte body, and a bottomed cylindrical shape containing the solid electrolyte body and having an inlet for a gas to be measured And the outer electrode of the closed end functions as a reference electrode in contact with a reference gas, and the outer electrode of the closed end functions as a measurement electrode in contact with the gas to be measured. In the oxygen sensor that narrows the measurement electrode by the outer surface of the closed end and the inner surface of the closed end of the outer tube,
The oxygen sensor, wherein the introduction port is formed in the outer tube so that the closed end portion of the solid electrolyte body and the measurement electrode are exposed. The oxygen sensor according to claim 1, wherein
Providing a protrusion projecting toward the measurement electrode on the inner surface of the closed end of the outer tube,
The oxygen sensor is characterized in that the measurement electrode is narrowed by the protrusion and the outer surface of the closed end. The oxygen sensor according to claim 1 or 2,
The measurement electrode includes a main measurement electrode installed on the outer surface of the closed end and an auxiliary measurement electrode installed on the outer surface of the main measurement electrode,
The oxygen sensor, wherein the auxiliary measurement electrode is formed larger than the main measurement electrode. The oxygen sensor according to any one of claims 1 to 3,
An oxygen sensor characterized in that a through-hole penetrating from the outer surface to the inner surface is formed at the tip of the outer tube. In the oxygen sensor according to any one of claims 1 to 4,
An oxygen sensor, wherein a catalyst member is provided on at least one of an inner surface and an outer surface of the outer tube. In the oxygen sensor according to any one of claims 1 to 5,
The oxygen sensor is characterized in that the solid electrolyte body is attached to the sensor body via an airtight case having an airtight structure.

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