JP2007248313A - Constant-potential electrolysis type gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant-potential electrolysis type gas sensor capable of preventing any electrolyte from leaking. <P>SOLUTION: The constant-potential electrolysis type gas sensor 100 comprises: a case body 1 equipped with a recessed section 13 for containing the electrolyte and a base section 19 for surrounding an aperture part 13a of the recessed section 13; a first electrode supporting membrane 3A; a second electrode supporting membrane 3B; a third electrode supporting membrane 3C; first, second and third leads 21A, 21B and 21C; a sealing member 5; and holding members 6, 7. The first electrode supporting membrane 3A is pressed by the sealing member 5 onto the base section 19 surrounding the aperture part of the recessed section 13, and the first, second and third leads 21A, 21B and 21C and electrodes 32A, 32B and 32C which are disposed in a stacked state in the recessed section 13, are brought into pressured contact with each other respectively by the first electrode supporting membrane 3A being pressed by the sealing member 5 onto the base section 19. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a constant potential electrolytic gas sensor, and more particularly to a constant potential electrolytic gas sensor having a configuration in which thin films on which electrodes are formed are stacked.

Conventionally, for example, detected gases such as sulfur dioxide (SO ₂ ), nitrogen oxide (NOx), carbon monoxide (CO) in exhaust gas from waste incinerators, boiler furnaces, engines, etc. are detected, and the amount is detected. There are potentiostatic gas sensors that are used to measure.

  The constant potential electrolytic gas sensor has a working electrode that detects a test gas, a counter electrode that allows current to flow between the working electrode, and a reference electrode that controls the potential of the working electrode. These working electrode, counter electrode, and reference electrode are arranged in a space partitioned by a porous gas-permeable membrane (gas diffusion membrane) as a diaphragm, and an electrolytic solution is accommodated in this space. The diaphragm is generally composed of a fluororesin-based water-repellent (hydrophobic) porous membrane such as PTFE (polytetrafluoroethylene). The test gas permeates the diaphragm, dissolves in the electrolyte, and contacts the working electrode. The test gas is electrolyzed at the working electrode in which the potential difference from the reference electrode is kept constant, and the electrolytic current flowing according to the electrochemical reaction between the working electrode and the counter electrode is measured. The constant potential electrolytic gas sensor is configured such that the electrolysis current value is proportional to the concentration of the test gas, and by measuring this electrolysis current value, it can be converted to the concentration of the test gas.

  Conventionally, there is a constant potential electrolytic gas sensor in which a diaphragm is provided on a contact surface between an electrolyte and a test gas, and a working electrode is formed on the electrolyte side of the diaphragm. This working electrode is formed on the diaphragm by a film forming method such as a method of attaching a conductor (noble metal or the like) by a sputtering method or a vapor deposition method, or a method of solidifying a conductor (noble metal or the like) with a resin ( For example, see Patent Document 1.) Some of the reference electrode and the counter electrode are formed on a film similar to the above diaphragm. In the present specification, a thin film having a working electrode, a reference electrode or a counter electrode attached to the surface is collectively referred to as an “electrode carrying film”. In addition, the thin films having the working electrode, the reference electrode, and the counter electrode attached to the surface are referred to as “working electrode carrying film”, “reference electrode carrying film”, and “counter electrode carrying film”, respectively.

  By the way, in the conventional constant potential electrolytic gas sensor using the electrode supporting film as described above, as shown in FIG. 5, the working electrode supporting film 203A, the reference electrode supporting film 203B, and the counter electrode supporting film 203C absorb the electrolytic solution. Some of them are housed in the sensor case 201 in a laminated structure in which the electrolyte solution holding members 204A and 204B are alternately sandwiched.

  That is, as shown in more detail in FIG. 6, the working electrode 232A, the reference electrode 232B, and the counter electrode 232C are formed on the water-repellent films 231A, 231B, and 231C, respectively, and the working electrode carrying film 203A, the reference electrode carrying film 203B, and the counter electrode A support film 203C is formed. Then, the working electrode support film 203A, the reference electrode support film 203B, and the counter electrode support film 203C are stacked via the first and second electrolyte solution holding members 204A and 204B. As described above, in the configuration using the electrode supporting film for the working electrode, the reference electrode, and the counter electrode, it is easy to make the electrode performance relatively uniform between the sensors, and in the configuration in which these electrode supporting film groups are stacked. , And has advantages such as simple structure and easy manufacture.

  In such a conventional constant potential electrolytic gas sensor, the lead wires 221A, 221B, and 221C for the working electrode 232A, the reference electrode 232B, and the counter electrode 232B are drawn from between the layers of the laminated structure, and the constant potential electrolytic gas sensor. Are respectively connected to contact pins 222A, 222B, and 222C for exchanging electrical signals with the outside.

The lead wires 221A, 221B, and 221C are water-repellent thin films that constitute the working electrode support film 203A, the reference electrode support film 203B, and the counter electrode support film 203C so that the electrolyte does not leak from the layers from which they are drawn. 231A, 231B, and 231C. Further, in order to maintain the measurement accuracy by limiting the test gas to be supplied only through the working electrode carrying film 203A, the working electrode carrying is carried out so that there is no gap between the working electrode carrying film 203A and the sensor case. The film 203A was pressed against the sensor case 201 with an elastic seal member 205 such as an O-ring or rubber packing.
Japanese Patent Laid-Open No. 9-43195

  However, as a result of studies by the present inventors, it has been found that the conventional constant potential electrolytic gas sensor has the following problems.

  First, as described above, in the potentiostatic gas sensor in which the working electrode support film 203A, the reference electrode support film 203B, and the counter electrode support film 203C are used and are housed in the sensor case 201 in a stacked configuration, the electrode support film is configured. An elastic polymer film is laminated, and the uppermost diaphragm (usually a working electrode support film) is pressed by an elastic seal member 205 such as an O-ring or rubber packing to perform sealing.

  Therefore, the method of tightening the electrode carrying films 203A, 203B, 203C with the O-ring or rubber packing on the sensor case 201 is likely to deteriorate, and the seal of the lead portions of the lead wires 221A, 221B, 221C from between the water-repellent thin films It may be insufficient. As a result, the electrolyte contained in the sensor case 201 leaks.

  Conventionally, for the purpose of removing interference gas, a filter (interference gas removal filter) 209 including an absorbent that absorbs interference gas is attached to the sensor case 201. Depending on the usage environment, the interference gas removal filter 209 may need to be replaced earlier than the life of the constant potential electrolytic gas sensor itself.

  However, conventionally, since the interference gas removal filter 209 is attached to the sensor case 201, there is a case where the sensor case 201 is likely to be distorted when the interference gas removal filter 209 is replaced. This distortion may reduce the sealing performance of the sealing member 205 such as an O-ring or rubber packing that is pressed against the sensor case 201, and may cause leakage of the electrolyte in the sensor case 201.

  When the electrolyte solution leaks and the amount of the electrolyte solution in the sensor case 201 decreases, the electrodes are electrically disconnected, causing an abnormal indication value. Alternatively, the electrolyte that oozes through the lead wires 221A, 221B, and 221C reaches the contact pins 222A, 222B, and 222C, and generates a corrosion potential, which may cause an abnormal indication value.

  Accordingly, an object of the present invention is to provide a constant potential electrolytic gas sensor capable of preventing leakage of an electrolytic solution.

  Another object of the present invention is to provide a constant potential electrolytic gas sensor capable of obtaining a stable indicated value by preventing electrical disconnection between electrodes due to a decrease in the amount of electrolyte.

  Still another object of the present invention is to provide a constant potential electrolytic gas sensor capable of preventing a corrosion potential of a contact pin due to a leaked electrolyte and obtaining a stable indicated value.

  The above object is achieved by the constant potential electrolytic gas sensor according to the present invention. In summary, the present invention relates to a constant potential electrolytic gas sensor that detects an electrolytic current of a test gas that flows between electrodes electrically connected by an electrolytic solution, and a case main body having a recess in which the electrolytic solution is accommodated; A first electrode disposed in the recess, the first electrode carrying film disposed in the case body so as to cover the opening of the recess; and a second electrode; A second electrode carrying film disposed in a laminated state with respect to the first electrode carrying film; a third electrode; and a laminated state with respect to the first and second electrode carrying films in the recess A third electrode-supporting film disposed; and first, second, and third disposed in contact with each of the first, second, and third electrodes in the recessed portion in a stacked state. A lead; disposed on a side surface of the first electrode-supporting film opposite to the concave side And a pressing member that presses the seal member against the first electrode carrying film and attaches to the case body, and the first electrode carrying film is formed by the seal member and the opening of the recess. The first, second, and third electrodes and the first, second, and third leads that are pressed by a base portion that surrounds the portion and are disposed in a stacked state in the recess are the first electrode The constant potential electrolytic gas sensor according to claim 1, wherein the supporting film is pressed against the pedestal portion by the seal member.

  According to an embodiment of the present invention, the constant potential electrolytic gas sensor further includes a first electrolyte holding member that absorbs an electrolyte between the first electrode supporting film and the second electrode supporting film. And a second electrolytic solution holding member that has absorbed the electrolytic solution between the second electrode supporting film and the third electrode supporting film.

  According to an embodiment of the present invention, the case body is further electrically connected to each of the first, second, and third leads, and exchanges electrical signals with the outside of the case body. First, second, and third contact members for the first, second, and third electrodes from the first, second, and third contact members to the first, second, and third electrodes, respectively. First, second, and third passages for guiding the three leads, and at least a part of each of the first, second, and third passages is liquid-tightly sealed. Filler is filled. The filler may be made of a chemical resistant resin. In addition, at least one or all of the first, second, and third passages may be open on the platform.

  According to a preferred embodiment of the present invention, the first electrode carrying film is sandwiched directly between the seal member and the base part over the entire circumference of the base part.

  According to one embodiment of the present invention, the constant potential electrolytic gas sensor further includes a detachable filter for removing an interference gas that interferes with measurement of the test gas, and the interference gas removal filter includes the interference gas removal filter. The interference gas removal filter is attached to the case body so that the pressing state of the seal member by the pressing member does not change when the interference gas removal filter is attached or detached. According to a preferred embodiment, the interference gas removal filter is attached to the case main body via a fixture connected to the case main body at a position different from a fixing portion of the pressing member with respect to the case main body. . The fixing portion of the pressing member with respect to the case main body is provided in the vicinity of the upstream end portion in the pressing direction of the first electrode carrying film by the pressing member in the case main body, and the connecting portion of the attachment tool to the case main body May be provided in the vicinity of the downstream end in the direction of the case body.

  According to the present invention, it is possible to prevent leakage of the electrolytic solution. In addition, according to the present invention, it is possible to prevent electrical disconnection between the electrodes due to a decrease in the amount of the electrolytic solution, and to obtain a stable indication value. Furthermore, according to the present invention, it is possible to prevent the occurrence of the corrosion potential of the contact pin due to the leaked electrolyte and obtain a stable indication value.

  Hereinafter, the constant potential electrolytic gas sensor according to the present invention will be described in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic cross section of one embodiment of a controlled potential electrolytic gas sensor according to the present invention. FIG. 2 shows an assembled partial cross section of one embodiment of a potentiostatic gas sensor.

  The constant potential electrolytic gas sensor 100 of the present embodiment is roughly divided into an electrolytic cell unit 110 and a filter unit 120. The electrolysis cell unit 110 constitutes a constant potential electrolysis gas sensor main body for measuring the test gas, and the filter unit 120 removes interference gas for the measurement of the test gas.

  First, the electrolytic cell unit 110 will be described. In the present embodiment, the electrolysis cell unit 110 is roughly composed of a case body 1 having a recess 13 that constitutes a storage unit for the electrolyte S, and electrode supporting film groups 3A, 3B, and 3C disposed on the case body 1. An O-ring 5 that is an elastic member as a sealing member, and a washer 6 and a case lid 7 as pressing members that are attached by pressing the sealing member 5 to the case body 1 are provided. The electrolysis cell unit 110 further connects the first, second, and third leads 21A, 21B, and 21C drawn from the electrodes included in the electrode supporting film groups 3A to 3C, and the first to third leads 21A to 21C. The first and second contact pins 22A, 22B, and 22C as contact members for exchanging electrical signals with the outside of the case body 1 are provided. The first to third leads 21A, 21B, and 21C are inserted into the case body 1, and the first, second, and third passages as the passages to which the first to third contact pins 22A to 22C are attached. Through-holes 15A, 15B, and 15C are formed.

  FIG. 3 shows the upper surface of the case body 1 of the constant potential electrolytic gas sensor 100 of this embodiment.

  The case main body 1 in FIGS. 1 and 2 shows a cross section taken along the line AA in FIG. 3, and in FIGS. 1 and 2, the first through-holes 15 </ b> A to 15 </ b> C are the first through holes. The first contact pin 22A among the holes 15A and the first to third contact pins 22A to 22C is shown.

  More specifically, the case main body 1 of the electrolytic cell unit 110 has a lower large-diameter portion 11 and an upper small-diameter portion 12 in FIGS. 1 and 2. The large diameter portion 11 has a substantially cylindrical shape, and the small diameter portion 12 has a substantially cylindrical shape concentric with the large diameter portion 11.

  The large-diameter portion 11 of the case body 1 is formed with a recess 13 having an opening 13 a on the meeting surface with the small-diameter portion 12. The recess 13 is formed as a substantially cylindrical hole. The inner diameter of the concave portion 13 is smaller than the inner diameter of the hollow portion 14 of the small diameter portion 12. Therefore, a substantially annular base 19 surrounding the opening 13 a of the recess 13 is formed on the meeting surface of the large diameter portion 11 and the small diameter portion 12. In addition, a space 18 having an inner diameter smaller than the inner diameter of the concave portion 13 is further formed as a pressure adjusting portion substantially at the center of the bottom of the concave portion 13.

  As shown in FIG. 3, first to third through holes 15 </ b> A to 15 </ b> C are formed on the base 19 of the large-diameter portion 11 along the edge of the opening 13 a of the recess 13, preferably at equal intervals. It is open. Each of the first to third through holes 15A to 15C penetrates the large diameter portion 11 of the case body 1 in the axial direction. The first to third contact pins 22A to 22C are attached so as to seal the end portions of the first to third through holes 15A to 15C on the side opposite to the base portion 19. In each of the first to second through holes 15A to 15C, one end of each of the first to third leads 21A to 21C is electrically connected to the first to third contact pins 22A to 22C. Connected.

  FIG. 4 shows the laminated structure of the electrode supporting film groups 3A to 3C with respect to the case body 1 in more detail. In the present embodiment, the electrode supporting film groups 3A to 3C include a working electrode supporting film 3A as a first electrode supporting film, a reference electrode supporting film 3B as a second electrode supporting film, and a third electrode supporting film. As the counter electrode supporting film 3C in this order from the outside of the recess 13 toward the bottom. The working electrode support film 3A, the reference electrode support film 3B, and the counter electrode support film 3C are electrically conductive on the porous gas permeable films (first, second, and third gas permeable films) 31A, 31B, and 31C, respectively. A working electrode 32A, a reference electrode 32B, and a counter electrode 32C made of a material are formed.

  A first water retention sheet 4A as a first electrolyte solution holding member is disposed between the working electrode support film 3A and the reference electrode support film 3B, and between the reference electrode support film 3B and the counter electrode support film 3C. The second water retention sheet 4B as the second electrolyte solution holding member is disposed in the.

  The working electrode support film 3 </ b> A is arranged at the interface between the test gas and the electrolyte S in the case body 1 so as to cover the opening 13 a of the recess 13 serving as a storage part for the electrolyte S, thereby forming a diaphragm. The working electrode 32A is formed on the recess 13 side of the first gas permeable membrane 31A, that is, on the surface in contact with the first water retention sheet 4A. The reference electrode 32B is formed on the surface of the second gas permeable membrane 31B on the side in contact with the first water retention sheet 4A. Furthermore, the counter electrode 32C is formed on the surface of the third gas permeable membrane 31C on the side in contact with the second water retention sheet 4B.

In the present embodiment, the constant potential electrolytic gas sensor 100 is configured as a carbon monoxide (CO) sensor. In this example, a thin film made of PTFE was used as the first to third gas permeable membranes 31A to 31C. As the gas permeable membrane, other porous polymer membranes such as silicone membranes can also be used. In this example, platinum thin films were used as the working electrode 32A, the reference electrode 32B, and the counter electrode 32C. In this embodiment, the working electrode 32A, the reference electrode 32B, and the counter electrode 32C are formed by applying a mixture of a film-forming material and an electrode material (conductive fine particles) to a polymer film and baking it. . That is, in the present embodiment, the working electrode 32A, the reference electrode 32B, and the counter electrode 32C are formed of platinum powder as conductive fine particles on the first to third gas permeable films (PTFE films) as polymer films. A PTFE resin powder as a film forming material was used to form a thin film. The thin films of the working electrode 32A, the reference electrode 32B, and the counter electrode 32 can be formed using other film forming methods such as vapor deposition and sputtering. Further, platinum is usually used as the working electrode 32A, but noble metals such as palladium, gold and silver, or carbon can also be used. As the reference electrode 32B, a noble metal such as platinum, gold or palladium, silver or silver chloride-plated silver, or carbon can be used. In addition, platinum is usually used as the counter electrode 32C, but noble metals such as palladium, gold, and silver can also be used. As the electrolytic solution S, 5M (= mol / L) sulfuric acid (H ₂ SO ₄ ) was used. As the electrolytic solution S, other acids such as phosphoric acid H ₂ PO ₄ or an alkaline solution may be used. The concentration of the electrolytic solution S is usually 1 to 10M. As the first and second electrolyte solution holding members 4A and 4B, non-woven sheets made of polyester fibers were used. As the first and second electrolyte solution holding members 4A and 4B, sponges, filter papers, and the like can be used.

  As described above, the electrode supporting film groups 3A to 3C include the working electrode supporting film 3A, the reference electrode supporting film 3B, and the counter electrode supporting film 3C in the state where the constant potential electrolytic gas sensor 100 is assembled, and the first and second water retaining films. It has a laminated structure laminated via sheets 4A and 4B. Then, one end portion of the first to third leads 21A to 21C is sandwiched and held between the layers so as to be in contact with the working electrode 32A, the reference electrode 32B, and the counter electrode 32C in this stacked structure.

  That is, one end of the first lead 21A is disposed between the working electrode 32A and the first water retention sheet 4A. One end of the second lead 21B is disposed between the first water retaining sheet 4A and the reference electrode 32B. Furthermore, one end portion of the third lead 21C is disposed between the second water retention sheet 4B and the counter electrode 32C. The first to third leads 21 </ b> A to 21 </ b> C drawn from the interlayer are each folded back along the inner wall of the recess 13 as desired, and opened to the top 19 of the case body 1. Introduced in 15A-15C. And it reaches 1st-3rd contact pin 22A-22B attached to the edge part on the opposite side to the base 19 of 1st-3rd through-hole 15A-15C. In this embodiment, as the first to third leads 21A to 21C, flat leads made of platinum, which is the same material as the working electrode 32A, the reference electrode 32B, and the counter electrode 32C, were used. The first to third contact pins were made of brass plated with gold.

  Here, the working electrode 32 </ b> A, the reference electrode 32 </ b> B, and the counter electrode 32 </ b> C are each formed in a substantially disk shape, and the diameter thereof is equal to or smaller than the inner diameter of the recess 13. Further, the second gas permeable membrane 31B, the third gas permeable membrane 31C, the first water retaining sheet 4A, and the second water retaining sheet 4B are each formed in a substantially disc shape, and the diameter thereof is that of the recess 13. It is equal to or smaller than the inner diameter. In the present embodiment, the diameters of the working electrode 32A, the reference electrode 32B, and the counter electrode 32C are smaller than the diameters of the second and third gas permeable membranes 31B and 31C, and the first and second water retaining sheets. The diameters of 4A and 4B are substantially the same as the diameters of the second and third gas permeable membranes 31B and 31C. On the other hand, the first gas permeable membrane 31 </ b> A is formed in a substantially disk shape having a diameter larger than the inner diameter of the concave portion 13 and equal to or smaller than the inner diameter of the hollow portion 14 of the small diameter portion 12. The members of these disk-shaped parts are arranged substantially concentrically with each other and substantially concentrically with the recess 13.

  Accordingly, the working electrode 32A, the reference electrode supporting film 3B (that is, the second gas permeable film 31B and the reference electrode 32B), the counter electrode supporting film 3C (that is, the third gas permeable film 31C and the counter electrode 32C), The first water retaining sheet 4A and the second water retaining sheet 4B are accommodated in the recess 13, but the first gas permeable membrane 31A is not disposed in the recess 13, and the first gas permeable membrane 31A A predetermined range on the inner side of the outer edge is disposed on the base 19 of the case body 1.

  When the electrode supporting film groups 3A to 3C and the first and second water retaining sheets 4A and 4B are arranged on the case body 1, first, the first to third leads 21A to 21C are first passed through the first to third penetrations. First to third ends of the first through third through holes 15A to 15C opposite to the base portion 19 are inserted through the holes 15A to 15C and electrically connected to one end of each. Third contact pins 22A to 22C are attached. Next, the counter electrode carrying film 3C is disposed in the recess 13, and then the third lead 21C is externally connected to the third through hole 15C opened on the base 19 so that one end of the third lead 21C contacts the counter electrode 32C. The third lead 21 </ b> C extending in the direction is bent along the inner wall of the recess 13. Next, the 2nd water retention sheet | seat 4B is arrange | positioned on the counter electrode carrying | support film | membrane 3C so that the 3rd lead | lead 21C may be pinched | interposed between 32C of counter electrodes. Next, the reference electrode carrying film 3B is disposed on the second water retaining sheet 4B, and then the second lead 21B is opened on the base 19 so that one end of the second lead 21B contacts the reference electrode 32B. The second lead 21 </ b> B extending outward from the two through holes 15 </ b> B is bent along the inner wall of the recess 13. Next, the first water retaining sheet 4A is disposed on the reference electrode supporting film 3B so that the second lead 21B is sandwiched between the first water retaining sheet 4A and the reference electrode 32B. Next, one end of the first lead 21A contacts the working electrode 32A of the working electrode carrying film 3A to be placed next from the first through hole 15A opened on the base 19 to the outside. The extending first lead 21A is bent. Since the working electrode 32 </ b> A is disposed in substantially the same plane as the base 19, the first lead A is hardly required to be bent along the inner wall of the recess 13. Finally, the working electrode support film 3A is disposed on the base 19 so that the first lead 21A is sandwiched between the working electrode 32A and the first water retention sheet 4A. The working electrode support film 3A is a base plate in a state in which the first and second water retention sheets 4A and 4B are sufficiently impregnated with the electrolytic solution S and the recessed portion 13 is filled with a predetermined amount of the electrolytic solution S. Arranged on the part 19.

  A washer 6 to which an O-ring 5 is attached is disposed on the case body 1 in a state where the electrode supporting film groups 3A to 3C and the first and second water retention sheets 4A and 4B are disposed on the case body 1. Then, the case lid 7 is attached to the case body 1 so as to press the washer 6 against the case body 1.

  That is, the washer 6 is a ring-shaped member having a substantially cylindrical center hole 61, and an outer edge portion on the case body 1 side is cut away to form a seal member holding portion (step portion) 62. The inner diameter of the center hole 61 of the washer 6 is equal to or larger than the inner diameter of the recess 13 of the case body 1. On the other hand, the maximum outer diameter of the washer 6 is equal to or smaller than the inner diameter of the hollow portion 14 of the small diameter portion 12 of the case body 1 and the opening portion 14a. And this washer 6 is arrange | positioned in the hollow part 14 of the small diameter part 12 of the case main body 1 from the side in which the O-ring 5 was provided.

  Thereby, the O-ring 5 is disposed in the vicinity of the outer edge portion of the working electrode carrying film 3 </ b> A disposed on the base 19. In the present embodiment, the first to third through holes 15 </ b> A to 15 </ b> C are opened from the edge of the recess 13 on the base 19. Therefore, the first gas permeable membrane 31A of the working electrode supporting membrane 3A is directly sandwiched between the O-ring 5 and the pedestal portion 19 over the entire circumference of the pedestal portion 19. The O-ring 5 is in pressure contact with the inner wall of the hollow portion 14 of the small diameter portion 12 of the case body 1. In addition to the O-ring 5, other elastic members such as rubber packing may be used as the seal member.

  The case lid 7 is a cap nut-like member, and a screw portion 73 that meshes with the screw portion 18 formed on the outer periphery of the small diameter portion 12 of the case main body 1 is formed on the inner peripheral surface. The case lid 7 has a center opening 71. The central opening 71 is substantially the same diameter as the central hole 61 of the washer 6 and is arranged concentrically with the central hole 61 of the washer 6 with the case lid 7 attached to the case body 1. After the washer 6 is disposed on the case main body 1, the case lid 7 is screwed into the small-diameter portion 12 of the case main body 1, whereby the washer 6 is attached to the case main body 1 by the flange portion 72 surrounding the central opening 71 of the case lid 7. Can be pressed.

  The case lid 7 is not limited to being fixed to the case main body 1 by screwing, and may be fixed to the case main body 1 by press fitting, for example. In this embodiment, the pressing member is divided into two members: a washer 6 that directly presses the O-ring 5 that is a sealing member, and a case lid 7 that presses the washer 6 and is attached to the case body 1. . Thus, when the case lid 7 is fixed to the case body 1 by screwing, the operation of pressing the seal member and the rotation operation for screwing are separated with a simple configuration, and the electrode carrying film is wrinkled. Generation | occurrence | production can be prevented suitably. However, the present invention is not limited to this, and the pressing member may be a single member or may be divided into a large number (three or more) members as desired.

  As described above, in the constant potential electrolytic gas sensor 100 of the present embodiment, the working electrode support film 3 </ b> A is formed on the base 19 surrounding the opening 13 a of the recess 13 of the case body 1 using the washer 6 and the case lid 7. It is pressed by the ring 5. In the figure, the first water retention sheet 4A, the reference electrode support film 3B, the second water retention sheet 4B, and the counter electrode support film 3C stacked in the lower layer than the working electrode support film 3A and disposed in the recess 13 Is pressed by the working electrode support film 3A. Accordingly, the recess 13 is sealed in a liquid-tight manner, and the working electrode 32A, the reference electrode 32B, the counter electrode 32C, and the first, second, and third leads 21A, Each of 21B and 21C is in pressure contact with each other.

  That is, the constant potential electrolysis gas sensor 100 of the present embodiment is provided with the base 19 for pressing and sealing only the uppermost working electrode support film 3A among the stacked electrode support films. As a result, the first gas permeable membrane 31A of the working electrode support membrane 3A arranged on the outermost part with respect to the electrolytic solution S accommodating portion, that is, the diaphragm can be firmly pressed against the base portion 19. Therefore, the recess 13 is sealed in a liquid-tight manner with respect to the side where the O-ring 5 of the working electrode support film 3A is provided, so that the electrolyte S does not leak from the recess 13 to the small diameter portion 12 side. it can.

  Further, the first water retaining sheet 4A, the reference electrode supporting film 3B, the second water retaining sheet 4B, and the counter electrode supporting film 3C disposed in the recess 13 are firmly pressed against the pedestal portion 19 as described above. The carrier film 3A is compressed in the recess 13. Accordingly, one end of each of the first to third leads 21A to 21C arranged between the layers is surely pressed and electrically connected to the working electrode 32A, the reference electrode 32B, or the counter electrode 32C. Thus, by sandwiching between the layers to obtain electrical connection between the first to third leads 21A to 21C and the respective electrodes, the structure of the potentiostatic gas sensor 100 is simplified and the manufacturing is easy. Instead, the first to third leads 21A to 21B, which are typically made of the same material (platinum), and the respective electrodes are simply electrically connected to each other by contact. Generation of an undesirable current can be prevented.

  As described above, in this embodiment, the first gas permeable membrane 31A made of a water-repellent PTFE membrane is directly pressed against the base 19 of the case body 1 for sealing. Therefore, the first gas permeable film 31A having the water repellency and the first through third through holes 15A to 15C opened at different positions in the circumferential direction of the pedestal 19 extend into the recess 13. Between the third leads 21A to 21C, a substantially complete liquid-tight state can be achieved in a normal use state. Compared with the conventional configuration described with reference to FIGS. 5 and 6, the liquid tightness in the lead-out portion of the lead wire is remarkably improved. However, when the internal pressure of the recess 13 changes due to a change in the temperature of the environment in which the constant potential electrolytic gas sensor 100 is used, it is conceivable that the liquid tightness is lowered.

  Therefore, in the constant potential electrolytic gas sensor 100 of the present embodiment, the first through third through holes 15A to 15C are further provided between the opening on the base 19 and the first to third contact pins 22A to 22C. Filling materials 23A, 23B, and 23C are filled so that at least a part of each, in the present embodiment, the whole is hermetically sealed. As the fillers 23A to 23C, those having sufficient resistance to the electrolytic solution S are used. The fillers 23A to 23C are preferably insulating materials so as not to generate an undesired current even if they contact the first to third leads 21A to 21C. As the fillers 23 </ b> A to 23 </ b> C, a chemical-resistant resin having sufficient resistance to the sulfuric acid used as the electrolytic solution S, for example, an adhesive can be suitably used. In this example, an epoxy resin adhesive was used as the fillers 23A to 23B.

  As described above, in the constant potential electrolytic gas sensor 100 according to the present embodiment, the first to third leads 21A to 21C are opened on the base 19 of the case body 1 after being drawn out from the stacked electrodes. The first through third through holes 15A through 15C are joined to the first through third contact pins 22A through 22C, and the first through third through holes 15A through 15C are filled with the fillers 23A through 23A. By filling each with 23C, the electrolytic solution S was prevented from reaching the first to third contact pins 22A to 22C. As a result, even if the electrolytic solution S passes through the first to third leads 21A to 21C between the first gas permeable membrane 31A and the pedestal 19, the first to third through holes 15A to 15C. Even when it reaches the opening, the electrolyte S is filled with the first to third contact pins 22A by the fillers 23A to 23C filled between the opening and the first to third contact pins 22A to 22C. It can prevent contacting to -22C.

  When the fillers 23A to 23C are used, the first to third through holes 15A to 15C may not be opened on the base portion 19. That is, in the present embodiment, all of the first to third through holes 15A to 15C are open on the base 19, but at least one or all of the first to third through holes 15A to 15C are open. May open in the recess 13. For example, at least one or all of the first to third through holes 15 </ b> A to 15 </ b> C may be opened at the bottom surface or the side wall of the recess 13, and the lead wire may be led to the electrode therefrom. Also in this case, it is possible to prevent the electrolyte from reaching the contact pin by the filler.

  Next, the filter unit 120 will be described. In the present embodiment, the filter unit 120 includes a filter attachment 8 and an interference gas removal filter 9. The interference gas removal filter 9 is detachably attached to the case body 1 by attaching the interference gas removal filter 9 to the filter attachment 8 attached to the case body 1.

  More specifically, the attachment 8 is a cylindrical member having a hollow portion 81, and the outer peripheral surface of the large-diameter portion 11 of the case body 1 is provided on the inner peripheral surface of one end portion (the lower side in the drawing) in the axial direction. A screw portion 82 is formed to be engaged with the screw portion 17 formed in the above. The attachment 8 is placed from the case lid 7 side of the case body 1 after the case lid 7 is attached, and is screwed into the large diameter portion 11.

  In addition, the fixture 8 is not limited to fixing to the case main body 1 by screwing, For example, you may fix to the case main body 1 by press fitting.

An interference gas removal filter 9 is attached to the other end (upper side in the figure) of the attachment 8 in the axial direction. The interference gas removal filter includes a filter main body 91 and a filter seal member 92 attached to the outer periphery of the filter main body 91. The interference gas removal filter 9 is firmly attached to the fixture 8 by press-fitting the filter seal portion 92 to the inner peripheral surface of the end of the fixture 8. The filter main body 91 has air permeability and allows the atmospheric gas of the constant potential electrolytic gas sensor 100 to pass toward the electrolytic cell unit 110, and the gas from the electrolytic cell unit 110 to the outside of the constant potential electrolytic gas sensor 100. Although it is allowed to pass through, an absorbent that absorbs interference gas that affects measurement in the electrolytic cell unit 110 is provided in the ventilation path. In the present embodiment, since the constant potential electrolytic gas sensor 100 is configured as a CO sensor, the filter main body 91 is provided with an absorbent that absorbs and removes NO ₂ that is an interference gas.

  In the present embodiment, the case main body 1, the washer 6, the case lid 7, and the fixture 8 are molded from plastic.

  Thus, in this embodiment, the interference gas removal filter 9 is attached to the case body 1 so that the pressing state of the O-ring 5 by the washer 6 and the case lid 7 does not change by the attachment / detachment of the interference gas removal filter 9. It is attached. More specifically, in the constant potential electrolytic gas sensor 100 of the present embodiment, an electrolysis cell portion (electrolysis cell forming component) 110 including the seal portion in the above-described base portion 19 and the filling portions of the fillers 23A to 23C, and interference gas. The attachment 8 to which the removal filter 9 is attached is made independent. The interference gas removal filter 9 is a portion that does not directly affect the pressing of the first gas permeable membrane 31A by the O-ring 5 in the electrolysis cell portion 110, which is the base portion (bottom portion) of the case body 1 in this embodiment. It attached to the electrolysis cell part 110 via the fixture 8 connected as another member with respect to the large diameter part 11 which is.

  In other words, in this embodiment, the interference gas removal filter 9 is attached to the case body 1 via the attachment 8 connected to the case body 1 at a position different from the fixing portion of the case lid 7 with respect to the case body 1. It is done. In particular, in the present embodiment, the fixing portion of the case lid 7 with respect to the case main body 1 is provided in the vicinity of the upstream end in the pressing direction of the working electrode support film 3A by the washer 6 and the case lid 7 in the case main body 1. 1 is provided in the vicinity of the downstream end of the case body 1 in the same direction. The connecting portion of the attachment 8 is a separate member from the washer 6 and the case lid 7 which are pressing members for the seal member, and is separated from the relatively thin small-diameter portion to which the washer 6 and the case 7 are attached. This corresponds to the relatively thick large-diameter portion 11 that is the base of the case body 1.

  As a result, the casing that accompanies the attachment / detachment of the interference gas removal filter 9, that is, the distortion of the fixture 8 in this embodiment, has a structure that does not affect the sealing performance of the sealing portion of the electrolytic cell portion 110. Even when the interference gas removal filter 9 is attached as described above, the structure in which the test gas passes only through the working electrode supporting film 3A and reaches the recess 13 is maintained.

  In order to verify the effect of the present invention, the following experiment was conducted using the constant potential electrolytic gas sensor 100 of the present example.

(Experimental example 1)
Ten constant potential electrolytic gas sensors (CO sensors) 100 of this example were prepared. And the electric current (residual current) value with respect to CO zero gas (CO concentration 0 ppm air) of each sensor was measured using the potentiostat circuit. Further, the potential difference between the working electrode 32A and the reference electrode 32B was measured using a potentiometer. As a result, in all the sensors, the residual current was 0 to 0.1 μA, and the potential difference was 0 to 0.6 mV. These measurements were performed in an environment at 25 ° C.

  Next, ten test sensors were set in a constant temperature and humidity tester, and a heat cycle test was performed. An operation in which the set temperature of the tester was temporarily increased from −10 ° C. to 50 ° C. and then decreased again to −10 ° C. in 2 hours was 10 cycles, and a heat cycle test of 10 cycles was performed.

  Then, after the heat cycle test, the residual current measurement and the potential difference measurement using CO zero gas were performed again in an environment of 25 ° C. As a result, the measurement results of the residual current value and the potential difference value were the same as before the heat cycle test with all ten sensors.

  The experiment as described above was similarly performed on a constant potential electrolytic gas sensor (CO sensor) having a laminated structure of conventional electrode supporting film groups as shown in FIGS. As a result, the residual current was 0 to 0.1 μA and the potential difference was 0 to 0.6 mV for all 10 test sensors before the heat cycle test, while 10 10 after the heat cycle test. Three of the test sensors had a residual current value of 3 μA (corresponding to a CO concentration of 100 ppm) or more and a potential difference of 3 to 6 mV. This is presumably because the liquid-tightness of the lead-out portion of the lead wire was lowered due to the change in the internal pressure of the electrolytic solution housing portion, and the electrode potential was shifted due to leakage of the electrolytic solution.

  Thus, according to the present embodiment, the leakage of the electrolytic solution S can be prevented satisfactorily, the electrical disconnection between the electrodes due to the decrease in the amount of the electrolytic solution S is prevented, and a stable indication value is obtained. be able to.

(Experimental example 2)
Ten constant potential electrolytic gas sensors (CO sensors) 100 of this example were prepared. And the test which attaches / detaches the interference gas removal filter 9 of each sensor repeatedly (about 100 times) without paying special attention to the distortion of the casing was performed. Then, after this attachment / detachment test, the residual current and potential difference were measured as in Experimental Example 1. As a result, the measured values of the residual current and the potential difference were the same as before the attachment / detachment test even after the attachment / detachment test (residual current 0 to 0.1 μA, potential difference 0 to 0.6 mV).

  The experiment as described above was similarly performed for a conventional constant potential electrolytic gas sensor (CO sensor) having a structure in which the pressing state of the seal member is easily changed by attaching and detaching the interference gas removal filter as shown in FIG. . In the constant potential electrolytic gas sensor shown in FIG. 5, the attachment part of the interference gas removal filter 209 and the pressing part 206 of the O-ring 205 serving as a seal member are provided in the vicinity of the same casing 201. As a result, the residual current was 0 to 0.1 μA and the potential difference was 0 to 0.6 mV in all 10 test sensors before the attachment / detachment test. Five of the detection sensors had a residual current value of 3 μA or more and a potential difference of 3 to 6 mV. This is considered to be because the electrode potential is shifted due to the liquid tightness of the seal portion of the electrolytic solution storage portion being lowered by the attaching / detaching operation of the interference gas removal filter, and the electrolytic solution leaking.

  As described above, according to this embodiment, even when the interference gas removal filter 9 is attached / detached, the leakage of the electrolytic solution S can be satisfactorily prevented, and the distance between the electrodes can be reduced by reducing the amount of the electrolytic solution S. Thus, the stable disconnection value can be obtained.

(Experimental example 3)
A sensor having a configuration in which the fillers 23A to 23C are removed from the constant potential electrolytic gas sensor (CO sensor) 100 of this example was prepared. And the test similar to the said experimental examples 1 and 2 was repeated. As a result, the same result as that of the constant potential electrolytic sensor 100 of this example could be obtained.

  However, in the sensor group excluding the fillers 23A to 23C, when the parts were observed after being stored for a long time after the test, the contact pins 22A to 22C were found to be corroded. When the sensor is used in such a state that the contact pin is corroded by the electrolytic solution, a contact pin corrosion potential is generated, which may affect the indicated value.

  Therefore, in order to prevent the corrosion potential of the contact pins 22A to 22C due to the leaked electrolyte S and further improve the reliability of the constant potential electrolytic gas sensor 100, by providing the fillers 23A to 23C, It is preferable to prevent the electrolyte solution S from leaking more reliably.

  As mentioned above, although this invention was demonstrated according to the specific Example, it should be understood that this invention is not limited to the above-mentioned embodiment.

For example, in the above-described embodiments, the constant potential electrolytic gas sensor has been described as being a CO sensor. However, as is well known to those skilled in the art, the constant potential electrolytic gas sensor is composed of sulfur dioxide (SO ₂ ), nitrogen dioxide ( It is also used for measuring other gases such as NO ₂ ) and nitric oxide (NO). The present invention can be equally applied to a constant-potential electrolysis gas sensor that uses a gas other than the CO gas as a detection target, and the same effect as described above can be obtained. The type of interference gas removal filter may be changed according to the type of test gas, and the principle of the present invention can be applied to a constant potential electrolytic gas sensor that does not have an interference gas removal filter.

It is sectional drawing of one Example of the constant potential electrolytic gas sensor which concerns on this invention. It is an assembly partial sectional view of one example of a controlled potential electrolysis type gas sensor concerning the present invention. FIG. 3 is a top view of a case body included in the constant potential electrolytic gas sensor shown in FIGS. 1 and 2. FIG. 3 is a schematic diagram for explaining a laminated configuration of an electrode supporting film group and an electrolyte solution holding member in the constant potential electrolytic gas sensor shown in FIGS. 1 and 2. It is typical sectional drawing of an example of the conventional constant potential electrolysis type gas sensor which has the laminated structure of an electrode support film group. It is a schematic diagram for demonstrating the laminated structure of the electrode supporting film group of the constant potential electrolytic gas sensor shown in FIG.

Explanation of symbols

1 Case body 3A Working electrode carrying film (first electrode carrying film)
3B Reference electrode support film (second electrode support film)
3C counter electrode support film (third electrode support film)
4A, 4B Water retention sheet (electrolyte holding member)
5 O-ring (seal member)
6 Washer (holding member)
7 Case lid (holding member)
8 Attachment 9 Interference gas removal filter 21A, 21B, 21C Lead 22A, 22B, 22C Contact pin (contact member)
23A, 23B, 23C Filler 31A, 31B, 31C Gas permeable membrane 32A Working electrode 32B Reference electrode 32C Counter electrode

Claims (9)

In a constant potential electrolytic gas sensor for detecting an electrolytic current of a test gas flowing between electrodes electrically connected by an electrolytic solution,
A case body provided with a recess for accommodating an electrolyte solution;
A first electrode disposed in the recess, the first electrode carrying film disposed in the case body so as to cover the opening of the recess;
A second electrode carrying film comprising a second electrode and disposed in a laminated state with respect to the first electrode carrying film in the recess;
A third electrode carrying film comprising a third electrode and disposed in a laminated state with respect to the first and second electrode carrying films in the recess;
First, second, and third leads disposed in contact with each of the first, second, and third electrodes in the recess in a stacked state;
A seal member disposed on a side surface of the first electrode-supporting film opposite to the concave portion;
A pressing member that presses the seal member against the first electrode-supporting film and attaches to the case body;
Have
The first electrode carrying film is pressed by the base member surrounding the opening of the recess by the seal member, and the first, second, and third electrodes arranged in a stacked state in the recess and the first electrode The constant potential electrolytic gas sensor, wherein the first, second, and third leads are pressed against each other when the first electrode-supporting film is pressed against the base portion by the seal member.   Furthermore, a first electrolyte solution holding member that absorbs an electrolyte solution is provided between the first electrode support film and the second electrode support film, and the second electrode support film and the third electrode support film are absorbed. The constant potential electrolytic gas sensor according to claim 1, further comprising a second electrolytic solution holding member that absorbs the electrolytic solution between the electrode supporting film and the electrode supporting film.   The case main body is further electrically connected to each of the first, second, and third leads, and performs first, second, and third for exchanging electric signals with the outside of the case main body. A contact member, and first, second, and third leads for respectively leading the first, second, and third leads from the first, second, and third contact members to the first, second, and third electrodes, respectively. 2 and a third passage, and is filled with a filler so as to liquid-tightly seal at least a part of each of the first, second, and third passages. The constant potential electrolytic gas sensor according to claim 1 or 2.   The constant potential electrolytic gas sensor according to claim 3, wherein the filler is made of a chemical resistant resin.   5. The constant potential electrolytic gas sensor according to claim 3, wherein at least one or all of the first, second, and third passages are opened on the base portion. 6.   The said 1st electrode carrying | support film | membrane is clamped directly between the said sealing member and the said base part over the perimeter of the said base part, The Claim 1 characterized by the above-mentioned. Constant potential electrolytic gas sensor.   Furthermore, the filter has a detachable filter for removing the interference gas that interferes with the measurement of the test gas, and the interference gas removal filter is configured to press the seal member by the pressing member by attaching / detaching the interference gas removal filter. The constant potential electrolytic gas sensor according to any one of claims 1 to 6, wherein the gas sensor is attached to the case main body so as not to change its state.   The interference gas removal filter is attached to the case main body via a fixture connected to the case main body at a position different from a fixing portion of the pressing member with respect to the case main body. 8. The constant potential electrolytic gas sensor according to 7.   The fixing portion of the pressing member with respect to the case main body is provided in the vicinity of the upstream end portion in the pressing direction of the first electrode carrying film by the pressing member in the case main body, and the connecting portion of the attachment tool to the case main body The constant potential electrolytic gas sensor according to claim 8, wherein the gas sensor is provided in the vicinity of a downstream end portion in the direction of the case body.

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