Gas sensor

Abstract

The present invention provides a gas sensor capable of measuring concentrations of O2, H2O, and CO2 in a gas to be measured in a designated space. In a gas sensor 100, a pump control unit adjusts, with an oxygen pump cell 21, the partial pressure of oxygen in a first internal cavity 20 so that substantially all water vapor and carbon dioxide in the gas to be measured is decomposed, adjusts, with a first measuring pump cell 50, the partial pressure of oxygen in a second internal cavity 40 so that hydrogen produced by the decomposition of water vapor is selectively burned, and adjusts, with a second measuring pump cell 41, the partial pressure of oxygen in the vicinity of the surface of an in-cavity second measuring electrode 44 so that carbon monoxide produced by the decomposition of carbon dioxide is selectively burned, and a concentration calculation unit calculates the water vapor concentration on the basis of the electric current flowing through the first measuring pump cell 50, calculates the carbon dioxide concentration on the basis of the electric current flowing in the second measuring pump cell 41, and calculates the oxygen concentration on the basis of the values of electric currents flowing respectively in the pump cells 21, 50, and 41.

Description

Gas Sensor

[0001] The present invention relates to a gas sensor including a sensor element using an oxygen ion conductive solid electrolyte. This application claims priority to Japanese Patent Application No. 2023-209401, filed on December 12, 2023, the contents of which are incorporated herein by reference.

[0002] In so-called controlled atmosphere (CA) storage / CA transportation, it is necessary to adjust the interior of a storage facility such as a storage facility or a transport container to a predetermined gas atmosphere. For example, Japanese Patent Application Laid-Open No. 2020-079686 and Japanese Patent Application Laid-Open No. 2022-041987 disclose an internal air conditioning device (air composition adjustment device) for adjusting the composition of the air inside a CA transport container. It is disclosed that the internal air conditioning device (air composition adjustment device) adjusts the oxygen concentration and carbon dioxide concentration inside the storage facility. Note that in CA storage / CA transportation, the temperature and humidity inside the storage facility are also usually adjusted.

[0003] Japanese Patent Application Laid-Open No. 2020-079686 and Japanese Patent Application Laid-Open No. 2022-041987 disclose that an air conditioning device (air composition conditioning device) is equipped with two gas sensors: an oxygen sensor that measures the oxygen concentration of the air inside the refrigerator, and a carbon dioxide sensor that measures the carbon dioxide concentration.

[0004] Japanese Patent Application Laid-Open No. 2020-079686 Japanese Patent Application Laid-Open No. 2022-041987 Japanese Patent Application Laid-Open No. 5918177 Japanese Patent Application Laid-Open No. 6469464

[0005] Japanese Patent Application Laid-Open Publication Nos. 2020-079686 and 2022-041987 disclose a zirconia current sensor as an oxygen sensor and a non-dispersive infrared (NDIR) sensor as a carbon dioxide sensor. In other words, two different types of gas sensors are used. Japanese Patent Application Laid-Open Publication No. 2020-079686 discloses that the interior air conditioning device may further include an ethylene sensor, but in that case, the number of gas sensors used would increase.

[0006] When an internal air conditioning device includes multiple gas sensors as described above, the device configuration becomes complex. Furthermore, a sensor case is required to house the multiple gas sensors, which may increase the volume occupied by the device within the storage cabinet. However, from the standpoint of storage and transportation efficiency, it is preferable to secure as much storage space as possible relative to the overall capacity of the storage cabinet.

[0007] Therefore, an object of the present invention is to provide a gas sensor that can simultaneously (in parallel) measure the concentrations of oxygen, water vapor, and carbon dioxide in a gas to be measured in a target space such as a storage facility used for CA storage / CA transportation.

[0008] As a result of extensive research, the inventors have invented a gas sensor that can simultaneously (in parallel) measure the concentrations of oxygen, water vapor, and carbon dioxide in a gas to be measured in a target space.

[0009] (1) A gas sensor for detecting oxygen, water vapor, and carbon dioxide in a measurement gas in a target space, comprising a sensor element and a control device for controlling the sensor element, wherein the sensor element comprises: a long, plate-shaped base portion including an oxygen ion conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on a surface of the base portion, a first internal space communicating with the gas inlet via a first diffusion-controlling passage, and a second internal space communicating with the first internal space via a second diffusion-controlling passage; an oxygen pump cell including an intra-space oxygen pump electrode disposed in the first internal space of the measurement gas flow space, and an extra-space oxygen pump electrode disposed at a position of the base portion different from the measurement gas flow space, the extra-space oxygen pump electrode corresponding to the intra-space oxygen pump electrode; a first measurement pump cell including a first in-space measurement electrode disposed in the second internal space of the measurement gas flow space and an external first measurement electrode disposed in the base portion at a position different from the measurement gas flow space and corresponding to the first in-space measurement electrode; a second measurement pump cell including a second in-space measurement electrode disposed in the second internal space of the measurement gas flow space or in a third internal space communicating with the second internal space via a third diffusion-controlling passage, on the opposite side of the second diffusion-controlling passage with respect to the first in-space measurement electrode; and an external second measurement electrode disposed in the base portion at a position different from the measurement gas flow space and corresponding to the second in-space measurement electrode; a reference gas chamber formed inside the base portion and separated from the measurement gas flow space; and a reference electrode disposed in the reference gas chamber, a pump control unit that controls the operations of the oxygen pump cell, the first measuring pump cell, and the second measuring pump cell; and a concentration calculation unit that calculates the concentrations of oxygen, water vapor, and carbon dioxide in the measurement gas, wherein the pump control unit operates the oxygen pump cell to pump oxygen out of the first internal space and adjusts the oxygen partial pressure in the first internal space so that substantially all of the water vapor and carbon dioxide in the measurement gas are decomposed in the first internal space;a gas sensor which operates the first measurement pump cell to pump oxygen into the second internal space and adjusts the oxygen partial pressure in the second internal space so that hydrogen produced by decomposition of the water vapor selectively combusts in the second internal space; operates the second measurement pump cell to pump oxygen near the surface of the second measurement electrode in the space and adjusts the oxygen partial pressure near the surface of the second measurement electrode in the space so that carbon monoxide produced by decomposition of the carbon dioxide selectively combusts near the surface of the second measurement electrode in the space; and the concentration calculation unit calculates the water vapor concentration in the measurement gas based on the value of the current flowing to the first measurement pump cell, calculates the carbon dioxide concentration in the measurement gas based on the value of the current flowing to the second measurement pump cell, and calculates the oxygen concentration in the measurement gas based on the value of the current flowing to the oxygen pump cell, the value of the current flowing to the first measurement pump cell, and the value of the current flowing to the second measurement pump cell.

[0010] Here, the target space in which the gas sensor detects oxygen, water vapor, and carbon dioxide may be a closed space or an airtight space, such as the interior space of a storage facility used for CA storage or CA transportation.

[0011] (2) The gas sensor according to (1), wherein the pump control unit adjusts an oxygen pump voltage applied between the intra-void oxygen pump electrode and the extra-void oxygen pump electrode of the oxygen pump cell to adjust the oxygen partial pressure in the first internal space so that substantially all of the water vapor and carbon dioxide in the measurement gas are decomposed in the first internal space; adjusts a first measurement pump voltage applied between the intra-void first measurement electrode and the extra-void first measurement electrode of the first measurement pump cell to adjust the oxygen partial pressure in the second internal space so that hydrogen produced by decomposition of the water vapor is selectively combusted in the second internal space; and adjusts a second measurement pump voltage applied between the intra-void second measurement electrode and the extra-void second measurement electrode of the second measurement pump cell to adjust the oxygen partial pressure near the surface of the intra-void second measurement electrode so that carbon monoxide produced by decomposition of the carbon dioxide is selectively combusted near the surface of the intra-void second measurement electrode.

[0012] (3) The gas sensor according to (1) or (2), wherein the pump control unit adjusts the oxygen partial pressure in the first internal space based on the value of the electromotive force generated between the oxygen pump electrode in the space and the reference electrode, adjusts the oxygen partial pressure in the second internal space based on the value of the electromotive force generated between the first measurement electrode in the space and the reference electrode, and adjusts the oxygen partial pressure near the surface of the second measurement electrode in the space based on the value of the electromotive force generated between the second measurement electrode in the space and the reference electrode.

[0013] (4) The gas sensor according to any one of (1) to (3), wherein the pump control unit adjusts the oxygen partial pressure in the second internal space so that it is greater than the oxygen partial pressure in the first internal space, and the oxygen partial pressure in the vicinity of the surface of the second measurement electrode in the space is equal to or greater than the oxygen partial pressure in the second internal space.

[0014] (5) The gas sensor according to any one of (1) to (4), wherein the sensor element includes a heater for heating the base portion, and the heater is disposed in the longitudinal direction of the base portion such that the highest temperature point of the base portion is located between the electrode end of the intra-void oxygen pump electrode that is closer to the intra-void first measurement electrode and the electrode end of the intra-void second measurement electrode that is farther from the intra-void first measurement electrode.

[0015] (6) The gas sensor according to any one of (1) to (5), wherein the sensor element further includes an ethylene detection electrode disposed on the surface of the base portion and having no catalytic activity against ethylene gas, and the concentration calculation portion calculates the ethylene concentration in the measurement gas based on an electromotive force generated between the ethylene detection electrode and the reference electrode.

[0016] (7) The gas sensor according to (6), wherein the ethylene detection electrode is disposed farther from the first measurement electrode inside the cavity than the oxygen pump electrode outside the cavity in the longitudinal direction of the base portion.

[0017] (8) The gas sensor according to (6) or (7) above, wherein the ethylene detection electrode is a cermet electrode of a metal and an oxygen ion conductive solid electrolyte, the metal is Au, or the metal is a Pt—Au alloy, and the area ratio of the portion of the surface of a metal particle covered with the gold Au to the portion of the surface of the platinum Pt exposed in the ethylene detection electrode is 0.25 or more.

[0018] (9) The gas sensor according to any one of (1) to (8) above, which is inserted directly through a wall that constitutes the target space.

[0019] (10) A gas composition adjusting storage container that includes a storage container and a gas sensor according to any one of (1) to (9) above that is provided in the storage container, and that adjusts the concentrations of oxygen, water vapor, and carbon dioxide within the storage container.

[0020] According to the present invention, it is possible to provide a gas sensor that can simultaneously (in parallel) measure the concentrations of oxygen, water vapor, and carbon dioxide in a measurement gas in a target space. By using the gas sensor of the present invention, the concentrations of oxygen, water vapor, and carbon dioxide can be measured using a single gas sensor, and therefore, in a gas composition adjustment storage that adjusts the composition of these gases, a gas composition adjustment mechanism inside the storage can be controlled using a single gas sensor.

[0021] 1 is a schematic diagram showing an example of the schematic configuration of a CA storage 501 including the gas sensor 100 of Embodiment 1. FIG. 2 is a schematic vertical cross-sectional view of a sensor element 101 in the longitudinal direction, showing an example of the schematic configuration of the gas sensor 100 of Embodiment 1. FIG. 3 is a block diagram showing the electrical connection relationship between a control device 90, and each pump cell 21, 50, 41, each sensor cell 80, 81, 82, 83 of the sensor element 101, and a heater unit 70 in the gas sensor 100 of Embodiment 1. FIG. 4 is a schematic diagram showing a graph (sensitivity characteristics) showing the correlation between the absolute values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 and the water vapor concentration and carbon dioxide concentration in a measurement gas. FIG. 5 is a schematic vertical cross-sectional view of a sensor element 201 in the longitudinal direction, showing an example of the schematic configuration of a gas sensor 200 of Embodiment 2. 1 is a block diagram showing the electrical connection relationships between a control device 290, and each of the pump cells 21, 50, and 41 of a sensor element 201, each of the sensor cells 80, 81, 82, 83, and 285, and a heater section 70 in a gas sensor 200 of Embodiment 2. FIG. 2 is a schematic vertical cross-sectional view of a sensor element 301 in the longitudinal direction, showing an example of the general configuration of a gas sensor 300 of Embodiment 3. FIG. 3 is a graph showing the relationship between the water vapor concentration and the water vapor detection current Ip1 in Example 1. FIG. 4 is a graph showing the relationship between the carbon dioxide concentration and the carbon dioxide detection current Ip2 in Example 1. FIG. 5 is a graph showing the relationship between the oxygen concentration and the pump current Ip0 in Example 1. FIG. 6 is a graph showing the relationship between the water vapor concentration and the pump current Ip0 in Example 1. FIG. 7 is a graph showing the relationship between the carbon dioxide concentration and the pump current Ip0 in Example 1. FIG. 8 is a graph showing the relationship between the ethylene concentration and the voltage V3 at the ethylene detection sensor cell 285 in Example 3.

[0022] The gas sensor of the present invention is a gas sensor for detecting oxygen, water vapor, and carbon dioxide in a measurement gas in a target space, and includes a sensor element and a control device for controlling the sensor element.

[0023] The gas sensor of the present invention includes a sensor element comprising: a long, plate-shaped base portion including an oxygen ion conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on a surface of the base portion, a first internal space communicating with the gas inlet via a first diffusion-controlling passage, and a second internal space communicating with the first internal space via a second diffusion-controlling passage; an oxygen pump cell including an intra-space oxygen pump electrode disposed in the first internal space of the measurement gas flow space and an external-space oxygen pump electrode disposed at a position different from the measurement gas flow space in the base portion and corresponding to the intra-space oxygen pump electrode; and a first measurement pump cell including a first intra-space measurement electrode disposed in the second internal space of the measurement gas flow space and an external-space first measurement electrode disposed at a position different from the measurement gas flow space in the base portion and corresponding to the first intra-space measurement electrode. a second measurement pump cell including: an in-space second measurement electrode disposed in the second internal space of the measurement gas flow space or in a third internal space communicating with the second internal space via a third diffusion-controlling passage, the in-space second measurement electrode being located on the opposite side of the second diffusion-controlling passage with respect to the in-space first measurement electrode; and an outside-space second measurement electrode disposed in a position different from the measurement gas flow space of the base portion and corresponding to the in-space second measurement electrode; a reference gas chamber formed inside the base portion and separated from the measurement gas flow space; and a reference electrode disposed in the reference gas chamber.

[0024] The control device included in the gas sensor of the present invention includes a pump control unit that controls the operations of the oxygen pump cell, the first measurement pump cell, and the second measurement pump cell, and a concentration calculation unit that calculates the concentrations of oxygen, water vapor, and carbon dioxide in the gas to be measured, wherein the pump control unit operates the oxygen pump cell to pump oxygen out of the first internal space and adjusts the oxygen partial pressure in the first internal space so that substantially all of the water vapor and carbon dioxide in the gas to be measured are decomposed in the first internal space, operates the first measurement pump cell to pump oxygen into the second internal space and adjusts the oxygen partial pressure in the second internal space so that hydrogen produced by decomposition of the water vapor is selectively combusted in the second internal space, and operates the second measurement pump cell to pump oxygen near the surface of the second measurement electrode in the space and adjusts the oxygen partial pressure near the surface of the second measurement electrode in the space so that carbon monoxide produced by decomposition of the carbon dioxide is selectively combusted near the surface of the second measurement electrode in the space, and the concentration calculation unit The water vapor concentration in the measurement gas is calculated based on the value of the current flowing through the first measurement pump cell, the carbon dioxide concentration in the measurement gas is calculated based on the value of the current flowing through the second measurement pump cell, and the oxygen concentration in the measurement gas is calculated based on the value of the current flowing through the oxygen pump cell, the value of the current flowing through the first measurement pump cell, and the value of the current flowing through the second measurement pump cell.

[0025] The gas sensor of the present invention is a gas sensor that measures the ambient gas in a target space. The target space may be a closed space or an airtight space. The target space may be openable or closable with a door or the like. The target space may be, for example, a storage facility such as a warehouse or a transport container. The gas sensor of the present invention may be used when adjusting such a target space to a desired gas composition. For example, the gas sensor may be used to control a gas composition adjustment device such as the interior air adjustment device (air composition adjustment device) disclosed in Japanese Patent Application Laid-Open No. 2020-079686 and Japanese Patent Application Laid-Open No. 2022-041987.

[0026] The gas composition adjusting device is provided, for example, in a storage facility used for so-called controlled atmosphere (CA) storage or CA transportation, and adjusts the interior of the storage facility to a predetermined gas atmosphere. The gas sensor is attached to a storage facility (hereinafter also referred to as a gas composition adjusting storage facility) that is capable of adjusting the gas composition inside the storage facility used for CA storage or CA transportation, and measures the oxygen concentration, water vapor concentration, and carbon dioxide concentration inside the storage facility. These measured values ​​can be used to control the gas composition adjusting device to adjust the gas composition inside the storage facility.

[0027] CA storage refers to storing plants such as fruits and vegetables in an environment where the temperature, humidity, and gas composition are controlled. Here, the gas species to be controlled as the gas composition are typically oxygen and carbon dioxide. Plants include fruits such as bananas and avocados, vegetables, grains, bulbs, and fresh flowers. By maintaining a gas atmosphere in the storage environment with a lower oxygen concentration and a higher carbon dioxide concentration than the atmosphere, plant respiration and decomposition of useful components are suppressed, thereby preventing quality changes. In CA storage, the temperature inside the storage facility is often maintained between 0°C and 30°C. Transporting plants such as fruits and vegetables in such an environment with controlled temperature, humidity, and gas composition is referred to as CA transportation.

[0028] Examples of storage facilities used for CA storage or CA transportation include storage facilities, refrigerated and frozen warehouses, room-temperature warehouses, marine transport containers, land transport containers, etc. In addition to these commercial storage facilities, storage facilities may also include household refrigerators, freezers, storage facilities, etc. The gas sensor of the present invention can be used to monitor the gas composition in such storage facilities and to control the gas composition adjustment mechanism.

[0029] The target space is not limited to a highly airtight space such as the inside of a storage cabinet, but may also be a less airtight space (a space with an opening or a space that is frequently opened and closed).

[0030] Hereinafter, examples of embodiments of the gas sensor of the present invention will be described in detail.

[0031] [Embodiment 1] The gas sensor of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of the general configuration of a CA storage 501 equipped with a gas sensor 100 of embodiment 1. The CA storage 501 includes a storage chamber 502 for storing fruits and vegetables, etc., and a gas composition adjusting device 503 for adjusting the gas composition in the storage chamber 502. The gas composition adjusting device 503 includes a gas composition adjusting mechanism 504 and a gas sensor 100. The gas sensor 100 adjusts the oxygen (O ) in the storage chamber 502. ２ , water vapor H ２ O, and carbon dioxide CO ２ 1 shows an example in which the gas sensor 100 is directly inserted through the wall of the CA storage 1.

[0032] 2 is a schematic vertical cross-sectional view in the longitudinal direction of the sensor element 101, illustrating an example of the schematic configuration of the gas sensor 100 of Embodiment 1. In the following, with reference to FIG. 2 , the upper side of FIG. 2 refers to the top, the lower side to the bottom, the left side of FIG. 2 refers to the leading end side, and the right side to the rear end side.

[0033] The gas sensor 100 also includes a control device 90 that controls the sensor element 101. Figure 3 is a block diagram showing the electrical connection between the control device 90 and the sensor element 101.

[0034] (Sensor Element) The sensor element 101 is a long plate-like element including a base portion 102 having a structure in which a plurality of oxygen ion conductive solid electrolyte layers are stacked. The long plate-like shape is also referred to as a long plate-like shape or a strip-like shape. The base portions 102 are each made of zirconia (ZrO ２The six layers are stacked in this order from bottom to top as viewed in the drawing: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, each of which is made of an oxygen ion conductive solid electrolyte layer such as SiO 2 . The solid electrolyte forming these six layers is dense and airtight. The six layers may all have the same thickness, or each layer may have a different thickness. The layers are bonded together via adhesive layers made of solid electrolyte, and the base portion 102 includes the adhesive layers. While FIG. 2 illustrates a layer structure consisting of six layers, the layer structure of the present invention is not limited to this and any number of layers and layer structure may be used.

[0035] The measurement gas flow space 15 has a gas inlet 10 opening on the surface of the base portion 102, a first internal space 20 communicating with the gas inlet 10 via a first diffusion-controlling passage 11 (first diffusion-controlling portion), and a second internal space 40 communicating with the first internal space 20 via a second diffusion-controlling passage 30 (second diffusion-controlling portion). In the first embodiment, the measurement gas flow space 15 further has a third internal space 61 communicating with the second internal space 40 via a third diffusion-controlling passage 60 (third diffusion-controlling portion). That is, the first embodiment shows an example of a configuration having three internal spaces.

[0036] A gas inlet 10 is formed at one longitudinal end (hereinafter referred to as the tip end) of the sensor element 101, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measurement gas flow space 15, i.e., the measurement gas flow portion, is formed in the longitudinal direction from the gas inlet 10 with a first diffusion-controlling passage 11, a buffer space 12, a fourth diffusion-controlling passage 13 (fourth diffusion-controlling portion), a first internal space 20, a second diffusion-controlling passage 30, a second internal space 40, a third diffusion-controlling passage 60, and a third internal space 61 adjacently and communicating with each other in this order.

[0037] The gas inlet 10, buffer space 12, first internal space 20, second internal space 40, and third internal space 61 are spaces inside the sensor element 101, which are defined by hollowing out the spacer layer 5, with an upper portion defined by the underside of the second solid electrolyte layer 6, a lower portion defined by the upper surface of the first solid electrolyte layer 4, and sides defined by the side surfaces of the spacer layer 5.

[0038] The first diffusion-controlled passage 11, the fourth diffusion-controlled passage 13, and the second diffusion-controlled passage 30 are each provided as two horizontally elongated slits (with their openings extending in the direction perpendicular to the plane of the drawing in FIG. 2). The first diffusion-controlled passage 11, the fourth diffusion-controlled passage 13, and the second diffusion-controlled passage 30 may have any shape that provides a desired diffusion resistance, and the shape is not limited to the slits.

[0039] The third diffusion-controlling passage 60 is provided as a single horizontally elongated slit (with the opening extending in the direction perpendicular to the plane of the drawing in FIG. 2 ) between the spacer layer 5 and the second solid electrolyte layer 6. The third diffusion-controlling passage 60 may have any shape that provides a desired diffusion resistance, and the shape is not limited to the slit.

[0040] Furthermore, a reference gas introduction space 43 is provided at a position farther from the tip side than the measurement gas flow space 15, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, and at a position defined at its sides by the side surfaces of the first solid electrolyte layer 4. The reference gas introduction space 43 has an opening at the other end (hereinafter referred to as the rear end) of the sensor element 101. For example, air is introduced into the reference gas introduction space 43 as a reference gas for concentration measurement.

[0041] The air introduction layer 48 is a layer made of porous alumina, and a reference gas is introduced into the air introduction layer 48 through the reference gas introduction space 43. The air introduction layer 48 is formed so as to cover the reference electrode 42. In this embodiment, the air introduction layer 48 and the reference gas introduction space 43 correspond to the reference gas chamber of the present invention.

[0042] The reference electrode 42 is an electrode disposed in the reference gas chamber. The reference electrode 42 is an electrode formed in a manner sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, the reference electrode 42 is surrounded by an air introduction layer 48 that is connected to the reference gas introduction space 43. That is, the reference electrode 42 is disposed so as to come into contact with the reference gas via the porous air introduction layer 48 and the reference gas introduction space 43. As will be described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20, the second internal space 40, and the third internal space 61. The reference electrode 42 is a porous cermet electrode (e.g., Pt and ZrO) that is rectangular in plan view. ２ The electrode may be formed as a cermet electrode.

[0043] In the measurement gas flow space 15 , the gas inlet 10 is open to the outside space, and the measurement gas is taken into the sensor element 101 from the outside space through the gas inlet 10 .

[0044] In this embodiment, the measurement gas is introduced into the measurement gas flow space 15 through the gas inlet 10 opening at the tip end surface of the sensor element 101, but the present invention is not limited to this. For example, the measurement gas flow space 15 does not need to have a recess for the gas inlet 10. In this case, the first diffusion-controlling passage 11 serves as both the gas inlet and the first diffusion-controlling passage.

[0045] Furthermore, for example, the measurement gas flow space 15 may have an opening on a side surface along the longitudinal direction of the base part 102, the opening communicating with the buffer space 12 or a position of the first internal space 20 close to the buffer space 12. In this case, the measurement gas is introduced from the side surface along the longitudinal direction of the base part 102 through the opening.

[0046] Furthermore, for example, the measurement gas flow space 15 may be configured so that the measurement gas is introduced through a porous body.

[0047] The first diffusion-controlling passage 11 is a portion that provides a predetermined diffusion resistance to the measurement gas taken in through the gas inlet 10 .

[0048] The buffer space 12 is a space provided to mitigate the influence of pressure fluctuations of the measurement gas on the detected value when the pressure of the measurement gas fluctuates. The sensor element 101 may have a structure without the buffer space 12.

[0049] The fourth diffusion-controlling passage 13 is a portion that provides a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 into the first internal space 20. The fourth diffusion-controlling passage 13 is provided in association with the provision of the buffer space 12.

[0050] When the buffer space 12 and the fourth diffusion-controlling passage 13 are not provided, the first diffusion-controlling passage 11 directly communicates with the first internal space 20 .

[0051] The first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the measurement gas introduced through the fourth diffusion-controlled passage 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21. That is, the main pump cell 21 functions as the oxygen pump cell of the present invention.

[0052] The main pump cell 21 is an electrochemical pump cell including an inner main pump electrode 22 of an intra-cavity oxygen pump electrode disposed in the first inner cavity 20 of the measurement gas flow cavity 15, and an outer pump electrode 23 of an extra-cavity oxygen pump electrode disposed at a position of the base 102 different from the measurement gas flow cavity 15 (on the outer surface of the base 102 in FIG. 2 ) and corresponding to the inner main pump electrode 22. The phrase "corresponding to the inner main pump electrode 22" means that the outer pump electrode 23 is provided on the inner main pump electrode 22 with a second solid electrolyte layer 6 interposed therebetween.

[0053] That is, the main pump cell 21 is an electrochemical pump cell including an inner main pump electrode 22 having a ceiling electrode portion 22 a provided on almost the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20, an outer pump electrode 23 provided on the upper surface of the second solid electrolyte layer 6 in a region corresponding to the ceiling electrode portion 22 a so as to be exposed to the external space, and the second solid electrolyte layer 6 sandwiched between these electrodes.

[0054] The inner main pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that define the first internal space 20 and the spacer layer 5 that provides the side walls. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal space 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. Side electrode portions (not shown) are formed on the side wall surfaces (inner surfaces) of the spacer layer 5 that constitute both side wall portions of the first internal space 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and are arranged in a tunnel-like structure at the locations where the side electrode portions are provided.

[0055] The inner main pump electrode 22 and the outer pump electrode 23 are porous cermet electrodes (electrodes in which a metal component and a ceramic component are mixed) that are rectangular in plan view. The metal component preferably contains a catalytically active noble metal (for example, at least one of Pt, Rh, Ir, Ru, and Pd). The ceramic component is not particularly limited, but it is preferable to use an oxygen ion conductive solid electrolyte, similar to the base portion 102. The inner main pump electrode 22 and the outer pump electrode 23 are, for example, Pt containing 0.1 wt. % to 30.0 wt. % Au and ZrO ２ The electrode may be a cermet electrode.

[0056] In the main pump cell 21, a pump voltage (oxygen pump voltage) Vp0 is applied between the inner main pump electrode 22 and the outer pump electrode 23 by a variable power supply 24, and a pump current Ip0 is passed between the inner main pump electrode 22 and the outer pump electrode 23 in a positive or negative direction, thereby making it possible to pump oxygen from the first internal space 20 out to the external space, or to pump oxygen from the external space into the first internal space 20.

[0057] The inner main pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., a main pump control oxygen partial pressure detection sensor cell 80. In the main pump control oxygen partial pressure detection sensor cell 80, an electromotive force (voltage V0) is generated between the inner main pump electrode 22 and the reference electrode 42 due to the difference in oxygen concentration between the atmosphere in the first internal space 20 and the reference gas in the reference gas introduction space 43.

[0058] The oxygen concentration (oxygen partial pressure) in the first internal space 20 can be determined by measuring the voltage V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump. Furthermore, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power supply 24 so that the voltage V0 is constant. This allows the oxygen partial pressure in the first internal space 20 to be maintained at a predetermined value.

[0059] The second diffusion-controlling passage 30 is a section that imparts a predetermined diffusion resistance to the measurement gas, the oxygen concentration (oxygen partial pressure) of which has been controlled by the operation of the main pump cell 21 in the first internal space 20, and guides the measurement gas into the second internal space 40.

[0060] The second internal space 40 is provided as a space for carrying out processing related to the measurement of the water vapor concentration in the measurement gas introduced through the second diffusion-controlled passage 30. When the first measuring pump cell 50 is operated, oxygen is supplied into the second internal space 40 from outside the sensor element 101.

[0061] The first measurement pump cell 50 is an electrochemical pump cell including a first measurement electrode 51, which is an intra-cavity first measurement electrode, disposed in the second internal space 40 of the measurement gas flow space 15, and an extra-cavity first measurement electrode disposed in a position of the base 102 different from the measurement gas flow space 15 and corresponding to the first measurement electrode 51. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the base 102 also functions as the extra-cavity first measurement electrode. "Corresponding to the first measurement electrode 51" means that the outer pump electrode 23 is provided on the first measurement electrode 51 via the second solid electrolyte layer 6.

[0062] That is, the first measurement pump cell 50 is an electrochemical pump cell including a first measurement electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode disposed at a position other than the measurement gas flow space 15, for example, outside the sensor element 101), and the second solid electrolyte layer 6.

[0063] The first measurement electrode 51 is disposed in the second internal space 40 in a tunnel-shaped structure similar to that of the inner main pump electrode 22 provided in the first internal space 20. That is, a ceiling electrode portion 51a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40. Side electrodes (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b are formed on both wall surfaces of the spacer layer 5 that provide the side walls of the second internal space 40, forming a tunnel-shaped structure.

[0064] The first measuring electrode 51 is a porous cermet electrode having a rectangular shape in a plan view, similar to the inner main pump electrode 22 and the outer pump electrode 23. The metal component preferably contains a catalytically active noble metal (for example, at least one of Pt, Rh, Ir, Ru, and Pd). The ceramic component is not particularly limited, but it is preferable to use an oxygen ion conductive solid electrolyte, similar to the base portion 102. For example, Pt containing 0.1 wt. % to 30.0 wt. % Au and ZrO ２ The electrode may be a cermet electrode.

[0065] In the first measurement pump cell 50, a pump voltage (first measurement pump voltage) Vp1 is applied between the first measurement electrode 51 and the outer pump electrode 23 by a variable power supply 52, and a pump current (water vapor detection current) Ip1 is caused to flow between the first measurement electrode 51 and the outer pump electrode 23, thereby enabling oxygen to be pumped into the second internal space 40. In Fig. 2, the direction in which oxygen is pumped into the second internal space 40 is shown as the negative direction.

[0066] The first measurement electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer 3 constitute an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 81 for controlling the first measurement pump. In the oxygen partial pressure detection sensor cell 81 for controlling the first measurement pump, an electromotive force (voltage V1) is generated between the first measurement electrode 51 and the reference electrode 42 due to the difference in oxygen concentration between the atmosphere in the second internal space 40 and the reference gas in the reference gas introduction space 43.

[0067] The oxygen concentration (oxygen partial pressure) in the second internal space 40 can be determined by measuring the voltage V1 in the oxygen partial pressure detection sensor cell 81 for controlling the first measurement pump. The pump voltage Vp1 of the variable power supply 52 is feedback-controlled based on the voltage V1 detected by the oxygen partial pressure detection sensor cell 81 for controlling the first measurement pump.

[0068] The third diffusion-controlling passage 60 is a section that imparts a predetermined diffusion resistance to the measurement gas, the oxygen concentration (oxygen partial pressure) of which has been controlled by the operation of the first measuring pump cell 50 in the second internal space 40, and guides the measurement gas into the third internal space 61.

[0069] The third internal space 61 is provided as a space for carrying out processing related to the measurement of the carbon dioxide concentration in the measurement gas introduced through the third diffusion-controlled passage 60. When the second measurement pump cell 41 is activated, oxygen is supplied into the third internal space 61 from outside the sensor element 101.

[0070] The second measurement pump cell 41 is an electrochemical pump cell including a second measurement electrode 44, which is an in-void second measurement electrode disposed in the third internal space 61 of the measurement gas flow space 15, and an outside-void second measurement electrode disposed in a position of the base 102 different from the measurement gas flow space 15 and corresponding to the second measurement electrode 44. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the base 102 also functions as the outside-void second measurement electrode. "Corresponding to the second measurement electrode 44" means that the outer pump electrode 23 is provided with the second measurement electrode 44 via the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4.

[0071] The second measurement pump cell 41 is an electrochemical pump cell comprising a second measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode disposed at a position other than the measurement gas flow space 15, for example, outside the sensor element 101), the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The second measurement electrode 44 is disposed on the opposite side of the first measurement electrode 51 from the second diffusion-controlling passage 30, i.e., farther from the second diffusion-controlling passage 30 than the first measurement electrode 51.

[0072] The second measurement electrode 44 is a porous cermet electrode having a rectangular shape in a plan view, similar to the inner main pump electrode 22, the outer pump electrode 23, and the first measurement electrode 51. The metal component preferably contains a catalytically active noble metal (for example, at least one of Pt, Rh, Ir, Ru, and Pd). The ceramic component is not particularly limited, but it is preferable to use an oxygen ion conductive solid electrolyte, similar to the base portion 102. For example, Pt containing 0.1 wt. % to 30.0 wt. % Au and ZrO ２ The electrode may be a cermet electrode.

[0073] In the second measurement pump cell 41, a pump voltage (second measurement pump voltage) Vp2 is applied between the second measurement electrode 44 and the outer pump electrode 23 by the variable power supply 46, and a pump current (carbon dioxide detection current) Ip2 is passed between the second measurement electrode 44 and the outer pump electrode 23, thereby making it possible to pump oxygen into the third internal space 61. In Figure 2, the direction in which oxygen is pumped into the third internal space 61 is shown as the negative direction.

[0074] In addition, in order to detect the oxygen partial pressure around the second measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the second measurement electrode 44, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 82 for controlling the second measurement pump. In the oxygen partial pressure detection sensor cell 82 for controlling the second measurement pump, an electromotive force (voltage V2) is generated between the second measurement electrode 44 and the reference electrode 42 due to the difference in oxygen concentration between the atmosphere in the third internal space 61 and the reference gas in the reference gas introduction space 43.

[0075] The oxygen concentration (oxygen partial pressure) in the third internal space 61 can be determined by measuring the voltage V2 in the oxygen partial pressure detection sensor cell 82 for controlling the second measurement pump. The pump voltage Vp2 of the variable power supply 46 is feedback-controlled based on the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for controlling the second measurement pump.

[0076] The second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42 constitute an electrochemical sensor cell 83, and the partial pressure of oxygen in the measurement gas outside the sensor can be detected by the electromotive force (voltage Vref) obtained by this sensor cell 83. In this way, the gas sensor 100 may be provided with the function of a so-called oxygen concentration cell.

[0077] Furthermore, in order to increase the oxygen ion conductivity of the solid electrolyte, the sensor element 101 includes a heater unit 70 that adjusts the temperature by heating and maintaining the temperature of the sensor element 101. The heater unit 70 includes a heater electrode 71, a heater 72, a heater lead 76, a through hole 73, a heater insulating layer 74, and a pressure release hole 75.

[0078] The heater electrode 71 is an electrode formed in a manner to contact the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to a heater power supply 77, which is an external power supply, it is possible to supply power to the heater section 70 from outside.

[0079] The heater 72 is an electrical resistor sandwiched between the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater electrode 71 via a heater lead 76 that is connected to the heater 72 and extends to the rear end side of the sensor element 101 in the longitudinal direction, and via a through hole 73. The heater 72 generates heat when power is supplied from the outside through the heater electrode 71, thereby heating and keeping warm the solid electrolyte that forms the sensor element 101.

[0080] The heater 72 is embedded throughout the entire area from the first internal space 20 to the third internal space 61, allowing the temperature of the sensor element 101 to be adjusted to a temperature at which the solid electrolyte is activated. The temperature needs only to be adjusted so that the main pump cell 21, the first measurement pump cell 50, and the second measurement pump cell 41 can operate. It is not necessary for these entire areas to be adjusted to the same temperature; the sensor element 101 may have a temperature distribution. The sensor element 101 (base portion 102) may have a temperature distribution in the longitudinal direction, or in the thickness direction and / or width direction. For example, the sensor element 101 may be heated so that the temperature of the solid electrolyte and each electrode around the measurement gas flow space 15 becomes approximately 750°C to 900°C.

[0081] Preferably, the heater 72 may be disposed in the longitudinal direction of the base portion 102 so that the highest temperature point of the base portion 102 is located between the electrode end of the intra-void oxygen pump electrode (inner main pump electrode 22) closest to the first intra-void measurement electrode (first measurement electrode 51) and the electrode end of the second intra-void measurement electrode (second measurement electrode 44) farthest from the first intra-void measurement electrode (first measurement electrode 51). That is, in the sensor element 101 (base portion 102), the position of the highest temperature (highest temperature point) in the longitudinal direction of the base portion 102 is preferably located rearward of the rear electrode end of the inner main pump electrode 22 and forward of the rear electrode end of the second measurement electrode 44. The highest temperature point may be located at the rear electrode end of the inner main pump electrode 22 or the rear electrode end of the second measurement electrode 44, but is preferably located rearward of the rear electrode end of the inner main pump electrode 22. More preferably, the heater 72 may be disposed in the longitudinal direction of the base portion 102 so that the hottest point of the base portion 102 is located between the electrode end of the first intra-void measurement electrode (first measurement electrode 51) that is closer to the intra-void oxygen pump electrode (inner main pump electrode 22) and the electrode end of the second intra-void measurement electrode (second measurement electrode 44) that is farther from the first intra-void measurement electrode (first measurement electrode 51). Here, the hottest point may be, for example, the position on the upper surface of the sensor element 101 in the longitudinal direction where the surface temperature is highest.

[0082] The temperature is lower than the maximum temperature point on the front end side of the sensor element 101, and lower than the maximum temperature on the rear end side of the sensor element 101. The temperature may gradually increase from the front end of the sensor element 101 to the maximum temperature point, and may decrease from the maximum temperature point toward the rear end.

[0083] If the heater 72 is arranged so that the hottest point is located further rearward than the rear electrode end of the inner main pump electrode 22, the temperature at the tip end of the sensor element 101 can be lowered, thereby reducing the thermal stress distribution due to the low-temperature measurement gas. Also, if the heater 72 is arranged so that the hottest point is located further frontward than the rear electrode end of the second measurement electrode 44, the area where the electrodes are located, i.e., the area where the measurement gas flow space 15 is located, can be efficiently heated.

[0084] The heater 72 may be designed as appropriate so that the hottest point in the longitudinal direction of the base portion 102 is at a desired position. For example, such a heater 72 may be realized by appropriately designing the thickness of the heating element (electrical resistor), the area of ​​the heating element (electrical resistor) in a plan view, the pattern arrangement (density and sparseness of the linear pattern, etc.), and the like.

[0085] In the sensor element 101 of this embodiment, the heater 72 is embedded in the base portion 102, but this is not limiting. The heater 72 may be disposed so as to heat the base portion 102. That is, the heater 72 may be disposed so as to heat the sensor element 101 to an extent that the main pump cell 21, the first measurement pump cell 50, and the second measurement pump cell 41 can be operated with oxygen ion conductivity. For example, the heater 72 may be embedded in the base portion 102 as in this embodiment. Alternatively, the heater portion 70 may be formed as a heater substrate separate from the base portion 102 and disposed adjacent to the base portion 102.

[0086] The heater insulating layer 74 is an insulating layer made of an insulator such as alumina and formed on the upper and lower surfaces of the heater 72 and heater lead 76. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and heater lead 76, and between the third substrate layer 3 and the heater 72 and heater lead 76.

[0087] The pressure release hole 75 penetrates the third substrate layer 3 and is formed so as to connect the heater insulating layer 74 to the reference gas introduction space 43. The pressure release hole 75 can mitigate an increase in internal pressure that accompanies a temperature increase within the heater insulating layer 74. Note that the pressure release hole 75 may be omitted.

[0088] Furthermore, a predetermined length of the surface of the sensor element 101 from the tip in the longitudinal direction may be covered with a porous protective layer (not shown). The porous protective layer is formed to protect the internal cavity and the region of the sensor element 101 where the electrodes are present from thermal shock due to splashing with water, etc. The porous protective layer is made of ceramics such as alumina, and may have a thickness of approximately 10 μm to 2000 μm. It is also preferable that the porous protective layer is formed to be able to withstand a force of up to approximately 50 N.

[0089] The above-described sensor element 101 is incorporated into the gas sensor 100 in such a manner that the front end of the sensor element 101 contacts the gas to be measured and the rear end of the sensor element 101 contacts the reference gas.

[0090] (Controller) The gas sensor 100 of this embodiment includes the sensor element 101 described above and a controller 90 that controls the sensor element 101. In the gas sensor 100, the electrodes 22, 23, 51, 44, and 42 of the sensor element 101 are electrically connected to the controller 90 via lead wires (not shown). FIG. 3 is a block diagram showing the electrical connections between the controller 90 and the pump cells 21, 50, and 41 of the sensor element 101, the sensor cells 80, 81, 82, and 83, and the heater unit 70. The controller 90 includes the variable power supplies 24, 52, and 46 described above, the heater power supply 77, and a controller 91. The controller 91 includes a heater controller 92, a pump controller 93, and a concentration calculator 94.

[0091] The control unit 91 is realized by a general-purpose or dedicated computer, and a CPU, memory, etc. installed in the computer realize the functions of a heater control unit 92, a pump control unit 93, and a concentration calculation unit 94. When the gas sensor 100 is used for adjusting the gas composition in an internal gas composition adjustment device such as a CA storage cabinet, some or all of the functions of the control device 90 (particularly the control unit 91) may be realized by the internal gas composition adjustment device.

[0092] The control unit 91 is configured to acquire electromotive forces (voltages V0, V1, V2, Vref) in the sensor cells 80, 81, 82, 83 of the sensor element 101, pump currents (Ip0, Ip1, Ip2) in the pump cells 21, 50, 41, and heater voltage Vh and heater current Ih in the heater unit 70. The control unit 91 is also configured to output control signals to the variable power supplies 24, 52, 46 and the heater power supply 77.

[0093] The heater control unit 92 may be configured to control the heater unit 70 (particularly the heater 72). The heater control unit 92 heats the heater 72 and maintains the temperature of the heater 72 at a desired temperature.

[0094] The heater control unit 92 preferably heats the base unit 102 so that the highest temperature point of the base unit 102 is located in the longitudinal direction of the base unit 102 between the electrode end of the oxygen pump electrode (inner main pump electrode 22) in the cavity that is closer to the first measurement electrode in the cavity (first measurement electrode 51) and the electrode end of the second measurement electrode (second measurement electrode 44) that is farther from the first measurement electrode in the cavity (first measurement electrode 51).

[0095] Various known control methods can be used to heat the heater 72. For example, the heater 72 can be heated by applying a constant voltage to it. The output of the heater power supply 77 can also be controlled based on the resistance value of the heater 72. Alternatively, the output of the heater power supply 77 can be controlled based on at least one of the resistance values ​​of the main pump cell 21, the first measurement pump cell 50, and the second measurement pump cell 41. The output of the heater power supply 77 can also be controlled based on at least one of the resistance values ​​of the main pump control oxygen partial pressure detection sensor cell 80, the first measurement pump control oxygen partial pressure detection sensor cell 81, the second measurement pump control oxygen partial pressure detection sensor cell 82, and the sensor cell 83.

[0096] For example, the heater control unit 92 feedback-controls the control signal output to the heater power supply 77 based on the heater resistance value Rh (= Vh / Ih) calculated from the heater voltage Vh and heater current Ih in the heater 72 so that the heater 72 reaches the target temperature.

[0097] The pump control unit 93 is configured to control the operation of the oxygen pump cell (in this embodiment, the main pump cell 21), the first measurement pump cell 50, and the second measurement pump cell 41 so as to measure the concentrations of oxygen, water vapor, and carbon dioxide in the gas to be measured.

[0098] The pump control unit 93 operates the oxygen pump cell (main pump cell 21) to pump oxygen out of the first internal space 20 and adjusts the oxygen partial pressure in the first internal space 20 so that substantially all of the water vapor and carbon dioxide in the measurement gas are decomposed in the first internal space 20; operates the first measurement pump cell 50 to pump oxygen into the second internal space 40 and adjusts the oxygen partial pressure in the second internal space 40 so that the hydrogen produced by the decomposition of the water vapor is selectively combusted in the second internal space 40; and operates the second measurement pump cell 41 to pump oxygen near the surface of the second measurement electrode (second measurement electrode 44) in the space (i.e., in the third internal space 61) and adjusts the oxygen partial pressure near the surface of the second measurement electrode (second measurement electrode 44) in the space (i.e., in the third internal space 61) so that the carbon monoxide produced by the decomposition of the carbon dioxide is selectively combusted near the surface of the second measurement electrode (second measurement electrode 44) in the space.

[0099] The pump control unit 93 may adjust the pump voltages (Vp0, Vp1, Vp2) applied to the pump cells 21, 50, 41 to adjust the oxygen partial pressures in the internal spaces 20, 40, 61. Furthermore, the pump control unit 93 may adjust the oxygen partial pressures in the internal spaces 20, 40, 61, for example, by performing the following feedback control based on the electromotive forces (voltages V0, V1, V2) generated in the sensor cells 80, 81, 82. Specifically, in this embodiment, the control is performed as follows.

[0100] The pump control unit 93 controls the electromotive force (voltage V0) generated between the oxygen pump electrode in the cavity (inner main pump electrode 22) and the reference electrode 42 to be a constant value (set value V0 ＳＥＴ The pump voltage Vp0 of the variable power supply 24 in the main pump cell 21 is feedback-controlled so that the set value V0 ＳＥＴ It is preferable to set the oxygen partial pressure in the atmosphere in the first internal space 20 to a value that will cause all or substantially all of the water vapor and carbon dioxide in the gas to be measured in the first internal space 20 to be decomposed.

[0101] The pump control unit 93 controls the pump so that the electromotive force (voltage V1) generated between the first measurement electrode (first measurement electrode 51) in the cavity and the reference electrode 42 is kept at a constant value (set value V1 ＳＥＴ The pump voltage Vp1 of the variable power supply 52 in the first measuring pump cell 50 is feedback-controlled so that the set value Vp1 is equal to the set value Vp1. ＳＥＴ may be set to a value that causes the oxygen partial pressure in the atmosphere in the second internal space 40 to be an oxygen partial pressure at which hydrogen produced by decomposition of the water vapor selectively burns in the second internal space 40. In other words, it may be set to a value that causes all or substantially all of the hydrogen produced by decomposition of the water vapor to combust near the surface of the first measurement electrode (first measurement electrode 51) in the space of the second internal space 40, and causes no or substantially no combustion of carbon monoxide produced by decomposition of the carbon dioxide near the surface of the first measurement electrode (first measurement electrode 51) in the space of the second internal space 40.

[0102] The pump control unit 93 controls the electromotive force (voltage V2) generated between the second measurement electrode (second measurement electrode 44) in the cavity and the reference electrode 42 to be a constant value (set value V2 ＳＥＴ The pump voltage Vp2 of the variable power supply 46 in the second measuring pump cell 41 is feedback-controlled so that the set value V2 ＳＥＴis preferably set to a value that causes the oxygen partial pressure in the atmosphere near the surface of the second measurement electrode (second measurement electrode 44) in the void (i.e., in the third internal void 61) to be an oxygen partial pressure at which the carbon monoxide produced by the decomposition of carbon dioxide selectively burns near the surface of the second measurement electrode (second measurement electrode 44) in the void. In other words, it is preferably set to a value that causes all or substantially all of the carbon monoxide produced by the decomposition of carbon dioxide to combust near the surface of the second measurement electrode (second measurement electrode 44) in the void.

[0103] The concentration calculation section 94 is configured to calculate the oxygen concentration, water vapor concentration, and carbon dioxide concentration in the measurement gas.

[0104] The concentration calculation unit 94 calculates the water vapor concentration in the measurement gas based on the value of the current (pump current Ip1) flowing through the first measurement pump cell 50, calculates the carbon dioxide concentration in the measurement gas based on the value of the current (pump current Ip2) flowing through the second measurement pump cell 41, and calculates the oxygen concentration in the measurement gas based on the value of the current (pump current Ip0) flowing through the oxygen pump cell (main pump cell 21), the value of the current (pump current Ip1) flowing through the first measurement pump cell 50, and the value of the current (pump current Ip2) flowing through the second measurement pump cell 41.

[0105] The concentration calculation unit 94 acquires the pump current Ip1 in the first measuring pump cell 50, and calculates the water vapor concentration (H ２ O concentration) and conversion parameter (current - H ２ O concentration conversion parameter) in the measurement gas ２ The O concentration is calculated and output as a measurement value of the gas sensor 100. Current -H ２ The O concentration conversion parameter is the pump current Ip1 and the H ２ The current -H is stored in advance in the memory of the control unit 91, which functions as the concentration calculation unit 94, as data representing the relationship between the current and the O concentration (for example, a linear relationship as shown in FIG. 4, which will be described later). ２ The O concentration conversion parameter can be determined appropriately by a person skilled in the art through experiments or the like in advance for the gas sensor 100. ２The O concentration conversion parameter may be, for example, a coefficient of an approximate expression (such as a linear function) obtained by experiment, or may be a function of the pump current Ip1 and the H in the measurement gas. ２ It may be a map showing the correspondence between the current and the O concentration. ２ The O concentration conversion parameter may be a parameter specific to each gas sensor 100, or may be a parameter commonly used by a plurality of gas sensors.

[0106] The concentration calculation unit 94 acquires the pump current Ip2 in the second measuring pump cell 41, and calculates the pump current Ip2 stored in advance and the carbon dioxide concentration (CO ２ Concentration) and conversion parameter (current - CO ２ Based on the CO concentration conversion parameter, ２ The concentration is calculated and output as a measurement value of the gas sensor 100. Current - CO ２ The concentration conversion parameters are the pump current Ip2 and the CO ２ The current - CO is stored in advance in the memory of the control unit 91, which functions as the concentration calculation unit 94, as data representing the relationship between the current and the concentration (for example, a linear relationship as shown in FIG. 4, which will be described later). ２ The concentration conversion parameter can be determined appropriately by a person skilled in the art through experiments or the like in advance for the gas sensor 100. Current - CO ２ The concentration conversion parameter may be, for example, a coefficient of an approximate expression (such as a linear function) obtained by experiment, or may be a value obtained by calculating the pump current Ip2 and the CO concentration in the measurement gas. ２ It may be a map showing the correspondence between the current and the CO concentration. ２ The concentration conversion parameter may be a parameter specific to each gas sensor 100, or may be a parameter commonly used by a plurality of gas sensors.

[0107] The concentration calculation unit 94 acquires the pump current Ip0 in the main pump cell 21, the pump current Ip1 in the first measuring pump cell 50, and the pump current Ip2 in the second measuring pump cell 41, and calculates the oxygen concentration (O ２ Concentration) and conversion parameter (current - O ２Based on the concentration conversion parameter, O in the measurement gas is ２ The concentration is calculated and output as a measurement value of the gas sensor 100. Current - O ２ The concentration conversion parameters are the pump currents Ip0, Ip1, and Ip2 (to be described later) and the O concentration in the measurement gas. ２ The data representing the relationship between the current and the concentration is stored in advance in the memory of the control unit 91, which functions as the concentration calculation unit 94. ２ The concentration conversion parameter can be determined appropriately by a person skilled in the art through experiments or the like in advance for the gas sensor 100. ２ The concentration conversion parameters may be, for example, coefficients of an approximate formula (linear function, etc.) obtained by experiment, or may be calculated by calculating the pump currents Ip0, Ip1, and Ip2 and the O concentration in the measurement gas. ２ It may be a map showing the correspondence between the current and the concentration. ２ The concentration conversion parameter may be a parameter specific to each gas sensor 100, or may be a parameter commonly used by a plurality of gas sensors.

[0108] <Oxygen O ２ , water vapor H ２ O, and carbon dioxide CO ２ Next, the gas sensor 100 having the above-described configuration is used to measure the concentration of oxygen O in the measurement gas in the target space. ２ , water vapor H ２ O, and carbon dioxide CO ２ A method for measuring the concentration of will be described below. As shown in FIG. 1, the case where the inside of a storage room 502 of a CA storage 501 is the target space will be described as an example.

[0109] The gas sensor 100 is disposed so that the tip side of the sensor element 101 is in contact with the ambient gas in the target space. The ambient gas (measurement gas) in the target space typically contains oxygen, water vapor, carbon dioxide, nitrogen, etc.

[0110] The measurement gas is introduced through the gas inlet 10, passes through the first diffusion-controlled passage 11, the buffer space 12, and the fourth diffusion-controlled passage 13 in this order, where a predetermined diffusion resistance is applied, and reaches the first internal space 20.

[0111] In the first internal space 20, the pump control unit 93 operates the main pump cell 21 as described above, so that the oxygen partial pressure in the measurement gas introduced into the first internal space 20 is low enough to decompose all or substantially all of the water vapor and carbon dioxide contained in the measurement gas (for example, 10 -10 ~10 -30 Oxygen is pumped out of the first internal space 20 so that the oxygen pressure in the first internal space 20 becomes approximately 100 bar (approximately 100 bar) atm. The fact that all or substantially all of the water vapor and carbon dioxide contained in the measurement gas are decomposed in the first internal space 20 means that the water vapor and carbon dioxide introduced into the first internal space 20 are not introduced into the second internal space 40.

[0112] When oxygen is pumped out of the first internal space 20 in this manner, a decomposition reaction of water vapor (2H ２ O → 2H ２ +O ２ ), and the decomposition reaction of carbon dioxide (2CO ２ →2CO+O ２ ) is promoted. Hydrogen and oxygen are generated by the decomposition of water vapor, and carbon monoxide and oxygen are generated by the decomposition of carbon dioxide. Of these, oxygen is pumped out by the main pump cell 21 together with oxygen gas that was present in the measurement gas. Meanwhile, hydrogen and carbon monoxide are introduced into the second internal space 40.

[0113] Preferably, the set value V0 of the voltage V0 is set so that the higher the oxygen partial pressure of the measurement gas that has reached the first internal space 20, the lower the oxygen partial pressure (target oxygen partial pressure) after adjustment in the first internal space 20. ＳＥＴ This can achieve a more reliable pumping of oxygen.

[0114] The measurement gas, which contains hydrogen produced by the decomposition of water vapor and carbon monoxide produced by the decomposition of carbon dioxide, passes through the second diffusion-controlling passage 30, where a predetermined diffusion resistance is applied, and reaches the second internal space 40.

[0115] In the second internal space 40, the pump control unit 93 operates the first measurement pump cell 50 as described above, thereby pumping oxygen into the second internal space 40. As a result, of the measurement gas containing hydrogen and carbon monoxide that has reached the vicinity of the surface of the first measurement electrode 51 in the second internal space 40, only hydrogen is selectively reacted with the oxygen present at that position and combusted. ２ +O ２ →2H ２ Oxygen is pumped in by the first measuring pump cell 50 so that the decomposition of oxygen into the gas under measurement is promoted and an amount of water vapor is generated again that correlates with the amount of water vapor contained in the gas under measurement introduced from the gas inlet 10. The correlation of the amount of water vapor means that the amount of water vapor contained in the gas under measurement introduced from the gas inlet 10 and the amount of water vapor generated again by burning the hydrogen produced by the decomposition of water vapor are the same or within a certain error range that is allowable from the viewpoint of measurement accuracy.

[0116] At this time, the pump current (water vapor detection current) Ip1 flowing through the first measurement pump cell 50 is approximately proportional to the concentration of water vapor generated by hydrogen combustion near the surface of the first measurement electrode 51 (the water vapor detection current Ip1 and the water vapor concentration are linearly related). Because the amount of water vapor generated by hydrogen combustion correlates with the amount of water vapor contained in the measurement gas introduced through the gas inlet 10, by detecting the water vapor detection current Ip1, the water vapor concentration in the measurement gas can be calculated based on the value of the detected water vapor detection current Ip1.

[0117] If water vapor is not present in the measurement gas introduced from the gas inlet 10, decomposition of water vapor does not occur in the first internal space 20, and hydrogen is not introduced into the second internal space 40. Therefore, the voltage V1 is set to the target value (set value V1) while a water vapor detection current Ip1 of a small magnitude corresponding to an offset current OFS (to be described later) flows. ＳＥＴ ) is maintained.

[0118] The measurement gas, which contains the combustion of hydrogen produced by the decomposition of water vapor and the carbon monoxide produced by the decomposition of carbon dioxide, passes through the third diffusion-controlling passage 60, where a predetermined diffusion resistance is applied, and reaches the third internal space 61.

[0119] In the third internal space 61, the pump control unit 93 operates the second measurement pump cell 41 as described above, thereby pumping oxygen into the third internal space 61. As a result, of the measurement gas containing carbon monoxide that has reached a position near the surface of the second measurement electrode 44 in the third internal space 61, only carbon monoxide is selectively reacted with oxygen present at that position and combusted. The combustion reaction of carbon monoxide (2CO + O ２ →2CO ２ ) is promoted, and oxygen is pumped in by the second measuring pump cell 41 so that an amount of carbon dioxide is generated again that correlates with the amount of carbon dioxide contained in the measurement gas introduced from the gas inlet 10. Note that the correlation of the amount of carbon dioxide means that the amount of carbon dioxide contained in the measurement gas introduced from the gas inlet 10 and the amount of carbon dioxide generated again by burning carbon monoxide produced by its decomposition are the same or within a certain error range that is allowable from the viewpoint of measurement accuracy.

[0120] At this time, the pump current (carbon dioxide detection current) Ip2 flowing through the second measurement pump cell 41 is approximately proportional to the concentration of carbon dioxide produced by the combustion of carbon monoxide near the surface of the second measurement electrode 44 (the carbon dioxide detection current Ip1 and the carbon dioxide concentration are linearly related). Because the amount of carbon dioxide produced by the combustion of carbon monoxide correlates with the amount of carbon dioxide contained in the measurement gas introduced through the gas inlet 10, by detecting the carbon dioxide detection current Ip2, the carbon dioxide concentration in the measurement gas can be calculated based on the value of the detected current.

[0121] If carbon dioxide is not present in the measurement gas introduced from the gas inlet 10, decomposition of carbon dioxide does not occur in the first internal space 20, and carbon monoxide is not introduced into the third internal space 61. Therefore, the voltage V2 is set to the target value (set value V2 ＳＥＴ ) is maintained.

[0122] By controlling the oxygen partial pressure as described above, hydrogen is more likely to be selectively combusted near the surface of the first measurement electrode 51 and carbon monoxide is more likely to be selectively combusted on the surface of the second measurement electrode 44. This is because hydrogen and carbon monoxide have different gas diffusion speeds, with hydrogen and carbon monoxide having faster diffusion speeds and being more likely to come into contact with oxygen and combust, and hydrogen and carbon monoxide are more likely to combine with oxygen, or in other words, to combust.

[0123] 4 is a graph (sensitivity characteristics) showing the correlation between the absolute values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 and the water vapor concentration and carbon dioxide concentration in the measurement gas. As mentioned above, the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 are negative current values, but for simplicity of explanation, the values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 are shown as absolute values ​​in FIG.

[0124] In FIG. 4 , the solid line L illustrates the ideal correlation between the water vapor detection current Ip1 and the water vapor concentration, and the ideal functional relationship between the carbon dioxide detection current Ip2 and the carbon dioxide concentration. The solid line L is a linear line with a non-zero intercept on the vertical axis. Note that for convenience, only one solid line L is illustrated in FIG. 4 . However, in reality, the sensitivity characteristics for water vapor and carbon dioxide are different, and therefore the correlations (slope and intercept values) do not usually match. Furthermore, when the water vapor concentration and carbon dioxide concentration are zero (a state in which water vapor and carbon dioxide are not present), the values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 should be zero. However, in reality, due to the influence of oxygen pumping by the main pump cell 21, there is a shortage of oxygen compared to the target oxygen concentration (oxygen partial pressure) near the surfaces of the first measuring electrode 51 and the second measuring electrode 44. Therefore, even in the absence of water vapor and carbon dioxide, the pumping currents required to achieve the target oxygen concentrations, i.e., the water vapor detection current Ip1 and the carbon dioxide detection current Ip2, flow slightly. The water vapor detection current Ip1 and the carbon dioxide detection current Ip2 at this time are particularly referred to as offset currents OFS.

[0125] The sensitivity characteristic shown by the solid line L in FIG. 4 is determined in advance, and the concentration calculation unit 94 calculates the current −H ２ O concentration conversion parameter and current-CO ２ The respective sensitivity characteristics are stored in advance as concentration conversion parameters. When actually detecting water vapor and carbon dioxide, the values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 are constantly measured, and the water vapor concentration and carbon dioxide concentration are calculated based on the individual measured values ​​and the pre-stored sensitivity characteristics.

[0126] As described above, the first measurement pumping cell 50 pumps oxygen into the vicinity of the surface of the first measurement electrode 51, and the second measurement pumping cell 41 pumps oxygen into the vicinity of the surface of the second measurement electrode 44, independently of each other. Therefore, the calculation of the water vapor concentration based on the water vapor detection current Ip1 and the calculation of the carbon dioxide concentration based on the carbon dioxide detection current Ip2 can be performed independently of each other. In other words, even if the measurement gas contains only water vapor or carbon dioxide, the gas sensor 100 can preferably obtain the concentration of either water vapor or carbon dioxide.

[0127] In this embodiment, in order to measure the water vapor concentration and carbon dioxide concentration accurately, it is necessary to reliably decompose the water vapor and carbon dioxide in the measurement gas in the first internal space 20 both when determining the sensitivity characteristics and during actual use, to reliably burn only hydrogen without burning carbon monoxide near the surface of the first measurement electrode 51, and to reliably burn carbon monoxide near the surface of the second measurement electrode 44.

[0128] To achieve this, it is preferable that the pump control unit 93 adjusts the oxygen partial pressure so that the oxygen partial pressure in the second internal space 40, particularly near the surface of the first measurement electrode 51, is higher than the oxygen partial pressure in the first internal space 20, and so that the oxygen partial pressure near the surface of the second measurement electrode 44 is equal to or higher than the oxygen partial pressure in the second internal space 40, particularly near the surface of the first measurement electrode 51. Specifically, the set value V0 of the electromotive force (voltage V0) generated between the oxygen pump electrode in the space (inner main pump electrode 22) and the reference electrode 42 is set to V0. ＳＥＴ , the set value V1 of the electromotive force (voltage V1) generated between the first measurement electrode (first measurement electrode 51) in the void and the reference electrode 42 ＳＥＴ , and the set value V2 of the electromotive force (voltage V2) generated between the second measurement electrode (second measurement electrode 44) in the void and the reference electrode 42 ＳＥＴ It is advisable to set it to a value that satisfies the above-mentioned relationship of oxygen partial pressure.

[0129] If the target oxygen partial pressure in the first internal space 20 is too high, the pumping of oxygen by the main pump cell 21 will be reduced, resulting in insufficient generation of hydrogen through the decomposition of water vapor and insufficient generation of carbon monoxide through the decomposition of carbon dioxide. In this case, the remaining oxygen and the measurement gas containing the remaining water vapor and carbon dioxide may be introduced near the surface of the first measuring electrode 51 or even near the surface of the second measuring electrode 44. As a result, the amount of oxygen pumped near the surfaces of the first measuring electrode 51 and the second measuring electrode 44 will be less than the amount that should be pumped, resulting in a sensitivity characteristic with a smaller slope, as shown by the dashed line L1 in FIG. 4, compared to the desired sensitivity characteristic (solid line L in FIG. 4). Therefore, when the gas sensor 100 is used with such partial pressure settings, the calculated water vapor and carbon dioxide concentrations will be lower than the actual values, even if the preset sensitivity characteristics are correct.

[0130] Furthermore, if the target oxygen partial pressure near the surface of the first measurement electrode 51 and the second measurement electrode 44 is too low, the oxygen pumping in each electrode may be insufficient, resulting in some hydrogen and carbon monoxide remaining unoxidized. In this case, the sensitivity characteristic is also likely to have a small slope, as shown by the dashed line L1 in Figure 4. Therefore, it becomes difficult to accurately calculate the concentration.

[0131] On the other hand, if the oxygen partial pressure near the surface of the first measurement electrode 51 is too high, carbon monoxide oxidation may also occur at that location, even though the desired sensitivity is to selectively oxidize only hydrogen. In this case, the gas sensor 100 will exhibit a sensitivity characteristic (dashed line L2 in FIG. 4 ) with a larger intercept and slope than the desired sensitivity characteristic (solid line L in FIG. 4 ) (the intercept value is the offset current OFS2). If the gas sensor 100 is used under such partial pressure settings, the calculated water vapor and carbon dioxide concentrations will be overestimated, even if the preset sensitivity characteristic is correct. Furthermore, if the oxygen partial pressure near the surface of the second measurement electrode 44 is too high, the offset current will be larger than the desired sensitivity characteristic (solid line L in FIG. 4 ), as shown by the offset current OFS2 in the sensitivity characteristic of dashed line L2.

[0132] In order to more reliably obtain the sensitivity characteristic as exemplified by the solid line L in FIG. 4, the oxygen partial pressure in the first internal space 20 should be set to 10 -10 atm~10 -30 atm, and the oxygen partial pressure in the second internal space 40, particularly near the surface of the first measuring electrode 51, is set to 10 -5 atm~10 -15 atm, and the oxygen partial pressure in the third internal space 61, particularly in the vicinity of the surface of the second measuring electrode 44, is set to 10 0 atm~10 -15 It is more preferable to set the pressure to 1000 kJ / cm@2 atm.

[0133] Next, measurement of oxygen concentration will be described. The pump control unit 93 operates the main pump cell 21 to pump oxygen from the first internal space 20, thereby decomposing all or substantially all of the water vapor and carbon dioxide contained in the measurement gas in the first internal space 20. At this time, the main pump cell 21 pumps out oxygen that was present in the measurement gas and oxygen produced by decomposition of water vapor and carbon dioxide. Meanwhile, the first measuring pump cell 50 pumps in oxygen for oxidizing hydrogen produced by decomposition of water vapor, and the second measuring pump cell 41 pumps in oxygen for oxidizing carbon monoxide produced by decomposition of carbon dioxide. Therefore, the difference C=C0-C1-C2 between the concentration of oxygen pumped out of the first internal space 20 (denoted as C0) and the concentration of oxygen pumped into the vicinity of the surface of the first measurement electrode 51 in the second internal space 40 and the vicinity of the surface of the second measurement electrode 44 in the third internal space 61 (denoted as C1 and C2, respectively) corresponds to the concentration of oxygen in the measurement gas introduced from the gas inlet 10. Since C0, C1, and C2 are values ​​approximately proportional to the pump currents Ip0, Ip1, and Ip2, respectively, the relationship between C0 and Ip0, the relationship between C1 and Ip1, and the relationship between C2 and Ip2 are determined in advance, and the concentration calculation unit 94 calculates these values ​​by calculating the current -O ２ By storing the pump currents Ip0, Ip1, and Ip2 in advance as concentration conversion parameters, the oxygen concentration in the measurement gas can be calculated from the detected values ​​of the pump currents Ip0, Ip1, and Ip2. Alternatively, the relationship between the value of |Ip0|-|Ip1|-|Ip2| (Ip0+Ip1+Ip2 in the gas sensor 100 of FIG. 2) and the oxygen concentration can be calculated in advance by the concentration calculation unit 94 by converting the currents Ip0, Ip1, and Ip2 into the oxygen concentration. ２ It may be stored in advance as a concentration conversion parameter.

[0134] Alternatively, the oxygen concentration may be calculated based on the electromotive force (voltage Vref) of the sensor cell 83 .

[0135] <Storage with Gas Sensor> The target space in which the gas sensor 100 measures the concentration may be, for example, a storage with a gas composition adjustment function, such as the CA storage 501 illustrated in FIG. 1 . The gas sensor 100 described above may be installed in a storage with a gas composition adjustment function for use. The gas composition adjustment storage (e.g., the CA storage 501) includes a storage and a gas sensor of the present invention installed in the storage, and is configured to adjust the concentrations of oxygen, water vapor, and carbon dioxide within the storage. The gas composition adjustment storage may further include a gas composition adjustment mechanism, such as the gas composition adjustment mechanism 504 illustrated in FIG. 1 . That is, the gas sensor 100 described above may be installed in a storage with a gas composition adjustment mechanism 504, such as the CA storage 501 illustrated in FIG. 1 .

[0136] As shown in FIG. 1 , the gas sensor 100 may be directly inserted through a wall (including a ceiling, floor, and side wall) that constitutes the target space (storage chamber 502 in FIG. 1 ). That is, the gas sensor 100 may be inserted into a through-hole drilled in the wall, and the tip side of the sensor element 101 may be in contact with the atmospheric gas in the storage chamber 502. The gas sensor 100 may be directly inserted into any appropriate position on the wall that constitutes the target space. The gas sensor 100 may be provided so that the tip side of the sensor element 101 is in contact with the atmospheric gas in the storage chamber 502. The tip of the sensor element 101 or the tip side of the gas sensor 100 may protrude into the storage chamber 502, or the tip may be located within the wall of the through-hole drilled in the wall.

[0137] In a storage facility with a gas composition adjustment function, such as the CA storage facility 501, the gas sensor 100 may measure the concentrations of oxygen, water vapor, and carbon dioxide in the measurement gas in the target space (storage chamber 502). Based on these measurement results, the gas composition in the target space can be adjusted. For example, based on the measurement values ​​of the gas sensor 100, the gas composition adjustment mechanism 504 may be operated to adjust the target space (storage chamber 502) to a desired gas composition. In such a storage facility, the oxygen and carbon dioxide concentrations, as well as the temperature and humidity, are controlled. Thus, the gas sensor of the present invention can be used to monitor the atmospheric gas in the storage facility and to control the gas composition. In other words, the gas sensor of the present invention can be used for CA storage control and CA storage facility gas composition control.

[0138] For example, in the indoor air conditioning device (air composition adjustment device) disclosed in Japanese Patent Application Laid-Open No. 2020-079686 and Japanese Patent Application Laid-Open No. 2022-041987, two gas sensors—an oxygen sensor for measuring oxygen concentration and a carbon dioxide sensor for measuring carbon dioxide concentration—are housed in a sensor case and placed inside the refrigerator. Although there is no disclosure regarding humidity control, it is believed that humidity control is typically performed using a separate hygrometer. Thus, when an indoor air conditioning device is equipped with multiple gas sensors, the device configuration becomes complex. Furthermore, since a sensor case is required to house multiple gas sensors, the volume occupied by the indoor air conditioning device within the storage cabinet is likely to increase. When multiple gas sensors of different types are housed in a single sensor case, interference between the gas sensors must also be considered, potentially resulting in a more complicated configuration.

[0139] On the other hand, by using the gas sensor of the present invention, it is possible to measure the concentrations of oxygen, water vapor, and carbon dioxide with a single gas sensor. In the above-described indoor air conditioning device used for gas composition for CA storage / CA transportation, the oxygen and carbon dioxide concentrations of the indoor air can be adjusted using a single gas sensor. Therefore, the configuration of the indoor air conditioning device can be simplified and the device capacity can be reduced. Furthermore, by using the gas sensor of the present invention, it is possible to measure the water vapor concentration, i.e., the absolute moisture content, and therefore the humidity control required for CA storage / CA transportation can also be performed. In other words, the measurement of the oxygen concentration and carbon dioxide concentration for adjusting the oxygen and carbon dioxide concentrations in the indoor air, as well as the measurement of the water vapor concentration (absolute moisture content) for humidity control, can be performed using a single gas sensor. In this respect, too, the device configuration can be simplified and its volume can be reduced. Therefore, a larger storage space can be secured relative to the overall capacity of the storage facility, which is preferable from the standpoint of storage efficiency and transportation efficiency.

[0140] 1, the gas sensor 100 can be inserted directly through the wall of the storage cabinet, eliminating the need for a sensor case and further simplifying the device configuration. When the gas sensor 100 is inserted directly through the wall of the storage cabinet, only the tip of the gas sensor 100 protrudes into the cabinet, or the gas sensor 100 is located almost entirely within the wall, so the temperature of the gas sensor 100, particularly the sensor element 101, has almost no effect on the temperature inside the cabinet.

[0141] Furthermore, one or more gas sensors 100 may be installed in a target space. For example, in the case of a large storage cabinet, multiple gas sensors 100 may be installed at any appropriate positions to measure the concentrations of oxygen, water vapor, and carbon dioxide at multiple positions within the storage cabinet. If there is a difference in the measured values ​​of the multiple gas sensors 100, adjustments may be made, for example, by circulating the gas within the storage cabinet using a circulator or the like to make the gas atmosphere within the storage cabinet uniform.

[0142] [Embodiment 2] As Embodiment 2, a gas sensor capable of measuring the ethylene concentration in addition to the concentrations of oxygen, water vapor, and carbon dioxide in a measurement gas will be described below with reference to the drawings. Fig. 5 is a schematic vertical cross-sectional view of a sensor element 201 in the longitudinal direction, showing an example of the general configuration of a gas sensor 200 of Embodiment 2. Fig. 6 is a block diagram showing the electrical connection between a control device 290 and the sensor element 201. In Figs. 5 and 6, the same components as those in the gas sensor 100 of Embodiment 1 shown in Figs. 2 and 3 are designated by the same reference numerals, and their description will be omitted.

[0143] In the gas sensor 200 of the second embodiment, the sensor element 201 further includes an ethylene detection electrode 284 that is disposed on the surface of the base portion 102 and does not have catalytic activity against ethylene gas.

[0144] In this embodiment 2, the ethylene detection electrode 284 is disposed on the upper surface of the second solid electrolyte layer 6, on a side farther from the first measurement electrode (first measurement electrode 51) inside the cavity than the outer pump electrode 23 of the oxygen pump electrode outside the cavity in the longitudinal direction of the base portion 102.

[0145] The ethylene detection electrode 284 is an electrode that does not have catalytic activity against ethylene gas. The term "not having catalytic activity against ethylene gas" means that ethylene decomposition does not occur at the ethylene detection electrode 284, or that the ethylene decomposition activity is suppressed to an extent that the ethylene concentration can be measured.

[0146] The ethylene detection electrode 284 may be a cermet electrode made of a metal and an oxygen ion conductive solid electrolyte, and may be porous.

[0147] The metal contained in the ethylene detection electrode 284 may be, for example, an alloy of platinum and gold (Pt—Au alloy). The oxygen ion conductive solid electrolyte may be, for example, ZrO ２ can be used.

[0148] In the ethylene detection electrode 284, catalytic activity with respect to ethylene gas is suppressed by appropriately determining the composition of the Pt—Au alloy. In other words, the decomposition reaction of ethylene gas in the ethylene detection electrode 284 is suppressed. The composition of the Pt—Au alloy, which has catalytic activity, may be determined so as to appropriately suppress catalytic activity with respect to ethylene gas depending on the expected ethylene gas concentration range. Because ethylene gas is not decomposed in the ethylene detection electrode 284, the potential of the ethylene detection electrode 284 is selectively varied in response to the concentration of ethylene gas. In other words, the ethylene detection electrode 284 is configured to have the characteristics of having a high concentration dependency of its potential with respect to ethylene gas, but a low concentration dependency of its potential with respect to other gas components.

[0149] More specifically, in the ethylene detection electrode 284, the area ratio (Au / Pt ratio) of the portion of the surface of the metal particle coated with gold Au to the portion where platinum Pt is exposed is preferably 0.25 or more.

[0150] As described above, the Au / Pt ratio is the area ratio of the portion coated with gold Au (portion where Au is present on the surface) to the portion where platinum Pt is exposed (portion where Pt is present on the surface) on the surface of the metal particle in the ethylene detection electrode 284. It is the area ratio of the metal and solid electrolyte constituting the cermet electrode on the metal particle surface. When the area of ​​the portion where Pt is exposed on the metal particle surface is equal to the area of ​​the portion coated with Au, the Au / Pt ratio is 1. More specifically, it is considered that the metal particle is in a state where an Au-rich Pt—Au alloy is formed near the surface of a Pt-rich Pt—Au alloy particle.

[0151] In this specification, the Au / Pt ratio is calculated using the detection values ​​for Au and Pt in the Auger spectrum obtained by performing AES (Auger electron spectroscopy) analysis on the surface of the metal particles, using the following formula: Au / Pt ratio=Au detection value / Pt detection value (1).

[0152] The Au / Pt ratio can also be calculated using the relative sensitivity factor method from the peak intensities of the detected peaks for Au and Pt obtained by XPS (X-ray photoelectron spectroscopy) analysis of the surface of the metal particles. The Au / Pt ratio value obtained by this method and the Au / Pt ratio value calculated based on the results of AES analysis can be considered to be substantially the same.

[0153] In the ethylene detection electrode 284, if the Au / Pt ratio is 0.25 or higher, the potential of the ethylene detection electrode 284 exhibits a significant dependence on the ethylene concentration. Therefore, for example, the ethylene concentration can be measured accurately in a concentration range of 0 ppm to 500 ppm. Furthermore, for example, if the ethylene detection electrode 284 has an Au / Pt ratio of 0.40 or higher, the ethylene concentration can be measured accurately even at lower concentrations (for example, a concentration range of 0 ppm to 100 ppm). There is no particular upper limit to the Au / Pt ratio. Therefore, in the ethylene detection electrode 284, the surfaces of the metal particles may be entirely made of Au. Alternatively, the metal particles may be composed solely of Au. However, when the ethylene detection electrode 284 made of a Pt—Au alloy is formed by screen printing and then co-firing (co-firing) the solid electrolyte layer and the electrode, as described below, the Au abundance ratio is preferably 2.30 or lower. This is because the melting point of Au (1064°C) is lower than the firing temperature, and therefore an excessively high Au abundance ratio would undesirably melt the ethylene detection electrode 284. This also applies when the ethylene detection electrode 284 is formed only from Au.

[0154] The ethylene detection electrode 284, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer 3 constitute an electrochemical sensor cell, i.e., an ethylene detection sensor cell 285.

[0155] In the ethylene detection sensor cell 285, based on the principle of mixed potential, ethylene C is detected in the vicinity of the ethylene detection electrode 284 and the vicinity of the reference electrode 42. ２ H ４The potential difference [electromotive force (voltage V3)] occurs due to the difference in concentration of C. Based on the electromotive force (voltage V3) generated at this time, the C in the measurement gas is ２ H ４ The concentration can be determined.

[0156] The position of the ethylene detection electrode 284 is not limited to the position shown in Fig. 5, and may be on the surface of the base portion 102. The ethylene detection sensor cell 285, which detects electromotive force, is considered to operate favorably at a lower temperature than the pump cells 21, 50, and 41 that pump oxygen in and out. For example, the ethylene detection electrode 284 may be disposed at a position whose temperature is lower than that of the pump cells 21, 50, and 41. When the heater 72 is positioned in the longitudinal direction of the base portion 102 so that the highest temperature point of the base portion 102 is between the electrode end of the intra-void oxygen pump electrode (inner main pump electrode 22) that is closer to the intra-void first measurement electrode (first measurement electrode 51) and the electrode end of the intra-void second measurement electrode (second measurement electrode 44) that is farther from the intra-void first measurement electrode (first measurement electrode 51), the ethylene detection electrode 284 is preferably positioned in the longitudinal direction of the base portion 102 on the side farther from the intra-void first measurement electrode (first measurement electrode 51) than the outer pump electrode 23 of the extra-void oxygen pump electrode, and is preferably positioned on the upper surface of the sensor element 101.

[0157] The sensor element 201 may further include a surface protective layer (not shown) on the upper surface of the second solid electrolyte layer 6, covering the ethylene detection electrode 284 and the outer pump electrode 23. The surface protective layer is provided to prevent poisoning substances contained in the measurement gas from adhering to the ethylene detection electrode 284 and the outer pump electrode 23. The surface protective layer may be, for example, porous alumina. However, the surface protective layer may be provided so as to have a pore diameter and a pore size that do not limit the flow of gas between the ethylene detection electrode 284 and the outer pump electrode 23 and the outside of the element. As with the sensor element 101 of the first embodiment, a predetermined length of the surface of the sensor element 201 extending from the tip in the longitudinal direction may be covered with a porous protective layer (not shown). Either or both of the surface protective layer and the porous protective layer may be provided.

[0158] 6 is a block diagram showing the electrical connections between the control device 290, the pump cells 21, 50, and 41 of the sensor element 201, the sensor cells 80, 81, 82, 83, and 285, and the heater unit 70. The concentration calculation unit 294 included in the control unit 291 of the control device 290 has the same configuration as the concentration calculation unit 94 of the first embodiment, and is also configured to calculate the ethylene concentration in the measurement gas based on the electromotive force (voltage V3) generated between the ethylene detection electrode 284 and the reference electrode 42 in the ethylene detection sensor cell 285.

[0159] The concentration calculation unit 294 acquires the electromotive force (voltage V3) in the ethylene detection sensor cell 285, and calculates the electromotive force (voltage V3) and the ethylene concentration (C ２ H ４ Concentration) and conversion parameter (electromotive force - C ２ H ４ Based on the concentration conversion parameter, ２ H ４ The concentration is calculated and output as a measurement value of the gas sensor 200. ２ H ４ The concentration conversion parameter is the electromotive force (voltage V3) and the C in the measurement gas. ２ H ４ The data representing the relationship between the electromotive force and the concentration is stored in advance in the memory of the control unit 291 that functions as the concentration calculation unit 294. ２ H ４ The concentration conversion parameter can be determined appropriately by a person skilled in the art through experiments or the like in advance for the gas sensor 200. ２ H ４ The concentration conversion parameter may be, for example, a coefficient of an approximate formula obtained by experiment, or may be a value obtained by calculating the voltage V3 and the C ２ H ４ It may be a map showing the correspondence between the electromotive force and the concentration. ２ H ４ The concentration conversion parameter may be a parameter specific to each gas sensor 200, or may be a parameter commonly used by a plurality of gas sensors.

[0160] The gas sensor 200 of the second embodiment can measure the concentrations of ethylene gas in addition to oxygen, water vapor, and carbon dioxide. Fruits and vegetables (fruits and vegetables) among the plants that are subject to CA storage / CA transportation often generate ethylene gas. Because ethylene gas has the effect of promoting the ripening of fruits and vegetables, it is preferable to keep the ethylene gas concentration low in a gas composition adjustment storage facility such as the CA storage facility 501 in order to maintain the freshness of the fruits and vegetables. The gas sensor 200 of the second embodiment can measure the ethylene gas concentration without adding any additional gas sensors, and therefore, the ethylene gas concentration can also be monitored without complicating the configuration of the gas composition adjustment storage facility.

[0161] [Embodiment 3] In Embodiments 1 and 2, the sensor element 101 and the sensor element 201 have three internal cavities, namely, the first internal cavities 20, the second internal cavities 40, and the third internal cavities 61. However, the gas sensor of the present invention is not limited to this. A gas sensor 300 may have two internal cavities, namely, the first internal cavities 20 and the second internal cavities 40, as in the case of a sensor element 301 shown in FIG. 7. FIG. 7 is a schematic vertical cross-sectional view in the longitudinal direction showing an example of the general configuration of a gas sensor 300 of Embodiment 3 including the sensor element 301. In FIG. 7, the same components as those in the gas sensor 100 of Embodiment 1 shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0162] In the sensor element 301, the measurement gas flow space 315 has a gas inlet 10 opening on the surface of the base portion 102, a first internal space 20 communicating with the gas inlet 10 via a first diffusion-controlling passage 11, and a second internal space 40 communicating with the first internal space 20 via a second diffusion-controlling passage 30. The second internal space 40 in the sensor element 301 is formed to extend further rearward in the longitudinal direction of the sensor element than the second internal space 40 in the sensor element 101.

[0163] The ceiling electrode portion 51a of the first measurement electrode 51 is provided on almost the entire lower surface of the second solid electrolyte layer 6 that defines the second internal space 40, and the bottom electrode portion 51b of the first measurement electrode 51 is provided on a portion of the upper surface of the first solid electrolyte layer 4.

[0164] The second measurement electrode 44 is disposed in the second internal space 40 on the opposite side of the first measurement electrode 51 from the second diffusion-controlling passage 30, generally speaking, farther from the second diffusion-controlling passage 30 than the first measurement electrode 51. The second measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 in the second internal space 40. The second measurement electrode 44 is covered with a third diffusion-controlling layer 360 that functions as a third diffusion-controlling passage. The third diffusion-controlling layer 360 is a porous alumina layer that provides a predetermined diffusion resistance to the measurement gas that is about to come into contact with the second measurement electrode 44 in the second internal space 40. In other words, the third diffusion-controlling layer 360 is provided for the purpose of limiting the amount of combustible gas that comes into contact with the second measurement electrode 44 and isolating the second measurement electrode 44 from the second internal space 40. The third diffusion-controlling layer 360 also functions as an electrode protection layer that protects the second measurement electrode 44 from adhesion of particles and the like.

[0165] In the oxygen partial pressure detection sensor cell 82 for controlling the second measurement pump, an electromotive force (voltage V2) is generated between the second measurement electrode 44 and the reference electrode 42 due to the difference in oxygen concentration between the atmosphere near the surface of the second measurement electrode 44 covered with the third diffusion-controlling layer 360 and the reference gas in the reference gas introduction space 43. In the third embodiment, the surface of the second measurement electrode 44 includes not only the portion in contact with the third diffusion-controlling layer 360 but also the walls of the numerous fine pores present inside the porous cermet that constitutes the second measurement electrode 44 and that communicate with the outside.

[0166] As described above, in the sensor element 301 of the third embodiment, the porous third diffusion-controlling layer 360 plays a role similar to that of the third diffusion-controlling passage 60 in the sensor element 101 of the first embodiment. Therefore, the oxygen concentration, water vapor concentration, and carbon dioxide concentration in the measurement gas in the target space can be measured in the same manner as in the gas sensor 100 of the first embodiment.

[0167] The gas sensor of the present invention is not limited to the above-described first to third embodiments. The present invention may include various types of gas sensors as long as they achieve the object of the present invention of simultaneously (parallelly) measuring the concentrations of oxygen, water vapor, and carbon dioxide in a measurement gas in a target space. For example, Japanese Patent Publication No. 5918177 and Japanese Patent Publication No. 6469464 may be referenced.

[0168] In the above-described first to third embodiments, the inner main pump electrode 22 is composed of a ceiling electrode portion 22a formed on the ceiling surface of the first internal space 20, a bottom electrode portion 22b formed on the bottom surface of the first internal space 20, and a side electrode portion formed on the side surface of the first internal space 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b. However, this is not limited to this. The inner main pump electrode 22 may be formed, for example, only on the ceiling surface of the first internal space 20. Alternatively, it may be formed only on the bottom surface of the first internal space 20. Furthermore, for example, when the inner main pump electrode 22 has a ceiling electrode portion 22a and a bottom electrode portion 22b, the ceiling electrode portion 22a and the bottom electrode portion 22b may be the same size or different sizes. The same applies to the first measurement electrode 51. Furthermore, although the measurement electrode 44 is formed on the bottom surface of the third internal space 61 in the above-described first and second embodiments and on the bottom surface of the second internal space 40 in the above-described third embodiment, the present invention is not limited to this. The measurement electrode 44 may be formed on the ceiling surface, or may be formed in a tunnel shape like the inner main pump electrode 22.

[0169] In the above-described first to third embodiments, the outer pump electrode 23 functions as three electrodes: the extra-void oxygen pump electrode in the main pump cell 21, the first extra-void measurement electrode in the first measurement pump cell 50, and the second extra-void measurement electrode in the second measurement pump cell 41. However, this is not limiting. For example, the extra-void oxygen pump electrode, the first extra-void measurement electrode, and the second extra-void measurement electrode may each be formed as separate electrodes. For example, one or more of the extra-void main pump electrode, the first extra-void measurement electrode, and the second extra-void measurement electrode may be provided separately from the outer pump electrode 23 on the outer surface of the base portion 102 so as to be in contact with the gas to be measured. Alternatively, the reference electrode 42 may also function as one or more of the extra-void oxygen pump electrode, the first extra-void measurement electrode, and the second extra-void measurement electrode.

[0170] In the gas sensor 100 of the first embodiment described above, the concentration calculation unit 94 is configured to calculate the water vapor concentration, the carbon dioxide concentration, and the oxygen concentration, but this is not limited thereto. The gas sensor 100 may calculate one or two of the water vapor concentration, the carbon dioxide concentration, and the oxygen concentration depending on the usage environment and the purpose of use of the gas sensor 100. Furthermore, the gas sensor 100 may output all of the water vapor concentration, the carbon dioxide concentration, and the oxygen concentration as measurement values, or may be configured to output one or two of them.

[0171] The present invention also includes the following gas sensor.

[0172] a gas sensor for detecting oxygen, water vapor, and carbon dioxide in a measurement gas, the gas sensor comprising: a sensor element; and a control device for controlling the sensor element, the gas sensor comprising: a long, plate-shaped base portion including an oxygen ion conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on a surface of the base portion, a first internal space communicating with the gas inlet via a first diffusion-controlling passage, and a second internal space communicating with the first internal space via a second diffusion-controlling passage; an oxygen pump cell including an intra-space oxygen pump electrode disposed in the first internal space of the measurement gas flow space, and an extra-space oxygen pump electrode disposed at a position of the base portion different from the measurement gas flow space, the extra-space oxygen pump electrode corresponding to the intra-space oxygen pump electrode; a first measurement pump cell including a first in-space measurement electrode disposed in the second internal space of the measurement gas flow space and an external first measurement electrode disposed in the base at a position different from the measurement gas flow space and corresponding to the first in-space measurement electrode; a second measurement pump cell including a second in-space measurement electrode disposed in the second internal space of the measurement gas flow space or in a third internal space communicating with the second internal space via a third diffusion-controlling passage, on the opposite side of the second diffusion-controlling passage with respect to the first in-space measurement electrode; and an external second measurement electrode disposed in the base at a position different from the measurement gas flow space and corresponding to the second in-space measurement electrode; a reference gas chamber formed inside the base at a distance from the measurement gas flow space; a reference electrode disposed in the reference gas chamber; and a heater for heating the base, The heater is disposed in the longitudinal direction of the base portion so that the highest temperature point of the base portion is located between the electrode end of the intra-void oxygen pump electrode that is closer to the intra-void first measurement electrode and the electrode end of the intra-void second measurement electrode that is farther from the intra-void first measurement electrode, and the control device includes: a pump control unit that controls the operations of the oxygen pump cell, the first measurement pump cell, and the second measurement pump cell; and a concentration calculation unit that calculates the concentrations of oxygen, water vapor, and carbon dioxide in the gas to be measured, and the pump control unitthe oxygen pump cell is operated to pump oxygen out of the first internal space and adjust the oxygen partial pressure in the first internal space so that substantially all of the water vapor and carbon dioxide in the measurement gas are decomposed in the first internal space; the first measurement pump cell is operated to pump oxygen into the second internal space and adjust the oxygen partial pressure in the second internal space so that hydrogen produced by the decomposition of the water vapor is selectively combusted in the second internal space; the second measurement pump cell is operated to pump oxygen near the surface of the second measurement electrode in the space and adjust the oxygen partial pressure near the surface of the second measurement electrode in the space so that carbon monoxide produced by the decomposition of the carbon dioxide is selectively combusted near the surface of the second measurement electrode in the space; the concentration calculation unit calculates the water vapor concentration in the measurement gas based on the value of the current flowing through the first measurement pump cell, and calculates the carbon dioxide concentration in the measurement gas based on the value of the current flowing through the second measurement pump cell; a gas sensor that calculates an oxygen concentration in a measurement gas based on a value of a current flowing through the oxygen pump cell, the value of the current flowing through the first measuring pump cell, and the value of the current flowing through the second measuring pump cell.

[0173] [Method for Manufacturing Gas Sensor] Next, an example of a method for manufacturing the above-described gas sensor will be described. ２ A sensor element can be fabricated by laminating a plurality of unfired sheet-shaped molded articles (so-called green sheets) containing an oxygen ion conductive solid electrolyte such as ethylenediaminetetraacetic acid (EPO) as a ceramic component, laminating the sheets, cutting the laminate, and firing the laminate. The fabricated sensor element can then be assembled into a gas sensor.

[0174] In the following, an example of fabricating the sensor element 101 made up of six layers as shown in FIG. 2 will be described.

[0175] First, zirconia (ZrO ２Six green sheets containing an oxygen ion conductive solid electrolyte such as SiO 2 as a ceramic component are prepared. A known forming method can be used to fabricate the green sheets. All six green sheets may be the same thickness, or the thickness may vary depending on the layer being formed. Holes and other features used for positioning during printing and lamination are formed in each of the six green sheets in advance using a known method, such as punching with a punching device, to form blank sheets. In the blank sheet used for the spacer layer 5, through-holes such as internal voids are also formed in a similar manner. Necessary through-holes are also formed in the other layers in advance.

[0176] Various patterns required for each layer are printed and dried on blank sheets used for the six layers: the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6. A known screen printing technique can be used to print the patterns, and known drying means can also be used for the drying process.

[0177] This process is repeated until various patterns are printed and dried on each of the six blank sheets. The six printed blank sheets are then stacked in a predetermined order while being positioned using sheet holes, etc., and then pressed together under predetermined temperature and pressure conditions to form a laminate. The pressing process is carried out by applying heat and pressure using a laminator such as a known hydraulic press. The temperature, pressure, and time for heating and pressing depend on the laminator used, but can be determined appropriately to achieve good lamination.

[0178] The obtained laminate contains a plurality of sensor elements 101. The laminate is cut into individual sensor elements 101. The cut laminate is fired at a predetermined firing temperature to obtain the sensor elements 101. That is, the sensor elements 101 are obtained by integral firing (co-firing) of the solid electrolyte layer and the electrodes. The firing temperature may be any temperature at which the solid electrolyte constituting the base portion 102 of the sensor element 101 is sintered into a dense body and the electrodes and the like maintain a desired porosity. For example, firing is performed at a firing temperature of about 1200°C or higher and 1500°C or lower.

[0179] The obtained sensor element 101 is incorporated into the gas sensor 100 in such a manner that the front end of the sensor element 101 contacts the gas to be measured and the rear end of the sensor element 101 contacts the reference gas.

[0180] Examples in which gas sensors were specifically fabricated and tested will be described below as examples, but the present invention is not limited to the following examples.

[0181] Example 1: Measurement of water vapor, carbon dioxide, and oxygen concentrations In Example 1, the gas sensor 100 shown in FIGS. 2 and 3 was used to detect water vapor and carbon dioxide concentrations, and the relationship between the water vapor concentration in the measurement gas and the water vapor detection current Ip1, and the relationship between the carbon dioxide concentration in the measurement gas and the carbon dioxide detection current Ip2 were evaluated. The relationship between the oxygen concentration in the measurement gas and the pump current Ip0 was also evaluated. In Example 1, when the oxygen partial pressure in the first internal space 20 was 10 －２５ atm, and the oxygen partial pressure in the second internal space 40 is 10 －１０ atm, and the oxygen partial pressure in the third internal space 61 is 10 －５ atm, the target values ​​of V0, V1, and V2 (V0 ＳＥＴ , V1 ＳＥＴ , and V2 ＳＥＴ ) was set.

[0182] The water vapor concentration measurement was performed using a model gas as the gas to be measured. The gas sensor 100 was attached to the measurement pipe and operated. The model gas was flowed through the measurement pipe, and the water vapor detection current Ip1 of the gas sensor was measured. The model gas had a flow rate of 5 L / min, and the gas temperature was set to room temperature (RT) to prevent condensation of water vapor. The following model gases were prepared. In the following, all concentration units are based on volume.

[0183] (Gas 1) Model gas for evaluating water vapor (not containing carbon dioxide): Water vapor concentrations of 0%, 2%, 4%, and 5%, oxygen concentration of 10%, balance nitrogen; (Gas 2) Model gas for evaluating water vapor (containing carbon dioxide): Water vapor concentrations of 0%, 2%, 4%, and 5%, carbon dioxide concentration of 10%, oxygen concentration of 10%, balance nitrogen.

[0184] (Gas 3) Model gas for carbon dioxide evaluation (no water vapor): Carbon dioxide concentrations 0%, 2%, 4%, 6%, 8% and 10%, oxygen concentration 10%, balance nitrogen; (Gas 4) Model gas for carbon dioxide evaluation (water vapor containing): Carbon dioxide concentrations 0%, 2%, 4%, 6%, 8% and 10%, water vapor concentration 3%, oxygen concentration 10%, balance nitrogen.

[0185] (Gas 5) Model gas for oxygen evaluation (containing water vapor): Oxygen concentrations of 0%, 5%, 10%, and 20%, water vapor concentration of 3%, balance nitrogen.

[0186] 8 is a graph showing the relationship between the water vapor concentration and the water vapor detection current Ip1 for the above-mentioned (Gas 1) and (Gas 2). The horizontal axis of the graph represents the H ２ The vertical axis represents the O concentration [%], and the vertical axis represents the current value [μA] of the water vapor detection current Ip1. Figure 8 also shows the relationship between the water vapor concentration and the carbon dioxide detection current Ip2 for the above (Gas 2).

[0187] 8, the water vapor detection current Ip1 was approximately proportional to the water vapor concentration for both gases containing carbon dioxide (Gas 1) and gases containing carbon dioxide (Gas 2), and both had approximately the same value. Furthermore, the carbon dioxide detection current Ip2 for (Gas 2) was constant regardless of the water vapor concentration.

[0188] 9 is a graph showing the relationship between the carbon dioxide concentration and the carbon dioxide detection current Ip2 for the above-mentioned (Gas 3) and (Gas 4). The horizontal axis of the graph represents the CO ２ The vertical axis represents the concentration [%], and the vertical axis represents the current value [μA] of the carbon dioxide detection current Ip2. Figure 9 also shows the relationship between the carbon dioxide concentration and the water vapor detection current Ip1 for the above (Gas 4).

[0189] 9, the carbon dioxide detection current Ip2 was approximately proportional to the carbon dioxide concentration for both gases containing no water vapor (Gas 3) and gases containing water vapor (Gas 4), and both had approximately the same value. Furthermore, the water vapor detection current Ip1 for gas 4 was constant regardless of the carbon dioxide concentration.

[0190] These results confirm that the concentrations of water vapor and carbon dioxide present in the measurement gas can be determined based on the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 by using the gas sensor 100. Furthermore, it was confirmed that the concentrations of water vapor and carbon dioxide can be measured regardless of whether they coexist in the measurement gas.

[0191] 10 is a graph showing the relationship between the oxygen concentration and the pump current Ip0 for the above (Gas 5). The horizontal axis of the graph represents the O concentration in the measurement gas. ２ The vertical axis represents the concentration [%], and the vertical axis represents the current value [μA] of the pump current Ip0. As described above, the pump current Ip0 is a current that flows when oxygen that was present in the measurement gas and oxygen generated by decomposition of water vapor and carbon dioxide are pumped out.

[0192] As shown in Figure 10, it was confirmed that the pump current Ip0 is approximately proportional to the oxygen concentration. Note that, for all oxygen concentrations, the water vapor (3%) and carbon dioxide (non-containing) concentrations are the same. That is, the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 are approximately the same.

[0193] 11 is a graph showing the relationship between the water vapor concentration and the pump current Ip0 for the above-mentioned (Gas 1) and (Gas 2). The horizontal axis of the graph represents the H ２ The vertical axis represents the carbon dioxide concentration [%], and the vertical axis represents the current value [μA] of the pump current Ip0. Figure 12 is a graph showing the relationship between the carbon dioxide concentration and the pump current Ip0 for the above (Gas 3) and (Gas 4). The horizontal axis of the graph represents the CO 2 concentration in the measurement gas. ２ The vertical axis indicates the concentration [%], and the vertical axis indicates the current value [μA] of the pump current Ip0.

[0194] 11 and 12, it was confirmed that, under the condition of a constant oxygen concentration (10%), the pump current Ip0 is approximately proportional to the water vapor concentration and the carbon dioxide concentration. As described above, the water vapor concentration can be calculated using the water vapor detection current Ip1, and the carbon dioxide concentration can be calculated using the carbon dioxide detection current Ip2. From these results, it was confirmed that the oxygen concentration can be calculated using the pump current Ip0, the water vapor detection current Ip1, and the carbon dioxide detection current Ip2.

[0195] [Example 2: Forced Load Test] In Example 2, a forced load test was performed on the sensor element 101 to verify whether cracks would occur in the internal structure of the sensor element 101. This test evaluates whether cracks would occur under conditions that are excessively harsher than the actual usage environment. Therefore, even if cracks occur in this test, it is considered that the sensor element can withstand actual usage.

[0196] The relationship between the highest temperature position in the longitudinal direction of the sensor element 101 and the occurrence of cracks was evaluated.

[0197] Gas sensors (Samples 1 to 9) were fabricated with different maximum temperature positions along the longitudinal direction of the sensor element 101. In all of Samples 1 to 9, the maximum surface temperature of the upper surface of the sensor element 101 was set to 900°C. The positions of the maximum temperature (900°C) were set to be 2 mm (Sample 1), 3 mm (Sample 2), 4 mm (Sample 3), 5 mm (Sample 4), 6 mm (Sample 5), 7 mm (Sample 6), 8 mm (Sample 7), 9 mm (Sample 8), and 10 mm (Sample 9) along the longitudinal direction from the tip of the sensor element 101. The position of the maximum temperature was adjusted by changing the position of the heater 72 along the longitudinal direction of the sensor element 101.

[0198] Gas sensors No. 1 to No. 9 were all fabricated in the same manner except for the position of the heater 72. Gas sensor No. 6 was the same as the gas sensor of Example 1. The positions of the electrodes in the longitudinal direction of the sensor element 101 were as follows:

[0199] Inner main pump electrode 22: from 2 mm to 4 mm in the longitudinal direction from the tip of the sensor element 101; first measurement electrode 51: from 5 mm to 7 mm in the longitudinal direction from the tip of the sensor element 101; second measurement electrode 44: from 7.5 mm to 8 mm in the longitudinal direction from the tip of the sensor element 101.

[0200] The relationship between the position of each electrode and the highest temperature position in Nos. 1 to 9 was as follows: In Nos. 1 to 3, the highest temperature position was within the range where the inner main pump electrode 22 was present. In No. 1, the highest temperature position was the leading end of the inner main pump electrode 22 in the longitudinal direction of the sensor element, and in No. 3, the highest temperature position was the rear end of the inner main pump electrode 22 in the longitudinal direction of the sensor element. In Nos. 4 to 6, the highest temperature position was within the range where the first measurement electrode 51 was present. In No. 4, the highest temperature position was the leading end of the first measurement electrode 51 in the longitudinal direction of the sensor element, and in No. 6, the highest temperature position was the rear end of the first measurement electrode 51 in the longitudinal direction of the sensor element. In No. 7, the highest temperature position was within the range where the second measurement electrode 44 was present (the rear end of the second measurement electrode 44 in the longitudinal direction of the sensor element). In Nos. 8 and 9, the highest temperature position was further rearward of the second measurement electrode 44.

[0201] The fabricated gas sensors 100 Nos. 1 to 9 were subjected to a crack evaluation. The gas sensors 100 were attached to a measurement pipe and operated. A model gas at 0°C was flowed through the measurement pipe for 60 minutes, and the gas sensors 100 were exposed to the model gas, and it was confirmed whether or not cracks occurred in the sensor element 101 of the gas sensor 100. The model gas was O ２ = 10% (remaining N ２) dry gas (gas not containing water vapor). Three gas sensors 100 of each of Nos. 1 to 9 were exposed to the model gas for 60 minutes. Thereafter, the sensor element 101 was removed from each gas sensor 100 and visually inspected for cracks. For each of Nos. 1 to 9, if cracks were found in one or more of the three sensors, it was evaluated as "cracks present," and if no cracks were found in any of the three sensors, it was evaluated as "cracks absent."

[0202] The maximum temperature positions (the longitudinal distance from the tip of the sensor element 101) and the crack evaluation results for Nos. 1 to 9 are shown in Table 1.

[0203]

[0204] It was confirmed that no cracks occurred in Nos. 4 to 9. In other words, it was confirmed that cracks could be suppressed even in the forced load test if the highest temperature position was located rearward of the rear end of the inner main pump electrode 22 in the longitudinal direction of the sensor element, or at or rearward of the tip of the first measurement electrode 51.

[0205] Example 3: Measurement of ethylene gas concentration In Example 3, the gas sensor 200 shown in FIGS. 5 and 6 was used to detect the ethylene concentration, and the relationship between the ethylene concentration in the measurement gas and the electromotive force (voltage V3) in the ethylene detection sensor cell 285 was evaluated.

[0206] The gas sensor 200 of Example 3 was the same as the gas sensor 100 of Example 1, except that it further included an ethylene detection electrode 284 and an ethylene detection sensor cell 285 .

[0207] The ethylene concentration measurement was carried out using a model gas as the gas to be measured. The gas sensor 200 was attached to the measurement pipe and driven. The model gas was flowed through the measurement pipe, and the voltage V3 at the ethylene detection sensor cell 285 of the gas sensor 200 was measured. The flow rate of the model gas was 5 L / min, and the gas temperature was 0°C. The model gas was ethylene C ２ H ４ Six types of model gases with different concentrations were used. ２ H ４The concentrations were 0 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm, respectively. The gas components other than ethylene gas were dry gases of oxygen (10%) and nitrogen (balance).

[0208] 13 is a graph showing the relationship between the ethylene concentration and the voltage V3 in the ethylene detection sensor cell 285. The horizontal axis of the graph represents the C ２ H ４ The vertical axis represents the concentration [ppm], and the vertical axis represents the EMF [mV], i.e., the voltage V3 [mV]. As shown in Fig. 13, it was confirmed that the voltage V3 at the ethylene detection sensor cell 285 increases as the ethylene concentration increases. From these results, it was confirmed that, by using the gas sensor 200, the concentration of ethylene gas present in the measurement gas can be determined based on the voltage V3 at the ethylene detection sensor cell 285.

[0209] As described above, the present invention provides a gas sensor capable of simultaneously (in parallel) measuring the concentrations of oxygen, water vapor, and carbon dioxide in a measurement gas in a target space. For example, the gas sensor of the present invention can measure the concentrations of oxygen and carbon dioxide using a single gas sensor. Therefore, in an interior air conditioning device such as that described above used for gas composition for CA storage / CA transportation, the oxygen and carbon dioxide concentrations of the interior air can be adjusted using a single gas sensor. This allows for a simpler configuration of the interior air conditioning device and a smaller device capacity. Furthermore, the gas sensor of the present invention can measure the water vapor concentration, i.e., the absolute moisture content, and therefore can perform humidity control required for CA storage / CA transportation. In other words, a single gas sensor can be used to measure the oxygen concentration and carbon dioxide concentration for adjusting the oxygen and carbon dioxide concentrations in the interior air, as well as the water vapor concentration (absolute moisture content) for humidity control. Furthermore, without being limited to these, the concentrations of oxygen, water vapor, and carbon dioxide can be measured in a desired target space.

[0210] 1 First substrate layer 2 Second substrate layer 3 Third substrate layer 4 First solid electrolyte layer 5 Spacer layer 6 Second solid electrolyte layer 10 Gas inlet 11 First diffusion-controlling passage 12 Buffer space 13 Fourth diffusion-controlling passage 15, 315 Measurement gas flow space 20 First internal space 21 Main pump cell 22 Inner main pump electrode 22a Ceiling electrode portion (of inner main pump electrode) 22b Bottom electrode portion (of inner main pump electrode) 23 Outer pump electrode 24 Variable power supply (of main pump cell) 30 Second diffusion-controlling passage 40 Second internal space 41 Second measurement pump cell 42 Reference electrode 43 Reference gas introduction space 44 Second measurement electrode 46 Variable power supply (of second measurement pump cell) 48 Air introduction layer 50 First measurement pump cell 51 First measurement electrode 51a Ceiling electrode portion (of first measurement electrode) 51b Bottom electrode portion (of first measurement electrode) 52 Variable power supply (of first measurement pump cell) 60 Third diffusion-controlling passage 360 ​​Third diffusion-controlling layer 61 Third internal space 70 Heater portion 71 Heater electrode 72 Heater 73 Through hole 74 Heater insulating layer 75 Pressure release hole 76 Heater lead 77 Heater power supply 80 Oxygen partial pressure detection sensor cell for controlling main pump 81 Oxygen partial pressure detection sensor cell for controlling first measurement pump 82 Oxygen partial pressure detection sensor cell for controlling second measurement pump 83 Sensor cell 284 Ethylene detection electrode 285 Ethylene detection sensor cell 90, 290 Control device 91, 291 Control unit 92 Heater control unit 93 Pump control unit 94, 294 Concentration calculation unit 100, 200, 300 Gas sensor 101, 201, 301 Sensor element 102 Base portion

Claims

1. A gas sensor for detecting oxygen, water vapor and carbon dioxide in a measurement gas in a target space, comprising a sensor element and a control device for controlling the sensor element, wherein the sensor element comprises: a long plate-shaped base portion including an oxygen ion conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on a surface of the base portion, a first internal space communicating with the gas inlet via a first diffusion rate-controlling passage, and a second internal space communicating with the first internal space via a second diffusion rate-controlling passage; an oxygen pump cell including an intra-space oxygen pump electrode disposed in the first internal space of the measurement gas flow space, and an extra-space oxygen pump electrode disposed in a position of the base portion different from the measurement gas flow space and corresponding to the intra-space oxygen pump electrode; a first measurement pump cell including an in-space first measurement electrode disposed in the second internal space of the measurement gas flow space and an outside-space first measurement electrode disposed at a position different from the measurement gas flow space of the base portion and corresponding to the in-space first measurement electrode; a second measurement pump cell including an in-space second measurement electrode disposed in the second internal space of the measurement gas flow space or in a third internal space communicating with the second internal space via a third diffusion rate-controlling passage and at a position opposite to the second diffusion rate-controlling passage with respect to the in-space first measurement electrode, and an outside-space second measurement electrode disposed at a position different from the measurement gas flow space of the base portion and corresponding to the in-space second measurement electrode; a reference gas chamber formed inside the base portion and separated from the measurement gas flow space; and a reference electrode disposed in the reference gas chamber, a pump control unit that controls operations of the oxygen pump cell, the first measuring pump cell, and the second measuring pump cell, and a concentration calculation unit that calculates concentrations of oxygen, water vapor, and carbon dioxide in the measurement gas, wherein the pump control unit operates the oxygen pump cell to pump oxygen out of the first internal space, and adjusts the oxygen partial pressure in the first internal space so that substantially all of the water vapor and carbon dioxide in the measurement gas are decomposed in the first internal space,a gas sensor which operates the first measurement pump cell to pump oxygen into the second internal space and adjusts the oxygen partial pressure in the second internal space so that hydrogen produced by decomposition of the water vapor selectively combusts in the second internal space; operates the second measurement pump cell to pump oxygen near a surface of a second measurement electrode in the space and adjusts the oxygen partial pressure near the surface of the second measurement electrode in the space so that carbon monoxide produced by decomposition of the carbon dioxide selectively combusts near the surface of the second measurement electrode in the space; and the concentration calculation unit calculates a water vapor concentration in the measurement gas based on a value of a current flowing through the first measurement pump cell, calculates a carbon dioxide concentration in the measurement gas based on the value of a current flowing through the second measurement pump cell, and calculates an oxygen concentration in the measurement gas based on the value of the current flowing through the oxygen pump cell, the value of the current flowing through the first measurement pump cell, and the value of the current flowing through the second measurement pump cell.

2. The gas sensor according to claim 1, wherein the pump control unit adjusts an oxygen pump voltage applied between the oxygen pump electrode inside the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell to adjust the oxygen partial pressure in the first internal cavity so that substantially all of the water vapor and carbon dioxide in the measured gas are decomposed in the first internal cavity, adjusts a first measurement pump voltage applied between the first measurement electrode inside the cavity and the first measurement electrode outside the cavity of the first measurement pump cell to adjust the oxygen partial pressure in the second internal cavity so that hydrogen produced by the decomposition of the water vapor is selectively combusted in the second internal cavity, and adjusts a second measurement pump voltage applied between the second measurement electrode inside the cavity and the second measurement electrode outside the cavity of the second measurement pump cell to adjust the oxygen partial pressure in the vicinity of the surface of the second measurement electrode inside the cavity so that carbon monoxide produced by the decomposition of the carbon dioxide is selectively combusted in the vicinity of the surface of the second measurement electrode inside the cavity.

3. The gas sensor described in claim 1, wherein the pump control unit adjusts the oxygen partial pressure in the first internal space based on the value of the electromotive force generated between the oxygen pump electrode in the space and the reference electrode, adjusts the oxygen partial pressure in the second internal space based on the value of the electromotive force generated between the first measurement electrode in the space and the reference electrode, and adjusts the oxygen partial pressure near the surface of the second measurement electrode in the space based on the value of the electromotive force generated between the second measurement electrode in the space and the reference electrode.

4. The gas sensor as described in claim 1, wherein the pump control unit adjusts the oxygen partial pressure in the second internal space so that it is greater than the oxygen partial pressure in the first internal space, and the oxygen partial pressure in the vicinity of the surface of the second measurement electrode in the space is equal to or greater than the oxygen partial pressure in the second internal space.

5. A gas sensor as described in claim 1, wherein the sensor element includes a heater for heating the base portion, and the heater is positioned in the longitudinal direction of the base portion so that the highest temperature point of the base portion is between the electrode end of the oxygen pump electrode in the void that is closer to the first measurement electrode in the void and the electrode end of the second measurement electrode in the void that is farther from the first measurement electrode in the void.

6. The gas sensor according to claim 1, wherein the sensor element further includes an ethylene detection electrode disposed on the surface of the base portion and having no catalytic activity against ethylene gas, and the concentration calculation portion calculates the ethylene concentration in the measured gas based on an electromotive force generated between the ethylene detection electrode and the reference electrode.

7. The gas sensor according to claim 6, wherein the ethylene detection electrode is disposed on a side farther from the first measurement electrode inside the cavity than the oxygen pump electrode outside the cavity in the longitudinal direction of the base portion.

8. The gas sensor according to claim 6, wherein the ethylene detection electrode is a cermet electrode of a metal and an oxygen ion conductive solid electrolyte, the metal is Au, or the metal is a Pt-Au alloy, and the area ratio of a portion of a surface of a metal particle of the ethylene detection electrode that is covered with the gold (Au) to a portion of the surface of the metal particle where the platinum (Pt) is exposed is 0.25 or more.

9. The gas sensor according to claim 1, which is inserted directly through a wall that defines the target space.

10. A gas composition adjusting storage container comprising a storage container and the gas sensor according to claim 1 provided in said storage container, which adjusts the concentrations of oxygen, water vapor and carbon dioxide within said storage container.

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