JPH0587773A - Gas sensor - Google Patents

Abstract

PURPOSE:To obtain a gas sensor capable of measuring the concns. of at least two kinds of gases at the same time. CONSTITUTION:A gas sensor is equipped with a ceramic heater 1, the stabilized zirconia plates 2,3 fixed to the upper and rear surfaces of said heater, the anodes 21, 31 and cathodes 22, 32 embedded in the stabilized zirconia plates 2, 3 in parallel, a gas lead-out means constituted of outlets 23, 33 and a gas restricting and introducing means constituted of a gas introducing part 26 and a gas diffusion control part 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for measuring the concentration of two or more kinds of gases such as oxygen, carbon dioxide and humidity.

[0002]

2. Description of the Related Art The following techniques are known as techniques for measuring the gas concentrations of two kinds of gases (for example, oxygen and water vapor). (A) The oxygen concentration is measured with an oxygen sensor, and the amount of water vapor is measured with a humidity sensor. (A) An oxygen sensor is used, and the applied voltage value at which the limiting current value proportional to the gas concentration is obtained is changed between when the oxygen concentration is measured and when the water vapor amount is measured.

[0003]

However, the above-mentioned conventional techniques have the following drawbacks. The former requires two types of sensors and is costly. The latter takes time to converge even if the applied voltage is changed, and the gas concentration of each gas cannot be measured in real time. An object of the present invention is to provide a gas sensor capable of simultaneously measuring gas concentrations of at least two kinds of gases.

[0004]

[Means for Solving the Problems] In order to solve the above problems,
The present invention has the following configurations. (1) A plate-shaped electrothermal heater exhibiting oxygen ion insulation, a solid electrolyte plate exhibiting good oxygen ion conductivity and fixed to the front surface and the back surface of the electrothermal heater, and a pair of these solid electrolyte plates. It is provided with a porous negative electrode and a positive electrode which are carried, and a gas restriction introducing means which is provided to each of the negative electrodes in order to restrict the diffusion of the gas to be measured. (2) A plate-shaped electrothermal heater exhibiting oxygen ion insulation, a solid electrolyte plate exhibiting good oxygen ion conductivity and fixed to the main end surface of the electrothermal heater, and a porous layer carried by the solid electrolyte plate. A negative electrode group and a positive electrode of high quality, and gas limiting introduction means provided to each of the negative electrodes in order to limit the diffusion of the gas to be measured.

[0005]

[Operation and effect of the invention]

(Claim 1) A solid electrolyte plate having good oxygen ion conductivity, which carries a pair of porous negative electrode and positive electrode, is fixed to the front and back surfaces of a plate-shaped electric heater having oxygen ion insulation. However, a gas restriction introducing means is provided to each negative electrode. Therefore, a voltage that gives a limiting current value proportional to the gas concentration of one type of gas is applied between the negative electrode and the positive electrode of one solid electrolyte plate, and the limiting current proportional to the gas concentration of another type of gas is applied. It becomes possible to apply a voltage for obtaining a value between the negative electrode and the positive electrode of the other solid electrolyte plate, and the gas sensor can simultaneously measure the gas concentrations of two kinds of gases. (Claim 2) A solid electrolyte plate having a good conductivity of oxygen ions, which carries a porous negative electrode group and a positive electrode, is fixed to the main end surface of a plate-shaped electric heater having an oxygen ion insulating property. The negative electrode is provided with a gas restriction introducing means. For this reason, it is possible to apply different voltages that obtain a limiting current value proportional to the gas concentration of the gas type to be detected between each negative electrode and positive electrode of the solid electrolyte plate. The gas concentration of gas can be measured.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First and second embodiments of the present invention (corresponding to claim 1) will be described with reference to FIGS. The gas sensor A of the first embodiment shown in FIGS. 1 and 2 is a ceramic heater 1 having an oxygen ion insulating property, and a solid electrolyte plate having good oxygen ion conductivity and fixed to the front surface and the back surface of the ceramic heater 1. The stabilized zirconia plates 2 and 3 and the positive electrode 2 embedded side by side in the stabilized zirconia plates 2 and 3.
1, a negative electrode 22, a positive electrode 31, a negative electrode 32, gas outlet holes 23 and 33 which are gas outlet means, and gas restriction introducing means. Further, in the gas sensor B of the second embodiment shown in FIG. 3, the positive electrode 21, the negative electrode 22, the positive electrode 31, and the negative electrode 32 are arranged side by side on the surfaces of the stabilized zirconia plates 2 and 3, and oxygen is provided. It is embedded in ceramic plates 4 and 5 which are mainly composed of alumina and which show ionic insulation.

The ceramic heater 1 is, as shown in FIG.
Tungsten 12 is embedded in a ceramic 11 composed mainly of alumina, and heat is generated by connecting platinum wires 13 and 14 to a heater power source (not shown), and positive electrodes 21, 31 and negative electrode 22. , 32 electrode portions 21a,
31a, 22a, and 32a are locally heated to 300 ° C to 700 ° C. In addition, 121 is a heat generating part, 122 is an electrode part, and 15 is a vent.

The stabilized zirconia plates 2 and 3 are solid electrolytes obtained by adding yttrium oxide as a stabilizer to zirconium oxide to form a solid solution. In this embodiment, the thickness is 0.3 m.
It has a size of m, 5 mm in length, and 23 mm in width. 2
0 is a vent.

The positive electrodes 21, 31 and the negative electrodes 22, 32 are
It is a porous platinum layer (thickness of several tens of μm) and is approximately 2 mm on a side.
Electrode parts 21a, 31a, 22a, 32a, narrow intermediate parts 21b, 22b (henceforth, some are not shown), and end parts 21c, 2 to which platinum wires 24, 25 are connected.
2c and.

The gas outlet holes 23 and 33 are connected to the electrode portion 21a,
It is a hole formed in the stabilized zirconia plates 2 and 3 at the position 31a and connects the electrode portions 21a and 31a to the outside.
The gas outlet holes 23 and 33 may be large so that the entire electrode portions 21a and 31a are exposed. The gas restriction introducing means is composed of a gas introduction section 26 in which the platinum layer of the intermediate section 22b is exposed on the outer wall surface of the stabilized zirconia plate 2, and a gas diffusion restriction section 27 that restricts the diffusion of the introduced gas.

Next, a manufacturing method (main part) of the gas sensors A and B will be described. In the ceramic heater 1, a heater pattern was printed with a paste made of tungsten on the upper surface of a 96 wt% alumina green sheet in which a window serving as a ventilation hole 15 was formed after firing, and platinum wires 13 and 14 were placed on the ends. After that, the same green sheet is covered, and this is sintered and integrated (see FIG. 4). After firing on the solid electrolyte green sheet in which a window serving as the vent hole 20 is formed after firing,
Platinum paste is printed so as to form the positive electrode 21 and the negative electrode 22, and the platinum wires 24 and 25 are placed on the ends, and then another solid electrolyte green sheet (in the case of the gas sensor A) or an alumina green sheet of the same shape ( Gas sensor B) is laminated and integrally fired at 1500 ° C. to manufacture a sensor element (front side in the drawing). Similarly, a platinum paste is printed so that the positive electrode 31 and the negative electrode 32 are formed after firing on the solid electrolyte green sheet having a window serving as a vent hole after firing, and platinum wires are placed on the ends, Another solid electrolyte green sheet (in the case of gas sensor A) or an alumina green sheet of the same shape (in the case of gas sensor B) is laminated and integrally fired at 1500 ° C. to manufacture a sensor element (the other side in the drawing).
Each sensor element is sealed (about 800 ° C.) on the back surface and the front surface of the ceramic heater 1 using sealing glass to become gas sensors A and B.

Next, the operation of the gas sensors A and B will be described.
It Place the gas sensors A and B in the gas to be measured and
Power is applied to the quater 1 and between the positive electrode 21 and the negative electrode 22, and
A voltage is applied between the positive electrode 31 and the negative electrode 32. Negative electrode 2
The oxygen inside the electrode portion 22a (32a) of 2 (32) is
Oxygen in the gas to be measured is turned on and becomes oxygen ions.
Depending on the applied voltage V, from the negative electrode 22 (32) to the positive electrode
21 (31) is pumped. At this time, the negative electrode 22
In (32), only the electrode portion 22a (32a) is locally heated.
The gas diffusion limiting portion 27 is filled to the extent that it exhibits oxygen ion conductivity.
Since it is not heated for a minute, oxygen is introduced from the gas introduction part 26 to the negative electrode
It diffuses in 22 (32). Here, the positive electrode 21 (3
1) -The current I flowing between the negative electrodes 22 (32) is shown in FIG.
It changes as shown. The applied voltage V has a voltage value V1 to V2.
Therefore, the amount of oxygen diffused into the negative electrode 22 (32) is
It is controlled by the gas introduction part 26 of the pole 22 (32),
The amount of diffusion is limited because it is limited according to the oxygen concentration in the gas.
As a result, the current value is also limited and the diffusion limit current value I_L1
And becomes the first flat portion F1. Applied voltage V is diffusion controlled
Voltage limit value I_L1Is higher than the obtained voltage value V2
(1.2 V or more) and the water vapor (moisture) in the measured gas
Electrolyzed and oxygen ions generated by the decomposition are positive electrode 2
Since it is pumped to 1 (31), the water vapor also becomes the negative electrode 22.
From the gas introduction portion 26 of (32) into the negative electrode 22 (32)
The current value increases in accordance with the amount of diffusion. Applied voltage V
If the voltage is further increased to V3 to V4, the current value becomes water.
Although it further increases depending on the vapor concentration, the negative electrode 22 (3
The amount of diffusion of water vapor is limited in the gas introduction section 26 of 2),
Along with this, the current value is also limited, and the diffusion control according to the water vapor concentration
Current limiting value I_L2And shows the second flat portion F2. example
For example, apply a voltage of V1 to V2 to the front sensor element.
Diffusion limited current value I _L1The diffusion limiting current value I_L1of
The oxygen concentration can be detected from the size. Also at the same time
Limit the diffusion by applying a voltage of V3 to V4 to the sensor element on the side
Current value I_L2The diffusion limiting current value I_L2The size of
Humidity can be detected.

The gas sensors A and B can simultaneously measure oxygen concentration and humidity in the gas to be measured in real time.

A third embodiment of the present invention (corresponding to claim 1) will be described with reference to FIGS. 6 and 7. The gas sensor C includes a ceramic heater 1 having an oxygen ion insulating property, and stabilized zirconia plates 2 and 3 which are fixed to a part of the front surface and the back surface of the ceramic heater 1 and are solid electrolyte plates having good oxygen ion conductivity. A positive electrode 21 and a negative electrode 22 arranged side by side in the stabilized zirconia plates 2 and 3 (hereinafter, some of the hidden electrodes are not shown), a gas outlet hole 23 serving as a gas outlet, and a gas. And a restriction introducing means. The second
As in the embodiment, two sets of positive electrode and negative electrode are arranged in parallel on the surfaces of the stabilized zirconia plates 2 and 3 and embedded in a ceramic plate mainly composed of alumina and exhibiting oxygen ion insulation. It may have a structure.

The ceramic heater 1 comprises platinum wires 13 and 14
The structure is the same as that of the first embodiment except that the heater energizing electrodes 131 and 141 exposed on the surface of the ceramic 11 are replaced. The stabilized zirconia plates 2 and 3 are the first
The solid electrolyte of the same material as that of the example, and the example of this example has a thickness of 0.3 mm, a length of 5 mm, and a width of 7 mm. The positive electrode 21 and the negative electrode 22 are porous platinum layers (thickness of several tens of μm), and the electrode portions 21 a, 2 a having a side of about 2 mm.
2a and narrow connecting portions 21d and 22d. The configurations of the gas outlet hole 23 and the gas restriction introducing means are the same as those in the first embodiment.

Next, a manufacturing method (main part) of the gas sensor C will be described. By the method according to the first embodiment, the tungsten 12 is embedded, the heater energizing electrodes 131 and 141, and the sensor electrodes 151 and 152 (ruthenium oxide) are surface-coated to manufacture the ceramic heater 1. Positive electrode 21, negative electrode 2 after firing on the solid electrolyte green sheet
The platinum paste is printed so as to be 2, and integrally baked at 1500 ° C. to manufacture the sensor element body (front side in the drawing). Similarly, the sensor element on the other side of the drawing is also manufactured. In order to electrically connect the positive electrode 21, the negative electrode 22 and the sensor electrodes 151, 152 inside, gold paste is applied between the sensor electrode 151 and the connecting portion 21d and between the sensor electrode 152 and the connecting portion 22d. The gas sensor C is completed by sealing each sensor element body to the back surface and the front surface of the ceramic heater 1 (about 800 ° C.) using a sealing glass (not shown).

The gas sensor C of this embodiment also operates in accordance with the gas sensors A and B, and can simultaneously measure the oxygen concentration and the humidity in the gas to be measured in real time. The gas sensor C of this embodiment can be manufactured at a lower cost than those of the first and second embodiments because the stabilized zirconia plates 2 and 3 can be reduced in size.

Fourth and fifth embodiments of the present invention (corresponding to claim 2) will be described with reference to FIGS. 8 and 9. As shown in FIG.
The gas sensor D of the fourth embodiment of the present invention comprises a ceramic heater 1 having an oxygen ion insulating property, and a stabilized zirconia plate which is a solid electrolyte plate fixed to the surface of the ceramic heater 1 and having good oxygen ion conductivity. 6, a positive electrode 61, a negative electrode 62, a negative electrode 63, which are embedded side by side in the stabilized zirconia plate 6, and a gas outlet hole 6 which is a gas outlet means.
4 and a gas restriction introducing means. Further, in the gas sensor E of the fifth embodiment shown in FIG. 9, the positive electrode 61 and the negative electrode 6
2, 63 are arranged side by side on the surface of the stabilized zirconia plate 6, and are embedded in a ceramic plate 7 mainly composed of alumina and exhibiting oxygen ion insulation.

The ceramic heater 1 is based on the product shown in FIG. 7, and has sensor electrodes 161, 162, 163 (ruthenium oxide) filmed thereon. This ceramic heater 1
Locally heats the electrode portions 61a, 62a, 63a. The size and material of the stabilized zirconia plate 6 are the same as in FIG. The positive electrode 61 and the negative electrodes 62 and 63 of the gas sensor D are
Stabilized zirconia plate 6 using the method according to the first embodiment
It is buried inside. In addition, the positive electrode 6 of the gas sensor E
1. The negative electrodes 62 and 63 are embedded in the ceramic plate 7 by using the method according to the second embodiment. Gas outlet hole 6
4. The configurations of the gas restriction introducing means 621 and 631 are substantially the same as those of the first embodiment.

Next, a manufacturing method (main part) of the gas sensors D and E will be described. By the method according to the third embodiment, the ceramic heater 1 is manufactured by embedding the tungsten 12, coating the heater energization electrodes 131, 141, and the sensor electrodes 161, 162, 163 (ruthenium oxide) on the surface. Positive electrode 6 after firing on the solid electrolyte green sheet
1. Platinum paste is printed so as to become the negative electrodes 62 and 63, and another solid electrolyte green sheet (gas sensor D),
Or same shape alumina green sheet (gas sensor E)
Are laminated and integrally fired at 1500 ° C. to manufacture a sensor element. In order to electrically connect the positive electrode 61, the negative electrodes 62, 63 and the sensor electrodes 161, 162, 163 inside, the sensor electrode 161 and the connecting portion 61b, the sensor electrode 162 and the connecting portion 62b, and the sensor electrode 163 and the connecting portion. Gold paste is applied between 63b. The sensor element body is sealed (about 800 ° C.) on the surface of the ceramic heater 1 using sealing glass (not shown), and the gas sensors D and E are completed.

The sensor electrode 161 is used as a reference electrode, for example, a voltage for measuring oxygen concentration is applied between the sensor electrode 161 and the sensor electrode 163, and a voltage for measuring humidity between the sensor electrode 161 and the sensor electrode 162. The gas sensors D, E are also connected to the gas sensors A, B, C
The same operation as described above can be performed, and the oxygen concentration and the humidity in the measured gas can be simultaneously measured in real time. The gas sensors D and E of the present embodiment can be manufactured at a lower cost than that of the third embodiment because the stabilized zirconia plate 6 can be further reduced in size (because one sheet is used).

The present invention includes the following embodiments in addition to the above embodiments. a. The number of negative electrode groups according to claim 2 is three or more, and the voltage applied between the negative electrode and the positive electrode is changed, respectively, and one gas sensor can simultaneously measure the gas concentrations of three or more types (in addition to CO ₂ and NO ₂ ). You can do it as well. b. In the second aspect, the gas sensor may be manufactured by fixing the solid electrolyte plates on both sides of the electric heater. c. The term “supported on the solid electrolyte plate” includes both a case where the solid electrolyte plate is closely attached to the front surface (or the back surface) and a case where the solid electrolyte plate is embedded in the solid electrolyte plate. d. The gas outlet holes 23, 33, 64 may have any size and shape as long as a flow rate higher than that of the gas restriction introducing means can be obtained.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a gas sensor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the gas sensor taken along the line H-H ′.

FIG. 3 is a structural explanatory view of a gas sensor according to a second embodiment of the present invention.

FIG. 4 is a structural explanatory view of a ceramic heater of the gas sensor according to the first and second embodiments.

FIG. 5 is a graph for explaining the operation of those gas sensors.

FIG. 6 is a structural explanatory view of a gas sensor according to a third embodiment of the present invention.

FIG. 7 is a structural explanatory view of a ceramic heater of the gas sensor.

FIG. 8 is a structural explanatory view of a gas sensor according to a fourth embodiment of the present invention.

FIG. 9 is a structural explanatory view of a gas sensor according to a fifth embodiment of the present invention.

[Explanation of symbols]

 A, B, C, D, E Gas sensor 1 Ceramic heater (electrothermal heater) 2, 3, 6 Stabilized zirconia plate (solid electrolyte plate) 21, 31, 61 Positive electrode 22, 32, 62, 63 Negative electrode 621, 631 Gas restriction introduction means

Claims (2)

[Claims] 1. A plate-shaped electrothermal heater exhibiting oxygen ion insulation, a solid electrolyte plate exhibiting good oxygen ion conductivity and fixed to a front surface and a back surface of the electrothermal heater, respectively. A gas sensor comprising a porous negative electrode and a positive electrode, which are carried in pairs, and gas limiting introduction means provided to each of the negative electrodes in order to limit the diffusion of the gas to be measured. 2. A plate-shaped electric heater which exhibits oxygen ion insulation, a solid electrolyte plate which exhibits good oxygen ion conductivity and is fixed to the main end surface of the electric heater, and a solid electrolyte plate which is carried by the solid electrolyte plate. A gas sensor comprising a porous negative electrode group and a positive electrode, and a gas restriction introducing means provided to each of the negative electrodes in order to restrict diffusion of a gas to be measured.