JPH06148137A - Oxygen sensor - Google Patents

Abstract

(57) [Summary] [Structure] The oxygen sensor 31 of the present invention comprises an ionic conductor 3
A pair of first electrodes 33, 34 is provided on the second surface 32 a, and the first electrodes 3 are provided at positions separated from the first electrodes 33, 34.
A pair of second electrodes 3 having an area smaller than 3, 34
5, 36 are provided, a sealing layer 37 that entirely covers the first electrode 34 and the second electrode 35 is provided, and a void portion 38 is provided between the sealing layer 37 and the ionic conductor 32. Electrode 33 of
A predetermined voltage is applied between the electrodes 34 and between the second electrodes 35 and 36, and the oxygen value in the sample gas is determined from the current value using oxygen ions taken into the ion conductor 32 from the second electrode 36 side as carriers. It is characterized in that the concentration is measured. [Effect] It is possible to reduce variations in ion current characteristics and widen the measurement range of oxygen concentration. Further, it is not necessary to attach electrodes to both surfaces of the ionic conductor, and the manufacturing process can be simplified and the manufacturing cost can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type oxygen sensor suitable for use in preventing oxygen deficiency accidents in basements and in combustion management of engines and boilers.

[0002]

2. Description of the Related Art Conventionally, a limiting current type oxygen sensor using stabilized zirconia as an ionic conductor has been proposed and put into practical use. This oxygen sensor uses zirconia (ZrO ₂ ) which is a type of ceramics, yttria (Y ₂ O ₃ ),
Stabilized zirconia in which several mol% of oxides such as magnesia (MgO) and calcia (CaO) are solid-solved is used as an ion conductor, and it is possible to detect a wide range of oxygen partial pressure, and the response speed is fast Since it has various features such as stable electromotive force and can be used in a high temperature atmosphere, it prevents oxygen deficiency accidents in closed rooms such as basements, measures oxygen concentration in molten steel, manages combustion in engines and boilers, and measures pollution. It is a sensor that is suitable for various purposes.

As an example of the oxygen sensor, a thick film type oxygen sensor as shown in FIG. 3 is known. The oxygen sensor 1 is stabilized zirconia (e.g., ZrO ₂ over 8
mol% Y ₂ O ₃ ) etc. and an ionic conductor 2 made of a thin solid electrolyte having ionic conductivity, and this ionic conductor 2
Porous platinum electrodes 3 and 4 respectively formed on both surfaces of each of the electrodes and to which a constant sensor monitoring voltage is applied, and bonded to the electrode 3 side of the ionic conductor 2 by crystallized glass 5 and 5, and
It is roughly composed of a ceramic cap 7 in which a gas diffusion hole 6 that penetrates vertically is formed in a central portion, and a heater 8 for heating formed on the upper surface of the ceramic cap 7. The ceramic cap 7 may be replaced with an inorganic porous material having extremely high oxygen permeability, such as porous alumina. In the oxygen sensor 1, if a predetermined voltage is applied to the heater 8 and a predetermined voltage is applied between the electrodes 3 and 4, the oxygen sensor 1 is taken into the ionic conductor 2 through the gas diffusion hole 6. Oxygen contained in the sample gas flows as ions in the ionic conductor 2 due to the oxygen pumping action, and the oxygen concentration in the sample gas is measured from the current value using the oxygen ions as carriers.

Further, like the oxygen sensor 11 shown in FIG.
Without forming the gas diffusion hole 6 in the ceramic cap 7, the gas diffusion hole 12 penetrating vertically in the center of the ionic conductor 2.
It is also known that formed. Also in the oxygen sensor 11 having this configuration, oxygen in the sample gas taken in through the gas diffusion holes 12 of the ionic conductor 2 flows as ions in the ionic conductor 2 due to the oxygen pumping action. The oxygen concentration in the sample gas is measured from the current value using as a carrier.

Further, like the oxygen sensor 21 shown in FIG.
There is also known a structure in which the entire upper portion of the electrode 3 of the ionic conductor 2 is covered with a ceramic cap 23 having an airtight glass film 22 formed on its inner surface. Also in the oxygen sensor 21 having this configuration, oxygen in the sample gas taken in from the gas diffusion holes 12 of the ionic conductor 2 flows as ions in the ionic conductor 2 due to the oxygen pumping action. The oxygen concentration in the sample gas is measured from the current value using as a carrier.

[0006]

By the way, in the above-described oxygen sensors 1 to 21, all the oxygen in the sample gas is taken into the ionic conductor 2 from the gas diffusion holes 6 and 12 and measured. , These gas diffusion holes 6, 12
The amount of oxygen passing through the chamber is liable to vary depending on the size of the gas diffusion holes 6 and 12 and the positions where they are formed, and there is a drawback in that variations in ion current characteristics tend to increase. Therefore,
Attempts have been made to control the shapes of the gas diffusion holes 6 and 12 with high accuracy in order to reduce the variations in the ion current characteristics, but it is extremely difficult in the actual manufacturing process. In addition, there is a problem in that calibration is required for each individual sensor element, which complicates the work, which complicates the manufacturing process and increases the manufacturing cost. In addition, in these oxygen sensors 1 to 21, the ionic conductor 2 is used.
It is necessary to accurately form the electrodes 3 and 4 on both surfaces by separate steps, which has a drawback that the manufacturing process becomes complicated and the manufacturing cost increases. These drawbacks hinder the introduction of an automated line, making it difficult to mass-produce these oxygen sensors 1 to 21.

Further, in these oxygen sensors 1 to 21, the limiting current value is determined to a certain specific value and cannot be set to an arbitrary value, so that the oxygen concentration measurement region is limited. There is. Therefore, when measuring a wide range of oxygen concentration from low concentration to high concentration, it is necessary to prepare a plurality of oxygen sensors having different limiting current values.

The present invention has been made in view of the above circumstances and provides an oxygen sensor having excellent characteristics such as high reliability, measurement of oxygen concentration in a wide range, mass production, and low cost. To provide.

[0009]

In order to solve the above problems, the present invention employs the following oxygen sensor. That is, at least a pair of first electrodes is provided on one surface of the ionic conductor, and the surface is separated from the first electrodes,
At least a pair of second electrodes having an area smaller than that of the first electrode is provided, and airtightness that entirely covers each of the first electrode and the second electrode is provided at the upper position of these electrodes. An encapsulating layer is provided, and a gap is provided between the encapsulating layer and the ionic conductor so that adjacent electrodes have different polarities from each other, and between the first electrodes and between the second electrodes, respectively. By applying a predetermined voltage to the second electrode, oxygen in the sample gas taken into the ionic conductor from the side of the second electrode flows as ions in the ionic conductor due to the oxygen pumping action. It is characterized in that the oxygen concentration in the sample gas is measured from a current value using as a carrier.

[0010]

In the oxygen sensor of the present invention, a predetermined voltage is applied between the first electrode and the second electrode so that the adjacent electrodes have different polarities from each other. Oxygen is taken into the ionic conductor from the side of the second electrode having a function as a gas diffusion hole, flows as an ion in the ionic conductor by the oxygen pumping action, and the oxygen ion serves as a carrier. The oxygen concentration in the sample gas is measured.

Here, since oxygen in the sample gas is taken into the ionic conductor from the second electrode side and measured, fluctuations in the amount of taken oxygen are reduced, and variations in ionic current characteristics are also reduced. It becomes unnecessary to control the shape of the gas diffusion hole with high precision as in the conventional case. Also,
By providing the first electrode and the second electrode on one surface of the ionic conductor, it is not necessary to attach electrodes to both surfaces of the ionic conductor in separate steps. Therefore, the manufacturing process is simplified and the manufacturing cost is reduced.

Further, by applying a predetermined voltage between the first electrodes and between the second electrodes so that the adjacent electrodes have different polarities, the limiting current value is set to an arbitrary value. It is possible to widen the measurement range of oxygen concentration. Therefore, it is possible to deal with the case of measuring a wide range of oxygen concentration from low concentration to high concentration, and it becomes unnecessary to prepare a plurality of oxygen sensors having different limiting current values.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the oxygen sensor of the present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view showing an oxygen sensor 31 of the present invention. The oxygen sensor 31 includes a stabilized zirconia (for example, ZrO ₂ -8 mol% Y
₂ O ₃ ), etc., the upper surface 32a of the thin ionic conductor 32.
First positive electrode 33 and first negative electrode 3 made of porous platinum
The second positive electrode 35 is made of porous platinum and has a smaller area than the electrodes 33 and 34 and is provided at a predetermined distance so as to face each other. And the second negative electrode 36 are provided at a predetermined interval so as to face each other.
A sealing layer 37 having airtightness that entirely covers these negative electrodes 34 and 35 is provided above the negative electrode 34 and the second positive electrode 35, and the sealing layer 37 and the ionic conductor 32 are A space 38 is provided between them. The sealing layer 37 is
A material having a smaller expansion coefficient than the ionic conductor 32, for example,
Glass having a high softening point such as potash glass or borosilicate glass is preferably used.

In this oxygen sensor 31, when a predetermined voltage is applied between the first positive electrode 33 and the first negative electrode 34, the second positive electrode 35 and the second negative electrode 36 are connected. The voltage between the two is smaller than the voltage due to the variable resistor R, and the first negative electrode 34 and the second negative electrode 36 are equipotential.

In this oxygen sensor 31, between the first positive electrode 33 and the first negative electrode 34 and the second positive electrode 35 so that the adjacent electrodes have mutually different polarities.
By applying a predetermined voltage between the second negative electrode 36 and the second negative electrode 36, oxygen in the sample gas is taken into the ionic conductor from the side of the second negative electrode 36 having a function as a gas diffusion hole. The oxygen concentration in the sample gas can be measured from the current value using the oxygen ions as carriers by flowing as ions in the ionic conductor 32 by the oxygen pumping action. Here, the oxygen in the sample gas is directly taken into the ionic conductor 32, so that the fluctuation of the taken-in oxygen amount becomes small and the variation in the ionic current characteristics also becomes small.

FIG. 2 is a diagram showing the limiting current characteristics of the oxygen sensor 31. This figure shows the magnitude of the current obtained when the oxygen sensor 31 is heated to 400 ° C. and the magnitude of the voltage applied between the first positive electrode 33 and the first negative electrode 34 is changed. It is a graphical representation of this. It can be seen from FIG. 2 that the oxygen sensor 31 exhibits very good limiting current characteristics. Moreover, the limiting current value can be set to an arbitrary value by changing the magnitude of the resistance value of the variable resistor R, and the measurement range of the oxygen concentration can be widened. Therefore, it is possible to deal with the case of measuring a wide range of oxygen concentration from low concentration to high concentration, and it is not necessary to prepare a plurality of oxygen sensors having different limiting current values.

As described above, according to the oxygen sensor 31 of the above-described embodiment, the first positive electrode 33 and the first negative electrode 34 are provided on the upper surface 32a of the ionic conductor 32, and these electrodes 33, These electrodes 3 are placed at a position away from 34.
A second positive electrode 35 and a second negative electrode 36 having an area smaller than that of the third and third electrodes 34, 34 are provided, and these electrodes 34, 3 are provided above the first negative electrode 34 and the second positive electrode 35.
Since the sealing layer 37 having the airtightness covering the entire No. 5 is provided and the void portion 38 is provided between the sealing layer 37 and the ionic conductor 32, the fluctuation of the amount of oxygen taken in can be reduced. It is possible to reduce variations in ion current characteristics. Therefore, it is not necessary to control the shape of the gas diffusion hole with high precision as in the conventional case, the manufacturing process can be simplified, and the manufacturing cost can be reduced.

Further, since the first electrodes 33, 34 and the second electrodes 35, 36 are provided on the upper surface 32a of the ionic conductor 32, it is not necessary to attach electrodes on both surfaces of the ionic conductor by separate steps. . Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced.

Further, the first positive electrode 33 and the first negative electrode 34 are arranged so that the adjacent electrodes have mutually different polarities.
Since a predetermined voltage is applied to each of the second positive electrode 35 and the second negative electrode 36, the limiting current value can be set to an arbitrary value and the oxygen concentration The measurement area can be expanded. Therefore, it is possible to deal with the case of measuring a wide range of oxygen concentration from low concentration to high concentration, and it is not necessary to prepare a plurality of oxygen sensors having different limiting current values.

[0020]

As described in detail above, according to the oxygen sensor of the present invention, at least a pair of first electrodes is provided on one surface of the ionic conductor and is separated from the first electrode on the surface. At least a pair of second electrodes having an area smaller than that of the first electrode is provided at the position, and the upper position of these electrodes entirely covers one of the first electrode and the second electrode. Since the sealing layer having airtightness is provided and the void portion is provided between the sealing layer and the ionic conductor, the fluctuation of the amount of oxygen taken in can be reduced and the variation of the ionic current characteristics can be reduced. be able to. Therefore, it is not necessary to control the shape of the gas diffusion hole with high precision as in the conventional case, the manufacturing process can be simplified, and the manufacturing cost can be reduced.

Since the pair of first and second electrodes is provided on one surface of the ionic conductor, it is not necessary to attach electrodes to both surfaces of the ionic conductor by separate steps. Therefore, the manufacturing process can be simplified and the manufacturing cost can be reduced.

Since a predetermined voltage is applied between the first electrodes and between the second electrodes so that the adjacent electrodes have different polarities from each other, the limiting current value is set to an arbitrary value. Can be set to, and the measurement region of oxygen concentration can be expanded. Therefore, it is possible to deal with the case of measuring a wide range of oxygen concentration from low concentration to high concentration, and it is not necessary to prepare a plurality of oxygen sensors having different limiting current values.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a limiting current characteristic of an oxygen sensor according to an embodiment of the present invention.

FIG. 3 is a front sectional view showing a conventional oxygen sensor.

FIG. 4 is a front sectional view showing a conventional oxygen sensor.

FIG. 5 is a front sectional view showing a conventional oxygen sensor.

[Explanation of symbols]

31 ... Oxygen sensor, 32 ... Ion conductor, 32a ... Top surface, 33 ... First positive electrode, 34 ... First negative electrode, 35 ...
2nd positive electrode, 36 ... 2nd negative electrode, 37 ... Sealing layer, 3
8 ... Void portion.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Kato 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Kiba Factory Ltd.

Claims (1)

[Claims] 1. An ionic conductor is provided with at least a pair of first electrodes on one surface thereof, and at least a pair of first electrodes having an area smaller than that of the first electrodes is provided on the surface at a position separated from the first electrodes. 2 electrodes are provided, and an airtight sealing layer that entirely covers each of the first electrode and the second electrode is provided at a position above these electrodes, and the sealing layer and the ionic conductivity are provided. A space is provided between the body and a predetermined voltage is applied between the first electrodes and between the second electrodes so that adjacent electrodes have different polarities from each other. Oxygen in the sample gas taken into the ionic conductor from the electrode side flows as ions in the ionic conductor due to the oxygen pumping action, and oxygen in the sample gas is determined from the current value using the oxygen ions as carriers. The concentration is measured And an oxygen sensor.