JPH0921782A - Oxygen concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen concentration sensor which does not need, for example, an accessory for supplying gas to the sensor, is simple since it does not require atmospheric bending, is compact, and can accurately measure oxygen concentration under a high-temperature environment. SOLUTION: The oxygen concentration sensor had at least two sets of a pair of electrodes 2 and 2' and 3 and 3' which face each other while holding zirconium films 1 and 1' where one surface is in contact with open air and the other surface is in contact with gas in a case, a set of a pair of electrodes out of them is a pumping cell for introducing oxygen from open air to the case, and the other set of a pair of electrodes are detection parts for measuring the oxygen concentration difference between the gas in the case and the open air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration sensor for measuring the oxygen concentration in gas, especially in high temperature gas.

[0002]

2. Description of the Related Art As a means for measuring the oxygen concentration in a gas, a magnetic method, a galvanic cell method, a zirconia method, etc. are known. Among them, the zirconia-type oxygen concentration measuring method utilizes the property that stabilized zirconia composed of zirconium oxide containing a small amount of yttrium oxide, etc. exhibits conductivity due to oxygen ions at high temperature and becomes a solid electrolyte.

Due to such properties of zirconia, a zirconia oxygen concentration sensor is used for measuring oxygen concentration in flue gas, engine exhaust gas of automobiles, or high temperature gas such as atmosphere gas in a blast furnace. In this sensor, as shown in FIG. 7, an electrode 2 (reference electrode) and an electrode 3 (detection electrode) are arranged at positions facing each other with the zirconia sintered body 1a interposed therebetween. The electrodes 2 and 3 are connected to voltage detecting means.

When a gas having a known oxygen concentration is brought into contact with the surface of the sintered body 1a on the electrode 2 side and a gas with an oxygen concentration to be measured is brought into contact with the surface of the electrode 3 side, a gap between the electrodes is generated according to the concentration ratio of these gases. The electromotive force is used to measure the oxygen concentration in the measurement target gas. The electrode 3 on the side of the gas to be measured is protected by the porous plate 4. This sensor is used by being fixed to a partition wall 5 such as a flue.

As described above, the zirconia-type oxygen sensor according to the prior art needs to be supplied with a gas having a known oxygen concentration such as air to the reference electrode as a reference gas, which makes it difficult to miniaturize the sensor and to install it at a certain place. It was limited. On the other hand, although air is usually used as the reference gas, when the target gas is combustion exhaust gas, the difference in oxygen concentration between these is 15 to 2
Since it was as small as 0%, the electromotive force between these electrodes was small, and therefore errors were likely to occur in measurement.

On the other hand, if there is a temperature difference between the electrode 2 and the electrode 3, there is a drawback that an accurate concentration difference cannot be detected. Here, for example, when the oxygen concentration is measured in an environment where the measurement atmosphere is 750 ° C., the temperature difference between these electrodes is 0.44.
If there is ℃, the measured value of the sensor is 1 in oxygen concentration.
It is said that an error corresponding to% occurs.

In order to solve the above problems, it is necessary to increase the measurement area of the sensor and to reduce the temperature difference between the electrodes caused by the reference gas or the like. There is no choice but to select the tubular shape as shown in Fig. 7, and there has been a demand for its improvement in the field in which particularly compactness is required such as measurement of oxygen concentration in combustion exhaust gas of automobiles. Further, since the electrode area of the sensor is large as described above, a large current is required for a heater (not shown) for heating, and it is necessary to secure a power source when applied to an automobile or the like.

Here, in order to miniaturize the sensor itself, for example, when the gas to be measured has a low oxygen concentration such as combustion exhaust gas, the electromotive force between the electrodes increases the concentration difference between the reference gas and the gas to be measured. Alternatively, a method of increasing sensitivity by supplying oxygen or a gas having a high oxygen concentration as a reference gas may be used. However, in this case, a reference gas supply means such as an oxygen cylinder is required as an accessory of the sensor, and as a result, convenience is significantly impaired.

[0009]

SUMMARY OF THE INVENTION The present invention does not require any accessories for supplying gas to the sensor, is simple and compact because it does not require an atmospheric electrode, and consumes less power to the heater. It is an object of the present invention to provide an oxygen concentration sensor that can perform accurate measurement in a high temperature environment.

[0010]

In order to solve the above-mentioned problems, the oxygen concentration sensor according to the present invention is faced with a zirconium film which is in contact with the outside air on one side and the gas in the case on the other side. Have two or more pairs of electrodes, one of which
A pair of electrode pairs is used as a pumping cell for introducing oxygen from the outside air into the case, and another pair of electrodes is used as a detection unit for measuring the oxygen concentration difference between the gas inside the case and the outside air.

In the above-mentioned case, a zirconium film is provided on each of two opposing walls, one of the zirconium films has an electrode pair used as a pumping cell, and the other zirconium film has an electrode pair serving as a detection section. This is preferable because the case can be made thinner and the oxygen concentration sensor can be made more compact.

Further, the oxygen concentration of the gas in the case becomes 100% as a result of pumping up, but strictly speaking, it is possible that it slightly varies due to the influence of the oxygen concentration of the outside air and leakage from the case. Therefore, for example, in the electrode pair serving as the detection unit, the electrode in the case of this electrode pair has a structure in which the electrode in the case contacts the gas in the case through a diffusion hole plate having fine holes that control the flow of the gas passing therethrough. If a voltage is applied to the electrode pair of this detection unit by electrical switching and the current value at that time is also measured, the oxygen concentration of the gas in the case can be measured using this electrode pair. . As a result, the concentration of the gas in the case can be checked at any time, and the measurement value of the detection unit can be calibrated, and as a result, the measurement value of the oxygen concentration sensor according to the present invention can be made more reliable. It is possible because it is possible.

Further, it is not a switching type as described above, but further has one set of electrode pairs, and the electrodes in the case of this electrode pair are provided with a diffusion hole plate having fine holes for controlling the flow of the gas passing therethrough. If there is an internal gas concentration calibration unit that has a structure for contacting the gas in the case and applying a voltage to this electrode pair and measuring the current value at that time, the oxygen concentration of the gas in the case is always checked. It is more preferable because it can be checked, and as a result, an accurate measured value can be obtained.

On the other hand, in the above case, if the pumping cell, the detection unit, and the internal gas concentration calibration unit are provided, the calibration unit and the like are covered with glass except for the portions through which these gases need to pass. It is possible to reduce the fluctuation of the gas concentration in the case due to the leakage of gas from the device or the influence of external gas, and to shorten the time required from the start of the pumping cell to the stabilization of the gas concentration in the case. It can be in a measurable state.

When a large current is applied to the zirconia film of the fixed electrolyte of the pumping cell for a long time, the zirconia (zirconium oxide) is partially reduced and deteriorated. Here, if gas leakage from the case is reduced by the glass coating as described above, it is possible not only to make quick measurement after starting the pumping cell operation but also to prevent deterioration of the zirconia film of the pumping cell, which is preferable. . Since the void in the case has a small volume, the oxygen concentration of the internal gas increases quickly due to pumping, which shortens the time required to reach the measurable state after the power is turned on, which is desirable.

The oxygen concentration sensor according to the present invention can be easily calibrated by using only air as follows. That is, the gas in the case is replaced with air by placing the sensor in air and setting the current supplied to the pumping cell to zero. Since the electromotive force at this time is 0, zero adjustment is performed by using this, and then the current supplied to the pumping cell is set to a predetermined value so that the gas concentration in the case becomes 100%.
%, And span adjustment is performed by the output at this time (electromotive force generated by air and 100% oxygen gas).

[0017]

The oxygen concentration sensor according to the present invention has a peculiar structure in which oxygen is introduced from the outside air into the case by the pumping cell so that the oxygen concentration in the case gas is 100%.
To keep. By measuring the potential difference between the electrodes inside and outside the case in the detection unit using the gas inside the case as a reference gas, the oxygen concentration of the outside air can be known from the potential difference between the electrodes.

That is, the potential difference E between the electrodes of the detection unit inside and outside the case is such that the oxygen concentration C of the gas inside the case is C when there is no pressure difference and temperature difference between the gas inside and outside the case at the temperature T (K).
1. The Nernst equation, the equation of state of gas, and the equation 1 derived from Faraday's law with the oxygen concentration C2 of the outside air.
The relationship is shown in E = RT / 4F × ln (C1 / C2) ... [Formula 1] In Formula 1, R is a gas constant and F is a Faraday constant.

As is clear from the equation (1), when the difference in oxygen concentration between the gas inside and outside the case is large, this potential difference becomes large. Therefore, for example, the present invention applies to oxygen in a gas having a low oxygen concentration in gas, such as combustion combustion exhaust gas. When applied to the concentration measurement, since the gas in the case is 100% oxygen gas, the concentration difference becomes large and a large signal can be obtained, so that the sensitivity is improved. Therefore, even if the electrode used in the oxygen concentration sensor according to the present invention has a small area, sufficient sensitivity can be obtained, and the sensor itself can be made extremely compact.

The above expression 1 is satisfied when the temperatures of both electrodes inside and outside the case of the detection unit are equal. Since the oxygen concentration sensor according to the present invention can be made compact, this temperature difference can be made extremely small, and therefore the error caused by the temperature difference between both electrodes can be made extremely small. Further, since it can be made compact as described above, the heater current for heating the zirconia film may be small, and thus it can be suitably applied to applications such as automobiles where the capacity of the power source is limited.

Further, since the reference gas is produced by the sensor itself pumping oxygen from the outside air, the reference gas supply means is not required. Therefore, the oxygen concentration sensor according to the present invention only needs to be electrically connected to the outside. Therefore, for example, when the sensor is moved to measure at a plurality of points,
Very easy.

[0022]

【Example】

[Embodiment 1] FIG. 1 shows a sectional view of an oxygen concentration sensor (Embodiment 1) according to an embodiment of the present invention. Reference numerals 1 and 1'in the drawing each denote a zirconia film having a thickness of 7 μm. 2
Electrodes 3 and 3 are connected to external voltage measuring means by lead wires or the like. Reference numerals 2'and 3'indicate electrodes of the pumping cell, which are connected to an external power source by a lead wire or the like. These electrodes 2, 3,
Since 2'and 3'are made of platinum and have fine holes,
The zirconia film on the back surface of these electrodes can also come into contact with the atmospheric gas.

The perforated plates 4 and 4'are plates made of alumina having a size of 3 cm × 4 cm and a thickness of 0.3 mm, and have gas permeability because they have fine holes. The detection part and the pumping cell are formed by a method of stacking on the perforated plates 4 and 4'by sputtering.

In the oxygen concentration sensor according to the present invention shown in FIG. 1, porous plates 4 and 4'having a detecting portion and a pumping cell, respectively, are adhered by an alumina-silica type inorganic adhesive Sumicelam SL50A-20 manufactured by Asahi Chemical Industry. Can be made. In addition, at the time of this bonding, there is a void 7 inside.
Is formed. A platinum heater (not shown) for heating the zirconia film is provided on the surfaces of the porous plates 4 and 4'which are not in contact with the respective electrodes.

This oxygen concentration sensor and the oxygen concentration sensor of the first embodiment are placed in air at room temperature, and a heater (not shown) having a detector and a pumping cell built therein is used to form 700.
The voltage applied to the pumping cell portion of the sensor was gradually increased while heating to 0 ° C. to increase the energizing current.
The situation at that time is shown in FIG. It has been found that when the value of the current flowing in the pumping cell exceeds 4 mA in this way, the voltage between the electrode pair of the detection unit does not change, that is, the oxygen concentration of the gas in the case of the sensor reaches equilibrium.

Example 2 An oxygen concentration sensor was obtained in exactly the same manner as the oxygen concentration sensor according to the present invention shown in Example 1. The glass coating material LS made by Tanaka Kikinzoku International Co., Ltd. is used for the oxygen concentration sensor except for the detector and the pumping cell which do not require gas permeability.
201 was applied and glass coating was performed (Example 2).
FIG. 3 shows a cross-sectional view thereof.

Under the same conditions as those for the oxygen concentration sensor of Example 1, the sensor coated with this glass was also examined for changes in the electromotive force of the detecting portion when the pumping current was changed. FIG. 4 shows the results. From FIG. 4, when the value of the current flowing in the pumping cell is about 1/10 of that of the sensor of the first embodiment, which is about 0.4 mA, there is no change in the voltage between the electrode pair of the detection unit, that is, It was found that the oxygen concentration of the gas in the case of the sensor reached equilibrium.

Example 2 coated with glass in this way
The amount of oxygen leaking from the oxygen concentration sensor according to Example 2 or the amount of gas (nitrogen, etc.) other than oxygen that intrudes from the outside of the sensor is much smaller than those in the oxygen concentration sensor according to Example 2. I understand.

[Embodiment 3] FIG. 5 shows the case where an oxygen concentration sensor according to the present invention is provided with an in-case gas concentration detection mechanism. A switch S is connected to the lead wire from the detection electrode. When the switch S is connected to the voltage detecting means, the oxygen concentration of the outside air can be measured, and when the detecting electrode is connected to the voltage applying means and the current detecting means, the oxygen concentration of the gas in the case can be measured.

The measurement of the oxygen concentration of the gas in this case is based on the following principle. That is, a voltage is applied to the electrode pair of the detection unit, and the detection unit functions as a pumping cell that moves oxygen from the inside of the case to the outside. As a result, the oxygen gas concentration decreases near the electrode 2 in the detection part of the porous plate 4,
As a result, oxygen gas is supplied by diffusion from the portion of the porous plate 4 that is in contact with the inner space 7 of the case and is rich in oxygen gas.

Here, the diffusion rate is determined by the shape of the porous plate 4 and the oxygen concentration difference (or oxygen partial pressure difference) between the supply source and the supply destination. Therefore, the perforated plate 4 is selected as a perforated plate 4 so that the amount of oxygen supplied by diffusion in the perforated plate 4 is sufficiently smaller than the pumping capacity of the detection unit, that is, the perforated plate having fine pores for controlling the flow of the permeating gas. However, if the current at the time of pumping is measured, it is possible to know the supply source, that is, the concentration of the gas in the case.

When pumping is performed in this manner, a gas flow accompanies the flow of oxygen, which causes a difference in oxygen concentration (or oxygen partial pressure) in the thickness direction of the porous plate 4. When only a small amount of electric current flows to measure the electromotive force, this gas flow is virtually absent, and therefore the difference in oxygen concentration (or oxygen partial pressure) in the thickness direction of the porous plate 4 can be ignored.

[Embodiment 4] The oxygen concentration sensor according to the present invention shown in the above-mentioned Embodiment 3 is for measuring the oxygen concentration of the outside air and the gas in the case by switching the operation of the detecting portion by the switch S. It was Here, the oxygen concentration sensor whose cross-sectional view is shown in FIG. 6 has a dedicated electrode pair for measuring the oxygen concentration of the gas in the case (Example 4). Since this can always measure the oxygen concentration of the gas in the case, it is possible to always accurately measure the oxygen concentration of the outside air.

[0034]

As described above, the oxygen concentration sensor according to the present invention does not require an accessory or the like for supplying a reference gas and does not require an atmospheric electrode, so it is simple, compact, and
Accurate measurement is possible in high temperature environment.

[Brief description of drawings]

FIG. 1 is a sectional view of an oxygen concentration sensor (Example 1) according to an example of the present invention.

FIG. 2 is a diagram showing a relationship between a pumping current and an electromotive force of a detection unit in the oxygen concentration sensor of Example 1.

FIG. 3 is a cross-sectional view (Example 2) of an oxygen concentration sensor of an example according to the present invention, a part of which is covered with glass.

FIG. 4 is a diagram showing a relationship between a pumping current and an electromotive force of a detection unit in the oxygen concentration sensor of Example 2.

FIG. 5 is a cross-sectional view of an oxygen concentration sensor according to an embodiment of the present invention, which has a mechanism for measuring the concentration of gas in a case.

FIG. 6 is a cross-sectional view of an oxygen concentration sensor according to an embodiment of the present invention, which has a mechanism for measuring the concentration of gas in a case.

FIG. 7 is a sectional view of an oxygen concentration sensor according to a conventional technique.

[Explanation of symbols]

 1 zirconia film 1'zirconia film 2 electrode 2'electrode 2 "electrode 3 electrode 3'electrode 3" electrode 4 perforated plate 4'perforated plate 5 partition wall 6 inorganic adhesive 7 void in case

Claims (5)

[Claims] 1. There are two or more pairs of electrodes facing each other with a zirconium film in contact with the gas in the case on one side and the outside air on the other side. An oxygen concentration sensor, comprising a pumping cell for introducing oxygen, and another pair of electrodes serving as a detection unit for measuring a difference in oxygen concentration between the gas inside the case and the outside air. 2. A zirconium film is provided on each of two walls facing each other in the case, and one of the zirconium films has an electrode pair used as a pumping cell, and the other zirconium film has an electrode pair serving as a detection unit. The oxygen concentration sensor according to claim 1, which is characterized in that. 3. The electrode pair serving as the detection unit has a structure in which the electrode in the case of the electrode pair comes into contact with the gas in the case through a diffusion hole plate having fine holes for controlling the flow of the gas passing therethrough. The oxygen concentration sensor according to claim 1 or 2, further comprising a mechanism for applying a voltage to the electrode pair by electrical switching and measuring a current value at that time. 4. In addition to the electrode pair used for the pumping cell and the electrode pair used as the detection section, there is further provided one pair of electrodes, and the electrodes in the case of this electrode pair control the flow rate of the gas passing therethrough. 2. A structure having a structure in which a gas in a case is contacted through a diffusion hole plate having fine holes, and a mechanism for applying a voltage to this electrode pair and measuring a current value at that time. Alternatively, the oxygen concentration sensor according to claim 2. 5. In the above case, when the pumping cell and the detection unit, and the internal gas concentration calibration unit are provided, the outer surface portion of the case other than the portion that needs to come into contact with gas is glass-coated. The oxygen concentration sensor according to any one of claims 1 to 4.