JPS5999244A - Detector for gaseous co - Google Patents

Abstract

PURPOSE:To detect selectively gaseous CO with good accuracy while eliminating the malfunction occuring in reducing gas by providing a gas sensitive element having sensitivity to CO and reducing gas and a gas sensitive element which does not react with CO and sensitivity to the reducing gas alone. CONSTITUTION:A gas sensitive body which is an oxide semiconductor consisting essentially of SnO2, ZnO and Fe2O3 and added with Nb<5+>, Sb<3+>, etc. according to need is formed by a vapor deposition method, etc. in the form of a thin film having 1,000Angstrom -1mum thickness on a ceramic substrate of Al2O3, BN, etc. which is a substrate having heat resistance and insulation characteristic. A pair of electrodes are provided thereon and further a catalyst layer consisting of a catalyst of at least one kind among Pt, Pd, Rh and a carrer of at least one kind among Al2O3, ZrO2, SiO2 is formed thereon, whereby a gas sensitive element having sensitivity to CO and reducing gas is obtd. Only the catalyst layer in the same constitution as mentioned above is formed of a carrier of one kind among Al2O3, ZrO2 and SiO2 and a catalyst of Ag, whereby a gas sensitive element for reference having sensitivity to the reducing gas is obtd. CO is selectively measured by two kinds of such elements.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a CO gas detection device.

[Technical background of the invention and its problems]

BACKGROUND ART Gas sensing elements have been known that use oxide semiconductors such as SnO, ZnO, and Fe2O3, which exhibit N-type semiconductor characteristics, as gas sensing bodies in order to detect reducing gases in the atmosphere. This utilizes the fA phenomenon in which when these oxide semiconductors come into contact with a reducing gas, their electrical conductivity increases, that is, their resistance value decreases.

There are those that use the gas sensitive material as a sintered body, and those that use it as a thin film formed by sputtering, vapor deposition, etc.
Regardless of whether it is a sintered body type or a thin film type gas-sensitive element, metal oxide semiconductors alone generally have low sensitivity as a gas-sensitive element, and the selectivity cannot be said to be comparable to that of light. Attempts have been made to increase the sensitivity of devices by using noble metals such as platinum (pt) and palladium (Pd) as catalysts. That is, methods have been adopted such as adding Pt or Pd to the entire gold ingot oxide semiconductor, or forming a catalyst layer supporting Pt or Pd on the metal oxide semiconductor.

Although such treatment improves sensitivity compared to the case without catalyst, it still does not exhibit sufficient sensitivity to reducing gases at low concentrations. Moreover, when various reducing gases are mixed, it is extremely difficult to selectively detect only one reducing gas with high sensitivity because malfunction of the element is induced by the influence of other reducing gases. Above all,
It has been extremely difficult to detect a gas such as Co, which has an adverse effect on the human body even at low concentrations, while excluding malfunctions caused by other reducing gases.

Furthermore, when it is assumed that the gas-sensitive element will be used in a general domestic vehicle, it is important to eliminate malfunctions caused by alcohol vapor.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a gas detection device that can selectively detect COO gas.

[Summary of the invention]

The present invention is a gas detection device equipped with a gas-sensitive element for emitting COO gas and a gas-sensitive confectionery for reference. power 1
The output is added for one hour to get used to the CO gas.

The gas-sensitive element for CO gas detection used in the present invention is COO
A gas sensitive body made of an oxidized semiconductor that is sensitive to reducing white gas containing gas and whose resistance value changes upon contact with the reducing gas, a pair of electrodes provided on this gas sensitive body, Pt,
Catalyst layer 4 of at least one of Pd, kLh and Al, 08. The catalyst is made of at least one type of carrier selected from ZrO2 and Si02, and has a catalyst j- provided on the gas sensitive body.

SnO is used as a semiconglomerate for use in gas sensitive materials.
, ZnO series, Fe, 03 series are used. Sn
O2 system.

ZnO thread, Fe, 0. The system monster Chihirotai are each S
nO,.

ZnO, upper "e, 08 is the main component, Nb"
, sb3+.

It contains subcomponents such as Cr3+, p, and t3+. This gas sensitive body may be either a thick film (sintered body) or a thin film, but a thin film sword is preferable because it has excellent responsiveness to gas and good immersion properties. Examples of methods for producing the gas sensitive thin film include vapor deposition, sputtering, and thermal decomposition of organic compounds of metals. This gas sensitive material is made of AI! which is a heat-resistant and insulating substrate. 20. ,BN,8
It is formed on a ceramic substrate such as I, N4, 5i02, etc., and the film thickness is preferably about 100A-1 μm, more preferably about 100OA-1 μm. This has a film thickness of 1μ
This is because if the value exceeds m, the sensitivity decreases to less than the sensitivity to reducing gases, and at the same time, its dispersion increases.

This gas sensitive body is provided with a pair of electrodes in order to detect the resistance value, and the W: pole only needs to be electrically connected to the gas sensitive body, and can be attached to either the gas sensitive body surface or the substrate surface. It may be provided. This electrode is formed of Au, Pt, etc. by a printing method, a vapor deposition method, a sputtering method, or the like. Normally, lead wires are connected to take out electrical signals from the gas-sensitive element, so the lead wire connection part is formed by a printing method that has a high adhesive strength with the substrate, and the contact part with the gas-sensitive element is formed by a vapor deposition method etc. It is also possible to form a thin film.

Further, the catalyst layer includes at least one catalyst metal selected from among Pt and Pd, and Az20. , ZrO,,S
It is preferable to use a carrier made of at least one type of iO□, and to have a porous structure that does not prevent the measurement atmosphere gas from coming into contact with the gas sensitive member. If it is porous like this, it can be used to create thick films using sintered bodies, sputtering methods, etc.
Both the Group N method and the thermal decomposition method of organic compounds of metals are suitable. This mediating metal is used to improve gas-sensitive characteristics such as gas responsiveness and gas selectivity.
The carrier is used to prevent deterioration of the gas-sensitive properties due to the catalytic metal being stuck in the gas-sensitive confectionery during use. In the case of a thick film, a film thickness of 10 to 5 Q prn is preferable; outside this range, pfR medium effects such as sensitivity and selectivity deteriorate. Further, in the case of a thin film, a temperature of 5 to 1QOOnm is preferably 8 degrees, and in the case of a thermal decomposition method, a range of about 1 to 1QQQnm is particularly preferable. Outside this range, not only the catalytic effects such as sensitivity and selectivity will be reduced, but also the gas response speed will be reduced.

The catalyst metal in this void layer is 0.05 to 2c in the case of a thick film.
1 wt%, preferably about 1 to 9 Qwt in the case of a thin film, and particularly preferably 1 to 80 wt% in the case of a sputtering method. Further, the ratio 4= of the catalyst metal is the Atsuko ratio, which is Pt −P
For d, Pt/Pd = o, 05~1,0,
In the case of Pd-11, h/Pd=u, 05-1.0
, for Pi-Rb, h/P is 20.05 ~
A range of 10 is preferred. Outside the above range, sufficient sensitivity and selectivity cannot be obtained, and if the amount of catalyst metal increases, the catalyst J- becomes responsible for the conductivity, making it difficult to measure the resistance value of the gas sensitive material. turn into.

In this way, the catalyst layer may be either a thick film or a thin film, but due to the lifespan of the gas-sensitive element and the gas responsiveness, sputtering method, evaporation method, thermal decomposition method of metal organic compounds, CVD method, etc. It is preferable to use a thin film formed through a sintering process. Further, in order to maintain the insulation between the catalyst layer and the sludge sensitive material, and to prevent diffusion of the catalyst metal, the catalyst layer may be provided via Ae2o, )-, etc.

The gas sensing element for discharging CO gas having the above configuration is sensitive to CO and other reducing gases (miscellaneous gases). In addition, gas-sensitive elements are generally equipped with a heater to heat the gas-sensitive body to ensure the same gas responsiveness, and measurement is performed by heating the gas-sensitive body. For example, by setting the temperature to a low temperature of about 120℃ or less, CO
Sensitivity to O20 is improved.

Next, the reference gas-sensitive element will be explained.

The reference gas-sensitive element is sensitive to reducing gases other than COO gas. The structure is the same as the above-mentioned gas sensitive element for COO gas emission, and the gas sensitive element used is also a 10J type, but the catalyst layer is different.

The catalyst number of the reference gas-sensitive element is k1203. ZrO
. , 5 in 2 and Al, and is preferably porous to the extent that it does not prevent the measurement atmosphere gas from coming into contact with the gas sensitive member.

This catalyst) may be either a thin film or a thick film, similar to the gas-sensitive element for lateral extraction of CO gas, but from the viewpoint of the life of the gas-sensitive element, gas response, etc., a sputtering method is preferred.

It is preferable to use a thin film formed without going through a sintering process such as a vapor deposition method or a thermal decomposition method of an organic compound of metal. The amount of As+ in the catalyst layer is preferably about 0.05 to 20 wt% in the case of a thick film, and 1 to 80 wt% in the case of a thin film; outside this range, sufficient sensitivity, selectivity, and moisture resistance cannot be obtained. If the amount of 82 is further increased, the catalyst layer will become electrically conductive. This catalyst layer has a thickness of 10 to 50 in the case of a thick film.
In the case of a thin film, it is preferably about 5 to 1100 Qn, and outside this range, the catalytic effect will decrease, and as the film becomes thicker, the gas response speed will also become slower.

The reference gas-sensitive element configured as above has virtually no sensitivity to COO20, and has no sensitivity to alcohol gas CH.
It has sensitivity to reducing gases (miscellaneous gases) such as 4, C, and H (1st grade).

In the present invention, as described above, an output having information on CO gas + miscellaneous gas from the gas-sensitive element for CO gas detection and a reference output having information on only miscellaneous gas from the reference gas-sensitive element are obtained separately. Therefore, the influence of miscellaneous gases can be easily removed from the output of the COO gas emitting gas sensitive element using the reference output from the reference gas sensitive element, and the selectivity of COO20 measurement is improved.

An example of a circuit configuration for driving a COO gas emitting device using such two gas-sensitive elements will be explained using a block diagram (FIG. 1).

The outputs from the gas-sensitive device AL for CO gas detection and the gas-sensitive element for reference (C) are input to the resistance-voltage conversion circuits (b) and (d), respectively, and converted into voltages vl and v2. .

The signal V from the reference gas-sensitive element output from the resistance-voltage conversion circuit (d) is the alarm level setting circuit (e).
is input, and an alarm level v; is output. This V and vl, which are the signals of the gas-sensitive confectionery for CO gas detection, are input to the voltage comparison circuit (f), and this voltage comparison circuit jj3
When it is determined in (f) that COO20 is present, an alarm signal S is output and input to the alarm circuit (g).

Next, the operation of this circuit will be explained.

The resistance value, which is the output from the gas-sensitive element a) for CO gas side discharge and the reference gas-sensitive element (C), changes depending on the measurement atmosphere. Generally, the change in resistance value in a gas-sensitive element is steep when the gas concentration is low, but as the gas concentration increases, the slope becomes gentler. This tendency also applies to mixed gases of two or more types. Also, when COO20 is introduced into reducing waste, the same amount of COO2 in the air
The change in resistance of the gas-sensitive element is smaller than when zero is introduced.

That is, as the concentration of CO gas in the atmosphere increases, the resistance change of the element with respect to a certain amount of CO gas becomes smaller. Therefore, it is necessary to change the alarm level depending on the number of miscellaneous gases in the measurement atmosphere. The alarm level setting circuit (e) sets this alarm level. The alarm level setting circuit (e) uses the signal vt (R2) from the reference gas-sensitive element (C) to determine the COO20 of the COO gas output gas-sensitive element (a) in an atmosphere containing miscellaneous gas. Outputs alarm level V:. The alarm level V changes depending on the concentration of such miscellaneous gas; and the gas sensing element for COO gas output (a)
The presence of the COO20 can be determined by comparing the signal vl from the voltage comparison circuit (f).

FIG. 2 shows changes in the physical gas characteristics according to the present invention depending on the miscellaneous gas concentration. Since both the gas-sensitive element for COO gas output and the reference gas-sensitive element respond to miscellaneous gases in the same way and change their resistance, the output from the resistance-voltage circuit has a characteristic 1 as shown by curve a in Figure 2.
Becomes raw. When a certain amount of COO20 is introduced into such an element, the COO gas-emitting gas-sensitive element exhibits a curve-like characteristic. Therefore, the 'nt pressure difference between curve a and curve A is COO2
As seen in the figure, even if the CO gas concentration is constant, the voltage difference between curve a and curve a varies greatly depending on the amount of miscellaneous gas. Therefore, by changing it as during measurement, it is possible to eliminate malfunctions caused by changes in the miscellaneous gas concentration.

As the resistance-voltage conversion circuit, for example, a circuit is used in which a passive element and a fixed resistor are connected in series, a constant voltage is applied, and the voltage across the fixed resistor is measured.

The alarm level setting circuit combines, for example, a normal operational amplifier and a reference voltage generation circuit, and calculates the difference between miscellaneous gas and COO20 using the output V2 (miscellaneous gas daughterness - voltage) from the reference gas-sensitive element using a preset function. It is converted into a gas-sensitive element output V1 for CO gas release in a mixed gas.

The voltage comparison circuit may be an ordinary electronic circuit, and the -1 notification circuit may be configured to generate and display an alarm using a buzzer, LED, etc., and to cut off the gas supply as necessary.

By using the circuit configured as above, the alarm level can be varied according to the concentration of miscellaneous gas, so COO20
It can be detected with good selectivity and high reliability.

〔Effect of the invention〕

As explained above, as in the present invention, a gas-sensitive element for CO detection that is sensitive to a reducing gas containing COO20,
OO20 can be used to detect CO gas with good selectivity by using a CO gas extraction device equipped with a reference gas-sensitive element that has no substantial sensitivity.
O20 can be detected.

[Embodiments of the invention]

Examples of the present invention will be described below.

(Example 1) Manufacturing of a gas-sensitive element for detecting g'yco gas will be described. FIG. 3 is a cross-sectional view of the gas-sensitive element.

An alumina substrate is used as the insulating group 'O, (]), and an electrode (2) is formed on the -force side. This electrode (2) has a lead wire connection portion (2a) and a signal extraction portion (2b).The lead wire connection portion (2a) is formed by baking Au paste.
A pair of comb-shaped electrodes are formed by sputtering Au in the signal extraction section (21) that comes into contact with the gas sensitive body (5). In addition, the back side of the insulating substrate ([) is I(,
A heater (3J) for heating the gas sensitive body made of uo2 paste or the like is used between a pair of electrodes (4).

Next, a gas sensitive body (5) is formed.

First, the combined amount of Sn is 0t.
A sample bath solution was prepared by dissolving the sample in n-butanol to give a concentration of JT%.

Apply this between a pair of electrodes (2) and leave it in the air for 1 hour.1. After that, the mixture was heated to 120°0 to vaporize II-butanol. The whole was then thermally decomposed in air at 400'O for 1 hour. This process of coating and thermal decomposition was repeated three times to form a gas sensitive member (5) made of a thin film of SnO with a thickness of about 0.3 μm.

Subsequently, catalyst No. 11# (6) is formed on the gas sensitive member (5).

4a of Pd and Pt (for example, Platinum Resinate, Pasium Resiné-1, manufactured by JI ES J, Ltd.) was added to the alkoxide of 8e, and diluted with butanol. This butanol solution was applied onto the gas sensitive member (5), and after drying at room temperature for 1 hour and at 150°C, 3Q1 was applied with 40Q'O.
A catalyst layer (6) made of pa-pt-8ttOs was formed by thermal decomposition of 1ta.

Examples of metal organic compounds used for forming such gas sensitive bodies and catalyst layers include Pt, Pd, l(, h, AJ.

Zr, 8i metal alcoholides, metal soaps, resin salts, complexes, and other commonly used organic compounds that decompose on heating to produce metals or metal oxides are used. Examples of organic compounds of these metals include Rinter Oil 2 Petroleum Ether, A solution mixed with an organic solvent such as hexanetoluene is applied to the surface of the gas sensitive member to form a film. The composition ratio of the catalyst layer can be easily controlled by changing the amount of the metal organic compound in this solution. Further, after the film is formed, it is preferable to perform a drying treatment at room temperature for about 1 hour and at 100 to 150°C for about 1 hour to evaporate the organic solvent and fix the metal organic compound on the gas sensitive member.

When heated, this metal organic compound easily thermally decomposes into metal or metal oxide. At this time AZ +
At least one of Zr+ St is oxidized to NZ2O3゜ZrO2 by reacting an organic compound with oxygen atoms in it or by heating in an oxygen-existing atmosphere.
,SiO,. In this way, by heating and decomposing an organic compound of a metal (including at least one catalytic metal among Pt, Pd, Pt, ZrO, S
102 (D), a catalyst layer consisting of at least one type of carrier can be used.

□′ As described above, the gas-sensitive element according to the present invention using the catalyst layer formed by the thermal decomposition method of a metal organic compound has extremely excellent responsiveness to the gas to be measured. This is considered to be because the catalyst layer formed by this method achieves a good porous state.

In other words, a porous state is required so as not to interfere with the contact between the gas sensitive body and the gas to be measured, but according to this method of thermal decomposition of organic compounds, the state in which the metal is dispersed in advance is required. This is thought to be because organic matter is removed from the surface, creating pores in this area.

Further, according to this thermal decomposition method of organic compounds, a catalyst layer having a desired composition ratio can be easily obtained by adjusting the amount of the metal organic compound in the organic medium. Furthermore, the metal organic compound is uniformly dispersed in the organic solvent, and a uniform composition can be achieved in the formed catalyst layer with good reproducibility, resulting in excellent reliability when mass-producing gas-sensitive elements.
ing.

Furthermore, regardless of the shape of the insulating substrate, a homogeneous film can be formed regardless of the shape of the insulating substrate, such as a flat plate or a cylindrical shape. Table 1 shows the sensitivity of the gas-sensitive element for CO gas detection to various gases as described above.

(Margin below) Table 1 Next, a reference gas-sensitive element is manufactured.

The structure is similar to that of the gas-sensitive element for detecting 1dcO gas (shown in FIG. 1), except that only the catalyst layer is changed. The catalyst layer is Ag-AI! 20. A system was prepared in the same manner as described above using an Al alkoxide and an Ag resin salt (for example, Silver Resinate (manufactured by ESL)) diluted with butanol.

The gas-sensitive characteristics of this reference gas-sensitive resistor are shown in Table 2.

Table 2 (Example-2) Table 3 shows the characteristics of a 7IC device having the same configuration as the gas-sensitive element shown in FIG. 1, with the gas-sensitive element and catalyst layer formed by sputtering.

Gas-sensitive confectionery receptor target for ocO gas detection Nb, O, / SnO, = 0. OQ
5 (Mole ratio) Film thickness 1000A Catalyst layer target AJ20. And this Al! 5Q for ρ
wt% of Pd Film thickness: 100A Gas sensitive element for O reference (same as gas sensitive element for CO gas detection) Catalyst layer target AJ20. And Kono At? 20. K vs. C2c
When forming a catalyst layer by a sputtering method, a material containing a catalyst metal and a carrier in a desired ratio may be used as a target, or a material containing a catalyst metal and a carrier in a desired ratio may be used as a target.
It is also possible to form a catalyst layer by forming a thin film using a material containing at least one of Si and Zr, and then performing thermal oxidation in an atmosphere containing oxygen. Also, catalytic metal and A/ as targets.

A material containing at least one of Si and Zr may be used, and sputtering may be performed in an atmosphere containing oxygen. In this case, in order to increase the stability of the oxide used as a carrier, it is preferable to perform a heat treatment in the air after forming the thin film. The same applies when a material containing a catalyst metal and a carrier is used as the target. In this way, the target used in the sputtering method may be a mixture of raw material powders, an alloy, or a target made of a single material (Targera) 4J coated with a part of its surface with another material. It may also be used as Furthermore, it may be carried out using a binary sputtering method, in which case various compositions can be realized with the same target.

Further, the catalyst layer is required to be in a porous state so as not to prevent contact between the gas sensitive body and the gas to be measured. When the catalyst layer is sufficiently thin, for example, when the film thickness is 10 nm or less, the thin film grows in the form of islands even if a normal sputtering method is used, so that a substantially porous state is realized. Also,
For example, by performing sputtering under a high gas pressure of Ar, O□N%'103, Torr, gas is trapped in the formed catalyst layer, and by removing this gas by heating, a porous state is achieved. You can also do that.

Furthermore, it is also possible to mix an organic substance such as PVA into the target and perform sputtering to form a catalyst layer containing the organic substance, and then remove the organic substance by heating to achieve a porous state.

Generally, gas-sensitive elements are equipped with a heater to heat the gas-sensitive element, but by making the catalyst layer thinner, the heat capacity becomes smaller, so the output of the heater can be suppressed, which reduces the lifespan of the heater. This will extend the life of the gas-sensitive element.

(Example 3) Formation of a catalyst layer of a gas sensitive element for detecting 0 ocO gas (Example 3) describes an example in which the gas sensitive body is the same as in Example 1 and the catalyst layer is formed into a thick film by coating and sintering. Nu(4
), PdC76 was dissolved in water to give Pd 1.0% by weight.
An aqueous solution of was prepared. Here, the surface area is about 100rr? /
2 A! ! , O, fine powder was immersed and thoroughly stirred. AI! ,
0. The fine powder was separated, dried under reduced pressure for 1.5 hours to remove moisture, and then evaporated to dryness. Then, it was ground in a mortar, and the resulting powder was placed in a quartz crucible and fired at 400°C.

This catalyst powder was put into an aluminum hydroxychloride aqueous solution (A/20.1%) to form a slurry. This slurry was applied onto the gas sensitive material, dried, and fired at 400''C to form a 20um thick Pd-supported A60.
．． A catalyst layer was formed.

Formation of catalyst layer of gas-sensitive element for 0 valley light AgN0. Al2O, is immersed in a predetermined amount of solution of
O.

On the other hand, the material was impregnated with as much as 10 wt% of Ag, dried, and then placed in a quartz crucible and fired at 400°C. This catalyst powder was mixed with an aqueous solution of aluminum hydroxychloride to form a slurry, which was spread over a gas sensitive material and dried for 40 minutes.
It was fired at 0° C. to form an Ag-supported catalyst layer having a thickness of μrn.

The catalyst metal of the gas-sensitive element having the thick film catalyst layer thus formed was changed, the gas-sensitive characteristics were measured, and the fourth
Shown in the table.

As explained above, the gas-sensitive element for CO gas detection according to the present invention has sensitivity to CO gas and miscellaneous gases such as alcohol, and the reference gas-sensitive element has substantial sensitivity to CO gas, such as alcohol. It can be seen that it has a sensitivity to miscellaneous gases. Therefore, the influence of miscellaneous gases such as alcohol can be easily removed from the output of the gas-sensitive element for CO gas detection by using the output of the reference gas-sensitive element, and CO gas can be detected with good selectivity. The gas-sensitive element for detecting CO gas is C) T4. Since the sensitivity to gases such as C, H, etc. is very low, the selectivity is even better.

The gas-sensitive element for CO gas detection and the gas-sensitive element for reference formed as described above may be fixed to the base, respectively.
In consideration of miniaturization of the device, etc., it may be fixed on one base. FIG. 4 shows, as a plan view, an embodiment in which a gas-sensitive element for CO gas detection and a gas-sensitive element for reference are fixed on one substrate.

A notch for a gas-sensitive element ml bookshelf is provided in an insulating base aυ made of glass epoxy resin. A conductor pattern α made of Cu foil is formed on both sides of this insulating substrate (1υ).
A gas-sensitive element for detecting CO gas and a gas-sensitive element for reference (10 is a cutout part (10 is a Pt1J-coated wire of about 100 μm on each surface)
4) is fixed and suspended. In addition, since gas-sensitive elements with different characteristics are provided on both sides of the base αυ, a notch (L) is provided to prevent the orientation from being incorrect when inserting the element into an external socket. It is preferable to apply Ni plating to the surface of the pattern plate.

In this example, a glass epoxy resin with a Cu foil formed on it was used, but AI! 20. A substrate on which Au is baked may also be used.

By adopting a structure in which two gas-sensitive elements are suspended in the notch in this manner, ventilation of the measurement atmosphere is improved.

Further, although gas-sensitive elements are normally operated at high temperatures (for example, 100° C. or higher), heat conduction to the base is almost only through the lead wires, and the heating efficiency of the gas-sensitive body by the heater of the gas-sensitive element is also improved.

Next, an example of a circuit configuration for operating the COO gas emitting device of the present invention will be explained using the block diagram shown in FIG. 81~ in the figure
S6 is an electrically responsive switch. First, when there is no miscellaneous gas in the air and the resistance of the reference gas-sensitive element (B) is high, the voltage across 1LLo is low. At this time, the first voltage comparison circuit Ov is activated.

and turn on 84. For this reason, the gas-sensitive element for COO gas output uses a relatively large resistor RL1 to output voltage, and compares the signal of the alarm level setting circuit (c) with the second voltage comparison circuit (c).
Comparison is made in c). With this kind of circuit configuration, COO20
When introduced, the resistance of the sensing element decreases, but the resistance of the reference gas-sensitive element (B) does not change, so the second voltage comparator circuit (c) uses the voltage across the terminal and the alarm level setting. The output of circuit (2) is input and judged. In this case, since only 11 gases are present, the degree of output saturation of the detection element is small and a sufficiently stable alarm can be obtained.

Next, when there is a miscellaneous gas in the air, the resistance of the reference gas-sensitive element decreases, and the voltage across the LO increases.In this case, the voltage across the LO becomes the first voltage. When the range of comparison circuit 011 is exceeded, the lth voltage comparison circuit 0υ stops operating, thus turning 81.84 OFF, and at the same time, the first voltage comparison circuit (2) operates and S2゜S turns ON. , RL2 and the alarm level setting circuit ←■ are activated.At this time, the resistance of the CO gas detection sensitive element (N) is also decreased due to the miscellaneous gas, so i, [I(, smaller than 1) When the gas to be detected is introduced in this state, the resistance of the gas-sensitive element AJ for discharging CO gas further changes, and the voltage across the puller 2 increases.This is controlled by the alarm level setting circuit (2). ) and the second voltage comparator circuit (27) to determine Hr.

In this case, gas-sensitive cable (A) for releasing COO gas due to miscellaneous gas.
Since the resistance value of is decreasing, the signal from COO20 is a curse,
It is better to use 1tL2 than to use (l(,Ll>几,2)
It can be threaded with high accuracy.

It goes without saying that even when the concentration of miscellaneous gases is high, this method can be used to accurately and reliably capture the gas to be detected and to issue an alarm. In Fig. 5, (8) and (9) respectively indicate the resistance-voltage conversion circuit, and (2), (4), (4), the first voltage comparator, (2), (C), and (4) indicate the alarm level. Each setting circuit is shown and operates in the same manner as above. or(
28) shows the alarm circuit.

COO gas was discharged in the presence of miscellaneous gas using the COO gas discharge device having such a configuration.

In a circuit similar to that shown in Fig. 5, S,, S6 are analog switches; tLo is constant RL□~RL3 is IM
Ω.

100 Ω and 10 Ω, and other ordinary electronic circuits were used.

For the measurement, 20ppm of COO20 was first introduced into the air, a circuit was set up to issue a warning at this value, and then the Ca2 degree at the time of alarm under miscellaneous gas (alcohol) was checked. The results are shown in Table 5.

Table 5 (unit: ppm) As is clear from Table 5, in the present invention, COO20 can be detected with very good stability.In the above embodiment, as shown in FIG. Although it is set in stages, it is also possible to use multiple stages to further improve accuracy. It goes without saying that it is also possible to have two stages if necessary.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a circuit for driving the COO gas emitting device of the present invention, Fig. 2 is a characteristic diagram of the sensitivity of the gas-sensitive element with respect to the concentration of miscellaneous gas, and Fig. 3 is the gas-sensitive element according to the present invention. FIG. 4 is a plan view showing an embodiment of the device of the present invention, and FIG. 5 is a block diagram showing an example of a circuit for driving the device of the present invention. Electrode...2 Gas sensitive body...5 Catalyst layer...6]! +'j, lJr ri', ↓j'J,'shi:
'+1. '11. (PPM) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] A gas sensitive body made of an oxide semiconductor whose resistance value changes when it comes into contact with a reducing gas, a pair of electrodes provided on this gas sensitive body, and one of Pt, Pd, R, and h. at least -go
Catalytic metal and AJ208. A gas-sensitive element for detecting CO gas, comprising a catalyst layer made of at least one type of carrier among ZrO2, 5i02, and provided on the gas-sensitive body; an oxide semiconductor whose resistance value changes upon contact with a reducing gas; A gas sensitive body consisting of a gas sensitive body, and a pair of oit poles cut into this gas sensitive body,! :, 7Ve, Ol, ZrO,, S 10
2(7) 5. A CO comprising at least one type of carrier and a catalyst layer made of A2 and provided on the gas sensitive body.
A CO gas detection device comprising a reference gas-sensitive element having substantially no sensitivity to gas.