JPH07218464A - Gas sensor - Google Patents

Abstract

PURPOSE:To make the bearing process of a gas sensor simpler so as to reduce the cost of the sensor by forming a pair of resistance thermometer bulbs composed of thick metallic films on a substrate and providing a trimming section to at least one of the bulbs. CONSTITUTION:A first resistance thermometer bulb 18, second resistance thermometer bulb 19, etc., are formed on a substrate 11. The bulb 19 has a resistance adjusting section 23 and a trimming section 47 is formed in the section 23. For example, platinum paste is screen-printed on a insulating substrate 11 made of alumina, etc., in the patterns of the bulbs 18 and 19 and a first pad 12, third pad 12A, and second pad 12B and baked after drying. Then a gas detecting coating layer 20 and compensating coating layer 21 are respectively formed on the bulbs 18 and 19. The trimming can be performed easily, because it is performed for making the resistances between the pads 12 and 12A and between the pads 12 and 12B equal to each other. A combustible gas burns in the layer 20 and, as a result, the resistance of the bulb 18 rises and a Wheatstone bridge circuit becomes unbalance and outputs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a gas sensor, and more particularly to a structure of a catalytic combustion type gas sensor which can be easily paired.

[0002]

2. Description of the Related Art There is known a catalytic combustion type gas sensor for detecting a combustible gas by utilizing a resistance change of a resistance temperature detector with a temperature change. FIG. 4 is a fragmentary perspective view showing a gas detecting element of a conventional catalytic combustion type gas sensor. Platinum coil 3
An alumina carrier 32 carrying a noble metal is fixed around the periphery of 1.

FIG. 5 is a connection diagram showing a detection circuit of a conventional catalytic combustion type gas sensor. R _{1 and} R _2, respectively _, are resistance values of fixed resistances, and R _{3 and} R _4, respectively _, are resistance values of the compensation element 33 and the gas detection element 34. The compensating element 33 has the same structure as the gas detecting element 34, but instead of the noble metal of the gas detecting element, lead oxide PbO 3 is carried. When no combustible gas is present, the Wheatstone bridge circuit is in balance, in the state of R ₁ × R ₄ = R ₂ × R ₃ , and the load 35
Output is 0V. When the atmosphere contains a combustible gas other than alcohol, the combustible gas burns in the gas detection element 34, the temperature of the platinum coil rises, and its resistance value R _4, increases. On the other hand, in the compensating element 33, the flammable gas except alcohol does not burn, and therefore the temperature rise does not occur due to the flammable gas except alcohol, so that the resistance value R _3, does not change due to the flammable gas. In this way, the balance of the Wheatstone bridge circuit is broken and an output is generated at the load 35.

When the atmosphere contains alcohol gas, the alcohol gas burns in both the gas detecting element 34 and the compensating element 33. Resistor R _{3 Therefore,} R _4, the Wheatstone balance of the bridge circuit does not produce output without collapse together increases. In this way, compensation for alcohol gas is performed. The compensating element 33 also compensates for temperature. Even if the temperature of the platinum coil of the compensating element 33 or the gas detecting element 34 changes due to the change of the room temperature, the temperature coefficient is the same as long as both are at the same temperature, and therefore the balance of the Wheatstone bridge circuit is not broken.

The gas detecting element 34 and the compensating element 33 of such a conventional catalytic combustion type gas sensor are prepared as follows. An outer diameter of 0.
A coil having a length of 6 mm, a winding number of 10 turns, and a length of 1.5 mm is manufactured. A paste containing a mixture of alumina powder and alumina sol is attached to the platinum coil and fired at 800 ° C. to fix the alumina carrier to the platinum coil. Impregnate an alumina carrier with a mixed catalyst solution of palladium oxide and platinum oxide, and
The gas detection element 34 was manufactured by carrying out thermal decomposition at 0 ° C. and supporting a mixed catalyst of palladium oxide and platinum oxide on an alumina carrier.

A paste prepared by mixing alumina powder and alumina sol is adhered to the platinum coil and fired at 800 ° C. to fix the alumina carrier to the platinum coil. A compensation element 33 was manufactured by impregnating an alumina carrier with a lead acetate solution and thermally decomposing it. The conventional catalytic combustion gas sensor as described above has features such as a simple operation principle, excellent long-term stability, and little influence of ambient temperature and humidity. It is widely used for gas detection with a power consumption of 0.1 to 1.0%.

[0007]

However, in the conventional catalytic combustion type gas sensor as described above, there are variations in the resistances of the gas detecting element and the compensating element obtained, and the Wheatstone bridge when the combustible gas does not exist. In order to reduce the balanced output of the circuit, it is necessary to perform a work called pairing in which elements with similar resistance characteristics are combined.
At this time, the pairing is one of the factors that increase the manufacturing cost of the catalytic combustion type gas sensor because of the complexity of the pairing work process and the reduction in the yield accompanying the pairing work process.

The present invention has been made in view of the above points, and a first object thereof is to provide a gas sensor in which the pairing process is simple and the cost can be easily reduced by improving the structure of the catalytic combustion gas sensor. A second object is to provide a gas sensor having a simple pairing process and high sensitivity to combustible gas.

A third object of the present invention is to provide a gas sensor in which the pairing process is simple and the space can be saved.

[0010]

The above first object is to provide a substrate, a first resistance temperature detector, a second resistance temperature detector, a gas detection coating layer, and a compensation coating layer, Has multiple pads,
The first resistance temperature detector is a thick metal film and is laminated on the substrate, and the second resistance temperature detector is a thick metal film and is laminated on the substrate. At least one of the resistors has a trimming portion, and the pad includes a first pad for commonly connecting one end of the first temperature sensing resistor and one end of the second temperature sensing resistor, and a first pad. A second pad connected to the other end of the resistance temperature detector and a third pad connected to the other end of the second resistance temperature detector, each of which is laminated on the substrate with a space therebetween. The gas detection coating layer is selectively laminated on the first resistance temperature detector and the substrate, and burns a combustible gas in a catalytic manner to raise the temperature of the first resistance temperature detector.
The compensation coating layer is achieved by being selectively laminated on the second resistance temperature detector and the substrate.

The second object is achieved by providing the substrate with a groove formed in the surface thereof at a position where at least the gas detection coating layer and the compensation coating layer are divided. Third
In addition to the configuration of the first aspect of the invention, the substrate further includes a first fixed resistor and a second fixed resistor, and at least one of the first fixed resistor and the second fixed resistor includes a trimming portion. It is achieved by

[0012]

According to the structure of the first aspect of the invention, at least one of the first resistance temperature detector and the second resistance temperature detector has a trimming portion. The resistance of the second resistance temperature detector can be matched with that of the second resistance temperature detector. According to the configuration of the second invention, the groove on the surface of the substrate serves as a thermal resistance that prevents movement of heat generated by the resistance temperature detector.

According to the structure of the third invention, since at least one of the first fixed resistor and the second fixed resistor has a trimming portion, the trimming portion is used to make the first fixed resistor and the second fixed resistor. Therefore, it is possible to match the resistance.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. Embodiment 1 FIG. 1 is a perspective plan view of a main part showing a gas sensor according to an embodiment of the first and second inventions.

FIG. 2 is a sectional view of the gas sensor shown in FIG. A first resistance temperature detector 18 and a second resistance temperature detector 1 are provided on an insulating substrate 11 made of alumina or the like having a groove 22.
A first pad 12, a third pad 12A, a second pad 12B, a gas detection coating layer 20, and a compensation coating layer 21, which commonly connect one end of 9, 18 and one end of 19, are formed,
The second resistance temperature detector 19 has a resistance adjusting section 23, and a trimming section 47 is formed in the resistance adjusting section 23.

Such a gas sensor is manufactured as follows. That is, the first resistance temperature detector 18 and the second resistance temperature detector 18 in which the platinum paste is illustrated on the insulating substrate 11 made of alumina or the like.
RTD 19, first pad 12, third pad 1
2A, the pattern of the second pad 12B is screen-printed, dried and baked at a temperature of 1100 ° C. to form a first resistance temperature detector 18. Second resistance temperature detector 19, first pad 1
2, the second pad 12A and the second pad 12B are the substrate 1
Baked on 1.

Gas detection coating layer 20 and compensation coating layer 21
Are formed as follows. First, the gas detection coating layer 2
No. 0 is immersing alumina powder in an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ , drying it and chloroplatinic acid H ₂ Pt at a temperature of 500 ° C. in air.
Cl ₆ was thermally decomposed and a platinum catalyst was supported on alumina powder at a ratio of 2% by weight. A binder was added to the alumina powder carrying the platinum catalyst and dispersed in ethyl carbitol to obtain a paste for the gas detection coating layer.

The paste of the gas detecting coating layer thus obtained was screen-printed in a predetermined pattern to obtain a molded body of the gas detecting coating layer. The compensating coating layer 21 is made of alumina powder and lead acetate.
Dip in an aqueous solution of (CH ₃ COO) ₂ Pb, dry and dry in air
Lead acetate (CH ₃ COO) ₂ Pb is thermally decomposed at a temperature of 0 ° C to produce lead oxide PbO.
Was supported on alumina powder at a ratio of 2% by weight. Lead oxide Pb
A binder was added to the O 2 -supported alumina powder and dispersed in ethyl carbitol to obtain a compensating coating layer paste.

The obtained paste of the compensating coating layer was screen-printed in a predetermined pattern to obtain a molded body of the compensating coating layer. The above-mentioned molded body of the gas detecting coating layer and the compensating coating layer was co-fired at a temperature of 600 ° C. to obtain a gas detecting coating layer 2
0 and the compensating coating layer 21 are respectively provided on the first resistance temperature detector 18
And was laminated on the second resistance temperature detector 19.

Subsequently, a portion corresponding to the resistance adjusting section 23 is irradiated with laser to form a trimming section 47, and the first pad 12 and the second pad are provided between the first pad 12 and the third pad 12A. The resistance between 12B was equalized. Trimming was performed using a YAG laser under the conditions of an output of 100 mW / cm ² and a scanning speed of 50 mm / s.

In the untrimmed state, the resistance adjusting unit 2
Due to 3, the resistance of the second resistance temperature detector 19 is smaller than the resistance of the first resistance temperature detector 18. Resistance adjuster 23
When the trimming portion 47 is formed, the resistance of the second resistance temperature detector gradually increases, and when the resistance becomes equal to the resistance of the first resistance temperature detector, the trimming ends. The trimming process can be carried out at room temperature or in the energized state.

Trimming is performed between the first pad 12 and the third pad 12A, and between the first pad 12 and the second pad 12A.
Since it is a process of equalizing the resistances between B, the operation is simple, and the matching of the resistances is surely realized, so that the yield of the gas sensor manufacturing is good. In the gas detection coating layer, combustible gas burns and the heat of combustion increases the resistance of the first resistance temperature detector. The groove 22 blocks the conduction of this combustion heat and prevents the resistance of the second resistance temperature detector from increasing, thereby increasing the non-equilibrium output of the Wheatstone bridge circuit. The groove 22 should be as deep as possible. The grooves 22 can intersect each other. Further, the groove 22 may be formed on either the front surface or the back surface of the substrate.
A plurality of spherical concave portions can be formed together with the groove 22. When spherical recesses are formed, the space between the recesses has a large thermal resistance. The substrate material preferably has low thermal conductivity, but partially stabilized zirconia can be used instead of alumina.

In the above example, the alumina powder carrying lead oxide is used as the compensating coating layer, but copper oxide may be carried instead of lead oxide, and the alumina powder carrying platinum oxide may be replaced with glass. You may coat. In the case of coating with glass, alumina powder carrying platinum oxide is applied, and then glass paste is applied and heat treatment is performed. Embodiment 2 FIG. 3 is a perspective plan view of a main part showing a gas sensor according to an embodiment of the third invention.

This embodiment differs from the first embodiment in that the fixed resistance is formed on the substrate together with the resistance temperature detector.
The second pad 12B and the third pad 12 are provided on the substrate 11.
A, a fourth pad 12D for commonly connecting one ends of the first pads 12, 15 and one end of 16, and a first resistance temperature detector 1
8, a second resistance temperature detector 19, a gas detection coating layer 20, a compensation coating layer 21, a first fixed resistor 15, and a second fixed resistor 16 are laminated.

A ruthenium oxide RuO ₂ -based resistance paste (GZK: manufactured by Tanaka Kikinzoku International) is screen-printed in the patterns shown by the first fixed resistance and the second fixed resistance. After being dried, it is heat-treated at a temperature of 850 ° C. for 10 minutes, and a first fixed resistor 15 and a second fixed resistor 16 having a film thickness of 12 μm are laminated on the substrate. Prior to trimming, the first fixed resistor 15 has a larger area than the second fixed resistor 16, and the trimming portion 17 is formed in the first fixed resistor 15.

When the first fixed resistor and the second fixed resistor are laminated, the resistance temperature detector and the fixed resistor are integrated, so that the space of the gas sensor can be saved and a compact gas sensor can be obtained.

[0027]

According to the present invention, since at least one of the first resistance temperature detector and the second resistance temperature sensor laminated on the same substrate has a trimming portion, the trimming portion is used. Since the resistances of the two resistance temperature detectors can be matched, the pairing process is simplified. In addition, the matching of resistance is always realized, and the yield of gas sensor manufacturing is improved.

Further, the groove on the surface of the substrate serves as a thermal resistance that prevents the movement of the heat generated in the resistance temperature detector, and prevents the resistance increase of the other resistance temperature detectors adjacent to the resistance temperature detector to prevent the unbalanced output of the Wheatstone bridge circuit. Enlarge. Further, the first resistance temperature detector and the second resistance temperature detector which are laminated on the same substrate together with the first resistance temperature detector
Fixed resistor and second fixed resistor are provided, and at least one of them has a trimming portion. Therefore, the trimming portion can be used to match the resistances of the two fixed resistors, and at the same time, the fixed resistor and the resistance temperature detector are fixed. A compact gas sensor with integrated resistance is obtained.

[Brief description of drawings]

FIG. 1 is a perspective plan view of a main part showing a gas sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view of the gas sensor shown in FIG.

FIG. 3 is a perspective plan view of essential parts showing a gas sensor according to another embodiment of the present invention.

FIG. 4 is a fragmentary perspective view showing a gas detection element of a conventional catalytic combustion gas sensor.

FIG. 5 is a connection diagram showing a detection circuit of a conventional catalytic combustion gas sensor.

[Explanation of symbols]

 Reference Signs List 11 substrate 12 first pad 12A third pad 12B second pad 12D fourth pad 14 trimming portion 15 first fixed resistor 16 second fixed resistor 17 trimming portion 18 first resistance temperature detector 19th 2 RTD 20 Gas detection coating layer 21 Compensation coating layer 22 Groove 23 Resistance adjusting portion 31 Platinum coil 32 Alumina carrier 33 Compensation element 34 Gas detection element 35 Load 36 Power supply 41 Substrate 42 Gas detection element 43 Compensation element 44 Electrode 45 Electrode 46 Heater 47 Trimming part

Claims (3)

[Claims] 1. A substrate, a first resistance temperature detector, a second resistance temperature detector, a gas detection coating layer, a compensation coating layer, and a plurality of pads. The temperature resistance element is a metal thick film and is laminated on the substrate, and the second temperature resistance element is a metal thick film and is laminated on the substrate. The first and second temperature resistance elements are at least One of them includes a trimming portion, the pad includes a first pad for commonly connecting one end of the first resistance temperature detector and one end of the second resistance temperature detector, and a first resistance temperature detector. Has a second pad connected to the other end of the second resistance temperature detector and a third pad connected to the other end of the second resistance temperature detector, and is laminated on the substrate separately from each other. The layer is selectively laminated on the first resistance temperature detector and the substrate, and combusts a combustible gas in a catalytic manner to raise the temperature of the first resistance temperature detector. , Compensating coating layer gas sensor, characterized by comprising selectively deposited on the second resistance temperature detector and the substrate. 2. The gas sensor according to claim 1, wherein the substrate has a groove formed on the surface thereof at a position where at least the gas detection coating layer and the compensation coating layer are divided. 3. A substrate, a first resistance temperature detector, a second resistance temperature detector, a gas detection coating layer, a compensation coating layer, a plurality of pads, and a first fixed resistance. , A second fixed resistance, the first RTD is a metal thick film and is laminated on the substrate, and the second RTD is a metal thick film and is laminated on the substrate. At least one of the first and second resistance temperature detectors includes a trimming portion, and the pad commonly connects one end of the first resistance temperature detector and one end of the second resistance temperature detector. A first pad, a second pad connected to the other end of the first resistance temperature detector, and a third pad connected to the other end of the second resistance temperature detector. At least one of the first and second resistance temperature detectors is provided with a trimming portion and is laminated on the substrate separately, and the gas detection coating layer is the first resistance temperature detector. The layer is selectively laminated on the substrate, and combustible gas is catalytically burned to raise the temperature of the first resistance temperature detector, and the compensation coating layer is formed on the second resistance temperature detector and the substrate. A first fixed resistor and a second fixed resistor are laminated on the substrate, and one end of the first fixed resistor is commonly connected to the second pad and One end of the second fixed resistor is commonly connected to the third pad, and the other end of the first fixed resistor and the other end of the second fixed resistor are further connected via a fourth pad provided on the substrate. A gas sensor characterized by being connected in common.