JPH0656371B2 - Gas detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas sensor using a tin oxide semiconductor as a gas sensor, and more particularly to a device for heating the gas sensor.

[Conventional technology]

A conventional gas sensor using a tin oxide semiconductor as a gas sensitive body is shown in FIG. 11, and this gas sensor has a tin oxide semiconductor 14 as a gas sensitive body on one surface of a sensor substrate 11 made of alumina across electrodes 12, 13. And a platinum thick film heater 17 is provided on the other surface of the sensor substrate 11 as shown in FIG. When such a gas sensor is used for a general household gas leak alarm, the platinum thick film heater 17 detects isobutane, methane and hydrogen as test gases by a gas sensor and obtains an output required as a gas leak alarm. Therefore, it is for always heating at 350 ℃ ~ 450 ℃.
Reference numerals 15, 16, 18, and 19 are lead wires.

The voltage applied to the heater for heating the platinum thick film heater 17 to 350 ° C. to 450 ° C. is several V (volts) to several tens of V, and AC which is a general household power source as a power source of the gas leak alarm device. When using 100V, a step-down transformer is used as shown in FIG. In FIG. 13, 1 is a commercial AC power source, 2 is a gas sensor, 3 is a step-down transformer, 4 is a voltage dividing resistor, and 5 is an output V necessary for operating an alarm buzzer or the like.
It is a load resistor to obtain ₀ . The secondary output of the step-down transformer 3 is connected to the stems 32 and 33 as shown in FIG. 3 via the lead wires 18 and 19 of the gas sensor 2,
The gas sensitive body is connected to the AC power source 1 via the lead wires 15 and 16 and the stems 34 and 35.

[Problems to be solved by the invention]

When a tin oxide semiconductor is used as a gas sensor and a gas sensor that uses a platinum thick film heater as a heating resistor for heating the gas sensor is used for a general household gas leak alarm, a transformer that steps down the commercial AC power supply is used. It is necessary and has a drawback that the gas leak alarm cannot be downsized, lightened and priced. Therefore, a heating resistor mainly containing ruthenium oxide (RuO ₂ ) is drawing attention as a heating resistor material that can directly apply 100 V AC without using a step-down transformer. However, when this ruthenium oxide heating resistor is used at a high temperature such as 350 ° C to 450 ° C for a long time in order to obtain the required output from a gas sensor that uses a tin oxide semiconductor as a gas sensor, evaporation of ruthenium oxide, etc. Therefore, there is a drawback that the electric resistance increases and the performance as a heating element deteriorates.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the conventional device, and to provide a gas detection device which can directly use a commercial power supply without using a step-down transformer and can be used for a long period of time. .

[Means for solving problems]

According to the present invention, according to the present invention, in a gas detection device having a gas sensitive body made of tin oxide semiconductor on one surface of a sensor substrate and a heating resistor on the other surface of the sensor substrate, The body is composed of a first exothermic resistor which is constantly heated to a predetermined temperature and a second exothermic resistor which is heated to a temperature higher than the predetermined temperature in response to a test gas. This is achieved by using a heating resistor of (1) as a heating resistor containing ruthenium oxide as a main component.

[Action]

By using a heating resistor containing ruthenium oxide as a main component as the first heating resistor and using a heating resistor containing tin oxide as a main component as the second heating resistor, the first heating resistor is always provided. Is heated at a predetermined temperature and reacts with the test gas in the atmosphere of the test gas to become a heating resistor.
By raising the temperature of the gas sensitive body and increasing its output by the heating resistor of (1), ruthenium oxide, which easily deteriorates at high temperature, can be used for a long time as the heating resistor material.

[Embodiment] FIGS. 1 to 3 show an embodiment of the present invention, respectively. In FIGS. 1 to 3, the same parts as those shown in FIGS. 11 to 12 are designated by the same reference numerals. The description is omitted.

1 is different from the conventional device in that the heating resistor 23 mainly composed of ruthenium oxide (RuO ₂ ) as the first heating resistor across the electrodes 21 and 22 is provided on the other surface of the sensor substrate 23.
And a heating resistor 24 containing tin oxide as a main component as a second heating resistor are juxtaposed, and the lead wires 2 are respectively connected to the electrodes 21 and 22.
5,26 are provided.

In this embodiment, the gas sensitive part made of tin oxide semiconductor 14 provided on one surface of the sensor substrate 11 and the heating resistors 23, 24 provided on the other surface of the sensor substrate 11 are manufactured by the screen printing method as follows. It First, in order to form the electrodes 12, 13, 21, 22 on the sensor substrate 11 made of alumina, platinum paste is applied to the sensor substrate 11 and baked. Next, a ruthenium oxide-based paste is applied in a predetermined shape between the electrodes 21 and 22 and baked in air at 850 ° C. for 30 minutes to obtain a ruthenium oxide-based heating resistor. This ruthenium oxide-based heating resistor is adjusted to a predetermined resistance value by the laser trimming method. A glass-based paste is applied onto the ruthenium oxide-based heating resistor and baked in air for 15 minutes to form an insulating layer. The gas sensitizer and the tin oxide semiconductor as the second heating resistor are formed by mixing the tin oxide powder obtained by oxidizing metal tin with nitric acid with a binder to form a paste, which is applied in a predetermined shape. After baking at 800 ℃ for 30 minutes, impregnate with an aqueous solution of palladium chloride
Gas treatment and heating resistor are obtained by treating at 600 ° C for 3 hours.

As shown in FIG. 3, the sensor element in which the gas sensitive body and the heating resistors 23 and 24 are formed as described above is connected to the electrodes 12, 13, 21, and 22 formed on the sensor substrate 11 with the lead wires 15 respectively. , 16,2
Bond 5,26 and these lead wires 15,16,25,26
Is connected to the stems 32 to 35 which are planted in the base 31, and the base 31 is covered with a stainless steel wire mesh (not shown) to form the gas sensor 20.

The gas sensor 20 assembled as shown in FIG. 3 is connected to the commercial AC power source 1 as shown in FIG. 4 and used as a gas leak alarm. In FIG. 4, the same parts as those of the conventional device shown in FIG. 13 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 4, reference numeral 1 indicates a commercial AC power source again, and a stem 32 to which the first heating resistor whose main component is ruthenium oxide and the second heating resistor whose main component is tin oxide of the gas sensor 20 are connected. , 33 are directly connected to the commercial AC power supply 1. In the basic electric circuit shown in FIG. 4, the resistance value of the first heating resistor whose main component is ruthenium oxide is
Trimmed to 28KΩ, commercial AC power supply 1 is 1
FIG. 7 shows the results of an experiment in which the output characteristics of the load resistor 5 were 00 V, the resistance value of the load resistor 5 was 8 KΩ, and the resistance value of the voltage dividing resistor 4 was 64 KΩ by an ordinary gas injection method. In FIG. 7, the vertical axis represents the output voltage (V), and the horizontal axis represents the isobutane concentration (%) as the test gas. In the above experiment, the gas sensor 20
Was heated to 300 ° C by the first heating resistor mainly composed of ruthenium oxide in clean air, but the resistance value of the second heating resistor mainly composed of tin oxide was 0.2% in isobutane. Became smaller and acted as a heater, and the gas sensor 20 was heated to 450 ° C. As shown in FIG. 8 as a comparative example, an output characteristic diagram of a gas sensor using a conventional platinum thick film heater, the gas sensor 20 according to this embodiment can obtain the same output characteristic as the conventional device. As another comparative example, FIG. 9 shows an output characteristic diagram in the case where only a heating resistor containing ruthenium oxide as a main component is used as the heating resistor.
In order to obtain the output characteristics shown in (a), it is necessary to increase the electric power of the heating resistor and maintain the temperature of the gas sensor at 450 ° C. In this case, thermal degradation of ruthenium oxide is promoted. It The output characteristic shown in (b) is the case where the gas sensor that does not cause the thermal deterioration of ruthenium oxide is heated to and maintained at 300 ° C. In this case, sufficient output characteristics cannot be obtained.

FIG. 10 shows the temporal stability of the output with respect to 0.2% isobutane in the gas sensor, where the vertical axis is the output voltage and the horizontal axis is the energization time (days). In FIG. 10, (C) is a gas sensor according to the present invention, (D) (E) is a comparative example, and only a heating resistor containing ruthenium oxide as a main component is used, and (D) is heated and maintained at 450 ° C. ) Is heated and maintained at 300 ° C. As is clear from this figure, the gas sensor according to the present invention can maintain stable output characteristics for a long period of time.

5 and 6 show another embodiment of the present invention.
The difference from the embodiment shown in the drawings and FIG. 2 is that the second heating resistor 24 is provided so as to overlap the first heating resistor 23. Of course, the first heating resistor 23 and the second heating resistor 24 are insulated from each other, and the second heating resistor 24 containing tin oxide as a main component is made to easily react with the test gas. It is provided above the first heating resistor 23. Also in this embodiment, sufficient output characteristics and stability with time are provided as in the embodiment shown in FIGS.

〔The invention's effect〕

As described above, according to the present invention, the sensor substrate has a gas sensitive body made of a tin oxide semiconductor on one surface thereof,
In a gas detection device having a heating resistor on the other surface of the sensor substrate, the heating resistor reacts with a first heating resistor that is constantly heated to a predetermined temperature and a test gas, and is higher than the predetermined temperature. A second heating resistor that is heated to a high temperature, and the first heating resistor is a heating resistor containing ruthenium oxide as a main component, so that the commercial power supply for household use Can be directly applied to the gas sensor for heating, and a required output can be obtained from the gas sensor, and a gas sensor that is stable for a long period of time can be provided.

[Brief description of drawings]

1 to 4 each show an embodiment of the present invention. FIG. 1 is a cross-sectional view of an essential part of a sensor element, FIG. 2 is a surface view as seen from the direction of arrow Q in FIG. 1, and FIG. Assembly drawing of the gas sensor, Fig. 4 is the basic electric circuit diagram of the gas leak alarm,
FIG. 6 and FIG. 6 are cross-sectional views and a surface view of a main part of a different embodiment of the present invention, FIGS. 7 to 9 are output characteristic diagrams showing the output characteristics of the gas sensor, and FIG. It is a characteristic view showing an output characteristic. 11 to 13 show a conventional device, respectively, and FIGS.
The figures show the front view of the gas sensitive part and the heater, respectively.
Figure 13 is a basic electric circuit diagram. 11: sensor substrate, 14: gas sensitive body, 23: first heating resistor containing ruthenium oxide as a main component, 24: second heating resistor containing tin oxide as a main component.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Issei Kubota 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (56) Reference JP-A-58-158549 (JP, A) Open Sho 59-184849 (JP, A) Actual Open Sho 56-65451 (JP, U)

Claims (2)

[Claims] 1. A gas detection element having a gas sensitive body made of tin oxide semiconductor on one surface of a sensor substrate and a heating resistor on the other surface of the sensor substrate, wherein the heating resistor is always It comprises a first heating resistor which is heated to a predetermined temperature and a second heating resistor which is heated to a temperature higher than the predetermined temperature in response to a gas to be detected, and the first heating resistor is oxidized. A gas detection device, which is a heating resistor containing ruthenium as a main component. 2. The gas detection device according to claim 1, wherein the second heating resistor is a heating resistor whose main component is tin oxide.