JPH0545322A - Gas detecting apparatus - Google Patents

Abstract

PURPOSE:To obtain a gas detecting apparatus having excellent reliability without resistance change in heater by preventing the increase in temperature of the gas detecting apparatus in gas to be detected. CONSTITUTION:An alumina substrate 4, a metal oxide semiconductor 3, a heater 2 and a PTC thermistor 6 are provided. The metal oxide semiconductor 3 and the heater 2 are formed on the substrate 4 and constituted as a gas sensor. The PTC thermistor 6 is connected to the heater 2 in series and provided at the close proximity to the metal oxide semiconductor 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to temperature control of a gas detection device, and more particularly to a structure of a gas sensor which prevents temperature rise of a gas sensor when detecting a combustible gas and is excellent in reliability.

[0002]

2. Description of the Related Art A metal oxide semiconductor adsorbs oxygen in air to increase its resistance, but adsorbs flammable gas in combustible gas to reduce its resistance. In the gas detection device, the gas sensor is heated to 300 ° C. to 400 ° C. and used in order to enhance the response of the gas reaction and the selectivity of the test gas.

Platinum or ruthenium oxide is used as the heating means, but recently ruthenium oxide, which is excellent in mass productivity, is often used. FIG. 7 is an electric circuit diagram showing a conventional general household gas leak alarm. Ruthenium oxide is used for the heater 2, and AC 100V is applied. The electric resistance of the heater is 20 KΩ, 0.5 W is consumed, and the sensitive body of the gas sensor can be heated and maintained at 380 ° C. The metal oxide semiconductor 3, which is a sensitive body, is connected in series with the load resistor 5 and AC 100V is applied. The heater 2 and the metal oxide semiconductor 3 are formed as a thick film on the substrate 4.
The output of the load resistor 5 is amplified by the amplifier circuit 7 and the thyristor 8
Buzzer 9 sounds via. In air, the temperature of the sensor of the gas sensor is 300 ° C as described above due to the heat generated by the heater.
Although the temperature is from 400 to 400 ° C., it is 500 to 600 ° C. in the test gas due to the heat generation of the sensitive body.

[0004]

It is considered that there is very little chance that a general household gas leak alarm will be placed in the gas under test. However, it is not preferred that the sensitive body of the gas sensor is heated to a high temperature of 500 ° C to 600 ° C. This is because the heater may be disconnected or the resistance of the metal oxide semiconductor may change. The present invention has been made in view of the above points, and an object thereof is to provide a gas detection device which prevents heat generation by a responsive body when detecting a combustible gas, does not cause a change in heater resistance, and is excellent in reliability.

[0005]

According to the present invention, the above objects are achieved by a substrate, a metal oxide semiconductor, a heater, and a PTC.
A thermistor is provided, and the metal oxide semiconductor and the heater are formed on a substrate to form a gas sensor. The PTC thermistor is connected in series with the heater and is provided close to the metal oxide semiconductor of the gas sensor. It is achieved by

[0006]

The function of the PTC thermistor increases when the temperature of the sensitive body of the gas sensor rises due to heat generation of the sensitive body. Therefore, the current supplied to the heater is reduced and the temperature rise of the gas sensor is suppressed. Since the temperature coefficient of resistance of the PTC thermistor is positive, the resistance increases as the temperature rises.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an electric circuit diagram showing a gas detection device according to an embodiment of the present invention. It differs from the conventional gas detection device in that the PTC thermistor 6 is connected to the heater 2 in series.
FIG. 4 is a perspective view showing a gas detection device according to an embodiment of the present invention. On the base 27, the stems 21, 22, 23,
24, 25, and 26 are provided, and the sensitive body of the gas sensor 28 is fixed to the stems 21 and 22 via the lead wires 14 and 15, and the heater of the gas sensor 28 is fixed to the stems 23 and 24 via the lead wires 18 and 19. The PTC thermistor 6 is fixed to the stems 25 and 26. The PTC thermistor 6 is provided close to the sensitive body of the gas sensor. The rise in temperature of the gas sensor is easily detected by the PTC thermistor.

FIG. 2 is a plan view showing a gas sensor according to an embodiment of the present invention. Platinum electrodes 12 and 13 and a tin oxide sensitizer 3 are laminated on a substrate 4 made of alumina. Lead wires 14 and 15 are pressed against the platinum electrodes 12 and 13, respectively.

FIG. 3 is a rear view showing a gas sensor according to an embodiment of the present invention. Platinum electrode 1 on alumina substrate 4
6, 17 and the heater 2 are laminated. Platinum electrodes 16, 1
Lead wires 18 and 19 are pressed against the wire 7. The heater 2 is mainly composed of ruthenium oxide.

Such a gas sensor is prepared as follows. Platinum paste is applied to an alumina substrate and fired to form platinum electrodes for the sensitive body and heater. Next, a ruthenium oxide paste is applied and baked to form a heater. The heater, which is a heating resistor, can be adjusted to a predetermined resistance value by a laser trimming method. The sensitive body can be manufactured by a screen printing method, a vapor deposition method, a sputtering method, or the like.

The sensitizer was prepared by mixing a tin oxide powder obtained by oxidizing metallic tin with nitric acid and a binder to prepare a paste. The paste was applied to a substrate and baked, and then impregnated with a palladium chloride solution and heat-treated. Prepared.

The resistance of the sensitive body is 200 KΩ or more in air, but 6 KΩ in the test gas (for example, 0.2% isobutane). When the load resistance is 6KΩ, the power consumed by the sensor is 0.4W or more, and the heater power consumption is 0.5.
When added to W, the total power consumption becomes 0.9 W or more, and the temperature of the gas sensor is 550 ° C.

When the gas sensor is placed in the test gas for a long time, the heater resistance gradually decreases. A heater containing ruthenium oxide as a main component shows no change in electric resistance when used at a temperature of the sensitive body of 450 ° C. or lower, but changes in electric resistance when used at 500 ° C. or higher.

When the PTC thermistor is connected in series with the heater, the heater resistance in air is 20 KΩ, the power consumption is 0.5 W, and the gas sensor responsive body temperature is 38.
At 0 ℃, it is the same as before.

On the other hand, in the test gas atmosphere, the temperature of the sensitive body of the gas sensor did not rise above 450 ° C., and the heater resistance did not change even when the test gas was left energized for a long time. This is because the PTC thermistor placed below the gas sensor is below 80 ° C in air and the electrical resistance is 100Ω.
In the test gas, the temperature of the gas sensor's sensitive body rises due to the heat generated by the sensitive body in the test gas, and the temperature of the PTC thermistor also rises, which increases the electrical resistance of the PTC thermistor and limits the current value flowing to ruthenium oxide. Is. The temperature of the PTC thermistor is 1 in the test gas atmosphere.
The temperature was 20 ° C., and the electric resistance had increased to 2 KΩ or more.

FIG. 5 is a diagram showing the change over time (characteristic a) in the heater resistance of the gas detecting apparatus according to the embodiment of the present invention in comparison with the conventional characteristic (characteristic b). The test gas is 0.
2% isobutane gas was used. The heater resistance of the conventional gas detecting device gradually decreases as the temperature of the gas sensor rises, but in the gas detecting device according to the embodiment of the present invention, the temperature of the sensitive body of the gas sensor does not rise and the change of the heater resistance is recognized. Absent.

FIG. 6 is a rear view showing a gas sensor of a gas detector according to another embodiment of the present invention. In this gas sensor, the sensitizer of tin oxide is the same as that described above.
In FIG. 6, in addition to the platinum electrodes 16 and 17, the lead wires 18 and 19, and the heater 2 being provided on the substrate 4, the platinum electrode 2
9, 30, 31, 32, PTC thermistors 33, 34,
Lead wires 35, 36, 37, 38 are provided. PTC
The thermistors 33 and 34 are connected in series with the heater 2.
The PTC thermistors 33 and 34 are lead titanate (PbTiO 3
_It is composed of a thick film whose main component is ₃ ). The PTC thermistors 33 and 34 have a Curie point near 200 ° C., and the temperature of the PTC thermistor rises above 20 ° C. when the sensitizer exceeds 400 ° C.
It becomes 0 ° C and it functions as a PTC thermistor.

[0018]

According to the present invention, the substrate, the metal oxide semiconductor, the heater, and the PTC thermistor are provided, and the metal oxide semiconductor and the heater are formed on the substrate to form a gas sensor. Since the thermistor is connected in series with the heater and is provided in the vicinity of the metal oxide semiconductor of the gas sensor, the resistance of the PTC thermistor when the temperature of the sensitive body of the gas sensor rises due to heat generation of the sensitive body in the test gas. Will immediately follow it and increase. Therefore, since the current supplied to the heater is reduced and the heater temperature is lowered, the heater temperature of the gas sensor is not increased by the temperature of the sensitive body and the resistance value is not changed as in the conventional case, and a highly reliable gas detection device can be obtained.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a gas detection device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a gas sensor according to an embodiment of the present invention.

FIG. 3 is a back view showing a gas sensor according to an embodiment of the present invention.

FIG. 4 is a perspective view showing a gas detection device according to an embodiment of the present invention.

FIG. 5 shows changes in heater resistance over time (characteristic b) of the gas detecting apparatus according to the embodiment of the present invention as compared with conventional characteristics (characteristic b)
Diagram shown in contrast to

FIG. 6 is a rear view showing a gas sensor of a gas detection device according to another embodiment of the present invention.

FIG. 7 is an electric circuit diagram showing a conventional general household gas leak alarm device.

[Explanation of symbols]

 1 AC 100V power supply 2 Heater 3 Sensitive body 4 Alumina substrate 5 Load resistance 6 PTC thermistor 7 Amplifying circuit 8 Thyristor 9 Alarm buzzer 12 Platinum electrode 13 Platinum electrode 14 Lead wire 15 Lead wire 16 Platinum electrode 17 Platinum electrode 18 Lead wire 19 Lead wire 21 Stem 22 Stem 23 Stem 24 Stem 25 Stem 26 Stem 27 Base 28 Gas Sensor 29 Platinum Electrode 30 Platinum Electrode 31 Platinum Electrode 32 Platinum Electrode 33 PTC Thermistor 34 PTC Thermistor 35 Lead Wire 36 Lead Wire 37 Lead Wire 38 Lead Wire

Claims (5)

[Claims] 1. A substrate, a metal oxide semiconductor, a heater,
A PTC thermistor, the metal oxide semiconductor and the heater are formed on a substrate to serve as a gas sensor, and the PTC thermistor is connected in series with the heater and is provided close to the metal oxide semiconductor of the gas sensor. A gas detection device characterized by being a thing. 2. The gas detection device according to claim 1, wherein P
The gas detection device, wherein the TC thermistor is provided independently of the substrate. 3. The gas detection device according to claim 1, wherein P
The gas detection device, wherein the TC thermistor is provided in the form of a thick film on the substrate. 4. The gas detection device according to claim 1, wherein the metal oxide semiconductor is tin oxide. 5. The gas detecting device according to claim 1, wherein the heater is a heating resistor containing ruthenium oxide as a main component.