JPH08220041A - Gas sensor - Google Patents

Abstract

(57) [Summary] [Structure] CO detection film 6 and CH4 detection film 8 on insulating substrate 4
The heater film 10 is provided on the lower surface of the CH4 detection film 8 on the back surface of the substrate 4. Lead wires 23, 23 on the CO detection film 6 side
Increase the thermal conductivity of. [Effect] The detection cycle time is shortened, and a sufficient temperature difference is provided between the CO detection film 6 and the CH4 detection film 8.

Description

Detailed Description of the Invention

[0001]

This invention relates to CO, methane and LPG.
The present invention relates to a gas sensor for simultaneously detecting a flammable gas such as

[0002]

The applicant has provided a heater film and a pair of metal oxide semiconductor films on the surface of a heat-resistant insulating substrate such as alumina, and detects water vapor on one side of the metal oxide semiconductor film and flammable gas on the other side. We have proposed a gas sensor designed to
-15057). In this case, the water vapor detection film is covered with a glass film to remove the sensitivity of the combustible gas, and a heater film is disposed on the water vapor detection film side to heat the water vapor detection film to a higher temperature than the combustible gas detection film.

Separately from this, the inventor has studied the simultaneous detection of CO and combustible gases such as CH4 and LPG with one gas sensor. In this case, the temperature of the gas sensor is periodically changed, and the maximum temperature of the combustible gas detection film is set to about 450 ° C. and the maximum temperature of the CO detection film is set to 300 ° C., for example.
The minimum temperature of the CO detection film is about room temperature to about 120 ° C. Then, the combustible gas is detected from the output of the combustible gas detection film at the maximum temperature and the like, and the CO is detected from the output of the CO detection film at the minimum temperature and the like. In order to put such a gas sensor into practical use, it is necessary to speed up the cooling of the CO detection film from the maximum temperature to the minimum temperature to shorten the detection cycle time. Further, when the combustible gas detection film is heated to a maximum temperature of 450 ° C., the temperature of the CO detection film is set to, for example, 30
It is necessary to keep the temperature at about 0 ° C. and to provide a sufficient temperature difference between them. It was found that if the above gas sensor is used for this purpose as it is, the detection cycle time cannot be shortened because the temperature difference between the CO detection film and the combustible gas detection film is small and the cooling of the CO detection film is slow.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to accelerate the cooling of the CO detection film to shorten the detection cycle time and to provide a sufficient temperature difference between the combustible gas detection film and the CO detection film. . An object of the present invention is to increase the temperature difference and shorten the detection cycle time. The object of claim 3 is to arrange the heater film on the back surface of the substrate and the combustible gas detection film or the CO detection film on the front surface of the substrate to reduce the substrate area, and to arrange the heater electrode and the common electrode on the front and back surfaces of the substrate. It is to be able to connect to both sides. The object of claim 4 is to strengthen the connection between the four electrodes and the lead wire.

[0005]

According to a first aspect of the present invention, in a gas sensor having a substantially rectangular heat-resistant insulating substrate, a CO detection film is provided in a first half portion, and a flammable gas detection film and a heater film are provided in a second half portion. And a common electrode connected to the CO detection film, a CO detection electrode connected to the CO detection film, a combustible gas detection electrode connected to the combustible gas detection film, and a heater electrode connected to the heater film. The first half connects the high thermal conductivity leads to two of the four electrodes and the second half connects the low thermal conductivity leads to the other two electrodes. A wire having high thermal conductivity such as Pt is used for the high thermal conductive lead wire, and a wire having low thermal conductivity such as Pt-W or Pt is used for the low thermal conductive lead wire.
Even when using, a wire having a wire diameter smaller than that of the high thermal conductive lead wire is used. The concept of the first half and the second half means that when the longitudinal direction of the substrate is taken to the left and right, for example, a CO detection film is provided on the right side and a flammable gas detection film and a heater film are provided on the left side. It does not mean that the flammable gas detection film or the heater film partially protrudes to the right of the center line of the substrate.

The invention of claim 2 is characterized in that the substrate is made of at least one member of the group consisting of glass, quartz, zirconia, titania, steatite, and forsterite. These materials have a fraction of the thermal conductivity of alumina, which is commonly used for gas sensor substrates.
The following materials. According to a third aspect of the present invention, the heater film is provided on the back surface of the substrate, the combustible gas detection film is provided on the front surface of the substrate, and the heater electrode and the common electrode are provided via the end face connecting portion provided on the end face of the substrate. And are connected to both front and back surfaces of the substrate. The invention of claim 4 is characterized in that the connecting portion of each electrode to the lead wire is covered with a conductive paste.

[0007]

In the invention of claim 1, since the heater film is arranged on the flammable gas detection film side, a temperature difference occurs between the heater film and the CO detection film. This temperature difference is promoted by heat dissipation from the high thermal conductive lead wire on the CO detection film side, and the cooling rate on the CO detection film side increases. For these reasons, flammable gas detection film and CO
It is possible to generate a large temperature difference with the detection film. Next, at the time of cooling, the CO detection film can be quickly cooled by the heat radiation from the high thermal conductive lead wire on the CO detection film side, and the minimum temperature of the combustible gas detection film can be increased. Because of these
Detection cycle time is shortened.

According to the second aspect of the present invention, the thermal conductivity of the substrate is reduced, the heat conduction from the heater film to the CO detection film is reduced, the temperature difference is increased, and the CO detection film is moved from the heater film side. Cools while suppressing the heat conduction of, and further shortens the cycle time. In the invention of claim 3, the heater film is arranged on the back surface of the combustible gas detection film to reduce the area of the substrate, and the front and back surfaces of the substrate are wired at the end face connection portion. In the invention of claim 4, the connecting portion of the electrode to the lead wire is covered with a conductive paste to reinforce the connecting portion.

[0009]

EXAMPLES Examples are shown in FIGS. In the figure,
2 is a gas sensor, 4 is a heat-resistant insulating substrate, such as crystallized glass, quartz, zirconia, titania, steatite (Mg
O.SiO2), forsterite (2MgO.SiO)
2) is preferable, and these have a thermal conductivity of about a fraction of 1 to 1/20 of that of alumina. Table 1 shows the thermal conductivity of the substrate 4. The substrate size is, for example, 1.5 × 2.5 mm and the thickness is about 0.3 mm, 6 is a CO detection film, 8 is a CH4 detection film and may be a film for LPG detection, and 10 is RuO2.
Etc. is a heater film. Here, the heater film 10 is arranged on the left half of the back surface of the substrate 4 in the figure, and the CO detection film 6 is arranged on the right half.
The CH4 detection film 8 and the heater film 10 are arranged in the left half part. C
The O detection film 6 and the CH4 detection film 8 are both made of SnO2 based metal oxide semiconductor films, but they are made of different materials.
For example, the CO detection film 6 has a small amount of catalyst such as Pd, and
4 The detection membrane 8 has a high catalyst content. Sn is used for the detection films 6 and 8.
A metal oxide semiconductor other than O2 may be used. 12 is a common electrode, 14 is a CO detection electrode, 16 is a CH4 detection electrode,
A heater electrode 18 is a film electrode made of gold, platinum, or the like. The common electrode 12 and the heater electrode 18 are connected to the end face connection portion 20.
The common electrode 12 is connected to each of the CO detection film 6, the CH4 detection film 8 and the heater film 10 through the wiring. The end face connecting portion 20 is made of a conductive paste such as gold on the substrate 4.
It is applied by coating on the cut-off corners and baked.

[0010]

[Table 1] Thermal conductivity of substrate material (J / sec · cm · deg) Material Thermal conductivity (25 ° C) Quartz 0.017 SiO2 glass 0.012 ZrO2 0.05 Titania 0.07 Steatite 0.025 Form Stellite 0.03 Alumina 0.3

The electrodes 12, 14, 16 and 18 are connected to the lead wires 22, 22, 23 and 23 by pads at the four corners of the substrate 4 by parallel gap welding or the like. Among these lead wires, 22 and 22 are low heat conductive lead wires, which are provided in the left half portion of the substrate 4 on which the combustible gas detection film 8 and the heater film 10 are provided.
Reference numerals 3 and 23 are high thermal conductive lead wires, which are provided in the right half portion of the substrate 4 provided with the CO detection film 6. High thermal conductive lead wires 23, 23
As the material, a thick material having a high thermal conductivity such as a Pt wire or an Au wire having a wire diameter of 70 μm is used. Low heat conduction lead wire 22,
22 is, for example, a thin Pt wire having a wire diameter of 50 to 60 μm and is used to reduce the thermal conductivity by utilizing the difference in wire diameter, or a Pt—W wire, a Pt—ZrO 2 wire, AP having a wire diameter of 50 to 70 μm.
A material having a low thermal conductivity such as an M wire (Au-Pd-Mo alloy wire) is used. The difference in the thermal conductivity between the low thermal conductivity lead wire 22 and the high thermal conductivity lead wire 23 is the difference in the wire diameter when the same wire is used, and the difference in the thermal conductivity when the materials having different heat conductivity are used. Cause by the difference. Reference numeral 24 is an external pin, which is fixed to a housing (not shown), and 26 is lead wires 22 and 23.
A conductive paste for reinforcing the connection to the electrodes 12, 14, 16, 18 of, for example, gold paste, platinum paste, Ni paste or the like is used. As shown in FIG. 1, the connection portions with the lead wires 22 and 23 are collected on one surface of the substrate 4 (here, the surface on which the CO detection film 6 and the CH4 detection film 8 are provided),
The end face connection portion 20 is used for double-sided wiring.

The gas sensor 2 of the embodiment may be modified, for example, like the gas sensor 40 of FIG. 4, in which 42 is a common electrode, 44 is a CO detection electrode, 46 is a CH4 detection electrode, and 48.
Is a heater electrode, both of which are film electrodes made of gold or platinum. The modification of FIG. 4 is similar to that of FIGS.
It is similar to the gas sensor of. As shown in FIGS. 1 and 4, the clearance between the pad and the CO detection film 6 is made smaller than the clearance between the heater film 10 and the CH4 detection film 8, and the heat radiation from the CO detection film 6 is increased.

The operation of the gas sensors 2 and 40 of the embodiment will be described. The operation cycle of the sensors 2 and 40 is, for example, 15 seconds to 30 seconds, of which 5 to 10 seconds are assigned to the high temperature side and 10 to 20 seconds are assigned to the low temperature side, and the heater film 10 is turned on at the high temperature side and at the low temperature side. The heater film 10 is turned off or the power consumption is reduced.
CH4 and LPG are detected from the resistance value of the CH4 detection film 8 immediately before the end on the high temperature side, and CO is detected from the resistance value of the CO detection film 6 immediately before the end on the low temperature side.

Explaining that the heater film 10 is turned off at the low temperature side, the heater film 10 and the CH4 detection film 8 are formed on the substrate 4.
Since the heat conduction from the heater film 10 to the CH4 detection film 8 is fast, the resistance value of the CH4 detection film is stable in about 5 to 10 seconds on the high temperature side, and the maximum temperature is, for example, 450.
℃. At this time, since the thermal conductivity of the lead wires 23, 23 is higher than that of the lead wires 22, 22, and the thermal conductivity of the substrate 4 is glass, zirconia, or the like, and the thermal conductivity is low, the maximum temperature of the CO detection film 6 is It will be about 300 ° C. Lead wire 23,
23 is a Pt wire having a wire diameter of 70 μm, and the lead wires 22 and 22 are
Is a Pt wire with a wire diameter of 60 μm, the thermal conductivity is 10: 7.
About. The lead wires 23, 23 are Pt wires having a wire diameter of 70 μm, and the lead wires 22, 22 are Pt wires having a wire diameter of 60 μm.
With the -W line, the thermal conductivity is about 4: 1. Further, the thermal conductivity of the substrate 4 is, as shown in Table 1, about a fraction of 1 to 1/20 of that of alumina. In addition to this, the CO detection film 6
The smaller clearance between the pad and the CO detection film 6 on the side also contributes to the generation of the temperature distribution. Because of these
The CO detection film 6 can be heated to an appropriate maximum temperature of about 300 ° C., and the CH4 detection film 8 can be heated to about 450 ° C. suitable for CH4 detection.

The heater film 10 is turned off, and the CO detection film 6 and C
When the H4 detection film 8 is cooled, the heat radiation from the lead wires 23, 23 is large, and the thermal conductivity of the substrate 4 is small.
4 Since there is little heat transfer from the detection film 8 and the heater film 10, C
The temperature of the O detection film 6 drops sharply, for example, to about 80 ° C. in about 10 to 20 seconds, and the CO detection film 6 at this temperature.
CO is detected from the resistance value of. During this time, the lead wires 22, 2
2 has a small heat dissipation and the substrate 4 has a low thermal conductivity, so that C
The H4 detection film 8 is not cooled so much and the minimum temperature is, for example, 20.
It will be about 0 ° C. Therefore, the gas sensors 2 and 40 can be driven at a cycle of about 15 to 30 seconds, the detection cycle time can be shortened, and a large temperature difference can be given to the CO detection film 6 and the CH4 detection film 8.

Since the lead wires 22 and 23 are all bonded on the same surface of the substrate 4, the bonding is easy and the vibration resistance is high. For example, if two lead wires 22 and 23 are arranged on the front and back of the substrate 4, damage in the drop test will be more than doubled. Next, the bonding portion is a conductive paste 2
Since it is reinforced with 6, vibration resistance is further improved.

[0017]

According to the first aspect of the present invention, the heat radiation from the high thermal conductive lead wire is used to accelerate the cooling of the CO detection film to shorten the cycle time of detection, and the combustible gas detection film and the CO
Provide a sufficient temperature difference with the detection film. According to the second aspect of the present invention, the heat conduction of the substrate is reduced, the temperature difference is increased, and the detection cycle time is reduced. According to the third aspect of the present invention, the heater electrode and the common electrode are wired on both the front and back surfaces of the substrate via the end face connecting portion to reduce the substrate area.
According to the invention of claim 4, the connection between the electrode and the lead wire is reinforced by the conductive paste, and the durability of the gas sensor against drop, vibration and the like is improved.

[Brief description of drawings]

FIG. 1 is a plan view of a gas sensor according to an embodiment.

FIG. 2 is a side view of a main part of the gas sensor according to the embodiment.

FIG. 3 is a rear view of the main part of the gas sensor according to the embodiment.

FIG. 4 is a plan view of a main part of a gas sensor according to a modified example.

[Explanation of symbols]

 2,40 Gas sensor 4 Substrate 6 CO detection film 8 CH4 detection film 10 Heater film 12,42 Common electrode 14,44 CO detection electrode 16,46 CH4 detection electrode 18 Heater electrode 20 End face connection part 22 Low thermal conductive lead wire 23 High thermal conductive lead Wire 24 pin 26 Conductive paste

Claims (4)

[Claims] 1. A substantially rectangular heat-resistant insulating substrate is provided with a CO detection film in the first half and a flammable gas detection film and a heater film in the second half, and a common electrode connected to each film, CO connected to the CO detection membrane
Four electrodes, a detection electrode, a combustible gas detection electrode connected to the combustible gas detection film, and a heater electrode connected to the heater film, are provided, and two electrodes among the four electrodes are provided in the first half part. A gas sensor in which a high thermal conductivity lead wire is connected and a low thermal conductivity lead wire is connected to the other two electrodes in the second half portion. 2. The substrate is glass, quartz, zirconia,
Characterized by comprising at least one member of the group consisting of titania, steatite, forsterite,
The gas sensor according to claim 1. 3. A heater film is provided on the back surface of the substrate, a flammable gas detection film and a CO detection film are provided on the front surface of the substrate, and a heater electrode and a common electrode are connected via an end face connecting portion provided on the end face of the substrate. The gas sensor according to claim 1, wherein the gas sensor is connected to both front and back surfaces of the substrate. 4. The gas sensor according to claim 1, wherein the connecting portion of each electrode to the lead wire is covered with a conductive paste.