JPH11304744A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas sensor which can suppress heat generated from the bend part of a heater. SOLUTION: In a gas sensor, a substrate 2 is provided, a detection part which is arranged on one face of the substrate 2 and which detects the concentration of a gas is provided, a linear heater 1 which is formed by combining straight-line parts with bend parts to be s shape corresponding to the detection part on the other face of the substrate 2 and which heats the detection part up to a temperature displaying its sensitivity is provided, electrode parts 3 which are installed on both ends of the heater 1 are provided, lead wires 9 by which the electrode parts 3 and lead pins 6 are connected electrically are provided, the bend parts of the heater 1 are formed to be curve-shaped, and the volume per same reference distance of the straight-line parts and the bend parts is made larger is set in such a way that it is larger than that in the bend parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for detecting the concentration of a combustible gas, toxic gas, water vapor, carbon dioxide gas or the like in an atmosphere.

[0002]

2. Description of the Related Art A gas sensor for detecting gas concentration includes S
nO2, solid electrolyte type, Zr
Many types such as those using O2 are known. Such gas sensors are widely used. For example, a carbon dioxide sensor is used for applications such as environmental measurement and horticulture.

Here, JP-A-4-24548, JP-A-6-182261, JP-A-6-88800, JP-A-5-142180, and JP-A-6-31 are disclosed.
No. 3410, Japanese Patent Application No. 7-165053,
A carbon dioxide sensor comprising a metal oxide, a perovskite compound and a carbonate, and a method for producing the same are disclosed.

Many of these gas sensors are heated at the time of use, and a heater for heating is mounted in the form of a coil, a thick film or the like. As for the material of the heater, RuO2, Pt, and the like have been studied and used. However, no special study has been made on the structure of the heater.

[0005]

A heater for generating heat from a material having a low resistance, such as Pt, used in a conventional gas sensor must have a thin linear structure due to its characteristics. Since the substrate on which the heater is formed is small, a part of the heater is bent to have a curved shape. Then
The bent portion used by the heater generates heat and its life is shortened.

Further, since the heater is often formed on the substrate by screen printing, the resistance cannot be adjusted after the heater is formed.

Further, since the resistance value of the heater is small,
If the resistance value of the entire sensor is not reduced, the amount of electric power except for the heater increases.

Accordingly, an object of the present invention is to provide a gas sensor capable of suppressing heat generation from a bent portion of a heater.

Another object of the present invention is to provide a gas sensor capable of adjusting the resistance value of a heater.

Another object of the present invention is to provide a gas sensor capable of reducing power consumption.

[0011]

In order to solve this problem, a gas sensor according to the present invention comprises a substrate, a detection unit disposed on one surface of the substrate and detecting a gas concentration, and a gas sensor on the other surface of the substrate. A linear heater formed by combining a linear portion and a bent portion in a shape corresponding to the detection portion, and heating the detection portion to a temperature at which the sensitivity is developed; electrode portions provided at both ends of the heater; and an electrode portion. A lead wire for electrically connecting a lead pin, wherein the bent portion of the heater is formed in a curved shape, and the volume of the straight portion and the bent portion per the same reference distance is larger in the bent portion. It is.

As a result, the amount of current flowing inside the bent portion is reduced, and heat generation from the bent portion can be suppressed.

In the gas sensor according to the present invention, in the above-described gas sensor, the heater has a resistance value adjusted by applying a predetermined metal material.

This makes it possible to adjust the resistance value of the heater to a constant value. Further, in the gas sensor according to the present invention, in the gas sensor described above, the lead wire is made of Ni or an alloy containing Ni.

As a result, the electric resistance of the lead wire is reduced, so that unnecessary heat generation is suppressed, and the power consumption can be reduced.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention corresponds to a substrate, a detection unit disposed on one surface of the substrate and detecting a gas concentration, and a detection unit on the other surface of the substrate. It is formed by combining a straight part and a bent part in the shape
A linear heater for heating the detection unit to a temperature at which the sensitivity is developed, electrode units provided at both ends of the heater, and a lead wire for electrically connecting the electrode unit to a lead pin; The part is formed in a curved shape, the volume per the same reference distance between the straight part and the bent part is a gas sensor in which the bent part is larger, the current flowing inside the bent part is reduced, Has the effect of suppressing heat generation of

According to a second aspect of the present invention, in the first aspect of the invention, the heater is a gas sensor in which a predetermined metal material is applied to adjust the resistance value. This has the effect that the adjustment can be made constant.

According to a third aspect of the present invention, in the first or second aspect, the lead wire is a gas sensor made of Ni or an alloy containing Ni. Heat generation is suppressed, and the power consumption can be reduced.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is a sectional view showing a gas sensor according to an embodiment of the present invention, and FIG. 2 is a plan view showing a heat generating portion of the gas sensor shown in FIG. In FIG. 2, the illustration of the glass material is omitted.

Inside the outer frame 8 having an opening formed therein, a heater 1 as a heat generating portion and a detecting portion 4 sensitive to gas are accommodated. The heater 1 is attached to one surface of a substrate 2 made of alumina ceramics, and the detection unit 4 is attached to the other surface of the substrate 2.

As shown, electrode portions 3 are formed at both ends of the heater 1, and the electrode portions 3 are electrically connected to lead pins 6 via lead wires 9. Also, heater 1
Is coated with a glass material 7 to prolong the service life by shielding from the external atmosphere.

On both sides of the detection section 4, detection electrodes 5 are provided. The detection electrode 5 is also connected to a lead pin 6 via a lead wire 9.

At the bottom of the outer frame 8, a lead pin 6 for extracting a signal from the detection unit 4 and supplying power to the heater 1 is fixed.

Next, a procedure for manufacturing a gas sensor having such a structure will be described. Commercially available barium carbonate, cerium oxide and copper oxide are weighed in a molar ratio of 20:45:35.

Next, these raw materials are put into alcohol, mixed and crushed using a rotary pot, and used as sensor raw materials for a carbon dioxide gas sensor. The raw material is formed into a disk having a diameter of 10 mm and a thickness of 0.4 mm using a press machine.

The sample thus obtained is fired in an electric furnace at 850 ° C. for 5 hours. A commercially available ruthenium oxide paste was applied to both sides of the fired sample,
A heat treatment is performed for minutes to form an electrode. The material of the electrode is gold, silver,
Platinum may be used. Finally, the sample on which the electrode was made was 1.5 m
When cut into a size of mx 1.1 mm, a detection unit 4 having a detection electrode 5 is created as shown in FIG.

The size of one piece after division is 2.8 mm.
5c with a cutting groove formed to be × 3.6 mm
When each part of the alumina substrate having a size of mx 5 cm x 0.3 mm is printed and then divided, a substrate 2 shown in Fig. 1 is obtained.

On one side of the substrate 2, a platinum paste is used to screen-print a 100 μm-wide linear heater as a heat-generating portion and a land portion as an electrode for energization. After drying, heat treatment is performed at 900 ° C. for 10 minutes to obtain the heater 1 and the electrode unit 3 shown in FIG. Note that the substrate 2 and its dimensions are not limited to the present embodiment, and the substrate may be any as long as it can withstand the temperature at which the sensor, such as zirconia, can be used.
Further, the material of the heater 1 is not limited to platinum, and for example, AgPd may be used. Further, the material of the land portion serving as the electrode portion 3 may be the same as that of the heater 1, but a material having low resistance such as Au or Ag may be used.

Here, the resistance value of the Pt heater at 143 locations in one of the prepared alumina substrates is from 3.4 Ω to 3.6 Ω.
Assume that Therefore, a tester is applied to the electrode portion 3 of the heater 1 to measure the resistance value, and Pt paste obtained by kneading Pt powder with isopropyl alcohol is applied to the linear heater 1 portion while confirming with a stereoscopic microscope, and the resistance value is measured. For example, it is adjusted to 3.4Ω. The material of the resistance value adjusting paste is preferably the same as the material of the heater 1, but various metal materials such as Ag powder may be used. Thereby, the resistance value of the heater 1 can be adjusted to be constant, and the quality can be stabilized.

After adjusting the resistance value of the heater 1 in this way, in order to prevent the deterioration of the heater 1, a glass paste is printed on the heater 1, dried, and then heat-treated at 900 ° C. for 10 minutes to coat the heater 1. Is applied.

The substrate 2 on which the heater 1 is formed is divided along the cutting groove, and the detection unit 4 is attached to the surface of the substrate 2 opposite to the surface on which the heater 1 is formed, using a ruthenium oxide paste. Also, for connection with the lead pin 6, the diameter is 0.1 m.
The electrodes 3, 5 on the substrate 2 are composed of a
To the position of using platinum paste. In addition, in order to increase the bonding strength of the detection unit 4, a land for bonding may be formed on the substrate 2 by printing and heat treatment, and the detection unit 4 may be bonded thereon. After paste drying, 800
Heat-treat at 10 ° C. for 10 minutes.

Next, a lead pin 6 for extracting a signal from the detection unit 4 and a lead pin 6 for supplying power to the heater 1 are penetrated and fixed to the bottom of the outer frame 8. Then, a lead wire 9 is connected to each lead pin 6 by welding. Although the lead pins 6 are linear in FIG. 1, they may be arranged in a rectangular shape, or may be arranged at an arbitrary position when more lead pins 6 are required.

Finally, when the whole is combined and fixed, a gas sensor is created. Although the gas sensor according to the present embodiment is a carbon dioxide gas sensor, the present invention is not limited to the carbon dioxide gas sensor, and may be applied to various sensors in which the detection unit 4 and the heater 1 are independently formed. it can. In addition, the detection unit 4 is formed by, for example, applying a paste in a thick film shape or forming a layer by vapor deposition.

An electric current is supplied to the heater 1 of the gas sensor thus prepared, and the temperature is adjusted to a temperature at which the sensitivity of the detecting section 4 is developed, and the carbon dioxide gas concentration is detected. In the present embodiment, it is confirmed that the temperature of the detection unit 4 is adjusted to, for example, a power amount of 0.8 W, which is about 500 ° C., and the sensitivity to carbon dioxide gas is developed. The sensitivity can be measured by a two-terminal method using, for example, an impedance analyzer 4192A manufactured by YHP, and the sample gas can be measured using dry air and carbon dioxide gas diluted with dry air.

The detection state of carbon dioxide gas is based on the capacity value (C0) of the sample heated to the measuring temperature measured with the air flowing therein, and the air adjusted to the carbon dioxide gas concentration of 2% is flowed. It can be captured by the change in capacitance value (C2%) when measured. Sensitivity is defined by the following equation.

Sensitivity = | 10 × Log (C2% / C0) | [dB] The larger the numerical value, the better the sensitivity. Therefore, when the sensitivity is 0 dB, it indicates that the capacitance value does not show a change with respect to the increase in the concentration of carbon dioxide, and that no carbon dioxide is detected.

According to the trial of the present inventor, in the gas sensor using the Ni wire having a diameter of 0.1 mm for the lead wire 9 formed in the present embodiment, when the heater power is 0.8 W, the carbon dioxide gas is converted to 3.4 dB. Of the carbon dioxide sensor using the lead wire 9 as a Pt wire having a diameter of 0.1 mm was 3.4.
1.2 W of heater power was required to obtain dB sensitivity. The reason why the Pt line requires more electric power than the Ni line seems to be that the resistance value of Ni is smaller than Pt. That is, according to the Chemical Handbook, the resistivity at 20 ° C. is 6.84 × 10 −6 Ωcm for Ni and 1 for Pt.
0.6 × 10 −6 Ωcm. The resistivity at 100 ° C. estimated from these resistivity is 10.6 × 10 −
6 Ωcm and Pt is 13.6 × 10 −6 Ωcm. Therefore, it is considered that since the resistance of the Ni wire is smaller than the resistance of the Pt wire, the heat generation of the lead wire 9 made of the Ni wire is reduced, and the power consumption as a whole is reduced.

When the diameter of the lead wire is large, its resistance value is small and the influence on heat generation is small. Therefore, the influence of the material of the lead wire becomes large as the diameter of the lead wire is small. As described above, by using the Ni wire for the lead wire, the resistance is reduced, unnecessary heat generation is suppressed, and the power consumption can be reduced. If the calorific value is large, the temperature of the entire sensor rises and the deterioration of the device is accelerated, and the life is shortened. Therefore, the life of the gas sensor can be prolonged by reducing the power consumption.

Here, the same effect can be obtained by using a Ni alloy suitable for the processing conditions at the time of producing the sensor and the use environment instead of Ni for the lead wire. That is, in the present invention, the same effect can be obtained even if an alloy having a lower resistivity than Pt is used for the lead wire. Note that Ni and Ni alloy are heat-resistant and corrosion-resistant materials having a long service life that can be used even when a heat treatment step is performed.

As described above, the heater 1 is prepared by forming a printing pattern, performing screen printing, and then performing heat treatment. When a material having a low resistivity, such as a Pt material, is used for the heater 1, it is necessary to make the heater 1 linearly thin and long.

Here, the length of a line passing through the center of the printed linear heater 1 is set as a reference distance. When the length of this line in the straight portion and the length of the bent portion are the same, the lengths of both are the same, and the same reference distance is set.

The heater 1 has a detection unit 4 attached to the back surface.
It is necessary to bend a part of the heater 1 to form a shape corresponding to the detection unit 4 because it is better to form a sheet having a shape close to the shape described above and heat it. At this time, if the bent portion is angular, heat is generated at the bent portion and deterioration is likely to occur.

Therefore, the curved portion is bent more easily than the straight portion, and is more likely to be degraded such as disconnection, dielectric breakdown and migration. This is because the inside and outside lengths of the curved portion are different, so that the inside heat generation increases. For example, 100μ between lines, 100μ line width
In this case, it is assumed that straight lines are connected by a semicircle having an inner radius of 50 μ and an outer radius of 150 μ. The overall volume is the same as the straight section, and the overall calorific value is the same as the straight section. However, the inner length is 157 μm and the outer length is 471 μm. If the thickness is constant, the resistance on the outer peripheral side is three times larger than that on the inner peripheral side. Therefore, a large amount of current flows inward, the amount of heat generation increases, and the temperature increases. The resistance value changes depending on the temperature, and the flow of current changes depending on the difference between DC and AC frequencies. Absent.

In order to avoid such development, the volume of the bent portion is increased by making the outer peripheral portion of the heater 1 elliptical, shifting the center position to increase the width, increasing the thickness, and the like. The volume of the bent portion is set to be equal to or larger than the linear portion by comparing the distances.

Then, although the entire current value is the same, the current flowing through the unit volume decreases by increasing the volume of the bent portion, and the current flowing inside decreases, so that the amount of heat generation can be suppressed. Thereby, the heat generation of the bent portion is suppressed, the deterioration of the heater 1 is reduced, and the life can be prolonged.

In order to suppress the heat generation at the bent portion, the inside shape may be changed. That is, if there is a portion having a small volume in the bent portion, heat is easily generated in the portion. Therefore, it is sufficient to make the bent portion larger in volume than the straight portion even when comparing each portion. Since the bent portion is often located at the end and there is no problem even if the heat generation is reduced, the heat generation is reduced by increasing the volume per the same reference distance as compared with the linear portion, and the deterioration of the heater 1 is suppressed. Is good.
As a result, the bent portion of the heater 1 does not generate heat and the heat balance is not deteriorated, and the characteristics can be stabilized by making the temperature uniform throughout the heater 1. Also,
Since the life of the bent portion that generates less heat is equal to or longer than that of the straight portion, the life of the heater 1 can be extended.

[0048]

As described above, according to the present invention, there is obtained an effective effect that the current flowing inside the bent portion is reduced and the heat generation from the bent portion can be suppressed.

By adjusting the resistance value of the heater by applying a predetermined metal material, it is possible to obtain an effective effect that the resistance value of the heater can be adjusted to be constant.

When the lead wire is made of Ni or an alloy containing Ni, the electric resistance of the lead wire is reduced, thereby suppressing unnecessary heat generation, and has an effective effect of reducing power consumption. can get.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a gas sensor according to an embodiment of the present invention.

FIG. 2 is a plan view showing a heat generating portion of the gas sensor of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 Substrate 3 Electrode part 4 Detection part 6 Lead pin 9 Lead wire

Claims (3)

[Claims] A substrate disposed on one surface of the substrate for detecting a gas concentration; and a linear portion and a bent portion formed on the other surface of the substrate in a shape corresponding to the detection portion. A linear heater for heating the detection unit to a temperature at which the sensitivity is developed; electrode units provided at both ends of the heater; and a lead wire for electrically connecting the electrode unit and a lead pin. The bent portion of the heater is formed in a curved shape, and the volume of the straight portion and the bent portion per the same reference distance is larger in the bent portion. 2. The gas sensor according to claim 1, wherein the heater has a resistance value adjusted by applying a predetermined metal material. 3. The gas sensor according to claim 1, wherein the lead wire is made of Ni or an alloy containing Ni.