JPH0815203A - Contact combustion type gas sensor - Google Patents

Abstract

PURPOSE:To provide a contact combustion type gas sensor whose resistance against wind speed is large and its dispersion is small, in which a cap for wind protection is fixed only by means of the shape of each of a metal net and a cap and its fitting method. CONSTITUTION:In a contact combustion type gas sensor provided with a gas sensor element 3 and a temperature compensation element in the inside enclosed by a base 1 and a metal net 5, while this metal net 5 is duplex and provided with a wind protection cap 6 between its duplex structure, a cap protrusion 6p protruding to the recessed side provided on the central spherical surface of the cap 6 is fitted in a recessed part 5h provided at the apex of an internal metal net 5a and pinched by two metal nets, thereby, the cap 6 is fixed. For fitting between the metal net 5 and the cap 6, the cap 6 may be fitted in the recessed part 5h of the metal net 5 in which the entire cap 6 may be fitted or plural claws are provided on the cap 6 and those may bite into the mesh of the metal net 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic combustion type gas sensor used for a gas leak alarm or the like.

[0002]

2. Description of the Related Art Catalytic combustion type gas sensors are widely used, for example, in gas leak alarms for detecting gas leaks of city gas, propane gas, etc. and issuing an alarm. The catalytic combustion gas sensor includes a gas sensor element whose resistance changes due to contact with gas and a temperature compensation element which has the same temperature characteristic resistance as the gas sensor element when not in contact with gas and has almost the same shape. It is a built-in device.

FIG. 4 is a circuit diagram of a gas leak alarm device. The gas sensor element 3 and the temperature compensating element 4 form two sides of a gas detection bridge circuit. When a constant voltage is applied between the voltage application terminals 9 of the circuit and the detectable gas is not in contact with the gas sensor element 3, the fixed resistors 7 and 8 have a potential difference between the signal output terminals 10. It is set not to occur. When the detectable gas comes into contact with the contact combustion gas sensor, that is, the gas sensor element 3, the resistance increases, the balance of the bridge circuit is lost, and a potential difference occurs between the signal terminals 10. This potential difference is the gas detection signal.

A cross-sectional view of a conventional catalytic combustion type gas sensor is shown in FIG. On the insulating base 1, four metal stems 2 (in the figure, the two rear stems hidden by the two stems 2 in the front of the drawing cannot be seen) are vertically penetrated and fixed to the base 1. Has been done. The four stems 2 are arranged so as to form a rectangular vertex. The gas sensor element 3 has its terminal portion welded over two adjacent stems. In FIG. 5, the temperature compensating element (not shown) overlaps with the gas sensor element 3, so that the terminal portion thereof is welded across the other two adjacent stems. The stem 2, the gas sensor element 3, and the temperature compensating element are covered by a fine mesh 5 attached to the inside of the peripheral edge of the base 1. The wire net 5 is doubled because the high temperature gas sensor element 3 does not serve as an ignition source even when a gas having a concentration higher than the explosion limit concentration reaches the contact combustion type gas sensor.

When the gas to be detected which has passed through the metal net 5 comes into contact with the gas sensor element 3, the gas to be detected is burned by the action of the catalyst carried by the gas sensor element 3, and the temperature of the gas sensor element 3 rises from a steady state. The resistance value is higher than that of the temperature compensation element. Since the catalytic combustion type gas sensor is exposed to the atmosphere passing through the wire net 5 as described above, the temperature of the gas sensor element 3 will be lowered if an excessively strong wind strikes the catalytic combustion, and the catalytic combustion will not be sufficiently carried out. May lead to excessive reduction of. In order to avoid this, a windshield cap 6 is attached to the top of the wire mesh. The cap 6 is a substantially spherical disk having a substantially spherical shape so as to follow the shape near the apex of the wire mesh, and is spot welded (welded portion 6w) to the apex of the inner wire mesh 5a. Outer wire mesh 5
b covers the cap 6 and the inner wire mesh 5a.

Inside the catalytic combustion type gas sensor, the gas sensor element 3 and the temperature compensating element are arranged at a short distance symmetrically with respect to the rotational symmetry axis of the base. When the center of the cap 6 is attached off the axis, the wind does not hit the two elements uniformly, and the temperature difference between the two elements occurs, which makes it seem as if gas was detected. Gives a false alarm. The wind speed at this time is called the wind speed. As for the catalytic combustion type gas sensor, it is desirable that the wind speed is high.

FIG. 6 shows a diagram showing the dependence of the wind speed resistance on the displacement of the cap. It can be seen that the wind speed decreases as the center of the cap deviates from the axis of rotational symmetry of the base. In practice, the wind speed is required to be 4 m / s or more, and the cap position distribution needs to be suppressed within ± 1 mm. The assembling process of this conventional catalytic combustion type gas sensor will be described below. After the gas sensor element 3 and the temperature compensating element are welded to the stem 2 of the base 1 already integrated, the inner wire mesh 5a
And adhere to the base 1. The cap 6 is placed on the apex of the inner wire net 5a, spot welding (welding portion 6w) is performed on the apex of the inner wire net 5a, and the outer wire net 5b is covered and bonded to the base 1.

[0008]

However, as is apparent from the above assembling process, the cap placed on the apex of the inner wire mesh is in a state of being able to move freely. There was a problem that the cap moved 1 mm or more before spot welding to the top of the wire mesh, spot welding was performed as it was, and a product having a low wind speed was produced.

An object of the present invention is to provide a contact combustion type gas sensor in which the position of the cap does not shift during the assembly process, the position of the cap can be accurately fixed, the wind speed is high, and the variation is small. Especially.

[0010]

In order to achieve the above-mentioned object, the present invention has a gas sensor element and a temperature compensating element inside a base and a double wire mesh. In a contact combustion type gas sensor having a windshield cap between wire meshes, a fitting portion for fixing the cap to the wire mesh is provided on at least one of the cap and the wire mesh contacting with the wire mesh, and the cap is fitted by the fitting portion. Then, the cap is fixed by fixing the cap to the wire and sandwiching it with two wire nets.

The fitting portion for fixing the cap to the wire netting by the fitting portion has a projection protruding to at least one of the double wire netting provided on the cap, as set forth in claim 2.
It is preferable that the projection is provided in the wire netting, and the projection is fitted in the recessed portion, and the projections are fitted to each other and sandwiched by two wire netting to fix the cap. Further, the fitting portion is composed of a concave portion into which the entire cap provided on the wire net is fitted as described in claim 3, and the cap is fixed by fitting the cap into the concave portion and further sandwiching it with two wire nets. Good to do.

Further, the fitting portion is composed of a plurality of claws provided on the cap as described in claim 4, and the claws are engaged with the claws of the wire mesh, and further sandwiched by two wire meshes to hold the cap. It is better to fix it.

[0013]

In the invention described in claim 1, since the fitting portions provided on at least one of the wire netting and the cap are fitted together, the cap is prevented from slipping on the wire netting after the fitting process. Further, since it is sandwiched by the two wire nets adhered to the base, movement of the cap in the direction perpendicular to the wire nets is also suppressed.

According to a second aspect of the present invention, the fitting portion between the wire mesh and the cap is formed by fitting projections and depressions provided on at least a part of each of the wire mesh and the cap.
In the one described in (4), the entire cap is fitted in the recessed part to which the entire cap provided in the wire mesh fits, or in the one described in claim 4, because the plurality of claws provided in the cap bite into the mesh of the wire mesh. The cap is prevented from moving during the process of covering the outer wire mesh.

In any case, after the outer wire mesh is covered and adhered, even if the cap is only lightly sandwiched between the wire meshes, the cap is prevented from moving in the direction perpendicular to the wire mesh. Therefore, the fitting and the biting of the claws do not come off, and it is possible to fix the product to the strength that can withstand a considerable impact.

[0016]

【Example】

Example 1 FIG. 1 shows a sectional view of a catalytic combustion type gas sensor according to an example of the present invention. 1 is different from the conventional example shown in FIG. 5 in that a small projection 6p is provided toward the concave side of the central spherical surface of the cap 6, and the contact combustion type gas sensor is oriented upward at the top of the wire mesh during the assembly process. Therefore, the concave portion 5h is provided at the apex of the inner wire mesh 5a. The recess 5h is sized to fit the protrusion 6p of the cap.

After the inner wire mesh 5a is adhered to the base 1, the projection 6p of the cap is fitted on the recess 5h of the inner wire mesh 5a, and then the outer wire mesh 5b is covered and adhered to the base 1 to complete the contact combustion type gas sensor. Let When the cap position accuracy was examined, the position shift was within ± 0.7 mm. These contact combustion type gas sensors were dropped from a height of 50 cm on a concrete floor by a drop impact test so that the wire mesh did not directly hit them, and then the cap position was measured. As a result, almost no change was observed. . Embodiment 2 FIG. 2 shows a sectional view of a catalytic combustion type gas sensor according to another embodiment of the present invention. The conventional example shown in FIG. 2 is different from the first example shown in FIG. 1 in that the contact combustion type gas sensor in the assembling process has an apex of the wire mesh facing upward,
The point is that the entire cap 6 is provided with a recess 5H that fits up to the middle of the thickness of the cap.

After adhering the inner wire mesh 5a, the cap 6 was fitted in the recess 5H, and then the outer wire mesh 5b was covered and adhered to the base 1 to complete the catalytic combustion type gas sensor.
When the cap position accuracy was examined, the position deviation was ±
It was within 0.7 mm. When these catalytic combustion type gas sensors were tested in the same manner as in Example 1, almost no change was observed in the cap position. Example 3 FIG. 3 shows a sectional view of a catalytic combustion type gas sensor according to another example of the present invention. Three cap claws 6t are provided at equal intervals on the edge of the cap 6 having no protrusion as in the first embodiment. The cap claw 6t has a substantially triangular shape with a sharp tip that fits into the stitches of the inner wire mesh 5a. Only by placing the cap 6 on the apex of the inner wire mesh 5a and pressing it lightly, the cap claws 6t bite into the stitches of the inner wire mesh 5a and did not move during the step of covering the outer wire mesh 5b. In order to fix the cap 6 more firmly, the inner wire mesh 5a is pushed by the cap claw 6t and is recessed by about 0.2 mm when the outer wire mesh 5b is covered.

After adhering the inner wire net 5a, the cap 6 was placed at a predetermined position, and the outer wire net 5b was covered and adhered to complete the contact combustion type gas sensor. When the cap position accuracy was examined, it was within ± 0.8 mm. When these catalytic combustion type gas sensors were tested in the same manner as in Example 1, almost no change was observed in the cap position. Example 4 In the above example, the gas sensor element was on the upper side of the base in the assembly process. However, the present invention can be applied even when the assembly process is upside down.

A small protrusion is provided at the center of the cap toward the convex portion of the spherical surface, and a convex portion having a size large enough to fit the protrusion of the cap is provided at the apex of the outer wire mesh. The apex of the outer wire mesh was supported as the lower side, and the protrusion of the cap was placed as the lower side in the outer wire mesh and fitted together. Then, the base to which the elements were already welded and the inner wire mesh was adhered was faced downward and placed in the outer wire mesh to bond the outer wire mesh and the base.

In this way, the exact same catalytic combustion gas sensor as in Example 1 could be manufactured.

[0022]

EFFECTS OF THE INVENTION At least a part of the wire mesh and the cap are provided with concavities and convexities and they are fitted together, or
Since the cap is provided with a plurality of claws and the claws are engaged with the mesh of the wire mesh, and the cap is covered with the second wire mesh in a semi-fixed state, the cap position does not shift during the assembly process. Therefore, the wind speed was high, the variation was reduced, and the manufacturing yield was improved. Further, since the cap position does not shift after manufacturing even if the cap is not welded to the wire mesh, the welding process can be omitted and the number of steps can be reduced.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a catalytic combustion type gas sensor according to another embodiment of the present invention.

FIG. 3 is a sectional view of a catalytic combustion type gas sensor according to another embodiment of the present invention.

[Figure 4] Gas detection bridge circuit diagram

FIG. 5 is a sectional view of a conventional catalytic combustion gas sensor.

FIG. 6 is a diagram showing the dependence of wind speed resistance on cap position deviation.

[Explanation of symbols]

 1 base 2 stem 3 gas sensor element 5 wire mesh 5a inner wire mesh 5b outer wire mesh 5h inner wire mesh recess 5H inner wire mesh recess 6 cap 6p cap projection 6t cap claw 6w weld 7 resistance 8 resistance 9 voltage application terminal 10 signal output terminal 10

Claims (4)

[Claims] 1. A contact combustion type gas sensor having a gas sensor element and a compensating element inside a base and a double wire mesh, and a windshield cap between the double wire meshes. Alternatively, a contact combustion type gas sensor characterized in that a fitting portion for fixing the cap to the wire net is provided on at least one of the wire nets that come into contact with the wire net, and the cap is fixed to the wire net by the fitting portion. 2. The catalytic combustion type gas sensor according to claim 1, wherein the cap has a protrusion protruding from at least one of the double wire mesh, and the metal mesh has a recess into which the protrusion is fitted. Contact combustion gas sensor. 3. The catalytic combustion type gas sensor according to claim 1, wherein the wire mesh is a recess into which the entire cap is fitted. 4. The contact combustion type gas sensor according to claim 1, wherein the cap has a plurality of claws that are bite into the mesh of the wire mesh.