JPH08101154A - Gas sensor - Google Patents

Abstract

PURPOSE: To provide an excellent S/N sensor free from being affected by winds by surrounding a gas sensing element and a compensating element with a cap which can disperse a combustible gas while a porous substance is interposed in between. CONSTITUTION: A gas sensing element and a compensating element supported by a stem are covered with a metal cap 65, and its fitting part is fitted to a sensor base. If it is structured so that the two elements are surrounded by a porous substance such as a quartz filter, the substance can withstand against the wind pressure but restricts influx of the air. However, covering with the cap 65 dispersing the combustible gas permits a gas quantity necessary for sensing the concentration to be supplied satisfactorily with dispersion to inside the cap 65. If, for example, the filter 62 of the cap 65 is supported by wire gauze 61A, 61B or by wire gauze 61A and metal paneling 63, a high sensitivity and withstand against winds are exerted in any case in measuring the gas sensing characteristics, etc.. of the sensors, and enhancement of the S/N ratio is obtained in the case of a large pressure loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a gas detection sensor, and more particularly to a cap for an element which enhances output stability against wind flow.

[0002]

2. Description of the Related Art As a gas sensor, an alarm described in Fuji Jikki Vol. 50, No. 8 (1977), pages 427 to 431 and Fuji Jikki Vol. 54, No. 8 (1981), pages 554 to 557. Gas sensors such as those used in gas appliances are known. FIG. 8 is a connection diagram showing a bridge circuit of the conventional gas sensor described in the Fuji Time Report.

This sensor comprises a gas detecting element 22 having a structure in which a platinum coil is covered with aluminum oxide carrying a catalyst,
The compensating element 23, which is inactive against combustible gas, is incorporated in the Wheatstone bridge circuit together with the two fixed resistors 21 and 21. Two fixed resistors 21 and 21 are connected in series, and a gas detecting element 22 and a compensating element 23 are connected in series, respectively. When the gas comes into contact, combustion occurs and a temperature change occurs in the platinum coil, causing an electric resistance change proportional to the gas concentration. In the compensating element 23, almost no temperature change occurs even if combustible gas comes in. Therefore, due to this minute electric resistance change, there is a difference between the middle of the two fixed resistors 21 and 21 and the middle of the gas detecting element 22 and the compensating element 23. The bridge output Vb generated in between changes, and a gas concentration change is detected.

In this conventional sensor, the gas detecting element and the compensating element are covered with metal net caps, respectively, but when exposed to wind, the gas detecting element and the compensating element are deprived of heat and the temperature is lowered, resulting in an electric resistance. Although changing, the effects are not the same, so that the temperature balance between the two elements is lost and the bridge output Vb fluctuates even if there is no combustible gas. This variation naturally affects the accuracy of the output value and greatly affects the quality of the sensor. Therefore, in gas leak alarms, etc., the sensor was housed in the housing so that the element was not exposed to strong wind.

In such a conventional sensor, since the two metal net caps occupy a large volume, it is necessary to install the sensor in a limited space such as for detecting exhaust gas when the water heater is incompletely burned or reduce the number of parts. The cost cannot be reduced. Therefore, a sensor in which a gas detecting element and a compensating element are bonded to a stem supported by three separate bases and housed in the same cap has been devised.

FIG. 5 is a perspective view showing another conventional gas sensor. A gas detecting element 5 and a compensating element 6 are supported by a stem 3 fixed to a sensor base 2 and a metal cap 1
Is covered. 4 is a temperature sensor. Such a gas sensor is formed as follows. A 60 μΦ platinum wire was formed into a coil shape to form porous γ-alumina on which platinum and palladium were supported in a fine particle state at a ratio of 1: 1 and adhered to the coil to prepare a gas detection element 5.
The compensating element 6 is a coil-shaped platinum wire to which only a γ-alumina porous carrier is attached, and these elements are supported by a sensor base 2 made of a plastic substrate as shown in FIG. The two stems 3 provided as electrodes were bonded by welding. The sensor base 2 made of a plastic base has a structure in which a cylinder is divided into three parts, and a gas detection element 5, a compensating element 6 and a temperature sensor 4 which are separately bonded are combined into one.
The fitting portion of the cap 1 is fitted to the sensor base 2 that supports the gas detecting element 5, the compensating element 6, and the temperature sensor 4 assembled in this manner to produce a gas detecting sensor.

FIG. 6 is a perspective view showing a metal cap of the different conventional gas sensor shown in FIG. A through hole 7 is provided in the metal cap. FIG. 7 is a diagram showing the dependency of the output of different conventional gas sensors shown in FIG. 5 on the number of through holes. In the case where the cap is made of metal or the like and the through holes 7 are simply provided, there is a proportional relationship between the logarithmic value of the total area (number) of the through holes 7 and the output sensitivity. There is a relationship that governs output sensitivity. The above fact indicates that under the conventional measurement conditions, the combustion is always performed in the cap with high efficiency, the supply of gas cannot catch up, and the reaction is always in a gas supply shortage state. Therefore, in order to maximize the output, it is necessary to maximize the opening area of the cap. However, in this case
On the contrary, if the opening area is made large and the sensitivity is increased, there is a problem that the output change due to the wind becomes large.

FIG. 9 is a diagram showing the relationship between the fluctuation value of the bridge voltage at a wind speed of 2 m / s (the fluctuation value for a wind speed of 0 m / s) and the output for a carbon monoxide gas of 3000 ppm.
It can be seen that the greater the output sensitivity, the greater the amount of fluctuation that is affected by the wind. Due to the S / N ratio, the operating point is set at the point where the Vb value is 0.2 mV.

[0009]

In order to make up for these drawbacks, a method of packing glass wool in a metal cap, winding the glass wool directly around the element, or forming a cap of unglazed ceramic to make it porous is also available. it was thought. However, when the glass wool is directly wound, the element is thermally affected, and water droplets attached to the cap surface due to dew condensation or the like propagate through the glass wool and soak into the element, which causes malfunction or malfunction. In addition, glass wool having a normal wire diameter of about 1 to 10 μm is not sufficient to suppress the influence on the wind, and it is necessary to increase the amount used, resulting in high cost. For unglazed ceramic caps, the price becomes high, and if the holes through which the gas passes are too small, the sensitivity will decrease, and it will be difficult to control the hole diameter to a certain size to obtain appropriate sensitivity. There was a problem that it was.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a gas detection sensor which is improved in the cap so that the generation of noise due to wind flow is small, the sensitivity is good, and the S / N ratio is excellent. .

[0011]

SUMMARY OF THE INVENTION According to the present invention, the above object is to incorporate a gas detecting element and a compensating element in each side of a bridge circuit to combust a combustible gas in the gas detecting element to thereby cause resistance of the gas detecting element. In a gas detection sensor that detects flammable gas by changing the bridge output due to temperature change, both the gas detection element supported by the stem and the compensating element are surrounded by a cap that diffuses the flammable gas through the porous body. Be achieved by

Further, the porous body of the above-mentioned gas detection sensor is preferably a glass fiber filter, silica fiber filter, alumina binder reinforced silica fiber filter or tetrafluoroethylene filter. Also, as the porous body of the above-mentioned gas detection sensor, the pressure loss is 10 mm when the ventilation speed is 5 cm / s.
It is preferable to use a porous body having a H ₂ o or higher.

Alternatively, it is effective that the porous body is supported by a wire mesh or a metal cylinder.

[0014]

According to the present invention, when the structure in which the gas detecting element and the compensating element are surrounded by a porous body such as a quartz filter or a ceramic filter is adopted, the porous body having resistance to wind pressure is Limit inflow. However, the amount of gas required for concentration detection is sufficiently supplied by diffusion into the cap.

[0015]

【Example】

Embodiment 1 An embodiment of the present invention will be described with reference to the drawings. The present embodiment differs from the conventional gas detection sensor in that a cap 65 is used instead of the cap 1.
1 shows a cap of a gas detection sensor according to an embodiment of the present invention, FIG. 1 (a) is a cross-sectional view of a double wire mesh structure, FIG.
1B is a sectional view of the metal spring ring gripping structure, FIG. 1C is a sectional view of only the filter, and FIG. 1D is a sectional view of the inner wire mesh structure. In the cap shown in FIG. 1A, the filter 62 is supported by two wire nets 61A and 61B inside and outside. In the cap shown in FIG. 1B, the filter 62 is supported by the outer wire mesh 61A and the metal spring ring 63. The filter in FIG. 1 (c) is self-supporting. The filter 62 of FIG. 1D is supported only by the inner wire net 61B. Table 1 shows the material and characteristics (pressure loss) of the filter suitable for the present invention.

[0016]

[Table 1]

The filter can be manufactured by cutting a sheet that is molded into a sheet as a standard product and cut.
It is also possible to form a cap shape from the beginning, and in any case, the same characteristics can be obtained by assembling in the same manner. For each sensor, gas detection characteristics (CO 300
Table 2 and Table 3 show the results of measurement of bridge output fluctuation values at 0 ppm, output mV) and wind speed of 2 m / s.

[0018]

[Table 2]

[0019]

[Table 3]

As a result, it was found that all the sensors exhibited higher sensitivity and resistance to wind than the conventional ones. It can be seen from Table 1 that the S / N ratio is improved when the pressure loss is large. That is, the filter NO, 3, 7 has a pressure loss of 150 m.
Larger at mH ₂ O and 110 mmH ₂ O values (see Table 1), these Vb
The fluctuation values are small at 0.03 mV and 0.05 mV (see Table 3). The outputs for CO 3000 ppm both show large values of about 3.4 mV (Table 2).

FIG. 2 is a diagram showing the relationship between the pressure loss at a ventilation velocity of 5 cm / s and the change in Vb value at a wind velocity of 2 m / s. The pressure loss was measured at an airflow rate of 5 cm / s, and the electrical characteristics were measured at a wind speed of 2 m / s. In FIG. 2, 10 indicates the structure of (a) shown in FIG. 1, 11 indicates the structure of FIG. (B), 12 indicates the structure of FIG. (C), and 13 indicates the structure of FIG.
The structure of each is shown. It has been found that when the pressure loss exceeds 10 mmH ₂ O when the aeration rate is 5 cm / s, the fluctuation amount of the Vb value with respect to the wind rapidly decreases. The filters used this time are all commercially available for less than 10 yen per cm ² , and can be provided at a sufficiently low cost compared to the conventional cap made of unglazed ceramic. Second Embodiment Another embodiment of the present invention will be described with reference to the drawings. In addition,
In this embodiment, the difference from the conventional gas detection sensor is that the circular portion of the conventional cap 1 is replaced with a filter,
The filter is that a cap 75 having a structure that is supported by a cylindrical peripheral portion and a circular wire net is used. FIG. 3 shows a cap of a gas detection sensor according to an embodiment of the present invention.
The cap shown in (a) of FIG.
3B is a cross-sectional view of the metal spring ring gripping structure, FIG. 3C is a cross-sectional view of the structure in which the filter is supported only by the peripheral edge of the cylinder, and the cap is shown in FIG. 3D. FIG. 4 is a cross-sectional view of an inner wire mesh structure.
In the cap shown in FIG. 3A, the filter 72 is supported by two wire nets 71A and 71B inside and outside. In the cap shown in FIG. 3B, the filter 72 has the outer wire mesh 7.
It is supported by 1A and a metal spring ring 73. The filter of FIG. 3 (c) is supported only by the peripheral edge of the cylinder. The filter 72 of FIG. 3D is supported only by the inner wire net 71B. The material and characteristics (pressure loss) of the filter suitable for the present invention are the same as in Table 1 of the first embodiment.

The filter can be manufactured by cutting a sheet that has been molded into a sheet as a standard product and cut.
It is also possible to form a cap shape from the beginning, and in any case, the same characteristics can be obtained by assembling in the same manner. For each sensor, gas detection characteristics (CO 300
Table 4 and Table 5 show the results of measurement of bridge output fluctuation values at 0 ppm output mV) and wind speed of 2 m / s.

[0023]

[Table 4]

[0024]

[Table 5]

As a result, it was found that all the sensors exhibited higher sensitivity and resistance to wind than the conventional sensors. It can be seen from Table 1 that the S / N ratio is improved when the pressure loss is large. That is, the filter NO, 3, 7 has a pressure loss of 150 m.
The values of mH ₂ O and 110 mmH ₂ O are large, and these Vb fluctuation values are 0.02.
Shows a value of mV, 0.03mV (see Table 5) and is small. CO 300
The outputs for 0 ppm both show large values of about 2.9 mV (Table 4).

FIG. 4 is a diagram showing the relationship between the pressure loss at a ventilation speed of 5 cm / s and the change in Vb value at a wind speed of 2 m / s. The pressure loss was measured at an airflow rate of 5 cm / s, and the electrical characteristics were measured at a wind speed of 2 m / s. In FIG. 4, 14 shows the structure of (a) shown in FIG. 1, 15 is the structure of FIG. (B), 16 is the structure of FIG. (C), and 17 is the structure of FIG.
The structure of each is shown. It can be seen that when the pressure loss exceeds 10 mmH ₂ O when the aeration rate is 5 cm / s, the fluctuation amount of the Vb value with respect to the wind rapidly decreases.

[0027]

According to the present invention, the gas sensing element and the compensating element are covered with the cap for diffusing the flammable gas through the porous body. It is possible to obtain a gas detection sensor which is prevented from being transported and has an excellent S / N ratio. A glass fiber filter, a silica fiber filter, a tetrafluoroethylene filter, or the like is effective as the porous body, and these filters can be mechanically supported by a wire mesh or the like to improve reliability. In addition, this cap can be manufactured at a lower cost as compared with a cap made of a porous ceramic sintered body or the like.

[Brief description of drawings]

1 shows a cap of a gas detection sensor according to an embodiment of the present invention, wherein the cap shown in FIG. 1 (a) is a cross-sectional view of a double wire mesh structure, and the cap shown in FIG. 1 (b) is a metal spring ring gripper. A sectional view of the structure, a cap shown in Fig. 1 (c) is a self-standing sectional view of only a filter, and a cap shown in Fig. 1 (d) is a sectional view of an inner wire mesh structure.

[Fig. 2] Pressure loss and wind speed of 2 m at a ventilation speed of 5 cm / s
Diagram showing the relationship of changes in Vb value in / s

3 shows a cap of a gas detection sensor according to another embodiment of the present invention, wherein the cap shown in FIG. 3 (a) is a sectional view of a double wire mesh structure, and the cap shown in FIG. 3 (b) is a metal. 3C is a sectional view of the structure in which the filter is supported only by the peripheral portion of the cylinder, and FIG. 3D is a sectional view of the inner wire mesh structure.

[Fig. 4] Pressure loss and wind speed of 2 m at a ventilation speed of 5 cm / s
Diagram showing the relationship of changes in Vb value in / s

FIG. 5 is a perspective view showing a different conventional gas sensor.

6 is a perspective view showing a metal cap of the conventional different gas sensor shown in FIG.

7 is a diagram showing the number dependence of the output holes of the output of the conventional different gas sensor shown in FIG.

FIG. 8 is a wiring diagram showing a bridge circuit of a conventional gas sensor.

FIG. 9 is a graph showing the relationship between the fluctuation value of the bridge voltage at a wind speed of 2 m / s and the output with respect to the carbon monoxide gas concentration of 3000 ppm.

[Explanation of symbols]

 1 Metal Cap 2 Sensor Base 3 Stem 4 Temperature Sensor 5 Gas Detection Element 6 Compensation Element 7 Flow Hole 21 Fixed Resistance 22 Gas Detection Element 23 Compensation Element 24 Bridge Output 25 Power Supply 61A Wire Mesh 61B Wire Mesh 62 Filter (Porous Body) 63 Metal Spring ring 64 Integrated part 65 Cap 71A Wire net 71B Wire net 72 Filter (porous body) 73 Metal spring ring 74 Metal cylinder 75 Cap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Kato 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Takashi Ishii 1 Nitta, Tanabe-ku, Kawasaki-ku, Kanagawa No. 1 in Fuji Electric Co., Ltd. (72) Inventor Fumihiro Inoue 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Within Fuji Electric Co., Ltd. (72) No. 1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 inside Fuji Electric Co., Ltd.

Claims (5)

[Claims] 1. A gas detecting element and a compensating element are respectively installed at the branches of a bridge circuit to burn combustible gas by the gas detecting element, and the bridge output is changed by changing the resistance temperature of the gas detecting element to generate the combustible gas. A gas detection sensor for detecting, wherein both the gas detection element and the compensating element supported by the stem are surrounded by a cap for diffusing a flammable gas through a porous body. 2. The gas detection sensor according to claim 1, wherein
Porous material is glass fiber filter, silica fiber filter,
A gas detection sensor, which is an alumina binder reinforced silica fiber filter or a tetrafluoroethylene fiber filter. 3. The gas detection sensor according to claim 1 or 2, wherein the pressure loss is 10 mm when the ventilation speed is 5 cm / s.
A gas detection sensor characterized by using a porous body having a H ₂ o or higher. 4. The gas detection sensor according to claim 1, wherein the porous body is supported by a wire mesh. 5. The gas detection sensor according to claim 1, wherein the porous body is supported by a metal cylinder.