JPH09229889A - Protecting cap for gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability by regulating opening area of a slit of a cap main body. SOLUTION: A plurality of window parts 7 are formed on the side face of the cap main body 5 covering a sensor element. A total opening area of slits 9 each formed between the front end part of a notched element 6 and the cap main body 5 of the plural window parts 7 is set to be 1.5mm<2> -6.0mm<2> per 1cm<3> internal cubic volume of the cap main body 5. Accordingly, a zero point of a gas sensor is less varied even when a wind velocity increases, a sensitivity change due to a gas substitution rate is decreased and a quick response to gas is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective cap for a gas sensor, and more particularly to an improvement of a protective cap for protecting a sensor element of a catalytic combustion type gas sensor.

[0002]

2. Description of the Related Art A catalytic combustion type gas sensor uses heated Pt.
The temperature rise caused by the combustible gas coming into contact with the catalyst and burning on the line is regarded as a change in the electrical resistance of the Pt line, and this is displayed as the detection value of the gas sensor. In this type of gas sensor, the sensor element is generally covered with a protective cap.

FIG. 6 and FIGS. 7A and 7B show a conventional example of a protective cap for a gas sensor.

FIG. 6 shows a first conventional example, in which a protective cap 2 to be covered on the outside of the sensor element 1 has a structure in which a fitting 4 is provided on the bottom of a wire net 3 in which a metal wire is woven in a cage shape.

7 (a) and 7 (b) show a second conventional example, in which the protective cap 2 covered on the outside of the sensor element 1 has a bottomed cylindrical metal cap body 5 with its open end facing down. The mounting member 4 is fixed to the open end. On the side surface of the cap body 5, a slit 9 is formed in each window portion 7 between the tip end portion of the notch piece 6 and the cap body 5 by bending the notch piece 6 obliquely inward.

[0006]

When the wire mesh type of the first conventional example is installed in a place where the wind speed is high, such as in the exhaust gas of a water heater, not only the zero point of the sensor fluctuates greatly due to the wind, but also However, there is a problem that it is susceptible to thermal deformation and deformation due to external stress, and a separate outer case is required to prevent this.

The metal cap type of the second conventional example prevents the wind from directly hitting the sensor element 1 by the notch piece 6, so that the zero point variation due to the wind is smaller than that of the wire mesh type. However, there is a problem that reliability is lacking due to the following problems.

That is, in general, in the case of the catalytic combustion type gas sensor, the sensor output is set to an electric output by picking up the calorific value of the gas reacted (oxidized) on the surface of the sensor element per unit time to obtain an electric output. The sensitivity of the sensor is likely to change due to the variation of the gas replacement rate, and such a change in sensitivity is unavoidable in the metal cap type gas sensor of the second conventional example. Further, the influence of the wind speed is improved as compared with that of the wire mesh type, but when the wind speed exceeds a certain level, it is unavoidable that the gas sensitivity changes. Further, in terms of gas responsiveness, the response time of 90% of the saturation value may be delayed.

As a result of various studies, the present inventors have found that the above-mentioned phenomenon is related to the opening area of the slit formed in the cap body 5, and have completed the present invention. .

Therefore, an object of the present invention is to provide a protective cap for a gas sensor having improved reliability by defining the opening area of the slit of the cap body.

[0011]

According to the present invention, a plurality of windows are formed on a side surface of a cap body that covers a sensor element, and one side edge of the window portion is connected to the side surface so as to be diagonally inside the cap body. In a protective cap for a gas sensor including a notch piece facing toward one side, a total opening area of a slit between a tip portion of the notch piece formed in each of the plurality of windows and the cap body is an inner volume of the cap body. 1.5 per cm ³
and it is characterized in that it is set mm ² ～6.0Mm at ^2.

The protective cap for a gas sensor having the above structure is
The wind that enters through the window is blocked by the cutout pieces, does not directly hit the sensor element, and the opening area of the slit is set in the optimum range, so even if the wind speed increases, the fluctuation of the zero point of the gas sensor In addition, the sensitivity change due to the gas replacement rate can be reduced, and the quick response to the gas can be obtained.

[0013]

FIG. 1 is a block diagram showing an embodiment of the present invention.
A description will be given based on FIG. The same members as those in FIG. 7 are designated by the same reference numerals.

The protective cap 2 has a bottomed cylindrical cap body 5 with its open end facing downwards, and this open end is attached to the mounting bracket 4.
It is fixed to. The cap body 2 is formed by pressing a stainless steel plate into a cylindrical shape with a bottom, and U-shaped notches 8 are formed on a side surface of the cap body 2 at a plurality of positions at equal intervals in the circumferential direction (in the illustrated embodiment, in the illustrated embodiment). 6 places) are formed. Therefore, on the side surface of the cap body 5, six notch pieces 6 defined by the U-shaped notch portion 8 are formed.

The cut-out piece 6 has three sides separated from the side surface of the cap body 2 by the cut-out portion 8, and the remaining one side is integrally connected to the side surface of the cap body 5. Then, the notch piece 6 uses the connecting portion with the side surface as a fulcrum to serve as the cap body 5.
By being bent obliquely inward, the window portions 7 through which gas flows are formed at six positions on the side surface of the cap body 5. The cut-out piece 6 faces obliquely inward and prevents the wind entering from the window 7 from directly hitting the sensor element 1. As the angle at which the cutout piece 6 is bent inward of the cap body 5 is larger, the slit 9 between the tip of the cutout piece 6 and the cap body 5 is larger.
Since the opening degree of the slit 9 becomes large, the opening degree of the slit 9 can be adjusted by adjusting the bending angle of the notch piece 6.

The shape of the cap body 5 is not limited to the above-mentioned cylindrical shape, but may be any shape such as a side surface having a polygonal tubular shape, or the entire cap body having a spherical shape or a polyhedron shape. Good.

In the protective cap for a gas sensor of the present invention, the slit 9 of the cap body 5 is set as follows. Here, the width of the slit 9 (the distance between the tip of the notch piece 6 and the cap body 5) is W, the length is L, and the opening area of one slit 9 is the unit opening area S0 (= W ×
L), the total opening area of all slits 9 is S (=
S0 x number of slits 9). Also, the internal space of the cap body 5 (the space up to the upper surface 4a of the mounting bracket 4)
The volume of is defined as the internal volume.

In the present invention, the slit 9 of the cap body 5 is used.
Is the minimum, and W = 0.5 mm, L = 1.0 mm, and the number of slits 9 installed = ³ per 1 cm ³ of the inner volume of the cap body 5, and the total opening area S is S = 0.5. ×
1.0 × 3 = 1.5mm ² which is the maximum,
W = 1.0 m per 1 cm ³ of the internal volume of the cap body 5
m, L = 1.0 mm, the number of slits 9 installed = 6, and the total opening area S is S = 1.0 × 1.0 × 6 = 6 mm
Set to ² .

By setting the slit 9 in the above-mentioned range, a gas sensor can be obtained which does not impair the sensitivity of the sensor, has a small gas sensitivity variation due to a change in wind speed, and has a quick gas responsiveness.

In order to prove this, a gas sensor covered with five kinds of protective caps 2 of A to E in Table 1 in which the configuration of the slit 9 of the cap body 5 was changed was prepared, and Experiment 1,
2, 3 and 4 were performed. In Experiments 1, 2, and 3, the inner volume of the cap body 5 was set to 1 cm ³ , and the sensor element 1
All used the same thing.

[0021]

[Table 1] Experiment 1. The gas sensor covered with the above five types of protective caps A to E was put in a desiccator, and the respective sensitivity measurements were performed in standard gas. The standard gas is CO (1000 p
A mixed gas of pm) + H ₂ (500 ppm) was used. The results are shown in Table 2 and FIG.

[0022]

[Table 2] From the results of Experiment 1 described above, it was found that when the slit 9 was narrowed down to the state A, the sensitivity was lowered to about 70% due to gas replacement.

Experiment 2. Using the same gas sensor as in Experiment 1, the sensitivity was measured in the same procedure while changing the wind speed from 0 to 3 m / s in the gas. The results are shown in Table 3 and FIG.

[0024]

[Table 3] From the results of Experiment 2 described above, it was found that when the slit 7 was expanded to the state of E, the maximum sensitivity increased by 15% at a wind speed of 3 m / s, which was a factor of sensitivity variation in actual use.

Experiment 3. The gas responsiveness of the gas sensor was compared under the same conditions as in Experiment 1. That is, the gas has a saturation value of 90
The response time of the sensor at% was measured. The results are shown in Table 4 and FIG.

[0026]

[Table 4] From the results of Experiment 3 above, there is no noticeable difference in response time between the gas sensors of the protective caps B, C, D and E, whereas
In the case of the protective cap A, 90% of the gas saturation value has a response time of about 60 seconds, which is a large delay.

Experiment 4. The inner volume of the cap body 5 is 2 cm
As a result of conducting the same experiments as in Experiments 1 to ³ for different cap bodies of ³ and 3 cm ³ , the same tendency as described above was obtained, and even when the total opening area was the same, the inner volume of the cap body 5 was 1 cm. Those outside the range of 1.5 to 6.0 mm ² per ³ cause various problems in sensitivity and responsiveness.

As is apparent from the above experimental results, the gas sensor using the protective cap having the slit structure of A has a problem in sensitivity and responsiveness, and the gas sensor using the protective cap of E has a problem of sensitivity due to wind. There is a problem of large fluctuations.

Therefore, the protective cap having the slit structure of B, C and D, that is, the inner volume of the cap body 5 is 1 cm.
The total opening area S of the slit 9 per ³ is 1.5 to 6 mm
A protective cap set to ² proved to be optimal.

[0030]

As described in detail above, according to the present invention,
The wind that enters through the window is blocked by the notch, does not directly hit the sensor element, and the total opening area of the slits is set in the optimum range, so even if the wind speed increases, the fluctuation of 0 point of the gas sensor Is small, sensitivity changes due to changes in the gas replacement rate can be reduced, and quick response can be obtained. As a result, a protective cap for a gas sensor with improved reliability can be provided. .

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a protective cap for a gas sensor of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a graph showing the results of experiment 1.

FIG. 4 is a graph showing the results of experiment 2.

FIG. 5 is a graph showing the results of experiment 3.

FIG. 6 is a side view of a protection cap for a gas sensor of a first conventional example.

7A and 7B show a gas sensor protection cap of a second conventional example, FIG. 7A is a side view thereof, and FIG. 7B is a sectional view taken along line bb of FIG.

[Explanation of symbols]

 1 Sensor Element 2 Protective Cap 5 Cap Body 6 Notch Piece 7 Window 9 Slit W Slit Width L Slit Vertical Length

Claims (1)

[Claims] 1. A plurality of windows are formed on a side surface of a cap body that covers a sensor element, and a cutout piece is provided continuously with the side surface at one side edge of the window portion and directed obliquely inward of the cap body. In the protective cap for a gas sensor, the total opening area of the slits between the cap body and the tip of the cutout piece formed in each of the plurality of windows is 1.5 mm ² per 1 cm ³ of the inner volume of the cap body. 6.
A protective cap for a gas sensor, which is set to be 0 mm ² .