JP2603633Y2 - Gas sensors and combustion appliances - Google Patents

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 a gas such as carbon monoxide, and to an improvement in a combustion apparatus provided with a gas sensor for detecting a gas concentration in exhaust gas.

[0002]

2. Description of the Related Art Conventionally, a catalytic combustion type gas sensor is configured as shown in FIG. 8, for example. In the figure, a gas sensor 1 includes a partition plate 3 erected on an upper surface of a base 2.
A sensing element 5 provided in one area partitioned by the partition plate 3 and a comparison element 6 provided in the other area.
And a temperature sensor 7 for temperature compensation arranged between these elements.

The sensing element 5 and the comparison element 6 are respectively provided on a pair of columnar support members 4 erected on the base 2.
4, 8, and 8 are fixedly supported by a platinum wire or the like.
On the other hand, the temperature sensor 7 has a cross-sectional diameter of about 0.4 m on the base 2.
The supporting member 9 is formed to have a predetermined height by a supporting member 9 formed of a nickel wire of m. The sensing element 5, the comparison element 6, and the temperature sensor 7 are formed in a mesh shape so as to allow gas to pass therethrough, or are covered with a cover (not shown) formed by providing a notch or the like. .

As a result, the sensing element 5 burns in contact with the flammable gas, and as the temperature rises, the electric resistance of the sensing element 5 changes to a value different from that of the comparison element 6. The change is taken out and the flammable gas is detected.

Further, since the characteristics of the sensing element 5 change depending on the ambient temperature, a temperature sensor 7 is provided, and based on the output value of the temperature sensor 7, the signal based on the current change is corrected to perform temperature compensation. It is supposed to do. Thereby, an accurate detection result is obtained.

FIG. 9 shows an example of a combustion apparatus in which the gas sensor 1 is used to detect, for example, the concentration of carbon monoxide in exhaust gas. In the drawing, a burning appliance 10 shows an example of a gas water heater, for example, and a case 1
1 has a combustion chamber 12 containing a large number of gas burners.
And a heat exchanger 13 for heating water introduced from the outside by a burner in the combustion chamber 12 to make it hot water.

In the water heater 20 of this type, the combustion chamber 12
A fan 14 is provided below the fuel cell 12 to supply combustion air to the combustion chamber 12. In addition, the heat exchanger 13
An exhaust passage 15 is provided above the fuel cell, and the combustion exhaust gas is discharged from the chimney 16 to the outside through the exhaust passage 15.

Further, in the exhaust passage 15, a portion where the exhaust components are mixed in a predetermined state is selected, and the chamber 1 is exhausted.
The gas sensor 1 is mounted in the chamber 17. In the gas sensor 1, a detection unit including the sensing element 5, the comparison element 6, and the temperature sensor 7 is exposed inside the chamber 17. Gas sensor 1
The sensor base including the base 2 of the
7 to be exposed to the outside.

Thus, the detecting section is arranged in the atmosphere in which the gas concentration is to be detected inside the chamber 17, and the sensor base extends outside the chamber 17 so that the wiring of the sensor extends.

Therefore, in such a water heater 20,
The combustion exhaust gas enters the chamber 17 while being mixed through the exhaust passage, and in the atmosphere in the chamber 17,
For example, the concentration of carbon monoxide or the like is detected by the gas sensor 1.

[0011]

By the way, in such a gas sensor 1, the sensor base is formed by a chamber 17.
It is exposed outside. For this reason, as shown in FIG. 9, outside air is taken into the appliance from an air inlet 19 provided on the side surface of the case 11 for cooling the electrical equipment board, and is circulated as indicated by an arrow A. May be caused.

Then, the outside air is supplied to the chamber 17.
Will come into contact with the sensor base of the gas sensor 1 that is exposed to the outside. Here, outside air A guided from the outside of the appliance
Is much lower than the ambient temperature in the chamber 17.
Therefore, when the outside air A comes into contact with the sensor base, the sensor base is cooled, and the sensor detecting unit including the sensing element, the comparison element, and the temperature sensor connected to the sensor base is also cooled.

Therefore, the sensor detecting section including the sensing element, the comparison element, and the temperature sensor detects the gas concentration under the influence of a low temperature different from the temperature in the chamber 17. For this reason, the sensor detection unit outputs a detection result different from the actual gas concentration in the chamber 17 due to the temperature characteristic, and there is a problem that the detection accuracy of the gas concentration is significantly reduced.

The present invention has been made in view of the above problems, and a first object of the present invention is to provide a gas which can accurately detect the concentration of a gas without being affected by the temperature of the outside air. It is to provide a sensor. It is a second object of the present invention to provide a combustion appliance having means for accurately detecting the concentration of gas in combustion exhaust gas without being affected by the outside air temperature.

[0015]

SUMMARY OF THE INVENTION The first object of the present invention is as follows.
According to the plan, a sensing element that is contact burnt with a combustible gas,
And a comparison element arranged corresponding to the sensing element.
In a gas sensor, the detection element consisting of the sensing element and the comparison element
The outlet is located in the atmosphere where the gas concentration is to be detected.
Arrange so that the body sensor base is exposed outside the above atmosphere.
And the outside air may come into contact with this exposed part.
Gas sensor equipped with an outside air shield to prevent
Is achieved. Further , according to the present invention, the first object is to provide a sensing element which is in contact with and combustible with a combustible gas, a comparison element arranged corresponding to the sensing element, and a temperature dependence of an output by the sensing element. In a gas sensor having a temperature sensor for compensating for the above, a detection unit including the sensing element, the comparison element, and the temperature sensor is disposed in an atmosphere in which a gas concentration is to be detected, and a base of the gas sensor is exposed outside the atmosphere. This is achieved by a gas sensor that is disposed so as to be in contact with the outside air and has an outside air shielding portion that prevents outside air from contacting the exposed portion.

A second object of the present invention is to burn fuel in an appliance.
Burn and discharge combustion gas to the outside through exhaust passage
In the combustion apparatus having the above configuration, a chip provided in the exhaust passage is provided.
Detection part consisting of sensing element and comparison element is exposed in the chamber
Gas chamber outside the chamber.
A gas sensor arranged so that the sensor base is exposed,
In the fixture, the gas sensor base is
Combustor comprising shielding means for preventing air contact
Is achieved by the tool. A second object of the present invention is,
In a combustion appliance configured to burn fuel in the appliance and discharge combustion gas to the outside through an exhaust passage, a sensing element, a comparison element, and a sensor are provided in a chamber provided in the exhaust passage.
A gas sensor arranged so that a detection portion constituted by a temperature sensor is exposed, and a gas sensor arranged so that a gas sensor base is exposed outside the chamber, and an outside air from outside the instrument with respect to the gas sensor base inside the instrument. This is achieved by a combustion apparatus comprising:

Preferably, the shielding means also serves as a heat-insulating plate disposed between the combustion section in the appliance and a control board of the combustion appliance to prevent heat from the combustion section from being transmitted to the control board. It can be configured.

Preferably, the heat insulating plate has an upper portion extended with respect to the appliance, so that the extended portion can be used as the shielding means. Preferably, the heat shield plate is formed by extending the entire cover side of the appliance, so that the extended portion can be used as the shielding means.

In the configuration of the present invention, the "outside air" is not only gas outside the appliance, such as a combustion appliance, but also gas such as air inside the appliance, which is cooled by air outside the appliance. Shall be included. That is, “outside air” refers to all gases except those in the atmosphere in which the gas concentration or the like is to be detected by the gas sensor.

[0020]

According to the above construction, the sensor base of the gas sensor of the present invention is provided with shielding means for shielding outside air. Therefore, without being affected by the outside air temperature,
The gas concentration can be accurately detected in the atmosphere to be detected.

Further, the combustion appliance of the present invention has shielding means for preventing outside air entering from outside the appliance from coming into contact with the sensor base of the gas sensor provided in the exhaust passage. For this reason, it is possible to prevent the sensor base from being cooled by the outside air and adversely affecting the detection unit of the sensor in relation to the temperature characteristics of the detection unit.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that the embodiments described below are
Since the present invention is a preferred embodiment of the present invention, various technically preferable limitations are provided, but the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description. It is not limited to.

FIG. 1 is a schematic sectional view showing a configuration of a gas sensor 20 according to a preferred embodiment of the present invention, and FIG. 2 is a schematic perspective view showing a main body of the gas sensor 20 with a cover removed. In FIG. 1, a gas sensor 20 is configured such that a stainless steel cap 21 is put on a detection unit 22 as a main body from above and fixed.

The cap 21 has, for example, a mesh structure around its periphery, so that gas can enter the inside thereof.

The detection unit 22 of the gas sensor includes a comparison element 23
And a sensing element 24 paired with the comparing element 23, a partition plate 26 for separating them, and a temperature sensor 25 disposed between the comparing element 23 and the sensing element 24. The comparison element 23 is formed of, for example, alumina. The comparison element 23 stands on the bottom plate 34, extends through the base 28, and extends a platinum wire 35 between a pair of support members 31, 31 extending in parallel to each other, and is fixed near the middle thereof. I have.

In this embodiment, the base 28 and the bottom plate 3
4 and a mounting member 29 described later form a sensor base 38. The supporting member 3 of the comparative element 23
In this embodiment, reference numerals 1 and 31 are formed of nickel columnar members having a cross-sectional diameter of approximately 1.0 mm.

The sensing element 24 is made of, for example, alumina and rhodium, and is arranged symmetrically with the comparison element 23 with the partition plate 26 interposed therebetween. Specifically, a pair of support members 32, 32 extending parallel to each other and extending upward in the figure through the base 28 are provided so as to stand on the bottom plate 34. A platinum wire 35 is stretched between the support members 32, 32, and the sensing element 24
Has been fixed.

The support members 32, 32 of the sensing element 24
Also, in this embodiment, the support members 31 of the comparative element 24,
31 is made of a nickel columnar member having a cross-sectional diameter of approximately 1.0 mm. Thus, the support members 31, 31, 32, and 32 are all configured to have the same heat capacity.

As shown in the figure, the base 28 is formed in a substantially cylindrical shape by using, for example, phenol resin or ceramics. The base 28 has support members 31, 31, 32, 32 extending relatively long from the bottom plate 24.
However, they are fixedly supported so as to maintain parallelism with each other.

Further, the comparison element 23 and the sensing element 2
4, a temperature sensor 25 is arranged above the partition plate 26. This temperature sensor 25 is also fixed near the middle between the two pairs of support members 33,33. The support members 33, 33 are provided so as to stand on the bottom plate 34, and extend upward outside the base 28 in the drawing. The support members 33, 3
3 may be provided so as to penetrate the base 28. This
Here, the temperature sensor 25 has the same configuration as the comparison element 23.
Therefore, the output of the comparison element 23 is separately and independently taken out.
By doing so, the comparison element 23 performs the function of the temperature sensor 25.
Can double.

Further, the support members 33, 33 are constituted by nickel columnar members having a cross-sectional diameter of approximately 1.0 mm. Thus, the support members 33, 33 and the support members 31, 31, 32, 32 of the comparison element and the sensing element are made of the same material and have the same shape, and therefore all have the same heat capacity. It is configured to have. still,
As described above, the comparison element 23 also serves as the temperature sensor 25.
In the case of such a configuration, the supporting members are 31, 31 and 32,
32, and these are made of the same material and the same shape.
It may be formed.

The gas sensor main body 22 configured as shown in FIG. 2 is mounted on the mounting member 2 as shown in FIG.
9 so as to be fitted inside. The mounting member 29 has an inner diameter substantially matching or slightly larger than the base 28, and has an external thread portion 28a
Are formed. Further, the mounting member 18 has a flange portion 37. The flange portion 37 is applied to, for example, the back surface of the mounting board 36 or the like, and the nut 35
Is screwed into the male screw portion 28a.

As described above, the detection section 22 which is the sensor main body of the gas sensor 20 is exposed on one side (the upper side in the drawing) of the mounting board 36 in the atmosphere in which the gas concentration or the like is to be detected. On the other hand, in the drawing, the sensor base 38 is exposed below the mounting board 36 so as to contact the outside air.

Here, the comparison element 23 and the sensing element 24
Is heated to, for example, 200 degrees Celsius by applying a predetermined voltage to obtain a predetermined output value, and has a characteristic that this output value changes with temperature. Therefore, the ambient temperature at that time is detected by the temperature sensor 25 as described later, and the output values of the comparison element 23 and the sensing element 24 are corrected based on the detected temperature.

However, in the case of the gas sensor 20, the comparison element 23 including this temperature sensor 25 and the sensing element 2
4 and the like are connected by support portions 31 and 32 to a sensor base portion 38 exposed to the outside air. For this reason, if the sensor base 38 is cooled by the outside air, the high temperature of the sensor detection unit 22 escapes to the sensor base 38 side, and the temperature becomes lower than the ambient temperature at which the gas concentration is to be detected.

Therefore, the comparison element 23 and the sensing element 2
The output value of 4 not only indicates an output value different from the actual gas concentration based on the temperature characteristic, but also the value of the temperature sensor 25 to be corrected is different from the actual ambient temperature. Therefore, in this embodiment, for example, a cover 27 as shown in FIG. 1 is provided, and the periphery of the sensor base 38 is covered with the cover 27, so that there is no contact with the outside air.

In this embodiment, the cover 27 is made of, for example, stainless steel and has holes 27a and 27b for preventing dew condensation. Thus, the cover 27a has an excellent ability to block the outside air temperature, and can be easily processed into a predetermined shape. The cover 27 may be attached from behind the sensor base 38 of the gas sensor 20 as shown in FIG. 1, for example. Alternatively, the sensor base 38 may be attached in advance so as to cover the periphery.

FIG. 3 shows an example in which such a gas sensor 20 is attached to, for example, a water heater 40 as a burning appliance. In the drawing, inside a case 41 of a water heater 40, there are provided a combustion chamber 42 accommodating a large number of gas burners, and a heat exchanger 43 for heating water introduced from the outside by the burners in the combustion chamber 42 to generate hot water. Have.

A fan (not shown) (for example, a sirocco fan) is provided below the combustion chamber 42 to supply combustion air to the combustion chamber 42. This air is
It is introduced into the appliance from outside the water heater 40 through, for example, an air intake 49. An exhaust passage 45 is provided above the heat exchanger 43, and the combustion exhaust is discharged from the chimney 46 to the outside through the exhaust passage 45.

Further, in the exhaust passage 45, a portion where the exhaust components are in a predetermined mixed state is selected, and a chamber 4 is formed.
The chamber 47 is provided with the gas sensor 20 described above. In the gas sensor 20, the detection unit 22 including the sensing element 23, the comparison element 24, and the temperature sensor 25 is exposed in an atmosphere inside the chamber 27 where the gas concentration is to be detected. Further, the sensor base 38 (see FIG. 1) of the gas sensor 20 is connected to the chamber 4 in the instrument.
7 to be exposed to the outside.

Therefore, in such a water heater 40,
The combustion exhaust gas enters the chamber 47 while being mixed through the exhaust passage 45, and the concentration of, for example, carbon monoxide is detected by the gas sensor 20 in the atmosphere in the chamber 47.

Here, a part of the outside air taken into the appliance from the outside of the water heater 40 through the air inlet 49 may be introduced as shown by an arrow A1, for example. That is, the outside air is supplied to the control board 41 of the water heater,
The control board passes over the heat insulating plate 48 provided to prevent the heat of the combustion section from being transmitted to the control board, and contacts the back side of the chamber 47.

The temperature of the outside air is significantly lower than the ambient temperature in the chamber 47, for example, about room temperature. The low-temperature outside air A1 touches an exposed portion of the gas sensor 20, and the cover 27 shown in FIG. 1 is provided at this portion. Thereby, the sensor base 3 of the gas sensor 20
8 is not cooled and does not adversely affect the detection unit 22 of the sensor. For this reason, the gas sensor 20
For example, the concentration of, for example, carbon monoxide in the exhaust gas of the water heater 40 can be appropriately detected.

That is, FIG. 4 shows an equivalent circuit of the gas sensor 20. In the circuit configuration as shown in the figure, the comparison element 23 and the sensing element 24 are connected to a power source, and a gas such as carbon monoxide is used. Used for detection.

In this case, when a combustible gas is brought into contact with the surface of the sensing element 24, the electric resistance of the sensing element 24 increases due to the reaction heat. That is, since the electric resistance of the comparison element 23 and the electric resistance of the sensing element 24 are different from each other, a change in current is extracted by a Wheatstone bridge as shown in the figure, and carbon monoxide is detected.

In this case, the change in the resistance value of the sensing element 24 is
It depends on the ambient temperature, and therefore, it is necessary to compensate for the temperature while monitoring the ambient temperature with the temperature sensor 25. FIG. 5 shows a block configuration of the device when the output detected by the gas sensor 20 is temperature compensated. In the figure, a gas sensor (CO sensor) 20 (the sensing element 2
The output signal from 4) is supplied to the signal processing / arithmetic unit 51. At the same time, the output signal of the temperature sensor 25 is also supplied to the signal processing / calculating section 51.

The signal processing / calculating section 51 processes the output signal of the temperature sensor 25 to detect the ambient temperature, and, based on this, calculates for compensating the output value of the CO sensor 20 (the sensing element 24). I do. Based on the calculation result, C
When the O concentration is detected and exceeds a predetermined standard, a predetermined alarm is displayed on the alarm display section 53 or a buzzer sounds. At the same time, for example, a signal is sent to the appliance stopping section 52 of the control board 44 of the water heater 40 to stop the combustion.

In this case, in the gas sensor (CO sensor) 20 of this embodiment, the supporting members 31, 32, and 33 supporting the comparing element 23, the sensing element 24, and the temperature sensor 25 are made of the same material and of the same size. , In the shape.

Therefore, since these heat capacities are almost the same, even if the ambient temperature of the sensor changes, this temperature change is transmitted through the support members 31, 32, 33 to the comparison elements 33, 33.
It is transmitted to the sensing element 24 and the temperature sensor 25 at the same time. As a result, the temperature compensation by the temperature sensor 25 is accurately performed, and the CO concentration is accurately detected.

As described above, the gas sensor 20 of this embodiment is
With this method, even when the ambient temperature changes, the detection accuracy does not transiently deteriorate, and the followability to the temperature change is extremely excellent.

Further, in addition to this, the gas sensor 20
Is not adversely affected by outside air, so that more accurate gas concentration detection is performed. For this reason,
In the water heater 40, for example, when incomplete combustion or the like occurs, the combustion is stopped at an appropriate timing to prevent an accident from occurring.

FIG. 6 shows a second embodiment of the water heater according to the present invention. In the figure, among the respective configurations of the water heater 60,
Since the portions denoted by the same reference numerals as those of the water heater 40 in FIG. 3 have the same configuration, duplicate description will be omitted. A conventional gas sensor 1 different from the gas sensor 20 of FIGS. 1 and 3 is mounted in the chamber 27 of the water heater 60.

For this reason, when the outside air comes into contact with the gas sensor 1, the detection accuracy deteriorates. Therefore, in the water heater 60, the outside air shielding means is formed by using the heat insulating plate 48.
That is, a control board 44 for controlling the operation of the water heater 60 is provided from the side of the case 41 of the water heater 60. If the heat of the combustion part 42 or the like is transmitted to the control board 44, it may cause a failure. Therefore, a heat-insulating plate 48 is provided between the high-heat portion including the combustion part 42 and the control board 44. I have.

In this embodiment, the heat insulating plate 48 is made of a metal such as an iron plate or other heat-resistant material. Further, the heat shield plate 48 is extended upward in the drawing as shown by the hatched portion at the upper portion, and the hatched portion serves as a shielding means 48a.

That is, the outside air A2 introduced into the apparatus from the air inlet 49 on the side of the case 41 passes through the control board 44 as shown in the example of FIG. Since it hits the portion 48a, it does not go around the back side of the chamber 27. For this reason, the sensor base exposed outside the chamber 27 of the gas sensor 1 is prevented from being cooled by the outside air A2.

Further, as shown in FIG. 7, when the water heater 60 is viewed from the side, the front side (left side in the figure) of the heat insulating plate 48, that is, the front cover 41a of the case 41
An example in which a second extension 48a (shown by a two-dot chain line) is formed on the side. According to this, as shown in FIG. 6, the outside air A3 introduced into the apparatus through the air intake 49 turns around the front side of the heat insulating plate 48, and
7 is prevented.

That is, such outside air A3 hits the second extension 48 as a shielding means, and
Flow to the side 7 is prevented. Therefore, the sensor base exposed outside the chamber 27 of the gas sensor 1
Cooling by the outside air A2 is effectively prevented.

Therefore, even in the present embodiment, the gas sensor 1 is not adversely affected by the outside air, so that the gas concentration can be detected more accurately. Thus, in the water heater 60, for example, when incomplete combustion or the like occurs, combustion is stopped at an appropriate timing, and occurrence of an accident can be prevented.

The present invention is not limited to the above embodiment. In the above-described example, the gas sensor itself is provided with the shielding means, and instead, the heat shield is provided with the outside air shielding means. However, the shielding means may be provided at a different place. As a result, the object of the present invention can be achieved if the outside air does not contact the sensor base of the gas sensor.

[0060]

As described above, according to the present invention, it is possible to provide a gas sensor which can accurately detect a gas without being affected by an outside air temperature lower than an ambient temperature at which a gas concentration or the like is to be detected. Can be. In addition, it is possible to provide a combustion device that can accurately detect the concentration of gas in exhaust gas and operate safely without being affected by outside air introduced into the device.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of a gas sensor of the present invention.

FIG. 2 is a schematic perspective view showing a state where a cover of the gas sensor of FIG. 1 is removed.

FIG. 3 is a schematic diagram showing a configuration of a main part of a combustion appliance including the gas sensor of FIG. 1;

FIG. 4 is a diagram showing an equivalent circuit of the gas sensor of FIG.

FIG. 5 is a block diagram illustrating a temperature compensation system of the gas sensor of FIG. 1;

FIG. 6 is a schematic front view showing a main part configuration of a second embodiment of the combustion appliance of the present invention.

FIG. 7 is a schematic side sectional view showing a main part of the combustion apparatus of FIG. 5;

FIG. 8 is a diagram showing an example of a conventional gas sensor.

FIG. 9 is a schematic perspective view showing a main part configuration of a conventional burning appliance.

[Explanation of symbols]

 Reference Signs List 20 gas sensor 22 sensor main body 23 comparison element 24 sensing element 25 temperature sensor 27 outside air shielding section 31 support member 32 support member 33 support member 48 heat shield plate 48a first outside air shielding section 48b second outside air shielding section

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Iizuka 3-4 Fukamidai, Yamato City, Kanagawa Prefecture Inside Gaster Co., Ltd. (72) Inventor Hideo Umeda 3-4 Fukamidai, Yamato City, Kanagawa Prefecture Gaster Co., Ltd. (56) References JP-A-55-125443 (JP, A) JP-A-51-106187 (JP, U) JP-A-58-154454 (JP, U) JP-A-2-6251 (JP, U) Japanese Utility Model Application Hei 2-32050 (JP, U) Japanese Utility Model Application Hei 4-129650 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 27/00-27/24 F23N 5/24 107

Claims (7)

(57) [Scope of request for utility model registration] 1. A gas sensor comprising: a sensing element which is burned in contact with a combustible gas; and a comparison element arranged corresponding to the sensing element. The gas sensor base is arranged so as to be exposed outside the above-mentioned atmosphere, and is provided with an outside air shielding portion for preventing outside air from contacting the exposed portion. A gas sensor, characterized in that: 2. A combustion device in which fuel is burned in the device and combustion gas is discharged to the outside through an exhaust passage, wherein a sensing element and a comparison element are provided in a chamber provided in the exhaust passage. A gas sensor arranged so that a detection part is exposed and a gas sensor base is arranged to be exposed outside the chamber, and outside air from outside of the instrument contacts the gas sensor base in the instrument. And a shielding means for preventing combustion. 3. A structure in which the shielding means is disposed between a combustion section in the appliance and a control board of the combustion appliance and also serves as a heat-insulating plate for preventing heat from the combustion section from being transmitted to the control board. 3. The combustion device according to claim 2 , wherein: 4. The combustion apparatus according to claim 3, wherein the heat-insulating plate has an upper portion extended with respect to the appliance, so that the extended portion serves as the shielding means. 5. The burning appliance according to claim 3, wherein the heat insulating plate is extended on a front cover side of the appliance so that the extended portion serves as the shielding means. 6. A gas sensor comprising: a sensing element which is burned in contact with a combustible gas; a comparing element arranged corresponding to the sensing element; and a temperature sensor for compensating a temperature dependency of an output by the sensing element. In the above, the detection unit including the sensing element, the comparison element, and the temperature sensor may include:
A gas sensor base is arranged in an atmosphere where the gas concentration is to be detected, and the gas sensor base is arranged so as to be exposed outside the above atmosphere, and an outside air shielding portion for preventing outside air from contacting the exposed portion is provided. A gas sensor characterized in that: 7. A combustion apparatus configured to burn fuel in the apparatus and discharge combustion gas to the outside through an exhaust passage, wherein a sensing element, a comparison element, and a temperature are provided in a chamber provided in the exhaust path. A gas sensor arranged so that a detection part constituted by a sensor is exposed, and a gas sensor base arranged so as to expose a gas sensor base outside the chamber; and an outside air from outside the instrument with respect to the gas sensor base in the instrument. And a shielding means for preventing contact.