JPH09243582A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the gas sensor, which can cool the actual exhaust gas in the vicinity of a gas detecting element and a compensating element and has the small temperature fluctuation at the zero-point output in a bridge circuit. SOLUTION: This gas sensor is constituted of an electrically insulating base 1, a gas detecting element D, which is mounted on two metallic pins 2 penetrating and fixed to the base, a compensating element C, which is mounted on other pins 2 by the same way, and a permeable cap 4 covering these two elements. In this gas sensor, a cooling body 71 made of metal, which absorbs the heat in the vicinity of the gas detecting element D and the compensating element C attached to the gas sensor as a unitary body and radiates the heat to the outside of the gas sensor, is provided.

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 incorporated in a water heater or the like for detecting incomplete combustion from actual exhaust gas.

[0002]

2. Description of the Related Art As a gas sensor incorporated in a water heater or the like to detect conventional incomplete combustion, the temperature of exhaust gas after combustion is about 300 ° C., high humidity, and NO _x. and SO _X such high contact combustion type gas sensor because such may include the impurities of environment resistance is used.

FIG. 5 is a view of a conventional catalytic combustion type gas sensor, (a) is a plan perspective view, and (b) is a XX cross section of (a) of the gas sensor installed in the gas sensor installation chamber of the water heater. It is a figure. A gas detecting element D and a compensating element C are respectively stretched by spot welding on each of two pins 4 which are fixed through the insulating material base 1. A heat shield plate 3 is erected between the two elements so that the heat when the gas detecting element burns the gas does not reach the compensating element. The element is covered with a breathable double wire mesh or ceramic cap 4. The whole is a gas sensor. The gas sensor is attached to a mounting plate 5 of a gas sensor installation chamber 6 provided on an exhaust wall of a water heater or the like. F1 represents a gas flow in the exhaust stack, and F2 represents a gas flow entering and exiting the installation chamber 6.
The element side of the mounting plate 5 has a high temperature atmosphere, and the other side has a normal temperature atmosphere.

For gas detection, a bridge circuit in which these two elements and two fixed resistors are incorporated in each branch is used. FIG. 6 is a bridge circuit diagram of catalytic combustion type gas detection. Series connection of two fixed resistors R1 and R2,
The gas detecting element D and the compensating element C are connected in parallel in series, and the two elements are energized and preheated by applying a voltage from the power source E to the bridge circuit. A load W is connected between the connection point of the two fixed resistors and the connection point of the gas detection element and the compensation element. When combustible gas comes into contact with the gas detection element D, combustion occurs, the temperature of the platinum coil rises, and the electrical resistance increases. In the compensating element C, the combustible gas does not burn even when it comes into contact with the combustible gas, and the electric resistance does not change. Due to this difference in electrical resistance, the bridge output generated at the load W is the output for incomplete combustion.

The bridge output when the combustible gas is not in contact is called the zero point output. Since the zero point output is added to the bridge output when the combustible gas is in contact, the zero point output should be small. In the vicinity of room temperature, the gas detecting element and the compensating element have the same temperature change, so that the zero point output hardly changes with temperature.

[0006]

However, the actual exhaust gas from the water heater (gas flow F1 in FIG. 5) is about 150 to the maximum.
The temperature is 300 ° C., and the temperature in the installation room is lower by about 50 ° C., but such a high temperature atmosphere exceeds the temperature compensation range of the compensating element. Therefore, the zero-point output may become large and the gas detection level may become unstable, so it was necessary to strictly perform temperature compensation of the zero-point output by an electronic circuit added to the bridge circuit. Also, because it is exposed to high temperatures,
There has been a problem that the gas detecting element and the compensating element have a short life.

The present invention has been made in view of the above problems, and an object thereof is to cool the actual exhaust gas in the vicinity of the gas detecting element and the compensating element, and the temperature fluctuation of the zero-point output when incorporated in the bridge circuit is small. Another object is to provide a gas sensor that does not require a temperature compensation circuit in the bridge circuit.

[0008]

In order to achieve the above object, an electrically insulating base and a gas detecting element stretched between two metallic pins fixed to the base by penetration are provided. , A gas sensor composed of a compensating element stretched on the other two pins and a breathable cap covering these two elements, in the vicinity of the gas detecting element and the compensating element integrally attached to the gas sensor. A metal cooling body that absorbs the heat of the above and radiates it to the outside of the gas sensor is provided.

The cooling body may be one or a plurality of flat plates that penetrate the base between the gas detecting element and the compensating element. It is preferable that the cooling body is a plate having a U-shaped cross section, and the U-shaped curved portion is on the heat absorbing portion side. The cooling body is preferably a plate having a plurality of fins.

Further, the electrically insulating base, the gas detecting element stretched on two metallic pins fixed to the base through the gas sensing element, and the other two pins are also stretched on the other gas detecting element. In a gas sensor including a compensating element and a breathable cap that covers these two elements, the cap that covers the gas detecting element and the compensating element is made of metal, and heat near the gas detecting element and the compensating element is absorbed by a tap. Then, a heat radiation portion for radiating heat to the outside of the gas sensor is formed integrally with the cap.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 FIG. 1 is a diagram of a gas sensor of an example according to the present invention,
(A) is a perspective plan view, (b) is a XX sectional view in (a). The same components as those of the conventional gas sensor are designated by the same reference numerals. The method of installing the gas sensor in the water heater or the like is the same as the conventional method (see FIG. 5).

The cooling body 71 is a single metal plate and is fixed between the gas detecting element D and the compensating element C by penetrating the base 1. The cooling body 71 avoids thermal interference between the gas detecting element D and the compensating element C as in the conventional heat shield plate 3, and
The temperature of the gas can be lowered by absorbing the heat of the actual exhaust gas inside the cap 4, that is, in the vicinity of the element and radiating the heat to the outside of the gas sensor at room temperature. As a result, the temperature of the element decreased and the temperature fluctuation of the zero point output became small.

In this embodiment, the number of cooling bodies 71 is one, but a plurality of cooling bodies 71 may be used to enhance the cooling effect. Example 2 FIG. 2 is a diagram of a gas sensor of another example according to the present invention, in which (a) is a perspective plan view and (b) is XX in (a).
It is sectional drawing. The cooling body 72 is formed by bending a metal plate into a U shape, and has a U-shaped bent portion on the element side of the base 1.
It became possible to enhance the cooling effect as compared with Example 1. This corresponds to the case of the two-body cooling body of Example 1, but the cooling body is connected on the element side, so the temperature difference between the elements was smaller.

The temperature of the element decreased, and the temperature fluctuation of the zero-point output decreased. Although the U-shaped bent portion is located on the element side of the base in the present embodiment, the U-shaped bent portion may be located on the opposite element side of the base. Example 3 FIG. 3 is a diagram of a gas sensor of another example according to the present invention, in which (a) is a perspective plan view and (b) is XX in (a).
It is sectional drawing. The cooling body 73 of this embodiment is made of metal and has fins made of a plurality of thin plates attached thereto.
Since the fins are attached, the cooling effect can be enhanced as compared with the cooling body of the first embodiment.

The temperature of the element was lowered, and the temperature fluctuation of the zero point output was reduced. Example 4 FIG. 4 is a diagram of a gas sensor of another example according to the present invention, in which (a) is a perspective plan view and (b) is XX in (a).
A sectional view, (c) is a bottom view of Fig. (A). The cooling body 74 is made of metal and has the same shape as the conventional cap 74a.
And a fin 74b divided into several pieces in the circumferential direction. A hole through which the fin 74b passes is formed in advance on the base 74 of the fin 74b, and the gas detecting element D and the compensating element C are formed.
After fixing to the pin 2, the fin 74b of the cooling body 74 was inserted into the hole.

The heat of the actual exhaust gas is absorbed by the cap portion 74a and radiated from the fins 74b to cool the gas in the cap. In this embodiment, since the cooling body covers the element, the cooling effect is larger than that in the other embodiments. The temperature of the element is lowered, the temperature fluctuation of the zero point output is reduced, and the temperature compensation circuit that has been added in the past is not necessary. It should be noted that, in place of the cooling body of another embodiment, for example, the heat shield plate 3, a cooling body 71 of the first embodiment, a cooling body 72 of the second embodiment, or a cooling body 73 of the third embodiment is added to this embodiment. If so, the cooling effect can be further enhanced.

[0017]

According to the present invention, the base is penetrated by an integral metal cooling body including a heat absorbing portion near the gas detecting element and the compensating element, and a heat radiating portion on the other side of the base integrally with the heat absorbing portion. The temperature of the zero point output of the bridge circuit is reduced by radiating the heat of the actual exhaust gas near the element to the outside of the base and lowering the element temperature within the temperature compensation range of the compensation element. You can Therefore, it is not necessary to add an electronic circuit for temperature compensation.

Further, since the ambient temperature of the element is lowered, the gas sensor has a long life.

[Brief description of drawings]

FIG. 1 is a diagram of an embodiment of a gas sensor according to the present invention, (a)
Is a perspective plan view, (b) is a sectional view taken along line XX in (a)

FIG. 2 is a diagram of another embodiment of the gas sensor according to the present invention,
(A) is a perspective plan view, (b) is a sectional view taken along line XX in (a)

FIG. 3 is a diagram of another embodiment of the gas sensor according to the present invention,
(A) is a perspective plan view, (b) is a sectional view taken along line XX in (a)

FIG. 4 is a diagram of another embodiment of the gas sensor according to the present invention,
(A) is a perspective plan view, (b) is a sectional view taken along line XX in (a), and (c) is a bottom view of (a).

FIG. 5 is a view of a conventional catalytic combustion type gas sensor, (a) is a plan perspective view, and (b) is a sectional view taken along line XX of (a) of the gas sensor installed in the gas sensor installation chamber of the water heater.

FIG. 6 is a bridge circuit diagram of catalytic combustion type gas detection.

[Explanation of symbols]

 1 Base 2 Pin 3 Thermal Shield Plate D Gas Detection Element C Compensation Element 4 Cap 5 Mounting Plate 6 Installation Room 71 Cooling Body 72 Cooling Body 73 Cooling Body 74 Cooling Body 74a Cap Part 74b Fin R1 Resistance R2 Resistance E Power Supply W Load

Claims (5)

[Claims] 1. An electrically insulative base, a gas detection element stretched on two metal pins fixed to the base, and a gas detection element stretched on another two pins. In a gas sensor including a compensating element and a gas-permeable cap that covers these two elements, a metal that is integrally attached to the gas sensor, absorbs heat in the vicinity of the gas detecting element and the compensating element, and dissipates the heat to the outside of the gas sensor. A gas sensor having a cooling body made of metal. 2. The gas sensor according to claim 1, wherein the cooling body is one or a plurality of flat plates that penetrate the base between the gas detecting element and the compensating element. 3. The cooling body is a plate having a U-shaped cross section, and U
The gas sensor according to claim 1, wherein the curved portion of the character shape is on the heat absorbing portion side. 4. The gas sensor according to claim 1, wherein the cooling body is a plate having a plurality of fins. 5. An electrically insulative base, a gas detection element stretched on two metallic pins fixed to the base by penetration, and a gas detection element stretched on another two pins as well. In a gas sensor including a compensating element and a breathable cap that covers these two elements, the cap that covers the gas detecting element and the compensating element is made of metal, and heat near the gas detecting element and the compensating element is absorbed by a tap. The gas sensor is characterized in that a heat radiating portion for radiating heat to the outside of the gas sensor is formed integrally with the cap.