JPH09170994A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor showing a low zero output variation of a zero point in an equilibrium state and a transient state even when a high-speed hot wind runs. SOLUTION: In the gas sensor, a gas direction element D and a compensation element C of a contact combustion type are suspended between two adjacent pins of four metallic pins 2, 3 penetrating and fixed to an electrically insulating base 1. A gas permeable gap covers the elements over the base. A lateral bar part 23 of a high heat conductive material is interposed between the metallic pins penetrating the electrically insulating base on which the gas detection element and the compensation element are supported. Accordingly, thermal bonding of the elements is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustible gas sensor attached to a water heater or the like having a wide temperature range of test gas.

[0002]

2. Description of the Related Art As an example of a conventional gas sensor, it is described in Fuji Jikki Vol. Combustible gas sensors such as those used in alarms are, for example, a gas detection element and a combustible gas detection device having a structure in which a metal coil such as a platinum coil is covered with a carrier such as aluminum oxide carrying a catalyst active against the combustible gas. It is composed of a compensating element which is inactive to the natural gas. FIG. 11 is a perspective view of a conventional catalytic combustion type gas sensor. A gas detecting element D and a compensating element C are stretched on each of two pins 2 and 3 which are fixed through the insulating material base 1. A heat shield 4 is erected between the two elements.
The element is covered with a breathable cap 5. The whole is gas sensor S.

For gas detection, these two elements and
A bridge circuit is used in which two fixed resistors are incorporated in each branch. FIG. 12 is a bridge circuit diagram of a catalytic combustion type gas sensor. The series connection of two fixed resistors R1 and R2 and the series connection of the gas detection element D and the compensation element C are connected in parallel, and the two elements are energized and preheated by the application of the voltage from the power source E to the bridge circuit. When combustible gas comes into contact with the gas detection element D, combustion occurs, causing a temperature change in the platinum coil and an electric resistance change proportional to the combustible gas concentration. In the compensating element C, even if combustible gas comes into contact, it does not burn, and therefore temperature change does not occur. Therefore, from this minute change in electrical resistance, the connection point between the two fixed resistors and the junction point between the gas detection element and the compensation element. Load connected between
The bridge output generated in W changes in proportion to the combustible gas, and the combustible gas concentration can be detected.

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.

[0005]

Actually, in order to quickly detect the incomplete combustion of the combustion equipment such as the gas water heater and the oil fan heater, incomplete combustion components (mainly in the combustion gas of the equipment) are mainly detected. It is desirable to bring the combustible gas sensor into contact with the carbon monoxide gas) at a high concentration before being diluted with the outside air, and the combustible gas sensor is attached to the exhaust side of the combustion chamber or an exhaust stack close to the combustion chamber. FIG. 13 is a sectional view when a gas sensor is attached to the exhaust stack.
The gas sensor S is connected via the sensor mounting box 7
Attached to stack 6. In such a case, the temperature of the exhaust gas G (hereinafter referred to as the detection gas) is generally
It becomes a high temperature of 100 ℃ or more, and depending on the model, it will be exposed to the detection gas that is several meters per second due to forced exhaust by the fan.

The inventors of the present invention take measures against high-speed hot air by adopting a special gas sensor cap so that the output of the sensor does not fluctuate even if hot air reaching several meters per second directly hits the gas sensor. Things are also known. In more detail, the output of the catalytic combustion type gas sensor is determined as follows.

The amount of heat Qh given by Joule heat generated by energizing the metal coils of the gas detecting element and the compensating element connected in series, and the heat conduction from each element to the metal pin through the lead portion of the metal coil. Amount of heat radiated
Qcond, the amount of heat radiated from the surface of each element to the atmosphere Qconv
And heat quantity Qrad radiated from the surface of the device by heat radiation
Are balanced to determine the temperatures of the metal coils of the gas detecting element and the compensating element. If flammable gas is present, the combustion heat Qgas of the gas is added to the Joule heat in the gas detection element. In this way, the bridge output is determined according to the coil resistance determined by the temperature of the metal coil of each element.

Among the above three types of heat radiation, for example, a diameter of 60 μm
Calculate the ratio of heat dissipation when a device with a 1.5 mm diameter porous alumina attached to a platinum coil is attached to a pin with a metal pin spacing of 5 mm that holds the gas detection device and the compensating device. be able to. According to the simulation, when the element temperature is 400 ° C or lower, the heat radiation amount Qrad due to heat radiation is 10% or less of the total heat radiation,
Most of the heat dissipation is about 1: 1 due to the heat dissipation Qcond due to heat conduction and the heat dissipation Qconv due to heat transfer to the atmosphere.

The heat dissipation Qcond due to heat conduction is proportional to the temperature difference between the coil temperature and the metal pin on which the element is stretched, and the heat dissipation Qconv due to heat transfer is proportional to the temperature difference between the porous alumina surface temperature and the atmospheric temperature. To do. 1 as shown in FIG.
In the structure in which the gas detecting element and the compensating element are housed in one cap, even if there is a difference in the cap temperature in the immediate vicinity of the gas detecting element and the compensating element, the air in the cap is sufficiently convected and the temperature of each element is equal. Therefore, even if there is a temperature distribution in the cap, there is little influence due to heat dissipation due to heat transfer.
On the other hand, between the pins holding the gas detecting element and the compensating element, a temperature difference occurs between the pins because the base is made of plastic that is generally electrically insulating and has low thermal conductivity. There is a difference in the coil temperatures of both elements, which causes the zero point output to fluctuate.

According to the conventional customer request, such a fluctuation of the zero point output is within the allowable range. However, awareness of intrinsic safety is increasing, and customer requirements for gas sensors that detect incomplete combustion have also become strict.
For example, the conventional requirement for zero-point output was 0 ppm ± 500 ppm when converted to CO gas, but now it is 0 ppm ± 250 ppm, which is twice as accurate as required. In order to meet such a demand for high accuracy, there has been a problem that the temperature difference between the gas detecting element and the compensating element due to the heat transmitted through the sensor mounting box cannot be ignored.

Further, in actuality, when the water heater is ignited, the temperature of the exhaust gas rapidly rises, and along with this, the temperature of the gas sensor mounting portion also sharply rises. At this time, a delicate temperature distribution different from the equilibrium state is created in the gas sensor mounting part,
As a result, an apparent transient output larger than the actual concentration of carbon monoxide gas is also a problem. The present invention has been made in view of the above problems, and an object thereof is to reduce the temperature difference between the metal pin that stretches the gas detection element and the compensating element even when high-speed hot air is flowing, thereby achieving an equilibrium state. Of course, another object of the present invention is to provide a gas sensor with reduced zero-point output fluctuation in a transient state.

[0012]

In order to achieve the above object, the contact combustion type gas detecting element and the compensating element are adjacent to each other by four metal pins which are fixed through the electrically insulating base. In a gas sensor which is stretched on each of the two, and a breathable cap covers these elements and covers the base, the electrically insulating base holding the gas detection element and the compensation element is fixed through. The metal pins shall be thermally bonded.

Of the two metal pins each holding the gas detecting element and the compensating element, at least electrically common metal pins are connected by a metal rod so that they are thermally coupled. Good to be In the above gas sensor,
When connecting metal pins that are electrically common to each other with a metal rod, it is preferable that the metal rod and the metal pin to be connected have an inverted U-shape or an inverted J-shape to be thermally coupled.

Alternatively, when connecting electrically common metal pins to each other with a metal rod, it is preferable that the metal rod and the metal pin to be connected are U-shaped to be thermally coupled. Alternatively, when metal pins that are electrically common to each other are connected with a metal rod, it is preferable that the metal rod and the metal pin to be connected have an H-shape to be thermally coupled.

Further, it is preferable that the metal pin holding the gas detecting element and the compensating element be thermally coupled by a metal plate having an electrically insulating film on the surface. In addition, the metal pin that stretches the gas sensing element and the compensating element consists of two inverted U-shaped pins, and the two inverted U-shaped pins are partially cut to provide electrical insulation. In addition, it is preferable that the cut portion is filled with a material having a thermal conductivity higher than that of air and having electric insulation.

Further, the shape of the metal pin holding the gas detecting element and the compensating element is based on the metal pin rather than the distance between the metal pins in the portion where the gas detecting element and the compensating element are stretched. It is preferable that the metal pin is thermally coupled by shortening the distance of the portion through which is fixed. In addition, since the electrically insulating base fixing the metal pin holding the gas detecting element and the compensating element is made of a material having high heat conduction, the metal pin is thermally coupled. good.

In the above gas sensor, the electrically insulating base fixing the metal pin holding the gas detecting element and the compensating element is preferably a ceramic containing aluminum nitride as a main component. Further, it is preferable that the metal pins are thermally coupled by embedding a metal plate in the electrically insulating base fixing the metal pins holding the gas detecting element and the compensating element.

The metal pins may be thermally coupled by combining at least two methods out of the above means. According to the present invention, the gas sensing element and the compensating element are stretched, and the metal pin fixed through the electrically insulating base is in mutual contact with the pin itself or through another metal rod or The enhanced thermal coupling due to the close proximity of each other or the interposition of a high thermal conductivity base improves the heat transfer between the pins. As a result, the temperature difference between the metal pins is alleviated, so that the accuracy of the sensor output in the absence of combustible gas, that is, the zero point output, can be significantly improved compared to the conventional case. Further, for the same reason, it can be expected that the zero-point output fluctuation in the transient state is significantly reduced.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The contents of the present invention will be described below with reference to Examples. In the drawings of the following embodiments, a heat shield plate and a breathable cap provided to prevent thermal interference between the gas detection element and the compensation element are omitted for clarity. Example 1 In this example, among the metal pins holding the gas detecting element and the compensating element, electrically common pins were connected by a metal rod to enhance thermal coupling. In order to make it possible, it has an inverted U-shaped structure. This coupling is intended to reduce the temperature difference between the gas detection element and the compensation element.

FIG. 1 is a perspective view of a gas sensor according to an embodiment of the present invention. (A) shows a metal pin having an inverted U-shaped structure,
(b) is the case of the inverted J-shaped metal pin, (c) is the case of the U-shaped metal pin, and (d) is the case of the H-shaped metal pin. The pins are stainless steel (SUS) rods with a diameter of 1 mm.The U-shaped and J-shaped horizontal bars 23 are made by bending the rods, and the H-shaped horizontal bars 23 are made by welding a short SUS rod to each pin. did. Each shape may be punched out from a SUS plate. The other members were the same as those of the conventional gas sensor. As the material of the pins, other materials such as nickel silver and manganin can be used.

The zero point output, which is the result of thermal coupling of the produced gas sensor, was examined as follows. Fig. 2 is a schematic sectional view of a gas sensor attached to a jig for producing a temperature difference between pins. This jig is a SUS plate 8 with a hole slightly larger than the gas sensor S cap.
The cap of the gas sensor is inserted without touching it, and the base is held by the SUS metal fitting 9 having the same hole and the step of the thickness of the base, and it can be stopped with two screws N1 and N2. A temperature difference was applied to the SUS plate 8 so that there was a temperature difference (ΔTs) between the two screws, and the zero point fluctuation at that temperature difference was investigated.

FIG. 3 is a graph of the zero point output with respect to the temperature difference (ΔTs) of the screw according to the embodiment of the present invention. Straight line a is for an inverted U-shaped pin, straight line b is for an inverted J-shaped pin, straight line c is for a U-shaped pin, straight line d is for a J-shaped pin, and straight line e is Is the case of a conventional gas sensor. In the conventional gas sensor, if there was a temperature difference of 10 ° C between the screw mounting positions, a zero point output of 1 mV occurred. This is equivalent to 500 ppm when converted to CO gas concentration. However, in the gas sensor according to the present invention, the zero-point fluctuation due to the temperature difference of 10 ° C. is 0.5 mV for the inverted U-shaped and inverted J-shaped pins, which is half that of the conventional gas sensor. In addition, the H-shaped type has the smallest zero-point output, and the U-shaped pin whose thermal coupling part is far from the element and outside the base is considerably smaller than the conventional gas sensor.

The position of the horizontal bar for thermal coupling may be at the upper part of the base or inside the base, but the more effective effect was at the time of connection at the upper part of the base. From the above, it can be estimated that the combination of the H-shape and the inverted U-shape or the inverted J-shape further lowers the zero-point output. Example 2 In this example, thermal coupling was strengthened by fixing a metal plate provided with an electric insulating film to the head of the metal pin that stretches the gas detection element and the compensation element. Since the pins are isolated from each other, this structure can be applied between pins that are not equipotential. FIG. 4 is a perspective view of a gas sensor according to another embodiment of the present invention. (A) is a disk, (b) is a ring, (c) is a cross shape, and (d) is ) Is a cross-sectional view of these.

The metal plate 23a was a 1 mm thick SUS plate. The ring shape and the cross shape aim to improve the flow of gas around the element. From the viewpoint of thermal coupling, the thinner the electric insulating film 23i, the better. In this embodiment, a commercially available water glass diluted with tap water was applied to form a film having a thickness of about 5 μm. Water glass was applied again to the metal plate provided with the electrically insulating film 23i made of water glass, and thereby adhered to the metal pin. The electric insulating film 23i may be a silicon oxide film formed by sputtering or CVD.

It was confirmed that even with the gas sensor having such a structure, there is little fluctuation in the zero-point output as in the first embodiment. Third Embodiment FIG. 5 is a perspective view of a gas sensor according to another embodiment of the present invention. In this embodiment, the upper portions of the metal pins 2 and 3 on which the gas sensing element and the compensating element are stretched are bent horizontal rods, and the tips thereof are bonded with a material that has greater thermal conductivity than air and has electrical insulation. Then, as a general inverted U-shaped pin,
Strengthened the thermal bond. The number of this horizontal bar and the bonded portion is 23b. An electrically insulating film may be sandwiched to ensure a non-contact between the two pins. Since the pins are isolated from each other, this structure can be applied between pins that are not equipotential.

The tip of the pin is a bent horizontal bar, and the tip is
It was filled and bonded with an inorganic adhesive exhibiting sufficient properties by heat treatment at 120 ° C or high-concentration water glass. The narrower the distance between the two pin tips, the stronger the thermal coupling, and the greater the effect of suppressing the fluctuation of the zero-point output. A difference with the conventional structure was confirmed at an interval of 3 mm or less. Embodiment 4 FIG. 6 is a perspective view of a gas sensor of another embodiment according to the present invention.

In this embodiment, the pin spacing of the portion 23c penetrating the base of the metal pin 2 or the pin 3 which stretches the gas detecting element and the compensating element holds the gas detecting element and the compensating element. The thermal coupling was strengthened by making the pin spacing narrower than that of the part. The structure shown in FIG.
The effect of the present invention was remarkable when the distance was less than half of the metal pin in the portion holding the gas detecting element and the compensating element with respect to the distance in the portion penetrating the pin. Example 5 In this example, instead of changing the morphology of the pins, the base material was replaced by a material with higher thermal conductivity and electrical insulation to enhance the thermal coupling between the pins.

A base was made of aluminum nitride, and a gas sensor having the same size and structure as the conventional one was made. Example 1
When the variation of the zero-point output point was examined by the same method as that of Example 1, the zero-point variation was reduced to 0.4 mV in this example. Embodiment 6 FIG. 7 is a cross-sectional view of a gas sensor of another embodiment according to the present invention. (A) is a case where the metal plate is below the base, (b) is a case where the metal plate is above the base, and (c) is ) Is a plan view of these.

Instead of changing the form of the pin, a metal plate
By embedding a metal plate 23d between the pins of the base so that the pins 23d and the pins are not in contact with each other, thermal coupling between the gas detection element and the metal pin that stretches the compensating element is strengthened. The metal plate 23d was a 2 mm thick SUS plate. Others have the same structure as the conventional one. The manufactured gas sensor was used in Example 1.
When the variation of the zero-point output point was examined by the same method as in Example 1, the zero-point variation was reduced to 0.7 mV in this example.

FIG. 8 is a sectional view of a metal-based gas sensor. The limit of enlarging the above metal plate is that the base 1m itself is a metal plate, and the pin penetrates the hole opened there,
Make sure the pins are in the original base material (
The structure is fixed by high heat resistant resin) or low melting point glass. The code of the fixed part is 1c. It can be easily estimated that such a fluctuation of the zero output point of the gas sensor is small. Example 7 In this example, two of the above examples were combined to further enhance the thermal coupling between the metal pins that span the gas sensing element and the compensating element.

FIG. 9 is a perspective view of a gas sensor of another embodiment according to the present invention. A composite gas sensor was manufactured for the case of the inverted U-shaped pin in Example 1 and for the case of non-contact adhesion of the tip of the inverted U-shaped pin in Example 3. The horizontal bar portion 23 connects pins having the same electric potential, and the horizontal bar and the adhesive portion 23b connect pins having different electric potentials, respectively, to enhance thermal coupling.

When the variation of the zero point output point of the produced gas sensor was examined by the same method as in Example 1, the zero point variation was reduced to 0.2 mV in this example. This value corresponds to a low concentration of ± 100 ppm in terms of CO gas concentration conversion. This composite gas sensor was attached to the exhaust pipe of an actual water heater, and the transient response output from ignition of the water heater to the equilibrium state of the gas sensor was examined.

FIG. 10 is a graph of transient response output in the water heater of the combined gas sensor of this embodiment. For comparison, the graph also shows the transient response output of the conventional gas sensor. The horizontal axis is the time after ignition of the water heater, and the vertical axis is the carbon monoxide gas concentration converted from the zero point output. Curve f
Is a gas sensor of the present invention, and curve g is a curve of a conventional gas sensor.

From this figure, it is understood that the curve of the conventional gas sensor shows an apparently high carbon monoxide gas concentration due to the fluctuation of the zero-point output, but the gas sensor of the present invention does not add the apparent concentration. As described above, the effect of the present invention can be recognized also for the transient response. It can be easily estimated that the zero-point variation can be further reduced even in the case of other combination types.

[0035]

According to the present invention, the gas detecting element and the compensating element are stretched, and the metal pin is fixed through the electrically insulating base through the pin itself or another rod made of metal. The enhanced thermal coupling, either by mutual contact or close proximity to each other, or by interposition of a base of high thermal conductivity, improves heat transfer between the pins. As a result, the temperature difference between the metal pins is alleviated, so that the accuracy of the sensor output in the absence of combustible gas, that is, the zero point output, can be significantly improved compared to the conventional case. Further, for the same reason, the zero point output fluctuation in the transient state can be significantly reduced.

Therefore, the gas sensor of the present invention can be applied to a gas water heater or the like where the temperature changes rapidly. Further, in the present invention, since a special structure or the like is unnecessary, the cost hardly rises as compared with the conventional gas sensor.

[Brief description of the drawings]

FIG. 1 is a perspective view of a gas sensor according to an embodiment of the present invention,
(a) is an inverted U-shaped metal pin, (b) is an inverted J-shaped metal pin, (c) is a U-shaped metal pin,
(d) is for H-shaped metal pin

FIG. 2 is a schematic sectional view of a gas sensor attached to a jig for producing a temperature difference between pins.

FIG. 3 is a graph of a zero point output with respect to a temperature difference (ΔTs) of a screw according to an embodiment of the present invention.

FIG. 4 is a perspective view of a gas sensor according to another embodiment of the present invention, where (a) is a disc, (b) is a ring, and (c).
Is a cross shape, (d) is a cross-sectional view of these

FIG. 5 is a perspective view of a gas sensor according to another embodiment of the present invention.

FIG. 6 is a perspective view of a gas sensor according to another embodiment of the present invention.

FIG. 7 is a cross-sectional view of a gas sensor of another embodiment according to the present invention, (a) shows a case where the metal plate is at the bottom of the base, (b) shows a case where the metal plate is at the top of the base, and (c) shows these. Plan view

FIG. 8 is a sectional view of a metal-based gas sensor.

FIG. 9 is a perspective view of a gas sensor according to another embodiment of the present invention.

FIG. 10 is a graph of transient response output in a water heater with a composite gas sensor.

FIG. 11 is a perspective view of a conventional contact combustion type combustible gas sensor.

FIG. 12 is a bridge circuit diagram of a catalytic combustion type gas sensor.

FIG. 13 is a sectional view when a gas sensor is attached to an exhaust stack.

[Explanation of symbols]

 D Gas detector C Compensator 1 Base 2 Pin 2a Pin 3 Pin 3a Pin 23 Horizontal bar 23a Metal plate 23b Horizontal bar and adhesive 23c Horizontal bar and adhesive 23d Metal plate 4 Thermal shield 5 Cap R1 Resistance R2 Resistance E Power supply W load 6 Exhaust stack 7 Gas sensor mounting part 8 SUS plate 9 Holding jig N1 screw N2 screw

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumihiro Inoue 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (12)

[Claims] 1. A contact combustion type gas detecting element and a compensating element are respectively stretched on two adjacent two of four metal pins which are fixedly penetrated through an electrically insulating base to form a breathable cap. In the gas sensor that covers these elements and covers the base, it is confirmed that the metal pin that is fixed through the electrically insulating base holding the gas detection element and the compensation element is thermally coupled. Characteristic gas sensor. 2. The gas sensor according to claim 1, wherein among the two metal pins each holding the gas detecting element and the compensating element, at least electrically common metal pins are metal rods. A gas sensor characterized by being thermally coupled by being connected. 3. The gas sensor according to claim 2, wherein when metal pins that are electrically common to each other are connected by a metal rod, the metal rod and the metal pin to be connected have an inverted U shape or an inverted J shape. The gas sensor is characterized by being thermally coupled. 4. The gas sensor according to claim 2, wherein when the metal pins that are electrically common to each other are connected by a metal rod, the metal rod and the metal pin to be connected are thermally coupled in a U shape. A gas sensor characterized in that 5. The gas sensor according to claim 2, wherein when the metal pins that are electrically common to each other are connected by the metal rod, the connecting metal rod and the metal pin are thermally coupled in an H shape. A gas sensor characterized in that 6. The gas sensor according to claim 1, wherein the metal pin holding the gas detecting element and the compensating element are thermally coupled by a metal plate having an electrically insulating film on the surface thereof. Gas sensor to do. 7. The gas sensor according to claim 1, wherein the metal pin holding the gas detecting element and the compensating element comprises two inverted U-shaped pins, and a part of the two inverted U-shaped pins. A gas sensor having electrical insulation by being cut, and the cut portion being filled with a material having higher thermal conductivity than air and having electric insulation. 8. The gas sensor according to claim 1, wherein the shape of the metal pin holding the gas detecting element and the compensating element is a distance between the metal pins holding the gas detecting element and the compensating element. The gas sensor is characterized in that the metal pins are thermally coupled to each other by shortening the distance of the portion where the metal pins are fixed through the base. 9. The gas sensor according to claim 1, wherein the electrically insulating base fixing the metal pin holding the gas detecting element and the compensating element is made of a material having high heat conductivity. A gas sensor characterized in that metal pins are thermally coupled. 10. The gas sensor according to claim 8, wherein
A gas sensor characterized in that an electrically insulating base fixing a metal pin holding a gas detecting element and a compensating element is a ceramic containing aluminum nitride as a main component. 11. The gas sensor according to claim 8, wherein
A gas sensor characterized in that the metal pins are thermally coupled by embedding a metal plate in an electrically insulating base fixing the metal pins holding the gas detecting element and the compensating element. 12. The gas sensor according to claim 1, wherein
A gas sensor according to any one of claims 2 to 11, characterized by combining at least two methods.