JP2000046775A - Contact combustion type gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a change of so-called a zero-point output of a contact combustion type gas sensor irrespective of the state or a mounting method. SOLUTION: A board of the contact combustion type gas sensor having a temperature compensating element C and a gas sensing element D fixed via pins P1 to P4 disposed through the board is constituted of a portion made of a metal having a large thermal conductivity such as an SUS or the like as shown in (a)-(c), and a portion B made of an insulating material. As shown in Fig. (d), the board is constituted of only the metal having a large thermal conductivity such as the SUS, and hence a temperature of the board is made uniform, thereby reducing a change of a zero-point output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to city gas, LP
The present invention relates to a gas sensor that is incorporated in a combustion appliance such as a water heater using a fuel such as gas or kerosene and detects carbon monoxide (CO) or hydrogen generated during incomplete combustion to prevent incomplete combustion.

[0002]

2. Description of the Related Art As a conventional example of this kind, for example, "Fuji Times", Vol. 50, No. 8, pp. 427-431 (197)
7), or a contact combustion type gas sensor used in an alarm device described in, for example, "Fuji Toho", Vol. 54, No. 8, pp. 554-557 (1981). This type of gas sensor is, for example, a gas detection element in which a porous ceramic is attached to a metal coil and a catalyst that oxidizes and combusts a combustible gas is carried, and a catalyst that does not carry a catalyst or carries a catalyst different from the oxidation catalyst. The temperature compensation element is arranged on the same substrate.

FIG. 5 is a perspective view showing this type of catalytic combustion type gas sensor. For example, P1 and P2 of pins fixed through the insulating material base B have gas sensing elements D
However, the temperature compensation element C is supported on P3 and P4, respectively. A heat shielding plate T is set up between these two elements C and D, and a permeable cap K is covered. For gas detection, a bridge circuit in which these two elements and a fixed resistor are incorporated in each branch is used. FIG.
An example is shown below. That is, the two fixed resistors R1 and R2
And a series circuit of the gas detection element D and the temperature compensation element C are connected in parallel, and when the power supply voltage E is applied, the two elements are energized and preheated.

Here, when a combustible gas comes into contact with the gas detecting element D, combustion takes place, causing a temperature change in the platinum coil, and a change in electric resistance proportional to the concentration of the combustible gas.
On the other hand, in the temperature compensating element C, even if the combustible gas comes in contact, the combustible gas does not burn, so that the temperature does not change. Therefore, the connection point of the two fixed resistors R1 and R2 is
Since the bridge output generated at the load Vb connected between the connection point of the gas detection element D and the temperature compensation element C changes in proportion to the flammable gas concentration, the flammable gas concentration can be detected. . The bridge output when the combustible gas is not in contact is called the zero point output, and the zero point output is added to the bridge output when the combustible gas is in contact. Is preferably smaller.

In fact, in order to quickly detect incomplete combustion of a combustion device such as a gas water heater or an oil fan heater, incomplete combustion components (mainly carbon monoxide gas) in the combustion gas of these devices are It is advisable to contact the contact combustion type gas sensor while the concentration is high before being diluted by the outside air,
The contact combustion type gas sensor is attached to the exhaust side of the combustion chamber or to an exhaust stack close to the combustion chamber. FIG. 7 shows an example in which a contact combustion type gas sensor is attached to an exhaust pipe.
A indicates a gas sensor mounting box, and M indicates an exhaust pipe.
In such a case, exhaust gas (also called detection gas) is generally used
Is heated to 100 ° C. or more, and depending on the model, it is exposed to a detection gas at a speed of several meters per second due to forced exhaust by a fan.

[0006]

The sensor mounting box installed in the exhaust stack has a delicate temperature distribution depending on the flow of the high-temperature exhaust gas, and an electric connection is established between the pins holding the gas detecting element and the temperature compensating element. Because the substrate is made of plastic that is insulative and has low thermal conductivity, a temperature difference occurs between the pins. Reflecting this, there is a difference between the coil temperatures of the two elements, which causes the zero point output to fluctuate. For the reasons mentioned above,
Since the magnitude of the zero-point output fluctuation also changes depending on the mounting direction of the contact combustion type gas sensor, erroneous mounting causes a zero-point fluctuation outside the allowable range. Therefore, one of the requirements is that there is no change in the zero point output even if this mounting is erroneous.

The present inventors have proposed a method of providing an inexpensive gas sensor by employing a special gas sensor cap so that the output of the sensor does not fluctuate even when hot air reaching several meters per second directly hits the gas sensor. The Japanese Patent Application 6-1
No. 83838, taking measures against hot air. Conventionally, the fluctuation of the zero point output and the allowable range have been considered. However, awareness of intrinsic safety has been increasing, and the demand for gas sensors for detecting incomplete combustion has also become more stringent. For example, the conventional requirement for zero point output is 0 ppm ± 500 ppm in terms of CO gas concentration.
Has been required to be twice as accurate as 0 ppm ± 250 ppm. For such a demand for high accuracy, there is a problem that a temperature difference between the gas detection element and the temperature compensation element due to heat transmitted through the sensor mounting box cannot be ignored.

Actually, when the water heater is ignited, the temperature of the exhaust gas rises sharply, and accordingly, the temperature of the gas sensor mounting portion also rises sharply. At this time, a subtle temperature distribution different from the equilibrium state is formed in the process of increasing the temperature in the gas sensor mounting portion, and as a result, an apparent transient output larger than the actual carbon monoxide gas concentration occurs. is there. Therefore, an object of the present invention is to reduce the temperature difference between the pins supporting the gas sensing element and the temperature compensating element even in a state where high-speed hot air is flowing, so that not only the equilibrium state but also the transient state and the mounting Irrespective of the above, it is to reduce the zero point output fluctuation.

[0009]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, there is provided a gas detecting element in which a porous ceramic is attached to a metal coil and a catalyst for oxidizing and burning a combustible gas is carried. And a temperature compensation element not carrying a catalyst or carrying a catalyst different from the oxidation catalyst, respectively, in a contact combustion type gas sensor in which the temperature compensation element is fixed through pins arranged through the substrate. It is composed of a portion made of a metal material having high conductivity and a portion made of an insulating material, and electrically insulates the pins and the substrate from each other.

In the first aspect of the present invention, a portion made of a metal material can be formed on the portion made of the insulating material (the second aspect of the invention), or a portion made of a metal material can be formed below the portion made of the insulating material. A portion made of a metal material can be formed on the substrate (the invention of claim 3), or a portion made of a metal material can be formed between the portions made of the insulating material (the invention of claim 4).

According to the fifth aspect of the present invention, the gas detecting element in which the porous ceramic is adhered to the metal coil and the catalyst for oxidizing and burning the combustible gas is carried, and the gas detecting element does not carry the catalyst or is different from the oxidation catalyst In a contact combustion type gas sensor in which a temperature compensation element carrying a catalyst is fixed via pins disposed through the substrate, the substrate is formed from a metal material having a large thermal conductivity, and the pin and the substrate are Are electrically insulated from each other.
In the first to fifth aspects of the present invention, the metal material may be austenitic stainless steel or copper (the sixth aspect of the invention).

[0012]

1 (a) to 1 (d) show an embodiment of the present invention. This is for explaining the structure of the substrate for fixing the pins, and a heat shield plate for preventing thermal interference is not shown here. FIG. 1 (e)
Indicates a conventional structure. That is, FIG. 1A shows a structure in which an austenitic stainless steel (SUS) metal plate is provided on an electric insulating material B (a metal upper type). At this time, it is necessary to insulate between the pins P1 to P4 and SUS. By doing so, the uniformity of the temperature inside the substrate is improved, and the temperature difference between the gas detection element and the temperature compensation element is reduced.

The example shown in FIG. 1A in which the uniformity of the temperature in the substrate is improved and the temperature difference between the gas detecting element and the temperature compensating element is reduced is deformed as shown in FIGS. It is possible. That is, FIG. 1B shows a structure in which a SUS metal plate is provided below the electric insulating material B (lower metal type), and FIG. 1C shows that the SUS metal plate is embedded between the electric insulating materials B. FIG. 1D shows a structure in which the entire substrate is a SUS metal plate (metal base type).
In these examples, a Cu metal plate can be used instead of a SUS metal plate. Also, the pin P1
Since P4 penetrates the substrate, it is needless to say that it is necessary to insulate the pin and the metal material in any case.

In FIG. 2, a temperature difference (Δ) is applied to the mounting screw portions N1 and N2 of the gas sensor S using a jig as shown in FIG.
An example of the result of examining the zero point fluctuation at that time with T) is shown. In the conventional structure shown in FIG. 1 (e), when there is a temperature difference of 10 ° C. in the mounting screw portion of the gas sensor, the zero point fluctuation of 1 mV is shown as shown by a circle in FIG.
With the structure as shown in FIG. 1A, the zero point fluctuation due to the temperature difference of 10 ° C. is 0.5 mV as shown by the mark Δ, and FIG.
In the case of (b), 0.8 mV as shown by a square in FIG. 2, and in the case of FIG. 1 (c), 0.65 m as shown by a circle in FIG.
V, in the case of FIG. 1 (d), 0.2
mV, which means that the respective values are reduced with respect to the conventional structure. Note that the mark Δ represents an example in which the substrate is made of Cu instead of SUS in FIG. 1A, and the zero point variation is 0.35 mV.

FIG. 4 shows an example of the result of examining the transient response output from when the gas sensor as described above is attached to the exhaust pipe of the water heater and when the gas sensor is brought into an equilibrium state after the water heater is ignited. In each case, the transient response output is lower than that of the conventional example, and it can be seen that the output is good.

[0016]

According to the present invention, since a metal material having a high thermal conductivity is used for a part or the whole of the substrate, even if a temperature difference occurs in the gas sensor mounting portion, this can be reduced. As a result, there is an advantage that a gas sensor with little zero point output fluctuation can be provided. Another advantage is that the cost is reduced because the structure is simple.

[Brief description of the drawings]

FIG. 1 is a perspective view for describing an embodiment of the present invention.

FIG. 2 is a graph showing a zero point output example of a conventional example and that of the present invention.

FIG. 3 is an explanatory view showing a mode of attaching a gas sensor to a jig.

FIG. 4 is a graph showing a transient response output when a gas sensor is attached to a water heater.

FIG. 5 is a perspective view showing a conventional example.

FIG. 6 is a bridge circuit showing a contact combustion type gas sensor.

FIG. 7 is an explanatory view of a mode of attaching a gas sensor to an exhaust pipe.

[Explanation of symbols]

A: gas sensor mounting box, B: base, C: temperature compensation element, D: gas detection element, E: power supply, K: cap, M: exhaust cylinder, MP: metal plate, N1, N2: mounting screws, P1 to P4 ... Pin, R1, R4 ... Resistance, S ... Gas sensor, T ... Heat shield plate, TL ... Low temperature part, TH ... High temperature part,
W: Exhaust flow.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tokumi Nagase 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in Fuji Electric Co., Ltd. (Reference) 2G060 AA02 AE19 AF07 AG03 BA03 BB05 BD02 HC02

Claims (6)

[Claims] 1. A gas detection element carrying a catalyst for oxidizing and burning a combustible gas by attaching porous ceramic to a metal coil, and a temperature at which a catalyst is not carried or a catalyst different from the oxidation catalyst is carried. In a contact combustion type gas sensor in which a compensating element and a fixing element are respectively fixed via pins arranged through the substrate, a portion made of a metal material having a large thermal conductivity,
A contact combustion type gas sensor comprising: a portion made of an insulating material; and wherein the pin and the substrate are electrically insulated from each other. 2. The catalytic combustion type gas sensor according to claim 1, wherein a portion made of a metal material is formed on the portion made of the insulating material. 3. The catalytic combustion type gas sensor according to claim 1, wherein a portion made of a metal material is formed below the portion made of the insulating material. 4. The catalytic combustion type gas sensor according to claim 1, wherein a portion made of a metal material is formed between the portions made of the insulating material. 5. A gas detection element having a porous ceramic attached to a metal coil and carrying a catalyst for oxidizing and burning a combustible gas, and a temperature at which a catalyst is not carried or a catalyst different from the oxidation catalyst is carried. In a contact combustion type gas sensor in which a compensating element and a compensating element are respectively fixed via pins disposed through the substrate, the substrate is formed from a metal material having a high thermal conductivity, and the pin and the substrate are electrically connected to each other. A contact combustion type gas sensor characterized by being insulated from a gas. 6. The catalytic combustion gas sensor according to claim 1, wherein the metal material is austenitic stainless steel or copper.