JP3167568B2 - Contact combustion type gas sensor - Google Patents

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 for detecting incomplete combustion of city gas or oil, and more particularly to a catalytic combustion type gas sensor for high-temperature combustion gas.

[0002]

2. Description of the Related Art As an example of a conventional gas sensor, Fuji Times Vol. 50, No. 8, pages 427 to 431 (197)
7), there is known a gas sensor used in an alarm described in Fuji Higashi Vol. 54, No. 8, pages 554 to 557 (1981). This gas sensor is composed of two elements, for example, a gas detecting element having a structure in which a platinum coil is covered with aluminum oxide carrying a catalyst, and a compensating element which is inert to combustible gas. For gas detection, a bridge circuit in which these two elements and two fixed resistors are incorporated in each branch is used. FIG. 4 is a bridge circuit diagram of the contact combustion type gas sensor. Two fixed resistors R
1, the series connection of R2 and the series connection of the gas detection element D and the temperature compensation element C are connected in parallel, and the two elements are energized and preheated by applying a voltage from the power supply voltage E to the bridge circuit. When the combustible gas comes into contact with the gas detection element D, combustion occurs, causing a temperature change in the platinum coil and a change in electric resistance in proportion to the concentration of the combustible gas. Since the temperature compensating element does not burn even when the combustible gas comes into contact and does not cause a temperature change, the minute electric resistance change causes the connection between the connection point of the two fixed resistances and the connection point of the gas detection element and the temperature compensation element. The bridge output generated at the load V connected therebetween changes in proportion to the flammable gas concentration, and the flammable gas concentration can be detected. The bridge output when the combustible gas is not in contact is called zero point output.

In practice, 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. It is necessary to contact the gas sensor while it is at a high concentration before it is diluted by the outside air.
For this purpose, the gas sensor needs to be attached to the exhaust side of the combustion chamber or to the exhaust stack close to the combustion chamber (hereinafter, referred to as the gas sensor).
These are called exhaust stacks). In the exhaust stack, the ambient temperature of the sensor is still high (approximately 200 ° C), and the change of the 0-point output may be excessive or the sensitivity of the gas sensor may be reduced, making it impossible to reliably detect incomplete combustion. There is. As a countermeasure, a temperature measuring element is placed near the gas detecting element and the temperature compensating element, thereby detecting the ambient temperature, calculating its output, and compensating for fluctuations in the zero-point output of the gas sensor and sensitivity reduction. There is a method. FIGS. 5A and 5B show a conventional gas sensor of a gas permeable cap used in such a system, wherein FIG. 5A is a perspective view and FIG. 5B is a perspective view of the cap. Six metal pins 2 are fixed through the base 1, and a gas detection element D, a temperature compensation element C, and a temperature measurement element T are bonded to each of the two pins 2. These three elements are covered with caps 4 with holes. A heat shield plate 3 stands between the gas detection element D and the temperature compensation element C. The perforated cap 4 has several holes 5 for ventilation. This cap with holes is a measure to prevent the airflow from directly hitting the elements and the temperature of each element to fluctuate or become non-uniform when a sensor with a normal wire mesh cap is placed in a large wind speed. It is.

[0004]

However, in the conventional catalytic combustion type gas sensor, a voltage of several volts is constantly applied to the gas detecting element and the temperature compensating element and is maintained at several hundred degrees Celsius. Even when not in contact with the gas, the heat is transmitted to the temperature measuring element, and the temperature compensation signal is disturbed. Further, if the gas to be detected is in contact, the disturbance of the temperature compensation signal is further increased due to the heat of combustion, and the fluctuation of the bridge output is increased.

Further, since the heat transfer from the gas detecting element and the temperature compensating element also changes depending on the attitude of the element, that is, the attitude of the contact combustion type gas sensor, there is a problem that the temperature compensation signal fluctuates accordingly. The purpose of this invention is
An object of the present invention is to provide a contact combustion type gas sensor capable of accurately detecting incomplete combustion without affecting the bridge output due to the heat retained by the gas detection element and the temperature compensation element, the heat generated by gas detection, and the attitude of the gas sensor. .

[0006]

According to the present invention, there is provided a metal pin having a contact-combustion type gas detecting element, a temperature compensating element, and a temperature measuring element fixed through an electrically insulating base. In a contact combustion type gas sensor in which a heat shield plate is provided between the gas detection element and the temperature compensation element and these elements are covered with a permeable cap, the gas detection element and the temperature compensation element contained within breathable inner cap, the cap temperature measuring element is held on the outside, and further breathable outer cap is put on the outside, the inner cap with the gas detection element and the temperature compensation element It has a heat shielding function between the two elements and the temperature measuring element.

[0007]

In the catalytic combustion type gas sensor according to the present invention, the gas detecting element and the temperature compensating element are covered, and the inner cap between these elements and the temperature measuring element is provided between the gas detecting element and the temperature compensating element whose temperature is higher than the ambient temperature. Thermal radiation is shielded from the temperature measuring element. The inner cap receives the heat radiation of the two high-temperature elements and becomes slightly higher in temperature than the ambient temperature. The heat radiation is received by the temperature measurement element but its influence is small, so the temperature of the temperature measurement element is independent of the position of the contact combustion type gas sensor. The temperature is maintained at about ambient temperature. The outer cap also prevents direct contact of the outside air with the temperature measuring element, and prevents the temperature measuring element from outputting an excessive temperature correction signal in response to a sudden temperature change.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 shows a catalytic combustion type gas sensor according to the present invention,
2A is a plan view, and FIG. 2B is a cross-sectional view taken along line AA in FIG. Each of the gas detecting element D, the temperature compensating element C, and the temperature measuring element T is held by two metal pins 2a, 2b, and 2c fixed through the base 1 of the insulator.

In the gas detection element D, an alumina carrier was attached to a platinum coil, and palladium was carried on the carrier as an oxidation active catalyst. The temperature compensating element C was an element in which only an alumina carrier was attached to a platinum coil. As the temperature measuring element T, a well-known small platinum resistance temperature detector was used. Between the gas detection element D and the temperature compensation element C, a shielding plate 3a for shielding heat is provided. These are covered with an inner cap 4a and fixed to the base B. The temperature measuring element T and the metal pin 2c holding the temperature measuring element T are outside the inner cap 4a.
Is covered with a cap 4b and fixed to the base 1. The caps 4a and 4b are made of stainless steel, and a plurality of (12) holes having a diameter of, for example, 2.5 mm are formed in the cylindrical portion similarly to the conventional cap. No hole is formed in the circular portion of the inner cap 4a so that the temperature measuring element T is not affected by heat radiation from the gas detecting element D and the temperature compensating element C. In order to avoid the influence of the attitude of the gas sensor, it is desirable that the temperature measuring elements are arranged symmetrically with respect to the center axis of the base or the cap.

Next, the contact combustion type gas sensor of the present invention was connected to the branch of the bridge circuit, and the fluctuation of the zero point output with respect to the ambient temperature of 25 to 250 ° C. was examined. Ambient temperature is 25-25
0 ° C., and the power supply voltage of the bridge circuit was 1.6 V. FIG. 2 is a diagram showing the fluctuation of the zero-point output (based on an ambient temperature of 25 ° C.) depending on the ambient temperature of the catalytic combustion type gas sensor of the present invention. FIG. 2 also shows the characteristics of a conventional catalytic combustion type gas sensor for comparison. Curve a shows the characteristics of the catalytic combustion type gas sensor of this embodiment, and curve b shows the characteristics of the conventional catalytic combustion type gas sensor. It can be seen that the curve a has a small change, and the fluctuation of the zero point output is improved.

Further, the dependence of the contact combustion type gas sensor on the attitude was examined. FIG. 3A is a perspective view showing the attitude of the sensor, and FIG. 3B is a graph of the attitude dependency of the zero point output of the contact combustion type gas sensor. As for the posture of the contact combustion type gas sensor, + z indicates vertically upward, the base is down, the cap is up, the gas detection element is on the −x side, and the temperature compensation element is + x
Side, and the sign is + z. The other posture is, for example, a case where the symbol + y is tilted in the (+ z) + y direction. The reference value was in the + z direction. Line c corresponds to the catalytic combustion type gas sensor of the present invention, and line d corresponds to the conventional catalytic combustion type gas sensor. From FIG. 3, it can be seen that the zero-point output of the contact combustion type gas sensor of the present invention is not affected by the sensor attitude at all. Second Embodiment In the first embodiment, the cap is made of metal. However, it is effective to fill not only other materials but also a fibrous material into the cap as in the first embodiment. Table 1 shows four examples in which the effect was confirmed.

[0012]

[Table 1]

[0013]

According to the contact combustion type gas sensor of the present invention, the gas detecting element and the temperature compensating element are housed in one cap, and the temperature measuring element is held outside the cap.
Because another cap is put on the outside,
The temperature measuring element is not affected by the heat radiation of the gas detecting element and the temperature compensating element having a temperature higher than the ambient temperature and the flow of the outside air, and is not affected by the attitude of the contact combustion type gas sensor itself. Therefore, the contact combustion type gas sensor can be attached to the exhaust stack of the combustion device having a high temperature and a high flow velocity in any posture, and the incomplete combustion can be accurately detected. Further, since the temperature measuring element is placed outside the inner cap, the ambient temperature can be reached before the gas detecting element and the temperature compensating element inside the temperature measuring element, so that a temperature measuring element having a larger heat capacity than these two elements can be used. . Further, no special design is required for the shape of the exhaust stack of the combustion device in order to mount the contact combustion type gas sensor of the present invention.

[Brief description of the drawings]

FIG. 1 is a catalytic combustion type gas sensor according to the present invention,
(A) is a plan view, and (b) is a cross-sectional view taken along the line AA of FIG.

FIG. 2 is a diagram of a change in a zero point output (based on 25 ° C.) according to an ambient temperature of the contact combustion type gas sensor of the present invention.

FIGS. 3A and 3B show the sensor attitude dependency of the zero-point output of the contact combustion type gas sensor of the present invention. FIG. 3A is a perspective view showing the sensor attitude, and FIG. Graph of

FIG. 4 is a bridge circuit diagram of a catalytic combustion type gas sensor.

FIG. 5 is a conventional gas sensor of a cap with a hole,
(A) is a see-through perspective view, (b) is a perspective view of a cap.

[Explanation of symbols]

 Reference Signs List 1 base 2 pin 3 shielding plate 3a shielding plate 4 cap 4a inner cap 4b outer cap 5 hole D gas detection element C temperature compensation element T temperature measurement element R1 fixed resistance R2 fixed resistance V load E power supply

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Ishii 2-2-1 Nagasaka, Yokosuka City, Kanagawa Prefecture Inside Fuji Electric Research Institute, Inc. (72) Inventor Kazunari Kubota 2-2-1 Nagasaka, Yokosuka City, Kanagawa Prefecture No. Within Fuji Electric Research Institute, Inc. (72) Inventor Toshiaki Kato 2-2-1 Nagasaka, Yokosuka City, Kanagawa Prefecture Inside Fuji Electric Research Institute, Inc. (72) Koichi Tsuda 2-2-1 Nagasaka, Yokosuka City, Kanagawa Prefecture No. Fuji Electric Research Institute, Inc. (56) References JP-A-4-291141 (JP, A) JP-A-7-14369 (JP, U) JP-A-7-18256 (JP, U) JP-A-7 −29454 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/00-27/24 G01N 25/28-25/32

Claims (1)

(57) [Claims] 1. A gas detection element of a contact combustion type, a temperature compensation element, and a temperature measurement element are held by a metal pin fixedly penetrated to an electrically insulating base. In a contact combustion type gas sensor in which a heat shield plate is provided between these elements and a gas permeable cap is put on these elements, the gas detection element and the temperature compensation element are housed in a gas permeable inner cap. outside temperature measuring element is held in its and breathable outer cap is put on the further outward, the inner cap is heat-shielding function between the two elements and the temperature measuring element with the gas detection element and the temperature compensation element A catalytic combustion type gas sensor comprising: