JPH0933472A - Gas detector - Google Patents

Abstract

(57) [Summary] [Object] To provide a gas detection device capable of detecting the concentration of a gas in a higher temperature range of two kinds of gases in which the temperature ranges having sensitivity overlap each other without using an arithmetic circuit. [Structure] The gas detection element can oxidize two kinds of gas in which a part of the temperature range having an oxidizing ability overlaps, and the first gas detection element D1
And the temperature compensating element C1 are housed in the air-permeable inner cap 4, the second gas detecting element D2 and the inner cap 4 are housed in the air-permeable outer cap 5, and are integrated using one base 1. , The first gas detecting element and the temperature compensating element are incorporated in a bridge circuit, these two elements are kept in a higher temperature range, and the second gas detecting element is kept at a temperature lower than the temperature range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting combustible gas.

[0002]

2. Description of the Related Art As an example of a conventional gas detection device, there is a Fuji Jikki Vol. 50 No. 8 (1977) or a Fuji Jikki 54.
A gas detection device such as that used in the gas alarm device described in Vol. 8 (1981) is known. These gas detection devices consist of a gas detection element in which the platinum coil is covered with a carrier such as aluminum oxide carrying a catalyst such as palladium, and a similar configuration that does not support the catalyst and is inert to combustible gas. A bridge circuit composed of an element and two fixed resistors is used. Further, the gas detecting element and the compensating element are housed in one breathable cap, and
Often used as one gas sensor. FIG. 6 is a bridge circuit diagram of a conventional gas detection device. 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, the power source E is connected to both ends of the series connection, and the load V is connected to the intermediate connection point of each series connection. Has been done. When the combustible gas comes into contact with the gas detection element that is energized and heated by the power source E, combustion occurs, causing a temperature change in the platinum coil and an electric resistance change proportional to the gas concentration. In the temperature compensating element C, even if a combustible gas comes into contact with the temperature compensating element C, the temperature compensating element C does not burn and the electric resistance does not change. The difference in these electric resistance changes gives a bridge output that changes in proportion to the gas concentration to the load V, and the gas concentration can be detected.

FIG. 7 is a graph showing the temperature dependence of the sensitivity of a conventional gas detection device in the gas detection element. The catalyst of the gas detection element is platinum and palladium, and the temperature compensation element does not carry the catalyst. Curve g is the sensitivity to hydrogen and curve h is the sensitivity to carbon monoxide. The sensitivity to carbon monoxide occurs at about 110 ° C. (lower limit temperature) or higher, and the sensitivity to hydrogen occurs at about 50 ° C. or higher.

When two kinds of combustible gases having overlapping sensitive regions coexist, if the gas detection element temperature is set to the lower limit temperature of the high sensitive region, only the gas in the low sensitive region is detected. However, when the temperature is higher than that, only the sum of the sensitivities of both gases can be obtained, and the concentration of each gas cannot be identified. Therefore, the following method is used to identify the concentration of each gas.

In the case of one gas detection element, it is operated at two temperatures above the above lower limit temperature to obtain a bridge output corresponding to it, and a gas concentration is obtained directly from the bridge output at a low temperature, and at a high temperature. The bridge output extrapolated from the above gas concentration is subtracted from the bridge output of 1 to obtain another gas concentration. When two gas detection elements are used, each gas detection element is incorporated in two sets of bridge circuits, and each gas detection element is set to two temperatures that are above the lower limit temperature of the higher one. Each gas concentration can be obtained from the bridge output of the temperature gas detection element by performing the same calculation as in the former case.

[0006]

However, in these methods, the accuracy of the concentration of the gas whose sensitive region is high is determined by both the concentration of the gas whose sensitive region is low and the bridge output (or sensitivity) for both gases. In order to reflect the above-mentioned variation, there is a drawback that the variation becomes maximum twice, or the detection calculation circuit is complicated, resulting in high cost.

In view of the above-mentioned drawbacks, an object of the present invention is to use a gas detecting element using the same catalyst as the conventional one, without degrading the accuracy of gas detection, and without requiring an arithmetic circuit leading to cost increase. An object of the present invention is to provide a gas detection device capable of detecting the concentrations of two kinds of gas having overlapping sensitive areas, which could not be directly detected in the past.

[0008]

In order to achieve the above object, a gas detecting element and a temperature compensating element are connected in a bridge circuit.
In a gas detector that is built in two branches and connected to a load on the output side of this bridge circuit, it is possible to oxidize two kinds of combustible gas, and one kind of combustible gas is above the first lower limit temperature. Is composed of two gas detection elements and a temperature compensating element, which are oxidizable with, and can oxidize another combustible gas at a second lower limit temperature or higher higher than the first lower limit temperature,
The first gas detecting element and the temperature compensating element are housed in a gas permeable inner cap, the second gas detecting element and the inner cap are housed in a gas permeable outer cap, and are integrated by using a base. The first gas detection element and the temperature compensation element are incorporated in the bridge circuit, these two elements are maintained at a temperature equal to or higher than the second lower limit temperature, and the second gas detection element is set to the first lower limit temperature and the second lower limit. The temperature shall be maintained between the temperatures.

Another temperature compensating element is installed between the inner cap and the outer cap, and this temperature compensating element and the second gas detecting element are incorporated in another bridge circuit. Further, it is preferable that the gas detecting element is a platinum coil to which an alumina carrier carrying a catalyst made of palladium and platinum is attached, and the temperature compensating element is a platinum coil to which only the alumina carrier is attached.

The inner cap is preferably made of porous alumina. Further, it is preferable that the outer cap is made of an airtight material, a ventilation window is provided in a part of the outer cap, and the second gas detection element is installed facing the window.

[0011]

According to the present invention, it is possible to oxidize two kinds of combustible gas, one kind of combustible gas can be oxidized at the first lower limit temperature or more, and another one kind of combustible gas. It is composed of two gas sensing elements which can be oxidized at a temperature higher than the first lower limit temperature and higher than the second lower limit temperature, and a temperature compensating element. Pay
The second gas sensing element and the inner cap are housed in a breathable outer cap and integrated using one base,
A first gas detecting element and a temperature compensating element are incorporated in the bridge circuit, these two elements are held at a temperature equal to or higher than a second lower limit temperature, and the second gas detecting element is set to the first lower limit temperature and the second lower limit temperature. Since it was decided to keep the temperature between the lower limit temperature,
The following effects occur.

The atmosphere containing two kinds of combustible gas first comes into contact with the second gas detecting element held at a temperature between the first lower limit temperature and the second lower limit temperature, and the first lower limit temperature. All the flammable gas at the temperature burns, but the flammable gas at the second lower limit temperature does not burn. Thus, only the second lower limit flammable gas contacts the first gas sensing element in the inner cap, which is incorporated in the bridge circuit together with the temperature compensating element, and produces a bridge output (sensitivity). If there is a temperature compensating element between the same inner and outer caps as the second gas detecting element, these can be incorporated into another bridge circuit to detect the combustible gas having the first lower limit temperature.

The gas detecting element is a platinum coil to which an alumina carrier carrying a catalyst made of palladium and platinum is attached, and the temperature compensating element is a platinum coil to which only the alumina carrier is attached. The combustible gas having the lower limit temperature of 1 corresponds to carbon monoxide gas, and the combustible gas having the first lower temperature limit corresponds to hydrogen gas. Further, since the inner cap is made of porous alumina, the air permeability is smaller than that of the wire mesh cap which is usually used, the combustible gas of the first lower limit temperature is completely burned, and the combustible gas of the second lower limit temperature is Purity improves.

Since the outer cap is made of an airtight material, and a wire mesh is provided as a breathable window in a part of the outer cap, and the second gas detecting element is installed facing this window, all of the test gas is the second gas.
The combustible gas having the first lower limit temperature is completely combusted by touching the gas detecting element.

[0015]

【Example】

Example 1 In this example, an example of detecting CO gas generated by incomplete combustion will be described. When incomplete combustion of city gas or propane gas occurs, along with the generation of carbon monoxide gas,
Hydrogen gas is always generated. However, if the fuel composition and combustion conditions are different, the generation ratio of them also changes, so C
A means for detecting only O gas is required. Here, an example has been described in which the CO gas concentration can be measured using the conventional gas detection element and temperature compensation element.

FIG. 1 is a perspective view of a gas sensor according to an embodiment of the present invention. The gas detection elements D1 and D2 have a diameter of 6
It is formed by sintering an alumina carrier carrying palladium as a catalyst on a resistance temperature detector composed of a coil of 0 μm platinum wire. The temperature compensating element C1 has the same structure as the gas detecting element and does not carry a catalyst. The inner cap 4 is made of porous alumina and is breathable. The outer cap 5 is made of a stainless steel plate, and a part of the side surface of the cylinder is provided with a metal wire window 5w made of stainless steel for ventilation.

The gas detecting elements D1 and D2 and the temperature compensating element C1 are electrically connected and fixed to each two conductive pins 2 which are fixed through the base 1 made of an electric insulating material. A heat shield plate 3 is provided on the base 1 between the gas detection element D1 and the temperature compensation element C1. The inner cap 4 is put on the two elements and the heat shield plate 3 to cover the base 1
Stuck to. Further, the inner cap 4 and the gas detection element D2 are covered with the outer cap 5 and fixed to the base 1. The window 5w is faced close to the gas detection element D2 so that the test gas first hits the gas detection element D2.

Further, the gas detecting element D1 and the temperature compensating element C1 are incorporated in one bridge circuit, and the gas detecting element D2 is connected to another power source to form a gas detecting device. This bridge output is the output and sensitivity of the gas detector. For single CO gas and hydrogen gas,
Since the element temperature dependence of the sensitivity of this gas detector is as already shown in FIG. 7 (prior art), from this data, the application method to the case where two kinds of gas coexist is described below. explain. The gas detection element D1 and the temperature compensation element C1 inside the inner cap 4 are energized so that the temperature of the elements becomes 170 ° C. (the power supply voltage of the bridge is 0.8).
V), the output was measured. Outer cap 5 and inner cap 4
The temperature of the gas detection element D2 between is about 100 ℃
The current was applied so that (the applied voltage was 0.25 V).

As the gas to be detected, the concentration of a mixed gas of hydrogen gas 0.5 to CO gas 1 was changed, and the output of the gas detector was examined. FIG. 2 is an output graph with respect to the gas concentration of the gas detector of the embodiment according to the present invention. The horizontal axis is the concentration of each component gas. Curve a is for CO gas and curve b is for hydrogen gas. From FIG. 2, it can be seen that the output characteristics for CO gas have a good linear relationship, and the output for hydrogen gas is almost 0 even if the concentration increases.

As described above, the gas detector of this embodiment was able to separate the CO gas concentration from the mixed gas of CO gas and hydrogen gas very well and measure it with high accuracy. Example 2 Similar to Example 1, another example of gas concentration detection in an incomplete combustion gas in which hydrogen and carbon monoxide are mixed will be described.

Although two sets and four elements are used in this embodiment, the gas detection elements D1 and D2 and the two temperature compensation elements C1 and C2 are the same as those in the first embodiment. Also, the inner cap and the outer cap were made of the same material as in Example 1. FIG. 3 is a perspective view of a gas sensor according to another embodiment of the present invention. Eight pins 2 are provided on the base 11, and a gas detection element D1 and a temperature compensation element C1 are bonded to each of the two inner pins. A heat shield plate 31 is provided on the base between these two elements. An inner cap 41 is put on these two elements and the heat shield plate 31 and fixed to the base 11. Furthermore, the inner cap 41
The gas detection element D2 and the temperature compensation element C2 are covered with an outer cap 51 and fixed to the base 11.

Further, the gas detecting element D1 and the temperature compensating element C1, and the gas detecting element D2 and the temperature compensating element C2 are respectively incorporated into one bridge circuit to form a gas detecting device. In the same manner as in Example 1, the concentration of the mixed gas having a ratio of 0.5 hydrogen gas to 1 CO gas as the test gas was changed, and the output of the gas detection device was examined. At this time, the two bridge circuits were operated at the same time. The element temperature of the gas detection element D1 and the temperature compensation element C1 in the inner cap is maintained at 170 ° C. (power supply voltage is 0.8 V), and the element temperature of the gas detection element D2 and the temperature compensation element C2 sandwiched between the two caps is about The temperature was maintained at 100 ° C. (power supply voltage was 0.5 V) and only hydrogen gas was burned.

FIG. 4 is an output graph with respect to the gas concentration of the gas detecting element in the inner cap of the gas detecting apparatus according to another embodiment of the present invention. The horizontal axis is the concentration of each component gas.
Curve c is the output for CO gas and curve d is the output for hydrogen gas. It can be seen from FIG. 4 that the output characteristics for CO gas have a good linear relationship, and the output for hydrogen gas is almost zero even if the concentration increases.

FIG. 5 is an output graph with respect to the gas concentration of the gas detecting element in the outer cap of the gas detecting apparatus according to another embodiment of the present invention. The horizontal axis is the concentration of each component gas.
Curve e is the output for CO gas and curve f is the output for hydrogen gas. It can be seen from FIG. 5 that the output characteristics for hydrogen gas have a good linear relationship, and the output for CO gas is almost 0 even if the concentration increases.

From the above, it was found that the present embodiment can independently and accurately detect the concentration of each component gas even in a mixed gas of hydrogen gas and CO gas.

[0026]

According to the present invention, two kinds of combustible gases can be oxidized, one kind of combustible gas can be oxidized at the first lower limit temperature or more, and another kind of combustible gas. Is composed of two gas sensing elements which can be oxidized at a temperature higher than the first lower limit temperature and higher than the second lower limit temperature, and a temperature compensating element. The second gas sensing element and the inner cap are housed in a breathable outer cap, and are integrated by using a base, and the first gas sensing element and the temperature compensation element are incorporated into the bridge circuit. The two elements are maintained at a temperature equal to or higher than the second lower limit temperature, and the second gas detection element is set to the first lower limit temperature and the second lower temperature limit.
Since the temperature is kept between the lower limit temperature of the first lower limit temperature, first, the combustible gas of the first lower limit temperature is burned by the second gas detection element, and only the combustible gas of the second lower limit temperature is inside. It enters the cap and produces a bridge output (sensitivity). That is, the combustible gas having the first lower limit temperature can be detected regardless of the presence of the combustible gas having the first lower limit temperature.
Therefore, a power supply for two temperatures and an arithmetic circuit are unnecessary.

If a temperature compensating element is provided between the inner and outer caps, which are the same as the second gas detecting element, these elements can be incorporated in another bridge circuit to detect the flammable gas having the first lower limit temperature. Since the gas detecting element is a platinum coil to which an alumina carrier carrying a catalyst composed of palladium and platinum is attached, and the temperature compensating element is a platinum coil to which only the alumina carrier is attached, the two types of gas are Carbon monoxide gas and hydrogen gas, for example, gas leak detection of city gas and incomplete combustion detection can be distinguished.

Also, since the inner cap is made of porous alumina, or the outer cap is made of an airtight material,
Since a wire mesh was provided as a breathable window in a part of the window and the second gas detection element was installed facing this window, the combustible gas of the first lower limit temperature was completely burned, and the second gas detection element was installed. Highly accurate detection of flammable gas at the lower limit temperature.

[Brief description of the drawings]

FIG. 1 is a perspective view of a gas sensor according to an embodiment of the present invention.

FIG. 2 is an output graph with respect to a gas concentration of a gas detection device according to an embodiment of the present invention.

FIG. 3 is a perspective view of a gas sensor according to another embodiment of the present invention.

FIG. 4 is an output graph with respect to a gas concentration of a gas detection element in an inner cap of a gas detection device according to another embodiment of the present invention.

FIG. 5 is an output graph with respect to a gas concentration of a gas detection element in an outer cap of a gas detection device according to another embodiment of the present invention.

FIG. 6 is a bridge circuit connection diagram of the gas detection device.

FIG. 7: Element temperature dependence of sensitivity of conventional gas detector

[Explanation of symbols]

 D gas detection element D1 gas detection element D2 gas detection element C temperature compensation element C1 temperature compensation element C2 temperature compensation element R1 resistance R2 resistance E power supply V load 1 base 11 base 2 pin 3 heat shield plate 4 inner cap 5 outer cap 5w window

Claims (5)

[Claims] 1. A gas detection device in which a gas detection element and a temperature compensation element are incorporated in two branch sides of a bridge circuit, and a load is connected to the output side of the bridge circuit, and two flammable gases are oxidized. Yes, one kind of combustible gas can be oxidized at a first lower limit temperature or higher, and another kind of combustible gas can be oxidized at a second lower limit temperature or higher higher than the first lower limit temperature. It is composed of two gas detecting elements and a temperature compensating element, the first gas detecting element and the temperature compensating element are housed in a gas permeable inner cap, and the second gas detecting element and the inner cap are gas permeable outside. The first gas detecting element and the temperature compensating element are integrated into the cap circuit by accommodating them in the cap, incorporating the first gas detecting element and the temperature compensating element into the bridge circuit, and keeping these two elements at a temperature equal to or higher than the second lower limit temperature. Set the sensing element to the first lower limit temperature Gas detecting apparatus characterized by holding at a temperature between 2 lower temperature limit. 2. The gas detection device according to claim 1,
A gas detecting apparatus, wherein another temperature compensating element is installed between the inner cap and the outer cap, and the temperature compensating element and the second gas detecting element are incorporated in another bridge circuit. 3. The gas detection device according to claim 1, wherein the gas detection element is a platinum coil to which an alumina carrier carrying a catalyst made of palladium and platinum is attached, and the temperature compensation element is platinum. A gas detection device characterized in that only an alumina carrier is attached to a coil. 4. The gas detecting device according to claim 1, wherein the inner cap is made of porous alumina. 5. The gas detection device according to claim 1, wherein the outer cap is made of an airtight material, a part of which is provided with a breathable window, and the second gas detection surface faces the window. A gas detector characterized in that the element is installed.