JPH09222406A - Method and apparatus for detection of gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique by which the concentration of a gas at a prescribed value or higher can be measured quickly and accurately while an apparatus is being operated at small electric power. SOLUTION: In a gas detection method, the concentration of a gas, to be detected, at a prescribed concentration or higher is detected by using gas detection elements which are built in the inside. Out of hot wire-type semiconductor gas detection elements forming a gas detection part 4 which covers a noble metal wire coil 3 and which uses a metal oxide semiconductor as a metal material, a first gas detection element 1 which is operated at room temperature and which can detect the gas and a second gas detection element 2 which is operated at a high temperature and which can detect the concentration of the gas are used. When the first gas detection element 1 displays an output at a prescribed value (a) or higher on the basis of the detection of the gas to be detected, the concentration of the gas to be detected is measured by the second gas detection element 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring the concentration of a gas to be detected having a predetermined concentration or higher by using a gas detection element incorporated therein.

[0002]

2. Description of the Related Art Conventionally, in order to measure the concentration of gas in an atmosphere, a gas detection device incorporating a gas detection element capable of measuring gas concentration at a high temperature operation is provided, and its output is constantly monitored and its output is measured. It was configured to measure the gas concentration. That is, in general, a hot-wire semiconductor gas detection element capable of measuring gas concentration has to operate at high temperature in order to obtain gas selectivity and to obtain an output of concentration information based on the gas detection. For example, when monitoring the carbon monoxide concentration using the gas detection element, there is a fact that the gas detection device provided with the gas detection element must be operated at all times. In order to operate the gas detection element at a high temperature, Joule heat is usually generated by energizing a noble metal wire coil or the like provided in the gas detection element, and the gas detection element is operated while being maintained at a high temperature. Was there.

[0003]

However, according to the above-mentioned conventional technique, if the gas detecting device is constantly operated at a high temperature, a large amount of electric power is required to maintain the gas detecting element at a high temperature. Since there is a need to supply power from an outlet, a gas detection device that can operate with a small amount of power has been desired. Therefore, it has been considered to detect gas using a gas detection element that can detect gas with low power, but such a gas detection element has a slow response until an output is obtained for gas, For a gas having a relatively low concentration, it takes about 15 minutes to obtain a stable output, which makes it difficult to detect the gas quickly.

In view of the above-mentioned drawbacks, an object of the present invention is to provide a gas detection device capable of quickly and accurately measuring the gas concentration exceeding a predetermined amount while operating with a small electric power.

[0005]

[Means for Solving the Problems]

[Structure 1] The characteristic means of the gas detection method of the present invention for achieving this object is to measure the concentration of a gas to be detected at a predetermined concentration or more by using a gas detection element incorporated therein. Among the hot-wire semiconductor type gas detection elements that cover the coil and form the gas sensitive part consisting mainly of metal oxide semiconductor, the first gas detection element that can detect gas at normal temperature operation and the gas concentration at high temperature operation Using a measurable second gas detection element, when the first gas detection element shows an output of a predetermined value or more based on detecting the detection gas, the detection gas by the second gas detection element Is to measure the concentration of.

[Operation and Effect] That is, since the hot wire semiconductor type gas detection element is a gas detection element which can obtain high gas selectivity by being formed with a small diameter, a small electric power is required when an electric current is applied to obtain an output. It can work. Further, when the concentration of carbon monoxide gas existing in the atmosphere is low and it is not usually necessary to measure the concentration of carbon monoxide gas,
Since only the first gas detection element capable of detecting gas at room temperature needs to be operated, a small amount of electric power can be used for most of the period in which gas detection is required. By the way, the first gas detection element requires a long time until a stable output is obtained in order to accurately measure the gas concentration, but it is also possible to grasp a rough gas concentration in a short time. Therefore,
When the gas concentration is high in the first gas detection element, or when an output that can be determined to reach a dangerous concentration is obtained, the second gas detection element is activated to measure an accurate gas concentration. As a result, it was possible to suppress the gas concentration measurement with the gas detection element maintained at a high temperature to the necessary minimum, and to reduce the power consumption.

[Structure 2] Further, a characteristic structure of the gas detecting device of the present invention is that a noble metal wire is used in a gas detecting device for measuring a concentration of a gas to be detected which is equal to or higher than a predetermined concentration by using a gas detecting element incorporated therein. Among the hot-wire semiconductor type gas detection elements that cover the coil and form the gas sensitive part consisting mainly of metal oxide semiconductor, the first gas detection element that can detect gas at normal temperature operation and the gas concentration at high temperature operation A switch that is provided with a measurable second gas detection element, and is capable of selectively switching the operation between detection of the detection gas by the first gas detection element and detection of the detection gas by the second gas detection element. A mechanism is provided, and when the output based on the detection of the gas to be detected by the first gas detection element exceeds a predetermined value, the detection of the gas to be detected by the first gas detection element is detected by the second gas detection element. Of detection gas When the output based on the detected gas detection of the second gas detection element is less than a predetermined value, the detection of the detected gas by the second gas detection element is detected by the first gas detection element. There is provided a control mechanism for switching the switching mechanism to switch to gas detection. Preferably, the first gas detection element has a tin oxide semiconductor containing at least one metal selected from palladium, platinum and gold. Any gas having a gas sensitive portion formed by adding at least 05 mol% but not more than 5 mol% may be used, and the second gas detecting element is a gas formed by adding lead, lanthanum and palladium to a tin oxide semiconductor. 0.045mo at least one metal of palladium, platinum and gold is added to a tin oxide semiconductor or a tin oxide semiconductor.
It is more preferable if it has a gas sensitive portion formed by adding 1% or less. [Effects] That is, in performing the above gas detection method, the first and second gas detection elements can be selectively used, and a gas detection device capable of performing gas detection operation with low power can be provided. . As a result, the power consumption of the gas detector as a whole can be set to an extremely low level,
For example, the gas detector can be made smaller, and the wiring from the power source can be eliminated by allowing it to operate with dry batteries, etc., and the gas detector can be ported or installed depending on the location of the outlet, etc. It is possible to greatly improve the usability of the gas detection device by eliminating the restrictions on the position.

Incidentally, as a technique for constantly monitoring the gas concentration in this way, carbon monoxide gas detection can be cited as an example. As a gas detection element for carbon monoxide gas detection, the first The gas detecting element may be any one having a gas sensitive portion formed by adding at least one metal of palladium, platinum and gold to a tin oxide semiconductor in an amount of 0.05 mol% or more and 5 mol% or less. Since the gas detection element has a high carbon monoxide gas selectivity at room temperature, it can efficiently detect only carbon monoxide gas even at room temperature operation, and even if it is a rough gas concentration,
Accurate gas detection is possible in the sense that it is not affected by other gases. The second gas sensing element has a gas sensitive portion formed by adding lead, lanthanum, or palladium to a tin oxide semiconductor, or at least one metal of palladium, platinum, and gold to a tin oxide semiconductor. If it has a gas sensitive part formed by adding 0.045 mol% or less, it has a high carbon monoxide gas selectivity and can detect carbon monoxide gas at high temperature quickly and accurately.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the gas detection device of the present invention incorporates first and second gas detection elements 1 and 2. As the first gas detection element 1, about 20 μm
A noble metal wire coil (platinum wire coil) 3 having a large diameter is covered with a tin oxide semiconductor having a diameter of 0.5 mm to form a gas sensitive portion 4. Palladium is added to the gas sensitive portion 4 in an amount of 0.05 to 5
Using a hot wire type semiconductor gas detection element having a normal temperature operation type and carbon monoxide gas selectivity to which mol% is added, similarly, as the second gas detection element 2, a platinum oxide coil 3 is covered with a tin oxide semiconductor. Of the gas sensitive portion 4 is formed using as a main material, and palladium is added to the gas sensitive portion 4 in an amount of 0.005 to 0.
A high temperature actuation type carbon monoxide gas-selective hot-wire semiconductor type gas sensing element to which 0.5 mol% and 0.5 to 5 mol% of lanthanum and 0.05 to 0.5 mol% of lead were added ( (Refer to FIG. 2), the gas can be freely detected. As shown in FIG. 1, the first and second gas detection elements 1 and 2 are connected to a detection circuit section 5 that incorporates a bridge circuit or the like and detects an output based on each element,
A circuit switching unit 6 is provided as a switching mechanism for switching which of the first and second gas detection elements 1 and 2 is connected to the detection circuit unit 5, and a power supply from a power source and the circuit switching are provided. The switching operation of the unit 6 is
A switching control unit 7 that controls switching based on outputs from the second gas detection elements 1 and 2 is provided, and the detection circuit unit 5 is provided.
On the basis of the output detected in (1), an alarm device 8 for generating an alarm sound when a gas concentration exceeding a predetermined value is detected is connected to form a gas detection device as a whole.

In the first gas detecting element 1, the resistance value of the first gas detecting element 1 changes corresponding to the carbon monoxide gas concentration due to adsorption of carbon monoxide gas at normal temperature. ing. Therefore, by repeating the operation of energizing for 1 millisecond for 10 seconds, it is possible to prevent the first gas sensing element from generating heat and obtain an output based on a change in the resistance value of the first gas sensing element 1, The concentration of carbon monoxide gas in contact with the first gas detection element 1 can be measured. In addition, such a first gas detection element 1
For 1 hour to perform the purging operation by exposing it to a high temperature of about 450 ° C.
By performing the operation at a rate of several seconds per several hours, stable operation can be performed for a long period of time.

When the carbon monoxide gas concentration information measured by the first gas detection element 1 reaches, for example, 60% or more of the saturated output of carbon monoxide gas of 50 ppm, When the energization is started, the second gas detection element 2 is controlled to a predetermined temperature by the Joule heat of the platinum wire coil 3, and the carbon monoxide gas is adsorbed,
The resistance value of the second gas detection element 2 changes according to the carbon monoxide gas concentration. Therefore, for example, if the output value after a predetermined time has passed from the start of energization, the carbon monoxide gas concentration can be quickly and accurately measured from the output.

When the output value based on the change in the resistance value of the second gas detection element 2 is less than a predetermined value, the switching control section 7 controls the detection circuit section 5 to change the detection circuit section 5 to the first gas detection element 1. In contrast to the above, the power supply is intermittently controlled, and when the output value based on the change in the resistance value of the first gas detection element 1 reaches a predetermined value, the detection circuit unit 5 is
The circuit switching unit 6 is switch-controlled and the power supply is controlled so that power is supplied to the second gas detection element 2 and the second gas detection element 2 can be maintained at a set temperature. The switch control mechanism is configured to operate.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

[Gas Sensing Element] An antimony chloride is added in a predetermined ratio to an aqueous solution of tin chloride having a predetermined concentration for adjustment. Aqueous ammonia is added dropwise to this aqueous solution to obtain a tin hydroxide precipitate. After washing the precipitate with water and drying, 650 ° C
And baked for 2 hours to obtain tin oxide. The tin oxide is pulverized into a fine powder and kneaded with water to obtain a tin oxide paste.

The tin oxide paste is applied so as to cover the periphery of the platinum coil 3, dried and fired at 600 ° C. for 1 hour to cover the platinum coil and provide the gas sensitive portion 4. Next, an aqueous palladium chloride solution is prepared in advance, and the aqueous palladium chloride solution is impregnated into the gas sensitive part 4 so that the amount of palladium with respect to the tin oxide is 0.05 to 5 mol%, and after this is dried, It heats at 600 degreeC for 1 hour, and a 1st gas detection element is obtained.

As shown in FIG. 3, the first gas detecting element 1 was found to have a high carbon monoxide gas selectivity with respect to hydrogen gas at room temperature. When the gas responsiveness is examined, it becomes as shown in FIG.
An accurate output can be obtained in about 15 minutes even with carbon monoxide gas of 50 ppm, but an output value of about 60% or more of the saturated output can be obtained in about 3 minutes, so that it can be obtained at room temperature in a short time. It can be seen that it is useful for grasping the rough concentration of carbon monoxide gas.

Similarly, the tin oxide paste is applied so as to cover the periphery of the platinum wire coil 3, dried and then baked at 600 ° C. for 1 hour to cover the platinum wire coil 3 and cover the gas sensitive portion. 4, the palladium salt aqueous solution, the lanthanum salt aqueous solution, and the lead salt aqueous solution are adjusted so that the amount of palladium with respect to the tin oxide is 0.005 to 0.05 mol with respect to the gas sensitive section 4.
%, The amount of lanthanum is 0.5 to 5 mol%, and the amount of lead is 0.
Each of the aqueous solutions is impregnated so as to have a concentration of 05 to 0.5 mol%, dried and then heated at 600 ° C. for 1 hour to obtain the second gas detection element 2. This second gas detection element 2 is shown in FIG.
As shown in, it has been found that it has an extremely high carbon monoxide gas selectivity with respect to hydrogen gas and hydrocarbon gas at a high temperature of 200 ° C to 250 ° C. I find it useful.

[Example of gas detection experiment] The first and second gas detection elements 1 and 2 are incorporated into the gas detection device, and
When an experiment was conducted to detect ppm carbon monoxide gas leakage, the results are shown in FIG. The switching of the gas detection device is controlled by the switching control unit 7 as follows. Normally, carbon monoxide gas is detected at room temperature, and an output is obtained for the concentration of the carbon monoxide gas of 500 ppm by energization. The detection of this carbon monoxide gas is 10
The operation of energizing for 1 millisecond per second is repeated. At this time,
The first gas detection element 1 did not generate heat, was maintained at room temperature, and consumed power at about 1 / 10,000 of the high temperature operation. An output based on a change in the resistance value of the first gas detection element 1 is obtained, the carbon monoxide gas concentration in the atmosphere in contact with the first gas detection element 1 is measured, and the first gas detection element 1 The carbon monoxide gas concentration information measured in
When it reaches 60% or more of the saturated output of carbon monoxide gas (primary detection line a), the circuit switching unit is switched to start energizing the second gas detection element 2 to detect the second gas. The element 2 is controlled at 250 ° C. In this way, if the output value of the second gas detection element 2 is obtained after a predetermined time from the start of energization, the carbon monoxide gas concentration can be accurately known from the output, and more than one minute after the carbon monoxide gas supply. In a short time of about 30 seconds, it was judged that the gas concentration obtained here exceeded the predetermined concentration (alarm line b), and the alarm sound of the alarm device could be sounded.

When performing such a gas detection method, especially when it is necessary to detect a low concentration carbon monoxide gas, for example, 50 ppm within 5 minutes, the first gas detection element 1 to be detected. Predetermined value a based on gas is 50 pp
If the output value of 60% of the saturated output in the gas of m is set, the second gas detection element 2 starts operating in about 3 minutes, and
The accurate concentration can be known in about 5 minutes, which is convenient for application to carbon monoxide alarms and the like.

Further, even if the carbon monoxide gas has a low concentration of about 50 to 100 ppm, the alarm sound can be emitted within 5 minutes, and it has been found that it can withstand practical use. Was completed.

[Another Embodiment] Another embodiment will be described below. As the first gas detection element 1, the palladium,
A comparative examination of the first gas detection element 1 in which the amount of at least one precious metal selected from platinum and gold was changed was as shown in FIG. The sensitivity ratio in the added amount of each noble metal is the ratio (sensitivity) to the added amount of each noble metal in which the sensitivity of the first gas detection element 1 to the carbon monoxide gas of 100 ppm is the highest. Ratio). From FIG. 7, the addition amount of each metal is 0.5 mo.
It can be seen that 1% or more and 1 mol% or less is particularly preferable.
Further, the second gas detection element 2 may have a gas sensitive portion formed by adding at least one noble metal of palladium, platinum and gold to a tin oxide semiconductor in an amount of 0.045 mol% or less. For example, as shown in FIG. 8, 0.003 mol% platinum is added to a tin oxide semiconductor.
If the added second gas sensing element 2 is used, 100p
It was found that an output equivalent to an output for 1000 ppm hydrogen gas was obtained with respect to pm carbon monoxide gas, and it was found to be useful for selectively detecting carbon monoxide gas. Further, these platinum, gold and palladium may be used alone or in combination of two or more.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a gas detection device.

FIG. 2 is a partially cutaway perspective view of a gas detection element.

FIG. 3 is a temperature-dependent gas detection characteristic diagram of the first gas detection element.

FIG. 4 is a response characteristic diagram of the first gas detection element.

FIG. 5 is a temperature-dependent gas detection characteristic diagram of the second gas detection element.

FIG. 6 is a diagram showing operation control of a gas detection device in a gas detection experiment example.

FIG. 7 is a noble metal addition amount-dependent gas detection characteristic diagram of the first gas detection element in another embodiment.

FIG. 8 is a concentration-dependent gas detection characteristic diagram of a second gas detection element according to another embodiment.

[Explanation of symbols]

 1 1st gas detection element 2 2nd gas detection element 3 Noble metal wire coil 4 Gas sensitive part 6 Switching mechanism 7 Control mechanism

Claims (5)

[Claims] 1. A gas detection method for measuring a concentration of a gas to be detected, which is equal to or higher than a predetermined concentration, by using a gas detection element incorporated therein, wherein a noble metal wire coil (3) is mainly covered with a metal oxide semiconductor. Of the hot-wire semiconductor type gas sensing element in which the gas sensitive part (4) as a material is formed, the first gas sensing element (1) capable of detecting gas at normal temperature operation and the first gas sensing element capable of measuring gas concentration at high temperature operation. The second gas detecting element (2) is used, and when the first gas detecting element (1) shows an output of a predetermined value (a) or more based on the detection of the gas to be detected, the second gas detecting element (2). A gas detection method for measuring the concentration of the gas to be detected according to (2). 2. A gas detection device for measuring the concentration of a gas to be detected, which is equal to or higher than a predetermined concentration, by using a gas detection element incorporated therein, the gas detection device covering a precious metal wire coil (3) and mainly comprising a metal oxide semiconductor. Of the hot-wire semiconductor type gas sensing element in which the gas sensitive part (4) as a material is formed, the first gas sensing element (1) capable of detecting gas at normal temperature operation and the first gas sensing element capable of measuring gas concentration at high temperature operation. A two gas detection element (2) is provided, and the detection of the detection gas by the first gas detection element (1) and the detection of the detection gas by the second gas detection element (2) are selectively operated. A switching mechanism (6) for enabling switching is provided, and when the output based on the detection of the gas to be detected by the first gas detection element (1) becomes a predetermined value (a) or more, the first gas detection element ( The detection of the gas to be detected by 1) is performed by the second gas detection element (2). When the output based on the detected gas detection of the second gas detection element (2) is less than a predetermined value (b), the detection of the detected gas by the second gas detection element (2) is performed. A gas detection device provided with a control mechanism (7) for switching and operating the switching mechanism (6) to switch detection of detection gas to detection of gas to be detected by the first gas detection element (1). 3. The gas sensitive part (1), wherein the first gas sensing element (1) is formed by adding at least one metal of palladium, platinum and gold to a tin oxide semiconductor in an amount of 0.05 mol% or more and 5 mol% or less. 4) which has 4).
The gas detection device according to any one of the preceding claims. 4. The carbon monoxide gas detection element, wherein the second gas detection element (2) has a gas sensitive portion (4) formed by adding lead, lanthanum and palladium to a tin oxide semiconductor. Item 2. A gas detection device according to items 2 to 3. 5. The second gas sensing element (2) has a gas sensitive portion (4) formed by adding 0.045 mol% or less of at least one metal of palladium, platinum and gold to a tin oxide semiconductor. The gas detection device according to claim 2, which has the gas detection device.