JP3549322B2 - Gas detection method and gas detection device - Google Patents

Description

[0001]
TECHNICAL 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 using a gas detection element incorporated therein.
[0002]
[Prior art]
Conventionally, to measure the concentration of gas in the atmosphere, a gas detection device that incorporates a gas detection element that can measure gas concentration at high temperature operation is installed, the output is constantly monitored, and the gas concentration is measured from the output. Had to be configured. That is, usually, the hot-wire semiconductor gas detection element capable of measuring gas concentration, while obtaining gas selectivity, in order to obtain the output of the concentration information based on the gas detection, must be operated at high temperature, For example, when monitoring the concentration of carbon monoxide using the gas detection element, there has been a situation in which a gas detection device provided with the gas detection element must be constantly operated. In order to operate the gas detecting element at a high temperature, Joule heat is generally generated by energizing a noble metal wire coil or the like provided in the gas detecting element, and the gas detecting element is operated while being maintained at a high temperature. I was
[0003]
[Problems to be solved by the invention]
However, according to the conventional technology described above, if the gas detection device is constantly operated at a high temperature, a large amount of power is required to maintain the gas detection element at a high temperature, and it is necessary to supply power from an outlet. Therefore, a gas detection device that can be operated with small electric power has been desired. Therefore, it has been considered to perform gas detection using a gas detection element that can detect gas with low power.However, such a gas detection element has a slow response until a gas output is obtained. For a gas having a very low concentration, it takes about 15 minutes to obtain a stable output, and there is a disadvantage that it is difficult to perform gas detection quickly.
[0004]
Therefore, an object of the present invention is to provide a gas detection device capable of quickly and accurately measuring a gas concentration of a predetermined amount or more while operating with small electric power in view of the above-described drawbacks.
[0005]
[Means for Solving the Problems]
[Configuration 1]
To achieve this object, the characteristic means of the gas detection method of the present invention is to cover the noble metal wire coil to measure the concentration of the gas to be detected having a predetermined concentration or more using the gas detection element incorporated therein. Among the hot-wire type semiconductor gas detection elements having a gas sensitive portion mainly composed of a metal oxide semiconductor, a first gas detection element capable of detecting gas at normal temperature operation and a second gas detection element capable of measuring gas concentration at high temperature operation Using a second gas detection element, when the first gas detection element shows an output of a predetermined value or more based on detection of the detection gas, the concentration of the detection gas is measured by the second gas detection element Is to do.
[0006]
(Function and effect)
That is, since the hot-wire semiconductor gas detection element is a gas detection element that can obtain high gas selectivity by being formed in a small diameter, it can operate with low power when energized to obtain an output. . In addition, when the concentration of carbon monoxide gas present in the atmosphere is low and it is not usually necessary to measure the concentration of carbon monoxide gas, only the first gas detection element that can detect gas at room temperature need be operated. Most of the time when gas must be detected, it can be operated with low power. By the way, the first gas detecting element requires a long time until a stable output is obtained in order to measure an accurate 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 an output that can be determined to be likely to reach the dangerous concentration is obtained, when the second gas detection element is activated, the accurate gas concentration is measured. As a result, the gas concentration measurement by the gas detection element maintained at a high temperature can be suppressed to a necessary minimum, and the power consumption can be reduced.
[0007]
[Configuration 2]
Further, the characteristic configuration of the gas detection device of the present invention is a gas detection device that measures the concentration of a gas to be detected having a predetermined concentration or more using a gas detection element incorporated therein. Among the hot-wire semiconductor gas detection elements that have a gas-sensitive part made mainly of semiconductor, the first gas detection element that can detect gas at normal temperature operation and the second gas detection element that can measure gas concentration at high temperature operation Element, and a switching mechanism is provided for enabling the operation of the detection of the gas to be detected by the first gas detection element and the detection of the gas to be detected by the second gas detection element. When the output based on the detection of the gas to be detected by the gas detection element is equal to or more than a predetermined value, the detection of the gas to be detected by the first gas detection element is switched to the detection of the gas to be detected by the second gas detection element, The said When the output based on the detection of the gas to be detected by the gas detection element is less than a predetermined value, the detection of the gas to be detected by the second gas detection element is switched to the detection of the gas to be detected by the first gas detection element. With the provision of a control mechanism for switching the switching mechanism,
Preferably, the first gas detection element has a gas sensing 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. Often,
The second gas detection element has a gas sensing portion formed by adding lead, lanthanum, and palladium to a tin oxide semiconductor, or a tin oxide semiconductor containing at least one metal of palladium, platinum, and gold. It is more preferable to have a gas-sensitive portion formed by adding 0.045 mol% or less.
(Function and effect)
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 a gas detection operation with low power can be provided.
As a result, the power consumption of the entire gas detection device can be set extremely small, so that the gas detection device can be made smaller, for example, can be operated with a dry battery, and the wiring from the power supply can be eliminated. Thus, the usability of the gas detection device can be greatly improved, for example, by providing portability to the gas detection device and eliminating restrictions on the installation position due to the position of an outlet or the like.
[0008]
As a technique for constantly monitoring the gas concentration as described above, carbon monoxide gas detection is given as an example, but as the gas detection element for carbon monoxide gas detection, the first gas detection element is used. Any gas detecting element may be used as long as it has a gas sensing 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. Has a high selectivity for carbon monoxide gas at room temperature, so it can efficiently detect only carbon monoxide gas even at room temperature operation and is not affected by other gases even if the gas concentration is rough. Thus, accurate gas detection becomes possible.
Further, the second gas detection element has a gas sensing portion formed by adding lead, lanthanum, and palladium to a tin oxide semiconductor, or at least one metal of palladium, platinum, and gold to a tin oxide semiconductor. Has a gas-sensitive portion formed by adding 0.045 mol% or less of, has high carbon monoxide gas selectivity and can quickly and accurately detect carbon monoxide gas at a high temperature.
[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 has first and second gas detection elements 1 and 2 incorporated therein.
As the first gas detecting element 1, a tin oxide semiconductor is provided at a diameter of 0.5 mm so as to cover a noble metal wire coil (platinum wire coil) 3 having a diameter of about 20 μm to form a gas sensing part 4. Using a normal temperature operating type carbon monoxide gas-selective hot-wire semiconductor gas detecting element in which 0.05 to 5 mol% of palladium is added to the part 4,
Similarly, as the second gas detecting element 2, a gas sensing portion 4 mainly composed of a tin oxide semiconductor is formed to cover the platinum wire coil 3, and 0.005 to 0.05 mol of palladium is contained in the gas sensing portion 4. %, And 0.5 to 5 mol% of lanthanum and 0.05 to 0.5 mol% of lead are used. 2), so that the gas can be detected freely.
As shown in FIG. 1, the first and second gas detection elements 1 and 2 are connected to a detection circuit unit 5 that incorporates a bridge circuit and 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 second gas detection elements 1 and 2 is connected to the detection circuit unit 5, and power is supplied from a power supply and switching of the circuit switching unit 6 is performed. A switching control section 7 for controlling the operation based on the outputs from the first and second gas detection elements 1 and 2 is provided, and the operation exceeds a predetermined value based on the output detected by the detection circuit section 5. An alarm device 8 for generating an alarm sound when a gas concentration is detected is connected to constitute a gas detection device as a whole.
[0010]
The resistance value of the first gas detecting element 1 changes in accordance with the concentration of carbon monoxide gas at normal temperature due to adsorption of carbon monoxide gas at normal temperature. Therefore, by repeating the operation of energizing for 1 millisecond per 10 seconds, while preventing the first gas detection element from generating heat, an output based on a change in the resistance value of the first gas detection element 1 is obtained. The concentration of carbon monoxide gas in contact with the first gas detection element 1 can be measured. In addition, such a first gas detecting element 1 can perform a stable operation for a long time by performing a purge operation of exposing to a high temperature of about 450 ° C. at a rate of several seconds per hour to several hours.
[0011]
The second gas detecting element 2 starts energization when the carbon monoxide gas concentration information measured by the first gas detecting element 1 reaches, for example, 60% or more of the saturated output of 50 ppm of carbon monoxide gas. Then, the second gas detecting element 2 is controlled to a predetermined temperature by the Joule heat of the platinum wire coil 3, and the resistance value of the second gas detecting element 2 is reduced by the adsorption of carbon monoxide gas. It changes according to the gas concentration. Therefore, for example, if an output value is obtained after a predetermined time from the start of energization, the concentration of carbon monoxide gas can be quickly and accurately measured from the output.
[0012]
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 sends the detection circuit section 5 to the first gas detection element 1 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 sets the detection circuit unit 5 to the second gas detection state. A switching control mechanism that controls the circuit switching unit 6 so as to supply power to the element 2 so that the second gas detection element 2 can be maintained at a set temperature, and controls the power supply. It has a working configuration.
[0013]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
[Gas detection element]
An aqueous solution of tin chloride having a predetermined concentration is adjusted by adding antimony chloride at a predetermined ratio. Aqueous ammonia is added dropwise to this aqueous solution to obtain a precipitate of tin hydroxide. The precipitate is washed with water, dried, and calcined at 650 ° C. for 2 hours to obtain tin oxide. The tin oxide is pulverized to a fine powder and kneaded with water to obtain a tin oxide paste.
[0015]
The tin oxide paste is applied so as to cover the periphery of the platinum coil 3, dried and baked at 600 ° C. for 1 hour, and a gas sensing part 4 is provided to cover the platinum coil.
Next, an aqueous solution of palladium chloride is prepared, and the gas-sensitive portion 4 is impregnated with the aqueous solution of palladium chloride such that the amount of palladium with respect to the tin oxide is 0.05 to 5 mol%. Heat at 600 ° C. for 1 hour to obtain a first gas detection element.
[0016]
As shown in FIG. 3, this first gas detecting element 1 has a high selectivity for carbon monoxide gas with respect to hydrogen gas at normal temperature, and furthermore, the gas responsiveness of this first gas detecting element 1 Fig. 4 shows that even with 50 ppm of carbon monoxide gas, an accurate output can be obtained in about 15 minutes, but an output value of about 60% or more of the saturated output in about 3 minutes. Can be obtained, which is useful for grasping the approximate concentration of carbon monoxide gas at room temperature in a short time.
[0017]
Similarly, the tin oxide paste is applied so as to cover the periphery of the platinum wire coil 3, dried and baked at 600 ° C. for 1 hour to provide the gas sensing portion 4 covering the platinum wire coil 3. At the same time, a palladium salt aqueous solution, a lanthanum salt aqueous solution, and a lead salt aqueous solution are adjusted, and the palladium amount with respect to the tin oxide is 0.005 to 0.05 mol%, Each of the aqueous solutions is impregnated so that the amount becomes 0.5 to 5 mol% and the amount of lead becomes 0.05 to 0.5 mol%, and after drying, it is heated at 600 ° C. for 1 hour to detect the second gas. Element 2 is obtained.
As shown in FIG. 5, the second gas detecting element 2 has an extremely high selectivity for carbon monoxide gas with respect to hydrogen gas and hydrocarbon gas at a high temperature of 200 ° C. to 250 ° C. It turns out that it is useful for measuring an accurate concentration of carbon gas.
[0018]
[Example of gas detection experiment]
An experiment was conducted in which the first and second gas detection elements 1 and 2 were incorporated into the gas detection device and a leakage of 500 ppm of carbon monoxide gas was performed. As a result, the results are as 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 500 ppm of carbon monoxide gas by energization. This detection of carbon monoxide gas repeats the operation of energizing for 1 millisecond per 10 seconds. At this time, the first gas detecting element 1 did not generate heat, was maintained at a normal temperature, and the power consumption was reduced to about 1/10000 of that at the time of high-temperature operation. An output based on a change in the resistance value of the first gas detection element 1 is obtained, and the concentration of carbon monoxide gas in the atmosphere in contact with the first gas detection element 1 is measured. When the carbon monoxide gas concentration information measured in step 1 reaches 60% or more (primary detection line a) of the saturation output of 50 ppm of carbon monoxide gas, the circuit switching unit is switched, and the second gas detection element 2 The energization is started, and the temperature of the second gas detection element 2 is controlled to 250 ° C. Thus, if the output value of the second gas detecting element 2 is obtained a predetermined time after the start of energization, the carbon monoxide gas concentration can be accurately known from the output, and moreover, it is almost one minute after the supply of the carbon monoxide gas. In a short time of about 30 seconds, it was determined that the gas concentration obtained here exceeded the predetermined concentration (warning line b), and the warning sound of the warning device could be sounded.
[0019]
When performing such a gas detection method, particularly when it is necessary to detect a low-concentration carbon monoxide gas, for example, 50 ppm within 5 minutes, the detection is performed based on the detected gas of the first gas detection element 1. If the predetermined value a is set to an output value of 60% of the saturation output in 50 ppm gas, the operation of the second gas detecting element 2 starts in about 3 minutes, and the accurate concentration in about 4 to 5 minutes. This is convenient when applied to an alarm or the like of carbon monoxide.
[0020]
In addition, even if the concentration of carbon monoxide gas was as low as about 50 to 100 ppm, an alarm sound could be sounded within 5 minutes, which proved to be sufficiently practical and could be used for a portable gas alarm. .
[0021]
[Another embodiment]
Hereinafter, another embodiment will be described.
FIG. 7 shows a comparison of the first gas sensing element 1 in which the amount of addition of at least one noble metal of palladium, platinum, and gold was variously changed. The sensitivity ratio of the amount of each noble metal to be added is such that the amount of each noble metal having the highest sensitivity to 100 ppm of carbon monoxide gas of the first gas sensing element 1 is defined as the sensitivity = 1 (sensitivity). Ratio). FIG. 7 shows that the addition amount of each metal is particularly preferably 0.5 mol% or more and 1 mol% or less.
Further, the second gas detection element 2 may have a gas sensing portion formed by adding at least one noble metal of palladium, platinum, and gold to a tin oxide semiconductor at a concentration of 0.045 mol% or less. For example, as shown in FIG. 8, if the second gas detection element 2 in which 0.003 mol% of platinum is added to a tin oxide semiconductor is used, the output with respect to 100 ppm of carbon monoxide gas and 1000 ppm of hydrogen gas is obtained. It can be seen that an output equivalent to the above is obtained, which is useful for selectively detecting carbon monoxide gas. These platinum, gold and palladium may be used alone or in combination of two or more.
[0022]
In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration of the accompanying drawings by the entry.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a gas detection device. FIG. 2 is a partially cutaway perspective view of a gas detection device. FIG. 3 is a temperature-dependent gas detection characteristic diagram of a first gas detection device. FIG. 4 is a response of the first gas detection device. FIG. 5 is a graph showing temperature-dependent gas detection characteristics of a second gas detection element. FIG. 6 is a view showing operation control of a gas detection device in a gas detection experiment example. FIG. 7 is a diagram showing a first gas detection element in another embodiment. Noble metal addition dependent gas detection characteristic diagram [FIG. 8] Concentration dependent gas detection characteristic diagram of second gas detection element in another embodiment [Description of reference numerals]
DESCRIPTION OF SYMBOLS 1 1st gas detection element 2 2nd gas detection element 3 noble metal wire coil 4 gas sensing part 6 switching mechanism 7 control mechanism

Claims (5)

A gas detection method for measuring the concentration of a gas to be detected having a predetermined concentration or more using a gas detection element incorporated therein,
Among the hot-wire semiconductor gas detection elements having a gas-sensitive portion (4) composed mainly of a metal oxide semiconductor and covering the noble metal wire coil (3), the first gas detection capable of detecting gas at normal temperature operation Using the element (1) and a second gas detection element (2) capable of measuring gas concentration at high temperature operation, a predetermined value (a) based on detection of the gas to be detected by the first gas detection element (1). A gas detection method for measuring the concentration of the gas to be detected by the second gas detection element (2) when the above output is indicated. A gas detection device for measuring the concentration of a gas to be detected having a predetermined concentration or more using a gas detection element incorporated therein,
Among the hot-wire semiconductor gas detection elements having a gas-sensitive portion (4) composed mainly of a metal oxide semiconductor and covering the noble metal wire coil (3), the first gas detection capable of detecting gas at normal temperature operation An element (1) and a second gas detection element (2) capable of measuring gas concentration at high temperature operation are provided, and detection of a gas to be detected by the first gas detection element (1) and the second gas detection element ( A switching mechanism (6) is provided for enabling the operation of the detection of the gas to be detected to be performed alternatively to the detection of the gas to be detected by 2), and the output based on the detection of the gas to be detected by the first gas detection element (1) is set to a predetermined value (a ), The detection of the gas to be detected by the first gas detection element (1) is switched to the detection of the gas to be detected by the second gas detection element (2). The output based on the detection of the gas to be detected was less than the predetermined value (b). A control mechanism for switching the switching mechanism (6) to switch the detection of the gas to be detected by the second gas detection element (2) to the detection of the gas to be detected by the first gas detection element (1). A gas detector provided with 7). The first gas detecting element (1) having a gas sensing part (4) formed by adding at least one kind of 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. The gas detection device according to claim 2, wherein The said 2nd gas detection element (2) is a carbon monoxide gas detection element which has a gas sensitive part (4) formed by adding lead, lanthanum, and palladium to a tin oxide semiconductor. The gas detection device according to any one of the preceding claims. The said 2nd gas detection element (2) has a gas sensitive part (4) formed by adding at least one kind of metal of palladium, platinum, and gold to a tin oxide semiconductor at 0.045 mol% or less. Item 3. The gas detection device according to item 2 or 3.

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