JP2002286672A - Gas detector and gas detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detector for minimizing interference from other gases for efficiently detecting a methane gas when detecting the methane gas, and minimizing power consumption. SOLUTION: In a gas sensor, an electrode is provided at a board having a heater, an oxide semiconductor covering the electrode is provided, and a catalyst layer is provided so that the oxide semiconductor can be covered. In the gas detection apparatus, gas to be detected is detected by turning on or off the voltage of the heater repeatedly, the ON heater on time of the heater voltage is set to a range of 20 seconds to four minutes, and the heater voltage OFF time is set to 20 minutes or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection device and a gas detection method, and more particularly to a gas containing methane as a main component such as methane or city gas (hereinafter referred to simply as "methane" or "methane"). The present invention relates to a gas detection device and a gas detection method capable of selectively detecting “methane gas” and suppressing power consumption.

[0002]

2. Description of the Related Art At present, natural gas is widely used as city gas, industrial gas / industrial gas, and gas for power generation, and it is important for security to detect the leak. is there.

However, when detecting leakage, there is a problem that it cannot be easily detected due to the presence of an interfering gas such as LP gas or an organic solvent gas such as alcohol.

Since the main component of natural gas is methane, in order to detect natural gas without being disturbed by an interfering gas, a sensor having high sensitivity to methane but low sensitivity to interfering gas is used. , It is necessary to selectively detect methane gas.

In practice, however, in order to increase the selectivity to methane, a catalyst layer for removing components other than methane is provided. However, usually, methane is also partially burned and removed at the same time. It was difficult to detect with high sensitivity and high selectivity.

Techniques for selectively detecting methane gas include, for example, Japanese Patent No. 3087978,
000-356614 or JP-A-2000-356614
There was one disclosed in JP-A-356615.

However, a gas sensor element that selectively detects methane gas, including these techniques, has a relatively high sensitivity to interfering gases, especially propane gas, to other interfering gases, and propane gas is not used. If so, it was difficult to selectively detect low concentrations of methane gas.

This is because the difference in chemical properties between methane and propane is smaller than that between methane and alcohol, methane and hydrogen, and propane is widely used in sensors for selectively detecting methane gas. This is probably due to the fact that the activated carbon filter is difficult to adsorb.

Further, in these applications, it is necessary to meet the needs of reducing the power consumption of the gas detector as much as possible and improving the convenience in use. That is, in order to selectively detect methane gas, it is necessary to raise the temperature of the gas sensor relatively high, and therefore, there is a problem that the power consumption of the gas sensor element increases.

In order to suppress the power consumption of the gas sensor, for example, Japanese Patent Publication No. 6-105234,
As disclosed in Japanese Patent Publication No. 10286, Japanese Utility Model Publication No. Hei 7-25885, and Japanese Patent No. 2911928, there is a technique for suppressing power consumption by intermittently driving a gas sensor.

However, these techniques have not been able to improve the performance of selectively detecting methane gas.

It is presumed that this is because the gas sensor is driven intermittently even if it is driven intermittently within a relatively short time range of several seconds to several minutes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to minimize the interference from other gases when detecting methane gas (ie, to efficiently detect methane gas). It is another object of the present invention to provide a gas detection device and a gas detection method capable of minimizing power consumption.

When the gas sensor is intermittently driven, the present invention selectively drives methane gas from the gas sensor by driving the gas sensor at a relatively long interval for a specific range of time. Among these performances, it has been found that sensitivity to propane gas can be suppressed and power consumption can be suppressed, and the present invention has been achieved.

[0015]

According to a first aspect of the present invention, there is provided a gas detection device, wherein an electrode is provided on a substrate provided with a heater, an oxide semiconductor covering the electrode is provided, and the oxide semiconductor is covered. A gas sensor in which a catalyst layer is provided on the gas sensor. The gas sensor is configured to detect a target gas by repeatedly applying ON / OFF of the voltage of the heater. Is set in the range of 10 seconds to 5 minutes, and the heater voltage OFF time is set to 10 minutes or more.

According to a second aspect of the present invention, there is provided a gas detection apparatus according to the first aspect, wherein the heater voltage is turned on.
The time is set in the range of 20 seconds to 4 minutes, and the heater voltage OFF time is set to 20 minutes or more.

According to a third aspect of the present invention, in the gas detection method, an electrode is provided on a substrate provided with a heater, an oxide semiconductor covering the electrode is provided, and a catalyst layer is provided so as to cover the oxide semiconductor. ON / OF of the heater voltage
A gas detection method using a gas detection device configured to detect a target gas by repeatedly applying F, wherein a heater voltage ON time is set within a range of 10 seconds to 5 minutes, and a heater voltage OFF is set. In this method, the time is set to 10 minutes or more.

According to a fourth aspect of the present invention, in the gas detection method according to the third aspect, the heater voltage ON time is set within a range of 20 seconds to 4 minutes, and the heater voltage OFF time is set to 20 minutes or more. It's a way to do it.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a substrate-type gas sensor using an oxide semiconductor such as tin oxide as a gas detection material is used as a gas sensor.

Specific examples of the oxide semiconductor include zinc oxide, indium oxide, iron oxide, and gallium oxide in addition to tin oxide. In the following, a description will be given using tin oxide as an example.

The substrate has a heater function on the back surface, the front surface, or the inside thereof. When a voltage is applied to the heater, heat is generated by heating the gas sensor, and the gas sensor detects gas when heated. . Therefore, the operation of the gas sensor can be controlled by controlling the application of the voltage of the heater.

As a material for the substrate, ceramics such as alumina or a silicon wafer can be used.

Then, a pair of electrodes for measuring the electric resistance of the gas detection material is formed on the substrate surface, and a tin oxide layer or a layer containing tin oxide as the gas detection material is formed thereon.

The tin oxide layer may be a thin film having a thickness of 10 μm or less, or a thick film having a thickness of about 10 μm to 100 μm. Further, a catalyst or a material such as alumina or silica may be mixed with tin oxide.

Further, a selective oxidation catalyst layer is provided on the tin oxide layer, that is, on the opposite side of the tin oxide layer as viewed from the substrate so as to cover the tin oxide layer.

The selective oxidation catalyst layer functions to control the gas components reaching the tin oxide layer. Specifically, methane as a detection target reaches the tin oxide layer without being oxidized and removed by the selective oxidation catalyst layer. The combustible gas serving as other obstructive components is oxidized and removed by the selective oxidation catalyst layer, and does not reach the oxidation gas layer very much. The degree of this oxidation removal depends on the type of flammable gas,
Components that are relatively easily oxidized, such as hydrogen and alcohols, are almost completely oxidized and removed, while components that are relatively hard to oxidize, such as propane gas, are not completely oxidized and removed, and a certain percentage of them are tin oxide layers. To reach.

The selective oxidation catalyst layer preferably contains 0.8% by weight of platinum, more preferably contains 1.0% by weight of platinum, and more preferably contains 1.2% by weight of platinum. More preferred. If the amount is less than 0.8% by weight, the effect of suppressing sensitivity to propane gas may not be sufficiently exhibited.

The thickness of the selective oxidation catalyst layer is not particularly limited, but is approximately 50 μm to 500 μm.

This gas sensor element is used in a state where it is supported on an electrode such as a metal pin by a thin metal lead wire such as platinum having a diameter of 1 mm or less.

The gas sensor element may be used in a metal or plastic case having a gas diffusion port.

At this time, an activated carbon filter may be inserted near the gas diffusion port or around the gas sensor element.

The activated carbon filter functions to enhance the gas selectivity for propane, which is one of the effects of the present invention. In actual use environment, oil mist,
Although it may be exposed to gas sensor poisoning components such as sulfurous acid gas and hydrogen sulfide, the activated carbon filter works to reduce the poisoning effect of these components.

The heater section for heating the gas sensor to be in an operating state has a circuit configuration in which the heater voltage is intermittently turned ON / OFF by a timer operation. This may be performed by a conventionally known method.

The ON time of the heater voltage application is 10 seconds to 5 seconds.
Minutes, preferably 20 seconds to 4 minutes, and the OFF time is 10 minutes or more, preferably 20 minutes or more, to obtain the effect of the present invention. Since the OFF time is set to 10 minutes or more, the gas cannot be detected during this time, but heater power consumption during this time is not required, and power consumption can be suppressed. When the ON time is shorter than 10 seconds, when it exceeds 5 minutes, and when the OFF time is shorter than 10 minutes, the interference by propane is so large that it cannot be ignored. This effect is more pronounced when an activated carbon filter is used.

A gas alarm (detector) may be configured by utilizing the above-described effects. That is, the resistance value of the tin oxide layer while the heater voltage is ON is measured using another electrode. Measurement of resistance value of tin oxide layer is ON
The operation may be performed after 10 seconds or more, preferably 20 seconds or more. Since the resistance value of the tin oxide layer decreases in the methane gas, the gas can be detected by monitoring the decrease in the resistance value of the tin oxide layer. Measure the resistance value of the tin oxide layer in the air containing a certain concentration of methane or in the air containing methane gas in advance, and calculate the concentration of the measurement gas or issue an alarm by comparing it with the measured value. Can be.

Here, the operation and effect of the present invention can be achieved without depending on the method of processing the sensor signal, that is, the method of calculating the density or the method of issuing an alarm.

[0037]

The present invention will be described in more detail with reference to the following Examples, which by no means limit the present invention.

Examples 1 and 2 and Comparative Examples 1 and 2 (Gas Detection Characteristics) FIG. 1 is a schematic structural view of a sensor used in Examples and Comparative Examples described later. In FIG.
The substrate (gas sensor substrate) is 2 mm as shown in FIG.
It is made of alumina having a square shape and a thickness of 0.5 mm, and a heater is formed on the back surface. An electrode is provided on the upper surface of the substrate, and the electrode is coated with a tin oxide layer (thin tin oxide) as an oxide semiconductor. The tin oxide layer has a thickness of 5 μm. Further, a catalyst layer (selective oxidation catalyst layer) is provided so as to cover the tin oxide layer.

The selective oxidation catalyst layer contains 1.3% by weight of platinum. The selective oxidation catalyst layer has a thickness of 300 μm.

In the first embodiment, the ON time is set to 2 minutes,
The time was set at 4 hours. In the second embodiment, the ON time / OF
Both the F times were set in the same manner as in Example 1, and in Example 2, as shown in FIG. 3, the performance was evaluated in a case with an activated carbon filter.

In Comparative Examples 1 and 2, the heater was always turned on without intermittent driving, and the performance was evaluated in the same manner as in Example 1. In Comparative Example 2, the performance was evaluated in the same manner as in Example 2 in a case with an activated carbon filter. The results are shown in FIGS.

(Off time characteristic) In order to grasp the optimum value of the OFF time, using the same gas sensor as in the first embodiment,
The characteristics were evaluated by changing the OFF time while keeping the ON time at 2 minutes. FIG. 6 shows the results. In FIG.
The graph above shows the case without an activated carbon filter.
The graph below shows the case with an activated carbon filter.

As can be seen from FIG. 6, if the OFF time is less than 10 minutes, the indicated concentration in propane is large, and the effect is not so significant. If the time is set to 20 minutes or more, a remarkable effect can be confirmed.

Therefore, as the OFF time, 10 minutes or more,
It can be seen that setting the time to preferably 20 minutes or more is good.

Although the effect of the present invention does not basically change even if the OFF time is lengthened, the time during which detection cannot be performed naturally becomes longer. What is necessary is just to determine by an interval.

(ON time characteristic) In order to grasp the optimum value of the ON time, the same gas sensor as that of the second embodiment is used.
The characteristics were evaluated by changing the ON time while keeping F at 4 hours. FIG. 7 shows the results. In FIG. 7, the upper graph shows the case without the activated carbon filter, and the lower graph shows the case with the activated carbon filter.

As can be seen from FIG. 7, when the ON time is less than 10 seconds, the error in the indicated concentration in methane is large, and the indicated concentration in propane is large. If the time is set to 20 seconds or more, a remarkable effect can be confirmed.

On the other hand, when the ON time exceeds 4 minutes, the instruction during propane becomes large again, and when it exceeds 5 minutes, it becomes even larger.

Therefore, the ON time is preferably from 10 seconds to 5 minutes, and more preferably from 20 seconds to 4 minutes.

(Long-term characteristics) In order to evaluate the state of deterioration of the detection function due to long-term use, the operation is continuously performed for one month.
One month later, the change over time (long-term characteristic) of the indicated concentration in the detection device was measured. The results are shown in Table 1 below.

[0051]

[Table 1]

From the figure, it can be seen that Example 1 and Example 2 have smaller changes over time of the detector indication in propane than Comparative Example, and are superior in durability.

[0053]

According to the present invention, when detecting methane gas, interference from other gases is minimized (that is, methane gas generation can be detected efficiently), and power consumption is minimized. Can be.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part showing an example of a gas detection device of the present invention.

FIG. 2 is an enlarged view of the gas sensor element in the previous figure.

FIG. 3 is a schematic explanatory view showing a state in which an activated carbon filter is further mounted on the gas detection device shown in FIG.

FIG. 4 is a graph showing the results of Examples 1 and 2.

FIG. 5 is a graph showing the results of Comparative Examples 1 and 2.

FIG. 6 is a graph showing an OFF time characteristic.

FIG. 7 is a graph showing ON time characteristics.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kota Yokoyama 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside Osaka Gas Co., Ltd. (72) Hiroichi Sasaki, Inventor Hirano-cho, Chuo-ku, Osaka-shi, Osaka 4-chome 1-2 F-Term in Osaka Gas Co., Ltd. (Reference) 2G046 AA19 BA02 BA04 BA09 BB02 BC01 BC09 BE03 DA05 DB07 DD03 EA03 EA04 EA08 EA09 EA11 EB06 FB02 FE31 FE39

Claims (4)

[Claims] An electrode is provided on a substrate provided with a heater, an oxide semiconductor covering the electrode is provided, and a catalyst layer is provided so as to cover the oxide semiconductor. A gas detection device configured to intermittently detect a target gas by repeatedly applying ON / OFF of the voltage of the heater, wherein the heater voltage ON time is set within a range of 10 seconds to 5 minutes. And a heater voltage OFF time set to 10 minutes or more. 2. The gas detection device according to claim 1, wherein the heater voltage ON time is set within a range of 20 seconds to 4 minutes, and the heater voltage OFF time is set to 20 minutes or more. A gas detection device characterized by the above-mentioned. 3. An electrode is provided on a substrate provided with a heater, an oxide semiconductor covering the electrode is provided, a catalyst layer is provided to cover the oxide semiconductor, and ON / OFF of a voltage of the heater is provided. A gas detecting method configured to intermittently detect a target gas by repeatedly applying the above method, wherein a heater voltage ON time is set within a range of 10 seconds to 5 minutes, and A gas detection method performed by setting the heater voltage OFF time to 10 minutes or more. 4. The gas detecting method according to claim 3, wherein the heater voltage ON time is set in a range of 20 seconds to 4 minutes, and the heater voltage OFF time is set to 20 minutes or more. The new gas detection method.