JPS5918657B2 - Gas detection device that selectively detects specific types of reducing gases - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas detection device that selectively detects a specific type of reducing gas.

It is widely known that the resistance value of metal oxide semiconductors changes depending on the atmospheric gas, and various applications have been proposed in Japanese Patent No. 568,957 and the like.

Conventional gas detection devices detect various reducing gases indiscriminately, so in actual use, the gases originally targeted for detection are those for alcohol gas detection and propane gas detection. Even if the atmosphere used contains unnecessary reducing gases other than the gas to be detected, It was not possible to distinguish between these during detection, and the equipment often responded to such unnecessary gases, causing malfunctions that were not intended for its intended purpose, resulting in extremely unreliable accuracy. . In view of the above points, the present invention selectively detects only a specific type of gas to be detected depending on the application, and can greatly reduce errors due to the influence of gases other than the detection target, thereby improving detection accuracy. Moreover, as long as the setting conditions are selected appropriately, it can exhibit the selective detection effect as described above for any gas, and can be suitably used for various purposes. It is an object of the present invention to provide a gas detection device in which the structure of the elements used is simple and compact, has excellent manufacturability, and can reduce costs.

First, to explain the principle of the present invention, in the present invention, two gas detection elements are used as elements for detecting gas, and each pixel element, together with the nl gas sensing section, is selectively oxidized by oxidation. A filter section is provided to block the permeation of certain reducing gases, so that only the reducing gases that pass through the filter section are sensed by the gas sensing section.

Depending on its ability as an oxidation catalyst, some of the above filters can react with one to several types of reducing gas in the atmosphere to convert it into an inert gas. It blocks almost all gases from permeating, while selectively allowing other gases that are difficult to oxidize to permeate. The material for a part of this filter is metal oxide semiconductor used in the gas sensing part, or Pd, Pt, RS.
A part of the filter is locally heated to a high temperature using a heater to make the oxidizing activity higher than that of the gas sensing part, thereby forming a part of the filter. In this case, the oxidizing ability of a portion of the filter changes depending on the heating temperature. The type of gas that passes through a portion of the filter depends on the degree of oxidizing ability of this portion of the filter. Therefore, by making the heating temperature of each filter part of each pixel element different, the type of gas that passes through each part of the filter, that is, the type of gas detected in each of the above-mentioned elements, can be changed. With this pixel element,
By selectively detecting several types of reducing gases from among the reducing gases in the atmosphere, depending on the oxidizing ability of a portion of each filter, and canceling out these two outputs, any of the above pixel elements can be detected. It detects only certain types of gases that are not detected in one case and detected in the other.
Here, in order to clarify that specific types of gases are selectively detected by the method described above, the graph in Figure 1 shows the oxidation ability and permeability of a filter made of an oxidation catalyst for various gases. Let me show you the relationship with gender.

In the same graph, the vertical axis represents the gas permeability, and the horizontal axis represents the oxidation ability of the filter, that is, the activity as an oxidation catalyst. In the curve A-E in the same graph, A is CO gas and B is H2 The graph shows the relationship between the oxidizing ability and transmittance of the filter for gases, C for ethanol, D for isobutane, and E for methane. As shown in the same graph, among these gases, CO
If the gas is the one whose permeation is most likely to be blocked and the filter has a relatively low oxidizing ability as indicated by the symbol a on the horizontal axis of the graph, the permeability of only CO gas will be extremely low, and the permeability of other gases will be almost completely blocked. It will pass through. This means that with this level of oxidation ability, CO gas, which is the most easily oxidized of the above gases, is oxidized by the catalytic action of the filter.
This is because the CO gas itself is oxidized to become inert CO2, and as a result, the permeation of the CO gas itself is almost blocked, while other gases that are less easily oxidized are permeated with almost no oxidation effect.
In addition, if the oxidizing ability of the filter is a little higher than this, as shown by the symbol b in the graph, in addition to CO gas, H gas, which is the next most easily oxidized gas, is also oxidized.
Since the value of 2α changes, the permeation of these two types of gases is mostly blocked and other gases are allowed to permeate. Similarly, as the oxidizing ability of the filter increases, the types of gases that are prevented from permeating increase in order of oxidizability. At the oxidizing ability, CO, H2, and alcohol are blocked from permeating, while isobutane and methane are allowed to permeate, and at the oxidizing ability shown by the symbol d, only methane is allowed to permeate. In the device used in the present invention as described above, the transmittance of each gas with respect to the oxidizing ability of the filter shown in this graph is not limited to the oxidizing ability of a portion of the filter of the device. This indicates how well this element detects gas compared to the case where the filter is not included, so if the oxidation ability of the filter part in the pixel element is made different, the detection rate in the pixel element can be improved. It can be seen that there are differences in the types of gases detected, and that it is possible to detect specific gases using the method described above. Hereinafter, embodiments of the present invention will be explained in detail with reference to FIGS. 2 and 3.

In FIG. 2, gas detection elements 1 and 2 are capable of selectively detecting gas, and both are small-shaped containers 2 and 2'' made of an insulating material such as airtight glass or ceramic. A gas sensing section 3, 3'' and a filter S4, 4'' are filled in the filter part 4,
Gas is introduced into the gas sensing portions 3, 3'' only through 4''.

In each of the pixel elements 1 and 1'', a single metal oxide semiconductor is used as a material for forming the gas sensing portion and a part of the filter, and by creating a partial temperature difference between the two, This is because the metal oxide semiconductor, which is known as the material of the gas sensor, also acts as an oxidation catalyst, and in particular, when kept at an appropriate temperature as a gas sensor, the gas When Tp comes into contact with it, its resistance value changes greatly and exhibits a gas sensing effect.Furthermore, when heated to a higher temperature, its function as an oxidation catalyst becomes stronger depending on the height of the temperature. At the same time, this method takes advantage of the property that the resistance value change with respect to gas becomes smaller as it becomes electrically close to a conductor. That is, the containers 2 and 2'' are filled with metal oxide semiconductors 5 and 5'', respectively, and , heaters 6 and 65, which also serve as one electrode of the element, are buried in the portions of the metal oxide semiconductors 5 and 5'' facing the opening side of the container.
′, the metal oxide semiconductors 5 and 5
'' is heated to a higher temperature as it approaches the opening side. Therefore, when the heaters 6 and 65 are energized, the portions of the metal oxide semiconductors 5 and 5 facing the opening side of the container are heated to a higher temperature. , which has an oxidation catalytic effect and is heated to a high temperature that is electrically close to a conductor, and acts as filter parts 4 and 4'', and the part inside these is heated to a relatively low temperature and acts as a gas sensing part. According to this structure, the heating temperature conditions for the filter portions 4 and 4'' by the heaters 6 and 6'' correspond to the oxidizing ability of the filter portion, that is, the horizontal axis in the graph of FIG. Depending on the heating conditions, a portion of the filter has permeability characteristics for various gases as shown in the graph of FIG. 1, and the element can also perform selective gas detection based on this characteristic. Therefore, the pixel 1
, 1" by changing the resistance value of each heater 6, 6" or by applying different voltages to each heater 6, the heating temperature of each filter part 4 and 4" is made different. , the pixel elements 1 and 1'' are configured to have different types of gas that can be detected. 7 and 71 are the other electrodes of the respective elements 1 and 1'', and 8 is a heater power source for each of the heaters 6 and 6''.

In such a structure of each element, the electrode and the heater may be provided separately, and the heater may be fitted onto the outer peripheral end of the container. Note that the metal oxide semiconductor in this specification does not simply mean units of SnO2, In2O3, and other various metal oxide semiconductors;
A broad term that includes mixtures of multiple types of metal oxide semiconductors, those to which catalysts such as Pd, Pt, Rh, Ru9Ag9Au are added, and those containing alumina, silica, etc. to increase mechanical strength. This means a metal oxide semiconductor.

] And these two elements 1, 1'' each have a resistance of 10
, 10'' are connected to the circuit power supply 9 in parallel with each other. An electric actuator 11 is connected between the parallel circuits, so that the voltage corresponding to the difference between the respective outputs of the pixel elements 1 and 1'' is The electric actuator 11 is provided with the electric power.

By appropriately setting the resistance value of each heater 6, 6'' of the pixel elements 1, 1'' and the voltage of the heater power supply 9, for example, the filter part 4 of one element 1 can be set as shown in FIG. When it is made to have an oxidizing ability as indicated by the symbol b in the graph, and the filter part 4'' of the other element 1'' is made to have an oxidizing ability as indicated by the symbol c in the graph of FIG. One of the above elements 1 contains CO among the gases in the same graph.
and H2 are hardly detected, while ethanol, isobutane,
When methane is detected, the other element 1'' has CO.H.
2. Ethanol is hardly detected, but isobutane and methane are detected.

Therefore, in this case, CO gas and H2 gas are connected to both terminals 1
, 1'' are hardly detected, and for isobutane and methane, both resistors 10, 1'' connected in series with the pixel elements 1, 1''
Since the respective output voltages applied to 0'' change almost equally and there is almost no difference between the outputs of the pixel elements 1 and 1'', the electrically actuated element 11 does not respond, and the pixel element 1 only responds to ethanol. , 1". The voltage corresponding to this difference is applied to the electric actuator 11 as the final output, and only ethanol is selectively detected.
However, in reality, even in such a case, some amount of H2 gas, etc., which is more easily oxidized than ethanol, is transmitted through the above-mentioned filter parts 4 and 4'' depending on their respective oxidation abilities.
In addition, the permeation of isobutane, which is less oxidized than ethanol, is blocked to some extent, so the final output as a voltage applied to the electric actuator 6 is slightly reduced even for these gases. Since the final output is much smaller than that for ethanol, there is no doubt that an excellent selective detection effect for ethanol can be obtained. In addition to this example, depending on how the temperature conditions that determine the oxidizing ability of each of the filter parts 4 and 4'' are set, for example, each of the filter parts 4 and 4'' may have a different symbol in the graph of FIG. When it has the oxidizing ability of a and b, H and gas are selectively detected according to the above operation, and when it has the oxidizing ability of c and d, isobutane is selectively detected. Thus, as long as the setting conditions for each filter portion 4, 4'' are appropriately selected according to the type of gas to be detected, it is possible to selectively detect a single desired specific type of gas.

Furthermore, by increasing the difference in oxidizing ability between the filter parts 4, 4', it is possible to selectively detect several types of gases whose transmittances change between them. In this way, it is possible to selectively detect a desired single type of gas or several types of gas, but when manufacturing the filter, set conditions such as heating temperature of a part of the filter suitable for detecting the desired gas. To determine this, it is necessary to experimentally investigate in advance the output of the element under various setting conditions for various standard gases for the sample, or the output applied to the electrically actuated object when the circuit as described above is constructed. This makes it possible to know the setting conditions suitable for obtaining a predetermined selective detection operation.

Further, as another embodiment of the device according to the present invention, as shown in FIG. 3, an integral structure in which two storage portions 2a and 2b, which correspond to each container of the pixel element in the above embodiment, are connected and arranged side by side may be used. good.

In this case as well, the other configurations are the same as in the previous embodiment. Further, the device of the present invention can optionally employ meters, alarms, ventilation fans, solenoid valves, and other various control devices as the electrically actuated objects, thereby providing alarm devices, gas flow path cutoff devices, fire prevention devices, etc. It can be used for various purposes such as ventilation equipment. As described above, the present invention uses two gas detection elements as elements for detecting gas, and each of these two gas detection elements heats the opening side of a metal oxide semiconductor filled in a cup-shaped container to a high temperature. By heating, this part is formed as a part of a filter that blocks the passage of a predetermined type of gas, and the other part of the semiconductor is formed as a gas sensing part, and each part of the filter of this pixel element is heated. By varying the heating temperature, the types of gas that each pixel element can detect are different, and the outputs of these two elements are offset, so that only one element can detect enough gas. By selectively detecting a specific type of reducing gas that is hardly detected by the other element, the influence of other reducing gases can be greatly reduced.

In other words, the relationship between the oxidizing ability of a part of the filter and the transmittance for various gases is as shown in the club in Figure 1. and a reducing gas with higher permeability than that, and a part of the filter of the other element has a higher permeability with almost no permeation of the target gas. By making the gas selectively permeable, there is a significant difference in the sensitivity of the pixel element for the reducing gas that is the target of detection, and the sensitivity of the pixel element for other reducing gases. The difference in sensitivity can be made very small. Therefore, the method described above exhibits a selective detection effect on the target specific type of reducing gas, and can greatly reduce the influence of reducing gases that are not the target of detection. Significantly improves accuracy for gas. Moreover, by adjusting the heating temperature of a part of each filter by each heater, a desired reducing gas can be selectively detected as described above, so it can be used for various purposes such as alcohol detection, propane gas detection, CO gas detection, etc. It can be used for. Furthermore, each element in the device of the present invention can be constructed by filling a gas sensing portion and a portion of the filter in a pot-shaped container made of a heat-resistant insulating material.
The container holds and protects the gas sensing part and a part of the filter, and also controls the direction of gas flow so that only the opening of the container needs to be filled with part of the filter. A portion of the filter is formed by giving a metal oxide semiconductor a temperature distribution.

Therefore, the structure is simple and compact, and manufacturing is easy. Furthermore, the presence of the cylindrical container makes it easy to heat and keep warm a part of the filter, making it possible to appropriately adjust the oxidation ability of the part of the filter of each element, and also adjusting the size, shape, etc. of the pixel element. It can be easily stabilized and errors caused by variations in these conditions can be prevented, and the gas selection detection function of the device can therefore be improved.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the oxidizing ability of a filter and the transmittance of various gases, and FIGS. 2 and 3 are circuit diagrams each showing a cross-sectional structure of a gas detection device showing an embodiment of the present invention. . 1.1″...Gas detection element, 2,2″, 2a,
2b...Container, 3,3''...Gas sensing section, 4,4゛...Filter section, 6,6'...
... Heater, 9 ... Circuit power supply, 10, 10'
...Electrically operated animal.

Claims (1)

[Claims] 1 (1) A pair of gas detection elements are provided, and (2) each of the elements includes a cup-shaped container made of a heat-resistant insulating material and a gas-sensitive metal oxide filled inside the container. By heating the semiconductor and the semiconductor disposed near the container opening with a temperature distribution with the container opening side as the high temperature side, the portion of the semiconductor on the container opening side is exposed to a predetermined type of gas. It consists of a heater that serves as a filter part that blocks transmission, the other part of this semiconductor as a gas sensing part, and a pair of electrodes connected to this gas sensing part, (3)
The heating temperature of each filter section by each heater of these two elements is different, (4) both of these elements are connected to a power supply in parallel with each other via a resistor, (5) and an electric current is connected between these parallel circuits. (6) an output for a specific type of gas that is detected by one of the two elements but not by the other is applied to the electric actuator; A gas detection device that selectively detects specific types of reducing gases.