JPS6140937B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gas leak alarm device using a gas detection element made of a metal oxide semiconductor, and its purpose is to detect combustible gases such as methane and butane (hereinafter referred to as detection gas). An object of the present invention is to provide a gas leak alarm device that does not malfunction due to other gases (alcohol vapor, water vapor). Generally, metal oxide semiconductors (SnO ₂ , ZnO,
It is known that materials (such as Fe ₂ O ₃ ) cause sensitive resistance changes when they come into contact with flammable gas while their surfaces are heated. Conventionally, gas detection elements that apply this principle to detect leaks of minute amounts of flammable gas (for example, LPG, city gas, etc.) have been put into practical use, and gas leak alarm devices using this gas detection element are commercially available. ing. However, in the case of this type of gas leak alarm device, detection gas (propane, the main component of LPG (however, isobutane is required to be tested according to the regulations), hydrogen, the main component of city gas, and hydrogen, the main component of natural gas. Increasing the gas detection sensitivity for the component methane) also increases the gas detection sensitivity for gases other than the detection gas (water vapor and alcohol vapor), which can cause gas leak alarms due to water vapor generated when water boils or alcohol vapor generated when drinking sake. There was a problem that the device would activate and cause false alarms. The present invention has been made in view of the above points. Examples will be described below using figures. 1st
The figure shows a circuit diagram of a gas leak alarm device according to the present invention. 1a and 1b are metal oxide semiconductors (SnO ₂ , ZnO , Fe ₂ O ₃ , etc.), and both gas detection elements 1a and 1b are heated by heaters 2a and 2b, respectively, and the element heating temperature is determined by the heater made of a constant voltage power supply circuit. The temperature is controlled to a predetermined temperature by control circuits 3a and 3b. The main gas detection element 1a is heated to a high temperature to increase the gas detection sensitivity for detection gases such as butane, hydrogen, and methane, and the sub-gas detection element 1b is used to detect gases other than the detection gas, namely water vapor and alcohol vapor. It is heated to a low temperature so that the sensitivity is high and the gas detection sensitivity of the detection gas is low. Figure 2 shows the gas detection sensitivity (resistance change rate △
R), and as is clear from the figure, the element heating temperature of gas sensing element 1a is _T2 gas sensing element 1
If the element heating temperature of b is T ₁ , gas detection element 1
The element a has a high gas detection sensitivity (large rate of change in resistance) for butane and methane, and the gas detection element 1b has a high gas detection sensitivity for water vapor, that is, humidity, and alcohol vapor. In this case, the gas detection element 1a has a certain degree of detection sensitivity for water vapor and alcohol vapor, and when the atmosphere becomes high humidity or high concentration alcohol vapor, the resistance of the gas detection element 1a changes significantly. Therefore, it is sensitive to virtually all combustible gases. 4a and 4b are comparison circuits consisting of operational amplifiers Oa and Ob and transistors Q ₁ a and Q ₁ b;
By applying the power supply voltage Vc output from the power supply circuit 5 to the gas detection elements 1a and 1b via load resistors R ₁ a and R ₁ b, the resistance change in the gas detection elements 1 a and 1 b was converted into a voltage change. The gas detection output is input to the positive input terminals of operational amplifiers Oa and Ob, and the negative input terminals of operational amplifiers Oa _{and Ob} are connected to resistors R ₂ a, R ₄ a and variable resistors.
Reference voltage generation circuits 7a and 7b that divide power supply voltage Vc with R ₁ a, resistors R ₂ b, R ₄ b, and variable resistor R ₃ b
Reference voltages V ₀ a and V ₀ b output from the two are applied. The output of the comparator circuit 4a and the output of the comparator circuit 4b inverted by the inverter circuit 8 are input to an AND circuit A that constitutes a gate circuit 8.
The alarm means 10 is controlled by the output _of
sounds. In the figure, AC is a commercial power supply, Tr is a step-down transformer, R ₅ a and R ₅ b are variable resistors that control the output voltages of the heater control circuits 3 a and 3 b, and LD is a light emitting diode. A gas leak has now occurred and the gas detection elements 1a, 1
When butane or methane comes into contact with b, the resistance of the gas detection element 1a decreases, and the voltage applied to the positive terminal of the operational amplifier (gas detection output) increases to the reference voltage V ₀ a applied to the negative terminal of the operational amplifier Oa. Comparison circuit 4a at the point when it becomes higher than
The output becomes H level. On the other hand, gas detection element 1b
The gas detection sensitivity for butane or methane is almost 0, the resistance of the gas detection element 1b does not change, and the output of the comparator circuit 4b is at L level. Therefore, the output of the inverter circuit 8 becomes H level, the inputs of AND circuit A both become H level, and H level is output from AND circuit A, transistor Q ₂ becomes conductive and electronic buzzer B sounds.
Alerts when a gas leak occurs. Next, when water vapor or alcohol vapor is generated and the high concentration alcohol vapor or water vapor comes into contact with the gas detection elements 1a and 1b, the resistance of the gas detection element 1a becomes low and the output of the comparison circuit 4a becomes H level. . However, at this time, the resistance of the gas detection element 1b becomes low, the output of the comparator circuit 4b becomes H level, and the output of the inverter circuit 8 becomes L level, so the output of the AND circuit A becomes L level, and the alarm means 10 Electronic buzzer B is not driven. Therefore, a gas leak alarm will not be erroneously issued due to alcohol vapor or water vapor. FIG. 3 shows another embodiment, in which the comparator circuit 4
A gate circuit 9 is formed by the contact r of the relay Ry controlled by the output of the relay Ry, and the output of the comparison circuit 4a is connected to the base of the electronic buzzer driving transistor through the gate circuit 9, and the alarm means 10 is activated. The contact r is opened when the output of the comparator circuit 4b is at H level. In the above embodiment, the element heating temperatures of the gas sensing elements 1a and 1b using the same metal oxide semiconductor are set to different values, so that the gas sensing characteristics of the gas sensing elements 1a and 1b are made to be different. , each gas sensing element 1 is made of different metal oxide semiconductors.
A, 1b may be formed to have desired gas detection characteristics, and will be explained in the following examples. It is preferable that the gas detection element 1b exhibits a large resistance change with respect to alcohol vapor and water vapor, and shows no or small resistance change with respect to butane and methane. Some metal oxide semiconductors having such gas sensing properties are made of 100-80% by weight copper oxide (Cu ₂ O, CuO) and 0-20% by weight palladium oxide (PdO). Copper oxide is P
It is a type semiconductor whose resistance value increases greatly when it comes into contact with alcohol vapor, and has high gas detection sensitivity for alcohol vapor, and almost no gas detection sensitivity for methane, and isobutane. Gas detection sensitivity is low for Therefore, copper oxide added with palladium oxide satisfies the gas detection characteristics required for the gas detection element 1b. Figure 4 shows gas detection element 1 whose main component is copper oxide.
This shows the manufacturing process of step b. In the mixing step, a total of 1 g of copper oxide as a main component and an additive (palladium oxide) are weighed and mixed for 30 minutes in a crusher. In the molding process, the mixed material is molded into a cylindrical shape with a diameter of 2 mm using a small press machine under a pressure of 2 tons/cm ² to form an element. At this time, two platinum wire electrodes were buried in each element at the same time, and the element weight was 15mg.
becomes. The product formed in this way is fired in the air (700℃, 3 hours) in the firing process, and in the mounting process, a platinum wire electrode is welded to a terminal block equipped with a heater to create a gas detection device with a predetermined shape. Element 1
Prepare b. Note that the element shape is not limited to the above-mentioned embodiments, and may be any shape including a sintered body, a thick film, and a thin film. The measurement results of the gas detection sensitivities of the gas detection elements 1b prepared in this manner with different amounts of added palladium oxide are shown in Table 1.
The gas detection sensitivity for alcohol vapor is much higher than the gas detection sensitivity for the detection gases except for. However, the measurement of gas detection sensitivity is 0.1
The resistance value Rg in a methane/ _isobutane /alcohol vapor atmosphere with _a concentration _of The element heating temperature was set to 450°C (the highest gas detection sensitivity) by adjusting the voltage applied to the heater.

[Table] Figures 5a and 5b show a gas leak alarm device constructed using the above-mentioned gas detection element 1b and a gas detection element 1a made of an N-type metal oxide semiconductor such as indium oxide (the circuit shown in Figure 1). Op amp in configuration
This figure shows the change in the gas detection output when the + and - inputs of ob are swapped.The gas detection output Vgb of the gas detection element 1b is as shown in Figure 5a. Gas detection output Vgb even if the concentration of detection gas such as
never becomes less than the reference voltage V ₀ b, and for alcohol vapor, at a gas concentration of 0.2%, it becomes less than the reference voltage V ₀ b, and the output of the comparator circuit 4b becomes H level. Therefore, the gas detection output Vgb of the gas detection element 1a changes as shown in _FIG . Even if the output is at H level, in the case of alcohol vapor, the output of comparison circuit 4b is at H level and becomes L level by inverter 8, so the output of AND circuit 9 becomes L level and electronic buzzer B is activated. doesn't work. However, in the case of methane/butane gas, the output of the comparator circuit 4b is always at the L level, and becomes the H level by the inverter 8.
The output of the AND circuit 9 becomes H level and the electronic buzzer B is activated. Next, another gas detection element 1b made of indium oxide (In ₂ O ₃ ) and a gas detection element 1a made of 10 to 0.01% by weight of palladium oxide (Pd) and 90 to 99.99% by weight of indium oxide were prepared. An example will be explained. Figure 6a shows the gas detection sensitivity of the gas detection element 1b made of indium oxide with respect to the element heating temperature T. As is clear from the figure, the gas detection sensitivity to the detection gas decreases as the element heating temperature decreases. The element heating temperature becomes almost 0 at 250°C. Therefore, by setting the element heating temperature to 250° C., it becomes insensitive to the detection gas and satisfies the conditions required of the gas detection element 1b. Figure 6b
shows the gas detection sensitivity of the gas detection element 1a made of indium oxide doped with palladium oxide. By setting the element heating temperature to 450°C, the gas detection sensitivity for both methane and isobutane gases can be increased. A highly sensitive gas leak alarm system can be obtained for both LPG and city gas leaks. The present invention is configured as described above, and a sub-gas detection element sensitive to non-detection target gas (gas other than combustible gas to be detected) is installed in parallel with the main gas detection element, and both gas detection elements are first and second comparison circuits that determine the voltage level of the detection element output;
A gate circuit is provided that selectively operates the alarm means based on the gas detection outputs outputted from both comparison circuits, so that the gas detection output of the gas to be detected is obtained from the first comparison circuit, and the gas detection output of the non-detection target gas is obtained from the first comparison circuit. Since the alarm means is activated only when the gas detection output is not obtained from the second comparison circuit, the main gas detection element that can detect many types of combustible gases is used, so the main gas is not detected. Even if the gas detection element becomes sensitive, the alarm means will not operate due to the non-detection target gas, and a gas leak alarm device with less false alarms due to the non-detection target gas can be obtained. In other words, if flammable gases such as methane or butane are detected individually, it is relatively easy to prevent false alarms caused by non-detectable gases such as alcohol or water vapor, but When a gas is used as a detection target gas, the sensor inevitably becomes sensitive to non-detection target gases, resulting in the problem of false alarms occurring. Therefore, in the present invention,
To solve this problem, a sub-gas detection element that is sensitive to the non-detection target gas is installed to detect the non-detection target gas separately, and when the non-detection target gas is detected, the main gas detection Even if a gas detection output based on the element output is obtained, the alarm means is not operated to prevent malfunctions, and there is an effect that a gas alarm device that is less likely to generate false alarms can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is a block circuit diagram of another embodiment, and Fig. 4 is a diagram showing the manufacturing process of a gas detection element. , FIGS. 5a and 5b are operation explanatory diagrams of still another embodiment, and FIGS. 6a and 6b are operation explanatory diagrams of still another embodiment. 1a and 1b are gas detection elements, 4a and 4b are comparison circuits, 9 is a gate circuit, and 10 is an alarm means.

Claims (1)

[Claims] 1. The resistance value of a gas detection element made of a metal oxide semiconductor whose resistance value changes when it comes into contact with a combustible gas in a heated state reaches a preset value, and the gas detection output increases. In a gas leak alarm system that activates the alarm means when a gas leak is detected, a main gas detection element and a sub-gas detection element with different gas detection characteristics are arranged in the same place, and combustible gas such as methane or butane is detected. A gas detection output is obtained from the first comparison circuit which inputs the voltage based on the resistance change of the main gas detection element that is sensitive to flammable gases, and the gas detection output is A gas leak alarm characterized in that a gate circuit is provided that operates an alarm means only when a gas detection output is not obtained from a second comparator circuit that inputs a voltage based on a resistance change of a sensitive sub-gas detection element. Device. 2. A main gas detection element and a sub gas detection element having different gas detection characteristics are constructed by setting the element heating temperatures of two gas detection elements made of the same metal oxide semiconductor to different values. A gas leak alarm device according to claim 1. 3. The gas leak alarm device according to claim 1, wherein the auxiliary gas detection element is formed of a metal oxide semiconductor in which 20% by weight or less of palladium oxide is added to copper oxide. 4 Sub-gas detection element made of indium oxide
Claim 1, characterized in that the main gas detection element is made of indium oxide heated to 200°C to 250°C and added with 10 to 0.01% by weight of palladium oxide, and heated to 350°C to 450°C. Gas leak alarm device.