Gas detector and gas detection method

Abstract

To provide a gas detector capable of accurately determining a detected gas.SOLUTION: A gas detector 100 comprises an MEMS type semiconductor gas sensor 1 which includes a sensitive part 11 and a heating part 12, and differs in detection sensitivity for a methane gas and an ethane gas with temperature, and a control part 2 which heats the sensitive part 11 up to a first temperature by driving the heating part 12 with pulses at predetermined intervals of time to perform first-temperature detection by the semiconductor gas sensor 1 at the predetermined intervals of time. The control part 2 determines which of a first gas including the methane gas and containing the ethane gas at less than a predetermined ratio and a second gas containing the ethane gas at the predetermined ratio or higher the detected gas is based upon a first detection result of the semiconductor gas sensor 1 at the first temperature and a second detection result of the semiconductor gas sensor 1 at a second temperature at which the detection sensitivity for the methane gas is lower than at the first temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas detector and a gas detection method. [Background technology]

[0002] BACKGROUND ART Gas detectors have been known in the past (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a gas detector equipped with a semiconductor gas sensor that detects methane gas. This gas detector is configured to detect city gas, which is mainly composed of methane gas, and thereby detect city gas leaks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-009263 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because the gas detector described in Patent Document 1 detects leaks of city gas, which is primarily composed of methane gas, by detecting methane gas, it is difficult to determine the type of gas detected, even when it detects methane gas that is not derived from city gas, such as that generated underground, or when it detects methane gas derived from city gas, and there is a risk of falsely detecting a city gas leak. Therefore, there is a need for a gas detector and gas detection method that can accurately determine the type of detected gas.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a gas detector and a gas detection method that are capable of accurately determining the detected gas. [Means for solving the problem]

[0007] In order to achieve the above object, a gas detector according to a first aspect of the present invention comprises: an MEMS-type semiconductor gas sensor including a sensitive portion and a heating portion that heats the sensitive portion to a predetermined temperature, and having detection sensitivity for methane gas and ethane gas that varies depending on the temperature; and a control portion that heats the sensitive portion to a first temperature by pulse driving the heating portion at predetermined time intervals, and performs detection by the semiconductor gas sensor at the first temperature at predetermined time intervals, wherein the control portion controls the semiconductor gas sensor to perform detection at a second temperature that is lower than the first temperature when the detection result at the first temperature exceeds a predetermined threshold, and the control portion determines whether the detected gas is a first gas that contains methane gas and has an ethane gas content of less than a predetermined percentage, or a second gas that contains methane gas and ethane gas at a predetermined percentage or more, based on the first detection result of the semiconductor gas sensor at the first temperature and the second detection result of the semiconductor gas sensor at the second temperature, which has a lower detection sensitivity for methane gas than the first temperature.

[0008] In a gas detector according to a first aspect of the present invention, the control unit determines whether the detected gas is a first gas containing methane gas and having an ethane gas content of less than a predetermined percentage, or a second gas containing methane gas and an ethane gas content of at least a predetermined percentage, based on a first detection result of the semiconductor gas sensor at a first temperature and a second detection result of the semiconductor gas sensor at a second temperature having a lower detection sensitivity for methane gas than the first temperature. Thus, by obtaining detection results at the first and second temperatures using the semiconductor gas sensor, it is possible to distinguish between the first gas containing methane gas and having an ethane gas content of less than a predetermined percentage, and the second gas containing methane gas and an ethane gas content of at least a predetermined percentage. This allows the detected gas to be determined accurately. As a result, erroneous gas detection can be suppressed.

[0009] In the gas detector according to the first aspect, the relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor at the second temperature is preferably greater than the relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor at the first temperature. This configuration makes it easier to determine whether the detected gas contains ethane gas based on the detection result at the second temperature. As a result, it is easier to determine whether the first gas or the second gas is present.

[0010] In the gas detector according to the first aspect, the first temperature is preferably 450° C. or higher and 600° C. or lower, and the second temperature is preferably 200° C. or higher and 400° C. or lower. With this configuration, it is possible to detect methane gas in a relatively high temperature range of 450° C. or higher and 600° C. or lower, and to detect whether or not ethane gas is present in the gas detector in a relatively low temperature range of 200° C. or higher and 400° C. or lower.

[0011] In the gas detector according to the first aspect, the control unit preferably controls the semiconductor gas sensor to pulse-drive the heating unit at predetermined time intervals to heat the sensitive unit to a first temperature and perform detection at the first temperature at predetermined time intervals, and, if methane gas is detected as a result of the first detection, to pulse-drive the heating unit to heat the sensitive unit to a second temperature and perform detection at the second temperature with the semiconductor gas sensor in addition to detection at the first temperature. With this configuration, if methane gas is not to be detected, the sensitive unit is not pulse-driven to heat to the second temperature to detect gas, thereby preventing the process leading up to detection of methane gas from becoming complicated.

[0012] In the gas detector according to the first aspect, the control unit preferably determines whether the detected gas is the first gas or the second gas based on a ratio between the first detection result and the second detection result. With this configuration, the ratio between the first detection result and the second detection result is used, so that the determination of whether the detected gas is the first gas or the second gas can be made with high accuracy regardless of the concentration of the detected gas.

[0013] In this case, the semiconductor gas sensor preferably includes a substrate, an electrode pattern provided on the substrate, a SnO2 sensitive layer covering the electrode pattern, and a palladium catalyst layer covering the SnO2 sensitive layer. By providing the palladium catalyst layer, the difference between the ratio of the first detection result to the second detection result when the first gas is detected and the ratio of the first detection result to the second detection result when the second gas is detected can be increased, thereby enabling the first gas and the second gas to be determined more accurately based on the ratio of the first detection result to the second detection result.

[0014] The gas detector according to the first aspect preferably further includes a communication unit capable of communicating with an external device, and the control unit controls the communication unit to communicate in different ways when it determines that the detected gas is the first gas and when it determines that the detected gas is the second gas. This configuration allows the mode of notification to the external device to differ depending on whether the detected gas is the first gas or the second gas. For example, when it determines that the detected gas is one of the first gas and the second gas, the communication unit may not communicate or the number of communication targets may be reduced. Furthermore, when it determines that the detected gas is the other of the first gas and the second gas, the communication unit may communicate or the number of communication targets may be increased.

[0015] The gas detector according to the first aspect preferably further includes an alarm unit that issues an alarm, and the control unit controls the alarm unit to issue an alarm in different manners when it is determined that the detected gas is the first gas and when it is determined that the detected gas is the second gas. With this configuration, the different manners of notification by the alarm unit allow the user to easily recognize whether the first gas or the second gas has been detected. For example, the user can be notified that the first gas, which includes potentially dangerous methane gas, has been detected, while also being notified in a manner that allows the user to determine whether the detected gas is a more dangerous second gas (e.g., city gas).

[0016] The gas detector according to the first aspect preferably further comprises a hydrogen sulfide sensor capable of detecting hydrogen sulfide gas, and the control unit, when the detection result of the semiconductor gas sensor at the first temperature exceeds a predetermined threshold, causes the hydrogen sulfide sensor to detect hydrogen sulfide gas and determines whether the detected gas contains hydrogen sulfide gas. With this configuration, when gas is detected by the semiconductor gas sensor at the first temperature, it can be easily determined whether the detected gas contains hydrogen sulfide gas based on the detection result of the hydrogen sulfide sensor. As a result, the detected gas can be determined with even greater accuracy.

[0017] In the gas detector according to the first aspect, the detection sensitivity of the semiconductor gas sensor for ethane gas at the first temperature is preferably substantially equal to that at the second temperature. With this configuration, the detection sensitivity of the semiconductor gas sensor for ethane gas is substantially equal to that at the first temperature and the second temperature, and the detection sensitivity of the semiconductor gas sensor for methane gas is lower at the second temperature than at the first temperature. Therefore, the accuracy of detecting ethane gas at the second temperature is relatively increased. Therefore, it is possible to easily determine whether the detected gas contains ethane gas based on the detection result at the second temperature. As a result, it is possible to easily determine whether the first gas or the second gas is present.

[0018] A gas detection method according to a second aspect of the present invention is a gas detection method for a gas detector equipped with an MEMS-type semiconductor gas sensor including a sensitive part and a heating part that heats the sensitive part to a predetermined temperature, and whose detection sensitivity for each of methane gas and ethane gas varies depending on the temperature, and comprises the steps of: heating the sensitive part to a first temperature by pulse driving the heating part at predetermined time intervals, and performing detection at the first temperature with the semiconductor gas sensor at predetermined time intervals; when the detection result at the first temperature exceeds a predetermined threshold, changing the driving of the heating part to perform detection with the semiconductor gas sensor at a second temperature heated to a temperature lower than the first temperature; and determining whether the detected gas is a first gas containing methane gas and having an ethane gas content less than a predetermined percentage, or a second gas containing methane gas and ethane gas at a predetermined percentage or more, based on the first detection result of the semiconductor gas sensor at the first temperature and the second detection result of the semiconductor gas sensor at a second temperature having a lower detection sensitivity for methane gas than the first temperature.

[0019] In a gas detection method according to a second aspect of the present invention, a first detection result of a semiconductor gas sensor at a first temperature and a second detection result of the semiconductor gas sensor at a second temperature, at which the detection sensitivity for methane gas is lower than that at the first temperature, are used to determine whether the detected gas is a first gas containing methane gas and having an ethane content less than a predetermined percentage, or a second gas containing methane gas and a predetermined percentage or more of ethane gas. By obtaining detection results at the first and second temperatures using the semiconductor gas sensor, it is possible to distinguish between the first gas containing methane gas and having an ethane content less than a predetermined percentage, and the second gas containing methane gas and a predetermined percentage or more of ethane gas. This provides a gas detection method capable of accurately determining the detected gas. As a result, erroneous gas detection can be suppressed. [Effects of the Invention]

[0020] According to the present invention, as described above, it is possible to determine the detected gas while preventing the device configuration from becoming complicated. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a block diagram showing a control configuration of the gas detector according to the embodiment. [Figure 2] 1 is a circuit diagram showing an example of the configuration of a gas sensor of a gas detector according to an embodiment; [Figure 3] 1 is a schematic plan view showing an example of the configuration of a gas sensor of a gas detector according to an embodiment; [Figure 4] 1 is a schematic cross-sectional view showing an example of the configuration of a gas sensor of a gas detector according to an embodiment; [Figure 5] FIG. 4 is a diagram showing an example of the relationship between gas sensitivity and temperature of a gas sensor of the gas detector according to the embodiment. [Figure 6] FIG. 10 is a graph showing the gas sensitivity at 300° C. of the gas sensor of the gas detector according to one embodiment. [Figure 7] FIG. 10 is a graph showing the gas sensitivity at 550° C. of the gas sensor of the gas detector according to one embodiment. [Figure 8] FIG. 10 is a diagram showing the sensor resistance value at 300° C. of the gas sensor of the gas detector according to the embodiment. [Figure 9] FIG. 10 is a diagram showing the sensor resistance value at 550° C. of the gas sensor of the gas detector according to the embodiment. [Figure 10] FIG. 10 is a diagram showing the dynamic resistance ratio at 300° C. of the gas sensor of the gas detector according to one embodiment. [Figure 11] FIG. 10 is a diagram showing the dynamic resistance ratio at 550° C. of the gas sensor of the gas detector according to the embodiment. [Figure 12] FIG. 2 is a diagram for explaining an example of driving a gas detector according to an embodiment. [Figure 13] 10 is a flowchart illustrating a gas detection process of the gas detector according to one embodiment. [Figure 14] FIG. 10 is a block diagram showing a control configuration of a gas detector according to a modified example of an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] The configuration of a gas detector 100 according to one embodiment will be described with reference to FIGS.

[0024] (Gas detector configuration) The gas detector 100 of this embodiment detects a target gas. When the gas detector 100 detects the target gas, it outputs an alarm to notify the user of a gas leak or the like. The target gas is a gas that the gas detector 100 is to detect. For example, the target gas is a fuel gas (city gas) containing methane gas as a main component.

[0025] 1, the gas detector 100 includes a semiconductor gas sensor 1, a control unit 2, a notification unit 3, and a communication unit 4. The semiconductor gas sensor 1, the control unit 2, the notification unit 3, and the communication unit 4 are housed within a housing of the gas detector 100. The gas detector 100 operates on power supplied from a commercial power source or on power from a battery (not shown).

[0026] The semiconductor gas sensor 1 includes a sensitive portion 11 and a heating portion 12 that heats the sensitive portion 11 to a predetermined temperature. The semiconductor gas sensor 1 has different detection sensitivities for methane gas and ethane gas depending on the temperature. The semiconductor gas sensor 1 is an MEMS-type gas sensor. In other words, the semiconductor gas sensor 1 is formed using MEMS (Micro Electro Mechanical Systems) technology, which forms a mechanical structure in a semiconductor substrate using a semiconductor manufacturing process. For example, the semiconductor gas sensor 1 has a side dimension of approximately 0.1 mm.

[0027] The semiconductor gas sensor 1 includes a measurement circuit as shown in Fig. 2. The measurement circuit includes a sensor section 1a, resistors R1 and R2, and a load resistor R3. A voltage is applied to the sensor section 1a, resistors R1 and R2, and load resistor R3 from a power source E. A sensor output value is output from a terminal A1 connected between the sensor section 1a and the load resistor R3, and a terminal A2 connected between the resistors R1 and R2.

[0028] The resistance value of the semiconductor gas sensor 1 changes when the gas to be detected is adsorbed. Therefore, the change in the electrical resistance of the semiconductor gas sensor 1 is extracted as a deviation voltage, which is used as the sensor output value, making it possible to measure the concentration of the gas to be detected.

[0029] Specifically, the sensitive part 11 of the semiconductor gas sensor 1 adsorbs oxygen in the air when heated to a predetermined temperature by the heating part 12. Furthermore, when a detection target gas (methane gas, ethane gas) is present, the oxygen adsorbed to the sensitive part 11 reacts with the gas, causing a change in the electrical resistance of the sensitive part 11. The semiconductor gas sensor 1 detects methane gas and ethane gas by measuring this change in electrical resistance.

[0030] The semiconductor gas sensor 1 can detect multiple types of gases using a common gas sensor element (sensitive part 11). Specifically, the sensitivity of the semiconductor gas sensor 1 changes for each type of gas depending on the temperature to which the sensitive part 11 is heated by the heating part 12. In the first embodiment, the semiconductor gas sensor 1 is provided with a single gas sensor element (sensitive part 11). In other words, the gas detector 100 detects a first gas and a second gas, which are different from each other, using the common semiconductor gas sensor 1.

[0031] As shown in FIGS. 3 and 4, the semiconductor gas sensor 1 includes a substrate 13, an electrode pattern 14 provided on the substrate 13 via an insulating film 13a, a SnO2 sensitive layer 15 covering the electrode pattern 14, and a palladium catalyst layer 16 covering the SnO2 sensitive layer 15. The substrate 13 is made of Si. A cavity C is formed in the substrate 13. The electrode pattern 14 is made of Pt. The electrode pattern 14 also serves as the sensitive part 11 and the heating part 12. In other words, the electrode pattern 14 is heated to a predetermined temperature by applying electricity. In addition, when a target gas is present in the electrode pattern 14, the resistance value changes, thereby changing the sensor output value.

[0032] The SnO2 sensitive layer 15 is formed by sintering a paste containing SnO2. The SnO2 sensitive layer 15 is doped with approximately 0.05 at% (atomic percent) to 0.2 at% of Sb (antimony) relative to the Sn (tin) in SnO2 (tin oxide). For example, the SnO2 sensitive layer 15 is formed by applying a paste of tin oxide semiconductor doped with 0.1 at% Sb and having a predetermined conductivity to a thickness of approximately 20 to 30 μm on the electrode pattern 14, and then heating and sintering it in an electric furnace. The doped Sb is, for example, antimony pentoxide (Sb2O5).

[0033] The palladium catalyst layer 16 is formed by sintering a paste containing palladium. For example, the palladium catalyst layer 16 is formed by adding an aqueous solution of palladium chloride to tin oxide by impregnation to a concentration of 10 mol%, baking the mixture in an electric furnace, pulverizing the mixture, kneading it with water to form a paste, applying it to the SnO2 sensitive layer 15 to a film thickness of about 20 to 30 μm, and heating and sintering it in an electric furnace.

[0034] The control unit 2 controls each part of the gas detector 100 (semiconductor gas sensor 1, notification unit 3, communication unit 4). The control unit 2 also controls the identification of the detected gas. The control unit 2 includes a processor such as a CPU (Central Processing Unit) and a memory such as a RAM (Random Access Memory). The control unit 2 also executes a predetermined program to perform control processing.

[0035] When a target gas is detected, the alarm unit 3 issues an alert using sound, light, or the like. The alarm unit 3 issues an alert in different ways depending on the type of gas detected. For example, the alarm unit 3 issues an alert in different ways when a first gas is detected and when a second gas is detected. The alarm unit 3 can issue an alert by varying the type, volume, length, etc. of the alerting sound. The alarm unit 3 can also issue an alert by varying the color of the alerting light, whether it flashes, where it emits light, etc.

[0036] For example, when the notification unit 3 indicates the determination result by emitting light such as an LED, it notifies the detection of methane gas by lighting up the LED yellow. Furthermore, if ethane gas is detected in a subsequent detection, the notification unit 3 notifies the detection of methane gas by lighting up another LED red in parallel with lighting up the LED yellow. That is, if the notification unit 3 notifies the detection of methane gas and then determines that the detected gas is a second gas (city gas) containing ethane gas, it notifies the detection of the second gas (city gas) containing ethane gas while leaving the notification of the detection of methane gas. Furthermore, if ethane gas is detected in a subsequent detection after the detection of methane gas, the notification unit 3 may notify the detection of methane gas by changing the LED that was lit yellow to a red LED. Furthermore, for example, when the notification unit 3 indicates the determination result by sound, it notifies the detection of methane gas by a short "beep, beep, beep" sound. Furthermore, if ethane gas is detected in subsequent detections, the notification unit 3 will notify the detection of ethane gas by issuing a long "beep, beep, beep" sound.

[0037] The communication unit 4 is capable of communicating with the external device 5. For example, the communication unit 4 communicates with the external device 5 via a network. Alternatively, the communication unit 4 may communicate with the external device 5 by being directly connected to the external device 5 via wired or wireless communication.

[0038] The control unit 2 heats the sensitive unit 11 to a first temperature by pulse-driving the heating unit 12 at predetermined time intervals, and performs detection of the semiconductor gas sensor 1 at the first temperature at predetermined time intervals. That is, the control unit 2 pulse-heats the sensitive unit 11 to the first temperature at which methane gas can be detected at predetermined time intervals, and performs detection of methane gas at predetermined time intervals. For example, the control unit 2 performs detection of the semiconductor gas sensor 1 at the first temperature at approximately 60-second intervals. The control unit 2 may perform detection during the entire period of the pulse during which the sensitive unit 11 is heated in a pulsed manner, or may perform detection during a part of the period (for example, a single point in time) of the pulse during which the sensitive unit 11 is heated in a pulsed manner.

[0039] Furthermore, when the detection result at the first temperature exceeds a predetermined threshold, the control unit 2 controls the semiconductor gas sensor 1 to perform detection at a second temperature that is lower than the first temperature. That is, the control unit 2 detects methane gas at the first temperature at predetermined time intervals, and when methane gas is detected, detects gas at the second temperature that is lower than the first temperature.

[0040] Here, in this embodiment, the control unit 2 determines whether the detected gas is a first gas containing methane gas and having an ethane gas content of less than a predetermined percentage, or a second gas containing methane gas and an ethane gas content of more than a predetermined percentage, based on the first detection result of the semiconductor gas sensor 1 at a first temperature and the second detection result of the semiconductor gas sensor 1 at a second temperature at which the detection sensitivity of methane gas is lower than that at the first temperature.

[0041] That is, when the first detection result of the semiconductor gas sensor 1 at the first temperature indicates that a gas containing methane gas is detected, the control unit 2 performs control to determine the type of the detected gas. The control unit 2 determines whether the detected gas is a first gas, which is a gas such as natural gas that has a low ethane content, or a second gas, which is city gas that has an ethane content of a predetermined percentage or more. By determining whether the first gas or second gas is a city gas (second gas), it is possible to identify whether the leak is city gas or not. As a result, it is possible to prevent the detected methane gas from being mistakenly detected as a city gas leak when it originates from natural gas.

[0042] As shown in Fig. 5, the semiconductor gas sensor 1 has different detection sensitivities for methane gas and ethane gas depending on the temperature. In the example shown in Fig. 5, the concentrations of methane gas and ethane gas are each 300 ppm. The detection sensitivity of the semiconductor gas sensor 1 for methane gas increases as the temperature increases. The detection sensitivity of the semiconductor gas sensor 1 for ethane gas reaches a peak at 400°C to 450°C, and then increases.

[0043] Moreover, the semiconductor gas sensor 1 has sensitivity characteristics as shown in Fig. 6 at 300°C. In the example shown in Fig. 6, at 300°C, the semiconductor gas sensor 1 has higher sensitivity characteristics to city gas than to methane gas. City gas contains, for example, 85% to 90% methane, 5 to 8% ethane, 2 to 4% propane, and 1 to 2% butane by volume.

[0044] Moreover, the semiconductor gas sensor 1 has sensitivity characteristics at 550° C. as shown in Fig. 7. In the example shown in Fig. 7, at 550° C., the semiconductor gas sensor 1 has higher sensitivity characteristics to methane gas than to city gas.

[0045] Moreover, at 300°C, the semiconductor gas sensor 1 has a sensor resistance value as shown in Fig. 8. In the example shown in Fig. 8, at 300°C, the sensor resistance value of the semiconductor gas sensor 1 for city gas is smaller than the sensor resistance value for methane gas.

[0046] Moreover, at 550° C., the semiconductor gas sensor 1 has a sensor resistance value as shown in Fig. 9. In the example shown in Fig. 9, at 550° C., the sensor resistance value of the semiconductor gas sensor 1 for methane gas is smaller than the sensor resistance value for city gas.

[0047] Furthermore, at 300°C, the semiconductor gas sensor 1 exhibits the dynamic resistance ratio shown in Fig. 10. The dynamic resistance ratio is the ratio of the resistance when a detectable gas is present to the resistance when air is present. In the example shown in Fig. 10, at 300°C, the dynamic resistance ratio of the semiconductor gas sensor 1 for city gas is smaller than the dynamic resistance ratio for methane gas.

[0048] Moreover, at 550°C, the semiconductor gas sensor 1 exhibits a dynamic resistance ratio as shown in Fig. 11. In the example shown in Fig. 11, at 550°C, the dynamic resistance ratio of the semiconductor gas sensor 1 for methane gas is smaller than the dynamic resistance ratio for city gas.

[0049] In this embodiment, for example, the first temperature is 450°C or higher and 600°C or lower, and the second temperature is 200°C or higher and 400°C or lower. The second temperature is preferably low. In other words, the lower the temperature, the greater the difference in sensitivity between methane gas and city gas. Therefore, it is possible to accurately distinguish between the first gas (methane gas) and the second gas (city gas) based on the detection result of the low second temperature. However, since the detection sensitivity of methane gas decreases as the temperature decreases, it is preferable that the second temperature is not too low. For example, the second temperature is preferably approximately 300°C. Furthermore, from the standpoint of gas selectivity and durability, it is preferable that the second temperature is not too high, and the second temperature is preferably 600°C or lower.

[0050] Furthermore, the detection sensitivity of the semiconductor gas sensor 1 to ethane gas at the first temperature is substantially equal to that at the second temperature. For example, when the first temperature is 550°C and the second temperature is 300°C, the detection sensitivity of the semiconductor gas sensor 1 to ethane gas is substantially equal, as shown in FIG.

[0051] Furthermore, the relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor 1 at the second temperature is greater than the relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor 1 at the first temperature. For example, when the first temperature is 550°C and the second temperature is 300°C, as shown in FIG. 5, the detection sensitivity of ethane gas of the semiconductor gas sensor 1 is approximately equal. Furthermore, the detection sensitivity of methane gas of the semiconductor gas sensor 1 at the first temperature (550°C) is higher than that at the second temperature (300°C). Therefore, the relative ratio, which is the value obtained by dividing the detection sensitivity of ethane gas of the semiconductor gas sensor 1 at the second temperature (300°C) by the detection sensitivity of methane gas, is greater than the relative ratio, which is the value obtained by dividing the detection sensitivity of ethane gas of the semiconductor gas sensor 1 at the first temperature (550°C) by the detection sensitivity of methane gas.

[0052] Furthermore, the control unit 2 pulse-drives the heating unit 12 at predetermined time intervals to heat the sensitive unit 11 to a first temperature, and performs detection at the first temperature at predetermined time intervals with the semiconductor gas sensor 1. Furthermore, when methane gas is detected as a first detection result, the control unit 2 controls the heating unit 12 to pulse-drive the sensitive unit 11 to a second temperature, and performs detection at the second temperature with the semiconductor gas sensor 1 in addition to detection at the first temperature.

[0053] For example, as shown in Figure 12, the control unit 2 controls the semiconductor gas sensor 1 to perform normal driving (see Figure 12(A)), in which gas detection is performed by the semiconductor gas sensor 1 at a first temperature at predetermined time intervals ta, and combined driving (see Figures 12(B)(C)), in which gas detection is performed by the semiconductor gas sensor 1 at both the first temperature and the second temperature when methane gas is detected.

[0054] As shown in Fig. 12(A), under normal circumstances (when methane gas is not being detected), the sensitive part 11 is heated to a first temperature by pulse driving the heating part 12 at predetermined time intervals ta, and detection is performed at the first temperature by the semiconductor gas sensor 1. In the example shown in Fig. 12(A), detection is performed by the semiconductor gas sensor 1 at the first temperature at time t1. Then, detection is performed by the semiconductor gas sensor 1 at the first temperature at time t2, which is the time interval ta after time t1. Thereafter, detection is performed by the semiconductor gas sensor 1 at the first temperature at times t3, t4, and so on, at intervals ta.

[0055] As shown in FIG. 12(B), when a gas detection result at a first temperature normally performed exceeds a predetermined threshold (when methane gas exceeding a predetermined concentration is detected), the control unit 2 controls gas detection at both the first temperature and the second temperature. In the example shown in FIG. 12(B), methane gas at a methane alarm level is detected at time t12, which is a time interval ta after time t11. Based on the detection of methane gas, the control unit 2 pulse-drives the heating unit 12 to heat the sensitive unit 11 to the second temperature at time t13, which is a timing before the time interval ta has elapsed since time t12, thereby performing detection at the second temperature with the semiconductor gas sensor 1. For example, the control unit 2 performs detection at the second temperature at time t13, which is ta / 2 after time t12, when detection at the first temperature was performed.

[0056] The control unit 2 also performs detection at the first temperature at time t14, which is a time interval ta after time t12. Based on the detection of methane gas at time t14, the control unit 2 also performs detection at the second temperature at time t15, which is a timing before the time interval ta has elapsed since time t14. The control unit 2 also performs detection at the first temperature at time t16, which is a time interval ta after time t14.

[0057] Furthermore, when alternately detecting at both the first temperature and the second temperature, if the detection result at the first temperature is equal to or lower than a predetermined threshold (methane gas exceeding a predetermined concentration is not detected), the control unit 2 stops detection at the second temperature, thereby returning to normal operation in which gas detection is performed by the semiconductor gas sensor 1 at the first temperature at predetermined time intervals ta.

[0058] 12(C), from time t21 to time t24, detection at the first temperature and detection at the second temperature are alternately performed. At time t25, the detection result at the first temperature is equal to or less than the predetermined threshold (methane gas exceeding the predetermined concentration is not detected). In this case, detection at the second temperature is stopped. Then, the control unit 2 performs detection at the first temperature from time t26, which is a time interval ta after time t25.

[0059] Furthermore, the control unit 2 determines whether the detected gas is the first gas or the second gas based on the ratio between the first detection result and the second detection result. Specifically, the control unit 2 calculates a determination value by dividing the second detection result (value at the second temperature) by the first detection result (value at the first temperature). If the calculated determination value is equal to or greater than a set threshold, the control unit 2 determines that the detected gas is the second gas (city gas). On the other hand, if the calculated determination value is less than the set threshold, the control unit 2 determines that the detected gas is the first gas (methane gas).

[0060] For example, if the first temperature is 550°C, the value when 3000 ppm methane gas is detected is 130 mV, and the value when 3000 ppm city gas is detected is 123 mV. If the second temperature is 300°C, the value when 3000 ppm methane gas is detected is 42 mV, and the value when 3000 ppm city gas is detected is 65 mV. In this case, the methane gas judgment value V11 is 42 mV / 130 mV ≒ 0.323. Furthermore, the city gas judgment value V12 is 65 mV / 123 mV ≒ 0.529. In this case, the difference between the judgment values ​​V11 and V12 is 0.206, which is a significant difference (0.1 or more). For example, if the first temperature is 550°C and the second temperature is 300°C, the threshold value for determining that the detected gas is the first gas (methane gas) may be 0.37, and the threshold value for determining that the detected gas is the second gas (city gas) may be 0.4. That is, the control unit 2 determines that the detected gas is the first gas (methane gas) when the determination value is 0.37 or less, and determines that the detected gas is the second gas (city gas) when the determination value is 0.4 or more. Furthermore, if the determination value is greater than 0.37 but less than 0.4, the control unit 2 repeats measurement and determination at the second temperature until the determination value becomes 0.37 or less or 0.4 or more. Alternatively, the threshold value for determining that the detected gas is the first gas and the threshold value for determining that the detected gas is the second gas may be a single value. For example, the determination value may be a value between 0.323 and 0.529 (e.g., 0.38). In this case, the control unit 2 may determine that the detected gas is the first gas (methane gas) when the judgment value is 0.38 or less, and may determine that the detected gas is the second gas (city gas) when the judgment value is greater than 0.38. The control unit 2 may also determine whether the detected gas is the first gas or the second gas by using an average of judgment values ​​calculated by measuring the gas multiple times at the first temperature and the second temperature.

[0061] For example, if the first temperature is 550°C, the value when 3000 ppm methane gas is detected is 130 mV, and the value when 3000 ppm city gas is detected is 123 mV. If the second temperature is 350°C, the value when 3000 ppm methane gas is detected is 60 mV, and the value when 3000 ppm city gas is detected is 80 mV. In this case, the methane gas judgment value V21 is 60 mV / 130 mV ≒ 0.462. Furthermore, the city gas judgment value V22 is 80 mV / 123 mV ≒ 0.650. In this case, the difference between the judgment value V21 and the judgment value V22 is 0.188, which is a significant difference (0.1 or more). For example, if the first temperature is 550°C and the second temperature is 350°C, the threshold value for determining that the detected gas is the first gas (methane gas) may be 0.5, and the threshold value for determining that the detected gas is the second gas (city gas) may be 0.6. That is, the control unit 2 determines that the detected gas is the first gas (methane gas) when the determination value is 0.5 or less, and determines that the detected gas is the second gas (city gas) when the determination value is 0.6 or more. Furthermore, if the determination value is greater than 0.5 but less than 0.6, the control unit 2 repeats measurement and determination at the second temperature until the determination value becomes 0.5 or less or 0.6 or more. Alternatively, the threshold value for determining that the detected gas is the first gas and the threshold value for determining that the detected gas is the second gas may be a single value. For example, the determination value may be a value between 0.462 and 0.650 (e.g., 0.55). In this case, the control unit 2 may determine that the detected gas is the first gas (methane gas) when the judgment value is 0.55 or less, and may determine that the detected gas is the second gas (city gas) when the judgment value is greater than 0.55.

[0062] For example, if the first temperature is 550°C, the value when 3000 ppm methane gas is detected is 130 mV, and the value when 3000 ppm city gas is detected is 123 mV. If the second temperature is 400°C, the value when 3000 ppm methane gas is detected is 86 mV, and the value when 3000 ppm city gas is detected is 102 mV. In this case, the methane gas judgment value V31 is 86 mV / 130 mV ≒ 0.699. Furthermore, the city gas judgment value V32 is 102 mV / 123 mV ≒ 0.829. In this case, the difference between the judgment value V31 and the judgment value V32 is 0.13, which is a significant difference (0.1 or more). For example, if the first temperature is 550°C and the second temperature is 400°C, the threshold value for determining that the detected gas is the first gas (methane gas) may be 0.75, and the threshold value for determining that the detected gas is the second gas (city gas) may be 0.77. That is, the control unit 2 determines that the detected gas is the first gas (methane gas) when the determination value is 0.75 or less, and determines that the detected gas is the second gas (city gas) when the determination value is 0.77 or more. If the determination value is greater than 0.75 but less than 0.77, the control unit 2 repeats measurement and determination at the second temperature until the determination value becomes 0.75 or less or 0.77 or more. Alternatively, the threshold value for determining that the detected gas is the first gas and the threshold value for determining that the detected gas is the second gas may be a single value. For example, the determination value may be a value between 0.699 and 0.829 (e.g., 0.76). In this case, the control unit 2 may determine that the detected gas is the first gas (methane gas) when the judgment value is 0.76 or less, and may determine that the detected gas is the second gas (city gas) when the judgment value is greater than 0.77.

[0063] The threshold value for determination is changed as appropriate depending on the first temperature and the second temperature. The threshold value for determination may be the same for both the first gas and the second gas.

[0064] Furthermore, the control unit 2 controls the communication mode of the communication unit 4 differently depending on whether the detected gas is determined to be the first gas (methane gas) or the second gas (city gas). For example, if the control unit 2 determines that the detected gas is the first gas (methane gas), the control unit 2 does not communicate via the communication unit 4. In other words, if the control unit 2 determines that the detected gas is the first gas (methane gas), it does not notify the external device 5. On the other hand, if the control unit 2 determines that the detected gas is the second gas (city gas), the control unit 2 notifies the external device 5 via the communication unit 4 that the second gas (city gas) has been detected. The control unit 2 may also communicate once when the detection result at the first temperature exceeds a threshold value (when methane gas exceeding a predetermined concentration is detected). In this case, the control unit 2 communicates via the communication unit 4 to notify the external device 5 that methane gas has been detected. The control unit 2 may also perform additional communication when the detection at the second temperature is performed and a gas is determined to be a gas. In this case, if the control unit 2 determines that the detected gas is the second gas (city gas), it additionally notifies the external device 5 via the communication unit 4 that the second gas (city gas) has been detected. On the other hand, if the control unit 2 determines that the detected gas is the first gas (methane gas), it does not issue an additional notification to the external device 5 via the communication unit 4. Furthermore, the control unit 2 may communicate with the external device 5 via the communication unit 4 in different ways depending on whether it has determined that the detected gas is the first gas (methane gas) or the second gas (city gas).

[0065] Furthermore, for example, when the control unit 2 detects methane gas, it notifies the external device 5 via the communication unit 4. If ethane gas is detected in a subsequent detection, the control unit 2 notifies the external device 5 via the communication unit 4 of the detection of ethane gas in parallel with the notification of the detection of methane gas. That is, the control unit 2 notifies the external device 5 via the communication unit 4 of the detection of methane gas, and then, if the control unit 2 determines that the detected gas is a second gas (city gas) containing ethane gas, it notifies the external device 5 of the detection of the second gas (city gas) containing ethane gas, while leaving the notification of the detection of methane gas intact. Furthermore, if ethane gas is detected in a detection after the detection of methane gas, the control unit 2 may change the notification of the detection of methane gas to a notification of the detection of the second gas (city gas) containing ethane gas and notify the external device 5 via the communication unit 4.

[0066] Furthermore, the control unit 2 controls the alarm unit 3 to issue an alert in different manners when it determines that the detected gas is the first gas (methane gas) and when it determines that the detected gas is the second gas (city gas). For example, the control unit 2 issues an alert by using different sounds and lights when it determines that the detected gas is the first gas (methane gas) and when it determines that the detected gas is the second gas (city gas). The control unit 2 may also issue an alert once the detection result at the first temperature exceeds a threshold value (when methane gas exceeding a predetermined concentration is detected). In this case, the control unit 2 issues an alert by using the alarm unit 3 that methane gas has been detected. Furthermore, the control unit 2 issues an alert in different manners when it detects the detected gas at the second temperature and determines that the detected gas is the first gas (methane gas) and when it determines that the detected gas is the second gas (city gas). That is, when the control unit 2 determines that the detected gas is the first gas (methane gas), it notifies the notification unit 3 of the possibility of an inflow of natural gas. Also, when the control unit 2 determines that the detected gas is the second gas (city gas), it notifies the notification unit 3 of the possibility of a city gas leak.

[0067] (Gas detection processing) Next, the gas detection process performed by the control unit 2 will be described with reference to FIG.

[0068] 13, the control unit 2 pulse-drives the heating unit 12 to heat the sensitive unit 11 to a first temperature at predetermined time intervals, thereby performing detection at the first temperature by the semiconductor gas sensor 1 at the predetermined time intervals. In step S2, the control unit 2 determines whether the detection result at the first temperature exceeds a predetermined threshold and whether methane gas exceeding a predetermined concentration has been detected. If methane gas is detected, the control unit 2 proceeds to step S3; if methane gas is not detected, the control unit 2 returns to step S1 and continues performing detection at the first temperature at predetermined intervals.

[0069] In step S3, the control unit 2 notifies the notification unit 3 that methane gas has been detected. The control unit 2 also notifies an external device via the communication unit 4 that methane gas has been detected. In step S4, the control unit 2 performs detection at a second temperature between detections at the first temperature. That is, the control unit 2 pulse-drives the heating unit 12 to heat the sensitive unit 11 to the second temperature, and performs detection by the semiconductor gas sensor 1 at the second temperature in addition to detection at the first temperature. In step S5, the control unit 2 determines whether the detected gas is a first gas containing methane gas and having an ethane gas content of less than a predetermined percentage, or a second gas containing methane gas and an ethane gas content of equal to or greater than a predetermined percentage, based on the first detection result of the semiconductor gas sensor 1 at the first temperature and the second detection result of the semiconductor gas sensor 1 at a second temperature at which the detection sensitivity for methane gas is lower than that at the first temperature.

[0070] In step S6, the control unit 2 determines whether the detected gas is the first gas (methane gas) or the second gas (city gas). If it is the first gas, the process proceeds to step S9, and if it is the second gas, the process proceeds to step S7. In step S7, the control unit 2 causes the notification unit 3 to issue a notification in a manner for the second gas (city gas).

[0071] In step S8, the control unit 2 notifies the external device that the second gas (city gas) has been detected via the communication unit 4. In step S9, the control unit 2 causes the notification unit 3 to issue a notification in the manner for the first gas (methane gas).

[0072] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0073] In this embodiment, as described above, the control unit 2 determines whether the detected gas is a first gas containing methane gas and having an ethane content less than a predetermined percentage, or a second gas containing methane gas and a predetermined percentage or more of ethane gas, based on the first detection result of the semiconductor gas sensor 1 at a first temperature and the second detection result of the semiconductor gas sensor 1 at a second temperature, which has a lower methane gas detection sensitivity than the first temperature. Thus, by obtaining detection results at the first and second temperatures using the semiconductor gas sensor 1, it is possible to distinguish between the first gas containing methane gas and having an ethane content less than a predetermined percentage, and the second gas containing methane gas and a predetermined percentage or more of ethane gas. This eliminates the need for multiple gas sensors, thereby preventing an increase in the number of parts. As a result, the detected gas can be determined without complicating the device configuration. As a result, erroneous gas detection can be prevented.

[0074] Furthermore, in this embodiment, as described above, the relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor 1 at the second temperature is greater than the relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor 1 at the first temperature. This makes it easier to determine whether the detected gas contains ethane gas based on the detection result at the second temperature. As a result, it is easier to determine whether the first gas or the second gas is present.

[0075] In this embodiment, as described above, the first temperature is 450° C. or higher and 600° C. or lower, and the second temperature is 200° C. or higher and 400° C. or lower. This makes it possible to detect methane gas in the relatively high temperature range of 450° C. or higher and 600° C. or lower, and to detect whether or not ethane gas is present in the relatively low temperature range of 200° C. or higher and 400° C. or lower.

[0076] Furthermore, in this embodiment, as described above, the control unit 2 pulse-drives the heating unit 12 at predetermined time intervals to heat the sensitive unit 11 to a first temperature and performs detection at the first temperature with the semiconductor gas sensor 1 at predetermined time intervals, and, if methane gas is detected as a result of the first detection, controls the heating unit 12 to pulse-drive the sensitive unit 11 to a second temperature and perform detection at the second temperature with the semiconductor gas sensor 1 in addition to detection at the first temperature. As a result, if methane gas is not to be detected, the sensitive unit 11 is not pulse-driven to be heated to the second temperature to detect gas, thereby preventing the process leading up to detection of methane gas from becoming complicated.

[0077] In this embodiment, as described above, the control unit 2 determines whether the detected gas is the first gas or the second gas based on the ratio between the first detection result and the second detection result. As a result, the ratio between the first detection result and the second detection result is used, and therefore the first gas and the second gas can be determined with high accuracy regardless of the concentration of the detected gas.

[0078] Furthermore, in this embodiment, as described above, the semiconductor gas sensor 1 includes a substrate 13, an electrode pattern 14 provided on the substrate 13, an SnO2 sensitive layer 15 covering the electrode pattern 14, and a palladium catalyst layer 16 covering the SnO2 sensitive layer 15. Thus, by providing the palladium catalyst layer 16, it is possible to increase the difference between the ratio of the first detection result to the second detection result when the first gas is detected and the ratio of the first detection result to the second detection result when the second gas is detected, and therefore it is possible to more accurately determine whether the first gas or the second gas is present based on the ratio of the first detection result to the second detection result.

[0079] Furthermore, in this embodiment, as described above, the control unit 2 controls the communication unit 4 to communicate in different ways when it determines that the detected gas is the first gas and when it determines that the detected gas is the second gas. This makes it possible to change the manner in which notification is sent to the external device 5 depending on whether it is the first gas or the second gas. For example, when it determines that the detected gas is one of the first gas and the second gas, it is possible to not communicate via the communication unit 4 or to reduce the number of targets for communication. Furthermore, when it determines that the detected gas is the other of the first gas and the second gas, it is possible to communicate via the communication unit 4 or to increase the number of targets for communication.

[0080] Furthermore, in this embodiment, as described above, the control unit 2 controls the notification unit 3 to issue a notification in different manners when it determines that the detected gas is the first gas and when it determines that the detected gas is the second gas. This allows the user to easily recognize whether the first gas or the second gas has been detected, based on the different notification manners of the notification unit 3.

[0081] Furthermore, in this embodiment, as described above, the detection sensitivity of the semiconductor gas sensor 1 for ethane gas at the first temperature is substantially equal to that at the second temperature. Therefore, since the detection sensitivity of the semiconductor gas sensor 1 for ethane gas is substantially equal at the first temperature and the detection sensitivity of the semiconductor gas sensor 1 for methane gas is lower at the second temperature than at the first temperature, the accuracy of detecting ethane gas at the second temperature is relatively increased. Therefore, it is possible to easily determine whether the detected gas contains ethane gas based on the detection result at the second temperature. As a result, it is possible to easily determine whether the first gas or the second gas is present.

[0082] (Variation) The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than the above description of the embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0083] For example, in the above embodiment, an example of a configuration in which one semiconductor gas sensor is provided in the gas detector is shown, but the present invention is not limited to this. In the present invention, a gas sensor for detecting other gases may be provided. For example, a gas sensor for detecting carbon monoxide gas may be provided separately. Also, a gas sensor for detecting hydrogen sulfide gas may be provided separately.

[0084] As shown in the modified example of FIG. 14, the gas detector 200 may include a semiconductor gas sensor 1, a control unit 2, a notification unit 3, a communication unit 4, and a hydrogen sulfide sensor 6. In this case, the control unit 2 may detect hydrogen sulfide gas using the hydrogen sulfide sensor 6 when the detection result of the semiconductor gas sensor 1 at the first temperature exceeds a predetermined threshold, and determine whether the detected gas contains hydrogen sulfide gas. With this configuration, when gas is detected by the semiconductor gas sensor 1 at the first temperature, it is possible to easily determine whether the detected gas contains hydrogen sulfide gas based on the detection result of the hydrogen sulfide sensor. As a result, the detected gas can be determined with greater accuracy. In other words, it is possible to determine whether the detected gas contains hydrogen sulfide gas and methane gas, which are generated from sewage or the like.

[0085] The hydrogen sulfide sensor 6 is a semiconductor gas sensor. It is formed using MEMS technology, which uses semiconductor manufacturing processes to form a mechanical structure in a semiconductor substrate. For example, the hydrogen sulfide sensor 6 has a side dimension of approximately 0.1 mm. The hydrogen sulfide sensor 6 also includes a substrate, an electrode pattern provided on the substrate, and a ZnO sensitive layer covering the electrode pattern. The ZnO sensitive layer also contains gallium. For example, the ZnO sensitive layer is doped with approximately 0.1 at% (atomic percent) to 1 at% of Ga (gallium) relative to the Zn (zinc) in ZnO (zinc oxide). For example, the ZnO sensitive layer is doped with 0.2 at% of Ga. The doped Ga is, for example, gallium oxide (Ga2O3). The hydrogen sulfide sensor 6 detects gas by heating the ZnO sensitive layer to a predetermined temperature using pulse drive.

[0086] In this case, the control unit 2 determines whether the detected gas is a first gas (methane gas) or a second gas (city gas), and also whether it is a third gas, including methane gas and hydrogen sulfide gas generated from sewage. When determining the third gas in addition to the first and second gases, the control unit 2 may communicate and notify the final result after a series of determinations, or may communicate and notify the result as appropriate for each determination. The manner of communication and notification may also be changed as appropriate depending on the determination results.

[0087] In the above embodiment, gas detection at the first temperature is performed at predetermined time intervals of approximately 60 seconds, but the present invention is not limited to this. In the present invention, gas detection at the first temperature may be performed at predetermined time intervals other than 60 seconds.

[0088] In the above embodiment, the first gas is methane gas and the second gas is city gas, but the present invention is not limited to this. In the present invention, the second gas may be a gas other than city gas that contains methane gas and ethane gas.

[0089] In the above embodiment, the detection sensitivity of the semiconductor gas sensor to ethane gas at the first temperature and the detection sensitivity of the semiconductor gas sensor to ethane gas at the second temperature are substantially equal, but the present invention is not limited to this. In the present invention, the detection sensitivity of the semiconductor gas sensor to ethane gas at the first temperature and the detection sensitivity of the semiconductor gas sensor to ethane gas at the second temperature may be different from each other.

[0090] In the above embodiment, the semiconductor gas sensor includes a SnO2 sensitive layer covering the electrode pattern and a palladium catalyst layer covering the SnO2 sensitive layer, but the present invention is not limited to this. In the present invention, the semiconductor gas sensor does not necessarily have to include a palladium catalyst layer covering the SnO2 sensitive layer. Furthermore, the sensitive layer covering the electrode pattern may be a sensitive layer other than SnO2.

[0091] In the above embodiment, an example of a configuration in which gas detection at the first temperature and gas detection at the second temperature are performed by separate pulse drives is shown, but the present invention is not limited to this. In the present invention, gas may be detected when the temperature rises to the second temperature during one heating cycle, and then detected again when the temperature further rises to the first temperature. Furthermore, gas may be detected when the temperature rises to the first temperature during one heating cycle, and then detected again when the temperature drops to the second temperature.

[0092] Furthermore, in the above embodiment, an example of a configuration in which the gas detector includes a communication unit and an alarm unit has been described, but the present invention is not limited to this. In the present invention, the gas detector may be provided with only one of the communication unit and the alarm unit. For example, the gas detector may not be provided with a communication unit. Furthermore, the gas detector may not be provided with an alarm unit. In this case, the alarm unit may be provided separately from the gas detector. Furthermore, even if the gas detector is provided with an alarm unit, the alarm may be performed by a device external to the gas detector.

[0093] In addition, in the above embodiment, an example of a configuration in which detection at the first temperature and detection at the second temperature are alternately performed when the detection result at the first temperature exceeds a predetermined threshold is shown, but the present invention is not limited to this. In the present invention, when the detection result at the first temperature exceeds a predetermined threshold, detection at the second temperature may be performed once for each of multiple detections at the first temperature, or detection at the first temperature may be performed once for each of multiple detections at the second temperature.

[0094] In the above embodiment, an example of a configuration in which, when detection at a first temperature and detection at a second temperature are performed, detection at the second temperature is stopped if the detection result at the first temperature becomes equal to or lower than a predetermined threshold is shown, but the present invention is not limited to this. In the present invention, when detection at a first temperature and detection at a second temperature are performed, detection at the second temperature may be stopped if the detection result at the first temperature becomes equal to or lower than the predetermined threshold multiple times.

[0095] In the above embodiment, for convenience of explanation, an example has been shown in which the control processing is explained using a flow-driven flowchart in which processing is performed sequentially according to a processing flow, but the present invention is not limited to this. In the present invention, the control processing may be performed by event-driven processing in which processing is performed on an event-by-event basis. In this case, the control processing may be performed completely event-driven, or may be performed by combining event-driven and flow-driven processing. [Explanation of symbols]

[0096] 1. Semiconductor gas sensor 2. Control section 3. Information Department 4. Communications Department 5 External equipment 6 Hydrogen sulfide sensor 11 Sensing part 12 Heating section 13 PCB 14 Electrode Pattern 15 SnO2 sensitive layer 16 Palladium catalyst layer 100 Gas Detector

Claims

1. a MEMS type semiconductor gas sensor including a sensitive part and a heating part for heating the sensitive part to a predetermined temperature, the MEMS type semiconductor gas sensor having different detection sensitivities for methane gas and ethane gas depending on the temperature; a control unit that heats the sensitive unit to a first temperature by pulse driving the heating unit at predetermined time intervals, and performs detection of the semiconductor gas sensor at the first temperature at predetermined time intervals, the control unit controls the semiconductor gas sensor to perform detection at a second temperature that is lower than the first temperature when the detection result at the first temperature exceeds a predetermined threshold value; The control unit determines whether the detected gas is a first gas containing methane gas and having an ethane gas content of less than a predetermined percentage, or a second gas containing methane gas and an ethane gas content of equal to or greater than a predetermined percentage, based on a first detection result of the semiconductor gas sensor at the first temperature and a second detection result of the semiconductor gas sensor at the second temperature, which has a lower detection sensitivity for methane gas than the first temperature.

2. 2. The gas detector according to claim 1, wherein a relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor at the second temperature is greater than a relative ratio of the detection sensitivity of ethane gas to the detection sensitivity of methane gas of the semiconductor gas sensor at the first temperature.

3. the first temperature is equal to or higher than 450°C and equal to or lower than 600°C, 2. The gas detector according to claim 1, wherein the second temperature is equal to or higher than 200°C and equal to or lower than 400°C.

4. 2. The gas detector according to claim 1, wherein the control unit controls the semiconductor gas sensor to perform detection at the first temperature at predetermined time intervals by pulsating the heating unit to heat the sensitive unit to the first temperature, and, when methane gas is detected based on the first detection result, controls the semiconductor gas sensor to perform detection at the second temperature in addition to detection at the first temperature by pulsating the heating unit.

5. 2. The gas detector according to claim 1, wherein the control unit determines whether the detected gas is the first gas or the second gas based on a ratio between the first detection result and the second detection result.

6. The semiconductor gas sensor includes a substrate, an electrode pattern provided on the substrate, and a SnO ２ Sensitive layer and the SnO ２ 6. The gas detector of claim 5, further comprising a palladium catalyst layer covering the sensitive layer.

7. Further comprising a communication unit capable of communicating with an external device; 2. The gas detector of claim 1, wherein the control unit controls the communication unit to have different communication modes when it determines that the detected gas is the first gas and when it determines that the detected gas is the second gas.

8. Further provided is a notification unit for making a notification, 2. The gas detector of claim 1, wherein the control unit controls the alarm unit to issue an alert in different manners when it determines that the detected gas is the first gas and when it determines that the detected gas is the second gas.

9. Further comprising a hydrogen sulfide sensor capable of detecting hydrogen sulfide gas, 2. The gas detector according to claim 1, wherein the control unit detects hydrogen sulfide gas using the hydrogen sulfide sensor when the detection result of the semiconductor gas sensor at the first temperature exceeds a predetermined threshold, and determines whether the detected gas contains hydrogen sulfide gas.

10. 2. The gas detector according to claim 1, wherein the detection sensitivity of said semiconductor gas sensor to ethane gas at said first temperature is substantially equal to that at said second temperature.

11. A gas detection method for a gas detector equipped with a MEMS type semiconductor gas sensor including a sensitive part and a heating part that heats the sensitive part to a predetermined temperature, and having detection sensitivities for methane gas and ethane gas that vary depending on temperature, comprising: a step of heating the sensitive part to a first temperature by pulse driving the heating part at predetermined time intervals, and performing detection of the semiconductor gas sensor at the first temperature at predetermined time intervals; a step of changing the driving of the heating unit to perform detection of the semiconductor gas sensor at a second temperature lower than the first temperature when the detection result at the first temperature exceeds a predetermined threshold; and determining whether the detected gas is a first gas containing methane gas and having an ethane gas content of less than a predetermined percentage, or a second gas containing methane gas and an ethane gas content of not less than a predetermined percentage, based on a first detection result of the semiconductor gas sensor at the first temperature and a second detection result of the semiconductor gas sensor at the second temperature, which has a lower detection sensitivity for methane gas than the first temperature.

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