JP2007271441A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor which enhances the discrimination properties with methane in the detection of hydrogen and enabling the detection of methane with high precision. <P>SOLUTION: The gas sensor includes a sensor part 3 equipped with a sensor element based on a metal oxide semiconductor and responding to methane and hydrogen, a heating control part 5 for controlling heating so as to periodically transiting the temperature of the sensor element between a high temperature state and a low temperature state, a resistance detection part 6a for detecting the sensor resistance of the sensor element and a gas decision part 6b for respectively deciding the presence of methane and hydrogen. The resistance detection part 6a detects not only first sensor resistance when the sensor element is set to the high temperature state but also second sensor resistance at an intermediate state wherein the sensor element is transited between the high temperature state and the low temperature state. The gas decision part 6b judges not only the presence of methane on the basis of the first sensor resistance but also the presence of hydrogen on the basis of the comparing result value of the second and first sensor resistances. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas detection device that detects methane by a change in electrical resistance of a sensor element mainly composed of a metal oxide semiconductor, and more specifically, methane detection by eliminating interference of miscellaneous gases such as hydrogen. It relates to accuracy improvement technology.

As a gas detector capable of discriminating and detecting hydrogen, which is a miscellaneous gas that interferes with detection of methane and methane detection, with one sensor element mainly composed of a metal oxide semiconductor, for example, the following patent documents 1 to 5 And the like. For example, as shown in FIG. 11, the sensor element has a structure in which a heating coil 22 for temperature adjustment of the sensor element 21 and an electrode 23 for sensor output are embedded in a metal oxide semiconductor 24 and integrated with the heating coil. There is. One end of the heating coil 22 is grounded, and the voltage value of the heating voltage V _HEAT applied to the other end of the heating coil 22 is periodically changed so that the temperature of the sensor element is low (approximately 80 ° C.) and high (approximately 400). The sensor element is controlled to be heated so as to periodically transition between [C. By providing the load resistor 25 on the electrode 23 of the sensor element 21, a voltage corresponding to the sensor resistance (the electric resistance value of the metal oxide semiconductor between the electrode 23 and the heating coil 22) is output to the electrode 23 as a sensor output. . The sensor resistance can be converted from the voltage value of the sensor output. As shown in FIG. 12, the temperature of the sensor element periodically changes following the periodic change of the heating voltage V _HEAT . The resistance value of the load resistor 25 is controlled to be an optimum value according to the temperature state of the sensor element.

In the conventional gas detector, carbon monoxide is selectively detected from the sensor output in the low temperature state (point C in FIG. 12), and the sensor in the high temperature state (point A in FIG. 12) that can be converted into sensor resistance. Methane is selectively detected from the output, and hydrogen is detected from the sensor output in an intermediate state (point B in FIG. 12) where the sensor resistance is converted to a low temperature state. The sensor element mainly composed of a metal oxide semiconductor such as SnO ₂ is shown in FIG. 13 for methane and carbon monoxide as detection target gas species and hydrogen as a miscellaneous gas that interferes with detection of the detection target gas. The sensitivity characteristics as shown are shown. In FIG. 13, the sensitivity of the sensor element, that is, the detection ability, is represented by a ratio (R _AIR / R _GAS ) between the sensor resistance in clean air and the sensor resistance in each gas atmosphere. As is clear from FIG. 13, the detection ability of methane is high in a high temperature state. Conversely, the detection ability of carbon monoxide is high in a low temperature state, and the detection ability of hydrogen is high in an intermediate state between the high temperature state and the low temperature state. However, because the hydrogen detection capability has a certain sensitivity even at low and high temperatures, it works as a miscellaneous gas that interferes with the detection of methane and carbon monoxide, and erroneously detects the presence of methane or carbon monoxide in a hydrogen atmosphere There is. Therefore, in the conventional gas detection device, the sensor resistance is obtained from the sensor output in the intermediate state, the presence of hydrogen is determined, and the sensitivity of methane and carbon monoxide is corrected based on the determination result. For example, if the sensor resistance in the high temperature state when the methane concentration is 3000 ppm is used as a threshold and the sensor resistance in the high temperature state is compared, the 3000 ppm methane concentration is detected and an alarm is output, and the presence of hydrogen is detected. Since the sensor resistance decreases even at the same methane concentration of 3000 ppm, a false alarm can be prevented in a state where the methane concentration is less than 3000 ppm by correcting the threshold value to be lower.

JP 2003-185610 A JP 2001-208711 A JP 2002-82083 A Japanese Unexamined Patent Publication No. 07-198644 JP 62-233842 A

However, in the hydrogen detection based on the sensor resistance in the intermediate state performed by the conventional gas detection device, as shown in FIG. 13, since methane sensitivity exists even in the intermediate state, there is a risk of erroneously detecting hydrogen in the methane atmosphere. was there. 14, the horizontal axis sensor resistance _{R H-CH4} (constant) normalized hot normalized resistance of the sensor resistance _{R H} in a high temperature state when the methane concentration 3000ppm at high temperature _{(R H / R H-CH4} ), And the vertical axis represents the normal normalized resistance (R _M / R _H-CH4 ) obtained by normalizing the sensor resistance R _M in the intermediate state with the sensor resistance R _{H-CH 4} (constant) in the high temperature state when the methane concentration is 3000 ppm. In the two-dimensional orthogonal coordinate space where the ambient temperature and relative humidity of the sensor element are 20 ° C. and 65%, the coordinate points when the methane concentration for the 190 measurement samples is 1000 ppm, 3000 ppm, 6000 ppm, and 10000 ppm, And the thing which plotted the coordinate point when hydrogen concentration is 500 ppm and 3000 ppm is shown, respectively. FIG. 14 shows that the coordinate point of hydrogen and the coordinate point of methane overlap in the vertical axis direction. That is, when it is determined detection hydrogen sensor resistance R _M in the intermediate state, is likely to erroneously detected methane atmosphere with hydrogen atmosphere. If a methane detection alarm is output when the methane concentration is 3000 ppm, a region where the high temperature normalization resistance ( _RH / _RH-CH4 ) on the horizontal axis in FIG. Since there are hydrogen coordinate points inside, if hydrogen cannot be detected correctly, the hydrogen atmosphere may be erroneously detected as a methane atmosphere.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas detection device that improves the discrimination from methane in hydrogen detection and enables highly accurate methane detection. It is in.

  In order to achieve the above object, a gas detection device according to the present invention includes a sensor element whose main component is a metal oxide semiconductor and whose electrical resistance changes in response to at least methane and hydrogen, and the temperature of the sensor element is high. A heating control unit that performs heating control so as to periodically transition between a low temperature state and a sensor resistance represented by an electric resistance value of the sensor element or an electric resistance equivalent value that can be converted into the electric resistance value A gas detection device comprising: a resistance detection unit; and a gas determination unit that individually determines the presence of methane and hydrogen based on the sensor resistance detected by the resistance detection unit, wherein the resistance detection unit includes: The sensor resistance when the sensor element is in the high temperature state is detected as a first sensor resistance by heating control by the heating control unit, and the sensor is detected by heating control by the heating control unit. The sensor resistance when the element is in an intermediate state transitioning between the high temperature state and the low temperature state is detected as a second sensor resistance, and the gas determination unit is configured to detect methane based on the first sensor resistance. The first characteristic is that the presence determination is performed and the presence determination of hydrogen is performed based on a comparison result value obtained by comparing the second sensor resistance with the first sensor resistance.

According to the gas detector of the first feature, since the gas determination unit performs the presence determination of hydrogen based on the comparison result value obtained by comparing the second sensor resistance and the first sensor resistance, the conventional second sensor resistance, That is, as compared with the case where the presence of hydrogen is determined based on the electrical resistance value (sensor resistance) in the intermediate state (see FIG. 14), as shown in FIG. 15, the discrimination from methane is improved and the hydrogen is more accurately detected. As a result, it is possible to determine the presence of methane with high accuracy. This is because the sensitivity of hydrogen and methane exists in both high temperature and intermediate states. Therefore, by comparing the sensor resistances in the high temperature state where methane sensitivity is remarkable and the intermediate state where hydrogen sensitivity is remarkable, This is based on the inventor's new knowledge that the discrimination between methane and methane can be improved. In FIG. 15, the vertical axis of the distribution chart shown in FIG. 14 is a comparison result value (R _{M) obtained} by dividing the second sensor resistance by the first sensor resistance from the high temperature normalized resistance (R _H / R _{H —CH 4} ). / R _H ) is a distribution map based on the same experimental sample re-displayed.

  Furthermore, in the gas detection device according to the present invention, in addition to the first feature, the gas determination unit is used for determining the first sensor resistance or a threshold for the first sensor resistance based on the comparison result value. The second feature is that the presence of methane is determined by correcting the threshold.

  According to the gas detector of the second feature, since the discrimination result between hydrogen and methane is improved by the comparison result value, the threshold for methane detection can be appropriately corrected in the hydrogen atmosphere, Prevents false detection of methane in a hydrogen atmosphere.

  Furthermore, in the gas detection device according to the present invention, in addition to the first or second feature, the gas determination unit determines whether hydrogen exists alone without coexisting with methane based on the comparison result value. A third feature is that the determination of the presence of methane is performed by correcting the threshold value used for determining the first sensor resistance or the threshold value for the first sensor resistance based on the determination result.

  According to the gas detector of the third feature, since the discrimination result between hydrogen and methane is improved by the comparison result value, the discrimination between hydrogen and methane mixed hydrogen is also improved. This makes it possible to more appropriately correct the threshold value that distinguishes between when hydrogen alone is detected and when hydrogen is detected in methane, thereby enabling highly accurate methane detection.

  Furthermore, in addition to the second or third feature, the gas detection device according to the present invention further includes a temperature sensor that measures an ambient temperature of the sensor element, and the gas determination unit includes the first sensor resistor or the A fourth feature is that a threshold value used for the threshold determination for the first sensor resistance is corrected based on the ambient temperature measured by the temperature sensor.

  According to the gas detector of the fourth feature, the second sensor resistance changes depending on the ambient temperature even when the hydrogen concentration is the same due to the temperature characteristics of the second sensor resistor with respect to the ambient temperature, and is used for determining the presence of hydrogen. Since the comparison result value also changes from the ambient temperature, the temperature characteristic of the second sensor resistor with respect to the ambient temperature is corrected by correcting the threshold used for the threshold determination for the first sensor resistor or the first sensor resistor based on the ambient temperature. High-accuracy methane detection considering

  Furthermore, in addition to any one of the above features, the gas detection device according to the present invention further includes: the metal oxide semiconductor of the sensor element further changes its electric resistance in response to carbon monoxide, and the resistance detection unit However, the sensor resistance when the sensor element is in the low temperature state is detected as a third sensor resistance by heating control by the heating control unit, and the gas determination unit detects carbon monoxide based on the third sensor resistance. The fifth feature is that when the presence determination is performed, the third sensor resistance or a threshold value used for threshold determination for the third sensor resistance is corrected based on the comparison result value.

  According to the gas detector of the fifth feature, hydrogen becomes a miscellaneous gas even in the presence determination of carbon monoxide. However, since the hydrogen detection accuracy is improved by the comparison result value, monoxide is oxidized in a hydrogen atmosphere. The threshold value for detecting carbon can be corrected appropriately, and erroneous detection of carbon monoxide in a hydrogen atmosphere can be prevented.

  Furthermore, in addition to the fifth feature, the gas detection device according to the present invention further includes a temperature sensor that measures the ambient temperature of the sensor element, and the gas determination unit includes the third sensor resistor or the third sensor. A sixth feature is that a threshold value used for the threshold value determination for resistance is corrected based on the ambient temperature measured by the temperature sensor.

  According to the gas detector of the sixth feature, the second sensor resistance changes depending on the ambient temperature even when the hydrogen concentration is the same due to the temperature characteristic of the second sensor resistor with respect to the ambient temperature, and is used for determining the presence of hydrogen. Since the comparison result value also changes from the ambient temperature, the temperature characteristic of the second sensor resistor with respect to the ambient temperature is corrected by correcting the third sensor resistor or the threshold used for the threshold determination for the third sensor resistor based on the ambient temperature. This makes it possible to detect carbon monoxide with high accuracy.

  Furthermore, in addition to any one of the above features, the gas detection device according to the present invention is a two-dimensional orthogonal coordinate in which the gas determination unit is defined by an increase / decrease direction of the first sensor resistance and an increase / decrease direction of the comparison result value. A seventh feature is that the presence of hydrogen is determined when a coordinate point determined by the first sensor resistance and the comparison result value exists in a predetermined region in the two-dimensional orthogonal coordinate space in the space. .

  According to the gas detector of the seventh feature, it is possible to simultaneously detect plural kinds of miscellaneous gases such as ethanol and dimethyl ether in addition to hydrogen. As a result, the selectivity of the detection target gas such as methane is improved.

  Hereinafter, embodiments of a gas detection device according to the present invention (hereinafter, abbreviated as “the device of the present invention” as appropriate) will be described with reference to the drawings.

<First Embodiment>
FIG. 1 shows a circuit configuration of the device 1 of the present invention. As shown in FIG. 1, the device 1 of the present invention includes two types of detection target gases, methane and carbon monoxide (CO), which are mainly composed of a metal oxide semiconductor, and hydrogen that interferes with detection of the detection target gas. The sensor unit 3 is configured to include a sensor element whose electric resistance changes in response to various gases, the nonvolatile storage means 4, and the temperature of the sensor element relative to the sensor unit 3 between the high temperature state and the low temperature state. Heating control unit 5 that performs heating control so as to make a transition, a determination unit 6 that determines whether or not to output an alarm based on a sensor output that is output from the sensor unit 3, and an alarm output determination of the determination unit 6 An alarm output unit 7 that outputs an alarm, a power supply unit 8 that supplies predetermined power to each unit of the device 1 of the present invention, and a thermistor that performs temperature detection for temperature correction in the alarm output determination process of the determination unit 6 Gas alarm with temperature sensor 9 Configured as. Further, as will be described later, a part of the heating control unit 5, a determination unit 6, and a part of the alarm output unit 7 are configured in the microprocessor 2.

As shown in FIG. 2, the sensor unit 3 includes a sensor element 11 including a semiconductor gas sensor that can selectively detect two types of detection target gases, methane and carbon monoxide, by driving control of a heater (heating coil) 10. The detection state of the detection target gas is configured to be output as an electrical signal. More specifically, the detection target gas includes a semiconductor gas sensor mainly composed of a metal oxide semiconductor such as SiO ₂ formed integrally with the heater 10. Two different load resistors R1 and R2 are provided in parallel between the sensor output terminal 12 of the sensor element 11 and the power supply voltage Vcc. However, the load resistor R2 forms a series circuit with the switching transistor T and is provided between the sensor output terminal 12 and the power supply voltage Vcc. With this configuration, the amplitude of the sensor output for detection / non-detection of the detection target gas due to the difference in temperature control of the heater 10 when the detection target gas is methane and carbon monoxide by the on / off operation of the switching transistor T. It becomes possible to adjust appropriately. The load resistors R1 and R2 are fixed resistors in this embodiment, and their resistance values are, for example, 100 kΩ and 10 kΩ, for example. It should be noted that the sensor output appearing on the sensor output terminal 12 is the electric power of the sensor element 11 between the sensor output terminal 12 and the ground terminal side of the heater 10 depending on the presence or absence of carbon monoxide when the temperature control of the heater 10 is around 100 ° C. The resistance changes when the resistance changes remarkably. Further, when the temperature control of the heater 10 is 400 to 500 ° C., the resistance changes depending on the presence or absence of methane. As will be described later, the switching transistor T is ON / OFF controlled by a control signal from the heating control unit 5 of the main body 1 in accordance with the drive control timing of the heater 10.

  In the present embodiment, the temperature control of the heater 10 of the sensor element 11 is performed by PWM (pulse width modulation) control of a constant voltage (for example, 3.3 V), that is, the voltage pulse applied to the heater 10 is turned on (voltage application). By controlling the time ratio (duty ratio) between the (state) and off (voltage non-applied state), the effective applied voltage is adjusted and the temperature applied to the sensor element 11 is controlled. An example of the applied voltage waveform by the PWM control of the heater 10 and an effective applied voltage waveform are shown in FIG. In the example shown in FIG. 3, the effective applied voltage is PWM controlled so as to be 0.9 V at a high temperature drive for 5 seconds and 0.2 V at a low temperature drive for 10 seconds. In FIG. 3, the temperature change applied to the sensor element 11 by the heating control with the applied voltage waveform is also shown below the applied voltage waveform.

  The non-volatile storage means 4 is composed of a non-volatile semiconductor memory such as an EEPROM that can electrically read, write, and erase information, and stores various information related to the device 1 of the present invention. As information stored in the non-volatile storage means 4, for example, the manufacturing date, manufacturing number, manufacturer name, product code, alarm output set value, and variation in detection characteristics of the sensor unit 3 are adjusted. Adjustment parameters, various parameters for detecting miscellaneous gases such as hydrogen, which will be described later, parameters for temperature correction, heating control unit 5 is a control parameter for heating control for sensor unit 3, and determination unit 6 is output from sensor unit 3. The determination reference value when the alarm output determination is performed based on the sensor output.

  The heating controller 5 includes a sensor driver 5a that drives a voltage pulse applied to the heater 10 of the sensor element 11, and a pulse controller 5b that controls the drive timing of the voltage pulse driven by the sensor driver 5a and the duty ratio of the voltage pulse. And is configured. The pulse control unit 5b of the heating control unit 5 is configured in the microprocessor 2, reads out the control parameter from the nonvolatile storage unit 4, and at the start timing, end timing, and duty ratio of each voltage pulse application of the control parameter, The drive timing and duty ratio of the corresponding voltage pulse are controlled, and according to the control, the sensor drive unit 5a drives the heater 10 in the sensor unit 3 so as to have the temperature control pattern shown in FIG. The microprocessor 2 includes a microcomputer incorporating a ROM and RAM for storing programs, and it does not matter whether the ROM or RAM is incorporated or provided externally.

The determination unit 6 includes a resistance detection unit 6a and a gas determination unit 6b. Resistance detection unit 6a includes a detection timing of the sensor output for methane detection of the control parameters stored in the nonvolatile storage unit 4 (t _H point in Fig. 3), the detection timing of the sensor output for hydrogen detection and (t _M point in FIG. 3), at the detection timing of the sensor output for carbon monoxide detector (t _L point in FIG. 3), reads the sensor output of each, from the sensor output read, methane detection the sensor resistance at time _{(t H)} as a first sensor resistance _{R H,} the sensor resistance in the hydrogen detection timing _{(t M)} as the second sensor resistance _{R M,} the third sensor to sensor resistance in the CO detection timing _{(t L)} It calculates as resistance _RL , respectively. As shown in FIG. 3, at the methane detection timing (t _H ) at 5 seconds after the start of the high temperature drive, the temperature of the sensor element 11 is in a high temperature state, and 5.6 seconds after the start of the high temperature drive (0.6 (Second) at the hydrogen detection timing (t _M ), the temperature of the sensor element 11 is in an intermediate state between the high temperature state and the low temperature state, and the CO detection timing (t _{In L} ), the temperature of the sensor element 11 is in a low temperature state. The sensor output at each detection timing _{(t H, t M, t} L) , each detection timing _{(t H, t M, t} L) number m seconds from the front leading to (e.g., 8m seconds) prescribed times intervals ( (For example, 16 times), and the average value is calculated and used.

Here, in order to read the sensor output within a voltage range where an appropriate resolution can be obtained, switching control of the load resistances R1 and R2 is performed by the heating control unit 5. The heating control unit 5 performs on / off control of the switching transistor T of the sensor element 11 in synchronization with the heating control of the temperature control pattern shown in FIG. Specifically, the methane detection timing (t _H ) and the hydrogen detection timing (t _M ) from the middle during high temperature driving (about 2.5 seconds after the start) to the middle during low temperature driving (about 5 seconds after the start) The switching transistor T is turned off during the period including the CO detection timing (t _L ) from the middle during the low temperature driving (about 5 seconds after the start) to the middle during the high temperature driving (about 2.5 seconds after the start). The switching transistor T is turned on. That is, the load resistance RL _HM when detecting methane and hydrogen is R1, and the load resistance RL _L when detecting carbon monoxide is R3 (= R1 · R2 / (R1 + R2)).

The gas determining unit 6b determines the presence of methane (whether the concentration is equal to or higher than the detection specified concentration) based on the first sensor resistance _RH detected by the resistance detecting unit 6a, and the gas detecting unit 6a detects the first detected by the resistance detecting unit 6a. The presence of carbon monoxide (whether the concentration is equal to or higher than the detection specified concentration) is determined based on the three-sensor resistance _RL . In addition, the gas determination unit 6b calculates the temperature correction coefficient for each of the first sensor resistance _RH and the third sensor resistance _RL used for the methane determination and the carbon monoxide determination from the ambient temperature detected by the temperature sensor 9. Make corrections. Further, the gas determination unit 6b includes a first sensor resistance R _H, which is detected by the resistance detection unit 6a on the basis of the comparison result value to be described later of the second sensor resistor R _M to determine the presence of hydrogen, the presence of hydrogen determination If it has been corrected, the first sensor resistance _RH and the third sensor resistance _RL are corrected. The gas determination unit 6b sets the methane detection bit in the built-in register to “1” when the methane concentration is equal to or higher than the methane detection regulation concentration, determines that a gas leak has occurred, and determines a gas leak determination signal. Is output. In addition, when the concentration of carbon monoxide is equal to or higher than the detection specified concentration, the gas determination unit 6b sets the CO detection bit in the built-in register to “1”, determines that it is in an incomplete combustion state, and performs incomplete combustion. Outputs a judgment signal. Further, when the gas determination unit 6b determines the presence of hydrogen based on the comparison result value, it sets the hydrogen detection bit in the built-in register to “1” and outputs a hydrogen detection signal.

  The determination unit 6 is configured in a microprocessor 2 provided in the main body unit 1, and a sensor output (analog value) is input from a predetermined analog port of the microprocessor 2, and an A / D conversion unit in the microprocessor 2. Sampled and digitized. The sampling timing at this time is defined by the detection timing of the sensor output of each detection target gas in the control parameters. Further, the temperature detection output (analog value) of the temperature sensor 9 is also input from a predetermined analog port of the microprocessor 2, sampled by the A / D converter in the microprocessor 2, and digitized.

  The alarm output unit 7 includes an optical alarm output unit 14 including an LED display circuit having three color (green, red, and yellow) LEDs 14a, an audio alarm output unit 15 including an audio circuit 15a and a speaker 15b, and an alarm output of the determination unit 6. A predetermined control signal for the external output circuit 16 that outputs the determination information to the outside according to the voltage level, the light alarm output unit 14, the sound alarm output unit 15, and the external output circuit 16 based on the alarm output determination of the determination unit 6 The alarm output control part 17 which outputs is comprised. Here, the alarm output control unit 17 is configured in the microprocessor 2 provided in the main body unit 1. Based on the alarm output determination (gas leak determination signal, incomplete combustion determination signal, hydrogen detection signal) of the determination unit 6, the alarm output control unit 17 is configured to output the light alarm output unit 14, sound, A predetermined control signal is output to the alarm output unit 15 and the external output circuit 16, and the light alarm output unit 14, the audio alarm output unit 15, and the external output circuit 16 are controlled so as to output a predetermined alarm. To do.

  The power supply unit 8 includes a power transformer, a smoothing circuit, a constant voltage circuit, and the like, and generates a DC low voltage (for example, 5 V, 3.3 V) from a commercial AC voltage 100 V for home use, for example.

  Next, each operation | movement of the methane detection process of the determination part 6 of this invention apparatus 1 shown in FIG. 1 and a hydrogen detection process, and CO detection process is demonstrated based on the flowchart shown in FIG. 4 thru | or FIG. The heating control unit 5 separately performs the above-described heating control and on / off control of the switching transistor T on the sensor element 11 in parallel. Note that the methane detection process, the hydrogen detection process, and the CO detection process are realized by the CPU executing a program describing each processing procedure in the microprocessor 2.

  First, methane detection processing (see FIG. 4) is started, and the determination unit 6 continues based on the determination results (methane detection bit, hydrogen detection bit) determined in the previous methane detection processing and hydrogen detection processing. The gas leak determination signal and the hydrogen detection signal are output (step # 1).

Then, the resistance detection part 6a reads the sensor output _{V M} at the sensor output _{V H} and hydrogen detection timing in the methane detection timing _{(t H) (t M)} ( Step # 2).

Next, the gas determination unit 6b determines the ambient temperature detected by the temperature sensor 9 at predetermined intervals (for example, 16 seconds) at a predetermined time (for example, 16 times) at the time of high-temperature driving closest to the methane detection timing (t _H ). The average value of these is read and the ambient temperature T is calculated (step # 3).

Then, the resistance detection section 6a, calculates the sensor output _{V H} and methane detection time of the load resistor _RL HM and (= R1) than the power supply voltage Vcc, from calculation formula shown in Formula 1 below, a first sensor resistance _{R H} (Step # 4).

(Equation 1)
R _H = V _H × RL _HM / (Vcc−V _H )

Next, the gas determination unit 6b calculates a temperature correction coefficient K _H when methane detection from ambient temperature T (step # 5). Specifically, the temperature correction coefficient K at the ambient temperature T is obtained by interpolating the temperature correction coefficients K _H when the ambient temperature stored in the nonvolatile storage means 4 is −10 ° C., 0 ° C., 20 ° C., and 50 ° C. _H is calculated.

Next, the gas determination unit 6b from the sensor resistance _{R H-CH4} (constant) and the temperature correction coefficient _{K H} of the first sensor resistor _{R H} and methane detection timing at methane concentration 3000ppm _{(t H),} the methane concentration 3000ppm Whether it is the above or not is determined by the determination formula shown in the following equation (step # 6). When the determination formula shown in Equation 2 is established, the methane determination (methane concentration is 3000 ppm or more) is made.

(Equation 2)
R _H / (R _{H—CH 4} × K _H ) <1

  In the case of methane determination in Step # 6 (YES), the process proceeds to the hydrogen detection process (see FIG. 5). If it is not methane determination (NO), the methane detection bit is reset to “0” without proceeding to the hydrogen detection process (see FIG. 5) (step # 7). Here, when the methane detection bit is “1”, the gas leak alarm is canceled. Further, following step # 7, assuming that hydrogen is not present without performing the hydrogen detection process, the hydrogen detection bit is reset to “0” (step # 8), and the CO detection process (see FIG. 6) is performed. Transition.

Next, the hydrogen detection process (see FIG. 5) will be described. If at step # 6 of methane detection processing (see FIG. 4) of methane determination (YES), the resistance detection unit 6a, the sensor output _{V M} and methane detection time of the load resistor _RL HM and (= R1) than the power supply voltage Vcc, The second sensor resistance _RM is calculated from the calculation formula shown in Equation 3 below (step # 11).

(Equation 3)
R _M = V _M × RL _HM / (Vcc−V _M )

Next, the gas determination unit 6b calculates a temperature correction coefficient K _S of the threshold value S when hydrogen is detected from the ambient temperature T (step # 12). Specifically, the temperature correction coefficient K at the ambient temperature T is obtained by interpolating each temperature correction coefficient K _S when the ambient temperature stored in the nonvolatile storage means 4 is −10 ° C., 0 ° C., 20 ° C., and 50 ° C. _S is calculated.

Next, the gas determination unit 6b, a second sensor resistance R _M of the first sensor resistance R _H in dividing the comparison result value and the threshold value S of the temperature correction coefficient K _S a multiplying temperature corrected threshold (S × K _S ) In accordance with the determination formula shown in the following equation 4, it is determined whether the atmosphere is a hydrogen-only atmosphere or a hydrogen-containing methane atmosphere (step # 13). When the determination formula shown in Equation 4 is satisfied, a hydrogen determination (hydrogen alone atmosphere or hydrogen-containing methane atmosphere) is made.

(Equation 4)
R _M / R _H <S × K _S

The threshold value S in the determination formula shown in Equation 4 was obtained from a plurality of samples in a methane atmosphere at various methane concentrations not containing hydrogen at a predetermined reference temperature and reference relative humidity (for example, 20 ° C., 65%). It is set slightly lower than the lower limit value of the distribution range of the plurality of R _M / _RH . For example, as shown in FIG. 7, when 1000 ppm of hydrogen is contained in the methane atmosphere at various methane concentrations, it can be seen that the distribution range of R _M / _RH moves downward. From this, it can be seen that the hydrogen alone atmosphere or the hydrogen-containing methane atmosphere can be detected by the judgment formula shown in Equation 4.

  If it is not a hydrogen determination in step # 13 (NO), the methane detection bit is set to “1”, a gas leak determination signal is output (step # 14), the hydrogen detection bit is reset to “0”, The process proceeds to the CO detection process (see FIG. 6) (step # 15).

  In the case of hydrogen determination in step # 13 (YES), the hydrogen detection bit is set to “1” and a hydrogen detection signal is output (step # 16).

Subsequently, in order to correct the methane determination performed in step # 6 of the methane detection process, the gas determination unit 6b performs the temperature correction coefficient K _F of the correction coefficient F during hydrogen detection from the ambient temperature T to the first sensor resistance _RH . Is calculated (step # 17). More specifically, the temperature correction coefficient K at the ambient temperature T is obtained by interpolating the temperature correction coefficients K _F when the ambient temperature stored in the nonvolatile storage means 4 is −10 ° C., 0 ° C., 20 ° C., and 50 ° C. _F is calculated. As the correction coefficient F, a value stored in the nonvolatile storage means 4 is read and used.

Next, the gas determination unit 6b includes the first sensor resistance _RH and the sensor resistance _RH-CH4 (constant) at the methane detection timing (t _H ) when the methane concentration is 3000 ppm, the temperature correction coefficient K _H , the correction coefficient F, and , the temperature correction coefficient _{K F,} the methane concentration at the time of hydrogen detecting whether or 3000 ppm, determined by the determination formula shown in equation 5 below (step # 18). When the determination formula shown in Equation 5 is satisfied, the methane determination (methane concentration is 3000 ppm or more) is made.

(Equation 5)
R _H / (R _{H —CH 4} × K _H × F × K _F ) <1

As shown in FIG. 7, in the hydrogen-containing methane atmosphere, even when the methane concentration is the same, R _H / R _{H —CH 4} shifts slightly lower, so that hydrogen detection using the correction coefficient F and the temperature correction coefficient K _F If there is no correction for time, there is a possibility that a methane concentration of 3000 ppm or higher is erroneously determined even if the methane concentration is less than 3000 ppm. The correction coefficient F and the temperature correction coefficient K _F are used to correct the shift due to the hydrogen content of the R _H / R _{H —CH 4} .

  In the case of methane determination in step # 16 (YES), the methane detection bit is set to “1”, a gas leak determination signal is output, and the routine proceeds to CO detection processing (see FIG. 6) (step # 19). If it is not methane determination (NO), the methane detection bit is reset to “0”, and the process proceeds to the CO detection process (see FIG. 6) (step # 20). Here, when the methane detection bit is “1”, the gas leak alarm is canceled.

  Next, the CO detection process (see FIG. 6) will be described. When shifting from the methane detection process (see FIG. 4) or the hydrogen detection process (see FIG. 5) to the CO detection process, the determination unit 6 first determines the determination results (CO detection bit, hydrogen detection bit) determined in the previous CO detection process. ), The incomplete combustion determination signal and the hydrogen detection signal are continuously output (step # 21).

Next, the resistance detection unit 6a reads the sensor output V _L at the CO detection timing (t _L ) (step # 22).

Next, the gas determination unit 6b determines the ambient temperature detected by the temperature sensor 9 at a predetermined interval (for example, an interval of 0.1 seconds) a predetermined number of times (for example, 16 times) at the time of low temperature driving closest to the CO detection timing (t _L ) The average value is read and set as the ambient temperature T (step # 23).

Next, the resistance detector 6a calculates the third sensor resistance R _L from the sensor output V _L , the load resistance RL _L (= R3) at the time of detecting carbon monoxide, and the power supply voltage Vcc according to the calculation formula shown below. Is calculated (step # 24).

(Equation 6)
R _L = V _L × RL _L / (Vcc−V _L )

Next, the gas determination unit 6b calculates a temperature correction coefficient K _L during the carbon monoxide sensing from the ambient temperature T (step # 25). Specifically, the ambient temperature which is stored in the nonvolatile storage means 4 -10 ° C., 0 ° C., 20 ° C., the temperature correction coefficient K in the ambient temperature T by interpolation processing each temperature correction coefficient K _L at 50 ° C. _L is calculated.

Next, when the hydrogen-detection bit is "1", the gas determination unit 6b calculates a temperature correction coefficient K _G of the correction coefficient G during hydrogen detection for the third sensor resistance R _L from ambient temperature T (step # 26). Specifically, -10 ° C. ambient temperature which is stored in the nonvolatile storage means 4, 0 ℃, 20 ℃, the temperature correction coefficient K in the ambient temperature T by interpolation processing each temperature correction coefficient K _G at 50 ° C. _G is calculated. As the correction coefficient G, a value stored in the nonvolatile storage means 4 is read and used. If the hydrogen detection bit is “0”, step # 26 is not executed and the process proceeds to the next step (step # 27).

Next, when the hydrogen detection bit is “0”, the gas determination unit 6b detects the sensor resistance R _L-CO (constant at the third sensor resistance R _L and the CO detection timing (t _H ) when the carbon monoxide concentration is 300 ppm. ) and the temperature correction coefficient _{K L,} determines the concentration of carbon monoxide is whether or 300 ppm, by determination formula shown in equation 7 below (step # 27). If hydrogen detection bit is "1", the third sensor resistance R _L by the presence of hydrogen is subjected to interference, in addition to the correction by the temperature correction coefficient K _L, also performs correction by the correction coefficient G. Therefore, the third sensor resistance R _L , sensor resistance R _L-CO (constant), temperature correction coefficient K _L , correction coefficient G, and temperature correction coefficient are determined as to whether or not the carbon monoxide concentration is 300 ppm or higher when hydrogen is detected. based on K _G, it determines the judgment formula shown in formula 8 below (step # 27). When the judgment formula shown in Formula 7 or Formula 8 is established, the CO judgment (the carbon monoxide concentration is 300 ppm or more) is made.

(Equation 7)
R _L / (R _L-CO × K _L ) <1

(Equation 8)
R _L / (R _L-CO × K _L × G × K _G ) <1

  In the case of CO determination in step # 27 (YES), the CO detection bit is set to “1”, an incomplete combustion determination signal is output, and the process returns to the methane detection process (see FIG. 4) (step # 28). If it is not the CO determination (NO), the CO detection bit is reset to “0” and the process returns to the methane detection process (see FIG. 4) (step # 29). Here, when the CO detection bit is “1”, the incomplete combustion alarm is canceled.

Second Embodiment
Next, another embodiment (second embodiment) of the device 1 of the present invention will be described with reference to the drawings.

  The circuit configuration of the inventive device 1 according to the second embodiment is exactly the same as that of the first embodiment. The device 1 of the present invention according to the second embodiment is different from the first embodiment in the processing algorithm of the hydrogen detection process by the gas determination unit 6b of the determination unit 6, and the methane detection process by the other components and the determination unit 6 and The processing procedure of the CO detection processing is the same as that in the first embodiment. Therefore, the description which overlaps with 1st Embodiment is omitted, and the hydrogen detection process in 2nd Embodiment is demonstrated.

  In the second embodiment, dimethyl ether (DME) other than hydrogen, ethanol, and the like also become miscellaneous gases in the detection of methane and carbon monoxide. In order to perform the detection process, detection of DME and ethanol is also performed simultaneously with the hydrogen detection process.

In FIG. 8, the horizontal axis represents the high-temperature normalized resistance (R _H / R _H-CH4 ) obtained by normalizing the first sensor resistance with the sensor resistance R _{H-CH 4} (constant) in a high temperature state when the methane concentration is 3000 ppm, In the two-dimensional orthogonal coordinate space in which the vertical axis represents the comparison result value (R _M / R _H ) between the second sensor resistance _RM and the first sensor resistance _RH , the ambient temperature and relative humidity of the sensor element are 20 ° C., Coordinate points when the methane concentration is 1000 ppm, 3000 ppm, 6000 ppm, and 10000 ppm, the coordinate points when the hydrogen concentrations are 500 ppm and 3000 ppm, the coordinate points when the DME concentration is 1000 ppm, and the ethanol concentration for 190 measurement samples at 65% Indicates a plot of coordinate points at 1000 ppm.

In the first embodiment, in step # 13 of the hydrogen detection process (see FIG. 5), the hydrogen alone atmosphere or the hydrogen-containing methane atmosphere can be detected by using the determination formula shown in Equation 4. However, as shown in FIG. 8, the comparison result value (R _M / R _H ) between the second sensor resistance _RM and the first sensor resistance _RH is significantly separated in the distribution range between the methane atmosphere and the hydrogen atmosphere. For DME and ethanol, since the methane atmosphere and the distribution range overlap, the determination formula shown in Equation 4 cannot detect the presence of DME and ethanol separately from methane.

Therefore, in the second embodiment, the increase / decrease direction of the high-temperature normalization resistance (R _H / R _{H-CH 4} ) without using the determination formula shown in Equation 4 used in Step # 13 of the hydrogen detection process (see FIG. 5). compared in result value two-dimensional orthogonal coordinate space is increased or decreased the direction defined in _(R M / R _H), at an elevated temperature normalized resistance _{(R H / R H-CH4} ) and the comparison result value _(R M / R _H) and Detection of miscellaneous gases such as hydrogen, DME, and ethanol is performed depending on whether or not the determined hydrogen detection coordinate points are present in a predetermined region in the two-dimensional orthogonal coordinate space. Hereinafter, in the second embodiment, “hydrogen detection” is synonymous with “miscellaneous gas detection”.

Specifically, as shown in FIG. 9, 2 broken lines (boundary lines) L passing through several reference coordinate points (for example, four points A, B, C, and D) in the two-dimensional orthogonal coordinate space. The coordinates of the reference coordinate points (R _H / R _{H -CH 4} , R _M / R _H ) are specified so that the coordinate points of hydrogen, DME, and ethanol fit on the right side and the lower side of the polygonal line L. To do. The broken line L extends from the reference coordinate point A to the opposite side to the reference coordinate point B in parallel to the vertical axis, and extends downward from the reference coordinate point D to the opposite side to the reference coordinate point C in parallel to the horizontal axis. It is defined to extend to the right. Therefore, the broken line L is a boundary line that divides the two-dimensional orthogonal coordinate space into a miscellaneous gas determination region and a miscellaneous gas non-determination region. The coordinate values of the reference coordinate points are set in advance at different ambient temperatures, for example, −10 ° C., 0 ° C., 20 ° C., and 50 ° C., and stored in the nonvolatile storage means 4. When the hydrogen detection coordinate points are located on the right side and the lower side of the polygonal line L, it is determined that there is a miscellaneous gas such as hydrogen (hydrogen determination), the hydrogen detection bit is set to “1”, and the hydrogen detection signal is Output.

Hereinafter, with reference to FIG. 10, the process sequence of the hydrogen detection process in 2nd Embodiment is demonstrated. If at step # 6 of methane detection processing (see FIG. 4) of methane determination (YES), the resistance detection unit 6a, the sensor output _{V M} and methane detection time of the load resistor _RL HM and (= R1) than the power supply voltage Vcc, The second sensor resistance _RM is calculated from the calculation formula shown in Equation 3 (step # 31).

Next, the gas determination unit 6b calculates the coordinate values of the reference coordinate points A to D that define the polygonal line L in the two-dimensional orthogonal coordinate space from the ambient temperature T (step # 32). Specifically, interpolation processing is performed based on the coordinate values of the reference coordinate points A to D when the ambient temperature is −10 ° C., 0 ° C., 20 ° C., and 50 ° C., and the reference coordinate points A to D at the ambient temperature T are detected. Each coordinate value (Xi, Yi) (i = A to D) is calculated. For example, when the ambient temperature T is 30 ° C., interpolation processing is performed based on the coordinate values of the reference coordinate points A to D at the ambient temperature of 20 ° C. and 50 ° C. Here, the X coordinate is the high-temperature normalized resistance (R _H / R _{H —CH 4} ) on the horizontal axis, and the Y coordinate is the comparison result value (R _M / R _H ) on the vertical axis.

Next, the gas determination unit 6b, a second sensor resistance R _M calculated in step # 31, the methane detection processing from the first sensor resistance R _H calculated in step # 4 (see FIG. 4), the hydrogen detecting coordinates The coordinate value (X0, Y0) of the point is obtained (step # 33).

  Next, the gas determination unit 6b determines that the coordinate values (X0, Y0) of the hydrogen detection coordinate points are the coordinate values (Xi, Yi) (i = A˜) of the reference coordinate points A to D calculated in step # 32. It is determined whether or not it exists on the miscellaneous gas region side (right side and lower side) of the broken line L defined in D) (step # 34). Specifically, the X coordinate X0 of the hydrogen detection coordinate point and the X coordinate of each of the reference coordinate points A to D are compared, and the Y coordinate Y0 of the hydrogen detection coordinate point and the reference coordinate points A to D are compared. The hydrogen detection coordinate point is located in the horizontal axis direction or the vertical axis direction with respect to the reference coordinate points A to D by comparison with the respective Y coordinates.

  If the hydrogen detection coordinate point is on the left side (X0 <XA) of the reference coordinate point A, the hydrogen determination is not performed. Further, if the hydrogen detection coordinate point is above the reference coordinate point A (Y0> YD), the hydrogen determination is not performed. In other cases, the determination is made as follows.

When the hydrogen detection coordinate point is in the middle of the reference coordinate points A and B (XA ≦ X0 <XB), the Y coordinate Y0 of the hydrogen detection coordinate point is X on the line segment connecting the reference coordinate points A and B. If the coordinates are below the Y coordinate Y _AB (X0) in X0 (Y0 ≦ Y _AB (X0)), the hydrogen determination is made. If the hydrogen detection coordinate point is in the middle of the reference coordinate points B and C (XB ≦ X0 <XC), the Y coordinate Y0 of the hydrogen detection coordinate point is X on the line segment connecting the reference coordinate points B and C. If the coordinate is below the Y coordinate Y _BC (X0) in X0 (Y0 ≦ Y _BC (X0)), the hydrogen determination is made. When the hydrogen detection coordinate point is in the middle of the reference coordinate points C and D (XC ≦ X0 <XD), the Y coordinate Y0 of the hydrogen detection coordinate point is X on the line segment connecting the reference coordinate points C and D. If the coordinate is below the Y coordinate Y _CD (X0) in X0 (Y0 ≦ Y _CD (X0)), the hydrogen determination is made. When the hydrogen detection coordinate point is on the right side (XD ≦ X0) of the reference coordinate point D, the Y coordinate Y0 of the hydrogen detection coordinate point is below the Y coordinate YD of the reference coordinate point D (Y0 ≦ YD). If there is, the hydrogen determination is made.

  If it is not hydrogen determination in step # 34 (NO), the methane detection bit is set to “1”, a gas leak determination signal is output (step # 35), the hydrogen detection bit is reset to “0”, The process proceeds to the CO detection process (see FIG. 6) (step # 36). In the case of hydrogen determination in step # 34, each process after step # 37 is performed. Since each process after step # 37 is the same as the process after step # 16 of the hydrogen detection process (see FIG. 5) in the first embodiment, a duplicate description is omitted.

  Next, another embodiment of the device of the present invention will be described.

<1> In the hydrogen detection process of the first embodiment (see FIG. 5), the determination formula (4) is used to determine whether the atmosphere is a hydrogen-only atmosphere or a hydrogen-containing methane atmosphere (step # 13). As described above, by preparing two threshold values S, it is possible to selectively determine not only the hydrogen-containing methane atmosphere but only the hydrogen-only atmosphere. Accordingly, when the hydrogen determination is made in step # 13, the hydrogen alone atmosphere is further detected using the second threshold value S ′ smaller than the threshold value S. In determining whether the methane concentration is 3000 ppm or more, the second correction coefficient F ′ and the temperature correction coefficient K _{F ′} may be used instead of the correction coefficient F and the temperature correction coefficient K _F at the time of hydrogen detection. I do not care. The correction coefficient F is a positive number smaller than 1, but the second correction coefficient F ′ is 1 or less and larger than the correction coefficient F. When the second correction coefficient F ′ and the temperature correction coefficient K _F are 1, the determination formula shown in Formula 5 is the same as the determination formula shown in Formula 2. That is, in the case of the hydrogen alone atmosphere, the correction at the time of hydrogen detection is not performed or the degree of the correction is weakened. Thereby, the methane detection sensitivity is not relaxed, and it becomes easy to make methane determination.

Similarly, when the atmosphere is hydrogen alone, the correction coefficient G and the temperature correction coefficient at the time of hydrogen detection are determined in step # 27 in the CO detection process (see FIG. 6) when the carbon monoxide concentration is 300 ppm or more. instead of K _G 'and temperature correction coefficient K _G' second correction factor G may be employed.

<2> In the above embodiments, as the comparison result value obtained by comparing the second sensor resistor R _M and the first sensor resistance R _H for use in hydrogen detection process, a second sensor resistance R _M in the first sensor resistance R _H As the comparison result value, for example, the difference between the second sensor resistance _RM and the first sensor resistance _{RH is} the sensor resistance R at the methane detection timing (t _H ) when the methane concentration is 3000 ppm. A value normalized by dividing by _H-CH4 (constant) may be used. As in the above embodiments, the discrimination from methane at the time of hydrogen detection is improved, and the presence determination of hydrogen can be performed with higher accuracy.

<3> In each of the embodiments described above, the first sensor resistance R _H , the second sensor resistance R _M , and the third sensor resistance R _L are calculated by the calculation formulas shown in Formulas 1, 3 and 6, respectively. Although calculated as a resistance value, each sensor resistance does not necessarily have to be calculated as an electrical resistance value. Each sensor resistance may be, for example, a value proportional to each electric resistance value and uniquely convertible to the electric resistance value. For example, each electric resistance value may be normalized by an electric resistance value (constant) in a clean air atmosphere (electric resistance equivalent value).

  <4> The methane detection process, the hydrogen detection process, and the CO detection process in each of the above embodiments are not limited to the processing procedures exemplified in the above embodiments. It can change suitably according to the meaning of the present invention. For example, in the first embodiment, the hydrogen detection process is performed after the methane detection process, but the process up to determining the presence of hydrogen in the hydrogen detection process may be performed before the methane detection process.

  <5> In each of the above embodiments, a case has been described in which two types of detection target gases, methane and carbon monoxide, are detected using one sensor element, but the detection target gas may be only methane.

  <6> In each of the above embodiments, the case where a constant voltage is applied to the heater 10 by PWM control is described as an example of the temperature control of the heater 10 of the sensor element 11. You may make it apply the voltage of 0.2V at the time of low temperature drive of 0.9V and 10 seconds.

  <7> Each voltage value, timing, gas concentration, and the like exemplified in the above embodiments are examples, and are not limited to the values exemplified in the above embodiments, and can be changed as appropriate.

  The gas detection device according to the present invention can be used for a gas detection device such as a gas alarm that detects gas leakage or incomplete combustion.

The circuit block diagram which shows the circuit structural example of the gas detection apparatus which concerns on this invention The circuit diagram which shows the circuit structural example of the sensor part which has the detection ability with respect to two types of detection object gas of methane and carbon monoxide in the gas detection apparatus which concerns on this invention Timing waveform diagram showing applied voltage waveform, effective applied voltage, temperature change, and sensor output detection timing when controlling the heater of the sensor unit shown in FIG. The flowchart which shows an example of the process sequence of the methane detection process by the gas detection apparatus which concerns on this invention The flowchart which shows an example of the process sequence of the hydrogen detection process by the gas detection apparatus which concerns on this invention The flowchart which shows an example of the process sequence of CO detection processing by the gas detection apparatus which concerns on this invention Methane atmospheres and various methanes with various methane concentrations in a two-dimensional orthogonal coordinate space with the horizontal axis representing the high-temperature normalized resistance (R _H / R _{H-CH 4} ) and the vertical axis representing the comparison result value (R _M / R _H ) Distribution chart plotting coordinate points of methane atmosphere with hydrogen concentration and hydrogen concentration of 1000ppm The methane concentration is 1000 ppm, 3000 ppm, 6000 ppm in a two-dimensional orthogonal coordinate space where the horizontal axis is the high temperature normalized resistance (R _H / R _{H —CH 4} ) and the vertical axis is the comparison result value (R _M / R _H ). Distribution chart plotting coordinate points at 10,000 ppm, coordinate points at 500 ppm and 3000 ppm for hydrogen concentration, coordinate points at 1000 ppm DME concentration, and coordinate points at 1000 ppm ethanol concentration The figure which shows the broken line (boundary line) for miscellaneous gas determination on the distribution map shown in FIG. 8, and the reference | standard coordinate point which prescribes | regulates it The flowchart which shows another example of the process sequence of the hydrogen detection process by the gas detection apparatus which concerns on this invention. The figure which shows one structural example of the sensor element which has a metal oxide semiconductor as a main component Timing waveform diagram showing heating voltage waveform and temperature change applied to sensor element shown in FIG. FIG. 11 is a sensitivity characteristic diagram schematically showing sensitivity characteristics of the sensor element shown in FIG. 11 with respect to methane, carbon monoxide and hydrogen. The ambient temperature of the sensor element and the ambient temperature of the sensor element in a two-dimensional orthogonal coordinate space with the horizontal axis as the high temperature normalized resistance (R _H / R _{H —CH 4} ) and the vertical axis as the intermediate normalized resistance (R _M / R _{H —CH 4} ) Distribution diagram plotting coordinate points when methane concentration is 1000ppm, 3000ppm, 6000ppm, 10000ppm, and when hydrogen concentration is 500ppm and 3000ppm at relative humidity of 20 ° C and 65%, respectively. The ambient temperature and relative humidity of the sensor element are within a two-dimensional orthogonal coordinate space with the horizontal axis representing the high-temperature normalized resistance (R _H / R _{H-CH 4} ) and the vertical axis representing the comparison result value (R _M / R _H ). Distribution chart plotting coordinate points at methane concentration of 1000 ppm, 3000 ppm, 6000 ppm, and 10000 ppm at 20 ° C. and 65%, and coordinate points at hydrogen concentrations of 500 ppm and 3000 ppm, respectively.

Explanation of symbols

1: Gas detection device according to the present invention 2: Microprocessor 3: Sensor unit 4: Non-volatile storage means 5: Heating control unit 5a: Sensor driving unit 5b: Pulse control unit 6: Determination unit 6a: Resistance detection unit 6b: Gas Judgment part 7: Alarm output part 8: Power supply part 9: Temperature sensor 10: Heater (heating coil)
11: Sensor element 12: Sensor output terminal 13: Power plug 14: Light alarm output unit (light notification signal output unit)
14a: LED
15: Audio alarm output unit 15a: Audio circuit 15b: Speaker 16: External output circuit 17: Alarm output control unit 18: Light notification signal control unit 21: Sensor element 22: Heating coil 23: Electrode 24: Metal oxide semiconductor 25: Load resistance R1, R2: Load resistance T: Switching transistor Vcc: Power supply voltage

Claims (7)

A sensor element whose electrical resistance changes in response to at least methane and hydrogen, the main component of which is a metal oxide semiconductor;
A heating control unit that performs heating control so that the temperature of the sensor element periodically transitions between a high temperature state and a low temperature state;
A resistance detector that detects a sensor resistance represented by an electrical resistance value of the sensor element or an electrical resistance equivalent value that can be converted into the electrical resistance value;
A gas determination device comprising: a gas determination unit that determines presence of methane and hydrogen separately based on the sensor resistance detected by the resistance detection unit;
The resistance detection unit detects the sensor resistance when the sensor element is in the high temperature state by heating control by the heating control unit as a first sensor resistance, and the sensor element is detected by heating control by the heating control unit. Detecting the sensor resistance when in an intermediate state transitioning between a high temperature state and the low temperature state as a second sensor resistance;
The gas determination unit determines the presence of methane based on the first sensor resistance, and determines the presence of hydrogen based on a comparison result value obtained by comparing the second sensor resistance and the first sensor resistance. Gas detection device.   The said gas determination part correct | amends the threshold value used for the threshold determination with respect to the said 1st sensor resistance or the said 1st sensor resistance based on the said comparison result value, The said methane presence determination is performed. The gas detection device according to 1.   The gas determination unit determines whether hydrogen exists alone without coexisting with methane based on the comparison result value, and the first sensor resistance or the first sensor resistance is determined based on the determination result. The gas detection device according to claim 1 or 2, wherein the presence of the methane is determined by correcting a threshold used for threshold determination. A temperature sensor for measuring the ambient temperature of the sensor element;
The said gas determination part correct | amends the threshold value used for the said threshold value determination with respect to the said 1st sensor resistance or the said 1st sensor resistance based on the said ambient temperature measured with the said temperature sensor, or 3. The gas detection device according to 3. The metal oxide semiconductor of the sensor element further changes its electrical resistance in response to carbon monoxide,
The resistance detection unit detects the sensor resistance when the sensor element is in the low temperature state by the heating control by the heating control unit as a third sensor resistance,
The gas determination unit is configured to determine the third sensor resistance or a threshold value for the third sensor resistance based on the comparison result value when determining the presence of carbon monoxide based on the third sensor resistance. The gas detection device according to any one of claims 1 to 4, wherein the correction is performed. A temperature sensor for measuring the ambient temperature of the sensor element;
The said gas determination part correct | amends the threshold value used for the said threshold value determination with respect to the said 3rd sensor resistance or the said 3rd sensor resistance based on the said ambient temperature measured with the said temperature sensor. The gas detector described.   In the two-dimensional orthogonal coordinate space defined by the increase / decrease direction of the first sensor resistance and the increase / decrease direction of the comparison result value, the gas determination unit is configured to determine a coordinate point determined by the first sensor resistance and the comparison result value. The gas detection device according to any one of claims 1 to 6, wherein the presence of hydrogen is determined when it exists in a predetermined region in a two-dimensional orthogonal coordinate space.