JP2006275606A - Gas detecting method and gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the identification accuracy of a gas component in a single gas sensor by well separating information related to the kind and information related to concentration of the gas component from the dynamic response to a temperature change by a metal oxide semiconductor gas sensor to take out the same. <P>SOLUTION: Since an n-order (n=1, 2, ...) differential waveform obtained by differentiating the dynamic response waveform of the gas sensor 10, obtained when the temperature of the gas sensor 10 is changed, passes the fixing point at a position different for every gas component without relying on the concentration of the gas component, the fixing point is preliminarily measured for every gas component to be stored in a fixing point data memory part 25. When a sample gas of which the component is unknown is analyzed, the dynamic response waveform, obtained when the temperature of the gas sensor 10 is changed, is acquired to be subjected to n-order differentiation in a differential operation processing part 22, and a gas kind judging processing part 23 judges which fixing point stored in the fixing point data memory part 25 the n-order differential waveform passes, thereby to identify the gas component on the basis of the judge result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas detection method and a gas detection apparatus using a metal oxide semiconductor sensor as a gas sensor.

  A metal oxide semiconductor gas sensor is a sensor in which a sensitive film made of a metal oxide semiconductor is formed between electrodes. When this sensitive film is heated to a high temperature, it is oxidized and reduced with gas components adhering to the surface of the sensitive film. Cause a reaction. In this process, movement of electrons occurs, the free electron density in the sensitive film and the thickness of the charge depletion layer change, and the resistance value between the electrodes changes. This type of gas sensor is widely used in, for example, a home gas leak detector.

  However, the metal oxide semiconductor gas sensor as described above responds to almost any gas as long as it is a reducing gas, and the gas components cannot be distinguished from a steady response. Therefore, for example, when it is desired to have selectivity for detecting a specific gas, it is necessary to adopt a configuration such as providing a filter that removes an undesired gas component in advance, which improves the selectivity of the gas component. It is one of the big issues.

  On the other hand, gas detectors capable of identifying and quantifying various types of gas components are required in a wide range of fields such as environmental measurement, inspection of foods and fragrances, criminal investigations, and various technologies have been proposed so far. Has been. A typical example is to obtain multidimensional information by arranging a plurality of gas sensors having different response characteristics by devising an added catalyst or the like. In such a configuration, gas components are identified and quantified by performing multivariate analysis processing such as principal component analysis and analysis processing using a neural network on multiple detection signals obtained by multiple gas sensors exposed to the same gas. Analysis is generally performed (see, for example, Patent Document 1).

  However, in such an apparatus, it is necessary to increase the number of gas sensors as the number of types of gas components that can be identified increases, and the amount of calculation for analysis processing becomes enormous. For this reason, an increase in the scale of the apparatus and an increase in costs are inevitable.

  On the other hand, as a method of obtaining multidimensional information from a single gas sensor, the temperature of the gas sensor (strictly speaking, the temperature of the sensitive film) is intentionally changed, and the dynamic change of the detection signal by the gas sensor is analyzed. A method of identifying and quantifying gas components by doing so is conventionally known (see, for example, Patent Documents 2, 3, and 4). For example, in Patent Document 2, the gas component is identified using the peak position and intensity of the gas sensor output when the temperature changes. However, none of the conventionally proposed methods has a fundamental problem that information on the type of gas component, that is, qualitative information, and information on the concentration of gas component, that is, quantitative information cannot be completely separated. is there. Therefore, it is difficult to obtain practically sufficient accuracy for both qualitative analysis (component identification) and quantitative analysis (concentration calculation). In addition, since it takes time to extract stable data in the analysis of the dynamic response in a periodic temperature change, it is not suitable for identifying and quantifying gas components in real time, for example, at the site of environmental measurement.

Japanese Patent Laid-Open No. 11-352088 JP-A-1-123848 Japanese Patent Laid-Open No. 3-123848 JP-A-7-311170

  If it is possible to satisfactorily separate the information on the type of gas component and the information on the concentration from the dynamic response waveform to the temperature change in the single gas sensor as described above, a single or a small number of gas sensors can be used. This makes it possible to identify many types of gas components. In addition, if the gas component can be accurately identified, it is possible to have such a high selectivity that apparently responds only to a specific gas.

  The present invention has been made in view of these points, and its main object is to achieve a high gas discrimination capability without complicated processing by using the dynamic response of a single gas sensor. An object of the present invention is to provide a gas detection method and a gas detection device.

  In the course of conducting research on dynamic response to temperature change of a metal oxide semiconductor gas sensor over a long period of time, the present inventor has a fixed point where the nth-order differential waveform related to time of the dynamic response waveform to temperature change is independent of concentration. And the fixing point was found to be different for each component (compound) contained in the gas. In other words, the position of the fixed point has only information (qualitative information) regarding the type of gas component, and does not have information (quantitative information) regarding the concentration. Therefore, when the type of component contained in the sample gas and its concentration are unknown, the nth-order differential waveform of the dynamic response waveform with respect to the temperature change of the metal oxide semiconductor gas sensor is displayed on the two-dimensional graph including the waveform. If it is checked whether it passes through such a fixed point, it becomes possible to specify the component regardless of the concentration.

The present invention is intended to solve the above-mentioned problems using such a principle, and the gas detection method according to the present invention detects a gas containing an unknown component by a gas sensor using a metal oxide semiconductor. In a gas detection method for identifying at least its components,
a) Under the condition where the sample gas is exposed to the gas sensor, the temperature of the gas sensor is changed within a range where the response operation is possible,
b) Measure the dynamic response of the detection signal of the gas sensor according to the temperature change,
c) nth order differential (n = 1, 2,...) waveform with respect to time of the dynamic response waveform and the nth order for the same gas component having different concentrations set on the graph on which the nth order differential waveform is drawn. Identifying the gas component contained in the sample gas based on the relationship with a fixed point where all of the differential waveforms pass in common and do not match for each type of gas component,
It is characterized by that.

A gas detection apparatus according to the present invention is an apparatus that embodies the gas detection method.
a) a gas sensor using a metal oxide semiconductor;
b) temperature control means for changing the temperature of the gas sensor within a range in which the response operation is possible;
c) a measurement control means for measuring a dynamic response of a detection signal of the gas sensor according to a temperature change by the temperature control means under a state in which the sample gas is exposed to the gas sensor;
d) nth-order differential (n = 1, 2,...) waveform with respect to time of the dynamic response waveform and nth-order for the same gas component having different concentrations set on the graph on which the n-order differential waveform is drawn. Qualitative means for identifying a gas component contained in the sample gas based on a relationship between a fixed point where all of the differential waveforms pass in common and do not coincide with each type of gas component;
It is characterized by having.

  Note that the “fixed point” in this specification does not mean a strict “point”, but is actually considered as a small region having an appropriate area in consideration of variations in conditions during analysis and changes over time. Can do.

  According to the gas detection method and the gas detection device of the present invention, the information on the type of the gas component is extracted without being influenced by the concentration of the gas component, and the gas component is identified based on the extracted information. And accurate identification is possible. If the gas component is specified, the concentration can be calculated based on, for example, the detection value of the gas sensor when a predetermined time has elapsed from the temperature change, with the condition of the type of the gas component narrowed down. Therefore, quantitative accuracy is also improved. This makes it possible to qualitatively and quantitatively determine a plurality of gas components with a single gas sensor, improving the operational efficiency of the gas sensor.

  Further, according to the gas detection method and the gas detection device according to the present invention, since necessary analysis processing such as n-th order differential calculation processing and determination processing such as whether a waveform passes through a fixed point is simple, Even an inexpensive processing device (for example, a personal computer) can perform analysis in real time. Therefore, it is easy to reduce the size and cost of the apparatus, and real-time measurement at the measurement location is also possible.

  As a preferable aspect of the gas detection device according to the present invention, the gas detection device includes a storage unit for previously checking and storing the fixed points for a plurality of types of gas components, and the qualitative unit is obtained by measuring a sample gas. The gas component can be identified by examining which of the fixed points for each gas component stored in the storage means passes through the nth-order differential waveform.

  That is, as described above, the position of the fixed point on the two-dimensional graph including the nth-order differential waveform is different for each type of gas component. Therefore, the measurement target is actually measured using a standard sample in advance. It is possible to obtain a fixed point for each gas component that can be stored in the storage means. According to this configuration, the processing content of the qualitative means is simple, which is advantageous for downsizing and cost reduction of the apparatus.

  In addition, when the difference (instrument difference) between the fixed points is large, the standard sample is measured for each device to obtain the fixed point, or the fixed point difference between the devices is corrected. Such arithmetic processing may be performed by each device. In addition, when the change with time of the fixed point is large, it is assumed that the change with time is assumed in advance and correction is performed according to the assumption, or the standard sample is measured again every time the apparatus is used for a predetermined time, for example. It is advisable to perform a fixed point calibration.

In the gas detection device according to the present invention, various metal oxide semiconductor gas sensors can be used as the gas sensor, for example, a widely used SnO ₂ sensor may be used. Thereby, not a special gas sensor but a general inexpensive gas sensor can be used.

  In addition, since the time change of a waveform will become small if the order n of a differentiation becomes large, generally n should be small, for example, it is good to set it as 1 or 2 (namely, it is set as a primary differentiation or a secondary differentiation). Further, not only one n but a plurality are selected, for example, based on both the relationship between the primary differential waveform and the fixed point related to the dynamic response time, and the relationship between the secondary differential waveform and the fixed point. You may make it identify a gas component.

  Hereinafter, the principle of gas component identification in the gas detection method and gas detection apparatus according to the present invention will be described together with the results of experiments conducted by the present inventors.

The temperature of the metal oxide semiconductor gas sensor (SnO ₂ gas sensor in this example) placed in a gas atmosphere containing a single component was raised from the first temperature T1 to the second temperature T2 within the temperature range in which gas can be detected. When the temperature changes, the detection signal of the gas sensor changes in a characteristic manner. This transient change is a dynamic response to a temperature change, but its response characteristic varies depending on the type of gas component and its concentration.

  FIG. 4 is a graph showing measured values of the surface temperature of the gas sensor when the heating current passed through the heater attached to the gas sensor at time 0 is increased stepwise in an experiment conducted by the present inventor. The temperature rises from T1 = about 410 [K] (about 140 ° C.) to T2 = about 520 [K] (about 250 ° C.) from time 0 to about 15 seconds. However, from the result of the response characteristics of the gas sensor 10 described later, this temperature change is delayed from the temperature change actually generated in the sensitive film of the gas sensor due to the limit of the temperature detection device used in this experiment. Conceivable. In any case, as the heating current increases, the temperature of the gas sensor 10 increases at an appropriate rate from the first temperature T1 to the second temperature T2, and the rate of increase increases gradually as the temperature approaches the second temperature T2. When the temperature reaches the vicinity of the second temperature T2, the temperature is substantially maintained by thermal equilibrium.

  FIG. 5 shows the above eight gas components of methanol, ethanol, benzene, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, and 2-butanol, and air as a dilution gas. It is a graph which shows the waveform which measured the dynamic response of the gas sensor 10 with respect to such temperature changes. The concentration of the gas component is three stages of 100, 200, and 300 ppm for each component.

  As can be seen from FIG. 5, the waveform shape of the dynamic response basically differs for each gas component, and also varies depending on the concentration. Therefore, it can be said that the waveform of this dynamic response includes information (qualitative information) regarding the type of gas component and information (quantitative information) regarding the concentration. However, it is difficult to completely separate qualitative information and quantitative information directly from this waveform shape.

  FIG. 6 is a graph showing waveforms obtained by first-order differentiation of the waveforms shown in FIG. 5 with respect to time. It can be seen from FIG. 6 that there is a difference in the waveform shape for each gas component, particularly in the initial 5 seconds of the temperature change. On the other hand, in the waveform shape after 7.5 seconds, there is almost no clear difference due to the gas component. Therefore, the present inventor has paid attention to the initial 5 second transient waveform fluctuation.

  FIG. 7 shows the dynamic response of the initial 5 seconds from the time of temperature change (time 0) for the sample gas containing each of the three gas components, ethanol, 1-butanol and 2-methyl-1-propanol. It is a graph which shows the result of having calculated | required in detail the primary differential waveform and secondary differential waveform regarding time. The primary differential waveform and the secondary differential waveform differ for each gas component, but pass through a fixed point that does not depend on the concentration on each two-dimensional graph, and the fixed point is different for each gas component. It can be seen that it exists in (time and differential value).

  For example, in the first derivative waveform for ethanol, there is one fixed point after about 0.5 seconds, and in the first derivative waveform for 1-butanol, after about 1.0 seconds and after about 3.6 seconds. In addition, there is one fixed point for each, and in the first derivative waveform for 2-methyl-1-propanol, after about 0.6, after about 2.1 seconds, and after about 3.4 seconds It can be seen that one fixed point exists at each of the three locations.

  Although FIG. 7 shows the result of only three kinds of gas components, the same result is obtained for the other gas components as described above, and the first-order differential waveform does not depend on the concentration but depends on the type of each component. Two-dimensional graph (including time on the horizontal axis and the primary differential value on the vertical axis) and a two-dimensional graph including the secondary differential waveform (graph on the horizontal axis with time and the vertical axis with the secondary differential value) Above, it has been found that each has a different fixed point.

  The graph shown in FIG. 8 summarizes the positions of the fixed points for the first-order differential waveforms of various gas components. In FIG. 8, the first-order differential waveform of 2-methyl-1-propanol having a concentration of 100 ppm is shown by a dotted line for reference. A similar graph can be created for the secondary differential waveform. As described above, the position of the fixed point on the two-dimensional graph with the horizontal axis representing time and the vertical axis representing the primary differential value (or secondary differential value) is clearly different for each gas component. Can be used.

  That is, the sample gas whose gas component is unknown is measured by the gas sensor by the method as described above, and the waveform of the dynamic response to the temperature change is acquired. Then, it is possible to examine which of the fixed points shown in FIG. 8 the waveform obtained by first-order differentiation of the dynamic response waveform with respect to time passes and identify the gas component from the result.

  Further, when it is known that the unknown gas component is one of the gas components shown in FIG. 8 (in other words, when there is no possibility of other gas components), the first derivative Rather than examining which of the fixed points the waveform passes through, for example, the correlation coefficient between the first derivative waveform and each fixed point or an index value indicating the correlation is calculated, and the correlation coefficient is the highest. It may be concluded that the gas component that is determined to be large, that is, the gas component that is determined to be the most probable is an unknown gas component. As a similar idea, the shortest distance between the primary differential waveform and each fixed point can be calculated, and the above identification can be performed based on the value. In any case, the fixed point does not have information on the concentration but has only information on the type of gas component, and on the two-dimensional graph including the first-order differential waveform or higher-order differential waveform and the differential waveform. The gas component can be identified from the relationship with the fixed point for each gas component positioned.

  The above is the principle of gas component identification of the gas detection method according to the present invention. Next, an embodiment of the gas detection apparatus according to the present invention using this principle will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of a gas detection apparatus according to this embodiment.

In this gas detector, a SnO ₂ gas sensor 10 is installed in a gas chamber 11 into which a sample gas to be analyzed is introduced. In order to reduce the influence of moisture contained in the sample gas, the sample gas may be sent into the gas chamber 11 after passing through the dehumidifying section. A heating current is supplied to the heater 10a attached to the gas sensor 10 from an external temperature control unit 12, and thereby the gas sensor 10 is heated to a predetermined temperature. The detection signal from the gas sensor 10 is converted into digital data by the A / D conversion unit 13 and input to the data processing unit 20. The data processing unit 20 includes a differential calculation processing unit 22, a gas type determination processing unit 23, a concentration calculation processing unit 24, a fixed point information storage unit 25, a calibration curve information storage unit 26, and the like as functional blocks. The operation of the temperature control unit 12, the data processing unit 20, and the like is comprehensively controlled by the control unit 14, and the control unit 14 displays an input unit 15 for an analyzer to give various instructions, an analysis result, and the like. A display unit 16 is connected.

  The data processing unit 20 and the control unit 14 can achieve their functions by executing a predetermined program on a personal computer, for example, and are configured by dedicated hardware including a digital signal processor or the like. You can also.

  FIG. 2 is a conceptual diagram showing the stored information in the fixed point information storage unit 25 included in the apparatus. As described above, the first-order differential waveform of the dynamic response for various components (compounds) to be detected has a fixed point that does not depend on the concentration. Therefore, this fixed point is examined in advance for each compound and is shown in FIG. They are stored in the fixed point information storage unit 25 in a table format as shown. In this example, for example, gas type A has fixed points a1 and a2, gas type B has fixed points b1, b2, and b3, and gas type C has fixed points c1 and c2. As described above, a fixed point of an n-order differential (n = 1, 2,...) Waveform such as a secondary differential waveform may be used instead of a fixed point of the primary differential waveform, or a plurality of n-order differentials may be used. The discriminability can be improved by using a fixed point of the waveform together.

  On the other hand, the calibration curve information storage unit 26 included in the apparatus stores information representing a calibration curve indicating the relationship between the detected value and the concentration obtained from the dynamic response of various compounds. For example, as can be seen from FIG. 5, the detected value after 10 seconds or 15 seconds from the time of temperature change differs depending on the concentration. Therefore, for example, a calibration as shown in FIG. 3 from the relationship between the concentration and the detected value for each compound. A line is created, an approximate polynomial representing the calibration curve is obtained, and the information is stored in the calibration curve information storage unit 26.

  Subsequently, a gas analysis operation in the gas detection apparatus of the present embodiment will be described. Under the control of the control unit 14, the temperature control unit 12 controls the heating current that flows through the heater 10a so that the temperature of the gas sensor 10 becomes the first temperature T1. Then, the temperature controller 12 increases the heating current so that the temperature of the gas sensor 10 changes from the first temperature T1 to the second temperature T2 (T2> T1) at a predetermined timing (for example, time t0) from that state. . Thereby, the temperature of the gas sensor 10 rises from the first temperature T1 to the second temperature T2. Even if the heating current increases stepwise, the temperature rise of the gas sensor 10 is not actually stepped due to the influence of heat capacity and the like. The first temperature T1 and the second temperature T2 may be appropriately set according to the category of the gas component to be detected. For example, when the detection target is an alcohol, T1 may be set to around 400 [K] and T2 may be set to around 500 [K] as described above.

  Upon receiving an instruction to start measurement from the control unit 14, the data processing unit 20 starts collecting data from the time t0, and takes in the detection signal converted into digital data at a predetermined sampling time interval by the A / D conversion unit 13. start. When the temperature of the gas sensor 10 rises from the first temperature T1 to the second temperature T2, the detection signal of the gas sensor 10 changes greatly, especially during the initial period of about 5 seconds, and then gently so as to approach the steady state. Change. The differential operation processing unit 22 receives the data having such time dependency, performs the differential operation processing in real time, creates primary differential waveform data, and sends it to the gas type discrimination processing unit 23.

  The gas type discrimination processing unit 23 reads information on the fixed point for each gas component as described above stored in the fixed point information storage unit 25, and the primary differential waveform data received from the differential calculation processing unit 22 Determine if it passes through a fixed point. Here, for example, even if the fixed points stored in the fixed point information storage unit 25 each indicate the coordinate position of a certain point, in consideration of variations in analysis conditions, analysis errors, etc., to a certain extent It is necessary to allow the deviation. Therefore, in practice, a predetermined range centered on the coordinate position indicated by the fixed point is defined as a detection range as the fixed point, and if the first-order differential waveform passes through this detection range, it is regarded as having passed through the fixed point. Perform the following process. As a result, the influence of variations in analysis conditions and various errors is reduced.

  The gas type discrimination processing unit 23 specifies which gas component is the unknown gas component based on the positional relationship between the first-order differential waveform and the fixed point as described above, and together with the control unit 14 as component type information. This is sent to the density calculation unit 24. The concentration calculation unit 24 receives the component information, reads out the calibration curve information corresponding to the component stored in the calibration curve information storage unit 26, and reproduces the calibration curve. Then, a detection value at a predetermined elapsed time (for example, after 15 seconds has elapsed) in the dynamic response waveform input to the data processing unit 20 is acquired, and the concentration is obtained from the detection value with reference to the reproduced calibration curve.

  The control unit 14 receives the component type information and the concentration information obtained as described above, and causes the display unit 16 to display them. As a result, the analyst can know the types and concentrations of the measured components of the unknown gas in a short time.

  Note that if the gas type discrimination processing unit 23 cannot find the one corresponding to the fixed point prepared in the fixed point information storage unit 25 as a result of the processing as described above, the gas type determination processing unit 23 passes through the control unit 14 as being undetectable. This can be displayed on the display unit 16.

  Note that the fixed point is not always constant and may change with time or may change depending on the analysis conditions (for example, the humidity of the sample gas). In addition, since there are generally some individual differences in the response characteristics of the gas sensor, it is considered that there are also differences between the devices at fixed points. Accordingly, for example, correction processing may be performed, or calibration processing may be performed based on the result of actual measurement of a standard sample, and the fixed point may be appropriately corrected and used.

  In the above-described embodiment, it is determined which fixed point the first-order differential waveform passes through. However, as described above, the correlation between the fixed point and the first-order (or n-th order) differential waveform is used. Thus, the type of gas component may be identified.

  In the above embodiment, the detection signal obtained by the gas sensor is processed almost in real time and the analysis result is output. However, the data obtained by A / D conversion of the detection signal is temporarily stored in the data memory, and then batch processing is performed. It is good also as a structure which performs an analysis process in process.

  Further, in the above embodiment, the case where the gas component is identified and quantified by one gas sensor has been described. However, two or more gas sensors having different response characteristics can be provided to increase the types of gas that can be identified, or The reliability of identification and quantification may be further increased.

  Further, since the above embodiment is an example of the present invention, any change, correction, addition, etc., as appropriate within the scope of the present invention, are included in the scope of the claims of the present application in addition to the above description. It is clear.

The block diagram of the gas detection apparatus by one Example of this invention. The conceptual diagram which shows the memory | storage information of the fixed point information storage part in FIG. The figure which shows an example of the calibration curve memorize | stored in the calibration curve information storage part in FIG. The graph which shows the change of the surface temperature of a gas sensor when the heating current sent through a gas sensor is increased in the step shape in the experiment by this inventor. The dynamic response of the gas sensor with respect to the temperature change in FIG. 4 is expressed by the following eight gas species: methanol, ethanol, benzene, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, and 2-butanol. The figure which shows the waveform measured about the air which is a dilution gas. The figure which shows the waveform acquired by carrying out the primary differentiation of each waveform shown in FIG. The figure which shows the primary differential waveform and the secondary differential waveform of the response characteristic of initial 5 second about three types of gases, ethanol, 1-butanol, and 2-methyl-1-propanol. The figure which plotted the fixed point about the primary differential waveform of various gas.

Explanation of symbols

10 ... SnO ₂ gas sensor 10a ... heater 11 ... gas chamber 12 ... temperature control unit 13 ... A / D conversion unit 14 ... controller 15 ... input unit 16 ... display unit 20 ... data processing unit 22 ... differential operation processing unit 23 ... Gas Species discrimination processing unit 24 ... concentration calculation processing unit
25 ... Fixed point information storage unit 26 ... Calibration curve information storage unit

Claims (5)

In a gas detection method for detecting a gas containing an unknown component by a gas sensor using a metal oxide semiconductor and identifying at least the component,
a) Under the condition where the sample gas is exposed to the gas sensor, the temperature of the gas sensor is changed within a range where the response operation is possible,
b) Measure the dynamic response of the detection signal of the gas sensor according to the temperature change,
c) nth order differential (n = 1, 2,...) waveform with respect to time of the dynamic response waveform and the nth order for the same gas component having different concentrations set on the graph on which the nth order differential waveform is drawn. Identifying the gas component contained in the sample gas based on the relationship with a fixed point where all of the differential waveforms pass in common and do not match for each type of gas component,
The gas detection method characterized by the above-mentioned. a) a gas sensor using a metal oxide semiconductor;
b) temperature control means for changing the temperature of the gas sensor within a range in which the response operation is possible;
c) a measurement control means for measuring a dynamic response of a detection signal of the gas sensor according to a temperature change by the temperature control means under a state in which the sample gas is exposed to the gas sensor;
d) nth-order differential (n = 1, 2,...) waveform with respect to time of the dynamic response waveform and nth-order for the same gas component having different concentrations set on the graph on which the n-order differential waveform is drawn. Qualitative means for identifying a gas component contained in the sample gas based on a relationship between a fixed point where all of the differential waveforms pass in common and do not coincide with each type of gas component;
A gas detection device comprising:   Storage means for preliminarily examining and storing the fixed points for a plurality of types of gas components is provided, and the qualitative means stores an nth-order differential waveform obtained by measuring a sample gas in the storage means. The gas detection device according to claim 2, wherein the gas component is identified by examining which of the fixed points for each gas component passes. The gas detection device according to claim _2, wherein the gas sensor is a SnO ₂ sensor. The gas detection method according to claim 1 or the gas detection device according to any one of claims 2 to 4, wherein n is 1 or 2.

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