Gas analysis method and gas analysis system

Abstract

This gas analysis method is for analyzing a sample gas by using a gas sensor in which an electrical characteristic value changes in response to adsorption of molecules. The gas analysis method includes: an acquisition step (S12) for acquiring, in a prescribed measurement period, a signal indicating an electrical characteristic value output by a gas sensor exposed to a sample gas while being increased or decreased in temperature; a correction step (S13) for correcting, on the basis of the temperature of the gas sensor measured by a temperature sensor in a prescribed measurement period, information pertaining to the signal acquired in the acquisition step; and an analysis step (S14) for analyzing the sample gas on the basis of the information corrected in the correction step.

Description

Gas analysis method and gas analysis system

[0001] The present disclosure relates to a gas analysis method and a gas analysis system.

[0002] Gas sensors whose electrical characteristics change in response to molecular adsorption are used for gas analysis, etc. In such gas sensors, the adsorption of molecules to the gas sensor can be controlled; for example, the state of adsorption of molecules to the gas sensor can be changed by changing the temperature of the gas sensor.

[0003] For example, Patent Document 1 discloses a technique for detecting gas by raising the temperature of a gas sensor to a high temperature and then lowering the temperature of the gas sensor to a suitable temperature for gas detection.

[0004] Japanese Unexamined Patent Publication No. 6-148116

[0005] The technology described in Patent Document 1 raises the temperature of a gas sensor to desorb gas (specifically, gas molecules to be detected) adsorbed on the gas sensor, thereby improving the stability of the gas sensor when detecting gas at an appropriate temperature. However, the technology described in Patent Document 1 poses a problem of long measurement times because it takes time for the temperature of the gas sensor to drop to the appropriate temperature and stabilize. On the other hand, when the electrical characteristic values ​​of a gas sensor are used in analysis, it is important to suppress a decrease in analytical accuracy even if the measurement time for analysis is shortened.

[0006] Therefore, the present disclosure provides a gas analysis method and a gas analysis system that can shorten the measurement time while suppressing a decrease in analytical accuracy.

[0007] A gas analysis method according to one aspect of the present disclosure is a gas analysis method for analyzing a sample gas using a gas sensor whose electrical characteristic value changes in response to molecular adsorption, and includes an acquisition step of acquiring a signal indicating the electrical characteristic value output by the gas sensor exposed to the sample gas as the temperature is increased or decreased during a predetermined measurement period; a correction step of correcting information about the signal acquired in the acquisition step based on the temperature of the gas sensor measured by a temperature sensor during the predetermined measurement period; and an analysis step of analyzing the sample gas based on the information corrected in the correction step.

[0008] A gas analysis system according to one aspect of the present disclosure includes a gas sensor whose electrical characteristic value changes in response to molecular adsorption; a temperature regulator that heats and / or cools the gas sensor; a temperature sensor that measures the temperature of the gas sensor; an acquisition unit that acquires a signal indicating the electrical characteristic value output by the gas sensor exposed to a sample gas while being heated or cooled by the temperature regulator during a predetermined measurement period; a correction unit that corrects information about the signal acquired by the acquisition unit based on the temperature of the gas sensor measured by the temperature sensor during the predetermined measurement period; and an analysis unit that analyzes the sample gas based on the information corrected by the correction unit.

[0009] These comprehensive or specific aspects may be realized by a system, an apparatus, a method, an integrated circuit, a computer program, or a non-transitory recording medium such as a computer-readable CD-ROM (Compact Disc-Read Only Memory), or may be realized by any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium.

[0010] According to the present disclosure, it is possible to shorten the measurement time while suppressing a decrease in analytical accuracy.

[0011] FIG. 1 is a block diagram showing a schematic configuration of a gas analysis system according to an embodiment. FIG. 2 is a top view showing an example of a gas sensor according to an embodiment. FIG. 3 is a schematic diagram showing an example of the configuration of an exposure section according to an embodiment. FIG. 4 is a diagram showing a temperature pattern of heating of a gas sensor. FIG. 5 is a diagram showing an example of a signal output from a gas sensor. FIG. 6 is a diagram showing the relationship between the temperature rise rate of a gas sensor and a feature amount. FIG. 7 is a diagram showing the result of principal component analysis of feature amounts before correction. FIG. 8 is a diagram showing the result of principal component analysis of feature amounts after correction. FIG. 9 is a flowchart showing an example of operation of a gas analysis system according to an embodiment. FIG. 10 is a diagram showing an example of temperature change of a gas sensor during a measurement period.

[0012] (Background to the Invention of One Aspect of the Present Disclosure) A gas sensor whose electrical characteristic value changes in response to molecular adsorption outputs a signal indicating the electrical characteristic value. When such a gas sensor is used for gas analysis, for example, the signal output from the gas sensor exposed to a sample gas is acquired, and the sample gas is analyzed using feature quantities extracted from the acquired signal. In this case, by exposing the gas sensor to the sample gas while the temperature of the gas sensor is stable, the signal output from the gas sensor also becomes stable.

[0013] However, as mentioned above, it takes time for the temperature of a gas sensor to stabilize. Therefore, one possible method to shorten the measurement time is to acquire a signal from the gas sensor while the temperature of the gas sensor exposed to the sample gas is being changed, that is, while the gas sensor is being heated or cooled. When the temperature of the gas sensor is changed, the state of adsorption of molecules to the gas sensor changes, and the signal output from the gas sensor also changes. Furthermore, the change in the state of adsorption of molecules to the gas sensor differs depending on the type of molecule. For these reasons, while the temperature of the gas sensor is changing, the gas sensor outputs a signal corresponding to the type and concentration of molecules contained in the sample gas, and the sample gas can be analyzed using this signal.

[0014] In such a method of acquiring a signal from a gas sensor while the temperature of the gas sensor is being changed, if the temperature pattern (e.g., temperature value and rate of temperature change) of the gas sensor during measurement is the same for each measurement, the signal output from the gas sensor will be stable. On the other hand, if the temperature pattern of the gas sensor during measurement changes from measurement to measurement, the waveform of the signal output from the gas sensor will also change for each measurement, even when measuring the same sample gas. The temperature pattern of the gas sensor during measurement can easily change due to fluctuations in the outside air temperature and changes in the characteristics of the heater used to heat the gas sensor. Therefore, in a method of acquiring a signal from a gas sensor while the temperature of the gas sensor is being changed, there is a problem in that the analysis accuracy decreases due to fluctuations in the temperature pattern of the gas sensor from measurement to measurement.

[0015] The present disclosure has been made in consideration of such problems, and provides a gas analysis method and a gas analysis system that can achieve both shortening the measurement time and suppressing a decrease in analytical accuracy.

[0016] (Summary of the Present Disclosure) As an overview of the present disclosure, examples of a gas analysis system and a gas analysis method according to the present disclosure will be described below.

[0017] For example, a gas analysis method according to a first aspect of the present disclosure is a gas analysis method for analyzing a sample gas using a gas sensor whose electrical characteristic value changes in response to molecular adsorption, and includes an acquisition step of acquiring a signal indicating the electrical characteristic value output by the gas sensor exposed to the sample gas as the temperature is increased or decreased during a predetermined measurement period, a correction step of correcting information about the signal acquired in the acquisition step based on the temperature of the gas sensor measured by a temperature sensor during the predetermined measurement period, and an analysis step of analyzing the sample gas based on the information corrected in the correction step.

[0018] As a result, in the acquisition step, the signal output by the gas sensor is acquired while the temperature is rising or falling, so there is no need to wait for the temperature of the gas sensor to stabilize, and measurement can be performed in a short time. Furthermore, because there is no need to wait for the temperature of the gas sensor to stabilize, even if the temperature of the gas sensor during a predetermined measurement period varies from measurement to measurement due to the external environment, etc., the information about the signal acquired in the acquisition step is corrected based on the temperature of the gas sensor in the correction step, and analysis can be performed using the corrected information, thereby improving analysis accuracy. Therefore, the gas analysis method according to this aspect can achieve both a short measurement time and suppression of a decrease in analysis accuracy.

[0019] Also, for example, a gas analysis method according to a second aspect of the present disclosure is the gas analysis method according to the first aspect, wherein the correction step corrects the information based on the rate of change of the temperature of the gas sensor during the specified measurement period.

[0020] This allows the information used for analysis to be corrected based on the rate of change in temperature, which is closely related to the state in which the gas sensor is being heated or cooled, thereby effectively preventing a decrease in analytical accuracy.

[0021] Furthermore, for example, a gas analysis method according to a third aspect of the present disclosure is the gas analysis method according to the first or second aspect, and in the correction step, the information is corrected based on a feature extracted from the signal acquired in the acquisition step.

[0022] This allows the feature amount extracted from the signal to be corrected, thereby reducing the amount of information to be corrected and the correction process.

[0023] Furthermore, for example, a gas analysis method according to a fourth aspect of the present disclosure is the gas analysis method according to the third aspect, wherein the characteristic amount includes a slope of a waveform of the signal.

[0024] The electrical characteristics of a gas sensor can also fluctuate due to temperature. Therefore, by correcting the slope of the signal waveform, which is easily affected by temperature increases or decreases in the gas sensor, a decrease in analytical accuracy can be effectively suppressed.

[0025] Furthermore, for example, a gas analysis method according to a fifth aspect of the present disclosure is the gas analysis method according to any one of the first to fourth aspects, wherein during the predetermined measurement period, the gas sensor is heated or cooled by a Peltier element or a heater.

[0026] This allows the temperature of the gas sensor to be increased or decreased with a simple configuration.

[0027] Also, for example, a gas analysis method according to a sixth aspect of the present disclosure is a gas analysis method according to any one of the first to fifth aspects, wherein in the acquisition step, the signal is acquired from the gas sensor arranged on the same substrate as the temperature sensor.

[0028] This makes it possible to improve the accuracy of measuring the temperature of the gas sensor measured by the temperature sensor.

[0029] Also, for example, a gas analysis method according to a seventh aspect of the present disclosure is a gas analysis method according to any one of the first to sixth aspects, wherein the acquisition step acquires the signal from the gas sensor via a network.

[0030] This makes it possible to easily acquire a signal from a gas sensor even if the gas sensor is located at a remote location.

[0031] Also, for example, a gas analysis method according to an eighth aspect of the present disclosure is a gas analysis method according to any one of the first to seventh aspects, in which, in the analysis step, odor molecules contained in the sample gas are identified as part of the analysis of the sample gas.

[0032] This makes it possible to identify odor molecules using a method that shortens the measurement time while preventing a decrease in analytical accuracy.

[0033] Furthermore, for example, a gas analysis system according to a ninth aspect of the present disclosure includes a gas sensor whose electrical characteristic value changes in response to molecular adsorption, a temperature regulator that heats and / or cools the gas sensor, a temperature sensor that measures the temperature of the gas sensor, an acquisition unit that acquires a signal indicating the electrical characteristic value output by the gas sensor exposed to sample gas while being heated or cooled by the temperature regulator during a predetermined measurement period, a correction unit that corrects information about the signal acquired by the acquisition unit based on the temperature of the gas sensor measured by the temperature sensor during the predetermined measurement period, and an analysis unit that analyzes the sample gas based on the information corrected by the correction unit.

[0034] As a result, similar to the gas analysis method according to the first aspect, it is possible to shorten the measurement time while suppressing a decrease in analytical accuracy.

[0035] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection forms, steps, step order, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0036] Furthermore, in this specification, terms indicating relationships between elements such as parallelism, terms indicating the shapes of elements, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0037] In addition, the drawings are not necessarily strict illustrations, and the same reference numerals are used to designate substantially the same components in the drawings, and redundant explanations are omitted or simplified.

[0038] (Embodiment) [Configuration] First, the configuration of a gas analysis system according to an embodiment will be described.

[0039] FIG. 1 is a block diagram showing a schematic configuration of a gas analysis system 100 according to this embodiment.

[0040] 1 , a gas analysis system 100 according to this embodiment includes a detection device 101 and an analysis device 102. The detection device 101 includes a gas sensor 10, a temperature regulator 20, a temperature sensor 30, an exposure unit 40, and a control unit 50. The analysis device 102 includes an acquisition unit 60, a correction unit 70, an analysis unit 80, and a memory 90.

[0041] The gas analysis system 100 analyzes the sample gas based on the output of the gas sensor 10 exposed to the sample gas. The sample gas includes molecules to be analyzed, such as volatilized organic compounds. The sample gas may include multiple types of molecules to be analyzed. The molecules to be analyzed may be inorganic gas molecules, such as ammonia, hydrogen sulfide, and carbon monoxide. The sample gas may be, for example, gas collected from food, exhaled breath collected from a human body, air surrounding a human body, or air collected from a room in a building.

[0042] The gas analysis system 100, for example, analyzes a sample gas by identifying molecules contained in the sample gas. For example, the gas analysis system 100 identifies which types of molecules are contained in the sample gas from among multiple types of molecules. The gas analysis system 100 may also be used to identify odors. In this case, the molecules to be identified are, for example, odor molecules, which are organic compounds that become odor components. The gas analysis system 100 may also perform an analysis to determine the concentration of a specific molecule contained in the sample gas.

[0043] The gas sensor 10 is a gas sensor whose electrical characteristic value changes in response to the adsorption of molecules to the gas sensor 10 (specifically, a sensitive part 11, which will be described later), and outputs a signal indicating the electrical characteristic value. For example, the gas sensor 10 outputs a signal that changes in response to the concentration of adsorbed molecules. The gas sensor 10 may be, for example, an electrochemical type, a semiconductor type, a field-effect transistor type, a surface acoustic wave type, a quartz oscillator type, or a resistance change type gas sensor.

[0044] Fig. 2 is a top view showing an example of a gas sensor 10 according to the present embodiment. As shown in Fig. 2, the gas sensor 10 includes, for example, a sensitive portion 11 and a pair of electrodes 12 and 13 electrically connected to the sensitive portion 11. In the example shown in Fig. 2, the gas sensor 10 is provided on a substrate 15.

[0045] The sensitive part 11 is, for example, a sensitive film whose electrical resistance, as an electrical characteristic value, changes in response to the adsorption of molecules. A signal indicating the electrical resistance of the sensitive part 11 of the gas sensor 10 is output, for example, as a voltage signal or a current signal via a pair of electrodes 12 and 13. The electrical resistance of the sensitive part 11 between the pair of electrodes 12 and 13 is converted into a voltage signal or a current signal, for example, by a detection circuit (not shown). The electrical resistance of the sensitive part 11 is converted into a voltage using, for example, a bridge circuit, and the voltage is amplified as necessary and output as a signal indicating the electrical resistance of the sensitive part 11. The gas sensor 10 outputs a signal that changes depending on the concentration of molecules adsorbed to the sensitive part 11. The ease of adsorption to the sensitive part 11 varies depending on the type of molecule. Furthermore, if different types of molecules are adsorbed by the sensitive part 11, the signal output from the gas sensor 10 may differ even for the same adsorption concentration.

[0046] The sensitive part 11 is composed of, for example, a resin material that is an adsorbent that adsorbs molecules to be analyzed by the gas analysis system 100, and conductive particles dispersed in the resin material. Examples of the resin material include polyalkylene glycol resin, polyester resin, and silicone resin. The resin material is, for example, a material commercially available as a stationary phase for gas chromatography columns. From the standpoint of durability and molecular adsorption, the resin material may be, for example, a silicone resin having various substituents, such as phenyl groups and methyl groups, on its side chain. When the resin material adsorbs molecules, the resin material expands, reducing the connections between the dispersed conductive particles and increasing the electrical resistance of the sensitive part 11.

[0047] Furthermore, the sensitive part 11 is not limited to being made of a resin material and conductive particles, but may be any material whose electrical resistance changes upon adsorption of molecules to be analyzed. The sensitive part 11 may be made of, for example, an inorganic material such as a metal oxide, or may be made of porous ceramics.

[0048] The gas analysis system 100 may include multiple gas sensors 10. In this case, the sensitivity characteristics of at least two of the multiple gas sensors 10 are different from each other. The sensitive portions 11 of at least two of the multiple gas sensors 10 are, for example, composed of different types of materials. For example, the types of organic compositions contained in the sensitive portions 11 are different. When the organic compositions are resin materials, different types of materials mean, for example, that at least one of the molecular weight and the composition formula is substantially different. Different types of materials exhibit different adsorption behaviors with respect to the same type of molecule. In other words, at least two of the multiple gas sensors 10 exhibit different molecular adsorption behaviors. In particular, when the materials have different composition formulas, the difference in molecular adsorption behavior is significant. Furthermore, the sensitive portions 11 of all of the multiple gas sensors 10 may be made of different materials. In this case, the multiple gas sensors 10 output different signals when adsorbing the same type of molecule. This allows different features to be extracted from the outputs of the multiple gas sensors 10, thereby improving the identification accuracy when using the gas analysis system 100 to identify molecules.

[0049] 1 , the temperature regulator 20 performs at least one of heating and cooling of the gas sensor 10 (specifically, the sensitive portion 11 of the gas sensor 10). The temperature regulator 20 operates under the control of the control unit 50. The temperature regulator 20 heats or cools the gas sensor 10 with a predetermined output, for example.

[0050] The temperature regulator 20 is, for example, a thermoelectric element that heats and / or cools the gas sensor 10. The temperature regulator 20 may be a heater that only heats, or an element that can heat and cool, such as a Peltier element. The temperature regulator 20 may also be a combination of multiple elements or devices. For example, the temperature regulator 20 may include a heater and a cooling fan to heat and cool the gas sensor 10. The temperature regulator 20 may also be a device that heats the gas sensor 10 via a medium such as a liquid.

[0051] The temperature sensor 30 measures the temperature of the gas sensor 10 (specifically, the sensitive part 11 of the gas sensor 10). The temperature sensor 30 is disposed near the sensitive part 11. The temperature sensor 30 may be in contact with the sensitive part 11 or may not be in contact with the sensitive part 11, as long as it can measure the temperature of the sensitive part 11. The temperature sensor 30 is, for example, a thermistor, a thermocouple, or a resistance temperature detector.

[0052] The exposure unit 40 is an exposure mechanism that exposes the gas sensor 10 to gas. Fig. 3 is a schematic diagram showing an example of the configuration of the exposure unit 40 according to this embodiment. As shown in Fig. 3, the exposure unit 40 includes, for example, a storage unit 41, a plurality of pipes 42 and 43, and an intake pump 44.

[0053] The accommodation unit 41 is a box-shaped container that accommodates the gas sensor 10, the temperature controller 20, and the temperature sensor 30. In the example shown in Fig. 3, the accommodation unit 41 accommodates a plurality of gas sensors 10. The plurality of gas sensors 10 are arranged in an array on the substrate 15, for example.

[0054] 3, the temperature controller 20 is arranged so as to be able to heat or cool a plurality of gas sensors 10 collectively. The plurality of gas sensors 10 are arranged on the same substrate 15 as the temperature sensor 30. This can improve the measurement accuracy of the temperature of the gas sensor 10 measured by the temperature sensor 30. Note that a plurality of temperature sensors 30 may be provided. In this case, one temperature sensor 30 is arranged on the substrate 15 for one or two or more gas sensors 10.

[0055] One end of each of a pipe 42 and a pipe 43 is connected to the housing 41. When the intake pump 44 is operated, gas flows from one end of the pipe 42 to one end of the pipe 43. The plurality of gas sensors 10 are arranged in the flow path through which the gas flows.

[0056] The piping 42 is a piping for sucking gas such as a sample gas to be analyzed from outside the exposure section 40. For example, by operating the suction pump 44, the sample gas is sucked from the piping 42, and the sucked sample gas is introduced into the storage section 41. The piping 42 may be provided with an automatic valve or a valve or the like for blocking the inflow of gas from outside the exposure section 40 to the storage section 41.

[0057] The pipe 43 is a pipe for discharging the gas inside the accommodation unit 41. For example, when the intake pump 44 is operated, the sample gas introduced into the accommodation unit 41 is discharged to the outside of the exposure unit 40.

[0058] The intake pump 44 is a pump for introducing gas into the inside of the storage unit 41 from the pipe 42 and discharging the introduced gas from the pipe 43. The intake pump 44 is provided in the pipe 43. The operation of the intake pump 44 is controlled by the control unit 50. The intake pump 44 may also be provided in the pipe 42.

[0059] The configuration of the exposure unit 40 is not limited to the configuration shown in Fig. 3, and is not particularly limited as long as it can expose the gas sensor 10 to the sample gas. For example, the exposure unit 40 may be configured not to include the intake pump 44, but to constantly flow a carrier gas into the accommodation unit 41 so that the sample gas is mixed into the carrier gas. Also, the exposure unit 40 may have a mechanism that can open the portion of the accommodation unit 41 above the gas sensor 10. Furthermore, the exposure unit 40 may further include various removal filters that remove moisture or particles from the sample gas, automatic valves such as electromagnetic adjustment valves that adjust the flow rate of each pipe, and check valves that prevent backflow in each pipe.

[0060] Furthermore, the exposure unit 40 may have a mechanism that can switch between the sample gas and a gas other than the sample gas and introduce it into the storage unit 41. For example, the pipe 42 may branch via a three-way valve, and the gas introduced into the storage unit 41 may be switched by operating the three-way valve. Examples of gases other than the sample gas include industrial or analytical air, inert gases that are substantially free of organic compounds, such as nitrogen or rare gases, and gases obtained by removing molecules that are easily adsorbed by the gas sensor 10 from the sample gas using a filter or the like.

[0061] Furthermore, the gas analysis system 100 does not need to include the exposure unit 40. For example, the gas sensor 10 may be exposed to the sample gas by placing the substrate 15 on which the gas sensor 10 is arranged in a space where the sample gas is present.

[0062] The control unit 50 controls the operation of the temperature regulator 20 and the exposure unit 40. For example, the control unit 50 controls the on / off of the intake pump 44 and the on / off of the heating or cooling of the temperature regulator 20. The control unit 50 may also output information indicating the timing of the operation of the temperature regulator 20 and the exposure unit 40 to the acquisition unit 60 and the correction unit 70.

[0063] Referring back to FIG. 1 , the acquisition unit 60 acquires a signal output from the gas sensor 10, which indicates an electrical characteristic value of the sensitive part 11 of the gas sensor 10. For example, the acquisition unit 60 acquires a signal output from the gas sensor 10 during a predetermined measurement period in which the gas sensor 10 is exposed to a sample gas and is being heated or cooled. The signal output from the gas sensor 10 during the predetermined measurement period is a signal for analyzing the sample gas. The acquisition unit 60 may extract a feature value from the acquired signal. Examples of the feature value include the magnitude of the acquired signal at a certain point in time, the amount and rate of change of the signal over a certain period, and the waveform slope. The extraction of the feature value may be performed by the correction unit 70 or the analysis unit 80. Furthermore, multiple feature values ​​may be extracted from the signal.

[0064] The correction unit 70 corrects the information about the signal acquired by the acquisition unit 60 based on the temperature of the gas sensor 10 measured by the temperature sensor 30 during a predetermined measurement period. The correction unit 70 corrects the information about the signal acquired by the acquisition unit 60 based on, for example, the rate of change in temperature of the temperature sensor 30 during the predetermined measurement period (i.e., the rate of temperature increase or decrease). The information about the signal acquired by the acquisition unit 60 is, for example, a feature extracted from the signal acquired by the acquisition unit 60. The information about the signal acquired by the acquisition unit 60 may be waveform data of the signal. The waveform data of the signal is data indicating the signal value of the signal over time. The correction unit 70 performs the correction using, for example, a correction parameter indicating the relationship between the temperature of the gas sensor 10 and the information about the signal acquired by the acquisition unit 60. Furthermore, when there are multiple gas sensors 10, the correction unit 70 applies individual correction parameters, etc., to each of the multiple gas sensors 10 to correct the information about the signal acquired by the acquisition unit 60.

[0065] The analysis unit 80 analyzes the sample gas based on the information corrected by the correction unit 70. For example, the analysis unit 80 identifies odor molecules contained in the sample gas as part of its analysis of the sample gas. For example, if the information corrected by the correction unit 70 is a feature, the analysis unit 80 analyzes the sample gas based on the corrected feature. Furthermore, for example, if the information corrected by the correction unit 70 is waveform data, the analysis unit 80 extracts a feature from the corrected waveform data and analyzes the sample gas based on the extracted feature.

[0066] The analysis unit 80 uses, for example, a trained logical model in analyzing the sample gas. The trained logical model receives, for example, the above-described feature quantities (the above-described corrected feature quantities or feature quantities extracted from the above-described corrected waveform data) corresponding to each gas sensor 10 as input, and outputs the analysis results of the sample gas.

[0067] The trained logical model is a logical model for analyzing a sample gas, and the trained logical model receives, for example, the above-described feature quantities as input and outputs the analysis results of the sample gas.

[0068] The trained logical model is constructed by performing machine learning using, for example, known analysis results and the above-mentioned feature quantities obtained when the sample gas that results in the analysis is used as training data. For example, a neural network, a random forest, a support vector machine, or a self-organizing map is used as the logical model in machine learning.

[0069] The analysis unit 80 displays the analysis results on, for example, a display (not shown) provided in the gas analysis system 100. The analysis unit 80 may output the analysis results to the memory 90 and store the analysis results in the memory 90. The analysis unit 80 may also output the analysis results to an external device.

[0070] The memory 90 is a storage device that stores the correction parameters used by the correction unit 70 and the trained logical model used by the analysis unit 80. The memory 90 is realized by, for example, a semiconductor memory.

[0071] The control unit 50, the acquisition unit 60, the correction unit 70, and the analysis unit 80 are realized by a microcomputer or a processor or the like that has built-in programs that perform the above-mentioned and later-described processes. In this case, the control unit 50, the acquisition unit 60, the correction unit 70, and the analysis unit 80 may each be realized by an individual microcomputer or processor or the like, or two or more of these functions may be realized by a single microcomputer or processor or the like. Therefore, the detection device 101 and the analysis device 102 may share one or more microcomputers or processors. Furthermore, the control unit 50, the acquisition unit 60, the correction unit 70, and the analysis unit 80 may each be realized by a dedicated logic circuit that performs the above-mentioned and later-described processes.

[0072] [Experiment to verify the effect of correction] In the gas analysis system 100 according to the present embodiment, a signal output by the gas sensor 10 while the temperature is increased or decreased during a predetermined measurement period is used for analysis, thereby enabling measurement in a short time. Furthermore, the correcting unit 70 corrects information related to the signal acquired by the acquiring unit 60 (for example, feature quantities extracted from the signal), thereby improving the accuracy of the analysis.

[0073] In this regard, the inventors conducted an experiment in which signals output from a plurality of gas sensors 10 were actually acquired, and verified the effect of correcting information relating to the acquired signals.

[0074] First, in this experiment, 16 gas sensors 10 with different materials for the sensitive part 11 (specifically, resin materials for the sensitive film) were prepared and arranged in an array on a substrate 15. These 16 gas sensors 10 were exposed to a sample gas and heated according to the temperature pattern shown in FIG. 4 , and signals output from each of the 16 gas sensors 10 were acquired. FIG. 4 illustrates the temperature pattern for heating the gas sensor 10. As shown in FIG. 4 , heating began one second after signal acquisition of the gas sensor 10 began. The gas sensor 10 was heated to 80°C while controlling the heating rate to three levels: 11°C / s, 12°C / s, and 13°C / s. The temperature of the gas sensor 10 at the start of signal acquisition was controlled to 40°C. Note that, although the temperature and heating rate of the gas sensor 10 were controlled in this experiment, the gas analysis system 100 does not require temperature control of the gas sensor 10; for example, the gas sensor 10 is heated or cooled at a constant output from the temperature controller 20.

[0075] The following three types of gas were used as sample gases: Gas air 00: Air Gas off 14: 2-tridecanone (odor molecules of the heat-deteriorated odor) + Air Gas off 18: Butyric acid (odor molecules of the putrid odor) + Air

[0076] In this experiment, the operation of acquiring signals from the gas sensors 10 exposed to each sample gas was performed 10 times for each level of temperature rise rate. Therefore, signals were acquired from each of the 16 gas sensors 10 under the condition of exposure to each sample gas (10 times x 3 levels of temperature rise rate). Figure 5 shows an example of a signal output from the gas sensor 10. Figure 5 shows a signal output from one of the 16 gas sensors 10 exposed to gas off 14.

[0077] As shown in Figure 5, the value of the signal output from the gas sensor 10 increases as the temperature of the gas sensor 10 increases. This increase in the value of the signal output from the gas sensor 10 is due to an increase in the electrical resistance of the sensitive part 11 due to the increase in temperature. In other words, the increase in the value of the signal output from the gas sensor 10 depends on the temperature characteristics of the electrical resistance of the gas sensor 10. Also, as shown in Figure 5, when the temperature rise rate of the gas sensor 10 (11°C / s, 12°C / s, and 13°C / s) is different, the slope of the increase in the value of the signal output from the gas sensor 10 also differs. Note that, depending on the material of the sensitive part 11, the electrical resistance may not increase easily or may decrease with an increase in temperature.

[0078] Furthermore, although the signal value output from the gas sensor 10 continues to increase over time, i.e., as the temperature of the gas sensor 10 increases, the rate of increase in the signal value output from the gas sensor 10 decreases as time passes. This is because molecules adsorbed to the sensitive part 11 are desorbed as the temperature increases, reducing the electrical resistance of the sensitive part 11. The gas analysis system 100 analyzes the sample gas based on changes in the signal value output from the gas sensor 10 due to such changes in the adsorption state of molecules. However, as shown in FIG. 5 , when the temperature rise rate of the gas sensor 10 varies, the signal waveform also varies, making it difficult to determine whether the change in the signal value output from the gas sensor 10 due to molecular adsorption is caused by temperature or by molecular desorption.

[0079] When the temperature of the gas sensor 10 decreases, the opposite phenomenon to the above occurs, and the electrical resistance of the sensitive part 11 decreases due to the change in temperature, and the degree of decrease in the value of the signal output from the gas sensor 10 decreases due to the adsorption of molecules to the sensitive part 11.

[0080] Next, feature quantities were extracted from the signals acquired in this experiment. The feature quantity was the slope of the signal waveform during the period P1, 2 to 3 seconds after the start of signal acquisition (1 to 2 seconds after the start of heating), as shown in Figure 5 . An approximate equation was then derived using the extracted feature quantity as a function of the heating rate. Figure 6 shows the relationship between the heating rate of the gas sensor 10 and the feature quantity. Figure 6 shows the relationship between the average feature quantity for each level of heating rate and the heating rate, without distinguishing between the types of sample gas. The average value is the average value of the feature quantities extracted from the signals of three types of sample gas x 10 times. Note that averaging the feature quantities is not required in deriving the approximate equation; the approximate equation may be derived without averaging the feature quantities.

[0081] As shown in Fig. 6, there is a strong correlation between the heating rate and the feature quantity, so if an approximation formula is used in which the feature quantity is a function of the heating rate, it is possible to correct the effect of the heating rate on the feature quantity. In the example shown in Fig. 6, the approximation is made with a linear formula of y = ax + b. Since y is the feature quantity and x is the heating rate, the feature quantity can be corrected by the heating rate by using the coefficient a of x as a correction parameter.

[0082] In this experiment, such an approximate formula was derived for each of the 16 gas sensors 10. That is, a correction parameter (coefficient a) corresponding to each of the 16 gas sensors 10 was determined.

[0083] Next, the effect of correction using the coefficient a determined as above will be described. The feature amount was corrected using the following formula.

[0084] Corrected feature amount = uncorrected feature amount + (reference heating rate - heating rate) × a

[0085] In this experiment, a heating rate of 12° C. / s was used as the reference heating rate. That is, when the heating rate was 12° C. / s, the pre-correction feature amount was used as the post-correction feature amount, when the heating rate was 11° C. / s, a was added to the pre-correction feature amount, and when the heating rate was 13° C. / s, a was subtracted from the pre-correction feature amount.

[0086] To verify the effect of the correction, principal component analysis was applied to each of the feature quantities before and after correction, and the analysis results were compared. FIG. 7 is a diagram showing the results of principal component analysis of the feature quantities before correction. FIG. 8 is a diagram showing the results of principal component analysis of the feature quantities after correction. As shown in FIGS. 7 and 8 , the 16 feature quantities before and after correction corresponding to each of the 16 gas sensors 10 were aggregated into two principal components, PCA1 and PCA2, by principal component analysis.

[0087] 7 , in the principal component analysis of the uncorrected feature values, the plotted points corresponding to each sample gas vary widely. For example, in the results using Gas Off 18, the plotted markers are clustered together at the same heating rate level, but are separated when the heating rate levels are different. Furthermore, there are markers plotted corresponding to Gas Off 14 and Gas Off 18 that are close to each other. In other words, when the uncorrected feature values ​​are used in the analysis, the analysis results vary depending on the heating rate, and misidentification is likely to occur when trying to distinguish between Gas Off 14 and Gas Off 18.

[0088] In contrast, as shown in Figure 8, in the principal component analysis of the corrected feature values, the markers plotted corresponding to each sample gas are closer together than before the correction. Furthermore, the markers plotted corresponding to Gas Off 14 and Gas Off 18 are farther apart than before the correction. Therefore, by using the corrected feature values ​​in the analysis, the variance in the analysis results is small, and Gas Off 14 and Gas Off 18 can be accurately distinguished from each other. In other words, by correcting the feature values ​​based on the temperature rise rate of the gas sensor 10, it is possible to suppress a decrease in analytical accuracy even when the temperature of the gas sensor 10 fluctuates between measurements.

[0089] [Operation] Next, the operation (processing) of the gas analysis system 100 according to this embodiment, that is, the gas analysis method, will be described.

[0090] 9 is a flowchart showing an example of the operation of the gas analysis system 100 according to this embodiment. In the following description, step S12 is an example of an acquisition step, step S13 is an example of a correction step, and step S14 is an example of an analysis step.

[0091] 9 , the exposure unit 40 exposes the gas sensor 10 to the sample gas (step S11). For example, the exposure unit 40 operates the intake pump 44 under the control of the control unit 50 to expose the gas sensor 10 to the sample gas.

[0092] Next, the acquisition unit 60 acquires a signal output by the gas sensor 10 while the temperature is rising or falling during a predetermined measurement period (step S12). For example, during the predetermined measurement period, the temperature regulator 20 heats or cools the gas sensor 10 at a constant output. The gas sensor 10 may be cooled by natural cooling. For example, a Peltier element or a heater is used as the temperature regulator 20. The acquisition unit 60 acquires a signal output from the gas sensor 10 while the temperature of the gas sensor 10 is rising or falling as a result of the gas sensor 10 being heated or cooled by the temperature regulator 20. After acquiring the signal output from the gas sensor 10, the acquisition unit 60 may extract feature quantities from the acquired signal.

[0093] Fig. 10 is a diagram schematically illustrating an example of a temperature change of the gas sensor 10 during a measurement period. Fig. 10 illustrates an example in which the temperature of the gas sensor 10 increases during the measurement period. In Fig. 10, the vertical axis represents the temperature of the gas sensor 10, and the horizontal axis represents time. Note that although the temperature changes linearly in Fig. 10, the temperature of the gas sensor 10 does not necessarily change linearly.

[0094] As shown in FIG. 10 , the temperature regulator 20 starts heating the gas sensor 10 at time t1, causing the gas sensor 10 to begin to increase in temperature. In the example shown in FIG. 10 , the measurement period Pm starts at time t1. The measurement period Pm ends at time t2, while the gas sensor 10 is still increasing in temperature. The length of the measurement period Pm is, for example, 0.5 seconds to 20 seconds, and may be 0.5 seconds to 10 seconds. The measurement period Pm is not particularly limited as long as it is a period during which the temperature of the gas sensor 10 increases or decreases, that is, a period during which the temperature of the gas sensor 10 continues to change in one direction. For example, the measurement period Pm may start after time t1, at which the temperature of the gas sensor 10 begins to change. Furthermore, in the example shown in FIG. 10 , the temperature regulator 20 continues to heat the gas sensor 10 after time t2, causing the gas sensor 10 to increase in temperature. However, the temperature regulator 20 may stop heating the gas sensor 10 at time t2.

[0095] 9 , the correction unit 70 then corrects the information about the signal acquired in step S12 based on the temperature of the gas sensor 10 measured by the temperature sensor 30 during a predetermined measurement period (step S13). The correction unit 70 corrects, for example, feature quantities extracted from the signal as information about the signal acquired in step S12. This reduces the amount of information to be corrected, thereby easing the correction process.

[0096] The feature quantity includes, for example, the slope of the signal waveform. As described above, the electrical characteristic value of the gas sensor 10 may fluctuate due to the influence of temperature. Therefore, by correcting the slope of the signal waveform, which is easily affected by an increase or decrease in the temperature of the gas sensor 10, it is possible to effectively suppress a decrease in analysis accuracy. Note that the feature quantity may include a value other than the slope of the signal waveform. Furthermore, when multiple feature quantities are extracted, all of the multiple feature quantities may be corrected, or only some of the feature quantities may be corrected.

[0097] The correction unit 70 also acquires the temperature of the gas sensor 10 from the temperature sensor 30 during a predetermined measurement period, and corrects the extracted feature quantity based on the acquired rate of change in the temperature of the gas sensor 10. This allows the feature quantity used for analysis to be corrected based on the rate of change in temperature, which is closely related to the state in which the gas sensor 10 is increasing or decreasing in temperature, thereby effectively preventing a decrease in analysis accuracy. The rate of change in the temperature of the gas sensor 10 may be the rate of change during a portion of the predetermined measurement period, or the rate of change during the entire predetermined measurement period. The rate of change in the temperature of the gas sensor 10 is calculated, for example, from the temperature at two certain points in time. The rate of change in the temperature of the gas sensor 10 may also be the differential value at a certain point in time of a function of time and temperature. The correction unit 70 may correct the extracted feature quantity based on the temperature of the gas sensor 10 at one or more points in time during the predetermined measurement period, instead of or in addition to the rate of change in the temperature of the gas sensor 10.

[0098] The correction unit 70 corrects the extracted feature quantity using, for example, a correction parameter stored in the memory 90. The correction parameter is a parameter indicating the relationship between the temperature of the gas sensor 10 and the information related to the signal acquired by the acquisition unit 60. The correction parameter is, for example, a coefficient of a function indicating the relationship between the temperature of the gas sensor 10 and the information related to the signal acquired by the acquisition unit 60. A specific example of the correction parameter is coefficient a of a linear expression indicating the relationship between the feature quantity and the rate of change in the temperature of the gas sensor 10, which is determined in advance by deriving an approximation formula through an experiment such as the above-mentioned verification experiment. The correction unit 70 corrects the feature quantity using, for example, the same method as described in the above-mentioned verification experiment. The function for deriving the correction parameter is not limited to a linear expression, but may be a polynomial expression of quadratic or higher order, or may be an exponential, logarithmic, or power expression. Instead of the correction parameter, a correction table for correction may be stored in the memory 90.

[0099] The correction parameters are determined, for example, by conducting a preliminary experiment or the like, based on information such as feature quantities extracted from the signal to be corrected and the target molecules contained in the sample gas. For example, an experiment similar to the above-described verification experiment is conducted using a sample gas containing the target molecules. Note that the preliminary experiment is not limited to the example of the verification experiment. For example, in the above-described verification experiment, the correction parameters were determined based on the feature quantities and the temperature rise rate (rate of temperature change) of the gas sensor 10, but the correction parameters may also be determined based on the feature quantities and the temperature of the gas sensor 10 at a certain point in time.

[0100] The correction unit 70 can also correct the waveform data of the signal as information related to the signal obtained in step S12. In this case, for example, the correction may be performed by calculation using a coefficient of the function of the rate of change of the temperature, or by using a correction parameter indicating the correlation between the temperature of the gas sensor 10 and the signal value of the signal output by the gas sensor 10.

[0101] Next, the analysis unit 80 analyzes the sample gas based on the information corrected in step S13 (step S14). The analysis unit 80 uses, for example, the trained logical model stored in memory 90, inputs the feature quantities corrected in step S13, and outputs the analysis results of the sample gas. The analysis results of the sample gas include, for example, whether or not the sample gas contains target molecules, the identification results of the molecules contained in the sample gas, the concentration of specific molecules in the sample gas, or the odor determination results of the sample gas. The analysis results of the sample gas in this case include, for example, whether or not the sample gas contains target odor molecules, the type of odor molecules contained in the sample gas, or the odor determination results of the sample gas.

[0102] In the operation of the gas analysis system 100 described above, if there are multiple gas sensors 10, for example, the multiple gas sensors 10 are collectively exposed to the sample gas and heated or cooled, and in steps S12 and S13, the above operations are performed for each individual gas sensor 10. Then, in step S14, the sample gas is analyzed based on the information corrected in step S13 corresponding to each of the multiple gas sensors 10.

[0103] As described above, the gas analysis method according to this embodiment is a gas analysis method for analyzing a sample gas using the gas sensor 10, whose electrical characteristic value changes in response to molecular adsorption. The gas analysis method includes an acquisition step (step S12), a correction step (step S13), and an analysis step (step S14). In the acquisition step, a signal indicating an electrical characteristic value output by the gas sensor 10 exposed to the sample gas while the temperature is increased or decreased during a predetermined measurement period is acquired. In the correction step, information about the signal acquired in the acquisition step is corrected based on the temperature of the gas sensor 10 measured by the temperature sensor 30 during the predetermined measurement period. In the analysis step, the sample gas is analyzed based on the information corrected in the correction step.

[0104] As a result, in the acquisition step, the signal output by the gas sensor 10 is acquired while the temperature is rising or falling, so there is no need to wait for the temperature of the gas sensor 10 to stabilize, and measurement can be performed in a short time. Furthermore, because there is no need to wait for the temperature of the gas sensor 10 to stabilize, even if the temperature of the gas sensor 10 during a predetermined measurement period varies from measurement to measurement due to the external environment, etc., the information about the signal acquired in the acquisition step is corrected based on the temperature of the gas sensor 10 in the correction step. Analysis can be performed using the corrected information, thereby improving analysis accuracy. Therefore, the gas analysis method according to this embodiment can achieve both a short measurement time and suppression of a decrease in analysis accuracy.

[0105] While the gas analysis method and gas analysis system according to the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications that a person skilled in the art can conceive of to the embodiments and other forms constructed by combining some of the components of the embodiments are also included in the scope of the present disclosure.

[0106] In the above embodiments, the acquisition unit 60 directly acquires the signal output from the gas sensor 10, but this is not limited thereto. For example, in step S12, the acquisition unit 60 may acquire the signal output from the gas sensor 10 via a network. Similarly, in step S13, the correction unit 70 may acquire the temperature of the gas sensor 10 from the temperature sensor 30 via a network. In this case, for example, the detection device 101 and the analysis device 102 each include a communication circuit and communicate with each other via the network. This communication may be wireless or wired. Furthermore, the communication method (communication standard) for this communication is not particularly limited. Furthermore, this communication may be communication via a wide area communication network such as the Internet.

[0107] Furthermore, in the above-described embodiment, a process executed by a specific processing unit may be executed by another processing unit. The order of multiple processes may be changed, or multiple processes may be executed in parallel. The allocation of components included in the gas analysis system 100 to multiple devices is an example. Components included in one device may be included in another device. For example, components included in one of the detection device 101 and the analysis device 102 may be included in the other of the detection device 101 and the analysis device 102. Furthermore, for example, the gas analysis system 100 may be realized by one device, or by three or more devices.

[0108] For example, the processing described in the above embodiments may be realized by centralized processing using a single device (system), or may be realized by distributed processing using multiple devices. Furthermore, the processor that executes the program may be a single processor or multiple processors. That is, centralized processing or distributed processing may be performed.

[0109] Furthermore, for example, in the above-described embodiments, all or some of the components of the gas analysis system according to the present disclosure may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a HDD or semiconductor memory.

[0110] Furthermore, the components of the gas analysis system according to the present disclosure may be configured with one or more electronic circuits, each of which may be a general-purpose circuit or a dedicated circuit.

[0111] The one or more electronic circuits may include, for example, a semiconductor device, an integrated circuit (IC), or a large-scale integration (LSI). The IC or LSI may be integrated on a single chip or on multiple chips. Although the IC or LSI is referred to here as an IC or LSI, the name may vary depending on the degree of integration, and may be called a system LSI, a very large-scale integration (VLSI), or an ultra-large-scale integration (ULSI). A field programmable gate array (FPGA), which is programmed after the LSI is manufactured, can also be used for the same purpose.

[0112] Furthermore, the general or specific aspects of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, or a computer program. Alternatively, the general or specific aspects may be realized as a computer-readable non-transitory recording medium such as an optical disk, a HDD, or a semiconductor memory on which the computer program is stored. Alternatively, the general or specific aspects of the present disclosure may be realized as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium.

[0113] For example, the present disclosure may be realized as a gas analysis method executed by a computer included in a gas analysis system, or as a program for causing a computer to execute such a gas analysis method. Furthermore, the present disclosure may be realized as a computer-readable non-transitory recording medium on which such a program is recorded.

[0114] The gas analysis method and gas analysis system according to the present disclosure are useful for analyzing gases, such as determining air quality or odors and identifying molecules in gases.

[0115] REFERENCE SIGNS LIST 10 Gas sensor 11 Sensing part 12, 13 Electrode 15 Substrate 20 Temperature regulator 30 Temperature sensor 40 Exposure part 41 Storage part 42, 43 Piping 44 Intake pump 50 Control part 60 Acquisition part 70 Correction part 80 Analysis part 90 Memory 100 Gas analysis system 101 Detection device 102 Analysis device

Claims

1. A gas analysis method for analyzing a sample gas using a gas sensor whose electrical characteristic value changes in response to molecular adsorption, comprising: an acquisition step of acquiring a signal indicating the electrical characteristic value output by the gas sensor exposed to the sample gas while the temperature is increased or decreased during a predetermined measurement period; a correction step of correcting information about the signal acquired in the acquisition step based on the temperature of the gas sensor measured by a temperature sensor during the predetermined measurement period; and an analysis step of analyzing the sample gas based on the information corrected in the correction step.

2. The gas analysis method according to claim 1, wherein in said correcting step, said information is corrected based on a rate of change in temperature of said gas sensor during said predetermined measurement period.

3. The gas analysis method according to claim 1 or 2, wherein in the correction step, a feature amount extracted from the signal acquired in the acquisition step is corrected as the information.

4. The gas analysis method according to claim 3, wherein the characteristic amount includes a slope of the waveform of the signal.

5. The gas analysis method according to claim 1 or 2, wherein the temperature of the gas sensor is increased or decreased by a Peltier element or a heater during the predetermined measurement period.

6. The gas analysis method according to claim 1 or 2, wherein in the acquiring step, the signal is acquired from the gas sensor arranged on the same substrate as the temperature sensor.

7. The gas analysis method according to claim 1 or 2, wherein in the acquiring step, the signal is acquired from the gas sensor via a network.

8. The gas analysis method according to claim 1 or 2, wherein in the analysis step, odor molecules contained in the sample gas are identified as the analysis of the sample gas.

9. A gas analysis system comprising: a gas sensor whose electrical characteristic value changes in response to molecular adsorption; a temperature regulator that at least one of heating and cooling the gas sensor; a temperature sensor that measures the temperature of the gas sensor; an acquisition unit that acquires a signal indicating the electrical characteristic value output by the gas sensor exposed to a sample gas while being heated or cooled by the temperature regulator during a predetermined measurement period; a correction unit that corrects information regarding the signal acquired by the acquisition unit based on the temperature of the gas sensor measured by the temperature sensor during the predetermined measurement period; and an analysis unit that analyzes the sample gas based on the information corrected by the correction unit.

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