Gas detection system and gas detection method

Abstract

A gas detection system (100) comprises: one or more sensor circuits (10) each having an impedance real part and an impedance imaginary part that are changed according to a gas to which that sensor circuit (10) is exposed; an AC signal source (30) for sequentially supplying a plurality of AC signals that have different frequencies to each of the one or more sensor circuits (10); and a measurement circuit (32) for measuring complex impedances that respectively correspond to the plurality of AC signals of each of the one or more sensor circuits (10).

Description

Gas detection system and gas detection method

[0001] The present disclosure relates to gas detection systems and methods.

[0002] Known methods for detecting and identifying gases include, for example, a method for detecting and identifying gases based on a signal obtained from a sensor exposed to the gas (see, for example, Patent Document 1).

[0003] In the invention described in Patent Document 1, an AC signal is applied to a sensor exposed to a gas, and the imaginary part of the impedance of the sensor (i.e., the imaginary component of the impedance) is determined, and a specific gas is identified with high sensitivity based on the imaginary part of the impedance of the sensor.

[0004] Japanese Patent Application Laid-Open No. 2002-139468

[0005] However, there is a demand for greater accuracy in gas identification.

[0006] Therefore, the present disclosure provides a gas detection system and the like that can improve the accuracy of gas identification.

[0007] A gas detection system according to one aspect of the present disclosure includes one or more sensor circuits whose real impedance part and imaginary impedance part change depending on the gas to which the sensor circuits are exposed, an AC signal source that sequentially supplies a plurality of AC signals having different frequencies to each of the one or more sensor circuits, and a measurement circuit that measures the complex impedance of each of the one or more sensor circuits corresponding to each of the plurality of AC signals.

[0008] A gas detection method according to one aspect of the present disclosure is a gas detection method for detecting a sample gas to which one or more sensor circuits are exposed, wherein each of the one or more sensor circuits changes its impedance real part and its impedance imaginary part depending on the gas to which it is exposed, and the gas detection method includes an AC signal supply step of supplying a plurality of AC signals having different frequencies to each of the one or more sensor circuits, an exposure step of exposing each of the one or more sensor circuits to the sample gas, and a measurement step of measuring a complex impedance of each of the one or more sensor circuits corresponding to the plurality of AC signals.

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

[0010] According to the gas detection system and the like according to one aspect of the present disclosure, it is possible to improve the accuracy of gas identification.

[0011] 1 is a block diagram showing a schematic configuration of a gas detection system according to an embodiment; FIG. 2 is a circuit diagram showing an equivalent circuit of a sensor circuit according to an embodiment; FIG. 3 is a schematic diagram showing an example of the configuration of an exposed portion according to an embodiment; FIG. 4 is a flowchart showing a gas detection method according to an embodiment; FIG. 5 is a graph showing the time waveform of the impedance real part and the time waveform of the impedance imaginary part of the sensor circuit according to an embodiment when the frequency of the AC signal is 1 kHz; FIG. 6 is a graph showing the time waveform of the impedance real part and the time waveform of the impedance imaginary part of the sensor circuit according to an embodiment when the frequency of the AC signal is 10 kHz; FIG. 7 is a graph showing the time waveform of the impedance real part and the time waveform of the impedance imaginary part of the sensor circuit according to an embodiment when the frequency of the AC signal is 100 kHz; FIG. 8 is a graph showing the time waveform of the impedance real part and the time waveform of the impedance imaginary part of the sensor circuit according to an embodiment when the frequency of the AC signal is 1 MHz; FIG. 9 is a graph showing the result of measuring the impedance real part while sweeping the frequency of the AC signal supplied to the sensor circuit of a first example embodiment; FIG. 10 is a graph showing the result of measuring the impedance imaginary part while sweeping the frequency of the AC signal supplied to the sensor circuit of a first example embodiment. 12 is a graph showing the results of measuring the real part of the impedance while sweeping the frequency of the AC signal supplied to the sensor circuit of the second example of the embodiment. 13 is a graph showing the results of measuring the imaginary part of the impedance while sweeping the frequency of the AC signal supplied to the sensor circuit of the first example of the embodiment. 14 is a graph showing an enlarged view of a part of FIG.

[0012] A gas detection system according to aspect 1 of the present disclosure includes one or more sensor circuits whose impedance real part (i.e., the real component of the impedance) and impedance imaginary part change depending on the gas to which the sensor circuits are exposed, an AC signal source that sequentially supplies a plurality of AC signals having different frequencies to each of the one or more sensor circuits, and a measurement circuit that measures the complex impedance of each of the one or more sensor circuits corresponding to each of the plurality of AC signals.

[0013] In this way, by measuring the real and imaginary impedance parts corresponding to each of the multiple AC signals from the sensor circuit, more information can be obtained than when measuring only the real and imaginary impedance parts corresponding to a single AC signal. This makes it possible to extract more feature quantities from the measurement results of these real and imaginary impedance parts. Therefore, by identifying the sample gas based on more feature quantities, it is possible to improve the accuracy of sample gas identification.

[0014] A gas detection system according to a second aspect of the present disclosure is the gas detection system according to the first aspect of the present disclosure, in which the one or more sensor circuits include a plurality of sensor circuits.

[0015] For example, if multiple sensor circuits have the same configuration, the reliability of the measurement results can be improved. Furthermore, if multiple sensor circuits have different configurations, more information about the sample gas can be obtained. Therefore, more feature quantities can be obtained, further improving the accuracy of identifying the sample gas.

[0016] A gas detection system according to a third aspect of the present disclosure is the gas detection system according to the second aspect of the present disclosure, in which the plurality of sensor circuits have different configurations from one another.

[0017] This makes it possible to obtain more information about the sample gas, and therefore more feature quantities, thereby further improving the accuracy of identifying the sample gas.

[0018] A gas detection system according to a fourth aspect of the present disclosure is the gas detection system according to any one of the first to third aspects of the present disclosure, in which the plurality of AC signals includes three or more AC signals.

[0019] This allows more information to be obtained about the sample gas, and therefore more feature quantities to be acquired, further improving the accuracy of identifying the sample gas.

[0020] A gas detection system according to a fifth aspect of the present disclosure is the gas detection system according to any one of the first to fourth aspects of the present disclosure, in which the frequencies of the plurality of AC signals are equal to or greater than 1 kHz and equal to or less than 1 MHz.

[0021] By using multiple AC signals with such frequencies, significant differences can be generated in the measurement results of the real and imaginary impedance parts corresponding to each AC signal, which allows more feature quantities to be obtained from the measurement results, thereby further improving the accuracy of sample gas identification.

[0022] A gas detection system according to a sixth aspect of the present disclosure is a gas detection system according to any one of the first to fifth aspects of the present disclosure, further comprising: an extraction circuit that extracts one or more feature quantities corresponding to the real impedance part and the imaginary impedance part of the complex impedance of each of the one or more sensor circuits measured by the measurement circuit; a memory that stores a learned logical model that identifies a gas to which each of the one or more sensor circuits is exposed; and an identification circuit that uses the learned logical model to identify a gas to which each of the one or more sensor circuits is exposed based on the extracted one or more feature quantities.

[0023] This makes it possible to easily and accurately identify the gas.

[0024] A gas detection system according to a seventh aspect of the present disclosure is the gas detection system according to the sixth aspect of the present disclosure, wherein the one or more feature quantities include a difference in shape between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance.

[0025] The difference between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance changes depending on the frequency of the AC signal, and the manner of this change often differs depending on the gas. Therefore, by extracting the difference in shape between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance, it is possible to extract a feature that is effective for improving the accuracy of gas identification.

[0026] A gas detection method according to aspect 8 of the present disclosure is a gas detection method for detecting a sample gas to which one or more sensor circuits are exposed, wherein each of the one or more sensor circuits changes its impedance real part and its impedance imaginary part depending on the gas to which it is exposed, and the gas detection method includes an AC signal supply step of supplying a plurality of AC signals having different frequencies to each of the one or more sensor circuits, an exposure step of exposing each of the one or more sensor circuits to the sample gas, and a measurement step of measuring a complex impedance of each of the one or more sensor circuits corresponding to the plurality of AC signals.

[0027] This provides the same effects as the gas detection system according to aspect 1 of the present disclosure.

[0028] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, or a recording medium.

[0029] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0030] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step order 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 that are not described in the independent claims that represent the highest concepts are described as optional components.

[0031] Furthermore, in this specification, terms indicating relationships between elements such as "identical" and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a range that is substantially equivalent, for example, a difference of about a few percent.

[0032] 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.

[0033] (Embodiments) A gas detection system and a gas detection method according to embodiments will be described.

[0034] [Configuration] The configuration of a gas detection system according to this embodiment will be described with reference to FIG.

[0035] FIG. 1 is a block diagram showing a schematic configuration of a gas detection system 100 according to this embodiment.

[0036] As shown in FIG. 1 , a gas detection system 100 according to this embodiment includes one or more sensor circuits 10, an AC signal source 30, and a measurement circuit 32. In this embodiment, the gas detection system 100 further includes an exposure unit 20, a control circuit 31, an extraction circuit 33, an identification circuit 34, and a memory 40. The gas detection system 100 identifies the sample gas based on the output of the sensor circuit 10 exposed to the sample gas. The sample gas includes, for example, a chemical substance to be identified. The sample gas may be, for example, a 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.

[0037] The gas detection system 100 identifies, for example, chemical substances contained in the sample gas. Specifically, the gas detection system 100 identifies which of a plurality of target substances to be identified is contained in the sample gas as a chemical substance. The gas detection system 100 may also identify whether or not the target substance to be identified is contained in the sample gas.

[0038] The substance to be identified is, for example, a volatile organic compound, but may also be an inorganic gas such as ammonia or carbon monoxide. The gas detection system 100 is used, for example, to identify odors. In this case, the volatile organic compound is, for example, a molecule that becomes an odor component.

[0039] The sensor circuit 10 is a sensor that outputs a signal corresponding to the gas to which it is exposed. In this embodiment, the sensor circuit 10 is a sensor whose real impedance part and imaginary impedance part change according to the gas to which it is exposed. The sensor circuit 10 is, 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 sensor.

[0040] The sensor circuit 10 includes, for example, a sensing unit and a pair of electrodes electrically connected to the sensing unit. The impedance of the sensing unit changes depending on, for example, the concentration of adsorbed gas. A signal corresponding to the impedance of the sensing unit of the sensor circuit 10 is measured by the measurement circuit 32 as, for example, a voltage signal or a current signal via the pair of electrodes.

[0041] In this embodiment, a mixture of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, polyethylene glycol, and ethyl cellulose is used as the sensing unit. However, the configuration of the sensing unit is not limited to this. For example, a mixture of polyvinyl formal, carbon black with a particle diameter of approximately 15 nm (e.g., Mitsubishi Chemical's carbon black #2300), a functional additive (e.g., Nagase & Co., Ltd.'s Synergist El-N6S), and a wetting and dispersing agent (e.g., BYK's DISPERBYK-2200) may also be used as the sensing unit.

[0042] The equivalent circuit of the sensor circuit 10 will be described with reference to Fig. 2. Fig. 2 is a circuit diagram showing the equivalent circuit of the sensor circuit 10 according to the present embodiment. As shown in Fig. 2, the equivalent circuit of the sensor circuit 10 has terminals 10Ta and 10Tb, resistive elements 10Ra and 10Rb, and a capacitive element 10C.

[0043] The terminals 10Ta and 10Tb correspond to a pair of electrodes of the sensor circuit 10.

[0044] The resistor element 10Ra is connected to the terminal 10Ta and is connected in parallel to the capacitor element 10C. The resistor element 10Ra is also connected in series to the resistor element 10Rb.

[0045] The capacitance element 10C is connected to the terminal 10Ta, and is connected in parallel to the resistance element 10Ra, and is also connected in series to the resistance element 10Rb.

[0046] The resistor element 10Rb is connected to the terminal 10Tb, and is connected in series with the resistor element 10Ra and the capacitor element 10C. If the resistor element 10Rb is sufficiently smaller than the resistor element 10Ra, the resistor element 10Rb may be ignored.

[0047] As described above, the sensor circuit 10 has a capacitance component, and therefore has not only a real impedance part but also an imaginary impedance part. The capacitance and resistance components of the sensor circuit 10 vary depending on the material of the sensing section, etc. The configuration of the sensor circuit 10 is not limited to the example shown in FIG. 2 . For example, the sensor circuit 10 may include an equivalent circuit shown in FIG. 2 and other elements connected to the equivalent circuit. For example, the sensor circuit 10 may include an inductor connected to a pair of electrodes (i.e., terminals 10Ta and 10Tb of the equivalent circuit shown in FIG. 2 ).

[0048] The gas detection system 100 includes, for example, multiple sensor circuits 10. That is, the one or more sensor circuits 10 according to the present embodiment include multiple sensor circuits 10. The multiple sensor circuits 10 may have different configurations. That is, at least two of the one or more sensor circuits 10 included in the gas detection system 100 may have different configurations. The sensing units of the multiple sensor circuits 10 may be made of, for example, different types of materials. Different types of materials exhibit different adsorption behaviors with respect to the same chemical substance. Therefore, the multiple sensor circuits 10 output different signals with respect to the same chemical substance. This allows different features to be extracted from the outputs of the multiple sensor circuits 10, thereby improving the accuracy of gas identification in the gas detection system 100.

[0049] The AC signal source 30 is a signal source that sequentially supplies a plurality of AC signals having different frequencies to each of the one or more sensor circuits 10. The plurality of AC signals may include three or more AC signals. In the present embodiment, the AC signal source 30 supplies a first AC signal, a second AC signal, a third AC signal, and a fourth AC signal having different frequencies to each of the one or more sensor circuits 10.

[0050] The AC signal source 30 sequentially supplies a first AC signal to each of the one or more sensor circuits 10, and then sequentially supplies a second AC signal to each of the one or more sensor circuits 10. Similarly, the AC signal source 30 sequentially supplies a third AC signal and a fourth AC signal to each of the one or more sensor circuits 10. Note that the AC signal source 30 may simultaneously supply AC signals to multiple sensor circuits 10.

[0051] The frequency of the AC signals supplied by the AC signal source 30 according to this embodiment is 1 kHz or more and 1 MHz or less. The frequency of the AC signals may be 100 Hz or more and 100 MHz or less.

[0052] The exposure unit 20 is an exposure mechanism that exposes the sensor circuit 10 to a gas under the control of the control circuit 31. Specifically, the exposure unit 20 exposes the sensor circuit 10 to the sample gas only during the second period of a measurement period consisting of a first period, a second period following the first period, and a third period following the second period. The exposure unit 20 may also expose the sensor circuit 10 to a reference gas during the first and third periods. The reference gas is a gas that serves as a reference for measurement, such as a gas that does not contain the target substance. The reference gas is a gas that is less likely to be adsorbed by the sensing unit of the sensor circuit 10 than the target substance. Specific examples of reference gases include inert gases such as air and nitrogen, and gases obtained by removing chemical substances from the sample gas using a filter or the like. By outputting a signal from the sensor circuit 10 exposed to the reference gas during the first and third periods, a reference signal corresponding to the ambient environment for each measurement can be obtained even when the ambient environment changes, and using such a signal can improve the accuracy of identification.

[0053] Here, a specific configuration of the exposure unit 20 will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing an example of the configuration of the exposure unit 20 according to this embodiment. Fig. 3 also shows a control circuit 31 and a sensor circuit 10. As shown in Fig. 3, the exposure unit 20 has, for example, a storage unit 21, a three-way electromagnetic valve 22, an intake pump 23, and a plurality of pipes 25a, 25b, 25c, 25d, and 25e.

[0054] One end of the pipe 25a is provided with an intake port 26a for introducing a sample gas. The intake port 26a is provided, for example, in a space filled with the sample gas. One end of the pipe 25b is provided with an intake port 26b for introducing a reference gas. The intake port 26b is provided, for example, in a space filled with the reference gas. One end of the pipe 25e is provided with an exhaust port 26e for discharging the introduced sample gas and reference gas.

[0055] The accommodation unit 21 is a box-shaped container that accommodates the sensor circuits 10. For example, a plurality of sensor circuits 10 are arranged in an array inside the accommodation unit 21. One end of each of the pipes 25c and 25d is connected to the accommodation unit 21. When the intake pump 23 (described later) is operated, gas flows from one end of the pipe 25c to one end of the pipe 25d. The plurality of sensor circuits 10 are arranged in the flow path through which the gas flows.

[0056] The sample gas introduced through intake port 26a is introduced into the storage section 21 via pipe 25a, three-way solenoid valve 22, and pipe 25c. The reference gas introduced through intake port 26b is introduced into the storage section 21 via pipe 25b, three-way solenoid valve 22, and pipe 25c. The sample gas and reference gas introduced into the storage section 21 are exhausted from exhaust port 26e via pipe 25d, intake pump 23, and pipe 25e.

[0057] The three-way solenoid valve 22 is a solenoid valve for switching the gas introduced into the storage section 21. The three-way solenoid valve 22 has an input port P1 connected to the other end of the pipe 25a, an input port P2 connected to the other end of the pipe 25b, and an output port P3 connected to the other end of the pipe 25c. The opening and closing of each port of the three-way solenoid valve 22 is controlled by the control circuit 31. The three-way solenoid valve 22 is switched, under the control of the control circuit 31, between a first state in which the input port P1 and the output port P3 are electrically connected and a second state in which the input port P2 and the output port P3 are electrically connected. In the first state, the input port P1 and the output port P3 are open, and the input port P2 is closed. In the second state, the input port P2 and the output port P3 are open, and the input port P1 is closed.

[0058] The intake pump 23 is a pump for introducing the sample gas and the reference gas into the storage section 21 and discharging the introduced sample gas and reference gas from the exhaust port 26e. The operation of the intake pump 23 is controlled by the control circuit 31. The intake port of the intake pump 23 is connected to the other end of the pipe 25d. The exhaust port of the intake pump 23 is connected to the other end of the pipe 25e.

[0059] With this configuration, when the intake pump 23 is operating and the three-way solenoid valve 22 is in the first state, the sample gas is introduced into the storage unit 21. As a result, the exposure unit 20 exposes the plurality of sensor circuits 10 to the sample gas. Also, when the intake pump 23 is operating and the three-way solenoid valve 22 is in the second state, the reference gas is introduced into the storage unit 21. As a result, the exposure unit 20 exposes the plurality of sensor circuits 10 to the reference gas.

[0060] The configuration of the exposure unit 20 is not limited to the configuration shown in FIG. 3 , and is not particularly limited as long as it can expose the sensor circuit 10 to the sample gas. The exposure unit 20 may be configured, for example, such that the sample gas and the reference gas are introduced into the storage unit 21 through separate pipes without passing through the three-way solenoid valve 22. The exposure unit 20 may also be configured without the intake pump 23, such that a carrier gas is constantly flowing into the storage unit 21 to mix the sample gas into the carrier gas. Alternatively, the reference gas may not be introduced, and the storage unit 21 may be evacuated by the intake pump 23 after the sensor circuit 10 is exposed to the sample gas. The exposure unit 20 may further include various removal filters for removing moisture or particles from the sample gas and the reference gas, electromagnetic adjustment valves for adjusting the flow rate of each pipe, check valves for preventing backflow in each pipe, and the like.

[0061] In this embodiment, the exposure unit 20 exposes the sensor circuit 10 to the reference gas in a first period and a third period, and exposes the sensor circuit 10 to the sample gas in a second period. In the gas detection system 100 according to this embodiment, the first period to the third period are repeated. That is, the period in which the sensor circuit 10 is exposed to the reference gas (the first period and the third period) and the period in which the sensor circuit 10 is exposed to the sample gas (the second period) are alternately repeated.

[0062] 1 again, as described above, the control circuit 31 controls the operation of the exposure unit 20, specifically, the operation of the three-way solenoid valve 22 and the suction pump 23. The control circuit 31 may also output information indicating the timing of the operation of the exposure unit 20 to the measurement circuit 32. Furthermore, the control circuit 31 controls the operation of the AC signal source 30. Specifically, the control circuit 31 controls the sensor circuit 10 to which the AC signal source 30 supplies an AC signal, and the frequency of the AC signal.

[0063] The measurement circuit 32 is a circuit that measures the complex impedance of each of the one or more sensor circuits 10 corresponding to each of the multiple AC signals. In this embodiment, the measurement circuit 32 measures the real impedance part and the imaginary impedance part of each of the one or more sensor circuits 10 based on the signal output from each of the one or more sensor circuits 10 during a measurement period. The measurement circuit 32 acquires, for example, a time waveform of the real impedance part and a time waveform of the imaginary impedance part of each of the one or more sensor circuits 10. The measurement circuit 32 acquires, for example, a voltage signal and a current signal as signals corresponding to the impedance of the sensor circuit 10. Note that the measurement circuit 32 may acquire only one of the voltage signal and the current signal as signals corresponding to the impedance of the sensor circuit 10. The measurement circuit 32 may include, for example, an LCR meter as a circuit for measuring the real impedance part and the imaginary impedance part. The measurement circuit 32 acquires information indicating the timing of controlling the exposure unit 20 from the control circuit 31. The measurement circuit 32 outputs the acquired signals and information to the extraction circuit 33.

[0064] The real and imaginary impedance parts of the complex impedance measured by the measurement circuit 32 may be the real and imaginary impedance parts of a normalized impedance. For example, the real and imaginary impedance parts may be normalized to 50 Ω.

[0065] The measurement circuit 32 may also measure the absolute value and phase of the complex impedance as the complex impedance. The measurement circuit 32 also includes a circuit for measuring a numerical value corresponding to the complex impedance. For example, the measurement circuit 32 may measure a complex admittance corresponding to the complex impedance. More specifically, the measurement circuit 32 may measure the real part and imaginary part of the complex admittance, the absolute value and phase of the complex admittance, or a normalized complex admittance.

[0066] The extraction circuit 33 extracts one or more feature quantities corresponding to the real impedance part and the imaginary impedance part of the complex impedance of each of the one or more sensor circuits 10 measured by the measurement circuit 32. When there are multiple sensor circuits 10, the extraction circuit 33 extracts one or more feature quantities from the signals output by each of the multiple sensor circuits 10. The one or more feature quantities include, for example, the difference in shape between the time waveform of the impedance real part and the time waveform of the impedance imaginary part of the sensor circuit 10.

[0067] The identification circuit 34 identifies the gas (i.e., sample gas) to which each of the one or more sensor circuits 10 is exposed based on one or more feature quantities extracted by the extraction circuit 33. In the present embodiment, the identification circuit 34 uses a trained logical model to identify the gas to which each of the one or more sensor circuits 10 is exposed based on one or more feature quantities extracted by the extraction circuit 33. The identification circuit 34, for example, identifies which of multiple identification target substances is contained in the sample gas. The identification circuit 34 may also identify whether or not the identification target substance is contained in the sample gas. The identification circuit 34 receives one or more feature quantities as input and outputs an identification result. The identification circuit 34 outputs information for displaying the identification result on a display (not shown) or the like provided in the gas detection system 100, for example. The identification circuit 34 may output information indicating the identification result to the memory 40 and store the information in the memory 40. The identification circuit 34 may also output information indicating the identification result to an external device.

[0068] The control circuit 31, the measurement circuit 32, the extraction circuit 33, and the identification circuit 34 are realized by a microcomputer or a processor that has a built-in program for performing the above-mentioned processing. The control circuit 31, the measurement circuit 32, the extraction circuit 33, and the identification circuit 34 may each be realized by a dedicated logic circuit that performs the above-mentioned processing.

[0069] The memory 40 is a storage device that stores the trained logic model used in the classification circuit 34. The memory 40 is realized by, for example, a semiconductor memory.

[0070] The trained logical model is a logical model that identifies the gas to which each of the one or more sensor circuits 10 is exposed. Specifically, the trained logical model is, for example, a logical model that identifies which of a plurality of identification target substances is contained in the sample gas. The trained logical model, for example, receives as input one or more feature quantities extracted by the extraction circuit 33, and outputs which of a plurality of identification target substances is contained in the sample gas. The trained logical model may also output whether or not the sample gas contains the identification target substance.

[0071] The trained logical model is constructed by performing machine learning using, for example, a known substance to be identified and one or more feature quantities extracted by the extraction circuit 33 using the known substance to be identified as training data. The method used to construct the logical model in machine learning is not particularly limited. For example, a neural network is used to construct the logical model in machine learning. That is, the trained logical model includes, for example, a neural network. For constructing the logical model in machine learning, a random forest, a support vector machine, a self-organizing map, or the like may also be used.

[0072] When the trained logical model includes a neural network, for example, one or more feature quantities are input to an input node of the neural network, and the output node outputs the probability that each of a plurality of identification target substances is contained in the sample gas. That is, the number of input nodes is the number of one or more feature quantities input, and the number of output nodes is the number of a plurality of identification target substances to be identified. The trained logical model outputs the identification target substance that has the highest probability of being output from the output node among the plurality of identification target substances. Furthermore, the trained logical model may output whether or not the identification target substance is contained in the sample gas based on the probability output from the output node, for example, based on whether or not the probability is equal to or greater than a threshold value.

[0073] Note that the gas detection system 100 may be configured, for example, as a single gas identification device including the above-described components, but may also be configured as a plurality of devices. When the gas detection system 100 is configured as a plurality of devices, the components of the gas detection system 100 may be distributed in any manner among the plurality of devices. For example, the gas detection system 100 may be configured as a measurement device including the sensor circuit 10, the exposure unit 20, the AC signal source 30, the control circuit 31, and the measurement circuit 32, and an identification device including the extraction circuit 33, the identification circuit 34, and the memory 40. In this case, the measurement device and the identification device may be connected via a communication network such as the Internet.

[0074] [Gas Detection Method] Next, a gas detection method executed in gas detection system 100 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a flowchart showing the gas detection method according to this embodiment.

[0075] The gas detection method according to the present embodiment is a method for detecting a sample gas to which one or more sensor circuits 10, the real part and imaginary part of which change in impedance depending on the gas to which they are exposed, are exposed. In the gas detection method according to the present embodiment, first, a plurality of AC signals having different frequencies are supplied to each of the one or more sensor circuits 10 using an AC signal source 30 (AC signal supply step S10).

[0076] Next, while the multiple AC signals are being supplied to each of the one or more sensor circuits 10, the one or more sensor circuits 10 are exposed to the sample gas using the exposure unit 20 (exposure step S20). In this embodiment, as described above, each of the one or more sensor circuits 10 is alternately exposed to the sample gas and the reference gas.

[0077] Next, the measurement circuit 32 measures the complex impedance of each of the one or more sensor circuits 10 corresponding to the multiple AC signals while each of the one or more sensor circuits 10 is exposed to the sample gas (measurement step S30). In this embodiment, in the measurement step S30, the measurement circuit 32 acquires the time waveform of the impedance real part and the time waveform of the impedance imaginary part of each of the one or more sensor circuits 10.

[0078] Next, the extraction circuit 33 extracts one or more feature quantities corresponding to the real impedance part and the imaginary impedance part of the complex impedance of each of the one or more sensor circuits 10 measured by the measurement circuit 32 (extraction step S40). In this embodiment, the one or more feature quantities include a difference in shape between the time waveform of the real impedance part and the time waveform of the imaginary impedance part.

[0079] Next, the identification circuit 34 uses the learned logical model to identify the gas to which each of the one or more sensor circuits 10 is exposed based on the one or more extracted features (identification step S50).

[0080] As described above, the gas detection method according to this embodiment detects and identifies the sample gas.

[0081] [Effects, etc.] The effects of the gas detection system 100 and gas detection method according to this embodiment will be described with reference to examples of measurement results using FIGS. 5 to 8. FIGS. 5, 6, 7, and 8 are graphs showing the time waveforms of the real part of impedance and the imaginary part of impedance, respectively, for the sensor circuit 10 according to this embodiment, when the AC signal frequencies are 1 kHz, 10 kHz, 100 kHz, and 1 MHz. The horizontal axis in FIGS. 5 to 8 represents time, the left vertical axis represents the normalized real part of impedance, and the right vertical axis represents the normalized imaginary part of impedance. In FIGS. 5 to 8, the scales and ranges of both vertical axes have been adjusted so that the positions and sizes of the time waveforms of the real part of impedance and the time waveforms of the imaginary part of impedance are aligned.

[0082] In this embodiment, nitrogen (N ２ ) was used, and benzaldehyde was used as the sample gas. The sensor circuit 10 was repeatedly exposed to the reference gas and the sample gas alternately for 30 seconds each. In this case, as shown in FIGS. 5 to 8 , both the real and imaginary impedance parts of the sensor circuit 10 increased upon exposure to the sample gas, but the time waveforms of the real and imaginary impedance parts varied depending on the frequency of the AC signal. For example, as shown in FIG. 5 , when the AC signal frequency was 1 kHz, the difference between the time waveforms of the real and imaginary impedance parts was small. As shown in FIG. 6 , when the AC signal frequency was 10 kHz, the difference between the time waveforms of the real and imaginary impedance parts was larger than when the AC signal frequency was 1 kHz. As shown in FIG. 7 , when the AC signal frequency was 100 kHz, the difference between the time waveforms of the real and imaginary impedance parts was even larger than when the AC signal frequency was 10 kHz. As shown in FIG. 8, when the frequency of the AC signal is 1 MHz, the difference between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance is smaller than the difference when the frequency of the AC signal is 10 kHz.

[0083] In this way, by measuring the real part and imaginary part of the impedance corresponding to each of the multiple AC signals from the sensor circuit 10, more information can be obtained than when measuring only the real part and imaginary part of the impedance corresponding to a single AC signal. This makes it possible to extract more feature quantities from the measurement results of these real part and imaginary part of the impedance. Therefore, with the gas detection system 100 and gas detection method according to this embodiment, the sample gas can be identified based on more feature quantities, thereby improving the accuracy of sample gas identification.

[0084] In the present embodiment, the one or more sensor circuits 10 may include a plurality of sensor circuits 10 .

[0085] For example, if the plurality of sensor circuits 10 have the same configuration, the reliability of the measurement results can be improved by measuring the real part and imaginary part of the impedance of each of the plurality of sensor circuits 10 .

[0086] Furthermore, when the plurality of sensor circuits 10 have different configurations, more information about the sample gas can be obtained, and therefore, more feature quantities can be obtained, further improving the accuracy of identifying the sample gas.

[0087] In the present embodiment, the plurality of AC signals may include three or more AC signals.

[0088] This allows more information to be obtained about the sample gas, and therefore more feature quantities to be acquired, further improving the accuracy of identifying the sample gas.

[0089] In this embodiment, the frequencies of the multiple AC signals may be 1 kHz or more and 1 MHz or less.

[0090] By using multiple AC signals with such frequencies, significant differences can be generated in the measurement results of the real and imaginary impedance parts corresponding to each AC signal, which allows more feature quantities to be obtained from the measurement results, thereby further improving the accuracy of sample gas identification.

[0091] In this embodiment, one or more feature quantities may be extracted corresponding to the real impedance part and the imaginary impedance part of the complex impedance of each of the one or more sensor circuits 10 measured by the measurement circuit 32 (in other words, the measurement step S30). Furthermore, a trained logical model that identifies the gas to which each of the one or more sensor circuits 10 is exposed may be used to identify the gas to which each of the one or more sensor circuits 10 is exposed based on the one or more extracted feature quantities.

[0092] This makes it possible to easily and accurately identify the gas.

[0093] In the present embodiment, the one or more feature amounts may include a difference in shape between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance.

[0094] As described above, the difference between the time waveform of the real part of the impedance of the sensor circuit 10 measured by the measurement circuit 32 and the time waveform of the imaginary part of the impedance changes depending on the frequency of the AC signal, and the manner of this change often differs depending on the gas. Therefore, by extracting the difference in shape between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance, it is possible to extract a feature amount that is effective for improving the accuracy of gas identification.

[0095] [Modification] A gas detection system and a gas detection method according to a modification of the present embodiment will be described. In the above, the time waveform of the impedance real part and the time waveform of the impedance imaginary part are acquired while one AC signal among a plurality of AC signals is supplied to each of one or more sensor circuits 10. However, the manner of detecting the complex impedance is not limited to the above. For example, while each of the one or more sensor circuits 10 is stably exposed to one sample gas, the complex impedance of each of the one or more sensor circuits 10 may be measured while changing the frequency of the AC signal supplied to each of the one or more sensor circuits 10. Subsequently, while each of the one or more sensor circuits 10 is stably exposed to another sample gas, the complex impedance of each of the one or more sensor circuits 10 may be measured while changing the frequency of the AC signal supplied to each of the one or more sensor circuits 10. In this way, the complex impedance of each of the one or more sensor circuits 10 for each of the multiple AC signals may be measured. In this way, the relationship between the multiple AC signals and the complex impedance of each of the one or more sensor circuits 10 may be measured for each gas to which the one or more sensor circuits 10 are exposed.

[0096] This detection mode will be described with reference to FIGS. 9 to 13 , showing measurement results. FIGS. 9 and 10 are graphs showing the results of measuring the real part of impedance and the imaginary part of impedance while sweeping the frequency of an AC signal supplied to a sensor circuit 10 according to a first example of the present embodiment. FIGS. 11 and 12 are graphs showing the results of measuring the real part of impedance and the imaginary part of impedance while sweeping the frequency of an AC signal supplied to a sensor circuit 10 according to a second example of the present embodiment. FIG. 13 is a graph showing an enlarged portion of FIG. 12 . The sensing sections of the first and second sensor circuits 10 each contain polyvinyl formal, carbon black, and a wetting and dispersing agent as main components, but the blending ratios of these components are different. The blending ratio of carbon black and wetting and dispersing agent in the sensing section of the sensor circuit 10 according to the second example is approximately half the blending ratio of carbon black and wetting and dispersing agent in the sensing section of the sensor circuit 10 according to the first example.

[0097] 9 and 10 show the measurement results (dashed line) of the first example sensor circuit 10 exposed to nitrogen and the measurement results (solid line) of the first example sensor circuit 10 exposed to sample gas A. FIGS. 11 to 13 show the measurement results (dashed line) of the second example sensor circuit 10 exposed to nitrogen, the measurement results (solid line) of the second example sensor circuit 10 exposed to sample gas A, the measurement results (dashed line) of the second example sensor circuit 10 exposed to sample gas B, and the measurement results (dashed line) of the second example sensor circuit 10 exposed to sample gas C. Nitrogen and sample gases A to C are different gases. The vertical axis on the left side of FIG. 13 shows the measurement results when the second example sensor circuit 10 is exposed to sample gas A and sample gas B, respectively, and the vertical axis on the right side of FIG. 13 shows the measurement results when the second example sensor circuit 10 is exposed to sample gas C and nitrogen, respectively.

[0098] 9 to 13, the waveforms showing the frequency characteristics differ between the real part of the impedance and the imaginary part of the impedance. Furthermore, the frequency characteristics of the real part of the impedance and the imaginary part of the impedance differ depending on the gas. Furthermore, the frequency characteristics of the real part of the impedance and the imaginary part of the impedance differ depending on the configuration of the sensing section of the sensor circuit 10.

[0099] Specifically, as shown in Figures 9 and 11, the real part of the impedance for AC signals, particularly in the low frequency range, differs depending on the gas. Furthermore, as shown in Figures 10, 12, and 13, the imaginary part of the impedance becomes minimal when the AC signal is at a predetermined frequency. The frequency of the AC signal at which the imaginary part of the impedance becomes minimal and the minimal value of the imaginary part of the impedance differ depending on the gas. Furthermore, comparing Figures 9 and 11 and comparing Figures 10 and 12 reveals that the frequency characteristics of the real part of the impedance and the imaginary part of the impedance differ depending on the configuration of the sensing unit of the sensor circuit 10.

[0100] By extracting feature quantities from the values ​​and waveforms of the real and imaginary impedance parts of the measurement results shown in Figures 9 to 13, it is possible to obtain the differences in frequency characteristics for each gas with high accuracy, thereby improving the accuracy of gas identification.

[0101] The sweep range of the frequency of the AC signal is not particularly limited and may be, for example, 4 MHz to 8 MHz, or may be narrower or wider than this range.

[0102] While the gas detection system 100 and the gas detection method 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 would occur to a person skilled in the art to the embodiments, as well as other forms constructed by combining some of the components of the embodiments, are also included in the scope of the present disclosure.

[0103] In the above embodiment, the exposure unit 20 exposes the sensor circuit 10 to the reference gas, but the configuration of the exposure unit 20 is not limited to this. The exposure unit 20 may have a period during which the sensor circuit 10 is not exposed to the sample gas. For example, the sample gas may be drawn in between two periods during which the sensor circuit 10 is exposed to the sample gas, exposing the sensor circuit 10 to a vacuum atmosphere.

[0104] In each of the above embodiments, each component 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 hard disk or semiconductor memory.

[0105] Furthermore, some or all of the functions of the gas detection system 100 according to each of the above-described embodiments may be realized by a processor such as a CPU executing a program.

[0106] Some of the components constituting the gas detection system 100 described above may be configured as an IC card or a standalone module that can be attached to or detached from each device. The IC card or the module is a computer system composed of a microprocessor, ROM, RAM, etc. The IC card or the module may include the ultra-multifunctional LSI described above. The IC card or the module achieves its functions when the microprocessor operates according to a computer program. The IC card or the module may be tamper-resistant.

[0107] The present disclosure may be the above-described methods. It may also be a computer program for implementing these methods on a computer, or a digital signal comprising the computer program. The present disclosure may also be a computer program or a digital signal recorded on a computer-readable non-transitory recording medium, such as a flexible disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray (registered trademark) Disc), semiconductor memory, or the like. It may also be a digital signal recorded on such a recording medium. The present disclosure may also be a computer program or a digital signal transmitted via a telecommunications line, a wireless or wired communication line, a network such as the Internet, data broadcasting, or the like. The present disclosure may also be a computer system including a microprocessor and a memory, in which the memory stores the computer program, and the microprocessor operates in accordance with the computer program. The present disclosure may also be implemented by another independent computer system by recording the program or the digital signal on the recording medium and transferring it, or by transferring the program or the digital signal via the network, or the like.

[0108] The gas detection system and gas detection method according to the present disclosure are useful for identifying chemical substances and the like in gas.

[0109] 10 Sensor circuit 10C Capacitive element 10Ra, 10Rb Resistive element 10Ta, 10Tb Terminal 20 Exposed portion 21 Storage portion 22 Three-way solenoid valve 23 Intake pump 25a, 25b, 25c, 25d, 25e Piping 26a, 26b Intake port 26e Exhaust port 30 AC signal source 31 Control circuit 32 Measuring circuit 33 Extraction circuit 34 Identification circuit 40 Memory 100 Gas detection system P1, P2 Input port P3 Output port

Claims

1. A gas detection system comprising: one or more sensor circuits whose real and imaginary impedance parts change depending on the gas to which they are exposed; an AC signal source that sequentially supplies a plurality of AC signals having different frequencies to each of the one or more sensor circuits; and a measurement circuit that measures the complex impedance of each of the one or more sensor circuits corresponding to each of the plurality of AC signals.

2. The gas detection system according to claim 1, wherein the one or more sensor circuits include a plurality of sensor circuits.

3. The gas detection system according to claim 2, wherein the plurality of sensor circuits have different configurations.

4. The gas detection system according to any one of claims 1 to 3, wherein the plurality of AC signals includes three or more AC signals.

5. The gas detection system according to any one of claims 1 to 3, wherein the frequencies of the plurality of AC signals are 1 kHz or more and 1 MHz or less.

6. The gas detection system according to any one of claims 1 to 3, further comprising: an extraction circuit that extracts one or more feature quantities corresponding to the real impedance part and the imaginary impedance part of the complex impedance of each of the one or more sensor circuits measured by the measurement circuit; a memory that stores a trained logical model that identifies a gas to which each of the one or more sensor circuits is exposed; and an identification circuit that uses the trained logical model to identify a gas to which each of the one or more sensor circuits is exposed based on the one or more extracted feature quantities.

7. The gas detection system according to claim 6, wherein the one or more feature quantities include a difference in shape between the time waveform of the real part of the impedance and the time waveform of the imaginary part of the impedance.

8. A gas detection method for detecting a sample gas to which one or more sensor circuits are exposed, wherein each of the one or more sensor circuits changes its impedance real part and its impedance imaginary part depending on the gas to which it is exposed, the gas detection method comprising: an AC signal supply step for supplying a plurality of AC signals having different frequencies to each of the one or more sensor circuits; an exposure step for exposing each of the one or more sensor circuits to the sample gas; and a measurement step for measuring the complex impedance of each of the one or more sensor circuits corresponding to the plurality of AC signals.

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