JP2018194314A - Gas analyzer and gas analysis method - Google Patents

Abstract

A gas analyzer and gas analysis method capable of obtaining high measurement accuracy for a measurement target gas containing a plurality of gas species are provided. A gas analyzer (100) includes a chamber (10), three or more gas sensors (30a, 30b, 30c) provided in the chamber and provided with gas-sensitive materials having different material configurations, and a plurality of gas sensors (10) having known components and concentrations. a storage unit 63 for pre-storing information for converting the responses of the gas-sensitive materials of the three or more gas sensors into concentrations for each of the gas types; a detection unit that detects a response of a material; and a converted concentration of the plurality of gas species is calculated using the information stored in the storage unit and the response detected by the detection unit, and one of the three or more gas sensors. a gas type identifying unit that identifies the gas type with the smallest variation among the differences between the converted concentrations of the specific gas sensor and the corresponding converted concentrations of the other two or more gas sensors. [Selection drawing] Fig. 2

Description

  This case relates to a gas analyzer and a gas analysis method.

  Techniques for detecting each gas type with respect to a gas including a plurality of gas types are disclosed (see, for example, Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 3-163343 JP 2008-292344 A JP 2000-55853 A

  However, with the above technique, it is difficult to obtain high measurement accuracy for a measurement target gas including a plurality of gas types.

  In one aspect, an object of the present invention is to provide a gas analysis apparatus and a gas analysis method capable of obtaining high measurement accuracy for a measurement target gas including a plurality of gas types.

  In one aspect, the gas analyzer includes a chamber, three or more gas sensors provided in the chamber, each having a gas-sensitive material having a different material structure, and a plurality of gas types whose components and concentrations are known. The storage unit stores in advance information for converting the response of each gas sensitive material of the three or more gas sensors into the concentration, and the response of each gas sensitive material of the three or more gas sensors to the measurement target gas is detected. Using the detection unit, the information stored in the storage unit, and the response detected by the detection unit, the converted concentration of the plurality of gas types is calculated, and each converted concentration of the specific gas sensor among the three or more gas sensors And a gas type specifying unit that specifies a gas type having the smallest variation among the differences between the corresponding converted concentrations of the other two or more gas sensors.

  High measurement accuracy can be obtained for a measurement target gas including a plurality of gas types.

It is a figure which illustrates the gas component of expiration. It is a schematic diagram which illustrates the whole structure of a gas analyzer. (A) is a figure which illustrates the whole structure of a gas sensor, (b) is a top view of a board | substrate, (c) is a bottom view of a board | substrate. CuBr to gas components, it is a diagram illustrating the rate of change in resistance of the SnO ₂ and WO _3. It is a figure which illustrates the flowchart showing the example of analysis of the gas seed | species contained in measurement object gas. (A)-(d) is a figure showing the example of an analysis. It is a figure showing the example of analysis.

  First, an outline of gas analysis will be described. In the following embodiments, the gas to be measured includes a plurality of different gas species, such as biological gas (exhaled breath, body odor, urine, sputum, stool) released from the body or excrement of humans or animals. is there. The gas analysis apparatus and the gas analysis method according to the present embodiment are, for example, a gas analysis apparatus and a gas analysis method for medical / healthcare that specify each gas type of biological gas.

  In an aging society, which is accelerating more and more, the total amount of medical expenses for people is increasing year by year. According to statistics from the Ministry of Health, Labor and Welfare in FY2015, the total amount of medical expenses for the public exceeded 40 trillion yen in FY2013 and has become a social problem. By disease, the proportion of diseases caused by lifestyle such as hypertension, diabetes, and cancer occupies the top. Therefore, the need for early detection of lifestyle-related diseases is increasing. Against this background, research has been conducted on breath analysis, which examines an indicator of the state of the body from biological gas, and on diagnostic methods based thereon.

  As exemplified in FIG. 1, human and animal breaths contain very low-concentration gas species that are released by vaporization of chemical substances in the blood in the lungs. Some of these are closely related to biological activity and disease. For example, ammonia gas contained in human breath is said to have a correlation with liver metabolism and H. pylori infection, which is a risk factor for gastric cancer. Nonanal, which is an aldehyde, is a substance that is a candidate for a lung cancer marker substance.

  In breath analysis, these gas species are analyzed, and it is effective for screening for improvement of lifestyle and early detection of disease by a simple means without the restraint of the body and blood collection by just breathing. Aims to detect specific substances.

  However, the biological gas contains a very large number of volatile gas species (200 or more in one theory). Most biological gases are reducing gases such as organic molecules (hydrocarbons) and have similar chemical properties. There are roughly two types of methods for analyzing such gas species.

  One is a method of performing measurement targeting a specific gas type using a large-scale analyzer represented by gas chromatography. In this method, the gas species can be analyzed in detail, but an expert operation is required. It takes several hours or more to obtain a result, and the apparatus is expensive and large. Therefore, this method is heavily used for research purposes because of the heavy testing burden.

  The other is a method of analyzing a difference in sensor response pattern due to gas using a device in which a large number of gas sensors are integrated. In this method, the time until the analysis result is obtained is fast, portable, and easy to use. On the other hand, the difference in sensitivity of the sensors is small, and it is difficult to distinguish a specific gas type from other gas types. Therefore, this method is not sufficient as an expiration analysis for examining an indicator of the body condition.

  Many conventional gas sensors are based on tin oxide. Each gas species can be identified by heating gas molecules and oxygen with a heater and detecting the amount of active oxygen adsorbed on the gas sensitive material as a resistance change of the semiconductor material. Selectivity (difference in response strength depending on the gas type) can be realized by selecting the main metal type, containing a noble metal having a gas catalytic action, the heating amount of the heater, and the like. However, in any case, only the balance between reducibility and oxygen was measured, and the selectivity was not large. For example, the selection ratio was a little less than 10, and there was almost no eigenvector orthogonality.

  For example, it is conceivable to use the techniques of Patent Documents 1 to 3. However, although the gas types can be classified by statistical processing, the principal component direction moves for each population. Therefore, it has been difficult to obtain a specific gas concentration index. That is, reproducibility was poor and there was no quantitative property. On the other hand, in the optical type, vibration type and the like, the unit system of the measurement result is completely different due to the difference in principle, and data conversion is necessary. For this reason, it is difficult to perform statistical processing with quantitativeness. Also, due to the difference in principle, it could not be formed integrally.

  Therefore, in the following embodiments, a gas analyzer and a gas analysis method that can obtain high measurement accuracy for a measurement target gas including a plurality of gas types will be described.

(Embodiment)
FIG. 2 is a schematic view illustrating the entire configuration of the gas analyzer 100. A gas to be measured by the gas analyzer 100 (hereinafter referred to as a measurement target gas) includes a plurality of types of gases. For example, the measurement target gas includes both a reducing gas and a basic gas. The reducing gas is a gas that is easily oxidized by oxygen, and includes organic compounds such as alcohols and ketones, hydrogen sulfide, and the like. The reducing gas is particularly generated in a process in which a living body decomposes hydrocarbons. The basic gas is a gas having basicity, and in particular, ammonia or the like generated in the process in which a living body decomposes protein. In the present embodiment, as an example, the measurement target gas includes ammonia as a basic gas, and includes hydrogen, acetone, ethanol, and the like as a reducing gas.

  As illustrated in FIG. 2, the gas analyzer 100 includes a purge gas supply unit 20 outside the chamber 10. In addition, the gas analyzer 100 includes a first gas sensor 30a, a second gas sensor 30b, a third gas sensor 30c, a fourth gas sensor 40, a temperature / humidity sensor 50, and the like inside the chamber 10. In addition, the gas analyzer 100 includes a calculation unit 60 outside the chamber 10. The calculation unit 60 includes an impedance measurement circuit 61, a calculation circuit 62, a memory 63, a transmission / reception unit 64, and the like. A processor or the like may be used as each circuit.

  A first inlet 11, a second inlet 12 and an outlet 13 are formed in the chamber 10. The first inlet 11 is an opening for supplying purge gas into the chamber 10. The second inlet 12 is an opening for supplying the measurement target gas into the chamber 10. The outlet 13 is an opening for discharging the purge gas or the measurement target gas from the chamber 10.

  A pipe from the purge gas supply unit 20 is connected to the first inlet 11. The second inlet 12 is provided with a check valve 14. The check valve 14 is configured to suppress gas outflow from the chamber 10 via the second inlet 12. A check valve 15 is provided at the outlet 13. The check valve 15 is configured to suppress gas inflow from the outside of the chamber 10 via the outlet 13.

  The purge gas supply unit 20 includes a filter 21 and a blower pump 22. The purge gas is not particularly limited, but is air or the like. The blower pump 22 sucks the purge gas through the filter 21 and supplies the purge gas into the chamber 10 through the pipe. The filter 21 removes dust and the like in the purge gas. By supplying the purge gas into the chamber 10 by the blower pump 22, the internal pressure of the chamber 10 is increased, and the gas inflow from the second inlet 12 is suppressed by the action of the check valve 14. When the internal pressure in the chamber 10 rises, the check valve 15 does not operate, so the purge gas is discharged from the outlet 13. Thereby, the inside of the chamber 10 can be purged.

  When analyzing the measurement target gas, the measurement target gas flows from the second inlet 12. The check valve 14 suppresses the outflow of the measurement target gas from the second inlet 12. The measurement target gas flows in the chamber 10 and is discharged from the outlet 13.

  The first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c have a configuration in which a heater 32 is provided on the lower surface of the substrate 31, and an electrode 33, a gas sensitive material 34, and an electrode 35 are provided on the upper surface of the substrate 31. FIG. 3A is a diagram illustrating the entire structure of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c. The substrate 31, the heater 32, the electrode 33, the gas sensitive material 34, and the electrode 35 illustrated in FIG. 2 are arranged in a housing 36 having a part of the opening. FIG. 3B is a top view of the substrate 31. FIG. 3C is a bottom view of the substrate 31. The substrate 31 is made of an insulating material such as alumina. The heater 32 is made of a material that generates heat when supplied with electricity, and is a NiCr thin film or the like. The electrode 33 is provided at one end of the gas sensitive material 34. The electrode 35 is provided at the other end of the gas sensitive material 34. Each of the electrodes 33 and 35 is connected to a terminal on the lower surface of the substrate 31 through a via. Thereby, the heater 32 and the gas sensitive material 34 are connected in parallel.

  The fourth gas sensor 40 has a configuration in which an electrode 42, a gas sensitive material 43, and an electrode 44 are provided on the upper surface of the substrate 41. The electrode 42 is provided at one end of the gas sensitive material 43. The electrode 44 is provided at the other end of the gas sensitive material 43.

  The gas sensitive materials 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c have different material configurations. Further, the gas sensitive material 43 of the fourth gas sensor 40 has a material configuration different from that of each gas sensitive material 34. Thereby, the 1st gas sensor 30a, the 2nd gas sensor 30b, the 3rd gas sensor 30c, and the 4th gas sensor 40 have a different selection ratio about the sensitivity to the measuring object gas containing a plurality of gas types.

  In the present embodiment, as an example, the gas sensitive material 34 is made of a material having high sensitivity to the reducing gas concentration. The gas sensitive material 34 is an oxide semiconductor of at least one of Sn (tin), W (tungsten), Zn (zinc), and In (indium), or a semiconductor whose main material is C (carbon). When the gas molecules and oxygen in the housing 36 are heated by the heater 32, the amount of active oxygen adsorbed on the gas sensitive material 34 changes. When the adsorption amount of active oxygen changes, the resistance of the gas sensitive material 34 changes. By detecting this resistance change, it is possible to detect the gas concentration of the measurement target.

  By changing the type and composition ratio of the metal constituting the oxide semiconductor, the gas sensitive material 34 can have selectivity (difference in response strength to the gas type). Alternatively, the gas-sensitive material 34 can be made selective by containing a gas-catalyzed noble metal in the gas-sensitive material 34 or changing the type and composition ratio of the noble metal. For example, the gas-sensitive material 34 contains an additive metal such as noble metals Pd (palladium), Pt (platinum) and the like, and base metals Al (aluminum), Pb (lead), etc., thereby determining the selection ratio between the gas species. can do. Alternatively, the gas sensitive material 34 can be made selective by changing the heating amount of the heater 32. In addition, it is preferable to make sensitivity larger than about 0.1 to 10 times with respect to acetone, ethanol, or the like.

  An organic thin film may be formed on the gas sensitive material 34 in order to provide a sensitivity difference with respect to VOC (volatile organic compound). When the organic thin film is formed, the sensitivity of the gas sensitive material 34 is relatively lowered. Therefore, it is desirable to form the organic thin film as thin as possible. For example, the monomolecular layer may be formed by applying gold particles to the surface of the gas sensitive material 34 and exposing it to a polymer gas. For example, it is preferable to use an amine-based, thiol-based, or silane-based coupling material.

  The first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c can detect the gas type and the gas concentration by detecting a change in the resistance value of the gas sensitive material 34. In the 1st gas sensor 30a, the 2nd gas sensor 30b, and the 3rd gas sensor 30c, the optimal detection temperature according to the gas kind made into a detection target exists. Therefore, when the gas concentration is measured, the inside of the housing 36 is set to the optimum detection temperature. Alternatively, the inside of the housing 36 is heated to the detection temperature within the detection temperature range including the optimum detection temperature by the heater 32 and used. On the other hand, when cleaning the gas sensitive material 34, the temperature in the housing 36 is increased to a cleaning temperature higher than the temperature at the time of gas detection, thereby desorbing contaminants adsorbed on the surface of the gas sensitive material 34. Can do.

On the other hand, in the present embodiment, as an example, the gas sensitive material 43 is made of a material having high sensitivity to the basic gas concentration. Copper ions (Cu ⁺ and Cu ²⁺ ) and silver ions (Ag ⁺ ) are present as mobile ions, thereby exhibiting high affinity with a basic gas. Therefore, in the present embodiment, the gas sensitive material 43 is mainly composed of a halide or oxide of copper or silver. As an example, copper bromide (I) (CuBr) which is a p-type semiconductor can be used.

  Since copper ions and silver ions have a high affinity for the basic gas, the basic gas strongly adsorbs to the gas sensitive material 43. By detecting a change in resistance of the gas sensitive material 43 in this case, the basic gas species and concentration can be measured. For example, copper ions and silver ions form a coordinate bond with the nitrogen atom of the amine. Thereby, copper ion and silver ion have high affinity with nitrogen. Therefore, basic gas such as ammonia can be measured by using copper ions or silver ions. Monovalent copper ions have a higher affinity for nitrogen than divalent copper ions. Therefore, it is preferable to use a monovalent copper ion halide or oxide.

  Since the fourth gas sensor 40 uses adsorption of gas molecules, heating with a heater is not essential. However, sensitivity and responsiveness can be improved by lowering the temperature at the time of adsorption and by increasing the temperature at the time of separation.

  An organic thin film may be formed on the gas sensitive material 43 in order to provide a sensitivity difference with respect to VOC (volatile organic compound). When the organic thin film is formed, the sensitivity of the gas sensitive material 43 is relatively lowered. Therefore, it is desirable to form the organic thin film as thin as possible. For example, the monomolecular layer may be formed by applying gold particles to the surface of the gas sensitive material 43 and exposing it to a polymer gas. For example, it is preferable to use an amine-based, thiol-based, or silane-based coupling material.

  The heat of the heater 32 may be transmitted downstream along the gas flow. Therefore, it is preferable that the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c are arranged on the outlet 13 side with respect to the fourth gas sensor 40. By doing in this way, the influence of the heat of the heater 32 with respect to the 4th gas sensor 40 can be suppressed.

FIG. 4 is a diagram illustrating the resistance change rate of CuBr, SnO ₂ and WO ₃ for each gas type. The vertical axis represents the normalized value of the resistance change rate. The MOS in the figure is a metal oxide semiconductor (Metal Oxide Semiconductor). The resistance change rate is normalized based on the resistance change rate with respect to 1 ppm of ammonia.

As illustrated in FIG. 4, SnO ₂ and WO ₃ can obtain a large resistance change rate with respect to a plurality of gas types. Therefore, the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c including SnO ₂ and WO ₃ as the gas sensitive material 34 have a low selection ratio. However, the resistance change rate differs depending on the gas type. Based on this difference, the concentration of each gas species can be accurately measured. Further, the rate of resistance change with respect to each gas type is different between SnO ₂ and WO ₃ . Therefore, using both SnO ₂ and WO ₃ makes the concentration measurement for each gas species more accurate.

  Next, CuBr provides a remarkably large resistance change rate with respect to the basic gas (ammonia) as compared with other gas types. On the other hand, the resistance of CuBr hardly changes against reducing gas. This is because copper or silver halides or oxides have a low affinity for reducing gases. Accordingly, the fourth gas sensor 40 including CuBr as the gas sensitive material 43 has a high selection ratio. By using a gas sensor including CuBr as the gas sensitive material 43, the basic gas concentration can be accurately measured.

  Thus, the selection ratio of these gas sensors can be varied by making the material configurations of the gas sensitive materials 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c different. Further, by making the material configuration of the gas sensitive material 43 of the fourth gas sensor 40 different from the material configuration of each gas sensitive material 34, the selection ratio of the fourth gas sensor 40 is changed to the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 40. It can be different from the selection ratio of the gas sensor 30c.

  By making the material configurations of the gas sensitive materials different, the selection ratio of the fourth gas sensor 40 can be set to a value larger than the selection ratio of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c. For example, the gas sensitive material 43 is mainly made of a halide or oxide of Cu or Ag, so that the fourth gas sensor 40 has a low sensitivity to a reducing gas and is particularly high to a basic gas. Has sensitivity. That is, the selection ratio of the fourth gas sensor 40 is increased. The gas sensitive material 34 is made of an oxide semiconductor whose main material is at least one of Sn, W, Zn and In, or a semiconductor whose main material is C, whereby the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor. While 30c has high sensitivity to reducing gas, it also has high sensitivity to basic gas. Thereby, the selection ratio of the fourth gas sensor 40 becomes larger than the selection ratio of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c.

  Referring to FIG. 2 again, the electrodes of the first gas sensor 30 a, the second gas sensor 30 b, the third gas sensor 30 c, and the fourth gas sensor 40 are connected to the impedance measurement circuit 61. Thereby, the impedance measurement circuit 61 measures the resistance of each gas sensitive material. Specifically, the impedance measurement circuit 61 measures the impedance of the gas sensitive material 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c, and measures the impedance of the gas sensitive material 43 of the fourth gas sensor 40. . The impedance measurement circuit 61 transmits the measurement result to the arithmetic circuit 62. The arithmetic circuit 62 calculates the concentration of each gas type of the measurement target gas. The transmission / reception unit 64 transmits the calculation result of the arithmetic circuit 62 to the external device.

  Next, an analysis example of the gas species contained in the measurement target gas will be described with reference to the flow of FIG. Here, as an example, the measurement target gas includes ammonia as a basic gas, and includes a plurality of reducing gases such as hydrogen, acetone, and ethanol as a reducing gas.

  Each gas sensor is not sensitive only to a specific gas type. That is, even if the resistance change of the gas sensitive material of each gas sensor is measured, it is difficult to specify which gas type the resistance change is. Therefore, in the present embodiment, by performing statistical processing or machine learning on the measurement result of the impedance of the gas sensitive material of each gas sensor, information converted into the concentration of each gas type is stored in the memory 63 in advance. deep.

  First, the learning result of the rate of change of the response (impedance) of the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 for each of the gas types 1 to m having known components and concentrations, It is stored in the memory 63 as matrix data (step S1).

  For example, a set as illustrated in FIG. Each element of the set of impedance changes is a time change rate of impedance with respect to each of a plurality of gas types. For example, the impedance change amount from when the gas species is introduced into the chamber 10 until the specified time elapses. Alternatively, element data may be obtained by examining the correlation between the gas concentration and the amount of impedance change with respect to a reference gas type (for example, ammonia) and converting the correlation into the concentration using the correlation.

Next, a database of correction equations when each gas type is introduced into the chamber 10 is created in advance (step S2). For example, a function f that defines Δz _n0m = f (C _m0 ) is defined. However, C _m0 is a gas concentration (initial value) in the gas type m. n is the number (1-4) of the gas sensor.

Next, the arithmetic circuit 62 changes the response rate (impedance time change rate) of the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 with respect to the measurement target gas x whose component or concentration is unknown. Is measured (step S3). FIG. 6B is a diagram illustrating measurement results. As illustrated in FIG. 6B, the impedance change rate of the first gas sensor 30a is Δz _1x . The impedance change rate of the second gas sensor 30b is Δz _2x . The impedance change rate of the third gas sensor 30c is Δz _3x . The impedance change rate of the fourth gas sensor 40 is Δz _4x .

Next, the arithmetic circuit 62 uses the measured values in FIG. 6B and the correction formula database created in step S2, and the gas types included in the measurement target gas x are the gas types on the database. A density conversion value when it is assumed to be present is calculated (step S4). The inverse function can be expressed as C _mx = f ⁻¹ (Δz _nx ). FIG. 6C shows the calculation result of the converted concentration value.

Next, the arithmetic circuit 62 calculates the difference between each concentration conversion value of the first gas sensor 30a to the third gas sensor 30c and the corresponding concentration conversion value of the fourth gas sensor 40 (step S5). FIG. 6D is a diagram illustrating a difference calculation result. The difference can be calculated using the following formula.
(A ₁₁ , A ₁₂ ,..., A _1m ) = (C ₁₁ , C ₁₂ ,..., C _1m ) − (C ₄₁ , C ₄₂ ,..., C _4m )
_{(A 21, A 22, ...} , A 2m) = (C 21, C 22, ..., C 2m) - (C 41, C 42, ..., C 4m)
(A ₃₁ , A ₃₂ ,..., A _3m ) = (C ₃₁ , C ₃₂ ,..., C _3m ) − (C ₄₁ , C ₄₂ ,..., C _4m )

The arithmetic circuit 62 includes (A ₁₁ , A ₂₁ , A ₃₁ ), (A ₁₂ , A ₂₂ , A ₃₂ ),..., (A _1m , A _2m , A _3m ), which are the same gas (same row) elements. The gas type k with the smallest variation is searched (step S6). At this time, elements including negative values are preferably excluded or set to zero. For the variation, for example, the minimum value may be found by using (maximum value−minimum value) / median value as an index, or by determining the variance. In the example of FIG. 7, for example, the gas type 2 is searched for as the gas type having the smallest variation.

Next, the arithmetic circuit 62 specifies the gas type k as the main component of the gas types excluding ammonia among the gas types included in the measurement target gas, and calculates the converted gas concentration of the gas type k = A _xk . To do. x has the highest sensitivity (Δz _n0m ) among the first gas sensor 30a to the third gas sensor 30c, thereby ensuring the highest accuracy. However, an average value of the first gas sensor 30a to the third gas sensor 30c may be adopted.

Then, the transmitting and receiving unit 64 outputs the _{C 41} as ammonia concentration, and outputs the _{A xk} as a main component gas concentration (step S7). With the above processing, the analysis of the measurement target gas is completed.

  According to the present embodiment, the gas sensitive materials 34 of the first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c have different material configurations. Further, the gas sensitive material 43 of the fourth gas sensor 40 has a material configuration different from that of each gas sensitive material 34. Accordingly, the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 have different selection ratios.

  Next, the fourth gas sensor 40 has a high sensitivity by calculating the difference between the respective concentration conversion values of the first gas sensor 30a to the third gas sensor 30c with respect to the measurement target gas and the corresponding concentration conversion value of the fourth gas sensor 40. Can be excluded. Next, by searching for the gas type having the smallest variation in the difference, it is possible to estimate the main component gas type other than the gas type with which the fourth gas sensor 40 has high sensitivity. Thereby, high measurement accuracy can be obtained for a measurement target gas including a plurality of gas types. In such processing, the calculation is simple, so that power consumption can be suppressed. Thereby, it can be applied to constant monitoring. Further, since it is not necessary to use a large arithmetic device, the device can be downsized.

  By making the selection ratio of the fourth gas sensor 40 larger than the selection ratio of the first gas sensor 30a to the third gas sensor 30c, the concentration measurement accuracy of the gas species with which the fourth gas sensor 40 has high sensitivity is improved.

  Further, in the measurement result of the fourth gas sensor 40, an error with respect to a gas type having low sensitivity is increased. In this case, a search is made for a gas type having the smallest variation in the difference between the respective concentration conversion values of the first gas sensor 30a to the third gas sensor 30c with respect to the measurement target gas and the corresponding concentration conversion value of the fourth gas sensor 40. Thus, the estimation accuracy of the main component gas species other than the gas species for which the fourth gas sensor 40 has high sensitivity is improved.

  In the above analysis example, the fourth gas sensor 40 uses the gas sensitive material 43 whose main material is a halide or oxide of Cu or Ag. The gas sensitive material 43 has high sensitivity to basic gas and low sensitivity to reducing gas. Thereby, high measurement accuracy with respect to the basic gas concentration is obtained. In the above analysis example, the ammonia concentration can be measured with high accuracy.

  By the way, in the body of an animal including a human, nitrogen is generated as ammonia during protein degradation in the digestive tract. Alternatively, microorganisms and anaerobic bacteria that live in the gastrointestinal tract decompose urea using urease enzyme to generate ammonia. A part of these ammonia is absorbed in the blood, and the rest is excreted as excrement. Blood containing nutrients absorbed from the digestive tract is collected in the liver as a portal vein.

  In the liver, nutrient substances are absorbed and metabolism having a detoxifying function is performed for toxins. In the case of ammonia, it is the latter, which is metabolized in the cycle of urea cycle in the liver and converted to urea. This urea is then filtered through the kidneys and excreted with the urine. In addition, when intense exercise causes muscle fatigue, ammonia is generated in the blood, which is similarly metabolized by the urea circuit in the liver through veins and converted to urea.

  With such a metabolic function, the biological ammonia concentration is kept below a certain level. Therefore, when there is a disease in the metabolic function of the liver and the liver function is lowered, the ammonia concentration is high, and in the undernutrition state, the ammonia concentration is low. However, it can be said that organisms always contain ammonia in blood as long as they are accompanied by nutrients and exercise. Since this ammonia is vaporized by capillaries in the lungs and skin, the breath and sweat of living things always contain a trace amount of ammonia.

  In the process of decomposing hydrocarbons, alcohols such as ethanol are generated. Further, when sugars are decomposed, ketones such as acetone are generated. Isoprene and the like are generated during the breakdown of cholesterol. In diseases such as cancer, various VOCs are generated by oxidative stress in the affected area and are vaporized through the blood and in the lungs and skin.

  According to the present embodiment, by using the gas sensitive material 43 mainly composed of a halide or oxide of Cu or Ag, it becomes possible to separate ammonia among various metabolic gases. . Furthermore, in addition to the concentration of the gas (ammonia) that is to be constantly monitored, the most dense gas species and concentration can be estimated as the main components. It is possible to improve estimation accuracy by excluding ammonia. By applying this embodiment and further installing a gas sensor, the number of detectable gas species can be increased and an electronic nose can be realized. By utilizing these, an electronic nose called a breath sensor using a gas sensor array for grasping the characteristics of breath and sweat components like a fingerprint can be constructed.

  Due to the ease of this embodiment, it is possible to continuously check the variation of the breath component due to lifestyle without suffering from pain such as blood collection. In addition, a breath pattern sensor can be mounted on a smart device or a wearable device, and the gas can be used as a means for continuously analyzing these gases like a thermometer. In addition, this technology can be used as a screening tool for improving lifestyle and early detection of diseases.

  In the above-described embodiment, the first gas sensor 30a, the second gas sensor 30b, the third gas sensor 30c, and the fourth gas sensor 40 are provided in the chamber, and three or more gas sensors each including a gas-sensitive material made of different materials. It is an example. The fourth gas sensor 40 is an example of a specific gas sensor among the three or more gas sensors. The first gas sensor 30a, the second gas sensor 30b, and the third gas sensor 30c are examples of two or more gas sensors other than the specific gas sensor. The memory 63 is an example of a storage unit that stores in advance information for converting the response of each gas sensitive material of the three or more gas sensors into a concentration for a plurality of gas types whose components and concentrations are known. The impedance measurement circuit 61 is an example of a detection unit that detects the response of each gas sensitive material of the three or more gas sensors to the measurement target gas. The arithmetic circuit 62 calculates the converted concentration of the plurality of gas types using the information stored in the storage unit and the response detected by the detection unit, and converts each specific gas sensor among the three or more gas sensors. It is an example of the gas type specific | specification part which specifies the gas type with the smallest variation among the difference of each density | concentration corresponding to a density | concentration and two or more other gas sensors.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Chamber 11 1st inlet 12 2nd inlet 13 Outlet 14, 15 Check valve 30a 1st gas sensor 30b 2nd gas sensor 30c 3rd gas sensor 32 Heater 34 Gas sensitive material 40 4th gas sensor 43 Gas sensitive material 60 Operation part 61 Impedance measurement Circuit 62 Arithmetic circuit 63 Memory 100 Gas analyzer

Claims (12)

A chamber;
Three or more gas sensors provided in the chamber, each comprising a gas sensitive material having a different material configuration;
A storage unit for storing in advance information for converting the response of each gas sensitive material of the three or more gas sensors into a concentration for a plurality of gas types whose components and concentrations are known;
A detection unit for detecting a response of each gas sensitive material of the three or more gas sensors to the measurement target gas;
Using the information stored in the storage unit and the response detected by the detection unit, the converted concentration of the plurality of gas types is calculated, and the converted concentration of the specific gas sensor among the three or more gas sensors and the other two A gas analyzer comprising: a gas type specifying unit that specifies a gas type having the smallest variation among the differences from the corresponding converted concentrations of the gas sensor.   2. The gas analyzer according to claim 1, wherein the gas sensitive material of the specific gas sensor is mainly composed of a halide or oxide of Cu or Ag. The other two or more gas sensors include a heater for heating the gas sensitive material,
The gas analyzer according to claim 2, wherein the specific gas sensor is arranged upstream of the other two or more gas sensors in the gas flow direction in the chamber.   The gas sensitive material of the other two or more gas sensors is an oxide semiconductor whose main material is at least one of Sn, W, Zn and In, or a semiconductor whose main material is C. The gas analyzer as described in any one of 1-3.   The gas analyzer according to any one of claims 1 to 4, wherein a selection ratio of the gas sensitive material of the specific gas sensor is larger than a selection ratio of the gas sensitive materials of the other two or more gas sensors. .   6. The gas analyzer according to claim 1, wherein a total number of the gas sensors is equal to or less than a total number of gas types stored in the storage unit. Information for converting the response of each gas sensitive material of three or more gas sensors provided in the chamber and having a different material configuration into a concentration for a plurality of gas types having known components and concentrations. , Store in advance in the storage unit,
Detecting the response of each gas sensitive material of the three or more gas sensors to the gas to be measured;
The converted concentration of the plurality of gas types is calculated using the information stored in the storage unit and the detected response, and the converted concentration of the specific gas sensor of the three or more gas sensors and the other two or more A gas analysis method characterized by identifying a gas type having the smallest variation among differences from corresponding conversion concentrations of a gas sensor.   The gas analysis method according to claim 7, wherein the gas sensitive material of the specific gas sensor is mainly composed of a halide or oxide of Cu or Ag. The other two or more gas sensors include a heater for heating the gas sensitive material,
The gas analysis method according to claim 8, wherein the specific gas sensor is disposed upstream of the other two or more gas sensors in the gas flow direction in the chamber.   The gas sensitive material of the other two or more gas sensors is an oxide semiconductor whose main material is at least one of Sn, W, Zn and In, or a semiconductor whose main material is C. The gas analysis method according to any one of 7 to 9.   The gas analysis method according to any one of claims 7 to 10, wherein a selection ratio of gas sensitive materials of the specific gas sensor is larger than a selection ratio of gas sensitive materials of the other two or more gas sensors. .   13. The gas analysis method according to claim 7, wherein a total number of the gas sensors is equal to or less than a total number of gas types stored in the storage unit.

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