Patent Publication Number: US-2022221397-A1

Title: Gas detection system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Japanese Patent Application No. 2019-100598 filed in Japan on May 29, 2019 and Japanese Patent Application No. 2019-100644 filed in Japan on May 29, 2019, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a gas detection system. 
     BACKGROUND ART 
     In the related art, there is known a system for detecting an odoriferous gas generated from feces discharged by a subject (for example, PTL 1). 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2016-142584 
     SUMMARY OF INVENTION 
     A gas detection system according to an embodiment of the present disclosure includes: 
     a sensor unit that outputs a signal corresponding to a concentration of a specific gas; 
     a concentration unit having therein an adsorbent that adsorbs a gas to be detected; 
     a supply unit capable of supplying a sample gas and a purge gas to the concentration unit; 
     a heater capable of heating the adsorbent; and 
     a control unit that controls the supply unit so that the sample gas passes through the concentration unit and then controls the supply unit so that the purge gas passes through the concentration unit while controlling the heater so that a temperature of the adsorbent increases, wherein 
     the control unit 
     stops passage of the purge gas to the concentration unit from a first point in time to a second point in time later than the first point in time, the first point in time being a point in time before or at which the temperature of the adsorbent reaches a desorption temperature of the gas to be detected, and, after the second point in time, performs control so that the purge gas passes through the concentration unit and is supplied to the sensor unit together with the gas to be detected in the concentration unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an external view of a gas detection system according to a first embodiment of the present disclosure. 
         FIG. 2  is a schematic diagram of the inside of a housing of the gas detection system illustrated in  FIG. 1 . 
         FIG. 3  is a functional block diagram of the gas detection system illustrated in  FIG. 1 . 
         FIG. 4  is a schematic graph of the concentration of a gas desorbed from an adsorbent adsorbing a predetermined gas, which is detected with a change in the temperature of the adsorbent. 
         FIG. 5  is a timing chart of an example operation of the gas detection system illustrated in  FIG. 1 . 
         FIG. 6  is a flowchart of an example operation of the gas detection system illustrated in  FIG. 1  during gas concentration. 
         FIG. 7  is a flowchart of an example operation of the gas detection system illustrated in  FIG. 1  during detection of the type and concentration of a gas. 
         FIG. 8  is timing chart of an example operation of a gas detection system according to a second embodiment of the present disclosure. 
         FIG. 9  is a timing chart describing another example of a first point in time and a second point in time in the present disclosure. 
         FIG. 10  is a functional block diagram of a gas detection system according to a modification of the first embodiment and the second embodiment of the present disclosure. 
         FIG. 11  is an external view of a gas detection system according to a third embodiment of the present disclosure. 
         FIG. 12  is a schematic diagram of the inside of a housing of the gas detection system illustrated in  FIG. 11 . 
         FIG. 13  is a functional block diagram of the gas detection system illustrated in  FIG. 11 . 
         FIG. 14  is a schematic graph of the concentration of a gas desorbed from an adsorbent adsorbing a predetermined gas, which is detected with a change in the temperature of the adsorbent. 
         FIG. 15  is a sectional view of the adsorbent in a concentration tank illustrated in  FIG. 12 . 
         FIG. 16  is a timing chart of an example operation of the gas detection system illustrated in  FIG. 11 . 
         FIG. 17  is a flowchart of an example operation of the gas detection system illustrated in  FIG. 11  during gas concentration. 
         FIG. 18  is a flowchart of an example operation of the gas detection system illustrated in  FIG. 11  during detection of the type and concentration of a gas. 
         FIG. 19  is timing chart of an example operation of a gas detection system according to a fourth embodiment of the present disclosure. 
         FIG. 20  is a flowchart of an example operation of the gas detection system according to the fourth embodiment of the present disclosure during gas concentration. 
         FIG. 21  is a schematic graph illustrating the relationship between the temperature of an adsorbent and the concentration of a gas desorbed from the adsorbent in a fifth embodiment of the present disclosure. 
         FIG. 22  is a functional block diagram of a gas detection system according to a modification of the third embodiment to the fifth embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A conventional system needs to improve the gas detection performance and the like. 
     The present disclosure relates to providing a gas detection system with improved gas detection performance and the like. 
     According to an embodiment of the present disclosure, a gas detection system with improved gas detection performance and the like can be provided. 
     Embodiments according to the present disclosure will be described hereinafter with reference to the drawings. The drawings are schematic illustrations. 
     First Embodiment 
     As illustrated in  FIG. 1 , a gas detection system  1  is installed in a toilet  2 . The toilet  2  may be, but is not limited to, a flush toilet. The toilet  2  includes a toilet bowl  2 A and a toilet seat  2 B. The gas detection system  1  may be installed in any portion of the toilet  2 . In one example, as illustrated in  FIG. 1 , the gas detection system  1  may be arranged from between the toilet bowl  2 A and the toilet seat  2 B to the outside of the toilet  2 . A portion of the gas detection system  1  may be embedded inside the toilet seat  2 B. The subject can discharge feces into the toilet bowl  2 A. The gas detection system  1  can acquire a gas generated from the feces discharged into the toilet bowl  2 A as a sample gas. The gas detection system  1  can detect the type of a gas contained in the sample gas, the concentration of the gas, and so on. The gas detection system  1  can transmit the detection results and so on to an electronic device  3 . The gas detection system  1  as illustrated in  FIG. 1  is also referred to as a “gas detection device”. 
     The uses of the gas detection system  1  are not limited to the use described above. For example, the gas detection system  1  may be installed in a refrigerator. In this case, the gas detection system  1  can acquire a gas generated from food as a sample gas. In another use, for example, the gas detection system  1  may be installed in a factory or a laboratory. In this case, the gas detection system  1  can acquire a gas generated from a chemical or the like as a sample gas. 
     The toilet  2  can be installed in a toilet room in a house, a hospital, or the like. The toilet  2  can be used by the subject. As described above, the toilet  2  includes the toilet bowl  2 A and the toilet seat  2 B. The subject can discharge feces into the toilet bowl  2 A. 
     The electronic device  3  is, for example, a smartphone used by the subject. However, the electronic device  3  is not limited to a smartphone. The electronic device  3  may be any electronic device. When brought into the toilet room by the subject, as illustrated in  FIG. 1 , the electronic device  3  can be present in the toilet room. However, for example, when the subject does not bring the electronic device  3  into the toilet room, the electronic device  3  may be present outside the toilet room. The electronic device  3  can receive the detection results from the gas detection system  1  via wireless communication or wired communication. The electronic device  3  can display the received detection results on a display unit  3 A. The display unit  3 A may include a display capable of displaying characters and the like, and a touch screen capable of detecting contact of a finger of the user (subject) or the like. The display may include a display device such as a liquid crystal display (LCD), an organic EL display (OELD: Organic Electro-Luminescence Display), or an inorganic EL display (IELD: Inorganic Electro-Luminescence Display). The detection method of the touch screen may be any method such as a capacitance method, a resistance film method, a surface acoustic wave method, an ultrasonic method, an infrared method, an electromagnetic induction method, or a load detection method. 
     As illustrated in  FIG. 2 , the gas detection system  1  includes a housing  10 , inflow paths  20  and  21 , and discharge paths  22 ,  23 , and  24 . The discharge path  22 , the discharge path  23 , and the discharge path  24  may merge in any location. The gas detection system  1  includes flow paths  30 ,  31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37 ,  38 , and  39 , valves  40 ,  41 ,  42 ,  43 , and  44 , and a supply unit  50 . The gas detection system  1  includes a concentration tank  60  serving as a concentration unit, a storage tank  70  serving as a reservoir, a chamber  80 , and a circuit board  90  serving as a circuit unit. As illustrated in  FIG. 3 , the gas detection system  1  includes, in the circuit board  90 , a storage unit  91 , a communication unit  92 , and a control unit  94 . The gas detection system  1  includes a sensor unit  93 . 
     The housing  10  houses various components of the gas detection system  1 . The housing  10  may be made of any material. For example, the housing  10  may be made of a material such as metal or resin. 
     As illustrated in  FIG. 1 , the inflow path  20  can be exposed to the inside of the toilet bowl  2 A. A portion of the inflow path  20  may be embedded in the toilet seat  2 B. A gas generated from feces discharged into the toilet bowl  2 A flows into the inflow path  20  as a sample gas. The sample gas flowing into the inflow path  20  is supplied to the concentration tank  60  through the flow paths  30 ,  31 , and  32 . As illustrated in  FIG. 1 , one end of the inflow path  20  may be directed to the inside of the toilet bowl  2 A. As illustrated in  FIG. 2 , the other end of the inflow path  20  may be connected to the valve  40 . The inflow path  20  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 1 , the inflow path  21  can be exposed to the outside of the toilet bowl  2 A. A portion of the inflow path  21  may be embedded in the toilet seat  2 B. For example, air in the toilet room, which is outside the toilet bowl  2 A, flows into the inflow path  21  as a purge gas. The purge gas flowing into the inflow path  21  is supplied to the storage tank  70  through the flow paths  30 ,  33 , and  34 . As illustrated in  FIG. 1 , one end of the inflow path  21  may be directed to the outside of the toilet  2 . As illustrated in  FIG. 2 , the other end of the inflow path  21  may be connected to the valve  40 . The inflow path  21  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 1 , a portion of the discharge path  22  can be exposed to the outside of the toilet bowl  2 A. The discharge path  22  as illustrated in  FIG. 2  discharges the exhaust from the chamber  80  to the outside. This exhaust can contain the sample gas and the purge gas, which have been subjected to detection processing. As illustrated in  FIG. 1 , one end of the discharge path  22  may be directed to the outside of the toilet  2 . As illustrated in  FIG. 2 , the other end of the discharge path  22  may be connected to the chamber  80 . The discharge path  22  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 1 , a portion of the discharge path  23  can be exposed to the outside of the toilet bowl  2 A. The discharge path  23  as illustrated in  FIG. 2  discharges the exhaust from the concentration tank  60  to the outside. This exhaust includes a gas not to be detected, which is generated in a concentration process of the sample gas described below. As illustrated in  FIG. 1 , one end of the discharge path  23  may be directed to the outside of the toilet  2 . As illustrated in  FIG. 2 , the other end of the discharge path  23  may be connected to the valve  43 . The discharge path  23  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 1 , a portion of the discharge path  24  can be exposed to the outside of the toilet bowl  2 A. The discharge path  24  as illustrated in  FIG. 2  discharges the residual gas or the like from the storage tank  70  to the outside. As illustrated in  FIG. 1 , one end of the discharge path  24  may be directed to the outside of the toilet  2 . As illustrated in  FIG. 2 , the other end of the discharge path  24  may be connected to the valve  44 . The discharge path  24  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 2 , one end of the flow path  30  is connected to the valve  40 . The other end of the flow path  30  is connected to one end of the flow path  31  and one end of the flow path  33 . The one end of the flow path  31  is connected to the other end of the flow path  30 . The other end of the flow path  31  is connected to the valve  41 . One end of the flow path  32  is connected to the valve  41 . The other end of the flow path  32  is connected to an inlet portion of the concentration tank  60 . The one end of the flow path  33  is connected to the other end of the flow path  30 . The other end of the flow path  33  is connected to the valve  42 . One end of the flow path  34  is connected to the valve  42 . The other end of the flow path  34  is connected to an inlet portion of the storage tank  70 . One end of the flow path  35  is connected to the valve  41 . The other end of the flow path  35  is connected to the valve  44 . One end of the flow path  36  is connected to an outlet portion of the concentration tank  60 . The other end of the flow path  36  is connected to the valve  43 . One end of the flow path  37  is connected to the valve  43 . The other end of the flow path  37  is connected to the chamber  80 . One end of the flow path  38  is connected to an outlet portion of the storage tank  70 . The other end of the flow path  38  is connected to the valve  44 . One end of the flow path  39  is connected to the valve  44 . The other end of the flow path  39  is connected to the chamber  80 . The flow paths  30  to  39  may be each constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 2 , the valve  40  is located among the inflow path  20 , the inflow path  21 , and the flow path  30 . The valve  40  includes a connection port connected to the inflow path  20 , a connection port connected to the inflow path  21 , and a connection port connected to the flow path  30 . The valve  40  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  40  as illustrated in  FIG. 2  switches the connection state among the inflow path  20 , the inflow path  21 , and the flow path  30  under the control of the control unit  94  as illustrated in  FIG. 3 . For example, the valve  40  switches the connection state among them to a state in which the inflow path  20  and the flow path  30  are connected to each other, a state in which the inflow path  21  and the flow path  30  are connected to each other, or a state in which the inflow path  20 , the inflow path  21 , and the flow path  30  are not connected to each other. 
     As illustrated in  FIG. 2 , the valve  41  is located among the flow path  31 , the flow path  32 , and the flow path  35 . The valve  41  includes a connection port connected to the flow path  31 , a connection port connected to the flow path  32 , and a connection port connected to the flow path  35 . The valve  41  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  41  as illustrated in  FIG. 2  switches the connection state among the flow path  31 , the flow path  32 , and the flow path  35  under the control of the control unit  94  as illustrated in  FIG. 3 . For example, the valve  41  switches the connection state among them to a state in which the flow path  31  and the flow path  32  are connected to each other, a state in which the flow path  35  and the flow path  32  are connected to each other, or a state in which the flow path  31 , the flow path  32 , and the flow path  35  are not connected to each other. 
     As illustrated in  FIG. 2 , the valve  42  is located between the flow path  33  and the flow path  34 . The valve  42  includes a connection port connected to the flow path  33 , and a connection port connected to the flow path  34 . The valve  42  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  42  as illustrated in  FIG. 2  switches the connection state between the flow path  33  and the flow path  34  under the control of the control unit  94  as illustrated in  FIG. 3 . For example, the valve  42  switches the connection state between them to a state in which the flow path  33  and the flow path  34  are connected to each other or a state in which the flow path  33  and the flow path  34  are not connected to each other. 
     As illustrated in  FIG. 2 , the valve  43  is located among the discharge path  23 , the flow path  36 , and the flow path  37 . The valve  43  includes a connection port connected to the discharge path  23 , a connection port connected to the flow path  36 , and a connection port connected to the flow path  37 . The valve  43  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  43  as illustrated in  FIG. 2  switches the connection state among the discharge path  23 , the flow path  36 , and the flow path  37  under the control of the control unit  94  as illustrated in  FIG. 3 . For example, the valve  43  switches the connection state among them to a state in which the discharge path  23  and the flow path  36  are connected to each other, a state in which the flow path  36  and the flow path  37  are connected to each other, or a state in which the discharge path  23 , the flow path  36 , and the flow path  37  are not connected to each other. 
     As illustrated in  FIG. 2 , the valve  44  is located among the discharge path  24 , the flow path  35 , the flow path  38 , and the flow path  39 . The valve  44  includes a connection port connected to the discharge path  24 , a connection port connected to the flow path  35 , a connection port connected to the flow path  38 , and a connection port connected to the flow path  39 . The valve  44  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  44  as illustrated in  FIG. 2  switches the connection state among the discharge path  24 , the flow path  35 , the flow path  38 , and the flow path  39  under the control of the control unit  94  as illustrated in  FIG. 3 . For example, the valve  44  switches the connection state among them to a state in which the discharge path  24  and the flow path  38  are connected to each other, a state in which the flow path  38  and the flow path  39  are connected to each other, or a state in which the flow path  35  and the flow path  38  are connected to each other. Alternatively, the valve  44  switches the connection state to a state in which the discharge path  24 , the flow path  35 , the flow path  38 , and the flow path  39  are not connected to each other. 
     As illustrated in  FIG. 2 , the supply unit  50  is attached to the flow path  30 . The supply unit  50  is capable of supplying the sample gas from the inflow path  20  to the concentration tank  60  under the control of the control unit  94  as illustrated in  FIG. 3 . Further, the supply unit  50  is capable of supplying the purge gas from the inflow path  21  to the storage tank  70  under the control of the control unit  94  as illustrated in  FIG. 3 . The arrow illustrated in the supply unit  50  indicates the direction in which the supply unit  50  sends a gas. The supply unit  50  may be constituted by a pump such as a piezoelectric pump or a motor pump. However, the supply unit  50  may be constituted by any component capable of supplying the sample gas from the inflow path  20  to the concentration tank  60 . 
     As illustrated in  FIG. 2 , the inlet portion of the concentration tank  60  is connected to the flow path  32 . The outlet portion of the concentration tank  60  is connected to the flow path  36 . The concentration tank  60  is supplied with the sample gas flowing in from the inflow path  20  through the flow paths  30 ,  31 , and  32 . In the concentration tank  60 , the sample gas is concentrated by processing described below. In this embodiment, the term “concentrating the sample gas” refers to increasing the concentration of a gas to be detected contained in the sample gas. An example of the gas to be detected will be described below. The sample gas concentrated in the concentration tank  60  is supplied to the chamber  80  through the flow paths  36  and  37 . 
     The concentration tank  60  may be formed by a container or the like having a rectangular parallelepiped shape, a cylindrical shape, a bag shape, or a shape such that it fits in a gap between various components housed inside the housing  10 . The concentration tank  60  includes an adsorbent  61 , support members  62  and  63 , and heaters  64 . 
     As illustrated in  FIG. 2 , the adsorbent  61  is placed in the concentration tank  60 . The adsorbent  61  may contain any material corresponding to the use of the gas detection system  1 . The adsorbent  61  may contain, for example, at least any one of activated carbon, silica gel, zeolite, or molecular sieve. The adsorbent  61  may be of a plurality of types or may contain a porous material. 
     The adsorbent  61  adsorbs the gas to be detected contained in the sample gas. When the sample gas is a gas generated from feces, examples of the gas to be detected include methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, and trimethylamine. The gas to be detected is, for example, a gas species that is contained in the odor of feces and is not contained in substances other than feces (such as flush water and urine) present in the toilet bowl  2 A. When the sample gas is a gas generated from feces, examples of the adsorbent  61  include activated carbon and molecular sieve. However, the combination of them may be appropriately changed according to the polarity of gas molecules to be adsorbed. 
     In response to the adsorbent  61  reaching a predetermined temperature by being heated by the heaters  64 , the gas to be detected, which is adsorbed by the adsorbent  61 , can be desorbed from the adsorbent  61 . The desorption of the gas to be detected from the adsorbent  61  increases the concentration of the gas to be detected in the concentration tank  60 . That is, the sample gas is concentrated. Typically, a gas can be desorbed from the adsorbent  61  within a predetermined temperature range. In this embodiment, the term “desorption temperature of a gas” refers to a temperature at which the amount of the gas desorbed from the adsorbent  61  reaches a peak within a predetermined temperature range in which the gas can be desorbed from the adsorbent  61 . 
       FIG. 4  is a schematic graph of the concentration of a gas desorbed from the adsorbent  61  adsorbing a predetermined gas, which is detected with a change in the temperature of the adsorbent  61 . In  FIG. 4 , the horizontal axis represents temperature. In  FIG. 4 , the vertical axis represents the concentration of the gas desorbed from the adsorbent  61 . The predetermined gas includes methyl mercaptan and water. Water can be desorbed from the adsorbent  61  in a predetermined temperature range including a temperature t 1 . The concentration (amount) of water desorbed from the adsorbent  61  reaches a peak at the temperature t 1 . Thus, the desorption temperature of water is the temperature t 1 . Methyl mercaptan can be desorbed from the adsorbent  61  in a predetermined temperature range including a temperature t 2 . The concentration (amount) of methyl mercaptan desorbed from the adsorbent  61  reaches a peak at the temperature t 2 . Thus, the desorption temperature of methyl mercaptan is the temperature t 2 . 
     The adsorbent  61  as illustrated in  FIG. 2  may adsorb a gas not to be detected contained in the sample gas. The gas not to be detected is also referred to as “noise gas”. When the sample gas is a gas generated from feces, examples of the gas not to be detected include ammonia and water. A gas may have a different desorption temperature depending on the type of the gas. Accordingly, the desorption temperature of the gas to be detected and the desorption temperature of the gas not to be detected may be different. For example, in  FIG. 4 , when the sample gas is a gas generated from feces, the gas to be detected is methyl mercaptan. Also, the gas not to be detected is water. As illustrated in  FIG. 4 , the temperature t 1 , which is the desorption temperature of water, is different from the temperature t 2 , which is the desorption temperature of methylcaptan. In this embodiment, the difference in desorption temperature between gases depending on the types of the gases is utilized to exclude the gas not to be detected contained in the sample gas from the sample gas by processing described below. The gas not to be detected, which is excluded from the sample gas, is discharged to the outside through the discharge path  23 . 
     The support member  62  as illustrated in  FIG. 2  supports the adsorbent  61  near the inlet portion of the concentration tank  60 . The support member  62  may be in powder or fiber form containing glass or fluorine resin. 
     The support member  63  as illustrated in  FIG. 2  supports the adsorbent  61  near the outlet portion of the concentration tank  60 . The support member  63  may be in powder or fiber form containing glass or fluorine resin. 
     The heaters  64  as illustrated in  FIG. 2  are capable of heating the adsorbent  61 . For example, the heaters  64  are energized under the control of the control unit  94  as illustrated in  FIG. 3  to heat the adsorbent  61 . The heaters  64  are disposed outside the concentration tank  60 . The heaters  64  may surround the outer sides of the concentration tank  60 . The heaters  64  may be resistance heaters, rubber heaters, or the like. 
     As illustrated in  FIG. 2 , the inlet portion of the storage tank  70  is connected to the flow path  34 . The outlet portion of the storage tank  70  is connected to the flow path  38 . The storage tank  70  is supplied with the purge gas flowing in from the inflow path  21  through the flow paths  30 ,  33 , and  34 . The storage tank  70  stores the supplied purge gas. The purge gas stored in the storage tank  70  is supplied to the chamber  80  through the flow paths  38  and  39 . The purge gas stored in the storage tank  70  is further supplied to the concentration tank  60  through the flow paths  38 ,  35 , and  32 . 
     The storage tank  70  may be formed by a container or the like having a rectangular parallelepiped shape, a cylindrical shape, a bag shape, or a shape such that it fits in a gap between various components housed inside the housing  10 . The storage tank  70  may have a larger capacity than the concentration tank  60 . The storage tank  70  includes an adsorbent  71  and support members  72  and  73 . 
     As illustrated in  FIG. 2 , the adsorbent  71  is placed in the storage tank  70 . The adsorbent  71  may contain any material corresponding to the use of the gas detection system  1 . The adsorbent  71  may contain, for example, at least any one of activated carbon, silica gel, zeolite, or molecular sieve. The adsorbent  71  may be of a plurality of types or may contain a porous material. 
     The adsorbent  71  may include an agent that adsorbs a gas to be detected contained in the purge gas. When the air in the toilet room is a purge gas, the purge gas may contain a gas to be detected. Since the adsorbent  71  adsorbs the gas to be detected contained in the purge gas, the purge gas in the storage tank  70  can be purified. When the sample gas is a gas generated from feces, examples of the adsorbent  71  that adsorbs the gas to be detected include activated carbon and molecular sieve. However, the combination of them may be appropriately changed according to the polarity of gas molecules to be adsorbed. 
     The adsorbent  71  may include an agent that adsorbs a gas not to be detected contained in the purge gas. When the air in the toilet room is a purge gas, the purge gas may contain a gas not to be detected. Since the adsorbent  71  adsorbs the gas not to be detected contained in the purge gas, the purge gas in the storage tank  70  can be purified. When the sample gas is a gas generated from feces, examples of the adsorbent  71  that adsorbs the gas not to be detected include silica gel and zeolite. However, the combination of them may be appropriately changed according to the polarity of gas molecules to be adsorbed. 
     The support member  72  supports the adsorbent  71  near the inlet portion of the storage tank  70 . The support member  72  may be in powder or fiber form containing glass or fluorine resin. 
     The support member  73  supports the adsorbent  71  near the outlet portion of the storage tank  70 . The support member  73  may be in powder or fiber form containing glass or fluorine resin. 
     As illustrated in  FIG. 2 , the chamber  80  includes therein a sensor unit  81 . The chamber  80  may include a plurality of sensor units  81 . The chamber  80  may be divided into a plurality of chambers. The sensor units  81  may be disposed in the resulting plurality of chambers  80 . The plurality of chambers  80  may be connected to each other. The chamber  80  is connected to the flow path  37 . The chamber  80  is supplied with the sample gas from the flow path  37 . The chamber  80  is further connected to the flow path  39 . The chamber  80  is supplied with the purge gas from the flow path  39 . The chamber  80  is further connected to the discharge path  22 . The chamber  80  discharges the sample gas and the purge gas, which have been subjected to detection processing, from the discharge path  22 . 
     As illustrated in  FIG. 2 , the sensor unit  81  is arranged in the chamber  80 . The sensor unit  81  outputs a signal corresponding to the concentration of a specific gas to the control unit  94 . The sensor unit  81  may include any sensor such as a semiconductor sensor, a contact combustion sensor, or a solid electrolyte sensor. The sensor unit  81  will be described hereinafter as being configured to output a voltage corresponding to the concentration of the specific gas to the control unit  94  as the signal corresponding to the concentration of the specific gas. However, the signal corresponding to the specific gas, which is output from the sensor unit  81 , is not limited to the voltage corresponding to the concentration of the specific gas. For example, the sensor unit  81  may output a current corresponding to the concentration of the specific gas to the control unit  94  as the signal corresponding to the concentration of the specific gas. The specific gas contains a specific gas to be detected and a specific gas not to be detected. When the sample gas is a gas generated from feces, examples of the specific gas to be detected include methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, and trimethylamine. When the sample gas is a gas generated from feces, examples of the specific gas not to be detected include ammonia and water. Each of the plurality of sensor units  81  can output a voltage corresponding to the concentration of at least any one of these gases to the control unit  94 . 
     The circuit board  90  as illustrated in  FIG. 3  has mounted therein wiring through which an electrical signal propagates, the storage unit  91 , the communication unit  92 , the control unit  94 , and the like. 
     The storage unit  91  as illustrated in  FIG. 3  is constituted by, for example, a semiconductor memory, a magnetic memory, or the like. The storage unit  91  stores various kinds of information and a program for operating the gas detection system  1 . The storage unit  91  may function as a work memory. 
     The communication unit  92  as illustrated in  FIG. 3  is capable of communicating with the electronic device  3  as illustrated in  FIG. 1 . The communication unit  92  may be capable of communicating with an external server. The communication method used when the communication unit  92  communicates with the electronic device  3  and the external server may be a short-range wireless communication standard, a wireless communication standard for connecting to a mobile phone network, or a wired communication standard. The short-range wireless communication standard may include, for example, WiFi (registered trademark), Bluetooth (registered trademark), infrared, NFC (Near Field Communication), and the like. The wireless communication standard for connecting to a mobile phone network may include, for example, LTE (Long Term Evolution), a fourth generation or higher mobile communication system, or the like. Alternatively, the communication method used when the communication unit  92  communicates with the electronic device  3  and the external server may be, for example, a communication standard such as LPWA (Low Power Wide Area) or LPWAN (Low Power Wide Area Network). 
     The sensor unit  93  as illustrated in  FIG. 3  may include at least any one of an image camera, a personal identification switch, an infrared sensor, a pressure sensor, or the like. The sensor unit  93  outputs a detection result to the control unit  94 . 
     For example, when the sensor unit  93  includes an infrared sensor, the sensor unit  93  detects reflected light from an object irradiated with infrared radiation from the infrared sensor, thereby being able to detect that the subject has entered the toilet room. The sensor unit  93  outputs, as a detection result, a signal indicating that the subject has entered the toilet room to the control unit  94 . 
     For example, when the sensor unit  93  includes a pressure sensor, the sensor unit  93  detects a pressure applied to the toilet seat  2 B as illustrated in  FIG. 1 , thereby being able to detect that the subject has sat on the toilet seat  2 B. The sensor unit  93  outputs, as a detection result, a signal indicating that the subject has sat on the toilet seat  2 B to the control unit  94 . 
     For example, when the sensor unit  93  includes a pressure sensor, the sensor unit  93  detects a reduction in the pressure applied to the toilet seat  2 B as illustrated in  FIG. 1 , thereby being able to detect that the subject has risen from the toilet seat  2 B. The sensor unit  93  outputs, as a detection result, a signal indicating that the subject has risen from the toilet seat  2 B to the control unit  94 . 
     For example, when the sensor unit  93  includes an image camera, a personal identification switch, and the like, the sensor unit  93  collects data, such as a face image, the sitting height, and the weight. The sensor unit  93  identifies and detects a person from the collected data. The sensor unit  93  outputs, as a detection result, a signal indicating the identified person to the control unit  94 . 
     For example, when the sensor unit  93  includes a personal identification switch or the like, the sensor unit  93  identifies (detects) a person in response to an operation of the personal identification switch. In this case, personal information may be registered (stored) in the storage unit  91  in advance. The sensor unit  93  outputs, as a detection result, a signal indicating the identified person to the control unit  94 . 
     The control unit  94  as illustrated in  FIG. 3  includes one or more processors. The one or more processors may include at least any one of a general-purpose processor that reads a specific program to execute a specific function, or a dedicated processor dedicated to a specific process. The dedicated processor may include an application specific IC (ASIC; Application Specific Integrated Circuit). The one or more processors may include a programmable logic device (PLD). The PLD may include an FPGA. (Field-Programmable Gate Array). The control unit  94  may include at least any one of an SoC (System-on-a-chip) or an SiP (System-in-a-Package) with which the one or more processors cooperate. 
     &lt;Purge Gas Storage Process&gt; 
     The control unit  94  can detect that the subject has risen from the toilet seat  2 B on the basis of the detection result of the sensor unit  93 . The control unit  94  performs control so that the air in the toilet room flows into the inflow path  21  as a purge gas after a predetermined first set time period has elapsed since it was detected that the subject rose from the toilet seat  2 B. The control unit  94  performs control so that the purge gas flowing in from the inflow path  21  is stored in the storage tank  70 . The first set time period may be appropriately set in consideration of the time period taken to replace the air in the toilet room with air outside the toilet room by using a ventilation fan or the like in the toilet room after the subject exits the toilet room. 
     For example, the control unit  94  causes the valve  40  as illustrated in  FIG. 2  to connect the inflow path  21  and the flow path  30  to each other, and causes the valve  42  as illustrated in  FIG. 2  to connect the flow path  33  and the flow path  34  to each other. Further, the control unit  94  causes the valve  44  as illustrated in  FIG. 2  to connect the flow path  38  and the discharge path  24  to each other. In addition, the control unit  94  controls the supply unit  50  to generate a flow of gas from the inflow path  21  toward the discharge path  24  through the flow paths  30 ,  33 , and  34 , the storage tank  70 , and the flow path  38 . As a result of generation of the flow of gas, the air in the toilet room flows into the inflow path  21  as a purge gas. The purge gas flowing in from the inflow path  21  is supplied to the storage tank  70  through the flow paths  30 ,  33 , and  34 . Since the purge gas is supplied to the storage tank  70 , the residual gas in the storage tank  70  is pushed out to the flow path  38  by the purge gas and discharged from the discharge path  24 . The control unit  94  stops the supply unit  50  at a point in time when a predetermined second set time period elapses after the purge gas starts to flow into the inflow path  21 . Further, the control unit  94  causes the valve  40  not to connect the inflow path  21  and the flow path  30  to each other, and causes the valve  42  not to connect the flow path  33  and the flow path  34  to each other. In addition, the control unit  94  causes the valve  44  not to connect the flow path  38  and the discharge path  24  to each other. With this configuration, the purge gas from the inflow path  21  is stored in the storage tank  70 . The second set time period may be appropriately set in consideration of the capacity of the storage tank  70  and the like. The purge gas stored in the storage tank  70  can come into contact with the adsorbent  71  in the storage tank  70 . Since the purge gas comes into contact with the adsorbent  71 , the gas to be detected and the gas not to be detected contained in the purge gas can be adsorbed by the adsorbent  71 . Since the gas to be detected and the gas not to be detected contained in the purge gas are adsorbed by the adsorbent  71 , the purge gas in the storage tank  70  can be purified. 
     &lt;Sample Gas Storage and Concentration Process&gt; 
     The control unit  94  as illustrated in  FIG. 3  can detect that the subject has sat on the toilet seat  2 B on the basis of the detection result of the sensor unit  93 . The control unit  94  performs control so that a gas generated from feces discharged into the toilet bowl  2 A flows into the inflow path  20  as a sample gas after a predetermined third set time period has elapsed since it was detected that the subject sat on the toilet seat  2 B. The control unit  94  performs control so that the sample gas flowing in from the inflow path  20  passes through the concentration tank  60 . The third set time period may be appropriately set in consideration of the time period taken until the subject defecates after the subject sits on the toilet seat  2 B. 
     For example, the control unit  94  causes the valve  40  as illustrated in  FIG. 2  to connect the inflow path  20  and the flow path  30  to each other, and causes the valve  41  to connect the flow path  31  and the flow path  32  to each other. Further, the control unit  94  causes the valve  43  as illustrated in  FIG. 2  to connect the flow path  36  and the discharge path  23  to each other. In addition, the control unit  94  controls the supply unit  50  as illustrated in  FIG. 2  to generate a flow of gas from the inflow path  20  toward the discharge path  23  through the flow paths  30 ,  31 , and  32 , the concentration tank  60 , and the flow path  36 . As a result of generation of the flow of gas, the sample gas flowing in from the inflow path  20  passes through the concentration tank  60 . 
     The control unit  94  as illustrated in  FIG. 3  performs control so that the sample gas passes through the concentration tank  60  to cause the adsorbent  61  to adsorb a detection target gas contained in the sample gas. For example, the control unit  94  may perform control so that the sample gas passes through the concentration tank  60  for a predetermined first time period. The first time period may be appropriately set in consideration of the amount of the gas to be detected that can be adsorbed by the adsorbent  61 . The control unit  94  may further control the supply unit  50  so that the flow rate of the sample gas passing through the inside of the concentration tank  60  is a first flow rate. The first flow rate may be appropriately set in consideration of the volumetric capacity of the concentration tank  60 , the area of the adsorbent  61 , or the like. Further, the control unit  94  may maintain the heaters  64  in a non-driven state while the sample gas passes through the inside of the concentration tank  60 . Since the heaters  64  are maintained in the non-driven state, the temperature of the adsorbent  61  can be room temperature. The control unit  94  may estimate the flow rate of the sample gas from at least any one of a driving voltage, a frequency, or the like of a pump or the like constituting the supply unit  50 . The gas detection system  1  may be provided with a flow rate sensor that detects the flow rate of the sample gas. In this configuration, the flow rate sensor outputs a detection signal indicating the flow rate of the sample gas to the control unit  94 . The control unit  94  detects the flow rate of the sample gas on the basis of the detection signal output from the flow rate sensor. The control unit  94  may also detect the flow rate of the purge gas in a manner that is the same as or similar to that of the sample gas. 
       FIG. 5  is a timing chart of an example operation of the gas detection system  1  illustrated in  FIG. 1 . The upper part of  FIG. 5  illustrates a change in the temperature of the adsorbent  61  with time. The central part of  FIG. 5  illustrates changes in the flow rates of gases in the concentration tank  60  with time. The lower part of  FIG. 5  illustrates a change in the concentration of the gas to be detected near the outlet portion of the concentration tank  60  with time. The control unit  94  may estimate the temperature of the adsorbent  61  from the current of the heaters  64  or the like. A temperature sensor may be disposed in the vicinity of the adsorbent  61 . In this configuration, the temperature sensor outputs a signal indicating the temperature in the vicinity of the adsorbent  61  to the control unit  94 . The control unit  94  may acquire the temperature of the adsorbent  61  on the basis of the detection signal output from the temperature sensor. 
     Time  50  as illustrated in  FIG. 5  is a point in time at which the third set time period elapses after the control unit  94  detects that the subject has sat on the toilet seat  2 B. At the time S 0 , the control unit  94  performs control so that a gas generated from feces discharged into the toilet bowl  2 A flows into the inflow path  20  as a sample gas. The control unit  94  further performs control so that the sample gas passes through the concentration tank  60 . In this case, the control unit  94  controls the supply unit  50  so that the flow rate of the sample gas passing through the concentration tank  60  is a first flow rate F 1 . Further, the control unit  94  maintains the heaters  64  in the non-driven state. Since the heaters  64  are maintained in the non-driven state, the adsorbent  61  is maintained at room temperature T 0 . The control unit  94  performs control so that the sample gas passes through the concentration tank  60  for the first time period from the time S 0  to time S 1 . 
     At the time S 0  as illustrated in  FIG. 5 , the sample gas starts to pass through the concentration tank  60 . Since the sample gas starts to pass through the concentration tank  60 , the adsorbent  61  starts to adsorb the gas to be detected contained in the sample gas. The sample gas in which the gas to be detected is adsorbed by the adsorbent  61  while passing through the concentration tank  60  is discharged from the discharge path  23 . If the sample gas contains a gas not to be detected, the gas not to be detected can also be adsorbed by the adsorbent  61  after the time S 0 . 
     The control unit  94  as illustrated in  FIG. 3  stops the passage of the sample gas to the concentration tank  60  at a point in time when the first time period elapses after the sample gas starts to pass through the concentration tank  60 . For example, the control unit  94  stops the supply unit  50  at a point in time when the first time period elapses. Further, the control unit  94  causes the valve  41  not to connect the flow path  31  and the flow path  32  to each other, and causes the valve  43  not to connect the flow path  36  and the discharge path  23  to each other. At the point in time when the first time period elapses, the control unit  94  brings the heaters  64  into the driven state to increase the temperature of the adsorbent  61 . 
     The time S 1  as illustrated in  FIG. 5  is the point in time when the first time period elapses after the sample gas starts to pass through the concentration tank  60 . At the time S 1 , the control unit  94  stops the passage of the sample gas to the concentration tank  60 . Stopping the passage of the sample gas to the concentration tank  60  reduces the flow rate of the gas in the concentration tank  60  to  0 . At the time S 1 , furthermore, the control unit  94  brings the heaters  64  into the driven state. Since the heaters  64  are brought into the driven state at the time S 1 , the temperature of the adsorbent  61  increases after the time S 1 . 
     In response to the temperature of the adsorbent  61  as illustrated in  FIG. 2  reaching a temperature T 1 , for example, the control unit  94  as illustrated in  FIG. 3  performs control so that the temperature of the adsorbent  61  is maintained as the temperature T 1  for a predetermined second time period. The second time period may be appropriately set in consideration of the amount of the gas not to be detected that can be contained in the sample gas. The temperature T 1  may be the desorption temperature of the gas not to be detected that can be contained in the sample gas. For example, when the gas not to be detected is water, the temperature T 1  can be the temperature t 1  as illustrated in  FIG. 4 . Since the adsorbent  61  is maintained at the temperature T 1 , the gas not to be detected can be desorbed from the adsorbent  61 . The control unit  94  performs control so that the purge gas passes through the concentration tank  60  while performing control so that the temperature of the adsorbent  61  is maintained as the temperature T 1 . The control unit  94  performs control so that the purge gas that has passed through the concentration tank  60  is discharged from the discharge path  23 . With this configuration, the gas not to be detected desorbed from the adsorbent  61  can be discharged from the discharge path  23  together with the purge gas. That is, the gas not to be detected desorbed from the adsorbent  61  can be removed from the concentration tank  60 . The control unit  94  may control the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the first flow rate. 
     For example, in response to the temperature of the adsorbent  61  as illustrated in  FIG. 2  reaching the temperature T 1 , the control unit  94  causes the valve  40  to connect the inflow path  21  and the flow path  30  to each other, and causes the valve  42  to connect the flow path  33  and the flow path  34  to each other. The control unit  94  further causes the valve  44  to connect the flow path  38  and the flow path  35  to each other, causes the valve  41  to connect the flow path  35  and the flow path  32  to each other, and causes the valve  43  to connect the flow path  36  and the discharge path  23  to each other. In addition, the control unit  94  controls the supply unit  50  to generate a flow of gas from the inflow path  21  toward the discharge path  23  through the flow paths  30 ,  33 , and  34 , the storage tank  70 , and the flow paths  38 ,  35 , and  32 , the concentration tank  60 , and the flow path  36 . As a result of generation of the flow of the gas, the purge gas passes through the concentration tank  60  and is discharged from the discharge path  23 . Since the purge gas passes through the concentration tank  60 , the gas not to be detected desorbed from the adsorbent  61  is removed from the concentration tank  60  and discharged from the discharge path  23 . 
     At time S 2  as illustrated in  FIG. 5 , the temperature of the adsorbent  61  reaches the temperature T 1 . The control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  is maintained as the temperature T 1  for the second time period from the time S 2  to time S 3 . Since the temperature of the adsorbent  61  is maintained as the temperature T 1  after the time S 2 , the gas not to be detected can be desorbed from the adsorbent  61 . Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is discharged from the discharge path  23  at the time S 2 . Since the purge gas passes through the concentration tank  60  and is discharged from the discharge path  23 , the gas not to be detected desorbed from the adsorbent  61  can be removed from the concentration tank  60  and discharged from the discharge path  23 . The control unit  94  may control the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the first flow rate F 1 . 
     At a point in time when the second time period elapses after the temperature of the adsorbent  61  as illustrated in  FIG. 2  reaches the temperature T 1 , the control unit  94  as illustrated in  FIG. 3  controls the heaters  64  so that the temperature of the adsorbent  61  increases. The control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  increases to a temperature T 2 . The temperature T 2  may be the desorption temperature of the gas to be detected contained in the sample gas. For example, when the gas to be detected is methyl mercaptan, the temperature T 2  can be the temperature t 2  as illustrated in  FIG. 4 . In response to the temperature of the adsorbent  61  reaching the temperature T 2 , the control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  is maintained as the temperature T 2 . 
     The time S 3  as illustrated in  FIG. 5  is a point in time at which the second time period elapses. At the time S 3 , the control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  increases. At time S 5 , the temperature of the adsorbent  61  reaches the temperature T 2 . The control unit  94  performs control so that the temperature of the adsorbent  61  is maintained as the temperature T 2  after the time S 5 . 
     In the present disclosure, the control unit  94  as illustrated in  FIG. 3  stops the passage of the purge gas to the concentration tank  60  from a first point in time to a second point in time later than the first point in time. The first point in time in the present disclosure is a point in time before or at which the temperature of the adsorbent  61  reaches the temperature T 2 . In the first embodiment, the first point in time is a point in time at which the temperature of the adsorbent  61  reaches a temperature T 3 . The temperature T 3  may be set on the basis of a temperature at which the gas to be detected starts to be desorbed from the adsorbent  61 . For example, when the gas to be detected is methyl mercaptan, the temperature T 3  can be a temperature t 3  as illustrated in  FIG. 4 . In the first embodiment, the second point in time is a point in time at which, for example, a predetermined third time period elapses after the temperature of the adsorbent  61  reaches the temperature T 2 . In response to the temperature of the adsorbent  61  reaching the temperature T 3 , the gas to be detected starts to be desorbed from the adsorbent  61  inside the concentration tank  60 . As a result of stopping the passage of the purge gas to the concentration tank  60  for a time period from the first point in time to the second point in time, a large amount of the gas to be detected that have been desorbed from the adsorbent  61  can remain in the concentration tank  60 . Since a large amount of the gas to be detected remains in the concentration tank  60 , the concentration of the gas to be detected in the concentration tank  60  can be increased. That is, the sample gas can further be concentrated in the concentration tank  60 . The third time period may be appropriately set in consideration of the amount of detection target gas that can be adsorbed by the adsorbent  61 . 
     For example, the control unit  94  stops the supply unit  50  in response to the temperature of the adsorbent  61  as illustrated in  FIG. 2  reaching the temperature T 3 . Further, the control unit  94  causes the valve  41  not to connect the flow path  31 , the flow path  32 , and the flow path  35  to each other, and causes the valve  43  not to connect the discharge path  23 , the flow path  36 , and the flow path  37  to each other. With this configuration, the passage of the purge gas to the concentration tank  60  is stopped. 
     The control unit  94  as illustrated in  FIG. 3  performs control so that the purge gas passes through the concentration tank  60  after the second point in time. In this embodiment, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  from the second point in time, that is, from the point in time at which the third time period elapses after the temperature of the adsorbent  61  reaches the temperature T 2 . The control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  together with the gas to be detected in the concentration tank  60 . With this configuration, the gas to be detected having an increased concentration in the concentration tank  60 , that is, the more concentrated sample gas in the concentration tank  60 , can be transported to the sensor unit  81  in the chamber  80  by the purge gas. The purge gas is also referred to as a “carrier gas” when used in gas transportation applications. 
     For example, at the second point in time, the control unit  94  causes the valve  40  as illustrated in  FIG. 2  to connect the inflow path  21  and the flow path  30  to each other, and causes the valve  42  to connect the flow path  33  and the flow path  34  to each other. The control unit  94  further causes the valve  44  to connect the flow path  38  and the flow path  35  to each other, causes the valve  41  to connect the flow path  35  and the flow path  32  to each other, and causes the valve  43  to connect the flow path  36  and the flow path  37  to each other. In addition, the control unit  94  controls the supply unit  50  to generate a flow of gas from the inflow path  21  toward the chamber  80  through the flow paths  30 ,  33 , and  34 , the storage tank  70 , and the flow paths  38 ,  35 , and  32 , the concentration tank  60 , and the flow paths  36  and  37 . As a result of generation of the flow of gas, the purge gas passes through the concentration tank  60  and transports the gas to be detected in the concentration tank  60  to the chamber  80 . 
     At time S 4  as illustrated in  FIG. 5 , the temperature of the adsorbent  61  reaches the temperature T 3 . That is, the time S 4  corresponds to the first point in time. At the time S 5 , the temperature of the adsorbent  61  reaches the temperature T 2 . The time period from the time S 5  to time S 6  is the third time period. That is, the time S 6  corresponds to the second point in time. The control unit  94  stops the passage of the purge gas to the concentration tank  60  from the time S 4  to the time S 6 . At the time S 6 , the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the chamber  80  together with the gas to be detected in the concentration tank  60 . The control unit  94  may perform control so that the purge gas passes through the concentration tank  60  for a time period from the time S 6  to time S 8 . The time period from the time S 6  to the time S 8  may be appropriately set in accordance with to the volumetric capacity of the storage tank  70  and the like. 
     The purge gas supplied from the inlet portion of the concentration tank  60  can gradually push out the gas to be detected in the concentration tank  60  toward the outlet portion of the concentration tank  60 . Accordingly, the concentration of the gas to be detected in the vicinity of the outlet portion in the concentration tank  60  may become maximum after a certain time period has elapsed since the start of supply of the purge gas to the concentration tank  60 , depending on the type of the gas to be detected. In the example as illustrated in  FIG. 5 , at time S 7 , the concentration of the gas to be detected in the vicinity of the outlet portion in the concentration tank  60  becomes a maximum value C 1 . That is, at the beginning when the purge gas starts to pass through the concentration tank  60 , the concentration of the detection target gas that is transported by the purge gas may not be so high. 
     Accordingly, the control unit  94  may exhaust the purge gas that has passed through the concentration tank  60  from, for example, the discharge path  23  without supplying the purge gas to the sensor unit  81  until a predetermined fourth time period elapses after the purge gas starts to pass through the concentration tank  60 . Further, the control unit  94  may supply the purge gas that has passed through the concentration tank  60  to the sensor unit  81  after the fourth time period has elapsed. In this case, the control unit  94  may cause the valve  43  to connect the flow path  36  and the discharge path  23  to each other until the fourth time period elapses after the purge gas starts to pass through the concentration tank  60 , thereby discharging the purge gas that has passed through the concentration tank  60  from the discharge path  23 . Further, after the fourth time period has elapsed, the control unit  94  may cause the valve  43  to connect the flow path  36  and the flow path  37  to each other to supply the purge gas that has passed through the concentration tank  60  to the sensor unit  81 . The fourth time period may be appropriately set in consideration of the length, cross-sectional area, and the like of the concentration tank  60 . The fourth time period may be about a time period from the time S 6  to time S 6   a  as illustrated in  FIG. 5 . The time S 6   a  is a time later than the time S 6  and is a time immediately before the time S 7 . Further, the control unit  94  may control the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the second flow rate. In  FIG. 5 , the control unit  94  may control the supply unit  50  so that the flow rate of the purge gas is a second flow rate F 2  after the time S 6 . The second flow rate is smaller than the first flow rate. The second flow rate may be appropriately determined in consideration of the volumetric capacity of the concentration tank  60 , the specifications of the valve  43 , and the like. Since the flow rate of the purge gas passing through the inside of the concentration tank  60  is set to the second flow rate smaller than the first flow rate, the control unit  94  can cause the valve  43  to smoothly switch the connection destination of the flow path  36  from the discharge path  23  to the flow path  37  after the lapse of the fourth time period. 
     &lt;Process for Detecting Type and Concentration of Gas&gt; 
     The control unit  94  performs control so that the purge gas stored in the storage tank  70  is supplied to the sensor unit  81  in the chamber  80 . For example, the control unit  94  causes the valve  40  to connect the inflow path  21  and the flow path  30  to each other, causes the valve  42  to connect the flow path  33  and the flow path  34  to each other, and causes the valve  44  to connect the flow path  38  and the flow path  39  to each other. Further, the control unit  94  controls the supply unit  50  to generate a flow of gas from the inflow path  21  toward the chamber  80  through the flow paths  30 ,  33 , and  34 , the storage tank  70 , and the flow paths  38  and  39 . As a result of generation of the flow of gas, the purge gas stored in the storage tank  70  is supplied to the sensor unit  81  in the chamber  80 . 
     The control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  together with the gas to be detected in the concentration tank  60  in the way described in the &lt;Sample Gas Storage and Concentration Process&gt; section described above. 
     The control unit  94  performs control so that the purge gas stored in the storage tank  70  and the sample gas concentrated in the concentration tank  60  are alternately supplied to the sensor unit  81  in the chamber  80 . The control unit  94  alternately supplies the purge gas and the concentrated sample gas to the chamber  80  to acquire a voltage waveform from the sensor unit  81  in the chamber  80 . The control unit  94  detects the type and concentration of a gas contained in the sample gas by, for example, machine learning for the acquired voltage waveform. The control unit  94  may transmit the detected type and concentration of the gas to the electronic device  3  via the communication unit  92  as a detection result. 
     [Operation of Gas Detection System] 
       FIG. 6  is a flowchart of an example operation of the gas detection system  1  illustrated in  FIG. 1  during gas concentration. The control unit  94  may start a process as illustrated in  FIG. 6  after the first set time period elapses after it is detected that the subject has risen from the toilet seat  2 B on the basis of the detection result of the sensor unit  93 . 
     The control unit  94  performs control so that the air in the toilet room flows into the inflow path  21  as a purge gas (step S 110 ). The control unit  94  performs control so that the purge gas flowing into the inflow path  21  is stored in the storage tank  70  (step S 111 ). 
     The control unit  94  performs control so that a gas generated from feces discharged into the toilet bowl  2 A flows into the inflow path  20  as a sample gas after the third set time period has elapsed since it was detected that the subject sat on the toilet seat  2 B (step S 112 ). The control unit  94  performs control so that the sample gas flowing in from the inflow path  20  passes through the concentration tank  60  for the first time period (step S 113 ). 
     The control unit  94  detects the lapse of the first time period after the sample gas starts to pass through the concentration tank  60  (step S 114 ). The control unit  94  stops the passage of the sample gas to the concentration tank  60  at the point in time at which the first time period elapses (step S 115 ). The control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  increases (step S 116 ). 
     The control unit  94  detects the temperature of the adsorbent  61  reaching the temperature T 1  (step S 117 ). In response to the temperature of the adsorbent  61  reaching the temperature T 1 , the control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  is maintained as the temperature T 1  for the second time period (step S 118 ). The control unit  94  performs control so that the purge gas passes through the concentration tank  60  while performing control so that the temperature of the adsorbent  61  is maintained as the temperature T 1  (step S 119 ). 
     The control unit  94  detects the lapse of the second time period after the temperature of the adsorbent  61  reaches the temperature T 1  (step S 120 ). The control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  increases at the point in time at which the second time period elapses (step S 121 ). 
     The control unit  94  detects the temperature of the adsorbent  61  reaching the temperature T 3  (step S 122 ). In response to the temperature of the adsorbent  61  reaching the temperature T 3 , the control unit  94  stops the passage of the purge gas to the concentration tank  60  (step S 123 ). 
     The control unit  94  detects the temperature of the adsorbent  61  reaching the temperature T 2  (step S 124 ). The control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  is maintained as the temperature T 2  (step S 125 ). 
     The control unit  94  detects the lapse of the third time period after the temperature of the adsorbent  61  reaches the temperature T 2  (step S 135 ). The control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  together with the gas to be detected in the concentration tank  60  at the point in time at which the third time period elapses (step S 127 ). 
     In the processing of step S 113 , the control unit  94  may control the supply unit  50  so that the flow rate of the sample gas passing through the inside of the concentration tank  60  is the first flow rate. In the processing of step S 117 , the control unit  94  may control the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the first flow rate. 
     In the processing of step S 127 , the control unit  94  may exhaust the purge gas that has passed through the concentration tank  60  from, for example, the discharge path  23  without supplying the purge gas to the sensor unit  81  until the fourth time period elapses after the purge gas starts to pass through the concentration tank  60 . Further, the control unit  94  may supply the purge gas that has passed through the concentration tank  60  to the sensor unit  81  after the fourth time period has elapsed. In this case, the control unit  94  may control the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the second flow rate. After the processing of step S 127  ends, the control unit  94  ends the gas concentration process. 
       FIG. 7  is a flowchart of an example operation of the gas detection system  1  illustrated in  FIG. 1  during detection of the type and concentration of a gas. 
     The control unit  94  performs control so that the purge gas stored in the storage tank  70  is supplied to the sensor unit  81  in the chamber  80  (step S 130 ). The control unit  94  executes the process as illustrated in  FIG. 6  to perform control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  together with the gas to be detected in the concentration tank  60  (step S 131 ). 
     The control unit  94  alternately executes the processing of step S 130  and the processing of step S 131  to perform control so that the purge gas in the storage tank  70  and the sample gas in the concentration tank  60  are alternately supplied to the sensor unit  81  in the chamber  80 . 
     The control unit  94  alternately supplies the purge gas and the concentrated sample gas to the chamber  80  to acquire a voltage waveform from the sensor unit  81  in the chamber  80  (step S 132 ). The control unit  94  detects the type and concentration of a gas contained in the sample gas by, for example, machine learning for the acquired voltage waveform (step S 133 ). After the processing of step S 133  ends, the control unit  94  ends the process for detecting the type and concentration of the gas. 
     As described above, in the gas detection system  1  according to the first embodiment, the control unit  94  stops the passage of the purge gas to the concentration tank  60  from the first point in time to the second point in time. Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  from the second point in time. With this configuration, the more concentrated sample gas in the concentration tank  60  can be supplied to the sensor unit  81  in the chamber  80  by the purge gas. Since the more concentrated sample gas is supplied to the sensor unit  81 , the gas to be detected contained in the sample gas can be more reflected in the voltage output from the sensor unit  81 . Since the gas to be detected is more reflected in the voltage output from the sensor unit  81 , the gas detection system  1  can more accurately detect the type and concentration of the gas contained in the sample gas. Accordingly, this embodiment can provide the gas detection system  1  with improved gas detection performance and the like. 
     Second Embodiment 
     A gas detection system according to a second embodiment of the present disclosure will be described hereinafter. The gas detection system according to the second embodiment can adopt a configuration that is the same as or similar to that of the gas detection system  1  according to the first embodiment. The following mainly describes differences from the first embodiment with reference to  FIGS. 1 to 3 . 
     As described above in the first embodiment, the control unit  94  as illustrated in  FIG. 3  controls the supply unit  50  so that the sample gas passes through the concentration tank  60  as illustrated in  FIG. 2 . In this case, the control unit  94  controls the supply unit  50  so that the flow rate of the sample gas passing through the concentration tank  60  is the first flow rate in a manner that is the same as or similar to that in the first embodiment. 
     As described above in the first embodiment, the control unit  94  as illustrated in  FIG. 3  controls the supply unit  50  so that the purge gas passes through the concentration tank  60  while controlling the heaters  64  to increase the temperature of the adsorbent  61  as illustrated in  FIG. 2 . In this case, the control unit  94  controls the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the first flow rate in a manner that is the same as or similar to that in the first embodiment. 
     As described above in the first embodiment, the control unit  94  as illustrated in  FIG. 3  stops the passage of the purge gas to the concentration tank  60  from the first point in time to the second point in time, and, from the second point in time, performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81 . In this case, in the second embodiment, the control unit  94  controls the supply unit  50  so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is a third flow rate. The third flow rate is larger than the first flow rate. The third flow rate may be appropriately determined in consideration of the volumetric capacity of the concentration tank  60 , a desired detection time period in the gas detection system  1 , and the like. Since the flow rate of the purge gas passing through the inside of the concentration tank  60  is set to the third flow rate larger than the first flow rate, the time taken to supply the sample gas in the concentration tank  60  to the chamber  80  by the purge gas can be shortened. With this configuration, the detection time period in the gas detection system  1  can be shortened. 
     In the following, the first point in time according to the second embodiment will be described as a point in time at which the temperature of the adsorbent  61  reaches the temperature T 3  in a manner that is the same as or similar to that in the first embodiment. The second point in time according to the second embodiment will be described as a point in time at which the third time period elapses after the temperature of the adsorbent  61  reaches the temperature T 2  in a manner that is the same as or similar to that in the first embodiment. The third time period according to the second embodiment may be appropriately set in consideration of the amount of detection target gas that can be adsorbed by the adsorbent  61  in a manner that is the same as or similar to that in the first embodiment. However, the third time period according to the second embodiment may be set independently of the third time period according to the first embodiment. For example, as described above, when the flow rate of the purge gas passing through the inside of the concentration tank  60  is set to the third flow rate, the time taken to supply the sample gas in the concentration tank  60  to the chamber  80  by the purge gas can be shortened. The third time period may be increased as the time taken to supply the sample gas to the chamber  80  is reduced. Increasing the third time period can increase the time for stopping the passage of the purge gas to the concentration tank  60 . Since the time for stopping the passage of the purge gas to the concentration tank  60  is increased, a larger amount of gas to be detected can be desorbed from the adsorbent  61  for a period during which the passage of the purge gas to the concentration tank  60  is stopped. That is, the sample gas can further be concentrated in the concentration tank  60 . Accordingly, a more concentrated sample gas can be supplied to the sensor unit  81 . 
       FIG. 8  is timing chart of an example operation of the gas detection system  1  according to the second embodiment of the present disclosure. The upper part of  FIG. 8  illustrates a change in the temperature of the adsorbent  61  with time. The central part of  FIG. 8  illustrates changes in the flow rates of gases in the concentration tank  60  with time. The lower part of  FIG. 8  illustrates a change in the concentration of the gas to be detected near the outlet portion of the concentration tank  60  with time. 
     From time S 0  to time S 5  as illustrated in  FIG. 8 , the control unit  94  performs control in a manner that is the same as or similar to that from the time S 0  to the time S 5  as illustrated in  FIG. 5 . At time S 4  as illustrated in  FIG. 8 , the temperature of the adsorbent  61  reaches the temperature T 3  in a manner that is the same as or similar to that in  FIG. 5 . That is, the time S 4  as illustrated in  FIG. 8  corresponds to the first point in time in a manner that is the same as or similar to that in  FIG. 5 . At the time S 5  as illustrated in  FIG. 8 , the temperature of the adsorbent  61  reaches the temperature T 2  in a manner that is the same as or similar to that in  FIG. 5 . 
     In  FIG. 8 , a time period from the time S 5  to time S 9  is the third time period. That is, the time S 9  corresponds to the second point in time. The control unit  94  stops the passage of the purge gas to the concentration tank  60  from the time S 4  to the time S 9 . At the time S 9 , the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the chamber  80  together with the gas to be detected in the concentration tank  60 . The control unit  94  performs control so that the flow rate of the purge gas is a third flow rate F 3 . At time S 10 , the concentration of the gas to be detected in the vicinity of the outlet portion in the concentration tank  60  becomes a maximum value C 2 . The control unit  94  may perform control so that the purge gas passes through the concentration tank  60  for a time period from the time S 9  to time S 11 . The time period from the time S 9  to the time S 11  may be appropriately set on the basis of the third flow rate F 3 . 
     As described above, in the gas detection system  1  according to the second embodiment, when performing control so that the purge gas passes through the concentration tank  60  from the second point in time, the control unit  94  performs control so that the flow rate of the purge gas passing through the inside of the concentration tank  60  is the third flow rate. The third flow rate is larger than the first flow rate. With this configuration, in the second embodiment, the detection time period in the gas detection system  1  can be shortened. 
     Other configurations and advantages of the gas detection system  1  according to the second embodiment are the same as or similar or to those of the gas detection system  1  according to the first embodiment. 
     (Modifications of First Embodiment and Second Embodiment) 
     Modifications of the first embodiment and the second embodiment will be described hereinafter. 
     For example, in the first embodiment described above, as illustrated in  FIG. 5 , the control unit  94  has been described as being configured to cause the purge gas to pass through the concentration tank  60  and to be supplied to the sensor unit  81  in the chamber  80  for the time period from the time S 6  to the time S 8 . However, the control of the control unit  94  is not limited to this. For example, the control unit  94  may alternately supply the sample gas in the concentration tank  60  and the purge gas in the storage tank  70  to the sensor unit  81  for the time period from the time S 6  to the time S 8 . In this case, the control unit  94  may detect the type and concentration of a gas contained in the sample gas on the basis of the voltage output from the sensor unit  81  around the time S 7  at which the concentration of the gas to be detected is the maximum value C 1 . This applies to the second embodiment in the same or similar manner. 
     For example, in the first embodiment and the second embodiment described above, the control unit  94  has been described as being configured to perform control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  together with the gas to be detected in the concentration tank  60  from the second point in time. However, in the present disclosure, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  together with the gas to be detected in the concentration tank  60  after the second point in time. For example, the gas detection system  1  may include a buffer tank between the concentration tank  60  and the chamber  80 . In this case, the control unit  94  may perform control so that the purge gas passes through the concentration tank  60  and is stored in the buffer tank from the second point in time. Further, after performing control so that the purge gas passes through the concentration tank  60  and is stored in the buffer tank, the control unit  94  may stop the supply of the purge gas to the concentration tank  60 . Since the supply of the purge gas to the concentration tank  60  is stopped, the gas to be detected desorbed from the adsorbent  61  can have uniform concentration in the buffer tank. In addition, after stopping the supply of the purge gas to the concentration tank  60 , the control unit  94  may perform control so that the sample gas stored in the buffer tank is supplied to the sensor unit  81  in the chamber  80 . With this configuration, the sample gas in which the gas to be detected has uniform concentration can be supplied to the sensor unit  81  in the chamber  80 . 
     For example, in the first embodiment and the second embodiment, the first point in time has been described as a point in time at which the temperature of the adsorbent  61  reaches the temperature T 3 . However, the first point in time is not limited to this. As described above, the first point in time in the present disclosure is a point in time before the temperature of the adsorbent  61  reaches the temperature T 2  or a point in time at which the temperature of the adsorbent  61  reaches the temperature T 2 . In the first embodiment and the second embodiment described above, furthermore, the second point in time has been described as a point in time at which the third time period elapses after the temperature of the adsorbent  61  reaches the temperature T 2 . However, the second point in time is not limited to this. As described above, the second point in time in the present disclosure is a point in time later than the first point in time. Another example of the first point in time and the second point in time will be described with reference to  FIG. 9 . 
       FIG. 9  is a timing chart describing another example of the first point in time and the second point in time in the present disclosure. At time S 3 , the control unit  94  controls the heaters  64  so that the temperature of the adsorbent  61  increases in a manner that is the same as or similar to that in  FIG. 5 . At time S 4 , the temperature of the adsorbent  61  reaches the temperature T 3  in a manner that is the same as or similar to that in  FIG. 5 . At time S 5 , the temperature of the adsorbent  61  reaches the temperature T 2  in a manner that is the same as or similar to that in  FIG. 5 . 
     For example, the first point in time may be a point in time at which the temperature T 3  is reached. That is, the time S 4  as illustrated in  FIG. 9  may correspond to the first point in time. The second point in time may be a point in time at which the temperature of the adsorbent  61  reaches the desorption temperature of the gas to be detected. That is, the time S 5  may correspond to the second point in time. In this case, the control unit  94  stops the passage of the purge gas to the concentration tank  60  for a time period A 1  from the time S 4  to the time S 5  as illustrated in  FIG. 9 . Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  from the time S 5  as illustrated in  FIG. 9 . With this configuration, the time period during which the passage of the purge gas to the concentration tank  60  is stopped can be shorter than that in a case where the purge gas is stopped from the time S 4  to the time S 6  as illustrated in  FIG. 5 , for example. Since the time period during which the passage of the purge gas is stopped is short, the amount of the gas to be detected that is not desorbed from the adsorbent  61  at the time S 5  as illustrated in  FIG. 9 , which is the second point in time, can be larger than the amount of the gas to be detected that is not desorbed from the adsorbent  61  at the time S 6  as illustrated in  FIG. 5 , which is the second point in time. Since the amount of the gas to be detected that is not desorbed from the adsorbent  61  at the second point in time is large, the gas to be detected can be desorbed from the adsorbent  61  even while the purge gas is controlled to pass through the concentration tank  60  from the second point in time. With this configuration, the sample gas in which the gas to be detected has a relatively high concentration can be continuously supplied to the sensor unit  81  for a longer period of time. 
     For example, the first point in time may be a point in time at which the temperature of the adsorbent  61  reaches the temperature T 2 . That is, the time S 5  as illustrated in  FIG. 9  may correspond to the first point in time. The second point in time may be a point in time at which the third time period elapses after the temperature of the adsorbent  61  reaches the temperature T 2 . A time period from the time S 5  to a time S 12  as illustrated in  FIG. 9  may be the third time period. That is, the time S 12  as illustrated in  FIG. 9  may correspond to the second point in time. In this case, the control unit  94  stops the passage of the purge gas to the concentration tank  60  for a time period A 2  from the time S 5  to the time S 12  as illustrated in  FIG. 9 . Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  from the time S 12  as illustrated in  FIG. 9 . With this configuration, the passage of the purge gas to the concentration tank  60  can be stopped after the temperature of the adsorbent  61  reaches the temperature T 2 . Since the passage of the purge gas to the concentration tank  60  is stopped after the temperature of the adsorbent  61  reaches the temperature T 2 , the probability that the gas not to be detected is desorbed from the adsorbent  61  can be reduced while the passage of the purge gas is stopped. Since the probability that the gas not to be detected is desorbed from the adsorbent  61  is reduced, the concentration of the gas to be detected can be increased. 
     For example, the first point in time may be a point in time at which the temperature of the adsorbent  61  exceeds the temperature T 1 , which is the desorption temperature of the detection target gas. That is, the time S 3  as illustrated in  FIG. 9  may correspond to the first point in time. The second point in time may be a point in time at which the third time period elapses after the temperature of the adsorbent  61  reaches the temperature T 2 . The time period from the time S 5  to the time S 12  as illustrated in  FIG. 9  may be the third time period. That is, the time S 12  as illustrated in  FIG. 9  may correspond to the second point in time. In this case, the control unit  94  stops the passage of the purge gas to the concentration tank  60  for a time period A 3  from the time S 3  to the time S 12  as illustrated in  FIG. 9 . Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  from the time S 12  as illustrated in  FIG. 9 . 
     For example, the first point in time may be a point in time at which the temperature of the adsorbent  61  exceeds the temperature T 1 , which is the desorption temperature of the detection target gas. That is, the time S 3  as illustrated in  FIG. 9  may correspond to the first point in time. The second point in time may be a point in time at which the temperature of the adsorbent  61  reaches the temperature T 2 . That is, the time S 5  as illustrated in  FIG. 9  may correspond to the second point in time. In this case, the control unit  94  stops the passage of the purge gas to the concentration tank  60  for a time period A 4  from the time S 3  to the time S 5  as illustrated in  FIG. 9 . Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  from the time S 5  as illustrated in  FIG. 9 . 
     For example, the first point in time may be a point in time at which the temperature of the adsorbent  61  exceeds the temperature T 1 , which is the desorption temperature of the detection target gas. That is, the time S 3  as illustrated in  FIG. 9  may correspond to the first point in time. The second point in time may be a point in time at which the temperature T 3  is reached. That is, the time S 4  as illustrated in  FIG. 9  may correspond to the second point in time. In this case, the control unit  94  stops the passage of the purge gas to the concentration tank  60  for a time period A 5  from the time S 3  to the time S 4  as illustrated in  FIG. 9 . Further, the control unit  94  performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80  from the time S 4  as illustrated in  FIG. 9 . 
     For example, in the first embodiment and the second embodiment described above, as illustrated in  FIG. 3 , the gas detection system  1  has been described as a single device. However, the gas detection system according to the present disclosure is not limited to the single device. The gas detection system according to the present disclosure may include a plurality of independent devices. For example, the first embodiment and the second embodiment described above may adopt a gas detection system  1 A having a configuration as illustrated in  FIG. 10 . 
     As illustrated in  FIG. 10 , the gas detection system  1 A includes a gas detection device  4  and a server device  5 . The gas detection device  4  and the server device  5  are capable of communicating with each other via a network  6 . A portion of the network  6  may be wired or wireless. The gas detection device  4  has a configuration that is the same as or similar to the configuration of the gas detection system  1  as illustrated in  FIG. 2  and  FIG. 3 . The server device  5  includes a storage unit  5 A, a communication unit  5 B, and a control unit  5 C. The control unit  5 C is capable of executing the processes of the control unit  94  as illustrated in  FIG. 3  described above. For example, the control unit  5 C stops the passage of the purge gas to the concentration tank  60  as illustrated in  FIG. 2  from the first point in time to the second point in time, and, after the second point in time, performs control so that the purge gas passes through the concentration tank  60  and is supplied to the sensor unit  81  in the chamber  80 . 
     Third Embodiment 
     As illustrated in  FIG. 11 , a gas detection system  101  is installed in a toilet  102 . The toilet  102  may be, but is not limited to, a flush toilet. The toilet  102  includes a toilet bowl  102 A and a toilet seat  102 B. The gas detection system  101  may be installed in any portion of the toilet  102 . In one example, as illustrated in  FIG. 11 , the gas detection system  101  may be arranged from between the toilet bowl  102 A and the toilet seat  102 B to the outside of the toilet  102 . A portion of the gas detection system  101  may be embedded inside the toilet seat  102 B. The subject can discharge feces into the toilet bowl  102 A. The gas detection system  101  can acquire a gas generated from the feces discharged into the toilet bowl  102 A as a sample gas. The gas detection system  101  can detect the type of a gas contained in the sample gas, the concentration of the gas, and so on. The gas detection system  101  can transmit the detection results and so on to an electronic device  103 . The gas detection system  101  as illustrated in  FIG. 11  is also referred to as a “gas detection device”. 
     The uses of the gas detection system  101  are not limited to the use described above. For example, the gas detection system  101  may be installed in a refrigerator. In this case, the gas detection system  101  can acquire a gas generated from food as a sample gas. In another use, for example, the gas detection system  101  may be installed in a factory or a laboratory. In this case, the gas detection system  101  can acquire a gas generated from a chemical or the like as a sample gas. 
     The toilet  102  can be installed in a toilet room in a house, a hospital, or the like. The toilet  102  can be used by the subject. As described above, the toilet  102  includes the toilet bowl  102 A and the toilet seat  102 B. The subject can discharge feces into the toilet bowl  102 A. 
     The electronic device  103  is, for example, a smartphone used by the subject. However, the electronic device  103  is not limited to a smartphone. The electronic device  103  may be any electronic device. When brought into the toilet room by the subject, as illustrated in  FIG. 11 , the electronic device  103  can be present in the toilet room. However, for example, when the subject does not bring the electronic device  103  into the toilet room, the electronic device  103  may be present outside the toilet room. The electronic device  103  can receive the detection results from the gas detection system  101  via wireless communication or wired communication. The electronic device  103  can display the received detection results on a display unit  103 A. The display unit  103 A may include a display capable of displaying characters and the like, and a touch screen capable of detecting contact of a finger of the user (subject) or the like. The display may include a display device such as a liquid crystal display (LCD), an organic EL display (GELD), or an inorganic EL display (IELD). The detection method of the touch screen may be any method such as a capacitance method, a resistance film method, a surface acoustic wave method, an ultrasonic method, an infrared method, an electromagnetic induction method, or a load detection method. 
     As illustrated in  FIG. 12 , the gas detection system  101  includes a housing  110 , inflow paths  120  and  121 , and discharge paths  122 ,  123 , and  124 . The discharge path  122 , the discharge path  123 , and the discharge path  124  may merge in any location. The gas detection system  101  includes flow paths  130 ,  131 ,  132 ,  133 ,  134 ,  135 ,  136 ,  137 ,  138 , and  139 , valves  140 ,  141 ,  142 ,  143 , and  144 , and a supply unit  150 . The gas detection system  101  includes a concentration tank  160  serving as a gas concentration unit, a storage tank  170  serving as a gas reservoir, a chamber  180 , and a circuit board  190  serving as a circuit unit. As illustrated in  FIG. 13 , the gas detection system  101  includes, in the circuit board  190 , a storage unit  191 , a communication unit  192 , and a control unit  194 . The gas detection system  101  includes a sensor unit  193 . 
     The housing  110  houses various components of the gas detection system  101 . The housing  110  may be made of any material. For example, the housing  110  may be made of a material such as metal or resin. 
     As illustrated in  FIG. 11 , the inflow path  120  can be exposed to the inside of the toilet bowl  102 A. A portion of the inflow path  120  may be embedded in the toilet seat  102 B. A gas generated from feces discharged into the toilet bowl  102 A flows into the inflow path  120  as a sample gas. The sample gas flowing into the inflow path  120  is supplied to the concentration tank  160  through the flow paths  130 ,  131 , and  132 . As illustrated in  FIG. 11 , one end of the inflow path  120  may be directed to the inside of the toilet bowl  102 A. As illustrated in  FIG. 12 , the other end of the inflow path  120  may be connected to the valve  140 . The inflow path  120  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 11 , the inflow path  121  can be exposed to the outside of the toilet bowl  102 A. A portion of the inflow path  121  may be embedded in the toilet seat  102 B. For example, air in the toilet room, which is outside the toilet bowl  102 A, flows into the inflow path  121  as a purge gas. The purge gas flowing into the inflow path  121  is supplied to the storage tank  170  through the flow paths  130 ,  133 , and  134 . As illustrated in  FIG. 11 , one end of the inflow path  121  may be directed to the outside of the toilet  102 . As illustrated in  FIG. 12 , the other end of the inflow path  121  may be connected to the valve  140 . The inflow path  121  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 11 , a portion of the discharge path  122  can be exposed to the outside of the toilet bowl  102 A. The discharge path  122  as illustrated in  FIG. 12  discharges the exhaust from the chamber  180  to the outside. This exhaust can contain the sample gas and the purge gas, which have been subjected to detection processing. As illustrated in  FIG. 11 , one end of the discharge path  122  may be directed to the outside of the toilet  102 . As illustrated in  FIG. 12 , the other end of the discharge path  122  may be connected to the chamber  180 . The discharge path  122  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 11 , a portion of the discharge path  123  can be exposed to the outside of the toilet bowl  102 A. The discharge path  123  as illustrated in  FIG. 12  discharges the exhaust from the concentration tank  160  to the outside. This exhaust includes a gas not to be detected, which is generated in a concentration process of the sample gas described below. As illustrated in  FIG. 11 , one end of the discharge path  123  may be directed to the outside of the toilet  102 . As illustrated in  FIG. 12 , the other end of the discharge path  123  may be connected to the valve  143 . The discharge path  123  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 11 , a portion of the discharge path  124  can be exposed to the outside of the toilet bowl  102 A. The discharge path  124  as illustrated in  FIG. 12  discharges the residual gas or the like from the storage tank  170  to the outside. As illustrated in  FIG. 11 , one end of the discharge path  124  may be directed to the outside of the toilet  102 . As illustrated in  FIG. 12 , the other end of the discharge path  124  may be connected to the valve  144 . The discharge path  124  may be constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 12 , one end of the flow path  130  is connected to the valve  140 . The other end of the flow path  130  is connected to one end of the flow path  131  and one end of the flow path  133 . The one end of the flow path  131  is connected to the other end of the flow path  130 . The other end of the flow path  131  is connected to the valve  141 . One end of the flow path  132  is connected to the valve  141 . The other end of the flow path  132  is connected to an inlet portion of the concentration tank  160 . The one end of the flow path  133  is connected to the other end of the flow path  130 . The other end of the flow path  133  is connected to the valve  142 . One end of the flow path  134  is connected to the valve  142 . The other end of the flow path  134  is connected to an inlet portion of the storage tank  170 . One end of the flow path  135  is connected to the valve  141 . The other end of the flow path  135  is connected to the valve  144 . One end of the flow path  136  is connected to an outlet portion of the concentration tank  160 . The other end of the flow path  136  is connected to the valve  143 . One end of the flow path  137  is connected to the valve  143 . The other end of the flow path  137  is connected to the chamber  180 . One end of the flow path  138  is connected to an outlet portion of the storage tank  170 . The other end of the flow path  138  is connected to the valve  144 . One end of the flow path  139  is connected to the valve  144 . The other end of the flow path  139  is connected to the chamber  180 . The flow paths  130  to  139  may be each constituted by a tubular member such as a resin tube or a metal or glass pipe. 
     As illustrated in  FIG. 12 , the valve  140  is located among the inflow path  120 , the inflow path  121 , and the flow path  130 . The valve  140  includes a connection port connected to the inflow path  120 , a connection port connected to the inflow path  121 , and a connection port connected to the flow path  130 . The valve  140  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  140  as illustrated in  FIG. 12  switches the connection state among the inflow path  120 , the inflow path  121 , and the flow path  130  under the control of the control unit  194  as illustrated in  FIG. 13 . For example, the valve  140  switches the connection state among them to a state in which the inflow path  120  and the flow path  130  are connected to each other, a state in which the inflow path  121  and the flow path  130  are connected to each other, or a state in which the inflow path  120 , the inflow path  121 , and the flow path  130  are not connected to each other. 
     As illustrated in  FIG. 12 , the valve  141  is located among the flow path  131 , the flow path  132 , and the flow path  135 . The valve  141  includes a connection port connected to the flow path  131 , a connection port connected to the flow path  132 , and a connection port connected to the flow path  135 . The valve  141  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  141  as illustrated in  FIG. 12  switches the connection state among the flow path  131 , the flow path  132 , and the flow path  135  under the control of the control unit  194  as illustrated in  FIG. 13 . For example, the valve  141  switches the connection state among them to a state in which the flow path  131  and the flow path  132  are connected to each other, a state in which the flow path  135  and the flow path  132  are connected to each other, or a state in which the flow path  131 , the flow path  132 , and the flow path  135  are not connected to each other. 
     As illustrated in  FIG. 12 , the valve  142  is located between the flow path  133  and the flow path  134 . The valve  142  includes a connection port connected to the flow path  133 , and a connection port connected to the flow path  134 . The valve  142  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  142  as illustrated in  FIG. 12  switches the connection state between the flow path  133  and the flow path  134  under the control of the control unit  194  as illustrated in  FIG. 13 . For example, the valve  142  switches the connection state between them to a state in which the flow path  133  and the flow path  134  are connected to each other or a state in which the flow path  133  and the flow path  134  are not connected to each other. 
     As illustrated in  FIG. 12 , the valve  143  is located among the discharge path  123 , the flow path  136 , and the flow path  137 . The valve  143  includes a connection port connected to the discharge path  123 , a connection port connected to the flow path  136 , and a connection port connected to the flow path  137 . The valve  143  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  143  as illustrated in  FIG. 12  switches the connection state among the discharge path  123 , the flow path  136 , and the flow path  137  under the control of the control unit  194  as illustrated in  FIG. 13 . For example, the valve  143  switches the connection state among them to a state in which the discharge path  123  and the flow path  136  are connected to each other, a state in which the flow path  136  and the flow path  137  are connected to each other, or a state in which the discharge path  123 , the flow path  136 , and the flow path  137  are not connected to each other. 
     As illustrated in  FIG. 12 , the valve  144  is located among the discharge path  124 , the flow path  135 , the flow path  138 , and the flow path  139 . The valve  144  includes a connection port connected to the discharge path  124 , a connection port connected to the flow path  135 , a connection port connected to the flow path  138 , and a connection port connected to the flow path  139 . The valve  144  may be constituted by a valve such as an electromagnetically driven valve, a piezoelectrically driven valve, or a motor-driven valve. 
     The valve  144  as illustrated in  FIG. 12  switches the connection state among the discharge path  124 , the flow path  135 , the flow path  138 , and the flow path  139  under the control of the control unit  194  as illustrated in  FIG. 13 . For example, the valve  144  switches the connection state among them to a state in which the discharge path  124  and the flow path  138  are connected to each other, a state in which the flow path  138  and the flow path  139  are connected to each other, or a state in which the flow path  135  and the flow path  138  are connected to each other. Alternatively, the valve  144  switches the connection state to a state in which the discharge path  124 , the flow path  135 , the flow path  138 , and the flow path  139  are not connected to each other. 
     As illustrated in  FIG. 12 , the supply unit  150  is attached to the flow path  130 . The supply unit  150  is capable of supplying the sample gas from the inflow path  120  to the concentration tank  160  under the control of the control unit  194  as illustrated in  FIG. 13 . Further, the supply unit  150  is capable of supplying the purge gas from the inflow path  121  to the storage tank  170  under the control of the control unit  194  as illustrated in  FIG. 13 . The arrow illustrated in the supply unit  150  indicates the direction in which the supply unit  150  sends a gas. The supply unit  150  may be constituted by a pump such as a piezoelectric pump or a motor pump. However, the supply unit  150  may be constituted by any component capable of supplying the sample gas from the inflow path  120  to the concentration tank  160 . 
     As illustrated in  FIG. 12 , the inlet portion of the concentration tank  160  is connected to the flow path  132 . The outlet portion of the concentration tank  160  is connected to the flow path  136 . The concentration tank  160  is supplied with the sample gas flowing in from the inflow path  120  through the flow paths  130 ,  131 , and  132 . In the concentration tank  160 , the sample gas is concentrated by processing described below. In this embodiment, the term “concentrating the sample gas” refers to increasing the concentration of a gas to be detected contained in the sample gas. An example of the gas to be detected will be described below. The sample gas concentrated in the concentration tank  160  is supplied to the chamber  180  through the flow paths  136  and  137 . 
     The concentration tank  160  may be formed by a container or the like having a rectangular parallelepiped shape, a cylindrical shape, a bag shape, or a shape such that it fits in a gap between various components housed inside the housing  110 . The concentration tank  160  includes an adsorbent  161 , support members  162  and  163 , and heaters  164 . 
     As illustrated in  FIG. 12 , the adsorbent  161  is placed in the concentration tank  160 . The adsorbent  161  may contain any material corresponding to the use of the gas detection system  1 . The adsorbent  161  may contain, for example, at least any one of activated carbon, silica gel, zeolite, or molecular sieve. The adsorbent  161  may be of a plurality of types or may contain a porous material. 
     The adsorbent  161  adsorbs the gas to be detected contained in the sample gas. When the sample gas is a gas generated from feces, examples of the gas to be detected include methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, and trimethylamine. The gas to be detected is, for example, a gas species that is contained in the odor of feces and is not contained in substances other than feces (such as flush water and urine, for example) present in the toilet bowl  102 A. When the sample gas is a gas generated from feces, examples of the adsorbent  161  include activated carbon and molecular sieve. However, the combination of them may be appropriately changed according to the polarity of gas molecules to be adsorbed. 
     In response to the adsorbent  161  reaching a predetermined temperature by being heated by the heaters  164 , the gas to be detected, which is adsorbed by the adsorbent  161 , can be desorbed from the adsorbent  161 . The desorption of the gas to be detected from the adsorbent  161  increases the concentration of the gas to be detected in the concentration tank  160 . That is, the sample gas is concentrated. Typically, a gas can be desorbed from the adsorbent  161  within a predetermined temperature range. In this embodiment, the term “desorption temperature of a gas” refers to a temperature at which the amount of the gas desorbed from the adsorbent  161  reaches a peak within a predetermined temperature range in which the gas can be desorbed from the adsorbent  161 . 
     The adsorbent  161  may adsorb a gas not to be detected contained in the sample gas. The gas not to be detected is also referred to as “noise gas”. When the sample gas is a gas generated from feces, examples of the gas not to be detected include ammonia and water. A gas may have a different desorption temperature depending on the type of the gas. Accordingly, the desorption temperature of the gas to be detected and the desorption temperature of the gas not to be detected may be different. In this embodiment, the difference in desorption temperature between gases depending on the types of the gases is utilized to exclude the gas not to be detected contained in the sample gas from the sample gas by processing described below. The gas not to be detected, which is excluded from the sample gas, is discharged to the outside through the discharge path  123 . 
       FIG. 14  is a schematic graph of the concentration of a gas desorbed from an adsorbent  161 X adsorbing a predetermined gas, which is detected with a change in the temperature of the adsorbent  161 X. The adsorbent  161 X does not have a pore  161   a  described below. In  FIG. 14 , the horizontal axis represents temperature. In  FIG. 14 , the vertical axis represents the concentration of the gas desorbed from the adsorbent  161 X. The predetermined gas includes a gas to be detected and a gas not to be detected. The gas not to be detected can be desorbed from the adsorbent  161 X in a predetermined temperature range including a temperature t 101 . The concentration (amount) of the gas not to be detected desorbed from the adsorbent  161 X reaches a peak at the temperature t 101 . Thus, the desorption temperature of the gas not to be detected is the temperature t 101 . The gas to be detected can be desorbed from the adsorbent  161 X in a predetermined temperature range including a temperature t 102 . The concentration (amount) of the gas to be detected desorbed from the adsorbent  161 X reaches a peak at the temperature t 102 . Thus, the desorption temperature of the gas to be detected is the temperature t 102 . As described above, the desorption temperature of the gas not to be detected, namely, the temperature t 101 , and the desorption temperature of the gas to be detected, namely, the temperature t 102 , are different. In this embodiment, the difference in desorption temperature between the gas not to be detected and the gas to be detected is utilized to exclude the gas not to be detected contained in the sample gas from the sample gas by processing described below. 
     As illustrated in  FIG. 15 , the adsorbent  161  has a pore  161   a . The pore  161   a  has a larger pore size than the effective molecular diameter (hereinafter, “effective molecular diameter” is also referred to simply as “molecular diameter”) of a gas to be detected  201  and the molecular diameter of a gas not to be detected  202 . In the present disclosure, the term “pore size” means the average diameter value of the pore  161   a  of the adsorbent  161  on the surfaces of the adsorbent  161 . The pore size of the pore  161   a  can be measured using, for example, a pore distribution measurement apparatus. In this case, the average value of the pore size can be calculated as, for example, the average pore size (4 V/A). That is, the average pore size can be determined from the specific surface area (A) and the total pore volume (V). The specific surface area can be determined by using a BET one point method. The total pore volume can be determined by using a one point method total pore volume. Since the specific surface area and the total pore volume are determined in this way, the average pore size can be easily determined. Alternatively, the pore size of the pore  161   a  can be easily measured by image analysis using a scanning electron microscope. 
     Since the pore size of the pore  161   a  is larger than the molecular diameters of the gases  201  and  202 , the gases  201  and  202  contained in the sample gas can enter the pore  161   a . Typically, a gas that has entered the pore  161   a  may be subjected to a suction force from the wall of the pore  161   a  present around the gas. That is, the adsorbent  161  having the pore  161   a  can apply a suction force to the gas that has entered the pore  161   a . The adsorbent  161  having the pore  161   a  can apply a suction force to the gas that has entered the pore  161   a , and can thus adsorb the gas more strongly than the adsorbent  161 X having no pore  161   a . Since the adsorbent  161  having the pore  161   a  can more strongly suck the gas than the adsorbent  161 X having no pore  161   a , the desorption temperature of the gas from the adsorbent  161  can be higher than the desorption temperature of the gas from the adsorbent  161 X. In other words, because the adsorbent  161  has the pore  161   a , the desorption temperature of the gas from the adsorbent  161  can be higher than the desorption temperature of the gas from the adsorbent  161 X having no pore  161   a . Accordingly, the desorption temperatures of the gases  201  and  202  from the adsorbent  161  having the pore  161   a  can be higher than the desorption temperatures of the gases  201  and  202  from the adsorbent  161 X having no pore  161   a.    
     When the sample gas is a gas generated from feces, as described above, the gas to be detected  201  as illustrated in  FIG. 15  can be any one of methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, or trimethylamine. When the sample gas is a gas generated from feces, as described above, the gas not to be detected  202  can be any one of water or ammonia. The molecular diameter of methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, and trimethylamine (which can be the gas to be detected  201 ) can be larger than the molecular diameter of water and ammonia (which can be the gas not to be detected  202 ). That is, when the sample gas is a gas generated from feces, the molecular diameter of the gas to be detected  201  can be larger than the molecular diameter of the gas not to be detected  202 . 
     In a configuration as illustrated in  FIG. 15  in which the molecular diameter of the gas  201  is larger than the molecular diameter of the gas  202 , if the gases  201  and  202  enter the pore  161   a , a gap generated between the gas  201  and the wall of the pore  161   a  can be smaller than a gap generated between the gas  202  and the wall of the pore  161   a . Since the gap generated between the gas  201  and the wall of the pore  161   a  is smaller than the gap generated between the gas  202  and the wall of the pore  161   a , the gas to be detected  201  can be more strongly subjected to a suction force from the wall of the pore  161   a  than the gas not to be detected  202 . As described above, because the adsorbent  161  has the pore  161   a , the desorption temperature of the gas from the adsorbent  161  can be higher than the desorption temperature of the gas from the adsorbent  161 X having no pore  161   a . As the suction force to which the gas is subjected from the wall of the pore  161   a  increases, because the adsorbent  161  has the pore  161   a , the degree of increase in the desorption temperature of the gas from the adsorbent  161  can be larger than that in the desorption temperature of the gas from the adsorbent  161 X having no pore  161   a . Accordingly, when the molecular diameter of the gas  201  is larger than molecular diameter of the gas  202 , the degree of increase in the desorption temperature of the gas to be detected  201  is larger than that of the gas not to be detected  202  because of the presence of the pore  161   a . With this configuration, the difference between the desorption temperature of the gas to be detected  201  and the desorption temperature of the gas not to be detected  202  in the adsorbent  161  can be larger than the difference between the desorption temperature of the gas to be detected  201  and the desorption temperature of the gas not to be detected  202  in the adsorbent  161 X. 
     For example, in the configuration as illustrated in  FIG. 14 , the molecular diameter of the gas to be detected is assumed to be larger than the molecular diameter of the gas not to be detected. As described above, the desorption temperature of the gas not to be detected from the adsorbent  161 X having no pore  161   a  is the temperature t 101 . In contrast, the desorption temperature of the gas not to be detected from the adsorbent  161  having the pore  161   a  is higher than the temperature t 101  and is equal to a temperature till. As described above, furthermore, the desorption temperature of the gas to be detected from the adsorbent  161 X having no pore  161   a  is the temperature t 102 . In contrast, the desorption temperature of the gas to be detected from the adsorbent  161  having the pore  161   a  is higher than the temperature t 102  and is equal to a temperature t 121 . As described above, the degree of increase in the desorption temperature of the gas to be detected is larger than that of the gas not to be detected because of the presence of the pore  161   a . With this configuration, the difference (t 121 −t 111 ) between the desorption temperature of the gas to be detected and the desorption temperature of the gas not to be detected in the adsorbent  161  can be larger than the difference (t 102 −t 101 ) between the desorption temperature of the gas to be detected and the desorption temperature of the gas not to be detected in the adsorbent  161 X. In this embodiment, increasing the difference between the desorption temperature of the gas to be detected and the desorption temperature of the gas not to be detected ensures that the gas not to be detected contained in the sample gas can be more reliably removed from the sample gas. 
     The density of the pore  161   a  in the adsorbent  161  as illustrated in  FIG. 15  may be appropriately selected according to the material of the adsorbent  161  and the type of the gas to be detected. The shape of the pore  161   a  is an inverted conical shape. However, the shape of the pore  161   a  is not limited to the inverted conical shape. For example, the shape of the pore  161   a  may be a cylindrical shape or the like. 
     The support member  162  as illustrated in  FIG. 12  supports the adsorbent  161  near the inlet portion of the concentration tank  160 . The support member  162  may be in powder or fiber form containing glass or fluorine resin. 
     The support member  163  as illustrated in  FIG. 12  supports the adsorbent  161  near the outlet portion of the concentration tank  160 . The support member  163  may be in powder or fiber form containing glass or fluorine resin. 
     The heaters  164  as illustrated in  FIG. 12  are capable of heating the adsorbent  161 . For example, the heaters  164  are energized under the control of the control unit  194  as illustrated in  FIG. 13  to heat the adsorbent  161 . The heaters  164  are disposed outside the concentration tank  160 . The heaters  164  may surround the outer sides of the concentration tank  160 . The heaters  164  may be resistance heaters, rubber heaters, or the like. 
     As illustrated in  FIG. 12 , the inlet portion of the storage tank  170  is connected to the flow path  134 . The outlet portion of the storage tank  170  is connected to the flow path  138 . The storage tank  170  is supplied with the purge gas flowing in from the inflow path  121  through the flow paths  130 ,  133 , and  134 . The storage tank  170  stores the supplied purge gas. The purge gas stored in the storage tank  170  is supplied to the chamber  180  through the flow paths  138  and  139 . The purge gas stored in the storage tank  170  is further supplied to the concentration tank  160  through the flow paths  138 ,  135 , and  132 . 
     The storage tank  70  may be formed by a container or the like having a rectangular parallelepiped shape, a cylindrical shape, a bag shape, or a shape such that it fits in a gap between various components housed inside the housing  110 . The storage tank  170  may have a larger capacity than the concentration tank  160 . The storage tank  170  includes an adsorbent  171  and support members  172  and  173 . 
     As illustrated in  FIG. 12 , the adsorbent  171  is placed in the storage tank  170 . The adsorbent  171  may contain any material corresponding to the use of the gas detection system  101 . The adsorbent  171  may contain, for example, at least any one of activated carbon, silica gel, zeolite, or molecular sieve. The adsorbent  171  may be of a plurality of types or may contain a porous material. 
     The adsorbent  171  may include an agent that adsorbs a gas to be detected contained in the purge gas. When the air in the toilet room is a purge gas, the purge gas may contain a gas to be detected. Since the adsorbent  171  adsorbs the gas to be detected contained in the purge gas, the purge gas in the storage tank  170  can be purified. When the sample gas is a gas generated from feces, examples of the adsorbent  171  that adsorbs the gas to be detected include activated carbon and molecular sieve. However, the combination of them may be appropriately changed according to the polarity of gas molecules to be adsorbed. 
     The adsorbent  171  may include an agent that adsorbs a gas not to be detected contained in the purge gas. When the air in the toilet room is a purge gas, the purge gas may contain a gas not to be detected. Since the adsorbent  171  adsorbs the gas not to be detected contained in the purge gas, the purge gas in the storage tank  170  can be purified. When the sample gas is a gas generated from feces, examples of the adsorbent  171  that adsorbs the gas not to be detected include silica gel and zeolite. However, the combination of them may be appropriately changed according to the polarity of gas molecules to be adsorbed. 
     The support member  172  supports the adsorbent  171  near the inlet portion of the storage tank  170 . The support member  172  may be in powder or fiber form containing glass or fluorine resin. 
     The support member  173  supports the adsorbent  171  near the outlet portion of the storage tank  170 . The support member  173  may be in powder or fiber form containing glass or fluorine resin. 
     As illustrated in  FIG. 12 , the chamber  180  includes therein a sensor unit  181 . The chamber  180  may include a plurality of sensor units  181 . The chamber  180  may be divided into a plurality of chambers. The sensor units  181  may be disposed in the resulting plurality of chambers  180 . The plurality of chambers  180  may be connected to each other. The chamber  180  is connected to the flow path  137 . The chamber  180  is supplied with the sample gas from the flow path  137 . The chamber  180  is further connected to the flow path  139 . The chamber  180  is supplied with the purge gas from the flow path  139 . The chamber  180  is further connected to the discharge path  122 . The chamber  180  discharges the sample gas and the purge gas, which have been subjected to detection processing, from the discharge path  122 . 
     As illustrated in  FIG. 12 , the sensor unit  181  is arranged in the chamber  180 . The sensor unit  181  outputs a signal corresponding to the concentration of a specific gas to the control unit  194 . The sensor unit  181  may include any sensor such as a semiconductor sensor, a contact combustion sensor, or a solid electrolyte sensor. The sensor unit  181  will be described hereinafter as being configured to output a voltage corresponding to the concentration of the specific gas to the control unit  194  as the signal corresponding to the concentration of the specific gas. However, the signal corresponding to the specific gas, which is output from the sensor unit  181 , is not limited to the voltage corresponding to the concentration of the specific gas. For example, the sensor unit  181  may output a current corresponding to the concentration of the specific gas to the control unit  194  as the signal corresponding to the concentration of the specific gas. The specific gas contains a specific gas to be detected and a specific gas not to be detected. When the sample gas is a gas generated from feces, examples of the specific gas to be detected include methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, and trimethylamine. When the sample gas is a gas generated from feces, examples of the specific gas not to be detected include ammonia and water. Each of the plurality of sensor units  181  can output a voltage corresponding to the concentration of at least any one of these gases to the control unit  194 . 
     The circuit board  190  as illustrated in  FIG. 13  has mounted therein wiring through which an electrical signal propagates, the storage unit  191 , the communication unit  192 , the control unit  194 , and the like. 
     The storage unit  191  as illustrated in  FIG. 13  can be constituted by, for example, a semiconductor memory, a magnetic memory, or the like. The storage unit  191  stores various kinds of information and a program for operating the gas detection system  101 . The storage unit  191  may function as a work memory. 
     The communication unit  192  as illustrated in  FIG. 13  is capable of communicating with the electronic device  103  as illustrated in  FIG. 11 . The communication unit  192  may be capable of communicating with an external server. The communication method used when the communication unit  192  communicates with the electronic device  103  and the external server may be a short-range wireless communication standard, a wireless communication standard for connecting to a mobile phone network, or a wired communication standard. The short-range wireless communication standard may include, for example, WiFi (registered trademark), Bluetooth (registered trademark), infrared, NFC, and the like. The wireless communication standard for connecting to a mobile phone network may include, for example, LTE, a fourth generation or higher mobile communication system, or the like. Alternatively, the communication method used when the communication unit  192  communicates with the electronic device  103  and the external server may be, for example, a communication standard such as LPWA or LPWAN. 
     The sensor unit  193  as illustrated in  FIG. 13  may include at least any one of an image camera, a personal identification switch, an infrared sensor, a pressure sensor, or the like. The sensor unit  193  outputs a detection result to the control unit  194 . 
     For example, when the sensor unit  193  includes an infrared sensor, the sensor unit  193  detects reflected light from an object irradiated with infrared radiation from the infrared sensor, thereby being able to detect that the subject has entered the toilet room. The sensor unit  193  outputs, as a detection result, a signal indicating that the subject has entered the toilet room to the control unit  194 . 
     For example, when the sensor unit  193  includes a pressure sensor, the sensor unit  193  detects a pressure applied to the toilet seat  102 B as illustrated in  FIG. 11 , thereby being able to detect that the subject has sat on the toilet seat  102 B. The sensor unit  193  outputs, as a detection result, a signal indicating that the subject has sat on the toilet seat  102 B to the control unit  194 . 
     For example, when the sensor unit  193  includes a pressure sensor, the sensor unit  193  detects a reduction in the pressure applied to the toilet seat  102 B as illustrated in  FIG. 11 , thereby being able to detect that the subject has risen from the toilet seat  102 B. The sensor unit  193  outputs, as a detection result, a signal indicating that the subject has risen from the toilet seat  102 B to the control unit  194 . 
     For example, when the sensor unit  193  includes an image camera, a personal identification switch, and the like, the sensor unit  193  collects data, such as a face image, the sitting height, and the weight. The sensor unit  193  identifies and detects a person from the collected data. The sensor unit  193  outputs, as a detection result, a signal indicating the identified person to the control unit  194 . 
     For example, when the sensor unit  193  includes a personal identification switch or the like, the sensor unit  193  identifies (detects) a person in response to an operation of the personal identification switch. In this case, personal information may be registered (stored) in the storage unit  191  in advance. The sensor unit  193  outputs, as a detection result, a signal indicating the identified person to the control unit  194 . 
     The control unit  194  as illustrated in  FIG. 13  includes one or more processors. The one or more processors may include at least any one of a general-purpose processor that reads a specific program to execute a specific function, or a dedicated processor dedicated to a specific process. The dedicated processor may include an application specific IC (ASIC). The one or more processors may include a programmable logic device (PLD). The PLD may include an FPGA. The control unit  194  may include at least any one of an SoC or an SiP with which the one or more processors cooperate. 
     &lt;Purge Gas Storage Process&gt; 
     The control unit  194  can detect that the subject has risen from the toilet seat  102 B on the basis of the detection result of the sensor unit  193 . The control unit  194  performs control so that the air in the toilet room flows into the inflow path  121  as a purge gas after a first specific time period has elapsed since it was detected that the subject rose from the toilet seat  102 B. The control unit  194  performs control so that the purge gas flowing in from the inflow path  121  is stored in the storage tank  170 . The first specific time period may be appropriately set in consideration of the time period taken to replace the air in the toilet room with air outside the toilet room by using a ventilation fan or the like in the toilet room after the subject exits the toilet room. 
     For example, the control unit  194  causes the valve  140  as illustrated in  FIG. 12  to connect the inflow path  121  and the flow path  130  to each other, and causes the valve  142  as illustrated in  FIG. 12  to connect the flow path  133  and the flow path  134  to each other. Further, the control unit  194  causes the valve  144  as illustrated in  FIG. 12  to connect the flow path  138  and the discharge path  124  to each other. In addition, the control unit  194  controls the supply unit  150  to generate a flow of gas from the inflow path  121  toward the discharge path  124  through the flow paths  130 ,  133 , and  134 , the storage tank  170 , and the flow path  138 . As a result of generation of the flow of gas, the air in the toilet room flows into the inflow path  121  as a purge gas. The purge gas flowing in from the inflow path  121  is supplied to the storage tank  170  through the flow paths  130 ,  133 , and  134 . Since the purge gas is supplied to the storage tank  170 , the residual gas in the storage tank  170  is pushed out to the flow path  138  by the purge gas and discharged from the discharge path  124 . The control unit  194  stops the supply unit  150  at a point in time when a second specific time period elapses after the purge gas starts to flow into the inflow path  121 . Further, the control unit  194  causes the valve  140  not to connect the inflow path  121  and the flow path  130  to each other, and causes the valve  142  not to connect the flow path  133  and the flow path  134  to each other. In addition, the control unit  194  causes the valve  144  not to connect the flow path  138  and the discharge path  124  to each other. With this configuration, the purge gas from the inflow path  121  is stored in the storage tank  170 . The second specific time period may be appropriately set in consideration of the capacity of the storage tank  170  and the like. The purge gas stored in the storage tank  170  can come into contact with the adsorbent  171  in the storage tank  170 . Since the purge gas comes into contact with the adsorbent  171 , the gas to be detected and the gas not to be detected contained in the purge gas can be adsorbed by the adsorbent  171 . Since the gas to be detected and the gas not to be detected contained in the purge gas are adsorbed by the adsorbent  171 , the purge gas in the storage tank  170  can be purified. 
     &lt;Sample Gas Storage and Concentration Process&gt; 
     The control unit  194  as illustrated in  FIG. 13  can detect that the subject has sat on the toilet seat  102 B on the basis of the detection result of the sensor unit  193 . The control unit  194  performs control so that a gas generated from feces discharged into the toilet bowl  102 A flows into the inflow path  120  as a sample gas after a third specific time period has elapsed since it was detected that the subject sat on the toilet seat  102 B. The control unit  194  performs control so that the sample gas flowing in from the inflow path  120  passes through the concentration tank  160 . For example, the control unit  194  performs control so that the sample gas passes through the concentration tank  160  and is discharged from the discharge path  123 . The third specific time period may be appropriately set in consideration of the time period taken until the subject defecates after the subject sits on the toilet seat  102 B. 
     For example, the control unit  194  causes the valve  140  as illustrated in  FIG. 12  to connect the inflow path  120  and the flow path  130  to each other, and causes the valve  141  to connect the flow path  131  and the flow path  132  to each other. Further, the control unit  194  causes the valve  143  as illustrated in  FIG. 12  to connect the flow path  136  and the discharge path  123  to each other. In addition, the control unit  194  controls the supply unit  150  as illustrated in  FIG. 12  to generate a flow of gas from the inflow path  120  toward the discharge path  123  through the flow paths  130 ,  131 , and  132 , the concentration tank  160 , and the flow path  136 . As a result of generation of the flow of gas, the sample gas flowing in from the inflow path  120  passes through the concentration tank  160 . 
     The control unit  194  as illustrated in  FIG. 13  performs control so that the sample gas passes through the concentration tank  160  to cause the adsorbent  161  to adsorb the gas to be detected contained in the sample gas. In this case, the control unit  194  maintains the heaters  164  in the non-driven state. Since the heaters  164  are maintained in the non-driven state, the temperature of the adsorbent  161  can be room temperature. The control unit  194  may perform control so that the sample gas passes through the concentration tank  160  for a first specified time period. The first specified time period may be appropriately set in consideration of the amount of the gas to be detected that can be adsorbed by the adsorbent  161 . Further, the flow rate of the sample gas passing through the inside of the concentration tank  160  may be appropriately set in consideration of the volumetric capacity of the concentration tank  160 , the area of the adsorbent  161 , or the like. The control unit  194  may estimate the flow rate of the sample gas from at least any one of a driving voltage, a frequency, or the like of a pump or the like constituting the supply unit  150 . The gas detection system  101  may be provided with a flow rate sensor that detects the flow rate of the sample gas. In this configuration, the flow rate sensor outputs a detection signal indicating the flow rate of the sample gas to the control unit  194 . The control unit  194  detects the flow rate of the sample gas on the basis of the detection signal output from the flow rate sensor. The control unit  194  may also detect the flow rate of the purge gas in a manner that is the same as or similar to that of the sample gas. 
       FIG. 16  is a timing chart of an example operation of the gas detection system  101  illustrated in  FIG. 11 .  FIG. 16  illustrates a change in the temperature of the adsorbent  161  with time. The control unit  194  may estimate the temperature of the adsorbent  161  from the current of the heaters  164  or the like. A temperature sensor may be disposed in the vicinity of the adsorbent  161 . In this configuration, the temperature sensor outputs a signal indicating the temperature in the vicinity of the adsorbent  161  to the control unit  194 . The control unit  194  may acquire the temperature of the adsorbent  161  on the basis of the detection signal output from the temperature sensor. 
     Time S 100  as illustrated in  FIG. 16  is a point in time at which the third specific time period elapses after the control unit  194  detects that the subject has sat on the toilet seat  102 B. At the time S 100 , the control unit  194  performs control so that a gas generated from feces discharged into the toilet bowl  102 A flows into the inflow path  120  as a sample gas. Further, the control unit  194  performs control so that the sample gas flowing into the inflow path  120  passes through the concentration tank  160 . In this case, the control unit  194  maintains the heaters  164  in the non-driven state. Since the heaters  164  are maintained in the non-driven state, the adsorbent  161  is maintained at room temperature T 100  after the time S 100 . The control unit  194  performs control so that the sample gas passes through the concentration tank  160  for the first specified time period from the time S 100  to time S 101 . Since the sample gas passes through the concentration tank  160 , the detection target gas contained in the sample gas is adsorbed by the adsorbent  161 . The sample gas in which the gas to be detected is adsorbed by the adsorbent  161  is discharged from the discharge path  123 . If the sample gas contains a gas not to be detected, the gas not to be detected can also be adsorbed by the adsorbent  161  after the time S 100 . 
     The control unit  194  as illustrated in  FIG. 13  stops the passage of the sample gas to the concentration tank  160  at a point in time when the first specified time period elapses after the sample gas starts to pass through the concentration tank  160 . For example, the control unit  194  stops the supply unit  150  at a point in time when the first specified time period elapses. Further, the control unit  194  causes the valve  141  not to connect the flow path  131  and the flow path  132  to each other, and causes the valve  143  not to connect the flow path  136  and the discharge path  123  to each other. At the point in time when the first specified time period elapses, the control unit  194  brings the heaters  164  into the driven state to increase the temperature of the adsorbent  161 . 
     In  FIG. 16 , the time S 101  is the point in time when the first specified time period elapses after the sample gas starts to pass through the concentration tank  60 . At the time S 101 , the control unit  194  stops the passage of the sample gas to the concentration tank  160 . At the time S 101 , furthermore, the control unit  194  brings the heaters  164  into the driven state. Since the heaters  164  are brought into the driven state at the time S 101 , the temperature of the adsorbent  161  increases after the time S 101 . 
     In response to the temperature of the adsorbent  161  as illustrated in  FIG. 12  reaching a temperature T 101 , the control unit  194  as illustrated in  FIG. 13  performs control so that the temperature of the adsorbent  161  is maintained as the temperature T 101  for a second specified time period. The second specified time period may be appropriately set in consideration of the amount of the gas not to be detected that can be contained in the sample gas. The temperature T 101  may be the desorption temperature of the gas not to be detected that can be contained in the sample gas. As illustrated in  FIG. 15 , when the adsorbent  161  has the pore  161   a , the temperature T 101  can be the temperature till as illustrated in  FIG. 14 . Since the adsorbent  161  is maintained at the temperature T 101 , the gas not to be detected can be desorbed from the adsorbent  161 . The control unit  194  performs control so that the purge gas passes through the concentration tank  160  while performing control so that the temperature of the adsorbent  161  is maintained as the temperature T 101 . For example, the control unit  194  performs control so that the purge gas that has passed through the concentration tank  160  is discharged from the discharge path  123 . With this configuration, the gas not to be detected desorbed from the adsorbent  161  can be discharged from the discharge path  123  together with the purge gas. That is, the gas not to be detected desorbed from the adsorbent  161  can be removed from the concentration tank  160 . The flow rate of the purge gas passing through the inside of the concentration tank  160  may be appropriately set in consideration of the volumetric capacity of the concentration tank  160 , the area of the adsorbent  161 , or the like. 
     For example, in response to the temperature of the adsorbent  161  as illustrated in  FIG. 12  reaching the temperature T 101 , the control unit  194  causes the valve  140  to connect the inflow path  121  and the flow path  130  to each other, and causes the valve  142  to connect the flow path  133  and the flow path  134  to each other. The control unit  194  further causes the valve  144  to connect the flow path  138  and the flow path  135  to each other, causes the valve  141  to connect the flow path  135  and the flow path  132  to each other, and causes the valve  143  to connect the flow path  136  and the discharge path  123  to each other. In addition, the control unit  194  controls the supply unit  150  to generate a flow of gas from the inflow path  121  toward the discharge path  123  through the flow paths  130 ,  133 , and  134 , the storage tank  170 , and the flow paths  138 ,  135 , and  132 , the concentration tank  160 , and the flow path  136 . As a result of generation of the flow of the gas, the purge gas passes through the concentration tank  160  and is discharged from the discharge path  123 . Since the purge gas passes through the concentration tank  160 , the gas not to be detected desorbed from the adsorbent  161  can be removed from the concentration tank  160  and discharged from the discharge path  123  by the purge gas. 
     In  FIG. 16 , at time S 102 , the temperature of the adsorbent  161  reaches the temperature T 101 . The control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 101  for the second specified time period from the time S 102  to time S 103 . Since the temperature of the adsorbent  161  is maintained as the temperature T 101  after the time S 102 , the gas not to be detected can be desorbed from the adsorbent  161 . Further, the control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is discharged from the discharge path  123  at the time S 102 . Since the purge gas passes through the concentration tank  160  and is discharged from the discharge path  123 , the desorbed gas not to be detected can be removed from the concentration tank  160  and discharged from the discharge path  123  by the purge gas. 
     At a point in time when the second specified time period elapses after the temperature of the adsorbent  161  as illustrated in  FIG. 12  reaches the temperature T 101 , the control unit  194  as illustrated in  FIG. 13  controls the heaters  164  so that the temperature of the adsorbent  161  increases to the temperature T 102 . The temperature T 102  may be the desorption temperature of the gas to be detected contained in the sample gas. As illustrated in  FIG. 15 , when the adsorbent  161  has the pore  161   a , the temperature T 102  can be the temperature t 121  as illustrated in  FIG. 14 . In  FIG. 16 , the time S 103  is a point in time at which the second specified time period elapses. In  FIG. 16 , at the time S 103 , the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  increases to the temperature T 102 . 
     In response to the temperature of the adsorbent  161  reaching the temperature T 102 , the control unit  194  as illustrated in  FIG. 13  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 102 . The control unit  194  controls the supply unit  150  so that the purge gas passes through the concentration tank  160  while controlling the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 102 . For example, the control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160 . With this configuration, the gas to be detected having an increased concentration in the concentration tank  160 , that is, the more concentrated sample gas in the concentration tank  160 , can be transported to the sensor unit  181  in the chamber  180  by the purge gas. The purge gas is also referred to as a “carrier gas” when used in gas transportation applications. The control unit  194  may perform control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160  for a third specified time period. The third specified time period may be appropriately set in consideration of the flow rate of the purge gas and the amount of the gas to be detected that can be adsorbed by the adsorbent  161 . Further, the flow rate of the purge gas passing through the concentration tank  160  as a carrier gas may be appropriately set in consideration of the amount of the gas to be detected that can be adsorbed by the adsorbent  161 , the cross-sectional area of the concentration tank  160 , and the like. 
     For example, in response to the temperature of the adsorbent  161  reaching the temperature T 102 , the control unit  194  causes the valve  140  as illustrated in  FIG. 12  to connect the inflow path  121  and the flow path  130  to each other, and causes the valve  142  to connect the flow path  133  and the flow path  134  to each other. The control unit  194  further causes the valve  144  to connect the flow path  138  and the flow path  135  to each other, causes the valve  141  to connect the flow path  135  and the flow path  132  to each other, and causes the valve  143  to connect the flow path  136  and the flow path  137  to each other. In addition, the control unit  194  controls the supply unit  150  to generate a flow of gas from the inflow path  121  toward the chamber  180  through the flow paths  130 ,  133 , and  134 , the storage tank  170 , and the flow paths  138 ,  135 , and  132 , the concentration tank  160 , and the flow paths  136  and  137 . As a result of generation of the flow of gas, the purge gas passes through the concentration tank  160  and transports the gas to be detected in the concentration tank  160  to the chamber  180 . 
     In  FIG. 16 , at time S 104 , the temperature of the adsorbent  161  reaches the temperature T 102 . After the time S 104 , the control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160  while performing control so that the temperature of the adsorbent  161  is maintained as the temperature T 102 . Further, the control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160  for the third specified time period from the time S 104  to time S 105 . 
     &lt;Process for Detecting Type and Concentration of Gas&gt; 
     The control unit  194  performs control so that the purge gas stored in the storage tank  170  is supplied to the sensor unit  181  in the chamber  180 . For example, the control unit  194  causes the valve  140  to connect the inflow path  121  and the flow path  130  to each other, causes the valve  142  to connect the flow path  133  and the flow path  134  to each other, and causes the valve  144  to connect the flow path  138  and the flow path  139  to each other. Further, the control unit  194  controls the supply unit  150  to generate a flow of gas from the inflow path  121  toward the chamber  180  through the flow paths  130 ,  133 , and  134 , the storage tank  170 , and the flow paths  138  and  139 . As a result of generation of the flow of gas, the purge gas stored in the storage tank  170  is supplied to the sensor unit  181  in the chamber  180 . 
     The control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160  in the way described in the &lt;Sample Gas Storage and Concentration Process&gt; section described above. 
     The control unit  194  performs control so that the purge gas stored in the storage tank  170  and the sample gas concentrated in the concentration tank  160  are alternately supplied to the sensor unit  181  in the chamber  180 . The control unit  194  alternately supplies the purge gas and the concentrated sample gas to the chamber  180  to acquire a voltage waveform from the sensor unit  181  in the chamber  180 . The control unit  194  detects the type and concentration of a gas contained in the sample gas by, for example, machine learning for the acquired voltage waveform. The control unit  194  may transmit the detected type and concentration of the gas to the electronic device  103  via the communication unit  192  as a detection result. 
     [Operation of Gas Detection System] 
       FIG. 17  is a flowchart of an example operation of the gas detection system  101  illustrated in  FIG. 11  during gas concentration. The control unit  194  may start a process as illustrated in  FIG. 17  after the first specific time period elapses after it is detected that the subject has risen from the toilet seat  102 B on the basis of the detection result of the sensor unit  193 . 
     The control unit  194  performs control so that the air in the toilet room flows into the inflow path  121  as a purge gas (step S 210 ). The control unit  194  performs control so that the purge gas flowing into the inflow path  121  is stored in the storage tank  170  (step S 211 ). 
     The control unit  194  performs control so that a gas generated from feces discharged into the toilet bowl  102 A flows into the inflow path  120  as a sample gas after the third specific time period has elapsed since it was detected that the subject sat on the toilet seat  102 B (step S 212 ). The control unit  194  performs control so that the sample gas flowing in from the inflow path  120  passes through the concentration tank  160  for the first specified time period (step S 213 ). In the processing of step S 213 , the control unit  194  maintains the heaters  164  in the non-driven state. 
     The control unit  194  detects the lapse of the first specified time period after the sample gas starts to pass through the concentration tank  160  (step S 214 ). The control unit  194  stops the passage of the sample gas to the concentration tank  160  at the point in time at which the first specified time period elapses (step S 215 ). The control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  increases (step S 216 ). 
     The control unit  194  detects the temperature of the adsorbent  161  reaching the temperature T 101  (step S 217 ). In response to the temperature of the adsorbent  161  reaching the temperature T 101 , the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 101  for the second specified time period (step S 218 ). The control unit  194  performs control so that the purge gas passes through the concentration tank  160  while performing control so that the temperature of the adsorbent  161  is maintained as the temperature T 101  (step S 219 ). In the processing of step S 219 , the control unit  194  performs control so that the purge gas that has passed through the concentration tank  160  is discharged from the discharge path  123 . 
     The control unit  194  detects the lapse of the second specified time period after the temperature of the adsorbent  161  reaches the temperature T 101  (step S 220 ). The control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  increases to the temperature T 102  at the point in time at which the second specified time period elapses (step S 221 ). 
     The control unit  194  detects the temperature of the adsorbent  161  reaching the temperature T 102  (step S 222 ). The control unit  194  performs control so that the purge gas passes through the concentration tank  160  (step S 224 ) while controlling the heaters  64  so that the temperature of the adsorbent  161  is maintained as the temperature T 102  (step S 223 ). In the processing of step S 224 , the control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160 . After the processing of step S 224  ends, the control unit  194  ends the gas concentration process. 
       FIG. 18  is a flowchart of an example operation of the gas detection system  101  illustrated in  FIG. 11  during detection of the type and concentration of a gas. 
     The control unit  194  performs control so that the purge gas stored in the storage tank  170  is supplied to the sensor unit  181  in the chamber  180  (step S 230 ). The control unit  194  executes the process as illustrated in  FIG. 17  to perform control so that the sample gas concentrated in the concentration tank  160  is supplied to the sensor unit  181  in the chamber  180  (step S 231 ). 
     The control unit  194  alternately executes the processing of step S 230  and the processing of step S 231  to perform control so that the purge gas in the storage tank  170  and the sample gas in the concentration tank  160  are alternately supplied to the sensor unit  181  in the chamber  180 . 
     The control unit  194  alternately supplies the purge gas and the concentrated sample gas to the chamber  180  to acquire a voltage waveform from the sensor unit  181  in the chamber  180  (step S 232 ). The control unit  194  detects the type and concentration of a gas contained in the sample gas by, for example, machine learning for the acquired voltage waveform (step S 233 ). After the processing of step S 233  ends, the control unit  194  ends the process for detecting the type and concentration of the gas. 
     As described above, in the gas detection system  101  according to the third embodiment, as illustrated in  FIG. 15 , the pore size of the pore  161   a  of the adsorbent  161  is larger than the molecular diameter of the gas to be detected  201  and the molecular diameter of the gas not to be detected  202 . Further, the molecular diameter of the gas to be detected  201  is larger than the molecular diameter of the gas not to be detected  202 . With this configuration, as described above, the difference (t 121 −t 111 ) between the desorption temperature of the gas to be detected and the desorption temperature of the gas not to be detected in the adsorbent  161  can be increased. That is, the difference between the temperature T 101  and the temperature T 102  as illustrated in  FIG. 16  can be increased. Since the difference between the temperature T 101  and the temperature T 102  is increased, the gas not to be detected can be more reliably removed from the sample gas. Since the gas not to be detected is more reliably removed from the sample gas, the gas detection system  101  can more accurately detect the type and concentration of the gas to be detected contained in the sample gas. Accordingly, the third embodiment can provide the improved gas detection system  101 . 
     Fourth Embodiment 
     A gas detection system according to a fourth embodiment of the present disclosure will be described hereinafter. The gas detection system according to the fourth embodiment can adopt a configuration that is the same as or similar to that of the gas detection system  101  according to the third embodiment. The following mainly describes differences from the third embodiment with reference to  FIGS. 11 to 13 . 
     When the sample gas is to be concentrated in the concentration tank  160  as illustrated in  FIG. 12 , the control unit  194  as illustrated in  FIG. 13  controls the supply unit  150  so that the sample gas passes through the concentration tank  160  as illustrated in  FIG. 12  in a manner that is the same as or similar to that in the third embodiment. In this case, in the fourth embodiment, the control unit  194  performs control so that the temperature of the adsorbent  161  is maintained as the temperature T 101 . As described above, the temperature T 101  may be the desorption temperature of the gas not to be detected that can be contained in the sample gas. Since the temperature of the adsorbent  161  is maintained as the temperature T 101  when the sample gas passes through the concentration tank  160  as illustrated in  FIG. 12 , the gas not to be detected contained in the sample gas can be discharged from the discharge path  123  as illustrated in  FIG. 12  without being adsorbed by the adsorbent  161  as illustrated in  FIG. 12 . Since the gas not to be detected contained in the sample gas is discharged from the discharge path  123  as illustrated in  FIG. 12  without being adsorbed by the adsorbent  161  as illustrated in  FIG. 12 , in the fourth embodiment, for example, the second specified time period for removing the noise gas as illustrated in  FIG. 16  can be reduced. With this configuration, in the fourth embodiment, the time taken to concentrate the sample gas in the concentration tank  160  can be shortened. 
       FIG. 19  is timing chart of an example operation of the gas detection system  101  according to the fourth embodiment of the present disclosure.  FIG. 19  illustrates a change in the temperature of the adsorbent  161  with time. 
     Time S 100  as illustrated in  FIG. 19  is a point in time at which the third specific time period elapses after the control unit  194  detects that the subject has sat on the toilet seat  102 B. At the time S 100 , the control unit  194  performs control so that a gas generated from feces discharged into the toilet bowl  102 A flows into the inflow path  120  as a sample gas. Further, the control unit  194  performs control so that the sample gas flowing into the inflow path  120  passes through the concentration tank  160 . Further, the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 101  after the time S 100 . The control unit  194  may control the heaters  164  before the time S 100  to increase the temperature of the adsorbent  161  in advance. For example, the control unit  194  may switch the heaters  164  from the non-driven state to the driven state at the point in time when the control unit  194  detects that the subject has sat on the toilet seat  102 B. Since the temperature of the adsorbent  161  is maintained as the temperature T 101  when the sample gas passes through the concentration tank  160 , the gas not to be detected contained in the sample gas can be discharged from the discharge path  123  as illustrated in  FIG. 12  without being adsorbed by the adsorbent  161 . Further, since the temperature of the adsorbent  161  is maintained as the temperature T 101  lower than the temperature T 102 , the gas to be detected contained in the sample gas can be adsorbed by the adsorbent  161 . 
     The control unit  194  as illustrated in  FIG. 13  may control the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 101  while controlling the supply unit  150  so that the sample gas passes through the concentration tank  160  for a fourth specified time period. In  FIG. 19 , the fourth specified time period is a time period from the time S 100  to time S 106 . The fourth specified time period may be appropriately set in consideration of at least any one of the amount of the gas to be detected that can be adsorbed by the adsorbent  161  or the amount of the gas not to be detected that can be contained in the sample gas. The fourth specified time period may be a time period equivalent to the first specified time period or the second specified time period as illustrated in  FIG. 16 . Alternatively, the fourth specified time period may be set independently of the first specified time period and the second specified time period. 
     At a point in time when the fourth specified time period elapses after the sample gas starts to pass through the concentration tank  160  as illustrated in  FIG. 12 , the control unit  194  as illustrated in  FIG. 13  controls the heaters  164  so that the temperature of the adsorbent  161  increases. The control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  increases to the temperature T 102  in a manner that is the same as or similar to that in the third embodiment. In response to the temperature of the adsorbent  161  reaching the temperature T 102 , the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 102  in a manner that is the same as or similar to that in the third embodiment. The control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160  while controlling the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 102  in a manner that is the same as or similar to that in the third embodiment. 
     In  FIG. 19 , the time S 106  is a point in time at which the fourth specified time period elapses. At the time S 106 , the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  increases to the temperature T 102 . At time S 107 , the temperature of the adsorbent  161  reaches the temperature T 102 . At the time S 107 , the control unit  194  controls the supply unit  150  so that the purge gas passes through the concentration tank  160  while controlling the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 102 . The control unit  194  performs control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160 . 
     The control unit  194  as illustrated in  FIG. 13  may perform control so that the purge gas passes through the concentration tank  160  and is supplied to the sensor unit  181  in the chamber  180  together with the gas to be detected in the concentration tank  160  for the third specified time period in a manner that is the same as or similar to that in the third embodiment. In  FIG. 19 , the third specified time period is a time period from the time S 107  to time S 108 . 
     [Operation of Gas Detection System] 
       FIG. 20  is a flowchart of an example operation of the gas detection system  101  according to the fourth embodiment of the present disclosure during gas concentration. The control unit  194  may start a process as illustrated in  FIG. 20  after the first specific time period elapses after it is detected that the subject has risen from the toilet seat  102 B on the basis of the detection result of the sensor unit  193 . 
     The control unit  194  executes the processing of steps S 240 , S 241 , S 242 , and S 243  in a way that is the same as or similar to that of the processing of steps S 210 , S 211 , S 212 , and S 213  as illustrated in  FIG. 17 . When executing the processing of step S 243 , the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 101  (step S 244 ). 
     The control unit  194  detects the lapse of the fourth specified time period after the processing of step S 213  is executed (step S 245 ). The control unit  194  executes the processing of step S 246  in a way that is the same as or similar to that of the processing of step S 215  as illustrated in  FIG. 17 . 
     The control unit  194  executes the processing of steps S 247 , S 248 , S 249 , and S 250  in a way that is the same as or similar to that of the processing of steps S 221 , S 222 , S 223 , and S 224  as illustrated in  FIG. 17 . After the processing of step S 250  ends, the control unit  194  ends the gas concentration process. 
     As described above, in the gas detection system  101  according to the fourth embodiment, when controlling the supply unit  150  so that the sample gas passes through the concentration tank  160  as illustrated in  FIG. 12 , the control unit  194  controls the heaters  164  so that the temperature of the adsorbent  161  is maintained as the temperature T 101 . With this configuration, in the gas detection system  101  according to the fourth embodiment, the time taken to concentrate the sample gas in the concentration tank  160  can be shortened. In the fourth embodiment, since the time taken to concentrate the sample gas in the concentration tank  160  is shortened, the detection time period in the gas detection system  101  can be shortened. 
     Other advantages and configurations of the gas detection system  101  according to the fourth embodiment are the same as or similar or to those of the gas detection system  101  according to the third embodiment. 
     Fifth Embodiment 
     A fifth embodiment describes the pore size of the pore  161   a  of the adsorbent  161 . The adsorbent  161  according to the fifth embodiment can be applied to the third embodiment and the fourth embodiment. 
     As described above, the pore size of the pore  161   a  of the adsorbent  161  as illustrated in  FIG. 15  is larger than the molecular diameter of the gas to be detected  201 . Further, the pore size of the pore  161   a  of the adsorbent  161  may be less than or equal to twice the molecular diameter of the gas to be detected  201 . 
       FIG. 21  is a schematic graph illustrating the relationship between the temperature of an adsorbent and the concentration of a gas desorbed from the adsorbent in the fifth embodiment of the present disclosure. Specifically, a curve P 1  and a curve P 2  are obtained by plotting the ratio of the gas to be detected to the gas not to be detected, desorbed from the adsorbent  161 , while changing the temperature of the adsorbent  161  that has adsorbed the gas to be detected and the gas not to be detected. In  FIG. 21 , acetone was used as a gas to be detected, and water was used as a gas not to be detected. The molecular diameter of acetone is 0.467 nm. The molecular diameter of water is 0.265 nm. In the curve P 1 , the adsorbent  161  with the pore  161   a  having a pore size of 5 nm was used. In the curve P 2 , the adsorbent  161  with the pore  161   a  having a pore size of 0.5 nm was used. In both the curve P 1  and the curve P 2 , the pore size of the pore  161   a  of the adsorbent  161  used is larger than the molecular diameter of acetone, namely, 0.467 nm, and the molecular diameter of water, namely, 0.265 nm. 
     A peak value indicated by the curve P 2  was about 10 times larger than a peak value indicated by the curve P 1 . These results indicate that a sample gas in which the detection target has a higher concentration is obtained when the adsorbent  161  with the pore  161   a  having a pore size of 0.5 nm is used than when the adsorbent  161  with the pore  161   a  having a pore size of 5 nm is used. The pore size of the pore  161   a  of the adsorbent  161  used in the curve P 1 , namely, 5 nm, is larger than twice the molecular diameter of acetone, namely, 0.467 nm (pore size of 5 nm&gt;molecular diameter of 0.467 nm×2). The pore size of the pore  161   a  of the adsorbent  161  used in the curve P 2 , namely, 0.5 nm, is less than or equal to twice the molecular diameter of acetone, namely, 0.467 nm (pore size of 0.5 nm molecular diameter of 0.467 nm×2). In a case where the pore size of the pore  161   a  is less than or equal to twice the molecular diameter of acetone, the gap generated between acetone and the pore  161   a  can be narrower than in a case where the pore size of the pore  161   a  is larger than twice the molecular diameter of acetone. Accordingly, in a case where the pore size of the pore  161   a  is less than or equal to twice the molecular diameter of acetone, acetone may be less likely to exit the pore  161   a  at temperatures, except for the desorption temperature of acetone, than in a case where the pore size of the pore  161   a  is larger than twice the molecular diameter of acetone. In contrast, both the pore size of the pore  161   a  of the adsorbent  161  used in the curve P 1 , namely, 5 nm, and the pore size of the pore  161   a  of the adsorbent  161  used in the curve P 2 , namely, 0.5 nm, are larger than about 1.8 times the molecular diameter of water, namely, 0.265 nm. Thus, water can mostly be desorbed from the adsorbent  161  at the desorption temperature of water in both the case where the pore size of the pore  161   a  is 5 nm and the case where the pore size of the pore  161   a  is 0.5 nm. With this configuration, the peak value indicated by the curve P 2  is considered to be about ten times larger than the peak value indicated by the curve P 1 . Accordingly, in a case where the pore size of the pore  161   a  is larger than the molecular diameter of the gas to be detected and is less than or equal to twice the molecular diameter of the gas to be detected (molecular diameter of 0.467 nm&lt;pore size of 0.5 nm molecular diameter of 0.467 nm×2), a sample gas in which the detection target has a high concentration is obtained. 
     As indicated by the curve P 1 , in a case where the pore size of the pore  161   a  of the adsorbent  161  was 5 nm, the desorption temperature of acetone was about 162 degrees. As indicated by the curve P 2 , in a case where the pore size of the pore  161   a  of the adsorbent  161  was 0.5 nm, the desorption temperature of acetone was about 167 degrees. In both the case where the pore size of the pore  161   a  was 5 nm and the case where the pore size of the pore  161   a  was 0.5 nm, the desorption temperature of acetone was higher than that in a case where the adsorbent had no pore  161   a . Further, the desorption temperature of acetone (167 degrees) in a case where the pore size of the pore  161   a  is 0.5 nm is higher by about 5 degrees than the desorption temperature of acetone (162 degrees) in a case where the pore size of the pore  161   a  is 5 nm. These results indicate that the desorption temperature of the gas to be detected is high in a case where the pore size of the pore  161   a  is larger than the molecular diameter of the gas to be detected and is less than or equal to twice the molecular diameter of the gas to be detected (molecular diameter of 0.467 nm&lt;pore size of 0.5 nm molecular diameter of 0.467 nm×2). 
     (Modifications of Third Embodiment to Fifth Embodiment) 
     Modifications of the third embodiment to the fifth embodiment will be described hereinafter. 
     For example, in the third embodiment to the fifth embodiment described above, as illustrated in  FIG. 13 , the gas detection system  101  has been described as a single device. However, the gas detection system according to the present disclosure is not limited to the single device. The gas detection system according to the present disclosure may include a plurality of independent devices. For example, the third embodiment to the fifth embodiment described above may adopt a gas detection system  101 A having a configuration as illustrated in  FIG. 22 . 
     As illustrated in  FIG. 22 , the gas detection system  101 A includes a gas detection device  104  and a server device  105 . The gas detection device  104  and the server device  105  are capable of communicating with each other via a network  106 . A portion of the network  106  may be wired or wireless. The gas detection device  104  has a configuration that is the same as or similar to the configuration of the gas detection system  101  as illustrated in  FIG. 12  and  FIG. 13 . The server device  105  includes a storage unit  105 A, a communication unit  105 B, and a control unit  105 C. The control unit  105 C is capable of executing the processes of the control unit  194  as illustrated in  FIG. 13  described above. For example, the control unit  105 C is capable of controlling the supply unit  150  so that the sample gas concentrated in the concentration tank  160  is supplied to the sensor unit  181  in the chamber  180 . 
     The configurations of the third embodiment to the fifth embodiment described above can be summarized in the following appendices. 
     (Appendix 1) 
     A gas detection system including: 
     a sensor unit that outputs a signal corresponding to a concentration of a specific gas; 
     a concentration unit having therein an adsorbent having a pore; and 
     a supply unit capable of supplying a sample gas to the concentration unit, wherein 
     the pore has a larger pore size than an effective molecular diameter of a gas to be detected and an effective molecular diameter of a gas not to be detected, the gas to be detected and the gas not to be detected being contained in the sample gas, and 
     the effective molecular diameter of the gas to be detected is larger than the effective molecular diameter of the gas not to be detected. 
     (Appendix 2) 
     The gas detection system according to appendix 1, wherein 
     the pore size is less than or equal to twice the effective molecular diameter of the gas to be detected. 
     (Appendix 3) 
     The gas detection system according to appendix 1 or 2, wherein 
     the gas to be detected includes at least one of methane, hydrogen, carbon dioxide, methyl mercaptan, hydrogen sulfide, acetic acid, or trimethylamine, and 
     the gas not to be detected includes at least one of water or ammonia. 
     (Appendix 4) 
     The gas detection system according to any one of appendices 1 to 3, further including 
     a heater capable of heating the adsorbent. 
     (Appendix 5) 
     The gas detection system according to appendix 4, further including 
     a control unit capable of controlling the supply unit so that the sample gas, which is concentrated in the concentration unit, is supplied to the sensor unit, wherein 
     when the sample gas is to be concentrated in the concentration unit, the control unit controls the supply unit so that the sample gas passes through the concentration unit, and then controls the heater so that a temperature of the adsorbent increases to a desorption temperature of the gas to be detected. 
     (Appendix 6) 
     The gas detection system according to appendix 5, wherein 
     when controlling the supply unit so that the sample gas passes through the concentration unit, the control unit maintains the heater in a non-driven state. 
     (Appendix 7) 
     The gas detection system according to appendix 5, wherein 
     when controlling the supply unit so that the sample gas passes through the concentration unit, the control unit controls the heater so that the temperature of the adsorbent is maintained as a desorption temperature of the gas not to be detected. 
     The drawings describing embodiments according to the present disclosure are schematic ones. Dimensional ratios and the like in the drawings do not necessarily match the actual ones. 
     While embodiments according to the present disclosure have been described with reference to the drawings and examples, it should be noted that various modifications or changes can be easily made by a person skilled in the art on the basis of the present disclosure. Accordingly, it should be noted that these modifications or changes fall within the scope of the present disclosure. For example, the functions and the like included in each component or the like can be rearranged in any manner that is not logically contradictory, and a plurality of components may be combined into one or divided. 
     In the present disclosure, descriptions such as “first” and “second” are identifiers for distinguishing the respective configurations. The configurations distinguished by the descriptions such as “first” and “second” in the present disclosure may be interchangeably numbered. The identifiers are exchanged simultaneously. Even after the identifiers are exchanged, the respective configurations are distinguishable. The identifiers may be deleted. Configurations without identifiers are distinguished using reference numerals. Only the description of identifiers such as “first” and “second” in the present disclosure should not be used for interpreting the order of the configurations or as a basis of the presence of identifiers with smaller numbers. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  1 A gas detection system 
               2  toilet 
               2 A toilet bowl 
               2 B toilet seat 
               3  electronic device 
               3 A display unit 
               4  gas detection device 
               5  server device 
               5 A storage unit 
               5 B communication unit 
               5 C control unit 
               6  network 
               10  housing 
               20 ,  21  inflow path 
               22 ,  23 ,  24  discharge path 
               30 ,  31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37 ,  38 ,  39  flow path 
               40 ,  41 ,  42 ,  43 ,  44  valve 
               50  supply unit 
               60  concentration tank (concentration unit) 
               61  adsorbent 
               62 ,  63  support member 
               64  heater 
               70  storage tank (reservoir) 
               71  adsorbent 
               72 ,  73  support member 
               80  chamber 
               81  sensor unit 
               90  circuit board 
               91  storage unit 
               92  communication unit 
               93  sensor unit 
               94  control unit 
               101 ,  101 A gas detection system 
               102  toilet 
               102 A toilet bowl 
               102 B toilet seat 
               103  electronic device 
               103 A display unit 
               104  gas detection device 
               105  server device 
               105 A storage unit 
               105 B communication unit 
               105 C control unit 
               106  network 
               110  housing 
               120 ,  121  inflow path 
               122 ,  123 ,  124  discharge path 
               130 ,  131 ,  132 ,  133 ,  134 ,  135 ,  136 ,  137 ,  138 ,  139  flow 
             path 
               140 ,  141 ,  142 ,  143 ,  144  valve 
               150  supply unit 
               160  concentration tank (concentration unit) 
               161  adsorbent 
               161   a  pore 
               162 ,  163  support member 
               164  heater 
               170  storage tank (reservoir) 
               171  adsorbent 
               172 ,  73  support member 
               180  chamber 
               181  sensor unit 
               190  circuit board 
               191  storage unit 
               192  communication unit 
               193  sensor unit 
               194  control unit 
               201 ,  202  gas