Patent Document

FIELD OF THE INVENTION 
   The present invention relates to a device for detecting hydrogen concentration and a method of detecting hydrogen concentration. 
   BACKGROUND OF THE INVENTION 
   There has heretofore been known a device, for detecting hydrogen concentration, which utilizes the fact that the thermal conductivity of hydrogen is higher than that of the air. 
   For example, a hydrogen concentration detecting device disclosed in JP-A-2003-130834 detects hydrogen concentration based on a difference in the change of resistance between a detector element and a reference element both of which containing a thermistor therein. 
   According to the hydrogen concentration detecting device disclosed in JP-A-2003-130834, however, a flow of gas such as the air or hydrogen around the detector element robs heat from the detector element causing a variation in the resistance thereof. Therefore, the value that is detected tends to be higher than the real hydrogen concentration. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a device, for detecting hydrogen concentration, which provides high precision detection and a method thereof. 
   According to the invention described in claims  1  to  20 , first and second electrophysical quantities, in first and second heat-generating resistors that vary depending upon the hydrogen concentration, also undergo a variation depending upon the flow of gas around the first and second heat-generating resistors. Therefore, the amounts of change in the first and second electrophysical quantities often include a component of change due to the hydrogen concentration and a component of change due to the gas flow. The first and second heat-generating resistors neighbor each other in the direction of gas flow and, the first and second electrophysical quantities similarly vary depending upon the hydrogen concentration. Therefore, there is almost no difference in the component of change due to the hydrogen concentration between the first electrophysical quantity and the second electrophysical quantity, but a difference occurs in the component of change due to the gas flow. Therefore, of the amount of change in the electrophysical quantities, the component of change due to the gas flow can be found based on a difference between the first electrophysical quantity and the second electrophysical quantity. 
   Owing to the above-mentioned principle, and according to the invention described in claims  1 – 20 , the component of change due to the gas flow in the amount of change in the target physical quantity which is one of either the first electrophysical quantity or the second electrophysical quantity, is calculated as a correction amount based on a difference between the first electrophysical quantity and the second electrophysical quantity. A difference between the correction amount and the amount of change in the target physical quantity, substantially represents a component of change due to the hydrogen concentration. Therefore, the hydrogen concentration can be precisely calculated based on the above difference. According to the invention described in claims  1 – 20 , it is possible to increase the precision for detecting the hydrogen concentration. 
   The first electrophysical quantity and the second electrohysical quantity may be power consumption values as in, for example, the invention described in claims  2  and  12 , or may be resistances as in the invention described in claims  3  and  13 . 
   According to the invention described in claims  4  and  14 , a deviation between the target physical quantity at a reference timing when the hydrogen concentration and the gas flow become substantially 0 around the first and second heat-generating resistors and the target physical quantity at the time of detecting the concentration, is regarded to be the amount of change in the target physical quantity. Therefore, the zero point in the amount of change represents the target physical quantity at the reference timing. The target physical quantity at the reference timing can be precisely known in advance, such as before the shipment of the device equipped with the first and second heat-generating resistors. Therefore, the amount of change in the target physical quantity can be precisely found from the target physical quantity, at the reference timing, as the zero point. 
   The first and second electrophysical quantities vary depending upon the temperature around the first and second heat-generating resistors (hereinafter simply referred to as an ambient temperature). 
   According to the invention described in claims  5  and  15 , therefore, the target physical quantity at the reference timing is varied based upon the ambient temperature. Therefore, an error due to a change in the ambient temperature hardly occurs in the amount of change in the target physical quantity with the target physical quantity at the reference timing as the zero point. According to the invention described in claims  6  and  16 , further, the amount of correcting the hydrogen concentration is calculated based on the difference between the first electrophysical quantity and the second electrophysical quantity and on the ambient temperature. Therefore, the correction amount that is calculated seldom contains an error caused by a change in the ambient temperature. According to the invention described in claims  7  and  17 , the hydrogen concentration is calculated based on a difference between the amount of change in the target physical quantity and the correction amount, and upon the ambient temperature. Therefore, the hydrogen concentration that is calculated seldom contains an error caused by a change in the ambient temperature. 
   According to the invention described in claims  8  and  18 , the ambient temperature is detected based on the resistance that varies in the temperature-detecting resistor. Here, the temperature-detecting resistor neighbors either the first heat-generating resistor or the second heat-generating resistor, and a correct ambient temperature can be found from the resistance of the temperature-detecting resistor. 
   According to the invention described in claims  9  and  19 , the first and second heat-generating resistors have straight portions perpendicular to the axes of the directions of gas flow. Therefore, the first and second electrophysical quantities vary sharply depending upon the gas flow, and improved sensitivity to the gas flow is obtained. 
   According to the invention described in claims  10  and  20 , the first and second heat-generating resistors are contained in a membrane to prevent the occurrence of a difference between the first electrophysical quantity and the second electrophysical quantity caused by factors other than the gas flow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a flowchart illustrating the operation of a device for detecting hydrogen concentration according to an embodiment of the present invention; 
       FIG. 2  is a block diagram illustrating the constitution of the device for detecting hydrogen concentration according to the embodiment of the present invention; 
       FIG. 3  is a longitudinal sectional view illustrating a sensing unit according to the embodiment of the present invention; 
       FIG. 4  is a transverse sectional view illustrating the sensing unit according to the embodiment of the present invention; 
       FIGS. 5A and 5B  are graphs illustrating the operation of the device for detecting hydrogen concentration according the embodiment of the present invention; 
       FIGS. 6A and 6B  are graphs illustrating the operation of the device for detecting hydrogen concentration according the embodiment of the present invention; 
       FIG. 7A  is a longitudinal sectional view illustrating the sensing unit according to a modified example of the first embodiment of the invention, and 
       FIG. 7B  is a transverse sectional view illustrating the sensing unit according to the modified example of the first embodiment of the invention; and 
       FIG. 8  is a longitudinal sectional view illustrating the sensing unit according to another modified example of the first embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An embodiment of the invention will now be described with reference to the drawings. 
     FIG. 2  illustrates a device for detecting hydrogen concentration according to an embodiment of the invention. The device  1  for detecting hydrogen concentration is installed in an engine compartment or a passenger compartment of an automobile that uses hydrogen as a fuel, and detects the concentration of hydrogen leaking into the compartment. The device  1  for detecting hydrogen concentration includes a sensing unit  2 , a current control unit  30  and an arithmetic and control unit  50 . 
   Referring to  FIGS. 3 and 4 , the sensing unit  2  is constituted by a housing  4 , a base body  11 , a membrane  12 , heat-generating resistors  14  and  15 , and a temperature-detecting resistor  16 . 
   The housing  4  includes a recessed accommodating portion  5  for accommodating and securing the base body  11 , and a flow path  6  for discharging the gas after the gas is introduced onto the membrane  12  from the compartment. 
   The base body  11  is made of single-crystal silicon in the shape of nearly a flat plate. The base body  11  has a cavity  20  penetrating in the direction of the thickness of the plate. The cavity  20  has its one opening  21  closed by the bottom wall of the recessed accommodating portion  5  of the housing  4  thereby to constitute a recessed portion. The other opening  22  of the cavity  20  is covered with the membrane  12  of the form of a thin film. The gas introduced into the housing  4  through the flow path  6  flows through the flow path  6  of the membrane  12  on the side opposite to the base body  11 . In  FIGS. 3 and 4 , the arrow X represents the forward direction of gas flow and the arrow Y represents the reverse direction of gas flow. 
   The membrane  12  is constituted by a silicon oxide film  24  and a silicon nitride film  25  laminated by a micro-machine technology. The membrane  12  on the side of the silicon oxide film  24  is secured to the outer peripheral side of the opening  22  of the base body  11 . The membrane  12  contains therein the heat-generating resistors  14  and  15  and holds them between the silicon oxide film  24  and the silicon nitride film  25  on the opening  22 . Therefore, the membrane  12  works as a heat-insulating member for insulating the heat between the heat-generating resistors  14  and  15  and, further, it works as a protection film for protecting the heat-generating resistors  14  and  15 . The membrane  12  further contains therein the temperature-detecting resistor  16  and holds it between the silicon oxide film  24  and the silicon nitride film  25 . 
   The heat-generating resistors  14 ,  15  and the temperature-detecting resistor  16  are formed by patterning a metal film such as a Pt film or a similar film. The temperature-detecting resistor  16 , the heat-generating resistor  14  and the heat-generating resistor  15  are arranged in this order along the forward direction X of gas flow. In the both directions X and Y of gas flow, therefore, the temperature detecting resistor  16  and the heat-generating resistor  14  neighbor each other, and the heat-generating resistor  14  and the heat-generating resistor  15  neighbor each other. The heat-generating resistors  14  and  15 , having the same specifications, assume a meandering shape each being bent at six places, and each forming four straight portions  14   a  and  15   a  perpendicular to the axes of the both directions X and Y of gas flow. Gaps between the four straight portions  14   a , gaps between the four straight portions  15   a , and gaps between the neighboring straight portions  14   a ,  15   a  (i.e., gaps between the heat-generating resistors  14  and  15 ) are set to be, for example, not larger than 1 mm. The temperature-detecting resistor  16  has a U-shape, is bent at two places, and forms two straight portions  16   a  perpendicular to the axes of the both directions X and Y of gas flow. The gap between the two straight portions  16   a  and the gap between the neighboring straight portions  16   a  and  14   a  (i.e., the gap between the temperature-detecting resistor  16  and the heat-generating resistor  14 ) are set to be, for example, not larger than 1 mm. 
   The current control unit  30  shown in  FIG. 2  is constituted by an electric circuit, and is electrically connected to the heat-generating resistors  14 ,  15  and to the temperature-detecting resistor  16 . The current control unit  30  supplies electric currents to the heat-generating resistors  14 ,  15  and to the temperature-detecting resistor  16  in a controlled manner. 
   Concretely speaking, the current control unit  30  carries out a feedback control operation while maintaining the resistances of the resistors  14  and  15  constant so that the heat-generating temperatures of the heat-generating resistors  14  and  15  become constant. In this case, the current control unit  30  of this embodiment works so that the resistances of the heat-generating resistors  14  and  15  become equal to each other, and that the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  similarly vary depending upon the hydrogen concentration around the resistors. Therefore, a correlation becomes in agreement between the power consumption values W 1 , W 2  and the hydrogen concentration when the gas flow becomes substantially 0 around the heat-generating resistors  14  and  15 . 
   As a result of feedback control by the current control unit  30 , the power consumption values W 1 , W 2  of the heat-generating resistors  14  and  15  vary as described below. 
   When the hydrogen concentration and the gas flow become substantially zero around the heat-generating resistors  14  and  15 , the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  assume nearly the same reference value W B . 
   When the hydrogen concentration becomes substantially zero but the gas flows around the heat-generating resistors  14  and  15 , the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  become greater than the reference value W B  and different from each other as shown in  FIG. 5B . When the gas is flowing in the forward direction X, in this case, the power consumption value W 1  of the heat-generating resistor  14  on the upstream side becomes greater than the power consumption value W 2  of the heat-generating resistor  15  on the downstream side. When the gas is flowing in the reverse direction Y, on the other hand, the power consumption value W 2  of the heat-generating resistor  15  on the upstream side becomes greater than the power consumption value W 1  of the heat-generating resistor  14  on the downstream side. In either case, the amounts C 1  and C 2  of change in the power consumption values W 1  and W 2  represented by deviations of the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  from the reference value W B , are solely components of change due to the gas flow. 
   When the hydrogen concentration becomes greater than zero but the gas flow becomes substantially zero around the heat-generating resistors  14  and  15 , the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  become greater than the reference value WB and become nearly equal to each other as shown in  FIG. 6A . Here, the amounts C 1  and C 2  of change in the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  are solely components of change due to the hydrogen concentration. 
   When the hydrogen concentration becomes greater than zero and the gas flows around the heat-generating resistors  14  and  15  as shown in  FIG. 6B , the power consumption values W 1  and W 2 , of the heat-generating resistors  14  and  15 , become greater than the reference value W B  and become different from each other. Here, when the gas is flowing in the forward direction X as shown in  FIG. 6B , the power consumption value W 1  of the heat-generating resistor  14  on the upstream side becomes greater than the power consumption value W 2  of the heat-generating resistor  15  on the downstream side. When the gas is flowing in the reverse direction Y, on the other hand, the power consumption value W 2  of the heat-generating resistor  15  on the upstream side becomes greater than the power consumption value W 1  of the heat-generating resistor  14  of the downstream side. In either case, the amounts C 1  and C 2  of change in the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  become the amounts obtained by adding the components of change due to the gas flow to the components of change due to the hydrogen concentration. Here, the amounts C 1  and C 2  of change in the power consumption values W 1  and W 2  are different from each other, as shown in  FIG. 6B , because there is a difference in the components of change, due to the gas flow, even though there is no difference in the components of change due to the hydrogen concentration. 
   When an instruction signal is received from the arithmetic and control unit  50 , further, the current control unit  30  supplies a predetermined voltage or a predetermined current to the temperature-detecting resistor  16 . Therefore, the resistance R of the temperature-detecting resistor  16  varies depending upon the temperature T around the temperature-detecting resistor  16 . In this embodiment, the temperature-detecting resistor  16  is located close to the heat-generating resistors  14  and  15 . Therefore, the ambient temperature T of the temperature-detecting resistor  16  is substantially in agreement with the ambient temperature of the heat-generating resistors  14  and  15 . 
   Referring to  FIG. 2 , the arithmetic and control unit  50  which is the “concentration detector means” is constituted chiefly by a microcomputer having a CPU  51 , a ROM  52  and a RAM  53 . The arithmetic and control unit  50  is electrically connected to the current control unit  30 , and receives, from the current control unit  30 , the signals representing the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15 , and the resistance R of the temperature-detecting resistor  16 . The arithmetic and control unit  50  has the CPU  51  execute a detection program, stored in the ROM  52 , to detect the ambient temperature T based on the resistance R and to detect the hydrogen concentration based on the ambient temperature T and on the power consumption values W 1 , W 2 . At this moment, the power consumption values W 1 , W 2  and the ambient temperature T are stored in the RAM  53 . 
   The steps successively executed by the arithmetic and control unit  50 , as the detection program is executed by the CPU  51 , will now be described in detail according to the flowchart of  FIG. 1 . 
   At step S 1 , first, an instruction signal is given to the current control unit  30  to supply a current to the temperature-detecting resistor  16  and, then, a signal representing the resistance R is received from the current control unit  30 . At step S 1 , further, an ambient temperature T is calculated based on the resistance R represented by the received signal, and is stored in the RAM  53 . The “temperature detecting means” is represented by a portion of the arithmetic and control unit  50  that executes the above step S 1 , by the temperature-detecting resistor  16  and by the current control unit  30 , and the “temperature detecting step” is represented by the above step S 1 . 
   At step S 2 , an instruction signal is given to the current control unit  30 , whereby signals representing the power consumption values W 1  and W 2  are received from the current control unit  30 , and the power consumption values W 1  and W 2  represented by the received signals are stored in the RAM  53 . 
   At step S 3 , attention is given to the one power consumption value W 1  to calculate a deviation between the power consumption value W 1  and the reference value W B , i.e., to calculate the amount C 1  of change in the power consumption value W 1 . In this embodiment, at this moment, the reference value WB is varied depending upon the ambient temperature T. The relationship between the reference value WB and the ambient temperature T has been measured in advance prior to the shipment of the device  1 , and has been stored in the ROM  52  in the form of a map of a function. At step S 3 , further, the amount C 1  of change that is calculated is stored in the RAM  53 . The “amount-of-change calculation means” is represented by a portion of the arithmetic and control unit  50  that executes the above step S 3 , and the “amount-of-change calculation step” is represented by the above step S 3 . 
   At step S 4 , a difference δ W , between the power consumption values W 1  and W 2 , is calculated and is stored in the RAM  53 . 
   At step S 5 , of the amount C 1  of change in the power consumption value W 1 , the component of change due to the gas flow is estimated as the correction amount C A  based on the difference δ W  between the power consumption values W 1  and W 2 . In this embodiment, in this case, the correction amount C A  is so calculated as to be proportional to the difference δ W , and the coefficient of proportion is varied depending upon the ambient temperature T. A correlation among the difference δ W , the ambient temperature T and the correction amount C A  has been stored in advance in the ROM  52  in the form of a map or a function. At step S 5 , further, the calculated correction amount C A  is stored in the RAM  53 . The “correction amount calculation means” is represented by a portion of the arithmetic and control unit  50  which executes the step S 5 , and the “correction amount calculation step” is represented by the step S 5 . 
   At step S 6 , a difference δ C  between the amount C 1  of change in the power consumption value W 1  and the correction amount C A  is calculated and is stored in the RAM  53 . 
   At step S 7 , the hydrogen concentration DH is calculated based on the difference δ C  between the amount C 1  of change in the power consumption value W 1  and the correction amount C A . In this embodiment, in this case, the correction amount D H  is so calculated as to be proportional to the difference δ C , and the coefficient of proportion is varied depending upon the ambient temperature T. A correlation among the difference δ C , the ambient temperature T and the calculated hydrogen concentration D H  has been stored in advance in the ROM  52  in the form of a map or a function. The “concentration calculation means” is represented by a portion of the arithmetic and control unit  50  which executes the step S 7 , and the “concentration calculation step” is represented by the step S 7 . 
   In this embodiment, which detects the hydrogen concentration as described above, the values C 1 , C A , δ C  and D H  calculated at steps S 3 , S 5 , S 6  and S 7  undergo changes as described above. 
   When the hydrogen concentration and the gas flow are substantially 0 around the heat-generating resistors  14  and  15 , the amount of change C 1  in the power consumption value W 1  and the correction amount C A  become 0, and the difference δ C  between C 1  and C A  becomes 0, too. Therefore, the hydrogen concentration D H  which varies in proportion to the difference δ C  becomes 0. 
   When the hydrogen concentration becomes substantially 0 but the gas flows around the heat-generating resistors  14  and  15 , the amount C 1  of change in the power consumption value W 1  becomes solely the component of change due to the gas flow, and becomes in agreement with the correction amount C A , whereby the difference δ C  between C 1  and C A  becomes 0. Therefore, the hydrogen concentration D H  that varies in proportion to the difference δ C  becomes 0. 
   When the hydrogen concentration becomes greater than 0 while the gas flow is substantially 0 around the heat-generating resistors  14  and  15 , the amount C 1  of change in the power consumption value W 1  is solely the component of change in the hydrogen concentration while the correction amount C A  is 0. Therefore, the difference δ C  between C 1  and C A  becomes in agreement with the component of change due to the hydrogen concentration. Accordingly, the hydrogen concentration D H  which varies in proportion to the difference δ C  precisely represents the real concentration. 
   When the hydrogen concentration is greater than 0 and the gas flows around the heat-generating resistors  14  and  15 , the amount C 1  of change in the power consumption value W 1  becomes the sum of the component of change due to the hydrogen concentration and the component of change due to the gas flow. Accordingly, the difference δ C  between the amount C 1  of change and the correction amount C A  becomes equal to the amount C 1  of change from which the component of change due to the gas flow is subtracted, and becomes in agreement with the component of change due to the hydrogen concentration. Therefore, the hydrogen concentration D H  which varies in proportion to the difference δ C  precisely represents the real concentration. 
   In this embodiment as described above, even when the gas flows around the heat-generating resistors  14  and  15 , the detected hydrogen concentration D H  is not affected by the gas flow. 
   At steps S 3 , S 5  and S 7 , further, the values C 1 , C A  and D H  are calculated by taking the ambient temperature T into consideration; i.e., the values C 1 , C A  and D H  are avoided from containing errors that stem from changes in the ambient temperature T. Therefore, the detected the hydrogen concentration D H  is not affected by a change in the ambient temperature T. 
   Further, the heat-generating resistors  14  and  15  have straight portions  14   a  and  15   a  perpendicular to the axes of the directions X, Y of gas flow. Therefore, the power consumption values W 1  and W 2  of the resistors  14  and  15  sensitively vary in response to the gas flow. At step S 5 , therefore, the correction amount C A  can be precisely obtained as a component of change due to the gas flow, making it possible to detect the hydrogen concentration DH which is hardly affected by the gas flow. 
   Further, the membrane  12  has the function of insulating the heat between the heat-generating resistors  14  and  15  and for protecting the resistors  14  and  15 , preventing the occurrence of difference between the power consumption values W 1  and W 2  of the heat-generating resistors  14 ,  15  due to factors other than the gas flow, such as mutual thermal action and shocks between the resistors  14  and  15 . Therefore, there is detected the hydrogen concentration D H  which is not affected by the mutual thermal action or shocks between the resistors  14  and  15 . 
   According to this embodiment as described above, the hydrogen concentration is detected highly precisely. 
   In the above-mentioned embodiment, the resistances of the heat-generating resistors  14  and  15  are maintained constant and equal to each other, and the hydrogen concentration is detected based on the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15 . It is, however, also possible to maintain the power consumption values W 1  and W 2  of the heat-generating resistors  14  and  15  constant and equal to each other, and to detect the hydrogen concentration based on the resistances of the heat-generating resistors  14  and  15 . 
   In the above embodiment, further, the heat-generating resistors  14  and  15  and the temperature-detecting resistor  16  are formed of a metal film such as a Pt film. These resistors  14 ,  15  and  16 , however, may be formed of a semiconductor film such as a polysilicon film. 
   According to the above embodiment, the temperature-detecting resistor  16  is provided neighboring the heat-generating resistor  14 . However, the temperature-detecting resistor  16  may be provided neighboring the heat-generating resistor  15 . 
   In the above embodiment, further, the ambient temperature T is detected by the temperature-detecting resistor  16 . However, the ambient temperature T may be detected by using any other widely-known temperature sensor. 
   At steps S 3 , S 5  and S 7  of the above embodiment, further, the values C 1 , C A  and D H  are calculated by taking the ambient temperature T into consideration. However, at least any one of the values C 1 , C A  and D H  may be calculated irrespective of the ambient temperature T. When the values C 1 , C A  and D H  are to be all calculated irrespective of the ambient temperature T, there is no need to provide the temperature-detecting resistor  16  or the temperature sensor in its place. 
   Further, according to a modified example of the above embodiment as illustrated in  FIG. 7 , the cavity  20  may be formed in the substrate  11  from the side of the front surface  62  of the flow path  6  by using a chemical that acts upon the substrate  11  without the cavity  20  by passing the chemical through at least one window  60  perforated in a portion of the membrane  12  surrounding the heat-generating resistors  14  and  15  in the direction of thickness. Here, as shown in  FIG. 7 , the cavity  20  may be formed to open on only the side of the front surface  62  without penetrating through the substrate  11 . According to another modified example shown in  FIG. 8 , further, a porous portion  70  may be formed instead of the cavity  20  by, for example, using a chemical that acts upon the substrate  11 . 
   At step S 3  of the above embodiment, further, a deviation between the power consumption value W 1  and the reference value WB is calculated as the amount C 1  of change in the power consumption value W 1  by detecting the power consumption value W 1  of the heat-generating resistor  14 . At step S 3 , however, it is also possible to calculate a deviation between the power consumption value W 2  and the reference value W B  as the amount C 2  of change in the power consumption value W 2  by detecting the power consumption value W 2  of the heat-generating resistor  15 . In this case, at step S 5 , of the amount C 2  of change in the power consumption value W 2 , a component of change due to the gas flow is estimated based on a difference δ W  between the power consumption values W 1  and W 2  and is regarded as the correction amount C A  to calculate, at step S 6 , a difference δ C  between the amount C 2  of change in the power consumption value W 2  and the correction amount C A  The above embodiment has dealt with a case where the present invention was applied to the device  1  for detecting the concentration of hydrogen leaking in the engine room or in the compartment of an automobile which uses hydrogen as a fuel. It is, however, also possible to apply the present invention to a device for detecting hydrogen concentration which detects the concentration of hydrogen fed to a fuel cell in the automobile that uses hydrogen as a fuel. Or, the invention may be applied to the device for detecting hydrogen-concentration which detects the concentration of hydrogen emitted to the exterior from the automobile that uses hydrogen as a fuel. Or, the invention may be applied to the device for detecting hydrogen concentration at a place other than an automobile that uses hydrogen as a fuel.

Technology Category: g