JP2017142130A - Nitrogen concentration measurement system and method for measuring nitrogen concentration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen concentration measurement system with which it is possible to easily measure the concentration of nitrogen included in a gas.SOLUTION: Provided is a nitrogen concentration measurement system comprising: a measurement unit 301 for measuring the measured value of an electric signal from a heat generating element that is in contact with a mixed gas to be measured, at each of a plurality of heat generation temperatures; a normalization unit 306 for normalizing the measured values of electric signals so that the values of electric signals from a heat generating element that is in contact with a reference gas not including nitrogen and in contact with a calibration gas are constant irrespective of heat generation temperatures; an expression storage unit 402 for preserving a nitrogen concentration calculation expression where normalized electric signals from heat generating elements at three heat generation temperatures at the least are an independent variable and a nitrogen concentration is a dependent variable; and a nitrogen concentration calculation unit 307 for assigning the measured values of normalized electric signals to the independent variables of the nitrogen concentration calculation expression, and calculating the concentration of nitrogen included in the mixed gas to be measured.SELECTED DRAWING: Figure 23

Description

  The present invention relates to a gas inspection technique, and relates to a nitrogen concentration measurement system and a nitrogen concentration measurement method.

Conventionally, when determining the calorific value of a mixed gas, it is necessary to analyze the components of the mixed gas using an expensive gas chromatography apparatus or the like. Further, by measuring the thermal conductivity of the mixed gas and the speed of sound in the mixed gas, methane (CH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ) contained in the mixed gas. ) Has been proposed (see, for example, Patent Document 1).

  However, the method disclosed in Patent Document 1 requires an expensive sound speed sensor for measuring sound speed in addition to the sensor for measuring thermal conductivity. In view of this, there has also been proposed a method for obtaining a heat generation amount of a mixed gas using a heat generating element that generates heat at a plurality of heat generation temperatures without using a sonic sensor (see, for example, Patent Documents 2, 3, 4, and 5). .

JP-T-2004-514138 Japanese Patent No. 5075986 Japanese Patent No. 5781968 JP2013-205109A Japanese Patent No. 5759780

  When nitrogen gas is contained in the mixed gas, the nitrogen gas is an incombustible component and the calorific value is zero. Therefore, it is preferable that the concentration of nitrogen gas can be measured in order to accurately know the calorific value of the mixed gas. Accordingly, an object of the present invention is to provide a nitrogen concentration measurement system and a nitrogen concentration measurement method that can easily measure the concentration of nitrogen contained in a gas.

  According to the aspect of the present invention, (a) a measurement unit that measures a measured value of an electric signal from a heating element that is in contact with a measurement target mixed gas at each of a plurality of exothermic temperatures, and (b) a hydrocarbon as a calibration component. A normalization unit that normalizes the measurement value of the electrical signal so that the value of the electrical signal from the heating element in contact with the reference gas not containing nitrogen and the calibration gas is constant regardless of the heating temperature; and (c) at least 3 A formula storage device for storing a nitrogen concentration calculation formula having normalized electric signals from the heating elements at two exothermic temperatures as independent variables and a nitrogen concentration as a dependent variable, and (d) an independent variable of the nitrogen concentration calculation formula, There is provided a nitrogen concentration measurement system comprising: a nitrogen concentration calculation unit that substitutes a measured value of a normalized electric signal and calculates a concentration of nitrogen contained in a measurement target mixed gas.

  In the above nitrogen concentration measurement system, the nitrogen concentration calculation unit corrects the first difference of the measured value of the normalized electrical signal in the first difference of the exothermic temperature by the correction coefficient and the corrected first difference. And the concentration of nitrogen contained in the measurement target mixed gas based on the evaluation value that is the difference between the second difference in the measured value of the normalized electrical signal in the second difference in the exothermic temperature, The correction coefficient may be set so that the evaluation value approaches 0 when a gas not containing nitrogen is in contact with the heating element.

  In the nitrogen concentration measurement system, the nitrogen concentration calculation unit multiplies the evaluation value by a second correction coefficient to calculate a nitrogen concentration, and the second correction coefficient is a dimensionless number. It may be set to convert to.

  In the above nitrogen concentration measurement system, the reference gas may be methane gas. Further, the normalization unit may normalize the measured value of the electric signal so that the value of the electric signal from the heating element in contact with the reference gas becomes 0 regardless of the heat generation temperature.

  In the above nitrogen concentration measurement system, the calibration gas may be a mixed gas. The calibration gas may be a span gas. The normalization unit may normalize the measured value of the electrical signal so that the value of the electrical signal from the heating element in contact with the calibration gas becomes 1 regardless of the heating temperature.

  In the above nitrogen concentration measurement system, the formula storage device further stores a calorific value calculation formula having the electrical signals from the heating elements at a plurality of exothermic temperatures as independent variables and the calorific value as a dependent variable, and measuring the above nitrogen concentration The system may further include a calorific value calculation unit that calculates the value of the calorific value of the measurement target mixed gas by substituting the measured value of the electrical signal from the heat generating element into the independent variable of the calorific value calculation formula.

  In the above nitrogen concentration measurement system, the number of the plurality of exothermic temperatures may be at least one obtained by subtracting 1 from the number of the plurality of types of gas components contained in the measurement target mixed gas.

  Further, according to the aspect of the present invention, (a) measuring a measured value of an electric signal from a heating element in contact with the measurement target mixed gas at each of a plurality of exothermic temperatures, and (b) using hydrocarbon as a calibration component Normalizing the measured value of the electric signal so that the value of the electric signal from the heating element in contact with the reference gas not containing nitrogen and the calibration gas is constant regardless of the heating temperature, and (c) at least three Prepared a nitrogen concentration calculation formula using the normalized electric signal from the heating element at the heat generation temperature as an independent variable and the nitrogen concentration as a dependent variable; and (d) normalized to an independent variable of the nitrogen concentration calculation formula. And a method of measuring the nitrogen concentration, comprising substituting the measured value of the electrical signal and calculating the concentration of nitrogen contained in the measurement target mixed gas.

  In calculating the nitrogen concentration in the above nitrogen concentration measurement method, the corrected first value obtained by multiplying the first difference in the normalized measurement value of the electrical signal in the first difference in the exothermic temperature by the correction coefficient is used. Based on the evaluation value that is the difference between the difference and the second difference in the normalized measurement value of the electrical signal in the second difference in the heat generation temperature, the concentration of nitrogen contained in the measurement target mixed gas is calculated and corrected The coefficient may be set so that the evaluation value approaches 0 when a gas not containing nitrogen is in contact with the heating element.

  In calculating the nitrogen concentration of the nitrogen concentration measurement method, the evaluation value is multiplied by a second correction coefficient to calculate the nitrogen concentration, and the evaluation value is a dimensionless number. May be set to be converted into a density unit.

  In the above method for measuring the nitrogen concentration, the reference gas may be methane gas. Further, the measured value of the electric signal may be normalized so that the value of the electric signal from the heating element in contact with the reference gas becomes 0 regardless of the heat generation temperature.

  In the above nitrogen concentration measurement method, the calibration gas may be a mixed gas. The calibration gas may be a span gas. Further, the measurement value of the electric signal may be normalized so that the value of the electric signal from the heating element in contact with the calibration gas becomes 1 regardless of the heating temperature.

  The above-mentioned nitrogen concentration measurement method prepares a calorific value calculation formula using an electrical signal from a heating element at a plurality of exothermic temperatures as an independent variable and the calorific value as a dependent variable, and as an independent variable of the calorific value calculation formula. The method further includes substituting the measured value of the electrical signal from the heating element to calculate the value of the calorific value of the measurement target mixed gas.

  In the above nitrogen concentration measurement method, the number of the plurality of exothermic temperatures may be a number obtained by subtracting 1 from the number of the plurality of types of gas components contained in the measurement target mixed gas.

  According to the present invention, it is possible to provide a nitrogen concentration measuring system and a nitrogen concentration measuring method capable of easily measuring the concentration of nitrogen contained in a gas.

It is a perspective view of the 1st microchip concerning an embodiment of the invention. It is sectional drawing seen from the II-II direction of FIG. 1 of the 1st microchip which concerns on embodiment of this invention. It is a perspective view of the 2nd microchip concerning an embodiment of the invention. It is sectional drawing seen from the IV-IV direction of FIG. 3 of the 2nd microchip which concerns on embodiment of this invention. It is a graph which shows the relationship between the thermal conductivity which concerns on embodiment of this invention, and a thermal radiation coefficient. It is a graph which shows the relationship between the temperature of the heat generating element which concerns on embodiment of this invention, and the thermal radiation coefficient of gas. It is a 1st graph which shows the relationship between the thermal conductivity which concerns on embodiment of this invention, and resistance of a heat generating element. It is a 2nd graph which shows the relationship between the thermal conductivity which concerns on embodiment of this invention, and resistance of a heat generating element. It is a 3rd graph which shows the relationship between the heat conductivity which concerns on embodiment of this invention, and resistance of a heat generating element. It is a 4th graph which shows the relationship between the heat conductivity which concerns on embodiment of this invention, and resistance of a heat generating element. It is a 1st graph which shows the relationship between the thermal conductivity which concerns on embodiment of this invention, and the drive power of a heat generating element. It is a 2nd graph which shows the relationship between the thermal conductivity which concerns on embodiment of this invention, and the drive power of a heat generating element. It is a graph which shows the relationship between the heat generation temperature of the heat generating element which concerns on embodiment of this invention, and the thermal conductivity of gas. It is a graph which shows the relationship between the heat generation temperature of the heat generating element which concerns on embodiment of this invention, and the normalized thermal conductivity of gas. It is a graph which shows the relationship between the heat_generation | fever temperature of the heat generating element which concerns on embodiment of this invention, and the normalized thermal conductivity of the gas whose nitrogen concentration is 0%. It is a graph which shows the relationship between the heat_generation | fever temperature of the heat generating element which concerns on embodiment of this invention, and the normalized thermal conductivity of gas whose nitrogen concentration is 3% or 4%. It is a graph which shows the relationship between the heat_generation | fever temperature of the heat generating element which concerns on embodiment of this invention, and the normalized thermal conductivity of the gas whose nitrogen concentration is 5% or 6%. It is a graph which shows the 1st difference of the measured value of the normalized electrical signal in the 1st difference of the exothermic temperature which concerns on embodiment of this invention. It is a graph which shows the 2nd difference of the measured value of the normalized electrical signal in the 2nd difference of the exothermic temperature which concerns on embodiment of this invention. It is a graph which shows the evaluation value which concerns on embodiment of this invention. It is a graph which shows the relationship between the corrected evaluation value which concerns on embodiment of this invention, and actual nitrogen concentration. It is a graph which shows the error of the measured value of nitrogen concentration concerning an embodiment of the invention. It is a mimetic diagram of a nitrogen concentration measuring system concerning an embodiment of the invention. It is a flowchart which shows the preparation method of the emitted-heat amount calculation formula which concerns on embodiment of this invention. It is a flowchart which shows the preparation method of the nitrogen concentration calculation formula which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  First, the microchip 8 used in the nitrogen concentration measurement system according to the embodiment will be described with reference to FIG. 1 which is a perspective view and FIG. 2 which is a cross-sectional view seen from the II-II direction. The microchip 8 includes a substrate 60 provided with a cavity 66, and an insulating film 65 disposed on the substrate 60 so as to cover the cavity 66. The thickness of the substrate 60 is, for example, 0.5 mm. The vertical and horizontal dimensions of the substrate 60 are, for example, about 1.5 mm. A portion of the insulating film 65 covering the cavity 66 forms a heat insulating diaphragm. Furthermore, the microchip 8 includes a heating element 61 provided in the diaphragm portion of the insulating film 65, a first temperature measuring element 62 and a second temperature measuring element 62 provided in the diaphragm portion of the insulating film 65 so as to sandwich the heating element 61. The temperature measuring element 63 and a heat retaining element 64 provided on the substrate 60 are provided.

  The diaphragm is provided with a plurality of holes. By providing a plurality of holes in the diaphragm, gas replacement in the cavity 66 is accelerated. Alternatively, the insulating film 65 may be disposed on the substrate 60 so as to cover the cavity 66 in a bridge shape as shown in FIG. 3 and FIG. 4 which is a cross-sectional view seen from the IV-IV direction. Also by this, the inside of the cavity 66 is exposed, and the replacement of the gas in the cavity 66 is accelerated.

  The heating element 61 shown in FIGS. 1 and 2 is arranged at the center of the diaphragm portion of the insulating film 65 covering the cavity 66. The heating element 61 is a resistor, for example, and generates heat when power is applied to heat the atmospheric gas in contact with the heating element 61. The first temperature measuring element 62 and the second temperature measuring element 63 are electronic elements such as passive elements such as resistors, for example, and output electric signals depending on the gas temperature of the atmospheric gas. In the following, an example in which the output signal of the first temperature measuring element 62 is used will be described. However, the present invention is not limited to this. For example, the output signal of the first temperature measuring element 62 and the output of the second temperature measuring element 63 are described. You may utilize the average value of a signal as an output signal of a temperature measuring element.

The heat retaining element 64 is a resistor, for example, and generates heat when supplied with electric power, and keeps the temperature of the substrate 60 constant. As a material of the substrate 60, silicon (Si) or the like can be used. As a material of the insulating film 65, silicon oxide (SiO ₂ ) or the like can be used. The cavity 66 is formed by anisotropic etching or the like. Further, platinum (Pt) or the like can be used as the material of the heating element 61, the first temperature measuring element 62, the second temperature measuring element 63, and the heat retaining element 64, and can be formed by a lithography method or the like. . Further, the heating element 61, the first temperature measuring element 62, and the second temperature measuring element 63 may be made of the same member.

  The microchip 8 is fixed to a container such as a chamber filled with atmospheric gas via a heat insulating member 18 disposed on the bottom surface of the microchip 8. By fixing the microchip 8 to the container via the heat insulating member 18, the temperature of the microchip 8 becomes less susceptible to the temperature fluctuation of the inner wall of the container.

A plurality of voltages are applied to the heating element 61 in stages. When three levels of voltage are applied to the heating element 61, the heating element 61 generates heat at three levels of temperature according to the applied voltage. Alternatively, when a five-step voltage is applied to the heating element 61, the heating element 61 generates heat at a five-step temperature according to the applied voltage. Hereinafter, the temperature of the heating element 61 to which the first voltage V _L1 is applied is T _H1 , the temperature of the heating element 61 to which the second voltage V _L2 is applied is T _H2 , and the third voltage V _L3 is applied. The temperature of the heating element 61 is T _H3 , the temperature of the heating element 61 to which the fourth voltage V _L4 is applied is T _H4 , and the temperature of the heating element 61 to which the fifth voltage V _L5 is applied is T _H5 . However, the number of voltages applied stepwise is not limited to these.

  A weak voltage is applied to the first temperature measuring element 62 so as not to cause the first temperature measuring element 62 to self-heat.

The resistance value of the heating element 61 varies depending on the temperature of the heating element 61. The relationship between the temperature _TH of the heating element 61 and the resistance value R _H of the heating element 61 is given by the following equation (1).
R _H = R _H-STD × [1 + α _H (T _H -T _H-STD ) + β _H (T _H -T _H-STD ) ² ] (1)
Here, T _H-STD represents the standard temperature of the heating element 61, and is 20 ° C., for example. R _H-STD represents the resistance value of the heating element 61 measured in advance at the standard temperature T _H-STD . α _H represents a first-order resistance temperature coefficient. β _H represents a second-order resistance temperature coefficient.

The resistance value R _H of the heating element 61 is given by the following equation (2) from the drive power P _H of the heating element 61 and the energization current I _H of the heating element 61.
R _H = P _H / I _H ² (2)
Alternatively, the resistance value R _H of the heating element 61 is given by the following equation (3) from the voltage V _H applied to the heating element 61 and the energization current I _H of the heating element 61.
R _H = V _H / I _H (3)

Here, the temperature _TH of the heating element 61 is stabilized when the heating element 61 and the ambient gas are in thermal equilibrium. The thermally balanced state is a state where the heat generation of the heating element 61 and the heat dissipation from the heating element 61 to the atmospheric gas are balanced. (4) below, as shown in the expression, the driving power P _H of the heater element 61 at equilibrium, by dividing the difference [Delta] T _H between the temperature T _I of the temperature T _H and the ambient gas of the heater element 61, the atmospheric gas A heat dissipation coefficient M _I is obtained. The unit of the heat dissipation coefficient M _I is, for example, W / ° C.
M _I = P _H / (T _H -T _I )
= P _H / ΔT _H = (V _H ² / R _H ) / ΔT _H・ ・ ・ (4)

From the above equation (1), the temperature T _H of the heater element 61 is given by the following equation (5).
_{T H = (1 / 2β H} ) × [-α H + [α H 2 - 4β H (1 - R H / R H-STD)] 1/2] + T H-STD ···(Five)
Therefore, the difference ΔT _H between the temperature T _H of the heating element 61 and the temperature T _{I of the} atmospheric gas is given by the following equation (6).
_{ΔT H = (1 / 2β H} ) × [-α H + [α H 2 - 4β H (1 - R H / R H-STD)] 1/2] + T H-STD - T I ··· ( 6)

The temperature T _{I of the} atmospheric gas approximates the temperature T _I of the first temperature measuring element 62 to which power that does not generate heat is given. The relationship between the temperature T _I of the first temperature measuring element 62 and the resistance value R _{I of} the first temperature measuring element 62 is given by the following equation (7).
R _I = R _I-STD × [1 + α _I (T _I -T _I-STD ) + β _I (T _I -T _I-STD ) ² ] (7)
T _I-STD represents the standard temperature of the first temperature measuring element 62 and is, for example, 20 ° C. R _I-STD represents the resistance value of the first temperature measuring element 62 measured in advance at the standard temperature T _I-STD . α _I represents the first-order resistance temperature coefficient. β _I represents a second-order resistance temperature coefficient. From the above equation (7), the temperature T _I of the first temperature measuring element 62 is given by the following equation (8).
_{T I = (1 / 2β I} ) × [-α I + [α I 2 - 4β I (1 - R I / R I-STD)] 1/2] + T I-STD ··· (8)

Therefore, the radiation coefficient M _I of the atmospheric gas is given by the following equation (9).
M _I = P _H / ΔT _H
= P _H / [(1 / 2β _H ) [-α _H + [α _H ² -4β _H (1-R _H / R _H-STD )] ^1/2 ] + T _H- STD-(1 / 2β _I ) [-α _I + [α _I ² -4β _I (1-R _I / R _I-STD )] ^1/2 ] -T _I-STD ] ... (9)

Since the energizing current I _H and the driving power P _H or voltage V _H of the heating element 61 can be measured, the resistance value R _H of the heating element 61 can be calculated from the above equation (2) or (3). Similarly, the resistance value R _{I of} the first temperature measuring element 62 can also be calculated. Therefore, by using the microchip 8, the heat radiation coefficient M _{I of the} atmospheric gas can be calculated from the above equation (9).

Note that, by keeping the temperature of the substrate 60 constant by the heat retaining element 64, the temperature of the ambient gas in the vicinity of the microchip 8 before the heat generating element 61 generates heat approximates the constant temperature of the substrate 60. For this reason, fluctuations in the temperature of the atmospheric gas before the heat generating element 61 generates heat are suppressed. By temperature variation further heated by the heating element 61 to the atmosphere gas is once suppressed, it is possible to calculate the radiation coefficient M _I with high accuracy.

Here, it is assumed that the atmospheric gas is a mixed gas, and the mixed gas is composed of four types of gas components: gas A, gas B, gas C, and gas D. The sum of the volume ratio V _A of gas _A , the volume ratio V _B of gas _B , the volume ratio V _C of gas _C , and the volume ratio V _D of gas D is 1, as given by the following equation (10). .
V _A + V _B + V _C + V _D = 1 (10)

The calorific value per unit volume of gas A is K _A , the calorific value per unit volume of gas B is K _B , the calorific value per unit volume of gas C is K _C , and the calorific value per unit volume of gas D is Is K _D , the calorific value Q per unit volume of the mixed gas is given by the sum of the volume ratio of each gas component multiplied by the calorific value per unit volume of each gas component. Therefore, the calorific value Q per unit volume of the mixed gas is given by the following equation (11). The unit of the calorific value per unit volume is, for example, MJ / m ³ .
Q = K _A × V _A + K _B × V _B + K _C × V _C + K _D × V _D ... (11)

Furthermore, the thermal conductivity per unit volume of gas A is C _A , the thermal conductivity per unit volume of gas B is C _B , the thermal conductivity per unit volume of gas C is C _C , and the per unit volume of gas D is When the thermal conductivity and C _D, thermal conductivity C _I of the mixed gas per unit volume is the volume ratios of the gas components, given by the sum of the values obtained by multiplying the thermal conductivity per unit volume of the gas components It is done. Accordingly, the thermal conductivity C _I per unit volume of the mixed gas is given by the following equation (12). The unit of thermal conductivity per unit volume is, for example, W / (mK).
C _I = C _A × V _A + C _B × V _B + C _C × V _C + C _D × V _D ... (12)

5, the first voltages V ₁ to the heating element 61, when the first voltage V ₁ is greater than the second voltage V _2, and a second voltage V ₂ is greater than the third voltage V ₃ was added It is a graph which shows the relationship between thermal conductivity and a heat dissipation coefficient. As shown in FIG. 5, the thermal conductivity and the heat dissipation coefficient are generally in a proportional relationship. Therefore, the radiation coefficient M _A gas A, the radiation coefficient of gas B M _B, when the radiation coefficient of gas C M _C, the radiation coefficient of the gas D and M _D, the radiation coefficient M _I of the mixed gas, the It is given as the sum of the volume fraction of the gas component multiplied by the heat dissipation coefficient of each gas component. Therefore, the heat dissipation coefficient M _I of the mixed gas is given by the following equation (13).
M _I = M _A × V _A + M _B × V _B + M _C × V _C + M _D × V _D ... (13)

Further, since the radiation coefficient of gas depends on the temperature T _H of the heater element 61, the radiation coefficient M _I of the mixed gas, as a function of the temperature T _H of the heater element 61 is given by the following equation (14).
M _I (T _H ) = M _A (T _H ) × V _A + M _B (T _H ) × V _B + M _C (T _H ) × V _C + M _D (T _H ) × V _D・ ・ ・ ( 14)

Therefore, the heat dissipation coefficient M _I1 (T _H1 ) of the mixed gas when the temperature of the heating element 61 is T _H1 is given by the following equation (15). The heat dissipation coefficient M _I2 (T _H2 ) of the mixed gas when the temperature of the heating element 61 is T _H2 is given by the following equation (16), and the heat dissipation coefficient of the mixed gas when the temperature of the heating element 61 is T _H3 : M _I3 (T _H3 ) is given by the following equation (17).
M _I1 (T _H1 ) = M _A (T _H1 ) × V _A + M _B (T _H1 ) × V _B + M _C (T _H1 ) × V _C + M _D (T _H1 ) × V _D・ ・ ・ ( 15)
M _I2 (T _H2 ) = M _A (T _H2 ) × V _A + M _B (T _H2 ) × V _B + M _C (T _H2 ) × V _C + M _D (T _H2 ) × V _D・ ・ ・ ( 16)
M _I3 (T _H3 ) = M _A (T _H3 ) × V _A + M _B (T _H3 ) × V _B + M _C (T _H3 ) × V _C + M _D (T _H3 ) × V _D・ ・ ・ ( 17)

Here, the heat dissipation coefficients M _A (T _H ), M _B (T _H ), M _C (T _H ), and M _D (T _H ) of each gas component are non-linear with respect to the temperature T _H of the heating element 61. If so, the above equations (15) to (17) have a linearly independent relationship. Further, the heat dissipation coefficients M _A (T _H ), M _B (T _H ), M _C (T _H ), and M _D (T _H ) of each gas component have linearity with respect to the temperature T _H of the heating element 61. Even in the case where the rate of change of the heat radiation coefficient M _A (T _H ), M _B (T _H ), M _C (T _H ), M _D (T _H ) of each gas component with respect to the temperature T _H of the heating element 61 is different. (15) to (17) have a linearly independent relationship. Further, when the equations (15) to (17) have a linearly independent relationship, the equations (10) and (15) to (17) have a linearly independent relationship.

FIG. 6 shows the heat release coefficients of methane (CH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ) contained in natural gas, and the heating element 61 that is a heating resistor. It is a graph which shows the relationship with temperature. The heat release coefficient of each gas component of methane (CH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ) has linearity with respect to the temperature of the heating element 61. However, the rate of change of the heat dissipation coefficient with respect to the temperature of the heating element 61 is different for each of methane (CH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ). Therefore, when the gas components constituting the mixed gas are methane (CH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ), the above (15) to (17 ) Has a linearly independent relationship.

The radiation coefficient M _A (T _H1 ), M _B (T _H1 ), M _C (T _H1 ), M _D (T _H1 ), M _A (T _H2 ) of each gas component in the equations (15) to (17) , M _B (T _H2 ), M _C (T _H2 ), M _D (T _H2 ), M _A (T _H3 ), M _B (T _H3 ), M _C (T _H3 ), M _D (T _H3 ) The value can be obtained in advance by measurement or the like. Therefore, when the simultaneous equations of (10) and (15) to (17) are solved, the volume ratio V _A of gas _A , the volume ratio V _B of gas _B , the volume ratio V _C of gas _C , and the volume of gas D Each of the rates V _D is given as a function of the heat release coefficient M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 ) of the mixed gas as shown in the following equations (18) to (21). It is done. In the following formulas (18) to (21), n is a natural number and f _n is a symbol representing a function.
V _A = f ₁ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )] (18)
V _B = f ₂ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )] (19)
V _C = f ₃ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )] (20)
V _D = f ₄ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )] (21)

Here, the following equation (22) is obtained by substituting the equations (18) to (21) into the above equation (11).
Q = K _A × V _A + K _B × V _B + K _C × V _C + K _D × V _D
= K _A × f ₁ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )]
+ K _B × f ₂ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )]
+ K _C × f ₃ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )]
+ K _D × f ₄ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )] (22)

As shown in the above equation (22), the calorific value Q per unit volume of the mixed gas is the heat dissipation coefficient M _I1 (T _H1 ) of the mixed gas when the temperature of the heating element 61 is T _H1 , T _H2 , T _H3. ), M _I2 (T _H2 ), M _I3 (T _H3 ) are given as equations. Therefore, the calorific value Q of the mixed gas is given by the following equation (23), where g ₁ is a symbol representing a function.
Q = g ₁ [M _I1 (T _H1 ), M _I2 (T _H2 ), M _I3 (T _H3 )] (23)

Therefore, if the above equation (23) is obtained in advance for a mixed gas composed of gas A, gas B, gas C, and gas D, the volume ratio V _A of gas _A , the volume ratio V _B of gas _B , and the gas C The present inventor has found that the calorific value Q per unit volume of the measurement target mixed gas whose volume ratio V _C and the volume ratio V _{D of the} gas D are unknown can be easily calculated. Specifically, using the above equation (9), the heat release coefficients M _I1 (T _H1 ), M _I2 (M _I2 ) of the measurement target mixed gas when the heat generation temperature of the heat generating element 61 is T _H1 , T _H2 , T _H3. By measuring T _H2 ) and M _I3 (T _H3 ) and substituting them into the equation (23), the calorific value Q of the measurement target mixed gas can be determined uniquely.

In the method described above, using the heat generating element 61 of the microchip 8 and the first temperature measuring element 62, the heat dissipation coefficients M _I1 (T _H1 ), M _I2 (T _H2 ), M of the measurement target mixed gas are used. Measure _I3 (T _H3 ) to determine calorific value Q. On the other hand, according to the following method, the calorific value Q of the mixed gas can be obtained using only the heating element 61 without using the first temperature measuring element 62 of the microchip 8.

As shown in the above equation (4), the heat dissipation coefficient M _{I of the} gas is proportional to the reciprocal (1 / R _H ) of the resistance R _H of the heating element 61. Further, as described above, the heat dissipation coefficient and the thermal conductivity are in a proportional relationship. For this reason, the reciprocal (1 / R _H ) of the resistance R _H of the heating element 61 and the thermal conductivity are in a proportional relationship. FIG. 7 illustrates the thermal conductivity and the reciprocal of the resistance _RH of the heating element 61 when the first voltage V ₁ , the second voltage V ₂ , and the third voltage V ₃ are applied to the heating element 61. 1 / R _H ). As shown in FIGS. 7 and 8, the thermal conductivity and the reciprocal (1 / R _H ) of the resistance R _H of the heating element 61 are proportional to each other as long as the voltage applied to the heating element 61 is constant. is there. As shown in FIGS. 9 and 10, the thermal conductivity and the resistance _RH of the heating element 61 are correlated if the voltage applied to the heating element 61 is constant. Furthermore, as shown in FIGS. 11 and 12, the thermal conductivity and the driving power of the heating element 61 are correlated if the voltage applied to the heating element 61 is constant.

Therefore, the resistance R _H reciprocal 1 / R _HA of the heater element 61 when in contact with the gas A, the resistance R _H reciprocal 1 / R _HB of the heater element 61 when in contact with the gas B, when in contact with the gas C resistor R _H reciprocal 1 / R _HC in the heater element 61, when the 1 / R _HD reciprocal of the resistance R _H of the heater element 61 when in contact with the gas D, by modifying the equation (12), a gas mixture reciprocal of the resistance R _H of the heater element 61 coming into contact with the (1 / R _HI) is given by the sum the volume ratios of the gas components, but multiplied by the reciprocal of the resistance R _H of the heater element 61 when in contact with the gas components It is done. Therefore, a constant voltage is applied, and the reciprocal (1 / R _HI ) of the resistance _RH of the heating element 61 in contact with the mixed gas is given by the following equation (24).
1 / R _HI = 1 / R _HA × V _A + 1 / R _HB × V _B + 1 / R _HC × V _C + 1 / R _HD × V _D ... (24)

Further, since the resistance R _H of the heating element 61 depends on the temperature T _H of the heating element 61, the reciprocal (1 / R _HI ) of the resistance R _H of the heating element 61 in contact with the mixed gas is the resistance of the heating element 61. As a function of the temperature T _H, the following equation (25) is given.
1 / R _HI (T _H )
= 1 / R _HA (T _H ) × V _A + 1 / R _HB (T _H ) × V _B + 1 / R _HC (T _H ) × V _C + 1 / R _HD (T _H ) × V _D・ ・·(twenty five)

Therefore, the reciprocal (1 / R _HI1 ) of the resistance R _H of the heating element 61 in contact with the mixed gas when the temperature of the heating element 61 is T _H1 is given by the following equation (26). Further, the reciprocal (1 / R _HI2 ) of the resistance R _H of the heating element 61 in contact with the mixed gas when the temperature of the heating element 61 is T _H2 is given by the following equation (27), and the temperature of the heating element 61 is T _H3. In this case, the reciprocal (1 / R _HI3 ) of the resistance _RH of the heating element 61 in contact with the mixed gas is given by the following equation (28).
1 / R _HI1 (T _H1 )
= 1 / R _HA (T _H1 ) × V _A + 1 / R _HB (T _H1 ) × V _B + 1 / R _HC (T _H1 ) × V _C + 1 / R _HD (T _H1 ) × ... (26)
1 / R _HI2 (T _H2 )
= 1 / R _HA (T _H2 ) × V _A + 1 / R _HB (T _H2 ) × V _B + 1 / R _HC (T _H2 ) × V _C + 1 / R _HD (T _H2 ) × V _D・ ・・ (27)
1 / R _HI3 (T _H3 )
= 1 / R _HA (T _H3 ) × V _A + 1 / R _HB (T _H3 ) × V _B + 1 / R _HC (T _H3 ) × V _C + 1 / R _HD (T _H3 ) × V _D・ ・・ (28)

The resistances R _HA (T _H1 ), R _HB (T _H1 ), R _HC (T _H1 ), R _HD (T _H1 ) of the heating element 61 when contacting each gas component in the formulas (26) to (28) , R _HA (T _H2 ), R _HB (T _H2 ), R _HC (T _H2 ), R _HD (T _H2 ), R _HA (T _H3 ), R _HB (T _H3 ), R _HC (T _H3 ), The value of R _HD (T _H3 ) can be obtained in advance by measurement or the like. Therefore, when the simultaneous equations of (10) and (26) to (28) are solved, the volume ratio V _A of gas _A , the volume ratio V _B of gas _B , the volume ratio V _C of gas _C , and the volume of gas D As shown in the following equations (29) to (32), the rates V _D are the resistances R _HI1 (T _H1 ), R _HI2 (T _H2 ), R _HI3 (T _H3 ) of the heating element 61 in contact with the mixed gas. Is given as a function of In the following formulas (29) to (32), n is a natural number and f _n is a symbol representing a function.
V _A = f ₅ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )] (29)
V _B = f ₆ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )] (30)
V _C = f ₇ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )] (31)
V _D = f ₈ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )] (32)

Here, the following equation (33) is obtained by substituting the equations (29) to (32) into the above equation (11).
Q = K _A × V _A + K _B × V _B + K _C × V _C + K _D × V _D
= K _A × f ₅ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )]
+ K _B × f ₆ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )]
+ K _C × f ₇ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )]
+ K _D × f ₈ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )] ・ ・ ・ (33)

As shown in the above equation (33), the calorific value Q per unit volume of the mixed gas is the resistance R _HI1 (T _H1) of the heating element 61 when the temperature of the heating element 61 is T _H1 , T _H2 , T _H3. ), R _HI2 (T _H2 ), R _HI3 (T _H3 ). Therefore, the calorific value Q of the mixed gas is given by the following equation (34), where g ₂ and g ₃ are symbols representing functions.
Q = g ₂ [1 / R _HI1 (T _H1 ), 1 / R _HI2 (T _H2 ), 1 / R _HI3 (T _H3 )]
= g ₃ [R _HI1 (T _H1 ), R _HI2 (T _H2 ), R _HI3 (T _H3 )] (34)

Therefore, if the above equation (34) is obtained in advance for the mixed gas composed of gas A, gas B, gas C, and gas D, the volume ratio V _A of gas _A , the volume ratio V _B of gas _B , and the gas C The present inventor has found that the calorific value Q per unit volume of the measurement target mixed gas whose volume ratio V _C and the volume ratio V _{D of the} gas D are unknown can be easily calculated. Specifically, the resistance values R _HI1 (T _H1 ), R _HI2 (T _H2 ), and R _HI3 (T _H3 ) of the heating element 61 when the heat generation temperatures are T _H1 , T _H2 , and T _H3 are measured. By substituting into the equation (34), the calorific value Q of the measurement target mixed gas can be uniquely obtained. In this case, the calorific value Q of the mixed gas can be obtained using only the heating element 61 without using the first temperature measuring element 62 of the microchip 8.

Furthermore, since the resistance R and the current I are correlated, the calorific value Q per unit volume of the mixed gas is such that the temperature of the heating element 61 is T _H1 , T _H2 , T _H3 , with g ₄ as a symbol representing a function. When the currents I _H1 (T _H1 ), I _H2 (T _H2 ), and I _H3 (T _H3 ) of the heating element 61 are used as variables, the following equation (35) is given.
Q = g ₄ [I _H1 (T _H1 ), I _H2 (T _H2 ), I _H3 (T _H3 )] (35)

Further, since the resistance R of the heating element 61 and the output signal AD of the analog-digital conversion circuit (hereinafter referred to as “A / D conversion circuit”) connected to the heating element 61 are correlated, the unit of the mixed gas The calorific value Q per volume is expressed by the output signal AD _H1 (T _H1 ) of the A / D conversion circuit when the temperature of the heating element 61 is T _H1 , T _H2 , T _H3 , where g ₅ is a symbol representing a function. It is given by the following equation (36) with AD _H2 (T _H2 ) and AD _H3 (T _H3 ) as variables.
Q = g ₅ [AD _H1 (T _H1 ), AD _H2 (T _H2 ), AD _H3 (T _H3 )] (36)

Therefore, the calorific value Q per unit volume of the mixed gas is represented by the following equation (37), and the heat generation temperature of the heat generating element 61 is T _H1 , T _H2 , T _H3, where g ₆ is a symbol representing a function. In this case, the electric signals S _H1 (T _H1 ), S _H2 (T _H2 ), and S _H3 (T _H3 ) from the heating element 61 are given by equations.
Q = g ₆ [S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 )] (37)

The gas components of the mixed gas are not limited to four types. For example, if the mixed gas comprises n types of gas components, as a symbol that represents the the g ₇ function given by the following equation (38), at least n-1 kinds of the heating temperatures _{T H1, T H2, T H3} , · ..., electric signals from the heater element 61 in the _{T Hn-1 S H1 (T} H1), S H2 (T H2), S H3 (T H3), ···, S Hn-1 (T Hn-1) An equation having as a variable is acquired in advance. Then, the heating element 61 in contact with the measurement target mixed gas whose volume ratio of each of the n types of gas components at the n-1 types of heat generation temperatures T _H1 , T _H2 , T _{H3 ,.} , Measured the values of electrical signals _SH1 ( _TH1 ), _SH2 ( _TH2 ), _SH3 ( _TH3 ),..., _SHn-1 ( _THn-1 ) from the equation (38). By substituting, the calorific value Q per unit volume of the measurement target mixed gas can be uniquely obtained. In addition, you may prepare two or more following (38) formulas for every temperature of mixed gas (atmosphere gas).
Q = g ₇ [S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), ..., S _Hn-1 (T _Hn-1 )] (38)

For example, the measurement target mixed gas is methane (CH ₄ ), ethane (C ₂ H ₅ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), carbon dioxide (CO ₂ ), and nitrogen (N ₂ ). If it made of six types of gases), at least five of the heating temperature _{T H1, T H2, T H3} , T H4, electric signals from the heater element 61 in the _{T H5 S H1 (T H1)} , S H2 (T H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) as variables. Then, the electric signal S from the heating element 61 in contact with the measurement target mixed gas whose volume ratio of each of the six types of gas components at the five types of heat generation temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5 is unknown. By measuring the values of _H1 ( _TH1 ), _SH2 ( _TH2 ), _SH3 ( _TH3 ), _SH4 ( _TH4 ), _SH5 ( _TH5 ) and substituting them into the following equation (39), It is possible to uniquely determine the calorific value Q per unit volume of the measurement target mixed gas.
Q = g ₇ [S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), S _H5 (T _H5 )] ・ ・ ・ (39)

However, the mixed gas, methane (CH ₄₎ as a gas component in addition to the propane (C ₃ H _8), a j is a natural number, methane (CH ₄₎ and other than propane (C ₃ H ₈₎ alkane (C _j H _{2j + 2} ), alkanes other than methane (CH ₄ ) and propane (C ₃ H ₈ ) (C _j H _{2j + 2} ), and mixtures of methane (CH ₄ ) and propane (C ₃ H ₈ ) (38) may be calculated. For example, ethane (C ₂ H ₆ ), butane (C ₄ H ₁₀ ), pentane (C ₅ H ₁₂ ), and hexane (C ₆ H ₁₄ ) are respectively represented by the following formulas (40) to (43): The equation (38) may be calculated by regarding the mixture as methane (CH ₄ ) and propane (C ₃ H ₈ ) multiplied by a predetermined coefficient.
C ₂ H ₆ = 0.5 CH ₄ + 0.5 C ₃ H ₈ ... (40)
C ₄ H ₁₀ = -0.5 CH ₄ + 1.5 C ₃ H ₈ ... (41)
C ₅ H ₁₂ = -1.0 CH ₄ + 2.0 C ₃ H ₈ ... (42)
C ₆ H ₁₄ = -1.5 CH ₄ + 2.5 C ₃ H ₈ ... (43)

Accordingly, the z as a natural number, a mixed gas consisting of n kinds of gas components methane (CH ₄₎ as a gas component in addition to the propane (C ₃ H _8), methane (CH ₄₎ and propane (C ₃ H ₈ ) if it contains z kinds of alkane (C _j H _{2j + 2)} other than, or an equation that the electrical signal S _H and the variables from the heater element 61 in at least n-z-1 different heat producing temperatures.

Further, when the type of the gas component of the mixed gas used in the calculation of the equation (38) is the same as the type of the gas component of the measurement target mixed gas whose calorific value Q per unit volume is unknown, the measurement target mixed gas Of course, the equation (38) can be used to calculate the calorific value Q. Further, when the measurement target mixed gas is composed of less than n kinds of gas components and less than n kinds of gas components are included in the mixed gas used in the calculation of the equation (38), Equation (38) can be used. For example, the mixed gas used in the calculation of the equation (38) has four types of gas components, methane (CH ₄ ), propane (C ₃ H ₈ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ). When it is included, the measurement target mixed gas may not contain nitrogen (N ₂ ) but may contain only three types of gas components, methane (CH ₄ ), propane (C ₃ H ₈ ), and carbon dioxide (CO ₂ ). The equation (38) can be used to calculate the calorific value Q of the measurement target mixed gas.

Further, when the mixed gas used for calculating the equation (38) contains methane (CH ₄ ) and propane (C ₃ H ₈ ) as gas components, the measurement target mixed gas is used for calculating the equation (38). Even if alkane (C _j H _{2j + 2} ) that is not contained in the mixed gas is included, the equation (38) can be used. This is because, as described above, the methane (CH ₄₎ and propane (C ₃ H ₈₎ other than the alkane _{(C j H 2j + 2)} , a mixture of methane (CH ₄₎ and propane (C ₃ H ₈₎ This is because it may be considered.

  Next, a method for measuring the nitrogen concentration will be described. As shown in FIG. 13, the thermal conductivity of the gas changes according to the heat generation temperature of the heat generating element 61. Here, the inventor has paid attention to the fact that nitrogen gas has a smaller rate of change in thermal conductivity with respect to the exothermic temperature than hydrocarbon gases such as methane, ethane, propane, and butane.

  In FIG. 14, the thermal conductivity value is normalized so that the thermal conductivity of methane is 0 regardless of the heating temperature of the heating element 61 and the thermal conductivity of propane is 1 regardless of the heating temperature of the heating element 61. It is a graph when it is converted. When normalizing, the value obtained by subtracting the value of thermal conductivity of methane at the same exothermic temperature from the value of each thermal conductivity is used as the value of heat conductivity of methane at the same exothermic temperature from the value of propane thermal conductivity at the same exothermic temperature. The conductivity value was divided by the subtracted value. As shown in FIG. 14, the difference in the rate of change in thermal conductivity with respect to the exothermic temperature between hydrocarbon gas and nitrogen gas becomes more prominent when the value of thermal conductivity is normalized.

  As described above, the value of the electrical signal from the heating element 61 reflects the value of the thermal conductivity of the gas in contact with the heating element 61. FIG. 15 shows the value of the electrical signal from the heating element 61 in contact with each of the 14 types of mixed gas containing methane gas and at least one of methane, ethane, propane, and butane and not containing nitrogen. It is a graph when the value of the electrical signal is normalized so that the value of the electrical signal at the time of contact with methane gas becomes 0 and the value of the electrical signal at the time of contact with a specific mixed gas becomes 1. A mixed gas that does not contain nitrogen gas has a small rate of change in the value of the normalized electrical signal with respect to the exothermic temperature.

  FIG. 16 shows values of electric signals from the heating element 61 in contact with each of four types of mixed gas containing at least one of methane, ethane, propane, and butane and containing 3 vol% or 4 vol% nitrogen. It is a graph when normalized under the same conditions. Comparing FIG. 15 and FIG. 16, the mixed gas containing nitrogen gas has a larger change rate of the value of the normalized electric signal with respect to the heat generation temperature than the mixed gas not containing nitrogen gas.

  FIG. 17 shows values of electrical signals from the heating element 61 in contact with each of five kinds of mixed gas containing at least one of methane, ethane, propane, and butane and containing 5 vol% or 6 vol% nitrogen. It is a graph when normalized under the same conditions. When FIG. 16 is compared with FIG. 17, the change rate of the value of the normalized electric signal with respect to the heat generation temperature is large in the mixed gas containing a large amount of nitrogen gas.

  Accordingly, the heat generation temperature when the value of the electric signal from the heating element 61 is normalized so that the value of the electric signal at the time of contact with each of at least two hydrocarbon-containing gases not containing nitrogen is constant. The magnitude of the rate of change in the value of the normalized electrical signal with respect to the value reflects the concentration of nitrogen contained in the mixed gas.

FIG. 18 shows normalized values S _H5N (T _H5 ) of electric signals at the highest heat generation temperature when 31 kinds of gas are brought into contact with the heat generation element 61 and the heat generation element 61 generates heat in five stages. The normalized value S _H4N (T _H4 ) of the electrical signal at the next highest exothermic temperature, the value d _{1 obtained} by multiplying the first difference by 100, and the actual nitrogen of each of the 31 gases It is the graph which plotted the value (vol%) of the density | concentration. FIG. 19 shows the normalized value S _H4N (T _H4 ) of the electrical signal at the next highest heating temperature after the highest heating temperature, and the normalized value S _H3N of the electrical signal at the next highest heating temperature after the highest heating temperature. and (T _H3), and the value d ₂ multiplied by 100 to the second difference is a graph plotting the actual nitrogen concentration value (vol%), the.

  In FIG. 18 and FIG. 19, multiplying the first and second differences of the normalized values of the electrical signal by 100 brings the first and second difference scales, which are dimensionless numbers, closer to the nitrogen concentration. Because. Therefore, the value multiplied by the first and second differences in order to bring the first and second difference scales closer to the nitrogen concentration is not limited to 100.

As shown in FIG. 18 and FIG. 19, values d ₁ and d _{2 obtained} by multiplying the difference between the normalized values of the electrical signals between the two exothermic temperatures by 100 generally reflect the nitrogen concentration. Actually, in gases No. 1 to No. 15 having a nitrogen concentration of 0%, values d ₁ and d _{2 obtained} by multiplying the difference value of the normalized value of the electric signal by 100 are not zero.

Therefore, as shown in the following equation (44), the corrected first difference d _C1 obtained by multiplying the first difference value d ₁ by the first correction coefficient A ₁ and the second difference value d _2. When a difference in, sets an evaluation value E is a value obtained by multiplying the scale correction factor a _S for correcting the scale.
E = (A ₁ × d ₁ -d ₂ ) × A _S
= (d _C1 -d ₂ ) × A _S ... (44)

Further, the first correction coefficient A ₁ is calculated so that the evaluation value E approaches 0 in the gases No. 1 to No. 15 in which the nitrogen concentration is actually 0% shown in FIGS. . In the examples shown in FIGS. 18 and 19, when the value of the _first correction coefficient A ₁ is 1.87, the evaluation value E is 0 in the gases No. 1 to No. 15 having a nitrogen concentration of 0%. Approached most. Note that the value 1.87 of the first correction coefficient A ₁ is an example and is not limited to this. FIG. 20 shows the evaluation value E of each of the 31 types of gas and the actual nitrogen concentration value (vol%) of each of the 31 types of gas when the value of the first correction coefficient A ₁ is 1.87. ) And are plotted.

  As shown in FIG. 20, the evaluation value E generally reflects the nitrogen concentration, but there is an error between the actual nitrogen concentration of the 16th to 31st gases and the evaluation value E.

Therefore, as shown in the following equation (45), a corrected evaluation value E _C obtained by multiplying the evaluation value E by the second correction coefficient A ₂ is set as a measured value of the concentration of nitrogen contained in the mixed gas.
E _C = A ₂ × E (45)

Further, in the gas having a nitrogen concentration of 4% to 6% from No. 24 to No. 31 shown in FIG. 20, the error between the actual value of the nitrogen concentration and the measured value E _{C of the} nitrogen concentration approaches zero. The value of the correction coefficient A ₂ of ₂ is calculated. In the example shown in FIG. 20, when the value of the second correction coefficient A ₂ is 1.27, the actual value of nitrogen concentration and the measured value E _{C of} nitrogen concentration in a gas having a nitrogen concentration of 4% to 6%. The error between and was closest to 0. Note that the value 1.27 of the second correction coefficient A ₂ is an example, and the present invention is not limited to this. Alternatively, the value of the second correction coefficient A ₂ may be calculated so that the error between the actual value of the nitrogen concentration and the measured value E _{C of the} nitrogen concentration approaches zero for all gases. FIG. 21 shows the actual values (vol%) of the nitrogen concentrations of the 31 kinds of gases and the nitrogen concentrations of the 31 kinds of gases when the value of the second correction coefficient A ₂ is 1.27. Is a graph in which measured values (corrected evaluation values) E _C are plotted. The measured value E _C of the nitrogen concentration of each of the 31 kinds of gases almost coincided with the actual value of the nitrogen concentration.

FIG. 22 is a graph showing an error of the measured value E _C of the nitrogen concentration with respect to the actual value of the nitrogen concentration. In all the gases from No. 1 to No. 31, the error in the measured value E _C of the nitrogen concentration was 0.2% or less.

Therefore, if the first correction coefficient A ₁ and the second correction coefficient A ₂ are calculated in advance using a plurality of gases whose actual values of nitrogen concentration are known as described above, the nitrogen concentration is unknown. It is the present inventor that the concentration of nitrogen contained in the measurement target mixed gas can be calculated by measuring the measured value of the electrical signal from the heating element 61 that contacts the measurement target mixed gas and generates heat at a plurality of heat generation temperatures. Found.

Specifically, as shown in the following equation (46), a nitrogen concentration calculation formula having a normalized electric signal from the heating element 61 at at least three heat generation temperatures as an independent variable and a nitrogen concentration as a dependent variable is previously set. prepare.
E _C = (A ₁ × (S _H5N (T _H5 ) -S _H4N (T _H4 ))-(S _H4N (T _H4 ) -S _H3N (T _H3 ))) × A _S × A ₂
= (A ₁ × d ₁ -d ₂ ) × A _S × A ₂
= (d _C1 -d ₂ ) × A _S × A ₂
= E × A ₂ ... (46)
In the equation (46), S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) are used as normalized electrical signals from the heating elements at at least three heating temperatures. Although an example is shown, it is arbitrary which heat generation temperature is used, and S _H1N (T _H1 ) and S _H2N (T _H2 ) may be used.

Even if the scale correction coefficient A _S is omitted, the scale correction can be performed using the second correction coefficient A ₂ ′. Therefore, as shown in the following equation (47), the normalized electric signal S _H3N from the heating element 61 including at least three heating temperatures includes the first correction coefficient A ₁ and the second correction coefficient A ₂ ′. A nitrogen concentration calculation formula may be prepared in advance, where (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) are independent variables and the nitrogen concentration E _C is a dependent variable.
E _C = (A ₁ × (S _H5N (T _H5 ) -S _H4N (T _H4 ))-(S _H4N (T _H4 ) -S _H3N (T _H3 ))) × A ₂ '
= (A ₁ × d ₁ -d ₂ ) _S × A ₂ '
= (d _C1 -d ₂ ) × A ₂ '(47)
In the following, the second correction coefficient A ₂ ′ capable of scale correction is also expressed as a _second correction coefficient A ₂ .

  Next, the measurement object mixed gas whose nitrogen concentration is unknown is brought into contact with the heating element 61, the measured values of the electrical signals from the heating element 61 at at least three heating temperatures are measured, and the measured values are normalized. Furthermore, by substituting the measured value of the normalized electrical signal into the independent variable of the nitrogen concentration calculation formula given by the above equation (46) or (47), the concentration of nitrogen contained in the measurement target mixed gas is calculated. It is possible to calculate.

  Here, the nitrogen concentration measurement system 20 according to the embodiment shown in FIG. 23 includes a reference gas not containing nitrogen, a calibration gas not containing nitrogen, a plurality of nitrogen-free mixed gases, and a plurality of nitrogen-containing mixed gases, respectively. Is provided with a chamber 101 which is a container to be injected.

Methane gas can be used as a reference gas having hydrocarbon as a calibration component. The calibration gas is a mixed gas containing a plurality of types of gas components, for example, _four types of methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), and butane (C ₄ H ₁₀ ). Any or all of the gas components are included. The calibration gas containing hydrocarbon as a calibration component is composed of, for example, the same components as natural gas or liquefied natural gas (LNG). A span gas can be used as the calibration gas.

Each of the plurality of nitrogen-free mixed gases includes a plurality of types of gas components. Each of the plurality of mixed gases is, for example, any or all of four kinds of gas components such as methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), and butane (C ₄ H ₁₀ ). including. Any or all of the plurality of mixed gases is natural gas or LNG.

Each of the plurality of nitrogen-containing mixed gases includes a plurality of types of gas components. Each of the plurality of mixed gases includes, for example, five kinds of gases such as methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), and nitrogen (N ₂ ). Contains any or all of the ingredients. Any or all of the plurality of mixed gases is natural gas or LNG.

The nitrogen concentration measurement system 20 further includes a microchip 8 disposed in the chamber 101 and including the heating element 61 shown in FIG. 1 or 3 that generates heat at a plurality of heat generation temperatures T _H. Hereinafter, an example in which the nitrogen concentration measurement system 20 includes the microchip 8 illustrated in FIG. 1 will be described. However, even if the nitrogen concentration measurement system 20 includes the microchip 8 illustrated in FIG. The operation of the nitrogen concentration measurement system 20 shown in FIG.

  The microchip 8 is disposed in the chamber 101 via the heat insulating member 18. The chamber 101 includes a reference gas, a calibration gas, a plurality of nitrogen-free mixed gases, and a flow path 102 for sending each of the plurality of nitrogen-containing mixed gases to the chamber 101, a reference gas, a calibration gas, and a plurality of nitrogen-free gases. A flow path 103 for discharging each of the contained mixed gas and each of the plurality of nitrogen-containing mixed gases from the chamber 101 is connected.

The nitrogen concentration measurement system 20 is further in contact with the reference gas and the measurement value of the reference electrical signal S _HA (T _H ) from the heating element 61 that generates heat at each of the plurality of heat generation temperatures T _H and the calibration gas. Each of the plurality of exothermic temperatures T _H in contact with the measured value of the calibration electric signal S _HB (T _H ) from the heating element 61 that generates heat at each exothermic temperature T _H and each of the plurality of nitrogen-free mixed gases. The measured value of the electrical signal S _H (T _H ) when nitrogen is not contained from the heating element 61 that generates heat at the temperature and the heating element 61 that is in contact with each of the plurality of nitrogen-containing mixed gases and generates heat at each of the plurality of heating temperatures T _H. The measurement part 301 which measures the measured value of the electrical signal _SH ( _TH ) at the time of nitrogen containing from is measured.

Nitrogen concentration measurement system 20 further includes reference gas, calibration gas, each of the known calorific value Q of a plurality of nitrogen-free mixed gas, and a plurality of nitrogen-containing gas mixture, and heating at a plurality of heat producing temperatures T _H The measured value of the reference electrical signal S _HA (T _H ) from the element 61, the measured value of the calibration electrical signal S _HB (T _H ), the measured value of the electrical signal S _H (T _H ) when nitrogen is not included, and the nitrogen content when based on the measurement values of the electric signals S _H (T _H), the electrical signals from the heater element 61 at a plurality of heat producing temperatures T _H S _H a (T _H) as independent variables and the calorific value Q as a dependent variable heating An expression creating unit 302 for creating an amount calculation expression is provided.

The nitrogen concentration measurement system 20 further has a measured value of the reference electrical signal S _HA (T _H ) from the heating element 61 in contact with the reference gas not containing nitrogen, regardless of the heating temperature of the heating element 61, and The reference electrical signal S _HA (T _H ) is set so that the measured value of the calibration electrical signal S _HB (T _H ) from the heating element 61 in contact with the calibration gas not containing nitrogen is constant regardless of the heating temperature of the heating element 61. ) Measurement value, calibration electric signal _SHB ( _TH ) measurement value, nitrogen-free electrical signal _SH ( _TH ) measurement value, and nitrogen-containing electrical signal _SH ( _TH ) measurement value Is provided with a normalization unit 306.

The formula creation unit 302 includes the reference gas, the calibration gas, the plurality of nitrogen-free mixed gases, and the known nitrogen concentration values of the plurality of nitrogen-containing mixed gases, and the heating element 61 at the plurality of heat generation temperatures T _H. The measured value of the reference electrical signal S _HA (T _H ), the measured value of the calibration electrical signal S _HB (T _H ), the measured value of the electrical signal S _H (T _H ) when not containing nitrogen, and the electrical signal S when containing nitrogen Based on the measured value of _H (T _H ), the normalized electrical signal S _HN (T _H ) from the heating element 61 at at least three exothermic temperatures T _H is an independent variable, and the nitrogen concentration is a dependent variable. Also create a concentration formula.

When the reference gas is supplied to the chamber 101, the heater element 61 shown in FIGS. 1 and 2 sequentially supplies driving power _{P H1, P H2, P H3} , P H4, P H5 from the driving circuit 303 shown in FIG. 23 It is done. When the driving powers P _H1 , P _H2 , P _H3 , P _H4 , and P _H5 are given, the heating element 61 in contact with the reference gas has five levels of temperatures T _H1 , T _H2 , T _H3 , T _H4 , and T _H5 . fever, reference electrical signal S _H1A at the heat producing temperature T _H1 (T _H1), the reference electric signal S _H2A at the heat producing temperature T _H2 (T _H2), the reference electrical signal at the heat producing temperature _{T H3 S H3A (T H3)} , heating temperature reference electrical signal S _H4A at T _H4 (T _H4), and outputs a reference electric signal S _H5A (T _H5) at a heat producing temperature T _H5.

After the reference gas is removed from the chamber 101, calibration gas is supplied to the chamber 101. When the calibration gas is supplied to the chamber 101, the heating element 61 in contact with the calibration gas generates heat at five stages of temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5 , and the calibration electricity at the heat generation temperature T _H1 . signal S _H1B (T _H1), the heat producing temperature T calibration electrical signal S _H2B in _H2 (T _H2), calibration electrical signal S _H3B at the heat producing temperature T _H3 (T _H3), an electrical signal for calibration at the heat producing temperature T _H4 S The calibration electric signal S _H5B (T _H5 ) at _H4B (T _H4 ) and the heat generation temperature T _H5 is output.

After the calibration gas is removed from the chamber 101, each of the plurality of nitrogen-free mixed gases is sequentially supplied to the chamber 101. When the first nitrogen-free mixed gas among the plurality of nitrogen-free mixed gases is supplied to the chamber 101, the heating element 61 shown in FIGS. 1 and 2 in contact with the first nitrogen-free mixed gas generates heat. temperature T _H1 nitrogen-free time of the electric signal S in _H1 (T _H1), the heat producing temperature T nitrogen-free time of the electric signal S _H2 in _H2 (T _H2), heating temperature T at nitrogen-free in _H3 electric signal S _H3 (T _H3 ), an electric signal S _H4 (T _H4 ) when nitrogen is not contained at an exothermic temperature T _H4 , and an electric signal S _H5 (T _H5 ) when no nitrogen is contained at an exothermic temperature T _H5 . For each well of other nitrogen-containing gas mixture, heating element 61, heating temperature T nitrogen-free time of an electrical signal at a _H1 S _H1 (T _H1), fever producing temperature T _H2, nitrogen-free time of the electric signal S _H2 in (T _H2), nitrogen-free time of an electrical signal at a heat producing temperature _{T H3 S H3 (T H3)} , heating nitrogen-free time of the electric signal S _H4 (T _H4 at the temperature T _H4), and nitrogen-free time electricity at the heat producing temperature T _H5 The signal S _H5 (T _H5 ) is output.

After each of the plurality of nitrogen-free mixed gases is removed from the chamber 101 illustrated in FIG. 23, each of the plurality of nitrogen-containing mixed gases is sequentially supplied to the chamber 101. When the first nitrogen-containing mixed gas among the plurality of nitrogen-containing mixed gases is supplied to the chamber 101, the heating element 61 shown in FIGS. 1 and 2 in contact with the first nitrogen-containing mixed gas has a heating temperature T _H1. Nitrogen-containing electrical signal S _H1 (T _H1 ), exothermic temperature T _H2 nitrogen-containing electrical signal S _H2 (T _H2 ), exothermic temperature T _H3 nitrogen-containing electrical signal S _H3 (T _H3 ), exothermic temperature T _An electrical signal S _H4 (T _H4 ) when nitrogen is contained in _H4 and an electrical signal S _H5 (T _H5 ) when nitrogen is contained at an exothermic temperature T _H5 are output. For each well of other nitrogen-containing gas mixture, heating element 61, the nitrogen-containing time an electrical signal at a heat producing temperature _{T H1 S H1 (T H1)} , fever producing temperature T _H2, nitrogenous during electric signal S _H2 in (T _H2), heat producing temperature T _H3 nitrogenous during electric signal S _H3 in (T _H3), heating temperature at the time the nitrogen content in T _H4 electric signal S _H4 (T _H4), and the heating temperature T nitrogenous during electric signal S _H5 in _H5 (T _H5 ) Is output.

  Note that the order of gases supplied to the chamber 101 shown in FIG. 23 is arbitrary. For example, the calibration gas may be supplied to the chamber 101 between a plurality of nitrogen-free mixed gases.

The microchip 8 is connected to a central processing unit (CPU) 300 that includes a measurement unit 301. An electrical signal storage device 401 is connected to the CPU 300. Measuring unit 301, the reference electrical signal S _H1A at a heat producing temperature T _H1, from the heater element 61 in contact with the reference gas (T _H1), the reference electric signal S _H2A at the heat producing temperature T _H2 (T _H2), the reference in the heat producing temperature T _H3 electrical signal S _H3A (T _H3), measures the measurement value of the reference electrical signal S _H4A at the heat producing temperature T _H4 (T _H4), and the reference electrical signal S _H5A at the heat producing temperature T _H5 (T _H5), electrical measurements Save in the signal storage device 401.

The measurement unit 301, calibration electrical signal S _H1B at a heat producing temperature T _H1, from the heater element 61 in contact with the calibration gas (T _H1), calibration electrical signal S _H2B at the heat producing temperature T _H2 (T _H2), heating temperature calibration electrical signal S _H3B at T _H3 (T _H3), calibration electrical signal S _H4B at the heat producing temperature T _H4 (T _H4), and the measured values of the calibration electrical signal S _H5B (T _H5) at a heat producing temperature T _H5 Measure and store the measured value in the electrical signal storage device 401.

Further, the measurement unit 301 is configured to _{display the} electric signal S _H1 (T _H1 ) when no heat is generated from the heating element 61 in contact with each of the plurality of nitrogen-free mixed gases, and the non-nitrogen content when the heat generation temperature is T _H2 . electric signal S _H2 (T _H2), nitrogen-free time of an electrical signal at a heat producing temperature _{T H3 S H3 (T H3)} , nitrogen-free time of the electric signal S _H4 at the heat producing temperature T _H4 (T _H4), and the heating temperature T _H5 The measured value of the electrical signal S _H5 (T _H5 ) when nitrogen is not contained in is measured, and the measured value is stored in the electrical signal storage device 401.

Furthermore, measuring unit 301, the heat generation temperature T when the nitrogen content in _H1 electric signal S _H1 (T _H1) from the heater element 61 coming into contact with the each of the plurality of nitrogen-containing mixed gas, nitrogen-containing time electrical signal at the heat producing temperature T _H2, S _H2 (T _H2), the heat producing temperature T nitrogenous when an electrical signal at a _H3 S _H3 (T _H3), heat producing temperature T _H4 nitrogenous during electric signal S _H4 in (T _H4), and when the nitrogen containing at the heat producing temperature T _H5 The measured value of the electrical signal S _H5 (T _H5 ) is measured, and the measured value is stored in the electrical signal storage device 401.

The electric signals S _H from the heater element 61, the heater element 61 the resistance value R _H, of the energizing current I _H, and the output signal AD _H of the connected A / D conversion circuit 304 to the heater element 61 of the heater element 61 Either may be sufficient.

The formula creation unit 302 included in the CPU 300 includes, for example, the known calorific value Q of each of the reference gas, the calibration gas, the plurality of nitrogen-free mixed gases, and the plurality of nitrogen-containing mixed gases, and the reference from the heating element 61. electrical signal _{S H1A (T H1), S} H2A (T H2), S H3A (T H3), S H4A (T H4), the measured value of S _H5A (T _H5), calibration electrical signal S _H1B (T _H1) , S _H2B (T _H2 ), S _H3B (T _H3 ), S _H4B (T _H4 ), S _H5B (T _H5 ) measured values, nitrogen non-oil- _free electrical signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), S _H5 (T _H5 ), and the nitrogen oil-containing electrical signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 A plurality of measured values of (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) are collected.

Further formula creation module 302, the value of the collected calorific value Q, the measured value of the reference electrical signal S _HA, measurements of the calibration electrical signal S _HB, measurement of nitrogen-oil-containing time electric signal S _H, and a nitrogen oil-containing Based on the measured value of the time electrical signal S _H , electrical signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ) from the heating element 61 are obtained by multivariate analysis. ), S _H5 (T _H5 ) is an independent variable, and a calorific value calculation formula is calculated with a calorific value Q as a dependent variable.

  “Multivariate analysis” means A. J Smol and B.M. In support vector regression, multiple regression analysis, and Japanese Patent Application Laid-Open No. 5-141999, disclosed in Scholkopf's “A Tutor on Support Vector Regression” (NeuroCOLt Technical Report (NC-TR-98-030), 1998). Includes the disclosed fuzzy quantification theory class II.

The normalizing unit 306 uses the measured values of the reference electrical signals S _H3A (T _H3 ), S _H4A (T _H4 ), S _H5A (T _H5 ) and the calibration electrical signal S _H3B (T _{H3), S H4B (T H4} ), the measured value of S _H5B (T _H5), nitrogen-oil-containing time electric signal _{S H3 (T H3), S} H4 (T H4), a plurality of measurements of S _H5 (T _H5) value, and nitrogen oilless when the electric signal _{S H3 (T H3), S} H4 (T H4), collecting a plurality of measured values of S _H5 (T _H5).

Further, the normalization unit 306 measures the measured value of the electrical signal S _H (T _H ) and the reference electrical signal S _HA (T _H ) at each of the plurality of heat generation temperatures, for example, as shown in the following equation (48). The difference between the two values is divided by the difference between the measured value of the calibration electrical signal S _HB (T _H ) and the measured value of the reference electrical signal S _HA (T _H ), and the normalized measured value S _{HN of} the electrical signal Calculate (T _H )
S _HN (T _H ) = (S _H (T _H ) -S _HA (T _H )) / (S _HB (T _H ) -S _HA (T _H )) (48)
When the above equation (48) is used, the measured value S _HAN (T _H ) of the normalized reference electrical signal becomes 0 regardless of the heat generation temperature. Further, the measured value S _HBN (T _H ) of the normalized electrical signal for calibration is 1 regardless of the heat generation temperature.

The formula creation unit 302 has a plurality of measured values S _H3N (T _H3 ), S _H4N (T _H4 ), S _H5N (T _H5 ) of the normalized nitrogen- _free oil signal and the normalized nitrogen- _containing oil signal. _Collect a plurality of measured values S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) of the electrical signal.

For each of the plurality of nitrogen-free mixed gases, the formula creating unit 302 generates the heat by using the difference between the heat generation temperature T _H5 and the heat generation temperature T _H4 as the first heat generation temperature difference as shown in the following formula (49). a normalized nitrogen-oil-containing time electric signal S _H5N (T _H5) at a temperature T _H5, a normalized nitrogen-oil-containing time electric signal S _H4N at the heat producing temperature T _H4 (T _H4), which is the difference, normalized The first difference value d ₁ of the converted nitrogen-free electrical signal is calculated.
d ₁ = S _H5 (T _H5 ) -S _H4 (T _H5 ) (49)

For each of the plurality of nitrogen-containing mixed gases, the formula creation unit 302 also uses the normalized nitrogen oil- _containing electric signal S _H5N (T _H5 ) at the exothermic temperature T _{H5 and} the normalized nitrogen oil- _containing at the exothermic temperature T _H4 . A first difference value d ₁ between the _hourly electrical signal S _H4N (T _H4 ) and the normalized nitrogen-containing _hourly electrical signal is calculated.

In addition, as shown in the following formula (50), the formula creation unit 302 sets the difference between the heat generation temperature T _H4 and the heat generation temperature T _H3 as the second difference in the heat generation temperature for each of the plurality of nitrogen-free mixed gases. , the heating temperature normalized nitrogen-oil-containing time an electrical signal at a _{T H4 S H4N (T H4)} , the heating temperature T normalized nitrogen-oil-containing time an electrical signal at a _H3 S _H3N (T _H3), is the difference Then, a second difference value d ₂ of the normalized electric signal without nitrogen is calculated.
d ₂ = S _H4 (T _H4 ) -S _H3 (T _H3 ) (50)

For each of the plurality of nitrogen-containing mixed gases, the formula creating unit 302 also normalizes the nitrogen-containing oil signal S _H4N (T _H4 ) at the exothermic temperature T _{H4 and} the normalized nitrogen-containing oil at the exothermic temperature T _H3 . A second difference value d ₂ between the _hourly electrical signal S _H3N (T _H3 ) and the normalized nitrogen-containing _hourly electrical signal is calculated.

For each of the plurality of nitrogen-free mixed gases, the equation creating unit 302 corrects the first difference value d ₁ multiplied by the _first correction coefficient A ₁ as shown in the following equation (51). An evaluation value E that is a difference value between the difference d _{C1 of 1} and the value d ₂ of the second difference is set. Further, the formula creation unit 302 calculates a value of the _first correction coefficient A ₁ such that the evaluation value E approaches 0 for each of the plurality of nitrogen-free mixed gases.
E = A ₁ × d ₁ -d ₂
= d _C1 -d ₂ ... (51)

Further, for example, as shown in the following formula (52), the formula creating unit 302 uses a corrected evaluation value E _C obtained by multiplying the evaluation value E by the second correction coefficient A ₂ to the nitrogen contained in the mixed gas. Set as a measured value of concentration. Further, the formula creating unit 302 performs the second operation such that the error between the known actual value of the nitrogen concentration and the measured value E _C of the nitrogen concentration approaches zero in each of the plurality of nitrogen-containing mixed gases. The value of the correction coefficient A ₂ is calculated. By multiplying the second correction coefficient A _2, is a dimensionless number evaluation value E is converted into concentration units.
E _C = E × A ₂ ... (52)

The formula creation unit 302 uses the calculated first correction coefficient A ₁ and second correction coefficient A ₂ to generate the current from the heating element 61 at at least three heating temperatures as shown in the above formula (47). A nitrogen concentration calculation formula is created with the normalized electrical signals S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) as independent variables and the nitrogen concentration E _C as a dependent variable.

  The nitrogen concentration measurement system 20 further includes a formula storage device 402 connected to the CPU 300. The formula storage device 402 stores the calorific value calculation formula created by the formula creation unit 302. The formula storage device 402 stores the nitrogen concentration calculation formula created by the formula creation unit 302. Further, an input device 312 and an output device 313 are connected to the CPU 300. As the input device 312, for example, a host computer, a communication device, a keyboard, and a pointing device such as a mouse can be used. As the output device 313, a liquid crystal display, an analog output receiver, an image display device such as a monitor, a printer, and the like can be used.

  Next, a method for creating a calorific value calculation formula according to the embodiment will be described using the flowchart shown in FIG.

(A) In step S100, a reference gas is introduced into the chamber 101 shown in FIG. In step S101, the drive circuit 303 applies drive power P _H1 to the heat generating element 61 shown in FIGS. 1 and 2, and causes the heat generating element 61 to generate heat at the heat generation temperature T _H1 . 23 measures the measured value of the reference electrical signal S _H1A (T _H1 ) from the heating element 61 that generates heat at the heating temperature T _H1 , and stores it in the electrical signal storage device 401.

(B) In step S102, the drive circuit 303 determines whether or not the temperature switching of the heating element 61 shown in FIGS. 1 and 2 has been completed. If the switching to the heat generation temperatures T _H2 , T _H3 , T _H4 , and T _H5 has not been completed, the process returns to step S101, and the drive circuit 303 shown in FIG. Heat is generated at an exothermic temperature _TH2 . 23 measures the measured value of the reference electrical signal S _H2A (T _H2 ) from the heating element 61 that is in contact with the reference gas and generates heat at the heating temperature T _H2 , and stores it in the electrical signal storage device 401. .

(C) Thereafter, the loop of step S101 and step S102 is repeated, and the measurement unit 301 shown in FIG. 23 is in contact with the reference gas and generates the reference electrical signal S _H3A (T _H3 ) from the heating element 61 that generates heat at the heating temperature T _H3. measurements, exothermic temperature reference from the heater element 61 that generates heat at T _H4 electric signal S _H4A measurements of (T _H4), and the reference electrical signal S _H5A from the heater element 61 that generates heat at a heat producing temperature T _H5 (T _H5 ) Is stored in the electrical signal storage device 401.

  (D) When the switching of the temperature of the heating element 61 is completed, the process proceeds from step S102 to step S103. In step S103, it is determined whether or not the gas switching has been completed. If switching from the reference gas to the calibration gas has not been completed, the process returns to step S100. In step S100, a calibration gas is introduced into the chamber 101 shown in FIG.

(E) The loop from step S101 to step S102 is repeated in the same manner as when the reference gas is introduced into the chamber 101. The measurement unit 301 is in contact with the calibration gas, and the calibration electric signals S _H1B (T _H1 ) and S _H2B (T _H2 ) from the heating element 61 that generates heat at the heat generation temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5. ), S _H3B (T _H3 ), S _H4B (T _H4 ), and S _H5B (T _H5 ) are measured and stored in the electrical signal storage device 401.

  (F) When the switching of the temperature of the heating element 61 is completed, the process proceeds from step S102 to step S103. In step S103, it is determined whether or not the gas switching has been completed. If switching from the calibration gas to each of the plurality of nitrogen-free mixed gases has not been completed, the process returns to step S100. In step S100, the first nitrogen-free mixed gas among the plurality of nitrogen-free mixed gases is introduced into the chamber 101 shown in FIG.

(G) The loop from step S101 to step S102 is repeated in the same manner as when the reference gas is introduced into the chamber 101. The measurement unit 301 is in contact with the first non-nitrogen-containing mixed gas, and the non-nitrogen-containing electric signal S _H1 (T _H (T) from the heating element 61 that generates heat at the exothermic temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5. The measured values of _H1 ), _SH2 ( _TH2 ), _SH3 ( _TH3 ), _SH4 ( _TH4 ), _SH5 ( _TH5 ) are measured and stored in the electrical signal storage device 401.

(H) Thereafter, the loop from step S100 to step S103 is repeated. Thus, the non-nitrogen containing electrical signal S _H1 (T _H1) from the heating element 61 in contact with each of the other non-nitrogen containing mixed gases and generating heat at the exothermic temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5. ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) are stored in the electrical signal storage device 401.

  (I) When the switching of the temperature of the heating element 61 is completed, the process proceeds from step S102 to step S103. In step S103, it is determined whether or not the gas switching has been completed. If switching from the plurality of nitrogen-free mixed gases to each of the plurality of nitrogen-containing mixed gases has not been completed, the process returns to step S100. In step S100, the first nitrogen-containing mixed gas among the plurality of nitrogen-containing mixed gases is introduced into the chamber 101 shown in FIG.

(J) The loop from step S101 to step S102 is repeated in the same manner as when the reference gas is introduced into the chamber 101. The measurement unit 301 is in contact with the first nitrogen-containing mixed gas, and the nitrogen-containing electric signal S _H1 (T _H1 ) from the heating element 61 that generates heat at the heat generation temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5. , S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) are measured and stored in the electrical signal storage device 401.

(K) Thereafter, the loop from step S100 to step S103 is repeated. As a result, the nitrogen-containing electrical signal S _H1 (T _H1 ), which is in contact with each of the other nitrogen-containing mixed gases and is generated from the heating element 61 that generates heat at the heat generation temperatures T _H1 , T _H2 , T _H3 , T _H4 , T _H5 , The measured values of S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) are stored in the electrical signal storage device 401.

(L) In step S104, the value of the known calorific value Q of each of the reference gas, the calibration gas, the plurality of nitrogen-free mixed gases, and the plurality of nitrogen-containing mixed gases is input from the input device 312 to the formula creating unit 302. To do. Further, the formula creating unit 302 receives the reference electrical signals S _H1A (T _H1 ), S _H2A (T _H2 ), S _H3A (T _H3 ), S _H4A (T _H4 ) from the electrical signal storage device 401. , the measured value of S _H5A (T _H5), calibration electrical signal _{S H1B (T H1), S} H2B (T H2), S H3B (T H3), S H4B (T H4), S H5B of (T _H5) A plurality of measured values of electrical signals _SH1 ( _TH1 ), _SH2 ( _TH2 ), _SH3 ( _TH3 ), _SH4 ( _TH4 ), _SH5 ( _TH5 ) when nitrogen is not contained, and A plurality of measured values of the electrical signals _SH1 ( _TH1 ), _SH2 ( _TH2 ), _SH3 ( _TH3 ), _SH4 ( _TH4 ), _SH5 ( _TH5 ) when nitrogen is contained are read.

(M) In step S105, the known calorific value Q of each of the reference gas, the calibration gas, the plurality of nitrogen-free mixed gases, and the plurality of nitrogen-containing mixed gases, and the reference electrical signal S _H1A from the heating element 61 _{(T H1), S H2A (} T H2), S H3A (T H3), S H4A (T H4), the measured value of S _H5A (T _H5), calibration electrical signal _{S H1B (T H1), S} H2B ( _{T H2), S H3B (T} H3), S H4B (T H4), the measured value of S _H5B (T _H5), nitrogen-free time of the electric signal _{S H1 (T H1), S} H2 (T H2), S H3 (T _H3 ), S _H4 (T _H4 ), a plurality of measured values of S _H5 (T _H5 ), and electrical signals SH ₁ (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ) when nitrogen is contained , S _H4 (T _H4 ), S _H5 (T _H5 ), and the formula creation unit 302 performs multivariate analysis such as support vector regression. By multivariate analysis such as support vector regression, the formula creating unit 302 generates electrical signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ) from the heating element 61. , S _H5 (T _H5 ) is an independent variable, and a calorific value calculation formula is calculated with a calorific value Q as a dependent variable. Thereafter, in step S106, the formula creation unit 302 stores the created calorific value calculation formula in the formula storage device 402, and the calorific value calculation formula creation method according to the embodiment ends.

  As described above, according to the method for creating the calorific value calculation formula according to the embodiment, it is possible to create a calorific value calculation formula that can uniquely calculate the calorific value Q of the measurement target mixed gas. .

  Next, a method of creating a nitrogen concentration calculation formula according to the embodiment will be described using the flowchart shown in FIG.

(A) In step S201, the normalization unit 306 receives the reference electrical signals S _H1A (T _H1 ), S _H2A (T _H2 ), S _H3A (T _H3 ), S from the electrical signal storage device 401. _H4A (T _H4), the measured value of S _H5A (T _H5), calibration electrical signal _{S H1B (T H1), S} H2B (T H2), S H3B (T H3), S H4B (T H4), S H5B (T _H5 ) measured value, electric signal SH ₁ (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), S _H5 (T _H5 ) when not containing nitrogen And a plurality of measured values of electrical signals _SH1 ( _TH1 ), _SH2 ( _TH2 ), _SH3 ( _TH3 ), _SH4 ( _TH4 ), _SH5 ( _TH5 ) when nitrogen is contained read out.

(B) In step S202, the normalization unit 306, for example, using the above equation (48), the measured value S _HAN (T _H ) of the normalized reference electrical signal becomes 0 regardless of the heat generation temperature, The non-nitrogen containing electrical signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (so that the measured value S _HBN (T _H ) of the calibrated electrical signal becomes 1 regardless of the heat generation temperature. A plurality of measured values of T _H3 ), S _H4 (T _H4 ), S _H5 (T _H5 ), and electric signals SH ₁ (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), Each of a plurality of measured values of S _H4 (T _H4 ) and S _H5 (T _H5 ) is normalized, and the measured values of the normalized electrical signal when no nitrogen is contained S _H1N (T _H1 ), S _H2N (T _H2 ) _{, S H3N (T H3),} S H4N (T H4), S H5N (T H5), and the measured value S _h1N (T _H1) of the normalized nitrogenous time electrical signals, S _H2N (T _{H2 , S H3N (T H3),} S H4N (T H4), calculates the S _H5N (T _H5).

(C) In step 203, the formula creation unit 302 receives from the normalization unit 306 the normalized measured value S _H3N (T _H3 ) of the non-nitrogen containing electric signal for each of the plurality of non-nitrogen containing mixed gases. S _H4N (T _H4 ), S _H5N (T _H5 ), and normalized nitrogen-containing electrical signal measurements S _H3N (T _H3 ), S _H4N (T _H4 ) for each of the plurality of nitrogen-containing mixed gases , S _H5N (T _H5 ).

(D) In step 204, the formula creating unit 302 uses the formula (49), for example, and normalizes nitrogen-free in the first difference in the exothermic temperature for each of the plurality of nitrogen-free mixed gases. A first difference value d ₁ of the hourly electrical signal is calculated. In addition, the formula creating unit 302 also calculates the _first difference value d ₁ of the normalized electrical signal when containing nitrogen in the first difference in the exothermic temperature for each of the plurality of nitrogen-containing mixed gases.

(E) In step 205, the formula creation unit 302 uses the above formula (50), for example, for each of the plurality of nitrogen-free mixed gases, normalized nitrogen-free in the second difference in the exothermic temperature A second difference value d ₂ of the hourly electrical signal is calculated. In addition, the formula creating unit 302 also calculates the _second difference value d ₂ of the normalized nitrogen-containing electrical signal in the second difference in the exothermic temperature for each of the plurality of nitrogen-containing mixed gases.

(F) In step 206, the formula creation unit 302 sets the first difference value d ₁ for each of the plurality of nitrogen-free mixed gases and the plurality of nitrogen-containing mixed gases, as shown in the formula (51) above. An evaluation value E which is a difference value between the corrected first difference d _C1 multiplied by the first correction coefficient A ₁ and the second difference value d ₂ is set. Further, the formula creation unit 302 calculates a value of the _first correction coefficient A ₁ such that the evaluation value E approaches 0 for each of the plurality of nitrogen-free mixed gases.

(G) In step S207, for example, as shown in the above equation (52), the equation creating unit 302 uses the evaluation value E _C obtained by multiplying the evaluation value E by the second correction coefficient A ₂ as a mixed gas. Is set as a measured value of the concentration of nitrogen contained in. Further, the formula creation unit 302 uses the second correction coefficient such that the error between the actual value of the nitrogen concentration and the measured value E _C of the nitrogen concentration approaches zero in each of the plurality of nitrogen-containing mixed gases. to calculate the value of a _2.

(H) In step S208, the formula creation unit 302 uses the calculated first correction coefficient A ₁ and second correction coefficient A ₂ to generate at least three heat generations as shown in the formula (47). A nitrogen concentration calculation formula is created with the normalized electrical signal from the heating element 61 at the temperature as an independent variable and the nitrogen concentration as a dependent variable. Thereafter, in step S209, the formula creation unit 302 stores the created nitrogen concentration calculation formula in the formula storage device 402, and the nitrogen concentration calculation formula creation method according to the embodiment ends.

  As described above, according to the method for creating a nitrogen concentration calculation formula according to the embodiment, it is possible to create a nitrogen concentration calculation formula that can uniquely calculate the nitrogen concentration value of the measurement target mixed gas.

  Next, functions of the nitrogen concentration measuring system 20 shown in FIG. 23 according to the embodiment when measuring the calorific value Q and the nitrogen concentration of the measurement target mixed gas whose calorific value Q and nitrogen concentration are unknown will be described. .

For example, methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), nitrogen (N ₂ ), carbon dioxide (CO ₂ ), etc. at unknown volume ratios A measurement target mixed gas such as natural gas whose calorific value Q and nitrogen concentration are unknown is introduced into the chamber 101. The heating element 61 of the microchip 8 shown in FIGS. 1 and 2 is sequentially supplied with driving powers P _H1 , P _H2 , P _H3 , P _H4 , and P _H5 from the driving circuit 303 shown in FIG. When the driving powers P _H1 , P _H2 , P _H3 , P _H4 , and P _H5 are given, the heating element 61 in contact with the measurement target mixed gas sequentially generates heat at, for example, five levels of heating temperature, and at the heating temperature T _H1 . electric signals S _H1 (T _H1), an electric signal S _H2 at heating temperatures T _H2 (T _H2), the electric signal S _H3 at the heat producing temperature T _H3 (T _H3), the electric signal S _H4 at the heat producing temperature T _H4 (T _H4) And an electric signal S _H5 (T _H5 ) at the heat generation temperature T _H5 is output.

The measuring unit 301 has an electric signal S _H1 (T _H1 ) at the heat generation temperature T _H1 from the heat generating element 61 in contact with the measurement target mixed gas, an electric signal S _H2 (T _H2 ) at the heat generation temperature T _{H2, and} an electricity at the heat generation temperature T _H3 . signal S _H3 (T _H3), the electric signal S _H4 at the heat producing temperature T _H4 (T _H4), and the measured values of the electric signals S _H5 (T _H5) at a heat producing temperature T _H5 measured, electric signal storage device measurements Save to 401.

As described above, the expression storage device 402 uses the electrical signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) as independent variables. And a calorific value calculation formula having the calorific value Q as a dependent variable is stored.

The nitrogen concentration measurement system 20 according to the embodiment further includes a calorific value calculation unit 305. The calorific value calculation unit 305 reads the calorific value calculation formula from the formula storage device 402. Further, the calorific value calculation unit 305 is configured to output the electric signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H4 ), S _H from the heating element 61 of the calorific value calculation formula. Electric signals S _H1 (T _H1 ), S _H2 (T _H2 ), S _H3 (T _H3 ), S _H4 (T _H (T _H5 )) read from the electric signal storage device 401 are _{added to} the independent variables of _H5 (T _H5 ). The measured values of _H4 ) and S _H5 (T _H5 ) are substituted, and the measured value of the calorific value Q of the measurement target mixed gas is calculated. A measurement result storage device 403 is further connected to the CPU 300. The calorific value calculation unit 305 stores the calculated value of the calorific value Q of the measurement target mixed gas in the measurement result storage device 403.

In addition, the normalization unit 306 reads the measured values of S _H3 (T _H3 ), S _H4 (T _H4 ), and S _H5 (T _H5 ) from the heating element 61 from the electric signal storage device 401, and normalizes the electric The signal measurement values S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) are calculated.

The nitrogen concentration measurement system 20 according to the embodiment further includes a nitrogen concentration calculation unit 307. The nitrogen concentration calculation unit 307 reads the nitrogen concentration calculation formula from the formula storage device 402. Further, the nitrogen concentration calculation unit 307 receives the normalized electric signal measurement values S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) from the normalization unit 306. Further, the nitrogen concentration calculation unit 307 is independent of the normalized electrical signals S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) of the nitrogen concentration calculation formula given by, for example, the equation (47). The measured values S _H3N (T _H3 ), S _H4N (T _H4 ), and S _H5N (T _H5 ) of the normalized electrical signal are substituted for the variables, and the concentration of nitrogen contained in the measurement target mixed gas is calculated. . The nitrogen concentration calculation unit 307 stores the calculated concentration value of nitrogen contained in the measurement target mixed gas in the measurement result storage device 403.

  In addition, each component of the nitrogen concentration measurement system 20 according to the embodiment does not need to be housed in the same casing, and at least a part of each component may be arranged separately.

According to the nitrogen concentration measurement system 20 according to the embodiment described above, the electrical signal S _H1 (T _H1 ), the heat signal from the heating element 61 in contact with the measurement target mixed gas can be used without using an expensive gas chromatography apparatus or sound velocity sensor. _{S H2 (T H2), S} H3 (T H3), S H4 (T H4), from the measured values of S _H5 (T _H5), values of the nitrogen concentration of the calorific value Q of the mixed gas to be measured mixed gas Can be measured.

Natural gas has a different component ratio of hydrocarbons depending on the gas field. Natural gas includes nitrogen (N ₂ ), carbon dioxide (CO ₂ ) and the like in addition to hydrocarbons. Therefore, the volume ratio of the gas component contained in the natural gas differs depending on the output gas field, and the calorific value Q of the natural gas is often unknown even if the type of the gas component is known. Moreover, even if it is the natural gas derived from the same gas field, the calorific value Q is not always constant and may change depending on the sampling time.

  Conventionally, when collecting the usage fee of natural gas, a method has been used in which charging is performed according to the volume of use, not the amount of heat Q used for natural gas. However, since the calorific value Q differs depending on the production gas field from which natural gas is derived, it is not fair to charge the volume used. On the other hand, if the nitrogen concentration measurement system 20 according to the embodiment is used, the type of gas component is known, but the volume ratio of the gas component is unknown. The calorific value Q of the gas can be easily calculated. Therefore, it becomes possible to collect a fair usage fee.

  In the gas business using LNG as a raw material, from the viewpoint of effective energy utilization, boil-off gas (BOG) tends to be mixed into city gas without being discarded. In the boil-off gas, methane is the main component, but nitrogen, which is a low boiling point component, may be contained at a high concentration. Since nitrogen is an incombustible component and the calorific value is zero, it is useful to be able to measure the concentration of nitrogen contained in the mixed gas in order to accurately grasp the calorific value of the mixed gas.

(Other embodiments)
As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, embodiments, and operation techniques should be apparent to those skilled in the art. It should be understood that the present invention includes various embodiments and the like not described herein.

8 Microchip 18 Heat insulation member 20 Nitrogen concentration measurement system 60 Substrate 61 Heating element 62 First temperature measuring element 63 Second temperature measuring element 64 Heat insulating element 65 Insulating film 66 Cavity 101 Chamber 102, 103 Flow path 300 Central processing unit 301 Measurement unit 302 Formula creation unit 303 Drive circuit 304 Conversion circuit 305 Heat generation amount calculation unit 306 Normalization unit 307 Nitrogen concentration calculation unit 312 Input device 313 Output device 401 Electric signal storage device 402 Formula storage device 403 Measurement result storage device

Claims (20)

A measuring unit for measuring a measured value of an electric signal from a heating element in contact with the measurement target mixed gas at each of a plurality of heating temperatures;
Normalization that normalizes the measured value of the electric signal so that the value of the electric signal from the heating element in contact with the reference gas not containing nitrogen and the calibration gas containing hydrocarbon as a calibration component is constant regardless of the heat generation temperature. And
A formula storage device for storing a nitrogen concentration calculation formula having normalized electric signals from the heating elements at at least three heating temperatures as independent variables and a nitrogen concentration as a dependent variable;
Substituting the normalized measured value of the electrical signal into the independent variable of the nitrogen concentration calculation formula, and calculating a concentration of nitrogen contained in the measurement target mixed gas;
A nitrogen concentration measurement system.   The nitrogen concentration calculator is configured to multiply the first difference of the measured value of the normalized electrical signal in the first difference of the exothermic temperature by a correction coefficient and the first difference of the exothermic temperature. A concentration of nitrogen contained in the measurement target gas mixture is calculated based on an evaluation value that is a difference between the second difference of the measured values of the normalized electrical signal in the difference of 2, and the correction coefficient is The nitrogen concentration measurement system according to claim 1, wherein the evaluation value is set to approach 0 when a gas not containing nitrogen is in contact with the heating element.   The nitrogen concentration calculator multiplies the evaluation value by a second correction coefficient to calculate the nitrogen concentration, and the second correction coefficient converts the evaluation value, which is a dimensionless number, into a concentration unit. The nitrogen concentration measurement system according to claim 2.   The nitrogen concentration measurement system according to any one of claims 1 to 3, wherein the reference gas is methane gas.   The said normalization part normalizes the measured value of the said electrical signal so that the value of the electrical signal from the said heat generating element which contact | connects the said reference gas may become 0 irrespective of heat_generation | fever temperature. The nitrogen concentration measurement system according to item 1.   The nitrogen concentration measurement system according to any one of claims 1 to 5, wherein the calibration gas is a mixed gas.   The nitrogen concentration measurement system according to any one of claims 1 to 6, wherein the calibration gas is a span gas.   The said normalization part normalizes the measured value of the said electric signal so that the value of the electric signal from the said heat generating element which contacts the said calibration gas may become 1 irrespective of heat_generation | fever temperature. The nitrogen concentration measurement system according to item 1. The equation storage device further stores a calorific value calculation formula having an electrical signal from the heating element at the plurality of exothermic temperatures as an independent variable and a calorific value as a dependent variable,
The heating value calculation part which calculates the value of the emitted-heat amount of the said measuring object mixed gas further by substituting the measured value of the electric signal from the said heat generating element for the said independent variable of the said emitted-heat amount calculation formula, The nitrogen concentration measuring system according to any one of 1 to 8.   10. The nitrogen concentration measurement system according to claim 9, wherein the number of the plurality of heat generation temperatures is at least a number obtained by subtracting 1 from the number of the plurality of types of gas components contained in the measurement target mixed gas. Measuring a measured value of an electrical signal from a heating element in contact with a measurement target mixed gas at each of a plurality of heating temperatures;
Normalize the measured value of the electric signal so that the value of the electric signal from the heating element in contact with the reference gas not containing nitrogen and the calibration gas containing hydrocarbon as a calibration component is constant regardless of the heating temperature. When,
Preparing a nitrogen concentration calculation formula with normalized electric signals from the heating elements at at least three exothermic temperatures as independent variables and nitrogen concentration as a dependent variable;
Substituting the normalized measured value of the electrical signal into the independent variable of the nitrogen concentration calculation formula, and calculating the concentration of nitrogen contained in the measurement target mixed gas;
A method for measuring nitrogen concentration.   In calculating the concentration of nitrogen, the corrected first difference obtained by multiplying the first difference of the normalized measurement value of the electrical signal in the first difference of the exothermic temperature by a correction coefficient, and the exothermic temperature Based on an evaluation value that is a difference between the second difference of the normalized measurement value of the electrical signal in the second difference, a concentration of nitrogen contained in the measurement target mixed gas is calculated, and the correction coefficient is The method for measuring a nitrogen concentration according to claim 11, wherein the evaluation value is set to approach 0 when a gas not containing nitrogen is in contact with the heating element.   In calculating the concentration of nitrogen, the nitrogen concentration is calculated by multiplying the evaluation value by a second correction coefficient, and the evaluation value is a dimensionless unit of the evaluation value where the second correction coefficient is a dimensionless number. The method for measuring a nitrogen concentration according to claim 12, which is converted.   The method for measuring a nitrogen concentration according to any one of claims 11 to 13, wherein the reference gas is methane gas.   15. The nitrogen according to claim 11, wherein the measured value of the electrical signal is normalized so that the value of the electrical signal from the heating element in contact with the reference gas becomes 0 regardless of the heating temperature. Concentration measurement method.   The method for measuring a nitrogen concentration according to claim 11, wherein the calibration gas is a mixed gas.   The method for measuring a nitrogen concentration according to any one of claims 11 to 16, wherein the calibration gas is a span gas.   18. The nitrogen according to claim 11, wherein the measured value of the electrical signal is normalized so that the value of the electrical signal from the heating element in contact with the calibration gas becomes 1 regardless of the heating temperature. Concentration measurement method. Preparing a calorific value calculation formula having an electrical signal from the heating element at the plurality of heat generation temperatures as an independent variable and a calorific value as a dependent variable;
Substituting the measured value of the electric signal from the heating element into the independent variable of the calorific value calculation formula, and calculating the calorific value of the measurement object mixed gas;
The method for measuring a nitrogen concentration according to any one of claims 11 to 18, further comprising:   The method of measuring a nitrogen concentration according to claim 19, wherein the number of the plurality of exothermic temperatures is at least a number obtained by subtracting 1 from the number of a plurality of types of gas components contained in the measurement target mixed gas.