Gas measuring device and method for determining the concentration of target components

Abstract

The concentration of each of a plurality of gas components is expressed as a corrected concentration obtained by subtracting, from a pre-correction concentration corresponding to a detected value for said gas component, a measurement error to which the measurement of said gas component is subject due to one or more interfering components affecting said gas component. The measurement error to which the measurement of the gas component is subject is expressed by a linear sum of corrected concentrations of the interfering components affecting said gas component and influence coefficients indicating the degree to which said interfering components influence the measurement of said gas component. According to the relationship between the corrected concentration and the pre-correction concentration for each of the plurality of gas components, the concentration of a component of interest is determined on the basis of the multiple influence coefficients and the respective detected values for said plurality of gas components.

Description

Technical Field

[0001] The present disclosure relates to a gas measurement device for measuring a sample gas containing a plurality of gas components whose absorption wavelength regions at least partially overlap each other, and a method for obtaining the concentration of a target component among the plurality of gas components.

Background Art

[0002] As a device for obtaining the concentration of a target component in a sample gas such as a gas discharged from a chemical plant or a steel mill, combustion gas from a boiler or a combustion furnace, air, or automobile exhaust gas, an infrared gas analyzer using the non-dispersive infrared absorption method (NDIR) is known.

[0003] In a gas measurement device such as an infrared gas analyzer that utilizes the light absorption characteristics of a target component, an error occurs in the measurement of the target component due to the influence of components other than the target component in the sample gas. Specifically, when an interfering component having an absorption wavelength region that at least partially overlaps with the absorption wavelength region of the target component is present in the sample gas, an error occurs in the measurement of the target component due to the influence of the interfering component.

[0004] Patent Document 1 discloses a measurement method for measuring the concentration of nitrous oxide, in which nitrous oxide and carbon dioxide, which is an interfering component with respect to nitrous oxide, are measured by infrared absorption analysis, and the measurement result of nitrous oxide is corrected using the measurement result of carbon dioxide.

[0005] Patent Document 2 discloses an analyzer in which an optical filter is arranged between a light source and a detector to cut off the absorption wavelength region of an interfering component.

[0006] Patent Document 3 discloses that an interfering component detector and a measurement component detector are optically arranged in series in this order from the other end side of the cell, and a measurement component is corrected and calculated using a detection signal obtained from the detector.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Patent No. 2952855 [Patent Document 2] Japanese Utility Model Publication No. 5-75654 [Patent Document 3] Japanese Patent Publication No. 2012-68164 [Overview of the project] [Problems that the invention aims to solve]

[0008] As disclosed in Patent Documents 1 to 3, in a gas measuring device that utilizes the infrared absorption characteristics of a target component, there is a need to determine the concentration of the target component while taking into account the influence of interfering components.

[0009] Although Patent Documents 1 to 3 disclose methods for determining the concentration of a target component while taking into account that the measurement of the target component is affected by interfering components, they did not take into account that the measurement of interfering components is affected by other components.

[0010] One objective of this disclosure is to more accurately determine the concentration of a target component contained in a sample gas, taking into account that the measurement of interfering components is affected by other components. [Means for solving the problem]

[0011] The gas measuring device of this disclosure measures a sample gas containing multiple gas components whose absorption wavelength ranges overlap by at least a portion of each other. The gas measuring device includes a detection unit that detects the amount of light in each absorption wavelength range of the multiple gas components by detecting light that has passed through the sample gas, and a calculation unit that determines the concentration of a target component among the multiple gas components based on the detected values ​​of each of the multiple gas components detected by the detection unit. A gas component having an absorption wavelength range that overlaps by at least a portion of the absorption wavelength range of one of the multiple gas components is an interference component with respect to that one gas component. The concentration of each of the multiple gas components is expressed as a corrected concentration obtained by subtracting the measurement error that one or more interference components have on the measurement of that gas component from the uncorrected concentration corresponding to the detected value of that gas component. The measurement error that has been applied to the measurement of the gas component is expressed as a linear sum of the corrected concentration of the interference component with respect to that gas component and an influence coefficient that indicates the degree to which the interference component has an effect on the measurement of that gas component. The calculation unit determines the corrected concentration of a target component as the concentration of that target component, based on multiple influence coefficients and the detected values ​​of each of the multiple gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the multiple gas components.

[0012] The method of this disclosure is a method for determining the concentration of a target component among a sample gas containing multiple gas components whose absorption wavelength ranges overlap by at least a portion of each other. The method includes the steps of: detecting light that has passed through the sample gas to detect the amount of light in each absorption wavelength range of the multiple gas components and obtaining a detected value for each of the multiple gas components; and determining the concentration of a target component among the multiple gas components based on the obtained detected values ​​for each of the multiple gas components. A gas component having an absorption wavelength range that overlaps by at least a portion of the absorption wavelength range of one of the multiple gas components is an interference component with respect to that one gas component. The concentration of each of the multiple gas components is expressed as a corrected concentration obtained by subtracting the measurement error that one or more interference components have on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error that has been applied to the measurement of the gas component is expressed as a linear sum of the corrected concentration of the interference component with respect to the gas component and an influence coefficient that indicates the degree to which the interference component has an effect on the measurement of the gas component. In the step of determining the concentration of the target component, the corrected concentration of the target component is determined as the concentration of the target component based on multiple influence coefficients and the detected values ​​of each of the multiple gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the multiple gas components. [Effects of the Invention]

[0013] According to this disclosure, the corrected concentration of the target component is expressed using the corrected concentration obtained by subtracting the measurement error that interferes with the measurement of the interfering component from the uncorrected concentration of the interfering component relative to the target component. Furthermore, the concentration of the target component is determined according to the relationship between the corrected concentration of the target component and the corrected concentration of the interfering component. Therefore, the concentration of the target component can be determined more accurately by taking into account that the measurement of the interfering component is affected by other components. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram illustrating a method for determining the concentration of a target component using a gas measuring device. [Figure 2] This is a schematic diagram illustrating a method for determining the influence coefficient in a gas measuring device. [Figure 3] It is a diagram showing the configuration of the gas measurement device. [Figure 4] It is a functional block diagram of the control unit. [Figure 5] It is a flowchart showing the processing of the control unit during the measurement of the sample gas. [Figure 6] It is a flowchart showing the processing of the control unit when calculating the influence coefficient. [Figure 7] It is the infrared absorption spectra of nitrous oxide and carbon dioxide. [Figure 8] It is the infrared absorption spectra of nitrous oxide, methane, and sulfur dioxide.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0016] §1 Application Example Referring to FIGS. 1 and 2, an example of a scenario to which the present invention is applied will be described. FIG. 1 is a schematic diagram showing a method for obtaining the concentration of a target component in a gas measurement device. FIG. 2 is a schematic diagram showing a method for obtaining an influence coefficient in a gas measurement device.

[0017] <Method for Obtaining the Concentration of the Target Component> Referring to FIG. 1, a method for obtaining the concentration of the target component will be described. The gas measurement device 1a includes a detection unit 100a and an arithmetic unit 200a. The detection unit 100a detects the amount of light in the absorption wavelength range of each of a plurality of gas components contained in the sample gas by detecting the transmitted light that has passed through the sample gas. The detection unit 100a sends the detection result to the arithmetic unit 200a. The arithmetic unit 200a is an arithmetic device that obtains the concentration of the components in the sample gas based on the detection result.

[0018] Each of the multiple gas components has its own unique absorption wavelength range. Transmitted light is partially absorbed and attenuated by each of the multiple gas components contained in the sample gas. Absorbance, which is the degree to which light is absorbed, is proportional to the concentration of the gas component. Therefore, the concentration of the gas component can be determined from the absorbance.

[0019] In the following, the gas component being measured may be referred to as the "target component." Furthermore, a gas component having an absorption wavelength range that overlaps, at least partially, with the absorption wavelength range of one gas component may be referred to as an "interfering component with respect to one gas component" or simply as an "interfering component." Additionally, the detection result obtained by detecting the light intensity within the absorption wavelength range of one gas component may be referred to as the "detected value of one gas component" or simply as the "detected value."

[0020] Now, consider the case where the target component and its interfering components are present in the sample gas. The detected value of the target component obtained by measuring the sample gas reflects not only the effect of light absorption by the target component, but also the effect of light absorption by the interfering components. Therefore, even if the absorbance in the absorption wavelength range of the target component is detected, the measurement of the target component's concentration will be inaccurate due to the influence of the interfering components.

[0021] The gas measuring device 1a according to this embodiment detects the target component and the interfering component with respect to the target component, and determines the concentration of the target component by correcting the detected value of the target component using the detected value of the interfering component.

[0022] In the example shown in Figure 1, the target component is denoted as component M, and the interfering components with respect to component M are components C1 and C2. The detection unit 100a includes a first detector 10a that detects the amount of light in the absorption wavelength range of component M, a second detector 10b that detects the amount of light in the absorption wavelength range of component C1, and a third detector 10c that detects the amount of light in the absorption wavelength range of component C2. The method for detecting the amount of light is not particularly limited. For example, the amount of light may be detected directly by a photoconductive element, or it may be detected indirectly by the change in internal pressure when transmitted light passes through a cell containing the gas to be detected.

[0023] The calculation unit 200a determines the concentration of component M based on the detected values ​​of each gas component sent from the detection unit 100a. The calculation unit 200a corrects the detected value of component M sent from the first detector 10a using the detected values ​​of component C1 and component C2 sent from the second detector 10b and third detector 10c, respectively, to determine the concentration of component M [M]. In the following, for a given component A, the uncorrected concentration corresponding to the detected value is denoted as A, and the corrected concentration is denoted as [A]. [M] is determined according to equation (1). [C1] is determined according to equation (2). [C2] is determined according to equation (3). Note that the uncorrected concentration corresponding to the detected value obtained from one detector is the concentration calculated based on the detected value obtained from that one detector, without using detected values ​​obtained from other detectors.

[0024]

number

[0025]

number

[0026]

number

[0027] a and b are influence coefficients that show the degree to which components C1 and C2 have an influence on the measurement of component M, respectively. c and d are influence coefficients that show the degree to which components M and C2 have an influence on the measurement of component C1, respectively. e and f are influence coefficients that show the degree to which components M and C1 have an influence on the measurement of component C2, respectively.

[0028] As shown in equations (1) to (3), the concentration of each of the multiple gas components in the sample gas is expressed as the corrected concentration obtained by subtracting the measurement error that one or more interfering components impose on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error that imposes on the measurement of the gas component is expressed as a linear sum of the corrected concentration of the interfering component and an influence coefficient that indicates the degree to which the interfering component has an effect on the measurement of the gas component.

[0029] The calculation unit 200a determines the corrected concentration of component M as the concentration of component M [M], based on the detected values ​​of each of the multiple gas components and the multiple influence coefficients a to f, according to the relationship between the corrected concentration and the uncorrected concentration shown in equations (1) to (3) above.

[0030] Specifically, the calculation unit 200a calculates the concentration [M] as follows. By solving the simultaneous equations (1) to (3), [M] can be expressed in terms of the uncorrected concentration (M, C1, and C2) corresponding to the detected value and the intermediate coefficient, as shown in equation (4) below. m1 to m3 are intermediate coefficients expressed using the influence coefficients a to f, respectively, and are expressed by equations (5) to (7). Also, k in equations (5) to (7) is expressed by equation (8).

[0031]

number

[0032]

number

[0033]

number

[0034]

number

[0035]

number

[0036] Furthermore, in the formula, a' is a-bf, b' is b-ad, c' is c-de, d' is d-bc, e' is e-cf, and f' is f-ae.

[0037] Since [M] can be expressed using the uncorrected concentrations M, C1, and C2, which correspond to the detected values, and intermediate coefficients m1 to m3, the calculation unit 200a stores the intermediate coefficients, for example, and calculates the concentration [M] of component M based on the detected values ​​and intermediate coefficients sent from the detection unit 100a.

[0038] Furthermore, similar to component M, the concentrations of components C1 and C2 can be expressed using M, C1, and C2, which correspond to the detected values, and an intermediate coefficient. Therefore, the calculation unit 200a can determine the concentrations of [C1] and [C2] based on the detected values ​​and intermediate coefficient sent from the detection unit 100a, just as it does for the concentration [M].

[0039] Furthermore, the method for determining the concentration according to multiple relational equations is not limited to the method described above. For example, the calculation unit 200a may perform the calculation using an influence coefficient instead of an intermediate coefficient.

[0040] As described above, the corrected concentration of the target component is expressed using the corrected concentration obtained by subtracting the measurement error caused by the interfering component from the uncorrected concentration of the interfering component relative to the target component. Furthermore, the concentration of the target component can be determined according to the relationship between the corrected concentration of the target component and the corrected concentration of the interfering component. Therefore, it is possible to determine the concentration of the target component more accurately by taking into account that the measurement of the interfering component is affected by other components.

[0041] Although an example with two interference components has been shown, there may be one or three or more interference components. Similarly, in this case as well, the gas measuring device 1a can determine the concentration of the target component based on multiple detected values ​​obtained by detecting the amount of light in each absorption wavelength range of multiple gas components according to the relationship between the corrected concentration and the uncorrected concentration, and multiple influence coefficients.

[0042] <Method for calculating the influence coefficient> Referring to Figure 2, we will explain how to determine the influence coefficients. We consider the influence coefficients that indicate the degree to which the first component influences the measurement of the second component. The detection unit 100a detects the amount of light in the absorption wavelength range of the second component by detecting light that has passed through a standard gas of known concentration consisting of the first component. The calculation unit 200a determines the influence coefficients that indicate the degree to which the first component influences the measurement of the second component, based on the detected value of the second component and the known concentration of the first component, according to the relationship between the corrected concentration and the uncorrected concentration of the second component. Specifically, each influence coefficient a to f is determined as follows.

[0043] Furthermore, the standard gas consisting of the first component does not need to contain any interfering components (for example, the second component) to the first component, and may contain gases such as nitrogen that do not affect the measurement of the first component.

[0044] The detection unit 100a detects a first standard gas containing component M at concentration x but not containing components C1 and C2 using the second detector 10b and the third detector 10c, respectively, to obtain the detected values ​​of component C1 and component C2. The calculation unit 200a calculates the influence coefficient c from the concentration x and the uncorrected concentration of component C1 corresponding to the detected value of component C1 detected by the second detector 10b, according to equation (2). Similarly, the calculation unit 200a calculates the influence coefficient e from the concentration x and the uncorrected concentration of component C2 corresponding to the detected value of component C2 detected by the third detector 10c, according to equation (3).

[0045] The detection unit 100a detects a second standard gas containing component C1 at concentration y but not containing components M and C2 using the first detector 10a and the third detector 10c respectively, and obtains the detected values ​​of component M and component C2. The calculation unit 200a calculates the influence coefficient a from the concentration y and the uncorrected concentration of component M corresponding to the detected value of component M detected by the first detector 10a, according to equation (1). Similarly, the calculation unit 200a calculates the influence coefficient f from the concentration y and the uncorrected concentration of component C2 corresponding to the detected value of component C2 detected by the third detector 10c, according to equation (3).

[0046] The detection unit 100a detects a third standard gas containing component C2 at concentration z but not containing components M and C1 using the first detector 10a and the second detector 10b respectively, and obtains the detected values ​​of component M and component C1. The calculation unit 200a calculates the influence coefficient b from the concentration z and the uncorrected concentration of component M corresponding to the detected value of component M detected by the first detector 10a, according to equation (1). Similarly, the calculation unit 200a calculates the influence coefficient d from the concentration z and the uncorrected concentration of component C1 corresponding to the detected value of component C1 detected by the second detector 10b, according to equation (2).

[0047] The calculation unit 200a stores the influence coefficients a to f obtained as described above and refers to them when measuring the sample gas to determine the concentration of the target component. In addition to the influence coefficients a to f, or instead of the influence coefficients a to f, the calculation unit 200a may also calculate and store an intermediate coefficient.

[0048] As described above, since the influence coefficients a to f are calculated based on measured values, influence coefficients that take into account individual differences in each gas measuring device can be obtained. Note that the influence coefficients a to f may be determined by the manufacturer before shipping the gas measuring device 1a to the user, or they may be determined by the user after shipping the gas measuring device 1a.

[0049] §2 Specific Examples Below, an example of a specific gas measuring device for implementing the method shown in Figures 1 and 2 will be described with reference to Figures 3 and 4.

[0050] <Configuration of the gas measuring device> Figure 3 shows the configuration of the gas measuring device. Gas measuring device 1 measures exhaust gas as a sample gas and determines the concentration of nitrous oxide (N2O) as the target component. Gas measuring device 1 also detects the amount of light in the absorption wavelength ranges of sulfur dioxide (SO2), methane (CH4), and carbon dioxide (CO2) as interference components of nitrous oxide. Gas measuring device 1 determines the concentration of nitrous oxide by correcting the detected value of nitrous oxide using the detected values ​​of sulfur dioxide, methane, and carbon dioxide. Specifically, exhaust gas includes gases emitted from chemical plants and steel mills, combustion gases from boilers and furnaces, and automobile exhaust gases. Furthermore, the sample gas is not limited to exhaust gas; for example, it may be atmospheric air.

[0051] Referring to Figure 3, the gas measuring device 1 comprises a detection unit 100, a control unit 200, an input unit 300, and a display unit 400. The detection unit 100 detects the amount of light in the absorption wavelength range of each of the multiple gas components in the sample gas. More specifically, the detection unit 100 detects the amount of light in the absorption wavelength range of nitrous oxide, sulfur dioxide, methane, and carbon dioxide.

[0052] The control unit 200 controls the detection unit 100. The control unit 200 also functions as a calculation device that determines the concentration of nitrous oxide based on the detection values ​​of each of the multiple gas components detected by the detection unit 100. The control unit 200 includes a processor 220, a memory 240, and an input / output interface (not shown) for inputting and outputting various signals.

[0053] Memory 240 includes, for example, ROM (Read Only Memory) and RAM (Random Access Memory). The processor 220 loads the program stored in ROM into RAM and executes it. The program stored in ROM is a program that describes the processing procedure of the control unit 200. ROM also stores various coefficients and relational formulas used to determine the concentration of nitrous oxide. The control unit 200 performs various processes to determine the concentration of nitrous oxide according to these programs, coefficients, and relational formulas. The processing is not limited to software; it can also be performed using dedicated hardware (electronic circuits).

[0054] The input unit 300 is a device that accepts user input such as a mouse or keyboard. For example, the input unit 300 accepts input of the gas component concentration in a standard gas and sends it to the control unit 200. The display unit 400 is a display device such as a liquid crystal panel, which displays, for example, the concentration of nitrous oxide determined by the control unit 200.

[0055] <Configuration of the detection unit> Referring to Figure 3, the detection unit 100 comprises a measuring gas line SL, a reference gas line RL, two switching valves 112 and 114, a first detection unit 120, a second detection unit 140, a motor 160, and a sector 180.

[0056] The measurement gas line SL is into which the measurement gas SG is introduced. The measurement gas SG is the gas to be measured in the detection unit 100, and includes the sample gas and the standard gas used for preparation before measuring the sample gas.

[0057] A reference gas RG is introduced into the reference gas line RL. The reference gas RG is a so-called zero gas, an inert gas such as nitrogen that does not absorb infrared radiation. Note that the reference gas RG can be any gas that does not interfere with any of the gas components measured by the detection unit 100, and may be a gas that absorbs infrared radiation.

[0058] The switching valve 112 is connected to the measurement gas line SL, the first line L1, and the third line L3. The switching valve 114 is connected to the reference gas line RL, the second line L2, and the fourth line L4.

[0059] The first line L1 is connected to the first detection unit 120. The second line L2 is connected to the second detection unit 140. The third line L3 is connected to the second line L2. The fourth line L4 is connected to the first line L1.

[0060] Specifically, the switching valve 112 is connected to the measurement gas line SL, the flow path connected to the first sample cell 122, and the flow path connected to the second sample cell 142. The switching valve 114 is connected to the reference gas line RL, the flow path connected to the first sample cell 122, and the flow path connected to the second sample cell 142.

[0061] The control unit 200 controls the switching valve 112 at predetermined intervals to switch the flow path connected to the measurement gas line SL to the flow path connected to the first detection unit 120 or the flow path connected to the second detection unit 140. The control unit 200 controls the switching valves 112 and 114 so that the reference gas line RL and the second sample cell 142 are connected while the measurement gas line SL and the first detection unit 120 are connected. The control unit 200 also controls the switching valves 112 and 114 so that the reference gas line RL and the first sample cell 122 are connected while the measurement gas line SL and the second sample cell 142 are connected.

[0062] As a result, the first detection unit 120 and the second detection unit 140 are alternately filled with the reference gas and the sample gas. More specifically, while the first detection unit 120 is being filled with the reference gas, the second detection unit 140 is being filled with the sample gas, and while the first detection unit 120 is being filled with the sample gas, the second detection unit 140 is being filled with the reference gas.

[0063] The motor 160 rotates the sector 180 according to commands from the control unit 200. The sector 180 is provided between the first sample cell 122 and the first light source 124, and between the second sample cell 142 and the second light source 144, as described later. The sector 180 has a light-shielding portion and a light-transmitting portion, and controls the irradiation and blocking of light from the first light source 124 to the first sample cell 122. The sector 180 also controls the irradiation and blocking of light from the second light source 144 to the second sample cell 142.

[0064] The first detection unit 120 detects the amount of light in the absorption wavelength range of the primary target component when measuring gas components using the gas measuring device 1. The first detection unit 120 comprises a first sample cell 122, a first light source 124, a first detector 10A for detecting the amount of light in the absorption wavelength range of nitrous oxide, an optical filter 20, and a first gas filter 30. The first sample cell 122, the first gas filter 30, the optical filter 20, and the first detector 10A are arranged on the first optical path IR1 of the first light source 124 in that order.

[0065] The second detection unit 140 detects the amount of light in the absorption wavelength range of interference components with respect to the primary target component during gas component measurement using the gas measuring device 1. The second detection unit 140 comprises a second light source 144, a second sample cell 142, a second gas filter 40, a second detector 10B for detecting the amount of light in the absorption wavelength range of sulfur dioxide, a third detector 10C for detecting the amount of light in the absorption wavelength range of methane, and a fourth detector 10D for detecting the amount of light in the absorption wavelength range of carbon dioxide. The second sample cell 142, the second gas filter 40, the second detector 10B, the third detector 10C, and the fourth detector 10D are arranged on the second optical path IR2 of the second light source 144 in that order, respectively.

[0066] As described above, the first detector 10A for detecting nitrous oxide is located on the first optical path IR1, which is separate from the second optical path IR2 where the detector for detecting the interference component of nitrous oxide is located. Therefore, the attenuation of light can be suppressed, and the decrease in the detection sensitivity of nitrous oxide can be prevented. In addition, since the multiple detectors for detecting the interference component of nitrous oxide (second detector 10B, third detector 10C, and fourth detector 10D) are arranged in series on the second optical path IR2, the overall size of the gas measuring device 1 can be suppressed.

[0067] <Configuration of the first detection unit> The first detection unit 120 detects the amount of light in the absorption wavelength range of the primary target component when measuring gas components using the gas measuring device 1. In this embodiment, the first detection unit 120 detects the amount of light in the absorption wavelength range of nitrous oxide. The first detection unit 120 comprises a first sample cell 122, a first light source 124, a first detector 10A, an optical filter 20, and a first gas filter 30.

[0068] The first light source 124 irradiates with light that includes at least the absorption wavelength range of the target component. The first light source 124 is not particularly limited and is, for example, a light source using nichrome wire.

[0069] The first sample cell 122, the first gas filter 30, the optical filter 20, and the first detector 10A are arranged in that order on the first optical path IR1 of the first light source 124. Although not shown in the figure, windows are formed on the first optical path IR1 at both ends of the first sample cell 122, the first gas filter 30, and the optical filter 20, through which light from the first light source 124 is transmitted. As a result, light from the first light source 124 is transmitted in the order of the first sample cell 122, the first gas filter 30, the optical filter 20, and the first detector 10A.

[0070] The first sample cell 122 is hollow inside and includes a gas inlet 122a and a gas outlet 122b. The measurement gas SG or reference gas RG is supplied from the first line L1 through the gas inlet 122a into the first sample cell 122 and discharged from the gas outlet 122b.

[0071] The first detector 10A detects the amount of light in the absorption wavelength range of nitrous oxide. The first detector 10A comprises a first housing 12A filled with nitrous oxide as a gas component, and a first detection unit 14A that detects the pressure inside the first housing 12A. In this embodiment, the first detector 10A indirectly detects the amount of light in the absorption wavelength range specific to nitrous oxide by detecting the pressure change inside the first housing 12A. The first detector 10A detects light from the first light source 124 that has been transmitted in the order of the first sample cell 122, the first gas filter 30, and the optical filter 20.

[0072] The optical filter 20 transmits light in a specific absorption wavelength range while blocking light in a specific absorption wavelength range. Nitrous oxide has a first absorption wavelength range (around 7.8 μm) and a second absorption wavelength range (around 4.5 μm), as will be described later with reference to Figures 7 and 8. Of the two absorption wavelength ranges, at least a portion of the second absorption wavelength range overlaps with the absorption wavelength range of carbon dioxide. The optical filter 20 blocks light in the second absorption wavelength range that overlaps with the absorption wavelength range of carbon dioxide, while transmitting light in the first absorption wavelength range. For example, the optical filter 20 blocks light with wavelengths of 5.5 μm to 6.5 μm or less, while transmitting light with wavelengths longer than 5.5 μm to 6.5 μm.

[0073] The first gas filter 30 is filled with an interference component gas having an absorption wavelength range that overlaps with at least a portion of the first absorption wavelength range of nitrous oxide. In this embodiment, the first gas filter 30 is filled with methane as the gas component.

[0074] Note that the arrangement order of the optical filter 20 and the first gas filter 30 may be reversed. Specifically, the first sample cell 122, optical filter 20, first gas filter 30, and first detector 10A may be arranged on the first optical path IR1 in that order.

[0075] <Second detection unit> The second detection unit 140 detects the amount of light in the absorption wavelength range of the interference component with respect to the primary target component when measuring gas components using the gas measuring device 1. In this embodiment, the second detection unit 140 comprises a second light source 144, a second sample cell 142, a second gas filter 40, a second detector 10B, a third detector 10C, and a fourth detector 10D.

[0076] The second light source 144 and the second sample cell 142 are common to the first light source 124 and the first sample cell 122 of the first detection unit 120, respectively. Specifically, the measurement gas SG or reference gas RG is supplied from the second line L2 to the second sample cell 142 through the gas inlet 142a of the second sample cell 142 and discharged from the gas outlet 142b.

[0077] The second sample cell 142, the second gas filter 40, the second detector 10B, the third detector 10C, and the fourth detector 10D are each arranged on the second optical path IR2 of the second light source 144 in that order. Although not shown in the figure, windows are formed at both ends of the second sample cell 142, the second gas filter 40, the second detector 10B, and the third detector 10C on the second optical path IR2, allowing light from the second light source 144 to pass through. The light from the second light source 144 passes through the second sample cell 142, the second gas filter 40, the second detector 10B, the third detector 10C, and the fourth detector 10D in that order.

[0078] The second detector 10B detects the amount of light in the absorption wavelength range of sulfur dioxide. The second detector 10B comprises a second housing 12B filled with sulfur dioxide as a gas component, and a second detection unit 14B that detects the pressure inside the second housing 12B. By detecting the pressure change inside the second housing 12B, the second detector 10B indirectly detects the amount of light in the absorption wavelength range specific to sulfur dioxide. The second detector 10B also detects light from the second light source 144 that has been transmitted in the order of the second sample cell 142 and the second gas filter 40.

[0079] The third detector 10C detects the amount of light in the absorption wavelength range of methane. The third detector 10C comprises a third housing 12C filled with methane as a gas component, and a third detection unit 14C that detects the pressure inside the third housing 12C. The third detector 10C indirectly detects the amount of light in the absorption wavelength range specific to methane by detecting the pressure change inside the third housing 12C. The third detector 10C detects light from the second light source 144 that has been transmitted in the order of second sample cell 142, second gas filter 40, and second detector 10B.

[0080] The fourth detector 10D detects the amount of light in the absorption wavelength range of carbon dioxide. The fourth detector 10D comprises a fourth housing 12D filled with carbon dioxide as a gas component, and a fourth detection unit 14D that detects the pressure inside the fourth housing 12D. The fourth detector 10D indirectly detects the amount of light in the absorption wavelength range specific to carbon dioxide by detecting the pressure change inside the fourth housing 12D. The fourth detector 10D detects light from the second light source 144 that has been transmitted in the order of second sample cell 142, second gas filter 40, second detector 10B, and third detector 10C.

[0081] The second gas filter 40 is filled with carbon dioxide. The second gas filter 40 reduces the influence of carbon dioxide on the measurements of sulfur dioxide and methane by reducing the amount of light in the absorption wavelength range of carbon dioxide, among the absorption wavelength ranges of sulfur dioxide and methane.

[0082] <Control Unit Software Configuration> Figure 4 is a functional block diagram of the control unit. The control unit 200 includes a pre-correction concentration calculation unit 222, a correction value calculation unit 224, a coefficient calculation unit 226, and a storage unit 228. Each function shown in Figure 4 is realized by the processor 220 executing a program. The storage unit 228 corresponds to the memory 240.

[0083] The uncorrected concentration calculation unit 222 determines the concentration of gas components in the sample gas by applying the detection signal (reference signal) when the reference gas is sent to the detection unit 100 and the detection signal (measurement signal) when the sample gas is sent to the detection unit 100 to a predetermined calculation formula. In other words, the reference signal and the measurement signal correspond to the "detected value".

[0084] The pre-correction concentration calculation unit 222 determines the pre-correction concentration of nitrous oxide based on the reference signal and measurement signal detected by the first detector 10A. Similarly, the pre-correction concentration calculation unit 222 determines the pre-correction concentration of sulfur dioxide based on the reference signal and measurement signal detected by the second detector 10B, the pre-correction concentration of methane based on the reference signal and measurement signal detected by the third detector 10C, and the pre-correction concentration of carbon dioxide based on the reference signal and measurement signal detected by the fourth detector 10D.

[0085] In this embodiment, the pre-correction concentration calculation unit 222 uses a reference gas, but the concentration may be calculated based on the measurement signal without using a reference gas. Furthermore, the gas measuring device 1 may obtain a reference signal using a reference cell filled with a reference gas and sealed, rather than circulating a reference gas.

[0086] The correction value calculation unit 224 corrects the detected value of nitrous oxide obtained by the detection unit 100 using the detected values ​​of carbon dioxide, methane, and sulfur dioxide, which interfere with the measurement of nitrous oxide, to determine the concentration of nitrous oxide. The concentrations of each gas component are determined according to the following equations (9) to (12). For a given component A, the pre-correction concentration corresponding to the detected value is denoted as A, and the corrected concentration is denoted as [A].

[0087]

number

[0088]

number

[0089]

number

[0090]

number

[0091] In equation (9), a, b, and g are influence coefficients indicating the degree to which nitrous oxide, sulfur dioxide, and carbon dioxide influence the measurement of methane, respectively. In equation (10), c, d, and h are influence coefficients indicating the degree to which methane, sulfur dioxide, and carbon dioxide influence the measurement of nitrous oxide, respectively. In equation (11), e, f, and i are influence coefficients indicating the degree to which methane, nitrous oxide, and carbon dioxide influence the measurement of sulfur dioxide, respectively.

[0092] As shown in equations (9) to (11), the concentration of each of the multiple gas components in the sample gas is expressed as the corrected concentration obtained by subtracting the measurement error that one or more interfering components impose on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error that imposes on the measurement of the gas component is expressed as a linear sum of the corrected concentration of the interfering component and an influence coefficient that indicates the degree to which the interfering component influences the measurement of the gas component.

[0093] Furthermore, in this embodiment, the sample gas is exhaust gas. The concentration of carbon dioxide in the exhaust gas is 100 times higher than the concentrations of other components (nitrous oxide, sulfur dioxide, and methane). In this embodiment, because the concentration of carbon dioxide is extremely high compared to the other components (nitrous oxide, sulfur dioxide, and methane), it is assumed that the other components have no effect on the measurement of carbon dioxide, as shown in equation (12).

[0094] The correction value calculation unit 224 determines the concentration of nitrous oxide based on the influence coefficients and the uncorrected concentrations of the gas components corresponding to each detected value, according to the relationship between equations (9) to (12). Specifically, by solving the simultaneous equations (9) to (12), the concentration of nitrous oxide is expressed as a linear sum of the uncorrected concentrations (N2O, CH4, SO2, CO2) corresponding to the detected values ​​and an intermediate coefficient expressed using multiple influence coefficients. Therefore, the correction value calculation unit 224 can determine the concentration of nitrous oxide based on the influence coefficients or intermediate coefficients and the uncorrected concentrations of the gas components corresponding to each detected value. Note that the method of determining the concentration according to the relationship between equations (9) to (12) is not limited to this method. For example, the correction value calculation unit 224 may perform the calculation using influence coefficients without using intermediate coefficients.

[0095] The coefficient calculation unit 226 determines the influence coefficients based on the detected value obtained by detecting a standard gas with a known concentration and the concentration of the standard gas input from the input unit 300. Specifically, the influence coefficients a to i in equations (9) to (11) are determined as follows.

[0096] The detection unit 100 detects a standard gas consisting of nitrous oxide of known concentration using the second detector 10B and the third detector 10C, respectively. Based on the multiple detection values ​​obtained and the known concentrations, the influence coefficients a and f in equations (9) and (11) are determined.

[0097] Specifically, the control unit 200 calculates the influence coefficient a by dividing the uncorrected concentration of methane corresponding to the detected value of the third detector 10C by the input nitrous oxide concentration, according to the relationship in equation (9). The control unit 200 calculates the influence coefficient f by dividing the uncorrected concentration of sulfur dioxide corresponding to the detected value of the second detector 10B by the input nitrous oxide concentration, according to the relationship in equation (11).

[0098] The detection unit 100 detects a standard gas consisting of sulfur dioxide of known concentration using the first detector 10A and the third detector 10C, respectively. Based on the multiple detection values ​​obtained and the known concentrations, the influence coefficients b and d in equations (9) and (10) are determined.

[0099] Specifically, the control unit 200 calculates the influence coefficient b by dividing the uncorrected concentration of methane corresponding to the detected value of the third detector 10C by the input sulfur dioxide concentration, according to the relationship in equation (9). The control unit 200 calculates the influence coefficient d by dividing the uncorrected concentration of nitrous oxide corresponding to the detected value of the first detector 10A by the input sulfur dioxide concentration, according to the relationship in equation (10).

[0100] The detection unit 100 detects a standard gas consisting of methane of known concentration using the first detector 10A and the second detector 10B, respectively. Based on the multiple detection values ​​obtained and the known concentrations, the influence coefficients c and e in equations (10) and (11) are determined.

[0101] Specifically, the control unit 200 calculates the influence coefficient c by dividing the uncorrected concentration of nitrous oxide corresponding to the detected value of the first detector 10A by the input methane concentration, according to the relationship in equation (10). The control unit 200 calculates the influence coefficient e by dividing the uncorrected concentration of sulfur dioxide corresponding to the detected value of the second detector 10B by the input methane concentration, according to the relationship in equation (11).

[0102] The detection unit 100 detects a standard gas consisting of carbon dioxide of known concentration using the first detector 10A, the second detector 10B, and the third detector, respectively. Based on the multiple detection values ​​obtained in this way and the known concentrations, the influence coefficients g, h, and i in equations (9) to (11) are determined.

[0103] Specifically, the control unit 200 calculates the influence coefficient g by dividing the uncorrected concentration of methane corresponding to the detected value of the third detector 10C by the input carbon dioxide concentration, according to the relationship in equation (9). The control unit 200 calculates the influence coefficient h by dividing the uncorrected concentration of nitrous oxide corresponding to the detected value of the first detector 10A by the input carbon dioxide concentration, according to the relationship in equation (10). The control unit 200 calculates the influence coefficient i by dividing the uncorrected concentration of sulfur dioxide corresponding to the detected value of the second detector 10B by the input carbon dioxide concentration, according to the relationship in equation (11).

[0104] The coefficient calculation unit 226 stores the calculated influence coefficients a to i in the storage unit 228. Alternatively, the coefficient calculation unit 226 may calculate an intermediate coefficient from the calculated influence coefficients a to i and store at least one of the influence coefficients and the intermediate coefficient in the storage unit 228. Alternatively, the coefficient calculation unit 226 may calculate only the intermediate coefficient without calculating the influence coefficients and store the calculated intermediate coefficient in the storage unit 228.

[0105] <Procedure for determining the concentration of the target component> The method for determining the concentration of the target component will be explained with reference to Figure 5. Figure 5 is a flowchart showing the processing of the control unit during sample gas measurement. In the following, steps will be abbreviated as "S".

[0106] In S12, the control unit 200 detects the light passing through the sample gas, thereby detecting the amount of light in each absorption wavelength range of multiple gas components, and obtains the detected values ​​for each of these multiple gas components from the detection unit 100. Specifically, the detection unit 100 detects the amount of light in each absorption wavelength range of nitrous oxide, sulfur dioxide, methane, and carbon dioxide. The detection unit 100 sends each detected value to the control unit 200.

[0107] In S14, the control unit 200 determines the concentration of nitrous oxide based on the detected values ​​of each of the multiple gas components. More specifically, the control unit 200 determines the concentration of nitrous oxide based on multiple influence coefficients a to f and the uncorrected concentrations of the gas components corresponding to each detected value, according to the relationships in equations (9) to (12) described above.

[0108] In S16, the control unit 200 displays the calculated nitrous oxide concentration on the display unit 400.

[0109] As described above, the control unit 200 determines the concentration of nitrous oxide in the sample gas.

[0110] <Method for calculating the influence coefficient> The method for determining the influence coefficient will be explained with reference to Figure 6. Figure 6 is a flowchart showing the processing of the control unit when calculating the influence coefficient.

[0111] In S22, the control unit 200 detects a standard gas consisting of nitrous oxide of known concentration using the second detector 10B and the third detector 10C, and acquires the detected values. In S24, the control unit 200 receives input of the nitrous oxide concentration from the input unit 300.

[0112] In S26, the control unit 200 determines an influence coefficient a, which indicates the degree to which nitrous oxide in equation (9) has an effect on the measurement of methane, and an influence coefficient f, which indicates the degree to which nitrous oxide in equation (11) has an effect on the measurement of sulfur dioxide.

[0113] In S28, the control unit 200 detects a standard gas consisting of sulfur dioxide of known concentration using the first detector 10A and the third detector 10C, and acquires the detected values. In S30, the control unit 200 receives input of the sulfur dioxide concentration from the input unit 300.

[0114] In S32, the control unit 200 determines an influence coefficient b, which indicates the degree to which sulfur dioxide in equation (9) has an effect on the measurement of methane, and an influence coefficient d, which indicates the degree to which sulfur dioxide in equation (10) has an effect on the measurement of nitrous oxide.

[0115] In S34, the control unit 200 detects a standard gas consisting of methane of known concentration using the first detector 10A and the second detector 10B, and acquires the detected values. In S36, the control unit 200 receives input of the methane concentration from the input unit 300.

[0116] In S38, the control unit 200 determines an influence coefficient c, which indicates the degree to which methane in equation (10) has an effect on the measurement of nitrous oxide, and an influence coefficient e, which indicates the degree to which methane in equation (11) has an effect on the measurement of sulfur dioxide.

[0117] In S40, the control unit 200 detects a standard gas consisting of carbon dioxide of known concentration using the first detector 10A, the second detector 10B, and the third detector 10C, and acquires the detected values. In S42, the control unit 200 receives the carbon dioxide concentration input from the input unit 300.

[0118] In S44, the control unit 200 determines the influence coefficient g, which indicates the degree to which carbon dioxide in equation (9) affects the measurement of methane; the influence coefficient h, which indicates the degree to which carbon dioxide in equation (10) affects the measurement of nitrous oxide; and the influence coefficient i, which indicates the degree to which carbon dioxide in equation (11) affects the measurement of sulfur dioxide.

[0119] As described above, the gas measuring device 1 determines an influence coefficient that indicates the degree to which an interfering component has an effect on the measurement of a particular gas component.

[0120] <Examples and Comparative Examples> Table 1 shows the results of an example in which the uncorrected concentration obtained when measuring the sample gas using the gas measuring device 1 shown in Figure 3 was corrected using the method according to this embodiment, and a comparative example in which the concentration was corrected using a conventional method.

[0121] [Table 1]

[0122] In the examples, the pre-correction concentrations were corrected according to equations (9) to (12) above. In the comparative examples, the pre-correction concentrations were corrected according to equations (13) to (15) below and equation (12) above. Note that the influence coefficients a to i are common to both the examples and the comparative examples.

[0123]

number

[0124]

number

[0125]

number

[0126] As shown in equations (13) to (15), in the comparative example, the uncorrected concentration corresponding to the detected value is corrected using the uncorrected concentration of the interfering component, without considering that the measurement of the interfering component is affected by other components. As shown in Table 1, there is a difference in the corrected concentration between the comparative example and the example. This difference is due to taking into account that the measurement of the interfering component is affected by other components, and by taking into account that the measurement of the interfering component is affected by other components, the concentration of the target component can be determined more accurately.

[0127] <Infrared absorption spectra of each gas component> The infrared absorption spectra of each gas component are described with reference to Figures 7 and 8. Figure 7 shows the infrared absorption spectra of nitrous oxide and carbon dioxide. Figure 8 shows the infrared absorption spectra of nitrous oxide, methane, and sulfur dioxide. In Figures 7 and 8, the solid lines represent the infrared absorption spectra of nitrous oxide. In Figure 7, the dashed lines represent the infrared absorption spectra of carbon dioxide. In Figure 8, the dashed lines represent the infrared absorption spectra of sulfur dioxide. In Figure 8, the dashed lines represent the infrared absorption spectra of methane. In Figures 7 and 8, the horizontal axis represents wavelength and the vertical axis represents absorbance.

[0128] As shown in Figures 7 and 8, nitrous oxide has absorption wavelength ranges around 4.5 μm and around 7.8 μm. As shown in Figure 7, carbon dioxide has an absorption wavelength range around 4.25 μm, which overlaps at least partially with the absorption wavelength range of nitrous oxide around 4.5 μm.

[0129] In this embodiment, the first detection unit 120 includes an optical filter 20 that does not transmit light in the second absorption wavelength range, which overlaps with the absorption wavelength range of carbon dioxide, while transmitting light in the first absorption wavelength range. As shown in Figure 3, the first detector 10A detects the light that has passed through the optical filter 20, and therefore detects the amount of light in the absorption wavelength range around 7.8 μm, rather than around 4.5 μm, where the absorption wavelength range of carbon dioxide overlaps.

[0130] As shown in Figures 7 and 8, when comparing the absorption wavelength range of nitrous oxide around 7.8 μm with the absorption wavelength range around 4.5 μm, the absorption around 7.8 μm detected by the first detector 10A is weaker than the absorption around 4.5 μm. However, in this embodiment, exhaust gas is assumed as the sample gas, and while the concentration of carbon dioxide in the exhaust gas is on the order of percent, the concentration of nitrous oxide is on the order of ppm. Since the concentration of carbon dioxide is much higher than that of nitrous oxide, the influence of carbon dioxide on the measurement of nitrous oxide is extremely large.

[0131] Therefore, the first detection unit 120 in this embodiment detects the amount of light in the absorption wavelength range around 7.8 μm, which does not overlap with the absorption wavelength range of carbon dioxide but has weak absorption. This reduces the influence of carbon dioxide present at high concentrations in the sample gas on the measurement of nitrous oxide, and enables measurement of nitrous oxide with higher accuracy.

[0132] Exhaust gas may contain carbon monoxide (CO). Although not shown in the diagram, the absorption wavelength range of carbon monoxide is around 4.7 μm, which overlaps with the absorption wavelength range of carbon monoxide around 4.5 μm. Therefore, by providing the optical filter 20, the influence of carbon monoxide on the measurement of nitrous oxide can be reduced, and nitrous oxide can be measured with higher accuracy.

[0133] The first detector 10A detects the amount of light in the absorption wavelength range around 7.8 μm within the absorption wavelength range of nitrous oxide. As shown in Figure 8, methane has an absorption wavelength range around 7.8 μm, and sulfur dioxide has an absorption wavelength range around 7.4 μm, and each gas component overlaps at least partially with the absorption wavelength range of nitrous oxide around 7.8 μm. Therefore, the detected value of the first detector 10A reflects not only the effect of light absorption by nitrous oxide, but also the effect of light absorption by sulfur dioxide and methane, respectively.

[0134] In this embodiment, the first detection unit 120 includes a first gas filter 30 filled with a gas component having an absorption wavelength range that overlaps at least partially with a first absorption wavelength range, which is different from a second absorption wavelength range that overlaps with the absorption wavelength range of carbon dioxide, within the absorption wavelength range of nitrous oxide. This reduces the amount of light in the absorption wavelength range of the gas component that overlaps at least partially with the first absorption wavelength range. As a result, the influence of the gas component that overlaps at least partially with the first absorption wavelength range on the measurement of nitrous oxide can be reduced, and nitrous oxide can be measured with higher accuracy.

[0135] In this embodiment, the first gas filter 30 is filled with methane gas. The absorption wavelength range of methane has a greater overlap with the absorption wavelength range of nitrous oxide compared to sulfur dioxide. Therefore, the influence of methane on the measurement of nitrous oxide is greater than that of sulfur dioxide. In this embodiment, the amount of light in the absorption wavelength range of methane, which has a large influence on the measurement of nitrous oxide, can be reduced, and nitrous oxide can be measured with higher accuracy.

[0136] In addition to the first gas filter 30 filled with methane, a gas filter filled with sulfur dioxide may also be provided on the first optical path IR1 between the first sample cell 122 and the first detector 10A. Furthermore, the gas component filled in the first gas filter 30 may be sulfur dioxide instead of methane.

[0137] The effect of the first gas filter 30 can be adjusted by changing the partial pressure of the filling gas or by changing the distance over which the light from the first light source 124 passes through the first gas filter 30. For example, increasing the partial pressure of the filling gas or increasing the distance over which the light from the first light source 124 passes through the first gas filter 30 will increase the effect of the first gas filter 30. However, increasing the effect of the first gas filter 30 will also decrease the amount of light in the absorption wavelength range of nitrous oxide detected by the first detector 10A, thus reducing the detection sensitivity of nitrous oxide. Therefore, the partial pressure of the filling gas and the distance over which the light from the first light source 124 passes through the first gas filter 30 are adjusted within a range that ensures the detection sensitivity of nitrous oxide.

[0138] In this embodiment, the first detection unit 120 cuts out light in the absorption wavelength range of carbon dioxide using the optical filter 20. However, carbon dioxide also absorbs light in the absorption wavelength range around 7.8 μm, albeit to a small extent. Furthermore, as mentioned above, the concentration of carbon dioxide in the exhaust gas is higher than that of nitrous oxide. As a result, even slight light absorption by carbon dioxide affects the measurement of nitrous oxide. Therefore, in this embodiment, the control unit 200 determines the concentration of nitrous oxide by assuming that carbon dioxide affects the measurement of nitrous oxide, as shown in equation (10).

[0139] Similarly, carbon dioxide also absorbs light in the absorption wavelength ranges of sulfur dioxide and methane, albeit to a small degree. The concentration of carbon dioxide in the exhaust gas is on the order of percent, while the concentrations of sulfur dioxide and methane are on the order of ppm. Therefore, the control unit 200 determines the concentration of nitrous oxide, taking into account the influence of carbon dioxide on the measurements of sulfur dioxide and methane, as shown in equations (9) and (11).

[0140] Furthermore, the second detection unit 140 according to this embodiment includes a second gas filter 40 filled with carbon dioxide. As described above, even slight absorption by carbon dioxide affects the measurement of sulfur dioxide and methane. Therefore, by including the second gas filter 40, the second detection unit 140 reduces the amount of light in the absorption wavelength range of carbon dioxide among the absorption wavelength ranges of sulfur dioxide and methane. As a result, the influence of carbon dioxide on the measurement of sulfur dioxide and methane can be reduced, and sulfur dioxide and methane can be measured with higher accuracy. However, if the effect of the second gas filter 40 is increased, the detection sensitivity of the fourth detector 10D will decrease. Therefore, the partial pressure of the gas filling the second gas filter 40 and the distance that light from the second light source 144 passes through the second gas filter 40 are adjusted within a range in which the detection sensitivity of carbon dioxide is ensured.

[0141] As shown in Figure 8, the absorption wavelength ranges of sulfur dioxide and methane partially overlap, so sulfur dioxide affects the measurement of methane. The second detection unit 140 has a second detector 10B, which is a second housing 12B filled with sulfur dioxide, positioned between the third detector 10C, which detects the amount of light in the absorption wavelength range of methane, and the second sample cell 142. Therefore, the third detector 10C detects the light that has passed through the second sample cell 142 and the second housing 12B in that order. As a result, the second housing 12B functions as a gas filter, reducing the amount of light in the absorption wavelength range of sulfur dioxide within the methane absorption wavelength range. Consequently, the measurement error of methane caused by sulfur dioxide can be reduced, and methane can be measured with higher accuracy.

[0142] Alternatively, the third detector 10C may be placed on the second optical path IR2 between the second sample cell 142 and the second detector 10B. This arrangement allows the third housing 12C, filled with methane, of the third detector 10C to function as a gas filter, reducing the light intensity in the methane absorption wavelength range within the sulfur dioxide absorption wavelength range. As a result, measurement errors in sulfur dioxide caused by methane can be reduced, enabling more accurate measurement of sulfur dioxide. The order of the second detector 10B and the third detector 10C is determined according to the desired accuracy for measuring either methane or sulfur dioxide.

[0143] In this embodiment, the gas measuring device 1 uses infrared light, but ultraviolet light may be used depending on the absorption wavelength range of the target component.

[0144] In this embodiment, the light intensity is indirectly detected by the change in internal pressure when transmitted light passes through a cell containing the gas to be detected. Alternatively, the light intensity may be detected directly by a photoconductive element or the like. Furthermore, the multiple detectors (first detector 10A to fourth detector 10D) included in the detection unit 100 share a common method for detecting light intensity. However, the multiple detectors may have different methods for detecting light intensity. For example, the first detector 10A and the fourth detector 10D, located furthest from the light source, may be detectors equipped with pyroelectric sensors, while the other second detector 10B and third detector 10C may have the configuration of the above embodiment.

[0145] Although the gas measuring device 1 is designed to measure exhaust gas, it can also measure other gases. Furthermore, the detection targets of each detector can be changed according to the target being measured. The optical filter 20, the first gas filter 30, and the second gas filter 40 can also be adjusted according to the target being measured.

[0146] The gas measuring device 1 is equipped with detectors for three types of interfering components: sulfur dioxide, methane, and carbon dioxide, in order to measure the concentration of nitrous oxide. However, the gas measuring device 1 only needs to be equipped with a detector for at least one of the interfering components of sulfur dioxide, methane, and carbon dioxide, and may also be equipped with detectors for other interfering components in addition to the three types of interfering component detectors.

[0147] The control unit 200 determines the concentration of nitrous oxide, assuming that other components have no effect on the measurement of carbon dioxide, as shown in equation (12).

[0148] Furthermore, the control unit 200 may determine the concentration of a target component by treating the influence of one or more interfering components on the measurement of a single gas component as zero if the measurement error of the interfering component on the measurement of the single gas component is sufficiently smaller than the concentration of the single gas component. The measurement error that the interfering component has on the measurement of a single gas component is obtained by multiplying the corrected concentration of the interfering component by an influence coefficient that indicates the degree to which the interfering component influences the measurement of the single gas component.

[0149] For example, if the measurement error caused by an interfering component to the measurement of one gas component is 1 / 1000 or less of the concentration of that gas component, the influence of that interfering component on the measurement of that gas component may be considered zero. Alternatively, if the measurement error caused by an interfering component to the measurement of one gas component is 1 / 100 or less of the concentration of that gas component, the influence of that interfering component on the measurement of that gas component may be considered zero. The criteria for considering the influence to be zero should be set according to the required accuracy of the gas measuring device 1 and the assumed maximum concentration of the interfering component in the sample gas.

[0150] For example, if the measurement error (d[SO2]) that sulfur dioxide imposes on the measurement of nitrous oxide is 1 / 100 or less of the concentration of nitrous oxide ([N2O]), the control unit 200 may determine the concentration of nitrous oxide by setting the influence coefficient d in equation (10) to zero.

[0151] In the above embodiment, the gas measuring device 1 determines the concentration of nitrous oxide using exhaust gas as the sample gas and nitrous oxide as the target component. However, the sample gas and target component may be other gases and components. For example, the gas measuring device 1 may be configured to measure a sample gas that contains two or more interfering components in addition to the target component. Even in this case, by arranging the detector for the target component and the detector for the interfering components on separate optical paths, and arranging each of the detectors for multiple interfering components in series on the same optical path, it is possible to suppress a decrease in the detection sensitivity of the target component and an increase in the size of the gas measuring device.

[0152] In the above embodiment, the control unit 200 performs both the control of the detection unit 100 and the calculation of the concentration. Alternatively, the gas measuring device 1 may include a separate control unit for controlling the detection unit 100 and a calculation unit for calculating the concentration. In this case, each of the control unit and the calculation unit includes a processor, memory, and an input / output interface.

[0153] [Aspect] Those skilled in the art will understand that the embodiments described above are specific examples of the following embodiments.

[0154] (Article 1) A gas measuring device according to one embodiment measures a sample gas containing multiple gas components whose absorption wavelength ranges overlap in at least part. The gas measuring device includes a detection unit that detects the amount of light in each absorption wavelength range of the multiple gas components by detecting light that has passed through the sample gas, and a calculation unit that determines the concentration of a target component among the multiple gas components based on the detected values ​​of each of the multiple gas components detected by the detection unit. A gas component having an absorption wavelength range that overlaps in at least part with the absorption wavelength range of one of the multiple gas components is an interference component with respect to that one gas component. The concentration of each of the multiple gas components is expressed as a corrected concentration obtained by subtracting the measurement error that one or more interference components have on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error that has been applied to the measurement of the gas component is expressed as a linear sum of the corrected concentration of the interference component with respect to the gas component and an influence coefficient that indicates the degree to which the interference component has an effect on the measurement of the gas component. The calculation unit determines the corrected concentration of the target component as the concentration of the target component, based on multiple influence coefficients and the detected values ​​of each of the multiple gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the multiple gas components.

[0155] According to the gas measuring device described in paragraph 1, the corrected concentration of the target component is expressed using the corrected concentration obtained by subtracting the measurement error caused by the interfering component from the uncorrected concentration of the interfering component relative to the target component. Furthermore, the concentration of the target component is determined according to the relationship between the corrected concentration of the target component and the corrected concentration of the interfering component. Therefore, the concentration of the target component can be determined more accurately by taking into account that the measurement of the interfering component is affected by other components.

[0156] (Section 2) In the gas measuring device described in Section 1, the detection unit detects the amount of light in the absorption wavelength range of the second component of the multiple gas components by detecting light that has passed through a standard gas whose concentration is known and which consists of the first component of the multiple gas components. The calculation unit determines an influence coefficient that indicates the degree to which the first component has an influence on the measurement of the second component, based on the detected value of the second component and the known concentration of the first component, according to the relationship between the corrected concentration and the uncorrected concentration of the second component.

[0157] According to the gas measuring device described in paragraph 2, the influence coefficient can be determined based on the measured values, and an influence coefficient that takes into account individual differences in the detector can be obtained.

[0158] (Article 3) In the gas measuring device described in Article 1 or Article 2, the corrected concentration of the target component is expressed as a linear sum of an intermediate coefficient, which is expressed by a plurality of influence coefficients, and the uncorrected concentration corresponding to the detected value of each of the plurality of gas components, based on a plurality of relational expressions that show the relationship between the corrected concentration and the uncorrected concentration for each of the plurality of gas components. The calculation unit determines the corrected concentration of the target component as the concentration of the target component based on the intermediate coefficient and the detected value of each of the plurality of gas components.

[0159] According to the gas measuring device described in paragraph 3, calculations to determine the concentration of the target component can be made easier, and the load on the calculation unit can be reduced.

[0160] (Article 4) In the gas measuring device described in any one of paragraphs 1 to 3, the multiple gas components include at least one component from carbon dioxide, methane, and sulfur dioxide, and nitrous oxide.

[0161] According to the gas measuring device described in paragraph 4, nitrous oxide, a greenhouse gas, can be measured with high accuracy using exhaust gas as the sample gas.

[0162] (Article 5) In the gas measuring device described in any one of paragraphs 1 to 4, the calculation unit shall, with respect to one or more interfering components for a single gas component, set the influence of the interfering component on the measurement of the single gas component to zero for interfering components whose measurement error on the measurement of the single gas component is 1 / 100 or less of the concentration of the single gas component.

[0163] According to the gas measuring device described in paragraph 5, calculations to determine the concentration of the target component can be made easier, and the load on the calculation unit can be reduced.

[0164] (Item 6) In the gas measuring device described in any one of items 1 to 4, the gas component among the multiple gas components that is different from the target component is carbon dioxide. The calculation unit determines the concentration of the target component, assuming that the other gas components do not have any effect on the measurement of carbon dioxide.

[0165] According to the gas measuring device described in paragraph 6, when measuring a sample gas containing high concentrations of carbon dioxide, such as exhaust gas, it is possible to easily calculate the concentration of the target component and reduce the load on the calculation unit.

[0166] (Section 7) A method relating to one embodiment is a method for determining the concentration of a target component among a sample gas containing multiple gas components whose absorption wavelength ranges overlap in at least part. The method includes the steps of: detecting light that has passed through the sample gas to detect the amount of light in each absorption wavelength range of the multiple gas components and obtaining a detected value for each of the multiple gas components; and determining the concentration of a target component among the multiple gas components based on the obtained detected values ​​for each of the multiple gas components. A gas component having an absorption wavelength range that overlaps in at least part with the absorption wavelength range of one of the multiple gas components is an interference component with respect to that one gas component. The concentration of each of the multiple gas components is expressed as a corrected concentration obtained by subtracting the measurement error that one or more interference components have on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error that has been given to the measurement of the gas component is expressed as a linear sum of the corrected concentration of the interference component with respect to the gas component and an influence coefficient that indicates the degree to which the interference component has an effect on the measurement of the gas component. In the step of determining the concentration of the target component, the corrected concentration of the target component is determined as the concentration of the target component based on multiple influence coefficients and the detected values ​​of each of the multiple gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the multiple gas components.

[0167] According to the method described in paragraph 7, the corrected concentration of the target component is expressed using the corrected concentration obtained by subtracting the measurement error caused by the interference component from the uncorrected concentration of the interfering component relative to the target component. Furthermore, the concentration of the target component is determined according to the relationship between the corrected concentration of the target component and the corrected concentration of the interfering component. Therefore, the concentration of the target component can be determined more accurately by taking into account that the measurement of the interfering component is affected by other components.

[0168] (Paragraph 8) The method described in Paragraph 7 further includes the step of determining an influence coefficient that indicates the degree to which an interfering component has an effect on the measurement of a gas component. The step of determining an influence coefficient includes the steps of detecting a detected value obtained by detecting the amount of light in the absorption wavelength range of a second component of a plurality of gas components by detecting light that has passed through a standard gas of known concentration consisting of a first component of a plurality of gas components, and determining an influence coefficient that indicates the degree to which the first component has an effect on the measurement of the second component, based on the detected value of the second component and the known concentration of the first component, according to the relationship between the corrected concentration and the uncorrected concentration of the second component.

[0169] According to the method described in Section 8, the influence coefficient can be determined based on measured values, and an influence coefficient that takes into account individual differences in detectors can be obtained.

[0170] (Clause 9) A gas measuring device according to one embodiment measures a sample gas containing multiple gas components whose absorption wavelength ranges overlap by at least a portion of each other. The gas measuring device includes a first detection unit for detecting a first component in the sample gas, a second detection unit for detecting a second component and a third component, each having absorption wavelength ranges that overlap by at least a portion of the absorption wavelength range of the first component in the sample gas, and a calculation unit for determining the concentration of the first component by correcting the detected value of the first component detected by the first detection unit using a plurality of detected values ​​detected by the second detection unit. The first detection unit includes a first light source, a first sample cell filled with the sample gas, and a first detector that detects light that has passed through the first sample cell and detects the amount of light in the absorption wavelength range of the first component. The first sample cell and the first detector are arranged in series on a first optical path of light irradiated from the first light source. The second detection unit includes a second light source, a second sample cell filled with a sample gas, a second detector that detects light passing through the second sample cell to detect the amount of light in the absorption wavelength range of the second component, and a third detector that detects light passing through the second sample cell to detect the amount of light in the absorption wavelength range of the third component. The second sample cell, the second detector, and the third detector are arranged in series on the second optical path of the light irradiated from the second light source.

[0171] According to the gas measuring device described in paragraph 9, by placing the detector for detecting the first component on a first optical path separate from the second optical path where the detector for components interfering with the detection of the first component is located, the attenuation of light can be suppressed, thereby preventing a decrease in the detection sensitivity of the first component. Furthermore, since the second and third detectors are arranged in series on the second optical path, the overall size of the gas measuring device can be kept down.

[0172] (Section 10) In the gas measuring apparatus described in Section 9, the sample gas is exhaust gas. The first component is nitrous oxide.

[0173] According to the gas measuring device described in paragraph 10, nitrous oxide, a greenhouse gas, can be measured using exhaust gas as the sample gas.

[0174] (Section 11) According to the gas measuring device described in Section 10, the first detector includes a first housing filled with a first component and a first detection unit for detecting the pressure inside the first housing. The first detection unit further includes an optical filter that does not transmit light in the second absorption wavelength range of nitrous oxide, which overlaps with the absorption wavelength range of carbon dioxide, while transmitting light in the first absorption wavelength range, and a first gas filter filled with a gas component having an absorption wavelength range that overlaps with at least a portion of the first absorption wavelength range. The optical filter and the first gas filter are arranged on a first optical path between a first sample cell and a first detector.

[0175] According to the gas measuring device described in paragraph 11, the influence of carbon dioxide present in high concentrations in exhaust gas on the measurement of nitrous oxide can be reduced, and the influence of gas components having an absorption wavelength range that overlaps with at least a portion of the first absorption wavelength range on the measurement of nitrous oxide can be reduced.

[0176] (Section 12) According to the gas measuring device described in Section 11, the gas component filled in the first gas filter is methane.

[0177] According to the gas measuring device described in paragraph 12, the influence on the measurement of nitrous oxide produced by methane present in the exhaust gas can be reduced.

[0178] (Section 13) In the gas measuring apparatus described in Sections 10 to 12, the second detection unit further includes a second gas filter filled with carbon dioxide, which is located on a second optical path between a second sample cell and a second detector.

[0179] According to the gas measuring device described in paragraph 13, the influence of carbon dioxide present in high concentrations in the exhaust gas on the measurement of the second and third components can be reduced.

[0180] (Section 14) In the gas measuring apparatus described in Sections 10 to 13, the second component is sulfur dioxide. The third component is methane. The second detector includes a second housing filled with the second component and a second detection unit for detecting the pressure inside the second housing. The third detector detects light that has passed through the second sample cell and the second housing in that order.

[0181] According to the gas measuring device described in paragraph 14, the second detector functions as a gas filter, reducing the influence of sulfur dioxide on methane measurement.

[0182] (Section 15) In the gas measuring apparatus described in Sections 10 to 13, the second detection unit further includes a fourth detector that detects light passing through the second sample cell and detects the amount of light in the absorption wavelength range of a fourth component in the sample gas that overlaps at least partially with the absorption wavelength range of the first component. The second component is sulfur dioxide. The third component is methane. The fourth component is carbon dioxide. The second sample cell, the second detector, the third detector, and the fourth detector are arranged in series on the second optical path in that order.

[0183] According to the gas measuring device described in paragraph 15, it is possible to obtain detection values ​​for multiple interfering components that affect the measurement of nitrous oxide, and thus measure the concentration of nitrous oxide more accurately.

[0184] The embodiments disclosed herein are intended to be implemented in appropriate combinations, to the extent that they do not contradict the technical invention. Furthermore, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the description of the embodiments described above, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0185] 1,1a Gas measuring device, 10A,10a First detector, 10B,10b Second detector, 10C,10c Third detector, 10D Fourth detector, 12A~12D First housing~Fourth housing, 14A~14D First detection unit~Fourth detection unit, 20 Optical filter, 30 First gas filter, 40 Second gas filter, 100,100a Detection unit, 112,114 Switching valve, 120 First detection unit, 122 First sample cell, 122a,142a Gas inlet, 122b,142b Gas outlet, 124 First light source, 140 Second detection unit, 142 Second sample cell, 144 Second light source, 160 Motor, 180 Sector, 200 Control unit, 200a Calculation unit, 220 Processor, 222 Pre-correction concentration calculation unit, 224 Correction value calculation unit, 226 Coefficient calculation unit, 228 Storage unit, 240 Memory, 300 Input unit, 400 Display unit, IR1 First optical path, IR2 Second optical path, L1~L4 First line~Fourth line, RG Reference gas, RL Reference gas line, SG Measurement gas, SL Measurement gas line.

Claims

1. A gas measuring device for measuring a sample gas containing multiple gas components whose absorption wavelength ranges overlap in at least part, A detection unit that detects the amount of light in each absorption wavelength range of the plurality of gas components by detecting the light that has passed through the sample gas, The system includes a calculation unit that determines the concentration of a target component among the plurality of gas components based on the detected values ​​of each of the plurality of gas components detected by the detection unit, A gas component having an absorption wavelength range that overlaps at least partially with the absorption wavelength range of one of the aforementioned gas components is an interference component with respect to that one gas component. The concentration of each of the aforementioned plurality of gas components is expressed as a corrected concentration obtained by subtracting the measurement error that one or more interfering components impose on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error in the measurement of the aforementioned gas component is expressed as a linear sum of the corrected concentration of the interfering component with respect to the gas component and an influence coefficient indicating the degree to which the interfering component influences the measurement of the gas component. Among the aforementioned plurality of gas components, the gas component different from the target component includes carbon dioxide. The calculation unit determines the corrected concentration of the target component as the concentration of the target component, based on a plurality of influence coefficients and the detected value of each of the plurality of gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the plurality of gas components, assuming that other gas components have no influence on the measurement of carbon dioxide.

2. The detection unit detects the amount of light in the absorption wavelength range of the second component of the plurality of gas components by detecting light that has passed through a standard gas whose concentration is known and which consists of the first component of the plurality of gas components. The gas measuring device according to claim 1, wherein the calculation unit determines an influence coefficient indicating the degree to which the first component influences the measurement of the second component, based on the detected value of the second component and the known concentration of the first component, according to the relationship between the corrected concentration and the uncorrected concentration of the second component.

3. Based on multiple relational expressions showing the relationship between the corrected concentration and the uncorrected concentration for each of the aforementioned multiple gas components, the corrected concentration of the target component is expressed as a linear sum of an intermediate coefficient represented by multiple influence coefficients and the uncorrected concentration corresponding to the detected value of each of the aforementioned multiple gas components. The gas measuring device according to claim 1 or 2, wherein the calculation unit determines the corrected concentration of the target component as the concentration of the target component based on the intermediate coefficient and the detected value of each of the plurality of gas components.

4. The gas measuring device according to claim 1 or claim 2, wherein the plurality of gas components include at least one component from methane and sulfur dioxide, and nitrous oxide.

5. The gas measuring device according to claim 1 or 2, wherein the calculation unit reduces the influence of one or more interfering components on the measurement of a gas component to zero for interfering components whose measurement error on the measurement of the gas component is 1 / 100 or less of the concentration of the gas component.

6. The gas measuring device according to claim 1 or 2, wherein the calculation unit, when the concentration of carbon dioxide in the sample gas is 100 times or more higher than the concentration of other gas components, determines the corrected concentration of the target component as the concentration of the target component, based on a plurality of influence coefficients and the detected value of each of the plurality of gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the plurality of gas components, assuming that other gas components have no influence on the measurement of carbon dioxide.

7. A method for determining the concentration of a target component in a sample gas containing multiple gas components whose absorption wavelength ranges overlap in at least part, The steps include: detecting the light that has passed through the sample gas to detect the amount of light in each of the absorption wavelength ranges of the plurality of gas components and obtaining the detected value of each of the plurality of gas components; The step includes determining the concentration of a target component among the plurality of gas components based on the detection values ​​of each of the plurality of gas components obtained, A gas component having an absorption wavelength range that overlaps at least partially with the absorption wavelength range of one of the aforementioned gas components is an interference component with respect to that one gas component. The concentration of each of the aforementioned plurality of gas components is expressed as a corrected concentration obtained by subtracting the measurement error that one or more interfering components impose on the measurement of the gas component from the uncorrected concentration corresponding to the detected value of the gas component. The measurement error in the measurement of the aforementioned gas component is expressed as a linear sum of the corrected concentration of the interfering component with respect to the gas component and an influence coefficient indicating the degree to which the interfering component influences the measurement of the gas component. Among the aforementioned plurality of gas components, the gas component different from the target component includes carbon dioxide. A method for determining the concentration of the target component, wherein, in the step of determining the concentration of the target component, the corrected concentration of the target component is determined as the concentration of the target component, based on a plurality of influence coefficients and the detected value of each of the plurality of gas components, according to the relationship between the corrected concentration and the uncorrected concentration for each of the plurality of gas components, assuming that other gas components have no influence on the measurement of carbon dioxide.

8. The method further includes the step of determining an influence coefficient that indicates the degree to which an interfering component has an effect on the measurement of a particular gas component, The step of determining the aforementioned influence coefficient is: The steps include: detecting light passing through a standard gas whose concentration is known and which consists of a first component among the plurality of gas components, thereby detecting the amount of light in the absorption wavelength range of a second component among the plurality of gas components and obtaining a detected value; The method according to claim 7, comprising the step of determining an influence coefficient indicating the degree to which the first component influences the measurement of the second component, based on the detected value of the second component and the known concentration of the first component, according to the relationship between the corrected concentration and the uncorrected concentration of the second component.

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