Measuring device and measuring method

Abstract

To enable high-concentration measurement.SOLUTION: A measurement device is provided, comprising: a setting unit for setting a wavelength modulation width; a light source measurement system configured to irradiate a target object with modulated light modulated with a modulation frequency f and provided with the wavelength modulation width set by the setting unit to measure 1f and 2f components of the modulated light after transmitting through the target object; and a computation unit configured to derive the concentration of the target object based on the 1f and 2f components measured by the light source measurement system, where the setting unit sets a wavelength modulation width that suppresses dependence on concentration of the 1f component at a concentration level of a given concentration upper limit or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a measurement device and a measurement method. [Background technology]

[0002] For example, Patent Document 1 discloses a method of setting the wavelength modulation width to 2.2 times the full width at half maximum of the gas absorption spectrum (the modulation current amplitude to 2.2 times the half width at half maximum) in order to maximize the signal strength obtained in gas concentration measurement using laser light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2866230 Summary of the Invention [Problem to be solved by the invention]

[0004] When the concentration of a gas is high, it may not be possible to properly measure the concentration simply by setting the wavelength modulation width to 2.2 times the full width at half maximum. The present invention makes it possible to measure high concentrations. [Means for solving the problem]

[0005] A measurement device according to one aspect includes a setting unit that sets a wavelength modulation width, a light source measurement system that irradiates an object with modulated light having the wavelength modulation width set by the setting unit and modulated at a modulation frequency f, and measures the 1f component and 2f component of the modulated light after passing through the object, and a calculation unit that calculates the concentration of the object based on the 1f component and 2f component measured by the light source measurement system, where the setting unit sets a wavelength modulation width that suppresses the concentration dependence of the 1f component at a concentration equal to or lower than a given upper concentration limit value.

[0006] A measurement method according to one aspect includes setting a wavelength modulation width, irradiating an object with modulated light having the set wavelength modulation width and modulated at a modulation frequency f, measuring the 1f component and the 2f component of the modulated light after passing through the object, and calculating the concentration of the object based on the measured 1f component and 2f component, wherein the setting includes setting a wavelength modulation width that suppresses the concentration dependency of the 1f component at a concentration equal to or lower than a given upper concentration limit value. Effect of the Invention

[0007] According to the present invention, high concentration measurements are possible. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of a schematic configuration of a measurement device 100 according to an embodiment. [Diagram 2] FIG. 13 is a diagram showing an example of an experimental result. [Diagram 3] FIG. 13 is a diagram showing an example of an experimental result. [Figure 4] FIG. 13 is a diagram showing an example of an experimental result. [Diagram 5] FIG. 4 is a diagram showing an example of a correspondence table 41. [Figure 6] 4 is a flowchart showing an example of a method for manufacturing the measurement device 100. [Figure 7] 4 is a flowchart showing an example of a measurement method using the measurement device 100. [Figure 8] FIG. 13 is a diagram showing an example of a schematic configuration of a measurement device 100 according to a modified example. [Figure 9] FIG. 13 is a diagram showing an example of a schematic configuration of a measurement device 100 according to another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. The same elements are given the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0010] FIG. 1 is a diagram showing an example of a schematic configuration of a measuring device 100 according to an embodiment. The measuring device 100 measures the concentration of an object using wavelength modulation spectroscopy (WMS). "Measurement" may be interpreted to include "detection", "sensing", and the like. An example of the object is gas G. An example of the gas concentration is column concentration. The column concentration is a value given by the product of the optical path length transmitted through gas G and the gas concentration, and is expressed in ppm·m. Hereinafter, "concentration" may be appropriately read as "column concentration" within a range without contradiction.

[0011] The measurement device 100 includes a setting unit 1, a light source measurement system 2, a calculation unit 3, and a storage unit 4. An example of information stored in the storage unit 4 is a correspondence table 41 described below.

[0012] The setting unit 1 sets parameters including the wavelength modulation width ΔλL, as will be described in detail later.

[0013] The light source measurement system 2 is a general term for the light source system and the measurement system. The light source system generates modulated light ML characterized by parameters set by the setting unit 1, and irradiates the gas G. The measurement system measures the modulated light ML after it has passed through the gas G.

[0014] As components of the light source system, the light source measurement system 2 includes an FG 21, a laser driver 22, a laser 23, and a light projection optical system 24. Modulated light ML generated and output by the FG 21, the laser driver 22, and the laser 23 is irradiated onto the gas G via the light projection optical system 24.

[0015] The FG 21 is a function generator, and generates an input signal Sin according to parameters set by the setting unit 1. The laser driver 22 is controlled by the input signal Sin from the FG 21, and drives the laser 23. In this example, the laser driver 22 generates a drive current Id for driving the laser 23. The laser 23 operates according to the drive current Id from the laser driver 22 (i.e., according to the set parameters), and outputs modulated light ML. The light projection optical system 24 guides the modulated light ML from the laser 23 to the gas G. The light projection optical system 14 is configured to include optical elements such as lenses and mirrors.

[0016] The parameters will now be described. The parameters define the operation of the laser 23. The modulated light ML output by the laser 23 is characterized by the parameters. Examples of the parameters are the central wavelength λc, modulation frequency f, and wavelength modulation width ΔλL of the modulated light ML. Note that temperature, pressure, and the like can also be parameters, but for ease of understanding, they are assumed to be constant.

[0017] The central wavelength λc is given by the value of the direct current component (DC value) of the drive current Id of the laser 13. The central wavelength λc is set to the absorption wavelength of the gas G. If it is assumed that the absorption spectrum of the gas G is a Lorentzian type, for example, the central wavelength of the absorption spectrum is set as the central wavelength λc.

[0018] The modulation frequency f is the modulation frequency of the modulated light ML, and is given by the frequency of the AC component of the drive current Id of the laser 23. The modulated light ML is light whose wavelength is modulated by a sine wave (constant frequency and amplitude) of the modulation frequency f, and contains a component with the same frequency as the modulation frequency f. The magnitude of this component is referred to as the "1f component."

[0019] The wavelength modulation width ΔλL is the wavelength modulation width of the modulated light ML, and is given by the AC component of the drive current Id of the laser 23. Unless otherwise specified, the wavelength modulation width ΔλL is expressed as a value normalized by the full width at half maximum ΔλG (=ΔλL / ΔλG). The full width at half maximum ΔλG is the full width at half maximum (FWHM) of the absorption spectrum of the gas G.

[0020] The modulated light ML from the projection optical system 24 passes through the gas G and reaches the scattering medium S. The modulated light ML after passing through the gas G is referred to as transmitted light TL and is illustrated. The scattering medium S reflects the transmitted light TL toward the receiving optical system 25. Examples of the scattering medium S include a wall, the ground, etc. A reflecting mirror may also be used. The transmitted light TL reflected by the scattering medium S passes through the gas G again and reaches the receiving optical system 25 described below. Note that, for convenience, in FIG. 1, the incident position and reflection position of the transmitted light TL at the scattering medium S are depicted as being different, but the incident position and reflection position may be the same.

[0021] The transmitted light TL also contains a component with a frequency twice the modulation frequency f. The magnitude of this component is called the "2f component." The 2f component is proportional to the concentration of the gas G.

[0022] As components of the measurement system, the light source measurement system 2 includes a light receiving optical system 25, a conversion unit 26, and a lock-in amplifier 27. The transmitted light TL extracted via the light receiving optical system 25 is converted into an electrical signal by the conversion unit 26. The 1f component and the 2f component are detected and measured by the lock-in amplifier 27.

[0023] The light receiving optical system 25 guides the transmitted light TL to the conversion unit 26. The light receiving optical system 25 includes optical elements such as lenses and mirrors.

[0024] The conversion unit 26 converts the transmitted light TL into an electrical signal. For example, the conversion unit 26 includes a photodiode (PD), peripheral circuits, etc. The transmitted light TL is converted into a photocurrent by the photodiode, and is converted into a voltage signal by the peripheral circuits. This signal is referred to as a measurement signal Sm and is illustrated.

[0025] The lock-in amplifier 27 detects the 1f component and the 2f component. The lock-in amplifier 27 is a phase-sensitive detector, and outputs an electrical signal corresponding to the 1f component and an electrical signal corresponding to the 2f component based on the reference signal Sref from the FG 21 and the measurement signal Sm from the conversion unit 26. The reference signal Sref is a sine wave signal having the same frequency as the modulation frequency f. The operating principle of the lock-in amplifier 27 is publicly known, so a detailed description will be omitted. A single lock-in amplifier that detects both the 1f component and the 2f component may be used, or two lock-in amplifiers, one that detects the 1f component and one that detects the 2f component, may be used.

[0026] The calculation unit 3 calculates the concentration of the gas G based on the 1f component and the 2f component detected by the lock-in amplifier 27. The calculation unit 3 calculates a value 2f / 1f by dividing the 2f component by the 1f component.

[0027] The 2f component is divided by the 1f component in order to obtain a value proportional to the concentration of the gas G without depending on the intensity of the transmitted light TL. Although the 2f component is proportional to the concentration of the gas G as described above, it also varies depending on the intensity of the transmitted light TL. The intensity of the transmitted light TL varies in various ways depending on the distance from the light projecting optical system 24 or the light receiving optical system 25 to the scatterer S, the surface condition of the scatterer S, etc. Like the 2f component, the 1f component also varies depending on the intensity of the transmitted light TL. By dividing the 2f component by the 1f component, the influence of the intensity of the transmitted light TL is removed (canceled).

[0028] The calculation unit 3 calculates the concentration of the gas G based on the value 2f / 1f proportional to the concentration of the gas G. An algorithm, table data, or the like may be used to convert the value 2f / 1f into a concentration.

[0029] For example, in the manner described above, the concentration of the gas G is measured. Note that the above-described configuration of the measurement device 100 is merely an example, and any configuration capable of measuring the concentration by the WMS may be adopted.

[0030] The setting of the wavelength modulation width ΔλL will be described. It is known that the signal to noise ratio (SNR) can be maximized by setting the wavelength modulation width ΔλL to 2.2 times the full width at half maximum ΔλG. Therefore, conventionally, the wavelength modulation width ΔλL is set to 2.2ΔλG.

[0031] The above method of dividing the 2f component by the 1f component is based on the premise that the 1f component has no concentration dependency. However, in reality, as the concentration of gas G increases, the 1f component begins to depend on the concentration. As the concentration of gas G increases, the concentration dependency of the 1f component becomes apparent. This is believed to be due to the fact that the absorption spectrum of gas G is not a perfect Lorentzian type but is asymmetric. As the concentration dependency of the 1f component becomes apparent, 2f / 1f becomes no longer proportional to the concentration, and the concentration of gas G cannot be measured properly. The disclosed technology addresses this problem by setting an appropriate wavelength modulation width ΔλL.

[0032] As described above, the wavelength modulation width ΔλL is set by the setting unit 1. The setting of the wavelength modulation width ΔλL by the setting unit 1 includes setting the wavelength modulation width ΔλL to be larger than 2.2ΔλG. By increasing the wavelength modulation width ΔλL, the concentration dependency of the 1f component is suppressed, as will be described later, and high concentration measurement becomes possible. A wide concentration measurement range, that is, a wide dynamic range (DR: Dynamic Range) is obtained. This will be described with reference to Figs. 2 to 4.

[0033] 2 to 4 are diagrams showing examples of experimental results. The gas used in the experiment was methane (CH4) gas. Five types of gas cells with concentrations of 500 ppm·m, 2500 ppm·m, 5000 ppm·m, 12500 ppm·m, and 25000 ppm·m were used. The central wavelength λc was set to 1653.73 nm. The wavelength modulation width ΔλL was set to four values: 2.2ΔλG, 3.3ΔλG, 4.4ΔλG, and 6.4ΔλG.

[0034] An example of the concentration dependence of the 1f component is shown in Figure 2. The horizontal axis of the graph indicates the concentration, and the vertical axis of the graph indicates the 1f component. The plots in the graph indicate the measured values ​​of the 1f component, and the graph lines connect the plots.

[0035] At low concentrations, the graph line is almost flat at any wavelength modulation width ΔλL, and the concentration dependence of the 1f component is suppressed (there is almost no concentration dependence). At high concentrations, the graph line is no longer flat. For example, when the wavelength modulation width ΔλL=2.2ΔλG, 4 A minimum appears near ppm·p, and concentration dependence becomes evident. When the wavelength modulation width ΔλL = 3.3ΔλG, it is thought that the minimum exists at a slightly higher concentration. As the wavelength modulation width ΔλL becomes smaller (approaching 2.2ΔλG), the minimum shifts to the low concentration side, which in turn makes the concentration dependence of the 1f component more evident. Conversely, it can be seen that by increasing the wavelength modulation width ΔλL, the minimum shifts to the high concentration side, suppressing the concentration dependence of the 1f component.

[0036] Figure 3 shows an example of the concentration dependence of the 2f component. The horizontal axis of the graph indicates the concentration, and the vertical axis of the graph indicates the 2f component. The plots in the graph indicate the measured values ​​of the 2f component, and the graph lines connect the plots. As explained above, the 2f component is proportional to the concentration, and this is the same for any wavelength modulation width ΔλL.

[0037] FIG. 4 shows an example of the concentration dependence of 2f / 1f. The horizontal axis of the graph indicates the concentration, and the vertical axis of the graph indicates 2f / 1f. The plots in the graph indicate the calculated values ​​of 2f / 1f, and the graph lines connect the plots. Where the concentration dependence of the 1f component is suppressed, 2f / 1f is proportional to the concentration, just like the 2f component. Where the concentration dependence of the 1f component is evident, the proportional relationship is lost. As can be seen, as the wavelength modulation width ΔλL approaches 2.2ΔλG, the proportional relationship is easily lost. Conversely, by increasing the wavelength modulation width ΔλL, it becomes easier to maintain the proportional relationship.

[0038] Based on the above findings, by setting the wavelength modulation width ΔλL to a value greater than 2.2ΔλG, the concentration dependence of the 1f component at high concentrations can be suppressed more than when the wavelength modulation width ΔλL = 2.2ΔλG. By selecting a wavelength modulation width ΔλL that suppresses the concentration dependence of the 1f component, high concentration measurement becomes possible.

[0039] On the other hand, if the wavelength modulation width ΔλL is set to a value greater than 2.2ΔλG, the SNR deviates from the optimum value. As the wavelength modulation width ΔλL deviates from 2.2ΔλG, the SNR decreases. From the viewpoint of SNR, it is desirable to set the wavelength modulation width ΔλL to as small a value as possible.

[0040] In this embodiment, the setting unit 1 determines whether the given upper concentration limit value C UL The wavelength modulation width ΔλL is set based on the concentration upper limit C UL is the upper limit value of the concentration of the gas G to be measured, and is a known value input to the setting unit 1 by, for example, a user operation. The setting unit 1 receives the given upper limit value C UL The wavelength modulation width ΔλL is set to suppress the concentration dependence of the 1f component at the following concentrations.

[0041] In one embodiment, the setting unit 1 sets the wavelength modulation width ΔλL by referring to a correspondence table 41 stored in the storage unit 4. This will be described with reference to FIG.

[0042] FIG. 5 is a diagram showing an example of the correspondence table 41. The correspondence table 41 shows the concentration upper limit CUL The wavelength modulation width ΔλL in the correspondence table 41 is described in correspondence with its upper concentration limit C UL The wavelength modulation width ΔλL suppresses the concentration dependence of the 1f component at the following concentrations. The wavelength modulation width ΔλL described in the correspondence table 41 may be the minimum wavelength modulation width ΔλL capable of suppressing the concentration dependence of the 1f component. The "minimum wavelength modulation width ΔλL" may be the minimum wavelength modulation width ΔλL among a finite number of wavelength modulation widths ΔλL (i.e., discrete values) that can be set in a preliminary experiment or an actual measurement.

[0043] In the example shown in FIG. 5, the upper concentration limit C UL A wavelength modulation width ΔλL of 2.2ΔλG corresponds to the upper concentration limit C of 5001 to 9000. UL A wavelength modulation width ΔλL of 3.3ΔλG corresponds to the upper concentration limit C of 9001 to 12000. UL A wavelength modulation width ΔλL of 4.4ΔλG corresponds to the upper concentration limit C of 12001 to 20000 or less. UL is associated with a wavelength modulation width ΔλL of 6.4ΔλG.

[0044] The correspondence table 41 may be a plurality of correspondence tables 41 prepared for each measurement target. For example, a correspondence table 41 may be prepared for each absorption spectrum of various gases G that may be the measurement target, and stored in the storage unit 4.

[0045] The setting unit 1 sets the wavelength modulation width ΔλL by referring to the correspondence table 41 stored in the storage unit 4. For example, given the upper concentration limit value C UL If the concentration upper limit C is less than 5000, the setting unit 1 sets the wavelength modulation width ΔλL to 2.2ΔλG. UL is 5001 or more and 9000 or less, the setting unit 1 sets the wavelength modulation width ΔλL to 3.3ΔλG. UL is 9001 or more and 12000 or less, the setting unit 1 sets the wavelength modulation width ΔλL to 4.4ΔλG. ULis equal to or greater than 12001 and equal to or less than 20000, the setting unit 1 sets the wavelength modulation width ΔλL to 6.4ΔλG. Naturally, the more precisely the correspondence table 41 specifies the wavelength modulation width ΔλL, the more precisely the wavelength modulation width ΔλL can be set.

[0046] An input signal Sin according to parameters including the wavelength modulation width ΔλL set by the setting unit 1 is generated by the FG 21. As described above, the modulated light ML characterized by the parameters is irradiated onto the gas G, and the concentration of the gas G is measured based on the 1f component and the 2f component in the transmitted light TL. Since the wavelength modulation width ΔλL is set to suppress the concentration dependency of the 1f component, the concentration can be appropriately measured even at high concentrations.

[0047] When the minimum wavelength modulation width ΔλL is set, the degradation of the SNR is minimized. Considering that the 2f component also becomes large in high concentration gas measurement, the impact of the degradation of the SNR is limited. As shown in Figure 3 described above, the amount of reduction in the 2f component when the wavelength modulation width ΔλL is increased is also limited.

[0048] 6 is a flowchart showing an example of preparation (manufacturing method) of measuring device 100. In the following, an example will be described in which each step is performed by a user of measuring device 100.

[0049] In step S1, the absorption spectrum of the gas G to be measured is investigated. For example, in the case of methane gas, the absorption spectrum of the methane gas is investigated.

[0050] In step S2, an appropriate absorption peak is selected and the central wavelength λc is determined. For example, in the case of methane gas, the central wavelength λc is determined to be 1653.73 nm.

[0051] In step S3, the correspondence table 41 is prepared and stored in the memory unit 4. As described above, the correspondence table 41 is ULand the wavelength modulation width ΔλL are described in correspondence with each other. For example, in the case of methane gas, a correspondence table 41 as shown in FIG. 5 described above is prepared based on the experimental results as shown in FIG. 2 and FIG. 4 described above, and is stored in the storage unit 4.

[0052] For example, in the manner described above, the measuring device 100 including the storage unit 4 in which the correspondence table 41 is stored is prepared (manufactured).

[0053] 7 is a flow chart showing an example of a measurement method using a measurement device. Descriptions of contents that overlap with those described above will be omitted as appropriate.

[0054] In step S11, the concentration upper limit C UL For example, the user of the measurement device 100 determines the upper concentration limit C UL Determine the upper concentration limit C UL Enter the upper concentration limit C UL is provided to the setting unit 1 of the measurement apparatus 100. Other parameters such as the central wavelength λc and the modulation frequency f may also be provided.

[0055] In step S12, the wavelength modulation width ΔλL is set. The setting unit 1 of the measurement device 100 sets the wavelength modulation width ΔλL based on the given upper concentration limit C UL and the wavelength modulation width ΔλL is set based on the correspondence table 41 stored in the storage unit 4. Other parameters such as the central wavelength λc and the modulation frequency f may also be set.

[0056] In step S13, modulated light ML is irradiated and the 1f component and the 2f component are measured. The light source measurement system 2 of the measurement device 100 generates modulated light ML characterized by set parameters and irradiates the gas G. The light source measurement system 2 also measures the 1f component and the 2f component of the modulated light ML that has transmitted through the gas G (i.e., the transmitted light TL).

[0057] In step S14, the concentration is calculated. The calculation unit 3 of the measurement device 100 calculates the concentration of the gas G based on the measured 1f component and 2f component.

[0058] For example, the concentration of the gas G is measured in the above manner.

[0059] The disclosed technology is not limited to the above-described embodiment, and some modified examples will be described.

[0060] 8 is a diagram showing an example of a schematic configuration of a measurement device 100 according to a modified example. In this example, the light source measurement system 2 of the measurement device 100 includes a laser driver 28 with a modulation function instead of the FG 21 and the laser driver 22 (FIG. 1). The laser driver 28 with a modulation function has both the functions of the FG 21 and the laser driver 22.

[0061] 9 is a diagram showing an example of a schematic configuration of a measurement device 100 according to another modified example. In this example, the measurement device 100 is an open-path type measurement device. The light projecting optical system 24 and the light receiving optical system 25 are disposed on opposite sides of the gas G. The other components are appropriately disposed according to the arrangement of the light projecting optical system 24 and the light receiving optical system 25. The concentration of the gas G can be measured even without the scatterer S (FIG. 1).

[0062] In the above embodiment, methane gas has been taken as an example of the gas G. However, the gas G may be a gas other than methane gas.

[0063] The techniques described above can be specified, for example, as follows. One of the techniques disclosed is a measurement device 100. As described with reference to FIG. 1 and the like, the measurement device 100 includes a setting unit 1, a light source measurement system 2, and a calculation unit 3. The setting unit 1 sets a wavelength modulation width ΔλL. The light source measurement system 2 irradiates an object (e.g., gas G) with modulated light ML having the wavelength modulation width ΔλL set by the setting unit 1 and modulated at a modulation frequency f, and measures the 1f component and 2f component of the modulated light ML (transmitted light TL) after passing through the object. The calculation unit 3 calculates the concentration of the object (e.g., column concentration) based on the 1f component and 2f component measured by the light source measurement system 2. The setting unit 1 calculates a concentration of the object (e.g., column concentration) based on a given concentration upper limit value C UL The wavelength modulation width ΔλL is set to suppress the concentration dependence of the 1f component at the following concentrations.

[0064] According to the above-mentioned measuring device 100, a given upper concentration limit C UL The wavelength modulation width ΔλL that suppresses the concentration dependence of the 1f component is set at the following concentrations: By using the wavelength modulation width ΔλL that suppresses the concentration dependence of the 1f component, the concentration of the target substance can be measured appropriately even if the concentration is high.

[0065] As described with reference to Fig. 1 and Fig. 5, the setting by the setting unit 1 may include setting a wavelength modulation width ΔλL larger than 2.2 times the full width at half maximum ΔλG of the absorption spectrum of the object. This makes it possible to suppress the concentration dependence of the 1f component more than when the wavelength modulation width ΔλL is set to 2.2ΔλG. This makes it possible to measure high concentrations accordingly.

[0066] As described with reference to FIG. 1 and FIG. 5, the measurement device 100 detects the upper concentration limit C UL and its upper concentration limit C UL The setting unit 1 may set the wavelength modulation width ΔλL by referring to the correspondence table 41 stored in the storage unit 4. For example, in this manner, a given concentration upper limit value C UL It is possible to set a wavelength modulation width ΔλL that suppresses the concentration dependence of the 1f component at the following concentrations.

[0067] As described with reference to FIG. 5 and the like, the correspondence table 41 is UL and its upper concentration limit C UL It may be described in correspondence with the minimum wavelength modulation width ΔλL that suppresses the concentration dependence of the 1f component at the following concentrations. This makes it possible to minimize the degradation of the SNR.

[0068] The measurement method described with reference to Fig. 7 etc. is also one of the techniques disclosed. The measurement method includes setting a wavelength modulation width ΔλL (step S12), irradiating a target (e.g., gas G) with modulated light ML having the set wavelength modulation width ΔλL and modulated at a modulation frequency f, measuring the 1f component and the 2f component of the modulated light ML (transmitted light TL) after passing through the target (step S13), and calculating the concentration of the target based on the measured 1f component and 2f component (step S14). UL A wavelength modulation width ΔλL is set to suppress the concentration dependency of the 1f component at the following concentrations (step S12). As explained above, high concentration measurement is also possible with this measurement method. [Explanation of symbols]

[0069] 1 Setting section 2 Light source measurement system 21 FG 22 Laser driver 23 Laser 24 Projection optical system 25 Light receiving optical system 26 Conversion unit 27 Lock-in amplifier 28 Laser driver with modulation function 3. Calculation section 4 Storage section 41 Correspondence table 100 Measuring Equipment G Gas (target object) S scatterer

Claims

1. A setting unit for setting a wavelength modulation width; a light source measurement system that irradiates an object with modulated light having a wavelength modulation width set by the setting unit and modulated at a modulation frequency f, and measures the 1f component and the 2f component of the modulated light after passing through the object; a calculation unit that calculates a concentration of the object based on the 1f component and the 2f component measured by the light source measurement system; Equipped with the setting unit sets a wavelength modulation width that suppresses the concentration dependency of the 1f component at a concentration equal to or lower than a given concentration upper limit value. Measuring equipment.

2. The setting by the setting unit includes setting a wavelength modulation width greater than 2.2 times the full width at half maximum of the absorption spectrum of the object.

2. The measuring device of claim 1.

3. A storage unit is further provided for storing a correspondence table that describes a correspondence between a concentration upper limit value and a wavelength modulation width that suppresses the concentration dependency of the 1f component at a concentration equal to or lower than the concentration upper limit value, The setting unit sets the wavelength modulation width by referring to the correspondence table stored in the storage unit.

3. The measuring device according to claim 1 or 2.

4. The correspondence table describes the upper concentration limit value and the minimum wavelength modulation width that suppresses the concentration dependency of the 1f component at a concentration equal to or lower than the upper concentration limit value.

4. The measuring device according to claim 3.

5. Setting a wavelength modulation width; Irradiating an object with modulated light having a set wavelength modulation width and modulated at a modulation frequency f, and measuring the 1f component and the 2f component of the modulated light after passing through the object; Calculating the concentration of the object based on the measured 1f component and 2f component; Including, By setting the wavelength modulation width, a wavelength modulation width that suppresses the concentration dependency of the 1f component at a concentration equal to or lower than a given upper concentration limit value is set. Measurement method.

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