Laser gas analyzer and laser gas analysis method

Abstract

To provide a laser gas analyzer that prevents the influence of the to-be-measured gas.SOLUTION: A laser gas analyzer for measuring a gas concentration of a to-be-measured gas present in a space to be measured by wavelength variable laser spectroscopy, comprises: a light-emitting unit having: a laser element configured to emit a laser beam; and a modulated light generation unit configured to sweep a wavelength in a wavelength band including a light absorption wavelength of an absorption line spectrum of the to-be-measured gas and supply a drive current to the laser element; and a light-receiving unit having a light-receiving element that receives the laser beam having passed through the space to be measured; and a received-light signal processing unit; wherein the received-light signal processing unit detects a temperature of a first to-be-measured gas from an absorption coefficient of the first to-be-measured gas at two wavelengths, measures a concentration of a second to-be-measured gas from an absorption coefficient of the second to-be-measured gas at one wavelength, and performs a temperature correction on the concentration of the second to-be-measured gas, based on the temperature.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to laser-based gas analyzers and methods. [Background technology]

[0002] Patent Document 1 discloses a laser gas analyzer that measures the gas concentration of a measurement target gas present in a measurement target space by wavelength tunable laser spectroscopy and wavelength-modulated optical spectroscopy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-106742 A Summary of the Invention [Problem to be solved by the invention]

[0004] When measuring the gas concentration of a target gas on-site, the gas temperature may change. It is required to measure the gas concentration of the target gas with high accuracy even when the gas temperature changes.

[0005] The present disclosure provides a laser gas analyzer that suppresses the influence of the temperature of the gas to be measured. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, there is provided a laser gas analyzer that measures a gas concentration of a target gas present in a target space by tunable laser spectroscopy, the laser gas analyzer comprising: a light emitting unit having a laser element that emits laser light in a wavelength band that includes an optical absorption wavelength of the absorption line spectrum of the target gas; and a modulated light generating unit whose wavelength is swept over a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the target gas and that supplies a drive current to the laser element; a light receiving unit that receives the laser light that has passed through the target space; and a light receiving signal processing unit that analyzes the target gas based on the amplitude of a detection waveform for a detection signal output from the light receiving element, wherein the light receiving signal processing unit detects the temperature of the first target gas from an absorption coefficient at two wavelengths of the first target gas, measures the concentration of the second target gas from an absorption coefficient at one wavelength of the second target gas, and performs temperature compensation for the concentration of the second target gas based on the temperature. Effect of the Invention

[0007] According to the laser gas analyzer of the present disclosure, the influence of the temperature of the measurement target gas can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the configuration of a laser gas analyzer according to the first embodiment. [Diagram 2] FIG. 2 is a graph showing the temperature dependence of the absorption spectrum of hydrogen gas. [Diagram 3] FIG. 3 is a diagram showing the temperature dependence of the absorption spectrum of hydrogen gas. [Figure 4] FIG. 4 is a diagram showing the temperature dependence of the absorption spectrum of oxygen gas. [Diagram 5] FIG. 5 is a diagram showing the temperature dependence of the absorption spectrum of oxygen gas. [Figure 6] FIG. 6 is a diagram for explaining temperature measurement using the absorption spectrum of oxygen gas. [Figure 7] FIG. 7 is a diagram for explaining correction of the gas concentration of hydrogen gas. [Figure 8] FIG. 8 is a diagram for explaining the process of the laser gas analyzer according to the first embodiment. [Figure 9] FIG. 9 is a diagram showing the configuration of a laser gas analyzer according to the second embodiment. [Figure 10] FIG. 10 is a diagram for explaining the process of the laser gas analyzer according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0010] In addition, in the description of the specification and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be denoted by the same reference numerals to avoid redundant explanation. In addition, in order to facilitate understanding, the scale of each part in the drawings may differ from the actual scale.

[0011] In the directions of parallel, right-angle, orthogonal, horizontal, vertical, up-down, left-right, front-back, etc., deviations are permitted to the extent that they do not impair the effects of the embodiment. The shape of the corners is not limited to right angles and may be rounded. Parallel, right-angle, orthogonal, horizontal, and vertical may include approximately parallel, approximately right-angle, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0012] For example, "approximately parallel" means that even if two lines or two surfaces are not completely parallel to each other, they can be treated as parallel to each other as long as it is within the range of manufacturing tolerance. As with "approximately parallel," "approximately right angle," "approximately perpendicular," "approximately horizontal," and "approximately vertical" are also intended to correspond to the respective terms as long as the relative positional relationship between the two lines or two surfaces is within the range of manufacturing tolerance.

[0013] <Laser gas analyzer according to the first embodiment> The laser gas analyzer according to the first embodiment is a laser gas analyzer that measures the gas concentration of a measurement target gas present in a measurement target space by tunable laser spectroscopy. The laser gas analyzer according to the first embodiment includes a light emitting unit and a light receiving unit.

[0014] The light emitting unit in the laser gas analyzer according to the first embodiment has a laser element that emits laser light in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the gas to be measured. The light emitting unit in the laser gas analyzer according to the first embodiment also has a modulated light generating unit that sweeps the wavelength in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the gas to be measured and supplies a drive current to the laser element.

[0015] The light receiving section in the laser gas analyzer according to the first embodiment has a light receiving element that receives the laser light that has passed through the measurement target space, and a light receiving signal processing section that performs analysis of the measurement target gas based on the amplitude of the detection waveform of the detection signal output from the light receiving element. The light receiving signal processing section in the laser gas analyzer according to the first embodiment detects the temperature from the absorption coefficients at two wavelengths of the first measurement target gas. The light receiving signal processing section in the laser gas analyzer according to the first embodiment measures the measurement target gas concentration from the absorption coefficient at one wavelength of the second measurement target gas, and performs temperature correction for the second measurement target gas based on the temperature detection result based on the first measurement target gas.

[0016] 1 is a diagram showing the configuration of a laser gas analyzer 1 which is an example of a laser gas analyzer according to the first embodiment. The laser gas analyzer according to the first embodiment will be described using the laser gas analyzer 1.

[0017] Each gas molecule has a unique light absorption wavelength and an absorption line spectrum that indicates the absorption intensity. Laser light is light with a narrow spectral line width at a specific wavelength. In a laser gas analyzer, a laser element emits laser light at a light absorption wavelength that is absorbed by a gaseous gas molecule, which is a measurement target gas, and the measurement target gas absorbs the laser light. The laser gas analyzer detects the presence or absence of a measurement target gas based on the amount of absorption of the laser light at the light absorption wavelength. In addition, the laser gas analyzer can detect the concentration of the measurement target gas because the amount of absorption of the laser light at the light absorption wavelength is proportional to the concentration of the measurement target gas.

[0018] The laser gas analyzer 1 measures the concentration of a specific gas contained in the gas flowing between the walls 50a and 50b. Furthermore, the laser gas analyzer 1 can detect the absence of gas if the gas concentration is 0 or a predetermined value or less. In other words, the laser gas analyzer 1 can detect the presence or absence of gas.

[0019] The laser gas analyzer 1 includes a light emitting unit 10, a light receiving unit 20, and a communication line 30. The communication line 30 communicates between the light emitting unit 10 and the light receiving unit 20 by electrical signals. Note that a communication unit such as a wireless or optical communication unit may be used instead of the communication line 30. The laser gas analyzer 1 can use the communication unit using the communication line, wireless, or optical communication.

[0020] The laser gas analyzer 1 emits detection light 40 from the light emitting unit 10. The detection light 40 is projected into a measurement target space between the walls 50a and 50b.

[0021] When detection light 40 is projected into the space to be measured, a portion of the amount of detection light 40 is absorbed by the specific gas. The remaining part of detection light 40 projected from light emitter 10 that is not absorbed, i.e., transmitted light, is incident on light receiver 20. Light receiver 20 detects the amount of the incident transmitted light. Light receiver 20 determines the concentration of the specific gas from the detected amount of transmitted light.

[0022] Next, each part will be described in detail.

[0023] [Light emitting part 10] The optical function of the light-emitting unit 10 will be described. The central wavelength of a specific absorption line spectrum absorbed by the gas to be measured is defined as λ. The light-emitting unit 10 emits detection light 40 toward the light-receiving unit 20 while modulating the wavelength at the central wavelength λ and its surrounding wavelengths. The detection light 40, which is a substantially parallel light, passes through the light-emitting unit window plate 14 and propagates inside the walls 50a, 50b, i.e., into the space through which gas including the gas to be measured flows.

[0024] The light-emitting section 10 includes at least a modulated light generating section 11 , a laser element 12 , a collimating lens 13 , a light-emitting section window plate 14 , and a light-emitting section container 15 .

[0025] (Modulated light generating unit 11) The modulated light generating unit 11 is a signal processing and current driving circuit. The light emitting unit 10 needs to irradiate laser light according to the light absorption characteristics of the gas to be measured. In addition, the light emitting unit 10 needs to convert the laser light into frequency-modulated modulated light. Therefore, the modulated light generating unit 11 supplies a driving current signal to the laser element 12 for emitting laser light according to the light absorption characteristics of the gas to be measured as frequency-modulated modulated light.

[0026] (laser element 12) The laser element 12 emits light at a central wavelength λ and wavelengths around it. The laser element 12 is, for example, a distributed feedback (DFB (Distributed Feedback)) laser. The laser element 12 may also be, for example, a VCSEL (Vertical Cavity Surface Emitting Laser Diode). Furthermore, the laser element 12 may also be, for example, a distributed Bragg Reflector (DBR) laser.

[0027] The emission wavelength of the laser element 12 can be variably controlled by the driving current and temperature. Therefore, the temperature is controlled so that the central wavelength of the laser light emitted by the laser element 12 becomes the central wavelength of the absorption line spectrum of the gas to be measured. In addition, the driving current is controlled so that the wavelengths around the central wavelength of the laser light are swept over time. Furthermore, a sine wave having an appropriate wavelength modulation amplitude and frequency is superimposed on the driving current so that the measurement can be performed with high sensitivity by wavelength modulation spectroscopy.

[0028] The light emitting point of the laser element 12 is disposed near the focal point of the collimator lens 13. The light emitted from the laser element 12 is incident on the collimator lens 13 while diffusing, and is converted into detection light 40 which is a substantially parallel light.

[0029] (Collimating lens 13) The collimating lens 13 is made of a material having high transmittance at the central wavelength λ and its surrounding wavelengths. The collimating lens 13 converts the detection light 40 emitted from the laser element 12 into a substantially parallel light. By converting the detection light 40 into a parallel light by the collimating lens 13, the light emitter 10 can transmit the detection light 40 to the light receiver 20 while suppressing loss due to diffusion.

[0030] In this embodiment, the collimator lens 13 is used, but the present invention is not limited to the collimator lens. For example, a parabolic mirror may be used instead of the collimator lens.

[0031] (Light emitting window panel 14) The light-emitting section window plate 14 is provided so as to close a hole made in a part of the light-emitting section container 15. The light-emitting section window plate 14 is located in the optical path of the detection light 40, and while transmitting the detection light 40, it prevents gas in the measurement target space from entering the inside of the light-emitting section 10. The light-emitting section window plate 14 prevents the optical elements, optical components, and electric / electronic circuits, etc., stored inside from directly coming into contact with the gas. The light-emitting section window plate 14 protects the optical elements, optical components, and electric / electronic circuits, etc., stored inside from directly coming into contact with the gas.

[0032] (Light emitting container 15) The light-emitting part container 15 contains optical elements, optical components, electric and electronic circuits, etc. The light-emitting part container 15 isolates the optical elements, optical components, electric and electronic circuits, etc. contained therein from the outside air. The light-emitting part container 15 protects the optical elements, optical components, electric and electronic circuits, etc. contained therein from wind, rain, dust, dirt, etc.

[0033] 1, holes are provided in walls 50a and 50b of a pipe or the like through which a gas containing a gas to be measured flows, and flanges 51a and 51b are fixed to the holes by welding or the like.

[0034] The light-emitting unit 10 includes an optical axis adjustment flange 52a on the light-emitting unit container 15. The optical axis adjustment flange 52a is attached to the flange 51a so as to be mechanically movable. The position of the light-emitting unit 10 can be adjusted by attaching it to the flange 51a via the optical axis adjustment flange 52a. The optical axis adjustment flange 52a adjusts the emission angle of the detection light 40. The optical axis adjustment flange 52a, together with the optical axis adjustment flange 52b, adjusts the detection light 40 emitted from the light-emitting unit 10 so that it is received by the light-receiving unit 20 with the maximum amount of light.

[0035] [Light receiving section 20] Next, the light receiving unit 20 will be described. The light receiving unit 20 receives the detection light 40 transmitted through the light receiving unit window plate 24, and analyzes the amount of light absorbed by the measurement target gas. The light receiving unit 20 at least includes a received light signal processing unit 21, a light receiving element 22, a condenser lens 23, the light receiving unit window plate 24, and a light receiving unit container 25.

[0036] (Light receiving signal processing unit 21) The received light signal processing unit 21 is a signal processing and light receiving circuit that calculates the gas concentration of the measurement target gas based on the received detection light 40. The received light signal processing unit 21 processes the signal obtained by converting the detection light 40 into an electrical signal by the light receiving element 22 to calculate the gas concentration of the measurement target gas. More specifically, the received light signal processing unit 21 extracts a frequency component that is twice the modulation frequency of the detection light 40 by a lock-in amplifier from the signal obtained by converting the detection light 40 into an electrical signal by the light receiving element 22. The received light signal processing unit 21 then calculates the gas concentration of the measurement target gas from the extracted component.

[0037] (Photodetector 22) The light receiving element 22 can be selected to be sensitive to the central wavelength λ and wavelengths around it.

[0038] (Condenser lens 23) The condenser lens 23 is made of a material with high transmittance at the central wavelength λ and its surrounding wavelengths. The condenser lens 23 condenses the detection light 40 onto the light receiving element 22, making it possible to obtain a high signal intensity. The detection light 40 is incident on the light receiving element 22, whose light receiving surface is disposed near the focal point of the condenser lens 23. Although the condenser lens 23 is used in this embodiment, a parabolic mirror, a doublet lens, a diffractive lens, or the like may also be used instead of the condenser lens 23.

[0039] The light receiving signal from the light receiving element 22 is sent as a detection signal to the light receiving signal processing unit 21. The light receiving signal processing unit 21 processes the detection signal to calculate the gas concentration.

[0040] (Light receiving window plate 24) The light-receiving unit window plate 24 is provided so as to close a hole made in a part of the light-receiving unit container 25. The light-receiving unit window plate 24 is located in the optical path of the detection light 40, and while transmitting the detection light 40, it prevents gas in the measurement target space from entering the inside of the light-receiving unit 20. The light-receiving unit window plate 24 prevents the optical elements, optical components, electric and electronic circuits, etc. stored inside from directly contacting the gas. The light-receiving unit window plate 24 protects the optical elements, optical components, electric and electronic circuits, etc. stored inside from directly contacting the gas.

[0041] (Light receiving container 25) The light-receiving unit container 25 contains optical elements, optical components, electric and electronic circuits, etc. The light-receiving unit container 25 isolates the optical elements, optical components, electric and electronic circuits, etc. contained therein from the outside air. The light-receiving unit container 25 protects the optical elements, optical components, electric and electronic circuits, etc. contained therein from wind, rain, dust, dirt, etc.

[0042] The light receiving unit 20 includes an optical axis adjustment flange 52b on the light receiving unit container 25. The optical axis adjustment flange 52b is attached to the flange 51b so as to be mechanically movable. The position of the light receiving unit 20 can be adjusted by attaching it to the flange 51b via the optical axis adjustment flange 52b. The optical axis adjustment flange 52b adjusts the incident angle of the detection light 40. The optical axis adjustment flange 52b, together with the optical axis adjustment flange 52a, adjusts the detection light 40 emitted from the light emitting unit 10 so that the maximum amount of light is received by the light receiving unit 20.

[0043] <Processing in the received light signal processing unit 21> The processing in the received light signal processing unit 21 will now be described.

[0044] In laser gas analyzers, the absorption strength of the gas to be measured may change due to changes in the environmental temperature. If the absorption strength of the gas to be measured changes, it may not be possible to obtain an accurate concentration.

[0045] When calibrating a laser gas analyzer, the environmental conditions are constant because corrections are made in a uniform temperature environment. However, the temperature in the actual installation environment, such as a flue, is not necessarily kept constant, and the temperature may fluctuate over time. Changes in temperature cause changes in the absorption strength of the gas being measured. If the absorption strength of the gas being measured changes due to changes in temperature, the measured concentration value of the gas being measured also changes.

[0046] For example, Figures 2 and 3 are diagrams showing the temperature dependence of the absorption spectrum of hydrogen gas. Figure 2 shows the absorption spectrum of hydrogen gas when the temperature is changed. Figure 3 shows the peak intensity in the absorption spectrum of hydrogen gas when the temperature is changed.

[0047] FIG. 2 is a diagram showing the absorption cross section of hydrogen gas in the wavelength range from wavelength λmin to wavelength λmax at a wavelength of around 2 nanometers. In the example shown in FIG. 2, the wavelength λmax is 0.0012 nanometers longer than the wavelength λmin. The horizontal axis of FIG. 2 is wavelength (unit: nanometers (nm)), and the vertical axis of FIG. 2 is absorption cross section (unit: molecules per square centimeter (cm 2 / molecule). Lines L11, L12, L13, L14, and L15 show the absorption cross sections at temperatures of 25°C, 200°C, 500°C, 600°C, and 1200°C, respectively. The horizontal axis of Fig. 3 shows temperature (unit: degree Celsius (°C)), and the vertical axis shows the absorption cross section at the peak in Fig. 2 (near wavelength λpeak).

[0048] As shown by line L2 in Figure 3, the absorption spectrum changes nonlinearly from room temperature (25°C) to 600°C. Therefore, in an environment where the temperature of the gas to be measured changes drastically, it is necessary to reduce measurement errors by performing temperature correction.

[0049] Laser gas analyzers can be calibrated under the same environmental conditions as when they were calibrated. However, if the temperature changes, the gas concentration measurement is performed with the absorption waveform dependent on the temperature, so the laser gas analyzer may not be able to obtain an accurate concentration of the target gas.

[0050] Therefore, the laser gas analyzer according to this embodiment performs measurement using absorption intensities at three or more wavelengths. The laser gas analyzer according to this embodiment performs temperature measurement using absorption intensities at two of the three wavelengths. The laser gas analyzer according to this embodiment performs concentration measurement using absorption intensity at the remaining wavelength, and performs temperature correction using the results of the temperature measurement.

[0051] The laser gas analyzer according to this embodiment performs temperature compensation by itself during measurement, and therefore can perform accurate concentration measurement in a wide range of temperature environments and in environments with rapid temperature changes.

[0052] The laser gas analyzer according to the first embodiment uses one laser to measure an absorption spectrum for measuring temperature and an absorption spectrum for measuring concentration. The laser gas analyzer according to the first embodiment is applied, for example, to a case where an absorption spectrum (absorption spectrum for measuring concentration) of a gas to be measured exists near a spectrum for measuring temperature. The laser gas analyzer according to the first embodiment is applied to a case where an absorption spectrum for measuring temperature and an absorption spectrum for measuring concentration exist within a sweep wavelength range of a single laser.

[0053] Specifically, a laser gas analyzer 1, which is an example of the laser gas analyzer according to the first embodiment, will be used for explanation. Here, a case will be explained in which the laser gas analyzer 1 measures temperature using oxygen gas and corrects the gas concentration of hydrogen gas.

[0054] FIG. 4 is a diagram showing the temperature dependence of the absorption spectrum of oxygen gas. FIG. 4 shows the absorption spectrum of oxygen gas when the temperature is changed. FIG. 4 is a diagram showing the absorption coefficient in the wavelength range from wavelength λmin1 to wavelength λmax1 in the vicinity of a wavelength of 760 nanometers. In the example of FIG. 4, wavelength λmax1 is 0.07 nanometers longer than wavelength λmin1. The horizontal axis of FIG. 4 is wavelength (unit: nanometers (nm)), and the vertical axis of FIG. 4 is absorption coefficient (unit: arbitrary unit). Lines L31, L32, and L33 show absorption coefficients at temperatures of 25° C., 400° C., and 1200° C., respectively.

[0055] As shown in FIG. 4, oxygen gas has two peaks, peak P1 and peak P2, between wavelength λmin1 and wavelength λmax1. The wavelength at peak P1 is wavelength λpeak1. The wavelength at peak P2 is wavelength λpeak2. The change in the absorption coefficient of oxygen gas with respect to temperature at peak P1 is different from the change in the absorption coefficient of oxygen gas with respect to temperature at peak P2. FIG. 5 is a diagram showing the temperature dependence of the absorption spectrum of oxygen gas. Specifically, FIG. 5 is a diagram showing the absorption coefficient at peak P1 and peak P2 in FIG. 4. The horizontal axis of FIG. 5 is temperature (unit: degree Celsius (°C)), and the vertical axis of FIG. 5 is absorption coefficient (unit: arbitrary unit). Line L41 and line L42 are absorption coefficients at peak P1 and peak P2, respectively. As shown in FIG. 5, the fluctuations of the absorption coefficient at peak P1 and peak P2 with respect to temperature are different. Therefore, the laser gas analyzer 1 estimates the temperature based on the ratio of the absorption coefficient at peak P1 to the absorption coefficient at peak P2.

[0056] Fig. 6 is a diagram for explaining temperature measurement using the absorption spectrum of oxygen gas. The horizontal axis of Fig. 6 is the ratio (unit: dimensionless) of the absorption coefficient at peak P1 to the absorption coefficient at peak P2, and the vertical axis of Fig. 6 is temperature (unit: degree Celsius (°C)).

[0057] 6, the temperature monotonically decreases with respect to the ratio of the absorption coefficient at peak P1 to the absorption coefficient at peak P2. Therefore, the laser gas analyzer 1 can calculate the temperature based on the ratio of the absorption coefficient at peak P1 to the absorption coefficient at peak P2.

[0058] Next, the temperature dependency of the gas concentration of hydrogen gas to be measured will be described. Fig. 7 is a diagram for explaining the correction of the gas concentration of hydrogen gas. The horizontal axis of Fig. 7 is temperature (unit: degree Celsius (°C)), and the vertical axis of Fig. 7 is the correction coefficient based on the gas concentration at a temperature of 25°C. As shown by line L6 in Fig. 7, if the temperature of the gas to be measured is known, the gas concentration of the gas to be measured can be corrected.

[0059] Next, a description will be given of the processing in the laser gas analyzer according to the first embodiment. Fig. 8 is a diagram for explaining the processing in the laser gas analyzer 1, which is an example of the laser gas analyzer according to the first embodiment.

[0060] 8, line La1 indicates the wavelength of the detection light 40 emitted from the laser element 12. Line Lb1 indicates the processed waveform in the received light signal processing unit 21. Line Lb1 indicates the output of a lock-in amplifier using a frequency twice the modulation frequency of the detection light 40 as a reference wave. Line Lb1 corresponds to the second derivative of the absorption spectrum. Time progresses in the direction of the arrow.

[0061] In the laser gas analyzer 1, it is assumed that the wavelength modulation period T1 of the detection light 40 includes both an absorption spectrum for measuring temperature and an absorption spectrum for measuring concentration.

[0062] As shown in Fig. 8, the laser gas analyzer 1 can acquire an absorption spectrum for measuring temperature SPT1, an absorption spectrum for measuring temperature SPT2, and an absorption spectrum for measuring concentration SPD. For example, the absorption spectrum for measuring temperature SPT1 and the absorption spectrum for measuring temperature SPT2 may be absorption spectra of the same measurement target gas, and the absorption spectrum for measuring concentration SPD may be an absorption spectrum of a different measurement target gas. To be more specific, the absorption spectrum for measuring temperature SPT1 and the absorption spectrum for measuring temperature SPT2 may be absorption spectra of oxygen gas, and the absorption spectrum for measuring concentration SPD may be an absorption spectrum of hydrogen gas. Note that, for example, the absorption spectrum for measuring temperature SPT1, the absorption spectrum for measuring temperature SPT2, and the absorption spectrum for measuring concentration SPD may be acquired from the same measurement target gas.

[0063] The laser gas analyzer 1 measures the peak intensity or the absorption coefficient at the peak for each of the absorption spectrum for temperature measurement SPT1 and the absorption spectrum for temperature measurement SPT2. Specifically, the light receiving signal processing unit 21 in the laser gas analyzer 1 measures the peak intensity or the absorption coefficient at the peak wavelength in the absorption spectrum for temperature measurement SPT1. In addition, the light receiving signal processing unit 21 in the laser gas analyzer 1 measures the peak intensity or the absorption coefficient at the peak wavelength in the absorption spectrum for temperature measurement SPT2.

[0064] Then, the laser gas analyzer 1 obtains a peak intensity ratio or an absorption coefficient ratio in the temperature measurement absorption spectrum SPT1 and the temperature measurement absorption spectrum SPT2. Specifically, the light receiving signal processor 21 in the laser gas analyzer 1 obtains a ratio (peak intensity ratio) between the peak intensity in the temperature measurement absorption spectrum SPT1 and the peak intensity in the temperature measurement absorption spectrum SPT2. Alternatively, the light receiving signal processor 21 in the laser gas analyzer 1 obtains a ratio (absorption coefficient ratio) between the absorption coefficient of the peak in the temperature measurement absorption spectrum SPT1 and the absorption coefficient of the peak in the temperature measurement absorption spectrum SPT2.

[0065] The laser gas analyzer 1 estimates the temperature based on the peak intensity ratio or absorption coefficient ratio thus determined. Specifically, the light receiving signal processor 21 in the laser gas analyzer 1 detects the temperature of the measurement target gas based on the peak intensity ratio or absorption coefficient ratio in the temperature measurement absorption spectrum SPT1 and the temperature measurement absorption spectrum SPT2.

[0066] For example, the light receiving signal processing unit 21 in the laser gas analyzer 1 may be provided with a temperature conversion table showing the relationship between the peak intensity ratio or the absorption coefficient ratio and the temperature (for example, FIG. 6).The light receiving signal processing unit 21 may then use the temperature conversion table to detect the temperature of the measurement target gas based on the measured peak intensity ratio or the absorption coefficient ratio.

[0067] The peak wavelength in the absorption spectrum for temperature measurement SPT1 is an example of the first wavelength, and the absorption coefficient at the peak wavelength in the absorption spectrum for temperature measurement SPT1 is an example of the first absorption coefficient. The peak wavelength in the absorption spectrum for temperature measurement SPT2 is an example of the second wavelength, and the absorption coefficient at the peak wavelength in the absorption spectrum for temperature measurement SPT2 is an example of the second absorption coefficient. The temperature conversion table is an example of the first table.

[0068] Furthermore, the laser gas analyzer 1 measures the gas concentration of the measurement target gas using the concentration measurement absorption spectrum SPD. Specifically, the light receiving signal processing unit 21 in the laser gas analyzer 1 measures the gas concentration of the measurement target gas based on the peak intensity in the concentration measurement absorption spectrum SPD.

[0069] The laser gas analyzer 1 corrects the target gas concentration measured using the concentration measurement absorption spectrum SPD based on the temperature estimated using the temperature measurement absorption spectrum SPT1 and the temperature measurement absorption spectrum SPT2. Specifically, the light receiving signal processing unit 21 in the laser gas analyzer 1 corrects the target gas concentration based on the temperature detected based on the peak intensity ratio or absorption coefficient ratio in the temperature measurement absorption spectrum SPT1 and the temperature measurement absorption spectrum SPT2.

[0070] For example, the light receiving signal processing unit 21 in the laser gas analyzer 1 may be provided with a concentration correction table indicating the relationship between the concentration of the measurement target gas and the temperature (e.g., FIG. 7). The light receiving signal processing unit 21 may then correct the measured concentration using the concentration correction table. The concentration correction table is an example of the second table.

[0071] According to the laser gas analyzer of the first embodiment, even if the temperature of the gas to be measured fluctuates, the influence of the temperature fluctuation of the gas to be measured is suppressed, and the gas concentration can be measured stably.

[0072] <Laser gas analyzer according to the second embodiment> Although the laser gas analyzer according to the first embodiment uses one laser, multiple lasers may be used. A case in which multiple lasers are used as the laser gas analyzer according to the second embodiment will be described.

[0073] The laser gas analyzer according to the second embodiment uses multiple lasers to measure an absorption spectrum for measuring temperature and an absorption spectrum for measuring concentration. The laser gas analyzer according to the second embodiment is applied, for example, to a case where an absorption spectrum of a measurement target gas (absorption spectrum for measuring concentration) does not exist near a spectrum for measuring temperature. The laser gas analyzer according to the second embodiment is applied to a case where an absorption spectrum for measuring temperature is present in the sweep wavelength range of one laser, and an absorption spectrum for measuring concentration is present in the sweep wavelength range of another laser.

[0074] FIG. 9 is a diagram showing the configuration of a laser gas analyzer 2 which is an example of the laser gas analyzer according to the second embodiment.

[0075] The laser gas analyzer 2, which is an example of the laser gas analyzer according to the second embodiment, measures the concentration of a specific gas contained in the gas flowing inside the walls 50a and 50b. The laser gas analyzer 2 differs from the laser gas analyzer 1, which is an example of the laser gas analyzer according to the first embodiment, in that the laser gas analyzer 2 includes laser elements 12a and 12b instead of the laser element 12. Although the laser gas analyzer 2 includes two laser elements, the number of laser elements included in the laser gas analyzer is not limited to two and may be three or more.

[0076] The laser element 12a emits a detection light 40a. The laser element 12b emits a detection light 40b. The laser gas analyzer 2 includes a combining element 16 that transmits the detection light 40a emitted from the laser element 12a onto an optical axis 41 and reflects the detection light 40b emitted from the laser element 12b onto the optical axis 41. The detection light 40b emitted from the laser element 12b is reflected by a surface 16a of the combining element 16.

[0077] The light receiving element 22 has a wavelength band capable of detecting the detection light 40a emitted from the laser element 12a and the detection light 40b emitted from the laser element 12b.

[0078] Next, a description will be given of the processing in the laser gas analyzer according to the second embodiment. Fig. 10 is a diagram for explaining the processing in the laser gas analyzer 2 which is an example of the laser gas analyzer according to the second embodiment.

[0079] In FIG. 10, lines La21 and L22 indicate the wavelengths of the detection light 40 emitted from the laser element 12a and the laser element 12b, respectively. Lines Lb21 and Lb22 indicate the processed waveforms in the received light signal processing unit 21 for the detection light 40a emitted from the laser element 12a and the detection light 40b emitted from the laser element 12b, respectively. Note that lines Lb21 and Lb22 indicate the output of a lock-in amplifier using a frequency twice the modulation frequency of the detection light 40a and the detection light 40b, respectively, as a reference wave. Each of lines Lb21 and Lb22 corresponds to the second derivative of the absorption spectrum. Note that time progresses in the direction of the arrows.

[0080] In the laser gas analyzer 2, it is assumed that the wavelength modulation period T21 of the detection light 40 emitted from the laser element 12a includes an absorption spectrum for temperature measurement. Also, in the laser gas analyzer 2, it is assumed that the wavelength modulation period T22 of the detection light 40 emitted from the laser element 12b includes an absorption spectrum for concentration measurement.

[0081] 10, the laser gas analyzer 2 can obtain an absorption spectrum for measuring temperature SPT1 and an absorption spectrum for measuring temperature SPT2 by the detection light 40a emitted from the laser element 12a. Also, the laser gas analyzer 2 can obtain an absorption spectrum for measuring concentration SPD by the detection light 40b emitted from the laser element 12b.

[0082] 10, by arranging the absorption spectrum for temperature measurement SPT1, the absorption spectrum for temperature measurement SPT2, and the absorption spectrum for concentration measurement SPD, the laser gas analyzer 2 can obtain an absorption spectrum similar to that of the laser gas analyzer 1. The laser gas analyzer 2 can then perform processing similar to that of the laser gas analyzer 1.

[0083] According to the laser gas analyzer of the second embodiment, even if the temperature of the gas to be measured fluctuates, the influence of the temperature fluctuation of the gas to be measured can be suppressed and the gas concentration can be stably measured. Moreover, according to the laser gas analyzer of the second embodiment, it is possible to handle various gases to be measured.

[0084] In the above specific example, the temperature is estimated using oxygen gas and the gas concentration of hydrogen gas is corrected, but the temperature measurement gas and the measurement target gas are not limited to the above example. Various gases can be used as the temperature measurement gas or the measurement target gas.

[0085] Although the laser gas analyzer has been described above by way of an embodiment, the present invention is not limited to the above embodiment. Various modifications and improvements, such as combinations or substitutions with part or all of other embodiments, are possible within the scope of the present disclosure. [Explanation of symbols]

[0086] 1, 2 Laser gas analyzer 10 Light emitting unit 11 Modulated light generation section 12, 12a, 12b Laser element 13 Collimating lens 14 Light emitting part window plate 15. Light-emitting container 16 Composite Elements 20 Light receiving part 21 Light receiving signal processing section 22 Photodetector 23 Condenser Lens 24 Light receiving window plate 25. Receiver container 30 Communication lines 50a, 50b Wall 51a, 51b flange 52a, 52b Optical axis adjustment flange

Claims

1. A laser gas analyzer for measuring a gas concentration of a measurement target gas present in a measurement target space by a tunable laser spectroscopy, a laser element that emits laser light having a wavelength band including an optical absorption wavelength of the absorption line spectrum of the measurement target gas; a light emitting unit having a wavelength swept in a wavelength band including an optical absorption wavelength of the absorption line spectrum of the measurement target gas, and a modulated light generating unit supplying a drive current to the laser element; a light receiving element that receives the laser light that has passed through the measurement target space; a light receiving unit having a light receiving signal processing unit that performs analysis of the measurement target gas based on the amplitude of a detection waveform of the detection signal output from the light receiving element; Equipped with the light receiving signal processing unit detects a temperature of the first measurement target gas from an absorption coefficient at two wavelengths of the first measurement target gas, measures a concentration of the second measurement target gas from an absorption coefficient at one wavelength of the second measurement target gas, and performs temperature compensation on the concentration of the second measurement target gas based on the temperature. Laser gas analyzer.

2. The light receiving signal processing unit includes: a first table indicating a relationship between a ratio of a first absorption coefficient at a first wavelength to a second absorption coefficient at a second wavelength for the first measurement gas and temperature; a second table showing a relationship between temperature and concentration of the second measurement target gas; Equipped with 2. The laser gas analyzer according to claim 1.

3. The light receiving signal processing unit includes: detecting the temperature of the first measurement target gas based on the ratio using the first table, and performing temperature correction on the concentration of the second measurement target gas based on the temperature of the first measurement target gas using the second table; 3. The laser gas analyzer according to claim 2.

4. A laser gas analysis method for measuring a gas concentration of a measurement target gas present in a measurement target space by a tunable laser spectroscopy, comprising: emitting a laser beam having a wavelength band including an optical absorption wavelength of the absorption line spectrum of the gas to be measured while sweeping the wavelength in the wavelength band including an optical absorption wavelength of the absorption line spectrum of the gas to be measured; receiving the laser light having passed through the measurement target space with a light receiving element; analyzing the measurement target gas based on the amplitude of a detection waveform of the detection signal output from the light receiving element; detecting a temperature of a first measurement target gas from an absorption coefficient of the first measurement target gas at two wavelengths, measuring a concentration of a second measurement target gas from an absorption coefficient of the second measurement target gas at one wavelength, and performing temperature compensation on the concentration of the second measurement target gas based on the temperature; Including, Laser-based gas analysis method.

5. A laser gas analyzer for measuring a gas concentration of a measurement target gas present in a measurement target space by a tunable laser spectroscopy, a first laser element that emits a first laser light in a first wavelength band that includes an optical absorption wavelength of an absorption line spectrum of a first measurement target gas; a second laser element that emits a second laser light in a second wavelength band that includes an optical absorption wavelength of an absorption line spectrum of a second measurement target gas; a light emitting unit having a modulated light generating unit whose wavelength is swept in the first wavelength band and the second wavelength band, and which supplies a drive current to each of the first laser element and the second laser element; a light receiving element that receives the first laser light and the second laser light that have passed through the measurement target space; a light receiving unit having a light receiving signal processing unit that performs analysis of the measurement target gas based on the amplitude of a detection waveform of the detection signal output from the light receiving element; Equipped with the light receiving signal processing unit detects a temperature of the first measurement target gas from an absorption coefficient at two wavelengths of the first measurement target gas, measures a concentration of the second measurement target gas from an absorption coefficient at one wavelength of the second measurement target gas, and performs temperature compensation on the concentration of the second measurement target gas based on the temperature. Laser gas analyzer.

6. A laser gas analysis method for measuring a gas concentration of a measurement target gas present in a measurement target space by a tunable laser spectroscopy, comprising: emitting a first laser light in a first wavelength band including an optical absorption wavelength of an absorption line spectrum of a first measurement target gas; emitting a second laser light in a second wavelength band including an optical absorption wavelength of an absorption line spectrum of a second measurement target gas; receiving the first laser light and the second laser light that have passed through the measurement target space with a light receiving element; detecting a temperature of the first measurement target gas from an absorption coefficient of the first measurement target gas at two wavelengths, measuring a concentration of the second measurement target gas from an absorption coefficient of the second measurement target gas at one wavelength, and performing temperature compensation on the concentration of the second measurement target gas based on the temperature; Including, Laser-based gas analysis method.

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