Laser gas analyzer

Abstract

To provide a laser gas analyzer that suppresses influence of moisture on a measurement target gas.SOLUTION: A laser gas analyzer for measuring concentration of a measurement target gas present in a measurement target space includes: a light emitting unit having a light emitting optical system including a laser element and a modulated light generation unit that supplies a drive current to the laser element such that a wavelength is swept and modulated in a first wavelength band including a light absorption wavelength of an absorption spectrum of the measurement target gas and a second wavelength band including the light absorption wavelength of the absorption spectrum of water; and a light receiving unit having a light receiving optical system and a light receiving signal processing unit that calculates concentration of the measurement target gas. The gas analyzer has a moisture correction processing unit that performs correction to eliminate noise caused by light absorption of water when calculating the concentration of the target gas being measured. The moisture correction processing unit determines whether correction is necessary based on temperature of the measurement target gas and performs correction when determining that the correction is necessary.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Gaseous gas molecules each have a unique absorption spectrum that represents their own optical absorption wavelength and absorption intensity. Laser light is light with a narrow spectral linewidth at a specific wavelength. A laser gas analyzer uses a laser element to emit laser light at an optical absorption wavelength that is absorbed by the gaseous gas molecules to be measured, causing the gas to absorb the laser light. The laser gas analyzer detects the presence or absence of the gas to be measured based on the amount of laser light absorbed at that optical absorption wavelength. In addition, the laser gas analyzer can also detect the concentration of the gas to be measured because the amount of laser light absorbed at the optical absorption wavelength is proportional to the concentration of the gas to be measured.

[0003] For example, Patent Document 1 discloses a laser gas analyzer that includes a light-emitting unit having a laser element that emits laser light in a wavelength band that includes the optical absorption wavelength of the absorption spectrum of the gas to be measured, and a light-receiving unit that has a light-receiving element that receives the laser light that has passed through the space to be measured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-106742 Summary of the Invention [Problem to be solved by the invention]

[0005] Such laser gas analyzers still have room for improvement in order to measure the concentration of a target gas with high accuracy. If the space where the target gas is present is, for example, a chimney or a furnace, and moisture is present in the space, and the optical absorption wavelength of water is near the optical absorption wavelength of the target gas, the measured value of the target gas may be attenuated, and the moisture may affect the measured value of the target gas as an error factor.

[0006] The present disclosure provides a laser gas analyzer that suppresses the influence of moisture on a gas to be measured. [Means for solving the problem]

[0007] One aspect of the present disclosure is a laser gas analyzer for measuring the concentration of a target gas present in a measurement space, the analyzer comprising: an emission optical system including a laser element that emits laser light in a wavelength band that includes the optical absorption wavelengths of the absorption spectrum of the target gas and the optical absorption wavelengths of the absorption spectrum of water; and a modulated light generating unit that supplies a drive current to the laser element so that the wavelength is swept and modulated through a first wavelength band that includes the optical absorption wavelengths of the absorption spectrum of the target gas and a second wavelength band that includes the optical absorption wavelengths of the absorption spectrum of water; a light receiving unit that includes a light receiving optical system that receives the laser light that has passed through the measurement space; and a light receiving signal processing unit that calculates the target gas concentration by processing a detection signal output from the light receiving optical system, the light receiving signal processing unit having a moisture correction processing unit that performs a correction to remove noise due to light absorption by water when calculating the target gas concentration, using a signal component that corresponds to the laser light in the second wavelength band and that is included in the detection signal; and the moisture correction processing unit determines whether the correction is necessary based on the temperature of the target gas, and performs the correction only if it is determined that the correction is necessary. [Effects of the Invention]

[0008] According to the laser gas analyzer of the present disclosure, the influence of moisture on the gas to be measured can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the configuration of a laser gas analyzer according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the absorption spectrum of a gas to be measured and the absorption spectrum of water. [Figure 3] FIG. 10 is a diagram showing a flow of processing of a detection signal. [Figure 4A] 10A and 10B are diagrams showing waveforms of modulated light emitted from a laser element. [Figure 4B] 10A and 10B are diagrams showing waveforms of received light signals processed in a received light signal processing unit; [Figure 5] FIG. 10 is a diagram showing the relationship between the temperature of the atmosphere and the moisture concentration. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] In the description of the specification and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be designated by the same reference numerals to avoid redundant explanation. In addition, the scale of each part in the drawings may differ from the actual scale to facilitate understanding.

[0012] The laser gas analyzer according to this embodiment is a laser gas analyzer that measures the concentration of a target gas present in a target space by tunable laser spectroscopy. The laser gas analyzer according to this embodiment includes a light-emitting unit and a light-receiving unit.

[0013] The light-emitting unit in the laser gas analyzer of this embodiment has an emission optical system including a laser element that emits laser light in a wavelength band that includes the optical absorption wavelengths of the absorption spectrum of the target gas and the optical absorption wavelengths of the absorption spectrum of water. The light-emitting unit in the laser gas analyzer of this embodiment also has a modulated light generating unit that supplies a drive current to the laser element so that the wavelength is swept and modulated in a first wavelength band that includes the optical absorption wavelengths of the absorption spectrum of the target gas and a second wavelength band that includes the optical absorption wavelengths of the absorption spectrum of water.

[0014] The light receiving unit in the laser gas analyzer according to this embodiment includes a light receiving optical system that receives the laser light that has passed through the measurement target space, and a light receiving signal processing unit that calculates the concentration of the measurement target gas by processing the detection signal output from the light receiving optical system. The light receiving signal processing unit in the laser gas analyzer according to this embodiment includes a moisture correction processing unit that performs correction to remove noise due to light absorption by water when calculating the concentration of the measurement target gas, using a signal component that corresponds to the laser light in the second wavelength band and is included in the detection signal. The moisture correction processing unit in the laser gas analyzer according to this embodiment determines whether correction is necessary based on the temperature of the measurement target gas, and performs correction to remove noise only if correction is determined to be necessary.

[0015] 1 is a diagram showing the configuration of a laser gas analyzer 1 according to this embodiment. The laser gas analyzer 1 will be used as an example of the laser gas analyzer according to this embodiment.

[0016] Gaseous gas molecules each have an absorption spectrum that represents a specific optical absorption wavelength and absorption intensity. Laser light is light with a narrow spectral linewidth at a specific wavelength. In a laser gas analyzer, a laser element emits laser light at an optical absorption wavelength that is absorbed by a target gas, which is a gaseous gas molecule, and the target gas absorbs the laser light. The laser gas analyzer then detects the presence or absence of a target gas based on the amount of laser light absorbed at the optical absorption wavelength. In addition, the laser gas analyzer can detect the concentration of a target gas because the amount of laser light absorbed at the optical absorption wavelength is proportional to the concentration of the target gas.

[0017] The laser gas analyzer 1 measures the concentration of a specific gas contained in the gas flowing between the walls 50a and 50b. The laser gas analyzer 1 can also detect the absence of gas if the gas concentration is 0 or below a predetermined value. In other words, the laser gas analyzer 1 can also detect the presence or absence of gas.

[0018] The laser gas analyzer 1 includes a light-emitting unit 10, a light-receiving unit 20, and a communication line 30a. The communication line 30a communicates between the light-emitting unit 10 and the light-receiving unit 20 via electrical signals. The laser gas analyzer 1 also includes a temperature sensor 60 that detects the temperature of the gas to be measured, and a communication line 30b. The communication line 30b transmits the electrical signal detected by the temperature sensor 60 to the light-receiving unit 20. Note that a communication unit such as a wireless or optical communication unit may be used instead of the communication lines 30a and 30b. The laser gas analyzer 1 can use a communication unit using these communication lines, wireless communication, or optical communication.

[0019] 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.

[0020] 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 light that is not absorbed from detection light 40 projected from light emitter 10, 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.

[0021] The optical function of the light-emitting unit 10 will now be described. FIG. 2 is a diagram showing the absorption spectrum of the gas to be measured and the absorption spectrum of water. The light absorption wavelength (peak wavelength) of the absorption spectrum is specific to the gas species. As shown in FIG. 2, the light absorption wavelength (peak wavelength) of the absorption spectrum of the gas to be measured is expressed as λ X The light absorption wavelength (peak wavelength) of the absorption spectrum of water (hereinafter sometimes referred to as the "first light absorption wavelength") is defined as λ Y1 The laser gas analyzer 1 selects the wavelength of the laser light emitted by the laser element 12 based on the absorption spectra of the gas to be measured and water. X , λ Y1The light-emitting unit emits detection light 40 toward the light-receiving unit 20 while modulating its wavelength with wavelengths at and around the wavelengths. The detection light 40, which is 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 containing the gas to be measured flows. Here, "substantially parallel" means that even if two lines or two surfaces are not completely parallel to each other, they can be treated as being parallel to each other as long as they are within a manufacturing tolerance.

[0022] In the example shown in Figure 2, the light absorption spectrum of water is min From wavelength λ max In the wavelength range up to the first optical absorption wavelength λ Y1 and the second optical absorption wavelength λ Y2 where the wavelength λ min From wavelength λ max The wavelength range up to the second optical absorption wavelength λ is a wavelength range that includes at least one optical absorption wavelength of the measurement target gas. Y2 is the optical absorption wavelength λ of the gas to be measured X The first optical absorption wavelength λ Y1 is the optical absorption wavelength λ of the gas to be measured X For the second optical absorption wavelength λ Y2 In the example shown in FIG. 2, the first optical absorption wavelength λ Y1 is the second optical absorption wavelength λ Y2 The second optical absorption wavelength λ is smaller than Y2 It may be larger than

[0023] The light absorption spectrum of water is min From wavelength λ max The light absorption spectrum of water may have three or more light absorption wavelengths in the wavelength range from λ min From wavelength λ max In the case where the optical absorption wavelength is three or more in the wavelength range up to the first optical absorption wavelength λ Y1 is the optical absorption wavelength λ of the gas to be measured among multiple optical absorption wavelengths. X The light absorption wavelength farthest from the X The wavelength with the largest difference from the first absorption wavelength is defined as the second absorption wavelength λ Y2 is the light absorption wavelength λ XThe wavelength where the difference between the wavelengths is smallest is defined as the light absorption wavelength.

[0024] The light-emitting unit 10 includes at least a modulated light generating unit 11 , a light-emitting optical system 16 including a laser element 12 and a collimating lens 13 , a light-emitting unit window plate 14 , and a light-emitting unit container 15 .

[0025] 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 absorption characteristics of the measurement target gas and water. 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 absorption characteristics of the measurement target gas as frequency-modulated modulated light.

[0026] Specifically, the modulated light generating unit 11 generates a modulated light having a wavelength λ of 1000 s, which is the optical absorption wavelength λ of the absorption spectrum of the measurement target gas. X and a first wavelength band R1 including the light absorption wavelength λ of the absorption spectrum of water. Y1 A drive current is supplied to the laser element 12 so that the wavelength is swept and modulated in a second wavelength band R2 including the first wavelength band R1 and the second wavelength band R2. The first wavelength band R1 and the second wavelength band R2 do not overlap.

[0027] The laser element 12 is, for example, a distributed feedback (DFB) laser. Alternatively, the laser element 12 may be, for example, a vertical cavity surface emitting laser diode (VCSEL). Furthermore, the laser element 12 may be, for example, a distributed Bragg reflector (DBR) laser.

[0028] The laser element 12 can variably control the emission wavelength by the drive current and temperature. Therefore, the central wavelength of the laser light emitted by the laser element 12 is set to the optical absorption wavelength λ of the absorption spectrum of the gas to be measured. X , or the light absorption wavelength λ of the absorption spectrum of water Y1The temperature is controlled so that the wavelength around the central wavelength of the laser light is swept over time. Furthermore, a sine wave having an appropriate wavelength modulation amplitude and frequency is superimposed on the drive current so that the wavelength can be measured with high sensitivity by wavelength modulation spectroscopy.

[0029] The laser element 12 emits light at a wavelength λ of the absorption spectrum of the gas to be measured. X , and the light absorption wavelength λ of the absorption spectrum of water Y1 The wavelength band including min ~λ max ) laser light with wavelength λ max is, for example, the wavelength λ min 1 nm larger than

[0030] The laser element 12 emits light at a first light absorption wavelength λ in the absorption spectrum of water. Y1 and the second optical absorption wavelength λ Y2 The laser beam emitted has a wavelength band including the first optical absorption wavelength λ Y1 is included in the second wavelength band R2 and has a second optical absorption wavelength λ Y2 is included in the first wavelength band R1.

[0031] The number of laser elements 12 is one. That is, the laser element 12 can emit laser light in the first wavelength band R1 and laser light in the second wavelength band R2 in a time-division manner.

[0032] The light emitting point of the laser element 12 is located 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 substantially parallel light.

[0033] The collimator lens 13 is configured to absorb light at a wavelength λ X , λ Y1 The collimator lens 13 is made of a material that has high transmittance at wavelengths around the wavelengths. The collimator lens 13 converts the detection light 40 emitted from the laser element 12 into approximately parallel light. By converting the detection light 40 into parallel light, the light emitter 10 can transmit the detection light 40 to the light receiver 20 while suppressing loss due to diffusion.

[0034] In this embodiment, the collimator lens 13 is used, but the present invention is not limited to this. For example, a parabolic mirror can be used instead of the collimator lens.

[0035] The light-emitting unit window plate 14 is provided to close a hole drilled in part of the light-emitting unit container 15. The light-emitting unit window plate 14 is located in the optical path of the detection light 40, and while allowing the detection light 40 to pass through, it prevents gas in the measurement target space from entering the light-emitting unit 10. The light-emitting unit window plate 14 prevents the optical elements, optical components, electrical and electronic circuits, etc. housed inside from coming into direct contact with the gas. In other words, the light-emitting unit window plate 14 protects the optical elements, optical components, electrical and electronic circuits, etc. housed inside from coming into direct contact with the gas.

[0036] The light-emitting portion container 15 houses optical elements, optical components, electric and electronic circuits, etc. inside. The light-emitting portion container 15 isolates the optical elements, optical components, electric and electronic circuits, etc. housed inside from the outside air. The light-emitting portion container 15 protects the optical elements, optical components, electric and electronic circuits, etc. housed inside from wind, rain, dust, dirt, etc.

[0037] 1, holes are formed in walls 50a and 50b of a pipe or the like through which a gas containing a measurement target gas flows, and flanges 51a and 51b are fixed to the holes by welding or the like.

[0038] The light-emitting unit 10 is provided with 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 light intensity.

[0039] Next, the light receiving unit 20 will be described. The light receiving unit 20 receives the detection light 40 that has passed through the light receiving unit window plate 24 and analyzes the amount of light absorbed by the gas to be measured. The light receiving unit 20 at least includes a received light signal processing unit 21, a light receiving optical system 26 including a light receiving element 22 and a condenser lens 23, the light receiving unit window plate 24, and a light receiving unit container 25.

[0040] The light receiving optical system 26 receives the laser light that has passed through the measurement target space. X , λ Y1 A light receiving element having sensitivity in the wavelength range of 1000 nm or the wavelengths around that wavelength can be selected.

[0041] The condenser lens 23 is configured to absorb light at a wavelength λ X , λ Y1 The light receiving element 22 is made of a material with high transmittance at wavelengths around the wavelength of the incident light. The condenser lens 23 condenses the detection light 40 onto the light receiving element 22, thereby obtaining a high signal intensity. The detection light 40 is incident on the light receiving element 22, whose light receiving surface is located 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 can also be used instead of the condenser lens 23. The detection light 40 received by the light receiving element 22 is converted into an electrical signal and sent to the light receiving signal processing unit 21 as a detection signal.

[0042] The received light signal processing unit 21 is a signal processing and light receiving circuit that calculates the concentration of the measurement target gas based on the received detection light 40. The received light signal processing unit 21 calculates the concentration of the measurement target gas by processing the detection signal output from the light receiving optical system 26.

[0043] The received light signal processing unit 21 has a moisture correction processing unit 211. The moisture correction processing unit 211 is a signal processing and light receiving circuit that removes noise due to light absorption by water when calculating the concentration of the measurement target gas. Specifically, the moisture correction processing unit 211 uses a signal component that is included in the detection signal and corresponds to the laser light in the second wavelength band R2 to perform correction that removes noise due to light absorption by water when calculating the concentration of the measurement target gas.

[0044] The light-receiving unit window plate 24 is provided to close a hole drilled in 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 allowing the detection light 40 to pass through, it prevents gas in the measurement target space from entering the light-receiving unit 20. The light-receiving unit window plate 24 prevents the optical elements, optical components, electrical and electronic circuits, etc. housed inside from coming into direct contact with the gas. In other words, the light-receiving unit window plate 24 protects the optical elements, optical components, electrical and electronic circuits, etc. housed inside from coming into direct contact with the gas.

[0045] The light-receiving unit container 25 houses 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. housed inside from the outside air. The light-receiving unit container 25 protects the optical elements, optical components, electric and electronic circuits, etc. housed inside from wind, rain, dust, dirt, etc.

[0046] 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 angle of incidence 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.

[0047] The temperature sensor 60 may be any sensor capable of measuring the temperature of the measurement target gas in the measurement target space. The temperature sensor 60 is fixed to the wall 50b, for example.

[0048] The processing in the light reception signal processing unit 21 will be described.

[0049] When water is present in the measurement space, the optical absorption of the target gas interferes with that of the water, making it difficult to accurately measure the target gas concentration, as shown in Figure 2. To eliminate the influence of water's optical absorption, one approach is to compare the optical absorption spectrum of water with that of the target gas and select a wavelength band within the target gas's absorption spectrum where the optical absorption spectrum of water is as minimal as possible. However, even if a wavelength has a large amount of optical absorption and is suitable for gas concentration measurement, it cannot be used if it interferes with the optical absorption wavelength of water, making it difficult to measure the target gas concentration with high accuracy. To accurately measure the target gas concentration, the target gas concentration must be corrected according to the moisture concentration.

[0050] Therefore, the laser gas analyzer 1 of this embodiment uses the laser element 12 to generate laser light in a first wavelength band R1 that includes the optical absorption wavelength of the gas to be measured and the second optical absorption wavelength of water, and a first optical absorption wavelength λ Y1 The moisture correction processing unit 211 uses the signal component corresponding to the laser light in the second wavelength band R2 to perform correction to remove noise due to light absorption by water when calculating the concentration of the gas to be measured.

[0051] Furthermore, since the moisture concentration varies depending on the temperature of the gas to be measured, the degree to which noise due to moisture affects the concentration of the gas to be measured varies depending on the temperature of the gas to be measured.

[0052] Therefore, in the laser gas analyzer 1 of this embodiment, the moisture correction processing unit 211 determines whether correction is necessary based on the temperature of the gas to be measured, and performs correction to remove noise only if it is determined that correction is necessary.

[0053] Fig. 3 is a diagram showing the flow of processing of a detection signal, Fig. 4A is a diagram showing the waveform of modulated light emitted from a laser element, and Fig. 4B is a diagram showing the processed waveform of a received light signal in a received light signal processing unit. Note that in Figs. 4A and 4B, time progresses in the direction of the arrows.

[0054] 3 is executed by the light receiving signal processing unit 21 and the moisture correction processing unit 211 included in the light receiving signal processing unit 21. The light receiving signal processing unit 21 first processes a light receiving signal corresponding to transmitted light after the modulated light (laser light) emitted from the laser element 12 shown in FIG. 4A is absorbed by the measurement target gas and moisture, and obtains a processed waveform shown in FIG. 4B (step S1).

[0055] As shown in FIG. 4B, the wavelength modulation period T1 of the detection light 40 includes the absorption spectrum of the measurement target gas, and the wavelength modulation period T2 includes the absorption spectrum of water. The laser gas analyzer 1 can alternately acquire the absorption spectrum of the measurement target gas and the absorption spectrum of water by time-sharing the sweep range of the first wavelength band R1 and the sweep range of the second wavelength band R2. This allows the laser gas analyzer 1 to perform moisture correction over time. In this case, if the change in the measurement environment (moisture concentration) is small, the received light signal processor 21 does not necessarily need to alternately acquire data on the measurement target gas and moisture, and the frequency of acquiring moisture data can be reduced.

[0056] Next, the received light signal processing unit 21 averages the obtained processed waveform of FIG. 4B (step S2). By averaging the waveform, noise can be reduced. Here, noise refers to noise caused by various factors such as light, circuit signal processing, and installation environment. Note that the noise in step S2 is different from noise caused by moisture.

[0057] In step S2, the processed waveform can be averaged, for example, by the following method. By changing the optical path length between the laser element 12 and the light-receiving element 22, the reflection position of the interference light in optical elements such as the collimator lens 13 and the condenser lens 23 changes, causing a phase shift. Therefore, the influence of optical interference can be reduced by periodically and repeatedly changing the optical path length within a small range and averaging multiple received light signals obtained during one period. Note that in step S2, increasing the number of averaging times increases the noise reduction effect, but also has the disadvantage of increasing the processing time, so it is necessary to set an appropriate number of averaging times.

[0058] Next, the received light signal processing unit 21 calculates the absorption intensity from the averaged waveform (step S3). The received light signal processing unit 21 detects the absorption position of the waveform and can calculate the absorption intensity by subtracting the minimum value from the maximum value of absorption. At this time, since there is a very rare case where an outlier due to a measurement error is included, the received light signal processing unit 21 may perform a calculation to remove the outlier.

[0059] Next, the light receiving signal processing unit 21 performs light intensity correction (step S4). The light receiving signal processing unit 21 calculates the ratio of the change in the amount of transmitted light during measurement to the amount of transmitted light during calibration, which serves as a reference, and can perform light intensity correction by multiplying the ratio by its reciprocal. This is a correction process when the amount of light changes due to factors other than light absorption by the gas to be measured, such as misalignment of the optical axis or contamination of the optical system.

[0060] After performing the light intensity correction process, the moisture correction processor 211 determines the gas temperature to determine whether moisture correction is required (step S5). The moisture correction processor 211 determines whether correction is required based on the temperature of the measurement target gas, and performs correction to remove noise due to light absorption by water only if it determines that correction is required (step S5: YES). Specifically, the moisture correction processor 211 determines that correction is required when the temperature of the measurement target gas is equal to or higher than a predetermined reference temperature T°C (step S5: YES), and determines that correction is not required when the temperature is lower than the reference temperature T°C (step S5: NO). The reference temperature can be a gas temperature at which the influence of moisture can be ignored. FIG. 5 shows the relationship between ambient temperature and moisture concentration. The moisture correction processor 211 can set the reference temperature, for example, based on the graph shown in FIG. 5. For example, the reference temperature T°C can be set to 0°C. However, in an environment where moisture has a significant effect, a lower temperature can be used as the reference temperature T°C. The moisture correction processing unit 211 can receive temperature data of the measurement object gas detected by the temperature sensor 60.

[0061] When it is determined that correction is necessary (step S5: YES), the moisture correction processing unit 211 performs moisture correction calculation (step S6). The procedure of the moisture correction calculation will be described in detail. First, the first light absorption wavelength λ of water is calculated. Y1 Absorption intensity A at Y1 Calculate the calculated absorption intensity A Y1 Using the following formula (1), the optical absorption wavelength λ of the gas to be measured is calculated. X Absorption intensity A of water at X Calculate. A X = α × A Y1 +β (1)

[0062] In the above formula (1), the coefficient α and the constant β may be obtained in advance. The coefficient α is, for example, Y1 Absorption intensity A at Y1 The optical absorption wavelength λ of the gas to be measured X Absorption intensity A of water at XThe constant β can be determined by the ratio of the wavelength λ Y1 and wavelength λ X The absorption intensity can be calculated by calculating the intercept of the simultaneous equation.

[0063] Next, the moisture correction processing unit 211 calculates the calculated light absorption wavelength λ of the measurement target gas. X Absorption intensity A of water at X and the optical absorption wavelength λ of the measured gas X Absorption intensity B at X Using the following formula (2), the optical absorption wavelength λ of the gas to be measured is calculated, after removing the noise due to the optical absorption of water. X Absorption intensity C X Calculate. C x =B X -A X ···(2)

[0064] Next, the light receiving signal processing unit 21 performs gas concentration calculation (step S7). In step S5, if the moisture correction processing unit 211 determines that correction is necessary (step S5: YES), the absorption intensity C of the measurement object gas calculated in step S6 is X On the other hand, in step S5, if the moisture correction processing unit 211 determines that correction is not necessary (step S5: NO), the processing of step S7 is started, and the light absorption wavelength λ of the measurement object gas after light intensity correction calculated in step S4 is calculated. X The gas concentration is calculated using the absorption intensity at 1000 kJ / s. The received light signal processing unit 21 can calculate the gas concentration by calculating the ratio of the calibration data to the full scale. The received light signal processing unit 21 may also perform processing such as moving average as necessary.

[0065] Finally, the received light signal processing unit 21 outputs the gas concentration calculated in step S7 (step S9), and the process ends. Through the above process, the concentration of the target gas from which noise due to light absorption by water has been removed, or the concentration of the target gas from which noise due to light absorption by water has not been removed, can be obtained. In the example shown in FIG. 3, the received light signal processing unit 21 performs the processes of steps S5 and S6 after the process of step S4, but this is not limiting, and the processes of steps S5 and S6 may be performed after the processes of other steps shown in FIG.

[0066] As described above, the laser gas analyzer 1 of this embodiment includes the light-emitting unit 10, which has the light-emitting optical system 16 including the laser element 12 and the modulated light generating unit 11, and the light-receiving unit 20, which has the light-receiving optical system 26 and the received-light signal processing unit 21. The received-light signal processing unit 21 also includes a moisture correction processing unit 211, which determines whether correction is necessary based on the temperature of the target gas and performs correction to remove noise only if correction is determined to be necessary. With this configuration, the laser gas analyzer 1 can perform correction to remove moisture-related noise as needed, i.e., depending on the degree of influence of moisture-related noise on the target gas concentration, and calculate the target gas concentration. Therefore, the laser gas analyzer 1 can suppress the influence of moisture on the target gas.

[0067] Furthermore, when the moisture influence level is stored in advance as a correction table and correction is performed to remove noise due to moisture, the correction table required differs depending on the measurement environment, and therefore a correction table needs to be set for each analyzer. However, with the laser gas analyzer 1, correction to remove noise due to moisture can be performed without setting a correction table in advance.

[0068] In the laser gas analyzer 1, the first wavelength band R1 and the second wavelength band R2 can be configured not to overlap. This allows the laser gas analyzer 1 to set, as the first wavelength band R1, a wavelength band that includes light absorption wavelengths that have a large amount of light absorption and are suitable for gas concentration measurement, and also allows the laser gas analyzer 1 to detect the amount of light absorption by water in the second wavelength band R2 and calculate the amount of light absorption by water in the first wavelength band R1 using, for example, the above-mentioned formula (1). Therefore, the laser gas analyzer 1 can perform correction to remove noise due to moisture in the first wavelength band R1 and calculate the concentration of the target gas, thereby improving the measurement accuracy of the target gas concentration.

[0069] The number of laser elements 12 can be one. Specifically, laser element 12 can emit laser light in a first wavelength band R1 and laser light in a second wavelength band R2 in a time-division manner. This allows laser gas analyzer 1 to perform correction to remove noise due to moisture over time and correct the concentration of the gas to be measured in accordance with changes in the moisture concentration in the space to be measured. Furthermore, laser gas analyzer 1 does not require the provision of a laser element for moisture detection in addition to a laser element for detecting the gas to be measured, and can utilize components of conventional laser gas analyzers.

[0070] The laser element 12 emits light at a first light absorption wavelength λ in the absorption spectrum of water. Y1 and the second optical absorption wavelength λ Y2 and emitting laser light in a wavelength band including a first optical absorption wavelength λ Y1 is included in the second wavelength band R2 and has a second optical absorption wavelength λ Y2 can be included in the first wavelength band R1. As a result, the laser gas analyzer 1 can set, as the first wavelength band R1, a wavelength band including a light absorption wavelength that has a large amount of light absorption and is suitable for gas concentration measurement, and can also set the first light absorption wavelength λ Y1 The amount of light absorption by water at the wavelength λ of the gas to be measured is detected, for example, using the above-mentioned formula (1). X Absorption intensity A of water at XTherefore, the laser gas analyzer 1 can perform a correction to remove noise due to moisture in the first wavelength band R1, calculate the concentration of the measurement target gas, and improve the measurement accuracy of the concentration of the measurement target gas.

[0071] The moisture correction processing unit 211 can determine that correction is necessary when the temperature of the measurement target gas is equal to or higher than a predetermined reference temperature T°C, and can determine that correction is not necessary when the temperature is below the reference temperature T°C. This allows the laser gas analyzer 1 to perform correction to remove moisture-induced noise and calculate the measurement target gas concentration when the degree of influence of moisture-induced noise on the measurement target gas concentration exceeds an allowable range. Furthermore, the laser gas analyzer 1 can calculate the measurement target gas concentration without performing correction to remove moisture-induced noise when the degree of influence of moisture-induced noise on the measurement target gas concentration is within an allowable range. This allows the laser gas analyzer 1 to further suppress the influence of moisture on the measurement target gas.

[0072] Although the laser gas analyzer has been described above using 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]

[0073] 1. Laser gas analyzer 10 Light-emitting part 11 Modulated light generation unit 12 Laser element 13 Collimating lens 14 Light-emitting window plate 15. Light-emitting container 16 Light Emitting Optical System 20 Light receiving part 21 Light receiving signal processing section 211 Moisture correction processing unit 22 Photodetector 23 Condenser lens 24 Light receiving window plate 25 Light receiving unit container 26 Light receiving optical system 30a, 30b communication line 40 Detected light 50a, 50b walls 51a, 51b flange 52a, 52b Optical axis adjustment flange 60 Temperature Sensor R1 First wavelength band R2 Second wavelength band

Claims

1. A laser gas analyzer for measuring the concentration of a measurement target gas present in a measurement target space, a light emitting unit including: an emission optical system including a laser element that emits laser light in a wavelength band that includes the optical absorption wavelengths of the absorption spectrum of the measurement target gas and the optical absorption wavelengths of the absorption spectrum of water; and a modulated light generating unit that supplies a drive current to the laser element so that the wavelength is swept and modulated in a first wavelength band that includes the optical absorption wavelengths of the absorption spectrum of the measurement target gas and a second wavelength band that includes the optical absorption wavelengths of the absorption spectrum of water; a light receiving unit including a light receiving optical system that receives the laser light that has passed through the measurement target space, and a light receiving signal processing unit that calculates the concentration of the measurement target gas by processing a detection signal output from the light receiving optical system; Equipped with the light receiving signal processing unit includes a moisture correction processing unit that performs correction to remove noise due to light absorption by water when calculating the concentration of the measurement target gas, using a signal component that is included in the detection signal and corresponds to the laser light in the second wavelength band, and The moisture correction processing unit determines whether or not the correction is necessary based on the temperature of the gas to be measured, and performs the correction only when it determines that the correction is necessary.

2. 2. The laser gas analyzer according to claim 1, wherein the first wavelength band and the second wavelength band do not overlap.

3. 3. The laser gas analyzer according to claim 2, wherein the number of the laser elements is one.

4. 4. The laser gas analyzer according to claim 3, wherein the laser element emits the laser light in the first wavelength band and the laser light in the second wavelength band in a time-division manner.

5. the laser element emits the laser light in a wavelength band including a first light absorption wavelength and a second light absorption wavelength of an absorption spectrum of water, The laser gas analyzer according to claim 4 , wherein the first optical absorption wavelength is included in the second wavelength band, and the second optical absorption wavelength is included in the first wavelength band.

6. 6. A laser gas analyzer according to claim 1, wherein the moisture correction processing unit determines that the correction is necessary when the temperature of the measurement target gas is equal to or higher than a predetermined reference temperature, and determines that the correction is unnecessary when the temperature is lower than the reference temperature.

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