Gas analysis system and gas analysis method

Abstract

To provide a gas analysis system and a gas analysis method which can measure density of a measuring object gas with high accuracy even if an absorption spectrum of the measuring object gas has an asymmetrical shape.SOLUTION: A gas analysis system 1 comprises: a semiconductor laser 13 emitting a laser beam wavelength-modulated with a modulation frequency fL; an optical modulation part (amplifier driving circuit 14, optical amplifier 15) intensity-modulating the laser beam emitted from the semiconductor laser 13 with a modulation frequency fB; a photodetector 17 receiving a laser beam transmitting through a measuring object gas GS; lock-in amplifiers 19a, 19b detecting a first component having a frequency n times (n is an integer of two or more) as large as modulation frequency fL included in a received optical signal outputted from the photodetector 17, a second component having a same frequency as the modulation frequency fB; and an operation part 21 acquiring density of the measuring object gas on the basis of the first component and the second component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas analysis system and a gas analysis method. [Background technology]

[0002] One type of gas analysis system that analyzes a gas to be measured measures the concentration of the gas to be measured based on the absorbance of light irradiated onto the gas to be measured. In such gas analysis systems, wavelength modulation spectroscopy (WMS) is sometimes used to improve the measurement accuracy (sensitivity). Wavelength modulation spectroscopy is a method of measuring the concentration of the gas to be measured based on the second harmonic component (2f component) obtained by irradiating the gas to be measured with laser light modulated (wavelength modulated) at a modulation frequency f and detecting the laser light that has passed through the gas to be measured.

[0003] In wavelength modulation spectroscopy, the ratio of the 2f component to the component of the detected modulation frequency f (1f component) is calculated to normalize the amount of received light, and then the concentration of the gas to be measured is often measured. This is to reduce the influence of fluctuations in the amount of received laser light caused by factors other than the gas to be measured. Note that wavelength modulation spectroscopy is sometimes called 2f detection. Patent Document 1 below discloses an example of a conventional gas analysis system that measures gas concentration using wavelength modulation spectroscopy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 014097 Summary of the Invention [Problem to be solved by the invention]

[0005] If the absorption spectrum of the measurement target gas is ideal, its shape will be symmetrical with respect to the central absorption frequency (central wavelength), and therefore the amplitude of the 1f component will depend only on the average power of the received light signal, and will not depend on the concentration of the measurement target gas. However, since the absorption spectrum of the measurement target gas actually has an asymmetric shape with respect to the central frequency (central wavelength), the amplitude of the 1f component will depend on the concentration of the measurement target gas, resulting in a problem of deterioration in the measurement accuracy of the concentration of the measurement target gas.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a gas analysis system and a gas analysis method that can measure the concentration of a target gas with high accuracy even if the shape of the absorption spectrum of the target gas is asymmetric. [Means for solving the problem]

[0007] In order to solve the above problems, a gas analysis system (1 to 3) according to one aspect of the present invention has a first modulation frequency (f L A light emitting element (13) that emits a laser beam that is wavelength-modulated at a second modulation frequency (f B the first modulation frequency, n is an integer greater than or equal to 2, and the second modulation frequency is n times the first modulation frequency, and a detection unit (19a, 19b, 23) detects a first component having a frequency that is n times the first modulation frequency (n is an integer greater than or equal to 2) and a second component having the same frequency as the second modulation frequency, which are included in a received light signal output from the light receiving element; and a calculation unit (21) that calculates the concentration of the gas to be measured based on the first component and the second component.

[0008] In the gas analysis system according to one aspect of the present invention, the second modulation frequency is set to a frequency that is an integer multiple of the first modulation frequency.

[0009] Here, in the gas analysis system according to one aspect of the present invention, the detection unit includes a lock-in amplifier (19a) that detects the first component and the second component contained in the received light signal by using a first reference signal having the same frequency as the first modulation frequency.

[0010] Alternatively, in a gas analysis system according to one aspect of the present invention, the detection unit includes a first lock-in amplifier (19a) that detects the first component included in the received light signal by using a first reference signal having the same frequency as the first modulation frequency, and a second lock-in amplifier (19b) that detects the second component included in the received light signal by using a second reference signal having the same frequency as the second modulation frequency.

[0011] Alternatively, in the gas analysis system according to one aspect of the present invention, the detection unit includes a signal processing unit (23) that detects the first component and the second component by performing synchronous detection processing or fast Fourier transform processing on the received light signal using a first reference signal having the same frequency as the first modulation frequency.

[0012] In the gas analysis system according to one aspect of the present invention, the calculation unit determines the concentration of the measurement target gas based on a value obtained by dividing the first component by the second component.

[0013] In addition, in a gas analysis system according to one embodiment of the present invention, the optical modulation unit includes an optical amplifier (15) that amplifies the laser light emitted from the light-emitting element in accordance with a supplied current, and a drive unit (14) that supplies the current modulated at the second modulation frequency to the optical amplifier to drive the optical amplifier.

[0014] A method for gas analysis according to one aspect of the present invention includes: L A first step (S11) of emitting a laser beam wavelength-modulated at a second modulation frequency (f B), a third step (S13) of receiving the laser light that has passed through the gas to be measured to obtain a received light signal, a fourth step (S14) of detecting a first component, which is a component having a frequency that is n times (n is an integer of 2 or more) the first modulation frequency and a second component, which is a component having the same frequency as the second modulation frequency, contained in the received light signal, and a fifth step (S15) of determining the concentration of the gas to be measured based on the first component and the second component. Effect of the Invention

[0015] According to the present invention, it is possible to measure the concentration of a gas to be measured with high accuracy even if the shape of the absorption spectrum of the gas to be measured is asymmetric. [Brief description of the drawings]

[0016] [Figure 1] 1 is a block diagram showing a configuration of a main part of a gas analysis system according to a first embodiment of the present invention. [Diagram 2] 1 is a flowchart showing a gas analysis method according to a first embodiment of the present invention. [Diagram 3] FIG. 4 is a block diagram showing a configuration of a main part of a gas analysis system according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a block diagram showing a configuration of a main part of a gas analysis system according to a third embodiment of the present invention. [Diagram 5] FIG. 13 is a diagram showing a simulation result of the concentration dependency of the measurement result obtained by the embodiment of the present invention. [Figure 6] FIG. 1 is a diagram showing experimental results of the concentration dependence of measurement results obtained by a conventional method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a gas analysis system and a gas analysis method according to embodiments of the present invention will be described in detail with reference to the drawings. First, an overview of the present embodiments will be described, and then each embodiment will be described in detail.

[0018] 〔overview〕 The embodiment of the present invention makes it possible to measure the concentration of a target gas with high accuracy even if the shape of the absorption spectrum of the target gas is asymmetric. That is, even if a component (1f component) having the same frequency as the modulation frequency f of the laser light among components obtained by detecting the laser light transmitted through the target gas depends on the concentration of the target gas, the embodiment of the present invention makes it possible to measure the concentration of the target gas with high accuracy.

[0019] In wavelength modulation spectroscopy, a modulated (wavelength modulated) laser light is irradiated onto a gas to be measured, and the laser light that has passed through the gas to be measured is received by a light receiving element to obtain a received light signal P(t), which is expressed by the following equation (1).

[0020]

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[0021] In the above equation (1), P0 is the average power of the received signal. L is the intensity modulation depth of the laser light, and ω L is the modulation frequency of the laser light, and t is the time. L is the angular frequency [rad / s]. The modulation frequency [Hz] is f L Then, ω L =2πf L Since the modulation (wavelength modulation) of the laser light is performed by changing the current injected into the laser diode, the laser light is not only wavelength modulated but also intensity modulated. Furthermore, α(ν) is the absorbance at frequency ν, C is the gas concentration of the measurement target gas, and L is the optical path length (the optical path length of the part where the measurement target gas exists).

[0022] where 2α(ν)CL≪1,η L If we set it to ≪1, the above equation (1) can be transformed into the following equation (2).

[0023]

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[0024] If the absorption spectrum (α(ν)) of the gas to be measured is an ideal Lorentzian spectrum, the above formula (2) can be expressed by the following formula (3).

[0025]

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[0026] In the above formula (3), α0 is the absorption coefficient that indicates the magnitude of the absorption peak. Also, x is v Lm is the modulation amplitude of the oscillation frequency of the laser light, and δ ν If the full width at half maximum of the absorption spectrum is x=ν Lm / δ ν This is shown by:

[0027] When the above equation (3) is expanded into a Fourier series, the angular frequency ω L The amplitude of the component (1f component) is expressed by (4) below, and the angular frequency is 2ω L The amplitude of the component (2f component) is expressed by the following (5).

[0028]

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[0029] Here, k in the above formula (5) is expressed by the following formula (6) using the above-mentioned x.

[0030]

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[0031] The concentration of the gas to be measured is expressed by the above formula (5) with the angular frequency 2ω L It can be calculated using the amplitude of the component (2f component) of the angular frequency 2ω LThe amplitude of the component is maximum when k expressed by the above equation (6) is maximum. k is x=ν Lm / δ ν The maximum (k = 0.343) is reached when k ≒ 2.2. In other words, the modulation amplitude ν Lm is the full width at half maximum of the absorption spectrum δ ν When the angular frequency is about 2.2 times L The amplitude of the component becomes maximum.

[0032] Here, the above condition (the modulation amplitude v Lm is the full width at half maximum of the absorption spectrum δ ν It can be said that the condition where the signal-to-noise ratio (SN ratio: approximately 2.2 times) is the best condition for measuring the concentration of the target gas. In other words, the above condition is the optimal sweep condition (modulation condition) of the laser light irradiated to the target gas. In conventional gas analysis systems, the modulation amplitude v Lm is set.

[0033] As shown in the following equation (7), the angular frequency 2ω expressed by the above equation (5) L The amplitude P2 of the component (2f component) and the angular frequency ω expressed by the above equation (4) L By calculating the ratio of the amplitude P1 of the component (1f component) to the amplitude P1 of the component (1f component), it is possible to obtain a signal whose concentration is independent of the average power P0 of the received light signal.

[0034]

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[0035] If the absorption spectrum of the gas to be measured is ideal (for example, a Lorentzian absorption spectrum), its shape will be symmetrical with respect to the central frequency (central wavelength) of the absorption. Therefore, the angular frequency ω LThe amplitude P1 of the 1f component depends only on the average power of the received light signal, and does not depend on the concentration of the gas to be measured. However, the absorption spectrum of the gas to be measured actually has an asymmetric shape with respect to the center frequency (center wavelength). Then, the angular frequency ω L The amplitude P1 of the 1f component depends on the concentration of the measurement target gas, and the measurement accuracy of the concentration of the measurement target gas deteriorates.

[0036] Regarding α(ν) in the above formula (2), the central frequency of the laser light ν L0 When expanded in a Fourier series around, it can be rearranged as shown in the following equation (8).

[0037]

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[0038] However, ν L is the angular frequency ω L is the wavelength of the laser light that changes with time, and ν L =ν L0 +ν Lm sinω L From the above equation (8), the signal related to the concentration is expressed as the modulation frequency ω L It can be seen that P1 in the above equation (7) appears as an integer multiple of the angular frequency ω L Since the amplitude is the amplitude of the 1f component (1f component), it can be seen from the second term on the right side of the above equation (8) that this is the sum of a signal that depends on the amount of returned light of the laser light and the concentration.

[0039] Figure 6 shows the experimental results of the concentration dependence of the measurement results obtained by the conventional method. The graphs shown in Figures 6(a) and (b) have concentration on the horizontal axis and signal intensity on the vertical axis. Figure 6(a) shows the concentration dependence of the (P2 / P1) value and the (P2 / P0) value, and Figure 6(b) shows the concentration dependence of the (P1 / P0) value.

[0040] 6(a), the value of (P2 / P0) increases almost in proportion to the concentration of the target gas, but the value of (P2 / P1) is no longer proportional to the concentration of the target gas when the concentration of the target gas becomes high. Also, referring to FIG. 6(a), the value of (P1 / P0) is no longer proportional to the concentration of the target gas when the concentration of the target gas becomes high.

[0041] As described above, when the absorption spectrum of the measurement target gas has an asymmetric shape with respect to the center frequency (center wavelength), the inventor of the present application L It was found that the amplitude of the 1f component (1f component) becomes concentration-dependent, degrading the measurement accuracy of the concentration of the target gas. To prevent this degradation of measurement accuracy, it is necessary to obtain the amount of returned laser light (average power P0 of the received signal) by another method.

[0042] Here, the following two methods are conceivable for determining the amount of returned laser light. A method for measuring the concentration signal and the amount of return light by separating them in time. How to change the modulation conditions of a laser diode However, the former method cannot eliminate the effect of time-varying laser light caused by environmental changes (e.g., rainfall), and as a result, the measurement accuracy may be deteriorated. Also, the latter method is undesirable because it changes the optimal sweep conditions (modulation conditions) of the laser light mentioned above.

[0043] In the embodiment of the present invention, first, a laser light wavelength-modulated at a first modulation frequency is intensity-modulated at a second modulation frequency. Next, the laser light that has passed through the gas to be measured is received, and a first component, which is a component having a frequency n times (n is an integer of 2 or more) the first modulation frequency contained in the received light signal, and a second component, which is a component having the same frequency as the second modulation frequency, are detected. Then, the concentration of the gas to be measured is obtained based on the first and second components. The first component is a component that depends on the concentration of the gas to be measured, while the second component does not depend on the concentration of the gas to be measured even if the shape of the absorption spectrum of the gas to be measured is asymmetric. This makes it possible to measure the concentration of the gas to be measured with high accuracy even if the shape of the absorption spectrum of the gas to be measured is asymmetric.

[0044] [First embodiment] Gas Analysis System Fig. 1 is a block diagram showing the configuration of the main parts of a gas analysis system according to a first embodiment of the present invention. As shown in Fig. 1, the gas analysis system 1 of this embodiment includes a gas analyzer 10 and a signal processing device 20, and measures the concentration of a measurement target gas GS by using wavelength modulation spectroscopy.

[0045] Specifically, the gas analysis system 1 of this embodiment has a modulation frequency f L (first modulation frequency), and the modulation frequency f B The laser light intensity-modulated at (second modulation frequency) is irradiated onto the measurement target gas GS. Then, the second harmonic component (2f L component: 1st component) and modulation frequency f B The same frequency component (f B The concentration of the measurement target gas GS is measured based on the modulation frequency f B is the modulation frequency f L The frequency is set to a value different from an integer multiple of .

[0046] The gas analyzer 10 includes a signal generator 11, a laser driver circuit 12, a semiconductor laser 13 (light-emitting element), an amplifier driver circuit 14 (light modulation section, driver section), an optical amplifier 15 (light modulation section), lenses 16a and 16b, a photodetector 17 (light-receiving element), an amplifier 18, a lock-in amplifier 19a (detection section, first lock-in amplifier), and a lock-in amplifier 19b (detection section, second lock-in amplifier). ...3 for irradiating a gas GS to be measured with a laser beam, a signal receiving the laser beam via the gas GS to be measured, and a signal receiving a component (2f L Component, f B Detecting components, etc.

[0047] The signal generator 11 outputs a control signal for controlling the laser driver circuit 12 and the amplifier driver circuit 14, and a reference signal used in the lock-in amplifiers 19a and 19b under the control of the signal processor 20. The control signal output from the signal generator 11 to the laser driver circuit 12 and the reference signal output from the signal generator 11 to the lock-in amplifier 19a have a modulation frequency f L The control signal output from the signal generator 11 to the amplifier driver circuit 14 and the reference signal output from the signal generator 11 to the lock-in amplifier 19b have a modulation frequency f B These are signals that are synchronized with each other. As the signal generator 11, for example, an arbitrary waveform generator, a function generator, or the like can be used.

[0048] The laser driving circuit 12 outputs a driving signal for driving the semiconductor laser 13 based on the control signal output from the signal generator 11. The driving signal output from the laser driving circuit 12 is, for example, a DC current having a constant magnitude (amplitude) and a modulation frequency f L The signal is a superimposed alternating current of modulation frequency f L The alternating current may be, for example, sinusoidal or non-sinusoidal.

[0049] The semiconductor laser 13 is driven by a drive signal output from the laser drive circuit 12, and emits a laser beam to be irradiated onto the measurement target gas GS. The laser beam emitted from the semiconductor laser 13 has, for example, a modulation center wavelength set to the center wavelength of the absorption spectrum of the measurement target gas GS, and a wavelength modulation width (modulation frequency f L ) is about 2.2 times the full width at half maximum of the absorption spectrum of the measurement target gas GS. As the semiconductor laser 13, for example, a QCL (Quantum Cascade Laser) or an ICL (Interband Cascade Laser) can be used.

[0050] The amplifier driver 14 outputs a drive signal for driving the optical amplifier 15 based on the control signal output from the signal generator 11. The drive signal output from the amplifier driver 14 is, for example, a DC current having a constant magnitude (amplitude) and a modulation frequency f B The signal is a superimposed alternating current of modulation frequency f B The alternating current may be, for example, sinusoidal or non-sinusoidal.

[0051] The optical amplifier 15 amplifies the laser light emitted from the semiconductor laser 13 in response to the current supplied from the amplifier driver circuit 14. The current supplied from the amplifier driver circuit 14 has a constant amplitude and a constant period (modulation frequency f B Therefore, the laser light emitted from the optical amplifier 15 changes with a modulation frequency f B The light is intensity-modulated by the optical amplifier 15. As the optical amplifier 15, for example, an optical fiber amplifier (OFA) or a semiconductor optical amplifier (SOA) can be used.

[0052] The lens 16a converts the laser light emitted from the optical amplifier 15 into parallel light. A collimator lens can be used as the lens 16a. Note that, instead of the lens 16a, other optical elements (for example, a parabolic mirror) can be used as long as they can convert the laser light emitted from the optical amplifier 15 into parallel light.

[0053] The laser light collimated by the lens 16a is irradiated onto the measurement target gas GS. Of the laser light irradiated onto the measurement target gas GS, the laser light that passes through the measurement target gas GS is reflected by a scatterer SM such as a wall, and then passes through the measurement target gas GS again to enter the lens 16b. The distance between the gas analyzer 10 and the scatterer SM may be any distance, but is set to, for example, about 100 m or less.

[0054] The lens 16b focuses the laser light transmitted through the measurement target gas GS onto the photodetector 17. A focusing lens can be used as the lens 16b. Note that, instead of the lens 16b, other optical elements (e.g., a parabolic mirror) can be used as long as the laser light transmitted through the measurement target gas GS can be focused onto the photodetector 17. The photodetector 17 converts the laser light focused by the lens 16b into an electrical signal and outputs it as a light receiving signal. For example, a PD (PhotoDiode) can be used as the photodetector 17.

[0055] The amplifier 18 amplifies the light-receiving signal output from the photodetector 17. The amplification factor of the amplifier 18 is set to an appropriate amplification factor, for example, according to the intensity of the laser light incident on the photodetector 17. When the photodetector 17 is a PD, the amplifier 18 can be an IV conversion circuit that converts a photocurrent output from the photodetector 17 as the light-receiving signal into a voltage.

[0056] The lock-in amplifiers 19a and 19b perform phase sensitive detection (PSD) using the reference signal output from the signal generator 11 to detect a specific frequency component from the received light signal amplified by the amplifier 18. Specifically, the lock-in amplifier 19a detects a 2f L The lock-in amplifier 19a detects the f component (first component) contained in the received light signal amplified by the amplifier 18 using a reference signal (second reference signal) output from the signal generator 11. B Detect the component (second component).

[0057] The signal processing device 20 includes a calculation unit 21 and an output unit 22, controls the operation of the gas analyzer 10, and measures the concentration of the measurement target gas GS using the detection results (detection results of the lock-in amplifiers 19a and 19b, etc.) of the gas analyzer 10. The signal processing device 20 is realized by a computer such as a personal computer, for example.

[0058] The calculation unit 21 calculates the concentration of the measurement target gas GS using the detection results of the gas analyzer 10 (detection results of the lock-in amplifiers 19a and 19b). L f detected by lock-in amplifier 19b for the component B The concentration of the measurement target gas GS is measured based on the ratio of the components. The reason for measuring the concentration of the measurement target gas GS based on the ratio is to reduce the influence of fluctuations in the amount of received laser light caused by factors other than the measurement target gas.

[0059] The output unit 22 outputs the calculation result of the calculation unit 21 to the outside. For example, the output unit 22 outputs information indicating the concentration of the measurement target gas GS measured by the calculation unit 21. In addition to the information indicating the concentration of the measurement target gas GS, the output unit 22 outputs L Information showing ingredients, f BThe output unit 22 may output information indicating the components and various other information. The output unit 22 may output a signal indicating this information to the outside, or may output this information to the outside by displaying it.

[0060] The calculation unit 21 and the output unit 22 provided in the signal processing device 20 are realized by a program for realizing these functions being executed by a CPU (Central Processing Unit) provided in a computer. In other words, the calculation unit 21 and the output unit 22 provided in the signal processing device 20 are realized by cooperation between software and hardware resources. Note that the signal processing device 20 may be realized using hardware such as a Field-Programmable Gate Array (FPGA), a Large Scale Integration (LSI), or an Application Specific Integrated Circuit (ASIC).

[0061] In the gas analysis system 1 of this embodiment, a light reception signal P(t) obtained by receiving the laser light transmitted through the measurement target gas GS by the photodetector 17 is expressed by the following equation (9).

[0062]

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[0063] In the above formula (9), η B is the intensity modulation depth by the optical amplifier 15. L =2πf L and ω B =2πf B The modulation frequency ω contained in the laser light emitted from the optical amplifier 15 is B The signal amplitude of the component with the same frequency as B Then, the signal amplitude P B is expressed by the following equation (10).

[0064]

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[0065] From the above formula (10), the intensity modulation degree η B By changing the signal amplitude P B It is clear that it is possible to control

[0066] The calculation unit 21 of the signal processing device 20 calculates 2f L Component amplitude P2 and f B Component amplitude P B By calculating the ratio of this to the average power P0 of the received light signal, a signal with a concentration that is independent of the average power P0 of the received light signal is obtained.

[0067]

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[0068] Even if the absorption spectrum of the measurement target gas GS is asymmetric with respect to the center frequency (center wavelength), B The amplitude of the component does not depend on the concentration of the measurement target gas GS. Therefore, in this embodiment, even if the shape of the absorption spectrum of the measurement target gas GS is asymmetric, the concentration of the measurement target gas GS can be measured with high accuracy.

[0069] Gas Analysis Method Fig. 2 is a flowchart showing a gas analysis method according to a first embodiment of the present invention. The process of the flowchart shown in Fig. 2 is started, for example, when a user issues an instruction to start measurement to the gas analysis system 1. The process of the flowchart shown in Fig. 2 may be repeatedly performed at predetermined time intervals.

[0070] When the measurement of the target gas GS is started, first, the signal generator 11 of the gas analyzer 10 is controlled by the signal processing device 20. As a result, the signal generator 11 transmits a modulation frequency f L At the same time, the signal generator 11 outputs a control signal having a modulation frequency fL The reference signal having the modulation frequency f L The control signal having the signal sig- nal and the reference signal are synchronous.

[0071] The signal generator 11 also outputs a modulation frequency f B At the same time, the signal generator 11 outputs a control signal having a modulation frequency f B The reference signal having the modulation frequency f B The control signal having the signal sig- nal and the reference signal are synchronous.

[0072] When a control signal from the signal generator 11 is input to the laser driver circuit 12, the laser driver circuit 12 outputs a drive signal for driving the semiconductor laser 13. When a control signal from the signal generator 11 is input to the amplifier driver circuit 14, the amplifier driver circuit 14 outputs a drive signal for driving the optical amplifier 15.

[0073] When a drive signal from the laser drive circuit 12 is supplied to the semiconductor laser 13, the semiconductor laser 13 emits a laser beam having a modulation frequency f L When the laser light emitted from the semiconductor laser 13 enters the optical amplifier 15, the laser light is modulated at a modulation frequency f by a driving current supplied from the amplifier driving circuit 14 to the optical amplifier 15. B The intensity is modulated by (step S12: second step).

[0074] The laser light emitted from the optical amplifier 15 (modulation frequency f B The laser light (intensity-modulated by ) is converted into a parallel beam by lens 16a and then irradiated onto the measurement target gas GS. Of the laser light irradiated onto the measurement target gas GS, the laser light that passes through the measurement target gas GS is reflected by a scatterer SM such as a wall, and then passes through the measurement target gas GS again to enter lens 16b.

[0075] The laser light is collected by the lens 16b and then converted into an electrical signal by the photodetector 17. The electrical signal converted by the photodetector 17 is output from the photodetector 17 as a received light signal (Step S13: third step). The received light signal output from the photodetector 17 is amplified by the amplifier 18 at a constant amplification factor and then input to the lock-in amplifiers 19a and 19b, respectively.

[0076] In the lock-in amplifier 19a, a reference signal (modulation frequency f L (a reference signal having a value of 2f L The lock-in amplifier 19b detects the reference signal (modulation frequency f B (a reference signal having a value of f B The component (second component) is detected (step S14: fourth step).

[0077] 2f detected by lock-in amplifier 19a L Component (first component) and f detected by lock-in amplifier 19b B The component (second component) is output to the signal processing device 20. The signal processing device 20 has a calculation unit 21 that calculates the concentration of the measurement target gas GS. Specifically, as shown in the above-mentioned formula (11), the 2f L The amplitude P2 of the first component and the f detected by the lock-in amplifier 19b B Amplitude P of the component (second component) B A calculation is then performed to obtain the ratio of the concentration of the measurement target gas GS to the concentration of the measurement target gas GS (step S15: fifth step).

[0078] As described above, in this embodiment, first, the modulation frequency f L The laser light is wavelength-modulated at a modulation frequency of f L After intensity modulation with , the laser light is irradiated onto the measurement target gas GS. Next, the laser light that has passed through the measurement target gas GS is received, and the 2f L Components of and fB Then, 2f L Components of and f B The concentration of the measurement target gas GS is calculated based on the components of 2f. L The components of are dependent on the concentration of the target gas GS, while f B The component does not depend on the concentration of the target gas GS even if the shape of the absorption spectrum of the target gas GS is asymmetric. This makes it possible to measure the concentration of the target gas GS with high accuracy even if the shape of the absorption spectrum of the target gas GS is asymmetric.

[0079] In addition, in this embodiment, since the concentration signal and the amount of return light of the laser light (average power P0 of the received light signal) are measured simultaneously, it is possible to eliminate the influence of time-dependent changes in the laser light due to environmental changes (e.g., rainfall). Also, in this embodiment, since the optimal sweep conditions (modulation conditions) of the laser light are not changed, it is possible to measure the concentration of the measurement target gas GS under the best signal-to-noise ratio, thereby achieving a wide dynamic range.

[0080] Second Embodiment Gas Analysis System Fig. 3 is a block diagram showing the configuration of the main parts of a gas analysis system according to a second embodiment of the present invention. In Fig. 3, the same components as those shown in Fig. 1 are denoted by the same reference numerals. A gas analysis system 2 of this embodiment has a configuration in which the gas analysis device 10 of the gas analysis system 1 shown in Fig. 1 is replaced with a gas analysis device 10A.

[0081] The gas analyzer 10A does not include the lock-in amplifier 19b included in the gas analyzer 10 shown in FIG. B The modulation frequency f LThat is, in gas analyzer 10A, the frequency of the control signal output from signal generator 11 to amplifier driver circuit 14 is set to an integer multiple of the frequency of the control signal output from signal generator 11 to laser driver circuit 12 and the frequency of the reference signal output from signal generator 11 to lock-in amplifier 19a. Gas analysis system 2 including such gas analyzer 10A aims to reduce costs by omitting lock-in amplifier 19b.

[0082] In this embodiment, the lock-in amplifier 19a receives the reference signal (modulation frequency f L (a reference signal having a value of 2f L Component (first component) and f B component (second component) is detected. Here, the modulation frequency f B is the modulation frequency f L Since the frequency is set to an integer multiple of , the 2f L Component (first component) and f B It is possible to detect the first component (the second component).

[0083] Gas Analysis Method The gas analysis system 2 of this embodiment is different from the gas analysis system 1 of the first embodiment in that the lock-in amplifier 19b is omitted, and basically, the gas concentration of the measurement target gas GS is measured by the same gas analysis method as in the first embodiment. Therefore, a detailed description of the gas analysis method is omitted.

[0084] In this embodiment, as in the first embodiment, first, the modulation frequency f L The laser light is wavelength-modulated at a modulation frequency of f L After intensity modulation with , the laser light is irradiated onto the measurement target gas GS. Next, the laser light that has passed through the measurement target gas GS is received, and the 2f L Components of and f B Then, 2f L Components of and f BThe concentration of the measurement target gas GS is calculated based on the components of the measurement target gas GS. This makes it possible to measure the concentration of the measurement target gas GS with high accuracy even if the shape of the absorption spectrum of the measurement target gas GS is asymmetric.

[0085] Also in this embodiment, the influence of the time change of the laser light due to the environmental change (for example, rainfall) can be eliminated. In addition, the concentration of the measurement target gas GS can be measured under the best signal-to-noise ratio, thereby realizing a wide dynamic range.

[0086] Third Embodiment Gas Analysis System Fig. 4 is a block diagram showing the main configuration of a gas analysis system according to a third embodiment of the present invention. In Fig. 4, the same components as those shown in Fig. 1 are denoted by the same reference numerals. A gas analysis system 3 of this embodiment is configured such that the gas analyzer 10 of the gas analysis system 1 shown in Fig. 1 is replaced with a gas analyzer 10B, and the signal processing device 20 is replaced with a signal processing device 20A.

[0087] The gas analyzer 10B is a gas analyzer 10 shown in FIG. 1 without the lock-in amplifiers 19a and 19b. B is the modulation frequency f L The modulation frequency f L 1. The signal processing device 20A has a configuration in which a signal processing unit 23 (detection unit) is added to the signal processing device 20 shown in Fig. 1. The gas analysis system 3 including such a gas analyzer 10B and signal processing device 20A aims to further reduce costs by omitting the lock-in amplifiers 19b, 19b.

[0088] In this embodiment, the reference signal (modulation frequency f L A reference signal having the above-mentioned characteristic is input to the signal processing device 20A. A signal output from an amplifier 18 included in the gas analyzing device 10B is also input to the signal processing device 20A.

[0089] The signal processing unit 23 of the signal processing device 20A receives the reference signal (with a modulation frequency f L A synchronous detection process is performed using a reference signal having a frequency of 2f L Components of and f B The signal processing unit 23 of the signal processing device 20A performs FFT (Fast Fourier Transform) processing to detect the 2f component included in the signal output from the amplifier 18. L Components of and f B The above components may also be detected.

[0090] Here, the signal processing unit 23 is realized by executing a program for realizing the functions of the signal processing unit 23 on a CPU provided in a computer. That is, the signal processing unit 23 is realized by cooperation between software and hardware resources. Note that the signal processing device 20A may be realized by using hardware such as an FPGA, an LSI, or an ASIC.

[0091] Gas Analysis Method The gas analysis system 3 of this embodiment is different from the gas analysis system 1 of the first embodiment in that the lock-in amplifiers 19a and 19b are omitted, and basically, the gas concentration of the measurement target gas GS is measured by the same gas analysis method as in the first embodiment. Therefore, a detailed description of the gas analysis method is omitted.

[0092] In this embodiment, as in the first embodiment, first, the modulation frequency f L The laser light is wavelength-modulated at a modulation frequency of f L After intensity modulation with , the laser light is irradiated onto the measurement target gas GS. Next, the laser light that has passed through the measurement target gas GS is received, and the 2f L Components of and f B Then, 2f L Components of and f BThe concentration of the measurement target gas GS is calculated based on the components of the measurement target gas GS. This makes it possible to measure the concentration of the measurement target gas GS with high accuracy even if the shape of the absorption spectrum of the measurement target gas GS is asymmetric.

[0093] Also in this embodiment, the influence of the time change of the laser light due to the environmental change (for example, rainfall) can be eliminated. In addition, the concentration of the measurement target gas GS can be measured under the best signal-to-noise ratio, thereby realizing a wide dynamic range.

[0094] [Simulation results] 5A to 5C are diagrams showing the results of a simulation of the concentration dependency of the measurement results obtained by the embodiment of the present invention. In the graphs shown in Fig. 5(a) to (c), the horizontal axis represents concentration and the vertical axis represents signal intensity.

[0095] Figure 5(a) shows the L = 1.0 [kHz], f B That is, the simulation results shown in FIG. 5(a) are obtained when ω B ≠mω L (m is an integer) is satisfied, and the measurement results are simulated for the gas analysis system 1 and the gas analysis method according to the first embodiment.

[0096] Figure 5(b) shows the L = 1.0 [kHz], f B That is, the simulation results shown in FIG. 5(b) are obtained when ω B =mω L (m is an integer) is satisfied (when m=11), and the measurement results are simulated for the gas analysis system 2 and the gas analysis method according to the second embodiment.

[0097] Figure 5(c) shows the L = 1.0 [kHz], f BThe simulation results shown in FIG. 5(c) are for ω B =(n / m)ω L (m, n are integers) is satisfied (when m=2, n=1). This simulation result also simulates the measurement results of the gas analysis system 2 and the gas analysis method according to the second embodiment.

[0098] In FIG. 5(a) to (c), the graphs shown by solid lines are the (P2 / P B ) is a graph showing the concentration dependence of 2f L Component amplitude P2 and f B Component amplitude P B This is a graph showing the concentration dependence of the ratio of P2 / P1 to P2. In contrast, the dashed line shows the concentration dependence of (P2 / P1) that was previously calculated. L Component amplitude P2 and f L 13 is a graph showing the concentration dependence of the ratio of the amplitude P1 of the component.

[0099] 5(a) to (c), the value of (P2 / P1) increases almost in proportion to the concentration of the measurement target gas GS when the concentration of the measurement target gas GS is low. However, when the concentration of the measurement target gas GS becomes high (approximately 6×10 4 [ppm m]), the value of (P2 / P1) decreases as the concentration of the measurement target gas GS increases. B ) increases almost in proportion to the concentration of the target gas GS, whether the concentration of the target gas GS is low or high. This confirms that the present embodiment has an improved concentration dependency compared to the conventional embodiment.

[0100] Although the gas analysis system and the gas analysis method according to the embodiment of the present invention have been described above, the present invention is not limited to the above embodiment and can be freely modified within the scope of the present invention. For example, in the above-mentioned embodiment, the modulation frequency fL The double wave component (2f L In this example, the concentration of the target gas GS was measured based on the modulation frequency f L The concentration of the measurement target gas GS may be measured based on the n-th harmonic component (n is an integer of 3 or more) of the above.

[0101] In the above embodiment, an example has been described in which the intensity of the laser light is modulated by the drive current supplied from the amplifier drive circuit 14 to the optical amplifier 15. However, the intensity modulation of the laser light only needs to be controlled independently of the wavelength modulation of the laser light, and is not limited to the above method of controlling the drive current supplied from the amplifier drive circuit 14 to the optical amplifier 15. For example, the intensity modulation of the laser light may be performed by physically intermittently cutting off the laser light using an optical chopper. [Explanation of symbols]

[0102] 1~3 Gas analysis system 13 Semiconductor laser 14 Amplifier driver circuit 15 Optical Amplifier 17 Photodetector 19a Lock-in amplifier 19b Lock-in amplifier 21 Arithmetic section 23 Signal Processing Section

Claims

1. a light emitting element that emits a laser beam whose wavelength is modulated at a first modulation frequency; an optical modulation unit that intensity-modulates the laser light emitted from the light emitting element at a second modulation frequency; a light receiving element that receives the laser light that has passed through the gas to be measured; a detection unit that detects a first component, which is a component having a frequency that is n times (n is an integer of 2 or more) the first modulation frequency, included in the light receiving signal output from the light receiving element, and a second component, which is a component having the same frequency as the second modulation frequency; a calculation unit that calculates a concentration of the measurement target gas based on the first component and the second component; A gas analysis system comprising:

2. 2. The gas analysis system according to claim 1, wherein the second modulation frequency is set to a frequency that is an integer multiple of the first modulation frequency.

3. 3. The gas analysis system according to claim 2, wherein the detection unit includes a lock-in amplifier that detects the first component and the second component contained in the received light signal by using a first reference signal having the same frequency as the first modulation frequency.

4. the detection unit includes a first lock-in amplifier configured to detect the first component included in the received light signal by using a first reference signal having the same frequency as the first modulation frequency; a second lock-in amplifier that detects the second component included in the received light signal by using a second reference signal having the same frequency as the second modulation frequency; The gas analysis system of claim 1 .

5. 2. The gas analysis system according to claim 1, wherein the detection unit includes a signal processing unit that detects the first component and the second component by performing synchronous detection processing or fast Fourier transform processing on the received light signal using a first reference signal having the same frequency as the first modulation frequency.

6. The gas analysis system according to claim 1 , wherein the calculation unit determines the concentration of the measurement target gas based on a value obtained by dividing the first component by the second component.

7. The optical modulation unit includes an optical amplifier that amplifies the laser light emitted from the light emitting element in accordance with a supplied current; a driver that supplies a current modulated at the second modulation frequency to the optical amplifier to drive the optical amplifier; 7. A gas analysis system according to claim 1, comprising:

8. A first step of emitting a laser beam wavelength-modulated at a first modulation frequency; a second step of intensity modulating the laser light at a second modulation frequency; a third step of receiving the laser light that has passed through the gas to be measured and obtaining a light receiving signal; a fourth step of detecting a first component, which is a component having a frequency n times (n is an integer equal to or greater than 2) the first modulation frequency included in the received light signal, and a second component, which is a component having the same frequency as the second modulation frequency; a fifth step of determining a concentration of the measurement target gas based on the first component and the second component; A gas analysis method comprising the steps of:

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