Gas analysis meter and method for analyzing gas

Abstract

To provide a gas analysis meter and a method for analyzing gas which can improve the accuracy of measuring the concentration of gas.SOLUTION: A gas analysis meter 10 includes an operation unit 181. The operation unit 181 calculates the intensities of a plurality of concentration signals based on the intensity of one concentration signal based on the intensity of one frequency composition of return light 102, which is multi-modulated measurement light 101 having returned through a measurement target gas 103 or each of the intensities of a plurality of frequency components of the return light, and calculates the measured value of the concentration of the measurement target gas 103 on the basis of the intensities of the plurality of concentration signals.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a gas analyzer and a gas analysis method.

Background Art

[0002] Conventionally, as described in Patent Document 1, an apparatus for measuring gas concentration using a laser beam is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Improvement in the measurement accuracy of gas concentration is required.

[0005] The present disclosure has been made in view of the above points, and an object thereof is to provide a gas analyzer and a gas analysis method capable of improving the measurement accuracy of gas concentration.

Means for Solving the Problems

[0006] (1) The gas analyzer according to some embodiments includes an arithmetic unit. The arithmetic unit calculates the intensity of one concentration signal based on the intensity of one frequency component of the return light that the multiply-modulated measurement light has passed through the measurement target gas and returned, or calculates the intensities of a plurality of concentration signals based on the intensities of the plurality of frequency components of the return light. The arithmetic unit calculates a measured value of the concentration of the measurement target gas based on the intensity of the one concentration signal or the intensities of the plurality of concentration signals.

[0007] The gas analyzer according to the present disclosure can, by using a double-modulated laser beam, make it difficult to reduce the intensity of the return light amount signal when the gas concentration increases, while maintaining the measurement accuracy of the gas concentration as compared with the case of using a single-modulated laser beam. By being able to suppress the amount of decrease in the intensity of the return light amount signal, the return light amount signal is less likely to decrease even when the gas concentration is high. As a result, even when the gas concentration is high, a state where the cause of the decrease in the return light amount signal cannot be determined is avoided.

[0008] Also, the gas analyzer according to the present disclosure can, by using a double-modulated laser beam, acquire a concentration signal so that the linearity of the calibration curve becomes high. By increasing the linearity of the calibration curve, a wide dynamic range measurement can be performed. As a result, the measurement accuracy of a wide range of gas concentrations is improved as compared with the case of using a single-modulated laser beam.

[0009] Also, the gas analyzer according to the present disclosure can, by using a double-modulated laser beam, acquire a concentration signal that avoids the frequency of a specific noise. By being able to acquire a concentration signal that avoids the frequency of a specific noise, the measurement accuracy of the gas concentration is improved.

[0010] (2) In the gas analyzer according to (1) above, the calculation unit may calculate a plurality of candidate values that are candidates for the measured value of the concentration of the gas to be measured based on the intensity of each of the plurality of concentration signals. The calculation unit may calculate the concentration of the gas to be measured based on the plurality of candidate values.

[0011] The gas analyzer according to the present disclosure can appropriately select high-sensitivity measurement and wide dynamic range measurement or avoid the frequency of a specific noise by calculating a plurality of candidate values based on the intensities of a plurality of frequency components. As a result, the measurement accuracy of the gas concentration is improved.

[0012] (3) In the gas analyzer according to (2) above, the calculation unit may select one of the plurality of candidate values as a measurement value of the concentration of the gas to be measured based on the signal-to-noise ratio of the concentration signal. By selecting a measurement value of the gas concentration from among the plurality of candidate values, the measurement accuracy of the gas concentration can be improved.

[0013] (4) In the gas analyzer according to (2) above, the calculation unit may calculate, as a measurement value of the concentration of the gas to be measured, an average value of at least two of the plurality of candidate values. By calculating the average value of the plurality of candidate values, a situation in which the measurement accuracy is significantly deteriorated due to an incorrect selection from the plurality of candidate values can be avoided. As a result, the measurement accuracy of the gas concentration is improved.

[0014] (5) The gas analyzer according to any one of (1) to (4) above may further include a light source that emits the measurement light and is configured to be able to set the modulation frequency of the measurement light. By configuring the light source to be able to set the modulation frequency, the measurement light is appropriately modulated according to the component to be measured. As a result, the measurement accuracy of the gas concentration is improved.

[0015] (6) A gas analysis method according to some embodiments includes a gas analyzer calculating an intensity of one concentration signal based on an intensity of one frequency component of return light that has passed through the gas to be measured and returned after being multi-modulated, or intensities of a plurality of concentration signals based on intensities of a plurality of frequency components of the return light, and calculating a measurement value of the concentration of the gas to be measured based on the intensity of the one concentration signal or the intensities of the plurality of concentration signals.

Advantages of the Invention

[0016] According to the gas analyzer and gas analysis method according to the present disclosure, the measurement accuracy of the gas concentration is improved.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

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Figure 5

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Figure 10

Figure 11

Mode for Carrying Out the Invention

[0018] (Comparative Example) The gas analyzer 90 according to the comparative example measures the concentration of the gas to be measured 903 based on the absorbance of the laser light transmitted through the gas to be measured 903. The method of measuring the gas concentration based on the absorbance of the laser light is also referred to as Wavelength Modulation Spectroscopy (WMS).

[0019] When the gas analyzer 90 measures the concentration of the gas to be measured 903 by WMS, it transmits the laser beam wavelength-modulated at a single frequency f through the gas to be measured 903, thereby obtaining a signal containing information on the concentration of the gas to be measured 903. The concentration of the gas to be measured 903 is proportional to the intensity of the frequency component of 2f, which is the second harmonic of the single modulation frequency, among the frequency components of the laser beam transmitted through the gas to be measured 903.

[0020] As shown in FIG. 1, the gas analyzer 90 according to the comparative example includes a waveform generator 91, a drive power supply 921, a light source 922, a driver 931, an optical amplifier 932, lenses 941 and 942, a photodetector 95, an amplifier 96, a lock-in amplifier (LIA) 97, and a signal processor 98.

[0021] The gas analyzer 90 emits the measurement light 901 from the lens 941 toward the gas to be measured 903. The measurement light 901 is light that is single-modulated at a single frequency.

[0022] The waveform generator 91 generates a signal waveform of the modulation frequency and outputs it to the drive power supply 921 and the LIA 97. The drive power supply 921 outputs a drive signal based on the signal waveform of the modulation frequency input from the waveform generator 91 to drive the light source 922. The drive signal is a signal in which an AC signal of a sine wave of the modulation frequency is superimposed on a DC signal. The light source 922 emits a laser beam whose frequency is modulated according to the signal waveform of the modulation frequency. The light source 922 is controlled such that the center wavelength of the modulation of the laser beam becomes the center wavelength of the absorption spectrum of the gas to be measured 903, and the wavelength modulation width of the laser beam becomes 2.2 times the FWHM of the absorption spectrum of the gas to be measured 903.

[0023] The optical amplifier 932 amplifies the laser beam emitted from the light source 922. The driver 931 drives the optical amplifier 932. The lens 941 converts the laser beam amplified by the optical amplifier 932 into parallel light and emits it as the measurement light 901 toward the gas to be measured 903.

[0024] After the measurement light 901 is emitted from the lens 941, it passes through the gas to be measured 903 and is reflected or scattered by a scatterer 904 such as a wall. The reflected or scattered light returns to the gas analyzer 90 through the gas to be measured 903. The light that returns to the gas analyzer 90 is also referred to as the return light 902. The return light 902 is incident on the lens 942. The gas analyzer 90 detects the return light 902 incident on the lens 942 with the photodetector 95, analyzes the frequency spectrum of the return light 902, and measures the concentration of the gas to be measured 903. The distance from the lenses 941 and 942 to the scatterer 904 is represented by L.

[0025] The lens 942 focuses the return light 902, which is the laser light that has passed through the gas to be measured 903 and is reflected or scattered by the scatterer 904 and returned to the gas analyzer 90, onto the photodetector 95. The photodetector 95 converts the return light 902 into an electrical signal and outputs it as a received light signal. The amplifier 96 amplifies the received light signal input from the photodetector 95 and outputs it as an amplified signal. The amplification factor of the signal in the amplifier 96 is appropriately set according to the intensity of the return light 902 incident on the photodetector 95.

[0026] The LIA 97 detects specific frequency components from the amplified signal using the signal waveform of the modulation frequency input from the waveform generator 91. Specifically, the LIA 97 detects the fundamental wave component and the second harmonic component of the modulation frequency from the amplified signal. The fundamental wave component of the modulation frequency is represented by P f and the second harmonic component of the modulation frequency is represented by P 2f .

[0027] The signal processing device 98 calculates the concentration of the gas to be measured 903 based on the fundamental wave component and the second harmonic component detected by the LIA 97. Specifically, the signal processing device 98 calculates the value obtained by dividing the intensity of the second harmonic component by the intensity of the fundamental wave component as the concentration signal. The concentration signal is represented by P C . The signal processing device 98 calculates the concentration of the gas to be measured 903 based on the calibration curve representing the relationship between the concentration signal and the concentration of the gas to be measured 903.

[0028] The gas analyzer 90 according to the comparative example measures the concentration of the gas to be measured 903 by executing the procedure of the flowchart shown in FIG. 2. The gas analyzer 90 emits laser light modulated at the modulation frequency f from the lens 941 (step S91). The gas analyzer 90 condenses the laser light that has passed through the gas to be measured 903 and returned with the lens 942 and receives it with the photodetector 95 (step S92). The gas analyzer 90 obtains, from the amplified signal obtained by amplifying the received signal, by the LIA 97, the component (P f ) of the first harmonic (f) of the modulation frequency and the component (P 2f ) of the second harmonic (2f) of the modulation frequency (step S93). The gas analyzer 90 calculates the concentration signal (P 2f ) by calculating P f / P C (step S94). The gas analyzer 90 calculates the concentration of the gas to be measured 903 based on the concentration signal and the calibration curve (step S95).

[0029] When measuring the concentration of the gas to be measured 903 with the gas analyzer 90 according to the comparative example, the following three problems may occur.

[0030] The first problem is the decrease in the intensity of the return light 902. As shown in FIG. 3, the higher the concentration of the gas to be measured 903, the lower the intensity of the return light 902. The horizontal axis of the graph in FIG. 3 represents the gas concentration. The vertical axis represents the intensity of the return light 902. The horizontal axis and the vertical axis are logarithmic axes. The gas concentration corresponds to the value obtained by integrating the concentration of the gas to be measured 903 in each part of the optical path through which the laser light passes along the optical path. The higher the gas concentration, the lower the intensity of the return light 902.

[0031] As described above, the intensity of the return light 902 decreases as the gas concentration increases. When the intensity of the return light 902 significantly decreases, it may become difficult for the gas analyzer 90 to detect the return light 902. When the gas concentration has increased due to gas leakage, the gas analyzer 90 may not be able to detect the gas leakage because it cannot detect the return light 902. In particular, when the gas analyzer 90 is used outdoors, there is a risk that it cannot distinguish between the case where the measurement light 901 is emitted toward the air or the like where the scatterer 904 does not exist and the case where the intensity of the return light 902 has significantly decreased due to the high gas concentration.

[0032] Also, in order to distinguish between the case where the scatterer 904 does not exist and the case where the gas concentration is high, it is conceivable to emit the measurement light 901 at a frequency of an off-peak that deviates from the absorption spectrum of the measurement target gas 903. However, the measurement time increases by changing the frequency and performing the measurement.

[0033] The second problem is the deterioration of the linearity of the calibration curve. As shown in FIG. 4, the calibration curve representing the relationship between the gas concentration and the concentration signal deviates from the straight line represented by the broken line. That is, the linearity of the calibration curve deteriorates. The horizontal axis of the graph in FIG. 4 represents the gas concentration. The vertical axis represents the concentration signal. The horizontal axis and the vertical axis are logarithmic axes. As a cause of the deterioration of the linearity of the calibration curve, for example, it is considered that the influence of the waveform distortion increases as the gas concentration increases. The deterioration of the linearity of the calibration curve causes a decrease in the measurement accuracy of the concentration of the measurement target gas 903.

[0034] The third problem is the influence due to the vibration of the scatterer 904. When the wall or pipe, etc., which is the scatterer 904, vibrates, the component of the vibration frequency of the scatterer 904 is superimposed on the return light 902. When the vibration frequency of the scatterer 904 is close to the modulation frequency of the laser light, the concentration signal is affected by the vibration of the scatterer 904. As a result, the measurement accuracy of the concentration of the measurement target gas 903 decreases.

[0035] As described above, there may be a problem when measuring the concentration of the gas 903 to be measured by the gas analyzer 90 according to the comparative example. It is required to achieve both measurement when the gas concentration is high and improvement or maintenance of measurement accuracy.

[0036] The gas analyzer 10 (see FIG. 5) according to the present embodiment can achieve both measurement when the gas concentration is high and improvement or maintenance of measurement accuracy. Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings.

[0037] (Overview of the gas analyzer 10 according to the present disclosure) The gas analyzer 10 according to the present disclosure measures the concentration of the gas 103 to be measured based on the absorbance of the laser light transmitted through the gas 103 to be measured using wavelength modulation spectroscopy (WMS). The gas analyzer 10 transmits laser light wavelength-modulated at a plurality of modulation frequencies through the gas 103 to be measured, thereby acquiring the frequency spectrum of the light that has passed through and returned from the gas 103 to be measured. The plurality of modulation frequencies are f L1 ~f Ln and are assumed to be represented. n is a natural number of 2 or more.

[0038] The laser light wavelength-modulated at a plurality of modulation frequencies includes components of frequencies represented by a linear combination of each modulation frequency. The frequency represented by the linear combination of each modulation frequency is also referred to as the linear combination frequency. The linear combination frequency includes a plurality of frequencies. Therefore, the frequency spectrum of the light that has passed through and returned from the gas 103 to be measured includes a plurality of frequency components.

[0039] The gas analyzer 10 acquires the intensity of one frequency component among the plurality of frequency components of the frequency spectrum of the light that has passed through and returned from the gas 103 to be measured as the intensity (P opt ) of the return light quantity signal. As the frequency of the component corresponding to the return light quantity signal, one of the plurality of modulation frequencies (f L1 ~f Ln ) may be selected. Also, as the frequency of the component corresponding to the return light quantity signal, one of the frequencies included in the linear combination frequency may be selected.

[0040] The gas analyzer 10 acquires, as signals of one or more frequency components, signals including information regarding the concentration of the measurement target gas 103 from among the frequency spectra of the light that has passed through and returned from the measurement target gas 103. The information regarding the concentration of the measurement target gas 103 is also referred to as concentration information. The intensity of the signal including the concentration information is P’ C1 ~P’ Cm and is assumed to be represented thereby. m is a natural number of 1 or more and may be determined independently of the value of n.

[0041] The gas analyzer 10 calculates the ratio of the intensity of the signal including the concentration information to the intensity of the return light amount signal. The ratio of the intensity of the signal including the concentration information (P’ opt ) to the intensity of the return light amount signal (P C1 ~P’ Cm ) is assumed to be represented by P C1 ~P Cm . Specifically, when i is a natural number of 1 or more and m or less, P Ci is calculated as P’ Ci / P opt .

[0042] P C1 ~P Cm is the intensity of the signal obtained by dividing the signal including the concentration information (P’ C1 ~P’ Cm ) by the intensity of the return light amount signal (P opt ) and is also referred to as the intensity of the concentration signal. That is, the concentration signal is a signal obtained by dividing the signal including the concentration information (P’ C1 ~P’ Cm ) by the intensity of the return light amount signal (P opt ). The concentration signal is a signal corresponding to the concentration of the measurement target gas 103 or a signal that can be converted into the concentration of the measurement target gas 103. The intensity of the concentration signal is a value corresponding to the concentration of the measurement target gas 103 or a value that can be converted into the concentration of the measurement target gas 103. On the other hand, P’ C1 ~P’ Cm is the intensity of the signal that is converted into the intensity of the concentration signal by dividing by the intensity of the return light amount signal and is also referred to as the intensity before conversion of the concentration signal.

[0043] The intensity of the concentration signal corresponds to the concentration of the gas to be measured 103. The gas analyzer 10 calculates the concentration of the gas to be measured 103 based on the intensity of the concentration signal. The gas analyzer 10 may calculate the concentration of the gas to be measured 103 from the intensity of the concentration signal based on a calibration curve, mathematical formula, table, etc. that specifies the relationship between the intensity of the concentration signal and the concentration of the gas to be measured 103.

[0044] The gas analyzer 10 may obtain the intensity of one concentration signal based on the intensity of one frequency component of the return light 102. That is, the gas analyzer 10 divides a signal (P’) C1 that includes one concentration information by the intensity (P) opt of the return light amount signal to calculate the intensity (P) C1 of the concentration signal. When the gas analyzer 10 obtains the intensity of one concentration signal, it calculates one candidate value as the measured value of the concentration of the gas to be measured 103 based on the obtained intensity of the one concentration signal.

[0045] The gas analyzer 10 may obtain the intensities of a plurality of concentration signals based on the intensities of a plurality of frequency components of the return light 102. That is, the gas analyzer 10 divides signals (P’ C1 ~P’ Cm ) that include a plurality of concentration information by the intensity (P) opt of the return light amount signal to calculate the intensities (P C1 ~P CmIt may calculate ( ). When the gas analyzer 10 acquires the intensities of a plurality of concentration signals, it calculates a plurality of values that are candidates for the measured value of the gas concentration based on each of the intensities of the acquired plurality of concentration signals. The values that are candidates for the measured value of the gas concentration are also referred to as candidate values of the gas concentration. That is, when the gas analyzer 10 acquires the intensities of a plurality of concentration signals, it may calculate a plurality of candidate values of the gas concentration. The gas analyzer 10 may select one value from among the plurality of candidate values of the gas concentration as the measured value of the concentration of the gas to be measured 103. The gas analyzer 10 may calculate the average value of the plurality of candidate values of the gas concentration as the measured value of the concentration of the gas to be measured 103. The gas analyzer 10 may calculate various other statistical values such as the median value of the plurality of candidate values of the gas concentration as the measured value of the concentration of the gas to be measured 103. That is, the gas analyzer 10 may calculate the measured value of the concentration of the gas to be measured 103 based on the plurality of candidate values of the gas concentration.

[0046] (Configuration example of the gas analyzer 10 according to the present disclosure) As shown in FIG. 5, the gas analyzer 10 according to an embodiment of the present disclosure includes a waveform generator 11, a drive power source 121, a light source 122, a driver 131, an optical amplifier 132, lenses 141 and 142, a photodetector 15, an amplifier 16, an A / D converter 17, and a signal processor 18.

[0047] The waveform generator 11 generates signal waveforms of a plurality of modulation frequencies used to multiplex-modulate the measurement light 101 and outputs them to the drive power source 121 and the A / D converter 17. The waveform generator 11 may include an oscillator or a function generator or the like. The waveform generator 11 may be configured to be able to set the modulation frequency. The waveform generator 11 may be configured to be able to set the number of modulation frequencies. That is, the waveform generator 11 may be configured to be able to set whether to generate a signal waveform for double modulation or a signal waveform for triple or higher modulation.

[0048] The drive power source 121 is a power source that drives the light source 122. The drive power source 121 drives the light source 122 based on the signal waveforms of a plurality of modulation frequencies input from the waveform generator 11. The drive power source 121 outputs a drive signal to drive the light source 122. The drive signal may be, for example, a signal in which each AC signal of a plurality of modulation frequencies is superimposed on a DC signal. The AC signal of the modulation frequency may be, for example, a sine-wave-shaped signal or a signal of other shapes. The drive power source 121 may be configured to include a transistor or a laser drive IC (Integrated Circuit) capable of supplying a drive current to the light source 122.

[0049] The light source 122 is a laser light source. The light source 122 emits laser light frequency-modulated according to the signal waveforms of a plurality of modulation frequencies. The light source 122 may be controlled so that the center wavelength of the modulation of the laser light becomes the center wavelength of the absorption spectrum of the measurement target gas 103. The light source 122 may be a semiconductor laser. The semiconductor laser may include, for example, a QCL (Quantum Cascade Laser) or an ICL (Interband Cascade Laser). By configuring the waveform generator 11 to be able to set the modulation frequency, the light source 122 is configured to be able to set the modulation frequency.

[0050] The optical amplifier 132 amplifies the laser light emitted from the light source 122. The optical amplifier 132 may include, for example, an OFA (Optical Fiber Amplifier) or an SOA (Semiconductor Optical Amplifiers). The driver 131 drives the optical amplifier 132. The driver 131 may be configured to include an element capable of supplying pump light or a drive current to the optical amplifier 132.

[0051] The lens 141 converts the laser light amplified by the optical amplifier 132 into parallel light and emits it as measurement light 101 toward the measurement target gas 103. The lens 141 may be configured to include a collimating lens. The lens 141 may be replaced with another optical element such as a parabolic mirror capable of converting the laser light into parallel light.

[0052] The lens 142 focuses the return light 102, which is the laser light emitted from and returned by the lens 141, onto the photodetector 15. The lens 142 may be configured to include a condenser lens. The lens 142 may be replaced with other optical elements such as a parabolic mirror that can focus the return light 102 onto the photodetector 15.

[0053] The photodetector 15 converts the return light 102 into an electrical signal and outputs it as a received light signal. The photodetector 15 may include, for example, a PD (Photo Diode) or the like.

[0054] The amplifier 16 amplifies the received light signal input from the photodetector 15 and outputs it as an amplified signal. The amplifier 16 may be configured to include elements such as a transistor. When the photodetector 15 is a PD, the amplifier 16 may include a circuit that converts the photocurrent output by the photodetector 15 into a voltage.

[0055] The A / D converter 17 converts the amplified signal input from the amplifier 16 into a digital signal and outputs it to the signal processing device 18.

[0056] The signal processing device 18 analyzes the digital signal and calculates the frequency spectrum of the return light 102. The signal processing device 18 may calculate the frequency spectrum by performing an FFT (Fast Fourier Transform) of the digital signal. The signal processing device 18 calculates a density signal based on the intensity of each frequency component included in the frequency spectrum of the return light 102. The signal processing device 18 calculates the density of the measurement target gas 103 from the density signal based on a calibration curve, relational expression, table, or the like that represents the relationship between the density signal and the density of the measurement target gas 103.

[0057] The signal processing device 18 includes an arithmetic unit 181, a storage unit 182, and an interface 183.

[0058] The arithmetic unit 181 may be configured to include a processor such as a CPU (Central Processing Unit) or a dedicated circuit such as an FPGA (Field Programmable Gate Array). The arithmetic unit 181 may be configured to execute a program that realizes the functions of the signal processing device 18.

[0059] The storage unit 182 may store various information used for the operation of the signal processing device 18, or a program that realizes the functions of the signal processing device 18. The storage unit 182 may function as a work memory of the arithmetic unit 181. The storage unit 182 may be configured by, for example, a semiconductor memory. The storage unit 182 may be configured integrally with the arithmetic unit 181 or separately.

[0060] The interface 183 may include a communication interface that communicates with, for example, the A / D converter 17 or the waveform generator 11 by wire or wirelessly. The communication interface may be configured to be communicable based on various communication standards such as RS-232C, RS-485, or LAN (Local Area Network). The communication standards are not limited to these examples and may be various other standards.

[0061] The interface 183 may include an input device that receives input from the user. The input device may include, for example, a keyboard or physical keys, or a pointing device such as a touch panel or touch sensor or mouse. The interface 183 may be configured to receive input from an external input device.

[0062] The interface 183 may include a display device that displays the measurement result of the gas concentration or the like. The display device may include various displays such as a liquid crystal display. The interface 183 may be configured to output the measurement result of the gas concentration or the like to an external display device.

[0063] The interface 183 may include an audio output device such as a speaker for emitting audio information such as an alarm sound according to the measurement result of the gas concentration. The interface 183 may be configured to output the audio information to an external speaker or the like.

[0064] The interface 183 is not limited to these examples and may be configured to include various other devices, or may be configured to connect to various other devices.

[0065] The signal processing device 18 may be, for example, a PC (Personal Computer). The signal processing device 18 is not limited to the above-described examples and may be configured in various modes. The signal processing device 18 may be configured integrally with the gas analyzer 10 or separately.

[0066] The signal processing device 18 may be configured to be able to set a modulation frequency for the waveform generator 11. The signal processing device 18 may be configured to be able to set the number of modulation frequencies. That is, the signal processing device 18 may be configured to be able to set whether to doubly modulate the laser beam or modulate it three or more times. The signal processing device 18 may set the modulation frequency based on an input from the user.

[0067] (Operation example of the gas analyzer 10 according to the present disclosure) As described above, the gas analyzer 10 according to an embodiment of the present disclosure emits measurement light 101 from a lens 141 toward a gas to be measured 103. The measurement light 101 is light that is multiplexed with a plurality of modulation frequencies. After the measurement light 101 is emitted from the lens 141, it passes through the gas to be measured 103 and is reflected or scattered by a scatterer 104 such as a wall. The reflected or scattered light returns to the gas analyzer 10 through the gas to be measured 103. The light that returns to the gas analyzer 10 is also referred to as return light 102. The return light 102 enters the lens 142. The gas analyzer 10 detects the return light 102 that has entered the lens 142, and analyzes the frequency spectrum of the return light 102 in the arithmetic unit 181 of the signal processing device 18 to measure the concentration of the gas to be measured 103. The distance from the lenses 141 and 142 to the scatterer 104 is represented by L.

[0068] <Frequency spectrum of the double-modulated laser light> In the present embodiment, the gas analyzer 10 emits laser light double-modulated with two modulation frequencies as the measurement light 101 to measure the concentration of the gas to be measured 103. The two modulation frequencies shall include a first modulation frequency (f 1 ) and a second modulation frequency (f 2 ). The linear combination frequency (f 1 ) in the laser light double-modulated with the first modulation frequency (f 2 ) and the second modulation frequency (f DM ) is represented by j·f 1 +k·f 2 . The coefficients j and k are integers.

[0069] The gas analyzer 10 detects the return light 102, in which the doubly modulated measurement light 101 has passed through and returned from the gas to be measured 103, with the photodetector 15, and analyzes the received light signal of the return light 102 with the signal processing device 18 to calculate the frequency spectrum of the return light 102. The frequency spectrum of the doubly modulated return light 102 is illustrated in the graph of FIG. 6. The horizontal axis of the graph in FIG. 6 represents the frequency. The vertical axis represents the intensity of each frequency component. The doubly modulated return light 102 is a laser beam in which an AC component of a first modulation frequency and a second modulation frequency is superimposed on a DC component. Therefore, the doubly modulated return light 102 has a DC component and components of linear combination frequencies of the first modulation frequency and the second modulation frequency.

[0070] Specifically, in the frequency spectrum of the doubly modulated return light 102 illustrated in FIG. 6, the intensity of the DC component is large. In addition, the intensity of the component of the first modulation frequency (f 1 ) and the intensity of the component of the second modulation frequency (f 2 ) are large. Also, the intensity of the component of the frequency (f 1 + f 2 ) which is the sum of the first modulation frequency and the second modulation frequency is large. Further, the intensity of the component of the frequency (2f 2 ) which is twice the second modulation frequency is larger than other frequency components.

[0071] <<Suppression of Decrease Amount of Return Light Quantity Signal>> As described above, the light quantity of the return light 102 decreases as the gas concentration increases. When the intensity of the return light quantity signal decreases until it becomes less than the noise level or less than the detection lower limit of the return light quantity signal, the gas analyzer 10 cannot determine whether the return light quantity signal has decreased due to the gas concentration being too high or due to the measurement light 101 being emitted into the air or the like. The reasons why the gas analyzer 10 cannot determine that the return light quantity signal has decreased may include, in addition to the measurement light 101 being emitted into the air, the incident angle of the measurement light 101 with respect to the scatterer 104 being shallow, or the measurement light 101 being incident on the scatterer 104 having a misaligned mirror surface.

[0072] When the double-modulated laser light is emitted as the measurement light 101, the frequency spectra of the measurement light 101 and the return light 102 include components of linearly combined frequencies in addition to the components of the modulation frequency. In other words, the modulation frequency widths of the measurement light 101 and the return light 102 are seemingly widened. As a result, the frequency components of the frequency spectrum of the return light 102 include frequency components that are deviated from the peak frequency of the absorption spectrum of the measurement target gas 103 and are less likely to be absorbed by the measurement target gas 103. The arithmetic unit 181 of the signal processing device 18 may calculate the intensity of the frequency components that are less likely to be absorbed by the measurement target gas 103 as the intensity of the return light amount signal. The arithmetic unit 181 may also calculate the sum of the intensities of a plurality of frequency components that are less likely to be absorbed by the measurement target gas 103 as the intensity of the return light amount signal.

[0073] Here, as a comparison target, it is assumed that the single-modulated measurement light 101 obtained by modulating the laser light only by the second modulation frequency (f 2 ) is emitted. The frequency spectrum of the return light 102 obtained in the single-modulation case is represented by a broken line in FIG. 6. The single-modulated return light 102 has, in addition to the DC component, a component of the first harmonic (f 2 ) of the modulation frequency and a component of the second harmonic (2f 2 ) of the modulation frequency.

[0074] In the single-modulation case, the component of the first harmonic of the modulation frequency is used as the return light amount signal. However, when the first harmonic of the modulation frequency is likely to be absorbed by the measurement target gas 103, the intensity of the return light amount signal is greatly reduced. On the other hand, the frequency spectrum of the double-modulated return light 102 has frequency components other than the first harmonic of the modulation frequency. Therefore, in the double-modulation case, a frequency component that is less likely to be absorbed by the measurement target gas 103 may be used as the return light amount signal. As a result, in the double-modulation case, the return light amount signal is selected so that the intensity of the return light amount signal is less likely to decrease than in the single-modulation case.

[0075] For example, as shown in FIG. 7, as the gas concentration increases, the intensity of the single-modulation return light 102 decreases significantly. On the other hand, the amount of decrease in the intensity of the double-modulation return light 102 is smaller than that in the case of single modulation. Specifically, when the gas concentration is 100 [%·m], the intensity of the double-modulation return light 102 is six times that of the single-modulation return light 102.

[0076] As described above, the gas analyzer 10 according to the present disclosure can suppress the amount of decrease in the return light amount signal. By being able to suppress the amount of decrease in the return light amount signal, even when the gas concentration is high, the return light amount signal is less likely to decrease. As a result, a state where it becomes impossible to determine whether the return light amount signal has decreased due to the gas concentration being too high or due to other causes is avoided.

[0077] <<High-sensitivity measurement>> As described above, the calculation unit 181 of the signal processing device 18 of the gas analyzer 10 divides the intensity (P’ C1 ~P’ Cm ) before conversion of the concentration signal by the intensity (P opt ) of the return light amount signal to calculate the intensity (P C1 ~P Cm ) of the concentration signal, and calculates the concentration of the measurement target gas 103 from the intensity of the concentration signal.

[0078] The calculation unit 181 selects one frequency component from a plurality of frequency components of the return light 102 as the return light amount signal. Further, the calculation unit 181 selects at least one frequency component from a plurality of frequency components of the return light 102 as the concentration signal.

[0079] In this operation example, the calculation unit 181 selects the component of the second modulation frequency (f 2 ) as the return light amount signal, and selects the component of the second harmonic (2f 2 ) of the second modulation frequency and the component of the frequency (f 1 +f 2 ) of the sum of the first modulation frequency and the second modulation frequency as the concentration signal.

[0080] In the frequency spectrum of the return light 102 illustrated in FIG. 6, the intensity of the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency is smaller than the intensity of the component at the second harmonic of the second modulation frequency. Therefore, when selecting the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal, even when the gas concentration is low, the intensity of the concentration signal becomes larger than the noise level. As a result, when selecting the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal, the gas concentration is measured with high sensitivity.

[0081] The relationship between the gas concentration and the intensity of the concentration signal is illustrated in the graph of FIG. 8. The horizontal axis of the graph in FIG. 8 represents the gas concentration. The vertical axis represents the intensity of the concentration signal. The relationship between the gas concentration and the intensity of the concentration signal when selecting the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal is represented by the points plotted as open circles (○) with "double modulation (high sensitivity)". As a comparison target, the relationship between the gas concentration and the intensity of the concentration signal in the case of single modulation is represented by the points plotted as solid circles (●) with "single modulation".

[0082] The noise level is represented by a dashed line in the graph of FIG. 8. The intensity of the concentration signal when selecting the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal is larger than the noise level even in the region where the gas concentration is low. Therefore, the measurement sensitivity of the gas concentration is maintained as compared with the case of single modulation.

[0083] As described above, in the case of single modulation, it may become impossible to determine whether the intensity of the return light quantity signal has decreased due to the gas concentration being too high, or due to causes such as the measurement light 101 being emitted into the air. That is, in the case of single modulation, it may become impossible to determine the cause of the decrease in the intensity of the return light quantity signal. On the other hand, by emitting the double-modulated laser light as the measurement light 101, a state where it becomes impossible to determine the cause of the decrease in the return light quantity signal can be avoided. That is, the gas analyzer 10 according to the present disclosure can avoid a state where it becomes impossible to determine the cause of the decrease in the return light quantity signal while maintaining the sensitivity of the gas concentration to be equivalent to that in the case of single modulation by using the double-modulated laser light.

[0084] <<Wide dynamic range measurement>> As described above, when the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal, the measurement sensitivity of the gas concentration is maintained in the same manner as in the case of single modulation. However, the calibration curve representing the relationship between the intensity of the concentration signal and the gas concentration when the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal deviates from the straight line as the gas concentration is higher, similar to the calibration curve in the case of single modulation. The gas analyzer 10 according to the present disclosure can improve the linearity of the calibration curve in the range where the gas concentration is high by using the double-modulated laser light.

[0085] Specifically, in FIG. 8, the calibration curve representing the relationship between the gas concentration and the intensity of the concentration signal when the component of the second harmonic of the second modulation frequency is selected as the concentration signal is represented by the points plotted as hollow triangles (△) as "double modulation (wide dynamic range)".

[0086] When the component of the second harmonic of the second modulation frequency is selected as the concentration signal, the calibration curve is linear over a wide range from a low gas concentration range (0.1 [% / m]) to a high gas concentration range (100 [% / m]). The high linearity of the calibration curve over a wide range of gas concentrations results in a wide dynamic range for measuring the gas concentration. That is, when the component of the second harmonic of the second modulation frequency is selected as the concentration signal, the dynamic range for measuring the gas concentration becomes wider.

[0087] The following reasons can be considered for the calibration curve being linear over a wide range of gas concentrations. The intensity of the component of the second harmonic of the second modulation frequency is smaller than the intensity of the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency. As a result, the intensity of the component of the second harmonic of the second modulation frequency is less likely to saturate than the intensity of the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency. In other words, the waveform of the component of the second harmonic of the second modulation frequency is less likely to be distorted in the high gas concentration range than the waveform of the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency. Waveform distortion affects the relationship between the gas concentration and the intensity of the concentration signal. Therefore, it is considered that the calibration curve is linear because the waveform is less likely to be distorted even in the high gas concentration range.

[0088] <<Selection between High-Sensitivity Measurement and Wide-Dynamic-Range Measurement>> As described above, when the arithmetic unit 181 of the signal processing device 18 of the gas analyzer 10 selects the component of the second harmonic of the second modulation frequency as the concentration signal, it can measure the gas concentration with a wide dynamic range. However, according to the graph illustrated in FIG. 8, the intensity of the concentration signal when measuring the gas concentration with a wide dynamic range is below the noise level in the range where the gas concentration is 1 [%·m] or less. That is, when measuring the gas concentration with a wide dynamic range, the measurement sensitivity decreases.

[0089] Conversely, when the arithmetic unit 181 selects a component having a frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal, the gas concentration can be measured with high sensitivity. However, according to the graph illustrated in FIG. 8, in the range where the gas concentration is 10 [%·m] or more, the linearity of the calibration curve representing the relationship between the gas concentration and the intensity of the concentration signal deteriorates. That is, when measuring the gas concentration with high sensitivity, the dynamic range becomes narrow.

[0090] As described above, wide dynamic range measurement and high sensitivity measurement may be in a trade-off relationship. The arithmetic unit 181 may measure the gas concentration by combining wide dynamic range measurement and high sensitivity measurement so as to complement each other so that the trade-off can be eliminated. Specifically, when the gas concentration is low, the arithmetic unit 181 may adopt the measurement value obtained by high sensitivity measurement, and when the gas concentration is high, the arithmetic unit 181 may adopt the measurement value obtained by wide dynamic range measurement.

[0091] In the calibration curve illustrated in FIG. 8, the concentration signal in the calibration curve of double modulation (wide dynamic range) sufficiently exceeds the noise level in the range where the gas concentration is 10 [%·m] or more. Therefore, in the range where the gas concentration is 10 [%·m] or more, the arithmetic unit 181 may select a component having a frequency that is twice the second modulation frequency as the concentration signal and adopt the measurement value of the wide dynamic range measurement, and in the range where the gas concentration is less than 10 [%·m], the arithmetic unit 181 may select a component having a frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal and adopt the measurement value of the high sensitivity measurement.

[0092] The boundary value of the gas concentration for selecting wide dynamic range measurement and high sensitivity measurement is not limited to the above-described example. In the calibration curve illustrated in FIG. 8, the concentration signal in the calibration curve of double modulation (wide dynamic range) is below the noise level in the range where the gas concentration is 1 [%·m] or less. Therefore, in the range where the gas concentration is 1 [%·m] or less, the arithmetic unit 181 may select a component having a frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal and adopt the measurement value of the high sensitivity measurement, and in the range where the gas concentration is greater than 1 [%·m], the arithmetic unit 181 may select a component having a frequency that is twice the second modulation frequency as the concentration signal and adopt the measurement value of the wide dynamic range measurement.

[0093] The calculation unit 181 adopts the measurement value of high-sensitivity measurement in the range where the gas concentration is 1 [%·m] or less, adopts the measurement value of wide-dynamic-range measurement in the range where the gas concentration is 10 [%·m] or more, and may appropriately select and adopt the measurement value of high-sensitivity measurement and the measurement value of wide-dynamic-range measurement in the range where the gas concentration is greater than 1 [%·m] and less than 10 [%·m].

[0094] As described above, the gas analyzer 10 can select different frequency components as concentration signals according to the gas concentration by using the doubly modulated laser light, and can improve the measurement accuracy of the gas concentration. On the other hand, in the case of single modulation, since the frequency component of the return light 102 is only the harmonic of the modulation frequency, it is difficult to select different frequency components as the concentration signal. That is, the gas analyzer 10 according to the present disclosure can improve the measurement accuracy of the gas concentration more than in the case of single modulation by using the doubly modulated laser light.

[0095] <<Influence by noise of a specific frequency>> Noise of a specific frequency such as the vibration frequency of the scatterer 104 may be superimposed on the return light 102. That is, the laser light used by the gas analyzer 10 to measure the gas concentration may be affected by noise of a specific frequency. The gas analyzer 10 according to the present disclosure can measure the gas concentration based on each of a plurality of frequency components included in the frequency spectrum of the return light 102 by using the doubly modulated laser light. When there is noise of a specific frequency, the gas analyzer 10 can reduce the influence of the noise and improve the measurement accuracy of the gas concentration by selecting a frequency component different from the noise.

[0096] For example, assume that the vibration frequency of the scatterer 104 coincides with the frequency (f 1 + f 2 ) which is the sum of the first modulation frequency and the second modulation frequency. In this case, as illustrated in FIG. 9, the second harmonic (2f 2For the noise level of the component of (), only the noise level of the frequency (f 1 + f 2 ) of the sum of the first modulation frequency and the second modulation frequency, represented by a two-dot chain line, becomes high.

[0097] When the gas concentration is 10 [%·m], the signal-to-noise ratio of the double modulation (high sensitivity) concentration signal, in which the component of the frequency (f 1 + f 2 ) of the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal, has decreased to 1.

[0098] On the other hand, since the noise level of the component of the frequency (2f 2 ) has not become high, the signal-to-noise ratio of the double modulation (wide dynamic range) concentration signal, in which the component of the second harmonic of the second modulation frequency is selected as the concentration signal, is 6, which is a sufficiently large value.

[0099] The graph of FIG. 10 shows the variations in the gas concentration calculated by the high-sensitivity measurement with a signal-to-noise ratio of 1 and the gas concentration calculated by the wide dynamic range measurement with a signal-to-noise ratio of 6, respectively. The horizontal axis of the graph of FIG. 10 represents each time when the gas concentration is calculated 100 times as a measurement point. The vertical axis represents the gas concentration calculated at each measurement point.

[0100] The variation in the gas concentration calculated by the high-sensitivity measurement with a signal-to-noise ratio of 1 is represented by a dashed line. The standard deviation representing the variation in the gas concentration calculated by the high-sensitivity measurement with a signal-to-noise ratio of 1 was 2.95.

[0101] The variation in the gas concentration calculated by the wide dynamic range measurement with a signal-to-noise ratio of 6 is represented by a solid line. The standard deviation representing the variation in the gas concentration calculated by the wide dynamic range measurement with a signal-to-noise ratio of 6 was 0.51.

[0102] When the calculation unit 181 of the signal processing device 18 of the gas analyzer 10 can obtain the SN ratio of the concentration signal in each measurement, among the gas concentration calculated by the high-sensitivity measurement and the gas concentration calculated by the wide dynamic range measurement, the gas concentration calculated by the measurement with the higher SN ratio may be selected as the measured value of the gas concentration. When the calculation unit 181 can obtain the SN ratio of the concentration signal in one measurement, it may determine whether to select the gas concentration calculated by that measurement as the measured value of the gas concentration based on the SN ratio. By selecting based on the SN ratio, the influence of noise is reduced.

[0103] The calculation unit 181 may also select the gas concentration with the smaller standard deviation as the measured value of the gas concentration. When the calculation unit 181 determines that the calculation accuracy of the gas concentration by one measurement has deteriorated, it may select the gas concentration calculated by the measurement with no deteriorated calculation accuracy as the measured value of the gas concentration. By selecting based on the standard deviation, the influence of noise is reduced.

[0104] When the calculation unit 181 cannot select either the gas concentration calculated by the high-sensitivity measurement or the gas concentration calculated by the wide dynamic range measurement, it may calculate the average value of the gas concentrations calculated by the two measurements as the measured value of the gas concentration.

[0105] The calculation unit 181 may calculate the root mean square of the gas concentration calculated by the high-sensitivity measurement and the gas concentration calculated by the wide dynamic range measurement as the average value of the gas concentrations calculated by the two measurements. In the graph of FIG. 10, the variation of the averaged gas concentration is represented by a broken line. The standard deviation representing the variation of the averaged gas concentration was 1.48.

[0106] The standard deviation of the averaged gas concentration is larger than the standard deviation of the gas concentration calculated by the wide dynamic range measurement with an SN ratio of 6, but smaller than the standard deviation of the gas concentration calculated by the high-sensitivity measurement with an SN ratio of 1. If the calculation unit 181 arbitrarily selects one gas concentration from the gas concentrations calculated by the two measurements, the measurement accuracy of the gas concentration will be significantly deteriorated by erroneously selecting the gas concentration with a larger variation.

[0107] The gas analyzer 10 can avoid a situation where the measurement accuracy is significantly deteriorated due to an incorrect selection when arbitrarily selecting one measurement from the two measurements by calculating the average value of the gas concentrations calculated by the two measurements as the measured value of the gas concentration.

[0108] The calculation unit 181 may determine whether to select one of the gas concentrations calculated by the two measurements as the measured value of the gas concentration, or to calculate the average value of the gas concentrations calculated by the two measurements as the measured value of the gas concentration, based on the user's setting. The calculation unit 181 may receive an input of the user's setting by the input device of the interface 183.

[0109] As described above, the gas analyzer 10 can execute a plurality of types of measurements in parallel, in which each of the plurality of frequency components is selected as a concentration signal, by using the doubly modulated laser light. The gas analyzer 10 may select the measured value of the gas concentration from the gas concentrations calculated by each type of measurement, or may calculate the average value of the gas concentrations calculated by each type of measurement as the measured value of the gas concentration. Since the gas analyzer 10 can execute a plurality of types of measurements in parallel, the measurement accuracy of the gas concentration can be improved without increasing the time required for the measurement of the gas concentration.

[0110] The gas concentration calculated by each of the two measurements corresponds to a candidate value of the gas concentration. The calculation unit 181 may select one of the two candidate values as the measured value of the gas concentration, or may calculate the average value of the two candidate values as the measured value of the gas concentration. The calculation unit 181 may select the measured value of the gas concentration from among the candidate values based on the gas concentration. The calculation unit 181 may select the measured value of the gas concentration from among the candidate values based on the signal-to-noise ratio of the concentration signal.

[0111] <Example of flowchart> The gas analyzer 10 may execute a gas analysis method including an example of the procedure of the flowchart illustrated in FIG. 11 in order to measure the concentration of the gas 103 to be measured. At least some of the procedures of the gas analysis method may be realized as a gas analysis program that causes the processor constituting the calculation unit 181 to execute. The gas analysis program may be stored in a non-transitory computer-readable medium.

[0112] The gas analyzer 10 emits laser light that is double-modulated at the first modulation frequency f 1 and the second modulation frequency f 2 (step S1). The gas analyzer 10 receives the laser light that has passed through the gas 103 to be measured and has been scattered or reflected by the scatterer 104 and returned (step S2). The calculation unit 181 of the signal processing device 18 of the gas analyzer 10 executes an FFT on the received signal of the laser light and calculates the frequency components of the laser light (step S3).

[0113] The calculation unit 181 calculates the value obtained by dividing the component of the second harmonic of the second modulation frequency by the component of the second modulation frequency as the intensity P C1 of the first concentration signal (step S4). The calculation unit 181 calculates the gas concentration based on the intensity P C1 of the first concentration signal (step S5).

[0114] The calculation unit 181 calculates the value obtained by dividing the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency by the component of the second modulation frequency as the intensity P C2 of the second concentration signal (step S6). The calculation unit 181 calculates the intensity P of the second concentration signalC2 Calculate the gas concentration based on this (step S7).

[0115] The calculation unit 181 calculates a measured value of the gas concentration based on the two types of gas concentrations calculated in the procedures from step S4 to S7 (step S8). Specifically, the calculation unit 181 may select one value of the gas concentration calculated based on the intensity of the first concentration signal and the gas concentration calculated based on the intensity of the second concentration signal, and calculate the selected value as the measured value of the gas concentration. The calculation unit 181 may also calculate the average value of the gas concentration calculated based on the intensity of the first concentration signal and the gas concentration calculated based on the intensity of the second concentration signal as the measured value of the gas concentration.

[0116] After executing the procedure of step S8, the gas analyzer 10 ends the execution of the procedure of the flowchart in FIG. 11.

[0117] (Summary) As described above, the gas analyzer 10 according to the present disclosure can, by using a doubly modulated laser beam, maintain the measurement accuracy of the concentration of the gas 103 to be measured compared to the case of using a singly modulated laser beam, and can make it difficult for the intensity of the return light amount signal to decrease when the gas concentration increases. By suppressing the amount of decrease in the intensity of the return light amount signal, the return light amount signal is less likely to decrease even when the gas concentration is high. As a result, even when the gas concentration is high, it is possible to avoid a state where it becomes impossible to determine whether the return light amount signal has decreased due to the gas concentration being too high or whether the return light amount signal has decreased due to the measurement light 101 being emitted into the air or the like.

[0118] The gas analyzer 10 according to the present disclosure can select a concentration signal so that the linearity of the calibration curve becomes high by using a doubly modulated laser beam. By increasing the linearity of the calibration curve, wide dynamic range measurement can be performed. As a result, the measurement accuracy of a wide range of gas concentrations is improved compared to the case of using a singly modulated laser beam.

[0119] The gas analyzer 10 according to the present disclosure can select a concentration signal by using a double-modulated laser beam, avoiding the frequency of specific noise caused by vibrations of the scatterer 104 or the like. By selecting the concentration signal while avoiding the frequency of the specific noise, the measurement accuracy of the gas concentration is improved.

[0120] As described above, the embodiments according to the present disclosure have been described with reference to the drawings. However, the specific configuration is not limited to this embodiment, and various modifications within the scope not departing from the gist of the present disclosure are also included.

[0121] In the above-described embodiment, an operation example of double-modulating the laser beam at two modulation frequencies has been described. As another embodiment, the gas analyzer 10 may multi-modulate the laser beam at three or more modulation frequencies.

[0122] In the above-described embodiment, an operation example of measuring the gas concentration by performing high-sensitivity measurement and wide-dynamic-range measurement in parallel has been described. As another embodiment, the gas analyzer 10 may measure the gas concentration by performing three or more types of measurements in parallel, and calculate three or more candidate values of the gas concentration. The calculation unit 181 may select one of the three or more candidate values of the gas concentration as the measured value of the gas concentration. The calculation unit 181 may calculate the average value of the three or more candidate values of the gas concentration as the measured value of the gas concentration, or may calculate the average value of some of the three or more candidate values of the gas concentration as the measured value of the gas concentration.

[0123] The gas analyzer 10 may select the same frequency component or different frequency components for each of the return light amount signal used to calculate the intensity of the concentration signal and the return light amount signal used to determine whether the cause of the decrease in the return light amount is due to the gas concentration being too high or the measurement light 101 being emitted into the air.

[0124] In the present embodiment, the gas to be measured 103 is oxygen (O 2 ), carbon monoxide (CO), or carbon dioxide (CO 2Assume that the gas contains a component to be measured such as []. The measurement target gas may contain one or more components to be measured. The gas analyzer 10 may set the modulation frequency according to the characteristics of the component to be measured. By configuring the light source 122 to be able to set the modulation frequency, the measurement light 101 is appropriately modulated according to the component to be measured. As a result, the measurement accuracy of the gas concentration is improved.

Explanation of Signs

[0125] 10 Gas analyzer (11: waveform generator, 121: drive power supply, 122: light source, 131: driver, 132: optical amplifier, 141, 142: lenses, 15: photodetector, 16: amplifier, 17: A / D converter, 18: signal processing device, 181: arithmetic unit, 182: storage unit, 183: interface) 101 Measurement light 102 Return light 103 Measurement target gas 104 Scatterer

Claims

1. A gas analyzer comprising a calculation unit, wherein the calculation unit, calculates the intensity of one concentration signal based on the intensity of one frequency component of the return light that the multiply-modulated measurement light has passed through the measurement target gas and returned, or the intensities of a plurality of concentration signals based on the intensities of a plurality of frequency components of the return light, and calculates a measured value of the concentration of the measurement target gas based on the intensity of the one concentration signal or the intensities of the plurality of concentration signals. Gas analyzer.

2. The calculation unit, calculates a plurality of candidate values that are candidates for the measured value of the concentration of the measurement target gas based on the intensities of the plurality of concentration signals, and calculates the concentration of the measurement target gas based on the plurality of candidate values. The gas analyzer according to claim 1.

3. The gas analyzer according to claim 2, wherein the calculation unit selects one of the plurality of candidate values as the measured value of the concentration of the measurement target gas based on the signal-to-noise ratio of the concentration signal.

4. The gas analyzer according to claim 2, wherein the calculation unit calculates the average value of at least two of the plurality of candidate values as the measured value of the concentration of the measurement target gas.

5. The gas analyzer according to any one of claims 1 to 4, further comprising a light source that emits the measurement light and is configured to be able to set the modulation frequency of the measurement light.

6. A gas analysis method including: the gas analyzer calculating the intensity of one concentration signal based on the intensity of one frequency component of the return light that the multiply-modulated measurement light has passed through the measurement target gas and returned, or the intensities of a plurality of concentration signals based on the intensities of a plurality of frequency components of the return light; and the gas analyzer calculating a measured value of the concentration of the measurement target gas based on the intensity of the one concentration signal or the intensities of the plurality of concentration signals.

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