Gas analyzer and gas analysis method

Abstract

The invention discloses a gas analyzer and a gas analysis method. A gas analyzer (10) is provided with a calculation unit (181). A calculation unit (181) calculates the intensity of one concentration signal based on the intensity of one frequency component of return light (102) obtained by the multiple modulated measurement light (101) passing through the gas to be measured (103) and returning, or the intensities of a plurality of concentration signals based on the respective intensities of a plurality of frequency components of the return light. The measurement value of the concentration of the gas to be measured (103) is calculated on the basis of the intensity of the one concentration signal or the intensities of the plurality of concentration signals.

Description

Technical Field

[0001] The present invention relates to a gas analyzer and a gas analysis method. Background Art

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

[0003] Patent Document 1: Japanese Patent Laid-Open No. 5-79976 Summary of the Invention

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

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

[0006] (1) The gas analyzer according to several 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 has passed through and returned from the measurement target gas of the measurement light after multiple modulations, or the intensities of multiple concentration signals based on the intensities of multiple 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 multiple concentration signals.

[0007] The gas analyzer according to the present invention uses a doubly modulated laser, so that compared with the case of using a singly modulated laser, the measurement accuracy of the gas concentration can be maintained, and it is difficult to reduce the intensity of the return light amount signal when the gas concentration increases. The decrease amount of the intensity of the return light amount signal can be suppressed, so that the return light amount signal is difficult to decrease even when the gas concentration is high. As a result, even when the gas concentration is high, a state in which the cause of the decrease in the return light amount signal cannot be discriminated is avoided.

[0008] In addition, the gas analyzer according to the present invention uses a doubly modulated laser, so that a concentration signal can be obtained in a manner that improves the linearity of the calibration line. Since the linearity of the calibration line is improved, a wide dynamic range measurement can be performed. As a result, compared with the case of using a singly modulated laser, the measurement accuracy of a wide range of gas concentrations can be improved.

[0009] In addition, the gas analyzer according to the present invention uses a doubly modulated laser, so that a concentration signal avoiding a specific noise frequency can be obtained. Since a concentration signal avoiding a specific noise frequency can be obtained, the measurement accuracy of the gas concentration can be improved.

[0010] (2) Based on the gas analyzer described in (1) above, it can be configured such that the arithmetic unit calculates a plurality of candidate values that are candidates for the measured value of the concentration of the gas to be measured, based on the intensities of the plurality of concentration signals respectively. The arithmetic unit can calculate the concentration of the gas to be measured based on the plurality of candidate values.

[0011] The gas analyzer according to the present invention calculates a plurality of candidate values based on the intensities of a plurality of frequency components, thereby enabling appropriate selection of high-sensitivity measurement and wide-dynamic-range measurement, and avoiding specific noise frequencies. As a result, the measurement accuracy of the gas concentration can be improved.

[0012] (3) Based on the gas analyzer described in (2) above, it can be configured such that the arithmetic unit selects one of the plurality of candidate values as the measured value of the concentration of the gas to be measured, based on the signal-to-noise ratio of the concentration signal. By selecting the measured value of the gas concentration from a plurality of candidate values, the measurement accuracy of the gas concentration can be improved.

[0013] (4) Based on the gas analyzer described in (2) above, it can be configured such that the arithmetic unit calculates the average value of at least two of the plurality of candidate values as the measured value of the concentration of the gas to be measured. By calculating the average value of a plurality of candidate values, the situation where the measurement accuracy deteriorates significantly due to an incorrect selection from a plurality of candidate values is avoided. As a result, the measurement accuracy of the gas concentration can be improved.

[0014] (5) Based on the gas analyzer described in any one of (1) to (4) above, it can be configured to 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. The light source is configured to be able to set the modulation frequency, thereby appropriately modulating the measurement light according to the component to be measured. As a result, the measurement accuracy of the gas concentration can be improved.

[0015] (6) The gas analysis method according to several embodiments includes the following steps: the gas analyzer calculates the intensity of one concentration signal based on the intensity of one frequency component of the return light that passes through and returns from the gas to be measured based on the measurement light after multiple modulations, or calculates the intensities of a plurality of concentration signals based on the intensities of a plurality of frequency components of the return light respectively; and

[0016] calculates the measured 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.

[0017] Effects of the Invention

[0018] According to the gas analyzer and gas analysis method of the present invention, the measurement accuracy of the gas concentration can be improved. Description of the Drawings

[0019] Figure 1 is a schematic diagram showing a structural example of a gas analyzer related to a comparative example.

[0020] Figure 2 is a flowchart showing the sequence of a gas analysis method related to a comparative example.

[0021] Figure 3 is a graph showing the relationship between the intensity of the returned light detected by the gas analysis method related to the comparative example and the gas concentration.

[0022] Figure 4 is a graph showing the relationship between the concentration signal calculated by the gas analysis method related to the comparative example and the gas concentration.

[0023] Figure 5 is a schematic diagram showing a structural example of a gas analyzer according to the present invention.

[0024] Figure 6 is a graph showing an example of the spectrum of the returned light.

[0025] Figure 7 is a graph showing an example of the relationship between the intensity of the returned light and the gas concentration.

[0026] Figure 8 is a graph showing an example of the relationship between the concentration signal and the gas concentration.

[0027] Figure 9 is a graph showing Figure 8 the case where the noise level increases at a frequency corresponding to double modulation (high sensitivity) in the graph.

[0028] Figure 10 is a graph showing the fluctuation of the measured value of the gas concentration.

[0029] Figure 11 is a flowchart showing an example of the sequence of a gas analysis method according to the present invention. Detailed Description of the Invention

[0030] (Comparative Example)

[0031] The gas analyzer 90 related to the comparative example measures the concentration of the measurement target gas 903 based on the absorbance of the laser transmitted through the measurement target gas 903. The method of measuring the gas concentration based on the absorbance of the laser is also called wavelength modulation spectroscopy (WMS).

[0032] When measuring the concentration of the gas to be measured 903 using a WMS, the gas analyzer 90 transmits a laser whose wavelength is modulated at a single frequency f through the gas to be measured 903, and acquires a signal including information related to 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 twice the single modulation frequency, in the frequency of the laser transmitted through the gas to be measured 903.

[0033] As Figure 1 shown, the gas analyzer 90 involved in 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 processing device 98.

[0034] 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 has been monotonically modulated at a single frequency.

[0035] 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. Based on the signal waveform of the modulation frequency input from the waveform generator 91, the drive power supply 921 outputs a drive signal and drives 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 whose frequency has been modulated according to the signal waveform of the modulation frequency. The light source 922 is controlled in such a way that the center wavelength of the modulation of the laser reaches the center wavelength of the absorption spectrum of the gas to be measured 903 and the wavelength modulation width of the laser reaches 2.2 times the FWHM of the absorption spectrum of the gas to be measured 903.

[0036] The optical amplifier 932 amplifies the laser emitted from the light source 922. The driver 931 drives the optical amplifier 932. The lens 941 converts the laser amplified by the optical amplifier 932 into parallel light and emits it as the measurement light 901 toward the gas to be measured 903.

[0037] 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 passes through the gas to be measured 903 and returns to the gas analyzer 90. The light returned to the gas analyzer 90 is also referred to as the return light 902. The return light 902 enters the lens 942. The gas analyzer 90 uses the photodetector 95 to detect the return light 902 entering the lens 942, analyzes the 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.

[0038] The lens 942 converges the return light 902, which is the laser that passes through the gas 903 to be measured, is reflected or scattered by the scatterer 904, and returns 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 of the amplifier 96 is appropriately set according to the intensity of the return light 902 incident on the photodetector 95.

[0039] The LIA 97 uses the signal waveform of the modulation frequency input from the waveform generator 91 to detect specific frequency components based on the amplified signal. Specifically, the LIA 97 detects the component of the first harmonic and the component of the second harmonic of the modulation frequency from the amplified signal. The component of the first harmonic of the modulation frequency is represented by P f The component of the second harmonic of the modulation frequency is represented by P 2f and is represented.

[0040] The signal processing device 98 calculates the concentration of the gas 903 to be measured based on the component of the first harmonic and the component of the second harmonic detected by the LIA 97. Specifically, the signal processing device 98 calculates the value obtained by dividing the intensity of the component of the second harmonic by the intensity of the component of the first harmonic as the concentration signal. The concentration signal is represented by P C and is represented. The signal processing device 98 calculates the concentration of the gas 903 to be measured based on the calibration line representing the relationship between the concentration signal and the concentration of the gas 903 to be measured.

[0041] The gas analyzer 90 involved in the comparative example measures the concentration of the gas 903 to be measured by executing the sequence of the flowchart shown in Figure 2 . The gas analyzer 90 emits the laser modulated at the modulation frequency f from the lens 941 (step S91). The gas analyzer 90 uses the lens 942 to converge the laser that passes through and returns from the gas 903 to be measured and receives the light using the photodetector 95 (step S92). The gas analyzer 90 uses the LIA 97 to obtain the component of the first harmonic (f) of the modulation frequency (P f ) and the component of the second harmonic (2f) of the modulation frequency (P 2f ) from the amplified signal after amplifying the received light signal (step S93). The gas analyzer 90 calculates the concentration signal (P 2f ) by calculating P f / P C using the signal processing device 98 (step S94). The gas analyzer 90 calculates the concentration of the gas 903 to be measured based on the concentration signal and the calibration line (step S95).

[0042] When measuring the concentration of the gas to be measured 903 using the gas analyzer 90 involved in the comparative example, the following three problems may occur.

[0043] As the first problem, a decrease in the intensity of the return light 902 can be cited. As Figure 3 shown, the higher the concentration of the gas to be measured 903, the smaller the intensity of the return light 902. Figure 3 In the curve graph, the horizontal axis 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 passes along the optical path. The higher the gas concentration, the more the intensity of the return light 902 decreases.

[0044] As described above, the higher the gas concentration, the smaller the intensity of the return light 902. When the intensity of the return light 902 decreases significantly, it is sometimes difficult for the gas analyzer 90 to detect the return light 902. When the gas concentration increases due to gas leakage, the gas analyzer 90 sometimes cannot detect the gas leakage because it cannot detect the return light 902. In particular, when the gas analyzer 90 is used outdoors, it may be impossible to distinguish between the case where the measurement light 901 is emitted into the air where there is no scatterer 904 and the case where the intensity of the return light 902 decreases significantly due to an increase in the gas concentration.

[0045] In addition, in order to distinguish between the case where there is no scatterer 904 and the case where the gas concentration increases, it is considered to emit the measurement light 901 at a frequency that is not a peak and deviates from the absorption spectrum of the gas to be measured 903. However, the measurement time is extended by changing the frequency for measurement.

[0046] As the second problem, a deterioration in the linearity of the calibration line can be cited. As Figure 4 shown, the calibration line showing the relationship between the gas concentration and the concentration signal deviates from the straight line represented by the dashed line. That is, the linearity of the calibration line deteriorates. Figure 4 In the curve graph, the horizontal axis represents the gas concentration. The vertical axis represents the concentration signal. The horizontal axis and the vertical axis are logarithmic axes. As a reason for the deterioration of the linearity of the calibration line, for example, it can be considered that the higher the gas concentration, the greater the influence of the waveform distortion. The deterioration of the linearity of the calibration line causes a decrease in the measurement accuracy of the concentration of the gas to be measured 903.

[0047] As the third problem, the influence of the vibration of the scatterer 904 can be cited. When the wall or pipe, etc. that 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, the concentration signal is affected by the vibration of the scatterer 904. As a result, the measurement accuracy of the concentration of the gas to be measured 903 decreases.

[0048] As described above, there are sometimes problems when measuring the concentration of the gas to be measured 903 using the gas analyzer 90 involved in the comparative example. It is required to achieve both the measurement in the case of increased gas concentration and the improvement or maintenance of the measurement accuracy.

[0049] The gas analyzer 10 according to this embodiment (refer to Figure 5 ) can achieve both the measurement in the case of increased gas concentration and the improvement or maintenance of the measurement accuracy. Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0050] (Outline of the gas analyzer 10 according to the present invention)

[0051] The gas analyzer 10 according to the present invention uses wavelength modulation spectroscopy (WMS) to measure the concentration of the gas to be measured 103 based on the absorbance of the laser after passing through the gas to be measured 103. The gas analyzer 10 causes the laser wavelength-modulated at a plurality of modulation frequencies to pass through the gas to be measured 103, thereby obtaining the spectrum of the light passing through and returning from the gas to be measured 103. The plurality of modulation frequencies are represented by f L1 ~f Ln . n is a natural number greater than or equal to 2.

[0052] The laser wavelength-modulated at a plurality of modulation frequencies includes components of frequencies represented by the linear coupling of each modulation frequency. The frequency represented by the linear coupling of each modulation frequency is also called the linear coupling frequency. The linear coupling frequency includes a plurality of frequencies. Therefore, the spectrum of the light passing through and returning from the gas to be measured 103 includes a plurality of frequency components.

[0053] The gas analyzer 10 obtains the intensity of one frequency component among the plurality of frequency components of the spectrum of the light passing through and returning from the gas to be measured 103 as the intensity (P opt ) of the return light amount signal. As the frequency of the component corresponding to the return light amount signal, one frequency among the plurality of modulation frequencies (f L1 ~f Ln ) can be selected. In addition, as the frequency of the component corresponding to the return light amount signal, one frequency included in the linear coupling frequency can be selected.

[0054] The gas analyzer 10 obtains signals of one or more frequency components in the spectrum of the light passing through and returning from the gas to be measured 103 as signals including information related to the concentration of the gas to be measured 103. The information related to the concentration of the gas to be measured 103 is also called concentration information. The intensity of the signal including the concentration information is represented by P' C1 ~P' CmIt is represented. m is a natural number greater than or equal to 1 and can be defined independently of the value of n.

[0055] The gas analyzer 10 calculates the ratio of the intensity of the signal including the concentration information to the intensity of the return light quantity signal. The intensity of the signal including the concentration information (P’ C1 ~P’ Cm ) relative to the intensity of the return light quantity signal (P opt ) is represented by P C1 ~P Cm . Specifically, when i is a natural number greater than or equal to 1 and less than or equal to m, P Ci is calculated by P’ Ci / P opt .

[0056] P C1 ~P Cm is the intensity of the signal obtained by dividing the signal including the concentration information (P’ opt ) by the intensity of the return light quantity signal (P C1 ~P’ Cm ), and is also called the intensity of the concentration signal. That is, the concentration signal is the signal obtained by dividing the signal including the concentration information (P’ opt ) by the intensity of the return light quantity signal (P C1 ~P’ Cm ). 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 quantity signal, and is also called the intensity before conversion of the concentration signal.

[0057] The intensity of the concentration signal corresponds to the concentration of the measurement target gas 103. The gas analyzer 10 calculates the concentration of the measurement target gas 103 based on the intensity of the concentration signal. The gas analyzer 10 can calculate the concentration of the measurement target gas 103 based on the intensity of the concentration signal according to a calibration line, mathematical formula, table, etc. that determines the relationship between the intensity of the concentration signal and the concentration of the measurement target gas 103.

[0058] The gas analyzer 10 can 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 can obtain the intensity of one concentration signal by dividing the signal including one concentration information (P’ opt ) by the intensity of the return light quantity signal (P C1) and calculates the intensity (P) of the concentration signal C1 ). When the intensity of one concentration signal is obtained, the gas analyzer 10 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.

[0059] The gas analyzer 10 can obtain the intensities of a plurality of concentration signals based on the intensities of the respective multiple frequency components of the return light 102. That is, the gas analyzer 10 can divide the signal (P’ opt ) including a plurality of concentration information by the intensity (P C1 ~P’ Cm ) of the return light amount signal to calculate the intensities (P C1 ~P Cm ) of the plurality of concentration signals. When the intensities of the plurality of concentration signals are obtained, the gas analyzer 10 calculates a plurality of values as candidates for the measured value of the gas concentration based on the obtained intensities of the plurality of concentration signals. The values as candidates for the measured value of the gas concentration are also referred to as candidate values of the gas concentration. That is, when the intensities of the plurality of concentration signals are obtained, the gas analyzer 10 can calculate a plurality of candidate values of the gas concentration. The gas analyzer 10 can select one value from 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 can 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 can 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 can 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.

[0060] (Structural example of the gas analyzer 10 according to the present invention)

[0061] As Figure 5 shown, the gas analyzer 10 according to one embodiment of the present invention includes a waveform generator 11, a drive power supply 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 processing device 18.

[0062] The waveform generator 11 generates signal waveforms of multiple modulation frequencies for multiplexing modulation of the measurement light 101 and outputs them to the drive power supply 121 and the A / D converter 17. The waveform generator 11 may include an oscillator or a function generator, etc. 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 to generate a signal waveform for double modulation, or to generate a signal waveform for modulation three or more times.

[0063] The drive power supply 121 is a power supply for driving the light source 122. The drive power supply 121 drives the light source 122 based on the signal waveforms of multiple modulation frequencies input from the waveform generator 11. The drive power supply 121 outputs a drive signal and drives the light source 122. The drive signal may be, for example, a signal obtained by superimposing an AC signal and a DC signal of each of the multiple modulation frequencies. 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 supply 121 may be configured to include a transistor or a laser drive IC (Integrated Circuit), etc., that can supply a drive current to the light source 122.

[0064] The light source 122 is a laser source. The light source 122 emits laser light that has been frequency-modulated according to the signal waveforms of multiple modulation frequencies. The light source 122 can be controlled so that the center wavelength of the modulation of the laser reaches 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), etc. The waveform generator 11 is configured to be able to set the modulation frequency so that the light source 122 is configured to be able to set the modulation frequency.

[0065] 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), etc. The driver 131 drives the optical amplifier 132. The driver 131 may be configured to include components that can supply pump light or a drive current, etc., to the optical amplifier 132.

[0066] The lens 141 converts the laser light amplified by the optical amplifier 132 into parallel light and emits it as the 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 other optical elements such as a parabolic mirror that can convert laser light into parallel light.

[0067] The lens 142 causes the return light 102, which is the laser light emitted from and returned by the lens 141, to converge on the light detector 15. The lens 142 can be configured to include a condenser lens. The lens 142 can be replaced with other optical elements such as a parabolic mirror that can cause the return light 102 to converge on the light detector 15.

[0068] The light detector 15 converts the return light 102 into an electrical signal and outputs it as a received light signal. The light detector 15 can include, for example, a PD (Photo Diode) or the like.

[0069] The amplifier 16 amplifies the received light signal input from the light detector 15 and outputs it as an amplified signal. The amplifier 16 can be configured to include components such as transistors. When the light detector 15 is a PD, the amplifier 16 can include a circuit that converts the photocurrent output from the light detector 15 into a voltage.

[0070] 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.

[0071] The signal processing device 18 analyzes the digital signal and calculates the spectrum of the return light 102. The signal processing device 18 can perform an FFT (Fast Fourier Transform) of the digital signal to calculate the spectrum. The signal processing device 18 calculates a concentration signal based on the intensities of the respective frequency components included in the spectrum of the return light 102. The signal processing device 18 calculates the concentration of the measurement target gas 103 based on the concentration signal according to a calibration line, a relational expression, a table, or the like indicating the relationship between the concentration signal and the concentration of the measurement target gas 103.

[0072] The signal processing device 18 includes an arithmetic unit 181, a storage unit 182, and an interface 183.

[0073] The arithmetic unit 181 can 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 can be configured to execute a program that implements the functions of the signal processing device 18.

[0074] The storage unit 182 can store various information for the operation of the signal processing device 18, or a program that implements the functions of the signal processing device 18. The storage unit 182 can function as a working memory for the arithmetic unit 181. The storage unit 182 can be constituted by, for example, a semiconductor memory. The storage unit 182 can be integrated with the arithmetic unit 181 or can be separately constituted.

[0075] The interface 183 may include a communication interface that communicates with, for example, the A / D converter 17 or the waveform generator 11 in a wired or wireless manner. The communication interface may be configured to communicate based on various communication standards such as RS-232C, RS-485, or LAN (Local Area Network). The communication standard is not limited to the above examples and may be other various standards.

[0076] The interface 183 may include an input device that accepts input from a user. The input device may include, for example, a keyboard or physical keys, and may also include a pointing device such as a touch panel, a touch sensor, or a mouse. The interface 183 may be configured to accept input from an external input device.

[0077] The interface 183 may have a display device that displays the measurement result of the gas concentration and 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 and the like to an external display device.

[0078] The interface 183 may have a voice output device such as a speaker that emits voice information such as an alarm sound corresponding to the measurement result of the gas concentration. The interface 183 may be configured to output the voice information to an external speaker and the like.

[0079] The interface 183 is not limited to the above examples and may be configured to include various other devices or to be connected to various other devices.

[0080] The signal processing device 18 may be, for example, a PC (Personal Computer). The signal processing device 18 is not limited to the above example and may be configured in various ways. The signal processing device 18 may be integrated with the gas analyzer 10 or may be configured separately.

[0081] The signal processing device 18 may be configured to be able to set the 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 double modulation or triple or more modulation of the laser. The signal processing device 18 may set the modulation frequency based on an input from a user.

[0082] (Operation example of the gas analyzer 10 according to the present invention)

[0083] As described above, a gas analyzer 10 according to an embodiment of the present invention emits measurement light 101 from a lens 141 toward a measurement target gas 103. The measurement light 101 is light that is multiplexed modulated at a plurality of modulation frequencies. After the measurement light 101 is emitted from the lens 141, it passes through the measurement target gas 103 and is reflected or scattered by a scatterer 104 such as a wall. The reflected or scattered light passes through the measurement target gas 103 and returns to the gas analyzer 10. 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 enters the lens 142, analyzes the spectrum of the return light 102 using an arithmetic unit 181 of a signal processing device 18, and measures the concentration of the measurement target gas 103. The distances from the lenses 141 and 142 to the scatterer 104 are represented by L.

[0084] <Spectrum of Laser after Double Modulation>

[0085] In the present embodiment, the gas analyzer 10 emits laser that has been double modulated at two modulation frequencies as the measurement light 101, and measures the concentration of the measurement target gas 103. The two modulation frequencies include a first modulation frequency (f 1 ) and a second modulation frequency (f 2 ). The linear coupling frequency (f 1 ) of the laser that has been double modulated at 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.

[0086] The gas analyzer 10 uses a photodetector 15 to detect the return light 102 that has passed through and returned from the measurement target gas 103 of the double modulated measurement light 101, and analyzes the received signal of the return light 102 using the signal processing device 18 to calculate the spectrum of the return light 102. In the Figure 6 graph, the spectrum of the double modulated return light 102 is shown as an example. Figure 6 In the graph of the

[0087] horizontal axis represents frequency. The vertical axis represents the intensity of each frequency component. The double modulated return light 102 is laser in which the AC components and the DC component of the first modulation frequency and the second modulation frequency are superimposed. Therefore, the double modulated return light 102 has a DC component and components of the linear coupling frequencies of the first modulation frequency and the second modulation frequency. Figure 6 Specifically, in the spectrum of the double modulated return light 102 shown as an example in the 1) and the intensity of the component of the second modulation frequency (f 2 ) increase. In addition, the intensity of the frequency (f 1 + f 2 ) which is the sum of the first modulation frequency and the second modulation frequency increases. In addition, the intensity of the frequency (2f 2 ) which is twice the second modulation frequency is greater than that of other frequency components.

[0088] <<Suppression of Decrease Amount of Return Light Quantity Signal>>

[0089] As described above, the higher the gas concentration, the lower the light quantity of the return light 102. When the intensity of the return light quantity signal decreases to be less than, for example, 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 decreases due to too high a gas concentration or due to the measurement light 101 being emitted into the air or the like. In addition to the measurement light 101 being emitted into the air, the reasons for which the gas analyzer 10 cannot determine that the return light quantity signal decreases may include that the incident angle of the measurement light 101 with respect to the scatterer 104 is small, or the measurement light 101 enters the scatterer 104 having mirrors with direction offsets.

[0090] When the doubly modulated laser is emitted as the measurement light 101, the spectra of the measurement light 101 and the return light 102 include components of linear coupling frequencies in addition to the components of the modulation frequencies. In other words, the modulation frequency widths of the measurement light 101 and the return light 102 are analogously expanded. As a result, the frequency components of the spectrum of the return light 102 include frequency components that deviate from the peak frequency of the absorption spectrum of the measurement target gas 103 and are difficult to be absorbed by the measurement target gas 103. The arithmetic unit 181 of the signal processing device 18 can calculate the intensity of the frequency components that are difficult to be absorbed by the measurement target gas 103 as the intensity of the return light quantity signal. The arithmetic unit 181 can calculate the sum of the intensities of the multiple frequency components that are difficult to be absorbed by the measurement target gas 103 as the intensity of the return light quantity signal.

[0091] Here, as a comparison object, it is assumed that the singly modulated measurement light 101 obtained by modulating the laser with the second modulation frequency (f 2 ) is emitted. The spectrum of the return light 102 obtained in the case of single modulation is represented by a dotted line in Figure 6 . The singly 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.

[0092] In the case of single modulation, the component of the 1-fold frequency of the modulation frequency is set as the return light signal. However, in the case where the 1-fold frequency of the modulation frequency is easily absorbed by the measurement object gas 103, the intensity of the return light signal is greatly reduced. On the other hand, the spectrum of the return light 102 of the double modulation has frequency components other than the 1-fold frequency of the modulation frequency. Therefore, in the case of double modulation, the frequency component that is difficult to be absorbed by the measurement object gas 103 can be set as the return light signal. As a result, in the case of double modulation, the return light signal is selected in a manner that the intensity of the return light signal is difficult to reduce compared with the case of single modulation.

[0093] For example Figure 7 As shown, the higher the gas concentration, the more the intensity of the single-modulated return light 102 decreases. On the other hand, the decrease in the intensity of the double-modulated return light 102 is less than that of the single-modulated case. Specifically, when the gas concentration is 100 [%·m], the intensity of the double-modulated return light 102 is 6 times that of the single-modulated return light 102.

[0094] As described above, the gas analyzer 10 according to the present invention can suppress the decrease in the return light signal. The decrease in the return light signal can be suppressed, so that the return light signal is difficult to decrease even when the gas concentration is high. As a result, it is possible to avoid a state where it is impossible to distinguish whether the return light signal decreases due to excessively high gas concentration or due to other reasons.

[0095] <<High-sensitivity measurement>>

[0096] As described above, the calculation unit 181 of the signal processing device 18 of the gas analyzer 10 uses the intensity (P opt ) divided by the pre-transformed intensity of the concentration signal (P' C1 ~P' Cm ) and calculate the intensity of the concentration signal (P C1 ~P Cm ), and calculate the concentration of the measured object gas 103 based on the intensity of the concentration signal.

[0097] The calculation unit 181 selects one frequency component from among the multiple frequency components of the return light 102 as the return light amount signal. In addition, the calculation unit 181 selects at least one frequency component from among the multiple frequency components of the return light 102 as the concentration signal.

[0098] In this operation example, the calculation unit 181 selects the second modulation frequency (f 2 ) as the return light signal, and select the 2nd modulation frequency (2f 2 ) and the frequency of the sum of the first modulation frequency and the second modulation frequency (f 1+f 2 The component of ) is used as the concentration signal.

[0099] In Figure 6 In the spectrum of the return light 102 shown as an example in, the intensity of the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency is greater than the intensity of the component at the second harmonic frequency of the second modulation frequency. Therefore, when the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal, even when the gas concentration is low, the intensity of the concentration signal is greater than the noise level. As a result, when the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal, the gas concentration is measured with high sensitivity.

[0100] Figure 8 The relationship between the gas concentration and the intensity of the concentration signal is shown as an example in the graph of. Figure 8 The horizontal axis of the graph of 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 the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal is represented by the points plotted with open circles (○) as "dual modulation (high sensitivity)". As a comparison object, 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 with solid circles (●) as "single modulation".

[0101] In Figure 8 In the graph of, the noise level is represented by a dotted line. The intensity of the concentration signal when the component at the frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal is also greater than the noise level in the region where the gas concentration is low. Therefore, compared with the case of single modulation, the measurement sensitivity of the gas concentration is maintained.

[0102] As described above, in the case of single modulation, it is sometimes impossible to determine whether the decrease in the intensity of the return light amount signal is caused by an excessive gas concentration or by the measurement light 101 being emitted into the air or other reasons. That is, in the case of single modulation, it is sometimes impossible to determine the reason for the decrease in the intensity of the return light amount signal. On the other hand, by emitting the dual-modulated laser as the measurement light 101, it is possible to avoid the state where the reason for the decrease in the return light amount signal cannot be determined. That is, the gas analyzer 10 according to the present invention can maintain the sensitivity of the gas concentration to be equivalent to that in the case of single modulation and can avoid the state where the reason for the decrease in the return light amount signal cannot be determined by using the dual-modulated laser.

[0103] <<Wide dynamic range measurement>>

[0104] As described above, when a component having a 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 the same as in the case of single modulation. However, a calibration line showing the relationship between the intensity of the concentration signal when a component having a frequency that is the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal and the gas concentration deviates more from a straight line as the gas concentration increases, just like the calibration line in the case of single modulation. The gas analyzer 10 according to the present invention can improve the linearity of the calibration line in a range where the gas concentration is relatively high by using the laser after double modulation.

[0105] Specifically, in Figure 8 , the calibration line showing the relationship between the gas concentration and the intensity of the concentration signal when a component having a frequency that is twice the second modulation frequency is selected as the concentration signal is represented by points drawn as hollow triangles (△) as "double modulation (wide dynamic range)".

[0106] The calibration line when a component having a frequency that is twice the second modulation frequency is selected as the concentration signal becomes straight over a wide range from a range where the gas concentration is relatively low (0.1 [%·m]) to a range where the gas concentration is relatively high (100 [%·m]). The linearity of the calibration line is high over a wide range of gas concentrations, thereby expanding the dynamic range of the measurement of the gas concentration. That is, when a component having a frequency that is twice the second modulation frequency is selected as the concentration signal, the dynamic range of the measurement of the gas concentration is expanded.

[0107] As a reason for the calibration line becoming straight over a wide range of gas concentrations, the following reason can be considered. The intensity of the component having a frequency that is twice the second modulation frequency is less than the intensity of the component having a frequency that is the sum of the first modulation frequency and the second modulation frequency. As a result, it is difficult for the intensity of the component having a frequency that is twice the second modulation frequency to saturate more than the intensity of the component having a frequency that is the sum of the first modulation frequency and the second modulation frequency. In other words, compared with the waveform of the component having a frequency that is the sum of the first modulation frequency and the second modulation frequency, the waveform of the component having a frequency that is twice the second modulation frequency is less likely to be distorted in a range where the gas concentration is relatively high. The distortion of the waveform affects the relationship between the gas concentration and the intensity of the concentration signal. Therefore, it can be considered that even in a range where the gas concentration is relatively high, the calibration line becomes straight because the waveform is less likely to be distorted.

[0108] <<Selection of High-Sensitivity Measurement and Wide-Dynamic-Range Measurement>>

[0109] As described above, when a component having a frequency that is twice the second modulation frequency is selected as the concentration signal, the arithmetic unit 181 of the signal processing device 18 of the gas analyzer 10 can measure the gas concentration within a wide dynamic range. However, according to Figure 8In the graph shown as an example in [reference], the intensity of the concentration signal when measuring the gas concentration within a wide dynamic range is less than the noise level within the range where the gas concentration is less than or equal to 1 [%·m]. That is, when measuring the gas concentration within a wide dynamic range, the measurement sensitivity decreases.

[0110] Conversely, in the case of selecting the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal, the arithmetic unit 181 can measure the gas concentration with high sensitivity. However, according to Figure 8 In the graph shown as an example in [reference], within the range where the gas concentration is greater than or equal to 10 [%·m], the linearity of the calibration line indicating 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 shrinks.

[0111] As described above, wide dynamic range measurement and high sensitivity measurement sometimes reach a trade-off state. The arithmetic unit 181 can combine wide dynamic range measurement and high sensitivity measurement in a complementary manner to measure the gas concentration in a way that can eliminate the trade-off state. Specifically, the arithmetic unit 181 can adopt the measurement value based on high sensitivity measurement when the gas concentration is low, and adopt the measurement value based on wide dynamic range measurement when the gas concentration is high.

[0112] In Figure 8 On the calibration line shown as an example in [reference], the concentration signal of the double modulation (wide dynamic range) calibration line is sufficiently greater than the noise level within the range where the gas concentration is greater than or equal to 10 [%·m]. Therefore, the arithmetic unit 181 can select the component of the second harmonic frequency of the second modulation frequency as the concentration signal within the range where the gas concentration is greater than or equal to 10 [%·m], and adopt the measurement value of wide dynamic range measurement. Within the range where the gas concentration is less than 10 [%·m], the arithmetic unit 181 can select the component of the 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 high sensitivity measurement.

[0113] The boundary value of the gas concentration for selecting wide dynamic range measurement and high sensitivity measurement is not limited to the above example. In Figure 8 In the calibration line shown as an example in [reference], the concentration signal of the double modulation (wide dynamic range) calibration line is less than the noise level within the range where the gas concentration is less than or equal to 1 [%·m]. Therefore, the arithmetic unit 181 can select the component of the frequency that is the sum of the first modulation frequency and the second modulation frequency as the concentration signal within the range where the gas concentration is less than or equal to 1 [%·m], and adopt the measurement value of high sensitivity measurement. Within the range where the gas concentration is greater than 1 [%·m], the arithmetic unit 181 can select the component of the second harmonic frequency of the second modulation frequency as the concentration signal, and adopt the measurement value of wide dynamic range measurement.

[0114] The operation unit 181 can adopt the measurement value of high-sensitivity measurement within the range where the gas concentration is less than or equal to 1 [%·m], adopt the measurement value of wide dynamic range measurement within the range where the gas concentration is greater than or equal to 10 [%·m], and appropriately select the measurement value of high-sensitivity measurement and the measurement value of wide dynamic range measurement within the range where the gas concentration is greater than 1 [%·m] and less than 10 [%·m].

[0115] As described above, the gas analyzer 10 can select different frequency components as the concentration signal according to the gas concentration by using the doubly modulated laser, and can improve the measurement accuracy of the gas concentration. On the other hand, in the case of single modulation, the frequency component of the return light 102 is only the double frequency of the modulation frequency, so it is difficult to select different frequency components as the concentration signal. That is, the gas analyzer 10 according to the present invention uses the doubly modulated laser, so that the measurement accuracy of the gas concentration can be improved compared with the case of single modulation.

[0116] <<Influence of noise of specific frequency>>

[0117] Sometimes, noise of a specific frequency such as the vibration frequency of the scatterer 104 is superimposed on the return light 102. That is, sometimes the laser used for the gas analyzer 10 to measure the gas concentration is affected by noise of a specific frequency. The gas analyzer 10 according to the present invention can measure the gas concentration based on a plurality of frequency components included in the spectrum of the return light 102 by using the doubly modulated laser. In the presence of noise of a specific frequency, the gas analyzer 10 selects a frequency component different from the noise, thereby being able to weaken the influence of the noise and improve the measurement accuracy of the gas concentration.

[0118] For example, assume that the vibration frequency of the scatterer 104 is consistent with the frequency (f 1 + f 2 ) of the sum of the first modulation frequency and the second modulation frequency. In this case, as Figure 9 illustrated by way of example, only the noise level of the frequency component of the sum of the first modulation frequency and the second modulation frequency (f 1 + f 2 ) represented by the double-dashed line is higher than the noise level of the double frequency (2f 2 ) of the second modulation frequency represented by the dashed line.

[0119] In the case where the gas concentration is 10 [%·m], the noise level of the frequency component of (f 1 + f 2 ) increases, and thus when the frequency component of the sum of the first modulation frequency and the second modulation frequency is selected as the concentration signal, the signal-to-noise ratio of the doubly modulated (high-sensitivity) concentration signal is reduced to 1.

[0120] On the other hand, the noise level of the component at the frequency (2f 2 ) does not increase, so that when the component at twice the second modulation frequency is selected as the concentration signal, the SN ratio of the concentration signal in the case of dual modulation (wide dynamic range) becomes a sufficiently large value of 6.

[0121] In the Figure 10 graph, the fluctuations of the gas concentration calculated by the high-sensitivity measurement with an SN ratio of 1 and the gas concentration calculated by the wide-dynamic-range measurement with an SN ratio of 6 are shown respectively. Figure 10 For the horizontal axis of the graph of , each time when the gas concentration is calculated 100 times is represented as a measurement point. The vertical axis represents the gas concentration calculated at each measurement point.

[0122] The fluctuation of the gas concentration calculated by the high-sensitivity measurement with an SN ratio of 1 is represented by a dotted line. The standard deviation representing the fluctuation of the gas concentration calculated by the high-sensitivity measurement with an SN ratio of 1 is 2.95.

[0123] The fluctuation of the gas concentration calculated by the wide-dynamic-range measurement with an SN ratio of 6 is represented by a solid line. The standard deviation representing the fluctuation of the gas concentration calculated by the wide-dynamic-range measurement with an SN ratio of 6 is 0.51.

[0124] When the arithmetic unit 181 of the signal processing device 18 of the gas analyzer 10 can obtain the SN ratio of the concentration signal of each measurement, it can select the gas concentration calculated by the measurement with a higher SN ratio among the gas concentration calculated by the high-sensitivity measurement and the gas concentration calculated by the wide-dynamic-range measurement as the measured value of the gas concentration. When the arithmetic unit 181 can obtain the SN ratio of the concentration signal of one measurement, it can select the gas concentration calculated by this measurement based on the SN ratio as the measured value of the gas concentration. By making a selection based on the SN ratio, the influence of noise is reduced.

[0125] The arithmetic unit 181 can select the gas concentration with a smaller standard deviation as the measured value of the gas concentration. When it is determined that the calculation accuracy of the gas concentration of one measurement deteriorates, the arithmetic unit 181 can select the gas concentration calculated by the measurement with undeteriorated calculation accuracy as the measured value of the gas concentration. By making a selection based on the standard deviation, the influence of noise is reduced.

[0126] When it is impossible to select either the gas concentration calculated by the high-sensitivity measurement or the gas concentration calculated by the wide-dynamic-range measurement, the arithmetic unit 181 can calculate the average value of the gas concentrations calculated by the two measurements as the measured value of the gas concentration.

[0127] 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. Figure 10 In the graph of , the fluctuation of the average gas concentration is indicated by a dotted line, which indicates that the standard deviation of the fluctuation of the average gas concentration is 1.48.

[0128] The standard deviation of the average 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. Assuming that the calculation unit 181 reluctantly selects one gas concentration from the gas concentrations calculated by the two measurements, the measurement accuracy of the gas concentration is greatly deteriorated due to the erroneous selection of the gas concentration with large fluctuations.

[0129] The gas analyzer 10 calculates the average value of the gas concentrations calculated by the two measurements as the measured value of the gas concentration, thereby preventing the measurement accuracy from being significantly deteriorated due to the erroneous selection when one measurement is forcibly selected from the two measurements.

[0130] The calculation unit 181 can 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 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 can accept the input of the setting from the user using the input device of the interface 183.

[0131] As described above, the gas analyzer 10 can perform multiple measurements in parallel by using a double-modulated laser, each of which selects multiple frequency components as a concentration signal. The gas analyzer 10 can select a measured value of the gas concentration from the gas concentrations calculated by various measurements, or can calculate the average value of the gas concentrations calculated by various measurements as the measured value of the gas concentration. The gas analyzer 10 can perform multiple measurements in parallel, thereby improving the measurement accuracy of the gas concentration without extending the time required for the measurement of the gas concentration.

[0132] The gas concentrations calculated by the two measurements correspond to candidate values ​​of the gas concentration. The operation unit 181 may select one of the two candidate values ​​as the measured value of the gas concentration, or may calculate the average of the two candidate values ​​as the measured value of the gas concentration. The operation unit 181 may select the measured value of the gas concentration from the candidate values ​​based on the gas concentration. The operation unit 181 may select the measured value of the gas concentration from the candidate values ​​based on the SN ratio of the concentration signal.

[0133] <Flowchart Example>

[0134] The gas analyzer 10 can perform a gas analysis method including the sequence example of the flowchart exemplified in Figure 11 in order to measure the concentration of the gas to be measured 103. At least a part of the sequence of the gas analysis method can be implemented as a gas analysis program for causing the processor constituting the arithmetic unit 181 to execute. The gas analysis program can be stored in a non-temporary computer-readable medium.

[0135] The gas analyzer 10 emits a laser beam 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 beam that has passed through the gas to be measured 103 and has been scattered or reflected by the scatterer 104 and returned (step S2). The arithmetic unit 181 of the signal processing device 18 of the gas analyzer 10 performs an FFT on the received light signal of the laser beam and calculates the frequency components of the laser beam (step S3).

[0136] The arithmetic 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 arithmetic unit 181 calculates the gas concentration based on the intensity P C1 of the first concentration signal (step S5).

[0137] The arithmetic 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 arithmetic unit 181 calculates the gas concentration based on the intensity P C2 of the second concentration signal (step S7).

[0138] The arithmetic unit 181 calculates the measured value of the gas concentration based on the two gas concentrations calculated in the order of steps S4 to S7 (step S8). Specifically, the arithmetic unit 181 can select one 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 arithmetic unit 181 can 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.

[0139] After the gas analyzer 10 executes the sequence of step S8, it ends Figure 11 the execution of the sequence of the flowchart.

[0140] (Summary)

[0141] As described above, the gas analyzer 10 according to the present invention uses doubly modulated laser light, so that, compared with the case of using singly modulated laser light, it is possible to maintain the measurement accuracy of the concentration of the gas to be measured 103 and it is difficult to reduce the intensity of the return light amount signal when the gas concentration increases. It is possible to suppress the reduction amount of the intensity of the return light amount signal, so that even when the gas concentration is high, the return light amount signal is difficult to decrease. As a result, even when the gas concentration is high, it is possible to avoid a state where it is impossible to determine whether the reduction of the return light amount signal is caused by an excessive gas concentration or by the measurement light 101 being emitted into the air or other reasons.

[0142] The gas analyzer 10 according to the present invention uses doubly modulated laser light, so that it is possible to select a concentration signal in a manner that improves the linearity of the calibration line. Since the linearity of the calibration line is improved, it is possible to perform wide dynamic range measurement. As a result, compared with the case of using singly modulated laser light, it is possible to improve the measurement accuracy of a wide range of gas concentrations.

[0143] The gas analyzer 10 according to the present invention uses doubly modulated laser light, so that it is possible to avoid the frequency of specific noise caused by vibration of the scatterer 104 or the like and select a concentration signal. By avoiding the frequency of specific noise and selecting a concentration signal, it is possible to improve the measurement accuracy of the gas concentration.

[0144] The embodiments of the present invention have been described above with reference to the drawings, but the specific structure is not limited to this embodiment, and various modifications within the scope not departing from the gist of the present invention are also included.

[0145] In the above embodiment, an operation example of doubly modulating the laser at two modulation frequencies has been described. As another embodiment, the gas analyzer 10 may perform multiple modulation of the laser at three or more modulation frequencies.

[0146] In the above 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 perform three or more kinds of measurements in parallel to measure the gas concentration and calculate three or more candidate values of the gas concentration. The arithmetic 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 arithmetic 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 a part of the three or more candidate values of the gas concentration as the measured value of the gas concentration.

[0147] As the return light quantity signal for calculating the intensity of the concentration signal, and each piece of information of the return light quantity signal used to determine whether the reason for the decrease in the return light quantity is too high gas concentration or the measurement light 101 is emitted into the air, etc., the gas analyzer 10 can select the same frequency component or different frequency components.

[0148] In the present embodiment, the measurement target gas 103 is set to a gas containing measurement target components such as oxygen (O 2 ), carbon monoxide (CO), or carbon dioxide (CO 2 ). The measurement target gas may contain one or more measurement target components. The gas analyzer 10 can set the modulation frequency according to the characteristics of the measurement target components. The light source 122 is configured to be able to set the modulation frequency so as to appropriately modulate the measurement light 101 according to the measurement target components. As a result, the measurement accuracy of the gas concentration can be improved.

[0149] Explanation of reference numerals

[0150] 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: operation unit, 182: storage unit, 183: interface)

[0151] 101 Measurement light

[0152] 102 Return light

[0153] 103 Measurement target gas

[0154] 104 Scatterer

Claims

1. A gas analyzer having a computing unit, wherein: The calculation unit calculates the intensity of one concentration signal based on the intensity of one frequency component of return light after multiply modulated measurement light passes through and returns from the measurement target gas, or the intensities of a plurality of concentration signals based on the intensities of a plurality of frequency components of the return light. A measured value of the concentration of the measurement target gas is calculated based on the intensity of the one concentration signal or the intensities of the plurality of concentration signals.

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

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

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

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

6. A gas analysis method, wherein: The gas analysis method comprises the following steps: The gas analyzer calculates the intensity of one concentration signal based on the intensity of one frequency component of return light after multiply modulated measurement light passes through and returns from the measurement target gas, or the intensities of multiple concentration signals based on the intensities of multiple frequency components of the return light; and The gas analyzer 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.

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