Gas absorption characteristic measurement device, temperature measurement device, concentration ratio measurement device, and gas absorption characteristic measurement method

Abstract

This gas absorption characteristic measurement device comprises: a first laser diode for oscillating a first laser beam having a first wavelength; a second laser diode for oscillating a second laser beam having a second wavelength different from the first wavelength; a first modulation unit configured to apply a first modulation signal having a predetermined modulation frequency to the first laser diode to modulate the first laser beam; a second modulation unit configured to apply, to the second laser diode, a second modulation signal having said modulation frequency and having a phase difference from the first modulation signal to modulate the second laser beam; a multiplexer configured to multiplex the first laser beam modulated using the first modulation signal and the second laser beam modulated using the second modulation signal to obtain a multiplexed laser beam; a detector configured to receive the multiplexed laser beam that is from the multiplexer so that a measurement target gas is irradiated therewith, and that is transmitted through the gas, thereby converting the multiplexed laser beam into a detection signal; and a signal acquisition unit for acquiring, from the detection signal, a first component signal including a component indicating the absorbance at the first wavelength and a second component signal including a component indicating the absorbance at the second wavelength, in the measurement target gas at the irradiation position of the multiplexed laser beam. The signal acquisition unit includes: a first demodulation part for demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (where n is an integer) the frequency of said modulation frequency; a second demodulation part for demodulating the detection signal using a second reference signal having said reference frequency and having a phase difference from the first reference signal; a first extraction part for extracting the first component signal as a DC component from a signal demodulated using the first reference signal; and a second extraction part for extracting the second component signal as a DC component from a signal demodulated using the second reference signal.

Description

Gas absorption characteristic measuring device, temperature measuring device, concentration ratio measuring device, and gas absorption characteristic measuring method

[0001] The present disclosure relates to a gas absorption characteristic measuring device, a temperature measuring device, a concentration ratio measuring device, and a gas absorption characteristic measuring method.This application claims priority based on Japanese Patent Application No. 2023-098191, filed with the Japan Patent Office on June 15, 2023, the contents of which are incorporated herein by reference.

[0002] It is known to measure values ​​indicating the state of a gas (for example, the temperature of the gas or the concentration of a component in the gas) in a non-contact manner using a laser beam.

[0003] Patent Document 1 describes an apparatus for measuring the temperature of high-temperature gas in a gas turbine using a laser beam. This apparatus uses a tunable diode laser to irradiate combustion gas with two laser beams having different wavelengths and detects the two laser beams that have passed through the combustion gas. The apparatus then obtains the absorbance of the combustion gas at each wavelength from a signal indicating the intensity of the detected laser beams, and determines the temperature of the combustion gas based on the ratio of these absorbances.

[0004] JP 2012-057623 A

[0005] The combustion gas temperature measuring device described in Patent Document 1 uses a tunable diode laser to switch between multiple laser beams with different wavelengths for irradiation and detection, which causes the irradiation and detection times of the multiple laser beams to be shifted, making it impossible to detect the absorbance of the combustion gas at each wavelength at the same time.

[0006] In a situation where the state of the gas to be measured changes over time, if the absorbance of the combustion gas at each wavelength cannot be detected simultaneously as described above, the ratio of these absorbances and the accuracy of the temperature determined from the ratio of these absorbances are thought to be low. In particular, in gases that flow at high speeds, such as combustion gases from a gas turbine, the state of the gas (temperature, etc.) at the position of the measurement target can change at high speeds, and the above-mentioned problem is thought to be significant.

[0007] In view of the above circumstances, at least one embodiment of the present invention aims to provide a gas absorption characteristics measuring device, a temperature measuring device, a concentration ratio measuring device, and a gas absorption characteristics measuring method that are capable of accurately obtaining the absorbance ratio of two laser beams having different wavelengths.

[0008] a first modulation unit configured to modulate the first laser light by applying a first modulation signal having a predetermined modulation frequency to the first laser diode; a second modulation unit configured to modulate the second laser light by applying a second modulation signal having the modulation frequency and having a phase difference with the first modulation signal to the second laser diode; a combiner configured to combine the first laser light modulated using the first modulation signal and the second laser light modulated using the second modulation signal to obtain a combined laser light; a detector configured to receive the combined laser light from the combiner that has been irradiated onto a gas to be measured and transmitted through the gas, and convert it into a detection signal; and a signal acquisition unit configured to acquire from the detection signal a first component signal including a component indicative of absorbance at the first wavelength in the gas to be measured at an irradiation position of the combined laser light and a second component signal including a component indicative of absorbance at the second wavelength. the signal acquisition unit includes: a first demodulation unit for demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (n is an integer) the modulation frequency; a second demodulation unit for demodulating the detection signal using a second reference signal that has the reference frequency and has a phase difference with the first reference signal; a first extraction unit for extracting the first component signal as a DC component from the signal demodulated using the first reference signal; and a second extraction unit for extracting the second component signal as a DC component from the signal demodulated using the second reference signal.

[0009] Furthermore, at least one embodiment of the present invention provides a temperature measuring device that includes the above-described gas absorption characteristic measuring device, wherein the signal analysis unit includes a temperature determination unit configured to determine the temperature of the gas at the irradiation position of the combined laser light on the gas to be measured based on the first component signal and the second component signal.

[0010] Furthermore, at least one embodiment of the present invention provides a concentration ratio measuring device that includes the above-described gas absorption characteristic measuring device, wherein the signal analysis unit includes a concentration ratio determination unit configured to determine the concentration ratio of the first substance to the second substance in the gas at the irradiation position of the combined laser light in the gas to be measured based on the first component signal and the second component signal.

[0011] a step of modulating the first laser light by applying a first modulation signal having a predetermined modulation frequency to the first laser diode; a step of modulating the second laser light by applying a second modulation signal having the modulation frequency and having a phase difference with the first modulation signal to the second laser diode; a step of combining the first laser light modulated using the first modulation signal and the second laser light modulated using the second modulation signal to obtain a combined laser light; a step of receiving from the combiner the combined laser light that has been irradiated onto a gas to be measured and transmitted through the gas and converting it into a detection signal; and a signal acquiring step of acquiring from the detection signal a first component signal including a component indicative of absorbance at the first wavelength in the gas to be measured at a position irradiated with the combined laser light and a second component signal including a component indicative of absorbance at the second wavelength, The method includes the steps of: demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (where n is an integer) the modulation frequency; demodulating the detection signal using a second reference signal having the reference frequency and having a phase difference with the first reference signal; extracting the first component signal as a DC component from the signal demodulated using the first reference signal; and extracting the second component signal as a DC component from the signal demodulated using the second reference signal.

[0012] According to at least one embodiment of the present invention, there are provided a gas absorption characteristic measuring device, a temperature measuring device, a concentration ratio measuring device, and a gas absorption characteristic measuring method that can accurately obtain the absorbance ratio of two laser beams having different wavelengths.

[0013] 10 is a schematic diagram of a gas absorption characteristic measuring device according to an embodiment; FIG. 11 is a schematic diagram of a gas absorption characteristic measuring device according to an embodiment; FIG. 12 is a graph schematically showing an absorption line of a gas to be measured and the waveform of a first laser beam modulated at a specified modulation frequency; FIG. 13 is a graph showing waveforms of signal intensity of first and second laser beams modulated with first and second modulation signals, respectively; FIG. 14 is a graph showing waveforms of signal intensity of a first reference signal and a second reference signal; FIG. 15 is a diagram for explaining extraction of a first component signal and a second component signal as DC components; FIG. 16 is a diagram for explaining extraction of a first component signal and a second component signal as DC components; FIG. 17 is a graph showing the correlation between the ratio of absorbance at two wavelengths showing the absorption peak of water and temperature; FIG. 18 is a graph showing time changes (measurement results) of absorbance at 1334 nm (first wavelength λa), absorbance at 1388 nm (second wavelength λb), and gas temperature (flame temperature); FIG. 19 is an enlarged view of FIG. 10 , showing the time of burner ignition. 10 is an enlarged view showing the burner extinguished state. FIG. 11 is a graph showing the difference in absorbance depending on the concentration of a substance in a gas. FIG. 12 is a graph showing the relationship between absorbance and temperature for each of different concentrations of a substance in a gas. FIG. 13 is a diagram showing a schematic diagram of mutual interference between two absorbance outputs. FIG. 14 is a graph showing the correlation between two absorbances and temperature.

[0014] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0015] 1 and 2 are schematic diagrams of a gas absorption characteristic measuring device according to one embodiment. As shown in Fig. 1, the gas absorption characteristic measuring device 1 includes a first laser diode 2, a second laser diode 4, a first modulator 6, a second modulator 8, a multiplexer 10, a detector 14, a signal acquirer 16, and a demodulated signal generator 18.

[0016] The first laser diode 2 is configured to emit a first laser beam 2 having a first wavelength λa, which is a wavelength that exhibits a specific absorption peak in the gas 12 (see FIG. 1) to be measured.

[0017] The second laser diode 4 is configured to emit a second laser beam having a second wavelength λb different from the first wavelength λa, the second wavelength λb being a wavelength that exhibits a specific absorption peak in the measurement target gas 12 (see FIG. 1 ) that is different from the first wavelength λa.

[0018] Each of the first laser diode 2 and the second laser diode 4 may be a distributed feedback laser (DFB-LD).

[0019] The first modulator 6 is configured to modulate the first laser beam by applying a first modulation signal having a predetermined modulation frequency (f) to the first laser diode 2. The first modulator 6 may include a modulator configured to modulate the first laser beam at a predetermined modulation frequency (f: e.g., 10 kHz) centered on the peak wavelength λa (see FIG. 3 ). Here, FIG. 3 is a graph schematically showing absorption lines of the measurement target gas 12 in the vicinity of the first wavelength λa and the waveform of the first laser beam modulated by the first modulator 6 at the predetermined modulation frequency (f: e.g., 10 kHz).

[0020] The second modulation unit 8 is configured to modulate the second laser light by applying a second modulation signal having the above-mentioned specified modulation frequency (f) and having a predetermined phase difference with the first modulation signal to the second laser diode 4. The second modulation unit 8 may include a modulator configured to modulate the second laser light at the above-mentioned specified modulation frequency (f: for example, 10 kHz) centered on the peak wavelength λb (see FIG. 3).

[0021] The phase difference between the first modulation signal and the second modulation signal is adjusted so that the phase difference between the first laser light modulated by the first modulation signal and the second laser light modulated by the second modulation signal becomes a predetermined phase difference Δθmod, which will be described later.

[0022] 4 is a graph showing waveforms of the signal intensities of the first and second laser beams modulated by the first and second modulation signals, respectively. In the case of a DFB laser, the injection current (drive current) of the DFB laser is oscillated (i.e., current modulation) to oscillate the wavelength at a modulation frequency (f) centered on a specific wavelength, as described above. At this time, the output fluctuates in proportion to the injection current into the DFB laser, so the signal intensity of the first laser beam (first laser beam modulated by the first modulation signal) emitted from the first laser diode oscillates at the modulation frequency (f) as shown in FIG. 4. Similarly, the signal intensity of the second laser beam (second laser beam modulated by the second modulation signal) emitted from the second laser diode oscillates at the modulation frequency (f) as shown in FIG. 4.

[0023] Note that the output (intensity) fluctuation of the DFB laser follows the current modulation with a certain delay, and this delay varies depending on the individual DFB laser. Therefore, the phase difference between the first modulated signal and the second modulated signal is almost the same as the phase difference Δθmod between the first laser light modulated by the first modulated signal and the second laser light modulated by the second modulated signal, but there is often a slight deviation.

[0024] The multiplexer 10 is configured to multiplex a first laser beam modulated using a first modulation signal and a second laser beam modulated using a second modulation signal to obtain a multiplexed laser beam. The multiplexer 10 may be an optical fiber coupler configured to mix the first laser beam modulated using the first modulation signal and the second laser beam modulated using the second modulation signal.

[0025] The combined laser light obtained by the combiner 10 is irradiated onto a gas 12 to be measured.

[0026] The detector 14 is configured to receive the combined laser light from the combiner 10 that is irradiated onto the gas 12 to be measured and transmitted through the gas 12, and convert it into a detection signal.

[0027] The signal acquirer 16 is configured to acquire a first component signal including a component indicating absorbance at a first wavelength λa and a second component signal including a component indicating absorbance at a second wavelength λb in the gas to be measured at the irradiation position of the combined laser beam from the detection signal detected by the detector 14. The demodulation signal generator 18 is configured to generate a demodulation signal having a predetermined reference frequency for demodulating the combined laser beam.

[0028] As shown in FIG. 2, the signal acquisition unit 16 includes a first demodulation unit 28, a second demodulation unit 32, a first extraction unit 30, and a second extraction unit 34.

[0029] The signal acquisition unit 16 is configured to receive the detection signal from the detector 14 and also receive the demodulation signal having a predetermined reference frequency from the demodulation signal generation unit 18 .

[0030] Here, the frequency of the demodulated signal (reference frequency) is 2n times (where n is an integer) the modulation frequency (f; for example, 10 kHz). As an example, the case where n=1 (i.e., the reference frequency is 2f; for example, 20 kHz) will be described below, but the frequency of the demodulated signal may be four times (reference frequency is 4f), six times (reference frequency is 6f), or eight times (reference frequency is 8f) the modulation frequency (f).

[0031] In the signal acquisition unit 16, the detection signal from the detector 14 is sent to a first demodulation unit 28 and a second demodulation unit 32, respectively.

[0032] In the signal acquisition unit 16, the demodulated signal from the demodulated signal generation unit 18 is sent to the phase shifter 26. The phase shifter 26 shifts the phase of the demodulated signal having the above-mentioned predetermined reference frequency and outputs it as a plurality of signals having mutually different phases.

[0033] More specifically, the phase shifter 26 is configured to send the demodulated signal from the demodulated signal generation unit 18 to the first demodulation unit 28 as a first reference signal at a predetermined phase (e.g., with a phase difference of zero degrees from the original demodulated signal), and to send the same demodulated signal to the second demodulation unit 32 as a second reference signal with a phase difference of Δθref from the first reference signal (i.e., for example, a phase difference of θref from the original demodulated signal).

[0034] The first demodulation unit 28 is configured to demodulate the detection signal from the detector 14 using the above-mentioned first reference signal. The first demodulation unit 28 may include a first multiplier configured to output the product of the detection signal and the first reference signal.

[0035] The second demodulation unit 32 is configured to demodulate the detection signal from the detector 14 using the above-mentioned second reference signal. The second demodulation unit 32 may include a second multiplier (a multiplier separate from the first multiplier) configured to output the product of the detection signal and the second reference signal.

[0036] 5 is a graph showing waveforms of the signal strength of the first reference signal and the second reference signal. As shown in FIG. 5, the first reference signal and the second reference signal have a common frequency, but there is a predetermined phase difference Δθref between them. In one embodiment, the phase difference Δθref between the first reference signal and the second reference signal is 90 degrees.

[0037] The first extractor 30 is configured to extract a first component signal, which is a DC component, from the signal demodulated using the first reference signal. The second extractor 34 is configured to extract a second component signal, which is a DC component, from the signal demodulated using the second reference signal.

[0038] The first extraction unit 30 and / or the second extraction unit 34 may include a low-pass filter configured to pass only frequency components of the signal to be processed (the signal demodulated using the first reference signal or the second reference signal) that are equal to or lower than a predetermined value. The first extraction unit 30 and / or the second extraction unit 34 may include a low-pass filter configured to pass only frequency components of the signal to be processed (the signal demodulated using the first reference signal or the second reference signal) that are equal to or lower than a predetermined value. －１ It may also include a low-pass filter of 100 kHz or less.

[0039] In some embodiments, the phase difference Δθdem between the component (2n-th harmonic component) of the reference frequency (2n×f) in the signal component derived from the first laser light contained in the detection signal and the component (2n-th harmonic component) of the reference frequency (2n×f) in the signal component derived from the second laser light contained in the detection signal (i.e., the phase difference Δθdem of the reference frequency component (2n-th harmonic component) in the detection signal), and the phase difference Δθmod between the first laser light modulated with the first modulation signal and the second laser light modulated with the second modulation signal, satisfy Δθmod = Δθdem / 2n.

[0040] When the phase difference Δθref between the first and second reference signals is 90 degrees, the phase difference Δθdem of the reference frequency component (2n-th wave component) in the detection signal can be set to 90 degrees (i.e., to set the phase difference Δθdem to 90 degrees, the phase difference between the first and second modulated signals can be adjusted so that the phase difference Δθmod of the modulated first and second laser beams is 90 degrees / 2n (45 degrees when n = 1)), and the first and second component signals can be extracted as DC components. This will be described with reference to FIGS. 6 to 8.

[0041] First, let us consider a case in which a first laser light modulated by a first modulation signal (f, here 10 kHz) having a first wavelength λa of the absorption peak of a specific substance contained in the gas to be measured is irradiated onto the gas to be measured (i.e., the first laser light is irradiated onto the gas without being multiplexed with the second laser light).

[0042] In this case, if the gas to be measured does not contain the above-mentioned specific substance, the first laser light modulated by the modulation signal (f, 10 kHz) is not absorbed at the first wavelength λa and passes through the gas. Therefore, as shown in Fig. 6, the detection signal detected by the detector 14 (solid line in Fig. 6) does not contain 2n x f components (2f component, 4f component, 6f component, etc.). Note that the dashed line in Fig. 6 indicates the waveform of the 2f component.

[0043] On the other hand, in a similar case, if the gas to be measured contains the above-mentioned specific substance, the first laser light modulated with a modulation signal (f, 10 kHz) is absorbed at a first wavelength λa. This first wavelength λa corresponds to the center of oscillation (signal intensity) of the modulated first laser light, and therefore the first wavelength λa is passed through twice during one oscillation period of the modulated first laser light. Therefore, as shown in FIG. 7 , the detection signal (solid line in FIG. 7 ) detected by the detector 14 contains 2n×f components (2f component, 4f component, 6f component, etc.). Note that the dashed line in FIG. 7 indicates the waveform of the 2f component.

[0044] In this embodiment, the gas to be measured is irradiated with first and second laser beams modulated by first and second modulation signals (f, here 10 kHz) with respect to a first wavelength λa and a second wavelength λb of two specific absorption peaks in the gas to be measured. Therefore, as shown in FIG. 8 , the detection signal (solid line in FIG. 8 ) detected by the detector 14 includes 2n×f components (2f components, 4f components, 6f components, etc.; hereinafter, also referred to as 2n-th harmonic components) corresponding to the first wavelength λa and the second wavelength λb, respectively. In the detection signal, the 2n×f components (e.g., 2f components) corresponding to each wavelength are superimposed signals that can be distinguished solely by phase difference. The phase difference Δθdem (see Figure 8) between the reference frequency component (2n x f component) in the signal component derived from the first laser light contained in the detection signal and the reference frequency component (2n x f component) in the signal component derived from the second laser light contained in the detection signal (i.e., the phase difference of the reference frequency component (2n x f component) in the detection signal) is expressed as Δθdem = 2n x Δθmod, and corresponds to the phase difference Δθmod between the first and second laser lights after modulation.

[0045] Here, consider the case where the phase difference Δθdem between the reference frequency components (2n×f components) in the detection signal is 90 degrees. That is, in an example where n = 1, the phases of the 2f components (2f: 20 kHz) of the first and second laser beams modulated with the first and second modulation signals (f: 10 kHz), respectively, are shifted by 90 degrees. For convenience, the 2f component for the first laser beam included in the detection signal will be referred to as the "measurement signal on the 0-degree phase side," and the 2f component for the second laser beam will be referred to as the "measurement signal on the 90-degree phase side." In this case, the phase difference Δθmod between the first laser beam (f: 10 kHz) modulated with the first modulation signal and the second laser beam (f: 10 kHz) modulated with the second modulation signal is 45 degrees (90 degrees / 2n).

[0046] Here, the 2f component included in the detection signal is expressed as sin(ωt+α), and the reference signal is expressed as sin(ωt+β). Considering that the detection signal is demodulated using the reference signal, the product of the 2f component of the detection signal and the reference signal can be expressed as follows: cos(β-α) / 2-cos(2ωt+α+β) / 2 ... (A) The first term in the above equation (A) is a DC component that does not oscillate with time, and the second term is a component that oscillates with time, so the latter can be removed using a low-pass filter or the like (first / second extraction unit). Here, if the phase difference between one 2f component included in the detection signal and the reference signal (2f) is 90 degrees, the first term in the above equation (A) will be zero.

[0047] That is, when the phase of the reference signal (2f) is adjusted to 0 degrees, the measurement signal on the phase 0 degree side can be obtained as a DC component from the first extraction unit 30 and the second extraction unit 34, and when the phase of the reference signal is adjusted to 90 degrees, the measurement signal on the phase 90 degree side can be obtained as a DC component from the first extraction unit 30 and the second extraction unit 34.

[0048] The first component signal and the second component signal (DC component) acquired in this manner by the first extraction unit 30 and the second extraction unit 34 indicate the absorbance at the first wavelength λa and the second wavelength λb, respectively.

[0049] The signal acquisition unit 16 may include a lock-in amplifier for detecting frequency components equal to the reference signal from the detection signal. Of the various signals contained in the measurement signal, only components equal to the reference signal frequency become DC and can pass through the first extraction unit 30 and the second extraction unit 34 (low-pass filters, etc.). Furthermore, other components are converted to AC signals with a frequency ≠ 0 Hz and are removed by the first extraction unit 30 and the second extraction unit 34 (low-pass filters, etc.). Therefore, only the targeted components can be converted to DC components and extracted. Alternatively, the lock-in amplifier may be a dual-phase lock-in amplifier having two systems, each using two reference signals with a phase shift of 90 degrees.

[0050] In the above-described embodiment, the gas to be measured is irradiated with a combined laser beam obtained by combining first and second laser beams having first and second wavelengths, respectively, and adding first and second modulation signals that are out of phase with each other, so that a single position can be simultaneously irradiated with laser beams having components of the first and second wavelengths (combined laser beam). Furthermore, the detection signal obtained by detecting the combined laser beam that has passed through the gas to be measured includes components of a frequency that is 2n times the modulation frequency (hereinafter also referred to as 2n-th harmonic components) in the signal component derived from the first laser beam and the component derived from the second laser beam, and the phase difference Δdem between these 2n-th harmonic components (phase difference at the demodulation frequency) corresponds to the phase difference Δθmod of the first and second laser beams modulated by the first and second modulation signals, respectively. Therefore, by demodulating the above-described detection signal using first and second reference signals having reference frequencies corresponding to the frequencies of the 2n-th harmonic components and a predetermined phase difference, first and second component signals indicating the absorbance at the wavelengths of the first and second laser beams can be independently extracted. This allows the absorbance (first and second component signals) at the first and second wavelengths at the same time at a single position (the irradiation position of the combined laser beam; the measurement position) of the target gas to be measured. That is, according to the above-described embodiment, the absorbance at two different wavelengths (the first and second wavelengths) at the same time at the same position of the target gas can be obtained, thereby enabling the ratio of the absorbance at the first and second wavelengths at the target gas position (measurement position) to be accurately obtained. Therefore, based on this absorbance ratio, a value indicating the state of the target gas at the position (such as temperature or concentration) can be accurately obtained.

[0051] Furthermore, in the above-described embodiment, the phase difference Δθref between the first reference signal and the second reference signal is 90 degrees, and the phase difference Δθdem of the reference frequency component (2n-th harmonic component) in the detection signal is approximately 90 degrees. Therefore, the signal obtained by demodulating the detection signal using the first reference signal and the signal obtained by demodulating the detection signal using the second reference signal each contain a DC component proportional to the intensity of the reference frequency component (frequency of the reference signal) in the detection signal. The magnitude of one of these DC components (first component signal) indicates the absorbance at the first wavelength, and the magnitude of the other DC component (second component signal) indicates the absorbance at the second wavelength. Therefore, the absorbance (first and second component signals) at the first and second wavelengths at the same time at a single position (irradiation position of the combined laser light) in the gas to be measured can be appropriately obtained.

[0052] Furthermore, in the above-described embodiment, since the phase difference Δθmod between the first and second laser beams modulated with the first and second modulation signals, respectively, is Δθdem / 2n, the phase difference between the components (components corresponding to the first and second wavelengths, respectively) having the same frequency as the reference frequency included in the detection signal of the combined laser beam transmitted through the measurement target gas is 90 degrees. Therefore, by demodulating such a detection signal using the first reference signal and the second reference signal, respectively, which have a phase difference of 90 degrees, it is possible to obtain signals each including a DC component (first component signal and second component signal) corresponding to the component having the same frequency as the reference frequency. Therefore, the DC components (first component signal and second component signal) can be extracted independently from these signals.

[0053] As shown in FIG. 1, the gas absorption characteristic measuring device 1 may include a signal analysis unit 20 for calculating a value indicating the state of the gas at the irradiation position of the combined laser light on the gas to be measured based on the first component signal and the second component signal.

[0054] In some embodiments, the signal analyzer 20 may include a temperature determiner configured to determine the temperature of the gas at the irradiation position of the combined laser light on the measurement target gas based on the first component signal and the second component signal. That is, the gas absorption characteristics measuring device 1 may function as a temperature measuring device.

[0055] In this case, the first laser diode 2 may be configured to emit a first laser light having a first wavelength λa, which is the wavelength of a first absorption peak of a substance contained in the gas to be measured, and the second laser diode 4 may be configured to emit a second laser light having a second wavelength λb, which is the wavelength of a second absorption peak of the same substance.

[0056] For example, the first laser diode 2 may be configured to emit a first laser light having a first wavelength λa (1334 nm), which is the wavelength of the absorption peak of water (water vapor, HO) contained in the gas to be measured (combustion exhaust gas, etc.), and the second laser diode 4 may be configured to emit a second laser light having a second wavelength λb (1388 nm), which is the wavelength of the second absorption peak of water.

[0057] According to the above-described embodiment, it is possible to obtain the absorbances of the measurement target gas at two different wavelengths (i.e., the first wavelength, which is the wavelength of the first absorption peak, and the second wavelength, which is the wavelength of the second absorption peak) at the same position and at the same time. This makes it possible to accurately obtain the ratio of the absorbances at the first / second wavelengths at that position of the measurement target gas. Therefore, it is possible to accurately obtain the temperature of the measurement target gas at that position based on this absorbance ratio.

[0058] 9 to 12, an example of measuring the flame temperature of a combustion burner will be described as an application example of the gas absorption characteristic measuring device 1 according to an embodiment to temperature measurement.

[0059] FIG. 9 is a graph showing the correlation between the ratio of absorbance at two wavelengths showing the absorption peak of water (water vapor, HO), 1334 nm (first wavelength λa) and 1388 nm (second wavelength λb), and temperature.

[0060] As shown in the graph of FIG. 9 , the higher the water temperature, the greater the absorbance (absorption intensity) at 1334 nm (first wavelength λa) and the smaller the absorbance (absorption intensity) at 1388 nm (second wavelength λb). The ratio of the absorbance at 1334 nm (first wavelength λa) to the absorbance at 1388 nm (second wavelength λb) changes depending on the temperature. Therefore, the water temperature can be determined from the ratio of the absorbance at 1334 nm (first wavelength λa) to the absorbance at 1388 nm (second wavelength λb). The correlation between the absorbance ratio and temperature shown in FIG. 9 is obtained in advance through experiments, etc.

[0061] The test method was as follows. Using the gas absorption characteristic measuring device 1 described above, a burner was installed so that the burner flame crossed the optical path of the combined laser beam from the combiner 10. The temperature of the burner flame at the height position of the combined laser beam was determined from the ratio of the absorbance at 1334 nm (first wavelength λa) to the absorbance at 1388 nm (second wavelength λb) obtained by the gas absorption characteristic measuring device 1 and the correlation between the absorbance ratio and temperature obtained in advance (see FIG. 9 ).

[0062] The test results are shown in Figures 10 to 12. Figure 10 is a graph showing the absorbance (LD1-absorption intensity) at 1334 nm (first wavelength λa), the absorbance (LD2-absorption intensity) at 1388 nm (second wavelength λb), and the time change (measurement results) of the gas temperature (flame temperature) obtained by the gas absorption characteristic measuring device 1. Figures 11 and 12 are enlarged views of the graph in Figure 10, with Figure 11 being an enlarged view showing the time when the burner is ignited (burner ON), and Figure 12 being an enlarged view showing the time when the burner is extinguished (burner OFF).

[0063] As shown in Fig. 10, the temperature of the burner flame at the height of the laser beam measured using the gas absorption characteristic measuring device 1 according to the embodiment was approximately 1500°C to 1600°C, which coincided with the temperature range measured using another method. Furthermore, as can be seen from Figs. 11 and 12, even when the temperature changed drastically, such as when the burner was ignited or extinguished, the temperature for each hour could be obtained with high accuracy.

[0064] In some embodiments, the signal analyzer 20 may include a concentration ratio determiner configured to determine the concentration ratio of the first substance to the second substance in the gas at the position where the combined laser light is irradiated on the gas to be measured, based on the first component signal and the second component signal. That is, the gas absorption characteristics measuring device 1 may function as a concentration ratio measuring device.

[0065] In this case, the first laser diode 2 is configured to emit a first laser light having a first wavelength λa, which is the wavelength of the absorption peak of a first substance contained in the gas to be measured, and the second laser diode 4 is configured to emit a second laser light having a second wavelength λb, which is the wavelength of the absorption peak of a second substance contained in the gas to be measured.

[0066] For example, the first laser diode 2 may be configured to emit a first laser light having a first wavelength λa (1.6537 μm), which is the wavelength of the absorption peak of methane (first substance) contained in the gas to be measured, and the second laser diode 4 may be configured to emit a second laser light having a second wavelength λb (1300 nm), which is the wavelength of the absorption peak of water (second substance) contained in the gas to be measured.

[0067] According to the above-described embodiment, it is possible to obtain the absorbances of the measurement target gas at two different wavelengths (i.e., a first wavelength that is the wavelength of the absorption peak of the first substance and a second wavelength that is the wavelength of the absorption peak of the second substance) at the same position and at the same time. This makes it possible to accurately obtain the ratio of the absorbances at the first / second wavelengths at that position of the measurement target gas. Therefore, based on this absorbance ratio, it is possible to accurately obtain the concentration ratio of the first substance to the second substance in the measurement target gas at that position.

[0068] In some embodiments, in the gas absorption characteristic measuring device 1, the phase difference Δθdem between the reference frequency components (2n-th harmonic components) in the signal components derived from the first laser beam and the second laser beam contained in the detection signal does not have to be 90 degrees. Specifically, the phase difference Δθdem may be greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees. In one embodiment, the phase difference Δθdem may be 135 degrees.

[0069] In the above-described embodiment, the phase difference Δθdem of the reference frequency component (2n-th harmonic component) included in the detection signal is set to a value greater than 0 degrees and less than 90 degrees, or a value greater than 90 degrees and less than 180 degrees. This makes it possible to increase or decrease the measurement sensitivity of the value (temperature, concentration, etc.) indicating the state of the gas being measured, which is indicated by the absorbance ratio at the first / second wavelength obtained from the measurement signal. This makes it possible to more accurately obtain the value indicating the state of the gas at the measurement position (the position irradiated with the combined laser light).

[0070] This will be described with reference to FIGS. 13 to 17, taking the case of measuring the temperature of gas as an example.

[0071] FIG. 13 is a graph showing the relationship between the temperature of the gas being measured and the magnitude of absorbance (absorption intensity, signal intensity), which differs depending on the concentration of the substance having the peak frequency of the measurement target (absorption intensity 1 (absorbance at a specific first wavelength) and absorption intensity 2 (absorbance at a specific second wavelength)). As can be seen from the graph in FIG. 13, the absorbance (absorption intensity) changes depending on the concentration of the substance in the gas, and generally, the higher the concentration, the higher the absorption intensity.

[0072] FIG. 14 is a graph showing the relationship between absorbance (absorption intensity) and temperature for different concentrations (high and low) of substances in a gas. As can be seen from FIG. 14, the absorption intensity varies depending on the substance concentration in the gas, but the line connecting points at the same temperature is a line passing through the origin. In other words, the temperature is determined by the absorbance ratio, regardless of the substance concentration in the gas. Therefore, the gas temperature can also be expressed as an angle (e.g., angle φ in the figure) based on the coordinate axis.

[0073] Incidentally, for example, as in the embodiment already described, when the phase difference (demodulation phase difference) Δθdem of the above-mentioned reference frequency component (2n-th wave component) included in the detection signal is 90 degrees, absorption intensity 1 (absorbance at the first wavelength) and absorption intensity 2 (absorbance at the second wavelength) are output from the signal acquisition unit 16 (lock-in amplifier, etc.) without mutual interference (see FIG. 15 ). The outputs at this time are designated X0 (absorbance intensity 1) and Y0 (absorbance intensity 2).

[0074] On the other hand, when the phase difference (demodulation phase difference) Δθdem of the above-mentioned reference frequency component (2n-th wave component) included in the detection signal is, for example, 135 degrees, the mutual interference between absorption intensity 1 (absorbance at the first wavelength) and absorption intensity 2 (absorbance at the second wavelength) is output from the signal acquisition unit 16 (see FIG. 15). In this case, the outputs X1 (absorption intensity 1) and Y1 (absorption intensity 2) are respectively expressed by the following equations: X1=X0-Y0×sin(45°) Y1=Y0-Y0×cos(45°)

[0075] 15 and 16 are diagrams that schematically show the mutual interference between the outputs indicating absorption intensity 1 and absorption intensity 2.

[0076] FIG. 17 is a graph showing the correlation between absorption intensity 1 and absorption intensity 2 and temperature. As shown in FIG. 17 , when the demodulation phase difference is 135 degrees, the angle around the origin indicating the same temperature range is larger than when the demodulation phase difference is 90 degrees. Therefore, by making the demodulation phase difference larger than 90 degrees (e.g., 135 degrees), the gas temperature can be measured with higher sensitivity. Similarly, when the demodulation phase difference is 45 degrees, the angle around the origin indicating the same temperature range is smaller than when the demodulation phase difference is 90 degrees. Therefore, by making the demodulation phase difference smaller than 90 degrees (e.g., 45 degrees), the gas temperature can be measured with lower sensitivity. In this way, the temperature measurement sensitivity can be adjusted by appropriately adjusting the demodulation phase difference.

[0077] The contents described in each of the above embodiments can be understood, for example, as follows.

[0078] [1] At least one embodiment of a gas absorption characteristic measuring device (1) according to the present invention includes: a first laser diode (2) for emitting a first laser beam having a first wavelength (λa); a second laser diode (4) for emitting a second laser beam having a second wavelength (λb) different from the first wavelength; a first modulation unit (6) configured to modulate the first laser beam by applying a first modulation signal having a predetermined modulation frequency to the first laser diode; a second modulation unit (8) configured to modulate the second laser beam by applying a second modulation signal having the modulation frequency and having a phase difference with the first modulation signal to the second laser diode; a combiner (10) configured to combine the first laser beam modulated using the first modulation signal and the second laser beam modulated using the second modulation signal to obtain a combined laser beam; and a detector (14) configured to receive the combined laser beam from the combiner that has been irradiated onto a gas (12) to be measured and transmitted through the gas, and convert the combined laser beam into a detection signal. and a signal acquisition unit (16) for acquiring from the detection signal a first component signal including a component indicative of absorbance at the first wavelength in the gas to be measured at the irradiation position of the combined laser light and a second component signal including a component indicative of absorbance at the second wavelength, wherein the signal acquisition unit includes: a first demodulation unit (28) for demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (n is an integer) the modulation frequency; a second demodulation unit (32) for demodulating the detection signal using a second reference signal having the reference frequency and having a phase difference with the first reference signal; a first extraction unit (30) for extracting the first component signal, which is a DC component, from the signal demodulated using the first reference signal; and a second extraction unit (34) for extracting the second component signal, which is a DC component, from the signal demodulated using the second reference signal.

[0079] In the configuration [1], the gas to be measured is irradiated with a combined laser beam obtained by combining first and second laser beams having first and second wavelengths, respectively, and adding first and second modulation signals that are out of phase with each other, so that a single position can be simultaneously irradiated with laser beams having components of the first and second wavelengths (combined laser beam). Furthermore, a detection signal obtained by detecting the combined laser beam that has passed through the gas to be measured includes components of a frequency that is 2n times the modulation frequency (hereinafter also referred to as 2n-th harmonic components) in each of the signal component derived from the first laser beam and the component derived from the second laser beam, and a phase difference Δdem between these 2n-th harmonic components (phase difference at the demodulation frequency) corresponds to the phase difference Δθmod of the first and second laser beams modulated by the first and second modulation signals, respectively. Therefore, by demodulating the above-described detection signal using first and second reference signals having reference frequencies corresponding to the frequencies of the 2n-th harmonic components and a predetermined phase difference, first and second component signals indicating the absorbance at the wavelengths of the first and second laser beams can be extracted independently. This allows the absorbance (first and second component signals) at the first and second wavelengths at the same time at a single position (the irradiation position of the combined laser beam; the measurement position) of the target gas to be measured. That is, according to the configuration [1] above, the absorbance at two different wavelengths (the first and second wavelengths) at the same time at the same position of the target gas can be obtained, thereby accurately obtaining the ratio of the absorbance at the first and second wavelengths at that position (measurement position) of the target gas. Therefore, based on this absorbance ratio, a value indicating the state of the target gas at that position (such as temperature or concentration) can be accurately obtained.

[0080] [2] In some embodiments, in the configuration of the above [1], a phase difference Δθref between the first reference signal and the second reference signal is 90 degrees.

[0081] In the configuration [2] above, since the phase difference between the first reference signal and the second reference signal is 90 degrees, the signal obtained by demodulating the detection signal using the first reference signal and the signal obtained by demodulating the detection signal using the second reference signal each contain a DC component proportional to the intensity of the reference frequency component (i.e., the 2n-th harmonic component) having a predetermined phase difference in the detection signal, and the magnitude of one of these DC components (the first component signal) indicates the absorbance at the first wavelength, and the magnitude of the other DC component (the second component signal) indicates the absorbance at the second wavelength. Therefore, it is possible to appropriately obtain the absorbance at the first and second wavelengths (the first and second component signals) at the same time at a single position (the irradiation position of the combined laser light) in the gas to be measured.

[0082] [3] In some embodiments, in the configuration of [1] or [2] above, the phase difference Δθdem between the reference frequency component in the signal component derived from the first laser light included in the detection signal and the reference frequency component in the signal component derived from the second laser light included in the detection signal (i.e., the phase difference of the reference frequency component (2n-th wave component) in the detection signal), and the phase difference Δθmod between the first laser light modulated with the first modulation signal and the second laser light modulated with the second modulation signal satisfy Δθmod = Δθdem / 2n.

[0083] In the configuration [3], the phase difference Δθmod between the first and second laser beams modulated with the first and second modulation signals, respectively, is set to satisfy Δθdem / 2n, so that the phase difference Δθdem between the reference frequency components (2n-th harmonic components) in the detection signal in the signal components originating from the first laser beam and the second laser beam, respectively, can be set to a desired value. For example, when the phase difference Δθref between the first and second reference signals is 90 degrees, the phase difference Δθmod between the modulated first and second laser beams can be set to 90 degrees / 2n in order to make the phase difference Δθdem the same as the phase difference Δθref of the reference signal. In the detection signal obtained in this manner, the phase difference between the reference frequency components originating from the first and second laser beams is Δθdem, and therefore, by demodulating this detection signal using a first reference signal and a second reference signal having a predetermined phase difference Δθref, it is possible to obtain signals each containing a DC component (first component signal and second component signal) corresponding to the component of the same frequency as the reference frequency. Therefore, it is possible to appropriately extract the DC components (first component signal and second component signal) from these signals.

[0084] [4] In some embodiments, in the configuration of [1] or [2] above, the first demodulation unit includes a first multiplier configured to output the product of the detection signal and the first reference signal, and the second demodulation unit includes a second multiplier configured to output the product of the detection signal and the second reference signal.

[0085] According to the configuration [4] above, the detection signal can be demodulated using the second reference signal by the second multiplier in parallel with the demodulation of the detection signal by the first reference signal by the first multiplier. Therefore, first and second component signals indicating the absorbance at the wavelengths of the first and second laser beams can be extracted in parallel and independently. Therefore, the absorbance (first and second component signals) at the first and second wavelengths at the same time at a single position (the irradiation position of the combined laser beam) in the gas to be measured can be acquired. That is, according to the configuration [2] above, the absorbance at two different wavelengths (the first and second wavelengths) at the same time at the same position (the irradiation position of the combined laser beam) in the gas to be measured can be appropriately acquired.

[0086] [5] In some embodiments, in the configuration of any one of the above [1] to [4], at least one of the first extraction unit and the second extraction unit has a cutoff frequency that is 10 times the modulation frequency. －１ Includes a low-pass filter of up to 1x.

[0087] In the configuration [1] above, by appropriately setting the phase difference Δθmod between the first laser light and the second laser light modulated with the first modulation signal and the second modulation signal, respectively, it is possible to arbitrarily set the phase difference (phase difference of the demodulation frequency) Δθdem of the reference frequency component (2n-th wave component) in the detection signal. The signal obtained by demodulating the detection signal using the first reference signal and the signal obtained by demodulating the detection signal using the second reference signal each contain a DC component proportional to the intensity of the reference frequency component (frequency of the reference signal) in the detection signal. The magnitude of one of these DC components (first component signal) indicates the absorbance at the first wavelength, and the magnitude of the other DC component (second component signal) indicates the absorbance at the second wavelength. Therefore, as in the configuration [5] above, by applying a low-pass filter to the demodulated signal, it is possible to appropriately extract the DC component while eliminating most of the components other than the DC component.

[0088] [6] In some embodiments, in the configuration of the above [3], the phase difference Δθdem of the reference frequency component in the detection signal is 90 degrees±10 degrees.

[0089] In the configuration [6] above, the phase difference Δθdem of the reference frequency component (2n-th harmonic component) in the detection signal is approximately 90 degrees. Therefore, the signal obtained by demodulating the detection signal using the first reference signal and the signal obtained by demodulating the detection signal using the second reference signal each contain a DC component proportional to the intensity of the reference frequency component in the detection signal (the frequency of the reference signal). The magnitude of one of these DC components (the first component signal) indicates the absorbance at the first wavelength, and the magnitude of the other DC component (the second component signal) indicates the absorbance at the second wavelength. Therefore, the absorbance at the first and second wavelengths (the first and second component signals) at the same time at a single position (the irradiation position of the combined laser light) in the gas to be measured can be appropriately obtained.

[0090] [7] In some embodiments, in the configuration of [3] above, the phase difference Δθdem of the reference frequency component in the detection signal is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

[0091] According to the configuration [7] above, the phase difference Δθdem of the reference frequency component (2n-th harmonic component) in the detection signal is set to a value greater than 0 degrees and less than 90 degrees, or a value greater than 90 degrees and less than 180 degrees, so that the measurement sensitivity of the value (temperature, concentration, etc.) indicating the state of the gas being measured, which is indicated by the absorbance ratio at the first / second wavelength obtained from the measurement signal, can be increased or decreased. This makes it possible to more accurately obtain the value indicating the state of the gas at the measurement position (the position irradiated with the combined laser light).

[0092] [8] In some embodiments, in any of the configurations [1] to [7] above, the first laser diode is configured to oscillate the first laser light having the first wavelength, which is the wavelength of a first absorption peak of a substance contained in the gas to be measured, and the second laser diode is configured to oscillate the second laser light having the second wavelength, which is the wavelength of a second absorption peak of the substance.

[0093] The ratio of absorbance at two different absorption peak wavelengths of a substance contained in a gas indicates the temperature of the substance. According to the configuration [8] above, it is possible to obtain the absorbance at two different wavelengths (i.e., the first wavelength, which is the wavelength of the first absorption peak, and the second wavelength, which is the wavelength of the second absorption peak) of the measurement target gas at the same position and at the same time. This makes it possible to accurately obtain the ratio of absorbance at the first / second wavelengths at that position of the measurement target gas. Therefore, based on this absorbance ratio, it is possible to accurately obtain the temperature of the measurement target gas at that position.

[0094] [9] In some embodiments, in any of the configurations [1] to [7] above, the first laser diode is configured to emit the first laser light having the first wavelength, which is the wavelength of an absorption peak of a first substance contained in the gas to be measured, and the second laser diode is configured to emit the second laser light having the second wavelength, which is the wavelength of an absorption peak of a second substance contained in the gas to be measured.

[0095] The ratio of absorbance at the wavelengths of the absorption peaks of two different substances contained in a gas indicates the concentration ratio of the substances in the gas. According to the configuration [9] above, it is possible to obtain the absorbance at two different wavelengths (i.e., a first wavelength that is the wavelength of the absorption peak of a first substance and a second wavelength that is the wavelength of the absorption peak of a second substance) at the same position and the same time in the measurement target gas. This makes it possible to accurately obtain the ratio of absorbance at the first / second wavelengths at that position in the measurement target gas. Therefore, based on this absorbance ratio, it is possible to accurately obtain the concentration ratio of the first substance to the second substance in the measurement target gas at that position.

[0096]

[10] In some embodiments, in any of the configurations [1] to [9] above, the gas absorption characteristic measuring device includes a signal analysis unit (20) for calculating a value indicating the state of the gas at the irradiation position of the combined laser light on the gas to be measured based on the first component signal and the second component signal.

[0097] According to the configuration

[10] , the absorbances of the target gas at two different wavelengths (first and second wavelengths) at the same time and at the same position can be obtained using the first and second component signals independently extracted from the detection signal. This allows the ratio of the absorbances of the target gas at the first and second wavelengths at that position to be accurately obtained. Therefore, based on this absorbance ratio, a value indicating the state of the target gas at that position (such as temperature or concentration) can be accurately obtained.

[0098]

[11] At least one embodiment of the temperature measuring device of the present invention comprises the gas absorption characteristic measuring device described in

[10] above, wherein the signal analysis unit includes a temperature determination unit configured to determine the temperature of the gas at the irradiation position of the combined laser light on the gas to be measured based on the first component signal and the second component signal.

[0099] According to the configuration

[11] above, it is possible to obtain the absorbances of the measurement target gas at two different wavelengths (i.e., the first wavelength, which is the wavelength of the first absorption peak, and the second wavelength, which is the wavelength of the second absorption peak) at the same position and at the same time. This makes it possible to accurately obtain the ratio of the absorbances at the first / second wavelengths at that position of the measurement target gas. Therefore, it is possible to accurately obtain the temperature of the measurement target gas at that position based on this absorbance ratio.

[0100]

[12] At least one embodiment of the concentration ratio measuring device of the present invention comprises the gas absorption characteristic measuring device described in

[10] above, wherein the signal analysis unit includes a concentration ratio determination unit configured to determine the concentration ratio of a first substance to a second substance in the gas at a position where the combined laser light is irradiated in the gas to be measured based on the first component signal and the second component signal.

[0101] According to the configuration

[12] above, it is possible to obtain the absorbances at two different wavelengths (i.e., a first wavelength that is the wavelength of the absorption peak of a first substance and a second wavelength that is the wavelength of the absorption peak of a second substance) at the same position and at the same time in the measurement target gas. This makes it possible to accurately obtain the ratio of the absorbances at the first and second wavelengths at that position in the measurement target gas. Therefore, based on this absorbance ratio, it is possible to accurately obtain the concentration ratio of the first substance to the second substance in the measurement target gas at that position.

[0102]

[13] A method for measuring absorption characteristics of a gas according to at least one embodiment of the present invention includes the steps of: oscillating a first laser beam having a first wavelength (λa) using a first laser diode (2); oscillating a second laser beam having a second wavelength (λb) different from the first wavelength using a second laser diode (4); modulating the first laser beam by applying a first modulation signal having a predetermined modulation frequency to the first laser diode; modulating the second laser beam by applying a second modulation signal having the modulation frequency and having a phase difference with the first modulation signal to the second laser diode; combining the first laser beam modulated by the first modulation signal and the second laser beam modulated by the second modulation signal to obtain a combined laser beam; receiving the combined laser beam that has been irradiated onto a gas to be measured and transmitted through the gas, and converting it into a detection signal; and a signal acquiring step of acquiring from the detection signal a first component signal including a component indicating absorbance at the first wavelength in the gas to be measured at the irradiation position of the combined laser light and a second component signal including a component indicating absorbance at the second wavelength, wherein the signal acquiring step includes: a step of demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (n is an integer) the modulation frequency; a step of demodulating the detection signal using a second reference signal having the reference frequency and having a phase difference with the first reference signal; a step of extracting the first component signal, which is a DC component, from the signal demodulated using the first reference signal; and a step of extracting the second component signal, which is a DC component, from the signal demodulated using the second reference signal.

[0103] In the method of

[13] , first and second laser beams having first and second wavelengths, respectively, are combined to be irradiated onto the gas to be measured, and first and second modulation signals having phases shifted from each other are added to the combined laser beam, so that a single position can be simultaneously irradiated with laser beams having components of the first and second wavelengths (combined laser beam). Furthermore, a detection signal obtained by detecting the combined laser beam that has passed through the gas to be measured includes components of a frequency 2n times the modulation frequency (hereinafter also referred to as 2n-th harmonic components) in the signal component derived from the first laser beam and the component derived from the second laser beam, and the phase difference Δdem between these 2n-th harmonic components (phase difference at the demodulation frequency) corresponds to the phase difference Δθmod between the first and second laser beams modulated with the first and second modulation signals, respectively. Therefore, by demodulating the above-described detection signal using first and second reference signals having reference frequencies corresponding to the frequencies of the 2n-th harmonic components and a predetermined phase difference, first and second component signals indicating the absorbance at the wavelengths of the first and second laser beams can be extracted independently. This allows the absorbance (first and second component signals) at the first and second wavelengths at the same time at a single position (the irradiation position of the combined laser beam; the measurement position) of the target gas to be measured. That is, according to the method of

[13] above, the absorbance at two different wavelengths (the first and second wavelengths) at the same time at the same position of the target gas can be obtained, thereby enabling the ratio of the absorbance at the first and second wavelengths at the target gas position (measurement position) to be accurately obtained. Therefore, based on this absorbance ratio, a value indicating the state of the target gas at the position (such as temperature or concentration) can be accurately obtained.

[0104] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0105] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0106] REFERENCE SIGNS LIST 1 absorption characteristic measuring device 2 first laser diode 2 first laser light 4 second laser diode 6 first modulator 8 second modulator 10 combiner 12 gas 14 detector 16 signal acquisition unit 18 demodulated signal generator 20 signal analyzer 26 phase shifter 28 first demodulator 30 first extractor 32 second demodulator 34 second extractor Δθmod phase difference between modulated first and second laser lights Δθdem phase difference of reference frequency component included in detection signal Δθref phase difference of reference signal φ angle

Claims

a first laser diode for oscillating a first laser beam having a first wavelength; a second laser diode for oscillating a second laser beam having a second wavelength different from the first wavelength; a first modulation unit configured to modulate the first laser beam by applying a first modulation signal having a predetermined modulation frequency to the first laser diode; a second modulation unit configured to modulate the second laser beam by applying a second modulation signal having the modulation frequency and a phase difference with the first modulation signal to the second laser diode; a combiner configured to combine the first laser beam modulated using the first modulation signal and the second laser beam modulated using the second modulation signal to obtain a combined laser beam; a detector configured to receive the combined laser beam from the combiner that has been irradiated to a gas to be measured and transmitted through the gas, and convert it into a detection signal; and a signal acquisition unit for acquiring from the detection signal a first component signal including a component indicative of absorbance at the first wavelength in the gas to be measured at a position irradiated with the combined laser beam and a second component signal including a component indicative of absorbance at the second wavelength, The signal acquisition unit includes: a first demodulation unit for demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (n is an integer) the modulation frequency; a second demodulation unit for demodulating the detection signal using a second reference signal having the reference frequency and having a phase difference with the first reference signal; a first extraction unit for extracting the first component signal as a DC component from the signal demodulated using the first reference signal; and a second extraction unit for extracting the second component signal as a DC component from the signal demodulated using the second reference signal.

2. The gas absorption characteristic measuring device according to claim 1, wherein the phase difference Δθref between the first reference signal and the second reference signal is 90 degrees.

3. A gas absorption characteristic measuring device as described in claim 1 or 2, wherein a phase difference between the reference frequency component in the signal component derived from the first laser light included in the detection signal and the reference frequency component in the signal component derived from the second laser light included in the detection signal is Δθdem, and a phase difference Δθmod between the first laser light modulated by the first modulation signal and the second laser light modulated by the second modulation signal satisfies Δθmod = Δθdem / 2n.

4. A gas absorption characteristic measuring device as described in claim 1 or 2, wherein the first demodulation unit includes a first multiplier configured to output the product of the detection signal and the first reference signal, and the second demodulation unit includes a second multiplier configured to output the product of the detection signal and the second reference signal.

5. At least one of the first extraction unit and the second extraction unit has a cutoff frequency of 10 times the modulation frequency. －１ The gas absorption characteristic measuring device according to claim 1 or 2, further comprising a low-pass filter having a filter width of 100 kHz or less.

6. The gas absorption characteristic measuring device according to claim 3, wherein the phase difference Δθdem of the reference frequency component in the detection signal is 90 degrees ±10 degrees.

7. The gas absorption characteristic measuring device according to claim 3, wherein the phase difference Δθdem of the reference frequency component in the detection signal is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

8. A gas absorption characteristic measuring device as described in claim 1 or 2, wherein the first laser diode is configured to oscillate the first laser light having the first wavelength which is the wavelength of a first absorption peak of a substance contained in the gas to be measured, and the second laser diode is configured to oscillate the second laser light having the second wavelength which is the wavelength of a second absorption peak of the substance.

9. A gas absorption characteristic measuring device as described in claim 1 or 2, wherein the first laser diode is configured to oscillate the first laser light having the first wavelength which is the wavelength of an absorption peak of a first substance contained in the gas to be measured, and the second laser diode is configured to oscillate the second laser light having the second wavelength which is the wavelength of an absorption peak of a second substance contained in the gas to be measured.

10. A gas absorption characteristic measuring device as described in claim 1 or 2, further comprising a signal analysis unit for calculating a value indicating the state of the gas at the irradiation position of the combined laser light of the gas to be measured based on the first component signal and the second component signal.

11. A temperature measuring device comprising the gas absorption characteristic measuring device according to claim 10, wherein the signal analysis unit includes a temperature determination unit configured to determine the temperature of the gas at the irradiated position of the gas to be measured, where the combined laser light is irradiated, based on the first component signal and the second component signal.

12. A concentration ratio measuring device comprising the gas absorption characteristic measuring device according to claim 10, wherein the signal analysis unit includes a concentration ratio determining unit configured to determine the concentration ratio of a first substance and a second substance in the gas at a position where the gas is irradiated with the combined laser light based on the first component signal and the second component signal.

13. A method for measuring a gas to be measured comprising the steps of: oscillating a first laser beam having a first wavelength using a first laser diode; oscillating a second laser beam having a second wavelength different from the first wavelength using a second laser diode; modulating the first laser beam by applying a first modulation signal having a predetermined modulation frequency to the first laser diode; modulating the second laser beam by applying a second modulation signal having the modulation frequency and having a phase difference with the first modulation signal to the second laser diode; obtaining a combined laser beam by combining the first laser beam modulated by the first modulation signal and the second laser beam modulated by the second modulation signal; receiving the combined laser beam that has been irradiated to a gas to be measured and transmitted through the gas and converting it into a detection signal; and acquiring from the detection signal a first component signal including a component indicative of absorbance at the first wavelength in the gas to be measured at a position irradiated with the combined laser beam and a second component signal including a component indicative of absorbance at the second wavelength, a step of demodulating the detection signal using a first reference signal having a reference frequency that is 2n times (n is an integer) the modulation frequency; a step of demodulating the detection signal using a second reference signal having the reference frequency and having a phase difference with the first reference signal; a step of extracting the first component signal as a DC component from the signal demodulated using the first reference signal; and a step of extracting the second component signal as a DC component from the signal demodulated using the second reference signal.

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