JP7543762B2 - Laser Gas Analyzer - Google Patents

Description

The present invention relates to a laser gas analyzer that analyzes the presence and concentration of various target gases in a space.

A laser gas analyzer that measures the concentration of a trace gas by wavelength modulation spectroscopy is known (see, for example, Patent Document 1). In addition, a method for removing noise has been devised to improve the signal-to-noise ratio of the laser gas analyzer (see, for example, Patent Document 2).
JP 2013-113647 A Patent No. 3943853

It is preferable for the laser gas analyzer to accurately remove periodic noise caused by optical interference.

In a first aspect of the present invention, a laser gas analyzer is provided. The laser gas analyzer may measure the concentration of a gas to be measured present in a space to be measured by wavelength modulation spectroscopy. The laser gas analyzer may include a laser element. The laser element may emit laser light modulated in a wavelength band including the absorption line spectrum of the gas to be measured. The laser gas analyzer may include a light receiving element. The light receiving element may detect the laser light that has passed through the space to be measured. The laser gas analyzer may include a detection unit. The detection unit may convert a light receiving signal of the light receiving element into a detection waveform. The laser gas analyzer may include a light receiving signal processing unit. The light receiving signal processing unit may measure the concentration of the gas to be measured based on the detection waveform. The light receiving signal processing unit may have a deletion waveform generating unit. The deletion waveform generating unit may generate a deletion waveform. The deletion waveform may be a waveform obtained by deleting a gas absorption waveform portion of the gas to be measured from the detection waveform. The received light signal processing unit may include a noise waveform generating unit. The noise waveform generating unit may generate a noise waveform by interpolating the deleted portion by calculating a sum model of sine waves from the remaining portion of the deleted waveform. The received light signal processing unit may include a corrected detection waveform generating unit. The corrected detection waveform generating unit may generate a corrected detection waveform by deleting the noise waveform from the detection waveform. The received light signal processing unit may include a concentration measuring unit. The concentration measuring unit may measure the concentration of the measurement target gas based on the corrected detection waveform. The noise waveform generating unit may calculate an amplitude estimate value and a frequency estimate value based on the deleted waveform. The noise waveform generating unit may limit a coefficient search range for the amplitude based on the amplitude estimate value. The noise waveform generating unit may limit a coefficient search range for the frequency based on the frequency estimate value.

The noise waveform generation unit may calculate the amplitude estimate and the frequency estimate by performing a Fourier transform on the deleted waveform. The noise waveform generation unit may limit the amplitude coefficient search range and the frequency coefficient search range based on the amplitude estimate and the frequency estimate, and then calculate a sum model of sine waves using the least squares method.

The deletion waveform generating unit may record deletion positions, which are positions at which the gas absorption waveform portion of the measurement target gas is deleted from the detection waveform. The deletion waveform may be generated by deleting the deletion positions in the detection waveform.

The amplitude coefficient search range may be 0.5 times or more and 2.0 times or less than the amplitude estimate. The frequency coefficient search range may be determined based on the frequency resolution when the deleted waveform is Fourier transformed. The frequency coefficient search range may be greater than or equal to the frequency estimate minus 100 Hz. The frequency coefficient search range may be less than or equal to the frequency estimate plus 100 Hz.

The received light signal processing unit may have a detection waveform correction unit. The detection waveform correction unit may obtain a correction term for the slope of the noise waveform using a noise waveform recorded in advance. The detection waveform correction unit may correct the slope of the detection waveform based on the correction term for the slope of the noise waveform. The received light signal processing unit may have a phase alignment unit. The phase alignment unit may align the phase of a corrected detection waveform obtained by correcting the detection waveform and a corrected noise waveform obtained by correcting the noise waveform. The received light signal processing unit may have a subtraction unit. The subtraction unit may subtract the corrected noise waveform from the corrected detection waveform to generate a subtracted detection waveform. The received light signal processing unit may have a concentration measurement unit. The concentration measurement unit may measure the concentration of the gas to be measured based on the subtracted detection waveform.

The detection waveform correction unit may use a prerecorded noise waveform to obtain a correction term for the DC component of the noise waveform. The detection waveform correction unit may correct the DC component of the detection waveform based on the correction term for the DC component of the noise waveform.

The phase alignment unit may calculate the time shift amount from the time difference between the maximum value of the corrected detection waveform in a detection range that does not include the gas absorption waveform portion of the gas to be measured and the maximum value of the corrected noise waveform in the detection range. The phase alignment unit may align the phases of the corrected detection waveform and the corrected noise waveform from the time shift amount.

1 shows an example of the configuration of a laser gas analyzer 100 according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a signal processing configuration of the laser gas analyzer 100. FIG. 2 is a block diagram showing an example of a signal processing block diagram of a received light signal processing unit 21. 4 is an example of a detected waveform 201 after the process of S102 in FIG. 3. 4 is an example of a deleted waveform 202 after the process in S103 of FIG. 3. 4 is an example of a noise waveform 203 after the process in S107 in FIG. 3. 4 is an example of a corrected detection waveform 204 after the process of S108 in FIG. 3. FIG. 13 is a diagram showing another example of a signal processing configuration of the laser gas analyzer 100. FIG. 9 is a block diagram showing an example of a signal processing block diagram of the light receiving signal processing unit 21 of FIG. 8 . FIG. 13 is a diagram illustrating an example of phase matching. FIG. 11 is a diagram illustrating an example of phase alignment according to a comparative example. 4 is a diagram showing an example of a method for acquiring a noise waveform 401 and a detection waveform 403. FIG.

The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

Figure 1 shows an example of the configuration of a laser gas analyzer 100 according to one embodiment of the present invention. The laser gas analyzer 100 of this example includes a light emitting unit 10, a light receiving unit 20, a light receiving signal processing unit 21, and a communication line 40. The light emitting unit 10 irradiates the measurement target space 2 with laser light 30. The light receiving unit 20 receives the laser light 30 propagated through the measurement target space 2. The light receiving unit 20 of this example receives the laser light 30 that has passed through the measurement target space 2, but the light receiving unit 20 of other examples may receive the laser light 30 that has been scattered or reflected in the measurement target space 2. The light receiving signal processing unit 21 may analyze the measurement target gas 1 in the measurement target space 2 based on the light receiving result in the light receiving unit 20. In other words, the light receiving signal processing unit 21 may measure the concentration of the measurement target gas 1 in the measurement target space 2 based on the light receiving result in the light receiving unit 20. The communication line 40 communicates between the light-emitting unit 10 and the light-receiving unit 20 using electrical signals. Also, a communication unit such as a wireless or optical communication unit may be used instead of the communication line 40.

In the laser gas analyzer 100 of this example, the light emitter 10 emits laser light 30. The laser light 30 is projected into the measurement target space 2 inside the piping walls 50a and 50b. A part of the amount of light of the laser light 30 is absorbed by the measurement target gas 1. The remaining light that is not absorbed, i.e., the transmitted light, is incident on the light receiver 20, and the amount of transmitted light is detected. The received light signal processor 21 calculates the concentration of the measurement target gas 1 based on the detected amount of transmitted light. In other words, the laser gas analyzer 100 may measure the concentration of the measurement target gas 1 present in the measurement target space 2 by wavelength modulation spectroscopy.

The measurement space 2 in this example is a tubular flue through which the measurement gas 1 passes. FIG. 1 shows the piping wall 50a and the piping wall 50b in a cross section of the tubular flue. The piping wall 50a is the wall on the light-emitting unit 10 side, and the piping wall 50b is the wall on the light-receiving unit 20 side. The laser gas analyzer 100 in this example measures the concentration of the measurement gas 1 contained in the gas flowing between the piping wall 50a and the piping wall 50b. The laser gas analyzer 100 in this example also includes a flange 51a and a flange 51b. The flange 51a is fixed to the piping wall 50a by welding or the like, and the flange 51b is fixed to the piping wall 50b by welding or the like.

The laser gas analyzer 100 of this example includes an optical axis adjustment flange 52a and an optical axis adjustment flange 52b. The optical axis adjustment flanges 52a and 52b are attached to the flanges 51a and 51b so as to be mechanically movable. The optical axis adjustment flange 52a fixes the light emitting unit 10 to the flange 51a. The optical axis adjustment flange 52b fixes the light receiving unit 20 to the flange 51b. The positions of the light emitting unit 10 and the light receiving unit 20 can be adjusted by the optical axis adjustment flanges 52a and 52b. The optical axis adjustment flange 52a adjusts the emission angle of the laser light 30, and the optical axis adjustment flange 52b adjusts the incidence angle of the laser light 30. The optical axis adjustment flanges 52a and 52b allow the laser light 30 emitted from the light emitting unit 10 to be received at the light receiving unit 20 with the maximum light amount.

The light-emitting unit 10 in this example has a laser drive current generating unit 11, a laser element 12, a collimating lens 13, a light-emitting unit window plate 14, and a light-emitting unit container 15. The light-emitting unit container 15 houses the laser drive current generating unit 11, the laser element 12, and the collimating lens 13. The light-emitting unit container 15 in this example is cylindrical with a bottom. The light-emitting unit container 15 is attached to an optical axis adjustment flange 52a. The light-emitting unit container 15 houses a light-emitting element, optical components, and an electric and electronic circuit inside, and isolates them from the outside air to protect them from wind, rain, dust, dirt, etc.

The light-emitting section window plate 14 is provided to open a hole in a part of the light-emitting section container 15 and close it. The light-emitting section window plate 14 is in the optical path of the laser light 30, and while allowing the laser light 30 to pass through, it prevents gas, including specific gases, from entering the inside of the light-emitting section 10. This prevents the light-emitting element, optical components, and electrical and electronic circuits from directly contacting the gas, protecting the inside. The laser light 30 passes through the light-emitting section window plate 14 and propagates into the inside of the piping walls 50a and 50b.

The laser drive current generating unit 11 generates a laser drive signal. In order to measure the concentration of the measurement target gas 1 by wavelength modulation spectroscopy, the laser drive current generating unit 11 irradiates a laser light 30 according to the absorption characteristics of the measurement target gas 1. The laser drive current generating unit 11 also irradiates the laser light 30, which is modulated light whose wavelength has been modulated. Therefore, the laser drive current generating unit 11 supplies a laser drive signal to the laser element 12 to emit the laser light 30. The laser drive current generating unit 11 also outputs the laser drive signal by superimposing an appropriate sine wave modulation so that measurement can be performed with high sensitivity by wavelength modulation spectroscopy. In this specification, the laser drive signal may be expressed as a drive current.

The laser element 12 emits laser light 30. The laser element 12 can control the wavelength of the laser light 30 by a laser drive signal (drive current) and temperature. Therefore, the central emission wavelength of the laser element 12 is temperature controlled to be the central wavelength of the absorption line spectrum of the gas to be measured 1. The central wavelength of the absorption line spectrum of the gas to be measured 1 is wavelength λ1. In addition, the laser drive signal (drive current) is controlled so that the wavelengths around wavelength λ1 are swept in time. The laser element 12 may emit laser light 30 modulated in a wavelength band including the absorption line spectrum of the gas to be measured 1. The laser element 12 is, for example, a DFB laser diode (Distributed Feedback Laser Diode), a VCSEL (Vertical Cavity Surface Emitting Laser), or a DBR laser diode (Distributed Bragg Reflector Laser Diode).

The laser light 30 emitted from the laser element 12 is collimated into parallel light by an optical system including a collimating lens 13. The collimated light passes through the center of the flange 51a and enters the inside of the flue between the pipe walls 50a and 50b. When the laser light 30 enters the inside of the flue, a portion of the wavelength component corresponding to the absorption wavelength of the gas 1 to be measured is absorbed as it passes through the gas 1 to be measured inside the flue.

The collimating lens 13 is made of a material that has high transmittance at wavelength λ1 and its surrounding wavelengths. The collimating lens 13 converts the laser light 30 into a nearly parallel light, which is then transmitted to the light receiving unit 20 while minimizing loss due to diffusion.

The light emitting point of the laser element 12 is located near the focal point of the collimating lens 13. The light emitted from the laser element 12 is diffused and enters the collimating lens 13, where it is converted into laser light 30, which is a substantially parallel light. Note that, in this embodiment, the collimating lens 13 is used as the parallel light conversion unit of the present invention, but this is not intended to be limited to a collimating lens. For example, a parabolic mirror can be used as the parallel light conversion unit instead of a collimating lens.

The light receiving unit 20 in this example has a light receiving signal processing unit 21, a light receiving element 22, a condensing lens 23, a light receiving unit window plate 24, a light receiving unit container 25, and a detection unit 26. The light receiving unit container 25 houses the light receiving signal processing unit 21, the light receiving element 22, and the condensing lens 23. The light receiving unit container 25 in this example is cylindrical with a bottom. The light receiving unit container 25 is attached to the optical axis adjustment flange 52b. The light emitting unit container houses a light emitting element, optical components, and an electric and electronic circuit inside, and isolates them from the outside air to protect them from wind, rain, dust, dirt, etc.

The light-receiving unit window plate 24 is provided so as to open a hole in a part of the light-receiving unit container 25 and close it. The light-receiving unit window plate 24 is in the optical path of the laser light 30, and while allowing the laser light 30 to pass through, it prevents gas, including specific gases, from entering the inside of the light-receiving unit 20. This prevents the light-emitting element, optical components, and electrical and electronic circuits from coming into direct contact with gas, protecting the inside.

The focusing lens 23 focuses the laser light 30 that has passed through the inside of the flue. The focusing lens 23 is made of a material that has high transmittance at wavelength λ1 and its surrounding wavelengths. The focusing lens 23 focuses the laser light 30 onto the light receiving element 22, making it possible to obtain a high signal strength.

The laser light 30 focused by the focusing lens 23 is received by the light receiving element 22. The light receiving element 22 is composed of a photodiode or the like, and one having sensitivity to the laser light 30 emitted from the laser element 12 is used. The light receiving element 22 is preferably sensitive to the entire wavelength sweepable range of the laser element 12. The light receiving element 22 converts the received light into an electrical signal and inputs it to the received light signal processing unit 21. For the light receiving element 22, a light receiving element having sensitivity to the wavelength λ ₁ and wavelengths around it can be selected. The light receiving element 22 may detect the laser light 30 that has passed through the measurement target space 2.

The detection unit 26 converts the light receiving signal of the light receiving element 22 into a detection waveform. The detection unit 26 is provided with a circuit that performs lock-in detection of the harmonics of the modulation frequency of the wavelength-modulated laser light, enabling highly sensitive gas detection. The light receiving signal processing unit 21 measures the concentration of the measurement target gas 1 based on the detection waveform detected by the detection unit 26.

Figure 2 is a diagram showing an example of the signal processing configuration of the laser gas analyzer 100. In Figure 2, the laser gas analyzer 100 includes a laser drive current generating unit 11, a laser element 12, a temperature control circuit 111, a control circuit 112, a light receiving element 22, a light receiving signal processing unit 21, and a detection unit 26. The detection unit 26 includes a preamplifier 121, a high-pass filter 122, a variable amplifier 123, and a lock-in detection circuit 124. The light receiving signal processing unit 21 includes an AD conversion unit 130, a deletion waveform generating unit 131, a noise waveform generating unit 132, a correction detection waveform generating unit 133, and a concentration measuring unit 134.

The temperature control circuit 111 controls and stabilizes the output and wavelength of the laser element 12 at a constant level. The output and wavelength of the laser element 12 vary with temperature. Therefore, it is preferable that the temperature control circuit 111 controls the laser element 12 to a constant temperature so that the output and wavelength of the laser element 12 do not vary with changes in the ambient temperature. The temperature control circuit 111 may have a temperature control element that controls the temperature of the laser element 12. The temperature control circuit 111 may have a Peltier element as the temperature control element. The temperature control circuit 111 may have a temperature sensor that detects the temperature of the laser element 12. The temperature control circuit 111 may have a thermistor as the temperature sensor.

The laser drive current generating unit 11 controls the drive current of the laser element 12 so that the wavelength emitted by the laser element 12 is swept near an absorption line of a specific wavelength and modulated by a predetermined signal. The laser drive current generating unit 11 may have a sweep signal generating unit, a modulation signal generating unit, and a current control unit. The sweep signal generating unit outputs a wavelength sweep drive signal that changes the emission wavelength of the laser element 12. The sweep signal generating unit sweeps the emission wavelength of the laser element 12 within a wavelength range including the absorption wavelength of the measurement target gas 1. The modulation signal generating unit outputs a sine wave high frequency modulation signal for modulating the emission wavelength of the laser element 12. The wavelength sweep drive signal and the high frequency modulation signal are superimposed and output to the current control unit as a laser drive signal. The current control unit supplies a current according to the input laser drive signal to the laser element 12.

The wavelength of the laser light 30 can be varied by increasing or decreasing the drive current, so that, for example, the drive current of the laser element 12 is swept so that it crosses the absorption lines of the components of the measurement target gas 1. In addition, in order to detect absorption with high sensitivity in the lock-in detection circuit 124, modulation is performed by superimposing a sine wave on the drive current. The wavelength sweep and modulation are repeated at the timing when the laser light 30 is turned on, based on the repeated output of the control circuit 112. The modulation frequency by the sine wave is set to be higher than the wavelength sweep frequency.

The control circuit 112 is a circuit that controls the timing of turning on and off the laser drive current generation unit 11. The control circuit 112 may cause the laser drive current generation unit 11 to output the drive current for the laser element 12 at the timing of turning on the laser light 30. The control circuit 112 does not need to cause the laser drive current generation unit 11 to output the drive current for the laser element 12 at the timing of turning off the laser light 30. This causes the laser element 12 to alternately turn on and off. It also controls the calculation timing of the concentration measurement unit 134.

The laser light 30, which passes through the gas and is partially absorbed by the components of the gas 1 to be measured, enters the light receiving element 22. The light receiving element 22 is an element sensitive to the wavelength of the laser light 30. If the wavelength of the laser light 30 is, for example, 760 nm to 763 nm, the light receiving element 22 can be, for example, a silicon photodiode. At this time, the light receiving element 22 may also receive light emitted from a space in which gas exists. In addition, if the light receiving element 22 is a photodiode, a dark current is generated. The sweep repetition period is selected to be short so that the fluctuation of the light receiving signal caused by noise such as dark current is sufficiently longer than the period of repeating the sweep of the laser light 30. The sweep repetition period is, in other words, the period of the high-frequency modulated signal output by the modulated signal generating unit.

The preamplifier 121 is a circuit that amplifies the signal from the light receiving element 22. For example, if the light receiving element 22 is a photodiode, it is a transimpedance amplifier that amplifies the current from the photodiode while converting it to a voltage. It is preferable to set the amplification factor of the preamplifier 121 to an extent that the signal from the preamplifier 121 is not saturated under conditions in which the laser light 30 is least attenuated, i.e., conditions in which there is no dust or the like on the optical path. By setting the signal so that it is not saturated under conditions in which the laser light 30 is least attenuated, it is possible to prevent the signal from the preamplifier 121 from being saturated.

The high-pass filter 122 removes the DC component contained in the signal from the preamplifier 121. The signal from the preamplifier 121 generally contains a DC component. The DC component is caused by, for example, light emitted from a space in which gas exists. If the light receiving element 22 is a photodiode, it is also caused by a dark current generated in the photodiode. The DC component contained in the signal from the preamplifier 121 has a time constant that is sufficiently longer than the period in which the laser light 30 is repeatedly swept. In other words, the DC component contained in the signal from the preamplifier 121 is a low frequency. Therefore, the DC component is removed by the high-pass filter 122, and the signal from the high-pass filter 122 has a waveform that crosses the reference voltage of 0V.

The cutoff frequency of the high-pass filter 122 is set so that the repetition frequency (the inverse of the repetition period) of the laser light 30 turning on and off and the frequency of the wavelength sweep and modulation signal of the laser light 30 are within the passband of the high-pass filter 122. Therefore, the signal due to the turning on and off of the laser light 30 and the wavelength sweep and modulation signal of the laser light 30 pass through with almost no change.

The reason why the high-pass filter 122 is provided immediately after the preamplifier 121 is that if the variable amplifier 123 amplifies the signal to a DC signal, the DC signal component increases relatively under poor measurement conditions, and the signal voltage saturates simply due to amplification. Examples of poor measurement conditions include when the light emitted from the space containing the gas is strong, when the dark current is large, and when the transmittance of the laser light 30 is low. To prevent saturation of the signal voltage, the high-pass filter 122 is provided immediately after the preamplifier 121.

The signal from the high-pass filter 122 mainly includes a signal for turning on and off the laser light 30 and a wavelength sweep and modulation signal for the laser light 30. Of these, the wavelength sweep and modulation signal wave when the laser light 30 is turned on fluctuates because the laser light 30 is scattered and attenuated due to, for example, fluctuations in the amount of dust coexisting in a space where gas is present. The scattering and attenuation of the laser light 30 due to fluctuations in the amount of dust, etc., is not wavelength-dependent within the wavelength sweep and modulation range of the laser light 30, and passes through the high-pass filter 122.

The variable amplifier 123 is an amplifier circuit that amplifies the signal from the high-pass filter 122 at a predetermined amplification factor. It is preferable to set the amplification factor so as not to saturate the signal from the high-pass filter 122. By providing the variable amplifier 123 and amplifying the signal from the high-pass filter 122, the concentration of a trace amount of the measurement target gas 1 can be detected.

The lock-in detection circuit 124 is a circuit that detects the signal of the modulation frequency component contained in the signal from the variable amplifier 123. The frequency used for lock-in detection can be selected to be, for example, twice the modulation frequency in the modulation signal generating section of the laser drive current generating section 11 as a reference. When the laser light 30 is swept so as to include the wavelength of the absorption line of the component of the measured gas 1, the output of the lock-in detection circuit 124 becomes a waveform with an extreme value based on the absorption line of the component of the measured gas 1.

For example, if the lock-in frequency is selected to be twice the modulation frequency, a waveform that can be approximated by the second derivative of the gas absorption waveform can be obtained. By using such lock-in detection, noise in frequency ranges other than the frequency used for lock-in detection can be significantly reduced, and only the minute signal of absorption by the measurement target gas 1 can be amplified. In other words, by using lock-in detection, scattering and attenuation of the laser light 30 due to fluctuations in the amount of dust, etc., as described above, is reduced. The signal output by the lock-in detection circuit 124 is input to the received light signal processing unit 21.

In addition to the absorption waveform due to gas, the signal from the lock-in detection circuit 124 is superimposed with noise due to distortion of the laser light 30, noise due to the circuit, and optical interference noise (interference noise) caused by multiple reflection of the laser light 30 on the window of the laser element 12, the window of the light receiving element 22, the lens end face, and inside the housing, which are components of the laser gas analyzer 100. Therefore, the signal-to-noise ratio of the signal deteriorates. One of the noises that causes the signal-to-noise ratio to deteriorate is interference noise. Interference noise is caused by two types of laser light. One is laser light that reaches the light receiving element 22 directly from the coherent light emitted from the laser light 30. The other is laser light that reaches the light receiving element 22 after multiple reflections occur on optical components, etc. Interference noise occurs when the laser light that reaches the light receiving element 22 directly and the laser light that reaches the light receiving element 22 with multiple reflections overlap and reach the light receiving element 22, causing interference and causing the intensity of light to fluctuate. The condition for constructive interference noise is expressed by the following equation 1. Moreover, the condition for destructive interference noise is expressed by the following equation 2. In the following, the difference in optical path length between the laser light that reaches the light receiving element 22 directly and the laser light that reaches the light receiving element 22 after multiple reflection is denoted as ΔL, the wavelength of the laser light is denoted as λ, and an integer is denoted as m.

Since the laser gas analyzer 100 performs measurements by sweeping the laser light 30, a periodic signal is generated that reaches a maximum each time the wavelength of the laser light 30 becomes an integer multiple of ΔL. The effect of interference noise changes depending on the positional relationship of the optical components, so if the housing supporting the optical components expands or contracts due to temperature or other factors, causing a slight change in the positional relationship of the optical components, the period and magnitude of the interference noise will fluctuate. Since temperature fluctuates over time, the magnitude of this noise also fluctuates over time, and the measured gas concentration value fluctuates due to the noise fluctuation, resulting in the problem of not being able to measure the concentration accurately.

The signal output by the lock-in detection circuit 124 is corrected and the concentration is calculated by the light receiving signal processing unit 21. The signal output by the lock-in detection circuit 124 is input to the AD conversion unit 130 and AD converted. That is, the signal output by the lock-in detection circuit 124 is converted into a digital signal. In the AD conversion unit 130, the AD converted signal is input to the deletion waveform generation unit 131. The deletion waveform generation unit 131, the noise waveform generation unit 132, and the correction detection waveform generation unit 133 are units that perform correction processing on the output signal of the lock-in detection circuit 124. The deletion waveform generation unit 131 may generate a deletion waveform by deleting the gas absorption waveform portion of the measurement target gas 1 of the detection waveform output by the detection unit 26. The noise waveform generation unit 132 may generate a noise waveform by interpolating the deletion portion by calculating a sum model of sine waves from the remaining portion of the deletion waveform generated by the deletion waveform generation unit 131. The sine wave sum model is a model in which a DC component is added to the sum of sine waves that differ in at least one of the amplitude, frequency, and phase. The corrected detection waveform generating unit 133 may generate the corrected detection waveform by deleting the noise waveform generated by the noise waveform generating unit 132 from the detection waveform output by the detection unit 26.

The concentration measurement unit 134 is a circuit that calculates the amplitude of the extreme value based on the gas absorption waveform from the corrected detection waveform generation unit 133. The concentration measurement unit 134 may calculate the amplitude of the extreme value of the gas absorption waveform based on the corrected detection waveform generated by the corrected detection waveform generation unit 133. The concentration measurement unit 134 may measure the concentration of the measurement target gas 1 based on the amplitude of the extreme value of the gas absorption waveform. In other words, the concentration measurement unit 134 may measure the concentration of the measurement target gas 1 based on the corrected detection waveform generated by the corrected detection waveform generation unit 133. The timing of calculating the amplitude of the extreme value of the gas absorption waveform may be controlled based on the control circuit 112. By measuring the concentration of the measurement target gas 1 based on the corrected detection waveform generated by the corrected detection waveform generation unit 133, periodic noise such as interference noise can be accurately removed, and highly accurate measurements can be performed.

Figure 3 is a block diagram showing an example of the signal processing of the received light signal processing unit 21. The processing contents of the received light signal processing unit 21 will be described in detail using Figure 3. First, the signal of the lock-in detection circuit 124 is AD converted and converted into a digital signal (S101). Next, a bandpass filter (not shown in Figure 2) is used to implement frequency restriction to extract only predetermined frequency components (S102). In order to improve the accuracy of noise estimation in data interpolation, the detection data after AD conversion is frequency restricted by a bandpass filter so that it contains as much of the frequency band of the gas absorption waveform as possible, and unnecessary components are removed.

After implementing the frequency restriction, the absorption waveform data portion is deleted from the time series data (S103). The deleted waveform generating unit 131 may generate the deleted waveform by deleting the absorption waveform data portion from the time series data.

Data interpolation is performed using the remaining portion of the deleted waveform. Data interpolation is performed by using an equation modeled as the sum of sine waves shown in the following equation 3, and calculating coefficients by the least squares method using the remaining data. In the following equation 3, v is the calculated data after interpolation, a _i , b _i , and c _i are coefficients related to the amplitude, frequency, and phase, respectively, d is the DC component, and t is the time (sampling point).

The data to be removed is periodic interference noise, so the data is estimated and interpolated using a sine wave sum model as described above. The number of sine waves in the combination, n, is 3, for example. The larger the number, the more complex the noise waveforms that can be estimated. However, the more coefficients that must be calculated, which increases the amount of calculations, so the number is set according to the signal processing resources.

The coefficients corresponding to frequency and amplitude may fall into a local solution because the amplitude, frequency, and phase can be arbitrarily determined, which may deteriorate the noise estimation accuracy. Therefore, the frequency estimate and amplitude estimate are determined by performing a Fourier transform on the data from which the absorption waveform portion has been deleted in advance, and the coefficient search range in the least squares method is limited before processing to calculate the coefficients. The phase coefficient is limited to a range of 0 to 2π, and since any value from 0 to 2π can be taken, the coefficient search range does not need to be limited. A Fourier transform is performed using the remaining portion of the deleted waveform (S104). A frequency estimate and an amplitude estimate are calculated by the Fourier transform (S105). In summary, the noise waveform generating unit 132 calculates an amplitude estimate and a frequency estimate by performing a Fourier transform on the deleted waveform. By using a Fourier transform, it is possible to obtain highly accurate amplitude estimates and frequency estimates.

After calculating the frequency estimate and the amplitude estimate, the coefficients are calculated by the least squares method (S106). The noise waveform generation unit 132 limits the amplitude coefficient search range and the frequency coefficient search range based on the amplitude estimate and the frequency estimate, and then calculates a sinusoidal sum model using the least squares method. By limiting the frequency and amplitude coefficient search ranges using the least squares method, it is possible to prevent falling into a local solution and to reliably calculate the coefficients. The noise waveform generation unit 132 may calculate the amplitude estimate and the frequency estimate based on the deleted waveform. The noise waveform generation unit 132 may limit the amplitude coefficient search range based on the amplitude estimate. The noise waveform generation unit 132 may limit the frequency coefficient search range based on the frequency estimate.

In this embodiment, both an amplitude estimate and a frequency estimate are obtained, and the coefficient search ranges for frequency and amplitude are limited, but an estimate of only one of them may be obtained, and the coefficient may be limited. In other words, the noise waveform generation unit 132 may calculate only an amplitude estimate based on the deleted waveform. Also, the noise waveform generation unit 132 may calculate only a frequency estimate based on the deleted waveform.

After calculating the coefficients, the interpolated data is used to generate a noise waveform (S107). The noise waveform is generated by interpolating the interpolated data into the deleted waveform. Then, the noise waveform is subtracted from the detected waveform to generate a corrected detected waveform (S108). The corrected detected waveform is used to perform absorption amplitude calculations and gas concentration calculations (S109).

Figure 4 is an example of the detection waveform 201 after processing in S102 in Figure 3. The vertical axis represents signal intensity, and the horizontal axis represents time. In Figure 4, the drive current of the laser element 12 is swept at a constant rate of change with respect to time, so the time on the horizontal axis corresponds one-to-one to the wavelength. In Figure 4, the peak of the gas absorption waveform is near the center of the horizontal axis. Periodic interference noise is superimposed on the gas absorption waveform that exists near the center of the horizontal axis. The time interval between the peak and bottom of the absorption waveform amplitude can be set arbitrarily depending on the laser sweep time and modulation amplitude, but for example, if the time interval between the peak and bottom is 1 ms to 2 ms, the bandpass filter is limited to approximately 100 Hz to 3000 Hz.

Figure 5 is an example of deleted waveform 202 after processing in S103 in Figure 3. The vertical and horizontal axes are the same as in Figure 4. Deleted waveform 202 has the gas absorption waveform present near the center of the horizontal axis deleted. Of the waveforms remaining after the gas absorption waveform in Figure 5 has been deleted, the waveform on the left is waveform 301 and the waveform on the right is waveform 302. When limiting the coefficient search range for frequency and amplitude, either waveform 301 or waveform 302 is used to perform frequency analysis such as FFT and calculate estimates of the noise amplitude and frequency.

The time on the horizontal axis corresponds one-to-one to the wavelength. Therefore, since the position of the absorption waveform is almost constant depending on the laser drive current, temperature control, and the type of gas to be detected, the position to be deleted is recorded in advance, and the data of that portion is deleted. In FIG. 5, the position of the absorption waveform is the position on the horizontal axis (time axis). When the horizontal axis is represented by wavelength, the position of the absorption waveform is the position on the wavelength axis. The deleted waveform generating unit 131 may record the deletion position, which is the position at which the gas absorption waveform portion of the measurement target gas 1 of the detection waveform is deleted, and generate the deleted waveform by deleting the deletion position in the detection waveform. By recording the deletion position, it is not necessary to determine the deletion position every time a correction process is performed, and there is less wasted processing, making it possible to perform measurements with many sampling points.

In this example, the amplitude was limited to 0.5 times or more and 2.0 times or less of the amplitude estimate value, and a search was performed. The amplitude coefficient search range may be 0.5 times or more and 2.0 times or less of the amplitude estimate value. The amplitude coefficient search range may also be 0.25 times or more and 4.0 times or less of the amplitude estimate value.

In this example, the frequency resolution in the frequency analysis is 100 Hz. The frequency resolution in the frequency analysis is the smallest unit in the frequency analysis (e.g., Fourier transform). Therefore, the frequency may be limited to the frequency estimate value ±100 Hz for the search. The frequency coefficient search range may be determined based on the frequency resolution when the deleted waveform is Fourier transformed. The frequency coefficient search range may be narrower as the frequency resolution increases. In addition, the frequency coefficient search range may be the frequency estimate value ± the frequency resolution. The frequency coefficient search range may be equal to or greater than the value obtained by subtracting 100 Hz from the frequency estimate value and equal to or less than the value obtained by adding 100 Hz to the frequency estimate value. Note that if the frequency resolution is sufficiently high, the frequency estimate value may be used as the frequency coefficient without performing a search.

After searching for amplitude and frequency, a combination of sine waves of 250 Hz, 1 kHz, and 1500 kHz was found. It was confirmed that a wide range of frequencies could be calculated, from small to large, within the frequency components restricted by the bandpass filter.

Figure 6 is an example of a noise waveform 203 after processing in S107 in Figure 3. The vertical and horizontal axes are the same as in Figure 4. The noise waveform 203 is generated by interpolating the waveform 303, which is the interpolation data, into the deleted waveform 202. It can be seen in Figure 6 that the frequency of the waveform 303 is close to the frequency of the interference noise.

Figure 7 is an example of a corrected detection waveform 204 after processing in S108 in Figure 3. The vertical and horizontal axes are the same as in Figure 4. The corrected detection waveform 204 is generated by subtracting the noise waveform 203 from the detection waveform 201. In Figure 7, the interference noise has been removed. Therefore, highly accurate concentration analysis is possible.

Figure 8 is a diagram showing another example of the signal processing configuration of the laser gas analyzer 100. The laser gas analyzer 100 in Figure 8 differs from the laser gas analyzer 100 in Figure 1 in the configuration of the received light signal processing unit 21. The other configuration of the laser gas analyzer 100 in Figure 8 may be the same as that of the laser gas analyzer 100 in Figure 1. The received light signal processing unit 21 in Figure 8 has an AD conversion unit 130, a detection waveform correction unit 141, a phase alignment unit 142, a subtraction unit 143, and a concentration measurement unit 134.

The AD converted signal from the AD converter 130 is input to the detection waveform correction unit 141. The detection waveform correction unit 141 corrects the detection waveform to a corrected detection waveform using a noise waveform recorded in advance. The noise waveform in this example does not include the gas absorption waveform of the measurement target gas 1. The noise waveform may be acquired in advance by controlling the temperature of the laser element 12 with the temperature control circuit 111. The noise waveform may also be acquired by removing the measurement target gas 1 from the measurement target space 2. The noise waveform may be recorded in the detection waveform correction unit 141, or the light receiving signal processing unit 21 may have a separate recording unit and the detection waveform correction unit 141 may refer to the recording unit.

The phase alignment unit 142 aligns the phase of the corrected detection waveform corrected by the detection waveform correction unit 141 and the corrected noise waveform obtained by correcting the noise waveform. The corrected noise waveform may be recorded in the detection waveform correction unit 141, like the noise waveform, or the light receiving signal processing unit 21 may have a separate recording unit and the detection waveform correction unit 141 may refer to the recording unit. The corrected noise waveform may also be generated in the detection waveform correction unit 141. By aligning the phases, it is possible to prevent noise from remaining uncancelled when subtracted by the subtraction unit 143.

The subtraction unit 143 subtracts the corrected noise waveform from the phase-aligned corrected detection waveform to generate a subtracted detection waveform. The concentration measurement unit 134 is a circuit that calculates the amplitude of the extreme value based on the subtracted detection waveform from the subtraction unit 143. The concentration measurement unit 134 may calculate the amplitude of the extreme value of the gas absorption waveform based on the subtracted detection waveform generated by the subtraction unit 143. The concentration measurement unit 134 may measure the concentration of the measurement target gas 1 based on the amplitude of the extreme value of the gas absorption waveform. In other words, the concentration measurement unit 134 may measure the concentration of the measurement target gas 1 based on the subtracted detection waveform generated by the subtraction unit 143. By measuring the concentration of the measurement target gas 1 based on the subtracted detection waveform generated by the subtraction unit 143, periodic noise such as interference noise can be accurately removed, and highly accurate measurements can be performed.

Figure 9 is a diagram showing an example of a block diagram of signal processing in the light receiving signal processing unit 21 in Figure 8. The processing contents of the light receiving signal processing unit 21 in Figure 8 will be described in detail using Figure 9. First, the signal of the lock-in detection circuit 124 is AD converted and converted into a digital signal (S401). Next, a frequency restriction is performed to extract only predetermined frequency components using a bandpass filter (not shown in Figure 8) (S402). In order to improve the noise estimation accuracy in data interpolation, the detection data after AD conversion is frequency restricted using a bandpass filter so that it contains only the frequency band of the gas absorption waveform as much as possible, and unnecessary components are removed.

Next, the light receiving signal processing unit 21 performs detection waveform correction or noise waveform correction (S403). If a noise waveform is to be recorded, the light receiving signal processing unit 21 performs noise waveform correction (S404). If a detection waveform is to be corrected, the light receiving signal processing unit 21 performs detection waveform correction (S408).

First, the noise waveform correction (S404) will be described. Due to factors such as the output of the laser element 12 and the nonlinearity of the current, the laser light 30 emitted from the laser element 12 generates an output in the high frequency component. Since the output of the high frequency component is not constant in the wavelength sweep range of the laser element 12, after lock-in detection, a slope and a DC component are generated as a noise waveform. A correction term for this noise waveform is obtained and recorded (S405). Specifically, a correction term for the slope of the noise waveform and a DC component of the noise waveform are obtained and recorded, respectively. The correction term for the slope of the noise waveform may be obtained by the least squares method. The correction term for the DC component of the noise waveform may be obtained by averaging. Then, a corrected noise waveform is obtained and recorded by using the correction term for the slope of the noise waveform and the correction term for the DC component of the noise waveform (S406). The corrected noise waveform V _noise '(t) is expressed by the following equation 4. In the following formula 4, V _noise (t) is a noise waveform, V _slope is a slope correction term, and V _dc is a DC component correction term. V _noise '(t) and V _noise (t) are functions of time t.

Next, the maximum value of the corrected noise waveform is detected and recorded (S407). The maximum value of the corrected noise waveform is used during phase alignment (S409). The detection range for the maximum value of the corrected noise waveform may be the entire corrected noise waveform or a part of the corrected noise waveform. The correction term, corrected noise waveform, and maximum value of the recorded noise waveform are recorded until the next time noise waveform correction (S404) is performed.

Next, the detection waveform correction (S408) will be described. The detection waveform correction unit 141 corrects the detection waveform to a corrected detection waveform by using a correction term for the slope of the noise waveform and a correction term for the DC component of the noise waveform (S408). That is, for the correction of the slope, a noise waveform recorded in advance is used to obtain a correction term for the slope of the noise waveform, and the slope of the detection waveform is corrected based on the correction term for the slope of the noise waveform. For the correction of the DC component, a noise waveform recorded in advance is used to obtain a correction term for the DC component of the noise waveform, and the DC component of the detection waveform is corrected based on the correction term for the DC component of the noise waveform. The corrected detection waveform V _gas '(t) is expressed by the following formula 5. In the following formula 5, V _gas (t) is the detection waveform, V _slope is the correction term for the slope recorded in the correction term recording (S406), and V _dc is the correction term for the DC component recorded in the correction term recording (S406). V _gas '(t) and V _gas (t) are functions of time t.

After performing the detection waveform correction (S408), the phase alignment unit 142 aligns the phase of the corrected detection waveform with that of the corrected noise waveform (S409). Phase alignment (S409) may not be performed and the corrected detection waveform and the corrected noise waveform may be directly subtracted. The phase alignment unit 142 detects the maximum value of the corrected detection waveform (S410), similar to recording the maximum value of the corrected noise waveform (S407). It is preferable that the detection range of the maximum value of the corrected detection waveform is a part of the corrected detection waveform excluding the gas absorption waveform portion of the gas to be measured. This is because the maximum value of the corrected detection waveform falls within that gas absorption waveform portion, making it difficult to align the phase with the corrected noise waveform.

Next, the phase matching unit 142 calculates a time shift amount t _shift from the time difference between the maximum value of the corrected detection waveform and the maximum value of the corrected noise waveform in a detection range that does not include the gas absorption waveform portion of the measurement target gas (S411). The phase matching unit 142 shifts the corrected noise waveform by the time shift amount t _shift to match the phase of the corrected detection waveform and the corrected noise waveform (S412). The phase matching unit 142 may match the phase of the corrected detection waveform and the corrected noise waveform from the time shift amount t _shift .

After phase alignment, the corrected noise waveform is subtracted from the corrected detection waveform to generate a subtracted detection waveform (S413). The subtracted waveform _Vsubtract (t) is expressed by the following equation 6. _Vsubtract (t) is a function of time t. The subtracted waveform is used to perform absorption amplitude calculation and gas concentration calculation (S414).

Figure 10 shows an example of phase alignment. Figure 10(a) shows an example of a noise waveform 401. The noise waveform 401 has a slope component and a DC component.

Figure 10(b) shows an example of the corrected noise waveform 402. The waveform in Figure 10(b) is obtained by removing the slope component and DC component from the waveform in Figure 10(a). As shown in Figure 10(b) , the maximum value in the detection range 501 of the corrected noise waveform 402 is A. The detection range 501 may be any range in which the peak of the corrected noise waveform 402 can be detected.

Figure 10(c) shows an example of a detection waveform 403. Similar to Figure 10(a), the detection waveform 403 has a slope component and a DC component.

Figure 10(d) shows an example of the corrected detection waveform 404. The waveform in Figure 10(d) has the slope and DC components removed from the waveform in Figure 10(c). As shown in Figure 10(d), the maximum value in the detection range 501 of the corrected detection waveform 404 excluding the gas absorption waveform portion of the measurement target gas is B. The detection range 501 in Figure 10(d) is the same as the detection range 501 in Figure 10(b), but may be different as long as the peak of the corrected detection waveform 404 can be detected. When the wavelength sweep time range is 0 ms to 10 ms (wavelength sweep time is 10 ms) and the gas absorption waveform portion of the measurement target gas is in the wavelength sweep time range of 3 ms to 8 ms, the detection range 501 is, for example, in the wavelength sweep time range of 0 ms to 2 ms.

Fig. 10E shows an example of phase alignment between the corrected noise waveform 402 and the corrected detection waveform 404. In Fig. 10E, the corrected noise waveform 402 is shifted by a time shift amount t _shift .

Figure 10(f) shows an example of the subtracted waveform 405. As shown in Figure 10(f), the subtracted waveform 405 has periodic noise removed, making it possible to perform accurate measurements.

Figure 11 is a diagram showing an example of phase alignment according to a comparative example. Figure 11(a) shows another example of a noise waveform 401. In Figure 11(a), the maximum value is calculated before correcting the noise waveform 401. Since the noise waveform 401 has a slope component, the maximum value is A', which is the end of the detection range 502.

Figure 11 (b) shows another example of the detection waveform 403. In Figure 11 (b), the maximum value is calculated before the detection waveform 403 is corrected. As shown in Figure 11 (b), the maximum value in the detection range 502 of the detection waveform 403 excluding the gas absorption waveform portion of the gas to be measured is B.

Fig. 11C shows an example of phase alignment between the noise waveform 401 and the detection waveform 403. In Fig. 11C, the noise waveform 401 is shifted by a time shift amount t _shift '.

11D is a diagram showing another example of the subtraction waveform 405. The subtraction waveform V _subtract (t) is expressed by the following equation 7.

Because the phases of the noise waveform 401 and the detection waveform 403 were shifted during phase alignment, the subtraction waveform 405 in FIG. 11(d) has residual noise compared to the subtraction waveform 405 in FIG. 10(f). For the above reasons, it is preferable to perform phase alignment after correcting the noise waveform 401 and the detection waveform 403, respectively.

Figure 12 is a diagram showing an example of a method for acquiring a noise waveform 401 and a detection waveform 403. In the example of Figure 12, the noise waveform 401 and the detection waveform 403 are acquired by controlling the temperature of the laser element 12 by the temperature control circuit 111. Figure 12 (a) shows an example of a laser drive current value controlled by the laser drive current generation unit 11. Figure 12 (b) is a diagram showing an example of the temperature of the laser element 12 controlled by the temperature control circuit 111. Figure 12 (c) is a diagram showing an example of a waveform when the laser drive current value and the temperature of the laser element 12 are controlled. In Figure 12, the horizontal axis (time) is shown uniformly.

As shown in FIG. 12, when acquiring the noise waveform 401, the temperature of the laser element 12 is set to T1, and when acquiring the detection waveform 403, the temperature of the laser element 12 is set to T2. The temperature T1 may be set so that the waveform does not include the gas absorption waveform of the measurement target gas 1. The temperature T2 may be set so that the waveform includes the gas absorption waveform of the measurement target gas 1. In addition, the laser drive current value is the same whether the noise waveform 401 or the detection waveform 403 is acquired. In this way, by controlling the laser drive current value and the temperature of the laser element 12, the noise waveform 401 and the detection waveform 403 can be acquired.

The laser gas analyzer 100 is ideal for measuring combustion exhaust gas from boilers, waste incineration, etc., and for combustion control. It is also useful as an analyzer for steel gas analysis [blast furnaces, converters, heat treatment furnaces, sintering (pellet equipment), coke ovens], fruit and vegetable storage and aging, biochemistry (microorganisms) [fermentation], air pollution [incinerators, flue gas desulfurization and denitrification], exhaust gas from internal combustion engines of automobiles and ships (removal testers), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growth, chemical analysis [oil refining plants, petrochemical plants, gas generating plants], environmental use [landing concentration, concentration inside tunnels, parking lots, building management], various physical and chemical experiments, etc.

The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

It should be noted that the order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically indicated as "before,""priorto," etc., and may be realized in any order unless the output of a previous process is used in a later process. Even if the operational flow in the claims, specifications, and drawings is described using "first,""next," etc. for convenience, it does not mean that it is essential to perform the process in this order.
[Item 1]
A laser gas analyzer that uses wavelength modulation spectroscopy to measure the concentration of a measurement target gas present in a measurement target space,
a laser element that emits laser light modulated in a wavelength band including an absorption line spectrum of the measurement target gas;
a light receiving element that detects the laser light that has passed through the measurement target space;
a detection unit that converts a light receiving signal of the light receiving element into a detection waveform;
a light receiving signal processing unit that measures the concentration of the measurement target gas based on the detected waveform;
Equipped with
The light receiving signal processing unit includes:
a deleted waveform generating unit for generating a deleted waveform by deleting a gas absorption waveform portion of the measurement target gas from the detection waveform;
a noise waveform generating unit that generates a noise waveform by interpolating the deleted portion by calculating a sum model of sine waves from the remaining portion of the deleted waveform;
a corrected detection waveform generating unit that removes the noise waveform from the detection waveform to generate a corrected detection waveform;
a concentration measuring unit that measures a concentration of the measurement target gas based on the corrected detection waveform;
having
The noise waveform generating unit is
calculating an amplitude estimate and a frequency estimate based on the deleted waveform;
limiting a coefficient search range for amplitude based on the amplitude estimate;
limiting a frequency coefficient search range based on the frequency estimate;
Laser gas analyzer.
[Item 2]
2. The laser gas analyzer according to claim 1, wherein the noise waveform generator calculates the amplitude estimate value and the frequency estimate value by performing a Fourier transform on the deleted waveform.
[Item 3]
3. The laser gas analyzer according to item 1 or 2, wherein the noise waveform generation unit limits a coefficient search range of the amplitude and a coefficient search range of the frequency based on the amplitude estimate value and the frequency estimate value, and then calculates the sum model of the sine wave by using a least squares method.
[Item 4]
The deleted waveform generating unit
a deletion position where a portion of the gas absorption waveform of the measurement target gas is deleted from the detection waveform is recorded;
generating the deleted waveform by deleting the deletion position in the detected waveform;
4. The laser gas analyzer according to any one of items 1 to 3.
[Item 5]
5. The laser gas analyzer according to claim 1, wherein a coefficient search range of the amplitude is equal to or greater than 0.5 times and equal to or less than 2.0 times the amplitude estimate value.
[Item 6]
3. The laser gas analyzer according to item 2, wherein the frequency coefficient search range is determined based on a frequency resolution when the deleted waveform is Fourier transformed.
[Item 7]
7. The laser gas analyzer according to item 6, wherein the frequency coefficient search range is equal to or greater than the frequency estimate value minus 100 Hz and equal to or less than the frequency estimate value plus 100 Hz.
[Item 8]
A laser gas analyzer that uses wavelength modulation spectroscopy to measure the concentration of a measurement target gas present in a measurement target space,
a laser element that emits a laser beam modulated in a wavelength band including an absorption line spectrum of the measurement target gas;
a light receiving element that detects the laser light that has passed through the measurement target space;
a detection unit that converts a light receiving signal of the light receiving element into a detection waveform;
a light receiving signal processing unit that measures the concentration of the measurement target gas based on the detected waveform;
Equipped with
The light receiving signal processing unit includes:
a detection waveform correction unit that uses a noise waveform recorded in advance to obtain a correction term for the slope of the noise waveform and corrects the slope of the detection waveform based on the correction term for the slope of the noise waveform;
a phase matching unit that matches the phases of a corrected detection waveform obtained by correcting the detection waveform and a corrected noise waveform obtained by correcting the noise waveform;
a subtraction unit that subtracts the corrected noise waveform from the corrected detection waveform to generate a subtracted detection waveform;
a concentration measuring unit that measures the concentration of the measurement target gas based on the subtraction detection waveform;
having
Laser gas analyzer.
[Item 9]
9. The laser gas analyzer according to item 8, wherein the detection waveform correction unit obtains a correction term for a DC component of the noise waveform using the noise waveform recorded in advance, and corrects the DC component of the detection waveform based on the correction term for the DC component of the noise waveform.
[Item 10]
The phase matching unit includes:
calculating a time shift amount from a time difference between a maximum value of the corrected detection waveform in a detection range not including a gas absorption waveform portion of the measurement target gas and a maximum value of the corrected noise waveform in the detection range;
aligning the phases of the corrected detection waveform and the corrected noise waveform based on the amount of time shift;
10. The laser gas analyzer according to item 8 or 9.

1: Gas to be measured, 2: Space to be measured, 10: Light emitting unit, 11: Laser drive current generating unit, 12: Laser element, 13: Collimating lens, 14: Light emitting unit window plate, 15: Light emitting unit container, 20: Light receiving unit, 21: Light receiving signal processing unit, 22: Light receiving element, 23: Condenser lens, 24: Light receiving unit window plate, 25: Light receiving unit container, 26: Detection unit, 30: Laser light, 40: Communication line, 50: Pipe wall, 51: Flange, 52: Optical axis adjustment flange, 100: Laser gas analyzer, 111: Temperature control circuit, 112: Control circuit, 121: Preamplifier, 122: High pass filter, 12 3: Variable amplifier, 124: Lock-in detection circuit, 130: AD conversion section, 131: Deleted waveform generation section, 132: Noise waveform generation section, 133: Corrected detection waveform generation section, 134: Concentration measurement section, 141: Detection waveform correction section, 142: Phase alignment section, 143: Subtraction section, 201: Detection waveform, 202: Deleted waveform, 203: Noise waveform, 204: Corrected detection waveform, 301: Waveform, 302: Waveform, 303: Waveform, 401: Noise waveform, 402: Corrected noise waveform, 403: Detection waveform, 404: Corrected detection waveform, 405: Subtracted waveform, 501: Detection range, 502: Detection range

Claims (7)

A laser gas analyzer that uses wavelength modulation spectroscopy to measure the concentration of a measurement target gas present in a measurement target space,
a laser element that emits a laser beam modulated in a wavelength band including an absorption line spectrum of the measurement target gas;
a light receiving element that detects the laser light that has passed through the measurement target space;
a detection unit that converts a light receiving signal of the light receiving element into a detection waveform;
a light receiving signal processing unit that measures a concentration of the measurement target gas based on the detection waveform,
The light receiving signal processing unit includes:
a deleted waveform generating unit for generating a deleted waveform by deleting a gas absorption waveform portion of the measurement target gas from the detection waveform;
a noise waveform generating unit that generates a noise waveform by interpolating the deleted portion by calculating a sum model of sine waves from the remaining portion of the deleted waveform;
a corrected detection waveform generating unit that removes the noise waveform from the detection waveform to generate a corrected detection waveform;
a concentration measuring unit that measures a concentration of the measurement target gas based on the corrected detection waveform,
The noise waveform generating unit is
calculating an amplitude estimate and a frequency estimate based on the deleted waveform;
limiting a coefficient search range for amplitude based on the amplitude estimate;
A laser gas analyzer that limits a frequency coefficient search range based on the frequency estimate. The laser gas analyzer according to claim 1 , wherein the noise waveform generator calculates the amplitude estimate value and the frequency estimate value by performing a Fourier transform on the deleted waveform. 3. The laser gas analyzer according to claim 1, wherein the noise waveform generator limits a coefficient search range of the amplitude and a coefficient search range of the frequency based on the amplitude estimate value and the frequency estimate value, and then calculates the sum model of the sine waves using a least squares method. The deleted waveform generating unit
a deletion position where a portion of the gas absorption waveform of the measurement target gas is deleted from the detection waveform is recorded;
The laser gas analyzer according to claim 1 , wherein the deleted waveform is generated by deleting the deletion position in the detected waveform. The laser gas analyzer according to claim 1 , wherein the coefficient search range of the amplitude is 0.5 times or more and 2.0 times or less of the amplitude estimate value. The laser gas analyzer according to claim 2 , wherein the frequency coefficient search range is determined based on a frequency resolution when the deleted waveform is subjected to a Fourier transform. 7. The laser gas analyzer according to claim 6, wherein the frequency coefficient search range is equal to or greater than a value obtained by subtracting 100 Hz from the frequency estimate value and equal to or less than a value obtained by adding 100 Hz to the frequency estimate value.

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