JP2021139868A - Laser type gas analyzer - Google Patents

Abstract

To provide a laser type gas analyzer with which it is possible to analyze a gas concentration with high accuracy.SOLUTION: The laser type gas analyzer comprises: a light source unit for emitting a frequency-modulated laser beam; a light receiving element for receiving a laser beam propagated via a measurement object space in which the gas to be measured exists; and a signal processing circuit for detecting a gas absorption waveform from the output signal of the light receiving element and measuring the concentration of the gas to be measured. The signal processing circuit includes a filter for removing the modulating frequency component of the laser beam, and a correction unit for correcting the modulating frequency of the laser beam or the frequency characteristic of the filter so that the noise of the gas absorption waveform becomes small.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laser gas analyzer that analyzes the presence / absence, concentration, etc. of various measurement target gases in the measurement target space.

A laser gas analyzer that irradiates a frequency-modulated laser beam into the measurement target space to measure the concentration is known. (See, for example, Patent Document 1).
Japanese Unexamined Patent Publication No. 2009-47677

It is preferable that the laser gas analyzer can analyze the gas concentration with high accuracy.

In the first aspect of the present invention, a laser gas analyzer is provided. The laser gas analyzer may include a light source unit. The light source unit may emit frequency-modulated laser light. The laser gas analyzer may include a light receiving element. The light receiving element may receive the laser beam propagated through the measurement target space in which the measurement target gas exists. The laser gas analyzer may include a signal processing circuit. The signal processing circuit may detect the gas absorption waveform by processing the output signal of the light receiving element, and measure the concentration of the gas to be measured from the gas absorption waveform. The signal processing circuit may have a filter. The filter may remove the modulated frequency component of the laser beam. The signal processing circuit may have a correction unit. The correction unit may correct the modulation frequency of the laser beam or the frequency characteristic of the filter so that the noise of the gas absorption waveform becomes small.

The correction unit may specify a specific modulation frequency in which the noise of the gas absorption waveform becomes smaller than the pre-correction modulation frequency, which is the modulation frequency before the change, by changing the modulation frequency of the laser beam. The correction unit may correct the modulation frequency of the laser beam to a specific modulation frequency.

The correction unit may correct the modulation frequency of the laser beam so as to approach the removal frequency of the filter.

The correction unit may change the modulation frequency of the laser beam in the sweep range, which is the range in which the modulation frequency is changed. The correction unit may specify the frequency at which the noise of the gas absorption waveform is minimized within the sweep range as the specific modulation frequency. The sweep range may include the pre-correction modulation frequency.

When the frequency at the end of the sweep range becomes the specific modulation frequency, the correction unit may shift the sweep range toward the end. The center of the sweep range before shifting may be the pre-correction modulation frequency.

The laser gas analyzer may include a gas temperature measuring unit. The gas temperature measuring unit may measure the temperature of the gas to be measured. The correction unit may control the sweep range based on the temperature of the gas to be measured. The correction unit may widen the sweep range when the temperature of the gas to be measured exceeds the threshold value. The correction unit may shift the sweep range based on the temperature change of the gas to be measured. The correction unit may change the direction of shifting the sweep range based on the direction of the temperature change of the gas to be measured.

The correction unit may detect the modulation frequency component each time the modulation frequency of the laser beam is corrected. The correction unit may correct the modulation frequency based on the modulation frequency component. The correction unit may correct the modulation frequency based on the change in the modulation frequency component.

Each time the correction unit corrects the modulation frequency of the laser beam, the correction unit may detect the modulation frequency component and the double modulation frequency component which is twice the frequency component of the modulation frequency component. The correction unit may correct the modulation frequency based on the ratio of the modulation frequency component to the double modulation frequency component.

The gas to be measured may be discharged from the exhaust gas device. The signal processing circuit may control the sweep range based on the operating condition of the exhaust gas device.

The correction unit may specify a specific removal frequency at which the noise of the gas absorption waveform becomes smaller than the noise before the removal frequency is changed by changing the removal frequency which is the center frequency or the cutoff frequency of the filter. The correction unit may correct the removal frequency of the filter to a specific removal frequency.

The correction unit may specify the specific removal frequency by changing the removal frequency of the filter in the change range including the removal frequency of the filter before correction. The correction unit may specify the specific removal frequency by changing the removal frequency of the filter in the change range centered on the removal frequency of the filter before correction. The correction unit may extend the change range when the specific removal frequency becomes the frequency at the end of the change range.

The correction unit may have a performance calculation unit that calculates the amount of residual noise as noise of the gas absorption waveform. The residual noise may be a frequency component other than the gas absorption waveform. The residual noise may be a modulation frequency component.

The outline of the above invention does not list all the necessary features of the present invention. Sub-combinations of these feature groups can also be inventions.

An example of the configuration of the laser gas analyzer 100 according to one embodiment of the present invention is shown. An example of the configuration of the light source unit 11 and the signal processing circuit 21 is shown. An example of the configuration of the signal processing circuit 21 is shown. The relationship between the output signal frequency and the removal frequency of the filter 214 when an error occurs is shown. It is a figure which shows the sweep range 60 of a modulation frequency. It is a figure which shows the example of the correction of a high frequency modulation signal. It is a figure which shows another example of correction of a high frequency modulation signal. It is a figure which shows an example of the block diagram of the correction process of the correction part 216. An example of the configuration of the laser gas analyzer 200 according to another embodiment of the present invention is shown. An example of the configuration of the signal processing circuit 221 according to another embodiment of the present invention is shown. An example of the configuration of the laser gas analyzer 300 according to another embodiment of the present invention is shown. An example of the configuration of the light source unit 311 and the signal processing circuit 321 according to another embodiment of the present invention is shown. An example of the configuration of the signal processing circuit 321 according to another embodiment of the present invention is shown. It is a figure which shows the change range 360 of the removal frequency. It is a figure which shows the example of the correction of the frequency characteristic of a filter 214. It is a figure which shows another example of the correction of the frequency characteristic of a filter 214. It is a figure which shows an example of the block diagram of the correction process of the correction part 316.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the inventions that fall within the scope of the claims. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

FIG. 1 shows an example of the configuration of the 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 signal processing circuit 21, and a communication line 40. The light emitting unit 10 irradiates the measurement target space 2 with the laser beam 30. The light receiving unit 20 receives the laser beam 30 propagated through the measurement target space 2 in which the measurement target gas 1 exists. The light receiving unit 20 of this example receives the laser light 30 transmitted through the measurement target space 2, while the light receiving unit 20 of another example receives the laser light 30 scattered or reflected in the measurement target space 2. You may. The signal processing circuit 21 may analyze the measurement target gas 1 in the measurement target space 2 based on the light reception result in the light receiving unit 20. That is, the signal processing circuit 21 may measure the concentration of the measurement target gas 1 in the measurement target space 2 based on the light reception result in the light receiving unit 20. The communication line 40 communicates between the light emitting unit 10 and the light receiving unit 20 by an electric signal. Further, instead of the communication line 40, a communication unit such as wireless or optical communication may be adopted.

The measurement target gas 1 may be included in the exhaust gas discharged from the exhaust gas device. That is, the gas 1 to be measured may be discharged from the exhaust gas device. The gas 1 to be measured is, for example, NH ₃ , HCl, O ₂ , CO, CO ₂ , and CH ₄ .

In the laser gas analyzer 100 of this example, the light emitting unit 10 emits the laser beam 30. The laser beam 30 is projected onto the measurement target space 2 inside the piping wall 50a and the piping wall 50b. A part of the light amount of the laser light 30 is absorbed by the gas 1 to be measured. The remaining unabsorbed light, that is, transmitted light is incident on the light receiving unit 20, and the amount of transmitted light is detected. The signal processing circuit 21 calculates the concentration of the gas 1 to be measured based on the amount of detected transmitted light. That is, the laser gas analyzer 100 may measure the concentration of the measurement target gas 1 existing in the measurement target space 2 by wavelength modulation spectroscopy.

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

The laser gas analyzer 100 of this example includes an optical axis adjusting flange 52a and an optical axis adjusting flange 52b. The optical axis adjusting flanges 52a and 52b are mechanically movably attached to the flanges 51a and 51b. The optical axis adjusting flange 52a fixes the light emitting portion 10 to the flange 51a. The optical axis adjusting flange 52b fixes the light receiving portion 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 adjusting flanges 52a and 52b. The optical axis adjusting flange 52a adjusts the emission angle of the laser beam 30, and the optical axis adjusting flange 52b adjusts the incident angle of the laser beam 30. The laser light 30 emitted from the light emitting unit 10 is received by the optical axis adjusting flanges 52a and 52b in the light receiving unit 20 with the maximum amount of light.

The light emitting unit 10 of this example includes a light source unit 11, a collimating lens 12, and a light emitting unit container 13. The light emitting unit container 13 accommodates the light source unit 11 and the collimating lens 12. The light emitting unit container 13 of this example has a bottomed cylindrical shape. The light emitting unit container 13 is attached to the optical axis adjusting flange 52a. The light emitting unit container 13 has a light emitting element, optical components, and an electric / electronic circuit built therein, and isolates them from the outside air to protect them from wind, rain, dust, dirt, and the like.

The light source unit 11 emits the laser beam 30. The light source unit 11 has a laser element whose wavelength of emitted light can be controlled. The laser beam 30 is frequency-modulated. The laser beam 30 emitted from the light source unit 11 is collimated into parallel light by an optical system including a collimating lens 12. The collimated light passes through the center of the flange 51a and is incident on the inside of the flue between the pipe wall 50a and the pipe wall 50b. When the laser beam 30 incident on the inside of the flue passes through the measurement target gas 1 inside the flue, a part of the wavelength component corresponding to the absorption wavelength of the measurement target gas 1 is absorbed.

The laser beam 30 emitted from the light source unit 11 is collimated into parallel light by an optical system including a collimating lens 12. The collimated light passes through the center of the flange 51a and is incident on the inside of the flue between the pipe wall 50a and the pipe wall 50b. The laser beam 30 emitted from the light source unit 11 is controlled so that the emission center wavelength becomes the center wavelength of the absorption line spectrum of the measurement target gas 1. The center wavelength of the absorption line spectrum of the gas 1 to be measured is defined as the wavelength λ1. Therefore, when the laser beam 30 incident on the inside of the flue passes through the measurement target gas 1 inside the flue, a part of the wavelength component corresponding to the absorption wavelength of the measurement target gas 1 is absorbed.

The collimating lens 12 is made of a material having high transmittance at the wavelength λ1 and the wavelengths around it. The collimated lens 12 converts the laser light 30 into substantially parallel light, and transmits the laser light 30 to the light receiving unit 20 while suppressing loss due to diffusion.

The light receiving unit 20 of this example includes a signal processing circuit 21, a light receiving element 22, a condensing lens 23, and a light receiving unit container 24. The light receiving unit container 24 houses the signal processing circuit 21, the light receiving element 22, and the condensing lens 23. The light receiving unit container 24 of this example has a bottomed cylindrical shape. The light receiving unit container 24 is attached to the optical axis adjusting flange 52b. The light emitting unit container 13 has a light emitting element, optical components, and an electric / electronic circuit built therein, and isolates them from the outside air to protect them from wind, rain, dust, dirt, and the like.

The condenser lens 23 collects the laser beam 30 that has passed through the inside of the flue. Like the collimating lens 12, the condenser lens 23 is made of a material having high transmittance at the wavelength λ1 and the wavelengths around the collimating lens 12. Since the laser beam 30 is focused on the light receiving element 22 by the condenser lens 23, high signal intensity can be obtained.

The laser beam 30 focused by the condenser lens 23 is received by the light receiving element 22. The light receiving element 22 is composed of a photodiode or the like, and is sensitive to the laser beam 30 emitted from the light source unit 11. The light receiving element 22 preferably has sensitivity to the entire wavelength sweepable range of the light source unit 11. The light receiving element 22 converts the received light into an electric signal and inputs it to the signal processing circuit 21. For the light receiving element 22, a light receiving element having sensitivity at _{the wavelength λ 1 and the wavelengths around the wavelength λ 1 can be selected.} The light receiving element 22 may detect the laser beam 30 that has passed through the measurement target space 2.

FIG. 2 shows an example of the configuration of the light source unit 11 and the signal processing circuit 21. The light source unit 11 includes a laser drive signal generation unit 111, a current control unit 114, a temperature control unit 115, a laser element 116, a thermistor 117, and a Perche element 118. In FIG. 5, the configuration of the signal processing circuit 21 other than the calculation unit 215 and the frequency control unit 218 is omitted.

The light source unit 11 includes a laser drive signal generation unit 111 having a sweep signal generation unit 112 and a modulation signal generation unit 113. The sweep signal generation unit 112 outputs a wavelength sweep drive signal that changes the emission wavelength of the laser element 116. The sweep signal generation unit 112 sweeps the emission wavelength of the laser element 116 within the wavelength range including the absorption wavelength of the gas 1 to be measured. The modulation signal generation unit 113 outputs a sine wave high-frequency modulation signal for frequency-modulating the emission wavelength of the laser element 116. The laser drive signal generation unit 111 superimposes a high frequency modulation signal on the wavelength sweep drive signal and outputs the signal. The high frequency modulation signal of the modulation signal generation unit 113 is set as a 1f signal.

The current control unit 114 supplies the laser element 116 with a current corresponding to the laser drive signal output by the laser drive signal generation unit 111. As a result, the laser element 116 emits the laser light 30 having a wavelength and an intensity corresponding to the laser drive signal.

The laser element 116 irradiates the measurement target space 2 with the laser beam 30. For example, a semiconductor laser that irradiates the measurement target space 2 with a laser beam. The laser element 116 has a property that the emission wavelength changes depending on the supplied current and the temperature of the laser element 116. That is, the laser element 116 can control the wavelength of the laser beam 30 by the laser drive signal (drive current) and the temperature. The laser element 116 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 Laser).

The thermistor 117 is a temperature sensor that detects the temperature of the laser element 116. The thermistor 117 may be arranged in close proximity to the laser element 116. The perche element 118 is a temperature control element that controls the temperature of the laser element 116. The thermistor 117 may be arranged between the Perche element 118 and the laser element 116. The thermistor 117 and the Perche element 118 may be connected to the temperature control unit 115.

The temperature control unit 115 controls the temperature of the laser element 116. The temperature control unit 115 may control the temperature of the laser element 116 by PID controlling the Pelche element 118. The temperature control unit 115 may control the temperature of the laser element 116 by PID controlling the Pelche element 118 based on the resistance value of the thermistor 117. The temperature control unit 115 may control the temperature of the laser element 116 by PID controlling the perche element 118 so that the resistance value of the thermistor 117 becomes constant. By controlling the temperature of the laser element 116, the emission wavelength of the laser element 116 can be stabilized.

The sweep signal generation unit 112 may output a trigger signal to the calculation unit 215 of the signal processing circuit 21. As a result, the signal processing circuit 21 can process the wavelength of the laser beam 30 output by the laser element 116 in association with the signal output by the light receiving element 22.

The frequency control unit 218 is connected to the modulation signal generation unit 113 to control the modulation frequency of the laser beam 30. The frequency control unit 218 may control the modulation frequency of the laser beam 30 based on the signal processing of the signal processing circuit 21.

FIG. 3 shows an example of the configuration of the signal processing circuit 21. The signal processing circuit 21 processes the output signal of the light receiving element 22, and measures the concentration of the measurement target gas 1 from the gas absorption waveform existing in the sweep range of the laser beam 30. The signal processing circuit 21 may detect the gas absorption waveform by processing the output signal of the light receiving element 22, and measure the concentration of the measurement target gas 1 from the gas absorption waveform.

The signal processing circuit 21 of this example includes an I / V converter 211, an oscillator 212, a synchronous detection circuit 213, a filter 214, a calculation unit 215, and a correction unit 216. Further, the correction unit 216 has a performance calculation unit 217 and a frequency control unit 218. The output current of the light receiving element 22 is converted into a voltage by the I / V converter 211. The output signal of the I / V converter 211 is input to the synchronous detection circuit 213.

The laser gas analyzer 100 of this example processes the 2f signal component of the voltage signal output by the light receiving element 22 as a gas absorption waveform. The 2f signal is a signal having a frequency twice that of the high-frequency modulated signal of the modulated signal generating unit 113 shown in FIG. Therefore, the 2f signal from the oscillator 212 is also input to the synchronous detection circuit 213. By inputting the 2f signal to the synchronous detection circuit 213, the gain of the double modulation frequency component, which is a component of the frequency twice that of the high frequency modulation signal, can be increased. Therefore, the synchronous detection circuit 213 extracts only the amplitude of the double frequency component of the high frequency modulated signal in the output signal of the I / V converter 211.

The filter 214 removes noise from the output signal of the synchronous detection circuit 213. The filter 214 may have digitally controllable frequency characteristics. The filter 214 may be a notch filter. The filter 214 may be an analog filter. The filter 214 is configured by an IC such as a programmable filter or a digital potentiometer as an example. The filter 214 may be a digital filter. The filter 214 is configured by a DSP or the like as an example.

In this example, since the 2f signal component of the voltage signal output by the light receiving element 22 is processed as a gas absorption waveform, the filter 214 may remove the 1f signal as noise. In other words, the filter 214 may be set to remove the 1f signal. The removal frequency of the filter 214 may be set to the 1f signal. The removal frequency of the filter 214 may be the center frequency (hereinafter referred to as the center frequency) in the range in which the filter 214 can be removed. Further, the removal frequency of the filter 214 may be the cutoff frequency of the filter 214. The output signal of the filter 214 is transmitted to the calculation unit 215, and the gas concentration of the gas 1 to be measured is measured. The filter 214 may remove the modulation frequency component of the laser beam 30.

The modulation signal generation unit 113 has individual differences and temperature characteristics for each individual IC. Therefore, the high-frequency modulated signal output by the modulated signal generation unit 113 may have an error from the ideal value of the output signal frequency.

FIG. 4 shows the relationship between the output signal frequency and the removal frequency of the filter 214 when an error occurs. The horizontal axis is the frequency, and the vertical axis is the gain of the frequency component when the output signal frequency is passed through the filter 214. If an error occurs, there will be a difference between the output signal frequency and the removal frequency of the filter 214. When there is no difference between the output signal frequency and the removal frequency of the filter 214, the gain of the frequency component from the filter 214 can be reduced. On the other hand, when there is a difference between the output signal frequency and the removal frequency of the filter 214, the gain of the frequency component from the filter 214 becomes large. Therefore, the noise removal performance of the filter 214 (1f signal in this example) deteriorates. It is conceivable to control the temperature of the modulated signal generation unit 113 in order to prevent an error from the ideal value of the output signal frequency, but the control may be insufficient due to factors other than the temperature characteristics.

The correction unit 216 corrects the high frequency modulation signal output by the modulation signal generation unit 113. The correction unit 216 includes a performance calculation unit 217 and a frequency control unit 218. The performance calculation unit 217 calculates the absorption waveform detection performance from the signal of the filter 214. The frequency control unit 218 calculates the control value of the high frequency modulation signal output by the modulation signal generation unit 113 based on the detection performance calculated by the performance calculation unit 217. The frequency control unit 218 transmits the control value to the modulation signal generation unit 113. In this example, the frequency control unit 218 is in the signal processing circuit 21, but may be in the light source unit 11. The frequency control unit 218 may be located in the modulation signal generation unit 113.

Since the correction unit 216 for correcting the high-frequency modulated signal output by the modulation signal generation unit 113 is provided, it is possible to prevent a difference between the output signal frequency and the removal frequency of the filter 214. Therefore, the filter removal performance can be maintained without setting a new filter. The correction unit 216 may correct the modulation frequency of the laser beam 30 so as to approach the removal frequency of the filter 214.

The method for measuring the concentration of the gas 1 to be measured will be described. First, the temperature of the laser element 116 is detected in advance by the thermistor 117. Further, the temperature control unit 115 controls the energization of the perche element 118 to adjust the temperature of the laser element 116 so that the gas 1 to be measured can be measured at the central portion of the wavelength sweep range. After that, the laser element 116 is driven to emit the laser beam 30 into the measurement target space 2 between the pipe wall 50a and the pipe wall 50b where the measurement target gas 1 exists. In the light receiving unit 20, the collected light is incident on the light receiving element 22.

When the laser beam 30 is not absorbed by the measurement target gas 1, the 2f signal is not detected by the synchronous detection circuit 213, so that the waveform of the output signal of the synchronous detection circuit 213 is substantially linear. On the other hand, when the laser beam 30 is absorbed by the measurement target gas 1, the 2f signal is detected by the synchronous detection circuit 213. The maximum value or the minimum value of the gas absorption waveform indicated by the 2f signal corresponds to the concentration of the gas 1 to be measured. Therefore, the calculation unit 215 may measure the maximum value or the minimum value of the gas absorption waveform to measure the gas concentration of the gas 1 to be measured. Further, a part or all of the gas absorption waveform may be integrated, and the gas concentration of the gas 1 to be measured may be calculated from the integrated value.

Further, there is a certain temporal correlation between the trigger signal output from the sweep signal generation unit 112 and the output signal of the synchronous detection circuit 213. That is, the gas absorption waveform and the timing at which the maximum value and the minimum value are generated can be detected almost accurately in advance with respect to the timing of the trigger signal, and high-precision measurement is possible by measuring with the trigger signal as a reference. ..

Next, the correction operation of the correction unit 216 will be described. The correction unit 216 controls the modulation frequency of the laser beam 30 and corrects the filter 214 so as to improve the noise removal performance, thereby improving the absorption waveform detection performance and making the density analysis more accurate. That is, the correction unit 216 corrects the modulation frequency of the laser beam 30 so that the noise of the gas absorption waveform becomes small. The correction unit 216 may perform a correction operation at a predetermined timing. The correction unit 216 may perform a correction operation at timings at regular intervals. The correction unit 216 may perform the correction operation at the timing when the detection performance of the absorption waveform becomes equal to or less than a predetermined threshold value. The correction unit 216 may perform the correction operation at the timing when the amount of change or the rate of change in the detection performance of the absorption waveform becomes equal to or higher than a predetermined threshold value.

In order to carry out the correction, the performance calculation unit 217 calculates the detection performance of the absorption waveform. In this example, the detection performance is the small amount of residual noise when a frequency component other than the absorption waveform is used as the noise component, and may be expressed simply as the small amount of noise. The detection performance may be a small residual noise component when a frequency component other than the absorption waveform is used as the noise component. The detection performance may be low noise. The detection performance may be a small frequency component other than the 2f signal component. The detection performance may be as small as the frequency component (modulation frequency component) of the 1f signal component. The detection performance may be a small frequency component other than the gas absorption waveform. That is, the correction unit 216 may detect the modulation frequency component every time the modulation frequency of the laser beam 30 is corrected, and correct the modulation frequency based on the modulation frequency component. The correction unit 216 may correct the modulation frequency based on the change in the modulation frequency component. Further, the detection performance may be a signal-to-noise ratio in which the absorption waveform is a signal component and the other frequency components are noise components. That is, each time the correction unit 216 corrects the modulation frequency of the laser beam 30, the correction unit 216 detects the modulation frequency component and the double modulation frequency component which is twice the frequency component of the modulation frequency component, and double-modulates the modulation frequency component. The modulation frequency may be corrected based on the ratio of frequency components. The detection performance may be a noise removal amount or a noise removal rate when a frequency component other than the absorption waveform is used as a noise component. Further, the detection performance can be calculated by the performance calculation unit 217 by frequency analysis such as FFT.

A modulation signal is transmitted from the frequency control unit 218 so as to change the modulation frequency in a range including the pre-correction modulation frequency, which is the pre-correction modulation frequency, at the timing of performing the correction operation, and is generated by the modulation signal generation unit 113. Change the frequency of. The sweep range may include the pre-correction modulation frequency. The sweep range may not change much, and it is preferable to start sweeping around the pre-correction modulation frequency. The correction unit 216 changes the modulation frequency of the laser beam 30 in the sweep range, which is the range in which the modulation frequency is changed.

FIG. 5 is a diagram showing a sweep range 60 of the modulation frequency. The horizontal axis is time and the vertical axis is the modulation frequency. In FIG. 5, the modulation frequency is changed in the sweep range 60, which is the range from the frequency f1 to the frequency f3.

As shown in FIG. 5, the change in modulation frequency may be a monotonous increase. The change in modulation frequency may be a monotonous decrease. Moreover, the change of the modulation frequency may be repeated. For example, when the frequency f1 is changed to the frequency f3, the frequency may be returned to the frequency f1 and the frequency may be changed to the frequency f3. By changing the iterative modulation frequency, the detection performance can be calculated accurately.

Further, the frequency f2, which is the center of the sweep range 60, may be the pre-correction modulation frequency. In other words, the frequency f2, which is the center of the frequency f1 and the frequency f3, may be the pre-correction modulation frequency. By sweeping around the pre-correction modulation frequency, a graph of detection performance centered on the pre-correction modulation frequency can be obtained. The frequency f2 is, for example, 10 kHz. The frequencies f1 and f3 may be determined by the frequency error. The frequency error may occur, for example, from the temperature range of the operating environment, the temperature characteristics of the ICs constituting the modulation signal generation unit 113, and the like. The frequencies f1 and f3 may be determined so as to surely include the estimated frequency error and f2. The frequency f1 is, for example, 5 kHz. The frequency f3 is, for example, 15 kHz. Further, in order to speed up the correction process, it is preferable to reduce the frequency range from f1 to f3 as much as possible.

FIG. 6 is a diagram showing an example of correction of a high frequency modulated signal. The horizontal axis is the modulation frequency, and the vertical axis is the amount of residual noise. The residual noise amount is an amount indicating the detection performance and can be calculated by the performance calculation unit 217. The performance calculation unit 217 may calculate the residual noise amount as the noise of the gas absorption waveform. The amount of residual noise may be expressed as the amount of residual noise. The modulation frequency is shown in the sweep range 60.

In FIG. 6, the modulation frequency at which the residual noise amount becomes the minimum value is defined as the specific modulation frequency f4. The specific modulation frequency f4 may be a frequency at which the residual noise amount takes a minimum value. The correction unit 216 corrects the modulation frequency to the specific modulation frequency f4, and ends the correction operation. The correction unit 216 may specify the frequency at which the noise of the gas absorption waveform is minimized within the sweep range 60 as the specific modulation frequency. By correcting the modulation frequency, highly accurate analysis is possible even when the frequency of the modulation frequency component of the laser beam 30 is different from the ideal value. In summary, the correction unit 216 identifies a specific modulation frequency in which the noise of the gas absorption waveform becomes smaller than the pre-correction modulation frequency, which is the modulation frequency before the change, by changing the modulation frequency of the laser light 30, and the laser light 30. The modulation frequency may be corrected to a specific modulation frequency.

FIG. 7 is a diagram showing another example of correction of a high frequency modulated signal. Similar to FIG. 6, the horizontal axis represents the modulation frequency and the vertical axis represents the residual noise amount.

In FIG. 7, the amount of residual noise becomes the minimum value at the frequency f1. That is, the frequency f1 becomes the specific modulation frequency. In this case, the residual noise amount may take a smaller value in the range lower than the frequency f1. Therefore, the correction operation is continued, and the sweep range 60 is shifted in the direction of the specific modulation frequency. Here, the shift means changing the sweep range 60 without changing the width of the sweep range 60. That is, the sweep range 60 may be shifted in the direction of the frequency f1. When the frequency at the end of the sweep range 60 becomes the specific modulation frequency, the correction unit 216 may shift the sweep range 60 toward the end. The ends of the sweep range 60 are frequencies f1 and frequency f3 in FIG. The correction operation may be repeated until the residual noise amount becomes the minimum value within the sweep range 60. The correction operation may be terminated with the frequency f1 as the specific modulation frequency.

FIG. 8 is a diagram showing an example of a block diagram of the correction process of the correction unit 216. After the correction is started, the modulation frequency is swept within the sweep range 60 (step S101). Next, the residual noise amount is calculated, and the relationship between the modulation frequency and the residual noise amount shown in FIGS. 6 and 7 is acquired (step S102).

A specific modulation frequency is acquired from the relationship between the acquired modulation frequency and the amount of residual noise (step S103). The specific modulation frequency may be a frequency at which the residual noise amount takes a minimum value. When the minimum value does not exist, the frequency may be the frequency at which the residual noise amount takes the minimum value. Then, it is confirmed whether the specific modulation frequency is located within the sweep range 60 (step S104). Being located between the sweep ranges 60 means that the specific modulation frequency is not located at the end of the sweep range 60.

If the specific modulation frequency is not located within the sweep range 60 (eg, FIG. 7), the sweep range 60 is shifted towards the specific modulation frequency (step S105). After shifting the sweep range 60, the modulation frequency is swept again in the shifted sweep range 60 to acquire a specific modulation frequency. In step S104, the sweep range 60 is shifted and the specific modulation frequency is updated until the specific modulation frequency falls within the sweep range 60.

When the specific modulation frequency is located within the sweep range 60 (for example, FIG. 6), the modulation frequency is corrected to the specific modulation frequency (step S106). After the correction, the correction process ends. Since the sweep range 60 is shifted and the specific modulation frequency is updated until the specific modulation frequency falls within the sweep range 60, it is possible to obtain the specific modulation frequency that minimizes the residual noise amount.

FIG. 9 shows an example of the configuration of the laser gas analyzer 200 according to another embodiment of the present invention. The laser gas analyzer 200 of FIG. 9 includes a signal processing circuit 221 and a gas temperature measuring unit 70, and a communication line 40 is extended to the gas temperature measuring unit 70. Different from 100. The other configuration of the laser gas analyzer 200 may be the same as that of the laser gas analyzer 100 of FIG. The configuration of the signal processing circuit 221 may be different from that of the signal processing circuit 21.

The gas temperature measuring unit 70 measures the temperature of the gas 1 to be measured. Therefore, it is located in the measurement target space 2. Inside the measurement target space 2, the gas temperature measuring unit 70 is preferably provided at a position as close as possible to the laser beam 30 and not interfering with the laser beam 30. The gas temperature measuring unit 70 may be provided on the pipe wall 50b. Further, the gas temperature measuring unit 70 may be provided on the pipe wall 50a. The gas temperature measuring unit 70 is, for example, a thermocouple. By including the gas temperature measuring unit 70, the laser type gas analyzer 200 can measure the temperature of the gas 1 to be measured in the space 2 to be measured. The measurement result of the gas temperature measuring unit 70 is sent to the signal processing circuit 221 via the communication line 40.

FIG. 10 shows an example of the configuration of the signal processing circuit 221 according to another embodiment of the present invention. The signal processing circuit 221 of FIG. 10 is different from the signal processing circuit 21 of FIG. 3 in that the gas temperature measuring unit 70 and the performance calculating unit 217 are connected. Other configurations of the signal processing circuit 221 may be the same as those of the signal processing circuit 21 of FIG.

The relationship between the modulation frequency and the amount of residual noise changes as the temperature changes. That is, the temperature of the gas 1 to be measured also causes a deviation from the removal frequency of the filter 214. Therefore, even if the specific modulation frequency is acquired under the condition of constant temperature, it is necessary to acquire and correct the specific modulation frequency again when the temperature changes. In this case, when the modulation frequency is corrected according to the block diagram of FIG. 8, the correction takes time (for example, the shift of the sweep range 60 is executed many times), and the temperature changes at the corrected timing. It may not be possible to measure in real time.

The correction unit 216 may control the sweep range 60 based on the temperature of the gas 1 to be measured. That is, it is possible to acquire in advance how much the relationship between the modulation frequency and the residual noise amount changes when the temperature of the gas 1 to be measured changes, and control the sweep range 60 based on the change rate acquired in advance. As a control example, the correction unit 216 may shift the sweep range 60 based on the temperature change of the gas 1 to be measured. Further, as a control example, the correction unit 216 may change the direction of shifting the sweep range 60 based on the direction of the temperature change of the gas 1 to be measured. When the temperature changes, the sweep range 60 is controlled based on the temperature, so that it is not necessary to repeatedly shift the sweep range 60, and real-time measurement is possible.

When the temperature of the gas 1 to be measured is high, the deviation from the removal frequency of the filter 214 becomes large. Therefore, the correction unit 216 may extend the sweep range 60 when the temperature of the gas 1 to be measured exceeds the threshold value. The size for expanding the sweep range 60 may be acquired in advance. The threshold value of the temperature of the gas 1 to be measured is, for example, 100 ° C. When the temperature of the gas 1 to be measured exceeds the threshold value, the specific modulation frequency can be quickly specified by expanding the sweep range 60.

Further, the temperature of the measurement target gas 1 changes depending on the operating condition of the exhaust gas device that discharges the measurement target gas 1. Therefore, the sweep range 60 may be controlled based on the operating condition of the exhaust gas device. For example, if the operating condition of the exhaust gas device continues for a long time, the temperature of the exhaust gas device becomes high and the temperature of the gas 1 to be measured becomes high, so that the sweep range 60 may be widened.

FIG. 11 shows an example of the configuration of the laser gas analyzer 300 according to another embodiment of the present invention. The laser gas analyzer 300 of FIG. 11 differs from the laser gas analyzer 100 of FIG. 1 in that it includes a light source unit 311 and a signal processing circuit 321 instead of the light source unit 11 and the signal processing circuit 21. The other configuration of the laser gas analyzer 300 may be the same as that of the laser gas analyzer 100 of FIG. The configuration of the light source unit 311 may be different from that of the light source unit 11. The configuration of the signal processing circuit 321 may be different from that of the signal processing circuit 21.

FIG. 12 shows an example of the configuration of the light source unit 311 and the signal processing circuit 321 according to another embodiment of the present invention. The signal processing circuit 321 of FIG. 12 is different from the signal processing circuit 21 of FIG. 2 in that it does not have a frequency control unit. Other configurations of the signal processing circuit 321 may be the same as those of the signal processing circuit 21 of FIG. In FIG. 12, the configuration of the signal processing circuit 321 other than the calculation unit 215 is omitted. The light source unit 311 of FIG. 12 is different from the light source unit 11 of FIG. 2 in that the modulation signal generation unit 113 is not connected to the frequency control unit. The other configuration of the light source unit 311 of FIG. 12 may be the same as that of the light source unit 11 of FIG.

FIG. 13 shows an example of the configuration of the signal processing circuit 321 according to another embodiment of the present invention. The signal processing circuit 321 of FIG. 13 differs from the signal processing circuit 21 of FIG. 3 in that it has a correction unit 316 instead of the correction unit 216. Other configurations of the signal processing circuit 321 may be the same as those of the signal processing circuit 21 of FIG. Further, the correction unit 316 is different from the correction unit 216 of FIG. 3 in that it has a filter control unit 318 instead of the frequency control unit 218. Other configurations of the correction unit 316 may be the same as the correction unit 216 of FIG.

The correction unit 316 corrects the frequency characteristics of the filter so that the noise of the gas absorption waveform becomes small. That is, the correction unit 216 corrects the modulation frequency to improve the detection performance of the absorption waveform, whereas the correction unit 316 corrects the frequency characteristic of the filter 214 to improve the detection performance. Since the correction unit 316 for correcting the frequency characteristics of the filter 214 is provided, it is possible to prevent a difference between the output signal frequency and the removal frequency of the filter 214. Therefore, the filter removal performance can be maintained without changing the modulation frequency.

The correction operation of the correction unit 316 of FIG. 13 will be described. The correction unit 316 controls the frequency characteristics of the filter 214 and corrects the filter 214 so as to improve the noise removal performance, thereby improving the absorption waveform detection performance and making the density analysis more accurate. The correction unit 316 may perform a correction operation at a predetermined timing. The correction unit 316 may perform a correction operation at timings at regular intervals. The correction unit 316 may perform the correction operation at the timing when the detection performance of the absorption waveform becomes equal to or less than a predetermined threshold value. The correction unit 316 may perform the correction operation at the timing when the amount of change or the rate of change in the detection performance of the absorption waveform becomes equal to or higher than a predetermined threshold value.

In order to carry out the correction, the performance calculation unit 217 calculates the detection performance of the absorption waveform. The detection performance in this example is the small residual noise when a frequency component other than the absorption waveform is used as the noise component as in the correction unit 216, and may be simply expressed as the small noise. The detection performance may be a small residual noise component when a frequency component other than the absorption waveform is used as the noise component. The detection performance may be low noise. The detection performance may be a small frequency component other than the 2f signal component. The detection performance may be as small as the frequency component (modulation frequency component) of the 1f signal component. The detection performance may be a small frequency component other than the gas absorption waveform. That is, each time the correction unit 316 corrects the frequency characteristic of the filter 214, the modulation frequency component may be detected and the frequency characteristic of the filter 214 may be corrected based on the modulation frequency component. The correction unit 316 may correct the frequency characteristic of the filter 214 based on the change in the modulation frequency component. Further, the detection performance may be a signal-to-noise ratio in which the absorption waveform is a signal component and the other frequency components are noise components. That is, each time the correction unit 316 corrects the frequency characteristic of the filter 214, the correction unit 316 detects the modulation frequency component and the double modulation frequency component which is twice the frequency component of the modulation frequency component, and the modulation frequency component and the double modulation frequency. The frequency characteristics of the filter 214 may be corrected based on the ratio of the components. The detection performance may be a noise removal amount or a noise removal rate when a frequency component other than the absorption waveform is used as a noise component. Further, the detection performance can be calculated by the performance calculation unit 217 by frequency analysis such as FFT.

The filter control unit 318 is connected to the filter 214 to control the frequency characteristics of the filter 214. The filter control unit 318 may control the frequency characteristic of the filter 214 based on the signal processing of the signal processing circuit 321. Controlling the frequency characteristic of the filter 214 may mean controlling the removal frequency of the filter 214. That is, the filter control unit 318 may control the center frequency of the filter 214. Further, the filter control unit 318 may control the cutoff frequency of the filter 214.

At the timing of performing the correction operation, a control value is transmitted from the filter control unit 318 so as to change the removal frequency within a range including the removal frequency before correction, and the removal frequency of the filter 214 is changed. The change range, which is the range in which the filter 214 is changed, may include the removal frequency before correction. The range of change may not change much, and it is preferable to start the change around the removal frequency before correction. The correction unit 316 changes the removal frequency of the filter 214 in the change range which is the range in which the filter 214 is changed.

FIG. 14 is a diagram showing a change range 360 of the removal frequency. The horizontal axis is time and the vertical axis is removal frequency. In FIG. 14, the removal frequency is changed in the change range 360, which is the range from the frequency cf1 to the frequency cf3.

As shown in FIG. 14, the change in the removal frequency may be a monotonous increase. The change in removal frequency may be a monotonous decrease. Moreover, the change of the removal frequency may be repeated. For example, when the frequency cf1 changes to the frequency cf3, the frequency cf1 may be returned again and the frequency cf3 may be changed. By changing the repetitive removal frequency, the detection performance can be calculated accurately.

Further, the frequency cf2, which is the center of the change range 360, may be the removal frequency before correction. In other words, the frequency cf2, which is the center of the frequency cf1 and the frequency cf3, may be the removal frequency before correction. By changing around the removal frequency before correction, it is possible to obtain a graph of detection performance centered on the removal frequency before correction. The frequency cf2 is, for example, 10 kHz. The frequencies cf1 and cf3 may be determined by the frequency error. The frequency error may occur, for example, from the temperature range of the operating environment, the temperature characteristics of the ICs constituting the modulation signal generation unit 113, and the like. The frequencies cf1 and cf3 may be determined so as to surely include the estimated frequency error and cf2. The frequency cf1 is, for example, 5 kHz. The frequency cf3 is, for example, 15 kHz. Further, in order to speed up the correction process, it is preferable to reduce the range of frequencies cf1 to cf3 as much as possible.

FIG. 15 is a diagram showing an example of correction of the frequency characteristic of the filter 214. The horizontal axis is the removal frequency, and the vertical axis is the amount of residual noise. The residual noise amount is an amount indicating the detection performance and can be calculated by the performance calculation unit 217. The amount of residual noise may be expressed as the amount of residual noise. The removal frequency is shown in the range of change 360.

In FIG. 15, the removal frequency at which the residual noise amount becomes the minimum value is defined as the specific removal frequency cf4. The specific removal frequency cf4 may be a frequency at which the residual noise amount takes a minimum value. The correction unit 316 corrects the removal frequency to the specific removal frequency cf4, and ends the correction operation. The correction unit 316 may specify the frequency at which the noise of the gas absorption waveform is minimized within the change range 360 as the specific removal frequency. By correcting the removal frequency, highly accurate analysis is possible even when the frequency of the modulation frequency component of the laser beam 30 is different from the ideal value. In summary, the correction unit 316 specifies a specific removal frequency at which the noise of the gas absorption waveform becomes smaller than the noise before changing the removal frequency by changing the removal frequency of the filter, and specifically removes the removal frequency of the filter 214. It may be corrected to the frequency. As described above, the frequency cf2, which is the center of the change range 360, may be the removal frequency before correction. Therefore, the correction unit 316 may specify the specific removal frequency by changing the removal frequency of the filter 214 in the change range including the removal frequency of the filter 214 before correction. Further, the correction unit 316 may specify the specific removal frequency by changing the removal frequency of the filter in the change range centered on the removal frequency of the filter 214 before correction.

FIG. 16 is a diagram showing another example of correction of the frequency characteristic of the filter 214. Similar to FIG. 15, the horizontal axis is the removal frequency and the vertical axis is the residual noise amount.

In FIG. 16, the amount of residual noise becomes the minimum value at the frequency cf1. That is, the frequency cf1 becomes the specific removal frequency. In this case, the residual noise amount may take a smaller value in the range lower than the frequency cf1. Therefore, the correction operation is continued and the change range 360 is expanded. Here, the expansion is to increase the width of the change range 360. The correction unit 316 may extend the change range 360 when the specific removal frequency becomes the frequency at the end of the change range 360. The correction operation may be repeated until the residual noise amount becomes the minimum value within the change range 360. The correction operation may be terminated with the frequency cf1 as the specific removal frequency.

FIG. 17 is a diagram showing an example of a block diagram of the correction process of the correction unit 316. After the correction is started, the removal frequency is changed within the change range 360 (step S301). Next, the residual noise amount is calculated, and the relationship between the removal frequency and the residual noise amount shown in FIGS. 15 and 16 is acquired (step S302).

A specific removal frequency is acquired from the relationship between the acquired removal frequency and the amount of residual noise (step S303). The specific removal frequency may be a frequency at which the residual noise amount takes a minimum value. When the minimum value does not exist, the frequency may be the frequency at which the residual noise amount takes the minimum value. Then, it is confirmed whether the specific removal frequency is located within the change range 360 (step S304). Being located within the range of change 360 means that the specific removal frequency is not located at the end of the range of change 360.

When the specific removal frequency is not located within the change range 360 (eg, FIG. 16), the change range 360 is extended (step S305). After expanding the change range 360, the removal frequency is changed again in the extended change range 360 to acquire the specific removal frequency. In step S304, the change range 360 is extended and the specific removal frequency is updated until the specific removal frequency falls within the change range 360.

When the specific removal frequency is located within the change range 360 (for example, FIG. 15), the removal frequency is corrected to the specific removal frequency (step S306). After the correction, the correction process ends. Since the specific removal frequency is updated by extending the change range 360 until the specific removal frequency falls within the change range 360, it is possible to obtain the specific removal frequency that minimizes the residual noise amount.

The laser gas analyzer 100, the laser gas analyzer 200, and the laser gas analyzer 300 are most suitable for measuring combustion exhaust gas such as boiler and dust incineration, and for combustion control. In addition, gas analysis for steel [blast furnace, converter, heat treatment furnace, sintering (pellet equipment), coke oven], fruit and vegetable storage and aging, biochemistry (microorganisms) [fermentation], air pollution [incinerator, flue gas desulfurization / Denitration], exhaust gas from internal combustion engines of automobiles and ships (excluding testers), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growing, chemical analysis [oil refining plant, petrochemical It is also useful as an analyzer for [plants, gas generation plants], environmental [landing concentration, concentration in tunnels, parking lots, building management], and various physics and chemistry experiments.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

The order of execution of each process such as operation, procedure, step, and step in the device, system, program, and method shown in the claims, specification, and drawings is particularly "before" and "prior to". It should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Even if the scope of claims, the specification, and the operation flow in the drawings are explained using "first", "next", etc. for convenience, it means that it is essential to carry out in this order. It's not a thing.

1 ... Measurement target gas, 2 ... Measurement target space, 10 ... Light emitting part, 11 ... Light source part, 12 ... Collimating lens, 13 ... Light emitting part container, 20 ... Light receiving part, 21 ... Signal processing Circuit, 22 ... Light receiving element, 23 ... Condensing lens, 24 ... Light receiving part container, 30 ... Laser light, 40 ... Communication line, 50 ... Piping wall, 51 ... Flange, 52 ... Optical axis Adjustment flange, 60 ... Sweep range, 70 ... Gas temperature measurement unit, 100 ... Laser gas analyzer, 111 ... Laser drive signal generator, 112 ... Sweep signal generator, 113 ... Modulation signal generator , 114 ... Current control unit, 115 ... Temperature control unit, 116 ... Laser element, 117 ... Thermista, 118 ... Perche element, 200 ... Laser gas analyzer, 211 ... I / V converter, 212 ... light source, 213 ... synchronous detection circuit, 214 ... filter, 215 ... calculation unit, 216 ... correction unit, 217 ... performance calculation unit, 218 ... frequency control unit, 221 ... signal processing circuit, 300 ... Laser gas analyzer, 311 ... Light source unit, 316 ... Correction unit, 318 ... Filter control unit, 321 ... Signal processing circuit, 360 ... Change range

Claims (21)

A light source unit that emits frequency-modulated laser light,
A light receiving element that receives the laser beam propagated through the measurement target space in which the measurement target gas exists, and a light receiving element that receives the laser beam.
It is provided with a signal processing circuit that detects a gas absorption waveform by processing the output signal of the light receiving element and measures the concentration of the measurement target gas from the gas absorption waveform.
The signal processing circuit
A filter that removes the modulation frequency component of the laser beam,
A laser gas analyzer having a correction unit for correcting the modulation frequency of the laser beam or the frequency characteristic of the filter so that the noise of the gas absorption waveform is reduced. The correction unit specifies a specific modulation frequency at which the noise of the gas absorption waveform becomes smaller than the pre-correction modulation frequency, which is the modulation frequency before the change, by changing the modulation frequency of the laser light, and the modulation frequency of the laser light. The laser gas analyzer according to claim 1, wherein the frequency is corrected to the specific modulation frequency. The laser gas analyzer according to claim 2, wherein the correction unit corrects the modulation frequency of the laser beam so as to approach the removal frequency of the filter. The correction unit
The modulation frequency of the laser beam is changed in the sweep range, which is the range in which the modulation frequency is changed.
The frequency at which the noise of the gas absorption waveform is minimized within the sweep range is specified as the specific modulation frequency.
The laser gas analyzer according to claim 2 or 3, wherein the sweep range includes the pre-correction modulation frequency. The laser gas analyzer according to claim 4, wherein the correction unit shifts the sweep range toward the end when the frequency at the end of the sweep range becomes the specific modulation frequency. The laser gas analyzer according to claim 5, wherein the center of the sweep range before shifting is the pre-correction modulation frequency. Further equipped with a gas temperature measuring unit for measuring the temperature of the gas to be measured,
The laser gas analyzer according to any one of claims 4 to 6, wherein the correction unit controls the sweep range based on the temperature of the gas to be measured. The laser gas analyzer according to claim 7, wherein the correction unit expands the sweep range when the temperature of the gas to be measured exceeds a threshold value. The laser gas analyzer according to claim 7 or 8, wherein the correction unit shifts the sweep range based on a temperature change of the gas to be measured. The laser gas analyzer according to claim 9, wherein the correction unit changes the direction of shifting the sweep range based on the direction of the temperature change of the gas to be measured. The correction unit
Each time the modulation frequency of the laser beam is corrected, the modulation frequency component is detected.
The laser gas analyzer according to any one of claims 2 to 10, wherein the modulation frequency is corrected based on the modulation frequency component. The laser gas analyzer according to claim 11, wherein the correction unit corrects the modulation frequency based on the change of the modulation frequency component. The correction unit
Every time the modulation frequency of the laser beam is corrected, the modulation frequency component and the double modulation frequency component which is twice the frequency component of the modulation frequency component are detected.
The laser gas analyzer according to any one of claims 2 to 10, wherein the modulation frequency is corrected based on the ratio of the modulation frequency component to the double modulation frequency component. The gas to be measured is discharged from the exhaust gas device and
The laser gas analyzer according to any one of claims 4 to 10, wherein the signal processing circuit controls the sweep range based on the operating state of the exhaust gas device. The correction unit specifies a specific removal frequency at which the noise of the gas absorption waveform becomes smaller than the noise before the removal frequency is changed by changing the removal frequency which is the center frequency or the cutoff frequency of the filter. The laser gas analyzer according to claim 1, wherein the removal frequency of the filter is corrected to the specific removal frequency. The laser gas analyzer according to claim 15, wherein the correction unit specifies the specific removal frequency by changing the removal frequency of the filter in a change range including the removal frequency of the filter before correction. The laser gas analysis according to claim 16, wherein the correction unit specifies the specific removal frequency by changing the removal frequency of the filter in the change range centered on the removal frequency of the filter before correction. Total. The laser gas analyzer according to claim 16 or 17, wherein the correction unit extends the change range when the specific removal frequency becomes a frequency at the end of the change range. The laser gas analyzer according to any one of claims 1 to 18, wherein the correction unit further includes a performance calculation unit that calculates the amount of residual noise as noise of the gas absorption waveform. The laser gas analyzer according to claim 19, wherein the residual noise is a frequency component other than the gas absorption waveform. The laser gas analyzer according to claim 19, wherein the residual noise is a modulation frequency component.

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