JP2021043117A - Laser type gas analyzer - Google Patents

Abstract

To provide a laser type gas analyzer that does not require a reference gas cell used for correction to prevent wavelength loss and reduces the cost through simplification of the device.SOLUTION: A laser type gas analyzer comprises a signal processing circuit for measuring the concentration of gas to be measured from a gas absorption waveform present in a first wavelength sweep range of a laser beam. The signal processing circuit includes a correction unit that identifies a position of a peak wavelength of the gas absorption waveform of the gas to be measured in a second wavelength sweep range based on a relative relationship of positions of peak wavelengths of a plurality of gas absorption waveforms detected by sweeping wavelengths of the laser beam in the second wavelength sweep range that is extended from the first wavelength sweep range, and corrects the first wavelength sweep range of the laser beam based on the identified position.SELECTED DRAWING: Figure 4

Description

The present invention relates to a laser gas analyzer that analyzes the presence / absence and concentration of various measurement target gases in a space, such as gas in a flue, exhaust gas, etc., by laser light.
[Prior art literature]
[Patent Document]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2009-47677 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-216385

It is preferable that the laser gas analyzer can analyze the gas with high accuracy even when the ambient temperature of the measurement space changes.

In the first aspect of the present invention, a laser gas analyzer is provided. The laser gas analyzer may include a light source unit that sweeps wavelengths and emits laser light. The laser gas analyzer may include a light receiving element. The light receiving element may receive the laser light propagated through the measurement space in which the gas to be measured exists. The laser gas analyzer may include a signal processing circuit. The signal processing circuit may process the output signal of the light receiving element and measure the concentration of the gas to be measured from the gas absorption waveform existing in the first wavelength sweep range of the laser beam. The signal processing circuit may have a correction unit. The correction unit is in the second wavelength sweep range of the gas absorption waveform of the gas to be measured by the relative relationship of the positions of the peak wavelengths of the plurality of gas absorption waveforms detected by sweeping the wavelengths of the laser light in the second wavelength sweep range. The position of the peak wavelength may be specified. The second wavelength sweep range may be extended beyond the first wavelength sweep range. The correction unit may correct the first wavelength sweep range of the laser beam based on the position of the peak wavelength in the second wavelength sweep range of the gas absorption waveform of the gas to be measured.

The correction unit corrects the first wavelength sweep range so that the position of the peak wavelength in the second wavelength sweep range of the gas absorption waveform of the gas to be measured specified by the signal processing circuit is within the first wavelength sweep range. It's okay. The correction unit corrects the first wavelength sweep range so that the position of the peak wavelength in the second wavelength sweep range of the gas absorption waveform of the gas to be measured specified by the signal processing circuit becomes the center of the first wavelength sweep range. You can do it.

The light source unit may have a laser drive signal generation unit. The laser drive signal generator may synthesize a wavelength sweep drive signal that changes the emission wavelength of the laser element and a high frequency modulation signal that modulates the emission wavelength, and output the laser drive signal as a laser drive signal. The light source unit may have a current control unit. The current control unit may convert the laser drive signal output from the laser drive signal generation unit into a current. The light source unit may have a laser element. The laser element may be supplied with the current output from the current control unit. The light source unit may have a temperature control unit. The temperature control unit may control the temperature of the laser element.

The waveform of the wavelength sweep drive signal may have an offset portion. The waveform of the wavelength sweep drive signal may have a portion that linearly changes the supply current to the laser element to gradually change the emission wavelength of the laser element. The waveform of the wavelength sweep drive signal may be a waveform that is repeated at regular intervals. The offset portion may be a value that supplies the laser element with a current equal to or greater than the threshold current value at which the light emission of the laser element is stable.

The correction unit may calculate the current control amount for correcting the first wavelength sweep range of the laser beam. The correction unit may correct the first wavelength sweep range of the laser beam by transmitting the current control amount to the current control unit. The correction unit may calculate the temperature control amount for correcting the first wavelength sweep range of the laser beam. The correction unit may correct the first wavelength sweep range of the laser beam by transmitting the temperature control amount to the temperature control unit.

The correction unit may store the relative relationship between the positions of the ideal peak wavelengths of the plurality of gas absorption waveforms. The plurality of gas absorption waveforms may include a gas absorption waveform of water vapor.

The laser gas analyzer may correct the first wavelength sweep range of the laser beam at a timing at regular intervals. The laser gas analyzer may observe the ambient temperature in the measurement space. The laser gas analyzer may correct the first wavelength sweep range of the laser beam at the timing when the amount of change or the rate of change in the temperature of the measurement space becomes equal to or higher than a predetermined threshold value. The laser gas analyzer may correct the first wavelength sweep range of the laser beam at the timing when the amount of change or the rate of change in the measured concentration of the gas to be measured becomes equal to or higher than a predetermined threshold value. The laser gas analyzer may correct the first wavelength sweep range of the laser beam at the timing when the gas absorption waveform of the gas to be measured is no longer detected.

The position of the peak wavelength of the gas absorption waveform may be determined by the point where the waveform obtained by oddly differentiating the gas absorption waveform intersects the horizontal axis passing through the origin. The position of the peak wavelength of the gas absorption waveform may be determined by the minimum value of the gas absorption waveform.

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 300 according to the comparative example is shown. An example of the gas absorption waveform detected by the laser gas analyzer 300 is shown. An example of the laser light wavelength sweep range of the laser element 316 is shown. 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 wavelength sweep drive signal is shown. An example of the configuration of the signal processing circuit 21 is shown. An example of the waveform obtained by odd-numbering the gas absorption waveform detected by the laser gas analyzer 100 is shown. An example of the case where the position of the peak wavelength of the gas absorption waveform of the gas to be measured is specified by the relative relationship of the three types of gases, gas A and gas B to be measured, is shown. HCl shows an example of a relationship between the wavelength and the absorption intensity with respect to (hydrogen chloride) and _H 2 O (water vapor). An example of the configuration of the laser gas analyzer 400 according to the comparative example is shown.

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 300 according to the comparative example. The laser gas analyzer 300 includes a laser element 316, a temperature sensor 317, and a temperature control element 315. The laser gas analyzer 300 analyzes the presence or absence or concentration of the gas to be measured in the measurement space. The laser element 316 analyzes the measurement target gas in the measurement space by irradiating the measurement space with a laser beam. For example, the laser element 316 analyzes the concentration of the gas to be measured based on the amount of attenuation of each wavelength component of the laser light in the measurement space. The laser element 316 has a property that the emission wavelength changes depending on the supplied current and the temperature of the laser element 316. The temperature control element 315 controls the temperature of the laser element 316. The temperature sensor 317 is arranged between the temperature control element 315 and the laser element 316 to detect the temperature. The temperature control element 315 controls the temperature of the laser element 316 based on the temperature detected by the temperature sensor 317.

The ambient temperature of the measurement space may change suddenly, such as when analyzing the concentration of combustion gas. In this case, the temperature of the laser element 316 changes due to the radiant heat from the measurement space, and a thermal gradient is generated between the temperature sensor 317 and the temperature control element 315. Therefore, the temperature of the laser element 316 may have an error with respect to the temperature of the control target.

FIG. 2 shows an example of the gas absorption waveform detected by the laser gas analyzer 300. When the laser beam from the laser element 316 passes through the measurement space, the component of _{wavelength λ A corresponding to the gas existing in the measurement space is absorbed.} The laser beam that has passed through the measurement space is converted into a voltage signal by the light receiving element. In this example, the double frequency component of the voltage signal output by the light receiving element is processed as a gas absorption waveform. By detecting the double frequency component of the voltage signal, the peak wavelength λ _A of the gas absorption waveform can be detected with high accuracy. Can estimate the type of gas present in the measurement space from the position of the peak wavelength lambda _A, it can be estimated the concentration of the gas from the amplitude value of the gas absorption waveform at the peak wavelength lambda _A.

FIG. 3 shows an example of the laser light wavelength sweep range of the laser element 316. The laser element 316 of this example changes the wavelength of the laser light to be output with the passage of time. In FIG. 3, the relationship between time and wavelength is shown by a dotted straight line. Further, in FIG. 3, an example of the gas absorption waveform detected at each time is schematically shown on the straight line. In FIG. 3, the gas absorption waveform of the gas to be measured is represented by a solid line, and the gas absorption waveform of another gas is represented by a dotted line. The gas absorption waveform is the same as the gas absorption waveform described with reference to FIG.

In FIG. 3, λ _rr is an ideal laser light wavelength sweep range, and λ _ll is a laser light wavelength sweep range when a wavelength loss occurs, which will be described later. The laser light wavelength sweep range λ _rr is a range including the wavelength of the light absorbed by the gas to be measured. If the temperature of the laser element 316 deviates from the control target temperature due to the heat gradient described above, the wavelength of the laser light changes due to the temperature characteristics of the laser element 316. Therefore, the laser light wavelength sweep range in the laser element 316 becomes _{λ ll} deviating from _{the ideal λ rr.} That is, the relative position of the peak wavelength of the gas absorption waveform of the gas to be measured deviates from the wavelength sweep range of the laser beam. Therefore, there may be a problem that the peak of the gas absorption waveform cannot be detected, or the gas absorption waveform of another gas is erroneously detected as the gas absorption waveform of the gas to be measured. This problem is called wavelength loss. Further, even when the concentration of the gas to be measured in the measurement space is low, the gas absorption waveform is not detected, so that the concentration analysis is difficult and it is also difficult to distinguish it from the wavelength loss, so that the correction is impossible.

Further, as a method for solving the above problem, there is a method of providing a reference gas cell in which a measurement target gas having a known concentration is sealed between the laser element and the measurement space, but there is a problem that the device becomes large. In addition, since it is necessary to fill the same gas as the gas to be measured, it is difficult to apply it to a gas that cannot or is difficult to fill in the reference gas cell. In addition, in order to use the reference gas cell, it is necessary to consider the gas leak of the reference gas cell itself. When the gas to be measured is HCL or the like which is a corrosive gas, if the same reference gas leaks, the surrounding optical parts Deteriorates. Further, it is necessary to consider the influence of the shaft shift due to the influence of vibration and the damage of the reference gas cell, and it is not desirable to use the reference gas cell itself.

FIG. 4 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, and a signal processing circuit 21. The light emitting unit 10 irradiates the measurement space with the laser beam 30. The light receiving unit 20 receives the laser beam 30 propagated through the measurement space. The light receiving unit 20 of this example receives the laser light 30 transmitted through the measurement space, but the light receiving unit 20 of another example may receive the laser light 30 scattered or reflected in the measurement space. The signal processing circuit 21 analyzes the measurement target gas in the measurement space based on the light reception result in the light receiving unit 20.

The measurement space of this example is a tubular flue through which the gas to be measured passes. FIG. 4 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 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 a mounting seat 52a and a mounting seat 52b. The mounting seat 52a fixes the light emitting portion 10 to the flange 51a. The mounting seat 52b fixes the light receiving portion 20 to the flange 51b.

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 houses 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 attachment seat 52a.

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 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 gas to be measured inside the flue, a part of the wavelength component corresponding to the absorption wavelength of the gas to be measured is absorbed.

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 signal processing circuit 21 may be provided outside the light receiving unit container 24. The light receiving unit container 24 of this example has a bottomed cylindrical shape. The light receiving unit container 24 is attached to the mounting seat 52b.

The laser beam 30 that has passed through the inside of the flue is condensed by the condenser lens 23 and 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.

The signal processing circuit 21 transmits a current control amount or a temperature control amount, which will be described later, to the light source unit 11 based on the input electric signal. The light receiving unit 20 may have a communication line 40 that connects the signal processing circuit 21 and the light source unit 11.

FIG. 5 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 Peltier element 118. The laser element 116 may have the same function as the laser element 316 in FIG. The laser element 116 is, for example, a semiconductor laser. The thermistor 117 may have the same function as the temperature sensor 317 in FIG. The Peltier element 118 may have the same function as the temperature control element 315 in FIG. The signal processing circuit 21 includes a calculation unit 215 and a control amount calculation unit 218. In FIG. 5, the configuration of the signal processing circuit 21 other than the calculation unit 215 and the control amount calculation 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 a wavelength range including the absorption wavelength of the gas to be measured. The modulation signal generation unit 113 outputs a sine wave high-frequency modulation signal for 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 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.

A thermistor 117 as a temperature detecting element is arranged in the vicinity of the laser element 116. Further, the Peltier element 118 is arranged close to the thermistor 117. The Peltier element 118 is PID-controlled by the temperature control unit 115 so that the resistance value of the thermistor 117 becomes a constant value. Thereby, the temperature of the laser element 116 is controlled. By controlling the temperature of the laser element 116, the emission wavelength of the laser element 116 is 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 current control unit 114 of this example is notified by the control amount calculation unit 218 of the signal processing circuit 21 of the current control amount for suppressing the wavelength loss described above. The current control amount is a control amount that adjusts the wavelength sweep range of the laser element 116 so that the absorption wavelength of the gas to be measured is included in the wavelength sweep range of the laser element 116. The current control amount may be a control amount that shifts the wavelength sweep range of the laser element 116 by a predetermined value.

The temperature control unit 115 of this example is notified by the control amount calculation unit 218 of the signal processing circuit 21 of the temperature control amount for suppressing the wavelength loss described above. The temperature control amount is a control amount that adjusts the temperature of the laser element 116 so that the absorption wavelength of the gas to be measured is included in the wavelength sweep range of the laser element 116. By adjusting the temperature of the laser element 116, the wavelength sweep range of the laser element 116 can be adjusted. The operation of the control amount calculation unit 218 will be described later.

FIG. 6 shows an example of a wavelength sweep drive signal. As shown in FIG. 6, the wavelength sweep drive signal is repeated at a constant cycle, and has a sweep portion S2 that linearly changes the supply current to the laser element 116 to gradually change the emission wavelength of the laser element 116. It is a signal. The sweep portion S2 gradually shifts the emission wavelength of the laser element 116 to enable sweeping of the emission wavelength.

The wavelength sweep drive signal has an offset portion S1 that does not sweep the emission wavelength but causes the laser element 116 to emit light. The offset portion S1 is a portion immediately before the sweep portion S2. The drive current supplied to the laser element 116 by the offset portion S1 is set to a value equal to or higher than the threshold current value at which the light emission of the laser element 116 is stable. Further, the wavelength sweep drive signal has a non-emission portion S3. The non-emission portion S3 is a portion that makes the drive current supplied to the laser element 116 substantially zero. The non-emission portion S3 is a portion immediately after the sweep portion S2. The wavelength sweep drive signal repeats parts S1 to S3.

A laser drive signal is generated by synthesizing the wavelength sweep drive signal and the high frequency modulation signal in the laser drive signal generation unit 111. The laser drive signal output from the laser drive signal generation unit 111 is converted into a current by the current control unit 114 and supplied to the laser element 116.

FIG. 7 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 gas to be measured from the gas absorption waveform existing in the sweep range of the laser beam 30.

The signal processing circuit 21 of this example includes an I / V converter 211, a synchronous detection circuit 213, a filter 214, a calculation unit 215, an oscillator 212, and a correction unit 216. 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.

A 2f signal (double wave signal) from the oscillator 212 is also input to the synchronous detection circuit 213. The 2f signal is a signal having a frequency twice that of the harmonic modulation signal of the modulation signal generation unit 113 shown in FIG. The synchronous detection circuit 213 extracts only the amplitude of the double frequency component of the harmonic modulation signal in the output signal of the I / V converter 211. The output signal of the synchronous detection circuit 213 is sent to the arithmetic unit 215 of the CPU or the like via the noise removing filter 214. The output signal of the filter 214 is transmitted to the correction unit 216.

A trigger signal is sent from the sweep signal generation unit 112 to the calculation unit 215. The trigger signal is a pulse-shaped signal that is output in synchronization with one cycle of the wavelength sweep drive signal.

A method for measuring the concentration of the gas 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 Peltier element 118 to adjust the temperature of the laser element 116 so that the gas 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 space between the pipe wall 50a and the pipe wall 50b where the gas to be measured 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 gas to be measured, the synchronous detection circuit 213 does not detect the double wave signal, 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, the synchronous detection circuit 213 detects the double wave signal. The maximum or minimum value of the gas absorption waveform indicated by the double wave signal corresponds to the concentration of the gas to be measured. Therefore, the calculation unit 215 may measure the maximum value or the minimum value of the gas absorption waveform, or integrate a part or all of the gas absorption waveform and calculate the concentration of the gas to be measured 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. ..

Further, the output signal of the filter 214 is sent to the correction unit 216. The correction unit 216 has a wavelength calculation unit 217 and a control amount calculation unit 218. The wavelength calculation unit 217 calculates the relative position of the peak wavelength of the gas absorption waveform by the measurement target gas within the wavelength sweep range based on the output signal of the filter 214. The control amount calculation unit 218 calculates the current control amount to be notified to the current control unit 114 or the temperature control amount to be notified to the temperature control unit 115 based on the relative position calculated by the wavelength calculation unit 217.

The operation of the laser gas analyzer 100 will be described. The laser gas analyzer 100 has two types of operation modes: a normal operation mode for measuring the gas to be measured and a correction operation mode for calculating the above-mentioned current control amount or temperature control amount. In the normal operation mode, the laser gas analyzer 100 sweeps the laser beam 30 in the first wavelength sweep range. For example, the first wavelength sweep range is a wavelength range centered on the absorption wavelength of the gas to be measured. As described above, when the first wavelength sweep range shifts due to the thermal gradient in the laser element 116 or the like, the absorption wavelength of the measurement target gas is not included in the first wavelength sweep range. It becomes difficult to detect the waveform.

In the correction operation mode, the laser beam 30 is swept in the second wavelength sweep range whose range is extended from the first wavelength sweep range. Therefore, even when the second wavelength sweep range is shifted, the gas absorption waveform by the measurement target gas is likely to be included in the sweep range. By expanding the wavelength sweep range, the gas absorption waveform by a gas other than the measurement target gas can be easily included in the second wavelength sweep range. When the gas existing in the measurement space is known, the position of the peak wavelength of the gas absorption waveform of each gas is also known. Therefore, it becomes easy to identify which gas absorption waveform is the gas absorption waveform of the gas to be measured based on the relative positions of the plurality of gas absorption waveforms. The position of the gas absorption waveform refers to the position on the wavelength axis. The wavelength range of the second wavelength sweep range may be 1.5 times or more, twice or more, or three times or more the wavelength range of the first wavelength sweep range. The second wavelength sweep range may be the maximum range in which the laser element 116 can sweep the wavelength.

Since the second wavelength sweep range is expanded from the first wavelength sweep range, the processing time becomes longer in the density calculation, and the responsiveness deteriorates. Further, it is preferable that the gas absorption waveform is amplified as much as possible within the measurement range and the concentration calculation is performed with high sensitivity. In this case, when a plurality of gases are detected in the second wavelength sweep range, they are amplified at the same amplification factor according to the maximum gas absorption waveform. Therefore, if the concentration of the gas to be measured is low, it is not sufficiently amplified and highly accurate analysis is performed. I can't. Therefore, when the concentration of the gas to be measured is low or the like, highly accurate analysis can be performed by detecting the gas absorption waveform by controlling the first wavelength sweep range.

The control amount calculation unit 218 controls the first wavelength sweep range so that the wavelength of the gas absorption waveform of the gas to be measured detected by the wavelength calculation unit 217 in the second wavelength sweep range is included. The control amount calculation unit 218 may control the first wavelength sweep range so that the position of the peak wavelength of the gas absorption waveform of the gas to be measured is the center wavelength of the first wavelength sweep range.

The correction operation may be performed at a predetermined timing. The correction operation may be performed at the timing of each fixed time elapse. Further, the atmospheric temperature in the measurement space may be observed, and the correction operation may be performed at the timing when the amount of change or the rate of change of the temperature becomes equal to or higher than a predetermined threshold value. Further, the correction operation may be performed at the timing when the amount of change or the rate of change in the measured concentration of the gas to be measured becomes equal to or higher than a predetermined threshold value. Further, the correction operation may be performed at the timing when the gas absorption waveform (peak) of the gas to be measured is no longer detected.

At the timing of performing the correction operation, a laser drive signal for wavelength sweeping in the second wavelength sweep range whose range is extended with respect to the first wavelength sweep range is generated from the sweep signal generation unit 112.

By extending the wavelength sweep range of the laser beam 30, in addition to the gas to be measured, the absorption wavelengths of a plurality of other gases existing in the measurement space may be included in the sweep range. In this case, the laser beam 30 emitted from the laser element 116 is absorbed by a plurality of gases in the measurement space. The gas existing in the measurement space may contain water vapor. The signal received by the light receiving element 22 is sent to the correction unit 216 as a signal having a plurality of gas absorption waveforms by the signal processing circuit 21. The plurality of gas absorption waveforms may include a gas absorption waveform of water vapor.

The correction unit 216 has a wavelength calculation unit 217 and a control amount calculation unit 218. The wavelength calculation unit 217 stores in advance the theoretical values of the absorption wavelengths of the gas to be measured and the gas used for correction other than the gas to be measured. The wavelength calculation unit 217 may save the relative relationship between the positions of the peak wavelengths at the ideal time of the plurality of gas absorption waveforms. The relative relationship between the positions of the peak wavelengths is, for example, the difference between the positions of the respective wavelengths. The wavelength calculation unit 217 calculates the position of the peak wavelength of each of the signals having a plurality of gas absorption waveforms input to the wavelength calculation unit 217.

FIG. 8 shows an example of a waveform obtained by odd-numbering the gas absorption waveform detected by the laser gas analyzer 100. The waveform shown in FIG. 8 is an odd-numbered waveform obtained from the waveform shown in FIG. Therefore, in the wavelength range shown in FIG. 8, the position of the peak wavelength is λ _A. In FIG. 8, the central horizontal axis is indicated by a dotted horizontal line.

_{When calculating the position λ A} of the peak wavelength of the gas absorption waveform, the wavelength at which the gas absorption waveform becomes the maximum value or the minimum value may be calculated. Therefore, the odd-numbered waveform of a signal having a plurality of gas absorption waveforms may be set as the position of the point where the central horizontal axis intersects. When a plurality of these intersections exist for one gas absorption waveform, the central one among them may be the position of the peak wavelength. The point where the odd-differentiated waveform intersects the central horizontal axis with a positive slope may be the position of the peak wavelength. The point where the odd-differentiated waveform intersects the central horizontal axis with a negative slope may be the position of the peak wavelength. Further, the minimum value of the gas absorption waveform may be set as the position of the peak wavelength. The maximum value of the gas absorption waveform may be the position of the peak wavelength.

The second wavelength sweep range is extended from the first wavelength sweep range. Therefore, when the wavelength of the laser beam 30 is swept in the second wavelength sweep range and the position of the peak wavelength is calculated, the position of the peak wavelength of the gas absorption waveform of the plurality of gases can be obtained. The position of the peak wavelength of the gas absorption waveform of each gas is ideally equal to the theoretical value of the position of the peak wavelength. However, in reality, the position of the peak wavelength of the gas absorption waveform of each gas differs from the theoretical value due to the wavelength loss. Therefore, in order to perform the correction operation, it is necessary to specify the position of the peak wavelength in the second wavelength sweep range of the gas absorption waveform of the gas to be measured from the calculated peak wavelength positions.

FIG. 9 shows an example in which the position of the peak wavelength of the gas absorption waveform of the gas to be measured is specified by the relative relationship of the three types of gases, the gas to be measured, the gas A, and the gas B. In FIG. 9, an example of the gas absorption waveform detected at each time is schematically shown on the straight line as in FIG. In FIG. 9, the gas absorption waveforms of the gas to be measured, the gas A, and the gas B are shown. The solid line is the ideal gas absorption waveform, and the dotted line is the actual gas absorption waveform. The ideal gas absorption waveform means a gas absorption waveform in which no wavelength loss occurs and the position of the peak wavelength does not change. The position of the peak wavelength of the ideal gas absorption waveform is equal to the theoretical value of the position of the peak wavelength of the gas absorption waveform of each gas. Let the positions of the peak wavelengths of the ideal gas absorption waveforms of the gas to be measured, gas A, and gas B be λ', λ _A ', and λ _B ', respectively. The actual gas absorption waveform means a gas absorption waveform in which the position of the peak wavelength is changed due to wavelength loss. The position of the peak wavelength of the actual gas absorption waveform is equal to the calculated value which is the position of the calculated peak wavelength. _{Let λ, λ A} , and λ _B be the positions of the peak wavelengths of the actual gas absorption waveforms of the gas to be measured, gas A, and gas B, respectively.

The gas absorption characteristics depend on the wavelength, and the relative relationship between the positions of the peak wavelengths of a plurality of gases is always kept constant. For example, the difference in the position of the peak wavelength of each gas absorption waveform is constant. Therefore, the position of the peak wavelength of the gas to be measured can be obtained from the acquired calculated value of the peak wavelength position of the plurality of gases and the theoretical value of the position of the peak wavelengths of the plurality of gases. The position of the peak wavelength of the gas to be measured can be calculated by the following formula.

_{λ ', λ A', λ} B ' is for a theoretical value, is known. λ _A and λ _B need to be specified from the position of the peak wavelength in the second wavelength sweep range. However, since _{the difference between λ A} and λ _B is kept constant, it can be easily specified. Therefore, the position λ of the peak wavelength of the actual gas absorption waveform of the gas to be measured can be calculated from λ', λ _A ', λ _B ', λ _A , and λ _B.

In FIG. 9, the magnitude relationship of various gases is λ _A <λ <λ _B , but the relationship is not limited to this, and if the relative position of λ is uniquely determined, for example, λ < The relationship may be _{λ A} <λ _B or λ _A <λ _{B <λ.} Further, as long as the relative position of λ is uniquely determined, two or more kinds of gas types may be used. As described above, the position of the peak wavelength in the second wavelength sweep range of the gas absorption waveform of the gas to be measured can be specified by the relative relationship of the positions of the peak wavelengths of the plurality of gases.

Figure 10 shows an example of a relationship between the wavelength and the absorption intensity with respect to HCl (hydrogen chloride) and _H 2 O (water vapor). A specific example of a method of calculating the position of the peak wavelength when the gas to be measured is HCl in the concentration measurement of the exhaust gas in the flue will be described with reference to FIG. In FIG. 10, the position of the peak wavelength of the gas absorption waveform of HCl is 1742.38 nm. Further, in the vicinity there is the position of the peak wavelength of of H _{2 O} gas absorption waveform. 10, the position of the peak wavelength of of _{H 2} O gas absorption waveform, 1742.51nm, 1742.60nm, is 1742.68Nm. The position of the peak wavelength of the gas absorption waveform shown in FIG. 10 is a theoretical value of the position of the peak wavelength of the gas absorption waveform.

The wavelength calculating unit 217, keep previously stored theoretical values of the position of the peak wavelength of HCl and H _{2 O} gas absorption waveform. In the example of FIG. 10, λ'= 1742.38 nm, λ _A '= 1742.51 nm, and λ _B '= 1742.60 nm. Further, 1742.68 nm may be used as the theoretical value of the position of the peak wavelength. Since H ₂ O exists in a constant concentration in the atmosphere, by expanding the wavelength sweep range of the second wavelength sweep range so as to include all these gas absorption waveforms, two peaks of the gas absorption waveform of _{H 2 O} Wavelength positions λ _A and λ _B can be detected. _{Therefore, the positions λ A} and λ _{B of the peak wavelength of H 2} O can be calculated from the received signal, and the position λ of the peak wavelength of the actual gas absorption waveform of HCl can be obtained by the above equation.

The correction unit 216 corrects the first wavelength sweep range of the laser beam 30 based on the position of the peak wavelength of the gas absorption waveform of the gas to be measured. By performing the correction, it becomes possible to detect the position of the peak wavelength of the gas absorption waveform of the gas to be measured in the first wavelength sweep range. Therefore, even when the concentration of the gas to be measured is low, the gas absorption waveform can be detected in the first wavelength sweep range, and highly accurate concentration analysis is possible.

The correction unit 216 corrects so that the gas absorption waveform of the gas to be measured can be detected in the first wavelength sweep range. The correction unit 216 may correct the first wavelength sweep range so that the position of the peak wavelength of the specified measurement target gas is within the first wavelength sweep range. The correction unit 216 may correct the first wavelength sweep range so that the position of the peak wavelength of the specified measurement target gas becomes the center of the first wavelength sweep range.

The control amount calculation unit 218 determines the current control amount or the temperature control amount for correcting the first wavelength sweep range. The current control amount and the temperature control amount may be obtained from the difference between the position of the peak wavelength of the actual gas absorption waveform and the center wavelength of the first wavelength sweep range.

An example of correction by current control is shown. The position λ of the peak wavelength of the calculated actual gas absorption waveform of the gas to be measured is sent to the control amount calculation unit 218. The control amount calculation unit 218 determines the current control amount so that the measurement target gas is at a predetermined position (for example, the center of the range) in the first wavelength sweep range. Considering that the current characteristic of the wavelength of the laser element 116 is about 12 pm / mA, the current control amount is determined by the following formula. The current control amount (correction amount to be added to the normal control) is dI [mA], the position of the peak wavelength of the actual gas absorption waveform of the gas to be measured is λ [pm], and the center wavelength of the first wavelength sweep range is λ _p [ pm]. The equation is an example in which the position of the peak wavelength of the gas absorption waveform of the gas to be measured is corrected so as to be the center of the first wavelength sweep range.

The correction unit 216 corrects the first wavelength sweep range of the laser beam 30 by transmitting the determined current control amount to the current control unit 114. Therefore, the current control makes it possible to detect the position of the peak wavelength of the gas absorption waveform of the gas to be measured in the first wavelength sweep range.

Further, the correction by temperature control may be performed instead of the current control. In that case, considering that the temperature dependence of the laser element 116 is about 100 pm / ° C., the temperature control amount is determined by the following formula. The temperature control amount (correction amount to be added to the normal control) is dT [° C], the position of the peak wavelength of the actual gas absorption waveform of the gas to be measured is λ [pm], and the center wavelength of the first wavelength sweep range is λ _p [ pm]. The equation is an example in which the position of the peak wavelength of the gas absorption waveform of the gas to be measured is corrected so as to be the center of the first wavelength sweep range.

The correction unit 216 corrects the first wavelength sweep range of the laser beam 30 by transmitting the determined temperature control amount to the temperature control unit 115. Therefore, the temperature control makes it possible to detect the position of the peak wavelength of the gas absorption waveform of the gas to be measured in the first wavelength sweep range.

FIG. 11 shows an example of the configuration of the laser gas analyzer 400 according to the comparative example. The laser gas analyzer 400 includes a laser element 416, a temperature sensor 417 temperature control element 415, and a reference gas cell 419. It differs from the laser gas analyzer 300 of FIG. 1 in that it has a reference gas cell 419. The other configuration of the laser gas analyzer 400 may be the same as that of the laser gas analyzer 300 of FIG.

The reference gas cell 419 is filled with a measurement target gas having a known concentration. By installing a measurement target gas having a known concentration between the laser element 416 and the measurement space, the laser light is input to the light receiving element through the measurement space after passing through the reference gas cell 419. Therefore, even when the measurement target gas in the measurement space has a low concentration, the peak of the gas absorption waveform can always be detected. In addition, by correcting the position of the gas absorption waveform detected in this way with respect to the wavelength sweep range of the laser beam, the gas absorption waveform of the gas to be measured can be reliably captured, even in an environment where there is a sudden change in ambient temperature. Stable and highly accurate concentration analysis can be performed.

The laser gas analyzer 100 is most suitable for measuring combustion exhaust gas such as boiler and garbage 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 / Desulfurization], exhaust gas from internal combustion engines of automobiles and ships (exhaust tester), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growth, chemical analysis [oil refining plant, petrochemical It is also useful as an analyzer for plants, gas generation plants], environmental use [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. It is clear from the description of the claims that such modified or improved forms may also be included in the technical scope of the present invention.

The order of execution of operations, procedures, steps, steps, etc. in the devices, systems, programs, and methods 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.

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 ... Mounting seat, 111 ... Laser drive signal generator, 112 ... Sweep Signal generator, 113 ... Modulation signal generator, 114 ... Current control, 115 ... Temperature control, 116 ... Laser element, 117 ... Thermista, 118 ... Perche element, 100 ... Laser gas analysis Total, 211 ... I / V converter, 212 ... Laser, 213 ... Synchronous detection circuit, 214 ... Filter, 215 ... Calculation unit, 216 ... Correction unit, 217 ... Wave frequency calculation unit, 218 ... Control amount calculation unit, 300 ... laser gas analyzer, 315 ... temperature control element, 316 ... laser element, 317 ... temperature sensor, 400 ... laser gas analyzer, 415 ... temperature control element, 416・ ・ Laser element, 417 ・ ・ Temperature sensor, 419 ・ ・ Reference gas cell

Claims (15)

A light source unit that sweeps wavelengths and emits laser light,
A light receiving element that receives the laser beam propagated through the measurement space in which the gas to be measured exists, and a light receiving element.
It is provided with a signal processing circuit that processes the output signal of the light receiving element and measures the concentration of the gas to be measured from the gas absorption waveform existing in the first wavelength sweep range of the laser beam.
The signal processing circuit is relative to the positions of the peak wavelengths of the plurality of gas absorption waveforms detected by sweeping the wavelength of the laser beam in the second wavelength sweep range extended from the first wavelength sweep range. In relation to this, the position of the peak wavelength of the gas absorption waveform of the measurement target gas in the second wavelength sweep range is specified, and the position of the peak wavelength of the gas absorption waveform of the measurement target gas in the second wavelength sweep range is set. A laser gas analyzer having a correction unit that corrects the first wavelength sweep range of the laser light based on the correction unit. The correction unit makes the position of the peak wavelength of the gas absorption waveform of the gas to be measured specified by the signal processing circuit in the second wavelength sweep range within the first wavelength sweep range. The laser gas analyzer according to claim 1, which corrects a one-wavelength sweep range. The correction unit performs the correction unit so that the position of the peak wavelength of the gas absorption waveform of the gas to be measured specified by the signal processing circuit in the second wavelength sweep range becomes the center of the first wavelength sweep range. The laser gas analyzer according to claim 2, which corrects the first wavelength sweep range. The light source unit
A laser drive signal generator that synthesizes a wavelength sweep drive signal that changes the emission wavelength of the laser element and a high-frequency modulation signal that modulates the emission wavelength and outputs it as a laser drive signal.
A current control unit that converts the laser drive signal output from the laser drive signal generation unit into a current, and a current control unit.
The laser element to which the current output from the current control unit is supplied, and
The laser gas analyzer according to any one of claims 1 to 3, further comprising a temperature control unit that controls the temperature of the laser element. The waveform of the wavelength sweep drive signal has an offset portion and a portion that linearly changes the supply current to the laser element to gradually change the emission wavelength of the laser element, and has a fixed period. It is a repeating waveform,
The laser gas analyzer according to claim 4, wherein the offset portion is a value that supplies a current equal to or greater than a threshold current value at which the light emission of the laser element is stable to the laser element. The correction unit
The current control amount for correcting the first wavelength sweep range of the laser beam is calculated.
The laser gas analyzer according to claim 4 or 5, wherein the first wavelength sweep range of the laser light is corrected by transmitting the current control amount to the current control unit. The correction unit
The temperature control amount for correcting the first wavelength sweep range of the laser beam is calculated.
The laser gas analyzer according to claim 4 or 5, wherein the temperature control amount is transmitted to the temperature control unit to correct the first wavelength sweep range of the laser light. The laser gas analyzer according to any one of claims 1 to 7, wherein the correction unit stores the relative relationship between the positions of the ideal peak wavelengths of the plurality of gas absorption waveforms. The laser gas analyzer according to any one of claims 1 to 8, wherein the plurality of gas absorption waveforms include the gas absorption waveform of water vapor. The laser gas analyzer according to any one of claims 1 to 9, wherein the first wavelength sweep range of the laser beam is corrected at a timing at regular time intervals. Claim 1 that observes the atmospheric temperature of the measurement space and corrects the first wavelength sweep range of the laser beam at the timing when the amount of change or the rate of change of the temperature of the measurement space becomes equal to or higher than a predetermined threshold value. 9. The laser gas analyzer according to any one of 9. According to any one of claims 1 to 9, the first wavelength sweep range of the laser beam is corrected at the timing when the amount of change or the rate of change in the measured concentration of the gas to be measured becomes equal to or higher than a predetermined threshold value. The laser gas analyzer described. The laser gas analyzer according to any one of claims 1 to 9, wherein the first wavelength sweep range of the laser beam is corrected at a timing when the gas absorption waveform of the gas to be measured is no longer detected. The laser gas analysis according to any one of claims 1 to 13, wherein the position of the peak wavelength of the gas absorption waveform is determined by the point where the waveform obtained by oddly differentiating the gas absorption waveform intersects the horizontal axis passing through the origin. Total. The laser gas analyzer according to any one of claims 1 to 13, wherein the position of the peak wavelength of the gas absorption waveform is determined by the minimum value of the gas absorption waveform.

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