JP2017101950A - Laser gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser gas analyzer which, even if including a mid-infrared laser element with a large calorific value, such as a quantum cascade laser (QCL), and being in such an environment that an ambient temperature changes, makes an oscillation wavelength of a laser beam constant by combining pulse drive and wavelength scan so as to achieve both heat generation suppression and temperature control of the mid-infrared laser element, so as to be able to accurately measure the concentration of gas.SOLUTION: In a laser gas analyzer, a reverse peak affected by optical absorption by a measurement object gas is detected from a signal component of a waveform of wavelength scan, so that temperature of a mid-infrared laser element is controlled to get close to a reference temperature on the basis of change of the reverse peak. Also, the variation of height of a pulse wave affected by the optical absorption by the measurement object gas is calculated from the signal component of a waveform of pulse drive, so that the concentration of the measurement object gas is calculated from the variation of the height of the pulse wave.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a laser type gas analyzer that measures the gas concentration of a measurement target gas with laser light.

It is known that each gas molecule / atom has its own light absorption spectrum. For example, FIG. 8 is an example of a light absorption spectrum of ammonia (NH ₃ ), the horizontal axis of the graph indicates the wavelength, and the vertical axis indicates the light absorption intensity.

  The laser gas analyzer detects the gas concentration of various gases using such a light absorption spectrum. The laser gas analyzer irradiates the measurement target gas with laser light from a semiconductor laser light source having an emission wavelength region including the wavelength of the light absorption spectrum of the measurement target gas. At this time, laser light is absorbed by the molecules and atoms of the measurement target gas.

Here, the attenuation at the center wavelength λ _c of the light absorption spectrum is proportional to the gas concentration. Therefore, a laser beam is irradiated to a gas having an oscillation wavelength of the center wavelength lambda _c, it is possible to estimate the gas concentration by multiplying an appropriate coefficient by measuring the amount of attenuation.

  The concentration measurement method by gas analysis using laser light is roughly classified into a differential absorption method and a frequency modulation method. Usually, the differential absorption method can measure the gas concentration with a relatively simple configuration. On the other hand, the frequency modulation method enables highly sensitive gas concentration measurement although signal processing is complicated.

  An apparatus for measuring a gas concentration by a differential absorption method is described in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 7-151681, “Gas Concentration Measuring Device”). As shown in FIG. 8 of Patent Document 1, this gas concentration measuring device is a device including a two-wavelength semiconductor laser, a gas cell, a light receiving lens, a light receiving unit, and a gas concentration measuring device.

Then, as shown in the concentration measurement principle by the differential absorption method of FIG. 9, a laser beam having an oscillation wavelength at the center wavelength λ _c of the absorption line, a laser beam having an oscillation wavelength at the center wavelength λ _r without the absorption line, The gas is irradiated with the two types of laser light, and the signal intensity difference obtained by subtracting the intensity of the signal output from each light receiving unit is multiplied by an appropriate proportionality constant to be converted into a concentration.

  An apparatus for measuring a gas concentration by a frequency modulation method is also described in, for example, Patent Document 1 described above. As shown in FIG. 7 of Patent Document 1, this gas concentration measuring device is a device including a frequency modulation type semiconductor laser, a gas cell, a light receiving lens, a light receiving unit, and a gas concentration measuring device.

Then, as shown in concentrations measuring principle according to the frequency modulation scheme of Figure 10, the center wavelength lambda _c, the output of the semiconductor laser is frequency-modulated at a modulation frequency f _m, is irradiated to the measurement target gas of interest. Since the absorption line of the gas is almost quadratic function with respect to the frequency twice the frequency of the signal (second harmonic) is obtained in the modulation frequency f _m in the role played light receiving portion of the absorption lines discriminator It is done. The fundamental wave by amplitude modulation can be estimated by performing envelope detection in the light receiving unit, and by synchronizing the ratio of the amplitude of the fundamental wave and the amplitude of the second harmonic wave, it is proportional to the gas concentration regardless of the amount of received light. To get a value.

  As a conventional gas analyzer using laser light, for example, a laser gas analyzer shown in FIG. 11 is known. This laser type gas analyzer is described in Patent Document 2 (Japanese Patent Laid-Open No. 2009-47677, title of the invention “laser type gas analyzer”).

  In FIG. 11, 101a and 101b are flue walls through which the measurement target gas flows. On these flue walls 101a and 101b, the light emitting portion flange 201a and the light receiving portion flange 201b are arranged at positions facing each other.

  A light emitting unit case 203a is attached to the light emitting unit flange 201a via a mounting bracket 202a. The light emitting unit case 203a incorporates optical components such as a laser light source 204 and a collimating lens 205. A light receiving part case 203b is attached to the light receiving part flange 201b via a mounting bracket 202b. The light receiving unit case 203b contains a lens 206, a light receiving element 207, and a light receiving unit circuit board 208 for processing the output signal of the light receiving element 207.

  In the above configuration, the laser light emitted from the laser light source 204 is applied to the inside of the flue, which is the measurement target space, and is applied to the light receiving element 207 in the light receiving unit case 203b disposed to face the laser light source 204.

  When the measurement target gas is present inside the flue due to this light reception, the laser light is absorbed. Therefore, the light absorption circuit board 208 is utilized by utilizing the fact that this light absorption is related to the concentration of the measurement target gas. The above received light signal processing circuit calculates the gas concentration to be measured. In the received light signal processing circuit, for example, a received light signal waveform as shown in FIG. 9 is obtained, and the gas concentration can be calculated from the signal intensity difference which is the difference between the maximum value and the minimum value of the signal.

These laser gas analyzers are also used to measure the exhaust gas inside the flue. Such exhaust gas contains SO ₂ gas. The spectral characteristic of SO ₂ gas absorbs light in the mid-infrared region as shown in FIG. Therefore, it is necessary to irradiate laser light in the mid-infrared region. As a laser element that emits the mid-infrared light, there is a quantum cascade laser (QCL). Patent Document 3 (Japanese Patent Laid-Open No. 2010-266303, “Laser Gas Analyzer”) is a laser type that emits laser light in the mid-infrared region using QCL in order to analyze SO ₂ gas. A gas analyzer is disclosed.

  Since QCL has a higher drive current and drive voltage and higher power consumption than other laser elements, it generates a large amount of heat. The conventional laser element has a power consumption of about 100 mA × 5 V = 0.5 W. On the other hand, QCL is 1 A × 10 V = 10 W, which is about 20 times the power consumption.

  Although the frequency modulation method described above with reference to Patent Document 1 can detect the gas concentration with very high accuracy, it is necessary to light the laser element for a long time. In the case of QCL, since the calorific value is large, if it is driven for a long time in a high temperature environment where a laser gas analyzer is installed, overheating may occur and the laser element may be destroyed.

  As a general method for overheating countermeasures, there is a gas concentration detection method using short pulse driving. In this method, a pulse driving current is applied to the QCL. As for the pulse width, the duty ratio can be set relatively freely so that the QCL does not cause overheating.

  This pulse drive current is precisely controlled to emit light having a wavelength at which the gas to be measured is absorbed. The amount of received light is maximum when there is no measurement target gas, and the amount of received light decreases when there is a measurement target gas. Since the degree of decrease in the amount of received light varies depending on the concentration of the measurement target gas, the gas concentration can be measured by detecting this amount of change.

Japanese Patent Laid-Open No. 7-151681 (paragraphs [0004], [0030], FIGS. 6, 7, etc.) Japanese Patent Laying-Open No. 2009-47677 (paragraphs [0029] to [0038], FIGS. 1 to 7 etc.) JP 2010-266303 A (paragraph [0033], FIG. 1 etc.)

  Laser gas analyzers that analyze exhaust gas are often installed near the flue. High temperature exhaust gas may circulate in the flue, and the environment around the flue becomes a high temperature environment. Furthermore, the normal flue is often exposed to the outside air, and the laser gas analyzer is also exposed to the outside air. In this case, the ambient temperature of the laser gas analyzer is constantly changed due to the influence of outside air such as wind.

  As a conventional technique, gas concentration detection by a shortened pulse drive, which is a general method for overheating, has been described. However, even if the current value is precisely controlled, in addition to the large amount of heat generated by the QCL, the area around the flue is not good. It is a stable high temperature environment, and the oscillation wavelength of the QCL is also affected by the influence of the ambient temperature. It has been found that the desired wavelength cannot be oscillated and it is difficult to accurately measure the gas concentration.

  Further, since the method of Patent Document 3 is a method that combines wavelength scanning and high-frequency modulation, even if the lighting time is pulsed, it is necessary to make the appearance frequency of the pulse larger than the modulation frequency, that is, light emission is longer than the stop time. For example, a problem has been found that it cannot be applied in an environment where the ambient temperature is high such that a high-temperature gas circulates.

  Therefore, the problem to be solved by the present invention is to have a combination of pulse driving and wavelength scanning even in an environment where the ambient temperature changes, including a mid-infrared laser element having a large calorific value such as QCL. An object of the present invention is to provide a laser type gas analyzer capable of accurately measuring the gas concentration by making the oscillation wavelength of the laser beam constant while achieving both suppression of heat generation of the mid-infrared laser element and temperature control of the mid-infrared laser element.

In order to solve the above problem, the invention according to claim 1
A mid-infrared laser element that emits a laser beam having a wavelength in the mid-infrared region including the center wavelength of the light absorption spectrum of the measurement target gas, and a laser beam having a wavelength that approximately matches the center wavelength of the light absorption spectrum of the measurement target gas. A temperature adjustment unit for adjusting the temperature of the mid-infrared laser element so as to be a reference temperature to be emitted, and a mid-infrared laser light emitting unit,
A temperature control unit that controls the temperature adjustment unit so that the mid-infrared laser element becomes the reference temperature, a pulsed pulse drive waveform, and a wavelength scan waveform that continuously changes the wavelength are included. A mid-infrared laser driving unit having a light-emitting driving unit that outputs a laser driving signal to the mid-infrared laser light-emitting unit;
A light-emitting side optical unit that collimates the laser light emitted from the mid-infrared laser light emitting unit and irradiates the measurement target space where the gas containing the measurement target gas exists;
A light receiving side optical unit that condenses the laser light emitted from the light emitting side optical unit;
A mid-infrared light receiving unit that receives the laser light collected from the light-receiving side optical unit and outputs it as an electrical mid-infrared light reception signal;
The signal component of the wavelength scan waveform is extracted from the mid-infrared light reception signal output from the mid-infrared light receiving unit, and an inverse peak affected by light absorption by the measurement target gas is detected from the signal component of the wavelength scan waveform. A temperature correction calculation unit that detects and transmits a correction temperature signal that brings the mid-infrared laser element close to a reference temperature based on a change in the reverse peak to the temperature control unit;
A signal component of the pulse drive waveform is extracted from the mid-infrared light reception signal output from the mid-infrared light receiving unit, and a pulse wave height affected by light absorption by the measurement target gas from the signal component of the pulse drive waveform is extracted. A gas concentration calculation unit that calculates a change amount and calculates a gas concentration of the measurement target gas from the change amount of the pulse wave height;
It was set as the laser type gas analyzer characterized by providing.

The invention according to claim 2
The laser gas analyzer according to claim 1, wherein
The correction temperature signal of the temperature correction calculation unit is the time from the start time of the wavelength scan waveform to the appearance of the bottom of the reverse peak affected by light absorption by the measurement target gas, which is half the scan time of the wavelength scan. The laser gas analyzer is characterized in that a signal for bringing the mid-infrared laser element closer to a reference temperature is set so as to be closer to the above time.

  According to the present invention, a mid-infrared laser device having a mid-infrared laser device having a large calorific value such as QCL and combining pulse driving and wavelength scanning even in an environment where the ambient temperature changes can be obtained. It is possible to provide a laser type gas analyzer capable of performing accurate gas concentration measurement by suppressing both heat generation and mid-infrared laser element temperature control, making the oscillation wavelength of laser light constant.

It is a block diagram of the laser type gas analyzer which concerns on the 1st form for implementing this invention. It is a block diagram of a mid infrared laser light emission part and a mid infrared laser drive part. It is explanatory drawing of a laser drive signal. It is a block diagram of a mid-infrared light receiving unit and a signal processing / driving unit. It is explanatory drawing of a mid-infrared received light signal. FIG. 6A is an explanatory diagram of temperature correction using a scan waveform, FIG. 6A is an explanatory diagram of temperature correction when the temperature rises, and FIG. 6B is an explanatory diagram of temperature correction when the temperature drops. It is a block diagram of the laser type gas analyzer which concerns on the 2nd form for implementing this invention. It is a diagram illustrating an optical absorption spectrum of ammonia (NH _3). It is a figure which shows the density | concentration measurement principle by a differential absorption system. It is a figure which shows the density | concentration measurement principle by a frequency modulation system. 2 is a configuration diagram of a conventional laser gas analyzer described in Patent Document 2. FIG. It is a diagram illustrating an optical absorption spectrum of sulfur dioxide (SO _2). It is a figure which shows the drive signal with respect to the laser element for the QCL calorific value reduction of the prior art described in patent document 3. FIG.

  Hereinafter, a first mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows the overall configuration of a laser gas analyzer according to this embodiment. The laser gas analyzer 1 includes a light emitting unit 10, a light receiving unit 20, and a communication line 30. Among these, the light emitting unit 10 and the light receiving unit 20 are fixed to the flue.

  The light emitting unit 10 further includes a light emitting unit case 11, a mid infrared laser light emitting unit 12, a light emitting side optical unit 13, a light emitting unit window 14, and a mid infrared laser driving unit 15. The light receiving unit 20 further includes at least a light receiving unit case 21, a mid-infrared light receiving unit 22, a light receiving side optical unit 23, a light receiving unit window 24, and a signal processing / driving unit 25, and notifies the gas concentration by the output unit 26.

  In FIG. 1, a light emitting portion flange 201a and a light receiving portion flange 201b are fixed to, for example, a flue wall 101a, 101b such as a flue through which the measurement target gas passes, by welding or the like.

  A light emitting unit case 11 is attached to the light emitting unit flange 201a via a mounting bracket 202a. Inside the light emitting unit case 11, there are a mid-infrared laser emitting unit 12 for emitting a mid-infrared laser beam and a lens. A light emitting side optical unit 13 is arranged. Further, by arranging the light emitting unit window 14 that transmits light having a wavelength in the mid-infrared region, the inside of the light emitting unit case 11 is secured.

  A mid-infrared laser driving unit 15 is connected to the mid-infrared laser light emitting unit 12. A current signal is sent from the mid-infrared laser drive unit 15 to the mid-infrared laser light-emitting unit 12 so that the mid-infrared laser light-emitting unit 12 emits mid-infrared light.

  The light emitted from the mid-infrared laser light emitting unit 12 is collimated by the light-emitting side optical unit 13 which is a lens to become parallel light, passes through the center of the light emitting unit flange 201a, and enters the flue interior 300 as the mid-infrared laser light 40. Irradiated. The mid-infrared laser beam 40 is affected by light absorption by the measurement target gas existing in the flue interior 300.

  On the other hand, the light receiving part case 21 is attached to the light receiving part flange 201b via a mounting bracket 202b. The mid-infrared laser beam 40 that has passed through the flue interior 300 is collected by the light-receiving side optical unit 23 that is airtightly arranged inside the light-receiving unit case 21 and is received by the mid-infrared light receiving unit 22. By arranging the window 24 that transmits light having a wavelength in the mid-infrared region, the inside of the light receiving unit case 21 is secured.

  Next, details of the operation of each unit will be described. As shown in detail in FIG. 2, the mid-infrared laser light emitting unit 12 includes a mid-infrared laser element 12a, a temperature detection unit (thermistor) 12b, and a heating / cooling unit (Peltier element) 12c. In the present embodiment, the temperature adjustment unit of the present invention is a combination of a temperature detection unit (thermistor) 12b and a heating / cooling unit (Peltier element) 12c.

Specifically, the mid-infrared laser element 12a is a quantum cascade laser (QCL) element. In this embodiment, sulfur dioxide gas (SO ₂ gas) is measured as a specific example of the measurement target gas. The quantum cascade laser (QCL) element emits mid-infrared laser light having a wavelength of 3 to 10 μm in the mid-infrared region including the light absorption spectrum of the measurement target gas (SO ₂ gas).

  The mid-infrared laser drive unit 15 further includes a command signal generation unit 15a, a laser drive signal generation unit 15b, and a temperature control unit 15c. The light emission drive unit of the present invention is a combination of the command signal generation unit 15a and the laser drive signal generation unit 15b in this embodiment.

  The mid-infrared laser driving unit 15 can change the emission wavelength of the mid-infrared laser light depending on the temperature. In FIG. 2, the temperature of the mid-infrared laser element 12a is detected by using a temperature detector 12b such as a thermistor. This temperature detection unit 12 b is connected to the temperature control unit 15 c of the mid-infrared laser driving unit 15.

  This temperature control unit 15c performs PID control or the like so that the resistance value obtained from the temperature detection unit 12b such as a thermistor becomes constant in order to stabilize the emission wavelength of the mid-infrared laser element 12a and adjust the emission wavelength. Thus, the temperature of the heating / cooling unit 12c such as a Peltier element is controlled, and the emission wavelength is controlled by adjusting the temperature of the mid-infrared laser element 12a.

Further, the mid-infrared laser driving unit 15 can change the emission wavelength of the mid-infrared laser light by a laser driving signal. Since the mid-infrared laser driving unit 15 emits a wavelength in the mid-infrared region, the laser driving signal by the current is controlled, and the wavelength at which the emission wavelength matches the absorption characteristic of the measurement target gas (SO ₂ gas) and its wavelength The mid-infrared laser light emitting unit 12 is caused to emit light so as to scan at a wavelength in the peripheral region.

  Next, the command signal generator 15a that determines the drive waveform of the laser drive signal will be described. The command signal generator 15a generates a command signal as shown in FIG. This command signal includes a pulsed pulse drive waveform and a wavelength scan waveform that continuously changes the wavelength.

Among the laser drive signals shown in FIG. 3, the pulse-like pulse drive waveform is a waveform in which a plurality of pulses having the same wavelength are continuously output. The wavelength of this pulse drive waveform is adjusted so that the gas absorption of the measurement target gas (SO ₂ gas) is the strongest wavelength.

Further, the wavelength scanning waveform to continuously change the wavelength, the wavelength scan, including portions having no absorption by the measurement target gas (SO ₂ gas). In this scan waveform, when the wavelength scan time is time T _S , the wavelength (point A in FIG. 3) of half time (T _S / 2) matches the light absorption characteristics of the measurement target gas (SO ₂ gas). The scan width is adjusted so that the center wavelength matches.

  When such a command signal is repeatedly input to the laser drive signal generation unit 15b at regular intervals, the laser drive signal generation unit 15b performs V / I conversion on the command signal to change the pulsed pulse drive waveform and wavelength. It is supplied to the mid-infrared laser element 12a as a laser drive signal having a current that includes both wavelength scan waveforms that are continuously changed. The laser element 12a outputs a mid-infrared laser beam 40 having a wavelength as shown in FIG.

Next, the mid-infrared light receiving unit 22 of the present invention will be described. As shown in FIG. 4, the mid-infrared laser light 40 that has propagated through the space where the measurement target gas (SO ₂ gas) exists and has absorbed the gas is condensed by the light-receiving side optical unit 23, and then the medium-red Light is received by the outer light receiving unit 22. The mid-infrared light receiving unit 22 outputs a mid-infrared light reception signal based on an electric signal according to the amount of received light.

  The mid-infrared light receiving unit 22 is an MCT (Mercury Cadmium Tellurium) photoconductive element having sensitivity to wavelengths in the mid-infrared region, and the mid-infrared light receiving signal output from the mid-infrared light receiving unit 22 is signal processing / driving. Input to the unit 25. The signal processing / driving unit 25 performs signal processing on the mid-infrared light reception signal of the mid-infrared light receiving unit 22, extracts a signal change component due to light absorption of the measurement target gas, calculates a gas concentration of the measurement target gas, It also controls heat generation suppression and oscillation wavelength stabilization of the mid-infrared laser element.

Next, details of the signal processing / driving unit 25 will be described. As shown in FIG. 4, the signal processing / driving unit 25 includes an I / V conversion unit 25a, a filter unit 25b, an initial setting storage unit 25c, and a calculation unit 25d. The initial setting storage unit 25c is registered at the time of factory shipment or calibration, and stores the maximum received light amount P _max and the span calibration value GA. The maximum received light amount _Pmax represents the maximum pulse height when a mid-infrared laser beam 40 having a wavelength as shown in FIG. 3 is received when there is no measurement target gas in the measurement target space.

  The mid-infrared light receiving signal input from the mid-infrared light receiving unit 22 to the signal processing / driving unit 25 is converted from a current signal to a voltage signal by the I / V conversion unit 25a. The voltage signal from which noise has been removed by the filter 25b is input to the arithmetic unit 25d. This voltage signal has an output waveform as shown in FIG. The calculation unit 25d calculates the gas concentration of the measurement target gas, and controls heat generation suppression and oscillation wavelength stabilization.

  Then, the process by the calculating part 25d in such a laser type gas analyzer is demonstrated. First, the calculation unit 25d functions as a temperature correction calculation unit of the present invention for suppressing heat generation and stabilizing the oscillation wavelength for the mid-infrared laser element 12a.

  The calculation unit 25d extracts the signal component of the wavelength scan waveform from the mid-infrared light reception signal output from the mid-infrared light reception unit 22 and noise-removed by the filter 25b. For example, digital data representing a wavelength scan waveform is registered in a memory built in the calculation unit 25d. Data representing the wave height at a certain time, and a large number of data in a period included in the scan width are registered.

The computing unit 25d detects a reverse peak affected by light absorption by the measurement target gas from the signal component of the wavelength scan waveform. Specifically, the time until the bottom of the reverse peak appears from the registered digital data is selected. This time is the time from the beginning of the scan waveform until the center of the reverse peak appears, such as T _f shown in FIG. _6A or T _d shown in FIG. 6B.

The calculation unit 25d controls the temperature control unit so that the mid-infrared laser element becomes the reference temperature based on the change in the reverse peak. For example, as shown in FIG. 6 (a), the scan waveform when the temperature of the mid-infrared laser element 12a rises shifts upward as indicated by an arrow a, so that the central wavelength absorbed by the measurement target gas (SO ₂ gas) A reverse peak appears at time _Tf . Therefore, if a reverse peak appears quickly in time, a temperature correction signal that lowers the temperature of the mid-infrared laser element 12a is transmitted to the temperature control unit 15c via the communication line 30, and the temperature control unit 15c The heating / cooling unit 12c is driven so as to lower the temperature of the mid-infrared laser element 12a. The temperature is decreased more as the time _Tf is smaller. For example, the temperature to be lowered by multiplying (T _S / 2-T _f ) by a coefficient may be calculated. Due to this cooling, the temperature of the mid-infrared laser element 12a is lowered, the scan waveform is returned to the normal time as shown by the arrow b, and the appearance time of the reverse peak returns to T _S / 2.

Further, as shown in FIG. 6B, the scan waveform when the temperature of the mid-infrared laser element 12a is lowered shifts downward as indicated by an arrow b, so that the measurement target gas (SO ₂ gas) absorbs the center. The wavelength arrives late and an inverse peak appears at time _Td . Therefore, if a reverse peak appears later in time, a temperature correction signal that increases the temperature of the mid-infrared laser element 12a is transmitted to the temperature control unit 15c via the communication line 30, and the temperature control unit 15c The heating / cooling unit 12c is driven so as to increase the temperature of the mid-infrared laser element 12a. As the time _Td increases, the temperature is increased. For example, the temperature to be raised by multiplying (T _d −T _S / 2) by a coefficient may be calculated. Due to the heating, the temperature of the mid-infrared laser element 12a rises, the scan waveform also returns to the normal time as shown by the arrow a, and the appearance time of the reverse peak returns to T _S / 2. In this way, the temperature of the mid-infrared laser element 12a is adjusted so that it does not affect the measurement of the gas concentration.

  These temperature correction signals change the time from the start time of the wavelength scan waveform to the appearance of the bottom of the reverse peak affected by light absorption by the measurement target gas, to half the scan time of the wavelength scan. It is a signal for heating and cooling as close to each other. By performing such temperature correction every time the scan waveform is acquired, the mid-infrared laser element is always maintained at the reference temperature, and the emission wavelength is maintained constant. This realizes oscillation wavelength control according to the temperature of the mid-infrared laser element.

Subsequently, the calculation unit 25d functions as a gas concentration calculation unit of the present invention.
First, the calculation unit 25d extracts a signal component of a pulse drive waveform from the mid-infrared light reception signal received from the mid-infrared light reception unit 22. For example, it registers as digital data in a memory built in the calculation unit 25d. Since the pulse width of this pulse drive waveform is sufficiently short, heat generation is suppressed when the laser light emitting element 12a such as QCL emits light.

The calculation unit 25d calculates a change amount of the pulse wave height affected by light absorption by the measurement target gas from the signal component of the pulse drive waveform. Digital data having a small value and digital data having a large value are acquired because they are in a pulse form, and digital data having a large value is selected from these. Since digital data with a large value is acquired for a plurality of pulses (10 pulses in FIG. 5) in one cycle of the pulse drive waveform, the average value of these is set as the pulse wave height P. Then, the calculation unit 25d reads the maximum received light amount _Pmax stored in the initial setting storage unit 25c, and acquires the change amount of the pulse wave height by the following equation.

[Equation 1]
Change amount of pulse wave height = (P _max −P)

  The calculation unit 25d calculates the measurement target gas concentration from the amount of change in the pulse wave height P. At this time, the calculation unit 25d reads the span calibration value GA stored in the initial setting storage unit 25c, and outputs a value obtained by correcting the light quantity by the following equation as a gas concentration.

[Equation 2]
Gas concentration to be measured (after correction) = (P _max −P) × GA

  The corrected measurement target gas concentration is sent to the output unit 26. The output unit 26 is, for example, a display device or an alarm device, or a transmission device that transmits to another computer. The concentration of the measurement target gas is detected in this way.

According to the present invention, a pulse drive waveform for detecting the concentration of a measurement target gas and a wavelength scan waveform for controlling the oscillation wavelength are combined, and the amount of heat generated as in QCL in an environment where the ambient temperature changes greatly. Even if a laser element having a large value is used, overheating is prevented by controlling the oscillation wavelength to be constant by wavelength scanning and by driving to reduce heat generation by pulse driving. Further, the wavelength of the pulse which is pulse-driven, the concentration of the measurement target gas (SO ₂ gas) is controlled so as to coincide with the center wavelength of the absorption, measured gas (SO ₂ gas) having absorption in the mid-infrared region Can be measured accurately.

  Next, a second embodiment for carrying out the present invention will be described with reference to the drawings. First, FIG. 7 shows a block diagram of a laser type gas analyzer according to the second embodiment. Among these, the laser gas analyzer 2 includes a light emitting unit 10 ′, a light receiving unit 20 ′, and a communication line 30. The light emitting unit 10 'and the light receiving unit 20' are fixed to the flue.

  The light emitting unit 10 ′ further includes a light emitting unit case 11, a mid infrared laser light emitting unit 12, a light emitting side optical unit 13 ′, a light emitting unit window 14, and a mid infrared laser driving unit 15. The light receiving unit 20 ′ further includes at least a light receiving unit case 21, a mid-infrared light receiving unit 22, a light receiving side optical unit 23 ′, a light receiving unit window 24, and a signal processing / driving unit 25, and notifies the gas concentration by the output unit 26. .

  The second embodiment is different from the first embodiment only in the light emitting side optical unit 13 ′ of the light emitting unit 10 ′ and the light receiving side optical unit 23 ′ of the light receiving unit 20 ′. Are the same components, and the same components are denoted by the same reference numerals and redundant description is omitted. Hereinafter, the light emitting side optical unit 13 ′ of the light emitting unit 10 ′ and the light receiving side optical unit 23 ′ of the light receiving unit 20 ′ which are different points will be described.

  In this embodiment, the light emitting side optical unit 13 ′ of the light emitting unit 10 ′ and the light receiving side optical unit 23 ′ of the light receiving unit 20 ′ are both parabolic mirrors. The emitted light from the mid-infrared laser light emitting unit 12 is collimated by a parabolic mirror as the light-emitting side optical unit 13 ′ to become parallel light, and passes through the center of the light-emitting unit flange 201a as smoke. The road interior 300 is irradiated.

  The mid-infrared laser beam 40 is affected by light absorption by the measurement target gas existing in the flue interior 300. Then, the mid-infrared laser beam 40 that has passed through the flue interior 300 is condensed by the light-receiving side optical unit 23 ′ that is a parabolic mirror in the light-receiving unit 20 ′ and received by the mid-infrared light receiving unit 22. The The following temperature control and concentration calculation are the same as in the first embodiment. This form is like this. In addition to this, the present invention can be implemented even if a configuration in which the light emitting side optical unit of the light emitting unit collimates the laser light and the light receiving side optical unit of the light receiving unit collects light is adopted. In both the first and second embodiments, the effects of the present invention can be achieved.

Although the present invention has been described above, the present invention can be variously modified. For example, according to the laser gas analyzer of the present invention, the measurement target gas has been described as an example of oxygen sulfide gas (SO ₂ ). However, the present invention is not limited to this, and the mid-infrared region is used. A gas such as CO, CO ₂ , CH ₄ , SO ₂ , NO, NO ₂ or the like having a light absorption spectrum at a wavelength of may be used. In that case, a laser emission unit having a wavelength capable of detecting other component gases is employed, and the calculation processing content of the calculation unit is changed so as to be detected at this wavelength.

  The laser-type oxygen gas analyzer of the present invention is optimal for ship exhaust gas measurement. In addition, gas analysis for steel [blast furnace, converter, heat treatment furnace, sintering (pellet equipment), coke oven], fruit and vegetable storage and ripening, biochemistry (microorganism) [fermentation], air pollution [incinerator, flue gas desulfurization / Denitration], automobile exhaust gas (remove tester), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growth, chemical analysis [oil refinery plant, petrochemical plant, gas generation plant], It is also useful as an analyzer for environmental [landing concentration, tunnel concentration, parking lot, building management], and various physics and chemistry experiments.

1, 2: Laser gas analyzer 10, 10 ': Light emitting unit 11: Light emitting unit case 12: Mid infrared laser light emitting unit 13, 13': Light emitting side optical unit 14: Light emitting unit window 15: Mid infrared laser drive Units 20, 20 ′: light receiving unit 21: light receiving unit case 22: mid-infrared light receiving unit 23, 23 ′: light receiving side optical unit 24: light receiving unit window 25: signal processing / driving unit 26: output unit 30: communication line 40 : Mid-infrared laser beam 101a, 101b: Flue wall 201a: Light emitting portion flange 201b: Light receiving portion flange 202a: Mounting bracket 202b: Mounting bracket 300: Inside the flue (measurement target space)

Claims (2)

A mid-infrared laser element that emits a laser beam having a wavelength in the mid-infrared region including the center wavelength of the light absorption spectrum of the measurement target gas, and a laser beam having a wavelength that approximately matches the center wavelength of the light absorption spectrum of the measurement target gas. A temperature adjustment unit for adjusting the temperature of the mid-infrared laser element so as to be a reference temperature to be emitted, and a mid-infrared laser light emitting unit,
A temperature control unit that controls the temperature adjustment unit so that the mid-infrared laser element becomes the reference temperature, a pulsed pulse drive waveform, and a wavelength scan waveform that continuously changes the wavelength are included. A mid-infrared laser driving unit having a light-emitting driving unit that outputs a laser driving signal to the mid-infrared laser light-emitting unit;
A light-emitting side optical unit that collimates the laser light emitted from the mid-infrared laser light emitting unit and irradiates the measurement target space where the gas containing the measurement target gas exists;
A light receiving side optical unit that condenses the laser light emitted from the light emitting side optical unit;
A mid-infrared light receiving unit that receives the laser light collected from the light-receiving side optical unit and outputs it as an electrical mid-infrared light reception signal;
The signal component of the wavelength scan waveform is extracted from the mid-infrared light reception signal output from the mid-infrared light receiving unit, and an inverse peak affected by light absorption by the measurement target gas is detected from the signal component of the wavelength scan waveform. A temperature correction calculation unit that detects and transmits a correction temperature signal that brings the mid-infrared laser element close to a reference temperature based on a change in the reverse peak to the temperature control unit;
A signal component of the pulse drive waveform is extracted from the mid-infrared light reception signal output from the mid-infrared light receiving unit, and a pulse wave height affected by light absorption by the measurement target gas from the signal component of the pulse drive waveform is extracted. A gas concentration calculation unit that calculates a change amount and calculates a gas concentration of the measurement target gas from the change amount of the pulse wave height;
A laser gas analyzer comprising: The laser gas analyzer according to claim 1, wherein
The correction temperature signal of the temperature correction calculation unit is the time from the start time of the wavelength scan waveform to the appearance of the bottom of the reverse peak affected by light absorption by the measurement target gas, which is half the scan time of the wavelength scan. The laser gas analyzer is characterized in that a signal for bringing the mid-infrared laser element closer to a reference temperature is set so as to be closer to a predetermined time.

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