JP2009041941A - Gas concentration measuring device and method - Google Patents

Gas concentration measuring device and method Download PDF

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JP2009041941A
JP2009041941A JP2007204369A JP2007204369A JP2009041941A JP 2009041941 A JP2009041941 A JP 2009041941A JP 2007204369 A JP2007204369 A JP 2007204369A JP 2007204369 A JP2007204369 A JP 2007204369A JP 2009041941 A JP2009041941 A JP 2009041941A
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measurement target
wavelength
light
target gas
laser
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Noritomo Hirayama
紀友 平山
Kazuhiro Koizumi
和裕 小泉
Shigeru Komine
繁 小峯
Yusuke Nakamura
裕介 中村
Hideo Kanai
秀夫 金井
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Fuji Electric Co Ltd
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Fuji Electric Systems Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To singly measure the concentration of a plurality of kinds of gases having absorption characteristics exceeding the wavelength variable range of a light-emitting element. <P>SOLUTION: A plurality of light-emitting elements 5a-5d for emitting laser beams having a wavelength corresponding to each absorption wavelength of at least two gases to be measured are provided in an optical system at the transmission side of a gas concentration measuring device. Laser beams are emitted in time series from the plurality of light-emitting elements 5a-5d having mutually different optical wavelengths. At least two gases to be measured having mutually different absorption wavelengths are permeated for detection by a single light receiving element 10. The amplitude ratio of a fundamental wave component to a double-wave component for a portion related to the absorption wavelength band of a specific constituent in gas to be measured is successively calculated by a signal processor 11, thus successively calculating the concentration of a specific constituent in the gas to be measured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明はガス濃度測定装置およびガス濃度測定方法に関し、特に、周波数変調されたレーザ光を用いてガスの濃度を測定する方法に適用して好適なものである。   The present invention relates to a gas concentration measuring apparatus and a gas concentration measuring method, and is particularly suitable for application to a method of measuring a gas concentration using a frequency-modulated laser beam.

気体状のガス分子にはそれぞれ固有の光吸収スペクトルが有ることが知られており、ガス分子の吸収線の中心周波数における減衰量はガスの濃度に比例する。このため、ガス分子の吸収線の中心周波数に一致した発振周波数をもつ半導体レーザ光をガスに照射し、その時のレーザ光の減衰量を測定することで、ガスの濃度を推定することができる（特許文献１）。   It is known that each gaseous gas molecule has its own light absorption spectrum, and the attenuation at the center frequency of the absorption line of the gas molecule is proportional to the gas concentration. For this reason, the gas concentration can be estimated by irradiating the gas with semiconductor laser light having an oscillation frequency that matches the center frequency of the absorption line of gas molecules, and measuring the attenuation of the laser light at that time ( Patent Document 1).

この原理を発展させたものとして２波長差分方式及び周波数変調方式があり、２波長差分方式では、半導体レーザの発振周波数はＴＨｚオーダの信号であることから、複雑な信号処理を行うことができないのに対して、周波数変調方式では、数ｋＨｚのベースバンド領域で信号処理を行うことができるという利点がある。
ここで、周波数変調方式では、ガスの吸収線幅よりもレーザ光の線幅の方が小さいことから、ガスの吸収波長と半導体レーザの発光波長とを合わせる必要がある。この方法として、予め測定したいガスと同じ成分を封入した参照ガスセルを用いる方法がある（特許文献２）。 The two-wavelength difference method and the frequency modulation method are developed from this principle. In the two-wavelength difference method, since the oscillation frequency of the semiconductor laser is a signal on the order of THz, complicated signal processing cannot be performed. On the other hand, the frequency modulation method has an advantage that signal processing can be performed in a baseband region of several kHz.
Here, in the frequency modulation method, since the line width of the laser beam is smaller than the absorption line width of the gas, it is necessary to match the absorption wavelength of the gas with the emission wavelength of the semiconductor laser. As this method, there is a method using a reference gas cell in which the same component as the gas to be measured is enclosed (Patent Document 2).

図１２（ａ）は、従来の周波数変調方式におけるガス濃度測定装置の概略構成を示す平面図、図１２（ｂ）は、従来の周波数変調方式におけるガス濃度測定装置の概略構成を示す側面図である。
図１２において、光源ユニットには、半導体レーザモジュール１２１、参照ガスセル１２２およびフォト検出器１２３が収容され、光源ユニットのケース本体１２６の底面には、冷却用フィン１２７が取り付けられたペルチェ素子１２８が配設されている。ここで、半導体レーザモジュール１２１には、周波数変調されたレーザ光を両面から出射する半導体レーザが配設されるとともに、コネクタ１２５ａを備えた光ケーブル１２５が延出され、半導体レーザから出射される一方の光が光ケーブル１２５を介して測定対象ガスの雰囲気に出射される。 FIG. 12A is a plan view showing a schematic configuration of a gas concentration measuring device in a conventional frequency modulation method, and FIG. 12B is a side view showing a schematic configuration of the gas concentration measuring device in a conventional frequency modulation method. is there.
In FIG. 12, the light source unit contains a semiconductor laser module 121, a reference gas cell 122, and a photo detector 123, and a Peltier element 128 to which a cooling fin 127 is attached is arranged on the bottom surface of the case body 126 of the light source unit. It is installed. Here, the semiconductor laser module 121 is provided with a semiconductor laser that emits frequency-modulated laser light from both sides, and an optical cable 125 including a connector 125a is extended to be emitted from the semiconductor laser. Light is emitted to the atmosphere of the measurement target gas via the optical cable 125.

また、参照ガスセル１２２は、半導体レーザの後ろ側の光路上に配設され、参照ガスセル１２２を通過したレーザ光は、参照ガスセル１２２の後ろ側に配設されたフォト検出器１２３によって受光検出される。
そして、参照ガスセル１２２を通過したレーザ光を参照しながらペルチェ素子１２８にて半導体レーザの温度制御を行い、２倍波と基本波との比が最大となるように半導体レーザの発光波長を制御することにより、ガスの吸収波長と半導体レーザの発光波長とを合わせることができる。
特開平７−１５１６８１号公報 特開２００１−２３５４１８号公報 The reference gas cell 122 is disposed on the optical path behind the semiconductor laser, and the laser light that has passed through the reference gas cell 122 is received and detected by a photo detector 123 disposed behind the reference gas cell 122. .
Then, the temperature of the semiconductor laser is controlled by the Peltier element 128 while referring to the laser light that has passed through the reference gas cell 122, and the emission wavelength of the semiconductor laser is controlled so that the ratio between the second harmonic and the fundamental wave is maximized. This makes it possible to match the absorption wavelength of the gas with the emission wavelength of the semiconductor laser.
Japanese Patent Laid-Open No. 7-151681 JP 2001-235418 A

しかしながら、従来の周波数変調方式におけるガス濃度の測定方法では、煙道などから排出される複数種類のガスの濃度を同時に計測する場合、１つの半導体レーザで可変できる波長の範囲が狭く、１台の成分計では１成分または特定の２成分しか計測できないため、単成分計を複数台設置する必要がある。このため、設置面積、設置工事費および光軸調整費などが設置台数に比例して増大し、計測システムの大型化や高価格化を招くという問題があった。
そこで、本発明の目的は、発光素子の波長可変範囲を超える吸収特性を持つ複数種類のガスの濃度を単成分計にて計測することが可能なガス濃度測定装置およびガス濃度測定方法を提供することである。 However, in the conventional gas concentration measurement method in the frequency modulation method, when simultaneously measuring the concentrations of a plurality of types of gases discharged from a flue or the like, the wavelength range that can be varied by one semiconductor laser is narrow, and one unit Since the component meter can measure only one component or two specific components, it is necessary to install a plurality of single component meters. For this reason, the installation area, the installation work cost, the optical axis adjustment cost, etc. increase in proportion to the number of installations, and there is a problem that the measurement system is increased in size and price.
Accordingly, an object of the present invention is to provide a gas concentration measuring apparatus and a gas concentration measuring method capable of measuring concentrations of a plurality of types of gases having absorption characteristics exceeding the wavelength variable range of the light emitting element with a single component meter. That is.

上述した課題を解決するために、請求項１記載のガス濃度測定装置によれば、２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を出射する複数の発光素子と、前記発光素子からそれぞれ出射されたレーザ光を共通の変調周波数で周波数変調させる高周波変調信号を発生する高周波変調信号発生部と、前記周波数変調されたレーザ光の発光波長にて測定対象ガスの特定の成分の吸収波長帯をそれぞれスキャンさせる波長走査駆動信号を発生する波長走査駆動信号発生器と、前記高周波変調信号および前記波長走査駆動信号に基づいて前記発光素子をそれぞれ駆動することにより、前記発光素子の発光波長を変調させるレーザ駆動信号発生部と、前記レーザ駆動信号発生部にて駆動される発光素子を時系列的に切り替える切り替え制御手段と、前記レーザ駆動信号発生部にて駆動されるレーザ光の発光波長が前記測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように前記発光素子の温度を設定する温度設定部と、前記レーザ駆動信号発生部にてそれぞれ周波数変調された複数のレーザ光を共通に検出する光検出部と、前記複数の発光素子から出射されたレーザ光を前記光検出部に導く光反射手段と、前記光検出部にて検出されたレーザ光から基本波成分を検出する基本波成分検出部と、前記光検出部にて検出されたレーザ光から２倍波成分を検出する２倍波成分検出部と、前記基本波成分と２倍波成分との振幅比に基づいて、前記レーザ光が透過した測定対象ガスの特定の成分の濃度をそれぞれ算出するガス濃度算出部とを備えることを特徴とする。   In order to solve the above-described problem, according to the gas concentration measuring device of claim 1, a plurality of light emitting elements that emit laser beams having wavelengths respectively corresponding to absorption wavelengths of two or more components of the measurement target gas; A high-frequency modulation signal generating unit that generates a high-frequency modulation signal for frequency-modulating the laser light emitted from each of the light-emitting elements with a common modulation frequency; and a specific gas to be measured at an emission wavelength of the frequency-modulated laser light A wavelength scanning drive signal generator for generating a wavelength scanning driving signal for scanning each absorption wavelength band of the component; and driving the light emitting element based on the high frequency modulation signal and the wavelength scanning driving signal, respectively, The laser drive signal generator for modulating the emission wavelength of the light source and the light emitting elements driven by the laser drive signal generator are switched in time series. And a temperature setting for setting the temperature of the light emitting element so that the emission wavelength of the laser light driven by the laser drive signal generator is in the absorption wavelength band of the specific component of the measurement target gas. , A light detection unit for commonly detecting a plurality of laser beams frequency-modulated by the laser drive signal generation unit, and a light reflection for guiding the laser beams emitted from the plurality of light emitting elements to the light detection unit Means, a fundamental wave component detector for detecting a fundamental wave component from the laser light detected by the light detector, and a second harmonic for detecting a second harmonic component from the laser light detected by the light detector. A component detection unit, and a gas concentration calculation unit that calculates a concentration of a specific component of the measurement target gas transmitted by the laser beam based on an amplitude ratio between the fundamental wave component and the second harmonic component. Features and That.

また、請求項２記載のガス濃度測定装置によれば、前記複数の発光素子の一部は、レーザ光の発光波長が前記測定対象ガスの吸収波長帯にかからないように選択されることを特徴とする。
また、請求項３記載のガス濃度測定方法によれば、２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を共通の変調周波数で周波数変調させるステップと、前記周波数変調されたレーザ光の発光波長が測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように、前記レーザ光をそれぞれ出射する発光素子の温度を設定するステップと、前記周波数変調されたレーザ光の発光波長を測定対象ガスの特定の成分の吸収波長帯がスキャンされるようにそれぞれ変化させながら、前記測定対象ガスに前記レーザ光を順次入射させるステップと、前記測定対象ガスを順次透過したレーザ光を共通の検出器にて検出するステップと、前記検出器にて順次検出されたレーザ光から基本波成分および２倍波成分を抽出するステップと、前記抽出された基本波成分および２倍波成分に基づいて、前記レーザ光が透過した測定対象ガスの特定の成分の濃度をそれぞれ算出するステップとを備えることを特徴とする。 According to the gas concentration measuring apparatus of claim 2, a part of the plurality of light emitting elements is selected so that an emission wavelength of a laser beam does not reach an absorption wavelength band of the measurement target gas. To do.
According to the gas concentration measurement method of claim 3, the step of frequency-modulating laser light having wavelengths respectively corresponding to the absorption wavelengths of the gas to be measured having two or more components at a common modulation frequency, and the frequency modulation Setting the temperature of each light emitting element that emits the laser light so that the emission wavelength of the laser light is applied to the absorption wavelength band of the specific component of the measurement target gas, and the emission of the frequency-modulated laser light Sequentially changing the wavelength so that the absorption wavelength band of a specific component of the measurement target gas is scanned, and sequentially entering the laser light into the measurement target gas; and laser light sequentially passing through the measurement target gas A step of detecting by a common detector, and a step of extracting a fundamental wave component and a second harmonic component from the laser light sequentially detected by the detector. And-up, on the basis of the extracted fundamental frequency component and second harmonic component, characterized in that it comprises a step of calculating the concentration of a particular component of the measurement object gas to the laser light is transmitted, respectively.

また、請求項４記載のガス濃度測定方法によれば、２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を共通の変調周波数で周波数変調させるステップと、前記周波数変調されたレーザ光の発光波長が測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように、前記レーザ光をそれぞれ出射する発光素子の温度を設定するステップと、前記周波数変調されたレーザ光の発光波長を測定対象ガスの特定の成分の吸収波長帯がスキャンされるようにそれぞれ変化させながら、前記測定対象ガスに前記レーザ光を順次入射させるステップと、前記測定対象ガスを順次透過したレーザ光を共通の検出器にて検出するステップと、前記検出器にて順次検出されたレーザ光から基本波成分および２倍波成分を抽出するステップと、前記抽出された基本波成分および２倍波成分に基づいて、前記レーザ光が透過した測定対象ガスの特定の成分の濃度をそれぞれ算出するステップと、前記測定対象ガスの吸収波長にかからない波長を有するレーザ光を前記変調周波数で周波数変調させるステップと、前記測定対象ガスの吸収波長にかからない波長を有するレーザ光を前記測定対象ガスに入射させるステップと、前記測定対象ガスの吸収波長にかからない波長を有するレーザ光を前記検出器にて検出するステップと、前記検出器にて検出された前記測定対象ガスの吸収波長にかからない波長を有するレーザ光から基本波成分および２倍波成分を抽出するステップと、前記測定対象ガスの吸収波長にかからない波長を有するレーザ光から抽出された基本波成分および２倍波成分に基づいて、前記レーザ光が透過した測定対象ガスの濃度を補正するステップとを備えることを特徴とする。   According to the gas concentration measuring method of claim 4, the step of frequency-modulating laser light having wavelengths respectively corresponding to the absorption wavelengths of the gas to be measured having two or more components at a common modulation frequency, and the frequency modulation Setting the temperature of each light emitting element that emits the laser light so that the emission wavelength of the laser light is applied to the absorption wavelength band of the specific component of the measurement target gas, and the emission of the frequency-modulated laser light Sequentially changing the wavelength so that the absorption wavelength band of a specific component of the measurement target gas is scanned, and sequentially entering the laser light into the measurement target gas; and laser light sequentially passing through the measurement target gas A step of detecting by a common detector, and a step of extracting a fundamental wave component and a second harmonic component from the laser light sequentially detected by the detector. And calculating the concentration of the specific component of the measurement target gas transmitted by the laser beam based on the extracted fundamental wave component and the second harmonic component, and the absorption wavelength of the measurement target gas. A step of frequency-modulating a laser beam having a wavelength that is not affected by the modulation frequency, a step of causing a laser beam having a wavelength that does not depend on the absorption wavelength of the measurement target gas to be incident on the measurement target gas, and an absorption wavelength of the measurement target gas A step of detecting a laser beam having a wavelength that is not affected by the detector, and extracting a fundamental wave component and a second harmonic component from the laser beam having a wavelength that is not affected by the absorption wavelength of the measurement target gas detected by the detector; A fundamental wave component extracted from a laser beam having a wavelength that does not depend on the absorption wavelength of the measurement target gas, and 2 Based on the wave component, characterized in that it comprises a step of correcting the concentration of the measurement target gas in which the laser light is transmitted.

以上説明したように、本発明によれば、発光波長が互いに異なる複数の発光素子からレーザ光を時系列的に出射させ、吸収波長が互いに異なる２成分以上の測定対象ガスを透過させてから、単一の光検出部にて検出することにより、単一の発光素子の波長可変範囲を超える吸収特性を持つ複数種類のガスの濃度を単成分計にて計測することが可能となり、計測システムの大型化や高価格化を抑制しつつ、煙道などから排出される複数種類のガスの濃度を計測することができる。   As described above, according to the present invention, laser light is emitted from a plurality of light emitting elements having different emission wavelengths from each other in time series, and two or more measurement target gases having different absorption wavelengths are allowed to pass through. By detecting with a single light detector, it is possible to measure the concentration of multiple types of gases with absorption characteristics exceeding the wavelength variable range of a single light emitting element with a single component meter. It is possible to measure the concentration of multiple types of gas discharged from a flue while suppressing the increase in size and price.

以下、本発明の実施形態に係るガス濃度測定装置について図面を参照しながら説明する。
図１は、本発明の一実施形態に係るガス濃度測定装置における光学系の概略構成を示す断面図である。
図１において、ガス濃度測定装置の送信側の光学系には、２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を出射する複数の発光素子５ａ〜５ｄ、発光素子５ａ〜５ｄからそれぞれ出射されたレーザ光の光軸を同一方向に一致させるプリズム型ミラー６が設けられている。なお、プリズム型ミラー６には、反射面を４面設けることができ、発光素子５ａ〜５ｄからそれぞれ出射されたレーザ光をプリズム型ミラー６の各面で反射させることにより、発光素子５ａ〜５ｄからそれぞれ出射されたレーザ光の光軸を同一方向に一致させることができる。なお、発光素子５ａ〜５ｄとしては、ＤＦＢレーザ（Ｄｉｓｔｒｉｂｕｔｅｄ Ｆｅｅｄｂａｃｋ Ｌａｓｅｒ）やＶＣＳＥＬ（Ｖｅｒｔｉｃａｌ Ｃａｖｉｔｙ Ｓｕｒｆａｃｅ Ｅｍｉｔｔｉｎｇ Ｌａｓｅｒ）などの半導体レーザを用いることができる。 Hereinafter, a gas concentration measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of an optical system in a gas concentration measuring apparatus according to an embodiment of the present invention.
In FIG. 1, the optical system on the transmission side of the gas concentration measuring device includes a plurality of light emitting elements 5a to 5d that emit laser beams having wavelengths respectively corresponding to absorption wavelengths of two or more components of the measurement target gas, and light emitting elements 5a. A prism-type mirror 6 is provided to match the optical axes of the laser beams emitted from .about.5d in the same direction. The prism-type mirror 6 can be provided with four reflecting surfaces, and the light beams emitted from the light-emitting elements 5a to 5d are reflected by the respective surfaces of the prism-type mirror 6 so that the light-emitting elements 5a to 5d are reflected. The optical axes of the laser beams respectively emitted from can be made to coincide with each other in the same direction. As the light emitting elements 5a to 5d, a semiconductor laser such as a DFB laser (Distributed Feedback Laser) or a VCSEL (Vertical Cavity Surface Emitting Laser) can be used.

また、ガス濃度測定装置の受信側の光学系には、測定対象ガスを透過したレーザ光を集光する集光レンズ９、測定対象ガスを透過したレーザ光を検出する受光素子１０が設けられている。なお、受光素子１０としては、例えば、フォトダイオードを用いることができる。そして、受光素子１０は、測定対象ガスを透過したレーザ光の基本波成分と２倍波成分との振幅比を算出する信号処理装置１１に接続されている。   The optical system on the receiving side of the gas concentration measuring device is provided with a condenser lens 9 that condenses the laser light that has passed through the measurement target gas, and a light receiving element 10 that detects the laser light that has passed through the measurement target gas. Yes. For example, a photodiode can be used as the light receiving element 10. The light receiving element 10 is connected to a signal processing device 11 that calculates an amplitude ratio between the fundamental wave component and the second harmonic component of the laser light that has passed through the measurement target gas.

ここで、発光素子５ａ〜５ｄおよびプリズム型ミラー６はハウジング４に収容されるとともに、集光レンズ９、受光素子１０、および信号処理装置１１はハウジング８に収容されている。そして、煙道などの測定対象ガスが流れる配管などの隔壁１ａ、１ｂには、固定フランジ２ａ、２ｂが溶接などの方法にて取り付けられる。そして、発光素子５ａ〜５ｄおよびプリズム型ミラー６が収容されたハウジング４は、光軸調整用の調整フランジ３ａを介してフランジ２ａに取り付けられるとともに、ウェッジ窓７ａにて配管内と仕切られている。また、集光レンズ９、受光素子１０、および信号処理装置１１が収容されたハウジング８は、光軸調整用の調整フランジ３ｂを介してフランジ２ｂに取り付けられるとともに、ウェッジ窓７ｂにて配管内と仕切られている。なお、ウェッジ窓７ａ、７ｂとしては、溶融石英などを材料として構成することができる。   Here, the light emitting elements 5 a to 5 d and the prism type mirror 6 are accommodated in the housing 4, and the condenser lens 9, the light receiving element 10, and the signal processing device 11 are accommodated in the housing 8. Then, fixed flanges 2a and 2b are attached to partition walls 1a and 1b such as pipes through which a measurement target gas flows such as a flue by a method such as welding. The housing 4 in which the light emitting elements 5a to 5d and the prism type mirror 6 are accommodated is attached to the flange 2a via the adjustment flange 3a for adjusting the optical axis, and is partitioned from the inside of the pipe by the wedge window 7a. . The housing 8 in which the condenser lens 9, the light receiving element 10, and the signal processing device 11 are accommodated is attached to the flange 2b via the adjustment flange 3b for adjusting the optical axis, and is connected to the inside of the pipe by the wedge window 7b. It is partitioned. The wedge windows 7a and 7b can be made of fused quartz or the like.

そして、中心周波数ｆｃ、変調周波数ｆｍで発光素子５ａ〜５ｄの出力が周波数変調されるとともに、測定対象ガスの特定の成分の吸収波長帯がそれぞれスキャンされるようにレーザ光の発光波長が変化されながら、発光素子５ａ〜５ｄからレーザ光が順次出射される。そして、発光素子５ａ〜５ｄから出射されたレーザ光は、プリズム型ミラー６にて受光素子１０の方向に反射された後、ウェッジ窓７ａを介して隔壁１ａ、１ｂ間の測定対象ガスを透過する。そして、測定対象ガスを透過したレーザ光は、測定対象ガスのガス分子の吸収線に対応した波長の吸収を受けた後、ウェッジ窓１ｂを介して集光レンズ９に入射し、集光レンズ９にて受光素子１０の受光面上に集光される。そして、受光素子１０にレーザ光が入射すると、受光素子１０にて電気信号に変換され、その電気信号が信号処理装置１１に送られる。そして、受光素子１０にて変換された電気信号が信号処理装置１１に送られると、測定対象ガスの特定の成分の吸収波長帯にかかる部分についての基本波成分と２倍波成分との振幅比が信号処理装置１１にて順次算出され、測定対象ガスの特定の成分の濃度を順次算出することができる。   The output of the light emitting elements 5a to 5d is frequency-modulated at the center frequency fc and the modulation frequency fm, and the emission wavelength of the laser light is changed so that the absorption wavelength band of a specific component of the measurement target gas is scanned. However, laser light is sequentially emitted from the light emitting elements 5a to 5d. The laser light emitted from the light emitting elements 5a to 5d is reflected by the prism type mirror 6 in the direction of the light receiving element 10, and then passes through the measurement target gas between the partition walls 1a and 1b through the wedge window 7a. . The laser light that has passed through the measurement target gas is absorbed at a wavelength corresponding to the absorption line of the gas molecules of the measurement target gas, and then enters the condenser lens 9 through the wedge window 1b. Is condensed on the light receiving surface of the light receiving element 10. When the laser light is incident on the light receiving element 10, the light receiving element 10 converts the laser light into an electric signal, and the electric signal is sent to the signal processing device 11. Then, when the electrical signal converted by the light receiving element 10 is sent to the signal processing device 11, the amplitude ratio between the fundamental wave component and the second harmonic component for the portion of the specific component of the measurement target gas that falls within the absorption wavelength band. Are sequentially calculated by the signal processing device 11, and the concentration of the specific component of the measurement target gas can be sequentially calculated.

これにより、発光波長が互いに異なる複数の発光素子５ａ〜５ｄからレーザ光を時系列的に出射させ、吸収波長が互いに異なる２成分以上の測定対象ガスを透過させてから、単一の受光素子１０にて検出することができる。このため、単一の発光素子５ａ〜５ｄの波長可変範囲を超える吸収特性を持つ複数種類のガスの濃度を単成分計にて計測することが可能となり、計測システムの大型化や高価格化を抑制しつつ、煙道などから排出される複数種類のガスの濃度を計測することができる。   Thereby, laser light is emitted from a plurality of light emitting elements 5a to 5d having different emission wavelengths in a time series, and two or more measurement target gases having different absorption wavelengths are transmitted, and then a single light receiving element 10 is received. Can be detected. For this reason, it becomes possible to measure the concentration of a plurality of types of gases having absorption characteristics exceeding the wavelength variable range of the single light emitting elements 5a to 5d with a single component meter, thereby increasing the size and cost of the measurement system. While suppressing, it is possible to measure the concentrations of a plurality of types of gases discharged from a flue or the like.

図２は、図１のガス濃度測定装置における送信側の信号処理部の概略構成を示すブロック図である。
図２において、ガス濃度測定装置の送信側には、複数の発光素子５ａ〜５ｄが設けられ、発光素子５ａ〜５ｄには、発光素子５ａ〜５ｄの温度をそれぞれ検出する温度検出素子１６ａ〜１６ｄおよび発光素子５ａ〜５ｄの温度をそれぞれ調整する温度調整素子１７ａ〜１７ｄが搭載されている。なお、温度検出素子１６ａ〜１６ｄとしては、例えば、サーミスタ、温度調整素子１７ａ〜１７ｄとしては、例えば、ペルチェ素子を用いることができる。また、温度検出素子１６ａ〜１６ｄは、発光素子５ａ〜５ｄに直接接触させることなく、アルミニウムなどの熱伝導性のよい材料に穴を空け、熱伝導性のよいシリコーンなどの樹脂を用いることで、サーミスタなどの温度検出素子１６ａ〜１６ｄをその穴に埋め込むようにしてもよい。 FIG. 2 is a block diagram showing a schematic configuration of a signal processing unit on the transmission side in the gas concentration measuring apparatus of FIG.
In FIG. 2, a plurality of light emitting elements 5a to 5d are provided on the transmission side of the gas concentration measuring device, and the temperature detecting elements 16a to 16d for detecting the temperatures of the light emitting elements 5a to 5d, respectively. Temperature adjusting elements 17a to 17d for adjusting the temperatures of the light emitting elements 5a to 5d are mounted. As the temperature detection elements 16a to 16d, for example, a thermistor, and as the temperature adjustment elements 17a to 17d, for example, Peltier elements can be used. In addition, the temperature detection elements 16a to 16d are not directly in contact with the light emitting elements 5a to 5d, but a hole is made in a material having good thermal conductivity such as aluminum, and a resin such as silicone having good thermal conductivity is used. Temperature detecting elements 16a to 16d such as thermistors may be embedded in the holes.

そして、ペルチェ素子などの温度調整素子１７ａ〜１７ｄは、温度検出素子１６ａ〜１６ｄが埋め込まれたアルミブロックを介して発光素子５ａ〜５ｄに装着することができる。
なお、発光素子５ａ〜５ｄの温度を制御する温度制御素子としては、例えば、マキシム社製ＭＡＸ１９７８やリニアテクノロジ社製ＬＴＣ１９２３などを用いることができる。 The temperature adjusting elements 17a to 17d such as Peltier elements can be attached to the light emitting elements 5a to 5d through an aluminum block in which the temperature detecting elements 16a to 16d are embedded.
As the temperature control element for controlling the temperature of the light emitting elements 5a to 5d, for example, MAX1978 manufactured by Maxim, LTC1923 manufactured by Linear Technology, or the like can be used.

また、発光素子５ａ〜５ｄからそれぞれ出射されたレーザ光を共通の変調周波数で周波数変調させる高周波変調信号を発生する高周波変調信号発生部１３ａ〜１３ｄ、周波数変調されたレーザ光の発光波長にて測定対象ガスの特定の成分の吸収波長帯をそれぞれスキャンさせる波長走査駆動信号を発生する波長走査駆動信号発生器１２、高周波変調信号発生部１３ａ〜１３ｄにてそれぞれ発生された高周波変調信号および波長走査駆動信号発生器１２にてそれぞれ発生された波長走査駆動信号に基づいて発光素子５ａ〜５ｄをそれぞれ駆動することにより、発光素子５ａ〜５ｄの発光波長を変調させるレーザ駆動信号発生部１４ａ〜１４ｄ、レーザ駆動信号発生部１４ａ〜１４ｄにてそれぞれ駆動される発光素子５ａ〜５ｄを時系列的に切り替える切り替え制御部１９、温度検出素子１６ａ〜１６ｄにて検出された温度に基づいて温度調整素子１７ａ〜１７ｄを駆動する温度制御回路１８ａ〜１８ｄが設けられている。   Further, high frequency modulation signal generators 13a to 13d that generate high frequency modulation signals for frequency-modulating the laser beams emitted from the light emitting elements 5a to 5d with a common modulation frequency, measured at the emission wavelength of the frequency modulated laser light The wavelength scanning drive signal generator 12 for generating the wavelength scanning drive signal for scanning the absorption wavelength band of the specific component of the target gas and the high frequency modulation signal and the wavelength scanning drive generated by the high frequency modulation signal generators 13a to 13d, respectively. Laser drive signal generators 14a to 14d that modulate the emission wavelengths of the light emitting elements 5a to 5d by driving the light emitting elements 5a to 5d based on the wavelength scanning drive signals respectively generated by the signal generator 12, and lasers The light emitting elements 5a to 5d respectively driven by the drive signal generators 14a to 14d are cut in time series. Switching control unit 19 to obtain, the temperature control circuit 18a~18d for driving the temperature adjustment element 17a~17d are provided on the basis of the temperature detected by the temperature detecting element 16 a to 16 d.

そして、温度検出素子１６ａ〜１６ｄにて検出された温度は温度制御回路１８ａ〜１８ｄに入力され、温度制御回路１８ａ〜１８ｄは、温度検出素子１６ａ〜１６ｄにて検出された温度に基づいて温度調整素子１７ａ〜１７ｄを駆動することにより、発光素子５ａ〜５ｄから出射されるレーザ光の発光波長が測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように発光素子５ａ〜５ｄの温度をそれぞれ制御する。例えば、温度制御回路１８ａ〜１８ｄは、温度検出素子１６ａ〜１６ｄとして用いられるサーミスタの抵抗値が一定になるように、温度調整素子１７ａ〜１７ｄとして用いられるペルチェ素子のＰＩＤ制御などを行うことにより、発光素子５ａ〜５ｄの温度を調整し、発光素子５ａ〜５ｄから出射されるレーザ光の発光波長を一定に保つことができる。   The temperatures detected by the temperature detection elements 16a to 16d are input to the temperature control circuits 18a to 18d, and the temperature control circuits 18a to 18d adjust the temperature based on the temperatures detected by the temperature detection elements 16a to 16d. By driving the elements 17a to 17d, the temperatures of the light emitting elements 5a to 5d are respectively set so that the emission wavelength of the laser light emitted from the light emitting elements 5a to 5d is applied to the absorption wavelength band of the specific component of the measurement target gas. Control. For example, the temperature control circuits 18a to 18d perform PID control of the Peltier elements used as the temperature adjustment elements 17a to 17d so that the resistance values of the thermistors used as the temperature detection elements 16a to 16d are constant. By adjusting the temperature of the light emitting elements 5a to 5d, the emission wavelength of the laser light emitted from the light emitting elements 5a to 5d can be kept constant.

そして、レーザ駆動信号発生部１４ａ〜１４ｄは切り替え制御部１９にて時系列的に選択されながら、波長走査駆動信号発生器１２にて発生された波長走査駆動信号および高周波変調信号発生部１３ａ〜１３ｄにてそれぞれ発生された高周波変調信号がレーザ駆動信号発生部１４ａ〜１４ｄに順次入力される。
そして、レーザ駆動信号発生部１４ａ〜１４ｄに順次入力された波長走査駆動信号および高周波変調信号は、レーザ駆動信号発生部１４ａ〜１４ｄにてそれぞれ合成され、電圧−電流変換処理が行われた後、発光素子５ａ〜５ｄに順次注入される。そして、発光素子５ａ〜５ｄに電流が順次注入されると、測定対象ガスの特定の成分の吸収波長帯をそれぞれスキャンする波長帯で発光素子５ａ〜５ｄが順次発光し、図１のプリズム型ミラー６を介して測定対象ガスに入射した後、受光素子１０にて検出される。 The laser drive signal generators 14a to 14d are selected in time series by the switching controller 19 while the wavelength scan drive signal and high frequency modulation signal generators 13a to 13d generated by the wavelength scan drive signal generator 12 are selected. Are sequentially input to the laser drive signal generators 14a to 14d.
Then, the wavelength scanning drive signal and the high frequency modulation signal sequentially input to the laser drive signal generators 14a to 14d are respectively combined by the laser drive signal generators 14a to 14d and subjected to voltage-current conversion processing. The light is sequentially injected into the light emitting elements 5a to 5d. When current is sequentially injected into the light emitting elements 5a to 5d, the light emitting elements 5a to 5d sequentially emit light in the wavelength bands for scanning the absorption wavelength bands of specific components of the measurement target gas, and the prism type mirror of FIG. After being incident on the measurement target gas via 6, the light receiving element 10 detects the light.

なお、図２の実施形態では、発光素子５ａ〜５ｄに対して波長走査駆動信号発生器１２を共通に設けるとともに、高周波変調信号発生部１３ａ〜１３ｄを個別に設ける方法について説明したが、高周波変調信号発生部１３ａ〜１３ｄは発光素子５ａ〜５ｄに対して共通に設けるようにしてもよい。ただし、受光素子１０にて検出された信号の信号処理を同一の回路で行えるようにするために、高周波変調信号の周波数は同一に設定するのが好ましい。なお、高周波変調信号の周波数は同一に設定した場合、波長スキャン幅や波長変調幅は互いに異なっていてもよい。   In the embodiment of FIG. 2, the wavelength scanning drive signal generator 12 is provided in common for the light emitting elements 5 a to 5 d and the high frequency modulation signal generators 13 a to 13 d are individually provided. The signal generators 13a to 13d may be provided in common for the light emitting elements 5a to 5d. However, it is preferable to set the frequency of the high frequency modulation signal to be the same so that the signal detected by the light receiving element 10 can be processed by the same circuit. When the frequency of the high frequency modulation signal is set to be the same, the wavelength scan width and the wavelength modulation width may be different from each other.

図３は、図１のガス濃度測定装置における受信側の信号処理部の概略構成を示すブロック図である。
図３において、ガス濃度測定装置の受信側には、発光素子５ａ〜５ｄからそれぞれ出射されたレーザ光を共通に検出する受光素子１０、受光素子１０から出力される電流を電圧に変換するＩ−Ｖ変換回路２５、高周波変調信号の２倍の周波数の信号を発生させる参照信号発生器２６、Ｉ−Ｖ変換回路２５の出力から高周波変調信号の２倍の周波数成分を抽出する同期検波器２７、同期検波器２７の出力から不要な帯域成分を除去するフィルタ２８が設けられている。 FIG. 3 is a block diagram showing a schematic configuration of a signal processing unit on the receiving side in the gas concentration measuring apparatus of FIG.
In FIG. 3, on the receiving side of the gas concentration measuring apparatus, a light receiving element 10 for commonly detecting the laser beams emitted from the light emitting elements 5a to 5d, and an I− for converting a current output from the light receiving element 10 into a voltage. A V conversion circuit 25; a reference signal generator 26 for generating a signal having a frequency twice that of the high frequency modulation signal; a synchronous detector 27 for extracting a frequency component twice the high frequency modulation signal from the output of the IV conversion circuit 25; A filter 28 for removing unnecessary band components from the output of the synchronous detector 27 is provided.

そして、発光素子５ａ〜５からそれぞれ出射されたレーザ光は測定対象ガスを通過すると、測定対象ガスの特定の成分による吸収量に対応した減衰を受けた後、受光素子１０に入射し、受光素子１０にてレーザ光が検出される。そして、受光素子１０にて検出された電流はＩ−Ｖ変換回路２５にて電圧に変換され、参照信号発生器２６にて発生された２倍周波数信号とＩ−Ｖ変換回路２５からの出力が同期検波器２７にて合成されることにより、Ｉ−Ｖ変換回路２５の出力から高周波変調信号の２倍の周波数成分が抽出され、フィルタ２８にてノイズが除去される。   Then, when the laser light emitted from each of the light emitting elements 5a to 5 passes through the measurement target gas, after being attenuated corresponding to the amount of absorption by a specific component of the measurement target gas, the laser light enters the light receiving element 10 and then enters the light receiving element. At 10, laser light is detected. The current detected by the light receiving element 10 is converted into a voltage by the IV conversion circuit 25, and the double frequency signal generated by the reference signal generator 26 and the output from the IV conversion circuit 25 are output. By synthesizing by the synchronous detector 27, a frequency component twice the high frequency modulation signal is extracted from the output of the IV conversion circuit 25, and noise is removed by the filter 28.

図４は、本発明の一実施形態に係る周波数変調方式によるガス濃度の測定原理を説明する図である。
図４において、中心周波数ｆｃ、変調周波数ｆｍで発光素子５ａ〜５ｄの出力をそれぞれ周波数変調し、測定対象ガスに照射されたものとする。ここで、測定対象ガスの吸収線は変調周波数に対してほぼ２次関数となっているので、この吸収線が弁別器の役割を果たし、受光素子１０では変調周波数ｆｍの２倍の周波数の成分（２倍波成分）が得られる。ここで、変調周波数ｆｍは任意の周波数でよいので、例えば、変調周波数ｆｍを数ｋＨｚ程度に選ぶと、ディジタル信号処理装置（ＤＳＰ）または汎用のプロセッサを用い高度な信号処理を施すことが可能となる。 FIG. 4 is a view for explaining the principle of measuring the gas concentration by the frequency modulation method according to one embodiment of the present invention.
In FIG. 4, it is assumed that the outputs of the light emitting elements 5a to 5d are frequency-modulated at the center frequency fc and the modulation frequency fm, respectively, and irradiated to the measurement target gas. Here, since the absorption line of the measurement target gas has a substantially quadratic function with respect to the modulation frequency, this absorption line serves as a discriminator, and the light receiving element 10 has a frequency component twice the modulation frequency fm. (Double wave component) is obtained. Here, since the modulation frequency fm may be an arbitrary frequency, for example, when the modulation frequency fm is selected to be about several kHz, it is possible to perform advanced signal processing using a digital signal processing device (DSP) or a general-purpose processor. Become.

そして、発光素子５ａ〜５ｄと受光素子１０との距離に起因するレーザ光の減衰量の影響を周波数変調方式にてキャンセルするためには、発光素子５ａ〜５ｄの出力に周波数変調を行うと同時に変調周波数ｆｍで振幅変調を行えばよく、発光素子５ａ〜５ｄの出力に周波数変調をかけることで振幅変調もかけることができる。そして、光検出側でエンベロープ検波をそれぞれ行うことで振幅変調による基本波成分を推定することができ、この基本波成分の振幅と２倍波成分の振幅の比を位相同期させて取ることで、発光素子５ａ〜５ｄと受光素子１０との距離に依存することなく、測定対象ガスの濃度に比例した値をそれぞれ得ることができる。   In order to cancel the influence of the attenuation amount of the laser light caused by the distance between the light emitting elements 5a to 5d and the light receiving element 10 by the frequency modulation method, the output of the light emitting elements 5a to 5d is simultaneously subjected to frequency modulation. Amplitude modulation may be performed at the modulation frequency fm, and amplitude modulation can also be performed by applying frequency modulation to the outputs of the light emitting elements 5a to 5d. Then, by performing envelope detection on the light detection side, the fundamental wave component by amplitude modulation can be estimated, and by taking the phase ratio of the ratio of the amplitude of the fundamental wave component and the amplitude of the second harmonic component, A value proportional to the concentration of the measurement target gas can be obtained without depending on the distance between the light emitting elements 5a to 5d and the light receiving element 10.

図５は、本発明の一実施形態に係る駆動電流と半導体レーザの発光波長との関係を示す図である。
図５において、発光素子５ａ〜５ｄからそれぞれ出射されるレーザ光の発光波長は駆動電流が増加するに従って長くなる。このため、発光素子５ａ〜５ｄの駆動電流を制御することにより、発光素子５ａ〜５ｄからそれぞれ出射されるレーザ光の発光波長を調整することができる。
図６は、本発明の一実施形態に係る温度と半導体レーザの発光波長との関係を示す図である。
図６において、発光素子５ａ〜５ｄからそれぞれ出射されるレーザ光の発光波長は温度が増加するに従って長くなる。このため、発光素子５ａ〜５ｄの温度を制御することにより、発光素子５ａ〜５ｄからそれぞれ出射されるレーザ光の発光波長を調整することができる。 FIG. 5 is a diagram showing the relationship between the drive current and the emission wavelength of the semiconductor laser according to one embodiment of the present invention.
In FIG. 5, the emission wavelength of the laser light emitted from each of the light emitting elements 5a to 5d becomes longer as the drive current increases. For this reason, the emission wavelength of the laser beam emitted from each of the light emitting elements 5a to 5d can be adjusted by controlling the drive current of the light emitting elements 5a to 5d.
FIG. 6 is a diagram showing the relationship between the temperature and the emission wavelength of the semiconductor laser according to one embodiment of the present invention.
In FIG. 6, the emission wavelength of the laser light emitted from each of the light emitting elements 5a to 5d becomes longer as the temperature increases. For this reason, the emission wavelength of the laser light emitted from each of the light emitting elements 5a to 5d can be adjusted by controlling the temperature of the light emitting elements 5a to 5d.

図７（ａ）は、図２の波長走査駆動信号発生器１２にて生成される電流波形を示す図、図７（ｂ）は、図２の高周波変調信号発生部１３ａ〜１３ｄにて生成される電流波形を示す図、図７（ｃ）は、図７（ａ）の電流波形と図７（ｂ）の電流波形とが合成された信号を印加した時に発光素子５ａ〜５ｄから出射される光の波長の変化を示す図である。
図７において、図２の波長走査駆動信号発生器１２にて発生される波長走査信号は、強度が一定に保たれた部分２０と、強度が台形状に直線的に増加する部分１９と、強度が０である部分２１とから構成することができる。ここで、強度が台形状に直線的に増加する部分１９は、測定対象ガスの特定の成分の吸収波長帯が走査されるように、発光素子５ａ〜５ｄからそれぞれ出射されるレーザ光の波長を徐々に変化させることができる。 7A is a diagram showing a current waveform generated by the wavelength scanning drive signal generator 12 of FIG. 2, and FIG. 7B is generated by the high frequency modulation signal generators 13a to 13d of FIG. FIG. 7C is a diagram showing the current waveform to be emitted from the light emitting elements 5a to 5d when a signal obtained by synthesizing the current waveform of FIG. 7A and the current waveform of FIG. 7B is applied. It is a figure which shows the change of the wavelength of light.
7, the wavelength scanning signal generated by the wavelength scanning drive signal generator 12 of FIG. 2 includes a portion 20 where the intensity is kept constant, a portion 19 where the intensity increases linearly in a trapezoidal shape, and an intensity. And a portion 21 in which is zero. Here, the portion 19 where the intensity increases linearly in a trapezoidal shape is the wavelength of the laser light emitted from each of the light emitting elements 5a to 5d so that the absorption wavelength band of a specific component of the measurement target gas is scanned. It can be changed gradually.

そして、測定対象ガスの濃度を測定する場合、図２の温度制御回路１８ａ〜１８ｄは、温度検出素子１６ａ〜１６ｄにて検出された温度を参照しながら温度調整素子１７ａ〜１７ｄを駆動することにより、波長走査信号の強度が直線的に増加する部分１９の中心付近で測定対象ガスの特定の成分の濃度が検出されるように、発光素子５ａ〜５ｄの温度をそれぞれ事前に設定する。   And when measuring the density | concentration of measurement object gas, the temperature control circuits 18a-18d of FIG. 2 drive temperature adjustment element 17a-17d, referring the temperature detected by temperature detection element 16a-16d. The temperatures of the light emitting elements 5a to 5d are set in advance so that the concentration of a specific component of the measurement target gas is detected near the center of the portion 19 where the intensity of the wavelength scanning signal increases linearly.

そして、図２の波長走査駆動信号発生器１２は、発光素子５ａ〜５ｄの発光をそれぞれ安定化させるために、波長走査信号の強度が一定に保たれた部分２０が発光素子５ａ〜５ｄのスレッショルドカレント以上になるようにして一定に保ちながら、波長走査信号の強度が一定に保たれた部分２０をレーザ駆動信号発生部１４ａ〜１４ｄに出力するとともに、高周波変調信号発生部１３ａ〜１３ｄは周波数が１０ｋＨｚ、波長変調幅が０．０２ｎｍの正弦波からなる高周波変調信号２２をレーザ駆動信号発生部１４ａ〜１４ｄにそれぞれ出力する。   The wavelength scanning drive signal generator 12 shown in FIG. 2 has a portion 20 where the intensity of the wavelength scanning signal is kept constant to stabilize the light emission of the light emitting elements 5a to 5d. While maintaining the current scanning current constant or higher, the portion 20 in which the intensity of the wavelength scanning signal is kept constant is output to the laser drive signal generators 14a to 14d, and the high frequency modulation signal generators 13a to 13d have a frequency. A high frequency modulation signal 22 composed of a sine wave having a frequency of 10 kHz and a wavelength modulation width of 0.02 nm is output to each of the laser drive signal generators 14a to 14d.

そして、波長走査信号の強度が一定に保たれた部分２０と高周波変調信号２２とはレーザ駆動信号発生部１４ａ〜１４ｄにてそれぞれ合成され、波長走査信号の強度が一定に保たれた部分２０と高周波変調信号２２が合成された信号に基づいて発光素子５ａ〜５ｄの電流がそれぞれ制御されることにより、測定対象ガスによる吸収を受けない波長を中心として１０ｋＨｚ程度の正弦波にてレーザ光が周波数変調される。   Then, the portion 20 where the intensity of the wavelength scanning signal is kept constant and the high frequency modulation signal 22 are respectively combined by the laser drive signal generators 14a to 14d, and the portion 20 where the intensity of the wavelength scanning signal is kept constant, By controlling the currents of the light emitting elements 5a to 5d based on the signal obtained by synthesizing the high frequency modulation signal 22, the laser light has a frequency of a sine wave of about 10 kHz around the wavelength that is not absorbed by the measurement target gas. Modulated.

そして、周波数変調されたレーザ光は測定対象ガスを通過すると、測定対象ガスによる吸収を受けることなく受光素子１０に入射し、受光素子１０にてレーザ光が検出される。そして、受光素子１０にて検出された電流はＩ−Ｖ変換回路２５にて電圧に変換され、参照信号発生器２６にて発生された２倍周波数信号とＩ−Ｖ変換回路２５からの出力が同期検波器２７にて合成されることにより、Ｉ−Ｖ変換回路２５の出力から高周波変調信号２２の２倍の周波数成分が抽出される。ここで、測定対象ガスによる吸収を受けない波長を中心としてレーザ光が周波数変調されると、Ｉ−Ｖ変換回路２５の出力から高周波変調信号２２の２倍の周波数成分が抽出されることはなく、同期検波器２７からの出力は一定となる。   When the frequency-modulated laser light passes through the measurement target gas, it enters the light receiving element 10 without being absorbed by the measurement target gas, and the laser light is detected by the light receiving element 10. The current detected by the light receiving element 10 is converted into a voltage by the IV conversion circuit 25, and the double frequency signal generated by the reference signal generator 26 and the output from the IV conversion circuit 25 are output. By synthesizing by the synchronous detector 27, a frequency component twice as high as the high frequency modulation signal 22 is extracted from the output of the IV conversion circuit 25. Here, when the laser light is frequency-modulated around a wavelength that is not absorbed by the measurement target gas, a frequency component that is twice the high-frequency modulation signal 22 is not extracted from the output of the IV conversion circuit 25. The output from the synchronous detector 27 is constant.

次に、図２の波長走査駆動信号発生器１２は、測定対象ガスの特定の成分の吸収波長帯をスキャンさせるために、波長走査信号の強度を台形状に直線的に増加させることで、波長走査信号の強度が台形状に直線的に増加する部分１９をレーザ駆動信号発生部１４ａ〜１４ｄに出力するとともに、高周波変調信号発生部１３ａ〜１３ｄは周波数が１０ｋＨｚ、波長変調幅が０．０２ｎｍの正弦波からなる高周波変調信号２２をレーザ駆動信号発生部１４ａ〜１４ｄにそれぞれ出力する。なお、波長走査駆動信号発生器１２は、測定対象ガスの特定の成分の吸収波長帯が走査されるように波長走査信号の波長スキャン幅を発光素子５ａ〜５ｄごとに個別に設定することができ、例えば、発光素子５ａから出射されたレーザ光にて、ＮＨ3ガスの濃度を測定する場合、波長走査駆動信号発生器１２は、発光素子５ａに対する波長スキャン幅を０．２ｎｍ程度に設定することができる。 Next, the wavelength scanning drive signal generator 12 in FIG. 2 linearly increases the intensity of the wavelength scanning signal in a trapezoidal shape in order to scan the absorption wavelength band of a specific component of the measurement target gas. A portion 19 where the intensity of the scanning signal linearly increases in a trapezoidal shape is output to the laser drive signal generators 14a to 14d, and the high frequency modulation signal generators 13a to 13d have a frequency of 10 kHz and a wavelength modulation width of 0.02 nm. A high frequency modulation signal 22 composed of a sine wave is output to each of the laser drive signal generators 14a to 14d. The wavelength scanning drive signal generator 12 can individually set the wavelength scanning width of the wavelength scanning signal for each of the light emitting elements 5a to 5d so that the absorption wavelength band of the specific component of the measurement target gas is scanned. For example, when measuring the concentration of NH 3 gas with the laser light emitted from the light emitting element 5a, the wavelength scanning drive signal generator 12 sets the wavelength scanning width for the light emitting element 5a to about 0.2 nm. Can do.

そして、波長走査信号の強度が台形状に直線的に増加する部分１９と高周波変調信号２２とはレーザ駆動信号発生部１４ａ〜１４ｄにてそれぞれ合成され、波長走査信号の強度が台形状に直線的に増加する部分１９と高周波変調信号２２とが合成された信号に基づいて発光素子５ａ〜５ｄの電流がそれぞれ制御されることにより、測定対象ガスの特定の成分の吸収波長帯を含むように１０ｋＨｚ程度の正弦波にてレーザ光が周波数変調される。   Then, the portion 19 where the intensity of the wavelength scanning signal linearly increases in a trapezoidal shape and the high frequency modulation signal 22 are synthesized by the laser drive signal generators 14a to 14d, respectively, and the intensity of the wavelength scanning signal is linearly shaped in a trapezoidal shape. The current of the light emitting elements 5a to 5d is controlled based on a signal obtained by synthesizing the portion 19 that increases in frequency and the high-frequency modulation signal 22, so that the absorption wavelength band of a specific component of the measurement target gas is 10 kHz. The laser beam is frequency-modulated with a sine wave of the order.

そして、周波数変調されたレーザ光は測定対象ガスを通過すると、測定対象ガスによる吸収量に対応した減衰を受けた後、受光素子１０に入射し、受光素子１０にてレーザ光が検出される。そして、受光素子１０にて検出された電流はＩ−Ｖ変換回路２５にて電圧に変換され、参照信号発生器２６にて発生された２倍周波数信号とＩ−Ｖ変換回路２５からの出力が同期検波器２７にて合成されることにより、Ｉ−Ｖ変換回路２５の出力から高周波変調信号２２の２倍の周波数成分が抽出される。
ここで、測定対象ガスの特定の成分の吸収波長帯を含むように周波数変調されたレーザ光は測定対象ガスの特定の成分による吸収量に対応した減衰を受けるため、同期検波器２７からの出力は測定対象ガスの特定の成分による吸収波形に対応した値となる。 When the frequency-modulated laser light passes through the measurement target gas, the laser light is attenuated corresponding to the amount of absorption by the measurement target gas, and then enters the light receiving element 10. The laser light is detected by the light receiving element 10. The current detected by the light receiving element 10 is converted into a voltage by the IV conversion circuit 25, and the double frequency signal generated by the reference signal generator 26 and the output from the IV conversion circuit 25 are output. By synthesizing by the synchronous detector 27, a frequency component twice as high as the high frequency modulation signal 22 is extracted from the output of the IV conversion circuit 25.
Here, since the laser light frequency-modulated to include the absorption wavelength band of the specific component of the measurement target gas is attenuated corresponding to the amount of absorption by the specific component of the measurement target gas, the output from the synchronous detector 27 Is a value corresponding to an absorption waveform due to a specific component of the measurement target gas.

図８は、図１のガス濃度測定装置における発光素子５ａ〜５ｄの駆動方法を示すタイミングチャートである。
図８において、測定対象ガスには吸収波長が互いに異なる４つの成分が含まれ、測定対象ガスの吸収波長帯は単一の発光素子５ａ〜５ｄの波長可変範囲を超えているものとする。
そして、発光素子５ａは、その波長可変範囲が測定対象ガスの第１の成分の吸収波長帯に対応するように発光波長を選択し、発光素子５ｂは、その波長可変範囲が測定対象ガスの第２の成分の吸収波長帯に対応するように発光波長を選択し、発光素子５ｃは、その波長可変範囲が測定対象ガスの第３の成分の吸収波長帯に対応するように発光波長を選択し、発光素子５ｄは、その波長可変範囲が測定対象ガスの第４の成分の吸収波長帯に対応するように発光波長を選択することができる。 FIG. 8 is a timing chart showing a driving method of the light emitting elements 5a to 5d in the gas concentration measuring apparatus of FIG.
In FIG. 8, it is assumed that the gas to be measured includes four components having different absorption wavelengths, and the absorption wavelength band of the gas to be measured exceeds the wavelength variable range of the single light emitting elements 5a to 5d.
The light emitting element 5a selects the emission wavelength so that the wavelength variable range corresponds to the absorption wavelength band of the first component of the measurement target gas, and the light emitting element 5b has the wavelength variable range of the measurement target gas. The light emission wavelength is selected so as to correspond to the absorption wavelength band of the second component, and the light emitting element 5c selects the emission wavelength so that the wavelength variable range corresponds to the absorption wavelength band of the third component of the measurement target gas. The light emitting element 5d can select the emission wavelength such that the wavelength variable range corresponds to the absorption wavelength band of the fourth component of the measurement target gas.

そして、図２の切り替え制御部１９は、レーザ駆動信号発生部１４ａ〜１４ｄを時系列的に選択し、発光素子５ａ〜５ｄを規定の時間だけ順次オンさせることにより、発光素子５ａ〜５ｄからそれぞれ出射されたレーザ光を測定対象ガスに順次入射させることができる。そして、測定対象ガスを透過したレーザ光は共通の受光素子１０にて順次検出され、測定対象ガスの４つの成分の濃度を順次算出することができる。   Then, the switching control unit 19 in FIG. 2 selects the laser drive signal generation units 14a to 14d in time series, and sequentially turns on the light emitting elements 5a to 5d for a specified time, so that the light emitting elements 5a to 5d are respectively turned on. The emitted laser light can be sequentially incident on the measurement target gas. And the laser beam which permeate | transmitted measurement object gas is sequentially detected by the common light receiving element 10, and the density | concentration of four components of measurement object gas can be calculated sequentially.

図９（ａ）は、ＮＨ3ガスの吸収スペクトラムの一例を示す図、図９（ｂ）は、ＨＣｌガスの吸収スペクトラムの一例を示す図、図９（ｃ）は、Ｈ2Ｓガスの吸収スペクトラムの一例を示す図、図９（ｄ）は、ＣＨ4ガスの吸収スペクトラムの一例を示す図、図１０は、図１のガス濃度測定装置における受光素子１０の検出感度を波長に対して示す図である。 9A shows an example of an absorption spectrum of NH 3 gas, FIG. 9B shows an example of an absorption spectrum of HCl gas, and FIG. 9C shows the absorption of H 2 S gas. FIG. 9D is a diagram showing an example of a spectrum, FIG. 9D is a diagram showing an example of an absorption spectrum of CH 4 gas, and FIG. 10 shows the detection sensitivity of the light receiving element 10 in the gas concentration measuring apparatus of FIG. FIG.

図９において、測定対象ガスには、ＮＨ3ガス、ＨＣｌガス、Ｈ2Ｓガス、ＣＨ4ガスの４種類が含まれているとする。この場合、この測定対象ガスの吸収特性を有する波長帯は１６００ｎｍ〜２０００ｎｍの範囲に及ぶため、単一の発光素子５ａ〜５ｄの波長可変範囲ではカバーすることができない。このため、発光素子５ａは、その波長可変範囲がＮＨ3ガスの吸収波長帯に対応するように発光波長を選択し、発光素子５ｂは、その波長可変範囲がＨＣｌガスの吸収波長帯に対応するように発光波長を選択し、発光素子５ｃは、その波長可変範囲がＨ2Ｓガスの吸収波長帯に対応するように発光波長を選択し、発光素子５ｄは、その波長可変範囲がＣＨ4ガスの吸収波長帯に対応するように発光波長を選択することができる。 9, the measurement target gas, and NH 3 gas, HCl gas, H 2 S gas contains four CH 4 gas. In this case, since the wavelength band having the absorption characteristics of the measurement target gas extends in the range of 1600 nm to 2000 nm, it cannot be covered by the wavelength variable range of the single light emitting elements 5a to 5d. Therefore, the light emitting element 5a selects the emission wavelength so that the wavelength variable range corresponds to the absorption wavelength band of NH 3 gas, and the light emitting element 5b has the wavelength variable range corresponding to the absorption wavelength band of HCl gas. The light emitting wavelength is selected as described above, and the light emitting element 5c selects the light emitting wavelength so that the wavelength variable range corresponds to the absorption wavelength band of the H 2 S gas, and the light emitting element 5d has the wavelength variable range within the CH 4 gas. The emission wavelength can be selected so as to correspond to the absorption wavelength band.

一方、受光素子１０としては、図１０に示すように、１６００ｎｍ〜２０００ｎｍの範囲に波長感度を持つフォトダイオードを選択することにより、ＮＨ3ガス、ＨＣｌガス、Ｈ2Ｓガス、ＣＨ4ガスの吸収特性をカバーすることができ、単一の受光素子１０を用いることで、ＮＨ3ガス、ＨＣｌガス、Ｈ2Ｓガス、ＣＨ4ガスの濃度を計測することができる。
なお、１６００ｎｍ〜２０００ｎｍの範囲に波長感度を持つフォトダイオードとしては、例えば、浜松フォトニクス製Ｇ８３７２−０１を用いることができる。 On the other hand, as the light receiving element 10, as shown in FIG. 10, absorption of NH 3 gas, HCl gas, H 2 S gas, and CH 4 gas is achieved by selecting a photodiode having a wavelength sensitivity in the range of 1600 nm to 2000 nm. The characteristics can be covered, and the concentration of NH 3 gas, HCl gas, H 2 S gas, and CH 4 gas can be measured by using a single light receiving element 10.
For example, G8372-01 manufactured by Hamamatsu Photonics can be used as the photodiode having wavelength sensitivity in the range of 1600 nm to 2000 nm.

図１１は、図３の同期検波器の出力波形の一例を示す図である。
図１１において、例えば、ＮＨ3ガスの吸光特性がある場合、図３の同期検波器２７の出力波形には、ピークが発生する。そして、吸光特性はピーク値がそのままガス濃度を表すため、ピークの振幅を測定したり、出力波形の変化部分を積分したりすることで、ＮＨ3ガスの濃度を測定することができる。
なお、上述した実施形態では、波長可変範囲が測定対象ガスの特定の成分の吸収波長帯にそれぞれ対応するように発光素子５ａ〜５ｄの発光波長を選択する方法について説明したが、全ての発光素子５ａ〜５ｄの発光波長を測定対象ガスの特定の成分の吸収波長帯にそれぞれ対応させる必要はなく、受光素子１０が感度を持つ範囲内において、複数の発光素子５ａ〜５ｄのうちの一部は、測定対象ガスによる吸収がない発光波長を選択するようにしてもよい。 FIG. 11 is a diagram illustrating an example of an output waveform of the synchronous detector of FIG.
In FIG. 11, for example, when there is an absorption characteristic of NH 3 gas, a peak occurs in the output waveform of the synchronous detector 27 in FIG. Since the peak value of the light absorption characteristic directly represents the gas concentration, the NH 3 gas concentration can be measured by measuring the amplitude of the peak or integrating the changed portion of the output waveform.
In the above-described embodiment, the method of selecting the emission wavelengths of the light emitting elements 5a to 5d so that the wavelength variable range corresponds to the absorption wavelength band of the specific component of the measurement target gas has been described. There is no need to correspond the emission wavelengths of 5a to 5d to the absorption wavelength bands of specific components of the measurement target gas, and within the range in which the light receiving element 10 has sensitivity, some of the plurality of light emitting elements 5a to 5d A light emission wavelength that is not absorbed by the measurement target gas may be selected.

例えば、複数の発光素子５ａ〜５ｄのうちの発光素子５ａについては、水分の吸収波長帯に対応するように発光波長を選択することができる。そして、発光素子５ａから出射されたレーザ光を測定対象ガスに透過させ、そのレーザ光を受光素子１０にて検出することにより、水分によるレーザ光の吸収量を測定することができる。そして、水分によるレーザ光の吸収量の測定結果に基づいて、発光素子５ｂ〜５ｄを用いて測定された測定対象ガスの特定の成分の濃度を補正することで、ダストの影響を除去することができ、測定対象ガスの特定の成分の濃度の測定精度を向上させることができる。   For example, for the light emitting element 5a among the plurality of light emitting elements 5a to 5d, the emission wavelength can be selected so as to correspond to the moisture absorption wavelength band. The amount of laser light absorbed by moisture can be measured by transmitting the laser light emitted from the light emitting element 5a through the measurement target gas and detecting the laser light by the light receiving element 10. Then, based on the measurement result of the amount of laser light absorbed by moisture, the influence of dust can be removed by correcting the concentration of a specific component of the measurement target gas measured using the light emitting elements 5b to 5d. It is possible to improve the measurement accuracy of the concentration of the specific component of the measurement target gas.

本発明の一実施形態に係るガス濃度測定装置における光学系の概略構成を示す断面図である。It is sectional drawing which shows schematic structure of the optical system in the gas concentration measuring apparatus which concerns on one Embodiment of this invention. 図１のガス濃度測定装置における送信側の信号処理部の概略構成を示すブロック図である。It is a block diagram which shows schematic structure of the signal processing part by the side of the transmission in the gas concentration measuring apparatus of FIG. 図１のガス濃度測定装置における受信側の信号処理部の概略構成を示すブロック図である。It is a block diagram which shows schematic structure of the signal processing part of the receiving side in the gas concentration measuring apparatus of FIG. 本発明の一実施形態に係る周波数変調方式によるガス濃度の測定原理を説明する図である。It is a figure explaining the measurement principle of the gas concentration by the frequency modulation system which concerns on one Embodiment of this invention. 本発明の一実施形態に係る駆動電流と半導体レーザの発光波長との関係を示す図である。It is a figure which shows the relationship between the drive current which concerns on one Embodiment of this invention, and the light emission wavelength of a semiconductor laser. 本発明の一実施形態に係る温度と半導体レーザの発光波長との関係を示す図である。It is a figure which shows the relationship between the temperature which concerns on one Embodiment of this invention, and the light emission wavelength of a semiconductor laser. 図７（ａ）は、図２の波長走査駆動信号発生器１２にて生成される電流波形を示す図、図７（ｂ）は、図２の高周波変調信号発生部１３ａ〜１３ｄにて生成される電流波形を示す図、図７（ｃ）は、図７（ａ）の電流波形と図７（ｂ）の電流波形とが合成された信号を印加した時に発光素子５ａ〜５ｄから出射される光の波長の変化を示す図である。7A is a diagram showing a current waveform generated by the wavelength scanning drive signal generator 12 of FIG. 2, and FIG. 7B is generated by the high frequency modulation signal generators 13a to 13d of FIG. FIG. 7C is a diagram showing the current waveform to be emitted from the light emitting elements 5a to 5d when a signal obtained by synthesizing the current waveform of FIG. 7A and the current waveform of FIG. 7B is applied. It is a figure which shows the change of the wavelength of light. 図１のガス濃度測定装置における発光素子５ａ〜５ｄの駆動方法を示すタイミングチャートである。5 is a timing chart showing a method for driving the light emitting elements 5a to 5d in the gas concentration measuring apparatus of FIG. 図９（ａ）は、ＮＨ3ガスの吸収スペクトラムの一例を示す図、図９（ｂ）は、ＨＣｌガスの吸収スペクトラムの一例を示す図、図９（ｃ）は、Ｈ2Ｓガスの吸収スペクトラムの一例を示す図、図９（ｄ）は、ＣＨ4ガスの吸収スペクトラムの一例を示す図である。9A shows an example of an absorption spectrum of NH 3 gas, FIG. 9B shows an example of an absorption spectrum of HCl gas, and FIG. 9C shows the absorption of H 2 S gas. FIG. 9D is a diagram illustrating an example of a spectrum, and FIG. 9D is a diagram illustrating an example of an absorption spectrum of CH 4 gas. 図１のガス濃度測定装置における受光素子１０の検出感度を波長に対して示す図である。It is a figure which shows the detection sensitivity of the light receiving element 10 in the gas concentration measuring apparatus of FIG. 1 with respect to a wavelength. 図３の同期検波器の出力波形の一例を示す図である。It is a figure which shows an example of the output waveform of the synchronous detector of FIG. 従来の周波数変調方式におけるガス濃度測定装置の概略構成を示す平面図である。It is a top view which shows schematic structure of the gas concentration measuring apparatus in the conventional frequency modulation system.

符号の説明Explanation of symbols

１ａ、１ｂ 隔壁
２ａ、２ｂ 固定フランジ
３ａ、３ｂ 調整フランジ
４、８ ハウジング
５ａ〜５ｄ 発光素子
６ プリズム型ミラー
７ａ、７ｂ 窓材
９ 集光レンズ
１０ 受光素子
１１ 信号処理装置
１２ 波長走査駆動信号発生器
１３ａ〜１３ｄ 高周波変調信号発生部
１４ａ〜１４ｄ レーザ駆動信号発生部
１６ａ〜１６ｄ 温度検出素子
１７ａ〜１７ｄ 温度調整素子
１８ａ〜１８ｄ 温度制御回路
１９ 切り替え制御部
２５ ＩＶ変換回路
２６ 参照信号発生器
２７ 同期検波器
２８ フィルタ DESCRIPTION OF SYMBOLS 1a, 1b Partition 2a, 2b Fixed flange 3a, 3b Adjustment flange 4, 8 Housing 5a-5d Light emitting element 6 Prism type mirror 7a, 7b Window material 9 Condensing lens 10 Light receiving element 11 Signal processing device 12 Wavelength scanning drive signal generator 13a to 13d High-frequency modulation signal generation unit 14a to 14d Laser drive signal generation unit 16a to 16d Temperature detection element 17a to 17d Temperature adjustment element 18a to 18d Temperature control circuit 19 Switching control unit 25 IV conversion circuit 26 Reference signal generator 27 Synchronous detection 28 Filter

Claims (4)

２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を出射する複数の発光素子と、
前記発光素子からそれぞれ出射されたレーザ光を共通の変調周波数で周波数変調させる高周波変調信号を発生する高周波変調信号発生部と、
前記周波数変調されたレーザ光の発光波長にて測定対象ガスの特定の成分の吸収波長帯をそれぞれスキャンさせる波長走査駆動信号を発生する波長走査駆動信号発生器と、
前記高周波変調信号および前記波長走査駆動信号に基づいて前記発光素子をそれぞれ駆動することにより、前記発光素子の発光波長を変調させるレーザ駆動信号発生部と、
前記レーザ駆動信号発生部にて駆動される発光素子を時系列的に切り替える切り替え制御手段と、
前記レーザ駆動信号発生部にて駆動されるレーザ光の発光波長が前記測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように前記発光素子の温度を設定する温度設定部と、
前記レーザ駆動信号発生部にてそれぞれ周波数変調された複数のレーザ光を共通に検出する光検出部と、
前記複数の発光素子から出射されたレーザ光を前記光検出部に導く光反射手段と、
前記光検出部にて検出されたレーザ光から基本波成分を検出する基本波成分検出部と、
前記光検出部にて検出されたレーザ光から２倍波成分を検出する２倍波成分検出部と、
前記基本波成分と２倍波成分との振幅比に基づいて、前記レーザ光が透過した測定対象ガスの特定の成分の濃度をそれぞれ算出するガス濃度算出部とを備えることを特徴とするガス濃度測定装置。 A plurality of light emitting elements that emit laser beams having wavelengths respectively corresponding to absorption wavelengths of two or more measurement target gases;
A high-frequency modulation signal generator for generating a high-frequency modulation signal for frequency-modulating the laser light emitted from each of the light emitting elements at a common modulation frequency;
A wavelength scanning drive signal generator for generating a wavelength scanning drive signal for scanning each absorption wavelength band of a specific component of the measurement target gas at the emission wavelength of the frequency-modulated laser light;
A laser drive signal generator for modulating the light emission wavelength of the light emitting element by driving the light emitting element based on the high frequency modulation signal and the wavelength scanning drive signal;
Switching control means for switching light emitting elements driven by the laser drive signal generation unit in time series;
A temperature setting unit for setting the temperature of the light emitting element so that the emission wavelength of the laser light driven by the laser drive signal generation unit is applied to the absorption wavelength band of the specific component of the measurement target gas;
A light detection unit for commonly detecting a plurality of laser beams, each of which is frequency-modulated by the laser drive signal generation unit;
A light reflecting means for guiding laser light emitted from the plurality of light emitting elements to the light detection unit;
A fundamental wave component detector that detects a fundamental wave component from the laser light detected by the light detector; and
A second harmonic component detection unit for detecting a second harmonic component from the laser light detected by the light detection unit;
A gas concentration comprising: a gas concentration calculation unit that calculates a concentration of a specific component of the measurement target gas transmitted by the laser beam based on an amplitude ratio between the fundamental wave component and the second harmonic wave component. measuring device. 前記複数の発光素子の一部は、レーザ光の発光波長が前記測定対象ガスの吸収波長帯にかからないように選択されることを特徴とする請求項１記載のガス濃度測定装置。   2. The gas concentration measuring apparatus according to claim 1, wherein a part of the plurality of light emitting elements is selected so that an emission wavelength of a laser beam does not reach an absorption wavelength band of the measurement target gas. ２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を共通の変調周波数で周波数変調させるステップと、
前記周波数変調されたレーザ光の発光波長が測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように、前記レーザ光をそれぞれ出射する発光素子の温度を設定するステップと、
前記周波数変調されたレーザ光の発光波長を測定対象ガスの特定の成分の吸収波長帯がスキャンされるようにそれぞれ変化させながら、前記測定対象ガスに前記レーザ光を順次入射させるステップと、
前記測定対象ガスを順次透過したレーザ光を共通の検出器にて検出するステップと、
前記検出器にて順次検出されたレーザ光から基本波成分および２倍波成分を抽出するステップと、
前記抽出された基本波成分および２倍波成分に基づいて、前記レーザ光が透過した測定対象ガスの特定の成分の濃度をそれぞれ算出するステップとを備えることを特徴とするガス濃度測定方法。 Frequency-modulating laser beams having wavelengths respectively corresponding to absorption wavelengths of two or more components of the measurement target gas with a common modulation frequency;
Setting the temperature of each of the light emitting elements that emits the laser light such that the emission wavelength of the frequency-modulated laser light is applied to the absorption wavelength band of a specific component of the measurement target gas;
Sequentially changing the emission wavelength of the frequency-modulated laser light so that the absorption wavelength band of a specific component of the measurement target gas is scanned, and sequentially making the laser light incident on the measurement target gas;
Detecting a laser beam sequentially transmitted through the measurement target gas with a common detector;
Extracting a fundamental wave component and a second harmonic component from the laser light sequentially detected by the detector;
Calculating a concentration of a specific component of the measurement target gas transmitted by the laser beam based on the extracted fundamental wave component and second harmonic component, respectively. ２成分以上の測定対象ガスの吸収波長にそれぞれ対応した波長を有するレーザ光を共通の変調周波数で周波数変調させるステップと、
前記周波数変調されたレーザ光の発光波長が測定対象ガスの特定の成分の吸収波長帯にそれぞれかかるように、前記レーザ光をそれぞれ出射する発光素子の温度を設定するステップと、
前記周波数変調されたレーザ光の発光波長を測定対象ガスの特定の成分の吸収波長帯がスキャンされるようにそれぞれ変化させながら、前記測定対象ガスに前記レーザ光を順次入射させるステップと、
前記測定対象ガスを順次透過したレーザ光を共通の検出器にて検出するステップと、
前記検出器にて順次検出されたレーザ光から基本波成分および２倍波成分を抽出するステップと、
前記抽出された基本波成分および２倍波成分に基づいて、前記レーザ光が透過した測定対象ガスの特定の成分の濃度をそれぞれ算出するステップと、
前記測定対象ガスの吸収波長にかからない波長を有するレーザ光を前記変調周波数で周波数変調させるステップと、
前記測定対象ガスの吸収波長にかからない波長を有するレーザ光を前記測定対象ガスに入射させるステップと、
前記測定対象ガスの吸収波長にかからない波長を有するレーザ光を前記検出器にて検出するステップと、
前記検出器にて検出された前記測定対象ガスの吸収波長にかからない波長を有するレーザ光から基本波成分および２倍波成分を抽出するステップと、
前記測定対象ガスの吸収波長にかからない波長を有するレーザ光から抽出された基本波成分および２倍波成分に基づいて、前記レーザ光が透過した測定対象ガスの濃度を補正するステップとを備えることを特徴とするガス濃度測定方法。 Frequency-modulating laser beams having wavelengths respectively corresponding to absorption wavelengths of two or more components of the measurement target gas with a common modulation frequency;
Setting the temperature of each of the light emitting elements that emits the laser light such that the emission wavelength of the frequency-modulated laser light is applied to the absorption wavelength band of a specific component of the measurement target gas;
Sequentially changing the emission wavelength of the frequency-modulated laser light so that the absorption wavelength band of a specific component of the measurement target gas is scanned, and sequentially making the laser light incident on the measurement target gas;
Detecting a laser beam sequentially transmitted through the measurement target gas with a common detector;
Extracting a fundamental wave component and a second harmonic component from the laser light sequentially detected by the detector;
Calculating a concentration of a specific component of the measurement target gas transmitted by the laser beam based on the extracted fundamental wave component and second harmonic wave component;
Frequency-modulating a laser beam having a wavelength that does not depend on the absorption wavelength of the measurement target gas with the modulation frequency;
Making the laser beam having a wavelength that does not depend on the absorption wavelength of the gas to be measured enter the gas to be measured;
Detecting a laser beam having a wavelength that does not depend on an absorption wavelength of the measurement target gas with the detector;
Extracting a fundamental wave component and a second harmonic component from a laser beam having a wavelength that does not depend on the absorption wavelength of the measurement target gas detected by the detector;
Correcting the concentration of the measurement target gas transmitted by the laser beam based on the fundamental wave component and the second harmonic component extracted from the laser beam having a wavelength that does not depend on the absorption wavelength of the measurement target gas. A characteristic gas concentration measurement method.
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