JP6148924B2 - Gas detector - Google Patents

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JP6148924B2
JP6148924B2 JP2013155478A JP2013155478A JP6148924B2 JP 6148924 B2 JP6148924 B2 JP 6148924B2 JP 2013155478 A JP2013155478 A JP 2013155478A JP 2013155478 A JP2013155478 A JP 2013155478A JP 6148924 B2 JP6148924 B2 JP 6148924B2
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absorption line
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JP2015025734A (en
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啓一 曽根
啓一 曽根
博之 玉本
博之 玉本
健 安部
健 安部
敏之 鈴木
敏之 鈴木
毅 原
毅 原
教明 山崎
教明 山崎
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Anritsu Corp
Tokyo Metropolitan Sewerage Service Corp
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Tokyo Metropolitan Sewerage Service Corp
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Description

本発明は、ガス検知器に関する。特に、二酸化炭素が高濃度で含まれる環境であっても硫化水素等有毒なガスを高感度に検出することが可能なガス検知器に関する。   The present invention relates to a gas detector. In particular, the present invention relates to a gas detector that can detect toxic gas such as hydrogen sulfide with high sensitivity even in an environment containing carbon dioxide at a high concentration.

特許文献１には、メタン等ガス分子の赤外光吸収特性を利用したガス検知器が開示されている。当該ガス検知器では、検出光として周波数変調した赤外レーザ光を用い、被検出ガスを通過した検出光の乱反射光を受光素子で受け、当該受光素子が出力する出力信号から、変調周波数に等しい周波数の基本波信号と変調周波数の２倍に等しい周波数の２倍波信号を検出する。そして、基本波信号に対する２倍波信号の強さから被検出ガスの濃度を算出している。   Patent Document 1 discloses a gas detector using infrared light absorption characteristics of gas molecules such as methane. The gas detector uses infrared laser light that is frequency-modulated as detection light, receives irregularly reflected light of detection light that has passed through the gas to be detected by the light receiving element, and is equal to the modulation frequency from the output signal output by the light receiving element. A fundamental wave signal of a frequency and a double wave signal of a frequency equal to twice the modulation frequency are detected. And the density | concentration of to-be-detected gas is computed from the strength of the 2nd harmonic signal with respect to a fundamental wave signal.

ところで、下水道等の地下管渠あるいは地下管路（以下、単に「管渠」と称する。）において、保守点検等、人手による作業を行う場合がある。管渠内は、酸素欠乏状態になる可能性があり、また、硫化水素等の有毒ガスが発生する可能性もあるため、管渠内における作業者の安全管理を図る観点から、いち早く硫化水素等有毒ガスの発生を検知する必要がある。このような場合、たとえば特許文献１に記載のガス検知器を用いることが可能である。   By the way, there are cases where manual work such as maintenance and inspection is performed in underground pipes such as sewers or underground pipes (hereinafter simply referred to as “pipe”). There is a possibility that the inside of the pipe will be deficient in oxygen, and toxic gases such as hydrogen sulfide may be generated. It is necessary to detect the generation of toxic gases. In such a case, for example, the gas detector described in Patent Document 1 can be used.

特開２００１−２３５４２０号公報JP 2001-235420 A

しかし、管渠の内部環境は通常の環境とは異なり、二酸化炭素を高濃度に含む特殊な環境である。このような二酸化炭素を高濃度に含む特殊環境において前記した赤外線吸収を利用したガス検知器を用いると、二酸化炭素による赤外線吸収の影響が大きく、たとえば硫化水素等の被検出ガスの信号が適正に検出できなくなる問題を本発明者らは認識した。   However, the internal environment of the tube is different from the normal environment and is a special environment containing carbon dioxide at a high concentration. When the above-described gas detector using infrared absorption is used in a special environment containing carbon dioxide at a high concentration, the influence of infrared absorption by carbon dioxide is large, and the signal of the gas to be detected such as hydrogen sulfide is appropriately set. The present inventors have recognized a problem that the detection becomes impossible.

本発明の目的は、硫化水素等の被検出ガスの検出において障害になり得る二酸化炭素が高濃度に存在する環境においても、被検出ガスを高感度に検出できるガス検知器を提供することにある。   An object of the present invention is to provide a gas detector that can detect a gas to be detected with high sensitivity even in an environment in which carbon dioxide that can be an obstacle in the detection of the gas to be detected such as hydrogen sulfide exists in a high concentration. .

上記課題を解決するために、本発明の態様においては、周波数変調されたレーザ光を検出光として放射する光源部と、前記検出光が物体に照射された場合に前記物体からの反射光を受光し、前記反射光に応じた受光信号を出力する受光部と、前記受光信号から、前記検出光の変調周波数に等しい周波数の基本波信号、および、前記変調周波数の２倍に等しい周波数の２倍波信号を検出する信号検出部と、前記基本波信号と前記２倍波信号の比に基づいて、背景ガスが存在する雰囲気における被検出ガスの濃度を計算する濃度計算部と、を有し、前記検出光の前記周波数変調における中心波長が、前記被検出ガスの複数の吸収線のうち「｜λｓ−λｂ｜≧２．７２×Δλｓ」の条件を満足する選択吸収線に合致するよう調整されたガス検知器を提供する。ただし、λｓは前記選択吸収線の波長、Δλｓは前記選択吸収線の半値全幅、λｂは前記背景ガスの吸収線波長を示す。   In order to solve the above-described problem, in an aspect of the present invention, a light source unit that emits frequency-modulated laser light as detection light, and receives reflected light from the object when the detection light is irradiated on the object. A light receiving unit that outputs a light reception signal corresponding to the reflected light, a fundamental wave signal having a frequency equal to the modulation frequency of the detection light, and a frequency equal to twice the modulation frequency from the light reception signal. A signal detection unit that detects a wave signal; and a concentration calculation unit that calculates the concentration of the gas to be detected in an atmosphere in which a background gas exists based on the ratio of the fundamental wave signal and the second harmonic signal; The center wavelength in the frequency modulation of the detection light is adjusted to match a selective absorption line satisfying the condition of “| λs−λb | ≧ 2.72 × Δλs” among the plurality of absorption lines of the detection gas. Gas detector To do. Where λs is the wavelength of the selective absorption line, Δλs is the full width at half maximum of the selective absorption line, and λb is the absorption line wavelength of the background gas.

前記選択吸収線の波形が、前記周波数変調により前記２倍波信号を発生するに十分な左右対称性および線幅の狭さを有したものであることが好ましい。前記被検出ガスとして、硫化水素ガスを例示することができ、前記背景ガスとして、二酸化炭素ガスを例示することができる。前記被検出ガスが硫化水素ガスであり、前記背景ガスが二酸化炭素ガスである場合、前記選択吸収線の波長として、１５７７．２ｎｍ、または１５７６．３ｎｍを例示することができる。   It is preferable that the waveform of the selective absorption line has sufficient left-right symmetry and narrow line width to generate the second harmonic signal by the frequency modulation. An example of the gas to be detected is hydrogen sulfide gas, and an example of the background gas is carbon dioxide gas. When the detection gas is hydrogen sulfide gas and the background gas is carbon dioxide gas, 1577.2 nm or 1576.3 nm can be exemplified as the wavelength of the selective absorption line.

ガス検知器１００の概要を示した構成図である。1 is a configuration diagram showing an outline of a gas detector 100. FIG. ２倍波信号の発生原理を説明した概念図である。It is the conceptual diagram explaining the generation principle of the 2nd harmonic signal. 二酸化炭素および硫化水素の吸収線を示したグラフである。2 is a graph showing absorption lines of carbon dioxide and hydrogen sulfide. 二酸化炭素および硫化水素の吸収線波長差を変化させたときの二酸化炭素吸収による硫化水素濃度値の減少度をシミュレートしたグラフである。It is the graph which simulated the decrease degree of the hydrogen sulfide concentration value by carbon dioxide absorption when changing the absorption line wavelength difference of carbon dioxide and hydrogen sulfide.

（実施形態１）
図１は、ガス検知器１００の概要を示した構成図である。ガス検知器１００は、光源部１０２、受光部１０４、信号検出部１０６、濃度計算部１０８、表示部１１０および制御部１１２を有する。ガス検知器１００は、光源部１０２から検出光１２０を放射し、背景ガス１３２とともに存在する被検出ガス１３０を通過した検出光１２０が物体１４０に反射されて生じた反射光１２２を受光し、当該反射光１２２から被検出ガス１３０の濃度を測定する。ここでいう濃度は、密度×長さの次元を有するコラム密度をいう。蜜度の単位が［％］あるいは［ｐｐｍ］であり長さの単位が［ｍ］である場合、コラム密度の単位は［％・ｍ］あるいは［ｐｐｍ・ｍ］となる。 (Embodiment 1)
FIG. 1 is a configuration diagram showing an outline of the gas detector 100. The gas detector 100 includes a light source unit 102, a light receiving unit 104, a signal detection unit 106, a concentration calculation unit 108, a display unit 110, and a control unit 112. The gas detector 100 radiates the detection light 120 from the light source unit 102, receives the reflected light 122 generated when the detection light 120 that has passed through the detection gas 130 that exists together with the background gas 132 is reflected by the object 140, and The concentration of the gas 130 to be detected is measured from the reflected light 122. The concentration here means a column density having a dimension of density × length. When the unit of honey is [%] or [ppm] and the unit of length is [m], the unit of column density is [% · m] or [ppm · m].

光源部１０２は、周波数変調されたレーザ光を検出光１２０として放射する。レーザ光を周波数変調することで後に説明するようにガス濃度に応じた２倍波信号が生じる。検出光１２０の波長（周波数）は、被検出ガス１３０に吸収され、背景ガス１３２に吸収されない波長が好ましい。この点は後に詳述する。被検出ガス１３０が硫化水素である場合、検出光１２０として発振波長が１．５７μｍ帯の赤外レーザ光を用いることができる。被検出ガス１３０がメタンである場合、検出光１２０として発振波長が１．６５μｍ帯の赤外レーザ光を用いることができる。なお、光源部１０２に半導体レーザ発振器を用いる場合、被検出ガス１３０が封入された標準セルを準備し、当該標準セルでの光吸収を参照して、検出光１２０の発振波長が被検出ガス１３０の吸収線の中心に一致するよう半導体レーザ発振器の動作温度等を調整することが好ましい。   The light source unit 102 emits frequency-modulated laser light as detection light 120. Frequency modulation of the laser light generates a second harmonic signal corresponding to the gas concentration as will be described later. The wavelength (frequency) of the detection light 120 is preferably a wavelength that is absorbed by the detection gas 130 and not absorbed by the background gas 132. This point will be described in detail later. When the gas to be detected 130 is hydrogen sulfide, an infrared laser beam having an oscillation wavelength of 1.57 μm band can be used as the detection light 120. When the gas to be detected 130 is methane, infrared laser light having an oscillation wavelength of 1.65 μm band can be used as the detection light 120. When a semiconductor laser oscillator is used for the light source unit 102, a standard cell in which the gas to be detected 130 is sealed is prepared, and the oscillation wavelength of the detection light 120 is determined by referring to light absorption in the standard cell. It is preferable to adjust the operating temperature or the like of the semiconductor laser oscillator so as to coincide with the center of the absorption line.

受光部１０４は、検出光１２０が物体１４０に照射された場合に物体１４０からの反射光１２２を受光し、反射光１２２に応じた受光信号を出力する。受光部１０４として、たとえばフォトダイオード、フォトマルチプライヤー等の光電変換素子とその駆動検出回路を例示することができる。受光部１０４には、たとえばバンドパスフィルタ等の光学フィルタ、スリット、分光機構等の適切な光学系を備えてもよい。   The light receiving unit 104 receives the reflected light 122 from the object 140 when the detection light 120 is irradiated on the object 140, and outputs a received light signal corresponding to the reflected light 122. Examples of the light receiving unit 104 include a photoelectric conversion element such as a photodiode and a photomultiplier and a drive detection circuit thereof. The light receiving unit 104 may include an appropriate optical system such as an optical filter such as a band pass filter, a slit, or a spectroscopic mechanism.

信号検出部１０６は、受光部１０４が出力した受光信号を受け、当該受光信号から、検出光１２０の変調周波数に等しい周波数の基本波信号、および、変調周波数の２倍に等しい周波数の２倍波信号を検出する。基本波信号および２倍波信号の検出には同期検波を用いる。図２は、２倍波信号が生じる原理を説明するための概念図である。検出光１２０が図２に示す変調波で周波数変調され、変調された検出光１２０の中心波長を図２に示すように吸収線の中心波長に一致させると、被検出ガス１３０を透過した光の強度信号には、変調周波数に等しい周波数の基本波信号に加えて変調周波数の２倍に等しい周波数の２倍波信号を含むようになる。すなわち、周波数変調における単位周期の間に、吸収線の中心より長波長側および短波長側のそれぞれにおいて透過光の強弱が生じる。この結果、被検出ガス１３０を通過した光には、変調周波数の２倍に等しい周波数の２倍波が含まれるようになる。なお、２倍波が適正に生成されるには、吸収線の形は中心波長を中心に対称であることが好ましく、吸収線の幅は周波数変調が可能な波長幅の程度に狭いことが好ましい。   The signal detection unit 106 receives the light reception signal output from the light reception unit 104, receives a fundamental wave signal having a frequency equal to the modulation frequency of the detection light 120 and a second harmonic wave having a frequency equal to twice the modulation frequency from the light reception signal. Detect the signal. Synchronous detection is used to detect the fundamental wave signal and the second harmonic signal. FIG. 2 is a conceptual diagram for explaining the principle of generating a second harmonic signal. When the detection light 120 is frequency-modulated with the modulated wave shown in FIG. 2 and the center wavelength of the modulated detection light 120 is matched with the center wavelength of the absorption line as shown in FIG. 2, the light transmitted through the detection gas 130 The intensity signal includes a double wave signal having a frequency equal to twice the modulation frequency in addition to a fundamental wave signal having a frequency equal to the modulation frequency. That is, the intensity of transmitted light is generated on each of the long wavelength side and the short wavelength side from the center of the absorption line during a unit period in frequency modulation. As a result, the light that has passed through the detection gas 130 includes a double wave having a frequency equal to twice the modulation frequency. In order to properly generate the second harmonic wave, the shape of the absorption line is preferably symmetric with respect to the center wavelength, and the width of the absorption line is preferably as narrow as the wavelength width capable of frequency modulation. .

以上のようにして。信号検出部１０６には、被検出ガス１３０の光吸収に起因して２倍波（２倍波信号）が含まれるようになる。一方、検出光１２０が物体１４０によって散乱され反射光１２２として検出される割合は、被検出ガス１３０の有無によって左右されないので、受光した反射光１２２に含まれる基本波（基本波信号）の強度に対する２倍波（２倍波信号）の強度を測定すれば、測定値は光路に沿った光吸収量（コラム密度）がわかる。   As above. The signal detection unit 106 includes a second harmonic (second harmonic signal) due to light absorption of the gas 130 to be detected. On the other hand, the ratio at which the detection light 120 is scattered by the object 140 and detected as the reflected light 122 does not depend on the presence or absence of the gas 130 to be detected. If the intensity of the second harmonic (second harmonic signal) is measured, the measured value indicates the amount of light absorption (column density) along the optical path.

濃度計算部１０８は、基本波信号と２倍波信号の比に基づいて、背景ガス１３２が存在する雰囲気における被検出ガス１３０の濃度（コラム密度）を計算する。なお、光吸収量（コラム密度）は光路に存在する被検出ガス１３０の分子数に比例するので光路長に依存することになるが、光路長が判明している場合には、コラム密度を光路長で除することで光路に沿った平均のガス密度（ガス濃度）を計算することができる。   The concentration calculation unit 108 calculates the concentration (column density) of the detection gas 130 in the atmosphere in which the background gas 132 exists based on the ratio of the fundamental wave signal and the second harmonic signal. The light absorption amount (column density) is proportional to the number of molecules of the gas 130 to be detected existing in the optical path, and therefore depends on the optical path length. However, when the optical path length is known, the column density is set to the optical path. By dividing by the length, the average gas density (gas concentration) along the optical path can be calculated.

ただし、上記の測定および計算は、検出光１２０が背景ガス１３２により影響を受けない場合に適正に成立する。よって、検出光１２０の波長は、被検出ガス１３０の複数の吸収線から、背景ガス１３２の吸収線と重ならない吸収線（選択吸収線）と合致するように調整する。選択吸収線の選択は、たとえば、吸収強度が強い、吸収線幅が狭い、吸収線波形の左右対称性が良い、光源である半導体レーザダイオードが入手可能である、という観点から、候補を絞り込む。   However, the above measurement and calculation are properly established when the detection light 120 is not affected by the background gas 132. Therefore, the wavelength of the detection light 120 is adjusted from the plurality of absorption lines of the detected gas 130 so as to match the absorption line (selective absorption line) that does not overlap with the absorption line of the background gas 132. The selection of the selective absorption line is narrowed down from the viewpoint that, for example, the absorption intensity is strong, the absorption line width is narrow, the left-right symmetry of the absorption line waveform is good, and the semiconductor laser diode as the light source is available.

さらに、近傍に水蒸気等の共存ガスの存在がない、あるいは影響が少ない、吸収線に絞りこむ。具体的には、検出光１２０の周波数変調における中心波長を、被検出ガス１３０の複数の吸収線のうち、「｜λｓ−λｂ｜≧２．７２×Δλｓ」の条件を満足する選択吸収線に合致するよう選択および調整する。ただし、λｓは選択吸収線の波長、Δλｓは選択吸収線の半値全幅、λｂは背景ガス１３２の吸収線波長を示す。   Further, the absorption lines are narrowed down so that there is no coexistence gas such as water vapor or the influence is small. Specifically, the center wavelength in the frequency modulation of the detection light 120 is a selective absorption line that satisfies the condition of “| λs−λb | ≧ 2.72 × Δλs” among the plurality of absorption lines of the detected gas 130. Select and adjust to match. Where λs is the wavelength of the selective absorption line, Δλs is the full width at half maximum of the selective absorption line, and λb is the absorption line wavelength of the background gas 132.

被検出ガス１３０が硫化水素ガスであり、背景ガス１３２が二酸化炭素ガスである場合についてより詳細に検討する。図３は、コラム密度が４０％・ｍの二酸化炭素の吸収線とコラム密度が３％・ｍの硫化水素の吸収線を示したグラフである。硫化水素の吸収線は、吸収強度が強い、吸収線幅が狭い、吸収線波形の左右対称性が良いという観点から絞り込んだ選択吸収線の候補である。なお、図示するように、選択吸収線Ａは背景ガスである二酸化炭素の吸収線から０．１７ｎｍ離れており、選択吸収線Ｂは、二酸化炭素の吸収線から０．１６ｎｍ離れている。一方、比較用吸収線は、二酸化炭素の吸収線から０．１０ｎｍしか離れていない。   The case where the gas 130 to be detected is hydrogen sulfide gas and the background gas 132 is carbon dioxide gas will be examined in more detail. FIG. 3 is a graph showing an absorption line of carbon dioxide having a column density of 40% · m and an absorption line of hydrogen sulfide having a column density of 3% · m. Hydrogen sulfide absorption lines are candidates for selective absorption lines narrowed down from the viewpoint of strong absorption intensity, narrow absorption line width, and good left-right symmetry of the absorption line waveform. As shown in the figure, the selective absorption line A is 0.17 nm away from the absorption line of carbon dioxide, which is the background gas, and the selective absorption line B is 0.16 nm away from the absorption line of carbon dioxide. On the other hand, the comparative absorption line is only 0.10 nm away from the carbon dioxide absorption line.

図４は、二酸化炭素および硫化水素の吸収線波長差を変化させたときの二酸化炭素吸収による硫化水素濃度値の減少度をシミュレートしたグラフである。二酸化炭素の濃度は４０％、硫化水素の濃度は１０ｐｐｍを想定した。また、吸収線プロファイルは、分子の熱運動に起因するドップラー広がり（ガウス型）と分子同士の衝突に起因する圧力広がり（ローレンツ型)との畳み込み（フォークト型)とした。比較用吸収線（１５７８．１ｎｍ）は、硫化水素の半値全幅で規格化した二酸化炭素吸収線との波長差が２．２であり、二酸化炭素の影響を大きく受けることがわかる。これに対し、選択吸収線Ｂ（１５７７．２ｎｍ）は、Ｈ２Ｓの半値全幅で規格化した二酸化炭素吸収線との波長差が３．３と十分離れており、二酸化炭素の吸収による影響は５％程度にとどまることがわかる。以上の結果、選択吸収線として、１５７６．３ｎｍの吸収線または１５７７．２ｎｍの吸収線が選択できる。 FIG. 4 is a graph simulating the degree of decrease in the hydrogen sulfide concentration value due to carbon dioxide absorption when the absorption line wavelength difference between carbon dioxide and hydrogen sulfide is changed. The concentration of carbon dioxide was assumed to be 40%, and the concentration of hydrogen sulfide was assumed to be 10 ppm. The absorption line profile was a convolution (Forked type) of Doppler broadening (Gaussian type) due to thermal motion of molecules and pressure broadening (Lorentz type) due to collision between molecules. The comparative absorption line (1578.1 nm) has a wavelength difference of 2.2 with respect to the carbon dioxide absorption line normalized by the full width at half maximum of hydrogen sulfide, and it can be seen that it is greatly affected by carbon dioxide. On the other hand, the selective absorption line B (1577.2 nm) has a wavelength difference of 3.3 from the carbon dioxide absorption line normalized by the full width at half maximum of H 2 S, which is sufficiently separated from the carbon dioxide absorption. It can be seen that it stays at around 5%. As a result, an absorption line of 1576.3 nm or an absorption line of 1577.2 nm can be selected as the selective absorption line.

表示部１１０は、濃度計算部１０８が計算した被検出ガス１３０の濃度を表示する。制御部１１２は、ガス検知器１００に含まれる各部の制御を実行する。   The display unit 110 displays the concentration of the detected gas 130 calculated by the concentration calculation unit 108. The control unit 112 performs control of each unit included in the gas detector 100.

ガス検知器１００によれば、背景ガス１３２が高濃度に存在する環境においても高精度に被検出ガス１３０の濃度を測定することができる。たとえば、管渠内の二酸化炭素が高い濃度で存在するような状況においても、有毒ガスである硫化水素を高精度に検出して、いち早く危険を察知でき、管渠内の作業者の安全を図ることができる。   According to the gas detector 100, the concentration of the detected gas 130 can be measured with high accuracy even in an environment where the background gas 132 exists at a high concentration. For example, even in a situation where the carbon dioxide in the pipe is present at a high concentration, hydrogen sulfide, which is a toxic gas, can be detected with high accuracy, and the danger can be immediately detected, thereby ensuring the safety of workers in the pipe. be able to.

以上、本発明を実施の形態を用いて説明したが、本発明の技術的範囲は上記実施の形態に記載の範囲には限定されない。上記実施の形態に、多様な変更または改良を加えることが可能であることが当業者に明らかである。その様な変更または改良を加えた形態も本発明の技術的範囲に含まれ得ることが、特許請求の範囲の記載から明らかである。   As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

１００…ガス検知器、１０２…光源部、１０４…受光部、１０６…信号検出部、１０８…濃度計算部、１１０…表示部、１１２…制御部、１２０…検出光、１２２…反射光、１３０…被検出ガス、１３２…背景ガス、１４０…物体。   DESCRIPTION OF SYMBOLS 100 ... Gas detector, 102 ... Light source part, 104 ... Light receiving part, 106 ... Signal detection part, 108 ... Concentration calculation part, 110 ... Display part, 112 ... Control part, 120 ... Detection light, 122 ... Reflected light, 130 ... Gas to be detected, 132 ... background gas, 140 ... object.

Claims (2)

周波数変調されたレーザ光を検出光として放射する光源部と、
前記検出光が物体に照射された場合に前記物体からの反射光を受光し、前記反射光に応じた受光信号を出力する受光部と、
前記受光信号から、前記検出光の変調周波数に等しい周波数の基本波信号、および、前記変調周波数の２倍に等しい周波数の２倍波信号を検出する信号検出部と、
前記基本波信号と前記２倍波信号の比に基づいて、背景ガスが存在する雰囲気における被検出ガスの濃度を計算する濃度計算部と、を有し、
前記被検出ガスが硫化水素ガスであり、前記背景ガスが二酸化炭素ガスであり、
前記検出光の前記周波数変調における中心波長が、前記被検出ガスの複数の吸収線のうち数１の条件、
（数１） ｜λｓ−λｂ｜≧２．７２×Δλｓ、を満足する選択吸収線に合致するよう調整され、
前記選択吸収線の波長λｓが、１５７７．２ｎｍ、または１５７６．３ｎｍである
ガス検知器。
ただし、Δλｓは前記選択吸収線の半値全幅、λｂは前記背景ガスの吸収線波長を示す。 A light source unit that emits frequency-modulated laser light as detection light;
A light receiving unit that receives reflected light from the object when the detection light is applied to the object, and outputs a light reception signal according to the reflected light;
A signal detection unit for detecting, from the received light signal, a fundamental wave signal having a frequency equal to the modulation frequency of the detection light and a second harmonic signal having a frequency equal to twice the modulation frequency;
A concentration calculator that calculates the concentration of the gas to be detected in the atmosphere in which the background gas exists based on the ratio of the fundamental wave signal and the second harmonic signal;
The gas to be detected is hydrogen sulfide gas, the background gas is carbon dioxide gas,
The center wavelength in the frequency modulation of the detection light is a condition of the number 1 among the plurality of absorption lines of the detection gas ,
(Expression 1) is adjusted so as to match a selective absorption line satisfying | λs−λb | ≧ 2.72 × Δλs ,
The gas detector, wherein the wavelength λs of the selective absorption line is 1577.2 nm or 1576.3 nm .
However, delta [lambda] s is the full width at half maximum of the selected absorption line, [lambda] b shows the absorption line wavelength of the background gas. 前記選択吸収線の形が、前記周波数変調により前記２倍波信号を発生するに十分な左右対称性および線幅の狭さを有したものである
請求項１に記載のガス検知器。 The gas detector according to claim 1, wherein a shape of the selective absorption line has sufficient left-right symmetry and a narrow line width to generate the second harmonic signal by the frequency modulation.
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