JPH07151681A - Gas density measuring apparatus - Google Patents
Gas density measuring apparatusInfo
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- JPH07151681A JPH07151681A JP32616393A JP32616393A JPH07151681A JP H07151681 A JPH07151681 A JP H07151681A JP 32616393 A JP32616393 A JP 32616393A JP 32616393 A JP32616393 A JP 32616393A JP H07151681 A JPH07151681 A JP H07151681A
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- signal
- phase
- frequency
- wave signal
- gas
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Abstract
Description
【0001】[0001]
【産業上の利用分野】この発明は、メタンガスや炭酸ガ
スなどのような特定のガスの濃度を光吸収スペクトル特
性を用いて高精度に測定するガス検出器において用いら
れるガス濃度測定装置に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration measuring device used in a gas detector for highly accurately measuring the concentration of a specific gas such as methane gas or carbon dioxide gas by using optical absorption spectrum characteristics. is there.
【0002】[0002]
【従来の技術】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、光源として
半導体レーザを用いたガス検出器は1965年ムーア
(C.B.Moore)によって初めて考案された。こ
の原理を簡単に以下に述べる。ガスの吸収特性の模式図
を図3に示す。ここで、吸収線の中心の周波数fc にお
ける減衰量はガスの濃度に比例する。したがって、fc
の発振周波数をもつ半導体レーザ光を作り、ガスに照射
し、その減衰量を測定し適当な係数を掛けることでガス
の濃度を推定することができる。2. Description of the Related Art It is known that gaseous gas molecules each have a unique light absorption spectrum, and a gas detector using a semiconductor laser as a light source was first introduced by CB Moore in 1965. Invented This principle will be briefly described below. A schematic diagram of gas absorption characteristics is shown in FIG. Here, the amount of attenuation at the frequency fc at the center of the absorption line is proportional to the gas concentration. Therefore, fc
The concentration of the gas can be estimated by producing a semiconductor laser beam having an oscillation frequency of, irradiating the gas, measuring the amount of attenuation, and multiplying it by an appropriate coefficient.
【0003】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、これらの方式が現在
では主流となっている。2波長差分方式についての詳細
な説明及び実験結果は、 ・K.Uehara: Appl.Phys.B,Vol.38,No.1,pp.37-40,1985. ・田井秀男、山本和成、阿部健、植木孝、田中弘明、上
原喜代治:計測自動制御学会論文集24,pp.452-458,1
988. ・田井秀男、田中弘明、上原喜代治:光学,Vol.19,No.
4,pp.238-244,1990. に開示されている。また、周波数変調方式についての詳
細な説明及び実験結果は、 ・D.T.Cassidy: Appl.Opt.,Vol.27,No.3,pp.610-614,1
988. ・田井秀男、松浦正行、田中弘明、上原喜代治:光学,V
ol.19,No.9,pp.616-619,1990. に開示されている。初めに、2波長差分方式について説
明し、その後、本発明に関わる周波数変調方式について
説明する。As a development of this principle, there are a two-wavelength difference method and a frequency modulation method, and these methods are now mainstream. Detailed explanation of the two-wavelength difference method and the experimental results are as follows: ・ K.Uehara: Appl.Phys.B, Vol.38, No.1, pp.37-40,1985. ・ Hideo Tai, Kazunari Yamamoto, Abe Ken, Takashi Ueki, Hiroaki Tanaka, Kiyoji Uehara: Transactions of the Society of Instrument and Control Engineers 24, pp.452-458,1
988. ・ Hideo Tai, Hiroaki Tanaka, Kiyoji Uehara: Optics, Vol.19, No.
4, pp.238-244, 1990. In addition, a detailed explanation of the frequency modulation method and the experimental results are as follows: DTCassidy: Appl.Opt.
988. ・ Hideo Tai, Masayuki Matsuura, Hiroaki Tanaka, Kiyoji Uehara: Optics, V
ol. 19, No. 9, pp. 616-619, 1990. First, the two-wavelength difference method will be described, and then the frequency modulation method according to the present invention will be described.
【0004】2波長差分方式を用いたガス検出器のブロ
ック図を図8に示す。ここで半導体レーザ11から受光部
14までの距離は任意の長さのガスセル12で測定出来るよ
うに可変となっている。したがって、距離が長くなると
レーザ光が発散して減衰することにより受光レンズ13で
集光し受光部14で受ける信号のレベルが小さくなり、そ
の結果、ガス濃度測定装置15はガスの濃度が増えたもの
と見積もってしまう。ここで述べているのは、半導体レ
ーザ11から受光部14までの距離に関してであり、ガスセ
ル12の長さに比例して見掛け上の減衰量も大きくなる
が、この量はガスセル12の長さで割ることでキャンセル
できる。この距離による影響を無くすために、実際に
は、吸収線の中心のfc と吸収線の無いfr の発振周波
数をもつ二つのレーザ光をガスに照射して、その比に適
当な比例定数を掛け濃度に換算する。この2波長差分方
式で問題となるのは、半導体レーザ11の発振周波数はT
Hzオーダの信号であり複雑な信号処理を行えないとい
うことである。また、安定して2波長の信号を生成する
のは非常に難しいという点である。FIG. 8 shows a block diagram of a gas detector using the two-wavelength difference method. Here, from the semiconductor laser 11 to the light receiving part
The distance to 14 is variable so that it can be measured by the gas cell 12 of an arbitrary length. Therefore, when the distance becomes long, the laser light diverges and is attenuated, so that the level of the signal collected by the light receiving lens 13 and received by the light receiving unit 14 becomes small, and as a result, the gas concentration measuring device 15 increases the gas concentration. I estimate it as something. What is stated here is the distance from the semiconductor laser 11 to the light receiving portion 14, and the apparent attenuation amount increases in proportion to the length of the gas cell 12, but this amount depends on the length of the gas cell 12. You can cancel by breaking. In order to eliminate the influence of this distance, in practice, two laser lights having an oscillation frequency of fc at the center of the absorption line and fr without the absorption line are irradiated to the gas, and the ratio is multiplied by an appropriate proportional constant. Convert to concentration. The problem with this two-wavelength difference method is that the oscillation frequency of the semiconductor laser 11 is T
This is a signal in the Hz order, which means that complicated signal processing cannot be performed. Moreover, it is very difficult to stably generate a signal of two wavelengths.
【0005】この問題を解決するために考案されたのが
次に述べる周波数変調方式であり、数kHz のベースバ
ンド領域で信号処理を行うことが可能となる。図4に周
波数変調方式の原理図を示す。中心周波数fc 、変調周
波数fm で半導体レーザの出力を周波数変調し、対象と
なるガスに照射する。ガスの吸収線は離調周波数に対し
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部では変調周波数fm の2倍の周波
数の信号(2倍波)が得られる。ここで、変調周波数f
m は任意の周波数でよいので、たとえば、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が可能となる。2波
長差分方式の説明で述べたことと同様に周波数変調方式
で距離の影響をキャンセルするためには、半導体レーザ
の出力を周波数変調を行うと同時に周波数fm で振幅変
調を行えばよいのであるが、半導体レーザの出力に周波
数変調を掛けると振幅変調も掛かるので、丁度これが利
用できる。そして、受光部でエンベロープ検波を行うこ
とで振幅変調による基本波を推定でき、この基本波の振
幅と前記2倍波の振幅の比を位相同期させて取ること
で、距離に関係なくガス濃度に比例した値を得ることが
できる。A frequency modulation method described below was devised to solve this problem, and it is possible to perform signal processing in a base band region of several kHz. FIG. 4 shows a principle diagram of the frequency modulation method. The output of the semiconductor laser is frequency-modulated at the center frequency fc and the modulation frequency fm, and the target gas is irradiated. Since the absorption line of gas is almost a quadratic function with respect to the detuning frequency, this absorption line plays the role of a discriminator, and a signal (double wave) having a frequency twice the modulation frequency fm is generated at the light receiving part. can get. Here, the modulation frequency f
Since m may be any frequency, for example, if it is selected to be several kHz, high-level signal processing can be performed using a digital signal processor (DSP) or a general-purpose processor. In order to cancel the influence of distance by the frequency modulation method as described in the explanation of the two-wavelength difference method, the output of the semiconductor laser may be frequency-modulated and at the same time the amplitude modulation may be performed at the frequency fm. If frequency modulation is applied to the output of the semiconductor laser, amplitude modulation is also applied, and this can be used exactly. Then, the fundamental wave by amplitude modulation can be estimated by performing envelope detection in the light receiving unit, and by taking the ratio of the amplitude of this fundamental wave and the amplitude of the second harmonic in phase synchronization, the gas concentration can be obtained regardless of the distance. A proportional value can be obtained.
【0006】ここで、実際には、図5に示すように、半
導体レーザの特性は様々な歪みを持っているので、前記
振幅は、ガウス平面で考えた場合、真円ではなく楕円と
か卵型とか、あるいは凸状であるが対称性の無い形状
(以後、楕円と総称する。)の半径となる。すなわち、
1点のみの周波数を抽出するための帯域幅無限小のバン
ドパスフィルターは実現不可能なので、前記歪みが基本
波及び2倍波に含まれてしまい楕円となる。従って、正
確にガスの濃度を推定しようとした場合、楕円の特性に
より生じるオフセット値が生じないように位相を同期さ
せ振幅値が最大あるいは最小となるように位相を調整す
る必要がある。Actually, as shown in FIG. 5, since the characteristics of the semiconductor laser have various distortions, the above-mentioned amplitude is not a perfect circle but an ellipse or an egg shape when considered in a Gaussian plane. Or the radius of a convex shape without symmetry (hereinafter collectively referred to as an ellipse). That is,
Since a bandpass filter with an infinitely small bandwidth for extracting the frequency of only one point cannot be realized, the distortion is included in the fundamental wave and the second harmonic wave and becomes an ellipse. Therefore, in order to accurately estimate the gas concentration, it is necessary to synchronize the phases so that the offset value caused by the characteristic of the ellipse does not occur and adjust the phase so that the amplitude value becomes maximum or minimum.
【0007】[0007]
【発明が解決しようとする課題】この周波数変調方式の
ガス検出器で用いられる従来のガス濃度測定装置は位相
同期式であり、その問題点は、位相同期を行うためにガ
ス濃度を推定する前に周波数変調による振幅が最大にな
るように位相を手動で少しずつずらしながら最大点また
は最小点を見つけなければならないということである。
現在この調整のために数分の時間が必要である。また、
位相同期を行うためには周波数の等しい信号をレファレ
ンスとして半導体レーザの変調部からガス濃度測定処理
部に持ってくる必要がある。そして、位相情報を処理す
る等の複雑な処理を行わなければならない。The conventional gas concentration measuring device used in the gas detector of this frequency modulation system is of the phase synchronization type, and its problem is that before estimating the gas concentration for phase synchronization. That is, the maximum point or the minimum point must be found while manually shifting the phase little by little so that the amplitude due to frequency modulation becomes maximum.
Currently, it takes a few minutes for this adjustment. Also,
In order to perform phase synchronization, it is necessary to bring signals having the same frequency as a reference from the modulator of the semiconductor laser to the gas concentration measurement processor. Then, complicated processing such as processing the phase information must be performed.
【0008】本発明の目的は、周波数変調方式を用いる
のであるが、従来のように位相同期のための校正を行わ
なくても済み、また、情報処理が複雑でないため安価な
低速のDSPあるいは安価な汎用のプロセッサの使用で
実現できるガス濃度測定装置を提供することである。The object of the present invention is to use a frequency modulation method, but it is not necessary to perform calibration for phase synchronization as in the prior art, and since information processing is not complicated, an inexpensive low speed DSP or an inexpensive DSP is used. Another object of the present invention is to provide a gas concentration measuring device that can be realized by using a general-purpose processor.
【0009】[0009]
【課題を解決するための手段】ガスの濃度を測定あるい
は推定する場合に必要となるパラメータは、被測定ガス
の吸収特性を帯びた光信号を受光器で検出し、得られた
電気信号がもつ基本波、すなわち、ガスセル(被測定ガ
ス)に向けて入射された半導体レーザ光を周波数変調す
るのに用いた周波数(fm)の基本波の信号成分と、被
測定ガスの吸収特性により励起された、基本波の2倍の
周波数(2fm)をもつ2倍波の信号成分との振幅比で
ある。しかしながら、現実には、様々な要因により目的
とする信号に歪みが含まれるため、基本波及び2倍波の
位相が変化すると前記振幅比は変化する。前記歪みは、
白色雑音のように平均化を行うだけでは取り除くことが
できないものであり、正確に振幅を求めることは不可能
である。[Means for Solving the Problems] The parameters necessary for measuring or estimating the concentration of gas have an electric signal obtained by detecting an optical signal having an absorption characteristic of the gas to be measured with a light receiver. The fundamental wave, that is, the signal component of the fundamental wave of the frequency (fm) used for frequency-modulating the semiconductor laser light incident on the gas cell (gas to be measured) and the absorption characteristic of the gas to be measured are excited. , The amplitude ratio with the signal component of the double wave having the frequency (2fm) double that of the fundamental wave. However, in reality, since the target signal contains distortion due to various factors, the amplitude ratio changes when the phases of the fundamental wave and the second harmonic wave change. The distortion is
Like white noise, it cannot be removed only by averaging, and it is impossible to accurately obtain the amplitude.
【0010】実験の結果、目的とする信号に含まれる歪
みは周期的であり、ガウス平面上でみると基本波及び2
倍波の軌跡は楕円軌道となることが分かった。そこで、
本発明ではガスの濃度の測度を振幅比ではなくガウス平
面上の楕円の面積比とした。この面積比を用いれば、位
相に関係なく面積比は一定であるので、従来のように基
本波及び2倍波の同相成分に対して振幅が最大(最小)
となるように手動で調整を行い、位相そのものを同期さ
せる必要はない。この発明では、検出された信号の同相
成分と直交成分とから振幅を求め、さらに疑似面積を求
めることができるような信号処理部を備えるようにし
た。As a result of the experiment, the distortion included in the target signal is periodic, and when viewed on the Gaussian plane, the fundamental wave and the 2
It was found that the locus of harmonics is an elliptical orbit. Therefore,
In the present invention, the measure of the gas concentration is not the amplitude ratio but the area ratio of the ellipse on the Gaussian plane. If this area ratio is used, the area ratio is constant regardless of the phase, so that the amplitude is maximum (minimum) with respect to the in-phase component of the fundamental wave and the second harmonic wave as in the past
There is no need to manually adjust so that the phase itself is synchronized. In the present invention, the signal processing unit is provided so that the amplitude can be obtained from the in-phase component and the quadrature component of the detected signal and the pseudo area can be obtained.
【0011】本発明の基本構成は図1(後に詳述する)
に示すように位相を少しずつずらしながら直交変調を、
基本波信号と2倍波信号それぞれに掛けることとし、同
相と直交との二つの成分をもつ信号(都合四つの信号)
を得るようにし、それぞれを積分した後に、二乗和を求
めて、再び積分し信号Aと信号Bとを得るようにしたも
のである。該信号A,Bはそれぞれが基本波及び2倍波
をガウス平面で表した場合の面積の測度となる。二つの
信号の比B/Aは被測定ガスの濃度を表す測度であるこ
とを、次に説明する。The basic configuration of the present invention is shown in FIG. 1 (detailed later).
Quadrature modulation while gradually shifting the phase as shown in
Signals with two components, in-phase and quadrature, to be applied to the fundamental wave signal and the second harmonic signal respectively (four signals for convenience)
To obtain the sum of squares, obtain the sum of squares, and integrate again to obtain the signal A and the signal B. Each of the signals A and B is a measure of the area when the fundamental wave and the second harmonic wave are represented by the Gaussian plane. It will be described below that the ratio B / A of the two signals is a measure of the concentration of the gas to be measured.
【0012】[0012]
【作用】この信号処理の原理について基本波の振幅推定
を例として詳細に説明する。入力信号を、The principle of this signal processing will be described in detail by taking the amplitude estimation of the fundamental wave as an example. Input signal,
【0013】[0013]
【数1】 [Equation 1]
【0014】と仮定する。ここで、ωm は基本波の角周
波数でωm =2πfm 、φは初期位相、aは振幅、n
(t) は外部からの雑音であり、ωm のみ既知とする。数
1で我々が求めなければならないパラメータは振幅aで
ある。まず、ベースバンド信号にするために入力信号x
(t) に角周波数ωm で直交変調を行うと、Assume that Where ω m is the angular frequency of the fundamental wave, ω m = 2πfm, φ is the initial phase, a is the amplitude, and n is
(t) is noise from the outside, and only ωm is known. The parameter we have to find in equation 1 is the amplitude a. First, the input signal x is converted to a baseband signal.
When quadrature modulation is performed on (t) with angular frequency ωm,
【0015】[0015]
【数2】 [Equation 2]
【0016】となる。数2の第2項は、白色雑音を周波
数推移させた項と考えることができるので、u(t) を平
均化することで無視できる程度に小さくできる。すなわ
ち、[0016] The second term of the equation 2 can be considered as a term in which white noise is frequency-shifted, and can be made negligibly small by averaging u (t). That is,
【0017】[0017]
【数3】 [Equation 3]
【0018】なお、本発明のガス濃度測定装置では、実
際の処理としては、後に述べるように、基本波と2倍波
の振幅の比をとるので、平均化の処理は行わない。数3
の結果を極座標で表すと、In the gas concentration measuring apparatus of the present invention, the averaging process is not performed as the actual process, as will be described later, because the ratio of the amplitudes of the fundamental wave and the double wave is taken. Number 3
If the result of is expressed in polar coordinates,
【0019】[0019]
【数4】 [Equation 4]
【0020】となる。この数4の第1項は同相成分、第
2項は直交成分と呼ばれる。したがって、数4から振幅
aを抽出するには同相及び直交成分をそれぞれ二乗して
加算し、さらに、平方根をとればよい。すなわち、ノル
ム演算を行えばよい。[0020] The first term of this equation 4 is called an in-phase component, and the second term is called a quadrature component. Therefore, in order to extract the amplitude a from Equation 4, the in-phase component and the quadrature component are each squared and added, and then the square root is taken. That is, the norm calculation may be performed.
【0021】[0021]
【数5】 [Equation 5]
【0022】ここで、直交変調部の位相を0から2πに
わたって変化させ、それぞれの角度に対する振幅を求め
て、それぞれの振幅を加算すると、楕円の面積と近似的
に等価な疑似面積が求められる。図1に示されるよう
に、上記の操作を基本波の角周波数ωm と2倍波の角周
波数2ωm にとり、得られる疑似面積の比を求めること
でガスの濃度に比例した値を得ることができる。Here, the phase of the quadrature modulator is varied from 0 to 2π, the amplitude for each angle is calculated, and the respective amplitudes are added to obtain a pseudo area approximately equivalent to the area of the ellipse. As shown in FIG. 1, a value proportional to the gas concentration can be obtained by taking the above operation for the angular frequency ωm of the fundamental wave and the angular frequency 2ωm of the second harmonic and obtaining the ratio of the obtained pseudo areas. .
【0023】[0023]
【実施例】図1に基づいて第1の実施例について説明す
る。基本波とその周波数の2倍の周波数を含む検出器の
信号である受信信号が、二つの直交変調部3,4に入力
される。基本波直交変調部3には基本波の角周波数ωm
の、また、2倍波直交変調部4には基本波の2倍の角周
波数2ωm の位相が順次増加する余弦波信号が加えられ
ている。前記位相は、0〜2πの範囲で位相信号発生部
6により順次段階的に増加される。本実施例では、位相
を0〜2πの範囲で順次段階的に増加させるようにして
いるが、減少させるようにしてもよく、要は0〜2πの
範囲にわたって順次変化させればよい。EXAMPLE A first example will be described with reference to FIG. The received signal, which is the signal of the detector including the fundamental wave and twice the frequency thereof, is input to the two quadrature modulators 3 and 4. The fundamental wave quadrature modulator 3 has an angular frequency ωm of the fundamental wave.
In addition, the cosine wave signal in which the phase of the angular frequency 2ωm, which is twice the fundamental wave, sequentially increases is added to the double wave quadrature modulator 4. The phase is sequentially and stepwise increased by the phase signal generator 6 in the range of 0 to 2π. In this embodiment, the phase is sequentially increased stepwise in the range of 0 to 2π, but it may be decreased, that is, the phase may be sequentially changed over the range of 0 to 2π.
【0024】前記余弦波信号から位相遅延器33,43 によ
り正弦波信号がつくられ、基本波信号及び2倍波信号と
それらの余弦波信号及び正弦波信号がそれぞれ乗算器3
1,32,41,42 で乗算される。この結果、基本波直交変調
部3からは前記数2の右辺の二つの項で記述される二つ
の信号が得られ、次の積分部5の積分器51,52,53,54
で、それぞれが積分され、前記数4で示される信号が、
それぞれの同相及び直交成分について得られる。積分部
5からの二つの信号は、二乗和演算部7に加えられ、乗
算器71,72,73,74 で二乗され、加算器75,76 で加算され
る。さらに、この信号は面積抽出部8で演算されること
で、数5で示される振幅を位相を段階的にずらしながら
加算することになりガウス平面における面積に相当する
信号が除算部10への第1の信号(分母となる信号)とさ
れる。A sine wave signal is generated from the cosine wave signal by the phase delay devices 33 and 43, and the fundamental wave signal and the second harmonic wave signal and those cosine wave signal and sine wave signal are respectively multiplied by a multiplier 3
It is multiplied by 1,32,41,42. As a result, two signals described by the two terms on the right side of the equation 2 are obtained from the fundamental wave quadrature modulator 3, and the integrators 51, 52, 53, 54 of the next integrator 5 are obtained.
Then, each of them is integrated, and the signal shown in the equation 4 is
Obtained for each in-phase and quadrature component. The two signals from the integrator 5 are added to the square sum calculator 7, squared by the multipliers 71, 72, 73, 74 and added by the adders 75, 76. Further, this signal is calculated by the area extraction unit 8 to add the amplitudes shown in Equation 5 while shifting the phase stepwise, and the signal corresponding to the area on the Gaussian plane is sent to the division unit 10. 1 signal (a denominator signal).
【0025】2倍波についても数2ないし数5において
角周波数ωm を2ωm とした演算処理がそれぞれ2倍波
直交変調部4、積分部5、二乗和演算部7、面積抽出部
8で行われて、除算部10への第2の信号(分子となる信
号)が得られる。除算部10では両信号の比B/Aが得ら
れ、この出力がガス濃度に比例する推定値とされる。With respect to the second harmonic wave, the arithmetic processing in which the angular frequency ωm is 2ωm in the equations 2 to 5 is performed in the second harmonic quadrature modulator 4, the integrator 5, the sum of squares calculator 7, and the area extractor 8, respectively. As a result, a second signal (a numerator signal) to the division unit 10 is obtained. The dividing unit 10 obtains the ratio B / A of both signals, and this output is an estimated value proportional to the gas concentration.
【0026】なお、Aの値が前もって測定され、かつ、
半導体レーザ11から受光部14までの距離が固定となって
いれば、Aを都度測定する必要はないので、Aを求める
側の、第1の余弦波信号発生部1、基本波直交変調部
3、積分部5、二乗和演算部7、及び面積抽出部8は不
要であり、除算部10に前記測定されたAを入力しておけ
ばよい。また、図1では積分部5の積分器51,52,53,54
と二乗和演算部7の乗算器71,72,73,74 とは各信号毎に
設けてあるが、メモリ又はレジスタを備えればこれらの
演算は一つの積分器及び乗算器で時分割で実施すること
も可能である。要は、作用のところで述べた数2ないし
数5の演算が行えればよい。Note that the value of A is measured in advance and
If the distance from the semiconductor laser 11 to the light receiving unit 14 is fixed, it is not necessary to measure A each time. Therefore, the first cosine wave signal generating unit 1 and the fundamental wave quadrature modulating unit 3 on the side for obtaining A are required. , The integration unit 5, the sum of squares calculation unit 7, and the area extraction unit 8 are unnecessary, and the measured A may be input to the division unit 10. In addition, in FIG. 1, the integrators 51, 52, 53, 54 of the integration unit 5 are
And the multipliers 71, 72, 73, 74 of the sum of squares operation unit 7 are provided for each signal. However, if a memory or a register is provided, these operations are performed by one integrator and multiplier in time division. It is also possible to do so. In short, it is only necessary to perform the operations of the equations 2 to 5 described in the operation.
【0027】図2に第2の実施例の構成を示す。第1の
実施例(図1)との違いは面積抽出部8での演算処理で
ある。前記信号A、Bに相当する疑似面積を、基本波に
ついては図6に示されるように半径an( n=1,2,
・・・N)を用いて、FIG. 2 shows the configuration of the second embodiment. The difference from the first embodiment (FIG. 1) is the arithmetic processing in the area extraction unit 8. The pseudo areas corresponding to the signals A and B have a radius an (n = 1, 2,
... N)
【0028】[0028]
【数6】 [Equation 6]
【0029】として、面積抽出部8で算出している。こ
こで、初期位相は非同期方式なのでガウス平面上のどこ
かは分からないが、基点とする点を位相角0とみなすこ
とで、数6を初期位相にかかわりなく用いることができ
る。また、2倍波は、前記Nは2πではなく4πにおけ
る指標となる。The area is calculated by the area extraction unit 8. Here, since the initial phase is an asynchronous method, somewhere on the Gaussian plane cannot be known, but by regarding the point serving as the base point as the phase angle 0, it is possible to use Equation 6 regardless of the initial phase. Further, the second harmonic is an index at 4π instead of 2π.
【0030】検出ガスとしてメタンガスを選択した場合
の実施例を以下に述べる。図7に本発明のガス濃度測定
装置を用いたガス検出器のブロック図を示す。この図で
半導体レーザ11はメタンガスの吸収線に中心周波数をも
つ波長1653.8nmのレーザである。このガス検出器では、
レーザ自身から生じる2倍波歪みをキャンセルするため
にフィードバック制御を行っている。また、周波数変調
の変調周波数を32.5kHz として変調指数を20%に設定し
た。演算処理部は、テキサス・インスツルメンツ社のD
SP(TMS320C25 )を用い、マスタークロックは50MHz
、サンプリングレートは260kHzである。An example in which methane gas is selected as the detection gas will be described below. FIG. 7 shows a block diagram of a gas detector using the gas concentration measuring device of the present invention. In this figure, the semiconductor laser 11 is a laser having a wavelength of 1653.8 nm and a center frequency in the absorption line of methane gas. With this gas detector,
Feedback control is performed to cancel the second harmonic distortion generated by the laser itself. Also, the modulation frequency was set to 32.5 kHz and the modulation index was set to 20%. The arithmetic processing unit is D of Texas Instruments Incorporated.
Using SP (TMS320C25), master clock is 50MHz
, The sampling rate is 260kHz.
【0031】[0031]
【発明の効果】本発明の構成によると、基本波と2倍波
の振幅をそれぞれの同相成分と直交成分とから演算によ
り求め、さらに、位相を変化させながら加算すること等
によりガウス平面上の疑似面積A,Bを求めている。そ
の後、信号Bと信号Aとの比を求めて、被測定ガスの濃
度を推定するものとしたから、位相同期の手動調整を必
要とせずにガス濃度測定を行うことができる。また、直
交変調部で用いる搬送波の周波数は多少ずれてもよいの
で、半導体レーザの変調部からレファレンスの信号を持
ってくる必要がない。さらに、位相情報を抽出する必要
がないため、アルゴリズムを簡略化でき、安価で汎用の
低速なプロセッサを用いることができる。According to the configuration of the present invention, the amplitudes of the fundamental wave and the second harmonic wave are calculated from the in-phase component and the quadrature component, and the addition is performed while changing the phase. Pseudo areas A and B are calculated. After that, since the ratio of the signal B and the signal A is obtained to estimate the concentration of the gas to be measured, the gas concentration can be measured without requiring manual adjustment of phase synchronization. Further, since the frequency of the carrier wave used in the quadrature modulator may be slightly shifted, it is not necessary to bring the reference signal from the modulator of the semiconductor laser. Furthermore, since it is not necessary to extract the phase information, the algorithm can be simplified and an inexpensive general-purpose low-speed processor can be used.
【図1】本発明の第1の実施例の構成を示す図。FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.
【図2】本発明の第2の実施例の構成を示す図。FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.
【図3】ガスの吸収特性の模式図。FIG. 3 is a schematic diagram of gas absorption characteristics.
【図4】周波数変調方式の原理図。FIG. 4 is a principle diagram of a frequency modulation method.
【図5】レーザ光が歪みを含んだ場合の周波数変調方式
を説明する図。FIG. 5 is a diagram illustrating a frequency modulation method when laser light includes distortion.
【図6】基本波のガウス平面上の軌跡を示す図。FIG. 6 is a diagram showing a locus of a fundamental wave on a Gaussian plane.
【図7】本発明のガス濃度測定装置を用いたガス検出器
のブロック図。FIG. 7 is a block diagram of a gas detector using the gas concentration measuring device of the present invention.
【図8】2波長差分方式を用いたガス検出器のブロック
図。FIG. 8 is a block diagram of a gas detector using a two-wavelength difference method.
1 第1の余弦波信号発生部 2 第2の余弦波信号発生部 3 基本波直交変調部 4 2倍波直交変調部 5 積分部 6 位相信号発生部 7 2乗和演算部 8 面積抽出部 9 制御器 10 除算部 11 半導体レーザ 12 ガスセル 13 受光レンズ 14 受光部 15 ガス濃度測定装置 1 1st cosine wave signal generation part 2 2nd cosine wave signal generation part 3 Fundamental wave quadrature modulation part 4 2nd harmonic quadrature modulation part 5 Integration part 6 Phase signal generation part 7 2 Sum calculation part 8 Area extraction part 9 Controller 10 Division unit 11 Semiconductor laser 12 Gas cell 13 Light receiving lens 14 Light receiving unit 15 Gas concentration measuring device
Claims (2)
波数変調された光を被測定ガスに入射して得られた、該
被測定ガスの吸収特性を帯びた光信号の基本波信号(周
波数fm )と2倍波信号(周波数2fm )とからガス濃
度を測定するガス濃度測定装置において、 前記所定の周波数の2倍の周波数(2fm )を有し、か
つ、位相が順次変化する余弦波信号を発生する余弦波信
号発生部(2)と、 被測定ガスの吸収特性を帯びた光信号を検出した電気信
号を受けて前記余弦波信号発生部からの余弦波信号で直
交変調を掛ける2倍波直交変調部(4)と、 前記2倍波直交変調部からそれぞれ出力される二つの互
いに直交する2倍波の複素信号をそれぞれ時間積分する
積分部(5)と、 位相角度が2πの範囲において順次段階的に変化する位
相信号を前記余弦波信号発生部に向けて出力する位相信
号発生部(6)と、 積分された二つの互いに直交する2倍波の複素信号の2
乗和を行う2乗和演算部(7)と、 該2乗和演算部の出力を前記位相角度の2πの範囲にわ
たって積分し直交座標における信号の疑似面積成分を求
める面積抽出部(8)と、 該面積抽出部の積分周期の終了時毎に、前記位相信号発
生部を所定位相ずつ歩進させる制御器(9)と、 前記面積抽出部で抽出された2倍波信号の疑似面積成分
と予め求められている基本波信号の疑似面積成分との比
を演算する除算部(10)とで成る信号処理部を有する
ことを特徴とするガス濃度測定装置。1. A fundamental wave signal (frequency) of an optical signal having absorption characteristics of the gas to be measured, obtained by injecting light amplitude-modulated and frequency-modulated at a predetermined frequency (fm) into the gas to be measured. fm) and a second harmonic signal (frequency 2fm) for measuring the gas concentration, which is a cosine wave signal having a frequency (2fm) which is twice the predetermined frequency and whose phase changes sequentially. And a cosine wave signal generating section (2) for generating an electric signal that detects an optical signal having an absorption characteristic of the gas to be measured, and performs quadrature modulation with the cosine wave signal from the cosine wave signal generating section. A quadrature wave modulation unit (4), an integration unit (5) for time-integrating two mutually orthogonal second-harmonic complex signals output from the second harmonic quadrature modulation unit, and a phase angle range of 2π Phase signal that changes stepwise at 2 of the phase signal generator for outputting toward the cosine wave signal generating section (6), integrated two double wave complex signals orthogonal to each other
A sum of squares operation unit (7) for performing sum of squares, and an area extraction unit (8) for integrating outputs of the sum of squares operation unit over a range of 2π of the phase angle to obtain a pseudo area component of a signal in rectangular coordinates. A controller (9) for stepping the phase signal generator by a predetermined phase at each end of the integration period of the area extractor; and a pseudo area component of the second harmonic signal extracted by the area extractor. A gas concentration measuring device comprising: a signal processing unit including a dividing unit (10) for calculating a ratio of a fundamental wave signal to a pseudo area component which is obtained in advance.
波数変調された光を被測定ガスに入射して得られた、該
被測定ガスの吸収特性を帯びた光信号の基本波信号(周
波数fm )と2倍波信号(周波数2fm )とからガス濃
度を測定するガス濃度測定装置において、 前記所定の周波数(fm )を有し、かつ、位相が順次変
化する余弦波信号を発生する第1の余弦波信号発生部
(1)と、 前記所定の周波数の2倍の周波数(2fm )を有し、か
つ、位相が順次変化する余弦波信号を発生する第2の余
弦波信号発生部(2)と、 被測定ガスの吸収特性を帯びた光信号を検出した電気信
号を受けて前記第1の余弦波信号発生部からの余弦波信
号で直交変調を掛ける基本波直交変調部(3)と、 被測定ガスの吸収特性を帯びた光信号を検出した電気信
号を受けて前記第2の余弦波信号発生部からの余弦波信
号で直交変調を掛ける2倍波直交変調部(4)と、 前記基本波直交変調部及び2倍波直交変調部からそれぞ
れ出力される二つの互いに直交する基本波の複素信号及
び二つの互いに直交する2倍波の複素信号とをそれぞれ
時間積分する積分部(5)と、 位相角度が2πの範囲において順次段階的に変化する位
相信号を前記第1の余弦波信号発生部及び第2の余弦波
信号発生部に向けて出力する位相信号発生部(6)と、 積分された二つの互いに直交する基本波の複素信号と積
分された二つの互いに直交する2倍波の複素信号とのそ
れぞれの2乗和を行う2乗和演算部(7)と、 該2乗和演算部の出力を前記位相角度の2πの範囲にわ
たって積分し直交座標における信号の疑似面積成分を求
める面積抽出部(8)と、 該面積抽出部の積分周期の終了時毎に、前記位相信号発
生部を所定位相ずつ歩進させる制御器(9)と、 前記面積抽出部で抽出された2倍波信号の疑似面積成分
と基本波信号の疑似面積成分との比を演算する除算部
(10)とで成る信号処理部を有することを特徴とする
ガス濃度測定装置。2. A fundamental wave signal (frequency) of an optical signal having absorption characteristics of the gas to be measured, obtained by injecting light amplitude-modulated and frequency-modulated at a predetermined frequency (fm) into the gas to be measured. fm) and a second harmonic signal (frequency 2fm) for measuring the gas concentration, a first cosine wave signal having a predetermined frequency (fm) and having a phase that changes sequentially. Cosine wave signal generator (1), and a second cosine wave signal generator (2) that generates a cosine wave signal having a frequency twice the predetermined frequency (2 fm) and a phase that changes sequentially. ), And a fundamental wave quadrature modulator (3) that receives an electrical signal obtained by detecting an optical signal having an absorption characteristic of the gas to be measured and performs quadrature modulation with the cosine wave signal from the first cosine wave signal generator. , An electrical signal that detects an optical signal with absorption characteristics of the gas to be measured Outputs from the second harmonic quadrature modulator (4) that receives the second quadrature cosine wave signal from the second cosine wave signal generator and performs the quadrature modulation with the cosine wave signal, and the fundamental quadrature modulator and the second harmonic quadrature modulator. An integrating unit (5) for time-integrating two mutually orthogonal fundamental wave complex signals and two mutually orthogonal second harmonic wave complex signals, and a phase signal that sequentially changes stepwise within a phase angle range of 2π. And a phase signal generator (6) for outputting to the first cosine wave signal generator and the second cosine wave signal generator, and two integrated orthogonal fundamental wave complex signals. A sum-of-squares operation unit (7) for performing a sum-of-squares of each of two mutually orthogonal second-harmonic complex signals, and an output of the sum-of-squares operation unit is integrated over a range of 2π of the phase angle and orthogonal Find the pseudo-area component of the signal at coordinates An area extraction section (8), a controller (9) for stepping the phase signal generation section by a predetermined phase at each end of the integration period of the area extraction section, and 2 extracted by the area extraction section. A gas concentration measuring device comprising: a signal processing unit including a dividing unit (10) for calculating a ratio of a pseudo area component of a harmonic signal and a pseudo area component of a fundamental wave signal.
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JP5326163A JP3051808B2 (en) | 1993-11-30 | 1993-11-30 | Gas concentration measurement device |
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---|---|---|---|
JP5326163A JP3051808B2 (en) | 1993-11-30 | 1993-11-30 | Gas concentration measurement device |
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ID=18184761
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