JP2001159608A - Gas concentration measuring apparatus - Google Patents
Gas concentration measuring apparatusInfo
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- JP2001159608A JP2001159608A JP2000309952A JP2000309952A JP2001159608A JP 2001159608 A JP2001159608 A JP 2001159608A JP 2000309952 A JP2000309952 A JP 2000309952A JP 2000309952 A JP2000309952 A JP 2000309952A JP 2001159608 A JP2001159608 A JP 2001159608A
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- harmonic
- component
- signal
- gas concentration
- frequency
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】この発明は、メタンガスや炭
酸ガスなどのガスの濃度を、それぞれのガス固有の吸収
スペクトルを利用することで高精度に測定するガス検出
器に於いて用いられるガス濃度測定処理装置に係り、特
に周波数変調法を用いたガス濃度測定処理装置に関する
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 measuring the concentration of a gas such as methane gas or carbon dioxide gas with high accuracy by utilizing an absorption spectrum peculiar to each gas. The present invention relates to a processing apparatus, and particularly to a gas concentration measurement processing apparatus using a frequency modulation method.
【0002】[0002]
【従来の技術】ガスには、それぞれガス分子固有の吸収
スペクトルが有り、レーザをこの吸収スペクトルの存在
する周波数で発振させることでガスの濃度を測定すると
いう試みは1965年にムーア(C.B.Moore) によって初めて
行われた。2. Description of the Related Art Each gas has an absorption spectrum peculiar to gas molecules, and an attempt to measure the concentration of a gas by oscillating a laser at a frequency where this absorption spectrum exists was made in 1965 by Moore (CBMoore). It was done for the first time.
【0003】この原理を下記で簡単に述べる。ガスの吸
収スペクトルは、そのガス分子の振動エネルギーに従っ
て様々な周波数に於いて極小値を持つが、そのうちの1
つを取り出すと図5に示されるような一般にローレンツ
型と呼ばれる特性になる。図5の横軸は周波数、縦軸は
透過率であり、この吸収スペクトルの極小値の周波数f
c における透過率は、ガスの濃度が高くなるにつれて小
さくなる。従って、fc の発振周波数を持つレーザ光を
ガスに照射して、その透過された信号を光検出器で受け
電気信号に変換し、透過率の変化量を算出すると、その
透過率の変化量がガスの濃度に比例するガス濃度の測度
となるので、この測度に予め濃度の分かっているガスを
測定する等して求めた係数を掛けることでガスの濃度を
測定することができる。[0003] This principle is briefly described below. The absorption spectrum of a gas has local minima at various frequencies according to the vibrational energy of the gas molecule.
When one is taken out, a characteristic generally called a Lorentz type is obtained as shown in FIG. The horizontal axis in FIG. 5 is frequency, and the vertical axis is transmittance. The frequency f of the minimum value of the absorption spectrum is shown.
The transmittance at c decreases as the gas concentration increases. Therefore, when the gas is irradiated with a laser beam having an oscillation frequency of fc, the transmitted signal is received by a photodetector and converted into an electric signal, and the change in transmittance is calculated. Since the gas concentration is proportional to the gas concentration, the gas concentration can be measured by multiplying this measure by a coefficient obtained by measuring a gas whose concentration is known in advance.
【0004】この原理に着目し発展させたものとして2
波長差分方式と周波数変調方式があり、これら2つの方
式が現在ではレーザを用いたガス濃度測定の主流となっ
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--4
0, 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, 19
88. ・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。Focusing on this principle and developing it, 2
There are a wavelength difference method and a frequency modulation method, and these two methods are currently the mainstream of gas concentration measurement using a laser. For a detailed description of the two-wavelength difference method and the experimental results, see K. Uehara: Appl. Phys. B, Vol. 38, No. 1, pp. 37--4.
0, 1985.Hideo Tai, Kazunari Yamamoto, Ken Abe, Takashi Ueki, Hiroaki Tanaka, Kiyoji Uehara: Transactions of the Society of Instrument and Control Engineers 24, pp.452--458, 19
88. ・ Hideo Tai, Hiroaki Tanaka, Kiyoji Uehara: Optics, Vol.19, No.
4, pp. 238-244, 1990.
【0005】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--6
14, 1988.田井秀男、松浦正行、田中弘明、上原喜代治: 光学,Vol.19, No.9,pp.616--619, 1990. に開示されている。[0005] Further, a detailed description of the frequency modulation method and experimental results are given in: DTCassidy: Appl. Opt., Vol. 27, No. 3, pp. 610--6.
14, 1988. Hideo Tai, Masayuki Matsuura, Hiroaki Tanaka, Kiyoji Uehara: Optics, Vol.19, No.9, pp.616--619, 1990.
【0006】初めに、2波長差分方式について説明し、
その後で本発明に関わる周波数変調方式について説明す
る。図10に2波長差分方式を用いたガス検出器のブロ
ック図を示す。図10で、周波数切り替え器40はレーザ
10の発振周波数をガスセル20のガスの吸収スペクトルで
透過率が極小となる周波数fc とガスの吸収スペクトル
が存在しない周波数fn を切り替えるためのものであ
る。光検出器30で電気信号に変換された信号は、レーザ
10の発振周波数fc ,fnを切り替えることで図5のよ
うに透過率が変わるので振幅値が変わり、その振幅の差
が透過率の変化量となりガスの濃度の測度となる。First, the two-wavelength difference method will be described.
After that, the frequency modulation method according to the present invention will be described. FIG. 10 shows a block diagram of a gas detector using the two-wavelength difference method. In FIG. 10, the frequency switch 40 is a laser
The oscillation frequency of 10 is used to switch between the frequency fc at which the transmittance is minimal in the gas absorption spectrum of the gas cell 20 and the frequency fn at which no gas absorption spectrum exists. The signal converted into an electric signal by the photodetector 30 is a laser
By switching the ten oscillation frequencies fc and fn, the transmittance changes as shown in FIG. 5, so that the amplitude value changes, and the difference between the amplitudes becomes the transmittance variation, which is a measure of the gas concentration.
【0007】ここで、一般の応用としてはレーザ10から
光検出器30までの光路長は可変とした方が都合がよい。
例えば、ガスの中を通るレーザ光の光路長が長いほど透
過率の変化が大きくなり高精度にガスの濃度測定を行う
ことができるので多重反射型のガスセルを選択したり、
持ち運びの容易さから小さなガスセルを選択したりする
場合があるからである。光路長が長くなるとレーザ光が
発散したり周囲の塵などの影響でレーザ光が減衰するの
で、ガス濃度測定処理装置80への入力信号の振幅が小さ
くなる。その結果、透過率の変化を表す振幅の差が小さ
くなり、ガス濃度測定処理装置80の出力値から換算され
るガスの濃度の値が減少するといった問題が生じる。上
記で述べた問題が生じないようにするため、その振幅の
差をガスの吸収スペクトルのない周波数の時の振幅で除
算するという手法が取られている。また、ガスの中を通
るレーザ光の光路長にその振幅の差は比例することにな
るから、濃度に換算するときは光路長で除算が行われ
る。このようにして求められたガス濃度の測度に適当な
比例定数を掛けることで、光路長に依存せずにガスの濃
度を得ることができる。Here, as a general application, it is convenient to make the optical path length from the laser 10 to the photodetector 30 variable.
For example, the longer the optical path length of the laser light passing through the gas, the greater the change in transmittance and the more accurately the gas concentration can be measured.
This is because a small gas cell may be selected for ease of carrying. When the optical path length becomes longer, the laser light diverges or the laser light is attenuated due to the influence of surrounding dust and the like, so that the amplitude of the input signal to the gas concentration measurement processing device 80 becomes smaller. As a result, a difference in amplitude representing a change in transmittance becomes smaller, and a problem arises in that the value of gas concentration converted from the output value of the gas concentration measurement processing device 80 decreases. In order to prevent the above-mentioned problem from occurring, a method is used in which the difference between the amplitudes is divided by the amplitude at a frequency having no gas absorption spectrum. In addition, since the difference in the amplitude is proportional to the optical path length of the laser light passing through the gas, when converting into the concentration, the division is performed by the optical path length. By multiplying the measure of the gas concentration thus obtained by an appropriate proportional constant, the gas concentration can be obtained without depending on the optical path length.
【0008】この2波長差分方式では、光検出器30で電
気信号に変換されガス濃度測定処理装置80への入力とな
る信号は直流の信号となるので、オペアンプのドリフト
などで生じた直流のオフセット成分を除去できないた
め、高精度にガスの濃度検出ができないという欠点があ
る。また、外来光の干渉により高精度にガスの濃度検出
ができないといった欠点もある。この欠点を改善するた
めに考案されたのが次に述べる周波数変調方式である。
この方式は直流のオフセット成分や外来光がが存在して
もガスの濃度測定に悪影響を及ぼさないように、交流成
分の信号だけでガスの濃度測定を行えるようにしたもの
である。In the two-wavelength difference method, since the signal which is converted into an electric signal by the photodetector 30 and which is input to the gas concentration measurement processing device 80 is a DC signal, the DC offset generated due to the drift of the operational amplifier or the like. Since components cannot be removed, there is a disadvantage that gas concentration cannot be detected with high accuracy. There is also a disadvantage that the concentration of gas cannot be detected with high accuracy due to interference of extraneous light. The frequency modulation method described below has been devised to improve this disadvantage.
In this method, the gas concentration can be measured only by the AC component signal so that the presence of a DC offset component or extraneous light does not adversely affect the gas concentration measurement.
【0009】図6に周波数変調方式の原理図を示す。中
心周波数をfc として、変調周波数fm でレーザを周波
数変調し、被測定ガスに照射する。ガスの吸収スペクト
ルはローレンツ型と呼ばれる特性を示し、離調周波数に
対してほぼ2次関数となるので、光検出器で電気信号に
変換された信号には、変調周波数の2倍の周波数の信号
(以後、この信号を2倍波信号という)が含まれる。こ
の信号の振幅値は、ガスの濃度が高くなると透過率が低
くなるので大きくなり、ガスの濃度の測度となり適当な
比例定数を掛けることでガスの濃度に換算できる。FIG. 6 shows the principle of the frequency modulation method. The laser is frequency-modulated at the modulation frequency fm with the center frequency being fc, and the laser is irradiated to the gas to be measured. Since the gas absorption spectrum shows a characteristic called Lorentz type and is almost quadratic function with respect to the detuning frequency, the signal converted into an electric signal by the photodetector includes a signal having a frequency twice as high as the modulation frequency. (Hereinafter, this signal is referred to as a second harmonic signal). The amplitude value of this signal increases as the gas concentration increases because the transmittance decreases and becomes a measure of the gas concentration, and can be converted into a gas concentration by multiplying by an appropriate proportional constant.
【0010】下記で、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光路長の影響をキャンセル
する方法について述べる。レーザを周波数変調するため
には電流制御を行わなければならない。この電流制御を
行いfm という周波数で周波数変調を掛けると、fm と
いう周波数で自動的に振幅変調も掛かる。このため、光
検出器で電気信号に変換された信号には振幅変調によっ
て生じたfm という周波数の信号も含まれる(以後、こ
の信号を基本波信号という)。この基本波を利用して、
2倍波の振幅値を基本波の振幅値で除算することで、光
路長が長くなることにより生じるレーザ光の発散あるい
は周囲の塵などの影響をキャンセルすることができ、こ
の値がガスの濃度の測度となる。このガス濃度測定のた
めの周波数変調法の基本波及び2倍波の振幅推定の方法
としては位相同期方式の位相敏感検波が用いられてい
る。In the following, a method of canceling the influence of the optical path length by the frequency modulation method will be described in the same manner as described in the description of the two-wavelength difference method. In order to frequency-modulate the laser, current control must be performed. When this current control is performed and frequency modulation is performed at the frequency fm, amplitude modulation is also automatically performed at the frequency fm. For this reason, the signal converted into an electric signal by the photodetector includes a signal having a frequency of fm generated by amplitude modulation (hereinafter, this signal is referred to as a fundamental signal). Using this fundamental wave,
Dividing the amplitude value of the second harmonic by the amplitude value of the fundamental wave cancels out the effect of laser light divergence or surrounding dust caused by an increase in the optical path length, and this value is determined by the gas concentration. Measure. As a method for estimating the amplitude of the fundamental wave and the second harmonic of the frequency modulation method for measuring the gas concentration, phase-sensitive phase-sensitive detection is used.
【0011】図11に周波数変調方式を用いた従来のガ
ス検出器を示す。この方式では、レーザ10の周波数変調
器50からリファレンスの信号をガス濃度測定装置90の基
本波位相敏感検波器91と2倍波位相敏感検波器92に接続
し、基本波の振幅値Aと2倍波の振幅値Bが最大となる
ように位相を手動で少しづつずらしながら位相同期をと
り、この校正で求められた振幅値Aを振幅値Bで除算す
ることでガスの濃度の測度が得られ適当な比例定数を掛
けることでガスの濃度に換算できる。FIG. 11 shows a conventional gas detector using a frequency modulation method. In this method, the reference signal from the frequency modulator 50 of the laser 10 is connected to the fundamental wave phase sensitive detector 91 and the second harmonic phase sensitive detector 92 of the gas concentration measuring device 90, and the amplitude values A and 2 The phase is manually shifted little by little so that the amplitude value B of the harmonic wave becomes the maximum, and the phase is synchronized. The amplitude value A obtained by this calibration is divided by the amplitude value B to obtain a measure of the gas concentration. By multiplying it by an appropriate proportional constant, it can be converted to the gas concentration.
【0012】[0012]
【発明が解決しようとする課題】周波数変調方式で従来
用いられている位相敏感検波では、レーザ10の周波数変
調器50からリファレンスの信号をガス濃度測定処理装置
90の基本波位相敏感検波器91と2倍波位相敏感検波器92
へ接続しなければならないといった問題が生じる。一例
として、水田で生じるメタンガスの濃度を測定する場
合、レーザ10とガス濃度測定処理装置90を数十m離す必
要があり、このような長距離のケーブルを用意するのは
非常に大変である。In the phase sensitive detection conventionally used in the frequency modulation method, a signal of a reference from a frequency modulator 50 of a laser 10 is processed by a gas concentration measurement processing apparatus.
90 fundamental wave phase sensitive detector 91 and 2nd harmonic phase sensitive detector 92
A problem arises that the user must connect to As an example, when measuring the concentration of methane gas generated in a paddy field, it is necessary to separate the laser 10 from the gas concentration measurement processing device 90 by several tens of meters, and it is very difficult to prepare such a long-distance cable.
【0013】また、位相敏感検波方式では、位相同期を
行うためにガスの濃度を推定する前に基本波及び2倍波
の振幅値が最大になるように手動で位相を少しずつずら
して最大点を見つけなければならず、数分の時間が必要
となるといった問題も生じる。In the phase sensitive detection method, the phase is manually shifted little by little so as to maximize the amplitude of the fundamental wave and the second harmonic before estimating the gas concentration in order to perform phase synchronization. Has to be found, which takes several minutes.
【0014】さらに、位相敏感検波はDSP (Digital Si
gnal Processor) や CPU (CentralProcessing Unit)な
どの処理速度では演算が間に合わないため、デジタル化
を行うことができず小型化および低コスト化ができな
い。本発明の目的は、従来の位相敏感検波を用いたガス
濃度測定処理装置の精度を維持しつつ、レーザの周波数
変調器からリファレンスの同期した信号をガス濃度測定
処理装置に接続する必要がなく、また校正のために手動
で位相を少しずつずらして振幅レベルの最大点を見つけ
るといった操作も必要なく、さらにDSP やCPU を用いて
回路の小型化、コストの削減を実現できるガス濃度測定
処理装置を提供することである。Further, the phase sensitive detection is performed by a DSP (Digital Si
Since the processing cannot be performed in time with the processing speed of a gnal processor) or a CPU (Central Processing Unit), it cannot be digitized and cannot be reduced in size and cost. An object of the present invention is to maintain the accuracy of a conventional gas concentration measurement processing device using phase-sensitive detection, and eliminate the need to connect a reference synchronized signal from the laser frequency modulator to the gas concentration measurement processing device. In addition, there is no need to manually shift the phase a little at a time for calibration to find the maximum point of the amplitude level.In addition, a gas concentration measurement processing device that can use DSPs and CPUs to reduce the size of the circuit and reduce costs To provide.
【0015】[0015]
【課題を解決するための手段】前記課題を解決するため
に、非同期方式の包絡線検波を採用することとし、第1
の発明では、さらに、高周波成分除去部を設けることと
した。また、第2の発明では、多重総和処理部を設ける
こととした。高周波成分除去部を設けた理由及び多重総
和処理部を設けた理由については作用の項で詳述する。In order to solve the above-mentioned problems, an asynchronous envelope detection is adopted.
According to the invention, a high-frequency component removing unit is further provided. In the second invention, a multiple sum processing unit is provided. The reason why the high-frequency component removing unit is provided and the reason why the multiple sum processing unit is provided will be described in detail in the section of operation.
【0016】〔作用〕非同期方式の包絡線検波を採用し
たので、リファレンスの同期した信号をガス濃度測定処
理装置に接続する必要がなく、また校正のために手動で
位相を少しずつずらして振幅レベルの最大点を見つける
といった操作も必要なく、さらに、DSP やCPU を用いて
の処理が可能となる。また、高周波成分除去部または多
重総和処理部で高周波成分を除去する。前に述べたよう
に、周波数変調方式でガスの濃度を測定する場合に必要
となるパラメータは、光検出器で電気信号に変換された
信号の基本波信号及び被測定ガスの吸収スペクトルによ
り生じる2倍波信号の振幅値である。2倍波信号の振幅
値を基本波信号の振幅値で除算するとガスの濃度の測度
となり、適当な定数を掛けることでガスの濃度に換算で
きる。[Operation] Since the asynchronous envelope detection is employed, there is no need to connect a reference-synchronized signal to the gas concentration measurement processor, and the amplitude level is manually shifted slightly for calibration. There is no need to find the maximum point, and processing using a DSP or CPU is possible. The high frequency component is removed by the high frequency component removing unit or the multiplex sum processing unit. As described above, the parameters necessary for measuring the gas concentration by the frequency modulation method include the fundamental wave signal of the signal converted into the electric signal by the photodetector and the absorption spectrum of the gas to be measured. This is the amplitude value of the harmonic signal. Dividing the amplitude value of the second harmonic signal by the amplitude value of the fundamental wave signal provides a measure of gas concentration, which can be converted to gas concentration by multiplying by an appropriate constant.
【0017】しかしながら、非同期方式の包絡線検波を
用いて基本波信号と2倍波信号の振幅の比を算出する
と、電源を入れ直すごとに、ガスの濃度が変化していな
いにも関わらず、この振幅の比が変わるといった現象が
生じる。電源を入れた状態では、この振幅の比は一定で
あり、電源を入れ直すとこの振幅の比が前の値と異なる
値で一定となるため、白色雑音のように平均化を用いて
この変動が生じないようにすることはできない。However, when the ratio of the amplitude of the fundamental wave signal to the amplitude of the second harmonic signal is calculated using the asynchronous envelope detection, this ratio is obtained every time the power is turned on again, even though the gas concentration does not change. A phenomenon such as a change in the amplitude ratio occurs. When the power is turned on, the ratio of this amplitude is constant, and when the power is turned on again, the ratio of this amplitude becomes constant at a value different from the previous value. It cannot be prevented.
【0018】前記現象について詳細に説明する。光検出
器で電気信号に変換された信号をDSP で処理するために
LPF(Low PassFilter) で高調波成分を除去するとADコン
バータで標本化した信号はThe above phenomenon will be described in detail. To process the signal converted by the photodetector into an electric signal by DSP
When harmonic components are removed by LPF (Low Pass Filter), the signal sampled by AD converter becomes
【0019】[0019]
【数1】 (Equation 1)
【0020】と表すことができる。ただし、第1項は基
本波成分、第2項は2倍波成分、第3項は白色雑音成分
であり、fm は基本波の周波数、fs はサンプリングレ
ート、θとφは初期位相である。ここで、数1を簡単に
表すためにIt can be expressed as Here, the first term is a fundamental wave component, the second term is a second harmonic component, the third term is a white noise component, fm is a fundamental wave frequency, fs is a sampling rate, and θ and φ are initial phases. Here, in order to simply represent Equation 1,
【0021】[0021]
【数2】 (Equation 2)
【0022】と置くと数1は## EQU2 ##
【0023】[0023]
【数3】 (Equation 3)
【0024】と書き直すことができる。ガスの濃度測定
のために必要となるのは数3の基本波の振幅Aと2倍波
の振幅Bである。まず、基本波の振幅Aを求めるため
に、ローカルの周波数を基本波の周波数として周波数推
移を行い、LPF で高調波成分を除去するとCan be rewritten. The amplitude A of the fundamental wave and the amplitude B of the second harmonic are required to measure the gas concentration. First, in order to obtain the amplitude A of the fundamental wave, a frequency transition is performed using the local frequency as the frequency of the fundamental wave, and harmonic components are removed by LPF.
【0025】[0025]
【数4】 (Equation 4)
【0026】従って、数4のノルムを求めるとTherefore, when the norm of Equation 4 is obtained,
【0027】[0027]
【数5】 (Equation 5)
【0028】となり、基本波の振幅Aが得られる。上で
述べたことと同様の操作を用いて2倍波の振幅Bを求め
ればよいように思われるが、低濃度のガスを測定する場
合、2倍波については問題が生じる。この理由は、低濃
度のガスを測定する場合、基本波成分の振幅値Aが2倍
波成分の振幅値Bよりもはるかに大きな値となるため
に、2倍波の周波数2fm で周波数推移を行った後のLP
F で、周波数推移されて高調波成分となった基本波成分
を十分に減衰できないからである。たとえ、周波数推移
を行う前処理としてHPF(High Pass Filter) を用いて基
本波成分を減衰させたとしても、より低濃度のガスに対
しては相対的に基本波の成分が2倍波成分よりも大きな
値を持ち、LPF で十分に減衰させることができず、結局
2倍波成分に影響を及ぼすことになる。ローカルの周波
数を2倍波の周波数として2倍波成分を抽出するために
周波数推移を行い、LPF を通すとその出力はThe amplitude A of the fundamental wave is obtained. It seems that the amplitude B of the second harmonic may be obtained by using the same operation as described above. However, when measuring a gas having a low concentration, a problem occurs with the second harmonic. The reason for this is that when measuring a gas having a low concentration, the amplitude value A of the fundamental wave component is much larger than the amplitude value B of the second harmonic component, so that the frequency transition at the second harmonic frequency 2fm is performed. LP after going
This is because the fundamental wave component that has been shifted in frequency and becomes a higher harmonic component cannot be sufficiently attenuated at F. Even if the fundamental component is attenuated using HPF (High Pass Filter) as a pre-process to change the frequency, the fundamental component is lower than the second harmonic component for lower concentration gas. Also has a large value and cannot be sufficiently attenuated by the LPF, which eventually affects the second harmonic component. With the local frequency as the frequency of the second harmonic, the frequency shift is performed to extract the second harmonic component.
【0029】[0029]
【数6】 (Equation 6)
【0030】となり、2倍波の振幅を推定するための直
流成分のみの信号とはならず、基本波成分が周波数推移
されることで生じる第2項、第3項の高調波成分が生じ
てしまう。数6をベクトルで表すと図7となる。また、
初期位相が異なる2つの2倍波信号の振幅値X0 、Y0
をベクトルで表すと図8となる。すなわち、電源を入れ
るタイミングにより、初期位相が変わると2倍波の振幅
値も変動してしまうことになる。As a result, the signal of only the DC component for estimating the amplitude of the second harmonic is not obtained, and the second and third harmonic components generated by shifting the frequency of the fundamental wave component are generated. I will. FIG. 7 shows Equation 6 as a vector. Also,
Amplitude values X0 and Y0 of two second harmonic signals having different initial phases
Is represented by a vector as shown in FIG. That is, if the initial phase changes according to the timing of turning on the power, the amplitude value of the second harmonic also changes.
【0031】一方、位相同期方式の位相敏感検波では振
幅値が最大となるように、ガスの濃度を測定する前に手
動で位相を調整しているのでこのような問題は生じな
い。本発明では、位相非同期方式の包絡線検波に高調波
成分除去部または多重総和処理部を設けて、2倍波の振
幅の測定において高調波成分を除去することで、2倍波
の振幅値の変動が生じないようにした。前記数6の第2
項、第3項の高調波成分はそれぞれ周波数fm と周波数
3fmの線スペクトルとなる。この高調波成分の信号
は、それぞれOn the other hand, in the phase-sensitive phase-sensitive detection of the phase synchronization system, such a problem does not occur because the phase is manually adjusted before measuring the gas concentration so that the amplitude value becomes maximum. In the present invention, a harmonic component removal unit or a multiplex sum processing unit is provided in the envelope detection of the phase asynchronous system, and the harmonic component is removed in the measurement of the amplitude of the second harmonic, whereby the amplitude value of the second harmonic is removed. No fluctuations occurred. 6 of the above
The harmonic components of the term and the third term are line spectra at the frequency fm and the frequency 3fm, respectively. The signals of this harmonic component are
【0032】[0032]
【数7】 (Equation 7)
【0033】で与えられるNの回数だけ加算すると、
(ここで、Mは任意の整数、G.C.M.(fs ,fm )はf
s とfm の最大公約数)By adding N times given by
(Where M is any integer and GCM (fs, fm) is f
greatest common divisor of s and fm)
【0034】[0034]
【数8】 (Equation 8)
【0035】[0035]
【0036】[0036]
【数9】 (Equation 9)
【0037】と打ち消され、高調波成分を除去できる。
従って、インパルス応答Thus, harmonic components can be removed.
Therefore, the impulse response
【0038】[0038]
【数10】 (Equation 10)
【0039】をもつ櫛形フィルタに数6で与えられる信
号を通すことで高調波成分を完全に除去できる。このこ
とを以下で周波数軸上で説明する。数10で与えられる
フィルタの周波数応答はThe harmonic component can be completely removed by passing the signal given by Equation 6 through a comb filter having the following. This will be described below on the frequency axis. The frequency response of the filter given by Equation 10 is
【0040】[0040]
【数11】 [Equation 11]
【0041】となる。一例として、M=1、fs =8f
m とするとN=8となり、数11で与えられる応答は、
図9に示されるようになり、周波数fm と周波数3fm
の領域の成分は完全に除去される。従って、数6で与え
られる信号を、数10で与えられるフィルタに通すこと
で、高調波成分が除去された2倍波の同相・直交成分B
×(eの−jφ乗)が得られ、数5と同様のノルム演算
を行うことで2倍波の振幅値Bを得ることができる。こ
の2倍波の振幅値Bには高調波成分が含まれていないの
で、電源を入れるごとにこの振幅値が変動するというこ
とはなくなり、高精度にガスの濃度を測定することがで
きる。## EQU1 ## As an example, M = 1, fs = 8f
m, N = 8 and the response given by equation 11 is
As shown in FIG. 9, the frequency fm and the frequency 3fm
The components in the region are completely removed. Therefore, by passing the signal given by equation (6) through the filter given by equation (10), the in-phase / quadrature component B of the second harmonic from which the harmonic component has been removed
× (e raised to the power of −jφ) is obtained, and the amplitude value B of the second harmonic can be obtained by performing the same norm operation as in Equation 5. Since the amplitude value B of the second harmonic does not include a harmonic component, the amplitude value does not change every time the power is turned on, and the gas concentration can be measured with high accuracy.
【0042】低濃度のガスを測定する場合は、基本波の
振幅値Aが2倍波の振幅値Bよりもはるかに大きな値と
なるために、上記で述べたように2倍波側に数10で与
えられるフィルタを入れたが、高濃度のガスを測定する
場合は、逆の基本波側に数10で与えられるフィルタを
入れる必要がある。このようにして求められた2倍波の
振幅値Bを基本波の振幅値Aで除算することで位相敏感
検波と同程度の精度でガスの濃度の測度が求まり、適当
な比例定数を掛けることでガスの濃度に換算できる。When measuring a gas having a low concentration, the amplitude value A of the fundamental wave is much larger than the amplitude value B of the second harmonic. Although the filter given by 10 is inserted, when measuring a gas with a high concentration, it is necessary to insert the filter given by Expression 10 on the opposite fundamental wave side. By dividing the amplitude value B of the second harmonic obtained in this way by the amplitude value A of the fundamental wave, a measure of the gas concentration can be obtained with the same accuracy as that of the phase sensitive detection, and multiplied by an appropriate proportional constant. Can be converted to gas concentration.
【0043】[0043]
【発明の実施の形態】被測定ガスがメタンガスである場
合の実施例を以下で述べる。レーザはメタンガスの吸収
スペクトルで透過率が極小となる波長1.6538μmの所に
中心周波数を設定し、周波数変調の変調周波数fm を 3
2.5kHzに設定し、最大周波数偏移を半値全幅で周波数変
調が掛かるように設定し、サンプリングレートfs を変
調周波数fm の8倍の260kHzに設定した。また、数7に
おいて、M=1として、数10のフィルタをN=8で実
現した。演算処理を行うためのDSP としてテキサス・イ
ンスツルメンツ社のTMS320C25を使用した。DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the gas to be measured is methane gas will be described below. The center frequency of the laser is set at a wavelength of 1.6538 μm where the transmittance is minimum in the absorption spectrum of methane gas, and the modulation frequency fm of the frequency modulation is set to 3
The frequency was set to 2.5 kHz, the maximum frequency shift was set so that frequency modulation was performed at the full width at half maximum, and the sampling rate fs was set to 260 kHz, eight times the modulation frequency fm. In addition, in Equation 7, M = 1 and the filter of Equation 10 is realized with N = 8. Texas Instruments TMS320C25 was used as a DSP for performing arithmetic processing.
【0044】以下で第1及び第2の発明のそれぞれの実
施例について説明する。実施例1(第1の発明)のガス
濃度測定処理装置を図2に示す。図2に示される基本波
直交復調部1では、入力信号s(n) を受け、その入力信
号は乗算器11でローカル信号13〔2cos(2πfm n/f
s)〕と乗算され、ローパスフィルタ(LPF )12でフィル
タリングされ、その結果が出力される。また、入力信号
s(n) は、乗算器14で前記ローカル信号13と直交するロ
ーカル信号16〔2sin(2πfm n/fs)〕と乗算され、
LPF15 でフィルタリングされ、その結果が出力される。The respective embodiments of the first and second inventions will be described below. FIG. 2 shows a gas concentration measurement processing apparatus according to the first embodiment (first invention). In the fundamental wave quadrature demodulation unit 1 shown in FIG. 2, an input signal s (n) is received, and the input signal is applied to a local signal 13 [2 cos (2πfm n / f) by a multiplier 11.
s)], filtered by a low-pass filter (LPF) 12, and the result is output. The input signal s (n) is multiplied by a local signal 16 [2 sin (2πfm n / fs)] orthogonal to the local signal 13 by a multiplier 14,
Filtered by LPF15 and the result is output.
【0045】高調波成分除去部3では、前記LPF12 の出
力を受け、数10のh(n) のインパルス応答をもつ櫛形
フィルタ31で高調波成分が除去され、入力信号s(n) の
同相成分が出力される。また、前記LPF15 の出力を受
け、h(n) のインパルス応答をもつ櫛形フィルタ32で高
調波成分が除去され、入力信号s(n) の直交成分が出力
される。The harmonic component removing unit 3 receives the output of the LPF 12 and removes the harmonic components by a comb filter 31 having an impulse response of h (n) of Formula 10, and removes the in-phase component of the input signal s (n). Is output. Further, the output of the LPF 15 is received, the harmonic component is removed by a comb filter 32 having an impulse response of h (n), and the quadrature component of the input signal s (n) is output.
【0046】測度演算部5では、前記櫛形フィルタ31の
出力である同相成分が乗算器51で2乗され、また前記櫛
形フィルタ32の出力である直交成分が乗算器52で2乗さ
れ、これらの2乗された値が加算器53で加算され、平方
根器54で平方根演算が行われ、基本波の振幅値Aが算出
され、この値が除算器59に分母として入れられる。2倍
波直交復調部2では、入力信号s(n) を受け、その入力
信号は乗算器21でローカル信号23〔2cos(4πfm n/
fs)〕と乗算され、LPF22 でフィルタリングされ、その
結果が出力される。また、入力信号s(n) は、乗算器24
で前記ローカル信号23と直交するローカル信号26〔2si
n(2πfm n/fs)〕と乗算され、LPF25 でフィルタリ
ングされ、その結果が出力される。In the measure calculation section 5, the in-phase component output from the comb filter 31 is squared by a multiplier 51, and the quadrature component output from the comb filter 32 is squared by a multiplier 52. The squared values are added by an adder 53, a square root operation is performed by a square root device 54, an amplitude value A of the fundamental wave is calculated, and this value is input to a divider 59 as a denominator. The second-harmonic quadrature demodulation unit 2 receives an input signal s (n), and the input signal is multiplied by a multiplier 21 into a local signal 23 [2 cos (4πfm n /
fs)], filtered by the LPF 22 and the result is output. Also, the input signal s (n) is
And a local signal 26 [2 si
n (2πfm n / fs)], filtered by the LPF 25, and the result is output.
【0047】高調波成分除去部4では、前記LPF22 の出
力を受け、数10のh(n) のインパルス応答をもつ櫛形
フィルタ41で高調波成分が除去され、入力信号s(n) の
同相成分が出力される。また、前記LPF25 の出力を受
け、h(n) のインパルス応答をもつ櫛形フィルタ42で高
調波成分が除去され、入力信号s(n) の直交成分が出力
される。測度演算部5では、前記櫛形フィルタ41の出力
である同相成分が乗算器55で2乗され、また前記櫛形フ
ィルタ42の出力である直交成分が乗算器56で2乗され、
これらの2乗された値が加算器57で加算され、平方根器
58で平方根演算が行われ、2倍波の振幅値Bが算出さ
れ、この値が除算器59に分子として入れられ、この2倍
波の振幅値Bを基本波の振幅値Aで除算した値がガスの
濃度の測度として出力される。The harmonic component removing unit 4 receives the output of the LPF 22 and removes the harmonic components by a comb filter 41 having an impulse response of h (n) of Formula 10, thereby removing the in-phase component of the input signal s (n). Is output. Further, the output of the LPF 25 is received, the harmonic component is removed by a comb filter 42 having an impulse response of h (n), and the quadrature component of the input signal s (n) is output. In the measure calculation unit 5, the in-phase component output from the comb filter 41 is squared by a multiplier 55, and the quadrature component output from the comb filter 42 is squared by a multiplier 56.
These squared values are added by the adder 57, and the square root
A square root operation is performed at 58 to calculate the amplitude value B of the second harmonic, and this value is input as a numerator into the divider 59, and a value obtained by dividing the amplitude value B of the second harmonic by the amplitude value A of the fundamental wave Is output as a measure of gas concentration.
【0048】この出力された値に所定の係数を掛けるこ
とでガスの濃度が求まる。実施例1では基本波側と2倍
波側にそれぞれ高調波成分除去部を設けたが、作用の項
で述べたように測定対象のガスの濃度によっては、一方
だけに設けることでもよい。実施例2(第2の発明)
は、実施例1の計算量を削減しDSP だけでなく汎用のCP
U でもガスの濃度測定処理を行えるようにしたものであ
る。計算量を削減するために、ガス濃度測定処理装置へ
の入力信号を標本化するためのサンプリングレートを基
本波の周波数の8倍(fs =8fm )に固定する。この
ようにサンプリングレートを定めると、基本波のローカ
ル信号の値は表1のようになる。The gas concentration is determined by multiplying the output value by a predetermined coefficient. In the first embodiment, the harmonic component removing sections are provided on the fundamental wave side and the second harmonic side, respectively. However, depending on the concentration of the gas to be measured, it may be provided on only one side as described in the section of the operation. Embodiment 2 (second invention)
Reduces the computational complexity of the first embodiment,
The gas concentration measurement process can be performed with U. In order to reduce the amount of calculation, the sampling rate for sampling the input signal to the gas concentration measurement processor is fixed to eight times the frequency of the fundamental wave (fs = 8fm). When the sampling rate is determined in this way, the values of the local signals of the fundamental wave are as shown in Table 1.
【0049】[0049]
【表1】 [Table 1]
【0050】nが8以上の時は、再び表1で示したロー
カル信号の値が繰り返されることになる。表1のローカ
ル信号cos(2πfm n/fs)の値が±1及び±1/√
(2)の時の演算用のレジスタをそれぞれa及びb、ロ
ーカル信号sin(2πfm n/fs)の値が±1及び±1/
√(2)の時の演算用のレジスタをそれぞれc及びd、
cos(4πfm n/fs)の値が±1の時の演算用のレジス
タをe、sin(4πfm n/fs)の値が±1の時の演算用
のレジスタをfとする。ガス濃度測定処理装置への入力
信号をs(n) とすると、実施例1の基本波直交復調部1
及び2倍波直交復調部2の同相および直交成分は、上記
で定義したレジスタを用いて表2に示される演算をn=
K(ただし、Kは8の倍数)まで繰り返し、When n is 8 or more, the values of the local signals shown in Table 1 are repeated again. The values of the local signal cos (2πfm n / fs) in Table 1 are ± 1 and ± 1 / √.
In the case of (2), the operation registers are a and b, respectively, and the value of the local signal sin (2πfm n / fs) is ± 1 and ± 1 /
レ ジ ス タ The operation registers at the time of (2) are c and d, respectively.
The register for operation when the value of cos (4πfm n / fs) is ± 1 is e, and the register for operation when the value of sin (4πfm n / fs) is ± 1 is f. Assuming that the input signal to the gas concentration measurement processing device is s (n), the fundamental wave quadrature demodulation unit 1 of the first embodiment
The in-phase and quadrature components of the second-harmonic quadrature demodulation unit 2 are calculated by using the registers defined above to calculate n =
K (where K is a multiple of 8)
【0051】[0051]
【表2】 [Table 2]
【0052】その後でAfter that
【0053】[0053]
【数12】 (Equation 12)
【0054】を計算することで、それぞれ求めることが
できる。ただし、表2のn mod8はnを8で除算したと
きの剰余を意味し、数12のAI とAQ はそれぞれ基本
波の同相成分と直交成分、BI とBQ はそれぞれ2倍波
の同相成分と直交成分である。。上記の演算は、総和演
算を行っているので実施例1の基本波直交復調部1と2
倍波直交復調部2の直交復調とLPF のフィルタ処理を行
ったことになり、さらにこの総和の繰り返し回数は、基
本波の周期の倍数となるので、高調波成分除去部3,4
のフィルタ処理も行ったことになる。また、実施例1の
除算器59で2倍波の振幅値Bを基本波の振幅値Aで除算
していることになるので、数12の繰り返し回数Kでの
除算は必要ない。Can be obtained by calculating. However, n mod8 in Table 2 means the remainder when n is divided by 8, AI and AQ in Equation 12 are the in-phase and quadrature components of the fundamental wave, and BI and BQ are the in-phase components of the second harmonic, respectively. It is an orthogonal component. . In the above calculation, since the sum calculation is performed, the fundamental wave quadrature demodulation units 1 and 2 of the first embodiment are used.
This means that the quadrature demodulation of the harmonic quadrature demodulation unit 2 and the filter processing of the LPF have been performed, and the number of repetitions of this sum is a multiple of the period of the fundamental wave.
Is also performed. Also, since the amplitude value B of the second harmonic is divided by the amplitude value A of the fundamental wave by the divider 59 of the first embodiment, the division by the repetition number K of Expression 12 is not necessary.
【0055】上で述べた、多重総和処理を用いた実施例
を図3に示す。また、多重総和処理部6の詳細を図4に
示す。図中a〜fは前記レジスタa〜fである。前記多
重総和処理部6では、入力信号s(n) を受けて、前述し
た演算処理を行い基本波の同相成分AI 、基本波の直交
成分AQ 、2倍波の同相成分BI および2倍波の直交成
分BQ が出力される。測度演算部7では、多重総和処理
部6で出力された4つの信号を受けて、基本波の同相成
分AI は乗算器71で2乗され、基本波の直交成分AQ は
乗算器72で2乗され、加算器73でそれらの2乗された値
は加算され、除算器77に分母として入れられる。2倍波
の同相成分BI は乗算器74で2乗され、2倍波の直交成
分BQ は乗算器75で2乗され、加算器76でそれらの2乗
された値は加算され、除算器77に分子として入れられ
る。除算器77では、除算を行いその値を出力し、平方根
器78では平方根演算を行いガス濃度の測度を出力する。
この出力された値に所定の係数を掛けることでガスの濃
度が求まる。FIG. 3 shows an embodiment using the multiple sum processing described above. FIG. 4 shows details of the multiplex sum processing unit 6. In the figure, a to f are the registers a to f. The multiplex sum processing unit 6 receives the input signal s (n) and performs the above-described arithmetic processing to perform the in-phase component AI of the fundamental wave, the quadrature component AQ of the fundamental wave, the in-phase component BI of the second harmonic, and the in-phase component BI of the second harmonic. An orthogonal component BQ is output. In the measure calculation unit 7, upon receiving the four signals output from the multiplex sum processing unit 6, the in-phase component AI of the fundamental wave is squared by the multiplier 71, and the quadrature component AQ of the fundamental wave is squared by the multiplier 72. Then, the squared values are added by the adder 73 and the sum is input to the divider 77 as a denominator. The in-phase component BI of the second harmonic wave is squared by the multiplier 74, the quadrature component BQ of the second harmonic wave is squared by the multiplier 75, and the squared values thereof are added by the adder 76. As a molecule. The divider 77 performs the division and outputs the value, and the square root device 78 performs the square root operation and outputs a measure of the gas concentration.
By multiplying the output value by a predetermined coefficient, the gas concentration is obtained.
【0056】第1または第2の発明によれば、実施例
1,2のようにDSP または汎用のCPUを用いてガス濃度
測定処理を行うことで、回路の小型化、低コスト化がで
き、また、扱う信号も従来の装置に用いられていた位相
敏感検波に比べて低周波であるので、周囲の温度や部品
の特性の経年変化等への依存が少なく、安定な測定がで
きる。According to the first or second aspect of the present invention, by performing gas concentration measurement processing using a DSP or a general-purpose CPU as in the first and second embodiments, the circuit can be reduced in size and cost. In addition, since the signal to be handled has a lower frequency than that of the phase sensitive detection used in the conventional apparatus, it is possible to perform stable measurement with little dependence on the ambient temperature and the secular change of the component characteristics.
【0057】[0057]
【発明の効果】本発明のガス濃度測定処理装置は、非同
期方式の包絡線検波を採用し、かつ、被測定ガスを透過
して得られた信号の高調波成分を除去する手段を設ける
こととしたから、レーザの周波数変調部からリファレン
スの同期した信号をガス濃度測定処理装置に接続すると
いう必要がなく、また、校正のために手動で位相を少し
ずつずらして振幅レベルの最大点を見つけるといった操
作も必要ない。しかも、従来のガス濃度測定処理装置が
採用していた位相敏感検波と同程度の精度でガスの濃度
測定ができる。また、DSP さらには汎用のCPU を用いて
ガス濃度測定処理を行うことができるので回路が小型
化、低コスト化できる。The gas concentration measurement processing apparatus of the present invention employs asynchronous envelope detection and has means for removing a harmonic component of a signal obtained by transmitting a gas to be measured. Therefore, there is no need to connect a reference-synchronized signal from the laser frequency modulation unit to the gas concentration measurement processing device, and manually shift the phase a little at a time for calibration to find the maximum point of the amplitude level. No action is required. In addition, the gas concentration can be measured with the same accuracy as the phase sensitive detection employed in the conventional gas concentration measurement processing device. In addition, since the gas concentration measurement process can be performed using a DSP or a general-purpose CPU, the circuit can be reduced in size and cost.
【図1】第1の発明のガス濃度測定処理装置のブロック
図。FIG. 1 is a block diagram of a gas concentration measurement processing device according to a first invention.
【図2】実施例1のガス濃度測定処理装置のブロック
図。FIG. 2 is a block diagram of a gas concentration measurement processing apparatus according to the first embodiment.
【図3】実施例2のガス濃度測定処理装置のブロック
図。FIG. 3 is a block diagram of a gas concentration measurement processing apparatus according to a second embodiment.
【図4】実施例2のガス濃度測定処理装置の多重総和処
理部の詳細を示すブロック図。FIG. 4 is a block diagram illustrating details of a multiple sum processing unit of the gas concentration measurement processing apparatus according to the second embodiment.
【図5】ガスの吸収スペクトルを示す図。FIG. 5 shows an absorption spectrum of a gas.
【図6】周波数変調方式の原理図。FIG. 6 is a principle diagram of a frequency modulation method.
【図7】2倍波直交復調後のベクトル図。FIG. 7 is a vector diagram after quadrature demodulation of a second harmonic.
【図8】初期位相が異なる2つの信号の2倍波直交復調
後のベクトル図。FIG. 8 is a vector diagram after two-wave quadrature demodulation of two signals having different initial phases.
【図9】櫛形フィルタの周波数応答を示す図。FIG. 9 is a diagram showing a frequency response of a comb filter.
【図10】2波長差分方式を用いたガス検出器のブロッ
ク図。FIG. 10 is a block diagram of a gas detector using a two-wavelength difference method.
【図11】従来の周波数変調方式を用いたガス検出器の
ブロック図。FIG. 11 is a block diagram of a gas detector using a conventional frequency modulation method.
1 基本波直交復調部 2 2倍波直交復調部 3,4 高調波成分除去部 5,7 測度演算部 6 多重総和処理部 DESCRIPTION OF SYMBOLS 1 Quadrature demodulator for fundamental wave 2 Quadrature demodulator for 2nd harmonic 3, 4 Harmonic component elimination unit 5, 7 Measure calculation unit 6 Multiple sum processing unit
─────────────────────────────────────────────────────
────────────────────────────────────────────────── ───
【手続補正書】[Procedure amendment]
【提出日】平成12年11月30日(2000.11.
30)[Submission date] November 30, 2000 (200.11.
30)
【手続補正1】[Procedure amendment 1]
【補正対象書類名】明細書[Document name to be amended] Statement
【補正対象項目名】特許請求の範囲[Correction target item name] Claims
【補正方法】変更[Correction method] Change
【補正内容】[Correction contents]
【特許請求の範囲】[Claims]
Claims (1)
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処理装置において、 前記光信号が電気信号に変換された入力信号を受け、基
本波信号の同相成分及び直交成分を求めて出力する基本
波直交復調部(1)と、前記入力信号を受け、2倍波信
号の同相成分及び直交成分を求めて出力する2倍波直交
復調部(2)と、前記基本波復調部から出力される同相
成分及び直交成分の信号を受け、それらの成分に含まれ
ている高調波成分を除去する基本波高調波成分除去部
(3)と、前記2倍波復調部から出力される同相成分及
び直交成分の信号を受け、それらの成分に含まれている
高調波成分を除去する2倍波高調波成分除去部(4)
と、前記基本波高調波成分除去部及び2倍波高調波成分
除去部から出力される同相成分及び直交成分の信号を受
け、ガスの濃度に比例するガス濃度の測度を求めて出力
する測度演算部(5)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処理装置。1. A fundamental wave signal (frequency) of an optical signal having an absorption characteristic of a gas to be measured, obtained by irradiating light having undergone amplitude modulation and frequency modulation at a predetermined frequency (fm) to the gas to be measured. fm) and a second harmonic signal (frequency 2fm), a gas concentration measurement processing device for receiving an input signal obtained by converting the optical signal into an electric signal, and converting an in-phase component and a quadrature component of a fundamental signal. A quadrature demodulation unit (1) for obtaining and outputting, a quadrature quadrature demodulation unit (2) for receiving the input signal and obtaining and outputting an in-phase component and a quadrature component of the second harmonic signal, and the fundamental wave demodulation A fundamental harmonic component elimination unit (3) for receiving in-phase and quadrature component signals output from the unit and removing harmonic components included in the components, and an output from the second harmonic demodulation unit. Receiving the in-phase component and quadrature component signals Double wave harmonic component removing unit for removing a harmonic component contained in the component (4)
And a measure calculation for receiving signals of the in-phase component and the quadrature component output from the fundamental harmonic component remover and the second harmonic component remover, and obtaining and outputting a gas concentration measure proportional to the gas concentration. A gas concentration measurement processing device comprising a signal processing unit comprising a unit (5).
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JP2000309952A JP3459399B2 (en) | 2000-10-10 | 2000-10-10 | Gas concentration measurement processing equipment |
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JP32616493A Division JPH07151682A (en) | 1993-11-30 | 1993-11-30 | Gas density measuring processor |
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JP3459399B2 JP3459399B2 (en) | 2003-10-20 |
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Cited By (7)
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JP2008175611A (en) * | 2007-01-17 | 2008-07-31 | Fuji Electric Systems Co Ltd | Device and method for measuring gas concentration |
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2008175611A (en) * | 2007-01-17 | 2008-07-31 | Fuji Electric Systems Co Ltd | Device and method for measuring gas concentration |
CN103048375A (en) * | 2013-01-22 | 2013-04-17 | 高清福 | Smart mobile terminal-based gas joint detection and alarming system |
CN104989953A (en) * | 2015-07-07 | 2015-10-21 | 成都国光电子仪表有限责任公司 | Multipoint monitoring system suitable for being distributed along natural gas pipeline |
CN105020587A (en) * | 2015-07-07 | 2015-11-04 | 成都国光电子仪表有限责任公司 | Natural gas station unattended operation system with good safety performance |
CN105156899A (en) * | 2015-08-07 | 2015-12-16 | 成都国光电子仪表有限责任公司 | Metering module structure used in natural gas extraction process |
CN105156900A (en) * | 2015-08-07 | 2015-12-16 | 成都国光电子仪表有限责任公司 | Natural gas remote-metering measurement unit |
CN105179947A (en) * | 2015-08-12 | 2015-12-23 | 成都国光电子仪表有限责任公司 | Metering method of flow computer for natural gas pipeline |
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