JP2009174920A - Optical combustible gas concentration detection method and optical combustible gas concentration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical combustible gas concentration detection method which enables the measurement of the concentrations of a plurality of kinds of gases at the same time and correction of the wavelength of the absorbing ray of each of the gases to accurately detect the concentration of the gas. <P>SOLUTION: A liquid branching means 13 for branching a laser beam is connected across a laser 2 and a light receiver 5, and a reference light path 14 not permitting a gas atmosphere to pass, a gas detecting light path 15 permitting the gas atmosphere to pass and a gas-in-air detecting light path 15R for measuring a component gas contained in air are connected to the light branching means 13. The wavelength of 1,650-1,690 nm of the laser beam is swept and the center wavelength of the laser beam is corrected from a gas signal component being the difference between the signal obtained from the gas detecting light path 15 and the signal obtained from the reference light path 14 and a reference gas signal component being the difference between the signals obtained from the gas-in-air detecting light path 15R and the reference light path 14 to measure the concentrations of propane gas, an isobutane gas, an n-butane gas and a methane gas contained in the gas atmosphere at the same time from transmitted light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an optical gas concentration detection method and an optical gas concentration detection device for detecting a gas concentration from a transmitted light through a laser light to be measured, and in particular, an optical combustible capable of simultaneously detecting the gas concentrations of a plurality of gases. TECHNICAL FIELD The present invention relates to a method for detecting a gas concentration and an optical flammable gas concentration detector.

  Gas molecules have a property of absorbing laser light having a specific wavelength (referred to as an absorption band), and the presence or absence of gas can be detected using this property. A gas detection method using laser light is used in fields such as industrial measurement and pollution monitoring, and gas can be detected remotely by transmitting laser light through an optical fiber.

  For example, in Patent Document 1, a semiconductor laser drive current is modulated with a high-frequency sine wave centered on a predetermined current value, and laser light whose wavelength and intensity are modulated is oscillated. This laser light is incident on an optical fiber and guided to a gas cell, gas of unknown concentration in the gas cell is transmitted, the transmitted light is guided to a light receiver by an optical fiber, and the received light signal is phase-sensitively detected to be a single detection signal. And the double detection signal are measured, the ratio of the first detection signal and the double detection signal, which is the output ratio of the gas signal, is obtained, and the concentration of the target gas is obtained from the output ratio of the gas signal.

JP-A-5-256769 JP-A-63-9843

  However, conventional optical gas concentration detection methods and apparatuses have been developed for the purpose of measuring one target gas such as methane gas. For this reason, there exists a problem that the density | concentration of multiple types of gas (for example, propane gas, isobutane gas, normal butane gas, methane gas etc.) cannot be detected correctly, respectively.

  In addition, in the conventional method and apparatus, when the absorption lines of the respective gases measured due to defects in the mounted parts are deviated, there is no means for correcting the deviation and the gas concentration cannot be detected accurately. As an example of a defect of a component mounted on the optical gas concentration detection device, there is deterioration of a Peltier element for controlling the temperature of the laser, deterioration of a power source for a Peltier element that supplies power to the Peltier element, and the like.

  That is, the laser oscillation wavelength deviates from the target value (set oscillation wavelength) to a different wavelength, and the measured gas absorption line deviates.

  Accordingly, an object of the present invention is to provide an optical combustible gas capable of simultaneously measuring the concentrations of propane gas, isobutane gas, normal butane gas, and methane gas, and accurately detecting the gas concentration by correcting the wavelength of the absorption line of each gas. An object of the present invention is to provide a concentration detection method and an optical combustible gas concentration detection device.

The present invention has been devised to achieve the above object. The invention of claim 1 modulates the wavelength of laser light and sweeps a predetermined sweep range, and passes this through a gas atmosphere to be measured. In the gas concentration detection method of detecting the intensity of the transmitted light obtained and detecting the gas concentration from the obtained signal,
An optical branching means for branching the laser beam is connected between the laser and the light receiver, and a reference optical path that does not pass through the gas atmosphere, a gas detection optical path that passes through the gas atmosphere, and components contained in the air. Connect with the gas detection optical path in the air to measure the gas,
The wavelength of the laser light is swept from around 1650 nm to around 1690 nm, and the gas signal component obtained by subtracting the signal obtained from the gas detection optical path and the signal obtained from the reference optical path, and the air gas detection optical path and the reference optical path are obtained. Light that simultaneously measures the concentration of propane gas, isobutane gas, normal butane gas, and methane gas contained in the gas atmosphere from the transmitted light by correcting the center wavelength of the laser light from a reference gas signal component obtained by subtracting the signal obtained It is a type combustible gas concentration detection method.

  The invention according to claim 2 uses methane gas as the component gas, and corrects the center wavelength of the laser beam by using a deviation from the center wavelength of the absorption spectrum of the methane gas. It is.

According to a third aspect of the present invention, there is provided a gas concentration detection device for modulating the wavelength of laser light, detecting the intensity of transmitted light obtained by passing the laser light through a gas atmosphere to be measured, and detecting the gas concentration from the obtained signal. ,
A light source unit that sweeps the wavelength of laser light from around 1650 nm to around 1690 nm, a reference optical path that does not pass through the gas atmosphere, a gas detection optical path that passes through the gas atmosphere, and in the air for measuring component gases contained in the air A gas detection optical path, and a light branching means for branching the laser light into each of these optical paths;
The laser from the gas signal component obtained by subtracting the signal obtained from the gas detection optical path and the signal obtained from the reference optical path, and the reference gas signal component obtained by subtracting the signal obtained from the air gas detection optical path and the reference optical path. An optical combustible gas concentration detection device comprising a signal processing unit that corrects the central wavelength of light and simultaneously measures the concentration of propane gas, isobutane gas, normal butane gas, and methane gas contained in the gas atmosphere from the transmitted light. is there.

  According to a fourth aspect of the present invention, there is provided the optical combustible gas concentration detection device according to the third aspect, wherein the light source unit, the air gas detection optical path, and the light branching unit are housed in a housing of the device main body.

  According to the present invention, the concentration of propane gas, isobutane gas, normal butane gas, and methane gas can be measured accurately at the same time, and the wavelength of each gas absorption line is corrected by correcting the center wavelength of the laser beam. Can be detected.

  First, the principle of a method for detecting a gas concentration using an optical fiber as a transmission path will be briefly described.

  In spectroscopic measurement, there is a frequency modulation method as a method for improving measurement sensitivity. First, when the frequency-modulated light is transmitted through the atmosphere containing the target gas, the detection signal of the transmitted light can be obtained as the fundamental component and the harmonic component of the same frequency as the modulation frequency in addition to the DC component. .

  Among these, when the phase-sensitive detection is performed on the fundamental wave component and the second harmonic component, the fundamental wave component corresponds to the first derivative of the absorption line, and the second harmonic component corresponds to the second derivative of the absorption line. For this reason, when laser light modulated with a drive current of a laser as a light source is transmitted through an atmosphere containing a specific gas and a specific component in a detection signal of the transmitted light is phase-sensitively detected, the gas concentration is detected from the detection signal. Information is obtained.

  Here, the phase sensitive detection refers to extracting only a component having a specific frequency and phase and measuring its amplitude.

  That is, in this method, in order to oscillate a laser beam having a wavelength and intensity corresponding to the drive current and temperature, the laser drive current is modulated around a predetermined current, and the center wavelength of the laser beam is swept to obtain a laser beam. The intensity of transmitted light obtained by passing through a gas atmosphere to be measured is detected, and the gas concentration is detected from a signal obtained by phase-sensitive detection of a specific component in this signal.

  The present invention is based on such a technique.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 is an overall configuration diagram of an optical combustible gas concentration detection device used for carrying out an optical combustible gas concentration detection method according to a preferred embodiment of the present invention.

  As shown in FIG. 1, an optical flammable gas concentration detection device (optical flammable gas concentration detection system) 1 (hereinafter referred to as device 1) is mainly used for leakage of city gas such as underground malls and high-rise buildings, and LNG tanks. The peripheral gas leak is detected at multiple points (plural points), a laser unit 3 as a light source unit for driving the laser to oscillate the laser beam, and an optical system 4 for guiding the oscillated laser beam, A plurality of (n + 1 in the figure) light receivers 5 that detect the laser light that has passed through the optical system 4 and a signal processing unit 6 that processes the detection signals are provided.

  The laser unit 3 includes a distributed feedback semiconductor laser (DFB-LD, hereinafter simply referred to as LD) 2 that oscillates laser light having a single wavelength, and the temperature of the LD 2 is controlled by a Peltier element power source 7 made of a semiconductor device. A Peltier element 8 for generating a signal, an oscillator (transmitter) 9 for outputting a sine wave signal having a predetermined frequency (variable), and a frequency multiplier 10 for generating a double wave signal having a frequency 2f from the sine wave signal having the frequency f. A bias current source 11 for applying a bias current to the LD 2, a sweeper 12 for determining how to sweep the bias current source 11, and a laser beam output from the LD 2 for branching to the optical system 4 for transmission. And a light splitter 13 such as a beam splitter.

  In the present embodiment, the oscillator 9 can output sine wave signals of at least four different frequencies f1, f2, f3, and f4 (eg, 10.1, 10.2, 10.3, and 10.4 kHz). it can. Further, the frequency multiplier 10 can generate a double wave signal of the frequencies 2f1 to 2f4 from the sine wave signals of the respective frequencies f1 to f4 from the oscillator 9.

  An inductance L is connected to the output side of the bias current source 11 in order to prevent the influence of the output of the oscillator 9, and a capacitor C for cutting a direct current component is connected to the output side of the oscillator 9. As the sweeper 12, a triangular wave sweeper or a sine wave sweeper is used.

  The optical system 4 is connected between the optical branching means 13 and the 0th light receiver 5 and is an optical fiber for an air gas detection optical path (air gas detection optical path for air) for measuring a predetermined component gas originally contained in the air. ) Connected in a loop between 15R and the air gas detector 16R provided in the middle of the optical fiber 15R for the air gas detection optical path, and the optical branching means 13 and the first light receiver 5, and passes through the gas atmosphere. A reference optical path optical fiber (reference optical path) 14 that is not connected, and a plurality of optical fibers that pass through the gas atmosphere (in FIG. (n−1) gas detection optical path optical fibers (gas detection optical paths or sensor optical paths) 15 and gas detection units (sensor units) 16 provided in the middle of the gas detection optical path optical fibers 15.

  Further, in FIG. 1, the gas detection optical path optical fiber 15R in the air is z0, the reference optical path optical fiber 14 is z1, and each gas detection optical path optical fiber 15 is numbered from z2 to zn in order from the top. The receiver 5 to which the fiber is connected is described.

  Each gas detection unit 16 is a container filled with a plurality of types of gases having unknown concentrations, which are measurement targets, or a container having an opening so that a gas atmosphere containing these gases is taken into the interior. It can be easily installed at the position. The in-air gas detection unit 16R is a container having the same configuration as each gas detection unit, and air in a place where an apparatus main body 1b described later is installed is taken into the inside.

  In the present embodiment, the plurality of types of gases are four types of gases, namely propane gas, isobutane gas (I-butane), normal butane gas (N-butane), and methane gas as combustible gases.

  The signal processing unit 6 includes a plurality of light receivers 5 that receive laser light that has passed through any one of the air detection optical path optical fiber 15R, the reference optical path optical fiber 14, and each gas detection optical path optical fiber 15. In synchronization with the frequencies f1 to f4 of the sine wave signal (* A in FIG. 1) from the oscillator 9 and the frequencies 2f1 to 2f2 of the sine wave signal (* B in FIG. 1) from the multiplier 10, Recording / calculating the phase detector 17 that performs phase sensitive detection of the output, the signal storage device 18 that temporarily stores the output signal from the phase detector 17 simultaneously, and the output ratio of 1f and 2f from the signal storage device 18 It consists of a computer 19 such as a personal computer for processing.

  The phase detector 17 phase-sensitively detects the received light signal of each transmitted light output from the optical fiber 15R for the gas detection optical path in the air, the optical fiber 14 for the reference optical path, and the optical fiber 15 for each gas detection optical path. A plurality of phase sensitive detection circuits 20 for obtaining the detection signal S1 and the double detection signal S2 are provided. As each phase sensitive detection circuit 20, a lock-in amplifier may be used. The computer 19 and the Peltier element power supply 7 are connected by a control signal line 21.

  Further, in the apparatus 1, at least the laser unit 3, preferably the apparatus main body 1b including the laser unit 3 and the signal processing unit 6 is housed in the housing 22, and the air gas detection unit 16R is filled with air. Yes.

  Next, an optical combustible gas concentration detection method using the apparatus 1 will be described.

  First, infrared absorption spectra of propane gas, isobutane gas, normal butane gas, and methane gas will be described with reference to FIG.

  As shown in FIG. 6, when the infrared absorption spectrum of each gas is viewed, the full width at half maximum is propane gas 0.37 nm, isobutane gas 0.907 nm, normal butane gas 0.714 nm, and methane gas 0.08 nm. As the amplitude value (also referred to as modulation amplitude width, modulation current amplitude width, or modulation wavelength width) of wavelength modulation (current modulation), a predetermined value at which the detection signal is substantially maximum is selected based on the above-described full width at half maximum.

  The predetermined modulation amplitude width here is set to the modulation amplitude width so that the detected double detection signal is large (preferably maximum), and the full width at half maximum of the infrared absorption spectrum of the target gas. It is obtained by multiplying by a predetermined coefficient (approximately 2 to 3).

  More specifically, in the method according to the present embodiment, first, the laser unit 3 is set to sweep the wavelength of the LD 2 from about 1650 nm to about 1690 nm, preferably from about 1685 nm to about 1690 nm. The wavelength of LD2 is swept by adding a triangular or sinusoidal bias current to LD2 by means of bias current source 11 and sweeper 12, and by sweeping the temperature of LD2 by means of Peltier element power supply 7 and Peltier element 8. There is a method of sweeping by changing to a wave shape or a sine wave shape. Since the change in the oscillation wavelength of the laser light with respect to the change in the temperature of the LD 2 is large, in this embodiment, the temperature of the LD 2 is changed and controlled by the Peltier element power supply 7 and the Peltier element 8 to sweep the wavelength of the laser light.

  Further, in the oscillator 9 of the laser unit 3, the modulation amplitude width by the drive current of the LD 2 is set to a predetermined value in correspondence with propane gas, isobutane gas, normal butane gas, and methane gas.

  In these setting states, the temperature of the Peltier element 8 is controlled by the power source 7 for the Peltier element, the temperature of the LD 2 is changed to a triangular wave shape or a sine wave shape, and the wavelength of the laser light is swept from around 1650 nm to around 1690 nm. The temperature of the laser is controlled to 25 ° C. ± 5 ° C., for example.

  In the present embodiment, the modulation amplitude width is uniformly set around 1.06 nm corresponding to propane gas, and the modulation frequency is also unified to a sine wave signal of f = 10 kHz.

  At the same time, an oscillator 9 that oscillates an alternating current having a uniform modulation frequency f, that is, a sinusoidal modulation current, superimposes a modulation current having a set modulation amplitude width on the bias current of the LD 2, and uses this as a drive current for the LD 2. To oscillate LD2. The laser light from the LD 2 is branched by the light branching means 13 and is incident on the in-air gas detection optical path optical fiber 15R, the reference optical path optical fiber 14, and each gas detection optical path optical fiber 15, respectively.

  The laser light incident on the in-air gas detection optical path optical fiber 15R is transmitted through the air of the in-air gas detector 16R, and the transmitted light is received by the zeroth light receiver 5. The laser light incident on the reference optical path optical fiber 14 is directly received by the first (z1) light receiver 5 in the signal processing unit 6. On the other hand, the laser light incident on each optical fiber 15 for gas detection optical path is transmitted through the gas atmosphere in each gas detection unit 15, and the transmitted light is 2nd to nth (z2 to zn) light receiving devices 5 respectively. Is received.

  Of the signals received by the light receivers 5, a signal (10 kHz) synchronized with the frequency f of the sine wave signal from the oscillator 9 and a signal (20 kHz) synchronized with the frequency 2 f of the sine wave signal of the frequency multiplier 10. Are detected by the phase detector 17 and the 1 × detection signal S <b> 1 and the 2 × detection signal S <b> 2 are respectively detected for the in-air gas detection optical path optical fiber 15 </ b> R, the reference optical path optical fiber 14, and each gas detection optical path optical fiber 15. Get. All the signals extracted by these phase detectors 17 are temporarily stored in the signal storage device 18.

  The computer 19 collects all the signals temporarily stored in the signal storage device 18 at the same time. First, as shown in FIG. 2, the output ratio Vb (of the gas signal obtained through the reference optical path optical fiber 14 is obtained. 2f) / Vb (1f) (reference) (2b in FIG. 2) while calculating the output ratio Vg (2f) / Vg () of the gas signal obtained by passing through each gas detection optical path optical fiber 15 1f) (gas) (2 g in FIG. 2) is calculated.

  Further, as shown in FIG. 3, the computer 19 outputs the gas signal output ratio Vb (2f) / Vb (1f) at a plurality of locations (multiple points) of the reference optical path optical fiber 14 and each gas detection optical path optical fiber 15. ) (Reference) and the difference (subtraction) between the output ratio Vg (2f) / Vg (1f) (gas) and calculate {Vg (2f) / Vg ( 1f) (gas)}-{Vb (2f) / Vb (1f) (reference)}.

  Since the gas signal component 31 is obtained by subtracting the output ratio of the reference gas signal from the output ratio of the gas signal of the target gas, the wavelength dependency of the laser unit 3, the optical branching unit 14, and the signal processing unit 6 is obtained. This is a gas signal that has been removed and is an accurate indicator of gas concentration.

  The computer 19 obtains the crest values hnb, hp, hm, hib which are the heights from the minimum value to the maximum value of the gas signal component 31, respectively, and obtains the crest values hnb, hp, hm, hib in advance with known concentrations. The gas concentration of each target gas is obtained simultaneously by applying a relational expression or relational table showing the relationship between each reference wave height value and each reference gas concentration obtained using the reference gas.

  In this case, the gas concentration of each target gas can be measured simultaneously from the peak values of propane gas around 1686.4 nm, isobutane gas around 1689 nm, normal butane gas around 1686.1 nm, and methane gas around 1687.3 nm.

  Further, in this embodiment, methane gas (about 2 ppm of methane gas is present in the air) is used as the component gas, and the computer 19 corrects the center wavelength of the laser beam by using a deviation from the center wavelength of the absorption spectrum of the methane gas. .

  More specifically, the computer 19 outputs the gas signal output ratio Vb (2f) / Vb (1f) obtained through the reference optical path optical fiber 14 simultaneously with the processing of the detection signal described in FIGS. ) (Reference) (2b in FIG. 4) while calculating the output ratio Vr (2f) / Vr (1f) of the in-air gas signal obtained through the in-air gas detection optical path optical fiber 15R. The gas in air) (2r in FIG. 4) is calculated in the same manner.

  Subsequently, as shown in FIG. 5, the computer 19 outputs the gas signal output ratio Vb (2f) / Vb (1f) (for a plurality of locations of the reference optical path optical fiber 14 and the air-in-gas detection optical path optical fiber 15R). The difference between the reference) and the output ratio Vr (2f) / Vr (1f) (in-air gas) is calculated, and as a reference gas signal component (correction signal) 51 (dotted line in FIG. 5), {Vr (2f) / Vr (1f) (gas in air)}-{Vb (2f) / Vb (1f) (reference)}.

  When the gas signal component 51 is shifted by a shift Δλ from the center wavelength 1687.3 nm of the absorption spectrum of methane gas stored in the computer 19 in advance, the personal computer 19 transmits a laser beam via the control signal line 21. A correction signal for correcting the center wavelength of the light is sent to the Peltier element power source 7 to control the wavelength. In general, although the oscillation wavelength of the LD 2 changes by about 0.1 nm / ° C., the temperature can be controlled by the Peltier element 8 with an accuracy of 1/1000 nm or less.

  In the example of FIG. 5, since the shift Δλ is shifted from the center wavelength 1687.3 nm of the absorption spectrum of methane gas to a shorter wavelength, the personal computer 19 outputs the output of the Peltier element power supply 7 so that the shift Δλ becomes zero. Decrease and raise the temperature of LD2.

  When the shift Δλ is shifted from the center wavelength 1687.3 nm of the absorption spectrum of methane gas toward the longer wavelength, the personal computer 19 increases the output of the Peltier element power supply 7 so that the shift Δλ becomes zero. The temperature of LD2 is lowered.

  Thereby, the personal computer 19 performs correction control of the Peltier element power supply 7 to correct the center wavelength of the laser beam and detect the correct concentrations of propane gas, isobutane gas, normal butane gas, and methane gas.

  The operation of this embodiment will be described.

  In the optical combustible gas concentration detection method according to the present embodiment, first, the wavelength of the laser light is swept from around 1650 nm to around 1690 nm.

  At this time, in accordance with all of propane gas, isobutane gas, normal butane gas, and methane gas, the modulation amplitude width by the drive current is set to a predetermined value and set by an oscillator 9 that outputs a signal of a unified frequency f, A modulation current having a set modulation amplitude width is superimposed on the bias current of LD2 to oscillate LD2. The laser light oscillated in this way is incident on the air detection optical path optical fiber 15R, the reference optical path optical fiber 14, and the gas detection optical path optical fibers 15, respectively.

  Further, the intensity of light from the optical fiber for reference optical path 14 and the intensity of transmitted light from each of the optical fibers for gas detection optical path 15 are detected, and the gas concentration is obtained from each obtained gas signal component.

  At the same time, the intensity of the light from the reference optical path optical fiber 14 and the intensity of the transmitted light from the in-air gas detection optical path optical fiber 15R are detected, and the deviation Δλ of the obtained gas signal component 51 is 0. The center wavelength of the laser light is corrected so that

  Thus, according to the optical flammable gas concentration detection method according to the present embodiment, the concentrations of propane gas, isobutane gas, normal butane gas, and methane gas contained in the gas atmosphere can be simultaneously measured (detected), and the center of the laser beam By correcting the wavelength, the gas concentration can be accurately detected by correcting the wavelength of the absorption line of each gas.

  That is, in the optical flammable gas concentration detection method according to the present embodiment, an air gas detection optical path optical fiber 15R having an air gas detection unit 16R is used, and based on a gas signal of transmitted light that has passed through the air. Thus, the center wavelength of the laser beam is corrected.

  Therefore, according to the optical flammable gas concentration detection method according to the present embodiment, absorption lines for each gas measured due to a failure of the mounted components while simultaneously measuring the concentrations of propane gas, isobutane gas, normal butane gas, and methane gas. Even when the gas is deviated from the true absorption line, the gas concentration can be detected with high accuracy.

  Further, according to the optical gas concentration detection system 1, the conventional system is slightly changed with respect to the oscillator 9, the sweeper 12, and the like, the in-air gas detection optical path optical fiber 15R having the in-air gas detection unit 16R, the control signal. The optical gas concentration detection method according to the present embodiment can be easily implemented simply by adding the line 21.

  In the above embodiment, the example has been described in which the frequency is unified by the oscillator 9 and the modulation amplitude width is unified, but wavelength modulation is performed with four different frequencies f1 to f4 and four different modulation amplitude widths. You may implement.

  As an example of the modulation amplitude width, when the propane gas is 1, the isobutane gas should be around 2.45 times, the normal butane gas should be around 1.93 times, and the methane gas should be around 0.22 times. That is, when the modulation amplitude width is set to a value close to 1.06 nm corresponding to propane gas, isobutane gas is set to 2.60 nm, normal butane gas is set to 2.05 nm, and methane gas is set to 0.23 nm.

  As an example of the modulation frequency of the four modulation signals, the propane gas modulation frequency f1 is 10.1 kHz, the isobutane gas modulation frequency f2 is 10.2 kHz, the normal butane gas modulation frequency f3 is 10.3 kHz, and the methane gas modulation frequency f4. It may be 10.4 kHz.

  In the above case, the actual output ratios obtained in the same manner as in FIG. Calculate with distinction as follows.

1 is an overall configuration diagram of an optical combustible gas concentration detection device showing a preferred embodiment of the present invention. It is a figure which shows the output ratio (2f / 1f) waveform of the gas signal after a reference | standard optical path and gas detection part permeation | transmission. It is a figure which shows the output signal (2f / 1f) difference waveform of the gas signal after a reference | standard optical path and gas detection part permeation | transmission. It is a figure which shows the output ratio (2f / 1f) waveform of the gas signal after permeation | transmission in the air gas detection optical path and a reference | standard optical path. It is a figure which shows the output signal (2f / 1f) differential waveform of the gas signal after permeation | transmission in the air gas detection optical path and a reference | standard optical path. It is a figure which shows the infrared absorption spectrum of each combustible gas.

Explanation of symbols

1 Optical gas concentration detector 2 Laser (DFB-LD)
3 Laser unit (light source unit)
4 Optical system 6 Signal processing unit 9 Oscillator 12 Sweeper 13 Optical branching means 14 Reference optical path optical fiber 15 Gas optical path optical fiber 15R In-air gas detection optical fiber 16 Gas detection unit 16R In-air gas detection unit 21 Control signal line

Claims (4)

Gas concentration detection method that modulates the wavelength of the laser light and sweeps a predetermined sweep range, detects the intensity of transmitted light obtained by passing the sweep range through the gas atmosphere to be measured, and detects the gas concentration from the obtained signal In
An optical branching means for branching the laser beam is connected between the laser and the light receiver, and a reference optical path that does not pass through the gas atmosphere, a gas detection optical path that passes through the gas atmosphere, and components contained in the air. Connect with the gas detection optical path in the air to measure the gas,
The wavelength of the laser light is swept from around 1650 nm to around 1690 nm, and the gas signal component obtained by subtracting the signal obtained from the gas detection optical path and the signal obtained from the reference optical path, and the air gas detection optical path and the reference optical path are obtained. The concentration of propane gas, isobutane gas, normal butane gas, and methane gas contained in the gas atmosphere is simultaneously measured from the transmitted light by correcting the center wavelength of the laser beam from the reference gas signal component obtained by subtracting the signal to be generated. An optical combustible gas concentration detection method.   The optical combustible gas concentration detection method according to claim 1, wherein methane gas is used as the component gas, and the center wavelength of the laser beam is corrected using a deviation from the center wavelength of the absorption spectrum of methane gas. In a gas concentration detection device that modulates the wavelength of laser light, detects the intensity of transmitted light obtained by passing the laser light through a gas atmosphere to be measured, and detects the gas concentration from the obtained signal.
A light source unit that sweeps the wavelength of laser light from around 1650 nm to around 1690 nm, a reference optical path that does not pass through the gas atmosphere, a gas detection optical path that passes through the gas atmosphere, and in the air for measuring component gases contained in the air A gas detection optical path, and a light branching means for branching the laser light into each of these optical paths;
The laser from the gas signal component obtained by subtracting the signal obtained from the gas detection optical path and the signal obtained from the reference optical path, and the reference gas signal component obtained by subtracting the signal obtained from the air gas detection optical path and the reference optical path. An optical flammability comprising a signal processing unit that simultaneously corrects the central wavelength of light and measures the concentration of propane gas, isobutane gas, normal butane gas, and methane gas contained in the gas atmosphere from the transmitted light. Gas concentration detector.   4. The optical combustible gas concentration detection device according to claim 3, wherein the light source unit, the air gas detection optical path, and the light branching unit are housed in a housing of the apparatus main body.

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