WO2012115150A1 - Dispositif de traitement de signal et dispositif de mesure laser - Google Patents

Dispositif de traitement de signal et dispositif de mesure laser Download PDF

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Publication number
WO2012115150A1
WO2012115150A1 PCT/JP2012/054277 JP2012054277W WO2012115150A1 WO 2012115150 A1 WO2012115150 A1 WO 2012115150A1 JP 2012054277 W JP2012054277 W JP 2012054277W WO 2012115150 A1 WO2012115150 A1 WO 2012115150A1
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Prior art keywords
frequency
light
unit
signal
laser
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PCT/JP2012/054277
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English (en)
Japanese (ja)
Inventor
明生 近藤
小林　靖之
義直 高桑
建二 茂木
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三菱重工業株式会社
株式会社ローラン
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Publication of WO2012115150A1 publication Critical patent/WO2012115150A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G01N2021/396—Type of laser source
    • G01N2021/399—Diode laser

Definitions

  • the present invention relates to a signal processing device and a laser measuring device used for laser measurement for calculating a physical quantity of a gas to be measured by laser absorption spectroscopy.
  • Patent Document 1 discloses a laser that oscillates a laser beam that is modulated by a current having a first alternating current component superimposed on a constant current and changes in wavelength according to temperature, and a laser beam that has passed through a detection atmosphere.
  • Current voltage converter light intensity voltage converter
  • two phase sensitive detectors for phase sensitive detection of the output voltage of the current voltage converter
  • 1 obtained from one phase sensitive detector
  • Patent Document 2 discloses a laser element that emits laser light, a frequency modulation unit that modulates the frequency of the laser light with a fundamental wave, a light detection unit that detects the frequency-modulated laser light, and a light detection unit.
  • a fundamental wave component detection unit that detects a fundamental wave component from the detected laser beam
  • a second harmonic component detection unit that detects a second harmonic component from the laser beam detected by the light detection unit
  • a light detection unit A gas concentration measuring device having a gas concentration calculating unit that calculates the concentration of a measurement target gas based on an amplitude ratio between a detected fundamental wave component and a second harmonic component is described.
  • the gas concentration measuring apparatus is based on an amplitude ratio calculation unit that calculates an amplitude ratio between a fundamental wave component and a second harmonic component detected from laser light, and an amplitude ratio between the fundamental wave component and the second harmonic component.
  • the temperature setting unit for setting the temperature of the laser element, and the amplitude ratio between the fundamental wave component and the second harmonic wave component when the wavelength modulation is performed based on the wavelength shifted from the absorption peak wavelength.
  • a drive current control unit that controls the drive current.
  • the physical quantity such as the concentration of the measurement target substance is obtained. It can be measured.
  • the gas concentration can be measured with high responsiveness by measuring the gas concentration using laser light.
  • the light reception signal generated by the light receiving unit receiving the laser light includes various noises. Therefore, various signal processes are performed to remove noise from the received light signal and extract a necessary component (for example, a signal component corresponding to a modulation frequency for performing wavelength modulation).
  • a necessary component for example, a signal component corresponding to a modulation frequency for performing wavelength modulation.
  • this signal processing there is a method of extracting a specific spectrum signal by performing lock-in processing and low-pass processing with a lock-in amplifier.
  • an FIR filter or the like is provided before processing by the lock-in amplifier to extract the frequency component to be processed by the lock-in amplifier. That is, a process for reducing frequency components other than the frequency to be processed by the lock-in amplifier is performed.
  • a specific frequency component is extracted using a large number of data immediately before (for example, 1024th order).
  • the FIR filter uses a value detected by storing and processing a large number of detection results immediately before in order to extract a target component from the light reception signal. For this reason, the amount of calculation to be stored and processed is large, and the calculation load increases.
  • the present invention has been made in view of the above, and provides a signal processing device and a laser measurement device capable of detecting a desired signal component from a received light signal with high accuracy with a small amount of calculation and a simple device configuration. For the purpose.
  • the present invention includes a measurement cell including an incident part and an emission part, and a laser having a wavelength region including an absorption wavelength unique to a gas to be measured.
  • a light emitting unit that modulates a wavelength with a modulation frequency and outputs the light, and enters the measurement cell; and receives the laser light that is incident from the incident unit, passes through the measurement cell, and is emitted from the emission unit.
  • a light receiving unit that outputs a received light amount as a light receiving signal, and is applied to a laser measuring device that calculates a physical quantity of a measurement target gas flowing through the measurement cell based on the light receiving signal, and the light receiving unit receives light
  • a signal processing apparatus that processes the received light signal and outputs a spectrum signal used to calculate a physical quantity of a gas to be measured flowing through the measurement cell, and converts the received light signal into digital data.
  • a designated frequency that is obtained by acquiring digital data for one frame of the received light signal converted by the conversion unit and the A / D conversion unit, and the obtained digital data for one frame is an integer multiple of the modulation frequency
  • a discrete Fourier transform is performed on each of the frequencies whose frequency is different by an integer multiple of the step frequency around the specified frequency, and the frequency is different by an integer multiple of the step frequency around the specified frequency.
  • a DFT calculation unit that calculates a DFT component, a convolution calculation unit that performs a convolution calculation on the DFT component calculated by the DFT calculation unit, and an inverse discrete Fourier transform on the result calculated by the convolution calculation unit.
  • an inverse DFT calculation unit for generating a spectrum signal.
  • the step frequency is preferably a frequency calculated by multiplying the detection interval of the received light signal by the number of frames.
  • the present invention is a laser measurement device, wherein the signal processing device according to any one of the above, a main pipe that can be connected to a flow path for fluid, and the main pipe A measuring cell including an incident part connected to and formed with a window part through which light can pass, an emission part connected to the main pipe and formed with a window part through which light can pass; A laser beam in a wavelength region including an absorption wavelength is output while modulating the wavelength at a modulation frequency, and a light emitting unit that is incident on the incident unit, incident from the incident unit, passes through the measurement cell, and is output from the output unit A light receiving unit that receives the laser beam and outputs the received light amount as a light reception signal, a physical quantity calculation unit that calculates a physical quantity of a measurement target gas flowing through the measurement cell based on the spectrum signal, A control unit for controlling the operation; Characterized in that it has.
  • the light emitting unit outputs laser light while sweeping the wavelength at a sweep frequency lower than the modulation frequency.
  • the DFT calculation unit obtains digital data for one cycle of the sweep frequency as data for one frame.
  • the step frequency is preferably the sweep frequency.
  • the DFT calculation unit uses only frequencies that differ by an integer multiple of the step frequency or an odd integer multiple of the step frequency as frequencies that are different from each other by an integer multiple of the step frequency around the designated frequency. .
  • the physical quantity calculated by the physical quantity calculator is preferably the concentration of the gas to be measured.
  • the physical quantity calculation unit calculates the concentration of the measurement target gas based on the intensity of the laser beam output from the light emitting unit and the intensity of the laser beam received by the light receiving unit.
  • the signal processing apparatus and the laser measuring apparatus according to the present invention have an effect that a desired signal component can be detected from a received light signal with high accuracy with a small amount of calculation and a simple apparatus configuration.
  • FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of a laser measuring apparatus having a signal processing apparatus of the present invention.
  • FIG. 2 is a block diagram illustrating a schematic configuration of a signal processing unit of the laser measurement apparatus illustrated in FIG. 1.
  • FIG. 3 is an explanatory diagram for explaining processing of the signal processing unit.
  • FIG. 4 is an explanatory diagram for explaining the processing of the signal processing unit.
  • FIG. 5A is a graph showing a detected waveform of the received light signal.
  • FIG. 5B is a graph showing an output waveform of a spectrum signal.
  • FIG. 5C is a graph showing an output waveform of a spectrum signal calculated using a lock-in amplifier.
  • FIG. 6A is a graph showing a detected waveform of the received light signal.
  • FIG. 6A is a graph showing a detected waveform of the received light signal.
  • FIG. 6B is a graph showing an output waveform of the spectrum signal.
  • FIG. 6C is a graph showing an output waveform of the spectrum signal.
  • FIG. 6D is a graph showing an output waveform of a spectrum signal.
  • FIG. 7A is a graph showing an output waveform of a spectrum signal.
  • FIG. 7B is a graph showing an output waveform of the spectrum signal.
  • FIG. 7C is a graph showing the output waveform of the spectrum signal.
  • FIG. 7D is a graph showing an output waveform of a spectrum signal.
  • FIG. 7E is a graph showing an output waveform of a spectrum signal.
  • FIG. 7F is a graph showing an output waveform of a spectrum signal.
  • FIG. 7G is a graph showing an output waveform of a spectrum signal.
  • FIG. 8 is a graph showing the output waveform of the spectrum signal.
  • the laser measurement device can measure physical quantities (concentrations, quantities) of substances (gases, specific components) to be measured contained in fluids such as various gases (gases) flowing through the flow path.
  • the laser measuring device may be attached to a diesel engine and measure the concentration of nitrogen oxides, sulfide oxides, carbon monoxide, carbon dioxide, ammonia, etc. contained in the exhaust gas discharged from the diesel engine.
  • the device for discharging (supplying) the substance (gas) to be measured is not limited to this, and can be used for various internal combustion engines such as a gasoline engine and a gas turbine.
  • Examples of the device having an internal combustion engine include various devices such as vehicles, ships, and generators.
  • the laser measuring device can also measure the concentration of the substance to be measured contained in the exhaust gas discharged from combustion equipment such as a garbage incinerator and boiler. In the following embodiments, the case where the concentration of the measurement substance contained in the exhaust gas flowing through the pipe is measured will be described.
  • FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of a laser measuring device having a signal processing device of the present invention.
  • the laser measurement device 10 includes a measurement cell 12 and measurement means 14.
  • the laser measuring device 10 is provided between the pipe 6 and the pipe 8 through which the exhaust gas A flows.
  • the exhaust gas A is supplied from the upstream side of the pipe 6, passes through the pipe 6, the laser measuring device 10, and the pipe 8, and is discharged to the downstream side of the pipe 8.
  • an exhaust gas A generator supply device
  • supply device supply device
  • the measurement cell 12 basically has a main tube 20, an incident tube 22, and an exit tube 24. Further, the incident tube 22 is provided with a window 26, and the exit tube 24 is provided with a window 28.
  • the main pipe 20 is a tubular tubular member, and has one end connected to the pipe 6 and the other end connected to the pipe 8. That is, the main pipe 20 is disposed at a position that becomes a part of the flow path through which the exhaust gas A flows. Thereby, the exhaust gas A flows in the order of the pipe 6, the main pipe 20, and the pipe 8. Further, the exhaust gas A flowing through the pipe 6 basically flows through the main pipe 20.
  • the incident tube 22 is a tubular member, and one end thereof is connected to the main tube 20. Further, in the main tube 20, the connection portion with the incident tube 22 is an opening having substantially the same shape as the opening (end opening) of the incident tube 22. That is, the incident tube 22 is connected to the main tube 20 in a state where air can flow.
  • a window 26 is provided at the other end of the incident tube 22 and is sealed by the window 26.
  • the window 26 is made of a light transmitting member such as transparent glass or resin. Thereby, the incident tube 22 is in a state where the end portion where the window 26 is provided is in a state where air is not circulated and light can pass therethrough.
  • the incident tube 22 is connected to the area of the opening at the end on the window 26 side (that is, the opening closed by the window 26) and the end on the main tube 20 side (that is, connected to the main tube 20).
  • the area of the opening) is substantially the same cylindrical shape.
  • the shape of the incident tube 22 is not limited to a cylindrical shape, and may be any shape as long as it is a cylindrical shape that allows air and light to pass therethrough.
  • the cross section may be a square, a polygon, an ellipse, or an asymmetric curved surface.
  • the shape of the cross section of a cylindrical shape and the shape from which a diameter changes with positions may be sufficient.
  • the exit tube 24 is a tubular member having substantially the same shape as the entrance tube 22, one end is connected to the main tube 20, and the other end of the exit tube 24 is provided with a window 28.
  • the exit tube 24 is also in a state where air can flow through the main tube 20, and an end portion provided with the window 28 is in a state where air does not flow and light can pass therethrough.
  • the emission tube 24 is disposed at a position where the central axis is substantially the same as the central axis of the incident tube 22. That is, the entrance tube 22 and the exit tube 24 are disposed at positions facing the main tube 20.
  • the exit tube 24 also has an area of an opening at the end on the window 28 side (that is, an opening closed by the window 28) and an end portion on the main tube 20 side (that is, a portion connected to the main tube 20).
  • the area of the opening) is substantially the same cylindrical shape.
  • the shape of the emission tube 24 is not limited to a cylindrical shape, and may be any shape as long as it has a cylindrical shape that allows air and light to pass therethrough.
  • the cross section may be a square, a polygon, an ellipse, or an asymmetric curved surface.
  • the shape of the cross section of a cylindrical shape and the shape from which a diameter changes with positions may be sufficient.
  • the emission tube 24 also has a shape in which a purge gas described later flows stably.
  • the measuring unit 14 includes a light emitting unit 40, an optical fiber 42, a light receiving unit 44, a light source driver 46, a signal processing unit (signal processing device) 47, a physical quantity calculating unit 48, a control unit 50,
  • the signal processing unit 47 and the physical quantity calculation unit 48 are provided separately, but may be provided integrally (as one processing unit).
  • the light source driver 46, the signal processing unit 47, the physical quantity calculation unit 48, and the control unit 50 may be provided integrally (as one processing unit).
  • the light emitting unit 40 includes a light emitting element that outputs (emits) laser light having a predetermined wavelength.
  • the light emitting element of the light emitting unit 40 is a light emitting element that can change the output wavelength (frequency) of the laser beam to be output with a predetermined wavelength width (frequency width).
  • a tunable semiconductor laser element LD: Laser Diode
  • the light emitting unit 40 outputs laser light in a wavelength region including a near infrared wavelength region that is absorbed by the substance to be measured. For example, when the measurement target is nitric oxide, the light emitting unit 40 outputs laser light in a wavelength range including a near infrared wavelength range that absorbs nitric oxide.
  • the light emitting unit 40 When the measurement target is nitrogen dioxide, the light emitting unit 40 outputs laser light in a wavelength region including a near infrared wavelength region that absorbs nitrogen dioxide. When the measurement target is nitrous oxide, the light emitting unit 40 outputs laser light in a wavelength range including a near-infrared wavelength range that absorbs nitrous oxide. When the measurement target is a plurality of substances, the light emitting unit 40 may include a plurality of light emitting elements that emit light in the wavelength ranges absorbed by the respective substances, and output light in the respective wavelength ranges. . The optical fiber 42 guides the laser light output from the light emitting unit 40 and causes the laser light to enter the measurement cell 12 through the window 26.
  • the light receiving unit 44 is a light receiving unit that receives the laser beam that has passed through the main tube 20 of the measurement cell 12 and that has been output from the window 28 of the emission tube 24.
  • the light receiving unit 44 includes, for example, a photodetector such as a photodiode (PD), receives the laser beam by the photodetector, and detects the intensity of the light.
  • the light receiving unit 44 sends the intensity (light quantity) of the received laser beam as a light reception signal to the signal processing unit 47.
  • the light source driver 46 has a function of driving the light emitting unit 40 and adjusts the wavelength and intensity of the laser light output from the light emitting unit 40 by adjusting the current and voltage supplied to the light emitting unit 40.
  • the light source driver 46 is an oscillator, and outputs laser light whose wavelength changes with time by supplying current and voltage to the light emitting unit 40 in a predetermined waveform.
  • the light source driver 46 of the present embodiment oscillates the wavelength of the laser beam at a set modulation frequency (for example, 100 kHz, 150 kHz), and the laser beam at a sweep frequency (0.1 kHz, 1 kHz) that is lower than the modulation frequency. Sweep the wavelength.
  • the laser beam output from the light emitting unit 40 becomes a laser beam in which the center of vibration oscillating at the modulation frequency changes based on the sweep frequency.
  • the light source driver 46 outputs information on the intensity of the laser beam output from the light emitting unit 40 to the physical quantity calculating unit 48 via the control unit 50.
  • the signal processing unit 47 processes a signal (light reception signal) generated when the light receiving unit 44 receives laser light. Specifically, the signal processing unit 47 removes a noise component included in the light reception signal, and extracts a component of the laser light output from the light emitting unit 40 and reaching the light receiving unit 44. A signal generated by extraction is hereinafter referred to as a spectrum signal. The processing of the signal processing unit 47 will be described later.
  • the physical quantity calculation unit 48 calculates the concentration of the exhaust gas flowing through the measurement cell 12 based on the spectrum signal output from the signal processing unit 47.
  • the physical quantity calculation unit 48 calculates the concentration of the substance to be measured based on the spectrum signal output from the signal processing unit 47 and the conditions under which the light source driver 46 is driven by the control unit 50.
  • the physical quantity calculation unit 48 calculates the intensity of the laser light output from the light emitting unit 40 based on the condition that the light source driver 46 is driven by the control unit 50, and is generated by the signal processing unit 47.
  • the intensity of the received laser beam is calculated based on the spectrum signal.
  • the physical quantity calculator 48 compares the intensity of the emitted laser light with the intensity of the received laser light, and calculates the concentration of the substance to be measured contained in the exhaust gas A.
  • the near-infrared wavelength laser beam L output from the light emitting unit 40 is a predetermined path from the optical fiber 42 to the measurement cell 12, specifically, the window 26, the incident tube 22, the main tube 20, After passing through the emission tube 24 and the window 28, the light reaches the light receiving unit 44.
  • the laser light L passing through the measurement cell 12 is absorbed. Therefore, the output of the laser beam L reaching the light receiving unit 44 varies depending on the concentration of the substance to be measured in the exhaust gas A.
  • the light receiving unit 44 converts the received laser light into a light reception signal.
  • the received light signal generated by the light receiving unit 44 is processed by the signal processing unit 47 and input to the physical quantity calculation unit 48 as a spectrum signal.
  • the control unit 50 and the light source driver 46 output the intensity of the laser light L output from the light emitting unit 40 to the physical quantity calculation unit 48.
  • the physical quantity calculation unit 48 compares the intensity of the light output from the light emitting unit 40 with the intensity calculated from the spectrum signal, and calculates the concentration of the measurement target substance of the exhaust gas A flowing in the measurement cell 12 from the decrease rate. To do.
  • the measuring means 14 uses the so-called TDLAS method (Tunable Diode Laser Absorption Spectroscopy), and based on the intensity of the output laser light and the received light signal detected by the light receiving unit 44.
  • the concentration of the substance to be measured in the exhaust gas A passing through the predetermined position in the main pipe 20, that is, the measurement position, can be calculated and / or measured.
  • the measurement means 14 can calculate and / or measure the concentration of the substance to be measured continuously.
  • the laser measuring device 10 may calculate the concentration of the substance to be measured included in the exhaust gas A based on only the spectrum signal, with the intensity of the laser light output from the light emitting unit 40 being constant.
  • the control unit 50 has a control function for controlling the operation of each unit, and controls the operation of each unit as necessary.
  • the control unit 50 controls not only the control of the measuring means 14 but also the overall operation of the laser measuring device 10. That is, the control unit 50 is a control unit that controls the operation of the laser measurement apparatus 10.
  • FIG. 2 is a block diagram showing a schematic configuration of a signal processing unit of the laser measuring apparatus shown in FIG.
  • the signal processing unit 47 processes the light reception signal sent from the light receiving unit 44 to generate a spectrum signal, and sends the generated spectrum signal to the physical quantity calculation unit 48.
  • the signal processing unit 47 includes an amplification A / D conversion unit (amplification analog-digital conversion unit) 62, a DFT (Discrete Fourier Transform) calculation unit 64, a temporary storage unit 65, a convolution calculation unit 66, and an inverse DFT (Discrete Fourier). Transform) calculation unit 68.
  • the amplification A / D converter 62 converts an analog light reception signal into a digital light reception signal, and further amplifies the output.
  • the amplification A / D conversion unit 62 sends the amplified digital light reception signal to the DFT calculation unit 64.
  • the DFT calculation unit 64 acquires digital data of the received light signal converted by the amplification A / D conversion unit 62 for one frame, and performs discrete Fourier transform (DFT, Discrete Fourier Transform) on the acquired digital data for one frame. Then, a DFT component (Fourier coefficient) is calculated for each of a designated frequency that is a frequency obtained by multiplying the modulation frequency by an integer and a frequency that differs from the designated frequency by an integral multiple of the step frequency.
  • the step frequency is a numerical value set in advance, and is a value that determines an interval between frequency components used for DFT and convolution processing described later.
  • the frequency for calculating the DFT component is ⁇ ⁇ n ⁇ .
  • the maximum value of n is a value that can be adjusted by setting.
  • the DFT calculation unit 64 calculates the DFT component (Fourier coefficient) of the specified frequency from the digital data for one frame by discrete Fourier transform, and each of the frequencies whose frequencies are different by an integer multiple of the step frequency with the specified frequency as the center.
  • the DFT component (Fourier coefficient) is calculated.
  • the DFT calculation unit 64 performs a discrete Fourier transform on f (t), which is a digital light reception signal, and calculates a DFT component F ( ⁇ ) of each frequency centered on the specified frequency. Note that ⁇ of the DFT component F ( ⁇ ) is ⁇ ⁇ n ⁇ .
  • a discrete Fourier transform is performed on g (t) which is a signal of a reference sine wave (sine wave of a specified frequency), and a DFT component G ( ⁇ ) of the reference sine wave is calculated.
  • G ( ⁇ ) may be calculated in advance and set in the convolution calculation unit 66.
  • a negative frequency DFT component (F ( ⁇ ), F) corresponding to a specified frequency and a frequency that is different from the specified frequency by an integral multiple of the step frequency.
  • G ( ⁇ )) is also calculated.
  • the temporary storage unit 65 is a storage unit that stores the calculation result (DFT component at each frequency) calculated by the DFT calculation unit 64.
  • the temporary storage unit 65 functions as a buffer that temporarily stores a calculation result required by the convolution calculation unit 66.
  • the calculation result calculated by the DFT calculation unit 64 is written, and the calculation result stored by the convolution calculation unit 66 is read out.
  • the calculation results stored in the temporary storage unit 65 are sequentially deleted from the temporary storage unit 65 by the DFT calculation unit 64 or the convolution calculation unit 66 by the overwriting process or the deletion process.
  • the convolution calculation unit 66 performs a convolution calculation on the DFT component calculated by the DFT calculation unit 64 stored in the temporary storage unit 65. Specifically, using the DFT component F ( ⁇ ) of each frequency centered on the designated frequency stored in the temporary storage unit 65 and the DFT component G ( ⁇ ) of the reference sine wave, Perform convolution calculations.
  • ⁇ is a value n ⁇ (n includes 0) that is an integral multiple of the step frequency.
  • G (f) has a value of 0 except when the absolute value of f is two positive and negative frequencies that are designated frequencies. For this reason, the object to be calculated by the convolution calculation of (Equation 2) is the frequency components of the designated frequencies f and ⁇ f. Further, since ⁇ is a value n ⁇ that is an integral multiple of the step frequency, one H ( ⁇ ) is calculated for each of 2n + 1 ⁇ .
  • FIG. 3 and FIG. 4 are explanatory diagrams for explaining the processing of the signal processing unit, respectively.
  • FIG. 3 is an explanatory diagram showing a result F ( ⁇ ) obtained by subjecting a received light signal (LD signal) to discrete Fourier transform and a result G ( ⁇ ) obtained by subjecting a reference sine wave to discrete Fourier transform.
  • the vertical axis represents intensity (size)
  • the horizontal axis represents frequency axis.
  • the designated frequency is 250 kHz
  • the step frequency is 1 kHz
  • the maximum value of the integer n is n.
  • the sampling frequency is 4 MHz and the sampling period ⁇ t is 2.5E ⁇ 7 seconds.
  • 1 / 2 ⁇ t corresponds to a half value (frequency) of the sampling frequency.
  • the laser measuring device 10 output laser light with a modulation frequency of 125 kHz and a sweep frequency of 1 kHz.
  • the convolution calculation unit 66 analyzes the specified frequency 250 kHz obtained by doubling the modulation frequency and components in the vicinity thereof among F ( ⁇ ) that can be calculated as shown in FIG. In the convolution calculation, a negative frequency corresponding to the specified frequency is also required, so that the frequency of ⁇ 250 kHz and its nearby components are also analyzed. That is, the convolution calculation unit 66 outputs a necessary DFT component from the output components surrounded by the region 100.
  • the designated frequency is 250 kHz
  • the step frequency is 1 kHz
  • the maximum value of the integer multiple coefficient n is 2. Therefore, F ( ⁇ 248), F ( ⁇ 249), F ( ⁇ 250), F ( ⁇ 251), F ( ⁇ 252), and G ( ⁇ 250) are used.
  • H (0) is calculated by summing up the calculated results.
  • H (1) is calculated using the following formula (4).
  • H (2) and (-2) are similarly calculated using formula (2).
  • the convolution calculator 66 calculates H ( ⁇ ) of a plurality of DFT components based on the conditions as described above.
  • the inverse DFT calculation unit 68 performs an inverse discrete Fourier transform on the result calculated by the convolution calculation unit 66 to generate a spectrum signal. Specifically, the inverse DFT calculation unit 68 uses the DFT component H ( ⁇ ) calculated by the convolution calculation by the convolution calculation unit 66 and the numerical value generation routine of the sine wave of the frequency ⁇ , and performs an inverse discrete Fourier transform. To output a spectrum signal (a signal obtained by extracting a predetermined spectrum component).
  • FIG. 5A is a graph showing a detection waveform of the received light signal.
  • FIG. 5B is a graph showing an output waveform of a spectrum signal.
  • FIG. 5C is a graph showing an output waveform of a spectrum signal calculated using a lock-in amplifier.
  • the vertical axis represents intensity
  • the horizontal axis represents time.
  • 5A the intensity on the vertical axis is the intensity of the received light signal (the intensity of transmitted light)
  • FIGS. 5B and 5C are the intensity of the spectrum signal on which the intensity on the vertical axis is calculated.
  • 5A and 5C the unit of time on the horizontal axis is ms, and in FIG.
  • the unit of time on the horizontal axis is s.
  • the laser measurement device 10 outputs laser light from the light emitting unit 40 with a modulation frequency of 125 kHz and a sweep frequency of 1 kHz.
  • the light reception signal of the laser beam that has passed through the exhaust gas to be measured output from the light emitting unit 40 has the waveform shown in FIG. 5A.
  • the received light intensity greatly increases with 1 ms as one cycle, and further, since the modulation frequency is 125 kHz, the sweep frequency with 0.008 ms as one cycle.
  • the received light intensity oscillates with an amplitude smaller than the amplitude due to. Note that there is a correlation between the wavelength (frequency) of laser light and the intensity.
  • the laser measuring apparatus 10 of the specific example has the same conditions as the above-described FIG. 3 and FIG. 4 for the received light signal shown in FIG. 5A, that is, the designated frequency is 250 kHz, the step frequency is 1 kHz, and the maximum value of the coefficient n is an integer multiple.
  • the received light signal shown in FIG. 5A is processed by a method using a conventional lock-in amplifier, and the output spectrum signal is shown in FIG. 5C.
  • the measurement result shown in FIG. 5C was calculated with the frequency of the reference sine wave set to 250 kHz.
  • the same waveform as that of the method using the conventional lock-in amplifier can be detected. Further, since the components to be detected are limited, the vibration of the waveform of the detection result can also be suppressed.
  • the relationship between the output of the spectrum signal and the concentration of the substance to be measured is associated by performing a test for calculating the correspondence before using the apparatus. Further, the absolute value of the detected intensity can be adjusted by adjusting the output intensity or the like.
  • the laser measuring apparatus 10 performs a discrete Fourier transform process on the digitized light reception signal, and the frequency differs by an integer multiple of the step frequency around the designated frequency that is a frequency obtained by multiplying the modulation frequency by an integer.
  • Each DFT component is calculated, a convolution process is performed with the DFT component and the DFT component of the reference sine wave (sine wave of the specified frequency), and a spectrum signal is obtained by performing an inverse discrete Fourier transform process on the calculation result.
  • the signal component of the absorption spectrum can be extracted from the received light signal with a small amount of calculation. That is, the laser measuring device 10 can extract a signal component necessary for calculating the physical quantity of the substance to be measured with a small calculation amount. Since the necessary calculations are reduced and the number of objects to be calculated is reduced, the configuration of the signal processing unit 47 can be simplified, so that the apparatus configuration can be simplified and the configuration of the control board (control circuit) is also simplified. can do.
  • the DFT calculation unit 64 since the DFT calculation unit 64 only needs to calculate the DFT component of the frequency necessary for the discrete Fourier transform, the calculation amount of the discrete Fourier transform can be reduced. In addition, since it is only necessary to extract the spectrum signal of the frequency to be measured and its surrounding frequency components, the discrete Fourier transform and the frequency around one specified frequency and its surrounding frequencies (frequency shifted by an integral multiple of the step frequency) and A convolution process may be performed. For this reason, the frequency component of a process target can be narrowed down and the increase in calculation amount can also be suppressed.
  • the designated frequency is twice the modulation frequency, but is not limited thereto.
  • the designated frequency can be a frequency that is an integral multiple of the modulation frequency.
  • the designated frequency is preferably twice the modulation frequency as in the present embodiment.
  • strength which arises by absorption of the light by the substance to be measured can be detected with a larger value. That is, the spectrum signal can be detected with a larger value (a value with a high S / N ratio).
  • FIG. 6A is a graph showing a detected waveform of the received light signal.
  • 6B to 6D are graphs each showing an output waveform of the spectrum signal.
  • the vertical axis is intensity and the horizontal axis is time.
  • the intensity on the vertical axis is the intensity of the received light signal
  • FIGS. 6B to 6D are the intensity of the spectrum signals on which the intensity on the vertical axis is calculated.
  • the unit of time on the horizontal axis is s.
  • the laser measuring apparatus 10 outputs laser light from the light emitting unit 40 with a modulation frequency of 100 kHz and a sweep frequency of 0.1 kHz.
  • the received light signal of the laser light output from the light emitting unit 40 and passing through the exhaust gas to be measured has the waveform shown in FIG. 6A.
  • the sweep frequency of the laser light is 0.1 kHz
  • 10 ms is one cycle of sweep
  • the modulation frequency is 100 kHz
  • 0.01 ms is one cycle of modulation.
  • the received light signal shown in FIG. 6A is processed by the signal processing unit 47 of the laser measuring device 10 with a setting in which the designated frequency is 200 kHz, the step frequency is 0.1 kHz, and the maximum value of the integer multiple coefficient n is 4.
  • Output a spectrum signal That is, the convolution process was performed using a 200 kHz component and 200 ⁇ 0.1 kHz, 200 ⁇ 0.2 kHz, 200 ⁇ 0.3 kHz, and 200 ⁇ 0.4 kHz components.
  • the output result is shown in FIG. 6B.
  • the modulation frequency is 100 kHz
  • the output (spectrum signal) of the target frequency can be detected by setting the modulation frequency to 200 kHz as in the above embodiment.
  • the signal processing unit 47 of the laser measuring apparatus 10 sets the specified frequency to 200 kHz, sets the step frequency to 0.1 kHz, sets an integer multiple coefficient n to a maximum value of 4 and an even number.
  • a spectrum signal was output after processing with a setting of (that is, an integer multiple of 2N and an integer having a maximum value 2 of N). That is, the convolution process was performed using the 200 kHz component and the 200 ⁇ 0.2 kHz and 200 ⁇ 0.4 kHz components. The output result is shown in FIG. 6C.
  • the intensity of the absorption spectrum (component reacting to the measurement) from which the distortion component included in the signal component is removed is calculated as a spectrum signal. can do. Thereby, the detection accuracy of a desired spectrum signal component can be maintained or improved.
  • the frequency to be calculated can be reduced.
  • the signal processing unit 47 of the laser measuring apparatus 10 sets the specified frequency to 200 kHz, sets the step frequency to 0.1 kHz, and sets the integer multiple coefficient n to a maximum value of 4 and an odd number (that is,
  • the spectrum signal was output after processing with the setting of an integer multiple of 2N-1 and an integer of 2 (the maximum value of N). That is, the convolution process was performed using the 200 kHz component and the 200 ⁇ 0.1 kHz and 200 ⁇ 0.3 kHz components. The output result is shown in FIG. 6D.
  • the intensity of the distortion component included in the signal component can be calculated by using only an odd number as a coefficient for multiplying the step frequency by an integer.
  • the distortion component is not affected by the absorption of the substance to be measured.
  • the laser measurement device 10 can use the distortion component for correction processing, calibration, and the like of the device.
  • the laser measurement device 10 calculates the intensity of the distortion component included in the signal component by using only an odd number as a coefficient for multiplying the step frequency by an integer in the signal processing unit 47, compares the result with a reference value, and the like. Measurement accuracy can be further improved by adjusting the conditions.
  • the laser measuring apparatus 10 switches between a mode that uses only odd numbers as a coefficient for multiplying a step frequency by an integer and a mode that uses only even numbers (or all integers) as a coefficient for multiplying a step frequency by an integer. In parallel, both correction processing and density measurement processing can be performed.
  • FIGS. 7A to 7G are graphs showing output waveforms of spectrum signals.
  • FIG. 7A to FIG. 7G show the intensities of the spectrum signals whose intensities on the vertical axis are calculated, and the time unit on the horizontal axis is s.
  • 7A to 7G are graphs showing the results of processing the received light signal shown in FIG.
  • FIG. 7A to FIG. 7G show the results of calculation using a designated frequency of 250 kHz, a step frequency of 1 kHz, and only an even number as a coefficient n.
  • FIG. 7A shows that the frequency to be analyzed is 5 points only in the even order (four frequencies shifted by an integral multiple of the designated frequency and the surrounding step frequency), that is, ⁇ 250 ⁇ 2N (N is an integer of 2 or less). ) Output in case of kHz. Therefore, in FIG. 7A, five frequencies of ⁇ 246 kHz, ⁇ 248 kHz, ⁇ 250 kHz, ⁇ 252 kHz, and ⁇ 254 kHz are analyzed.
  • FIG. 7B shows an output when the frequency to be analyzed is 7 points only in the even order, that is, ⁇ 250 ⁇ 2N (N is an integer of 3 or less) kHz.
  • FIG. 7C shows an output when the frequency to be analyzed is 9 points only in the even order, that is, ⁇ 250 ⁇ 2N (N is an integer of 4 or less) kHz.
  • FIG. 7D shows an output when the frequency to be analyzed is 11 points only in the even order, that is, ⁇ 250 ⁇ 2N (N is an integer of 5 or less) kHz.
  • FIG. 7E shows the output when the frequency to be analyzed is 15 points only in the even order, that is, ⁇ 250 ⁇ 2N (N is an integer of 7 or less) kHz.
  • FIG. 7F shows an output when the frequency to be analyzed is an even-order 21 point, that is, ⁇ 250 ⁇ 2N (N is an integer of 10 or less) kHz.
  • FIG. 7G shows the output when the frequency to be analyzed is an even-order 31 point, that is, ⁇ 250 ⁇ 2N (N is an integer of 15 or less) kHz.
  • various spectrum signals can be detected by setting the number of frequencies to be analyzed in various settings. Further, since any spectrum signal can detect a spectrum change caused by absorption based on the maximum value and the minimum value of the spectrum signal, the concentration of the substance to be measured can be preferably measured. Note that the laser measuring device 10 can obtain the same effect as increasing the cutoff frequency of the low-pass filter of the lock-in amplifier by increasing the number of frequencies to be analyzed.
  • the designated frequency can be various values that are integer multiples of the modulation frequency.
  • FIG. 8 is a graph showing an output waveform of the spectrum signal.
  • the vertical axis represents output, and the horizontal axis represents time with the unit s.
  • FIG. 8 shows the result of calculation using the received light signal shown in FIG. 5A with the specified frequency of 500 kHz, the step frequency of 1 kHz, and only the even number as the coefficient n.
  • the frequency to be analyzed is 31 points only in the even order. As shown in FIG. 8, even when a frequency that is four times the modulation frequency is used as the designated frequency, a change in the absorption spectrum (spectrum to be detected) included in the modulation frequency can be detected.
  • a fourth-order differential waveform of the spectrum is detected.
  • a frequency other than twice the modulation frequency in this way, a change in the absorption spectrum (detection target spectrum) can be detected even when there is a noise component at a frequency twice the modulation frequency.
  • the frequency higher than 2 times, such as 4 times the modulation frequency is difficult to detect the absorption spectrum (spectrum to be detected) because the signal intensity is small, but the laser measuring device 10 can accurately detect the target spectrum. Since it can be detected, an absorption spectrum (a spectrum to be detected) can be preferably detected.
  • the laser measuring device 10 preferably has the step frequency equal to the sweep frequency as in the present embodiment.
  • the step frequency By making the step frequency the same as the sweep frequency, it is possible to more suitably detect a change in the absorption spectrum (spectrum to be detected) included in the modulation frequency.
  • the step frequency is preferably a frequency calculated by multiplying the detection interval of the received light signal by the number of one frame. That is, it is preferable that the step frequency is a frequency at which the time required to acquire the light reception signal for one frame is one cycle.
  • the step frequency is preferably 1 kHz. Thereby, a spectrum signal can be detected with higher accuracy.
  • the laser measuring apparatus 10 preferably uses an integral multiple of the number of data that can be acquired in one cycle of the sweep frequency as the number of data for one frame of the received light signal. As a result, the spectrum signal can be detected with higher accuracy when the wavelength is swept at the sweep frequency.

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Abstract

L'invention concerne un dispositif de traitement de signal et un dispositif de mesure laser comportant un convertisseur A/N qui convertit un signal de réception de lumière en données numériques, une unité de calcul de DFT (transformée de Fourier discrète) qui obtient une partie à trame unique de données numériques pour le signal de réception de lumière converti par le convertisseur A/N, une transformée de Fourier discrète transformant la partie à trame unique de données numériques obtenue à l'aide d'une fréquence spécifiée qui est une fréquence de modulation multipliée par un nombre entier et de fréquences présentant la fréquence spécifiée en tant que fréquence centrale et différant par un multiple entier de la fréquence échelonnée, et qui calcule une composante DFT à l'aide de la fréquence spécifiée et des fréquences présentant la fréquence spécifiée en tant que fréquence centrale et différant par un multiple entier de la fréquence échelonnée, une unité de calcul convolutionnel qui effectue un calcul convolutionnel sur la composante DFT calculée par l'unité de calcul, et une unité de calcul de DFT inverse qui effectue une transformation de Fourier discrète inverse sur le résultat calculé par l'unité de calcul convolutionnel, et qui génère un signal spectroscopique.
PCT/JP2012/054277 2011-02-25 2012-02-22 Dispositif de traitement de signal et dispositif de mesure laser WO2012115150A1 (fr)

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JPWO2016174761A1 (ja) * 2015-04-30 2017-06-22 富士電機株式会社 船舶用レーザ式ガス分析計
CN110865042A (zh) * 2019-11-26 2020-03-06 东北石油大学 气体浓度检测方法、装置和系统

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JP2005502895A (ja) * 2001-09-19 2005-01-27 ジュール マイクロシステムズ カナダ インコーポレイテッド 信号整合フィルタリングを組み込んだ分光計
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JP2010169487A (ja) * 2009-01-21 2010-08-05 Mitsubishi Heavy Ind Ltd 濃度計測装置及び濃度計測方法
JP2010169449A (ja) * 2009-01-20 2010-08-05 Mitsubishi Heavy Ind Ltd 濃度計測装置及び濃度計測方法

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JP2007127425A (ja) * 2005-10-31 2007-05-24 Univ Of Tsukuba 光断層画像化法における補正方法
JP2010169449A (ja) * 2009-01-20 2010-08-05 Mitsubishi Heavy Ind Ltd 濃度計測装置及び濃度計測方法
JP2010169487A (ja) * 2009-01-21 2010-08-05 Mitsubishi Heavy Ind Ltd 濃度計測装置及び濃度計測方法

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Publication number Priority date Publication date Assignee Title
JPWO2016174761A1 (ja) * 2015-04-30 2017-06-22 富士電機株式会社 船舶用レーザ式ガス分析計
CN110865042A (zh) * 2019-11-26 2020-03-06 东北石油大学 气体浓度检测方法、装置和系统

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