WO2012115150A1 - Signal processing device and laser measurement device - Google Patents

Signal processing device and laser measurement device 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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French (fr)
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/en

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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.

Abstract

A signal processing device and a laser measurement device, having: an A/D converter that converts a light reception signal to digital data; a DFT calculation unit that obtains a one-frame portion of the digital data for the light reception signal converted by the A/D converter, discrete Fourier transforms the obtained one-frame portion of digital data using a specified frequency, which is a modulation frequency multiplied by an integer, and frequencies having the specified frequency as the center frequency and differing by an integral multiple of the step frequency, and calculates a DFT component using the specified frequency and frequencies having the specified frequency as the center frequency and differing by an integral multiple of the step frequency; a convolutional calculation unit that performs convolutional calculation on the DFT component calculated by the DFT calculation unit; and an inverse DFT calculation unit that performs inverse discrete Fourier transformation of the result calculated by the convolutional calculation unit, and generates a spectroscopic signal.

Description

信号処理装置およびレーザ計測装置Signal processing apparatus and laser measuring apparatus
　本発明は、レーザ吸収分光法により測定対象のガスの物理量を算出するレーザ計測に用いる信号処理装置およびレーザ計測装置に関する。 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.
　管路内を流れるガス（気体）を分析する方法として、レーザ光を測定光として用いる方法がある。例えば、特許文献１には、一定電流に重畳された第１の交流成分を有する電流で変調され、温度に応じて波長が変化するレーザ光を発振するレーザと、検知雰囲気通過後のレーザ光の強度を電圧に変換する電流電圧変換器（光強度電圧変換器）と、該電流電圧変換器の出力電圧を位相敏感検波する２つの位相敏感検波器と、一方の位相敏感検波器から得られる１次の位相敏感検波信号と他方の位相敏感検波器から得られる２次の位相敏感検波信号とに基づいて検知雰囲気の濃度を検知するガス検知装置が記載されている。 There is a method of using laser light as measurement light as a method of analyzing gas (gas) flowing in the pipe. For example, 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) for converting intensity into voltage, two phase sensitive detectors for phase sensitive detection of the output voltage of the current voltage converter, and 1 obtained from one phase sensitive detector There is described a gas detection device that detects the concentration of a detection atmosphere based on a next phase sensitive detection signal and a secondary phase sensitive detection signal obtained from the other phase sensitive detector.
　また、特許文献２には、レーザ光を出射するレーザ素子と、レーザ光を基本波で周波数変調する周波数変調部と、周波数変調されたレーザ光を検出する光検出部と、光検出部にて検出されたレーザ光から基本波成分を検出する基本波成分検出部と、光検出部にて検出されたレーザ光から２倍波成分を検出する２倍波成分検出部と、光検出部にて検出された基本波成分と２倍波成分との振幅比に基づいて測定対象ガスの濃度を算出するガス濃度算出部と、を有するガス濃度測定装置が記載されている。また、当該ガス濃度測定装置は、レーザ光から検出された基本波成分と２倍波成分との振幅比を算出する振幅比算出部と、基本波成分と２倍波成分との振幅比に基づいてレーザ素子の温度を設定する温度設定部と、吸収ピーク波長からシフトされた波長を基準とする波長変調を行った時の基本波成分と２倍波成分との振幅比に基づいてレーザ素子の駆動電流を制御する駆動電流制御部とを備える。 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, and 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.
特許第２７９６６４９号公報Japanese Patent No. 2796649 特開２００８－１４７５５７号公報JP 2008-147557 A
　特許文献１および特許文献２に記載されているように、測定光として波長変調を行いつつ出力したレーザ光を用い、当該レーザ光の吸収を計測することで、測定対象物質の濃度等の物理量を計測することができる。レーザ光を用いてガス濃度を計測することで高い応答性でガス濃度を計測することができる。 As described in Patent Document 1 and Patent Document 2, by using the laser light output while performing wavelength modulation as the measurement light, and measuring the absorption of the laser light, 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.
　ここで、受光部がレーザ光を受光して生成する受光信号には、種々のノイズが含まれる。そのため、受光信号からノイズを除去し、必要な成分（例えば波長変調を行う変調周波数に対応する信号成分）を抽出するために各種信号処理を行う。この信号処理としては、ロックインアンプで、ロックイン処理およびローパス処理を行い特定のスペクトル信号を抽出する方法がある。しかしながら、検出対象の信号はノイズに対して出力が小さいため、高精度な検出を行う場合は、ロックインアンプによる処理前にＦＩＲフィルタ等を設け、ロックインアンプの処理対象の周波数成分を抽出する、つまりロックインアンプの処理対象の周波数以外の周波数成分を低減させる処理を行う。 Here, 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). As 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. However, since the signal to be detected has a small output against noise, when performing highly accurate detection, 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.
　ここで、ＦＩＲフィルタを用いた処理では、直前の多数（例えば１０２４次）のデータを用いて特定の周波数成分を抽出する。このように、ＦＩＲフィルタは、受光信号から対象の成分を抽出するために、直前の多数の検出結果を記憶・処理して検出した値を使用する。このため、記憶・処理する計算量が多く計算負荷が大きくなってしまう。 Here, in the process using the FIR filter, a specific frequency component is extracted using a large number of data immediately before (for example, 1024th order). As described above, 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.
　本発明は、上記に鑑みてなされたものであって、少ない計算量かつ簡単な装置構成で受光信号から所望の信号成分を高い精度で検出することができる信号処理装置およびレーザ計測装置を提供することを目的とする。 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.
　上述した課題を解決し、目的を達成するために、本発明は、入射部と出射部を備え、かつ、流体が流れる計測セルと、測定対象のガスに固有な吸収波長を含む波長域のレーザ光を変調周波数で波長を変調しつつ出力し、前記計測セルに入射させる発光部と、前記入射部から入射され、前記計測セルを通過し、前記出射部から出射された前記レーザ光を受光し、受光した光量を受光信号として出力する受光部と、を有し、前記受光信号に基づいて前記計測セルを流れる測定対象のガスの物理量を算出するレーザ計測装置に適用され、前記受光部が受光した前記受光信号を処理し、前記計測セルを流れる測定対象のガスの物理量の算出に用いるスペクトル信号を出力する信号処理装置であって、前記受光信号をデジタルデータに変換するＡ／Ｄ変換部と、前記Ａ／Ｄ変換部で変換された前記受光信号の１フレーム分のデジタルデータを取得し、取得した１フレーム分のデジタルデータを、前記変調周波数を整数倍した周波数である指定周波数および前記指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれで離散フーリエ変換（Discrete　Fourier　Transform）し、前記指定周波数および前記指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれでＤＦＴ成分を算出するＤＦＴ計算部と、前記ＤＦＴ計算部で算出した前記ＤＦＴ成分に対して畳み込み計算する畳み込み計算部と、前記畳み込み計算部で計算した結果に対し逆離散フーリエ変換を行い、スペクトル信号を生成する逆ＤＦＴ計算部と、を含むことを特徴とする。 In order to solve the above-described problems and achieve the object, 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. And 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. And an inverse DFT calculation unit for generating a spectrum signal.
　ここで、前記ステップ周波数は、前記受光信号の検出間隔と１フレーム分の個数との乗算で算出される周波数であることが好ましい。 Here, the step frequency is preferably a frequency calculated by multiplying the detection interval of the received light signal by the number of frames.
　上述した課題を解決し、目的を達成するために、本発明はレーザ計測装置であって、上記のいずれかに記載の信号処理装置と、流体を流す流路と連結可能な主管、前記主管に連結し、光が通過可能な窓部が形成された入射部、前記主管に連結し光が通過可能な窓部が形成された出射部と、を含む計測セルと、測定対象のガスに固有な吸収波長を含む波長域のレーザ光を変調周波数で波長を変調しつつ出力し、前記入射部に入射させる発光部と、前記入射部から入射され、前記計測セルを通過し、前記出射部から出射された前記レーザ光を受光し、受光した光量を受光信号として出力する受光部と、前記スペクトル信号に基づいて、前記計測セルを流れる測定対象のガスの物理量を算出する物理量算出部と、各部の動作を制御する制御部と、を有することを特徴とする。 In order to solve the above-described problems and achieve the object, 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.
　また、前記発光部は、変調周波数よりも低い周波数の掃引周波数で波長を掃引しつつレーザ光出力することが好ましい。 Moreover, it is preferable that the light emitting unit outputs laser light while sweeping the wavelength at a sweep frequency lower than the modulation frequency.
　また、前記ＤＦＴ計算部は、前記掃引周波数の１周期分のデジタルデータを１フレーム分のデータとして取得することが好ましい。 Further, it is preferable that the DFT calculation unit obtains digital data for one cycle of the sweep frequency as data for one frame.
　また、前記ステップ周波数は、前記掃引周波数であることが好ましい。 The step frequency is preferably the sweep frequency.
　また、前記ＤＦＴ計算部は、前記指定周波数を中心として周波数が前記ステップ周波数の整数倍分異なる周波数として、前記ステップ周波数の偶数の整数倍分または奇数の整数倍分異なる周波数のみを用いることが好ましい。 Preferably, 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. .
　また、前記物理量算出部が算出する物理量は、前記測定対象のガスの濃度であることが好ましい。 The physical quantity calculated by the physical quantity calculator is preferably the concentration of the gas to be measured.
　また、前記物理量算出部は、前記発光部から出力したレーザ光の強度と、前記受光部で受光したレーザ光の強度とに基づいて、前記測定対象のガスの濃度を算出することが好ましい。 Moreover, it is preferable that 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.
　本発明にかかる信号処理装置およびレーザ計測装置は、少ない計算量かつ簡単な装置構成で受光信号から所望の信号成分を高い精度で検出することができるという効果を奏する。 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.
図１は、本発明の信号処理装置を有するレーザ計測装置の一実施形態の概略構成を示す模式図である。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. 図２は、図１に示すレーザ計測装置の信号処理部の概略構成を示すブロック図である。FIG. 2 is a block diagram illustrating a schematic configuration of a signal processing unit of the laser measurement apparatus illustrated in FIG. 1. 図３は、信号処理部の処理を説明するための説明図である。FIG. 3 is an explanatory diagram for explaining processing of the signal processing unit. 図４は、信号処理部の処理を説明するための説明図である。FIG. 4 is an explanatory diagram for explaining the processing of the signal processing unit. 図５Ａは、受光信号の検出波形を示すグラフである。FIG. 5A is a graph showing a detected waveform of the received light signal. 図５Ｂは、スペクトル信号の出力波形を示すグラフである。FIG. 5B is a graph showing an output waveform of a spectrum signal. 図５Ｃは、ロックインアンプを用いて算出したスペクトル信号の出力波形を示すグラフである。FIG. 5C is a graph showing an output waveform of a spectrum signal calculated using a lock-in amplifier. 図６Ａは、受光信号の検出波形を示すグラフである。FIG. 6A is a graph showing a detected waveform of the received light signal. 図６Ｂは、スペクトル信号の出力波形を示すグラフである。FIG. 6B is a graph showing an output waveform of the spectrum signal. 図６Ｃは、スペクトル信号の出力波形を示すグラフである。FIG. 6C is a graph showing an output waveform of the spectrum signal. 図６Ｄは、スペクトル信号の出力波形を示すグラフである。FIG. 6D is a graph showing an output waveform of a spectrum signal. 図７Ａは、スペクトル信号の出力波形を示すグラフである。FIG. 7A is a graph showing an output waveform of a spectrum signal. 図７Ｂは、スペクトル信号の出力波形を示すグラフである。FIG. 7B is a graph showing an output waveform of the spectrum signal. 図７Ｃは、スペクトル信号の出力波形を示すグラフである。FIG. 7C is a graph showing the output waveform of the spectrum signal. 図７Ｄは、スペクトル信号の出力波形を示すグラフである。FIG. 7D is a graph showing an output waveform of a spectrum signal. 図７Ｅは、スペクトル信号の出力波形を示すグラフである。FIG. 7E is a graph showing an output waveform of a spectrum signal. 図７Ｆは、スペクトル信号の出力波形を示すグラフである。FIG. 7F is a graph showing an output waveform of a spectrum signal. 図７Ｇは、スペクトル信号の出力波形を示すグラフである。FIG. 7G is a graph showing an output waveform of a spectrum signal. 図８は、スペクトル信号の出力波形を示すグラフである。FIG. 8 is a graph showing the output waveform of the spectrum signal.
　以下に、本発明にかかる信号処理装置およびレーザ計測装置の一実施形態を図面に基づいて詳細に説明する。なお、この実施形態によりこの発明が限定されるものではない。なお、レーザ計測装置は、流路を流れる種々の気体（ガス）等の流体に含まれる測定対象の物質（ガス、特定の成分）の物理量（濃度、量）を計測することができる。レーザ計測装置は、例えば、ディーゼルエンジンに取付、ディーゼルエンジンから排出される排ガスに含まれる窒素酸化物、硫化酸化物、一酸化炭素、二酸化炭素、アンモニア等の濃度等を計測してもよい。なお、測定対象の物質（ガス）を排出（供給）する装置は、これに限定されず、ガソリンエンジンや、ガスタービン等種々の内燃機関に用いることができる。また、内燃機関を有する装置としては、車両、船舶、発電機等種々の装置が例示される。さらに、レーザ計測装置は、ゴミ焼却炉、ボイラ等の燃焼機器から排出される排ガスに含まれる測定対象の物質の濃度等を計測することもできる。なお、以下の実施形態では、配管を流れる排ガスに含まれる測定物質の濃度を計測する場合として説明する。 Hereinafter, an embodiment of a signal processing device and a laser measurement device according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. Note that 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. For example, 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. Further, 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.
　図１は、本発明の信号処理装置を有するレーザ計測装置の一実施形態の概略構成を示す模式図である。図１に示すようにレーザ計測装置１０は、計測セル１２と、計測手段１４と、を有する。ここで、レーザ計測装置１０は、排ガスＡが流れる配管６と配管８との間に設けられている。また、排ガスＡは、配管６の上流側から供給され、配管６、レーザ計測装置１０、配管８を通過し、配管８よりも下流側に排出される。なお、配管６の上流側には、排ガスＡの発生装置（供給装置）が配置されている。 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. As shown in FIG. 1, the laser measurement device 10 includes a measurement cell 12 and measurement means 14. Here, the laser measuring device 10 is provided between the pipe 6 and the pipe 8 through which the exhaust gas A flows. Further, 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. Note that an exhaust gas A generator (supply device) is disposed upstream of the pipe 6.
　計測セル１２は、基本的に主管２０と、入射管２２と、出射管２４とを有する。また、入射管２２には、窓２６が設けられており、出射管２４には、窓２８が設けられている。主管２０は、筒状の管状部材であり、一方の端部が配管６と連結され、他方の端部が配管８と連結されている。つまり、主管２０は、排ガスＡが流れる流路の一部となる位置に配置されている。これにより、排ガスＡは、配管６、主管２０、配管８の順に流れる。また、配管６を流れる排ガスＡは、基本的に全て主管２０を流れる。 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.
　入射管２２は、管状部材であり、一方の端部が主管２０に連結されている。また、主管２０は、入射管２２との連結部が、入射管２２の開口（端部の開口）と略同一形状の開口となっている。つまり、入射管２２は、主管２０と、空気の流通が可能な状態で連結されている。また、入射管２２の他方の端部には、窓２６が設けられており、窓２６により封止されている。なお、窓２６は、光を透過する部材、例えば、透明なガラス、樹脂等で構成されている。これにより、入射管２２は、窓２６が設けられている端部が、空気が流通しない状態で、かつ、光が透過できる状態となる。 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.
　入射管２２は、図１に示すように、窓２６側の端部の開口（つまり、窓２６により塞がれている開口）の面積と、主管２０側の端部（つまり、主管２０と連結している部分の開口）の面積とが実質的に同一の円筒形状である。なお、入射管２２の形状は円筒形状に限定されず、空気および光を通過させる筒型の形状であればよく、種々の形状とすることができる。例えば、断面が四角、多角形、楕円、非対称曲面となる形状としてもよい。また筒形状の断面の形状、径が位置によって変化する形状でもよい。 As shown in FIG. 1, 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. For example, the cross section may be a square, a polygon, an ellipse, or an asymmetric curved surface. Moreover, the shape of the cross section of a cylindrical shape and the shape from which a diameter changes with positions may be sufficient.
　出射管２４は、入射管２２と略同一形状の管状部材であり、一方の端部が主管２０に連結され、出射管２４の他方の端部には、窓２８が設けられている。出射管２４も、主管２０と空気が流通可能な状態で、窓２８が設けられている端部が、空気が流通しない状態で、かつ、光が透過できる状態となる。また、出射管２４は、中心軸が入射管２２の中心軸と略同一となる位置に配置されている。つまり、入射管２２と出射管２４とは、主管２０の対向する位置に配置されている。 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. Further, 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.
　また、出射管２４も、窓２８側の端部の開口（つまり、窓２８により塞がれている開口）の面積と、主管２０側の端部（つまり、主管２０と連結している部分の開口）の面積とが実質的に同一の円筒形状である。なお、出射管２４も形状は円筒形状に限定されず、空気および光を通過させる筒型の形状であればよく、種々の形状とすることができる。例えば、断面が四角、多角形、楕円、非対称曲面となる形状としてもよい。また筒形状の断面の形状、径が位置によって変化する形状でもよい。なお、出射管２４も、後述するパージガスが安定して流れる形状とすることが好ましい。 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. For example, the cross section may be a square, a polygon, an ellipse, or an asymmetric curved surface. Moreover, the shape of the cross section of a cylindrical shape and the shape from which a diameter changes with positions may be sufficient. In addition, it is preferable that the emission tube 24 also has a shape in which a purge gas described later flows stably.
　次に、計測手段１４は、発光部４０と、光ファイバ４２と、受光部４４と、光源ドライバ４６と、信号処理部（信号処理装置）４７と、物理量算出部４８と、制御部５０と、を有する。なお、本実施形態では、信号処理部４７と、物理量算出部４８と、を別々に設けたが一体で（１つの処理部として）設けてもよい。また、光源ドライバ４６と、信号処理部４７と、物理量算出部４８と、制御部５０と、を一体で（１つの処理部として）設けてもよい。 Next, 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, Have In the present embodiment, the signal processing unit 47 and the physical quantity calculation unit 48 are provided separately, but may be provided integrally (as one processing unit). In addition, 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).
　発光部４０は、所定波長のレーザ光を出力（発光）させる発光素子を有する。なお、発光部４０の発光素子は、出力するレーザ光の出力波長（周波数）を所定の波長幅（周波数幅）で変化させることができる発光素子である。発光素子としては、波長可変の半導体レーザ素子（ＬＤ：Laser　Diode）を用いることができる。発光部４０は、測定対象の物質が吸収する近赤外波長域を含む波長域のレーザ光を出力する。例えば、計測対象が一酸化窒素の場合、発光部４０は、一酸化窒素を吸収する近赤外波長域を含む波長域のレーザ光を出力する。また、計測対象が二酸化窒素の場合、発光部４０は、二酸化窒素を吸収する近赤外波長域を含む波長域のレーザ光を出力する。また、計測対象が亜酸化窒素の場合、発光部４０は、亜酸化窒素を吸収する近赤外波長域を含む波長域のレーザ光を出力する。なお、測定対象が複数の物質である場合、発光部４０は、夫々の物質が吸収する波長域の光を発光する発光素子を複数備え、それぞれの波長域の光を出力するようにしてもよい。光ファイバ４２は、発光部４０から出力されたレーザ光を案内し、窓２６から計測セル１２内に入射させる。 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). As the light emitting element, a tunable semiconductor laser element (LD: Laser Diode) can be used. 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. 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.
　受光部４４は、計測セル１２の主管２０の内部を通過し、出射管２４の窓２８から出力されたレーザ光を受光する受光部である。なお、受光部４４は、例えば、フォトダイオード（ＰＤ、Photodiode）等の光検出器を備え、光検出器によってレーザ光を受光し、その光の強度を検出する。受光部４４は、受光したレーザ光の強度（光量）を受光信号として、信号処理部４７に送る。 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.
　光源ドライバ４６は、発光部４０を駆動する機能を有し、発光部４０に供給する電流、電圧を調整することで、発光部４０から出力されるレーザ光の波長、強度を調整する。光源ドライバ４６は、発振器であり、電流、電圧を所定の波形で発光部４０に供給することで時間により波長が変化するレーザ光を出力させる。本実施形態の光源ドライバ４６は、設定された変調周波数（例えば、１００ｋＨｚ、１５０ｋＨｚ）でレーザ光の波長を振動させ、変調周波数よりも低い周波数である掃引周波数（０．１ｋＨｚ、１ｋＨｚ）でレーザ光の波長を掃引する。これにより、発光部４０から出力されるレーザ光は、変調周波数で振動する振動の中心が、掃引周波数に基づいて変化するレーザ光となる。光源ドライバ４６は、制御部５０を介して物理量算出部４８に、発光部４０から出力しているレーザ光の強度の情報を出力する。 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. Thereby, 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.
　信号処理部４７は、受光部４４がレーザ光を受光することで生成した信号（受光信号）を処理する。具体的には、信号処理部４７は、受光信号に含まれるノイズ成分を除去し、発光部４０から出力され受光部４４に到達したレーザ光の成分を抽出する。なお、抽出して生成される信号を以下スペクトル信号という。また、信号処理部４７の処理については後述する。 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.
　物理量算出部４８は、信号処理部４７から出力されたスペクトル信号に基づいて、計測セル１２を流れる排ガスの濃度を算出する。物理量算出部４８は、信号処理部４７から出力されたスペクトル信号と、制御部５０により光源ドライバ４６を駆動させている条件とに基づいて、計測対象の物質の濃度を算出する。具体的には、物理量算出部４８は、制御部５０により光源ドライバ４６を駆動させている条件に基づいて発光部４０から出力されるレーザ光の強度を算出し、信号処理部４７で生成されたスペクトル信号に基づいて受光したレーザ光の強度を算出する。物理量算出部４８は、この発光したレーザ光の強度と受光したレーザ光の強度と比較し、排ガスＡに含まれる測定対象の物質の濃度を算出する。 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. Specifically, 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.
　具体的には、発光部４０から出力された近赤外の波長域のレーザ光Ｌは、光ファイバ４２から計測セル１２の所定経路、具体的には、窓２６、入射管２２、主管２０、出射管２４、窓２８を通過した後、受光部４４に到達する。このとき、計測セル１２内の排ガスＡ中に測定対象の物質が含まれていると、計測セル１２を通過するレーザ光Ｌが吸収される。そのため、レーザ光Ｌは、排ガスＡ中の測定対象の物質の濃度によって、受光部４４に到達するレーザ光の出力が変化する。受光部４４は、受光したレーザ光を受光信号に変換する。受光部４４で生成された受光信号は、信号処理部４７で処理されスペクトル信号として物理量算出部４８に入力される。また、制御部５０および光源ドライバ４６は、発光部４０から出力したレーザ光Ｌの強度を物理量算出部４８に出力する。物理量算出部４８は、発光部４０から出力した光の強度と、スペクトル信号から算出される強度とを比較し、その減少割合から計測セル１２内を流れる排ガスＡの測定対象の物質の濃度を算出する。このように計測手段１４は、いわゆるＴＤＬＡＳ方式（Tunable　Diode　Laser　Absorption　Spectroscopy：可変波長ダイオードレーザー分光法）を用いることで、出力したレーザ光の強度と、受光部４４で検出した受光信号とに基づいて主管２０内の所定位置、つまり、測定位置を通過する排ガスＡ中の測定対象の物質の濃度を、算出および／または計測することができる。また、計測手段１４は、連続的に測定対象の物質の濃度を、算出および／または計測することができる。なお、レーザ計測装置１０は、発光部４０から出力されるレーザ光の強度を一定として、スペクトル信号のみ基づいて排ガスＡに含まれる測定対象の物質の濃度を算出してもよい。 Specifically, 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. At this time, if the substance to be measured is contained in the exhaust gas A in the measurement cell 12, 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. In addition, 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. Thus, 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. Moreover, 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.
　制御部５０は、各部の動作を制御する制御機能を有し、必要に応じて、各部の動作を制御する。なお、制御部５０は、計測手段１４の制御のみならず、レーザ計測装置１０の全体の動作を制御する。つまり、制御部５０は、レーザ計測装置１０の動作を制御する制御部である。 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.
　次に、レーザ計測装置１０の信号処理部４７の構成を説明し、信号処理部４７による受光信号の処理について説明する。ここで、図２は、図１に示すレーザ計測装置の信号処理部の概略構成を示すブロック図である。図２に示すように、信号処理部４７は、受光部４４から送られた受光信号を処理してスペクトル信号を生成し、生成したスペクトル信号を物理量算出部４８に送る。信号処理部４７は、増幅Ａ／Ｄ変換部（増幅アナログデジタル変換部）６２と、ＤＦＴ（Discrete　Fourier　Transform）計算部６４と、一時記憶部６５と、畳み込み計算部６６と、逆ＤＦＴ（Discrete　Fourier　Transform）計算部６８と、を有する。 Next, the configuration of the signal processing unit 47 of the laser measurement apparatus 10 will be described, and the processing of the received light signal by the signal processing unit 47 will be described. Here, FIG. 2 is a block diagram showing a schematic configuration of a signal processing unit of the laser measuring apparatus shown in FIG. As shown in FIG. 2, 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.
　増幅Ａ／Ｄ変換部６２は、アナログの受光信号をデジタルの受光信号に変換し、さらにその出力を増幅する。増幅Ａ／Ｄ変換部６２は、増幅したデジタルの受光信号をＤＦＴ計算部６４に送る。 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.
　ＤＦＴ計算部６４は、増幅Ａ／Ｄ変換部６２で変換された受光信号のデジタルデータを１フレーム分取得し、取得した１フレーム分のデジタルデータを、離散フーリエ変換（ＤＦＴ、Discrete　Fourier　Transform）し、変調周波数を整数倍した周波数である指定周波数および当該指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれについてのＤＦＴ成分（フーリエ係数）を算出する。なお、ステップ周波数とは、予め設定した数値であり、ＤＦＴおよび後述する畳み込み処理に用いる周波数成分の間隔を決定する値である。つまり、指定周波数をαとし、ステップ周波数をβとし、ｎを０以上の整数とした場合、ＤＦＴ成分を算出する周波数は、α±ｎβとなる。なお、ｎの最大値は、設定により調整することができる値である。 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. That is, when the designated frequency is α, the step frequency is β, and n is an integer greater than or equal to 0, the frequency for calculating the DFT component is α ± nβ. The maximum value of n is a value that can be adjusted by setting.
　これにより、ＤＦＴ計算部６４は、離散フーリエ変換により１フレーム分のデジタルデータから指定周波数のＤＦＴ成分（フーリエ係数）を算出しかつ指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれのＤＦＴ成分（フーリエ係数）を算出する。このようにＤＦＴ計算部６４は、デジタルの受光信号であるｆ（ｔ）に対して離散フーリエ変換を行い、指定周波数を中心とした各周波数のＤＦＴ成分Ｆ（ω）を算出する。なお、ＤＦＴ成分Ｆ（ω）のωはα±ｎβである。また、参照正弦波（指定周波数の正弦波）の信号であるｇ（ｔ）に対して離散フーリエ変換を行い、参照正弦波のＤＦＴ成分Ｇ（ω）を算出する。なお、Ｇ（ω）は予め算出しておき、畳み込み計算部６６に設定しておいてもよい。また、ＤＦＴ計算部６４は、畳み込み計算部６６で必要となるため、指定周波数及び指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数に対応するマイナス周波数のＤＦＴ成分（Ｆ（ω）、Ｇ（ω））も算出する。なお、離散フーリエ変換では、マイナス周波数のＤＦＴ成分はＦ（－ｋ）＝Ｆ＊（ｋ）となるため、正周波数の複素共役で算出することができる。 As a result, 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. As described above, 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 (ω) of each frequency centered on the specified frequency. Note that ω of the DFT component F (ω) is α ± nβ. Also, 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 (ω) of the reference sine wave is calculated. G (ω) may be calculated in advance and set in the convolution calculation unit 66. Further, since the DFT calculation unit 64 is necessary for the convolution calculation unit 66, a negative frequency DFT component (F (ω), 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 (ω)) is also calculated. In the discrete Fourier transform, the negative frequency DFT component is F (−k) = F * (k), and therefore can be calculated with a complex conjugate of the positive frequency.
　一時記憶部６５は、ＤＦＴ計算部６４で算出された算出結果（各周波数におけるＤＦＴ成分）を記憶する記憶部である。なお、一時記憶部６５は、畳み込み計算部６６で必要な算出結果を一時的に記憶するバッファとして機能する。一時記憶部６５は、ＤＦＴ計算部６４により算出された算出結果が書き込まれ、畳み込み計算部６６により記憶した算出結果が読み出される。また、一時記憶部６５に記憶された算出結果は、自身、ＤＦＴ計算部６４または畳み込み計算部６６により上書き処理や削除処理により順次一時記憶部６５から消去される。 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. In the temporary storage unit 65, 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.
　畳み込み計算部６６は、一時記憶部６５に記憶されたＤＦＴ算出部６４で算出したＤＦＴ成分に対して畳み込み計算する。具体的には、一時記憶部６５に記憶した指定周波数を中心とした各周波数のＤＦＴ成分Ｆ（ω）と、参照正弦波のＤＦＴ成分Ｇ（ω）とを用いて、下記式（１）の畳み込み計算を実行する。 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 (ω) of each frequency centered on the designated frequency stored in the temporary storage unit 65 and the DFT component G (ω) of the reference sine wave, Perform convolution calculations.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　ここで、（式１）の畳み込み計算は、下記式（２）に示すように展開することができる。本実施形態のΔはステップ周波数の整数倍の値ｎβ（なおｎは０を含む）である。 Here, the convolution calculation of (Expression 1) can be expanded as shown in the following Expression (2). In the present embodiment, Δ is a value nβ (n includes 0) that is an integral multiple of the step frequency.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ここで、本実施形態の畳み込み計算において、Ｇ（ｆ）はｆの絶対値が指定周波数である正負の２周波数の場合以外に値が０となる。このため、（式２）の畳み込み計算で計算する対象は、指定周波数ｆと－ｆの周波数成分となる。また、Δはステップ周波数の整数倍の値ｎβであるため、２ｎ＋１個のΔに対して各１個のＨ（Δ）が算出される。 Here, in the convolution calculation of the present embodiment, 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 Δ is a value nβ that is an integral multiple of the step frequency, one H (Δ) is calculated for each of 2n + 1 Δ.
　以下、具体例を用いて、信号処理部４７の畳み込み処理を説明する。ここで、図３および図４は、それぞれ信号処理部の処理を説明するための説明図である。なお、図３は、受光信号（ＬＤ信号）を離散フーリエ変換した結果Ｆ（ω）と、参照正弦波を離散フーリエ変換した結果Ｇ（ω）を示す説明図である。また、図３は、縦軸が強度（大きさ）であり、横軸が周波数軸である。 Hereinafter, the convolution processing of the signal processing unit 47 will be described using a specific example. Here, 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 (ω) obtained by subjecting a received light signal (LD signal) to discrete Fourier transform and a result G (ω) obtained by subjecting a reference sine wave to discrete Fourier transform. In FIG. 3, the vertical axis represents intensity (size), and the horizontal axis represents frequency axis.
　図３および図４に示す具体例では、指定周波数を２５０ｋＨｚとし、ステップ周波数を１ｋＨｚとし、整数倍の係数ｎの最大値を２とした。また、サンプリング周波数は４ＭＨｚでありサンプリング周期Δｔは２．５Ｅ－７秒である。また、１／２Δｔは、サンプリング周波数の半分の値（周波数）に相当する。なお、レーザ計測装置１０は、変調周波数を１２５ｋＨｚとし、掃引周波数を１ｋＨｚとしてレーザ光を出力した。以上の条件で、受光信号（ＬＤ信号）を離散フーリエ変換すると、Ｆ（ω）として、図３に示すように、変調周波数１２５ｋＨｚの倍の周波数である２５０ｋＨｚの周辺（周波数２４８ｋＨｚから２５２ｋＨｚ）に出力９２が算出される。また、畳み込み計算で必要となる、対応するマイナス周波数（周波数－２５２ｋＨｚから－２４８ｋＨｚ）の出力９４も算出される。また、同様に、参照正弦波を離散フーリエ変換すると、Ｇ（ω）は、図３に示すように、参照正弦波の周波数である２５０ｋＨｚの周辺に出力９６が算出される。また、離散フーリエ変換では、対応するマイナス周波数の出力９８も算出される。 In the specific examples shown in FIGS. 3 and 4, the designated frequency is 250 kHz, the step frequency is 1 kHz, and the maximum value of the integer n is n. The sampling frequency is 4 MHz and the sampling period Δt is 2.5E −7 seconds. Moreover, 1 / 2Δt 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. Under the above conditions, when the received light signal (LD signal) is subjected to discrete Fourier transform, as F (ω), as shown in FIG. 3, it is output around 250 kHz (frequency from 248 kHz to 252 kHz), which is twice the modulation frequency of 125 kHz. 92 is calculated. In addition, an output 94 having a corresponding negative frequency (frequency of −252 kHz to −248 kHz) necessary for the convolution calculation is also calculated. Similarly, when the reference sine wave is subjected to discrete Fourier transform, an output 96 of G (ω) is calculated around 250 kHz, which is the frequency of the reference sine wave, as shown in FIG. In the discrete Fourier transform, a corresponding negative frequency output 98 is also calculated.
　畳み込み計算部６６は、図３に示すように算出することができるＦ（ω）のうち、変調周波数を２倍した指定周波数２５０ｋＨｚ及びその近傍の成分を解析対象とする。なお、畳み込み計算では、指定周波数に対応するマイナス周波数も必要となるため、周波数－２５０ｋＨｚ及びその近傍の成分も解析対象とする。つまり、畳み込み計算部６６は、領域１００に囲われた出力成分から必要なＤＦＴ成分を出力する。ここで、本実施形態では、指定周波数を２５０ｋＨｚとし、ステップ周波数を１ｋＨｚとし、整数倍の係数ｎの最大値が２であるため、Ｈ（Δ）の算出には、Ｆ（±２４８）、Ｆ（±２４９）、Ｆ（±２５０）、Ｆ（±２５１）、Ｆ（±２５２）と、Ｇ（±２５０）と、を用いる。畳み込み計算部６６は、上記ＤＦＴ成分を用いて、Δ＝０、±１、±２ｋＨｚのＨ（Δ）を算出する。つまり、Ｈ（－２）、Ｈ（－１）、Ｈ（０）、Ｈ（１）、Ｈ（２）を算出する。例えば、Ｈ（０）は、下記式（３）を用いて、算出する。 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 (ω) 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. Here, in this embodiment, the designated frequency is 250 kHz, the step frequency is 1 kHz, and 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. The convolution calculation unit 66 calculates H (Δ) of Δ = 0, ± 1, ± 2 kHz using the DFT component. That is, H (−2), H (−1), H (0), H (1), and H (2) are calculated. For example, H (0) is calculated using the following formula (3).
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　つまり、図４に示すように、Δ＝０の場合は、Ｆ（２５０）の成分とＧ（－２５０）の成分とを乗算し、Ｆ（－２５０）の成分とＧ（２５０）の成分とを乗算して算出する。また、この算出した結果を合計することで、Ｈ（０）を算出する。また、Ｈ（１）は、下記式（４）を用いて、算出する。 That is, as shown in FIG. 4, when Δ = 0, the component of F (250) and the component of G (−250) are multiplied, and the component of F (−250) and the component of G (250) Multiply by Further, H (0) is calculated by summing up the calculated results. H (1) is calculated using the following formula (4).
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　図４に示すように、Δ＝１の場合は、Ｆ（２５１）の成分とＧ（－２５０）の成分とを乗算し、Ｆ（－２４９）の成分とＧ（２５０）の成分とを乗算して算出する。また、この算出した結果を合計することで、Ｈ（１）を算出する。また、Ｈ（－１）は、下記式（５）の計算式で算出する。 As shown in FIG. 4, when Δ = 1, the component of F (251) and the component of G (−250) are multiplied, and the component of F (−249) and the component of G (250) are multiplied. To calculate. Further, H (1) is calculated by summing up the calculated results. H (−1) is calculated by the following equation (5).
Figure JPOXMLDOC01-appb-M000005
Figure JPOXMLDOC01-appb-M000005
　さらに、式は示さないがＨ（２）、（－２）も同様に上記式（２）を用いて計算を行う。畳み込み計算部６６は、以上のようにして、条件に基づいて、複数のＤＦＴ成分のＨ（Δ）を算出する。 Furthermore, although formulas are not shown, H (2) and (-2) are similarly calculated using formula (2). The convolution calculator 66 calculates H (Δ) of a plurality of DFT components based on the conditions as described above.
　逆ＤＦＴ計算部６８は、畳み込み計算部６６で計算した結果に対し、逆離散フーリエ変換を行い、スペクトル信号を生成する。具体的には、逆ＤＦＴ計算部６８は、畳み込み計算部６６で畳み込み計算されて算出されたＤＦＴ成分のＨ（Δ）と、周波数Δの正弦波の数値生成ルーチンを用いて、逆離散フーリエ変換を行い、スペクトル信号（所定のスペクトル成分を抽出した信号）を出力する。 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 (Δ) calculated by the convolution calculation by the convolution calculation unit 66 and the numerical value generation routine of the sine wave of the frequency Δ, and performs an inverse discrete Fourier transform. To output a spectrum signal (a signal obtained by extracting a predetermined spectrum component).
　次に、具体的な処理例について説明する。ここで、図５Ａは、受光信号の検出波形を示すグラフである。図５Ｂは、スペクトル信号の出力波形を示すグラフである。図５Ｃは、ロックインアンプを用いて算出したスペクトル信号の出力波形を示すグラフである。なお、図５Ａから図５Ｃは、ともに縦軸を強度とし、横軸を時間とした。なお、図５Ａは、縦軸の強度が受光信号の強度（透過光の強度）であり、図５Ｂおよび図５Ｃは、縦軸の強度が算出されたスペクトル信号の強度である。また、図５Ａおよび図５Ｃは、横軸の時間の単位がｍｓであり、図５Ｂは、横軸の時間の単位がｓである。ここで、レーザ計測装置１０は、図５Ａから図５Ｃに示す計測において、変調周波数を１２５ｋＨｚとし、掃引周波数を１ｋＨｚとして発光部４０からレーザ光を出力した。この条件で、発光部４０から出力された測定対象の排ガスを通過したレーザ光の受光信号は、図５Ａに示す波形となる。図５Ａに示すように、レーザ光は、掃引周波数が１ｋＨｚであるため、１ｍｓを１周期として受光強度が大きく振幅し、さらに、変調周波数が１２５ｋＨｚであるため、０．００８ｍｓを１周期として掃引周波数による振幅よりも小さい振幅で受光強度が振動している。なお、レーザ光の波長（周波数）と強度とは相関関係がある。 Next, a specific processing example will be described. Here, 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. In FIGS. 5A to 5C, the vertical axis represents intensity, and 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), and 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. 5B, the unit of time on the horizontal axis is s. Here, in the measurement shown in FIGS. 5A to 5C, 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. Under this condition, 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. As shown in FIG. 5A, since the laser beam has a sweep frequency of 1 kHz, 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.
　具体例のレーザ計測装置１０は、図５Ａに示す受光信号を上述した図３および図４と同様の条件、つまり、指定周波数を２５０ｋＨｚとし、ステップ周波数を１ｋＨｚとし、整数倍の係数ｎの最大値を３１で処理し、スペクトル信号を出力した。出力したスペクトル信号を図５Ｂに示す。また、比較のために、図５Ａに示す受光信号を従来のロックインアンプを用いた方式で処理し、出力したスペクトル信号を図５Ｃに示す。なお、図５Ｃに示す計測結果は、参照正弦波の周波数を２５０ｋＨｚとして算出した。 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. Was processed at 31 to output a spectrum signal. The output spectrum signal is shown in FIG. 5B. For comparison, 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.
　図５Ｂおよび図５Ｃに示すように、本実施形態のレーザ計測装置１０を用いた場合でも、従来のロックインアンプを用いた方式と同様の波形を検出することができる。また、検出対象の成分を限定しているため、検出結果の波形の振動も抑制することができる。なお、スペクトル信号の出力と測定対象の物質の濃度との関係は、装置の使用前に対応関係を算出する試験を行うことで、対応付ける。また、検出強度の絶対値は、出力強度等を調整することで調整することもできる。 As shown in FIG. 5B and FIG. 5C, even when the laser measurement device 10 of the present embodiment is used, 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.
　このように、レーザ計測装置１０は、デジタル化した受光信号に離散フーリエ変換処理を行い、変調周波数を整数倍した周波数である指定周波数および指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれのＤＦＴ成分を算出し、そのＤＦＴ成分と、参照正弦波（指定周波数の正弦波）のＤＦＴ成分とで、畳み込み処理を行い、その算出結果に逆離散フーリエ変換処理を行ってスペクトル信号を算出（検出）することで、少ない計算量で受光信号から吸収スペクトルの信号成分を抽出することができる。つまり、レーザ計測装置１０は、少ない計算量で、測定対象の物質の物理量の算出に必要な信号成分を抽出することができる。必要な計算が少なくなり、計算対象も少なくなるため、信号処理部４７の構成も簡単にすることができるため、装置構成を簡単にすることができ、制御基板（制御回路）の構成も簡単にすることができる。 As described above, 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. By calculating (detecting), 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.
　具体的には、比較例で用いたロックインアンプを用いた信号処理では、ＦＩＲフィルタで１つの信号の処理を行うために直前の多数のフレーム分のデータを記憶・処理して移動平均を算出する必要がある。これに対して、本実施形態は、１フレーム分のデータに対して離散フーリエ変換を行い、設定された周波数毎のＤＦＴ成分（フーリエ係数）を算出し、算出した複数のＤＦＴ成分を組み合わせ計算する畳み込み処理を行い、その結果を逆離散フーリエ変換することで、スペクトル信号を算出することができる。これにより、計算量を少なくすることができ、かつ、処理対象の信号成分を飛躍的に少なくすることができる。 Specifically, in the signal processing using the lock-in amplifier used in the comparative example, in order to process one signal with the FIR filter, data for a large number of immediately preceding frames is stored and processed to calculate a moving average. There is a need to. In contrast, in the present embodiment, discrete Fourier transform is performed on data for one frame, a DFT component (Fourier coefficient) for each set frequency is calculated, and a plurality of calculated DFT components are combined and calculated. A spectrum signal can be calculated by performing convolution processing and performing inverse discrete Fourier transform on the result. As a result, the amount of calculation can be reduced, and the signal components to be processed can be dramatically reduced.
　また、ＤＦＴ計算部６４は、離散フーリエ変換で必要な周波数のＤＦＴ成分のみを算出すればよいため、離散フーリエ変換の計算量も少なくすることができる。また、測定対象の周波数およびその周辺の周波数成分のスペクトル信号を抽出すればよいため、１つの指定周波数およびその周辺の周波数（ステップ周波数の整数倍分ずれた周波数）に対して、離散フーリエ変換および畳み込み処理を行えばよい。このため、処理対象の周波数成分を絞り込むことができ、計算量の増加も抑制できる。なお、上記実施形態では、一例として、指定周波数として変調周波数の２倍の周波数としたが、これに限定されない。指定周波数は、変調周波数の整数倍の周波数を用いることができる。なお、指定周波数は、本実施形態のように、変調周波数の２倍の周波数とすることが好ましい。これにより、測定対象の物質による光の吸収で生じる強度の変動をより大きい値で検出することができる。つまり、スペクトル信号をより大きい値（Ｓ／Ｎ比が高い値）で検出することができる。 In addition, 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. In the above-described embodiment, as an example, 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. Note that the designated frequency is preferably twice the modulation frequency as in the present embodiment. Thereby, the fluctuation | variation of the intensity | 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).
　次に、図６を用いて、レーザ計測装置１０の信号処理部４７の処理の他の実施形態について説明する。ここで、図６Ａは、受光信号の検出波形を示すグラフである。図６Ｂから図６Ｄは、それぞれスペクトル信号の出力波形を示すグラフである。なお、図６Ａから図６Ｄは、ともに縦軸を強度とし、横軸を時間とした。なお、図６Ａは、縦軸の強度が受光信号の強度であり、図６Ｂから図６Ｄは、縦軸の強度が算出されたスペクトル信号の強度である。また、図６Ａから図６Ｄは、横軸の時間の単位がｓである。 Next, another embodiment of the processing of the signal processing unit 47 of the laser measuring device 10 will be described with reference to FIG. Here, 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. In FIGS. 6A to 6D, the vertical axis is intensity and the horizontal axis is time. 6A, the intensity on the vertical axis is the intensity of the received light signal, and FIGS. 6B to 6D are the intensity of the spectrum signals on which the intensity on the vertical axis is calculated. 6A to 6D, the unit of time on the horizontal axis is s.
　図６Ａから図６Ｄに示す計測において、レーザ計測装置１０は、変調周波数を１００ｋＨｚとし、掃引周波数を０．１ｋＨｚとして発光部４０からレーザ光を出力した。この条件で、発光部４０から出力され測定対象の排ガスを通過したレーザ光の受光信号は、図６Ａに示す波形となる。図６Ａに示すように、レーザ光は、掃引周波数が０．１ｋＨｚであるため、１０ｍｓが掃引の１周期となり、さらに、変調周波数が１００ｋＨｚであるため、０．０１ｍｓが変調の１周期となる。 6A to 6D, 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. Under this condition, 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. As shown in FIG. 6A, since the sweep frequency of the laser light is 0.1 kHz, 10 ms is one cycle of sweep, and furthermore, since the modulation frequency is 100 kHz, 0.01 ms is one cycle of modulation.
　この図６Ａに示す受光信号を、レーザ計測装置１０の信号処理部４７が、指定周波数を２００ｋＨｚとし、ステップ周波数を０．１ｋＨｚとし、整数倍の係数ｎの最大値を４とした設定で処理してスペクトル信号を出力した。つまり、２００ｋＨｚの成分と、２００±０．１ｋＨｚ、２００±０．２ｋＨｚ、２００±０．３ｋＨｚ、２００±０．４ｋＨｚの成分を用いて、畳み込み処理を行った。出力結果を図６Ｂに示す。図６Ｂに示すように、変調周波数が１００ｋＨｚの場合は、変調周波数を２００ｋＨｚとすることで上記実施形態と同様に対象の周波数の出力（スペクトル信号）を検出することができる。 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. As shown in FIG. 6B, when 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.
　次に、図６Ａに示す受光信号を、レーザ計測装置１０の信号処理部４７が、指定周波数を２００ｋＨｚとし、ステップ周波数を０．１ｋＨｚとし、整数倍の係数ｎを、最大値が４でかつ偶数（つまり、整数倍の係数２Ｎで、かつＮの最大値２の整数）とした設定で処理してスペクトル信号を出力した。つまり、２００ｋＨｚの成分と、２００±０．２ｋＨｚ、２００±０．４ｋＨｚの成分を用いて、畳み込み処理を行った。出力結果を図６Ｃに示す。 6A, 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.
　図６Ｃに示すように、ステップ周波数を整数倍する係数に偶数のみを用いることで、信号成分に含まれる歪み成分を除去した吸収スペクトル（測定に反応している成分）の強度をスペクトル信号として算出することができる。これにより、所望のスペクトル信号成分の検出精度を維持または向上させることができる。ステップ周波数を整数倍する係数に奇数を用いないことで、計算対象の周波数を少なくすることができる。 As shown in FIG. 6C, by using only an even number as a coefficient for multiplying the step frequency by an integer, 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. By not using an odd number as a coefficient for multiplying the step frequency by an integer, the frequency to be calculated can be reduced.
　図６Ａに示す受光信号を、レーザ計測装置１０の信号処理部４７が、指定周波数を２００ｋＨｚとし、ステップ周波数を０．１ｋＨｚとし、整数倍の係数ｎを、最大値が４でかつ奇数（つまり、整数倍の係数２Ｎ－１で、かつＮの最大値２の整数）とした設定で処理してスペクトル信号を出力した。つまり、２００ｋＨｚの成分と、２００±０．１ｋＨｚ、２００±０．３ｋＨｚの成分を用いて、畳み込み処理を行った。出力結果を図６Ｄに示す。 6A, 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.
　図６Ｄに示すように、ステップ周波数を整数倍する係数に奇数のみを用いることで、信号成分に含まれる歪み成分の強度を算出することができる。ここで、歪み成分は、測定対象の物質の吸収の影響を受けない。このため、レーザ計測装置１０は、歪み成分を装置の補正処理、キャリブレーション等に用いることができる。レーザ計測装置１０は、信号処理部４７でステップ周波数を整数倍する係数に奇数のみを用いることで、信号成分に含まれる歪み成分の強度を算出し、その結果と基準値等を比較し、各種条件を調整することで、計測精度をより向上させることができる。なお、レーザ計測装置１０は、ステップ周波数を整数倍する係数に奇数のみを用いるモードと、ステップ周波数を整数倍する係数に偶数のみ（または全ての整数）を用いるモードと、を切り換えるまたは２つのモードを並列で処理することで、補正処理と、濃度の計測処理の両方を行うことができる。 As 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. Here, the distortion component is not affected by the absorption of the substance to be measured. For this reason, 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.
　また、信号処理部４７の処理対象の周波数、つまり、指定周波数をαとし、ステップ周波数をβとし、ｎを０以上の整数とした場合のα±ｎβに用いるｎの最大値は任意の値とすることができる。つまり、畳み込み処理に用いるＤＦＴ成分の数は、２ｎ＋１個数とすることができる。ここで、図７Ａから図７Ｇは、それぞれスペクトル信号の出力波形を示すグラフである。図７Ａから図７Ｇは、それぞれ縦軸の強度が算出されたスペクトル信号の強度であり、横軸の時間の単位がｓである。なお、図７Ａから図７Ｇは、図５Ａに示す受光信号を、ｎの最大値をそれぞれの値として信号処理部４７で処理した結果を示すグラフである。また、図７Ａから図７Ｇは、指定周波数を２５０ｋＨｚとし、ステップ周波数を１ｋＨｚとし、係数ｎとして偶数のみを用いて計算を実行した結果である。 The maximum frequency of n used for α ± nβ when the frequency to be processed by the signal processing unit 47, that is, the designated frequency is α, the step frequency is β, and n is an integer of 0 or more is an arbitrary value. can do. That is, the number of DFT components used for the convolution process can be 2n + 1. Here, 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. 5A by the signal processing unit 47 with the maximum value of n as the respective values. 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.
　ここで、図７Ａは、解析対象の周波数を、偶数次のみ５点（指定周波数とその周辺のステップ周波数の整数倍分ずれた４つの周波数）、つまり±２５０±２Ｎ（Ｎは２以下の整数）ｋＨｚとした場合の出力である。したがって、図７Ａは、±２４６ｋＨｚ、±２４８ｋＨｚ、±２５０ｋＨｚ、±２５２ｋＨｚ、±２５４ｋＨｚの５つの周波数を解析対象としている。また、図７Ｂは、解析対象の周波数を偶数次のみ７点、つまり±２５０±２Ｎ（Ｎは３以下の整数）ｋＨｚとした場合の出力である。図７Ｃは、解析対象の周波数を偶数次のみ９点、つまり±２５０±２Ｎ（Ｎは４以下の整数）ｋＨｚとした場合の出力である。図７Ｄは、解析対象の周波数を偶数次のみ１１点、つまり±２５０±２Ｎ（Ｎは５以下の整数）ｋＨｚとした場合の出力である。図７Ｅは、解析対象の周波数を偶数次のみ１５点、つまり±２５０±２Ｎ（Ｎは７以下の整数）ｋＨｚとした場合の出力である。図７Ｆは、解析対象の周波数を偶数次の２１点、つまり±２５０±２Ｎ（Ｎは１０以下の整数）ｋＨｚとした場合の出力である。図７Ｇは、解析対象の周波数を偶数次の３１点、つまり±２５０±２Ｎ（Ｎは１５以下の整数）ｋＨｚとした場合の出力である。 Here, 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.
　図７Ａから図７Ｇに示すように、解析対象の周波数の個数を種々の設定とすることで、種々のスペクトル信号を検出することができる。またいずれのスペクトル信号としても、スペクトル信号の最大値と最小値に基づいて吸収により生じるスペクトル変化を検出することができるため、好適に測定対象の物質の濃度を計測することができる。なお、レーザ計測装置１０は、解析対象の周波数の個数を増加させることで、ロックインアンプのローパスフィルタのカットオフ周波数を増加させることと同様の効果を得ることができる。 As shown in FIGS. 7A to 7G, 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.
　また、上述したように、指定周波数は、変調周波数の整数倍の種々の値とすることができる。ここで、図８は、スペクトル信号の出力波形を示すグラフである。図８は、縦軸が出力であり、横軸が単位をｓとした時間である。なお、図８は、図５Ａに示す受光信号を、指定周波数を５００ｋＨｚとし、ステップ周波数を１ｋＨｚとし、係数ｎとして偶数のみを用いて計算を実行した結果である。また、図８は、解析対象の周波数を偶数次のみ３１点としている。図８に示すように、指定周波数として、変調周波数の４倍の周波数を用いても、変調周波数に含まれる吸収スペクトル（検出対象のスペクトル）の変化を検出することができる。なお、指定周波数として、変調周波数の４倍の周波数を用いて解析を行うとスペクトルの４次微分波形が検出される。このように変調周波数の２倍以外の周波数を用いることで、変調周波数の２倍の周波数にノイズ成分がある場合も吸収スペクトル（検出対象のスペクトル）の変化を検出することができる。また、変調周波数の４倍等、２倍より周波数の高い周波数は、信号強度が小さいため吸収スペクトル（検出対象のスペクトル）を検出しにくいが、レーザ計測装置１０は、対象のスペクトルを高精度に検出できるため好適に吸収スペクトル（検出対象のスペクトル）を検出することができる。 Also, as described above, the designated frequency can be various values that are integer multiples of the modulation frequency. Here, FIG. 8 is a graph showing an output waveform of the spectrum signal. In FIG. 8, 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. In FIG. 8, 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. If analysis is performed using a frequency that is four times the modulation frequency as the designated frequency, a fourth-order differential waveform of the spectrum is detected. By using 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. In addition, 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.
　また、レーザ計測装置１０は、本実施形態のようにステップ周波数を、掃引周波数と同一周波数とすることが好ましい。ステップ周波数を掃引周波数と同一とすることで、より好適に変調周波数に含まれる吸収スペクトル（検出対象のスペクトル）の変化を検出することができる。 Further, the laser measuring device 10 preferably has the step frequency equal to the sweep frequency as in the present embodiment. 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.
　なお、ステップ周波数は、受光信号の検出間隔と１フレーム分の個数との乗算で算出される周波数とすることが好ましい。つまり、ステップ周波数は、１フレーム分の受光信号を取得するのに要する時間が１周期となる周波数とすることが好ましい。１フレームが４０００点で、受光信号の検出間隔（サンプリング周期）が４ＭＨｚの場合は、ステップ周波数を１ｋＨｚとすることが好ましい。これにより、スペクトル信号をより高精度で検出することができる。 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. When one frame is 4000 points and the detection interval (sampling period) of the received light signal is 4 MHz, the step frequency is preferably 1 kHz. Thereby, a spectrum signal can be detected with higher accuracy.
　また、レーザ計測装置１０は、掃引周波数の１周期で取得できるデータ数の整数倍を、受光信号の１フレーム分のデータ数とすることが好ましい。これにより、掃引周波数で波長を掃引している場合により高い精度でスペクトル信号を検出することができる。 In addition, 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.
　６、８　配管
　１０　レーザ計測装置
　１２　計測セル
　１４　計測手段
　２０　主管
　２２　入射管
　２４　出射管
　２６、２８　窓
　４０　発光部
　４２　光ファイバ
　４４　受光部
　４６　光源ドライバ
　４７　信号処理部
　４８　物理量算出部
　５０　制御部
　６２　増幅Ａ／Ｄ変換部
　６４　ＤＦＴ計算部
　６５　一時記憶部
　６６　畳み込み計算部
　６８　逆ＤＦＴ計算部 6, 8 Piping 10 Laser measuring device 12 Measuring cell 14 Measuring means 20 Main tube 22 Incident tube 24 Emission tube 26, 28 Window 40 Light emitting unit 42 Optical fiber 44 Light receiving unit 46 Light source driver 47 Signal processing unit 48 Physical quantity calculating unit 50 Control unit 62 Amplification A / D converter 64 DFT calculator 65 Temporary storage 66 Convolution calculator 68 Inverse DFT calculator

Claims (9)

  1. 　入射部と出射部を備え、かつ、流体が流れる計測セルと、測定対象のガスに固有な吸収波長を含む波長域のレーザ光を変調周波数で波長を変調しつつ出力し、前記計測セルに入射させる発光部と、前記入射部から入射され、前記計測セルを通過し、前記出射部から出射された前記レーザ光を受光し、受光した光量を受光信号として出力する受光部と、を有し、前記受光信号に基づいて前記計測セルを流れる測定対象のガスの物理量を算出するレーザ計測装置に適用され、
    　前記受光部が受光した前記受光信号を処理し、前記計測セルを流れる測定対象のガスの物理量の算出に用いるスペクトル信号を出力する信号処理装置であって、
    　前記受光信号をデジタルデータに変換するＡ／Ｄ変換部と、
    　前記Ａ／Ｄ変換部で変換された前記受光信号の１フレーム分のデジタルデータを取得し、取得した１フレーム分のデジタルデータを、前記変調周波数を整数倍した周波数である指定周波数および前記指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれで離散フーリエ変換し、前記指定周波数および前記指定周波数を中心として周波数がステップ周波数の整数倍分異なる周波数のそれぞれでＤＦＴ成分を算出するＤＦＴ計算部と、
    　前記ＤＦＴ計算部で算出した前記ＤＦＴ成分に対して畳み込み計算する畳み込み計算部と、
    　前記畳み込み計算部で計算した結果に対し逆離散フーリエ変換を行い、スペクトル信号を生成する逆ＤＦＴ計算部と、を含むことを特徴とする信号処理装置。     A measurement cell that includes an incident part and an emission part, and in which a fluid flows, and outputs laser light in a wavelength region that includes an absorption wavelength specific to the gas to be measured while modulating the wavelength with the modulation frequency, and enters the measurement cell A light emitting unit to be received, and a light receiving unit that is incident from the incident unit, passes through the measurement cell, receives the laser light emitted from the emitting unit, and outputs the received light amount as a light reception signal, Applied to a laser measuring device that calculates a physical quantity of a gas to be measured flowing through the measurement cell based on the received light signal,
    A signal processing device that processes the light reception signal received by the light receiving unit and outputs a spectrum signal used for calculation of a physical quantity of a gas to be measured flowing through the measurement cell,
    An A / D converter for converting the received light signal into digital data;
    The digital data for one frame of the received light signal converted by the A / D conversion unit is obtained, and the designated frequency and the designated frequency are obtained by multiplying the obtained digital data for one frame by an integral multiple of the modulation frequency. A DFT component is calculated by performing a discrete Fourier transform on each of frequencies different from each other by an integer multiple of the step frequency, and calculating a DFT component at each of the designated frequency and each frequency different from the designated frequency by an integer multiple of the step frequency. A calculation unit;
    A convolution calculator that performs a convolution calculation on the DFT component calculated by the DFT calculator;
    A signal processing apparatus comprising: an inverse DFT calculation unit that performs inverse discrete Fourier transform on a result calculated by the convolution calculation unit and generates a spectrum signal.
  2. 　前記ステップ周波数は、前記受光信号の検出間隔と１フレーム分の個数との乗算で算出される周波数であることを特徴とする請求項１に記載の信号処理装置。 2. The signal processing apparatus according to claim 1, wherein the step frequency is a frequency calculated by multiplying the detection interval of the received light signal by the number of one frame.
  3. 　請求項１または２に記載の信号処理装置と、
    　流体を流す流路と連結可能な主管、前記主管に連結し、光が通過可能な窓部が形成された入射部、前記主管に連結し光が通過可能な窓部が形成された出射部と、を含む計測セルと、
    　測定対象のガスに固有な吸収波長を含む波長域のレーザ光を変調周波数で波長を変調しつつ出力し、前記入射部に入射させる発光部と、
    　前記入射部から入射され、前記計測セルを通過し、前記出射部から出射された前記レーザ光を受光し、受光した光量を受光信号として出力する受光部と、
    　前記スペクトル信号に基づいて、前記計測セルを流れる測定対象のガスの物理量を算出する物理量算出部と、
    　各部の動作を制御する制御部と、を有することを特徴とするレーザ計測装置。     The signal processing device according to claim 1 or 2,
    A main pipe connectable to a flow path for fluid, an incident part connected to the main pipe 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 measuring cell including
    A light emitting unit that outputs laser light in a wavelength region including an absorption wavelength unique to a gas to be measured while modulating the wavelength at a modulation frequency, and that is incident on the incident unit;
    A light receiving portion that is incident from the incident portion, passes through the measurement cell, receives the laser light emitted from the emission portion, and outputs the received light amount as a light reception signal;
    A physical quantity calculation unit that calculates a physical quantity of a gas to be measured flowing through the measurement cell based on the spectrum signal;
    And a control unit that controls the operation of each unit.
  4. 　前記発光部は、変調周波数よりも低い周波数の掃引周波数で波長を掃引しつつレーザ光出力することを特徴とする請求項３に記載のレーザ計測装置。 4. The laser measuring apparatus according to claim 3, wherein the light emitting unit outputs a laser beam while sweeping a wavelength at a sweep frequency lower than a modulation frequency.
  5. 　前記ＤＦＴ計算部は、前記掃引周波数の１周期分のデジタルデータを１フレーム分のデータとして取得することを特徴とする請求項４に記載のレーザ計測装置。 The laser measurement apparatus according to claim 4, wherein the DFT calculation unit acquires digital data for one cycle of the sweep frequency as data for one frame.
  6. 　前記ステップ周波数は、前記掃引周波数であることを特徴とする請求項４または５に記載のレーザ計測装置。 6. The laser measuring apparatus according to claim 4, wherein the step frequency is the sweep frequency.
  7. 　前記ＤＦＴ計算部は、前記指定周波数を中心として周波数が前記ステップ周波数の整数倍分異なる周波数として、前記ステップ周波数の偶数の整数倍分または奇数の整数倍分異なる周波数のみを用いることを特徴とする請求項６に記載のレーザ計測装置。 The DFT calculation unit uses only frequencies that differ by an integer multiple of the step frequency or an integer multiple of the odd number as the frequency that differs by an integer multiple of the step frequency around the designated frequency. The laser measurement device according to claim 6.
  8. 　前記物理量算出部が算出する物理量は、前記測定対象のガスの濃度であることを特徴とする請求項３から７のいずれか一項に記載のレーザ計測装置。 The laser measurement apparatus according to any one of claims 3 to 7, wherein the physical quantity calculated by the physical quantity calculation unit is a concentration of the measurement target gas.
  9. 　前記物理量算出部は、前記発光部から出力したレーザ光の強度と、前記受光部で受光したレーザ光の強度とに基づいて、前記測定対象のガスの濃度を算出することを特徴とする請求項８に記載のレーザ計測装置。 The physical quantity calculation unit calculates the concentration of the gas to be measured 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. 8. The laser measuring device according to 8.
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