JP2012173176A - Signal processor and laser measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processor and a laser measurement device that can detect a desired signal component from a light reception signal with high precision.SOLUTION: The signal processor includes a crystal filter which passes an output of a transmissive frequency band including a transmissive frequency and attenuates an output of a band other than the transmissive frequency band, an oscillator which oscillates a frequency of the difference between the transmissive frequency and a specified frequency, and a downstream-side frequency converter which mixes the signal oscillated by the oscillator with the signal passed through the crystal filter, and converts an output of the transmissive frequency of the signal passed through the crystal filter into an output of the specified frequency, and further includes a signal processing part including a filter processing part which reduces an output of a frequency other than the specified frequency and a spectrum signal extractor (for example, a lock-in detector) which extracts a spectrum signal by performing spectrum signal extraction processing (for example, lock-in processing) on the signal having been processed by the filter processing part.

Description

  The present invention relates to a signal processing apparatus and a laser measurement apparatus used for laser measurement for calculating a physical quantity of a gas to be measured by laser absorption spectroscopy.

  As a method for analyzing a gas (gas) flowing through a pipe, there is a method using laser light as measurement light. 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. Light intensity voltage converter for converting intensity into voltage, two phase sensitive detectors for phase sensitive detection of the output voltage of the light intensity voltage converter, and primary phase sensitive detection obtained from one of the phase sensitive detectors A gas detection device is described that detects the concentration of a detection atmosphere based on a signal and a secondary phase sensitive detection signal obtained from the other 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, 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.

Japanese Patent No. 2796649 JP 2008-147557 A

  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.

  The received light signal generated by the light receiving unit receiving the laser beam 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, a bandpass filter, etc. are provided before processing by the lock-in amplifier, The frequency component is extracted, that is, the frequency component other than the frequency to be processed by the lock-in amplifier is reduced.

  Here, in the process using the FIR filter or the band pass filter, there are cases where the noise cannot be sufficiently reduced, and it is necessary to perform many calculations in order to sufficiently reduce the noise.

  The present invention has been made in view of the above, and an object of the present invention is to provide a laser measuring apparatus capable of detecting a desired signal component from a light reception signal with high accuracy.

  In order to solve the above-described problems and achieve the object, the present invention modulates the wavelength of a measurement cell in which a fluid flows and a laser beam in a wavelength region including an absorption wavelength specific to a measurement target gas with a modulation frequency. A light-emitting unit that outputs 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 outputs the received light amount as a light-receiving signal. And a light receiving unit, 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 light reception signal, processes the light reception signal received by the light receiving unit, and the measurement cell A signal processing device for outputting a spectrum signal used for calculation of a physical quantity of a gas to be measured flowing through the filter processing unit for reducing output of a frequency other than the designated frequency, and the filter processing unit A spectrum signal extractor for performing a spectrum signal extraction process on the processed signal and extracting the spectrum signal, wherein the filter processing unit passes an output of a transmission frequency band including a transmission frequency, and transmits the transmission frequency band A crystal filter that attenuates an output other than the above, an oscillator that oscillates a difference frequency between the transmission frequency and the specified frequency, a signal oscillated from the oscillator and a signal that has passed through the crystal filter, and A downstream frequency converter that converts the output of the transmission frequency of the signal that has passed through the filter into the output of the specified frequency.

  Here, it is preferable that the signal processing apparatus further includes an upstream frequency conversion unit that converts a component of a specified frequency included in the light reception signal into a component of a frequency included in the transmission frequency.

  The upstream frequency converting unit mixes the signal oscillated from the oscillating unit and the light receiving signal, and converts the component of the specified frequency included in the light receiving signal into the component of the frequency included in the transmission frequency. It is preferable.

  Moreover, it is preferable that the said oscillator can change the frequency of the signal to output.

  Moreover, it is preferable that the designated frequency is a frequency obtained by multiplying the modulation frequency by two or more times as an integer.

  The light reception signal preferably has an output of the transmission frequency that is an output of the designated frequency of the spectrum signal.

  Moreover, it is preferable that the transmission frequency is a frequency obtained by multiplying the modulation frequency by an integer of 2 or more.

  Further, it is preferable to further include a low-pass filter that is disposed between the downstream frequency converter and the spectral signal extractor and reduces an output of a frequency equal to or higher than the specified frequency from a signal that has passed through the downstream frequency converter. .

  An amplifier that is disposed between the low-pass filter and the spectral signal extractor and that amplifies the signal that has passed through the downstream frequency converter, and a coil coupling that is disposed between the low-pass filter and the amplifier. It is preferable to further include

  Also, an amplifier that is disposed between the crystal filter and the downstream frequency converter, amplifies a signal that has passed through the crystal filter, and a coil coupling that is disposed between the crystal filter and the amplifier, It is preferable to further have.

  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 measurement cell including an incident part connected to and formed with a window part through which light can pass, and an emission part formed with a window part connected to the main pipe and 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.

  Here, the physical quantity calculated by the physical quantity calculator is preferably the concentration of the gas to be measured.

  The physical quantity calculation unit preferably 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 device and the laser measurement device according to the present invention have an effect that a desired signal component can be detected from the received light signal with high accuracy.

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. 3A is an explanatory diagram for explaining processing of the signal processing unit. FIG. 3B is an explanatory diagram for explaining processing of the signal processing unit. FIG. 3C is an explanatory diagram for explaining processing of the signal processing unit. FIG. 3D is an explanatory diagram for explaining processing of the signal processing unit. FIG. 3E is an explanatory diagram for explaining processing of the signal processing unit. FIG. 4 is a graph showing characteristics of the crystal filter. FIG. 5A is a graph showing an example of a spectrum detected by the path of the signal processing unit. FIG. 5B is a graph showing an example of a spectrum detected by the path of the signal processing unit. FIG. 5C is a graph showing an example of a spectrum detected by the path of the signal processing unit. FIG. 5D is a graph illustrating an example of a spectrum detected by the path of the signal processing unit. FIG. 5E is a graph illustrating an example of a spectrum detected by the path of the signal processing unit. FIG. 6 is a schematic diagram showing a schematic configuration of another embodiment of the laser measuring device. FIG. 7 is a schematic diagram showing a schematic configuration of another embodiment of the laser measuring device. FIG. 8 is a schematic diagram showing a schematic configuration of another embodiment of the laser measuring device. FIG. 9 is an explanatory diagram for explaining processing of the signal processing unit.

  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 various gases (gases) and fluids such as liquids 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 apparatus for discharging (supplying) the 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. Furthermore, the laser measuring device can also measure the concentration of a measurement target substance contained in exhaust gas discharged from combustion equipment such as a garbage incinerator or a 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 apparatus having a signal processing apparatus 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 downstream from the pipe 8. An exhaust gas generator (supply device) is disposed upstream of the pipe 6.

  The measurement cell 12 basically includes 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 has one end 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.

  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.

  The exit tube 24 is a tubular member having substantially the same shape as the entrance tube 22. One end of the exit tube 24 is connected to the main tube 20, and a window 28 is provided at the other end of the exit tube 24. 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.

  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.

  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).

  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. Further, when the measurement target is nitrogen dioxide, the light emitting unit 40 outputs laser light including a near-infrared wavelength region that absorbs nitrogen dioxide. Further, when the measurement target is nitrous oxide, the light emitting unit 40 outputs laser light including a near infrared wavelength region 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 light that passes through the inside of the main tube 20 of the measurement cell 12 and is 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 vibrates the wavelength of the laser light at a set modulation frequency (for example, 100 kHz, 125 kHz). 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. 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.

  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 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. As described above, the measuring unit 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.

  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.

  Next, the configuration of the signal processing unit 47 of the laser measurement apparatus 10 will be described using FIGS. 2 to 4, 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. 3A to 3E are explanatory diagrams for explaining processing of the signal processing unit, respectively. FIG. 4 is a graph showing characteristics of the crystal filter. 3A to 3E are graphs schematically showing the relationship between the signal frequency and the output (intensity), that is, the graph showing the relationship between the frequency calculated when the signal is subjected to frequency analysis and the output. In FIGS. 3A to 3E, the vertical axis is output and the horizontal axis is frequency. FIG. 4 is a graph showing the frequency characteristics of the crystal filter. The vertical axis represents gain [dB], and the horizontal axis represents frequency [MHz].

  The signal processing unit 47 shown in FIG. 2 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 extracts a spectrum signal by performing a spectrum processing extraction process (for example, a lock-in process) on the signal processed by the filter processing unit 62 and a filter processing unit 62 that reduces the output of frequencies other than the specified frequency. A spectral signal extractor (for example, lock-in detector) 64. Here, the designated frequency is a frequency of a spectrum signal extracted by the spectrum signal extractor 64 and includes a component of an absorption spectrum that is a detection target. In the present embodiment, as the designated frequency, a frequency obtained by multiplying the modulation frequency by two or more and an integer is used.

  In the following description, it is assumed that a laser beam having a modulation frequency of 125 kHz is output and a spectrum signal is generated with a specified frequency of 250 kHz. That is, in the example described below, the light reception signal generated by the light receiving unit 44 receiving the laser light has an absorption spectrum component that is generated when the substance to be measured absorbs the laser light and has an even multiple of 125 kHz. include. Therefore, the signal processing unit 47 of the laser measuring apparatus 10 performs processing for extracting a component of the designated frequency by setting the frequency of 250 kHz out of the frequencies including the component of the absorption spectrum as the frequency of the analysis target (measurement target), that is, the designated frequency. Do. In the received light signal sent to the filter processing unit 62, a noise component is superimposed on a 250 kHz component that is a specified frequency. Therefore, as shown in FIG. 3A, the light reception signal is in a state where the output is distributed in each frequency component. The signal processing unit 47 performs processing for extracting a component of the designated frequency to be analyzed from the received light signal on which noise is superimposed as shown in FIG. 3A.

  The filter processing unit 62 includes an oscillator 70, an up converter (upstream frequency converter) 72, a crystal filter 74, a coil coupling 76, an amplifier 77, a down converter (downstream frequency converter) 78, and a low pass. A filter 80, a coil coupling 82, and an amplifier 84 are included.

  The oscillator 70 is a signal generator that generates and outputs a signal having a set frequency. The oscillator 70 generates a signal having a difference frequency (oscillation frequency) between a specified frequency and a frequency (transmission frequency) passing through a crystal filter 74 described later, and sends the signal to the up-converter 72 and the down-converter 78. In the present embodiment, the oscillator 70 outputs a signal having an oscillation frequency of 10.45 MHz. That is, a signal composed of a component having a frequency of 10.45 MHz is output.

  The up-converter (upstream frequency converter) 72 is a mixer (frequency converter, mixer) that mixes the received light signal and the signal sent from the oscillator 70 according to the heterodyne theorem. The up-converter 72 generates a signal in which each frequency component of the received signal is increased by the oscillation frequency and reduced by the oscillation frequency. That is, the up-converter 72 generates a signal that expands the received signal in both positive and negative directions with the oscillation frequency as a reference. That is, if the oscillation frequency is f and each frequency fa of the received signal, the output of the frequency fa is the output of f ± fa. The received signal shown in FIG. 3A passes through an up converter (upstream frequency converter) 72 to become a signal shown in FIG. 3B. Here, in the signal shown in FIG. 3B, the component of the specified frequency (250 kHz) of the received light vibration is a 10.2 MHz component obtained by adding ± 0.25 MHz to the oscillation frequency 10.45 MHz and a 10.7 MHz component. The up converter 72 sends the processed signal to the crystal filter 74.

  The crystal filter 74 is a filter that selectively transmits a transmission frequency component, which is a predetermined frequency, and removes and reduces frequency components other than the transmission frequency. The crystal filter 74 is a filter that uses a crystal resonator, and selectively transmits a component in a certain frequency band having a transmission frequency (a frequency component that resonates with the crystal resonator) as a center frequency. The frequency component (output) other than the fixed frequency band is reduced. Here, the crystal filter 74 of the present embodiment is a filter having a transmission frequency of 10.7 MHz as shown in FIG. Here, the gain on the vertical axis in FIG. 4 is the same as the transmittance at each frequency, and the output is transmitted as the gain is closer to 0, and the output is increased as the negative component of the gain is larger (closer to −90 dB). To reduce. The crystal filter 74 hardly transmits the frequency component having a gain of −80 dB. The crystal filter 74 transmits a certain amount of output of frequency components in the range of 10.69 MHz or more and less than 10.71 MHz around 10.7 MHz, and reduces the output of other frequency components. As a result, as shown in FIG. 3C, the signal transmitted through the crystal filter 74 becomes a signal having a dominant frequency component centered on the transmission frequency of 10.7 MHz. The crystal filter 74 performs processing (filter processing) on the signal sent from the up-converter 72, and sends the processed signal (the signal that has passed through the crystal filter 74) to the coil coupling 76 (amplifier 77).

  The coil coupling 76 is disposed between the crystal filter 74 and the amplifier 77. The coil coupling 76 is a device that matches the circuit constant of the input part of the operational amplifier used in the amplifier 77, and is arranged in a matching part with other parts of the amplifier 77. The coil coupling 76 is constituted by a pair of coils, one coil is connected to the crystal filter 74 and the other coil is connected to the amplifier 77. The coil coupling 76 has a pair of coils facing each other, transmits a signal sent from the crystal filter 74 from one coil to the other coil, and sends it to the amplifier 77. The coil coupling 76 can suppress thermal noise generated at the matching portion of the amplifier 77 by transmitting a signal through a pair of coils.

  The amplifier 77 amplifies the signal sent from the crystal filter 74 and passed through the coil coupling 76 (a signal obtained by removing and reducing a frequency component other than the frequency region centered on the transmission frequency from the received light signal). The amplifier 77 sends the amplified signal to the down converter 78.

  The down converter (downstream frequency converter) 78 is a mixer (frequency converter, mixer) that mixes the signal sent from the amplifier 77 and the signal sent from the oscillator 70 by the heterodyne theorem. The down-converter 78 has the same configuration as the up-converter 72, and generates a signal having a component in which each frequency component of the signal transmitted from the amplifier 77 is increased by an oscillation frequency and a component in which the oscillation frequency is decreased. That is, the down-converter 78 generates a signal obtained by developing the signal sent from the amplifier 77 in both positive and negative directions with reference to the oscillation frequency. The signal that has passed through the down converter 78 becomes the signal shown in FIG. 3D. Here, in the signal shown in FIG. 3D, the component of the transmission frequency (10.7 MHz) is a component of 250 kHz obtained by adding ± 10.7 MHz to the oscillation frequency of 10.45 MHz and a component of 21.15 MHz. The down converter 78 sends the processed signal to the low pass filter 80.

  The low-pass filter 80 is disposed between the down converter 78 and the coil coupling 82. The low-pass filter 80 is a filter that transmits a component having a frequency equal to or lower than a set threshold frequency and reduces a component having a frequency that is higher than the threshold frequency. The frequency band component is transmitted, and the frequency band component centered on the frequency obtained by adding the oscillation frequency to the transmission frequency is reduced. As the low-pass filter 80, it is preferable to use a filter that reduces a frequency component of 1 MHz or higher (transmits a frequency component of less than 1 MHz as it is). In the present embodiment, the frequency band component centered at 250 kHz is transmitted, and the frequency band component centered at 21.15 MHz is reduced.

  The coil coupling 82 is disposed between the low pass filter 80 and the amplifier 84. The coil coupling 82 is a device that matches the circuit constant of the input part of the operational amplifier used in the amplifier 84 and is arranged in a matching part with other parts of the amplifier 84. The coil coupling 82 is composed of a pair of coils, one coil is connected to the low-pass filter 80, and the other coil is connected to the amplifier 84. The coil coupling 82 has a pair of coils facing each other, transmits a signal sent from the low-pass filter 80 from one coil to the other coil, and sends it to the amplifier 84. The coil coupling 76 can suppress thermal noise generated at the matching portion of the amplifier 84 by transmitting a signal through a pair of coils.

  The amplifier 84 amplifies the signal sent from the low-pass filter 80 and passed through the coil coupling 82 (a signal obtained by removing and reducing a frequency component other than the specified frequency from the received light signal). As a result, the signal passing through the amplifier 84 becomes the signal shown in FIG. 3E. The signal shown in FIG. 3E is a signal in which the frequency band component centered at 21.15 MHz is reduced and the frequency band component centered at 250 kHz is dominant when the signal shown in FIG. In addition, the frequency band component centered at 250 kHz is amplified. The amplifier 84 sends the amplified signal to the spectrum signal extractor 64.

  Next, the spectrum signal extractor 64 performs a spectrum signal extraction process using the specified frequency as a reference frequency for the received light signal that has been processed by the filter processing unit 62 and whose frequency components other than the specified frequency are reduced. As a result, a spectrum signal of the designated frequency is generated from the received light signal in which the frequency components other than the designated frequency are reduced. As the spectrum signal extractor 64, as exemplified above, a lock-in detector that performs lock-in processing can be used. By using a lock-in detector, a spectrum signal can be extracted with high accuracy with an inexpensive configuration. Note that the type of the spectral signal extractor 64 is not limited to the lock-in detector. The spectrum signal extractor 64 sends the detected spectrum signal to the physical quantity calculator 48. The signal processing unit 47 generates and / or extracts a spectrum signal from the received light signal as described above.

  Next, the processing of the signal processing unit 47 will be described in more detail with reference to FIGS. 4 and 5A to 5E, which are examples of specific signal measurement results. FIG. 5A to FIG. 5E are graphs showing examples of spectra detected by the path of the signal processing unit. 5A to 5E, the vertical axis represents voltage (output) [dBV], and the horizontal axis represents frequency [MHz]. In the following description, a description will be given of a case where a laser beam having a modulation frequency of 100 kHz is output, a specified frequency is 200 kHz, and an oscillation frequency of the oscillator is 10.5 MHz to generate a spectrum signal.

  First, as shown in FIG. 5A, the spectrum of the received light signal (input spectrum input to the signal processing unit 47) is in a state in which the output is distributed to each frequency component. Here, in the received light signal shown in FIG. 5A, the 100 kHz component of the modulation frequency is −10.93 dBV, and the 200 kHz component of the specified frequency is −53.16 dBV. Thus, in the received light signal, the difference between the 200 kHz component to be analyzed and the 100 kHz component of noise is −42.23 dB, and the analysis target component has an output smaller than the 100 kHz component that is the noise component. Yes.

  Thereafter, the signal subjected to frequency conversion (up-conversion) by the up-converter 72 has an output distribution shown in FIG. 5B. As shown in FIG. 5B, the up-converted signal has a substantially target waveform on the frequency axis centering on the oscillation frequency of 10.5 MHz. In the up-converted signal, the 10.60 MHz component obtained by frequency conversion of the modulation frequency of 100 kHz is -17.74 dBV, and the 10.7 MHz component obtained by frequency conversion of the specified frequency of 200 kHz is -60.20 dBV. Thus, in the up-converted signal, the difference between the 10.7 MHz component to be analyzed and the 10.6 MHz noise component is −42.46 dB. In addition, the component of each frequency has decreased by processing by the up-converter 72.

  Thereafter, the signal passing (transmitting) through the crystal filter 74 has an output distribution shown in FIG. 5C. Note that the graph shown in FIG. 5C shows only the frequency range of 10 MHz to 11 MHz. As shown in FIG. 5C, the signal that has passed through the crystal filter 74 transmits components in the frequency region centered on the transmission frequency of 10.7 MHz, and reduces the components in other frequency regions. As a result, the signal having passed through the crystal filter 74 has a frequency 10.60 MHz component of −101.25 dBV and a 10.7 MHz component of −60.72 dBV. In this way, the signal that has passed through the crystal filter 74 allows the 10.7 MHz component to be analyzed to pass substantially as it is, and reduces the 10.6 MHz component of noise. As a result, the difference between the 10.7 MHz component to be analyzed and the 10.6 MHz noise component is 37.53 dB, and the analysis target component is larger than the noise component.

  Thereafter, the frequency-converted (down-converted) signal by the down converter 78 has an output distribution shown in FIG. 5D. In FIG. 5D, the horizontal frequency axis is a logarithmic axis. As shown in FIG. 5D, the down-converted signal has a substantially target waveform on the frequency axis with the oscillation frequency of 10.5 MHz as the center, and the 10.7 MHz component to be analyzed includes the 200 kHz component and the frequency 21. 2MHz component. In addition, the 10.6 MHz component of noise is a component having a frequency of 100 kHz and a component having a frequency of 21.3 MHz. That is, the component of 10.7 MHz or less is a component having the same frequency as the frequency of the signal before processing by the up-converter 72. The down-converted signal has a component of 100 kHz of −89.59 dBV and a component of 200 kHz of the designated frequency of −59.80 dBV. Thus, in the down-converted signal, the difference between the 200 kHz component to be analyzed and the 100 kHz noise component is 29.79 dB.

  Thereafter, the signal passing through the low-pass filter 80 has an output distribution shown in FIG. 5E. 5E also uses the frequency axis on the horizontal axis as a logarithmic axis, as in FIG. 5D. The low-pass filter 80 used in this specific example is a filter that reduces components having a frequency of 1 MHz or more. As shown in FIG. 5E, the signal that has passed through the low-pass filter 80 has a component with a frequency of 1 MHz or more reduced and a component with a frequency of 21.2 MHz. Further, the component with a frequency of 100 kHz and the component with a frequency of 200 kHz are transmitted almost as they are. The signal that has passed through the low-pass filter 80 has a component of 100 kHz of −89.61 dBV and a component of 200 kHz of the designated frequency of −60.06 dBV. Thus, in the signal that has passed through the low-pass filter 80, the difference between the 200 kHz component to be analyzed and the 100 kHz noise component is 29.55 dB. The signal that has passed through the low-pass filter 80 is then amplified by the amplifier 84 and is then subjected to spectrum signal extraction processing by the spectrum signal extractor 64, thereby generating a spectrum signal from which the designated frequency component has been extracted.

  As described above, the signal processing unit 47 of the laser measurement device 10 uses the specified frequency component of the received light signal as the transmission frequency component of the crystal filter 74, and then transmits (passes) the signal to the crystal filter 74. Noise can be efficiently removed or reduced from the received light signal. In other words, by performing the filtering process with the crystal filter 74 that can reduce the frequency components other than the transmission frequency (a constant frequency region centered on the transmission frequency) at a high rate, components other than the specified frequency component of the received light signal can be efficiently obtained. It can be removed and reduced. In addition, a constant frequency range centered on the transmission frequency can be made narrower than other filters. Thereby, the component of the designated frequency can be extracted with high accuracy. For example, as in the present embodiment, even when 200 kHz is the specified frequency and there is a large noise component at 100 kHz, the noise component can be suitably reduced.

  As in the present embodiment, the up-converter 72 and the oscillator 70 convert the light reception signal component of the light reception signal into the transmission frequency component of the crystal filter 74, so that the light reception signal is received by the crystal filter 74d regardless of the frequency of the specified frequency. The components of the designated frequency can be transmitted and the components of other frequencies can be removed and reduced.

  Further, by down-converting the signal transmitted through the crystal filter 74 by the down converter 78, the processing by the spectrum signal extractor 64 can be simplified. Furthermore, since one oscillator 70 supplies signals to the up-converter 72 and the down-converter 78, the number of oscillators can be reduced. Further, the frequency including the component to be analyzed can be set to the same frequency when the signal processing unit 47 is input and when it is output.

  In addition, noise is efficiently removed or reduced from the received light signal, and the difference between the output of the specified frequency component and the output of the noise component is reduced, thereby amplifying the signal after the noise removal and before the spectral signal extraction processing. The output of the component of the designated frequency can be further amplified before the spectrum signal extraction process. Here, the amplifier 84 sets the amplification ratio based on the signal size when the signal is amplified to a size applicable to the measurement range of the spectrum signal extractor 64. Therefore, the difference between the output of the specified frequency component and the output of the noise component is reduced, so that the output of the specified frequency component is more than the case where the output of the noise component is a certain amount larger than the output of the specified frequency component. It can be greatly amplified. That is, even if the signal is amplified more greatly, the output can be suppressed to a size applicable to the measurement range of the spectrum signal extractor 64. Thereby, the output of the component of the designated frequency can be detected with higher accuracy. Further, since a crystal filter may be provided as the filter, the apparatus configuration can be simplified.

  Furthermore, since the noise can be suitably reduced, the output of the designated frequency can be suitably detected even when the measurement range of the spectrum signal extractor is small. As a result, the spectral signal extractor can be made inexpensive while the performance is maintained, and the laser measuring device can also be made inexpensive.

  Next, another embodiment of the laser measuring device will be described with reference to FIG. FIG. 6 is a schematic diagram showing a schematic configuration of another embodiment of the laser measuring device. The embodiment of the laser measuring apparatus shown in FIG. 6 is basically the same as the laser measuring apparatus shown in FIGS. 1 and 2 except for the configuration of the signal processing unit. Further, in the signal processing unit 147 shown in FIG. 6, the same components as those of the signal processing unit 47 shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The signal processing unit 147 illustrated in FIG. 6 includes a filter processing unit 162 and a spectrum signal detector 64. The filter processing unit 162 includes an oscillator 70, a crystal filter 74, a coil coupling 76, an amplifier 77, a down converter (downstream frequency converter) 78, a low-pass filter 80, a coil coupling 82, and an amplifier 84. And having.

  The oscillator 70 is a signal generator that generates and outputs a signal having a set frequency. The oscillator 70 generates a signal having a difference frequency (oscillation frequency) between the designated frequency and the transmission frequency and sends the signal to the down converter 78.

  Thus, the signal processing unit 147 is the same as the signal processing unit 47 except for the point that it does not include an up-converter. Even in the case of the configuration of the laser measuring apparatus of the present embodiment, the light receiving unit 44 receives the laser light, and the component of the absorption spectrum to be analyzed included in the generated light reception signal becomes the component of the transmission frequency. The frequency component transmitted through the crystal filter 74 can be the frequency component to be measured.

  As described above, the component of the absorption spectrum to be analyzed included in the light reception signal generated by the light receiving unit 44 is the component of the transmission frequency, so that the component of the absorption spectrum to be analyzed can be changed from the light reception signal without providing an up-converter. Can be extracted. For example, when the transmission frequency is 10.7 MHz as in the above embodiment, the analysis target can be set to 10.7 MHz by setting the modulation frequency of the laser light to 5.35 MHz.

  Next, another embodiment of the laser measuring device will be described with reference to FIG. FIG. 7 is a schematic diagram showing a schematic configuration of another embodiment of the laser measuring device. The embodiment of the laser measurement device shown in FIG. 7 is basically the same as the laser measurement device shown in FIGS. 1 and 2 except for the configuration of the signal processing unit. Also, in the signal processing unit 247 illustrated in FIG. 7, the same components as those of the signal processing unit 47 illustrated in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The signal processing unit 247 illustrated in FIG. 7 includes a filter processing unit 262 and a spectrum signal extractor 64. The filter processing unit 262 includes an up converter 20, a variable frequency oscillator 270, an oscillator 271, a crystal filter 74, a coil coupling 76, an amplifier 77, a down converter (downstream frequency converter) 78, and a low pass filter. 80, a coil coupling 82, and an amplifier 84.

  The variable frequency oscillator 270 is a signal generator that can arbitrarily vary the oscillation frequency. The variable frequency oscillator 270 can change the oscillation frequency in multiple stages or change the oscillation frequency with time. The frequency variable oscillator 270 can change the frequency based on the difference frequency between the specified frequency and the frequency passing through the crystal filter 74 (transmission frequency) as the oscillation frequency. The variable frequency oscillator 270 sends the generated signal to the up-converter 72.

  The oscillator 271 is a signal generator that generates and outputs a signal having a set frequency. The oscillator 271 generates a signal having a difference frequency (oscillation frequency) between the designated frequency and the transmission frequency and sends the signal to the down converter 78.

  The signal processing unit 247 can select the frequency to be analyzed of the signal included in the received light signal by using the frequency variable oscillator 270 as the oscillator that supplies the signal to the up-converter 72. That is, by changing the oscillation frequency of the signal input to the up-converter 72, the frequency component of the received light signal that passes through the crystal filter can be changed. The laser measuring device can extract signal components based on each modulation frequency by one light receiving unit 44 even when a plurality of laser beams are incident on the light receiving unit 44 at different modulation frequencies.

  Further, by sweeping (modulating) the oscillation frequency of the signal output from the frequency variable oscillator 270, even when the modulation frequency is unstable, a component due to the absorption spectrum included in the signal can pass through the crystal filter 74. it can.

  Further, the signal from the oscillator 271 is sent to the down-converter 78 so that, of the signals that pass through the crystal filter 74 and reach the spectral signal extractor 64, the town conversion of the component of the transmission frequency when passing through the crystal filter 74 is performed. The subsequent frequency can be made constant. Thereby, the component which permeate | transmitted the crystal filter 74 can be extracted by a spectrum signal extraction process, without changing a designated frequency.

  Next, another embodiment of the laser measuring device will be described with reference to FIGS. 8 and 9. FIG. 8 is a schematic diagram showing a schematic configuration of another embodiment of the laser measuring device. Moreover, FIG. 9 is explanatory drawing for demonstrating the process of a signal processing part. The embodiment of the laser measurement apparatus shown in FIG. 8 is basically the same as the laser measurement apparatus shown in FIGS. 1 and 2 except for the configuration of the signal processing unit. In addition, in the signal processing unit 347 illustrated in FIG. 8, the same components as those of the signal processing unit 46 illustrated in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. A signal processing unit 347 shown in FIG. 8 is obtained by adding a self-diagnosis function and a calibration function to the signal processing device 47.

  The signal processing unit 347 illustrated in FIG. 8 includes a filter processing unit 362, a spectral signal extractor 64, a memory 366, a built-in signal generator 368, and a signal merge unit 369. Since the filter processing unit 362 has the same configuration as the filter processing unit 62, detailed description thereof is omitted. The memory 366 is a storage device, acquires information on the signal generated by the spectrum signal extractor 64, and stores the acquired own signal and the conditions for generating the signal. The signal built-in generator 368 is an oscillator that generates and outputs a signal, and generates and outputs a signal based on an instruction input to the control unit 50. The signal merge unit 369 is disposed between the light receiving unit 44 and the filter processing unit 362, and sends a signal sent from the light receiving unit 44 to the filter processing unit 362. The signal merge unit 369 is further connected to the built-in signal generator 368, and sends the signal sent from the built-in signal generator 368 to the filter processing unit 362.

  The signal processing unit 347 is configured as described above. The signal processing unit 347 executes diagnosis and calibration of the filter processing unit 362 and the spectrum signal extractor 364 based on the information stored in the memory 366 based on the control of the control unit 50. Note that the signal processing unit 347 may have a control function instead of the control unit 50. The control unit 50 outputs a signal from the signal built-in generation unit 368, and acquires a signal that has passed through the filter processing unit 362 and reached the spectrum signal extractor 64 from the signal merge unit 369. The control unit 50 detects white noise generated by being transmitted through the path of the signal processing unit 347 based on the signal reaching the spectrum signal extractor 64, and based on the result, diagnoses the circuit of the signal processing unit 347. Or perform calibration. For example, as shown in FIG. 9, it is detected whether the component of the specified frequency 250 kHz is a waveform 380, a waveform 382 having a larger output than the waveform 380, or a waveform 384 having a smaller output than the waveform 380, and the signal processing unit 347 Determine the degradation state. Further, signals with different intensities are sequentially output from the built-in signal generator 368, and it is determined whether the output is proportional to the output, such as waveforms 380, 382, and 384, and the input (light receiving signal) is determined. The relationship with the output (spectrum signal) is detected, and the apparatus is calibrated.

  As described above, the signal processing unit 347 generates a signal that changes to a light reception signal, detects white noise in the system, and accumulates the result, thereby executing self-diagnosis and calibration in the system. Can do. In addition, since the self-diagnosis becomes possible, it is possible to solve the problem. Various methods can be used for self-diagnosis and calibration. Further, when a problem occurs, the user may be notified.

  Further, as described above, the designated frequency can be various values that are integral multiples of the modulation frequency. Even when a frequency that is four times the modulation frequency is used as the designated frequency, a change in the absorption spectrum (detection target spectrum) 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.

  Further, in the signal processing unit of the laser measurement device, it is preferable to provide a coil coupling at a connection part (a matching part of an operational amplifier constituting the amplifier or the like) between the amplifier and other members as in the above embodiment. By using a coil coupling for the matching portion, thermal noise or the like can be suppressed. In addition, since the said effect can be acquired, although it is preferable to use a coil coupling for the connection part of an amplifier and another member, it is not limited to this, A various connection member can be used.

  Moreover, in the said embodiment, although the signal which permeate | transmitted the crystal filter 74 was filtered by the low-pass filter, it is not limited to this. A band pass filter can also be used as the filter. If the signal component is sufficiently large, the amplifiers 77 and 84 may not be provided.

  The laser measuring device preferably sweeps the wavelength of the laser beam output from the light emitting unit 40 at a sweep frequency (for example, 0.1 kHz, 1 kHz) that is a frequency lower than the modulation frequency. By sweeping the laser light at the sweep frequency, it is possible to correct even if the absorption wavelength of the substance to be measured is shifted or the output wavelength of the laser light fluctuates, and the physical quantity of the substance to be measured is more accurate. Can be measured. Here, it is preferable that the vibration width of the laser light wavelength based on the modulation frequency be smaller than the change width of the laser light wavelength based on the sweep frequency. 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.

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 Filter processing unit 64 Spectral signal extractor 70 Oscillator 72 Up converter 74 Crystal filter 76, 82 Coil coupling 77, 84 Amplifier 78 Down converter 80 Low pass filter

Claims (13)

A measurement cell through which a fluid flows, a laser beam in a wavelength region including an absorption wavelength specific to a gas to be measured, with a wavelength modulated and output, and a light emitting unit that is incident on the measurement cell, and incident from the incident unit And a light receiving unit that receives the laser light emitted from the emitting unit and outputs the received light amount as a light reception signal, and the measurement cell is configured based on the light reception signal. Applied to a laser measuring device that calculates the physical quantity of the gas to be measured,
A signal processing device that processes a light reception signal received by the light receiving unit and outputs a spectrum signal used to calculate a physical quantity of a gas to be measured flowing through the measurement cell;
A filter processing unit for reducing an output of a frequency other than the designated frequency;
A spectrum signal extractor that performs a spectrum signal extraction process on the signal processed by the filter processing unit and extracts the spectrum signal;
The filter processing unit passes the output of the transmission frequency band including the transmission frequency, and attenuates the output other than the transmission frequency band,
An oscillator that oscillates a difference frequency between the transmission frequency and the designated frequency;
A downstream frequency converter that mixes a signal oscillated from the oscillator and a signal that has passed through the crystal filter, and converts an output of a transmission frequency of the signal that has passed through the crystal filter into an output of the specified frequency; A signal processing device comprising:   The signal processing apparatus according to claim 1, further comprising an upstream frequency conversion unit configured to convert a component of a specified frequency included in the light reception signal into a frequency component included in the transmission frequency.   The upstream frequency converting unit mixes the signal oscillated from the oscillating unit and the light reception signal, and converts the component of the specified frequency included in the light reception signal into the component of the frequency included in the transmission frequency. The signal processing apparatus according to claim 2, wherein:   The signal processing apparatus according to claim 1, wherein the oscillator is capable of changing a frequency of an output signal.   5. The signal processing apparatus according to claim 1, wherein the designated frequency is a frequency obtained by multiplying the modulation frequency by two or more and an integer.   The signal processing apparatus according to claim 1, wherein an output of the transmission frequency of the light reception signal is an output of the designated frequency of the spectrum signal.   The signal processing apparatus according to claim 6, wherein the transmission frequency is a frequency obtained by multiplying the modulation frequency by two or more and an integer.   It further comprises a low-pass filter that is disposed between the downstream frequency converter and the spectral signal extractor and reduces an output of a frequency equal to or higher than the specified frequency from a signal that has passed through the downstream frequency converter. The signal processing device according to any one of claims 1 to 7. An amplifier that is disposed between the low-pass filter and the spectral signal extractor and amplifies the signal that has passed through the downstream frequency converter;
The signal processing device according to claim 8, further comprising a coil coupling disposed between the low-pass filter and the amplifier. An amplifier that is disposed between the crystal filter and the downstream frequency converter and amplifies a signal that has passed through the crystal filter;
The signal processing apparatus according to claim 1, further comprising a coil coupling disposed between the crystal filter and the amplifier. A signal processing device according to any one of claims 1 to 10,
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.   The laser measurement apparatus according to claim 11, wherein the physical quantity calculated by the physical quantity calculation unit is a concentration of a gas to be measured.   The physical quantity calculation unit calculates the concentration of the substance 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. 12. The laser measuring device according to 12.

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