JP2013072730A - Substance measurement apparatus and substance measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure concentration, quantity, etc., of a measurement target substance included in flowing gas with high responsiveness and accuracy.SOLUTION: A substance measurement apparatus for measuring a measurement target substance included in flowing gas includes: a measurement cell in which the gas flows; a laser light irradiation unit for switching a state in which laser light having a wave length modulated within a certain wave length including the wave length of the measurement target substance is made to enter the measurement cell and a state in which the laser light is made not to enter the measurement cell; a light reception device for receiving the laser light emitted from the measurement cell; a first reflection part arranged between the measurement cell and the laser light irradiation unit for reflecting the laser light; a second reflection part arranged between the measurement cell and the light reception device for reflecting the laser light; and an analysis device for detecting the measurement target substance included in the flowing gas on the basis of attenuation of the intensity of the light in which the laser light irradiation unit has switched from a state for making the laser light enter the measurement cell to a state for making it not to enter the measurement cell and which has been received by the light reception device.

Description

  The present invention relates to a substance measuring apparatus and a substance measuring method for measuring a measurement target substance contained in a flowing gas flowing in a pipeline.

  For example, gas discharged from a combustion engine such as an internal combustion engine or an incinerator is a mixed gas in which various substances (gaseous substances, particulate substances, etc.) are mixed. Thus, various substances are contained in the substance contained in the mixed gas. For this reason, there are cases where it is desired to detect a specific substance in the mixed gas for various purposes, for example, whether the mixed gas contains a toxic substance. In some cases, it is desirable to detect the concentration and amount of a specific substance contained in a mixed gas for testing, evaluation, and the like. On the other hand, various apparatuses for measuring the concentration and amount of a specific substance (measuring substance) from a mixed gas composed of a plurality of gaseous substances have been proposed. For example, Patent Literature 1 and Patent Literature 2 use cavity ring-down spectroscopy that measures the amount of light leaked from a measurement cell and measures a substance to be measured based on attenuation of the measured amount of light. An apparatus for analyzing a sample to be measured is described.

JP 2004-333337 A JP 2006-138727 A

  The devices described in Patent Document 1 and Patent Document 2 use cavity ring-down spectroscopy, and can ensure a longer optical path length than the total length of the measurement cell by circulating measurement light in the light path. It is also possible to lengthen the distance passing through the region where the flow gas (sample) to be measured is arranged. Thereby, measurement with high accuracy can be performed.

  Here, in cavity ring-down spectroscopy, light having an absorption wavelength of a measurement target substance is used as measurement light incident on a measurement cell. For this reason, if the wavelength of the incident measurement light deviates from the absorption wavelength of the measurement target substance, a measurement error occurs.

  The present invention has been made in view of the above, and is a substance measuring apparatus and a substance measuring method capable of measuring the concentration, amount, etc., of a measurement target substance contained in a circulating gas with high responsiveness and high accuracy. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the present invention provides a substance measuring device for measuring a measurement target substance contained in a circulation gas, the measurement cell through which the circulation gas flows, and the measurement target substance. A laser light irradiation unit that switches between a state in which laser light having a wavelength modulated in a wavelength range including an absorption wavelength is incident on the measurement cell and a state in which the laser light is not incident on the measurement cell; and a light receiving device that receives the laser light emitted from the measurement cell; A first reflection unit disposed between the measurement cell and the laser light irradiation unit to reflect the laser beam, and a second reflection unit disposed between the measurement cell and the light receiving device to reflect the laser beam. And, based on the attenuation of the intensity of the light received by the light receiving device switched from the state in which the laser light irradiation unit is incident on the measurement cell to the state in which the laser light is not incident, And having a an analysis device for detecting the target substance contained in the passing gas.

  Here, the laser light irradiation unit preferably has a modulation period of the laser light of 20 μs or less. By setting the modulation period of the laser light to 20 μs or less, it is possible to make one modulation period of the laser light shorter than a general ring down time of about several tens of μs.

  In the laser beam irradiation unit, the modulation period of the laser beam is preferably 1 μs or less.

  Moreover, it is preferable that the said 1st reflection part and the said 2nd reflection part are optical mirrors with a reflectance of 99% or more.

  A first optical member connected to the laser light irradiation unit and the measurement cell and guiding the laser light; a second optical member connected to the light receiving device and the measurement cell; and guiding the laser light; It is preferable to further have.

  A first optical fiber that is connected to the laser light irradiation unit and the measurement cell and guides the laser light; and a second optical fiber that is connected to the laser light irradiation unit and the measurement cell and guides the laser light. The first reflecting part is a fiber Bragg grating composed of a plurality of high refractive index layers arranged in the first optical fiber, and the second reflecting part is the second light. A fiber Bragg grating composed of a plurality of high refractive index layers disposed in the fiber is preferable.

  A third optical fiber having one end connected to the first optical fiber, the other end connected to the second optical fiber, and inserted into the measurement cell; The optical fiber preferably includes a region where the core is exposed in a part of the measurement cell.

  It is preferable that the first optical fiber, the second optical fiber, and the third optical fiber are one optical fiber having no connection portion.

  The laser light irradiation unit is preferably provided with a shutter that is disposed on the laser light passing path and switches between a state of being incident on the measurement cell and a state of not being incident upon opening and closing.

  Moreover, it is preferable that the said laser beam irradiation unit is equipped with the mechanism which switches the emission direction of the said laser beam, and switches the state which enters into the said measurement cell, and the state which does not enter.

  Moreover, it is preferable that the said analysis apparatus detects the density | concentration of the said measuring object substance contained in the said circulation gas.

  In order to solve the above-described problems and achieve the object, the present invention is configured such that a laser beam is incident from one end of a measurement cell in which reflection portions are arranged at both ends and a flow gas flows, A substance measurement method for detecting a laser beam emitted from an end and measuring a measurement target substance contained in the flow gas, the step of flowing the flow gas into the measurement cell, and absorption of the measurement target substance A step of causing a laser beam modulated in a wavelength range including a wavelength to be incident from the one end of the measurement cell, a step of stopping the incidence of the laser beam on the measurement cell, and the other of the measurement cell. Based on a light receiving step for receiving the laser light output from the end, and attenuation of the intensity of the light received after switching from a state in which the laser light is incident on the measurement cell to a state in which the laser light is not incident , And having a detecting step of detecting the target substance contained in the circulation gas.

  The present invention has an effect that the concentration, amount, and the like of the measurement target substance contained in the circulation gas can be measured with high responsiveness and high accuracy.

FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of a concentration measuring apparatus. FIG. 2A is a waveform diagram showing an example of the wavelength of laser light output from the semiconductor laser oscillation device. FIG. 2B is an explanatory diagram for explaining the relationship between the wavelength of the laser beam output from the semiconductor laser oscillation device and the absorbance of the measurement target substance. FIG. 3 is an explanatory diagram for explaining an example of the operation of the high-speed laser intensity modulation device. FIG. 4 is a flowchart for explaining the operation of the concentration measuring apparatus. FIG. 5 is a graph showing the relationship between the received light intensity detected by the light receiving device and time. FIG. 6A is an explanatory diagram illustrating the relationship between the wavelength of the laser beam output from the semiconductor laser oscillation device and the absorbance of the measurement target substance. FIG. 6B is a graph showing the relationship between the received light intensity detected by the light receiving device and time. FIG. 6C is an explanatory diagram for explaining an example of a measurement result. FIG. 7 is a graph showing the relationship between the received light intensity detected by the light receiving device and time. FIG. 8 is an explanatory diagram for explaining an example of a measurement result. FIG. 9 is a schematic diagram showing a schematic configuration of another embodiment of the concentration measuring apparatus. FIG. 10 is a schematic diagram showing a schematic configuration of another embodiment of the concentration measuring apparatus. FIG. 11 is an enlarged schematic view of the FBG shown in FIG. FIG. 12A is a graph showing the relationship between the intensity of laser light output from the laser light irradiation unit and time. FIG. 12B is a graph showing the relationship between the received light intensity detected by the light receiving device and time. FIG. 13 is a schematic diagram showing a schematic configuration of another embodiment of the concentration measuring apparatus. FIG. 14 is a schematic diagram showing the optical fiber shown in FIG. 13 in an enlarged manner. FIG. 15 is a schematic diagram illustrating an example of a laser beam irradiation unit. FIG. 16 is a schematic diagram illustrating an example of the operation of the laser light irradiation unit.

  Hereinafter, an embodiment of a substance measuring device and a substance measuring method 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. For example, in this embodiment, as the substance measuring device and the substance measuring method, the concentration of the measurement target substance contained in the circulation gas is measured, but the present invention is not limited to this, and the amount of the measurement target substance contained in the gas is determined. You may measure. The substance measuring device and the substance measuring method can use various gases flowing through the pipeline as circulation gas. For example, a substance measuring device can be attached to a diesel engine, exhaust gas discharged from the diesel engine can be used as a circulation gas, and a measurement target substance contained in the circulation gas can be measured. The engine that discharges exhaust gas, that is, a device that discharges (supplies) 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, it is also possible to measure various substances contained in the circulation gas as the measurement target substance using the gas discharged from the waste incinerator as the circulation gas.

[Embodiment 1]
FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of the concentration measuring apparatus of the present invention. The concentration measurement apparatus 10 is a substance measurement apparatus that measures the concentration of a measurement target substance contained in a circulation gas. As shown in FIG. 1, the concentration measuring apparatus 10 includes a measuring cell unit 12, a laser light irradiation unit 14, a light receiving device 16, an analyzing device 18, a control device 20, a first reflecting unit 46, and a second reflecting unit 46. And a reflection part 48.

  The measurement cell unit 12 constitutes a measurement area for measuring a measurement target substance including a route for guiding the circulation gas G and the circulation gas. The measurement cell unit 12 includes a measurement cell 40, an inflow pipe 42, and a discharge pipe 44.

  The measurement cell 40 is a cylindrical member, and the flow gas G flows inside. A first reflecting portion 46 is arranged at one end of the measurement cell 40 in the cylindrical shape (left side in FIG. 1, the upper surface of the cylindrical shape), and on the other end portion (right side in FIG. 1, the lower surface of the cylindrical shape). A second reflecting portion 48 is disposed. That is, the measurement cell 40 has a shape in which the upper surface and the lower surface of the cylindrical shape are closed by the first reflecting portion 46 and the second reflecting portion 48, respectively. Thereby, as for the measurement cell 40, the both ends in which the 1st reflection part 46 and the 2nd reflection part 48 are provided will be in the state which does not distribute | circulate air. The first reflection part 46 and the second reflection part 48 will be described later.

  The inflow pipe (sampling pipe) 42 is a pipe for supplying the measurement target circulation gas G to the measurement cell 40. For example, the inflow pipe 42 is connected to the measurement target pipe and collects a part of the circulation gas G flowing through the measurement target pipe. The inflow pipe 42 has one end (upstream end in the flow direction of the flow gas G) connected to a supply device that supplies the flow gas G, and the other end (in the flow direction of the flow gas G). The downstream end portion is connected to the first reflecting portion 46 side of the side surface (circumferential surface) of the measurement cell 40. One end of the discharge pipe 44 is connected to the second reflecting portion 48 side of the side surface (circumferential surface) of the measurement cell 40, and the other end is connected to a more downstream pipe.

  The measurement cell unit 12 supplies the flow gas G supplied to the inflow pipe 42 from the inflow pipe 42 to the measurement cell 40. Further, the measurement cell unit 12 discharges the circulating gas G flowing through the measurement cell 40 from the discharge pipe 44 to the outside. In this way, the measurement cell unit 12 forms a flow path through which the flow gas G supplied from the measurement target gas supply means flows in the order of the inflow pipe 42, the measurement cell 40, and the discharge pipe 44.

  Further, the measurement cell unit 12 may further include a pump that sucks air in a direction in which the flow gas G flows from the inflow pipe 42 toward the measurement cell 40 and flows from the measurement cell 40 toward the discharge pipe 44. . In this case, the pump is preferably disposed in the discharge pipe 44 on the downstream side of the measurement cell 40 in the flow direction of the circulation gas G. The measurement cell unit 12 can appropriately adjust the flow rate of the flow gas G flowing in the order of the inflow pipe 42, the measurement cell 40, and the discharge pipe 44 by sucking the flow gas G with a pump.

  The first reflection unit 46 and the second reflection unit 48 are optical mirrors that reflect light. The surface of the first reflecting portion 46 that faces the second reflecting portion 48 is a reflecting surface. The surface of the second reflecting portion 48 that faces the first reflecting portion 46 is a reflecting surface. Specifically, the first reflecting portion 46 and the second reflecting portion 48 are optical mirrors having a reflectance of 99% or more, and in this embodiment, the reflectance is about 99.99%. The first reflection unit 46 and the second reflection unit 48 reflect almost all the light (99% or more) of the light (laser light) that has arrived, and transmit some of the light (less than 1%). .

  Thereby, the light traveling from the first reflecting portion 46 to the second reflecting portion 48 in the measurement cell 40 is reflected by the first reflecting portion 46 and becomes light directed from the second reflecting portion 48 to the first reflecting portion 46. In addition, the light that travels from the second reflecting portion 48 to the first reflecting portion 46 in the measurement cell 40 is reflected by the second reflecting portion 48 and becomes light that travels from the first reflecting portion 46 to the second reflecting portion 48. Thereby, the light traveling substantially parallel to the cylindrical shape of the measurement cell 40 is reflected by the first reflection unit 46 and the second reflection unit 48 and reciprocates in the measurement cell 40. Further, a part of the light traveling back and forth between the first reflecting part 46 and the second reflecting part 48, and less than 1% of the light not reflected by the first reflecting part 46 or the second reflecting part 48, 2 The light is emitted from the reflection portion 48 to the outside of the measurement cell 40. Thereby, the light traveling back and forth in the measurement cell 40 is gradually emitted from the first reflection unit 46 or the second reflection unit 48 to the outside of the measurement cell 40 every time it is reflected by the first reflection unit 46 or the second reflection unit 48. The This will be described later together with the measurement operation.

  Next, the laser beam irradiation unit 14 will be described. The laser light irradiation unit 14 includes a semiconductor laser oscillation device 22, a laser control device 24, an optical fiber 25, a high-speed laser intensity modulation device 26, and a beam stopper 28.

  The semiconductor laser oscillator 22 outputs laser light having a wavelength including a wavelength that is absorbed by the measurement target substance (hereinafter referred to as an absorption wavelength). The semiconductor laser oscillation device 22 has a semiconductor laser (laser diode, LD) as a light emitting element. In this embodiment, the semiconductor laser oscillation device 22 using a semiconductor laser as a light emitting element is used as a light emitting device that outputs laser light. However, the light emitting device is not limited to this. The light emitting device may be any mechanism that outputs laser light. The semiconductor laser oscillation device 22 can adjust the wavelength and intensity of the laser beam to be output based on the input signal.

  The laser control device 24 generates a laser control signal and sends it to the semiconductor laser oscillation device 22. The laser control signal is a signal for controlling the wavelength and intensity of the laser beam output from the semiconductor laser oscillator 22. The semiconductor laser oscillator 22 generates a laser control signal that periodically changes the wavelength of the laser light. The semiconductor laser oscillation device 22 outputs laser light based on the laser control signal generated by the laser control device 24. As a result, the semiconductor laser oscillation device 22 outputs laser light whose wavelength changes periodically.

Here, FIG. 2A is a waveform diagram showing an example of the wavelength of the laser beam output from the semiconductor laser oscillation device. FIG. 2B is an explanatory diagram for explaining the relationship between the wavelength of the laser beam output from the semiconductor laser oscillation device and the absorbance of the measurement target substance. In the graph shown in FIG. 2A, the vertical axis represents the wavelength λ of the laser beam, and the horizontal axis represents time. In the graph shown in FIG. 2B, the vertical axis represents the absorbance of the measurement target substance, and the horizontal axis represents the wavelength. The graph shown in FIG. 2B schematically shows the waveform 60 of the laser beam output from the semiconductor laser oscillation device 22 in addition to the absorption line 62 indicating the absorbance distribution of the measurement target substance. The semiconductor laser oscillation device 22 of the present embodiment outputs laser light whose wavelength is modulated with a sine wave as shown in FIG. 2A. Laser light, as shown in FIG. 2A, period t, and the next wavelength modulation width alpha, wavelength center becomes lambda _0. As shown in FIG. 2B, λ ₀ of the wavelength center of the sine wave of the laser light is the same wavelength as the absorption center wavelength of the measurement target material (the wavelength at which the absorption line 62 has the highest absorbance and the absorbance has the maximum value h). is there. The wavelength modulation width α is wider than the spectral width 64 of the absorption line 62. As described above, the semiconductor laser oscillation device 22 outputs laser light including the absorption center wavelength of the substance to be measured and modulated with a wavelength width wider than the spectral width 64 of the absorption line 62.

  The optical fiber 25 has one end connected to the semiconductor laser oscillation device 22 and the other end connected to the high-speed laser intensity modulation device 26. The optical fiber 25 guides the laser light output from the semiconductor laser oscillation device 22 to the high-speed laser intensity modulation device 26.

The high-speed laser intensity modulation device 26 is a device capable of switching the direction in which incident light is output. That is, the high-speed laser intensity modulation device 26 can deflect the traveling direction of the incident light and output it in a plurality of directions. As the high-speed laser intensity modulation device 26, a modulation signal is directly applied to an AO deflector (AOD, AO Deflectors), an acoustooptic device (AOM, Acoustic Optics Modulator) that modulates TeO ₂ or the like with a piezoelectric element, or LiNbO ₃ or the like. An electro-optic element (EOM, Electro-Optic Modulator) can be used. As the high-speed laser intensity modulation device 26, a device using a direct modulation method can also be used. An apparatus using the direct modulation method modulates the output by superimposing a rectangular wave pulse and a modulation wave on the laser injection current because the output of the semiconductor laser is proportional to the injection current. The apparatus using the direct modulation method further modulates the intensity while maintaining the laser wavelength at the absorption wavelength by controlling the laser wavelength with the element temperature. The high-speed laser intensity modulation device 26 has a first direction in which the laser light output from the semiconductor laser oscillation device 22 and guided by the optical fiber 25 is directed toward the end of the measurement cell 40 where the first reflection portion 46 is disposed. Can be output in the second direction toward the beam stopper 28. That is, the high-speed laser intensity modulation device 26 can output the laser light L1 incident on the end portion of the measurement cell 40 where the first reflecting portion 46 is disposed and the laser light L2 incident on the beam stopper 28. it can.

FIG. 3 is an explanatory diagram for explaining an example of the operation of the high-speed laser intensity modulation device. The high-speed laser intensity modulator 26 receives the ON / OFF signal shown in FIG. 3 from the controller 20, and switches the direction in which the laser beam is output based on the input signal. The high-speed laser intensity modulation device 26 of the present embodiment outputs laser light L1 incident on the end of the measurement cell 40 where the first reflecting portion 46 is disposed when the signal is OFF, and a beam stopper when the signal is ON. The laser beam L2 incident on the beam 28 is output. Therefore, when the signal shown in FIG. 3, a high speed laser intensity modulator 26 outputs the laser beam L2 incident on a beam stopper 28 until the time t _1, between the time t ₁ of time t _2, the measurement cell 40 the first reflecting part 46 outputs a laser beam L1 incident on the end that is arranged to output a laser beam L2 incident to the time t ₁ after the beam stopper 28.

  The beam stopper 28 is a device that absorbs incident laser light. The beam stopper 28 includes a cooling mechanism that suppresses a temperature rise caused by absorbing laser light.

  The laser light irradiation unit 14 is configured as described above, and a laser control signal is transmitted from the laser control device 24 to the semiconductor laser oscillation device 22. The semiconductor laser oscillation device 22 outputs laser light whose wavelength is modulated at a constant period based on the laser control signal, and causes the output laser light to enter the optical fiber 25. The optical fiber 52 guides the incident laser light and makes it incident on the high-speed laser intensity modulator 26. The high-speed laser intensity modulation device 26 switches between a state in which the laser light is incident in the measurement cell 40 and a state in which the laser light is incident on the beam stopper, based on a signal from the control device 20. That is, the high-speed laser intensity modulation device 26 switches between a state of outputting the laser light L1 and a state of outputting the laser light L2. In this way, the laser beam irradiation unit 14 causes the laser beam L1 whose wavelength is modulated at a constant period to enter the measurement cell 40. Further, the laser light irradiation unit 14 switches between a state in which the laser light L <b> 1 whose wavelength is modulated at a certain period is incident on the measurement cell 40 and a state in which the laser light L <b> 1 is not incident.

  The light receiving device 16 is a light receiving unit that receives the laser light that passes through the measurement cell 40 and is output from the second reflecting unit 48. The light receiving device 16 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 device 16 sends the intensity of the received laser light to the analyzing device 18 as a received light intensity signal. The light receiving device 16 preferably includes a signal processing unit that removes a noise component from a signal received by the light receiving device 16 from a signal received by the light receiving unit. The signal processing unit can use a low-pass filter that reduces high frequency components of the signal, a lock-in amplifier (phase sensitive detector) that extracts only a predetermined frequency component, or the like. The light receiving device 16 can generate a light reception intensity signal from which noise has been removed by processing the light reception signal of the light reception unit in the signal processing unit.

  The analysis device 18 measures the concentration of the measurement target substance contained in the circulation gas G based on the received light intensity signal transmitted from the light receiving device 16, that is, based on the intensity of the laser light detected by the light receiving device 16. A method for measuring the concentration of the analyzer 18 will be described later.

  The control device 20 has a control function for controlling the operations of the analysis device 18, the laser control device 24, and the high-speed laser intensity modulation device 26, and controls the operation of each unit as necessary. Specifically, the control device 20 controls the frequency, intensity, output timing, and the like of the control signal generated by the laser control device 24. The control device 20 controls the timing at which the high-speed laser intensity modulation device 26 changes the direction in which the laser beam is output and the direction in which the laser beam is output. The control device 20 also sets conditions necessary for analysis in the analysis device 18. The concentration measuring apparatus 10 is configured as described above.

  Next, the operation of the concentration measuring apparatus 10 will be described with reference to FIGS. 1 and 4. FIG. 4 is a flowchart for explaining the operation of the concentration measuring apparatus. The control device 20 of the concentration measuring device 10 starts circulation of the flow gas as step S12. When starting the flow of the flow gas in step S12, the control device 20 drives the laser light irradiation unit 14 and starts outputting the laser light in step S14. Here, as described above with reference to FIGS. 2A and 2B, the laser beam irradiation unit 14 outputs the sine wave laser beam L whose wavelength changes at a predetermined period. In addition, the high-speed laser intensity modulation device 26 of the laser beam irradiation unit 14 is in an ON state in the initial state. That is, the high-speed laser intensity modulation device 26 outputs the laser light L2. Thereby, the laser beam irradiation unit 14 causes the laser beam L2 to enter the beam stopper 28 when the output of the laser beam is started in step S14.

  When the controller 20 drives the laser beam irradiation unit 14 in step S14 and starts outputting the laser beam, the controller 20 turns off the high-speed laser intensity modulator (modulator) 26 in step S16. That is, the control device 20 switches the signal sent to the high-speed laser intensity modulation device 26 from ON to OFF, and changes the state where the high-speed laser intensity modulation device 26 outputs the laser light L2 from the state where the high-speed laser intensity modulation device 26 outputs the laser light L2. Thereby, the laser beam irradiation unit 14 causes the laser beam L1 to enter the measurement cell 40.

  Here, the laser beam irradiation unit 14 irradiates the first reflection unit 46 with the laser beam L1 and causes the laser beam L1 that has passed through the first reflection unit 46 to enter the measurement cell 40. Here, since the 1st reflection part 48 is an optical mirror with a high reflectance as mentioned above, the laser beam L3 which injects into the measurement cell 40 turns into a laser beam whose output is lower than the laser beam L1. The laser beam L3 incident on the measurement cell 40 travels in the measurement cell 40, is alternately reflected by the first reflection unit 46 and the second reflection unit 48, and reciprocates in the measurement cell 40. Thereby, the laser beam L3 passes through the region filled with the flow gas G of the measurement cell 40 a plurality of times.

  In step S16, the control device 20 turns off the modulation device, causes the laser light L1 to enter the measurement cell 40, and starts the incidence of the laser light L3 into the measurement cell 40. In step S18, threshold time ≦ elapsed time. Determine if there is. Here, the elapsed time is an elapsed time since the high-speed laser intensity modulator 26 is turned on, and the threshold time is a preset time. That is, the control device 20 determines whether or not the laser light L1 is incident (irradiated) on the measurement cell 40 (the first reflection unit 46 thereof) for a time equal to or longer than a preset threshold time.

  When it is determined in step S18 that the threshold time is not equal to the elapsed time (No in step S18), the control device 20 proceeds to step S18. That is, the control device 20 repeats the determination in step S18 until the elapsed time becomes equal to or greater than the threshold time. If the control device 20 determines in step S18 that the threshold time ≦ the elapsed time (Yes in step S18), the control device 20 proceeds to step S20. In the present embodiment, the determination criterion is not particularly limited, based on whether the threshold time has elapsed.

  If the control device 20 determines Yes in step S18, the control device 20 turns on the modulation device in step S20. That is, the control device 20 switches the signal sent to the high-speed laser intensity modulation device 26 from OFF to ON, and the high-speed laser intensity modulation device 26 changes from a state in which the laser light L2 is output to a state in which the laser light L1 is output. Switch. Thereby, the laser beam irradiation unit 14 stops the incidence of the laser beam L1 to the measurement cell 40 and causes the laser beam L2 to enter the beam stopper 28.

  If the modulation device is turned on in step S20, the control device 20 detects the received light intensity signal in step S22. That is, the control device 20 uses the light receiving device 16 to detect the intensity of the laser light L4 incident on the light receiving device 16 and detect the received light intensity signal. The control unit 20 may drive the light receiving device 16 in advance and detect the received light intensity signal even at a stage prior to step S20. The control device 20 analyzes the received light intensity signal detected by the light receiving device 16 during the time when the modulation device is turned on in step S20 and the predetermined time after the modulation device is turned on in step S20.

  After detecting the received light intensity signal in step S22, the control device 20 calculates the density from the ring down time in step S24. A detection method for detecting the density from the ring down time will be described later.

  When detecting the intensity of the laser beam in step S20, the control device 20 detects the density in step S22. The control device 20 uses the analysis device 18 to detect the concentration of the measurement target substance contained in the circulating gas G flowing through the measurement region using the results of step S18 and step S20.

  When the concentration is detected in step S24, the control device 20 determines whether the measurement is finished (whether the detection of the concentration of the measurement target substance is finished) in step S26. If it is determined in step S26 that the process has not ended (No), the control device 20 proceeds to step S16 and executes the processes from step S16 to step S24. Moreover, when it determines with the control apparatus 20 having been measurement completion (Yes) by step S26, this process is complete | finished.

  Next, the density detection operation executed in step S24 will be described. FIG. 5 is a graph showing the relationship between the received light intensity detected by the light receiving device and time. In the graph shown in FIG. 5, the vertical axis represents received light intensity and the horizontal axis represents time. The graph shown in FIG. 5 is shown in a standardized state where the maximum value of the received light intensity is 1. Here, the control apparatus 20 measures the density | concentration of a measuring object substance using cavity ring down spectroscopy (CRD spectroscopy, CRDS, Cavity Ring Down Spectroscopy).

  In the concentration measuring apparatus 10, when the laser light L 1 is incident on the measurement cell 40 from the laser light irradiation unit 14 for a predetermined time and becomes stable, the laser light L 3 having a constant intensity reciprocates in the measurement cell 40. Each time it moves and is reflected by the first reflecting portion 46 and the second reflecting portion 48, a laser beam having a constant intensity passes through the first reflecting portion 46 and the second reflecting portion 48. As a result, the laser beam L4 is output from the second reflecting portion 48.

  When the incidence of the laser light L1 from the laser light irradiation unit 14 to the measurement cell 40 is stopped from the stable state, the concentration measurement apparatus 10 enters a state in which no new laser light is incident on the measurement cell 40. In the concentration measuring apparatus 10, even when the incidence of the laser beam L 1 on the measurement cell 40 is stopped, the laser beam L 3 reciprocating in the measurement cell 40 is reflected by the first reflecting unit 46 and the second reflecting unit 48. Each time, a part of the laser light passes through the first reflecting part 46 and the second reflecting part 48. For this reason, the intensity of the laser beam L3 is gradually attenuated, and the intensity of the laser beam L4 output from the second reflecting portion 48 is also gradually attenuated. The control device 20 detects the attenuation (change in the received light intensity signal) of the laser light L4 that passes through the second reflecting portion 48 of the measurement cell 40 and then enters the light receiving device 16 after stopping the incidence of the laser light. Here, the intensity of the laser beam L4 detected by the light receiving device 16 gradually decreases as shown in FIG. In the example shown in FIG. 5, the incidence of the laser beam L1 is stopped at time 0 and the measurement of the received light signal is started.

  The control device 20 performs analysis by the analysis device 18 based on the detection result of the attenuation of the intensity of the laser light L4. Here, in the concentration measuring apparatus 10, when the measurement target substance is contained in the flow gas G in the measurement cell 40, when the laser light passes through the flow gas G, the absorption wavelength component of the laser light is absorbed by the measurement target substance. As a result, the output of the laser light is attenuated. Further, the greater the amount of the measurement target substance contained in the circulating gas G, that is, the higher the concentration, the greater the amount of laser light attenuation. For this reason, as shown in FIG. 5, the light reception intensity when there is no flow gas G measurement target substance (no gas in the figure) is also the light reception intensity when there is a flow gas G measurement target substance (wavelength modulation in the figure). Decays (decreases) more in a shorter time. In addition, in FIG. 5, the case where the laser beam which does not modulate a wavelength at the wavelength with the highest absorbance of the measurement target substance, that is, the center wavelength is used is also shown for reference (center wavelength in the figure).

  The analysis device 18 detects the received light intensity of the laser beam L4 that is attenuated based on the above relationship, and detects the ring-down time that is the time from the detection result until the attenuation rate of the intensity of the laser beam L4 reaches a predetermined ratio. To do. The analysis device 18 stores the relationship between the ring town time calculated in the experiment conducted in advance and the concentration of the measurement target substance, and calculates the concentration of the measurement target substance based on the relationship and the detected ring down time. To do.

  As described above, the concentration measurement apparatus 10 causes the laser light to enter the measurement cell 40 sandwiched between the reflection portions having high reflectance at both ends of the laser light path, and the measurement that occurs after the laser light is stopped. Based on the attenuation of the laser beam output from the cell 40, the concentration of the measurement target substance contained in the flowing gas G flowing in the measurement cell 40 is measured using cavity ring-down spectroscopy. Thereby, the concentration measuring apparatus 10 can dramatically increase the optical path length through which the laser light passes through the flow gas with respect to the length of the measurement cell 40, for example, the same as the measurement cell having a measurement length of 10 km. The output of the laser beam that has passed through the circulation gas G by the distance can be detected. Thereby, the density | concentration of a measuring object substance is detectable with high precision.

  In addition, the concentration measuring apparatus 10 outputs laser light output from the laser light emitting unit 14 and makes the laser light incident on the measurement cell 40 be laser light whose wavelength is modulated in a wavelength range including the absorption wavelength of the measurement target substance. Measurement can be simplified, and the concentration of the measurement target substance can be measured in a short time with high accuracy.

  Here, FIG. 6A is an explanatory view illustrating the relationship between the wavelength of the laser beam output from the semiconductor laser oscillation device and the absorbance of the measurement target substance. FIG. 6B is a graph showing the relationship between the received light intensity detected by the light receiving device and time. FIG. 6C is an explanatory diagram for explaining an example of a measurement result. 6A to 6C show an example in which a pulse wave having a predetermined wavelength is used as a laser beam unlike the present invention.

  For example, the laser light incident on the measurement cell 40 from the laser light emitting unit 14 is a pulse wave having one wavelength as shown by a laser wavelength 70 as shown in FIG. 6A. In this case, when the laser wavelength 70 coincides with the peak of the absorption line 64 (wavelength having the highest absorbance), as shown in the measurement result at the wavelength center in FIG. 6B, there is no gas, that is, the measurement result when the measurement target substance is not included. On the other hand, the attenuation of the received light intensity increases.

  However, in the concentration measuring device, the wavelength of the laser beam output varies depending on the state of the laser beam emitting unit 14, for example, the temperature of the light source, or the center wavelength of the absorption wavelength varies depending on the measurement environment. Therefore, when using a pulse wave as the laser beam, the concentration measuring apparatus 10 changes the wavelength of the laser beam to be output at a constant wavelength interval as shown in FIG. Measure the concentration. Thus, by measuring each of the plurality of wavelengths, the measurement result at the absorption wavelength of the measurement target substance can be detected, and the concentration of the measurement target substance can be measured.

  On the other hand, as described above, the concentration measuring apparatus 10 according to the present embodiment uses the laser light incident on the measurement cell 40 as a laser light whose wavelength is modulated in a wavelength range including the absorption wavelength of the measurement target substance. . Thereby, the concentration measuring apparatus 10 can change the wavelength of the laser light output depending on the state of the laser light emitting unit 14, for example, the temperature of the light source, or even if the center wavelength of the absorption wavelength changes depending on the measurement environment. The incident laser beam can be a laser beam including the center wavelength of the absorption wavelength. For this reason, the same measurement result can be obtained even when the center wavelength of the laser beam to be modulated deviates from the center wavelength of the absorption wavelength of the measurement target substance. That is, similar results can be obtained even if the conditions change. As described above, the concentration measuring apparatus 10 can measure the concentration of the measurement target substance with high accuracy even in one measurement.

  Next, an example of the measurement result will be described with reference to FIGS. FIG. 7 is a graph showing the relationship between the received light intensity detected by the light receiving device and time. FIG. 8 is an explanatory diagram for explaining an example of a measurement result. In this measurement, when there is no substance to be measured in the flow gas and the laser beam is modulated, and when the gas to be measured contains a constant concentration of the measurement target substance and the laser beam is modulated, the flow gas The gas concentration was measured for each of the cases where the substance to be measured contains a constant concentration and the laser light is not modulated (the wavelength is set constant for the device setting).

  FIG. 7 shows the attenuation of the received light intensity detected by the measurement under each of the three conditions. As shown in FIG. 7, when there is no measurement target substance in the flow gas and the laser beam is modulated (no target gas in the figure, with modulation), the flow gas contains a constant concentration of the measurement target substance. In addition, the time until the received light intensity becomes zero is longer than when the laser light is modulated (with target gas in the figure, with modulation). Also, in the figure, when the target gas is present and modulated, the received light intensity is higher than when the gas to be measured contains a certain concentration of the substance to be measured and the laser light is not modulated (with target gas and not modulated in the figure). The time until becomes zero becomes longer. As shown in FIG. 7, the responsiveness from the start of detection until the ring-down time is reached is faster when measurement is performed without modulation than when measurement is performed by modulating laser light.

  Next, FIG. 8 shows the measurement results of the density of the measurement under each of the three conditions. In FIG. 8, in each case, the measurement was performed a plurality of times in a certain time for the same circulating gas. As shown in FIG. 8, when the measurement is performed without modulating the laser beam, the detected value varies more than when the measurement is performed by modulating the laser beam. Here, in the measurement, since the circulation gas containing the measurement target substance having the same concentration is used, the fluctuation becomes a detection error. That is, as shown in FIG. 8, the detection accuracy can be further increased by performing measurement by modulating the laser beam.

  As described above, the concentration measuring apparatus 10 can measure the concentration with higher accuracy than the case where the concentration is detected by one measurement without modulating the wavelength. In addition, the concentration measuring apparatus 10 can detect the concentration by one measurement as compared to the case where the wavelength is changed with a constant wavelength width, the measurement is performed without modulating the wavelength for each wavelength, and the concentration is detected. The concentration can be measured in a short time. In addition, when the concentration measuring apparatus 10 changes the wavelength with a constant wavelength width and performs measurement without modulating the wavelength for each wavelength, in order to perform measurement at the center wavelength of the absorption wavelength with high accuracy, Although it is necessary to increase the number of times and the measurement takes time, the concentration measuring apparatus 10 can measure the concentration with the same degree of accuracy in one measurement. As described above, the concentration measuring apparatus 10 can achieve both high responsiveness and robustness at a high level.

  Further, the concentration measuring apparatus 10 further improves the robustness by setting the wavelength modulation width α of the laser light to be wider than the spectral half width of the absorption line of the substance to be measured, preferably 2.2 times or more. Can do. In other words, by making the wavelength modulation width α of the laser light sufficiently wider than the spectral width of the absorption line of the measurement target substance, the center wavelength of the modulation of the laser light and the center wavelength (peak wavelength) of the absorption line of the measurement target substance Even if the deviation is larger, a range in which the absorbance of the measurement target substance is a certain ratio or more can be included in the modulation width.

  Further, the concentration measuring apparatus 10 needs to make the modulation period t of the laser light sufficiently shorter than the ring-down time. Furthermore, the concentration measuring apparatus 10 preferably sets the laser light modulation period t to 1/4 or less of the ring-down time, and more preferably 1/20 or less of the ring-down time. Here, since the general ring-down time is normally about several tens of μs, the concentration measuring apparatus 10 sets the laser light modulation period t to 20 μs or less by setting the laser light modulation period t to 20 μs or less. It can be made sufficiently shorter than the ring down time. The concentration measuring apparatus 10 can sufficiently shorten the cycle with respect to the time until the ring-down time by setting the laser light modulation cycle t to preferably 5 μs or less, and more preferably 1 μs or less. Measurement can be performed in a state where a minute laser beam is incident. Specifically, by setting the laser light modulation period t to 5 μs or less, the laser light modulated during the ring-down time can be incident for four periods or more. Further, by setting the modulation period t of the laser light to 1 μs or less, the laser light modulated during the ring-down time can be incident for 20 periods or more. Thereby, measurement accuracy can be made higher.

  Here, the concentration measuring apparatus 10 can use various substances contained in the circulation gas as measurement target substances by adjusting the apparatus. Moreover, as a measurement object substance, the various substances contained in distribution | circulation gas can be made into object. The measurement target substance exists in the circulating gas as a suspended particulate matter (SPM, Suspended Particulate Matter), a particulate matter (PM, Particulate Matter, Particulate), a gaseous matter, or the like. As the measurement target substance, various substances having an absorption wavelength (a wavelength at which the absorbance increases) in a wavelength range that can be output by laser light can be used.

  Here, it is preferable to use a laser beam in the near-infrared wavelength region as the laser beam. Thereby, even if it is in the state where components other than a measuring object substance were mixed in circulation gas, the concentration of a measuring object substance can be measured appropriately. That is, it is possible to make it difficult for components other than the measurement target substance to become noise. As a result, it is possible to eliminate or reduce the filter and the dehumidifying process, and to shorten the time from when the circulation gas is supplied from the circulation gas supply source until the measurement is performed and the measurement result is calculated. it can. That is, the measurement time delay can be reduced. Thereby, responsiveness can be made high.

  Further, as described above, the measurement cell unit 12 is provided with a pump that sucks air in the direction in which the flow gas G flows from the inflow pipe 42 toward the measurement cell 40 and flows from the measurement cell 40 toward the discharge pipe 44. May be. In this case, the pump is preferably disposed in the discharge pipe 44 on the downstream side of the measurement cell 40 in the flow direction of the circulation gas G. The measurement cell unit 12 can appropriately adjust the flow rate of the flow gas G flowing in the order of the inflow pipe 42, the measurement cell 40, and the discharge pipe 44 by sucking the flow gas G with a pump.

  The concentration measuring apparatus is not limited to the above embodiment, and can be various embodiments. Hereinafter, other embodiments will be described with reference to FIGS. 9 to 16.

[Embodiment 2]
FIG. 9 is a schematic diagram showing a schematic configuration of another embodiment of the concentration measuring apparatus. The concentration measuring apparatus 100 shown in FIG. 9 includes a measuring cell unit 12, a laser light irradiation unit 104, a light receiving device 16, an analyzing device 18, a control device 20, a first reflecting unit 46, and a second reflecting unit 48. And having. Furthermore, the concentration measuring apparatus 100 includes an optical fiber 112 and connecting optical systems 114 and 116. Here, the concentration measurement apparatus 100 is the same as the concentration measurement apparatus 10 except for the configuration of the laser light irradiation unit 104, the optical fiber 112, and the connection optical systems 114 and 116. Description of the configuration of the concentration measuring apparatus 100 that is the same as that of the concentration measuring apparatus 10 is omitted.

  The laser light irradiation unit 104 includes a semiconductor laser oscillation device 22, a laser control device 24, an optical fiber 25, and an optical shutter 110. Since the semiconductor laser oscillation device 22, the laser control device 24, and the optical fiber 25 have the same configuration as the laser light irradiation unit 14 described above, the description thereof is omitted.

  The high-speed light shutter 110 is a device equipped with the functions of the high-speed laser intensity modulation device 26 and the beam stopper 28 of the laser light irradiation unit 14. The high-speed light shutter 110 is a mechanism capable of switching between a state of blocking the passage of the laser light and a state of passing the laser light (a state where the passage of the laser light is not blocked) on the passage path of the laser light. Here, as the high-speed optical shutter 110, for example, a liquid crystal shutter used in a liquid crystal display device can be used. The high-speed optical shutter 110 is in a state where the laser light is not incident on the measurement cell 40 by blocking the passage of the laser light, and the laser light is incident on the measurement cell 40 by allowing the laser light to pass. State. Further, in the high-speed light shutter 110, the state where the passage of the laser light is blocked is turned on, and the state where the laser light is passed is turned off.

  The laser light irradiation unit 104 is configured as described above, and a laser control signal is transmitted from the laser control device 24 to the semiconductor laser oscillation device 22. The semiconductor laser oscillation device 22 outputs laser light whose wavelength is modulated at a constant period based on the laser control signal, and causes the output laser light to enter the optical fiber 25. The optical fiber 52 guides the incident laser light and makes it incident on the high-speed optical shutter 110. Based on the signal from the control device 20, the high-speed optical shutter 110 allows the laser light to pass therethrough and makes the laser light enter the measurement cell 40, and blocks the laser light and does not allow the laser light to enter the measurement cell 40. Switch between states. In this way, the laser beam irradiation unit 104 also makes the measurement cell 40 enter the laser beam whose wavelength is modulated at a constant period. The laser light irradiation unit 104 switches between a state in which the laser light is incident on the measurement cell 40 and a state in which the laser light is not incident.

  Next, the optical fiber 112 has one end connected to the high-speed optical shutter 110 and the other end connected to the connection optical system 114. The connecting optical system 114 connects the optical fiber 112 and the first reflecting portion 46. The connection optical system 114 is a connector or the like, and connects two connected members (the optical fiber 110 and the first reflecting portion 46) in a state where laser light can pass between the two members. As described above, the high-speed optical shutter 110 and the first reflection unit 46 are connected by the optical fiber 112 and the connection optical system 114. As a result, the laser light incident from the high-speed optical shutter 110 toward the measurement cell 40 passes through the optical fiber 112 and then passes through the connection optical system 114 and enters the first reflecting portion 46.

  The connection optical system 116 connects the second reflection unit 48 and the light receiving device 16. The connection optical system 116 is a connector or the like, and is coupled between the second reflecting unit 48 and the light receiving device 16 in a state where laser light can pass.

  The concentration measuring apparatus 100 switches between a state in which laser light is incident on the measuring cell 40 and a state in which it is not incident by providing a high-speed optical shutter 110 instead of the high-speed laser intensity modulator 26 and the beam stopper 28. As described above, by using the high-speed optical shutter 110, it is possible to appropriately switch between a state in which the laser light is incident on the measurement cell 40 and a state in which the laser light is not incident. Further, the concentration measuring apparatus 100 can suppress the output of laser light to the outside when the laser light is not incident on the measurement cell 40 by using the high-speed light shutter 110.

  The concentration measurement apparatus 100 outputs from the laser light irradiation unit 104 by providing the optical fiber 112 and the connection optical system 114 between the high-speed optical shutter 110 and the measurement cell 40 (the first reflection unit 46 connected to the measurement cell 40). The laser beam thus made can be guided to the measurement cell 40 by an optical member. Similarly, the measuring cell 40 (the second reflecting portion 48 connected to the light receiving device 16) and the light receiving device 16 are connected by the connecting optical system 116, so that the laser beam output from the measuring cell 40 is received by the optical member by the optical member. Can be guided to. The concentration measuring apparatus 100 can transmit the laser light with higher accuracy by providing an optical fiber or an optical connection system in the laser light path between the components. Further, by guiding the laser beam with an optical fiber, the laser beam can be guided along a route other than a straight line. Thereby, the apparatus can be made compact and the arrangement of the apparatus can be simplified.

[Embodiment 3]
FIG. 10 is a schematic diagram showing a schematic configuration of another embodiment of the concentration measuring apparatus. 10 includes a measurement cell unit 202, a laser beam irradiation unit 104, a light receiving device 16, an analysis device 18, a control device 20, an FBG (Fiber Bragg Grating) 220, 240. Furthermore, the concentration measuring apparatus 200 includes optical fibers 218 and 230 and connecting optical systems 114, 232 and 234. Here, the concentration measuring apparatus 200 has the other configuration except for the configuration of the measuring cell unit 202, the FBGs 220 and 240, the optical fibers 218 and 230, and the connecting optical systems 114, 232, and 234. 100. Description of the configuration of the concentration measuring apparatus 200 that is the same as that of the concentration measuring apparatus 100 is omitted.

  The measurement cell unit 202 constitutes a measurement area for measuring a path for guiding the flow gas G and a measurement target substance contained in the flow gas. The measurement cell unit 202 includes a measurement cell 210, an inflow pipe 212, and a discharge pipe 214.

  The measurement cell 210 is a hollow quadrangular prism-shaped member, and the circulation gas G flows inside. An inflow pipe 212 is arranged at one end (upper side in FIG. 10, upper surface of the quadrangular column) of the hollow prismatic shape of the measurement cell 210, and at the other end (lower side in FIG. 10, lower surface of the quadrangular column). Is provided with a discharge pipe 214. In other words, the measurement cell 210 has a quadrangular prism-shaped upper and lower surfaces open to which the inflow pipe 212 and the exhaust pipe 214 are connected. In the measurement cell 210, the connection optical system 114 is connected to one side surface of the quadrangular prism, and the connection optical system 232 is connected to the side surface opposite to the side surface to which the optical member 114 is connected. Here, in the measurement cell 210, the side surface to which the connection optical system 114 is connected and the side surface to which the connection optical system 232 is connected are parallel surfaces.

  The inflow pipe (sampling pipe) 212 is a pipe that supplies the flow gas G to be measured to the measurement cell 210. One end of the inflow pipe 42 is connected to a supply device that supplies the circulating gas G, and the other end is connected to the upper surface of the measurement cell 210. The discharge pipe 214 has one end connected to the lower surface of the measurement cell 210 and the other end connected to a more downstream pipe.

  The measurement cell unit 202 supplies the flow gas G supplied to the inflow pipe 212 to the measurement cell 210 from the inflow pipe 212. In addition, the measurement cell unit 202 discharges the circulating gas G flowing through the measurement cell 210 to the outside from the discharge pipe 214. In this way, the measurement cell unit 202 forms a flow path through which the flow gas G supplied from the measurement target gas supply means flows in the order of the inflow pipe 212, the measurement cell 210, and the discharge pipe 214.

  Next, the optical fibers 218 and 230 and the connection optical systems 114, 232, and 234 will be described. The optical fiber 218 and the connection optical system 114 are disposed between the high-speed optical shutter 110 and the measurement cell 210. The optical fiber 230 and the connecting optical systems 323 and 324 are disposed between the measurement cell 210 and the light receiving device 16.

  The optical fiber 218 has one end connected to the high-speed optical shutter 110 and the other end connected to the connection optical system 114. The connection optical system 114 connects the optical fiber 128 and the side surface of the measurement cell 210. The connection optical system 114 is a connector or the like, and connects two connected members (the optical fiber 218 and the measurement cell 210) in a state where laser light can pass between the two members. Thus, the high-speed optical shutter 110 and the measurement cell 210 are connected by the optical fiber 218 and the connection optical system 114.

  The optical fiber 230 has one end connected to the connection optical system 232 and the other end connected to the connection optical system 234. The connection optical system 232 connects the side surface of the measurement cell 210 and the optical fiber 230. The connection optical system 234 connects the optical fiber 230 and the light receiving device 16. Thus, the measurement cell 210 and the light receiving device 16 are connected by the optical fiber 230 and the connection optical systems 232 and 234.

  Next, FBGs (Fiber Bragg Gratings) 220 and 240 will be described. The FBG 220 is provided in an end region of the optical fiber 218 on the connection optical system 114 side (that is, the measurement cell 210 side). The FBG 220 is an optical member having a function similar to that of the first reflection unit 46 and includes a plurality of high refractive index layers 222. The FBG 240 is provided in the end region of the optical fiber 230 on the connection optical system 232 side (that is, the measurement cell 210 side). The FBG 240 is an optical member having a function similar to that of the second reflection unit 48 and includes a plurality of high refractive index layers 242. The FBG 220 and the FBG 240 are arranged at positions facing each other with the measurement cell 210 in between. Further, since both the FBG 220 and the FBG 240 are provided in the optical fibers 218 and 230 that are laser beam passage paths, they are arranged in the laser beam passage path.

  Hereinafter, the FBG 240 as a representative of the two FBGs 220 and 240 will be described with reference to FIG. FIG. 11 is an enlarged schematic view of the FBG shown in FIG. The FBG 240 includes a plurality of high refractive index layers 242 arranged at a predetermined interval in the laser beam path direction at the core of the optical fiber 230. The FBG 240 periodically changes the refractive index by disposing a plurality of high refractive index layers 242 in the core of the optical fiber 230. In this way, the FBG 240 provides a Bragg reflection condition created by the period of the grating by providing a periodic change of the refractive index in the laser beam passage path and causing the periodic change of the refractive index to function as a grating (diffraction grating). Only the light of the wavelength which fills is reflected. Thereby, FBG240 can reflect the wavelength of a laser beam. Further, the FBG 240 is caused by the same reflection at the boundary between the plurality of high refractive index layers 242. Further, since the FBG 240 passes laser light that satisfies a predetermined condition, a part of the laser light that has reached the FBG 240 (light of less than 1%) passes through the FBG 240 and reaches the light receiving device 16.

  As a result, the concentration measuring apparatus 200 reciprocates as the laser light is reflected between the FBG 220 and the FBG 240 with the measurement cell 210 interposed therebetween. That is, the light traveling from the FBG 220 toward the FBG 240 is reflected by the FBG 240 and becomes light traveling from the FBG 240 toward the FBG 220. The light traveling from the FBG 240 toward the FBG 220 is reflected by the FBG 220 and becomes light traveling from the FBG 220 toward the FBG 240. Further, a part of the light traveling back and forth between the FBG 220 and the FBG 240, that is, less than 1% of light that is not reflected by the FBG 220 or the FBG 240, is emitted outward from the FBG 220 or the FBG 240 in a direction away from the measurement cell 210. As a result, the light traveling back and forth in the measurement cell 212 is gradually emitted to the outside from between the FBG 220 and the FBG 240 every time it is reflected by the FBG 220 and the FBG 240.

  The concentration measuring apparatus 200 can also reciprocate the laser beam in the measurement cell 210 by using the FBGs 220 and 240 as a reflection part that reflects light across the measurement cell 210, and performs cavity ring-down spectroscopy. The used concentration measurement can be performed. FIG. 12A is a graph showing the relationship between the intensity of laser light output from the laser light irradiation unit and time. FIG. 12B is a graph showing the relationship between the received light intensity detected by the light receiving device and time. Here, the concentration measuring apparatus 200 uses the FBGs 222 and 240 formed of a plurality of high refractive index layers 222 and 242 as a reflection unit. For this reason, as shown in FIG. 12A, the concentration measuring apparatus 200 switches the laser light output from the laser light irradiation unit from being output to the measurement cell 210 at time 0 to not being output. As shown in FIG. 12B, the light receiving signal is detected by the light receiving device 16 at regular time intervals, and the detection intensity attenuates stepwise. As shown in FIG. 12B, the concentration measuring apparatus 200 can detect the ring-down time and detect the concentration by analyzing the received light signals detected at regular time intervals as in the above embodiment.

  In addition, the concentration measuring apparatus 200 can be made more compact than using an optical mirror by using the FBGs 220 and 240 disposed inside the optical fiber as a reflecting portion. Moreover, since it is not necessary to provide an optical mirror at the end of the measurement cell, the shape of the measurement cell can be reduced. Since the measurement cell can be reduced in size, measurement can be suitably performed even when the amount of circulating gas is small.

[Embodiment 4]
FIG. 13 is a schematic diagram showing a schematic configuration of another embodiment of the concentration measuring apparatus. 13 includes a measurement cell unit 302, a laser light irradiation unit 104, a light receiving device 16, an analysis device 18, a control device 20, an FBG (Fiber Bragg Grating) 320, 330. Further, the concentration measuring apparatus 300 includes an optical fiber 312 and connecting optical systems 314 and 316. Here, the concentration measurement apparatus 300 is the same as the concentration measurement apparatus 200 except for the configuration of the measurement cell unit 302, the FBGs 320 and 330, the optical fiber 312, and the connection optical systems 314 and 316. is there. Description of the configuration of the concentration measuring apparatus 300 that is the same as that of the concentration measuring apparatus 300 is omitted.

  The measurement cell unit 302 constitutes a measurement area for measuring a path for guiding the flow gas G and a measurement target substance contained in the flow gas. The measurement cell unit 302 has a measurement cell 310. The measurement cell 310 is a hollow pipe, and the circulating gas G flows inside. The flowing gas G flows from one of the hollow prismatic shapes of the measurement cell 210 to the other. The measurement cell 310 has an optical fiber 312 inserted therein.

  Next, the optical fiber 312 and the connection optical systems 314 and 316 will be described. The optical fiber 312 has one end connected to the connection optical system 314 and the other end connected to the connection optical system 316. Further, part of the optical fiber 312 passes through the inside of the measurement cell 310. A part of the optical fiber 312 disposed in the measurement cell 310 becomes a fiber sensor region 340. The fiber sensor area 340 will be described later. The connection optical system 314 connects the high-speed optical shutter 110 and the optical fiber 312. The connection optical system 114 is a connector or the like, and connects two connected members in a state where laser light can pass between the two members. The connection optical system 316 connects the optical fiber 312 and the light receiving device 16. Thus, the high-speed optical shutter 110 and the light receiving device 16 are connected by the optical fiber 312 that passes through the inside of the measurement cell 310 and the connection optical systems 314 and 316.

  Here, FIG. 14 is a schematic diagram showing the optical fiber shown in FIG. 13 in an enlarged manner. The fiber sensor region 340 is in a state in which the core 314 is exposed because the clad 316 is not provided among the core 314 and the clad 316 constituting the optical fiber. In the fiber sensor region 340, the core 314 is exposed, so that part of the laser light leaks and irradiates near-field light (evanescent light). This near-field light (evanescent light) is irradiated with a constant intensity. The absorption wavelength component of the near-field light (evanescent light) is absorbed by the measurement target substance. For this reason, if there is a substance to be measured in the region irradiated with near-field light (evanescent light), the output of the laser light passing through the optical fiber 312 is attenuated. By providing the fiber sensor region 340, the concentration measuring device 300 can attenuate the output of the laser beam based on the concentration of the measurement target substance without directly entering the laser beam into the measurement cell. Thereby, it can measure similarly to the said embodiment.

  Next, FBG (Fiber Bragg Grating) 320 and 330 will be described. Here, the basic configuration of the FBGs 320 and 330 is the same as that of the FBGs 220 and 240 except that the optical fiber to be arranged is the optical fiber 312. The FBG 320 is provided closer to the high-speed optical shutter 110 than the fiber sensor region 340 of the optical fiber 312. The FBG 320 is an optical member having a function similar to that of the first reflection unit 46 and includes a plurality of high refractive index layers 322. The FBG 330 is provided closer to the light receiving device 16 than the fiber sensor region 340 of the optical fiber 312. The FBG 320 is an optical member having a function similar to that of the second reflection unit 48 and includes a plurality of high refractive index layers 332.

  As a result, the concentration measuring apparatus 300 also reciprocates while the laser beam is reflected between the FBG 320 and the FBG 330 with the fiber sensor region 340 interposed therebetween. The light traveling back and forth in the fiber sensor region 340 is gradually emitted to the outside from between the FBG 320 and the FBG 330 every time it is reflected by the FBG 320 and the FBG 330.

  By providing the fiber sensor region 340, the concentration measuring apparatus 300 can perform measurement while maintaining the state in which the laser light is guided by the optical fiber. Thereby, since the distance which a laser beam transmits in space can be shortened, the loss of a laser beam can be decreased more. Further, since the high-speed optical shutter 110 and the light receiving device 16 can be connected by a single optical fiber, the number of connecting portions between optical members can be reduced, and in this respect also, the loss of laser light can be reduced.

  Moreover, since the concentration measuring apparatus 200 can pass an optical fiber through the measurement cell, the measurement cell can have various structures. Thereby, the apparatus can be made compact. Moreover, since it can also arrange | position directly to piping through which the distribution | circulation gas G of a measuring object flows, the responsiveness of measurement can be made higher.

(Embodiment 5)
In the above embodiment, the number of the semiconductor laser oscillation devices of the laser light irradiation unit is one, but a plurality of semiconductor laser oscillation devices may be provided. FIG. 15 is a schematic diagram illustrating an example of a laser beam irradiation unit. FIG. 16 is a schematic diagram illustrating an example of the operation of the laser light irradiation unit. The laser light irradiation unit 414 shown in FIG. 15 includes a first semiconductor laser oscillation device 422a, a second semiconductor laser oscillation device 422b, a third semiconductor laser oscillation device 422c, a laser control device 424, and a first high-speed optical shutter 432a. A second high-speed optical shutter 432b, a third high-speed optical shutter 432c, and a multiplexing unit 436. The laser beam irradiation unit 414 includes optical fibers 430a, 430b, 430c, 434a, 434b, 434c, and 438 that connect the respective units.

  The first semiconductor laser oscillating device 422a, the second semiconductor laser oscillating device 422b, and the third semiconductor laser oscillating device 422c have the same configuration and function except that the wavelengths of laser beams to be output are different from each other. This is the same as the laser oscillation device 22. The laser control device 424 sends a control signal to the first semiconductor laser oscillation device 422a, the second semiconductor laser oscillation device 422b, and the third semiconductor laser oscillation device 422c, and outputs laser light whose wavelength is oscillated from each of them. .

  The first high-speed light shutter 432a, the second high-speed light shutter 432b, and the third high-speed light shutter 432c are mechanisms for switching whether or not to block the incident laser light, as with the high-speed light shutter 110. The first high-speed optical shutter 432a is connected to the first semiconductor laser oscillation device 422a through an optical fiber 430a. The first high-speed optical shutter 432a is connected to the multiplexing unit 436 through an optical fiber 434a. The second high-speed optical shutter 432b is connected to the first semiconductor laser oscillation device 422b through an optical fiber 430b. The second high-speed optical shutter 432b is connected to the multiplexing unit 436 through an optical fiber 434b. The third high-speed optical shutter 432c is connected to the third semiconductor laser oscillation device 422c through an optical fiber 430c. The third high-speed optical shutter 432c is connected to the multiplexing unit 436 through an optical fiber 434c.

  The multiplexing unit 436 is a coupler that connects the three optical fibers 434 a, 434 b, 434 c and one optical fiber 438. The multiplexing unit 436 causes the laser light incident from each of the three optical fibers 434 a, 434 b, and 434 c to enter the optical fiber 438. The optical fiber 328 is connected to the measurement cell directly or via a connection optical system.

  The laser light irradiation unit 414 is configured as described above. The control device switches ON and OFF of the first high-speed light shutter 432a, the second high-speed light shutter 432b, and the third high-speed light shutter 432c of the laser light irradiation unit 414, that is, by switching between passing and blocking of the laser light, The laser beam that passes through the multiplexing unit 436 and enters the measurement cell can be switched. For example, as shown in FIG. 16, only the laser beam output from the first semiconductor laser oscillation device 422a is passed through the first high-speed optical shutter 432a, and the concentration of the measurement target substance is measured with the laser beam. Thereafter, only the laser beam output from the second semiconductor laser oscillation device 422b is passed by the second high-speed optical shutter 432b, and the concentration of another measurement target substance is measured by the laser beam. Laser light output from the third semiconductor laser oscillation device 422c is passed by the third high-speed optical shutter 432c, and the concentration of another measurement target substance is measured by the laser light.

  Thus, the laser beam irradiation unit 414 can measure the concentrations of the three different measurement target substances contained in the flow gas by sequentially entering the laser beams having three different wavelengths. In addition, the time required for one measurement is sufficiently shorter than the time required for the flow gas to pass through the measurement cell, so that it can be considered that the same flow gas has been measured. In the above embodiment, there are three combinations of the semiconductor laser light emitting device and the high-speed shutter, but the number is not particularly limited. When the output of the laser beam can be switched on the oscillation device side, a high-speed optical shutter may be provided on the downstream side of the multiplexing unit. In addition, you may enable it to output the laser beam of the absorption wavelength of several measurement object material with one semiconductor laser oscillation apparatus.

  In the above embodiments, the concentration of the measurement target substance contained in the flow gas is measured. However, the present invention is not limited to this, and the amount of the measurement target substance can also be calculated.

10, 100, 200, 300 Concentration measuring device 12, 202, 302 Measuring cell unit 14, 104, 414 Laser light irradiation unit 16 Light receiving device 18 Analyzing device 20 Control device 22 Semiconductor laser oscillation device 24, 424 Laser control device 26 High-speed laser Intensity modulator 28 Beam stopper 112, 218, 230, 312, 430a, 430b, 430c, 434a, 434b, 434c, 438 Optical fiber 40, 210, 310 Measurement cell 42, 212 Inflow pipe 44, 214 Exhaust pipe 46 First reflection Part 48 Second reflecting part 110 High-speed optical shutter 114, 116, 232, 234, 314, 316 Connection optical system 220, 240, 320, 330 FBG
222, 242, 322, 332 High refractive index layer 314 Core 316 Clad 340 Sensor region 422a First semiconductor laser oscillation device 422b Second semiconductor laser oscillation device 422c Third semiconductor laser oscillation device 432a First high-speed optical shutter 432b Second high-speed light Shutter 432c Third high-speed optical shutter 436 Multiplexing section

Claims (12)

A substance measuring device for measuring a measurement target substance contained in a circulating gas,
A measurement cell through which the flow gas flows;
A laser light irradiation unit that switches between a state in which laser light having a wavelength modulated in a wavelength range including an absorption wavelength of the measurement target substance is incident on the measurement cell and a state in which the laser light is not incident;
A light receiving device for taking a laser beam emitted from the measurement cell;
A first reflection unit disposed between the measurement cell and the laser beam irradiation unit to reflect the laser beam;
A second reflection unit that is disposed between the measurement cell and the light receiving device and reflects laser light;
The measurement target substance contained in the flowing gas is detected based on the attenuation of the intensity of the light received by the light receiving device that has been switched from the state in which the laser light irradiation unit is incident on the measurement cell to the state in which the laser light is not incident. A substance measuring apparatus comprising: an analyzing apparatus;   The substance measuring apparatus according to claim 1, wherein the laser light irradiation unit has a modulation period of the laser light of 20 μs or less.   The substance measuring apparatus according to claim 1, wherein the laser light irradiation unit has a modulation period of the laser light of 1 μs or less.   4. The substance measuring apparatus according to claim 1, wherein the first reflecting unit and the second reflecting unit are optical mirrors having a reflectance of 99% or more. 5. A first optical member connected to the laser beam irradiation unit and the measurement cell and guiding the laser beam;
5. The substance measuring device according to claim 1, further comprising a second optical member connected to the light receiving device and the measurement cell and guiding the laser beam. A first optical fiber connected to the laser light irradiation unit and the measurement cell and guiding the laser light;
A second optical fiber that is connected to the laser light irradiation unit and the measurement cell and guides the laser light;
The first reflecting part is a fiber Bragg grating composed of a plurality of high refractive index layers arranged in the first optical fiber,
4. The substance according to claim 1, wherein the second reflecting portion is a fiber Bragg grating including a plurality of high refractive index layers arranged in the second optical fiber. 5. Measuring device. A third optical fiber having one end connected to the first optical fiber, the other end connected to the second optical fiber, and inserted into the measurement cell;
The material measuring apparatus according to claim 6, wherein the third optical fiber includes a region where a core is exposed in a part of the measurement cell.   The substance measuring apparatus according to claim 7, wherein the first optical fiber, the second optical fiber, and the third optical fiber are one optical fiber having no connection portion.   9. The laser light irradiation unit is provided on a passage path of the laser light, and includes a shutter that switches between a state of entering and not entering the measurement cell by opening and closing. The substance measuring device according to any one of the above.   The said laser beam irradiation unit is provided with the mechanism in which the emission direction of the said laser beam is switched, and the state which makes it enter into the said measurement cell and the state which does not enter are provided. The substance measuring apparatus described.   11. The substance measuring apparatus according to claim 1, wherein the analysis apparatus detects a concentration of the measurement target substance contained in the flow gas. A laser beam is incident from one end of a measurement cell in which reflection portions are arranged at both ends and the flow gas flows, and the laser beam emitted from the other end of the measurement cell is detected and included in the flow gas A substance measurement method for measuring a measurement target substance,
Flowing the flow gas through the measurement cell;
Injecting from the one end of the measurement cell a laser beam whose wavelength is modulated in a wavelength range including the absorption wavelength of the measurement target substance;
Stopping the incidence of the laser beam on the measurement cell;
A light receiving step for receiving the laser light output from the other end of the measurement cell;
A detection step of detecting the measurement target substance contained in the flow gas based on attenuation of the intensity of light received after switching from a state in which laser light is incident on the measurement cell to a state in which it is not incident. Substance measurement method.

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