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WO2017029792A1 - 濃度測定装置 - Google Patents

濃度測定装置 Download PDF

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Publication number
WO2017029792A1
WO2017029792A1 PCT/JP2016/003669 JP2016003669W WO2017029792A1 WO 2017029792 A1 WO2017029792 A1 WO 2017029792A1 JP 2016003669 W JP2016003669 W JP 2016003669W WO 2017029792 A1 WO2017029792 A1 WO 2017029792A1
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WIPO (PCT)
Prior art keywords
light
reflected light
concentration measuring
detection signal
incident
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP2016/003669
Other languages
English (en)
French (fr)
Inventor
出口　祥啓
正明 永瀬
山路　道雄
池田　信一
西野　功二
将慈 河嶋
一輝 田中
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fujikin Inc
University of Tokushima NUC
Original Assignee
Fujikin Inc
University of Tokushima NUC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fujikin Inc, University of Tokushima NUC filed Critical Fujikin Inc
Priority to US15/748,264 priority Critical patent/US10976240B2/en
Priority to JP2017535234A priority patent/JP6811966B2/ja
Priority to KR1020177032581A priority patent/KR102082172B1/ko
Priority to CN201680025238.7A priority patent/CN107923841B/zh
Publication of WO2017029792A1 publication Critical patent/WO2017029792A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/3103—Atomic absorption analysis
    • G—PHYSICS
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
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    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G01J3/0218—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using optical fibers
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    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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    • G—PHYSICS
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    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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    • G01N21/59—Transmissivity
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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    • G—PHYSICS
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G—PHYSICS
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    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
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    • G01J2003/102—Plural sources
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G01N2021/155—Monitoring cleanness of window, lens, or other parts
    • G01N2021/157—Monitoring by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N2021/3129—Determining multicomponents by multiwavelength light
    • G01N2021/3133—Determining multicomponents by multiwavelength light with selection of wavelengths before the sample
    • G—PHYSICS
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N2021/3148—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths using three or more wavelengths
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N2021/558—Measuring reflectivity and transmission
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G—PHYSICS
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    • G01N2201/062—LED's
    • G01N2201/0627—Use of several LED's for spectral resolution
    • G—PHYSICS
    • G01—MEASURING; TESTING
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    • G01N2201/08—Optical fibres; light guides
    • G—PHYSICS
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    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/12—Circuits of general importance; Signal processing
    • G01N2201/121—Correction signals
    • G01N2201/1211—Correction signals for temperature

Definitions

  • the present invention relates to a concentration measuring device for measuring a gas concentration based on the principle of absorptiometry.
  • a purge gas is supplied to the optical system, and active oxygen is generated for the purge gas, so that the stain containing organic substances as a main component is decomposed before adhering to the optical system or decomposed and removed even after the adhering dirt.
  • a gas concentration measuring device that can do this has been proposed (Patent Document 1, etc.).
  • the equipment for supplying the purge gas is expensive, and the equipment for generating active oxygen incurs further high cost.
  • deposits that cannot be removed using purge gas or active oxygen it is more efficient to replace the light incident window or measurement cell when deposits adhere to the light incident window. .
  • the above conventional technique cannot cope with a measurement error due to deterioration of the light source.
  • the present invention mainly provides a concentration measuring device that can detect that deposits have adhered to the light incident window, and also provides a concentration measuring device that can accurately measure the concentration without flowing purge gas or the like. Objective.
  • the light to be measured in the measurement cell is detected by detecting the transmitted light that has passed through the measurement cell in which the light incident window and the light exit window are opposed to each other.
  • a density measuring device for measuring density comprising a reflected light detector for detecting reflected light from the light incident window.
  • the second aspect of the present invention further includes a notifying unit for notifying that a detection signal of the reflected light detected by the reflected light detector has deviated from a predetermined range in the first aspect.
  • a third aspect of the present invention further includes a calculation unit for correcting the detection signal of the transmitted light using the detection signal of the reflected light by the reflected light detector in the first aspect.
  • the optical system further includes an incident optical fiber that guides light incident on the light incident window from a light source, and the reflected light detector receives the reflected light.
  • a reflection measuring optical fiber for guiding light is provided.
  • an end of the incident optical fiber on the side of the light incident window and an end of the light receiving side of the optical fiber for reflection measurement are disposed adjacent to each other.
  • a plurality of light sources each emitting light of different wavelengths and at least one combination of light of different wavelengths emitted by the plurality of light sources.
  • a wave combiner and the combined light combined by the combiner is incident on the light incident window.
  • an oscillation circuit device that causes drive currents of different frequencies to flow through the plurality of light sources is further provided.
  • the seventh aspect further includes a calculation unit that performs frequency analysis on the detection signal of the transmitted light detector using fast Fourier transform.
  • the ninth aspect further includes a calculation unit that performs frequency analysis on the detection signal of the reflected light detector using fast Fourier transform.
  • the light source of light incident on the incident window includes a light source that emits ultraviolet light.
  • the calculation unit calculates an intensity change of the reflected light for each different wavelength from a detection signal of the reflected light detector.
  • the type of surface deposit on the light incident window is determined based on an intensity change of the reflected light for each wavelength.
  • a thirteenth aspect of the present invention is the ratio of the intensity of the transmitted light and the intensity of the reflected light from the detection signal of the transmitted light detector and the detection signal of the reflected light detector in the first aspect.
  • the calculation unit outputs that the rate of change in the ratio between the intensity of the transmitted light and the intensity of the reflected light has deviated from a predetermined range.
  • the surface deposit can be detected by detecting the reflected light reflected by the surface deposit inside the measurement cell by detecting the reflected light from the light incident window.
  • the measurement error caused by the surface deposit can be compensated.
  • the ratio between the intensity of the transmitted light and the intensity of the reflected light is calculated, it is possible to determine whether the measurement error is due to deterioration of the light source or due to the adhered matter by the change in the ratio. .
  • FIG. 5 is a spectrum diagram showing an amplitude spectrum after frequency analysis of the waveform data of FIG. 4 by fast Fourier transform.
  • a light entrance window 3 and a light exit window 5 are arranged so as to face each other, and a measurement cell 4 having an inflow port 4 a and an outflow port 4 b for a fluid to be measured is entered into the measurement cell 4 through the light incidence window 3.
  • Light sources 12 to 15 that generate incident light L, transmitted light detector 6 that detects transmitted light that has passed through measurement cell 4, and reflected light detector that detects reflected light LR from the inside of the measurement cell of light incident window 3 7 and a calculation unit 8a that calculates the concentration of the fluid to be measured based on the detection signal of the transmitted light detector 6.
  • the light entrance window 3 and the light exit window 5 are preferably made of sapphire glass that is resistant to ultraviolet light and is mechanically and chemically stable, but other stable materials such as quartz glass are used. It can also be used.
  • the incident light L is guided from the light sources 12 to 15 by the incident optical fiber 2, passes through the light incident window 3, and enters the measurement cell 4.
  • the incident light L is light obtained by combining light having a plurality of wavelengths in the ultraviolet region by WDM (wavelength division multiplexing) multiplexers 17, 18, and 19.
  • LEDs are used as the light sources 12 to 15.
  • the light sources 12 to 15 are supplied with drive currents having different frequencies by the oscillation circuit device 20. Since the transmitted light detector 6 and the reflected light detector 7 cannot detect the difference in wavelength, the transmitted light detector 6 and the reflected light detector 7 are caused to flow by supplying drive currents having different frequencies to the light sources 12 to 15, respectively.
  • the LEDs 12 to 15 having different wavelengths can be distinguished from the detected detection signal.
  • the light wavelength of the light source 12 is 365 nm
  • the light wavelength of the light source 13 is 310 nm
  • the light wavelength of the light source 14 is 280 nm
  • the light wavelength of the light source 15 is 255 nm
  • the frequency of the drive current of the light source 12 is The frequency of the driving current of the light source 13 is 192 Hz
  • the frequency of the driving current of the light source 14 is 168 Hz
  • the frequency of the driving current of the light source 15 is 144 Hz.
  • FIG. 3 shows the waveforms of the light sources 12-15.
  • the combiner 17 combines the light of the light source 12 and the light of the light source 13 into a combined light A, and the combiner 18 combines the combined light A with the light of the light source 14 into a combined light B. 19 multiplexes the light from the light source 15 with the combined light B to obtain combined light C. Therefore, the combined light C includes four different wavelengths.
  • FIG. 4 shows the waveform of the combined light C detected by the photodiode.
  • Incident light L composed of the combined light C is guided through the incident optical fiber 2, passes through the light incident window 3, and enters the measurement cell 4.
  • a light emitting element other than the LED for example, an LD (laser diode) may be used.
  • the incident light L guided by the incident optical fiber 2 is converted into parallel light by the collimating lens 21 (FIG. 2), passes through the light incident window 3, and enters the measurement cell 4.
  • the reflected light detector 7 includes a reflection measurement optical fiber 7 a that receives and guides the reflected light LR reflected by the light incident window 3.
  • the reflected light detector 7 uses an optical sensor such as a photodiode or a phototransistor as a light receiving element.
  • the reflected light detector 7 outputs a voltage proportional to the irradiation amount to the control calculation unit 8 through the electric wiring 22.
  • the end 2a of the incident optical fiber 2 on the light incident window 3 side and the light receiving side end 7a1 of the reflection measuring optical fiber 7a are disposed adjacent to each other, and the reflected light LR. Is efficiently received.
  • one incident optical fiber 2 is shown in the illustrated example, it may be two or more.
  • the transmitted light detector 6 uses a light sensor such as a photodiode or a phototransistor as a light receiving element.
  • the transmitted light detector 6 outputs a voltage proportional to the transmitted light to the control calculation unit 8 when the transmitted light L that has passed through the measurement cell 4 is irradiated.
  • the light receiving element of the transmitted light detector 6 is installed in the measurement cell 4, but in order to avoid the influence of heat transmitted from the gas in the measurement cell 4 to the transmitted light detector 6,
  • the calculation unit 8a of the control calculation unit 8 calculates the concentration of the fluid to be measured from the detection signal of the transmitted light detected by the transmitted light detector 6 based on the absorptiometry.
  • the control calculation unit 8 displays the calculated density on the display unit 9 such as a liquid crystal panel.
  • the transmitted light detector 6 detects the transmitted light after the incident light L combined with a plurality of frequencies passes through the measurement cell 4.
  • a detection signal of the transmitted light detected by the transmitted light detector 6 is A / D converted and transmitted as a digital signal to the arithmetic unit 8a.
  • the arithmetic unit 8a performs frequency analysis by fast Fourier transform, and the amplitude of each frequency component. Converted to a spectrum.
  • FIG. 5 is a spectrum diagram showing an amplitude spectrum after frequency analysis by fast Fourier transform. In FIG. 5, the frequency on the horizontal axis indicates the frequency of the drive current, and the amplitude on the vertical axis indicates the intensity.
  • FIG. 5 is a spectrum diagram showing an amplitude spectrum after frequency analysis by fast Fourier transform. In FIG. 5, the frequency on the horizontal axis indicates the frequency of the drive current, and the amplitude on the vertical axis indicates the intensity.
  • non-absorbing state a state in which there is no light absorption such as a state in which a fluid to be measured having absorption characteristics is not flowing or a state in which nitrogen gas without light absorption is flowing (hereinafter referred to as “non-absorbing state”).
  • non-absorbing state a state in which nitrogen gas without light absorption is flowing
  • I 0 is the intensity of incident light incident on the measurement cell
  • I is the intensity of transmitted light that has passed through the measurement cell
  • ⁇ is the molar extinction coefficient (m 2 / mol)
  • L is the optical path length (m) of the measurement cell
  • C is the concentration (mol / m 3 ).
  • the molar extinction coefficient ⁇ is a coefficient determined by the substance.
  • (I 0 / I) in the above formula (1) is expressed by the amplitude peak value (P 0 ) in the non-absorbing state of the amplitude spectrum shown in FIG. ) change between (with P 0 / P) and regarded, it is possible to determine the absorbance a lambda. If the absorbance A lambda is obtained, it is possible to determine the concentration C of the fluid to be measured from the above equation (1).
  • the peak value (P 0 ) of the amplitude in the non-absorbing state of the amplitude spectrum can be stored in advance in a memory or the like in the control calculation unit 8 for each frequency of the drive current.
  • the detection signal of the reflected light LR of the reflected light LR of the combined light is also A / D converted and transmitted as a digital signal to the arithmetic unit 8a, and the frequency is analyzed by fast Fourier transform in the arithmetic unit 8a. It is converted into an amplitude spectrum of frequency components.
  • the initial value (S 0 ) of the amplitude peak value of the amplitude spectrum is recorded in a memory or the like in the control calculation unit 8 for each frequency, and is used for density correction or the like described later.
  • a notification unit 23 When the detection signal of the reflected light LR detected by the reflected light detector 7 deviates from a predetermined range, a notification unit 23 is provided to notify it.
  • the predetermined range can be determined in advance by experiments or the like.
  • the notification unit 23 notifies when the output voltage of the reflected light detector 7 is out of the predetermined range.
  • the notification unit 23 can be, for example, an alarm generator that generates an alarm. Or the notification part 23 can also be set as the indicator which displays a warning.
  • the calculation unit 8a performs calculation processing for correcting the detection signal of the transmitted light detector 6 using the detection signal of the reflected light LR by the reflected light detector 7, and reduces the transmitted light due to the reflected light LR. The amount can be corrected.
  • the rate of change (S / S 0 ) between the peak value (S) at the time of concentration measurement of the amplitude spectrum of the reflected light LR and the above-described initial value (S 0 ), and the amplitude spectrum of the transmitted light rate of change of the peak value of the initial value and the measured density values (P / P 0) is obtained in advance by experiment and the like and, by using the relationship between the rate of change (S / S 0), the rate of change (P / P 0 ) can be corrected.
  • the corrected (P / P 0 ) is obtained.
  • correction can be made for each of the four wavelengths. Since the absorption spectrum differs depending on the type of gas, it is possible to measure the concentration with higher accuracy by combining the wavelength with absorption and the wavelength without absorption. Depending on the type of gas to be measured, correction is not performed for all wavelengths, but only necessary wavelengths among a plurality of wavelengths, for example, only two types of four wavelengths can be corrected.
  • a temperature detector can be installed at an appropriate location, and the output value (concentration measurement value) can be corrected by the measured temperature.
  • the concentration measuring apparatus having the above-described configuration can detect the reflected light LR reflected by the surface deposit inside the measurement cell of the light incident window 3, the transmitted light from the light incident window 3 caused by the surface deposit is detected. Can be detected.
  • the reflected light detector 7 informs that the detection signal of the reflected light LR has deviated from a predetermined range by an alarm or a warning by a liquid crystal display or the like, thereby knowing the maintenance time such as replacement of the light incident window 3. Can do.
  • the transmitted light accompanying the reflected light LR is based on the detected value of the reflected light LR by the reflected light detector 7. By correcting the amount of decrease, it is possible to compensate for the measurement error caused by the surface deposit on the light incident window 3.
  • the surface deposit on the light incident window 3 changes in characteristics depending on the type thereof, for example, can be decomposed and removed by heating the measurement cell 4, or needs to be replaced completely after being fixed completely. There are things. Since the surface deposit has different characteristics depending on the type, the wavelength dependency of the light to be absorbed varies depending on the type. The wavelength dependence depending on the kind of the surface deposit can be previously made into a database by experiments or the like. By monitoring the intensity change of the reflected light LR for each of a plurality of different wavelengths, the type of the surface deposit can be determined. If the type of the surface deposit can be determined, a display such as “heating of the measurement cell” or “replacement of the light incident window” can be displayed on the display unit 9 according to the type. As described above, the detection signal detected by the reflected light detector 7 is converted into an amplitude spectrum as shown in FIG. 5, and the change in amplitude at each frequency is changed to the intensity change of the reflected light having a different wavelength. Can be seen.
  • the calculation unit 8a uses the detection signal of the transmitted light detector 6 and the detection signal of the reflected light detector 7 to determine the intensity (I 1 ) of the transmitted light that has passed through the measurement cell 4, and The ratio (I 1 / I 2 ) with the intensity (I 2 ) of the reflected light LR from the light incident window 3 is calculated.
  • the ratio (I 1 / I 2 ) By monitoring the ratio (I 1 / I 2 ), it is possible to determine the presence or absence of surface deposits on the light incident window 3. For example, when the intensity of the reflected light LR is reduced, it may be due to surface deposits on the light incident window 3 or due to deterioration over time of the light sources 12-15. When the light source deteriorates with time, it is considered that the ratio of the intensity of the transmitted light and the intensity of the reflected light does not change. However, when surface deposits on the light incident window 3 occur, the ratio between the intensity of the transmitted light and the intensity of the reflected light is considered to change. Therefore, by looking at the change in the ratio (I 1 / I 2 ), it is possible to determine the presence or absence of surface deposits in distinction from the deterioration of the light source.
  • the computing unit 8a monitors the ratio between the intensity of the transmitted light and the intensity of the reflected light, determines whether or not the ratio (I 1 / I 2 ) changes within a predetermined range, and determines the predetermined range. When deviating, an error signal can be output. The error signal can be displayed on the display unit 9. The error signal may prompt the replacement of the light incident window 3.
  • the light used for the measurement can be light in a wavelength region other than the ultraviolet region.
  • the light source can be light in a wavelength region other than the ultraviolet region.
  • combined light having a plurality of different frequencies is used as the light source, but a light source having a single wavelength can also be used.
  • the reflected light detector 7 can be provided with a photodiode in the vicinity of the light incident window 3 and the optical fiber can be omitted.

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Abstract

光入射窓と光出射窓とが対向配置された測定セルを通過する透過光を検出することにより前記測定セル内の被測定流体の濃度を測定するための濃度測定装置であって、前記光入射窓の反射光を検出する反射光検出器を備える。

Description

濃度測定装置
　本発明は、吸光光度法の原理に基づいてガス濃度を測定するための濃度測定装置に関する。
　従来、この種の濃度測定装置では、被測定流体が供給される測定セルの光入射窓に光源から所定波長の光を入射し、測定セル内を通過した透過光を受光素子で受光することにより吸光度を測定し、吸光度から濃度を求めている。
　しかしながら、この種の濃度測定装置では、光入射窓への被測定流体由来の付着物、或いは、光源の劣化等により、測定誤差を生じる。
　そのため、例えば、光学系にパージガスを供給するとともに、前記パージガスに対して活性酸素を発生させて、有機物を主成分とする汚れを光学系に付着前に分解し又は汚れが付着した後も分解除去することができるガス濃度測定装置が提案されている（特許文献１等）。
特開２０１３－１１７４１８号公報
　しかしながら、パージガスを供給する設備はコスト高となるし、加えて活性酸素を発生させる設備は更なるコスト高を招く。また、堆積物が付着する前からパージガスを流し続けることもコスト面から好ましくない。さらに、パージガスや活性酸素を用いても除去できないような堆積物もある等、場合によっては、光入射窓に堆積物が付着した場合には光入射窓或いは測定セルを交換した方が効率が良い。また、上記従来技術では、光源の劣化による測定誤差には対応できない。
　そこで本発明は、光入射窓に堆積物が付着したことを検知し得る濃度測定装置を提供し、併せてパージガス等を流さずとも濃度を精度よく測定し得る濃度測定装置を提供することを主たる目的とする。
　上記目的を達成するため、本発明の第１の態様は、光入射窓と光出射窓とが対向配置された測定セルを通過した透過光を検出することにより前記測定セル内の被測定流体の濃度を測定するための濃度測定装置であって、前記光入射窓の反射光を検出する反射光検出器を備える。
　本発明の第２の態様は、前記第１の態様において、前記反射光検出器により検出された前記反射光の検出信号が所定範囲を逸脱したことを知らせる通知部を更に備える。
　本発明の第３の態様は、前記第１の態様において、前記反射光検出器による前記反射光の検出信号を用いて、前記透過光の検出信号を補正する演算部を更に備える。
　本発明の第４の態様は、前記第１の態様において、前記光入射窓に入射させる光を光源から導光する入射用光ファイバーを更に備え、前記反射光検出器が、前記反射光を受光し導光する反射測定用光ファイバーを備える。
　本発明の第５の態様は、前記第４の態様において、前記入射用光ファイバーの前記光入射窓の側の端部と前記反射測定用光ファイバーの受光側端部とが隣接して配設される。
　本発明の第６の態様は、前記第１の態様において、其々が異なる波長の光を発する複数の光源と、前記複数の光源が発する異なる複数の波長の光を合波する少なくとも一つの合波器と、が更に備えられ、前記合波器により合波された合波光が前記光入射窓に入射される。
　本発明の第７の態様は、前記第６の態様において、前記複数の光源の其々に異なる周波数の駆動電流を流す発振回路装置が更に備えられる。
　本発明の第８の態様は、前記第７の態様において、前記透過光検出器の検出信号を高速フーリエ変換を用いて周波数解析する演算部を更に備える。
　本発明の第９の態様は、前記第７の態様において、前記反射光検出器の検出信号を高速フーリエ変換を用いて周波数解析する演算部を更に備える。
　本発明の第１０の態様は、前記第１の態様において、前記入射窓に入射する光の光源が、紫外光を発光する光源を含む。
　本発明の第１１の態様は、前記第９の態様において、前記演算部が、前記反射光検出器の検出信号から、異なる波長毎の前記反射光の強度変化を演算する。
　本発明の第１２の態様は、前記第１１の態様において、各波長毎の前記反射光の強度変化に基づいて光入射窓の表面付着物の種類を判定する。
　本発明の第１３の態様は、前記第１の態様において、前記透過光検出器の検出信号と前記反射光検出器の検出信号とから、前記透過光の強度と前記反射光の強度との比率を演算する演算部を更に備える。
　本発明の第１４の態様は、前記第１３の態様において、前記演算部が、前記透過光の強度と前記反射光の強度との比率の変化割合が所定範囲を逸脱したことを出力する。
　本発明によれば、光入射窓の前記反射光を検出することにより、測定セル内側の表面付着物により反射された前記反射光を検出することで、前記表面付着物を検出することができる。
　また、前記反射光の検出信号が所定範囲を逸脱したことを通知することで、メンテナンス時期を知ることができる。
　さらに、前記反射光検出器による前記反射光の検出信号を用いて、前記反射光に伴う前記透過光の減少量を補正することにより、前記表面付着物に起因する測定誤差を補うことができる。
　さらに、前記透過光の強度と前記反射光の強度との比率を演算すれば、その比率の変化によって測定誤差が光源の劣化に依るものか付着物に依るものかを判別することも可能となる。
本発明に係る濃度測定装置の第１実施形態を示す部分断面図である。 図１の濃度測定装置の要部を拡大して示す断面図である。 波長の異なる複数の発光素子の其々に異なる周波数の駆動電流を流した場合に生じる光の波形を示す波形図である。 図３の異なる波長をもつ複数の波形を合波器によって合波した光の波形を示す波形図である。 図４の波形データを高速フーリエ変換により周波数解析した後の振幅スペクトルを示すスペクトル図である。
　本発明に係る濃度測定装置の一実施形態について、以下に図１～図５を参照して説明する。
　濃度測定装置１は、光入射窓３と光出射窓５とが対向配置され被測定流体の流入口４ａ及び流出口４ｂを備える測定セル４と、光入射窓３を通して測定セル４内に入射させる入射光Ｌを発生させる光源１２～１５と、測定セル４を通過した透過光を検出する透過光検出器６と、光入射窓３の測定セル内側からの反射光ＬＲを検出する反射光検出器７と、透過光検出器６の検出信号に基づいて被測定流体の濃度を演算する演算部８ａと、を備える。
　光入射窓３及び光出射窓５は、紫外光等に対しても耐性を有し、機械的・化学的に安定なサファイアガラスが好適に用いられるが、他の安定な素材、例えば石英ガラスを用いることもできる。入射光Ｌは、入射用光ファイバー２により光源１２～１５から導光され、光入射窓３を透過して、測定セル４内に入射する。
　入射光Ｌは、図示例では、紫外領域の複数の波長の光をＷＤＭ（波長分割多重方式）の合波器１７，１８，１９で合成した光である。光源１２～１５として図示例ではＬＥＤが用いられている。光源１２～１５は、発振回路装置２０により其々に異なる周波数の駆動電流が流される。透過光検出器６及び反射光検出器７が波長の違いを検知できないため、光源１２～１５の其々に異なる周波数の駆動電流を流すことにより、透過光検出器６及び反射光検出器７が検出した検出信号から、異なる波長のＬＥＤ１２～１５を区別できるようにしている。
　図示例において、光源１２の光の波長は３６５ｎｍ、光源１３の光の波長は３１０ｎｍ、光源１４の光の波長は２８０ｎｍ、光源１５の光の波長は２５５ｎｍであり、光源１２の駆動電流の周波数は２１６Ｈｚ，光源１３の駆動電流の周波数は１９２Ｈｚ、光源１４の駆動電流の周波数は１６８Ｈｚ、光源１５の駆動電流の周波数は１４４Ｈｚである。図３は、光源１２～１５の各波形を示している。
　合波器１７は光源１２の光と光源１３の光を合波して合波光Ａとし、合波器１８は合波光Ａに光源１４の光を合波して合波光Ｂとし、合波器１９は合波光Ｂに光源１５の光を合波して合波光Ｃとする。従って、合波光Ｃには、４つの異なる波長が含まれている。図４は、フォトダイオードで検出した合波光Ｃの波形を示している。
　合波光Ｃからなる入射光Ｌが、入射用光ファイバー２を通じて導光され、光入射窓３を透過し、測定セル４内に入射される。光源としては、ＬＥＤ以外の他の発光素子、例えばＬＤ（レーザーダイオード）を用いることもできる。
　入射用光ファイバー２により導光された入射光Ｌは、コリメートレンズ２１（図２）により平行光とされて、光入射窓３を透過し、測定セル４内に入る。
　反射光検出器７は、光入射窓３で反射された反射光ＬＲを受光し且つ導光する反射測定用光ファイバー７ａを備える。反射光検出器７は、受光素子として、フォトダイオード、フォトトランジスター等の光センサーが用いられる。反射光検出器７は、受光した反射光ＬＲが照射されると、照射量に比例した電圧を、電気配線２２を通じて制御演算部８に出力する。
　図２に示されているように、入射用光ファイバー２の光入射窓３の側の端部２ａと反射測定用光ファイバー７ａの受光側端部７ａ１とは、隣接して配設され、反射光ＬＲを効率よく受光するようになっている。入射用光ファイバー２は、図示例では１本示されているが、２本以上であってもよい。
　透過光検出器６は、受光素子としてフォトダイオード、フォトトランジスター等の光センサーが用いられる。透過光検出器６は、測定セル４を通過した前記透過光Ｌが照射されると前記透過光に比例した電圧を制御演算部８に出力する。
　図示例においては測定セル４に透過光検出器６の受光素子が設置されているが、測定セル４内のガスから透過光検出器６へ伝わる熱の影響を回避するため、測定セル４の前記透過光を、測定セル４の光出射窓５の外側に接続されたコリメーター及び光ファイバー（図示せず。）を介して、測定セル４から離れた位置に配置した透過光検出器６の受光素子で受光させることもできる。
　制御演算部８の演算部８ａでは、吸光光度法に基づき、透過光検出器６によって検出された前記透過光の検出信号から、被測定流体の濃度を演算する。制御演算部８は、算出された濃度を液晶パネル等の表示部９に表示する。
　透過光検出器６は、複数の周波数が合波された入射光Ｌが測定セル４を通過した後の透過光を検出する。透過光検出器６で検出された前記透過光の検出信号は、Ａ／Ｄ変換されてデジタル信号として演算部８ａに伝送され、演算部８ａで高速フーリエ変換により周波数解析され、各周波数成分の振幅スペクトルに変換される。図５は、高速フーリエ変換による周波数解析後の振幅スペクトルを表すスペクトル図である。図５において、横軸の周波数は駆動電流の周波数を示し、縦軸の振幅は強度を示している。図５は、吸光特性を持つ被測定流体を流していない状態、或いは、光の吸収の無い窒素ガスを流している状態のように、光の吸収が無い状態（以下、「無吸収状態」という。）を示している。被測定流体としての有機金属材料を測定セル４に流すと、図５のスペクトル図において吸収がある波長の周波数の振幅が減少する。
　吸収がある波長の振幅スペクトルの振幅の変化から、ランベルト・ベールの法則に基づき、吸光度Ａλを求める下記式（１）により、吸光度Ａλを算出することができる。
　Ａλ＝ｌｏｇ１０（Ｉ０／Ｉ）＝αＬＣ　・・・・（１）
　但し、Ｉ０は測定セルに入射する入射光の強度、Ｉは測定セルを通過した透過光の強度、αはモル吸光係数（ｍ２／ｍｏｌ）、Ｌは測定セルの光路長（ｍ）、Ｃは濃度（ｍｏｌ／ｍ３）である。モル吸光係数αは物質によって決まる係数である。
　即ち、上式（１）の（Ｉ０／Ｉ）を、図５に示した振幅スペクトルの無吸収状態の振幅のピーク値（Ｐ０）と振幅スペクトルの濃度測定時の振幅のピーク値（Ｐ）との変化（Ｐ０／Ｐ）と看做して、吸光度Ａλを求めることができる。吸光度Ａλが求まれば、上式（１）から被測定流体の濃度Ｃを求めることができる。
　振幅スペクトルの前記無吸収状態の振幅のピーク値（Ｐ０）は、駆動電流の周波数ごとに制御演算部８内のメモリ等に予め記憶され得る。
　合波後の光の反射光ＬＲの反射光検出器７による検出信号も、Ａ／Ｄ変換されてデジタル信号として演算部８ａに伝送され、演算部８ａで高速フーリエ変換により周波数解析されて、各周波数成分の振幅スペクトルに変換される。光入射窓３に被測定流体由来の堆積物の付着量が増加すると、振幅スペクトルの振幅が変化する。振幅スペクトルの振幅のピーク値の初期値（Ｓ０）は、周波数ごとに制御演算部８内のメモリ等に記録され、後述する濃度補正等に用いられる。
　反射光検出器７により検出された反射光ＬＲの検出信号が所定範囲から逸脱した場合に、それを知らせる通知部２３を備える。前記所定範囲は予め実験等により定めることができ、例えば、反射光検出器７の出力電圧が所定範囲から外れた場合に通知部２３が通知する。通知部２３は、例えばアラームを発するアラーム発生器とすることができる。或いは、通知部２３は、警告を表示させる表示器とすることもできる。
　反射光検出器７による反射光ＬＲの検出信号の値が変化すると、透過光検出器６の検出信号の値が減少し、測定誤差を生じる。そのため、演算部８ａは、反射光検出器７による反射光ＬＲの検出信号を用いて、透過光検出器６の検出信号に補正を加える演算処理を行い、反射光ＬＲに伴う前記透過光の減少量を補正することができる。
　補正方法としては、例えば、反射光ＬＲの振幅スペクトルの濃度測定時におけるピーク値（Ｓ）と上記した初期値（Ｓ０）との変化率（Ｓ／Ｓ０）と、前記透過光の振幅スペクトルの初期値と濃度測定値のピーク値の変化率（Ｐ／Ｐ０）との関係を予め実験等により求めておき、前記関係と変化率（Ｓ／Ｓ０）を用いて、変化率（Ｐ／Ｐ０）を補正することができる。補正された（Ｐ／Ｐ０）を用いて上記式（１）により補正された濃度が得られる。
　本実施形態では、４波長の其々について補正がなされ得る。ガスの種類により吸収スペクトルが異なるため、吸光のある波長と吸光のない波長を組合せることにより、より精度の高い濃度測定が可能となる。測定するガス種によっては、全ての波長の其々について補正するのではなく、複数波長のうちの必要な波長のみ、例えば４波長のうち２種類の波長についてのみ補正することもできる。
　また、構成機器の温度依存性及び被測定流体の温度変動があるため、適宜箇所に温度検出器を設置し、測定した温度により出力値（濃度測定値）を修正することもできる。
　上記構成を有する濃度測定装置は、光入射窓３の測定セル内側の表面付着物により反射された反射光ＬＲを検出することができるので、表面付着物に起因する光入射窓３の前記透過光の減少を検出することができる。
　また、反射光検出器７により反射光ＬＲの検出信号が所定範囲を逸脱したことを、アラームや液晶表示などによる警告等によって通知することで、光入射窓３の交換等のメンテナンス時期を知ることができる。
　さらに、光入射窓３の付着物によって透過光検出器６の検出信号の値が減少しても、反射光検出器７による反射光ＬＲの検出値に基づいて、反射光ＬＲに伴う前記透過光の減少量を補正することにより、光入射窓３の表面付着物に起因する測定誤差を補うことができる。
　光入射窓３上の表面付着物は、その種類に応じて特性が変わり、例えば、測定セル４を加熱することにより分解除去できるものや、完全に固着して光入射窓３の交換が必要なもの等がある。前記表面付着物は、その種類に応じて特性が異なるため、種類によって吸収する光の波長依存性も異なる。前記表面付着物の種類に依る波長依存性は予め実験等によりデータベース化しておくことができる。複数の異なる波長ごとに、反射光ＬＲの強度変化をモニタリングすることにより、前記表面付着物の種類を判定することができる。前記表面付着物の種類を判定できれば、その種類に応じて、“測定セルの加熱”或いは“光入射窓の交換”等の表示を表示部９に表示させることもできる。上記したように反射光検出器７で検出された検出信号は図５に示されるような振幅スペクトルに変換され、其々の周波数における振幅の変化を其々異なる波長の前記反射光の強度変化と看做すことができる。
　また、他の一態様において、演算部８ａは、透過光検出器６の検出信号と反射光検出器７の検出信号とから、測定セル４を通過した前記透過光の強度（Ｉ１）と、光入射窓３の反射光ＬＲの強度（Ｉ２）との比率（Ｉ１／Ｉ２）を演算する。
　比率（Ｉ１／Ｉ２）をモニタリングすることで、光入射窓３上の表面付着物の有無を判定することが可能となる。例えば、反射光ＬＲの強度が低下した場合、光入射窓３上の表面付着物に起因する場合と、光源１２～１５の経時劣化に起因する場合とがあり得る。光源の経時劣化が生じる場合は、前記透過光の強度と前記反射光の強度の比率は変化しないと考えられる。しかしながら、光入射窓３上の表面付着物が生じる場合は、前記透過光の強度と前記反射光の強度との比率は変化すると考えられる。従って、比率（Ｉ１／Ｉ２）の変化をみることにより、光源の劣化と区別して、表面付着物の有無を判別することができる。
　演算部８ａは、前記透過光の強度と前記反射光の強度との比率をモニタリングし、比率（Ｉ１／Ｉ２）の変化割合が所定範囲に有るか無いかを判定し、前記所定範囲を逸脱したときにエラー信号を出力することができる。エラー信号は、表示部９に表示され得る。エラー信号は、光入射窓３の交換を促すものとすることができる。
　本発明は、上記実施形態に限定解釈されるものではなく、本発明の趣旨を逸脱しない範囲において種々の変更が可能である。例えば、測定に用いられる光は、紫外領域以外の波長領域の光も利用可能である。また、上記実施形態では複数の異なる周波数の合波光を光源に用いたが、単一波長の光源を用いることもできる。また、反射光検出器７は、光入射窓３の近傍にフォトダイオードを設置して、光ファイバーを省略することも可能である。
１　濃度測定装置
２　入射用光ファイバー
３　光入射窓
４ａ　流入口
４ｂ　流出口
４　測定セル
５　光出射窓
６　透過光検出器
７　反射光検出器
７ａ　反射測定用光ファイバー
８ａ　演算部
１２～１５　光源
２０　発振回路装置
２３　通知部

Claims (14)

  1. 　光入射窓と光出射窓とが対向配置された測定セルを通過した透過光を検出することにより前記測定セル内の被測定流体の濃度を測定するための濃度測定装置であって、前記光入射窓の反射光を検出する反射光検出器を備える、前記濃度測定装置。
  2. 　前記反射光検出器により検出された前記反射光の検出信号が所定範囲を逸脱したことを知らせる通知部を更に備える、請求項１に記載の濃度測定装置。
  3. 　前記反射光検出器による前記反射光の検出信号を用いて、前記透過光の検出信号を補正する演算部を更に備える、請求項１に記載の濃度測定装置。
  4. 　前記光入射窓に入射させる光を光源から導光するための入射用光ファイバーを更に備え、
    　前記反射光検出器が、前記反射光を受光し導光する反射測定用光ファイバーを備えている、請求項１に記載の濃度測定装置。
  5. 　前記入射用光ファイバーの前記光入射窓側の端部と前記反射測定用光ファイバーの受光側端部とが隣接して配設されている、請求項４に記載の濃度測定装置。
  6. 　其々が異なる波長の光を発する複数の光源と、前記複数の光源が発する異なる複数の波長の光を合波する少なくとも一つの合波器と、を更に備え、前記合波器により合波された合波光が前記光入射窓に入射される、請求項１に記載の濃度測定装置。
  7. 　前記複数の光源の其々に異なる周波数の駆動電流を流す発振回路装置を更に備える、請求項６に記載の濃度測定装置。
  8. 　前記透過光検出器の検出信号を高速フーリエ変換を用いて周波数解析する演算部を更に備える、請求項７に記載の濃度測定装置。
  9. 　前記反射光検出器の検出信号を高速フーリエ変換を用いて周波数解析する演算部を更に備える、請求項７に記載の濃度測定装置。
  10. 　前記入射窓に入射する光の光源が紫外光を発光する光源を含む、請求項１に記載の濃度測定装置。
  11. 　前記演算部は、前記反射光検出器の検出信号から、異なる波長毎の前記反射光の強度変化を演算する、請求項９に記載の濃度測定装置。
  12. 　前記演算部は、各波長毎の前記反射光の強度変化に基づいて前記光入射窓の表面付着物の種類を判定する、請求項１１に記載の濃度測定装置。
  13. 　前記透過光検出器の検出信号と前記反射光検出器の検出信号とから、前記透過光の強度と前記反射光の強度との比率を演算する演算部を更に備える、請求項１に記載の濃度測定装置。
  14. 　前記演算部は、前記透過光の強度と前記反射光の強度との前記比率の変化割合が所定範囲を逸脱したことを出力する、請求項１３に記載の濃度測定装置。
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