Classifications

• • 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
  • G01N21/59—Transmissivity
• • 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
  • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
  • G01N21/274—Calibration, base line adjustment, drift correction
• • 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
  • G01N21/85—Investigating moving fluids or granular solids
  • G01N21/8507—Probe photometers, i.e. with optical measuring part dipped into fluid sample

Definitions

• the present invention relates to an optical probe for measuring absorption at several wavelengths.
• the field of the invention is that of optical absorption spectrometry analysis of a fluid, gas or liquid medium.
• Such an analysis is performed by means of an optical probe which comprises an analysis cell provided with a transmission module and a detection module.
• the transmission module comprises a light source arranged behind a diffusion window on the body of this transmission module.
• a filter is arranged between the source and the window (monochromatic or quasi-monochromatic analysis).
• the detection module comprises a detector disposed behind a window on the body of this detection module.
• a filter is arranged between the window and the detector.
• the medium to be analyzed is between the transmission module and the detection module.
• the analysis is carried out in two stages.
• the calibration consists of carrying out an absorption measurement on a reference medium.
• the measurement itself consists of performing the same operation on the critical medium to be analyzed. The absorption of the critical medium is weighted by that of the reference medium.
• document FR 2 939 894 proposes an optical absorption measurement probe which comprises a first cell or analysis cell, this first cell comprising a transmission module and a detection module capable of producing a detection signal.
• This optical probe also comprises a second cell or monitoring cell capable of producing a monitoring signal, this monitoring cell being arranged on the optical path connecting the transmission module to the detection module.
• the present invention thus relates to an optical probe which makes it possible to measure the absorption at several wavelengths by means of two cells.
• an optical probe comprises:
• a first cell which comprises a first transmission module and a first detection module able to produce a first detection signal
• a second cell which comprises a second detection module able to produce a first monitoring signal of the first transmission module
• control circuit for producing a first measurement signal by weighting the first detection signal by means of the first monitoring signal
• the second cell comprising a second transmission module
• the second detection module is able to produce a second detection signal
• the first detection module is able to produce a second monitoring signal of the second transmission module .
• the cells are each in the form of a sealed body having an active face.
• the cells are each arranged behind a window on its active face.
• each detection module is placed behind a partially reflecting plate which adjoins the corresponding porthole.
• the detectors are identical.
• the active faces of these cells are vis-à-vis.
• the first measurement signal Qm is the ratio of the detection signal to the monitoring signal.
• the control circuit having in memory the following values:
• this control circuit produces an absorption value Am derived from the following expression:
• control circuit is provided with a temperature compensation.
• the temperature compensation is carried out by means of two constants K1, K2, a calibration temperature ⁇ and the temperature ⁇ at which the measurement is made from the following expression:
• one of the emission modules comprises two sources illuminating the detection module which faces it by means of a partially reflecting plate.
• FIG. 1 a perspective view of an optical absorption measurement probe
• FIG. 2 a sectional diagram of the mechanical assembly of this optical probe, in particular:
• FIG. 3 a schematic diagram of the electrical assembly of this optical probe
• the optical probe is presented as two distinct elements, the first cell C1 and the second cell C2.
• these two cells are each a cylindrical body. They are connected by a connecting means which here takes the form of an upper spar L1 and a lower spar L2. The connection is thus made that the two cylindrical bodies are coaxial.
• the faces opposite these two bodies are henceforth denominated active faces. Naturally, the medium to be analyzed is between these two active faces.
• the first cell C1 essentially comprises a first LED1 transmission module, for example a light-emitting diode, and a first detection module D1.
• first two modules LED1, D1 are arranged behind a first window H1 which materializes the active face of the first cell C1. Depending on the nature of this source, it may be necessary to provide a bandpass filter between it and the H1 porthole. If the emission module is a light-emitting diode that has a relatively narrow emission spectrum, the filter is not always essential.
• the first detection module comprises a first detector D1 which is arranged behind this first port H1 in the vicinity of the first transmission module LED1.
• a first partially reflective plate PR1 is interposed between the first window H1 and the first detector D1. This plate can also be integrated into the porthole.
• the second cell C2 comprises a second LED2 transmission module and a second detection module D2.
• These two second modules LED2, D2 are arranged behind a second window H2 which materializes the active face of the second cell C2.
• the second detection module comprises a second detector D2 which is arranged behind this second window H2 in the vicinity of the second emission module LED2.
• a second partially reflective plate PR2 is interposed between the second window H2 and the second detector D2.
• cells C1, C2 are of course sealed. They are each provided with a wall on the opposite side to its active face.
• the term porthole must be understood in its broadest sense, that is to say transparent surface.
• the second detector D2 is identical to the first D1.
• the two portholes H1, H2 are of the same nature.
• the mechanical arrangement of the probe is thus made that the light beam from the first emission module LED1 successively passes through the first window H1, the medium to be analyzed and the second window H2. This beam then reaches the second partially reflective plate PR2 on which it is partly transmitted to the second detector D2 and partly reflected towards the first porthole H1 to finally cross the first partially reflective plate PR1 and reach the first detector D1.
• the light beam from the second emission module LED2 successively passes through the second porthole H2, the medium to be analyzed and then the first porthole H1.
• This beam then reaches the first partially reflecting plate PR1 on which it is partly transmitted to the first detector D1 and partly reflected to the second window H2 to finally cross the second partially reflective plate PR2 and reach the second detector D2.
• the portholes H1, H2 are substantially perpendicular to the axis of the probe.
• the configuration making it possible to illuminate the two detectors D1, D2 each with the two emission modules LED1, LED2 is obtained by arranging the detectors parallel to the axis of the probe and by inclining the emission modules with respect to this axis. .
• the second detector D2 is interposed on the optical path that connects the first LED1 emission module to the first detector D1.
• the first detector D1 is interposed on the optical path which connects the second emission module LED2 to the second detector D2.
• the control circuit CC receives:
• the absorption coefficient more particularly Ar this coefficient in the reference medium (stored by the control circuit CC) and Am this coefficient in the medium to be analyzed
• the attenuation coefficients reflect the fact that the detectors do not receive all the luminous flux emitted in their directions. They depend on geometrical considerations and are therefore independent of the absorption coefficients which in turn depend on the physicochemical properties of the medium analyzed.
• the intensity received by the second detector is:
• the intensity received by the first detector is:
• the second port H2 is designed so that these two intensities 12, M are of the same order of magnitude.
• the partial reflection of this porthole can be obtained in various ways, in particular by:
• the measurement Q is thus defined as the ratio of the intensity received by the first detector D1 to that received by the second detector D2:
• This reference measurement is also stored by the control circuit CC.
• control circuit thus produces the desired absorption coefficient
• ⁇ . ( ⁇ ) ⁇ 1 ( ⁇ ) / ⁇ 2 ( ⁇ )
• the calibration is then performed in a reference medium whose absorption is known at the calibration temperature ⁇ :
• a first solution is to activate sequentially these transmission modules.
• a second solution consists in modulating these emission modules according to two different frequencies.
• the detectors, each tuned to one of these frequencies, are then used in synchronous detection, a technique well known to those skilled in the art.
• the detectors are centered on two distinct lengths.
• the invention is also applicable if they have the same spectral response, which provides redundancy.
• the required geometrical configuration is obtained by tilting the windows H1, H2 with respect to the axis of the probe and by arranging the two detectors D1, D2 and the two modules of FIG. emission LED1, LED2 parallel to this axis.
• the description made with reference to FIG. 2a applies without modification.
• the first cell C1 is arranged as in the second option described with reference to Figure 2b.
• the second cell C2 further comprises a second detection module D2 identical to that described above but the second transmission module is now different.
• the second transmission module is now composed of a first SEa and a second SEb light source which illuminates a semireflecting plate SR.
• the geometry of the assembly is thus made that the beam coming from the first source SEa crosses the semi-reflecting plate SR to reach the first detector D1 and that the beam coming from the second source SEb is reflected by this plate SR always intended for the first D1 detector.
• the two light sources are centered on two distinct wavelengths. The invention also applies if they emit the same spectrum, which makes it possible to overcome a failure of one of the sources.
• the optical probe according to the present invention performs an absorption measurement by comparing the optical properties of a critical medium with that of a reference medium.
• the calibration is carried out once and for all before the commissioning of this probe because the monitoring cell makes it possible to overcome the various drifts mentioned above in the introduction. It may be occasionally repeated from time to time, if only for security reasons.
• a further advantage of the present invention is that the two cells may be identical. It follows that the number of subsets of the probe is very small, which is favorable for manufacturing.

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• Engineering & Computer Science (AREA)
• Mathematical Physics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Theoretical Computer Science (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)

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• 2010
  • 2010-07-19 FR FR1003015A patent/FR2962805B1/fr not_active Expired - Fee Related
• 2011
  • 2011-07-18 JP JP2013520175A patent/JP2013534638A/ja active Pending
  • 2011-07-18 EP EP11757354.3A patent/EP2596333A1/fr not_active Withdrawn
  • 2011-07-18 CA CA2805205A patent/CA2805205C/fr not_active Expired - Fee Related
  • 2011-07-18 WO PCT/FR2011/000420 patent/WO2012010748A1/fr active Application Filing
  • 2011-07-18 CN CN2011800429933A patent/CN103080728A/zh active Pending
  • 2011-07-18 US US13/811,106 patent/US20130194576A1/en not_active Abandoned

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