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WO1980001953A1 - Agencement pour la mesure, dans un milieu compressible, de la densite locale et de sa variation dans le temps - Google Patents

Agencement pour la mesure, dans un milieu compressible, de la densite locale et de sa variation dans le temps Download PDF

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Publication number
WO1980001953A1
WO1980001953A1 PCT/EP1980/000017 EP8000017W WO8001953A1 WO 1980001953 A1 WO1980001953 A1 WO 1980001953A1 EP 8000017 W EP8000017 W EP 8000017W WO 8001953 A1 WO8001953 A1 WO 8001953A1
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WIPO (PCT)
Prior art keywords
measuring
detectors
measurement
volume
refractive index
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Ceased
Application number
PCT/EP1980/000017
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German (de)
English (en)
Inventor
B Lehmann
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Individual
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Publication of WO1980001953A1 publication Critical patent/WO1980001953A1/fr
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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
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods

Definitions

  • the invention relates to an optically and optoelectronically acting device with which it is possible to locally measure the refractive index of an optically transparent medium and its rapid changes over time and thereby to the corresponding local density or its temporal change changes, for example within the flow of a compressible fluid.
  • the invention also relates to this radiation and to media which it penetrates largely without scattering.
  • a method that has recently been used frequently for the purpose of local density measurement is methods which use the Raman solution of narrowband light. Such methods require highly sensitive equipment and experienced scientific staff and will therefore mainly be reserved for use in the laboratory.
  • the invention described here permits the local measurement of the refractive index and its rapid changes over time with the aid of a device which, if necessary, can be combined in a compact measuring unit and transported to the location of the measurement as a closed unit. Since the refractive index of a medium is in many cases directly related to its density, a corresponding refractive index measurement makes it possible to measure and track the associated local density of the medium over time.
  • the invention takes advantage of a long-known but little-used fact.
  • a locally localized real interference fringe system is used as a sectional image through an interference layer system in the intersection area of two to one another - 3 - » -
  • the distance a 0 of the interference fringes depends on the convergence angle ___ 0 of both light bundles according to the relationship
  • ⁇ is the output wavelength of the laser light that is still unaffected by changes in the refractive index
  • n is the refractive index valid for this initial or reference state, which therefore prevails before irradiation into the measuring medium.
  • the non-indicated state is the state in the region of interest of the measurement volume, which is identical to the cutting volume of the light beam, the wavelength, the refractive index n and the cutting angle prevailing there - the light beam.
  • the distance between the interference fringes changes inversely proportional to the refractive index.
  • the invention now solves the problem in that the cutting volume of the beam bundles as a measurement volume with the aid of a sufficiently long focal length image is reproduced one or more times and is finally projected through a strongly magnifying micro-optics into the istrian area, in which there is sufficient integrity-sensitive optoelectronic Detectors.
  • the focal length of the first imaging optics should be chosen at least so large that the optics themselves do not mechanically influence the measurement object, for example a flow.
  • the intermediate image enables the micro-objective to be brought up for sufficient magnification right up to the image of the measurement volume itself, without having to be introduced into the flow, which would disturb it in an intolerable form.
  • the system exists strongly
  • optoelectronic detectors are used, which are provided with a pinhole, the diameter of which is small enough to detect only a small part of the flank of an intensity strip.
  • the pinhole can be replaced by a narrow slit, which must then be aligned parallel to the strip system.
  • Two such detectors which are expediently of approximately the same sensitivity, are aligned in such a way that their distance perpendicular to the strip direction actuates approximately half of the projected strip width or an odd multiple thereof.
  • the difference between the electrical signals of these two fixing detectors becomes zero when their diaphragms select areas of the same flank height of the intensity profile of the strips. If this is not the case, the differential voltage is used to generate a lateral displacement of the projected strip system in such a way that it occupies this excellent position and the differential signal thus becomes zero. In this way, the position of a reference point of a fixed phase position in the projected strip system is fixed locally, which is a prerequisite for the further measurement.
  • the interference strip offset to be compensated for in the manner described perpendicular to the strip direction can be any interference strip offset to be compensated for in the manner described perpendicular to the strip direction.
  • the lateral offset is compensated for by one or more electro-optical cells, for example Eckels or Kerr cells, which are inserted into one or both of the incident laser light bundles in front of the measuring location and controlled by the electrical difference signal of the two fixing detectors mentioned above via an electronic control system stem can be activated electrically.
  • the refractive index changes which can thus be generated in the cell produce corresponding phase shifts of the light waves of the two coherent laser light bundles with respect to one another, as a result of which the interference fringe system in the measurement volume undergoes the necessary position correction in the measurement volume due to lateral migration, which correction occurs both in the intermediate images and in the projected strip system ⁇ occurs.
  • a further route can be followed by displacing the micro-objective used for the enlargement of the strip perpendicular to the direction of the strip to the extent that a correction of the position of the projected strip system is necessary.
  • This can be achieved by mounting the micro-objective on, for example, a piezo body, which in turn is controlled by the differential voltage of the fixing detectors.
  • this position correction receives the minimum time constant necessary for the measurement problem in order to be able to follow the greatest occurring speed of change of position, which is possible with the help of modern electronic control technology without difficulty.
  • a differential voltage is then generated with two detectors, which is related to the strip spacing.
  • these two measuring detectors one of which can also be identical to one of the fixing detectors, are arranged at a distance of approximately half a strip spacing or an odd multiple thereof.
  • the electrical difference signal generated by the measuring detectors is then proportional to the strip spacing a.
  • Aligning the detectors to about half the height of the intensity edges is not absolutely necessary, but maximizes the sensitivity of the measuring device and the approximation to a linearity between the difference signal and the strip spacing.
  • the case of half the strip spacing of the measuring detectors or the odd multiple thereof is a way of maximizing the difference signal compared to all other cases.
  • One of the measuring detectors can be arranged on one side of the pair of fixing detectors, taking into account the criteria mentioned. - B -
  • the relationship between the difference signal of the measuring detectors and the strip spacing is generally not exactly linearly proportional, the actual relationship for the direct conclusion from the difference signal to the refractive index must be taken into account. This necessity can be avoided by using the measurement signal as a control signal for a zero method.
  • a further intermediate image of the measurement volume is generated within an electro-optical cell (e.g. Pockels or Kerr cell).
  • the refractive index of the cell which can be changed by the voltage applied to this cell, is controlled by the measuring voltage via an electronic control circuit so that it adjusts itself again to zero or to a fixed reference value. Then the stripe spacing of the intermediate image within the cell is equal to that of the value predetermined by the reference value of the difference signal.
  • the activation voltage for the cell is a measure of the current refractive index or the current density of the medium in the measurement volume.
  • the refraction is also based on a reference value - 9 -
  • Fig. 1 shows two at the angle "** ⁇ * overlapping mutually coherent laser light beams 1 and 1 • which form the measurement volume 2 in its sectional area. - 10- -
  • FIG. 2 shows the common cutting area of the light beams 1 and 1 ', the measuring volume 2, in a greatly enlarged form, with the stationary interference surfaces which are parallel to one another and which appear through the vertical cut with the plane of the drawing as interference strips 3 with the distance a from one another nen.
  • the refractive index n is present in the area of the measuring volume.
  • the piezzoelectric or magnetostrictive body 12 represents a possible alternative to the electro-optical cell 11 11 *
  • control circuit 10 can, likewise activated by the control circuit 10, shift the micro-optics 6 perpendicular to the strip system in such a way that undesired lateral displacements of the strip system in the registration area 7 are corrected by making the difference signal from 9 zero.
  • Another pair of detectors 8 ′′ and 8 ′ ′′ serves to register the desired measurement signal U (t). Both detectors can also be arranged separately on each side of the fixing detectors 8 and 8 1 . Alternatively, one of the registration detectors 8 "and 8 '" can be replaced by one of the fixing detectors 8 or 8'.
  • An electronic circuit 9 ' forms the electrical difference signal of the two measuring detectors 8 "and 8"', which is proportional to the strip spacing a and thus inversely proportional to the refractive index or the density of the medium in the area of the measuring volume 2. It is converted into the measurement signal U (t) by the electronics 13.
  • FIG. 4 again shows schematically the projected interference fringe system 3 "with the sinusoidal intensity curve and the arrangement of the detectors 8, 8", 8 "and 8 '” which is in principle optimal for this purpose, of which here the parallel to the slit diaphragms 17, 17 ', 17 “and 17'” aligned with the interference fringes between the maxima 15 and the mini a 16 of the intensity curve are indicated.
  • Strip system when changing the strip spacing a ".
  • the difference in intensity between the detector positions 8" and 8 "'or the corresponding electrical difference signal is then clearly related to the strip spacing. Because of the generally small change in the strip spacing, the uniqueness of the display is normally not clear at risk.
  • the distance between the detector pairs 8 and 8 'or 8 "and 8"' covered stripes can be used to adapt the measurement conditions to the respective measurement problem within wide limits and to optimally design the sensitivity of the measurement arrangement.
  • FIG. 5 essentially shows the arrangement according to FIG. 3, but with an additional intermediate image 2 ′′ of the measurement volume with the intensity stripe system 3 ′′, which is generated within an electro-optical cell 19.
  • the optics 18 then generate the intermediate image 2 'for the subsequent projection of the strip system by the micro objective 6.
  • An additional electronic control circuit 14 is now controlled by the differential signal of the measuring detectors from the circuit 9 1 and in turn activates the cell 1. Via the refractive index which is variable by the activation voltage in the cell 19, the strip spacing in the strip system 3 '' can be influenced in such a way that it is always kept constant, which is achieved by adjusting the difference signal from 9 'to zero or a predetermined reference value.
  • the voltage V ⁇ t) taken from FIG. 14 and used to activate the cell 19 is then a measure of the deviation of the refraction ' 1 3 "
  • the zero method acting in this way enables a large temporal resolution of the refractive index changes to be measured and thus the density changes in the measurement volume, is distinguished by a high sensitivity and is independent of the non-linearities of the intensity curve on the flanks of the interference fringes used.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'agencement pour la mesure de la densite locale et de sa variation dans le temps est base sur la mesure de l'indice de refraction local et de ses variations. L'agencement est notamment utilise pour la mesure de la densite locale de milieux compressibles lorsque ces milieux eux-memes, par exemple sous la forme d'un ecoulement de gaz ou de liquide, ne doivent pas etre perturbes. L'agencement de mesure est applicable a l'examen d'ecoulements a vitesse voisine ou superieure a celle du son ou de l'ecoulement de milieux presentant des gradients de temperature ainsi qu'au domaine de l'acoustique d'ecoulement. Le probleme a resoudre a cet effet est de fournir un agencement aisement transportable et simple a manier, grace auquel il est possible de mesurer, au moyen de la mesure de l'indice de refraction correspondant, la densite locale du milieu a l'endroit ou dans le volume de mesure et de suivre son evolution dans le temps. Pour resoudre ce probleme, deux faisceaux de rayonnement laser (1, 1') coherents entre eux sont diriges de maniere a se couper dans le volume de mesure (2), de sorte que des franges d'interference (3) espacees entre elles d'une distance (a) apparaissent a cet endroit. A l'aide d'une optique (5) puissante suffisamment eloignee du volume de mesure (2), une image optique intermediaire des franges d'interference (3') est engendree et ensuite, a l'aide d'un micro-objectif (6), une image fortement agrandie d'une coupe transversale de ce volume de mesure est projetee dans une zone d'enregistrement sous la forme d'un systeme de franges d'interferences paralleles (3''). A cet endroit, des detecteurs sensibles a l'intensite par exemple des detecteurs opto-electroniques (8, 8', 8'', 8'''), sont disposes d'une maniere determinee. Par un reglage de zero du signal differentiel fourni par les detecteurs (8 et 8'), on fixe dans l'espace la valeur extreme particuliere de l'intensite des franges d'interference (3'') apparaissant entre ceux-ci et cette valeur sert ainsi de point de reference pour l'elargissement du
PCT/EP1980/000017 1979-03-14 1980-03-13 Agencement pour la mesure, dans un milieu compressible, de la densite locale et de sa variation dans le temps Ceased WO1980001953A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2910428 1979-03-14
DE19792910428 DE2910428A1 (de) 1979-03-14 1979-03-14 Vorrichtung zur messung der lokalen dichte und deren zeitliche aenderungen in kompressiblen medien

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Publication Number Publication Date
WO1980001953A1 true WO1980001953A1 (fr) 1980-09-18

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PCT/EP1980/000017 Ceased WO1980001953A1 (fr) 1979-03-14 1980-03-13 Agencement pour la mesure, dans un milieu compressible, de la densite locale et de sa variation dans le temps

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EP (1) EP0025448A1 (fr)
DE (1) DE2910428A1 (fr)
WO (1) WO1980001953A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0179522A3 (fr) * 1984-10-09 1989-04-26 Quantum Diagnostics, Ltd. Appareil et procédé pour analyser un objet par perturbation des franges d'interférence
FR2781883A1 (fr) * 1998-07-28 2000-02-04 Centre Nat Rech Scient Dispositif optique d'observation des gaz par croisement de deux faisceaux de lumiere diffusee a partir de la meme region par les non-uniformites de l'indice optique
KR101721469B1 (ko) * 2016-03-25 2017-04-10 국방과학연구소 렌즈릿어레이의 다중 하부개구 분할을 이용한 레이저매질 온도특성 측정 장치 및 방법
AT520087A4 (de) * 2017-04-19 2019-01-15 Univ Wien Tech Verfahren zur kontaktlosen Bestimmung von Strömungsparametern

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2209406C1 (ru) * 2002-10-08 2003-07-27 Атнашев Виталий Борисович Интерферометр (варианты)
US8885174B2 (en) 2009-02-24 2014-11-11 Lyncee Tec S.A. Monitoring energy and matter fluxes by use of electromagnetic radiations

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3354311A (en) * 1965-08-23 1967-11-21 Boeing Co Fringe movement detector including dual photocells
US3572882A (en) * 1969-11-28 1971-03-30 Us Air Force Variable reference phase holocamera to compensate for object motion
US3639063A (en) * 1970-03-06 1972-02-01 Boeing Co Interference fringe movement detector

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3354311A (en) * 1965-08-23 1967-11-21 Boeing Co Fringe movement detector including dual photocells
US3572882A (en) * 1969-11-28 1971-03-30 Us Air Force Variable reference phase holocamera to compensate for object motion
US3639063A (en) * 1970-03-06 1972-02-01 Boeing Co Interference fringe movement detector

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
IEEE Transactions on Aerospace and Eletronics Systems, Band AES-13, No.2, veroffenlicht im Marz 1977, New York (US) G.Smeets: "Flow diagnostics by Laser Anemometry", Seiten 82-90, siehe insbesondere seiten 83,88; figuren 3,16,18. *
Journal of Scientific Instruments, Band 43, No. 12, veroffenlicht im Dezember 1966, London (GB), L. Tanner: "The design of laser interferometers for use influidmechanics", Seiten 878-886, siehe insbesondere Seiten 883-884. *
Optics and Laser Technology, Band 3, No. 4, veroffenlicht im November 1971, IPC Business Press in Heywards Heath (GB), M.Rudd: "The laser anemometer-a review", Seiten 200-207, siehe insbesondere Seiten 201,203. *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0179522A3 (fr) * 1984-10-09 1989-04-26 Quantum Diagnostics, Ltd. Appareil et procédé pour analyser un objet par perturbation des franges d'interférence
FR2781883A1 (fr) * 1998-07-28 2000-02-04 Centre Nat Rech Scient Dispositif optique d'observation des gaz par croisement de deux faisceaux de lumiere diffusee a partir de la meme region par les non-uniformites de l'indice optique
WO2000006995A1 (fr) * 1998-07-28 2000-02-10 Centre National De La Recherche Scientifique (Cnrs) Procede et dispositif optique pour la mesure des caracteristiques dynamiques d'un milieu gazeux
KR101721469B1 (ko) * 2016-03-25 2017-04-10 국방과학연구소 렌즈릿어레이의 다중 하부개구 분할을 이용한 레이저매질 온도특성 측정 장치 및 방법
AT520087A4 (de) * 2017-04-19 2019-01-15 Univ Wien Tech Verfahren zur kontaktlosen Bestimmung von Strömungsparametern
AT520087B1 (de) * 2017-04-19 2019-01-15 Univ Wien Tech Verfahren zur kontaktlosen Bestimmung von Strömungsparametern

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Publication number Publication date
DE2910428A1 (de) 1980-09-18
EP0025448A1 (fr) 1981-03-25

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