WO1990015308A1 - Process and system for measuring a physical size in gas and/or liquid - Google Patents

Process and system for measuring a physical size in gas and/or liquid Download PDF

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Publication number
WO1990015308A1
WO1990015308A1 PCT/NO1990/000094 NO9000094W WO9015308A1 WO 1990015308 A1 WO1990015308 A1 WO 1990015308A1 NO 9000094 W NO9000094 W NO 9000094W WO 9015308 A1 WO9015308 A1 WO 9015308A1
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WIPO (PCT)
Prior art keywords
light
fiber
measuring
sensor
optic fibers
Prior art date
Application number
PCT/NO1990/000094
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French (fr)
Inventor
Carl Nilsson
Original Assignee
Chr. Michelsens Institutt
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
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Publication of WO1990015308A1 publication Critical patent/WO1990015308A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres

Definitions

  • the present invention relates to a process for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid with a measuring medium consisting of light which is excited via optic fibers in connection with a sensor and associated light detector.
  • the invention also relates to a measuring system for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid, by means of light as measuring medium, via optic fibers in connection with a sensor.
  • a measuring system for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid, by means of light as measuring medium, via optic fibers in connection with a sensor.
  • One of the most usual ways of effecting measurements in fiber optic sensors in connection with measurements in gas or liquid is to transmist light (visible or infra red) through an optic fiber to a sensor where the intensity of the light is changed by the physical size one desires to measure, for example pressure, temperature, etc. This light is thereafter reflected back in the same fiber in which the light is excited or trans ⁇ mitted back via another fiber to a light detector which converts light signals from the sensor to an electrical signal.
  • the problem with such a measuring method is that the light is exposed to scattering and absorption in the optic fibers on the way forwardly to and backwardly from the sensor. Since this loss can be readily altered over time, for example as a result or bending and/or stretching of the fibers, temperature variations and processes of ageing (hydrogen absorption) it is difficult to achieve high accuracy with these types of sensor without recali ⁇ brating the measuring system quite frequently.
  • intensity modulated fiber optic sensor systems there exists as far as we know only one other general technique which can be used to eliminate the effect of alterations in the loss of transmission in optic fibers.
  • This method aims at transmitting light having at least two different wave lengths (often a broad spectrum) to the sensor, which is constructed so that it affects the intensity to the light differently at different wave lengths.
  • wave length method in English often called wave length reference method
  • the wave length method requires a far more complicated detector design than according to the invention, since the light intensity must be measured as a function of wave length.
  • the wave length method a separate arrangement in order to be able to compensate for drift in the intensity of the light source, here also as a function of wave length. This contributes furthermore to increase the com ⁇ plexity in relation to this invention.
  • the aim is a simpler system than the known systems, and the objective is to be able to achieve cheaper and better fiber optic sensor systems than those on the market to-day.
  • the aim is to compensate for such variations in the fiber losses continuously and while the measurements are in progress.
  • the process according to the invention is characterised in that the sensor communicates with two mutually separated light sources (light-emitting diodes) and with two mutually separated light detectors (photo-diodes) via two separate, individually two-way light-conducting optic fibers, in that there is measured separately one after the other the intensity I_, and I Uber of the light from a first of the light sources in each of the optic fibers and the measurements are stored in a microprocessor, and thereafter the intensities I' n an ⁇ - - , - ) - ⁇ of tne light from the second of the light sources are measured in each of the optic fibers, and the measurements are stored in the microprocessor, the light, which is excited from a respective one of the light sources, being conducted with a first fraction (R, , R ⁇ ) back from the sensor through the light-exciting fiber and with a second fraction (F, , F Formula) from the light-exciting fiber via the sensor to the remaining fiber, and finally a physical measurement variable R, ,
  • I D1 I 'D2 /I D2 I 'D1 R 1 R 2 /F 1 F 2'
  • R, and R ⁇ indicate the fraction of light which is reflected back through the first and second fiber respectively
  • F, and F 2 indicate the fraction of light which is coupled via the second fiber and the first fiber respectively to its associated detec ⁇ tor, the effect of light loss in the optic fibers being elimated in the result of the measurement.
  • the measuring system according to the invention is charac ⁇ terised in that the sensor is connected to two mutually separated light sources (for example light-emitting diodes) and to two mutually separated light detectors (for example photo-diodes) via two separate, individually two-way light-conducting optic fibers, the fibers being connected via one end of their respective Y- direction coupling to the sensor and via the other end of their respective Y-direction coupling being connected, at a first branch, to their respective separate light source (light-emitting diodes) and, at a second branch, being connected to an associated light detector (photo-diode) , which with their respective conduc ⁇ ting connections are connected to a microprocessor, and that the light, which is excited from a respective one of the light sources, is adapted to be conducted with a first fraction (R, , R ⁇ ) back via the light-exciting fiber and with a second fraction criz, F caution) from the light-exciting fiber to the remaining fiber, the measurement results being adapted to
  • Fig. 1 shows a flow sheet of the meaturing system according to the invention.
  • Fig. 2 shows schematically a cross-section of a sensor for use in the measuring system as shown in Fig. 1.
  • Fig. 1 there are shown two light sources in the form of two light-emitting diodes LI and L2 which are individually connected to a common sensor S and to their respective light detectors in the form of a photo-diode Dl and Dl respectively by means of two optic fibers OF1 and OF2 and two fiber optic Y- direction couplings Yl and Y2.
  • the photo-diodes Dl and D2 are connected by means of their respective electrical conducting connections 10 and 11 to a microprocessor ⁇ P .
  • ⁇ P microprocessor
  • each of the conductors 10 and 11 there is inserted in series an amplifier 12 and 13 respectively and an A/D converter 14 and 15 respectively.
  • Generally measuring is effected by alternately activating the light sources LI and L2.
  • LI When LI is lighted, light having the intensity I, is coupled to the optic fiber OF1 via the Y-direc ⁇ tion coupling Yl.
  • the fiber 0F1 ⁇ as a transmission factor T, , where T, is greater than 0 and less than 1. Consequently the light has an intensity I- j T, when it arrives at the sensor S.
  • the transmission factor T will vary over time as a result of varying fiber loss.
  • K is the coupling factor of the Y-coupler.
  • the detector or the photo-diode Dl will thereby emit via the conductor 10 an electrical signal which is proportional to the light intensity by the diode Dl.
  • the signal will therefore change, if the trans ⁇ mission factor T, of the fiber changes.
  • a light fraction F, where F, is less than 1-R, will also be coupled over into the second fiber OF2 which has a transmission factor T»(t).
  • R is the coefficient of reflection or the fraction of reflected light
  • I is the distance between the fibers
  • n is the index of refraction of the medium
  • NA is the numerical "aperatur" for the fibers
  • r is the radius to the light-conducting core of the fibers .
  • the calculated size in formula (7) is totally independent of the transmission factors of the fibers, the coupling factors of the Y coupler and the intensity of the light source.
  • the size as indicated in formula (7) will be able to be used for measuring the physical variable size without this being affected by the transmission loss of the fibers or drift in the light intensity of the light source. This applies so long as the changes in the transmission losses are slow relative to the measuring cycle. In the vast majority of cases this will not be any problem in practice.
  • the measurements will often be able to be conductd in the course of milliseconds, while the undesired drift in transmission loss or the intensity of the light source will have time constants of the magnitude of hours or days or months.
  • Fig. 2 shows a sensor S, where the principle of measurement as described above can be utilised.
  • the illustrated sensor S is employed for measuring the index of refraction in gases or liquids.
  • the sensor S acts in that reflected fraction R between an end surface of an optic fiber and a gas/liquid varies with the refractive index of the gas/liquid. This fraction R is given by the following:
  • Formula (8) R where n f and n are respectively the refractive index of the fiber and the gas/liquid.
  • n f and n are respectively the refractive index of the fiber and the gas/liquid.
  • n f is about 1.65.
  • gases have a refractive index of between 1.0 and 1.10.
  • Most liquids have a refractive index between 1.30 and 1.45.
  • the reflected fraction R will consequently vary between about 0.05 and 0.0013. Consequently by measuring the intensity of the reflected light, one will get a measurement of the index of refraction.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Arrangements Characterized By The Use Of Fluids (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Testing Or Calibration Of Command Recording Devices (AREA)

Abstract

A process for measuring a physical size, such as pressure, temperature and the like in gas and/or liquid, employs a measuring medium consisting of light which is excited via optic fibers in connection with a sensor (S) and associated light detector (D1, D2). The measurements are effected via two separate, individually two-way light-conducting optic fibers (OF1, OF2), and the measuring results are stored in a micro-processor (νP). Finally a physical measurement variable R1, R2, F1, F2 is correspondingly measured, by means of the formula: ID1I'D2/ID2I'D1 = R1R2/F1F2, the effect of light loss in the optic fibers (OF1, OF2) being eliminated in the measuring result. A measuring system for use in the process comprises a sensor (S) which is connected to two mutually separated light-emitting diodes (L1, L2) and to two mutually separated light detectors (D1, D2) via two separate, individually two-way light-conducting optic fibers (OF1, OF2), with their repective Y-direction couplings (Y1, Y2). An associated light detector (D1, D2) is connected with its respective conducting connection to a micro-processor ($(m)P).

Description

PROCESS AND SYSTEM FOR MEASURING A PHYSICAL SIZE IN-GAS-AND/OR LIQUID.
The present invention relates to a process for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid with a measuring medium consisting of light which is excited via optic fibers in connection with a sensor and associated light detector.
The invention also relates to a measuring system for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid, by means of light as measuring medium, via optic fibers in connection with a sensor.
One of the most usual ways of effecting measurements in fiber optic sensors in connection with measurements in gas or liquid is to transmist light (visible or infra red) through an optic fiber to a sensor where the intensity of the light is changed by the physical size one desires to measure, for example pressure, temperature, etc. This light is thereafter reflected back in the same fiber in which the light is excited or trans¬ mitted back via another fiber to a light detector which converts light signals from the sensor to an electrical signal.
The problem with such a measuring method is that the light is exposed to scattering and absorption in the optic fibers on the way forwardly to and backwardly from the sensor. Since this loss can be readily altered over time, for example as a result or bending and/or stretching of the fibers, temperature variations and processes of ageing (hydrogen absorption) it is difficult to achieve high accuracy with these types of sensor without recali¬ brating the measuring system quite frequently.
As regards intensity modulated fiber optic sensor systems, there exists as far as we know only one other general technique which can be used to eliminate the effect of alterations in the loss of transmission in optic fibers. This method aims at transmitting light having at least two different wave lengths (often a broad spectrum) to the sensor, which is constructed so that it affects the intensity to the light differently at different wave lengths.
By assuming that light having different wave lengths is exposed to the same loss of transmission in the fibers, it is possible to compensate for the changes in fiber loss by measuring the intensity of the light from the sensor as a function of the wave length.
However it is a well known fact that changes in fiber loss, which for example are due to flexing of the fiber, are somewhat dependent on wave length. Therefore with the known wave length method one does not manage to eliminate 100 per cent the effect of varied fiber loss.
Another thing is that the wave length method (in English often called wave length reference method) requires a far more complicated detector design than according to the invention, since the light intensity must be measured as a function of wave length. In addition one must have for the wave length method a separate arrangement in order to be able to compensate for drift in the intensity of the light source, here also as a function of wave length. This contributes furthermore to increase the com¬ plexity in relation to this invention.
In recent years there have come on the market several sensor systems based on the wave length method. According to the invention the aim is a simpler system than the known systems, and the objective is to be able to achieve cheaper and better fiber optic sensor systems than those on the market to-day. With the present invention the aim is to compensate for such variations in the fiber losses continuously and while the measurements are in progress.
The process according to the invention is characterised in that the sensor communicates with two mutually separated light sources (light-emitting diodes) and with two mutually separated light detectors (photo-diodes) via two separate, individually two-way light-conducting optic fibers, in that there is measured separately one after the other the intensity I_, and I „ of the light from a first of the light sources in each of the optic fibers and the measurements are stored in a microprocessor, and thereafter the intensities I'n an<- - , -)-ι of tne light from the second of the light sources are measured in each of the optic fibers, and the measurements are stored in the microprocessor, the light, which is excited from a respective one of the light sources, being conducted with a first fraction (R, , R~) back from the sensor through the light-exciting fiber and with a second fraction (F, , F„) from the light-exciting fiber via the sensor to the remaining fiber, and finally a physical measurement variable R, , R„ , F, , F~ is correspondingly measured, by means of the formula:
ID1I'D2/ID2I'D1 = R1R2/F1F2'
where R, and R~ indicate the fraction of light which is reflected back through the first and second fiber respectively, and F, and F2 indicate the fraction of light which is coupled via the second fiber and the first fiber respectively to its associated detec¬ tor, the effect of light loss in the optic fibers being elimated in the result of the measurement.
The measuring system according to the invention is charac¬ terised in that the sensor is connected to two mutually separated light sources (for example light-emitting diodes) and to two mutually separated light detectors (for example photo-diodes) via two separate, individually two-way light-conducting optic fibers, the fibers being connected via one end of their respective Y- direction coupling to the sensor and via the other end of their respective Y-direction coupling being connected, at a first branch, to their respective separate light source (light-emitting diodes) and, at a second branch, being connected to an associated light detector (photo-diode) , which with their respective conduc¬ ting connections are connected to a microprocessor, and that the light, which is excited from a respective one of the light sources, is adapted to be conducted with a first fraction (R, , R~) back via the light-exciting fiber and with a second fraction („, F„) from the light-exciting fiber to the remaining fiber, the measurement results being adapted to be stored and processed in the microprocessor.
Further features of the invention will be evident from the following description having regard to the accompanying drawings, in which:
Fig. 1 shows a flow sheet of the meaturing system according to the invention.
Fig. 2 shows schematically a cross-section of a sensor for use in the measuring system as shown in Fig. 1.
In Fig. 1 there are shown two light sources in the form of two light-emitting diodes LI and L2 which are individually connected to a common sensor S and to their respective light detectors in the form of a photo-diode Dl and Dl respectively by means of two optic fibers OF1 and OF2 and two fiber optic Y- direction couplings Yl and Y2. The photo-diodes Dl and D2 are connected by means of their respective electrical conducting connections 10 and 11 to a microprocessor μP . In each of the conductors 10 and 11 there is inserted in series an amplifier 12 and 13 respectively and an A/D converter 14 and 15 respectively.
Generally measuring is effected by alternately activating the light sources LI and L2. When LI is lighted, light having the intensity I, is coupled to the optic fiber OF1 via the Y-direc¬ tion coupling Yl. The fiber 0F1 } as a transmission factor T, , where T, is greater than 0 and less than 1. Consequently the light has an intensity I-jT, when it arrives at the sensor S. The transmission factor T, will vary over time as a result of varying fiber loss. The transmission factor T, can therefore be written as a function of the time, that is to say T, = T-, (t) . When the light arrives at the sensor S a fraction R, of the light is reflected back through the light-exciting fiber OF., to the diode D, . The reflected light fraction R_ has the following intensity, expressed by:
Formula (1) I χ = I-^ t^ ^
where K, is the coupling factor of the Y-coupler. The detector or the photo-diode Dl will thereby emit via the conductor 10 an electrical signal which is proportional to the light intensity by the diode Dl. The signal will therefore change, if the trans¬ mission factor T, of the fiber changes.
A reflection coefficient indicates how large is the portion (fraction R of the light which is reflected at a boundary surface between two optic mediums. If the intensity of the incident light is Iu_, the intensity of the reflected light will be I _. = RI_ _>. R is determined by the indices of refraction of the two medium and the angle of incidence. When one says that a fraction R of the light is reflected, this means that the coefficient of reflection is equal to R.
In the sensor S a light fraction F, , where F, is less than 1-R, , will also be coupled over into the second fiber OF2 which has a transmission factor T»(t). The fractions F, and F_ indicate how large a portion of the light which is coupled over between the fibers in the sensor. If light having intensity I leaves the one fiber, light which becomes coupled over into the second fiber will have an intensity l f = I0. For a sensor geometry as shown in Fig. 1 and 2 F (F, and F„ ) is given by:
Figure imgf000007_0001
rn g
where R is the coefficient of reflection or the fraction of reflected light, I is the distance between the fibers, n is the index of refraction of the medium, NA is the numerical "aperatur" for the fibers and r is the radius to the light-conducting core of the fibers . The intensity of the light which reaches forward to the detector or the diode D2 is consequently expressed by:
Formula (2) I 2 = 1^(t)Fχ 2(t)K2
where K„ is the coupling factor for Y2. By measuring these signals and thereafter calculating the ratio In,/I _ one will find the size in the following:
Formula (3) I D1/I D2 = ι(t)Ri/ 2 (t)FlK2
This size is thereafter stored in the microprocesor and there¬ after by extinguishing the source of light LI and lighting the source of light L2 one will measure the equivalent signals in the diodes Dl and D2 by the following:
Formula (4) I'D2 = I2T2(t)2R2K2 and
Formula (5) I'D1 = 1^ ( )F2TL(t)Kχ
where R- indicates the fraction of reflected light back in the fiber 0F2 and F„ indicates the coupling from fiber OF2 to fiber OF1. In practice one will often have R, = R„ and F, = F„. In the same way one arrives at the ratio in the following:
Formula (6) I'D2/I,D1 = 2(t)R2K2 Tl( ~)F2K1
By multiplying formula (3) with formula (6) one will find the following:
Formula (7) 1^1 'D2 ID2I'D1 = Rχ FlF2
One sees that the calculated size in formula (7) is totally independent of the transmission factors of the fibers, the coupling factors of the Y coupler and the intensity of the light source. By providing that the sensor is made so that the relevant measurement variable can affect the fractions
Figure imgf000009_0001
and/or the fractions F,F-, the size as indicated in formula (7) will be able to be used for measuring the physical variable size without this being affected by the transmission loss of the fibers or drift in the light intensity of the light source. This applies so long as the changes in the transmission losses are slow relative to the measuring cycle. In the vast majority of cases this will not be any problem in practice. The measurements will often be able to be conductd in the course of milliseconds, while the undesired drift in transmission loss or the intensity of the light source will have time constants of the magnitude of hours or days or months.
Fig. 2 shows a sensor S, where the principle of measurement as described above can be utilised. The illustrated sensor S is employed for measuring the index of refraction in gases or liquids. The sensor S acts in that reflected fraction R between an end surface of an optic fiber and a gas/liquid varies with the refractive index of the gas/liquid. This fraction R is given by the following:
Formula (8) R =
Figure imgf000009_0002
where nf and n are respectively the refractive index of the fiber and the gas/liquid. For most optic fibers the refractive index nf is about 1.65. Depending upon pressure, temperature and gas type most gases have a refractive index of between 1.0 and 1.10. Most liquids have a refractive index between 1.30 and 1.45. Over this field the reflected fraction R will consequently vary between about 0.05 and 0.0013. Consequently by measuring the intensity of the reflected light, one will get a measurement of the index of refraction.
By using two identical fiber probes OF1 and OF2, which point right up to each other, some of the light from the one fiber Ofl will be coupled over to the second fiber 0F2. The intensity of the light which becomes coupled over will increase with an increasing index of refraction, the reflection being reduced and the numerical "apertur" of the fiber diminished with an in¬ creasing index of refraction.
By alternately measuring reflected light and transmitted light from the optic fibers - by alternately exciting the sources of light - one will be able to get a measure of the gas/liquid refractive index by calculating the expression as indicated in formula (7), which is independent of the transmission loss of the fibers and independent of drift in the sources of light.

Claims

CLAIMS,
1. Process for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid with a measuring medium consisting of light which is excited via optic fibers in connection with a sensor (S) and associated light detector (photo-diode Dl, D2) , characterised in that the sensor (S) communicates with two mutually separated light sources (for example light-emitting diodes LI, L2) and with two mutually separated light detectors (for example photo-diodes Dl, D2) via two separate, individually two-way light-conducting optic fibers (OF1, OF2), in that there is measured separately one after the other the intensity ID, and I _ of the light from a first (LI) of the light sources in each of the optic fibers (OF1 and 0F2) and the measurements are stored in a microprocessor (μP) , and there¬ after the intensities I'D2 an~~ ~ ' r,± °^ t^ιe li ht from the second (L2) of the light sources are measured in each of the optic fibers (OF1 and Of2) , and the measurements are stored in the microprocessor, the light, which is excited from a respective one of the light sources (LI, L2) , being conducted with a first fraction (R, , R^ back through the light-exciting fiber and with a second fraction (F, , F2) from the light-exciting fiber to the remaining fiber, and finally a physical measurement variable R- , R„ , F,, F is correspondingly measured, by means of the formula: ID1I ,D2/ID2I'D1 _ R1R2/F1F2'
where R, and R~ indicate the fraction of light which is reflected back through the first (OF1) and the second (OF2) fiber respec¬ tively, and F-, and F„ indicate the fraction of light which is coupled via the second fiber (0F2) and the first fiber (OF2) respectively to its associated detector, the effect of light loss in the optic fibers (OFl, OF2) being eliminated in the result of the measurement.
2. Measuring system for measuring a physical size, such as pressure, temperature, and the like in gas and/or liquid, by means of light as measuring medium, via optic fibers in connection with sensor (S), characterised in that the sensor (S) is connected to two mutually separated light sources (light- emitting diodes LI, L2) and to two mutually separated light detectors (photo-diodes Dl and D2) via two separate, individually two-way light-conducting optic fibers (OFl, OF2) , the fibers being connected via one end of their respective Y-direction couplings (Yl, Y2) to the sensor (S) and via the other end of their respective Y-direction couplings being connected, at a first branch, to their respective separate light sources (light-emitting diodes LI, L2) and, at a second branch, being connected to an associated light detector (photo-diode Dl', D2), which with their respective conducting connections are connected to a microprocessor (μP), and that the light, which is excited from a respective one of the light sources (LI, L2), is adapted to be conducted with a first fraction (R, , R„) back through the light-exciting fiber and with a second fraction (F, , F„ ) from the light-exciting fiber to the remaining fiber, the mneasurement results being adapted to be stored and processed in the micro¬ processor.
PCT/NO1990/000094 1989-06-07 1990-05-25 Process and system for measuring a physical size in gas and/or liquid WO1990015308A1 (en)

Applications Claiming Priority (2)

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NO892327 1989-06-07
NO892327A NO167691C (en) 1989-06-07 1989-06-07 PROCEDURE AND SYSTEM FOR AA MEASURING A PHYSICAL SIZE IN GAS AND / OR LIQUID.

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106706562A (en) * 2017-01-12 2017-05-24 天津大学 All-optical-fiber based gas-liquid mixed measurement device and remote gas-liquid mixed measurement system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4281245A (en) * 1978-06-02 1981-07-28 Asea Aktiebolag Fiber optical measurement apparatus
DE3408417C1 (en) * 1984-03-08 1984-12-13 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 8000 München Fibre-optic measuring device
US4687927A (en) * 1984-12-13 1987-08-18 Kabushiki Kaisha Toshiba Pressure measuring system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4281245A (en) * 1978-06-02 1981-07-28 Asea Aktiebolag Fiber optical measurement apparatus
DE3408417C1 (en) * 1984-03-08 1984-12-13 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 8000 München Fibre-optic measuring device
US4687927A (en) * 1984-12-13 1987-08-18 Kabushiki Kaisha Toshiba Pressure measuring system

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AU5678790A (en) 1991-01-07
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NO892327D0 (en) 1989-06-07

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