GB2144534A - Optical monitoring apparatus - Google Patents

Optical monitoring apparatus Download PDF

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Publication number
GB2144534A
GB2144534A GB08416376A GB8416376A GB2144534A GB 2144534 A GB2144534 A GB 2144534A GB 08416376 A GB08416376 A GB 08416376A GB 8416376 A GB8416376 A GB 8416376A GB 2144534 A GB2144534 A GB 2144534A
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GB
United Kingdom
Prior art keywords
light beam
light
transducer
spectrometer
transducer means
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.)
Granted
Application number
GB08416376A
Other versions
GB8416376D0 (en
GB2144534B (en
Inventor
David Niall Macfadyen
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.)
Thales Optronics Ltd
Original Assignee
Thales Optronics Ltd
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 Thales Optronics Ltd filed Critical Thales Optronics Ltd
Publication of GB8416376D0 publication Critical patent/GB8416376D0/en
Publication of GB2144534A publication Critical patent/GB2144534A/en
Application granted granted Critical
Publication of GB2144534B publication Critical patent/GB2144534B/en
Expired legal-status Critical Current

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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
    • 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
    • G01D5/32—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 with attenuation or whole or partial obturation of beams of light
    • G01D5/34—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 with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/36—Forming the light into pulses
    • G01D5/38—Forming the light into pulses by diffraction gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/12—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance
    • G01K11/14—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance of inorganic materials

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Optical Transform (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

The apparatus (10) comprises a broad band light source (11) coupled by optical fibres (12) to a spectrometer (15) arranged to provide spatial separation of the wavelengths of the light emitted by source (11). The spatially separated wavelengths are incident on a transducer formed by gratings (14A,14B) and the resultant light is collected by collector (16) and transmitted by fibre optics (17) to an interpretation means (20), interpretation means (20) comprises spectrometer (21) providing spatial separation of the wavelengths of the light provided by fibre (17) and these are incident on a CCT array (22) which is driven to provide electrical output signals in series. The electrical output signals are fed through a low pass filter (24) to a comparator (25) which also receives a reference signal from an oscillator (26). Comparator (25) measures phase difference, the magnitude of which corresponds to the variation sensed by transducer (14A, 14B) arising from variation of a parameter being measured. It is started that pressure may be measured using an elasto-optic (photoelastic) material e.g. polyurethane rubber or that temperature may be measured using a temperature sensitive birefringent material e.g. lithium niobate. <IMAGE>

Description

SPECIFICATION Optical monitoring apparatus This invention relates to optical monitoring apparatus.
Recently, increased attention has been given to monitoring apparatus incorporating optical interrogation of transducers for detection of such parameters as displacement, temperature and pressure particularly for utilising the advantages of optical fibres in data transmission. Primarily the known apparatus operates on the basis of variation in light intensity arising from parameter variation as sensed by a transducer. However, this arrangement requires the optical fibres to be of predetermined fixed length and of predetermined attenuation characteristics if unambiguous results are to be achieved and no account is taken of ageing of the light source.
It is an object of the present invention to provide a new and improved form of optical monitoring apparatus which obviates or mitigates the disadvantages of the known optical monitoring apparatus.
According to the present invention there is provided optical monitoring apparatus comprising transducer means responsive to variations in a predetermined parameter, lightdelivery means arranged for delivering an interrogating light beam from a light source to said transducer means, light-collecting means arranged for collecting the interrogated light beam from said transducer means and delivering the interrogated light beam to signal interpretation means, wherein the transducer means iniposes a cyclic modulation in a characteristic of the light beam and phase variation of said cyclic modulation is imposed by variation in said predetermined parameter, and the interpretation means comprises means for isolating the cyclic modulation of said characteristic from the interrogated light beam and phase sensitive detection means for establishing the phase difference thereof with respect to a reference modulation.
By virtue of the present invention measurement of parameter variation by way of phase difference techniques renders the measurement independent of signal intensity and of variation therein so that the apparatus neither requires a calibrated light source nor calibrated optical fibres in the light-delivery means and in the light-collecting means.
The predetermined parameter may, for example, be displacement or pressure or temperature. A convenient displacement sensitive transducer means comprises a pair of copianar moor6 gratings the grating lines of one being at a small angle to the grating lines of the other grating. A convenient temperature sensitive transducer means comprises a temperature sensitive birefringent material such as lithium niobate. A convenient pressure sensitive transducer means comprises an elastooptic (photo-elastic) material such as polyurethane rubber.
The light-beam characteristic which is cyclically modulated may be intensity within a wavelength band or polarisation within a wavelength band.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, in which: Fig. 1 shows the embodiment schematically with waveform diagrams to facilitate understanding.
The apparatus 10 shown in the drawing comprises a white light source 11 connected by way of optical fibres 1 2 forming a light delivery means to a transducer means 1 3. The means 1 3 comprises a pair of copp-planar moor8 grating plates 1 4A, 1 4B of which plate 1 4A is fixedly mounted and plate 1 4B is movably mounted so as to follow the displacement parameter being monitored. Means 1 3 also comprises a spectrometer 15 connected to the end of fibres 1 2 for the purposes of providing spatial separation of different wavelengths forming the light beam provided from source 11. Spectrometer 1 5 conveniently is formed by a diffraction grating.The lines of the grating plates 14A, 1 4B are disposed at a small angle to each other so that fringes, for example, sinusoidal are interrogated by the spatially separated beam wavelengths and impose thereon a spatially cyclic modulation in the intensity of the interrogating light beam.
The interrogated light beam is collected within transducer means 1 3 by a collector 1 6 and transmitted to an interpreting means 20 by an optical fibre collecting means 1 7. Interpreting means 20 comprises a further spectrometer 21, preferably identical to spectrometer 15, for spatially separating the modulated wavelengths and a light-sensitive CCD array 22 for effecting opto-electric signal conversion. The array 22 is arranged to receive the individual wavelength signals in parallel from the spectrometer 21 and is clocked by a clock source 23 to deliver the individually corresponding electrical signals in series.The electrical output of array 22 is passed through a high frequency (low pass) filter 24 in order to isolate the cyclic modulation imposed by the means 1 3 and fed into a phase comparator 25 to which a reference modulation is also applied and the phase difference identified by the comparator 25 is a measure of the displacement of grating plate 1 4B from its datum position. The reference modulation applied to comparator 25 is fed directly from a free-running oscillator 26 the frequency of which is initially locked to provide null output from the comparator 25 when the plate 1 4B is in its datum position. Clock source 23 is also operated by oscillator 26 for example by incorporating zero crossing detectors and one or more counters.
It will be evident that the reference frequency of the oscillator 26 is related to the cyclic variation imposed on the characteristic of the interrogating light beam by means of plates 1 4A, 1 4B. In fact this is determined by the particular angle between the lines of the two plates and accordingly the apparatus 10 may be incorporated into a multiplexed arrangement utilising identical components in each channel but having the plates of each channel disposed at different angles to each other. The relationship of phase to displacement is not altered by this technique; the phase/displacement relationship is varied by variation of the line pitch of the plates.
The apparatus 10 is relatively inexpensive to manufacture arising from the absence of calibration components, non-aging components and a certain degree of commonality in components. The quality of the two spectrometers for example does not require to be particularly great to permit accurate measurement of parameter variation.

Claims (7)

1. Optical monitoring apparatus comprising transducer means responsive to variations in a predetermined parameter, light-delivery means arranged for delivering an interrogating light beam from a light source to said transducer means, light-collecting means arranged for collecting the interrogated light beam from said transducer means and delivering the interrogated light beam to signal interpretation means, wherein the transducer means imposes a cyclic modulation in a characteristic of the light beam and phase variation of said cyclic modulation is imposed by variation in said predetermined parameter, and the interpretation means comprises means for isolating the cyclic modulation of said characteristic from the interrogated light beam and phase sensitive detection means for establishing the phase difference thereof with respect to a reference modulation.
2. Apparatus as claimed in claim 1, wherein the transducer means imposes a cyclic modulation in the intensity within a predetermined wavelength band of the interrogating light beam.
3. Apparatus as claimed in claim 1, wherein the transducer means imposes a cyclic modulation in the polarisation within a predetermined wavelength band of the interrogating light beam.
4. Apparatus as claimed in any preceding claim, wherein the transducer means comprises a spectrometer for providing spatial separation of different wavelengths forming the interrogating light beam.
5. Apparatus as claimed in any preceding claim, wherein the interpretation means comprises a spectrometer for providing spatial separation of different wavelengths forming the interrogated light beam and a light-sensitive CCD array for effecting opto-electric conversion of signals received in parallel from the spectrometer of the interpretation means.
6. Apparatus as claimed in claim 5, wherein the interpretation means comprises clock means for driving the CCD array to deliver its output electrical signals in series, a low pass filter for receiving said series electrical signals and a phase comparator having one input connected to the output of the low pass filter, a modulated reference signal being applied to the other input of the comparator.
7. Optical monitoring apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.
GB08416376A 1983-07-26 1984-06-27 Optical monitoring apparatus Expired GB2144534B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB838320107A GB8320107D0 (en) 1983-07-26 1983-07-26 Optical monitoring apparatus

Publications (3)

Publication Number Publication Date
GB8416376D0 GB8416376D0 (en) 1984-08-01
GB2144534A true GB2144534A (en) 1985-03-06
GB2144534B GB2144534B (en) 1987-01-07

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Family Applications (2)

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GB838320107A Pending GB8320107D0 (en) 1983-07-26 1983-07-26 Optical monitoring apparatus
GB08416376A Expired GB2144534B (en) 1983-07-26 1984-06-27 Optical monitoring apparatus

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB838320107A Pending GB8320107D0 (en) 1983-07-26 1983-07-26 Optical monitoring apparatus

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Country Link
GB (2) GB8320107D0 (en)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2176284A (en) * 1985-06-11 1986-12-17 Anthony John Asbury Device for detecting displacement
EP0214040A2 (en) * 1985-08-19 1987-03-11 Tacan Aerospace Corporation Fiber-optic sensor
EP0214845A2 (en) * 1985-09-06 1987-03-18 The University Of Liverpool Device and method for determining displacement
FR2595820A1 (en) * 1986-03-13 1987-09-18 Bertin & Cie OPTICAL FIBER DEVICE FOR REMOTELY DETECTING A PHYSICAL SIZE, ESPECIALLY TEMPERATURE
GB2190193A (en) * 1986-05-01 1987-11-11 Bicc Plc Movement detection
GB2191286A (en) * 1986-06-03 1987-12-09 Bicc Plc Temperature measurement
GB2202937A (en) * 1987-03-17 1988-10-05 Univ Liverpool Optical displacement sensor
WO1989008238A1 (en) * 1988-02-24 1989-09-08 Hughes Aircraft Company Comb filter pressure/temperature sensing system
FR2641861A1 (en) * 1989-01-18 1990-07-20 Photonetics OPTOELECTRONIC MEASURING DEVICE
FR2643145A1 (en) * 1989-02-14 1990-08-17 Bertin & Cie METHOD AND DEVICE FOR DETECTING AND MEASURING A PHYSICAL SIZE
EP0582442A2 (en) * 1992-07-31 1994-02-09 Hamamatsu Photonics K.K. An optical fiber component characteristics measuring apparatus

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1325452A (en) * 1970-03-25 1973-08-01 Nat Res Dev Optical measuring apparatus

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1325452A (en) * 1970-03-25 1973-08-01 Nat Res Dev Optical measuring apparatus

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2176284A (en) * 1985-06-11 1986-12-17 Anthony John Asbury Device for detecting displacement
EP0214040A2 (en) * 1985-08-19 1987-03-11 Tacan Aerospace Corporation Fiber-optic sensor
EP0214040A3 (en) * 1985-08-19 1988-10-05 Tacan Aerospace Corporation Fiber-optic sensor and method of use
EP0214845A2 (en) * 1985-09-06 1987-03-18 The University Of Liverpool Device and method for determining displacement
EP0214845A3 (en) * 1985-09-06 1989-03-01 The University Of Liverpool Device and method for determining displacement
FR2595820A1 (en) * 1986-03-13 1987-09-18 Bertin & Cie OPTICAL FIBER DEVICE FOR REMOTELY DETECTING A PHYSICAL SIZE, ESPECIALLY TEMPERATURE
US4822999A (en) * 1986-05-01 1989-04-18 Parr David T Apparatus and method for detecting movement of an object
GB2190193A (en) * 1986-05-01 1987-11-11 Bicc Plc Movement detection
GB2190193B (en) * 1986-05-01 1990-03-28 Bicc Plc Movement detection
GB2191286B (en) * 1986-06-03 1990-07-04 Bicc Plc Temperature measurement
GB2191286A (en) * 1986-06-03 1987-12-09 Bicc Plc Temperature measurement
GB2202937A (en) * 1987-03-17 1988-10-05 Univ Liverpool Optical displacement sensor
GB2202937B (en) * 1987-03-17 1991-02-27 Univ Liverpool Optical sensor
AU606798B2 (en) * 1988-02-24 1991-02-14 Hughes Aircraft Company Comb filter pressure/temperature sensing system
WO1989008238A1 (en) * 1988-02-24 1989-09-08 Hughes Aircraft Company Comb filter pressure/temperature sensing system
GR1000329B (en) * 1988-02-24 1992-06-25 Hughes Aircraft Co Comb filter pressure temperature sensing system
FR2641861A1 (en) * 1989-01-18 1990-07-20 Photonetics OPTOELECTRONIC MEASURING DEVICE
EP0390615A2 (en) * 1989-01-18 1990-10-03 Photonetics Opto-electronic measuring device
EP0390615A3 (en) * 1989-01-18 1990-10-10 Photonetics Opto-electronic measuring circuit
FR2643145A1 (en) * 1989-02-14 1990-08-17 Bertin & Cie METHOD AND DEVICE FOR DETECTING AND MEASURING A PHYSICAL SIZE
EP0387115A1 (en) * 1989-02-14 1990-09-12 Bertin & Cie Procedure and device to detect and measure a physical entity
WO1990009564A1 (en) * 1989-02-14 1990-08-23 Bertin & Cie Process and device for detecting and measuring a physical quantity
US5200796A (en) * 1989-02-14 1993-04-06 Bertin & Cie Method and apparatus for detecting and measuring a physical magnitude
EP0582442A2 (en) * 1992-07-31 1994-02-09 Hamamatsu Photonics K.K. An optical fiber component characteristics measuring apparatus
EP0582442A3 (en) * 1992-07-31 1994-05-18 Hamamatsu Photonics Kk An optical fiber component characteristics measuring apparatus
US5493406A (en) * 1992-07-31 1996-02-20 Hamamatsu Photonics K.K. Apparatus for measuring spectral characteristics of an optical fiber component

Also Published As

Publication number Publication date
GB8320107D0 (en) 1983-08-24
GB8416376D0 (en) 1984-08-01
GB2144534B (en) 1987-01-07

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PCNP Patent ceased through non-payment of renewal fee