GB2211605A - Optical fibre distributor sensor - Google Patents
Optical fibre distributor sensor Download PDFInfo
- Publication number
- GB2211605A GB2211605A GB8829109A GB8829109A GB2211605A GB 2211605 A GB2211605 A GB 2211605A GB 8829109 A GB8829109 A GB 8829109A GB 8829109 A GB8829109 A GB 8829109A GB 2211605 A GB2211605 A GB 2211605A
- Authority
- GB
- United Kingdom
- Prior art keywords
- digital
- optical fibre
- analogue
- scattered
- sensing system
- 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
Links
- 239000013307 optical fiber Substances 0.000 title claims abstract description 15
- 238000012935 Averaging Methods 0.000 claims abstract description 11
- 230000003287 optical effect Effects 0.000 claims description 18
- 239000000835 fiber Substances 0.000 description 16
- 238000003491 array Methods 0.000 description 5
- 230000001902 propagating effect Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
Classifications
-
- 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
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in 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
- G01D5/353—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 influencing the transmission properties of an optical fibre
- G01D5/35383—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 influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
- G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
- G01M11/3145—Details of the optoelectronics or data analysis
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Testing Of Optical Devices Or Fibers (AREA)
- Measuring Temperature Or Quantity Of Heat (AREA)
Abstract
An optical fibre distributed sensing system, e.g. for temperature, includes a multi-channel averaging circuit arrangement comprising an analogue-to-digital converter 10 which receives an analogue electrical input corresponding to back-scattered or returned light along an optical fibre sensor 5. The digital output therefrom is fed sequentially to respective digital storage devices 11 of a digital storage arrangement and the data stored for corresponding elements of each back-scattered or returned light signal is then clocked out simultaneously into a digital adder 15. The output from the adder is fed to a processor 24 for providing an indication of the averaged signal waveform in respect of successive waveforms with reduced noise. <IMAGE>
Description
IMPROVEMENTS RELATING TO OPTICAL SENSING SYSTEMS
This invention relates to optical sensing systems of the kind in which successive optical pulse signals of a particular wavelength are transmitted along an optical fibre sensor which extends over a path the temperature profile or some other parameter profile of which it is required to monitor. Time-related back-scattered or returned light resulting from the pulses propagating along the fibre sensor may be detected and measured by means of an optical time-domain reflectometer which accordingly provides an indication of the temperature distribution along the fibre sensor.
The utilisation of back-scattered or returned light for determining the profile of an external parameter causing variations in scattering or return of the light along the fibre sensor enables optical fibres to be monitored either to check their basic transmission
characteristics or, alternatively, to monitor external physical parameters, such as temperature, along the fibre.
However, the back-scattered or return signals from the fibre
sensor are generally weak and give rise to a very noisy electrical
signal in the reflectometer. Consequently, a high degree of signal
averaging of the return signals in response to successive optical
pulses propagating along the fibre sensor is required in order to
establish accurate parameter distribution measurement.
For the purpose of signal averaging an optical sensing system
of the kind set forth above may be provided with a principally
analogue multi-channel signal averaging circuit comprising a
plurality of charge-coupled device arrays each consisting of a multiplicity of devices capable of storing all the successive elements of a signal waveform corresponding to the return optical signal of back-scattered light, in which the charge-coupled device arrays are arranged to be rendered operative sequentially for storing incoming signal waveforms under the control of timing means, in which following the storage of a predetermined number of signal waveforms in the respective charge-coupled device arrays the groups of signal waveform elements stored in the charge-coupled device arrays are fed sequentially into an averaging circuit and in which the averaged groups of signal elements may be fed into an analogue-to-digital converter prior to being fed into a processor for providing an indication of the averaged signal waveforms in respect of the successive incoming waveforms to the circuit arrangement.
One disadvantage of such a multi-channel signal averaging circuit is that the charge-coupled devices produce additional noise and temperature offsets.
According to the present invention there is provided an optical fibre sensing system utilising back-scattered or returned light signals along an optical fibre sensor for establishing the scattering or light return profile along the fibre sensor, in which a multi-channel averaging circuit arrangement comprises an analogue-to-digital converter which receives an analogue electrical input corresponding to back-scattered or returned light along said fibre sensor, in which the digital output from the analogue-to-digital converter is fed sequentially to respective digital storage devices of a digital storage arrangement and in which the digital data stored in the respective storage devices corresponding to groups of elements of the back scattered or returned light signal is clocked out simultaneously into a digital adder the output from which may, if an analogue output is required be fed into a digital-to-analogue converter and which may thereafter be fed into a processor for providing an indication of the averaged signal waveform in respect of the successive incoming waveforms from the optical sensing system.
The present invention replaces the analogue charge-coupled device storage components of the previously referred to averaging circuit arrangement with digital components and thereby eliminates from the arrangement the aforesaid additional noise and temperature offsets produced by the charge-coupled device arrays.
By way of example the present invention will now be described with reference to the accompanying drawings in which:
Figure 1 shows a block schematic diagram of an optical sensing system with a multi-channel averaging circuit arrangement; and,
Figure 2 shows typical waveforms of sensed parameters and signals of the system of Figure 1.
Referring to Figure 1 of the drawings the optical sensing system depicted shows a pulsed laser source 1 which produces successive optical pulses of a particular frequency which are transmitted through optical fibres 2 and 3 and an optical coupler 4 to an optical sensor fibre 5. The optical fibre sensor 5 will be located along the path to be monitored by the system in order to determine a particular parameter profile of said path. In respect of each optical pulse propagating along the fibre sensor 5 a very small proportion of the light at each position along the fibre will be reflected back along the fibre sensor 5 due to backscattering which sill be dependent on the particular external parameter (eg. temperature) influencing the fibre sensor. This very weak time-related back-scattered light signal will be returned to the input end of the sensor.
This reflective action of the sensor fibre 5 is illustrated in the waveform diagram of Figure 2 in which one of the successive optical pulses launched into the optical fibre sensors is shown at 6 in section( a) of the figure. An exemplary temperature profile along the fibre sensor 5 is depicted at 7 in section(b). The resultant backscattered light signal returning along the sensor is shown at 8 in section (c). This signal will be a very low level and would give rise to a very noisy electrical signal if it were fed directly into an optoelectrical reflectometer. Accordingly, these back-scattered signals need to be averaged over a large number of cycles in order to achieve an accurate measurement of the back-scattered light levels.
For this purpose a large number of successive light pulses, such as the pulse 6, need to be transmitted down the fibre sensor and the resultant back-scattered signals, such as the signal 8, suitably averaged.
The averaging of these signals is achieved by feeding a succession of back-scattered light signals, such as the signal 8, into an opto-electric device 9 and then into an analogue-to-digital converter 10 which samples the analogue output from the device 9 (see sampling pulses 20 in section (d)) of Figure 2. The digital outputs corresponding to the respective back-scattered light signals (eg.
signal 8) from the converter 10 are applied sequentially to digital shift registers four of which are shown at 11, 12, 13 and 14 under the control of clock counter 25. When the digital elements corresponding to a predetermined number of back-scattered light signals have been stored in the digital shift registers, the stored digital information will be simultaneously clocked out of all the shift registers, one digital signal element at a time, into a digital adder 15 which effectively averages corresponding digital elements of the stored digital signals corresponding to successive back-scattered light signals to provide a digital averaged signal output shown at 21 in section (f) of Figure 2 the sampled output from the converter 10 in respect of one return signal being shown at 22 in section (e).
This output may be converted to an analogue signal by a digital-to-analogue converter 23 and then fed to a processor 24 which gives an indication of the average signal waveform in respect of the successive incoming signal waveforms to the circuit arrangement, or the output from the adder 15 may be fed directly to the processor 24.
Claims (4)
1. An optical fibre sensing system utilising back-scattered or returned light signals along an optical fibre sensor for establishing the scattering or light return profile along the optical fibre sensor, in which a multi-channel averaging circuit arrangement comprises an analogue-to-digital converter which receives an analogue electrical input corresponding to back-scattered or returned light along said optical fibre sensor, in which the digital output from the analogue-todigital converter is fed sequentially to respective digital storage devices of a digital storage arrangement and in which the digital data stored in the respective storage devices corresponding to groups of elements of the back-scattered or returned light signal is clocked out simultaneously into a digital adder the output from which is applied to a processor which provides an indication of the averaged signal waveform in respect of the successive incoming waveforms from the optical sensing system.
2. An optical fibre sensing system as claimed in claim 1, in which the digital storage devices comprise shift registers which are stepped under the control of a clock counter.
3. An optical fibre sensing system as claimed in claim 1 or claim 2, in which the output from the digital adder is applied to a digitalto-analogue converter before being applied to the processor.
4. An optical fibre sensing system substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB878730061A GB8730061D0 (en) | 1987-12-23 | 1987-12-23 | Improvements relating to optical sensing systems |
Publications (3)
Publication Number | Publication Date |
---|---|
GB8829109D0 GB8829109D0 (en) | 1989-01-25 |
GB2211605A true GB2211605A (en) | 1989-07-05 |
GB2211605B GB2211605B (en) | 1991-12-18 |
Family
ID=10628994
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB878730061A Pending GB8730061D0 (en) | 1987-12-23 | 1987-12-23 | Improvements relating to optical sensing systems |
GB8829109A Expired - Fee Related GB2211605B (en) | 1987-12-23 | 1988-12-14 | Improvements relating to optical sensing systems |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB878730061A Pending GB8730061D0 (en) | 1987-12-23 | 1987-12-23 | Improvements relating to optical sensing systems |
Country Status (1)
Country | Link |
---|---|
GB (2) | GB8730061D0 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0457941A1 (en) * | 1990-05-21 | 1991-11-27 | Kabushiki Kaisha Toshiba | Apparatus and method for measuring temperatures by using optical fiber |
US5178465A (en) * | 1990-07-11 | 1993-01-12 | Fujikura Ltd. | Optical fiber laying structure for electric power cable line trouble occurrence location detecting system |
US5217306A (en) * | 1991-03-02 | 1993-06-08 | Fujikura Ltd. | Temperature distribution analyzer using optical fiber |
WO1995016902A1 (en) * | 1993-12-14 | 1995-06-22 | Antel Optronics Inc. | High dynamic range otdr data acquisition circuit |
DE102004015945B3 (en) * | 2004-03-25 | 2005-12-29 | Ufz-Umweltforschungszentrum Leipzig-Halle Gmbh | Determining the temperature of a medium comprises coupling electromagnetic radiation with a Raman-active substance via an optical fiber, arranging the Raman-active substance in the medium and further processing |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0122953A1 (en) * | 1983-04-23 | 1984-10-31 | ANT Nachrichtentechnik GmbH | Method for the determination of the backscatter diagram of a beam waveguide |
-
1987
- 1987-12-23 GB GB878730061A patent/GB8730061D0/en active Pending
-
1988
- 1988-12-14 GB GB8829109A patent/GB2211605B/en not_active Expired - Fee Related
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0122953A1 (en) * | 1983-04-23 | 1984-10-31 | ANT Nachrichtentechnik GmbH | Method for the determination of the backscatter diagram of a beam waveguide |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0457941A1 (en) * | 1990-05-21 | 1991-11-27 | Kabushiki Kaisha Toshiba | Apparatus and method for measuring temperatures by using optical fiber |
US5178465A (en) * | 1990-07-11 | 1993-01-12 | Fujikura Ltd. | Optical fiber laying structure for electric power cable line trouble occurrence location detecting system |
US5217306A (en) * | 1991-03-02 | 1993-06-08 | Fujikura Ltd. | Temperature distribution analyzer using optical fiber |
WO1995016902A1 (en) * | 1993-12-14 | 1995-06-22 | Antel Optronics Inc. | High dynamic range otdr data acquisition circuit |
DE102004015945B3 (en) * | 2004-03-25 | 2005-12-29 | Ufz-Umweltforschungszentrum Leipzig-Halle Gmbh | Determining the temperature of a medium comprises coupling electromagnetic radiation with a Raman-active substance via an optical fiber, arranging the Raman-active substance in the medium and further processing |
Also Published As
Publication number | Publication date |
---|---|
GB2211605B (en) | 1991-12-18 |
GB8730061D0 (en) | 1988-02-03 |
GB8829109D0 (en) | 1989-01-25 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19921214 |