GB2312503A - Two-part balancing coil assembly compensates for vibration - Google Patents
Two-part balancing coil assembly compensates for vibration Download PDFInfo
- Publication number
- GB2312503A GB2312503A GB9608656A GB9608656A GB2312503A GB 2312503 A GB2312503 A GB 2312503A GB 9608656 A GB9608656 A GB 9608656A GB 9608656 A GB9608656 A GB 9608656A GB 2312503 A GB2312503 A GB 2312503A
- Authority
- GB
- United Kingdom
- Prior art keywords
- coils
- assembly according
- coil
- optical fibre
- support 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.)
- Withdrawn
Links
- 239000013307 optical fiber Substances 0.000 claims abstract description 40
- 230000003287 optical effect Effects 0.000 claims abstract description 21
- 239000000835 fiber Substances 0.000 claims abstract description 13
- 230000005534 acoustic noise Effects 0.000 claims abstract description 5
- 230000007613 environmental effect Effects 0.000 abstract description 9
- 239000006260 foam Substances 0.000 abstract description 7
- 230000000694 effects Effects 0.000 description 5
- 230000000712 assembly Effects 0.000 description 2
- 238000000429 assembly Methods 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000013016 damping Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000008393 encapsulating agent Substances 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
-
- 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
Abstract
A balancing coil assembly for a time-multiplexed pulsed heterodyne optical fibre sensing system is disclosed. The balancing coil assembly comprises a continuous length of optical fibre 30, 32 wound in two coils 12, 14 on a common support 16. The two coils are separated by a dividing wall 24 integrally formed with spools 26, 28. The spools are coated with a vibration insulating foam layer 34 which fully encases the optical fibre 30, 32. When the assembly is exposed to environmental influences such as vibration or acoustic noise, the vibration is applied by the support (18, fig. 1) to the coils 12, 14 along their common axis. Changes in optical path length of each coil induced by the vibration are substantially equal and opposite, and thus the net change in the assembly is small or negligible, and spurious signals are avoided. The sensing system might be an optical fibre hydrophone, or it might detect changes in pressure, temperature, stress and/or strain along a fibre.
Description
IMPROVEMENTS RELATING TO OPTICAL FIBRE SENSING SYSTEMS
This invention relates to optical fibre sensing systems and relates more specifically to optical fibre coil assemblies for incorporation in such systems.
In many coherent optical fibre sensing systems, sensor and balancing optical fibre coils are provided. The sensor coil or coils are sensitive to the measurand, such as pressure in the case of hydrophone based sensing systems. The balancing coil acts to delay a light pulse or a modulated light signal.
In the case of heterodyne optical fibre sensing systems the balancing coil causes a predetermined optical path length difference in order to delay a first modulated light signal with respect to a second modulated light signal. In this way balanced interferometric techniques can be used.
In a typical time-multiplexed pulsed heterodyne optical fibre sensing system two light pulses which are spaced in time are transmitted along a sensor optical fibre. The sensor optical fibre has partially reflective discontinuities or junctions along its length. Small proportions of the light pulses (effectively return signals) are reflected back along the fibre from each fibre discontinuity. The signals reflected back from the successive discontinuities are caused to interfere with the signals reflected from the preceding discontinuities in order to produce heterodyning. This provides a detectable beat signal, the modulation of which is dependent upon the optical path lengths of optical fibre sensor coils between the discontinuities. As the optical path lengths change the modulation changes.
A problem in such systems is that the balancing coils are sensitive to acoustic and vibrational noise. In environments where such disturbances are present, they may apply force to the balancing coil which can change its optical path length which in turn may introduce spurious effects in the system. This can cause, for example optical phase noise.
A solution which has been adopted is to provide optical fibre balancing coils which are insensitive to environmental influences thus reducing the spurious effects in the system.
Such a balancing coil is shown in British Patent No. 2250588 which shows the use of two coils each of which is affected by environmental influences. By causing the effect generated in each coil to be opposite, the net effect can be cancelled out. However, it is very difficult to remove completely the effects of environmental influences and some spurious signals usually remain.
It is an object of the invention to provide a system which is less sensitive to environmental influences. It is another object of the invention to provide such a system which is simpler than known systems.
According to a first aspect the invention provides a balancing coil assembly for an optical fibre sensing system comprising a first coil, a second coil and a support means in which the first and second coils are supported on the support means.
Preferably the environmental influences are vibration and/or acoustic noise.
Preferably the coils are disposed on a common axis. The common axis may extend vertically and the coils may be disposed one above the other. In another embodiment the coils are mounted on separate axes whch are substantially parallel to each other. Preferably the assembly is orientated such that vibrational motion occurs along an axis parallel to the axes or the common axis of the fibre coils. The coils may be adjacent. Preferably the support rneans or a region or part of the support means may be present between the coils.
Preferably the each coil is located on a spool comprised by the support means. Preferably the coils are located on parts of the support means which are spaced apart from each other.
The support means may comprise a base or divider. The support means may be adapted to receive vibrational force and apply it to each of the coils. The support means apply vibrational force to each of the coils in equal measure. Preferably the first and second coils have substantially equal optical path lengths. Preferably the dimensions of each coil are substantially the same.
A problem with concentric coils is that vibration related optical characteristics may differ for each coil because they have different dimensions and are not mounted on a common support. It may be difficult to match vibration related optical characteristics in such prior art assemblies. By providing similar sized coils mounted on a common support, matching of characteristics may be easier.
One or more optical characteristics of the coil may change in response to environmental influences. An optical characteristic which may change is optical path length. The amount by which the optical characteristic or characteristics change may be equal and opposite in each coil. Thus the net change in the balancing coil assembly may be substantially zero.
According to a second aspect the invention provides an optical fibre sensing system comprising a balancing coil assembly according to the first aspect of the invention.
Preferably the optical fibre sensing system comprises a balancing circuit. The balancing circuit may comprise a first optical fibre arm and a second optical fibre arm, there being a balancing coil assembly in one of the arms. Preferably at a first end, the optical fibre arms are optically linked by a coupler. Light may be fed through the coupler into each arm. Preferably at a second end, the optical fibre arms are optically linked by a coupler.
Light pulses may be fed through the coupler to sensor means. The sensor means may comprise a coil or coils. It may be an array of coils. The coils may be connected in series.
Alternatively the sensor means may be one or more non-coiled lengths of optical fibre.
Preferably light in each arm is modulated into pulses by a respective modulator. The modulators may produce modulated light pulses having a slightly different frequency in each arm.
One aspect of the present invention is directed to optical fibre hydrophones, in which the balancing coil may be exposed to environmental influences such as vibration and airborne acoustic pressures. It is also applicable to other optical fibre sensing systems in which a degree of insensitivity to environmental influences is required. The sensing system may be a terrestrial based system. Light pulses may be fed into a length of optical fibre extending around the circumference or perimeter of an area, such as a perimeter fence. The length of optical fibre may be buried.
The sensing system may be an interferometric reflectometric sensor system.
The system may detect pressure or temperature applied to a fibre. It may detect stress and/or strain along a fibre.
In an embodiment having a plurality of sensors, they may be in individual zones, a zone being defined at a first end and a second end by partially reflective discontinuities or junctions.
An embodiment of the invention will now be described, by way of example only, with reference to the accompanying figures in which:
Figure 1 shows a balancing coil assembly; and
Figure 2 shows part of the assembly of Figure 1.
Figure 1 shows a side view of a balancing coil assembly 10. The assembly 10 comprises a first coil 12 and a second coil 14 supported on a rigid former 16. The coils 12, 14 are formed of a single optical fibre which is wound to form coil 12 and then wound to form coil 14. The coils 12, 14 together comprise a single balancing coil (the word "coil" being used loosely).
The former 16 is supported in a frame 18. The former 16 is rigidly mounted in frame 18.
Vibrations in the frame 18 are conveyed to the former 16. The frame 18 is surrounded by a layer 20 of acoustic damping material which is intended to isolate the coils 12, 14 to some extent from vibration, particularly airborne acoustic noise. The layer 20 is encased in a box 22. The outer dimensions of the box are approximately 100mm by 100mm.
Further details of the coils 12, 14 and former 16 are shown in Figure 2. This shows a cross sectional view through part of the assembly of Figure 1.
As can be seen the former 16 comprises a dividing wall or base 24 integrally formed with spools 26, 28 extending from either side. Fibre 30, 32 is wound onto the spools 26, 28 to form coils 12, 14 respectively. In the embodiment shown the fibre 30, 32 is wound onto a layer of foam 34 which coats the spools 26, 28, the layer comprising a vibration insulating layer. Other layers of foam 34 are provided such that there is foam 34 between the fibre 30, 32 and the wall 24 and on all other sides of the fibre 30, 32. Thus the fibre is fully encased in foam 34. The foam 34 is surrounded by a coating of encapsulant 36.
The diameters of the coils 12, 14 are about 50mm. The combined height of the coils stacked one on top of the other is about 60mm.
The balancing coil assembly 10 is provided with damping materials (the layer 20 and foam 34) which reduces the amount of vibration which affects the coils. This vibration is mechanical vibration and acoustic disturbance. However, some vibration will inevitably get through to affect the coils 12, 14. Therefore the assembly 10 is constructed such that changes induced in the optical path length of the coils 12, 14 are equal and opposite thus producing no net change.
The assembly 10 is orientated such that vibrational motion is induced along an axis 36 about which the coils are wound. Vibrational motion along this axis does not cause a net change in the optical path length of the balancing coil assembly 10. It is believed by the inventors that if the former 16 is vibrating along the axis 36, as it and coils 12, 14 move upwards, coil 12 will be placed under compression and coil 14 will be placed under tension ("compression" and "tension" being relative terms) and vice versa for a downward movement.. Therefore any change in optical path length induced by the force applied to the coils caused by vibration should be equal and opposite in each coil.
The invention provides a simple balancing coil assembly which is relatively insensitive to vibration. Use of two similar coils enables matching of of optical changes in each coil to be straightforward.
Claims (16)
1. A balancing coil assembly for an optical fibre sensing system comprising a first
coil, a second coil and a support means in which the first and second coils are
supported on the support means.
2. An assembly according to Claim 1 in which the coils are disposed on a common
axis.
3. An assembly according to Claim 1 or Claim 2 in which the coils are spaced apart
on a common axis and separated by a region or part of the support means.
4. An assembly according to Claim 3 which is orientated such that vibrational motion
occurs along an axis parallel to the common axis of the fibre coils.
5. An assembly according to any preceding claim in which each coil is located on a
spool comprised by the support means.
6. An assembly according to any preceding claim in which the support means
comprises a base or divider.
7. An assembly according to any preceding claim in which the support means is
adapted to receive vibrational motion and apply it to each of the coils.
8. An assembly according to Claim 6 in which the support means applies the
vibrational motion to each of the coils in equal measure.
9. An assembly according to Claim 7 or Claim 8 in which an optical characteristic of
the first and second coils changes in response to the vibrational motion.
10. An assembly according to Claim 9 in which an amount by which the optical
characteristic changes is equal and opposite in each coil.
11. An assembly according to any of Claims 7 to 10 in which the vibrational motion
is caused by acoustic noise.
12. An assembly according to any preceding claim in which the dimensions of each
coil are substantially the same.
13. A balancing coil assembly substantially as described herein with reference to
Figures 1 and 2 of the accompanying drawings.
14. An optical fibre sensing system comprising a balancing coil assembly according to
any preceding claim.
15. An optical fibre sensing system according to Claim 14 comprising an optical fibre
hydrophone.
16. An optical fibre sensing system substantially as described herein with reference to
Figures 1 and 2 of the accompanying drawings.
16. An optical fibre sensing system according to Claim 14 which is a terrestrial based
system.
17. An optical fibre sensing system substantially as described herein with reference to
Figures 1 and 2 of the accompanying drawings.
Amendments to the claims have been filed as follows 1. A balancing coil assembly for an optical fibre sensing system comprising a first coil, a second coil and a support means in which the first and second coils are
supported on the support means in which the coils are disposed on a common axis
and are spaced apart along the common axis.
2. An assembly according to claim 1 in which the coils are separated by a region or
part of the support means.
3. An assembly according to claim 1 or claim 2 which is orientated such that
vibrational motion occurs along an axis parallel to the common axis of the fibre
coils.
4. An assembly according to any preceding claim in which each coil is located on a
spool comprised by the support means.
5. An assembly according to any preceding claim in which the support means
comprises a base or divider.
6. An assembly according to any preceding claim in which the support means is
adapted to receive vibrational motion and apply it to each of the coils.
7. An assembly according to claim 6 in which the support means applies the
vibrational motion to each of the coils in equal measure.
8. An assembly according to claim 6 or claim 7 in which an optical characteristic of
the first and second coils changes in response to the vibrational motion.
9. An assembly according to claim 8 in which an amount by which the optical
characteristic changes is equal and opposite in each coil.
10. An assembly according to any of claims 6 to 9 in which the vibrational motion is
caused by acoustic noise.
11. An assembly according to any preceding claim in which the outer dimensions of
each coil are substantially the same.
12. A balancing coil assembly substantially as described herein with reference to
Figures 1 and 2 of the accompanying drawings.
13. An optical fibre sensing system comprising a balancing coil assembly according to
any preceding claim.
14. An optical fibre sensing system according to claim 13 comprising an optical fibre
hydrophone.
15. An optical fibre sensing system according to claim 13 which is a terrestrial based
system.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9608656A GB2312503A (en) | 1996-04-26 | 1996-04-26 | Two-part balancing coil assembly compensates for vibration |
| KR1019970014629A KR970071037A (en) | 1996-04-26 | 1997-04-19 | Fiber optic detection system |
| FR9705143A FR2748107A1 (en) | 1996-04-26 | 1997-04-25 | BALANCING WINDING ASSEMBLY AND FIBER OPTIC DETECTION SYSTEM |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9608656A GB2312503A (en) | 1996-04-26 | 1996-04-26 | Two-part balancing coil assembly compensates for vibration |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9608656D0 GB9608656D0 (en) | 1996-12-04 |
| GB2312503A true GB2312503A (en) | 1997-10-29 |
Family
ID=10792688
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9608656A Withdrawn GB2312503A (en) | 1996-04-26 | 1996-04-26 | Two-part balancing coil assembly compensates for vibration |
Country Status (3)
| Country | Link |
|---|---|
| KR (1) | KR970071037A (en) |
| FR (1) | FR2748107A1 (en) |
| GB (1) | GB2312503A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2002055970A1 (en) * | 2001-01-11 | 2002-07-18 | Litton Systems, Inc. | Fiber optic displacement sensor |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2250588A (en) * | 1990-12-06 | 1992-06-10 | Marconi Gec Ltd | Optical fibre coil with self adjusting pressure compensation |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61118095A (en) * | 1984-11-14 | 1986-06-05 | Hitachi Ltd | Acceleration suppressing type optical fiber hydrophone |
| GB2189110B (en) * | 1986-03-17 | 1989-11-15 | Plessey Co Plc | Improvements relating to optical fibre hydrophones |
| GB2221120B (en) * | 1988-07-20 | 1992-07-15 | Plessey Co Plc | A hydrophone |
-
1996
- 1996-04-26 GB GB9608656A patent/GB2312503A/en not_active Withdrawn
-
1997
- 1997-04-19 KR KR1019970014629A patent/KR970071037A/en not_active Application Discontinuation
- 1997-04-25 FR FR9705143A patent/FR2748107A1/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2250588A (en) * | 1990-12-06 | 1992-06-10 | Marconi Gec Ltd | Optical fibre coil with self adjusting pressure compensation |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6563967B2 (en) | 2000-01-27 | 2003-05-13 | Northrop Grumman Corporation | Fiber optic displacement sensor |
| WO2002055970A1 (en) * | 2001-01-11 | 2002-07-18 | Litton Systems, Inc. | Fiber optic displacement sensor |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2748107A1 (en) | 1997-10-31 |
| KR970071037A (en) | 1997-11-07 |
| GB9608656D0 (en) | 1996-12-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |