GB2214771A - Optical fibre pressure or weight transducer - Google Patents
Optical fibre pressure or weight transducer Download PDFInfo
- Publication number
- GB2214771A GB2214771A GB8900183A GB8900183A GB2214771A GB 2214771 A GB2214771 A GB 2214771A GB 8900183 A GB8900183 A GB 8900183A GB 8900183 A GB8900183 A GB 8900183A GB 2214771 A GB2214771 A GB 2214771A
- Authority
- GB
- United Kingdom
- Prior art keywords
- fibre
- transducer
- pressure sensitive
- pressure
- changes
- 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- Withdrawn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 title claims abstract description 16
- 239000000835 fiber Substances 0.000 claims abstract description 34
- 230000005540 biological transmission Effects 0.000 claims abstract description 7
- 230000035945 sensitivity Effects 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 5
- 230000004044 response Effects 0.000 abstract description 2
- 238000005303 weighing Methods 0.000 description 5
- 239000003990 capacitor Substances 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 244000043261 Hevea brasiliensis Species 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000007767 bonding agent Substances 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 235000009508 confectionery Nutrition 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 229920003052 natural elastomer Polymers 0.000 description 1
- 229920001194 natural rubber Polymers 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 229920002379 silicone rubber Polymers 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
- G08B13/181—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems
- G08B13/183—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier
- G08B13/186—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier using light guides, e.g. optical fibres
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G19/00—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups
- G01G19/02—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups for weighing wheeled or rolling bodies, e.g. vehicles
- G01G19/022—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups for weighing wheeled or rolling bodies, e.g. vehicles for weighing wheeled or rolling bodies in motion
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances
- G01G3/12—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing
- G01G3/125—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing wherein the weighing element is an optical member
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
- G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
-
- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/01—Detecting movement of traffic to be counted or controlled
- G08G1/02—Detecting movement of traffic to be counted or controlled using treadles built into the road
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Fluid Pressure (AREA)
Abstract
A pressure or weight transducer comprises an optical fibre (10) which is located on a flat rigid surface (12). A constant light signal is fed into one end of the fibre from a control unit (13). The control unit (13) includes a receiver at the other end of the fibre which detects changes in the light transmission level and produces an output signal which is either calibrated to be proportional to the changes in pressure or weight applied to the fibre or to change from a first to second state in response to that pressure exceeding a predetermined threshold. The transducer may be used to count vehicles on a road, for weight measurement, and for burglar alarms. <IMAGE>
Description
OPTICAL FIBRE PRESSURE TRANSDUCER
The present invention relates generally to the field of fibre optics and in particular the invention provides a new application for optical fibres as pressure transducers
The present invention consists in a pressure transducer comprising a length of optical fibre, a portion of which is arranged to be located on a rigid, substantially flat surface to define a pressure sensitive region of the fibre1 a transmitter arranged to transmit a fixed level light signal through the fibre from an input end to an output end thereof, a receiver arranged to monitor the light signal arriving at the output end of the fibre and to produce a receiver signal which is a function of changes in the output level of the light signal detected by the receiver, such that the receiver signal is responsive to changes in the transmission characteristics of the fibre as a result of pressure being applied to the fibre in the pressure sensitive region.
The principle of the present invention may be applied to various applications, including analog applications such as the measurement of weight or pressure, in which case the receiver signal can be calibrated in accordance with the parameter to be measured and the resulting signal level displayed using either an electromechanical meter or an analog to digital converter and a digital read-out.
Alternatively the receiver signal may be compared with a predetermined threshhold and deviations above that threshhold detected. This latter arrangement is most useful in applications such as pressure sensors in household alarm systems, in which case the optical fibre may be laid under the carpet or other floor covering, or event counters such as traffic counters used by road authbrities for monitoring vehicular traffic densities.
Several embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 schematically illustrates an arrangement which might be used in a traffic counting application or a household alarm application of the present invention;
Figure 2 illustrates in plan view an apparatus which might be used in an application of the invention for weight measurement;
Figure 3 illustrates a side view of the apparatus of
Figure 2;
Figure 4 illustrates a transmitter circuit which may be used with embodiments of the present invention; and
Figure 5 illustrates a receiver circuit which may be used in traffic counting and household alarm embodiments of the invention and with minor modification can also be used in weight measurement applications of the invention.
Referring to Figure 1, all embodiments of the present invention employ a loop of optical fibre 10, having at least one portion 11 which is located on a substantially flat rigid surface 12. The two ends of the cable 10 are respectively connected to photo-optic transmitter and receiver devices mounted in a control unit 13. In embodiments of the invention where the extremity of the loop 14 does not form part of the pressure sensitive region of the optical fibre, the loop is mounted on an end plate 15 such that changes in the transmission characteristics of the fibre will not be caused as a result of small movements in the fibre when in use.
The fibre chosen for use in preferred embodiments of the invention is RS (362-047) Single Core Polymer cable constructed of a lam single-step-index plastic fibre sheathed in a PVC jacket. This cable was chosen for its strength and durability, ease of handling and cost.
Termination of the fibre is achieved using a RS (456-598) single way plug.
When employing the present invention as a traffic counter, various suitable methods of positioning and fixing the optical fibre on the road surface exist, including bonding the fibre directly to the road surface with a suitable bonding agent, sheathing the optical fibre in a natural rubber or silicon rubber sheath and attaching this to the road surface with suitable fasteners such as staples and, for more permanent installations, cutting a shallow groove in a road surface and locating the fibre in the groove beneath a suitable flexible putty.
In applications where the present invention is used as a pressure sensitive device in burglar alarms, the fibre optic cable could simply be laid over a floor surface and covered by a carpet or mat or other floor covering, or alternatively the fibre could be incorporated into a pressure sensitive mat.
Referring to Figures 2 and 3, a simple and effective weight transducer can be achieved by bonding a length of optical fibre 20 to a rigid base plate 22, over which is located a pressure pad 24 which in turn supports a weighing plate 23 to provide a surface onto which the object to be weighed may be placed. In this embodiment the bottom surface of the pressure pad 24 defines the pressure sensitive region 21 of the optical fibre 20 and as the length of this region is fixed by the dimensions of the pressure pad 24 a reproducible and well defined relationship will exist between the weight applied to the weighing plate 23 and the transmission characteristics of the cable 20. It has been found that the linearity of the transmission characteristic of the optical fibre is sufficient to enable weight measurement over useful ranges of values.It will also be recognised that the range of weights for which the weighing device may be employed is dependent on the length of the region 21 under the pressure pad 24 and therefore weighing apparatus of different capacities can be manufactured simply by altering the dimensions of the pressure pad 24.
Referring to Figures 4 and 5 it will be seen that, since a coherent beam of light is not required for embodiments of the present invention, a standard LED can be used. In the described embodiment, a RS High Radiance
Emitter (633-701) diode was employed, having a transmission wavelength of 830nm, which lies in the optimum wavelength region for photo diode response. The detector chosen is a RS PIN photodiode (303-292) which is inexpensive and readily available. Both the emitter and detector are housed within a standard RS "Sweet Spot"
Housing (456-605) (not shown), allowing the optical fibre to be easily replaced if damaged, and also enabling the control unit to be disconnected from the optical fibre and removed to another site without having to remove the fibre itself.
Referring to Figure 5, the receiver diode D2 is connected to a high gain input amplifier comprising IC1 and negative feedback resistor R2. In the illustrated circuit, the output of IC1 is then capacitor coupled via C1 to the input of a second amplifier stage comprising IC2 and resistors R4, R5 and R6 and having a variable gain in the range of 10 to 500. The input to the second stage amplifier is biassed to the centre of the supply range by a resistor R3.The embodiment of the receiver circuit illustrated in Figure 5 is useful for counting and detecting applications where it is only necessary to detect a reasonably rapid transition from one output level to another, and the AC coupling between the two amplifier stages enables multiple events to be detected even under the circumstances where a first event may not have been completed (i.e. the pressure had not been removed from the fibre) before a second event is initiated. This features is particularly useful in traffic counting applications where vehicles may sometimes come to a halt on the detector cable. With prior art pneumatic traffic counters such an event would cause the counter to stop counting until the offending vehicle was removed from the detector tube.
In counting and detecting applications, the output of the second stage amplifier would typically be connected to the input of a threshhold detecting circuit which was in turn connected to the input of a counter or alarm circuit. The sensitivity of the detector or counter circuit would then be adjusted by varying the gain of the second stage amplifier using variable resistor R5. In the traffic counting application, for example, this would enable the threshhold of the detector circuit to be varied such that the circuit would only count vehicles above a certain threshhold weight. This might be useful, for example, where only the number of trucks or heavy vehicles using a particular road is required to be known.Alternatively, if it is desirable to detect the passage of all vehicles including light-weight vehicles such as bicycles, the threshhold level could be set at a very low level, thus providing another advantage of the present invention over prior art traffic counters, which were generally incapable of detecting light vehicles such as push-bikes.
If it is desirable to detect the passage of vehicles in a particular range of weights, then it is a simple matter to install two traffic counters at a single point in the road, with each counter being set to a different threshhold weight and the difference in counts being monitored. Similarly, it is possible to counter the number of vehicles using specific lanes in a multi-lane road by installing individual optical fibre loops extending to the centre of each of the lanes on the road (i.e. to monitor three lanes, three loops would be used, with each loop extending to the centre-line of a respective one of the lanes).In this way, the longest fibre-optic cable would measure the traffic density in its respective lane and the difference between the counts detected by the counters of adjacent lanes would provide the traffic density for the remaining two lanes. To facilitate such differential counting techniques, a number of counters could be provided in one instrument, together with logic circuits connected between adjacent receivers to derive pulses which can be counted to provide the difference count.
In weighing applications, resistor R3 and capacitor C1 would be removed from the circuit of
Figure 5 to enable DC coupling to be employed between the amplifier stages in order that a steady state analog signal representative of the mass applied to the transducer could be obtained. In such applications, additional scaling and biassing of the output of the second stage amplifier may. be required in order to display the output of the apparatus using conventional display devices such as moving coil meters and digital read-outs.
In some applications, particularly weight-measuring applications, where actual signal levels are important, it may sometimes be necessary to provide temperature correction circuits and more sophisticated current regulating circuits for the transmitter diode D1 of
Figure 4 and it may also be necessary in some instances to provide band limiting of the input amplifier in order to minimise noise.
It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention as described above without departing from the spirit or scope of the invention as broadly described.
Claims (12)
1. A pressure transducer comprising a length of optical fibre, a portion of which is arranged to be located on a rigid, substantially flat surface to define a pressure sensitive region of the fibre, a transmitter arranged to transmit a fixed level light signal through the fibre from an input end to an output end thereof, a receiver arranged to monitor the light signal arriving at the output end of the fibre and to produce a receiver signal which is a function of changes in the output level of the light signal detected by the receiver, such that the receiver signal is responsive to changes in the transmission characteristics of the fibre as a result of pressure being applied to the fibre in the pressure sensitive region.
2. The transducer of claim 1 wherein the fibre is arranged in a loop with the input and output ends located adjacent to one another.
3. The transducer of claim 2 wherein the fibre is doubled to form said loop with outward and inward running halves of the fibre laid adjacent to one another and a central folded portion of the fibre being bonded to a base to prevent significant changes in stress occurring in the region as a result'of movement.
4. The transducer according to claim 3 wherein the pressure sensitive region is divided with a part being located on each of the outward and inward running halves of the fibre.
5. The transducer according to any one of the preceding claims wherein the pressure sensitive region is mounted on a base which forms said flat surface.
6. The transducer according to any one of claims 1 to 4 wherein the fibre is sheathed and the pressure sensitive region is arranged to be located in a groove cut into a rigid surface, the groove. being of a depth less than the outside diameter of the fibre and its sheath and the bottom of the groove forming said flat surface.
7. The transducer according to any one of claims 1-4 wherein the pressure sensitive region of the fibre is incorporated in a mat to form a pressure sensitive mat.
8. The transducer according to any one of claims 1-4 wherein the pressure sensitive region of the fibre is mounted between two rigid members a first one of which forms said flat surface such that the transducer is respons e to pressure applied to t second of said members in a direction towards the first
9. The transducer of claim 8 wherein the second member is significantly shorter than the first such that forces applied to the transducer are concentrated over a short portion of the fibre to increase the sensitivity of the transducer.
10. The transducer according to any one of the preceding claims wherein the receiver is responsive to changes in the output level of said light signal to produce an output having one of two states depending upon whether the light signal is above or below a predetermined threshold.
11. The transducer according to any one of claims 1-10 wherein the receiver is responsive to changes in the output level of said light signal to produce an output signal which is proportional to the changes in the pressure applied to the transducer which cause the changes in the light output signal.
12. A transducer substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPI619488 | 1988-01-06 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8900183D0 GB8900183D0 (en) | 1989-03-01 |
| GB2214771A true GB2214771A (en) | 1989-09-13 |
Family
ID=3772707
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8900183A Withdrawn GB2214771A (en) | 1988-01-06 | 1989-01-05 | Optical fibre pressure or weight transducer |
Country Status (3)
| Country | Link |
|---|---|
| CN (1) | CN1035355A (en) |
| AU (1) | AU2770189A (en) |
| GB (1) | GB2214771A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2673749A1 (en) * | 1991-03-08 | 1992-09-11 | Electronique Controle Mesure | Device for detecting passage over a roadway, and its installation method |
| EP0747678A1 (en) * | 1995-06-09 | 1996-12-11 | Seb S.A. | Force measuring device with optical sensor compensating off-centre loading, particularly for weighing persons and process for producing such an apparatus |
| US5952647A (en) * | 1996-03-20 | 1999-09-14 | Seb S.A. | Force measuring apparatus with optical sensor enabling limitation of eccentricity defects in particular for bathroom scales and method of manufacturing apparatus of this kind |
| WO2002065426A1 (en) * | 2001-02-15 | 2002-08-22 | Qinetiq Ltd | Traffic monitoring |
| EP1571433A2 (en) * | 2004-03-05 | 2005-09-07 | Denso Corporation | Load sensor mounting device with sensor-protective structure |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4082692B2 (en) * | 2004-03-18 | 2008-04-30 | 株式会社デンソー | Pedestrian detection device |
| CN1308660C (en) * | 2004-06-18 | 2007-04-04 | 梁少华 | Optical fiber weighing system |
| CN110371835A (en) * | 2019-08-27 | 2019-10-25 | 刘彬 | The optical fiber type pedestrian of a kind of escalator or moving sidewalk passes in and out terraced monitoring device |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2145515A (en) * | 1983-08-20 | 1985-03-27 | Nmi Ltd | Crack or strain monitor systems |
| GB2145516A (en) * | 1983-08-20 | 1985-03-27 | Nmi Ltd | Crack or strain monitors |
| GB2145517A (en) * | 1983-08-20 | 1985-03-27 | Nmi Ltd | Crack or strain monitors |
| GB2199938A (en) * | 1987-01-20 | 1988-07-20 | De La Rue Syst | Force detection assembly |
| EP0278143A1 (en) * | 1987-02-13 | 1988-08-17 | G2 SYSTEMS CORPORATION (a California corporation) | Structural monitoring system using fiber optics |
| GB2201511A (en) * | 1987-02-26 | 1988-09-01 | Bicc Plc | Optical sensors |
-
1989
- 1989-01-04 AU AU27701/89A patent/AU2770189A/en not_active Abandoned
- 1989-01-05 CN CN 89100128 patent/CN1035355A/en active Pending
- 1989-01-05 GB GB8900183A patent/GB2214771A/en not_active Withdrawn
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2145515A (en) * | 1983-08-20 | 1985-03-27 | Nmi Ltd | Crack or strain monitor systems |
| GB2145516A (en) * | 1983-08-20 | 1985-03-27 | Nmi Ltd | Crack or strain monitors |
| GB2145517A (en) * | 1983-08-20 | 1985-03-27 | Nmi Ltd | Crack or strain monitors |
| GB2199938A (en) * | 1987-01-20 | 1988-07-20 | De La Rue Syst | Force detection assembly |
| EP0278143A1 (en) * | 1987-02-13 | 1988-08-17 | G2 SYSTEMS CORPORATION (a California corporation) | Structural monitoring system using fiber optics |
| GB2201511A (en) * | 1987-02-26 | 1988-09-01 | Bicc Plc | Optical sensors |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2673749A1 (en) * | 1991-03-08 | 1992-09-11 | Electronique Controle Mesure | Device for detecting passage over a roadway, and its installation method |
| EP0747678A1 (en) * | 1995-06-09 | 1996-12-11 | Seb S.A. | Force measuring device with optical sensor compensating off-centre loading, particularly for weighing persons and process for producing such an apparatus |
| FR2735231A1 (en) * | 1995-06-09 | 1996-12-13 | Seb Sa | OPTICAL SENSOR FORCE MEASURING APPARATUS FOR LIMITING EXCENTRATION DEFECTS, IN PARTICULAR FOR A WEIGHTING, AND METHOD OF MAKING SAME |
| US5952647A (en) * | 1996-03-20 | 1999-09-14 | Seb S.A. | Force measuring apparatus with optical sensor enabling limitation of eccentricity defects in particular for bathroom scales and method of manufacturing apparatus of this kind |
| WO2002065426A1 (en) * | 2001-02-15 | 2002-08-22 | Qinetiq Ltd | Traffic monitoring |
| US7068186B2 (en) | 2001-02-15 | 2006-06-27 | Qinetiq Limited | Traffic monitoring |
| EP1571433A2 (en) * | 2004-03-05 | 2005-09-07 | Denso Corporation | Load sensor mounting device with sensor-protective structure |
| EP1571433A3 (en) * | 2004-03-05 | 2006-05-10 | Denso Corporation | Load sensor mounting device with sensor-protective structure |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8900183D0 (en) | 1989-03-01 |
| CN1035355A (en) | 1989-09-06 |
| AU2770189A (en) | 1989-07-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |