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WO1996031762A1 - Mesure de temperatures - Google Patents

Mesure de temperatures Download PDF

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Publication number
WO1996031762A1
WO1996031762A1 PCT/GB1996/000818 GB9600818W WO9631762A1 WO 1996031762 A1 WO1996031762 A1 WO 1996031762A1 GB 9600818 W GB9600818 W GB 9600818W WO 9631762 A1 WO9631762 A1 WO 9631762A1
Authority
WO
WIPO (PCT)
Prior art keywords
light
wavelength
temperature
sensor element
pulses
Prior art date
Application number
PCT/GB1996/000818
Other languages
English (en)
Inventor
Steven John Butcher
David Armitage
Richard Smith
James David Hobby
Donald Harry Maguire Kings
Original Assignee
Cookson Group Plc
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 Cookson Group Plc filed Critical Cookson Group Plc
Priority to AU51597/96A priority Critical patent/AU5159796A/en
Publication of WO1996031762A1 publication Critical patent/WO1996031762A1/fr

Links

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
    • G01K11/3206—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 at discrete locations in the fibre, e.g. using Bragg scattering
    • 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

Definitions

  • This invention relates to a method of temperature measurement and to apparatus and to a temperature sensor element for use in the method.
  • Optical fibres are known to provide a suitable means of conducting signals between local and remote stations by amplitude or phase modulated light beams.
  • a problem with such measurement is that mechanical or other interference to which the fibres are subjected may induce optical noise or spurious signals.
  • a method of temperature measurement comprising the steps of directing a measuring pulse of light of a first wavelength through a sensor element formed of a material exhibiting temperature dependent absorption at the first wavelength, directing a reference pulse of light of a second wavelength through the sensor element, the second wavelength being selected such that light of the second wavelength is transmitted through the element substantially independently of temperature variation, sensing by means of a receiver the intensities of the measuring and reference pulses after transmission through the sensor element to generate signals V, and V- respectively, sensing during a dwell period the output V 3 of the receiver in the absence of the measuring and reference pulses and processing the signals V. and V- to provide an output signal Z representative of temperature and having a value Z * (V. - V 3 ) / (V- - V 3 ) .
  • An advantage of such a method is that the effects of electronic noise and drift in the processing stage and optical noise in the stage of transmitting light to and from the sensor element may both be cancelled by subtracting V- from both V 1 and V-.
  • the measuring pulse of light is generated repeatedly by operation of a first source which is maintained in a temperature controlled environment in order to stabilise the value of the first wavelength.
  • the operation of said first source is controlled by means of an optical feedback circuit such that the intensities of the successive measuring pulses are maintained constant .
  • the output wavelength of typically available light sources such as light emitting diodes (EDs)
  • EDs light emitting diodes
  • the value of V. can be very sensitive to changes in the wavelength of the measuring pulses of light. Maintaining the output intensity of the first source constant by optical feedback control can significantly improve accuracy of temperature measurement.
  • Figure 1 is a schematic representation of a first embodiment
  • Figure 2 is a graphical representative showing the temperature dependent absorption characteristic of a sensor element shown at three distinct temperatures
  • Figure 3 is a graphical representation of the spectra of light transmitted to the sensor element during successive measuring and reference pulses in accordance with the embodiment of Figure 1;
  • Figure 4 is a schematic representation of the sensor configuration of a second embodiment in which the sensor element is coupled to a single optical fibre;
  • Figure 5 is a schematic representation of the sensor element of the embodiment of Figure 4 coupled to a single optical fibre
  • Figure 6 is a schematic representation of a further sensor element arrangement using a single optical fibre
  • Figure 7 is a schematic representation of the sensor configuration of a third embodiment in which the sensor element is coupled to two optical fibres.
  • Figure 8 is a schematic representation of a modification to the embodiment of Figure 4 and including a beam splitting cube.
  • a first embodiment of the present invention comprises a sensor element 1 located at a remote station 2 and connected to first and second optical fibres 3 and 4 so that light enters the sensor element from the first optical fibre 3 and is collected and channelled into the second optical fibre 4 after transmission through the sensor element.
  • the sensor element 1 is an optical filter glass of type Schott RG665 which transmits light in a waveband above a threshold or cut off wavelength and absorbs light in a shorter wavelength band below the cut off wavelength as described below with reference to Figure 2.
  • Pulses of light from first and second light sources 5 and 6 at a local station 7 are directed into the first optical fibre 3 via a first optical fibre coupler 8 and, after having passed through the sensor element 1, are conducted via the second optical fibre 4 to a receiver 9 also located at the local station.
  • the first and second light sources 5 and 6 are constituted by LEDs (light emitting diodes) whose operation is controlled by a LED controller 13.
  • the LEDs are precision aligned with respect to optical fibres 30,31 respectively, thereby ensuring efficient coupling, and the fibres 30,31 are input to the first optical fibre coupler 8, thereby directing the light pulses to the first optical fibre 3.
  • a second optical coupler 14 separates a proportion of the light transmitted into the first optical fibre 3 into a third optical fibre 15 connected to a photodiode 16 whose output is fed back to the LED controller.
  • LED controller 13 is operable to trigger the first and second light sources 5 and 6 to generate pulses of light of constant predetermined intensity, the intensity being sensed and fed back to provide an optical feedback signal to the LED controller via the third optical fibre 15 and the photodiode 16.
  • the first and second light sources 5 and 6 are selected to have spectra which peak sharply at wavelengths of 665 nanometres and 850 nanometres respectively as shown in Figure 3 where a first peak 33 represents the output of the first light source 5 and second peak 34 represents the output of the second light source 6.
  • the receiver 9 is a silicon PIN photodiode which is sensitive to light over a bandwidth which includes both of these wavelengths.
  • the first and second light sources 5 and 6 are separately pulsed so that not more than one of the peaks 33 and 34 will be present in the spectrum at any given time. Operation of the sources 5 and 6 is controlled by controller 13 which first delivers a firing pulse to the first source 5, thereby generating a measuring pulse of light conducted via the first optical fibre 3 to the sensor element 1, the measuring pulse being conducted after transmission through the sensor element to the receiver 9.
  • the first light source 5 is temperature stabilised by locating the LED within a thermally insulated enclosure 28, the temperature within the enclosure being maintained at a constant level by means of heat dissipated from a power resistor which consumes current determined by a thermistor (not shown) .
  • a thermistor not shown
  • Alternative arrangements may be used in which Peltier heater/cooler devices regulate the temperature within the enclosure. The effect of temperature regulation on the first light source 5 is to maintain the wavelength of light emitted by the LED constant.
  • the controller 13 After the measuring pulse, the controller 13 generates a further firing pulse directed to the second source 6 to produce a reference pulse of light conducted to the sensor element 1 via the first optical fibre 3, and after transmission through the sensor element the reference pulse is conducted via the second optical fibre 4 to the receiver 9.
  • the controller 13 then de-actuates the first and second sources 5,6 during a dwell period prior to delivering a firing pulse to the first source 5 to recommence the sequence. This firing sequence is repeated cyclically, the period of the complete cycle being 10msec.
  • Output signal voltages V., V- and V 3 are derived from the receiver 9 and correspond to the received light intensity during the measuring pulse, the reference pulse and the dwell period respectively.
  • the signal voltages V., V- and V 3 are derived by means of amplifier 21 which receives as its input the output of the receiver 9 which in the preferred embodiment is a photodiode, the output of amplifier 21 being fed to an analogue switch device 22.
  • a clock 23 controls synchronised operation of both the controller 13 and the switch device 22 so that the output of the switch device is switched between lines V., V- and V 3 depending on whether the controller 13 is driving the measuring pulse, the reference pulse or dwell period respectively.
  • the outputs V 1 , V- and V " 3 are integrated by means of capacitors 24, 25 and 26 respectively before being fed to the inputs of a processor 27.
  • V 3 obtained during the dwell period provides an indication of the level of both optical and electronic background noise in the apparatus.
  • This signal may therefore be used to correct the values of V, and V-.
  • a display device 17 receives a display output signal which is derived from the signal Z in a manner which allows the numerical value displayed to be proportional to temperature and calibrated as required.
  • the display 17 may therefore be utilised to indicate the temperature of the remote location 2 in any suitable scale such as degrees Celsius.
  • the light received at the receiver 9 is spectrally modulated by transmission through the sensor element 1 because the sensor element 1 absorbs light selectively according to wavelength as illustrated in Figure 2 where curve 10 illustrates a variation of light transmission with increasing wavelength at normal temperature. From the curve it is apparent that 50% transmission occurs at a cut off wavelength of about 665 nanometres wavelength. Curve
  • the filter element 12 illustrates the variation of transmission as a function of wavelength when the filter element is at a temperature of 100°C below normal temperature, the cut off wavelength here being at about 650 nm.
  • the curves 10, 11 and 12 therefore represent a characteristic of spectral modulation which varies as a function of temperature of the sensor element 1, this spectral modulation being present in the received light thereby enabling the temperature to be remotely determined by analysis of the received light in the receiver 9.
  • the light incident on the sensor element 1 during the measuring pulse via the first optical fibre 3 therefore contains a first peak 33 in the spectrum centred on 665 nanometres wavelength, this first wavelength being selected to coincide with a region of curve 10 shown in Figure 2 at which the transmission of light through the sensor element is sensitive to temperature.
  • Light incident on the sensor element 1 during the reference pulse has a spectrum constituted by the second peak 34 centred on 850 nanometres wavelength, this second wavelength being selected to coincide with portions of the curves 10, 11 and 12 of Figure 2 at which light is transmitted through the sensor element in a manner which is insensitive to temperature change .
  • the response time to changes of temperature at the remote location 2 will depend upon the thermal inertia of the filter element 1 and the extent to which it is thermally insulated.
  • the effect of temperature change on the outputs V 1 , V. and Z may be understood by considering with reference to Figure 2 the effect of an increase in temperature at the remote station from normal to 1C0° above normal temperature.
  • Curve 10 corresponds to the relative transmission of the material of the sensor element at normal temperature and it will be observed that the measuring pulse wavelength of 665 nm corresponds to approximately 50% transmission.
  • the increase in temperature by 100°C results in the relative transmission being reduced to about 10% for the measuring pulse at 665 nm, as determined by curve 11.
  • This reduction in transmission results in the received measuring pulse as measured by the receiver 9 being of significantly decreased intensity, thereby reducing the value of V..
  • the transmission at the 850 nm wavelength of the reference pulse is however unaffected by this change in temperature so that V- remains unchanged.
  • V 3 can be expected to remain constant in the absence of external perturbations so that the value of Z responds to this increase in temperature by being reduced in value according to the above algorithm.
  • the amplifier 18 applies inversion to the variation in Z in the sense that progressive decrease in Z is inverted to provide a progressively increasing output of amplifier 18, thereby providing a corresponding increase in the display output signal whose value is displayed by the display device 17, typically being calibrated in degrees centigrade.
  • the effect of decrease in temperature to 100° below normal temperature follows the reverse pattern in which increased transmission of light is indicated by curve 12 in Figure 2, the value of V 1 thereby being increased so as to increase Z and resulting after inversion in a decrease in the display output signal.
  • light is transmitted to and from the remote location by first and second optical fibres 3 and 4.
  • the second embodiment allows a single optical fibre 3 to extend between the local and remote stations 7 and 2, the single fibre being arranged to carry both transmitted and received light simultaneously.
  • Light passing through the sensor element 1 is reflected back through the sensor element by a reflector 29 to be returned to the local station 7 via the optical fibre 3.
  • the returned light is divided by means of a third optical coupler 52 which directs returned light to the receiver 9 via an additional fibre 54.
  • the reflector 29 may be a mirror or retroreflecting device.
  • light transmitted through the sensor element 1 may for example be reflected at a mirrored end surface 44 of the sensor element as shown in Figure 5 so as to be collected by a lens 46 and returned into the first fibre 3.
  • the fibre 3 may be coupled directly to the sensor element 1 without including any lens provided that a mirrored end surface 45 of the sensor element is curved to constitute a concave mirror which acts to focus the light back into the first fibre 3.
  • the sensor element 1 may alternatively be coupled to both first and second optical fibres 3,4 and additionally may be provided with a reflector 29 which reflects light back through the sensor element to be collected and transmitted via the second optical fibre.
  • the arrangement shown in Figure 4 may be modified as shown in Figure 8 by the inclusion of a beam splitting cube 50 at the local station 7 in place of the second and third optical couplers 14 and 52.
  • the light pulses from the first and second sources 5 and 6 is input to the beam splitting cube 50 via a collimator 51, the cube being arranged such that 50% of the light input emerges into the first optical fibre 3 and the remainder is deflected into the third optical fibre 15 to be detected by the photodiode 16 as part of an optical feedback circuit maintaining constant intensity of the pulses.
  • Light retroreflected from the reflector 29 is returned via the first optical fibre 3 to the beam splitting cube 50 where 50% of the received light is deflected into an additional optical fibre 54 so as to be measured by the receiver 9.
  • the beam splitting cube 50 is arranged such that the retroreflected light cannot enter the third optical fibre 15 and therefore overcomes a potential problem associated with optical fibre couplers in which some stray light may be misdirected, the result of such stray light in the case of the arrangement of Figure 4 being that a small proportion of retroreflected light may enter the third optical fibre 15 and thereby introduce an erroneous feedback signal into the optical feedback circuit.
  • the optical fibres may be 50/125 micron or 100/140 micron communication fibres. These fibres are inexpensive and can be used with low attenuation over long distances. It has been found for example that such fibres provide satisfactory results between local and remote stations separated by 1km.
  • lenses may be used to couple optical fibres to the sensor element material in order to minimise losses.
  • identical photodiodes are employed for both the receiver 9 and the optical feedback photodiode 16.
  • the sensor element may alternatively be formed of a semiconductor material provided that appropriate values of the first and second wavelengths are selected.
  • the second source 6 may optionally be located within the thermally insulated enclosure 28 with the first source 5 as shown in Figure 8. This will stabilise the value of the second wavelength and remove a possible source of error associated with wavelength dependent absorption by the sensor element in the region of the second wavelength.
  • the sensors 9 and 16 may also be located in the thermal enclosure 28 to minimise temperature effects on the sensor outputs.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)

Abstract

On mesure des températures à distance en envoyant par fibres optiques une impulsion de mesure d'une première longueur d'onde à un capteur constitué d'un matériau dont le degré d'absorption à cette première longueur d'onde est fonction de la température. On envoie également à travers ce capteur une impulsion de référence d'une seconde longueur d'onde, celle-ci étant sélectionnée pour transiter par le capteur de manière sensiblement indépendante aux variations de température. Un récepteur détermine l'intensité des impulsions de mesure et de référence après leur transit par le capteur dans le but de générer des signaux V1 et V2, respectivement. On mesure également la sortie V3 du récepteur au cours d'une période d'arrêt en l'absence d'impulsion de mesure ou de référence. On fixe une valeur Z désignant la température du capteur à partir de la formule Z = (V1 - V3)/( V2 - V3). On évite des erreurs dépendantes de la longueur d'onde en conservant à la source lumineuse une température constante. Une rétroaction optique garantit que la source lumineuse soit excitée de manière à produire des impulsions d'une intensité constante.
PCT/GB1996/000818 1995-04-03 1996-04-03 Mesure de temperatures WO1996031762A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU51597/96A AU5159796A (en) 1995-04-03 1996-04-03 Temperature measurement

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9506867.2 1995-04-03
GBGB9506867.2A GB9506867D0 (en) 1995-04-03 1995-04-03 Temperature measurement

Publications (1)

Publication Number Publication Date
WO1996031762A1 true WO1996031762A1 (fr) 1996-10-10

Family

ID=10772428

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1996/000818 WO1996031762A1 (fr) 1995-04-03 1996-04-03 Mesure de temperatures

Country Status (3)

Country Link
AU (1) AU5159796A (fr)
GB (1) GB9506867D0 (fr)
WO (1) WO1996031762A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0852330A1 (fr) * 1996-12-31 1998-07-08 Schott Glas Procédé et dispositif pour la mesure de la température opérationnelle à au moins un endroit d'un corps en verre ou en vitrocéramique, qui est soumis aux grandes varations de la tepérature opérationnelle
WO1998036253A1 (fr) * 1997-02-17 1998-08-20 Luxcom Engineering Module emetteur-recepteur pour capteurs a fibres de verre
US8277119B2 (en) * 2006-12-19 2012-10-02 Vibrosystm, Inc. Fiber optic temperature sensor

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0006530A1 (fr) * 1978-06-26 1980-01-09 Asea Ab Capteur de température à fibres optiques
EP0210719A2 (fr) * 1985-04-25 1987-02-04 Advanced Fiberoptics Technologies Corporation Appareil de mesure de températures à fibres optiques

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0006530A1 (fr) * 1978-06-26 1980-01-09 Asea Ab Capteur de température à fibres optiques
EP0210719A2 (fr) * 1985-04-25 1987-02-04 Advanced Fiberoptics Technologies Corporation Appareil de mesure de températures à fibres optiques

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0852330A1 (fr) * 1996-12-31 1998-07-08 Schott Glas Procédé et dispositif pour la mesure de la température opérationnelle à au moins un endroit d'un corps en verre ou en vitrocéramique, qui est soumis aux grandes varations de la tepérature opérationnelle
WO1998036253A1 (fr) * 1997-02-17 1998-08-20 Luxcom Engineering Module emetteur-recepteur pour capteurs a fibres de verre
US8277119B2 (en) * 2006-12-19 2012-10-02 Vibrosystm, Inc. Fiber optic temperature sensor

Also Published As

Publication number Publication date
GB9506867D0 (en) 1995-05-24
AU5159796A (en) 1996-10-23

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