Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
  • G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
  • H10N10/80—Constructional details
  • H10N10/81—Structural details of the junction
  • H10N10/817—Structural details of the junction the junction being non-separable, e.g. being cemented, sintered or soldered

Definitions

• the invention relates to a method for measuring the sensitivity of a radiative fluxmeter, the corresponding radiatim fluxmeter and the use of such a fluxmeter.
• the measurement of the thermal radiation emitted by a surface, more specifically designated as the target surface, is important in practice, such an operation in particular making it possible to measure the temperature of the target surface remotely.
• thermopile detectors are particular thermal detectors, which convert the radiation to be measured into a rise in temperature of a thermally insulated surface element.
• the equilibrium temperature, measured by the hot junctions of the thermopile is influenced by convection exchanges and it is therefore essential to encapsulate these detectors in a sealed housing, of the T05 type for example, in order to eliminate all disturbances due to air movements.
• the radiative fluxmeters are thermal sensors capable of allowing the measurement of a density of radiation flux, independently of the convective exchanges with the ambient medium. These devices have the advantage, compared to other thermal sensors, of being able to be used in the absence of encapsulation.
• the sensitive element is a planar thermopile mounted on an insulating support of very low thickness. contact with a metal sheet of high thermal conductivity. Given the small thickness of the insulating sheet, all temperature variations are passed through the support on the thermoelectric junctions. These variations are not detected because the differential structure of the thermopile detector makes it possible to eliminate the effect of temperature drift from all of the thermoelectric junctions.
• thermo ⁇ elements are covered with a layer absorbing the incident thermal radiation while the cold junctions are covered with a layer reflecting this radiation.
• the electric voltage generated by it is directly proportional to the density of the radiation flux. This density is positive when the radiation is absorbed, and negative otherwise.
• the thermal conduction between thermoelectric junctions is increased to the maximum so that the output voltage is not influenced by air movements, which can be compared to an increase in apparent conductivity of the fluid surrounding the radiative fluxmeter.
• a radiative heat flow meter of this type has been disclosed by the French Patent Application No. 86 07072 ⁇ in the name of the Applicant.
• the sensitive element no longer having to be thermally insulated, it is no longer necessary to produce sensors of small dimension, with a view to their encapsulation.
• current radiative fluxmeters have an active surface, a measurement surface, which can reach several square decimeters.
• Their sensitivity, expressed in ⁇ V / W / m 2 is very important since it is proportional to the number of thermo-elements distributed on the active surface of the radiative fluxmeter.
• a symmetrical structure to measure thermal radiation is important with regard to the processes of measuring quantities which are reduced. directly or indirectly to the measurement of thermal radiation or of the coefficient of sensitivity to thermal radiation.
• This same symmetrical structure of the radiative fluxmeters implies, in accordance with the studies and observations carried out by the inventors, a symmetrical operation of these very radiative fluxmè ⁇ , the output voltage being positive when the measurement surface absorbs radiation, and negative in the opposite case , because the absorbent surfaces of the measurement surface are brought to a higher temperature when absorbing radiation and to a lower temperature when radiation is emitted from the measurement surface.
• the radiation measurement is reduced to a temperature difference measurement, the sensitivity coefficient of the radiation fluxmeter being independent of the temperature thereof.
• the present invention relates to the implementation of a method for measuring the sensitivity of a radiative fluxmeter, in order to carry out a temperature self-calibration of this type of device.
• Another object of the present invention is the implementation of a specific radiative fluxmeter, allowing a sensitivity measurement and an automatic self-calibration whatever the temperature thereof.
• Another object of the present invention is further, from the aforementioned specific radiative fluxmeter, and taking into account the fact of the latter's sensitivity to temperature, the production of detectors of physical phenomena whose intrinsic parameters influence directly the operation of the aforementioned radiative fluxmeter, in particular of the coefficient of sensitivity, at a given temperature thereof.
• this radiative fluxmeter being provided with a measurement surface at a temperature T "with respect to at least one surface target at a temperature T c placed in an ambient medium, the radiative flux or power density exchanged between the measurement surface and the target surface verifying the relationship:
• this radiative fluxmeter comprising a sensitive surface formed by a support made of dielectric material provided with a continuous meandering band of a first conductive material and of discontinuous zones of a second material conductor, having a thermoelectric power different from that of the first conductive material and greater electrical conductivity, to form a chain of elementary thermocouples making it possible to deliver, for a temperature T m of this chain, a corresponding electric voltage of thermocouple V m , in presence of at least one target surface at a temperature T c , when the radiative fluxmeter, the sensitive surface and the target surface are in the same ambient medium, quable in that it further comprises a circuit for controlling the exchange of heat energy between the radiative fluxmeter and the ambient medium, making it possible to generate an exchange of heat energy between the radiative fluxmeter and the ambient medium and a circuit measurement, following this exchange, of the temperature variation ⁇ m of the measurement surface and the voltage variation ⁇ V B delivered by the thermocouple chain.
• a module for calculating and controlling the sensitivity S ac of the radiative fluxmeter with respect to the target surface is provided, the sensitivity being defined as the ratio of the variation in the voltage ⁇ V B delivered by the radiative fluxmeter to the variation temperature ⁇ T B of the measurement surface.
• the method and the radiation fluxmeter, objects of the present invention find application in the industry of instrumentation and control of thermal radiation, temperature control, and corresponding regulation processes.
• FIG. 2a shows an exploded view of a radiative fluxmeter specially adapted for the implementation of the method of the invention, in a first simplified variant
• FIG. 2cl shows a top view of a third variant embodiment of a radiative fluxmeter more specifically adapted to a fire detector application
• Figure 2c2 shows a longitudinal sectional view along a sectional plane Q of Figure 2cl;
• FIG. 1 a shows a sensitivity diagram of a radiative fluxmeter according to the invention, in an applica ⁇ tion to a dew point detector of the liquid phase of an ambient medium at a determined temperature.
• the radiative fluxmeter for which the sensitivity measurement method can be implemented is either a radiative fluxmeter as described in the art by French patent application no. 86 07072 in the name of the applicant, that is, on the contrary, a radiative fluxmeter specially adapted for the implementation of the method as will be described later in the description.
• the latter comprise a measurement surface at a temperature T ⁇ vis-à-vis a target surface at a temperature T c .
• the radiative fluxmeter for which the sensitivity measurement method in accordance with the object of the present invention is implemented is placed in an ambient medium and the power density, expressed in W / m 2 , or radiative flux exchanged between the surface the target surface then checks the relationship:
• ⁇ denotes the Boltzmann constant ⁇ c and ⁇ B denote the emissivity coefficient of the target and measurement surfaces respectively; T c and T B denote the absolute temperature of the target and measurement surfaces considered. More generally, it is indicated that, although the target surface can be constituted by a discrete target surface at a temperature T c , it is recalled that this can on the contrary be constituted by a plurality of delocalized elementary target surfaces and playing the role of a target surface equivalent to a corresponding temperature T c .
• the method, object of the present invention for measuring the sensitivity of a radiative fluxmeter as previously described, and in particular because of the symmetrical operation of the latter, as mentioned previously in the description, can be implemented. works for a multiplicity of target surfaces considered and, ultimately, in the absence of a target surface, when the aforementioned radiation fluxmeter is in an ambient atmosphere in thermal equilibrium with respect to this ambient atmosphere. Under these conditions, it is recalled that at the temperature T c of the target surface can then be substituted a temperature called ambient temperature, denoted T a , with which the radiative fluxmeter is in thermal equilibrium.
• the radiative fluxmeter subjected to the sensitivity measurement method delivers a corresponding electric voltage of thermocouple V B.
• the abovementioned initial conditions being specified and represented in step 1000 of FIG. 1a, it is indicated that the method for measuring the sensitivity of the radiative fluxmeter considered then consists, as represented in step 1001 of the aforementioned figure, of causing an exchange of heat energy between the radiative fluxmeter and the ambient environment.
• step 1001 is followed by a step 1002 consisting in measuring, following this exchange, the temperature variation ⁇ T B of the measurement surface of the radiative fluxmeter as well as of course the voltage variation ⁇ V B delivered by the radiative fluxmeter.
• This voltage variation is none other than the voltage variation of thermo ⁇ couples delivered by the radiative fluxmeter considered following the exchange of heat energy previously mentioned.
• Step 1002 is then followed by a step 1003 consisting in establishing the sensitivity, denoted S BC , of the radiative fluxmeter with respect to the target surface where, where appropriate, with respect to the ambient medium such as ratio of the voltage variation delivered by the radiative flux meter to the temperature variation ⁇ T B of the measurement surface.
• S BC the sensitivity
• thermocouple voltage V B delivered by the radiative fluxmeter is in a temperature range between -15 ° and 250 ° to 350 ° C, substantially linear.
• FIG. 1b which represents a sectional view of a radiative fluxmeter of the prior art as described in patent application n ° 86 07 072 previously mentioned in the description and in which, as a reminder, A denotes a substantially rectangular insulating support, B a meandering conductive strip of an alloy called constantan, C denotes electrically conductive rectangular plates, made of copper for example, and D denotes an insulating resin with high emissive power filling the corresponding spaces between the plates C above the areas of the meander band B not covered with plates C and also covering the plates C in the form of a thin film Da.
• E and F denote an alternation of reflective zones E with low emissivity and zones F with high emissivity on the first end Ca and the second end Cb of each plate C.
• FIG. 1b a top view of Figure 1b and in particular the meander line B thus constituted.
• the exchange of heat energy between the radiative fluxmeter and the ambient medium can consist in making a calorific contribution, denoted + Q, on the radiative fluxmeter, the temperature variation ⁇ T M then being positive and consisting of an increase in temperature relative to the initial temperature of the measurement surface S B.
• the measurement surface S B is then formed by the space formed by the meander line B as shown in FIG.
• thermocouple voltage V B being substantially linear in this temperature range
• the exchange of heat energy between the radiative fluxmeter and the ambient medium can also consist in carrying out a heat shrinkage, denoted -Q, with the radiative fluxmeter considered.
• the temperature variation ⁇ T B then consists of a decrease, denoted - ⁇ T B , in the temperature of the measurement surface S B relative to the initial temperature.
• thermocouple voltage V B the variation in voltage delivered, variation in thermocouple voltage V B , is positive + ⁇ V B during a calorific contribution + Q, and negative and equal to -V m when the heat exchange consists of a heat shrinkage -Q.
• FIG. 1dl there is shown an assembly enabling a sensitivity measurement of the radiative fluxmeter to be carried out in a substantially automatic manner.
• the radiative fluxmeter as shown in the aforementioned Figure ldl, is interconnected by means of two interfacing circuits such as sample-swimming circuits for example, denoted ECH lr ECH 2 , to a microcontroller circuit for example , the sampling circuit ECr ⁇ being able to be connected at the output of the thermocouple voltage V B delivered by the radiative fluxmeter to measure a value of flux or energy density, noted ⁇ , which is converted into the value of a voltage V B of measurement corresponding to a measurement of the thermocouple voltage.
• sample-swimming circuits for example, denoted ECH lr ECH 2
• a microcontroller circuit for example
• the sampling circuit ECr ⁇ being able to be connected at the output of the thermocouple voltage V B delivered by the radiative fluxmeter to measure a value of flux or
• the radiative fluxmeter can be provided with a temperature sensor denoted CT, which is connected to the input of the sample generator ECH 2 to deliver a voltage V ⁇ representative of the temperature of the measurement surface.
• CT temperature sensor
• the sampler circuits such as ECHi and ECH 2 are connected to the microcontroller, which then makes it possible to deliver a value of the target temperature T c under the conditions previously mentioned in the description.
• the microcontroller is also relayed to a power circuit, which makes it possible to carry out the heat exchange controlled by the intermediary of a heat exchanger controlled placed in the vicinity of the corresponding radiative fluxmeter.
• the power circuit is a circuit generating heat energy by Joule effect for example while the heat exchanger controlled is a resistive circuit, which receives electrical energy generated by the power circuit to transform it into heat energy bringing the heat exchange corresponding Q to the radiative fluxmeter considered.
• the measurement process can consist in carrying out a series of successive heat exchanges according to specific cycles or phases represented by phasel, phase2 on the figure ld2.
• Radiative flux i.e.
• the radiative fluxmeter with automatic sensitivity calibration comprises a sensitive surface formed by a support made of dielectric insulating material, bearing the reference A as in the radiative fluxmeters of the prior art, and provided with a continuous meandering strip B made of a first conductive material and of discontinuous zones made of a second conductive material having a thermoelectric power different from that of the first conductive material and greater electrical conductivity.
• This meander line B makes it possible to form a chain of elementary thermocou ⁇ ples to deliver, for a temperature T B of this chain, an electric voltage of corresponding thermocouples V B in the presence of a target surface at a temperature T c , or, at the very least, a plurality of target surfaces as described above in the description, when the radiative fluxmeter, the sensitive surface and the target surface are in the same ambient medium in a given thermal equilibrium situation.
• the radiative fluxmeter with automatic sensitivity calibration according to the invention further comprises a controlled device for exchanging heat energy between the radiative fluxmeter and the ambient medium making it possible to generate an energy exchange. calorific between this radiative fluxmeter and the aforementioned ambient medium.
• the controlled device for exchanging heat energy bears the reference 1.
• thermocouple chain a measurement device 2 following this exchange of the temperature variation ⁇ T B of the measurement surface and of the voltage variation ⁇ V B delivered by the thermocouple chain is provided, this measurement device bearing the reference 2 on Figure 2a.
• the radiative fluxmeter thus constituted is a radiative fluxmeter of the family previously mentioned in the description, which makes it possible to measure the only radiative component of the heat flux independently of the convective exchanges with the surrounding air.
• the thermopile is thus constituted by the meanderriform line B in CHROMEL or CONSTANTAN of small thickness, from 5 to 25 ⁇ m, etched in the form of meandering lines on the insulating support A, which can be an insulator flexible, KAPTON or NYLON for example, and covered by a large number of electrolytic deposits, copper or gold for example, regularly distributed along the length of the aforementioned meandering ribbon.
• the electrolytic deposition imposes its thermal and electric properties so that the circuit behaves like a large number of planar thermocouples electrically connected in cascade, the thermoelectric junctions being located on the border lines of the electrolytic deposits.
• the use of photolithography and chemical etching techniques makes it possible to produce planar thermopiles comprising a density of thermocouples of the order of 1500 / cm 2 .
• the upper coating shown exploded in FIG. 2a actually comes directly onto the meander line B, this coating possibly being made of a material absorbing infrared radiation.
• the device 2 for measuring the temperature variation ⁇ T B which is then formed for example by a resistive line 2 formed by a gold film in the form of Greek with a very small thickness of a few ⁇ for example.
• the upper part of the sensor formed by the upper covering has the function of generating tangential thermal gradients between the junctions of the thermopile, so as to generate the output voltage V B , this voltage being positive when the front face of the sensor, i.e. the upper coating, absorbs the radiation during positive heat exchange + Q for example, and on the contrary negative in the opposite case, when the heat exchange consists of a heat shrinkage -Q for example.
• the temperature rise ⁇ T B of the sensitive surface S B is then transmitted entirely by the upper coating to the device 2 formed by the resistive line, which sees its resistance modified due to this variation in temperature.
• the control of exchange of heat energy can be carried out by a switch connected in series with the resistive element 1, this switch being denoted I and shown schematically in Figure 2a.
• the controlled switch thus makes it possible to deliver a supply voltage to the resistive line 1, which by the Joule effect makes it possible to bring the corresponding heat energy.
• the radiative flowmeter with automatic sensitivity calibration as shown in FIG. 2a can also include sampling interfacing circuits as shown in FIG.
• the ECHi circuit being connected at the output of the meandering line.
• B and the ECH 2 sampling circuit being on the contrary connected to the resistive line 2 allowing the measurement of temperature rise.
• the power circuit can then be directly connected to the switch I, which is controlled by the microcontroller to carry out the phases 1 and 2 previously described in connection with FIG. Ld2.
• the controlled heat exchange device 1 formed by the resistive line 1 and the switch I is placed in the vicinity of the meandering continuous band B forming the chain of elementary thermocouples, the switch I being connected in operation at the power source, that is to say the above-mentioned electric power source.
• the resistive line 2 in the form of a Greek, constituting the device for measuring the temperature variation ⁇ T B of the measurement surface S B , thus forms a resistive film placed in the vicinity of the continuous strip with meanders B forming the chain of elementary thermocouples and is thermally coupled to it.
• a metal plate 3 can be associated with the insulating support A, this metal plate 3 being placed on the rear face of the thermopile support, which can thus be made isothermal by the aforementioned metal sheet 3.
• the temperature of the metal foil 3 is the initial temperature of the radiative flux meter which is the subject of the present invention and that, of course, this initial temperature can be either controlled or regulated in order to obtain specific effects in particular applications as will be described later in the description.
• FIG. 2bl Another alternative embodiment of the radiative fluxmeter specially adapted for implementing the method which is the subject of the present invention will now be described in conjunction with FIG. 2bl and FIGS. 2b2, 2b3.
• the support base formed by the metal sheet 3 constitutes a heat exchanger with the sensitive surface S B.
• the heat exchanger is provided with a device for supplying the latter with a heat transfer fluid represented by the reference 30 in the aforementioned FIG. 2bl, the heat transfer fluid being denoted fc.
• This arrangement makes it possible to control and regulate the heat exchange between the support base and the sensitive surface S ⁇ mentioned above.
• the upper coating can be chosen so as to provide the emissivity contrast to generate the tangential thermal gradients or to allow the measurement of the average temperature of the radiative fluxmeter by variation of the electrical resistance of this coating.
• the resistive line 2 can advantageously be connected in operation to an equilibrium displacement measuring circuit of the resistance variation due to the temperature variation D ⁇ T M of the resistive film, following the exchange of heat energy.
• this equilibrium displacement circuit can comprise, as shown in FIG.
• FIGS. 2cl and 2c2 A more detailed description of a radiative fluxmeter in accordance with the object of the present invention, more particularly intended for use as a fire detector, will now be given in conjunction with FIGS. 2cl and 2c2, FIG. 2c2 being a view in section along the section plane Q of FIG. 2cl.
• the support base 3 of the sensitive surface further comprises an inlet nozzle for a pressurized gas, air or an inert gas for example, and a housing L intended for receiving the sensitive surface, that is to say the corresponding radiation fluxmeter on which the metal layer 3 has however been removed or reduced.
• the support base 3 can be constituted by a copper block, the gas inlet nozzle, as shown in FIG. 2c2, being in communication with a chamber Ch allowing the gas to be pressurized and an orifice outlet, denoted S, in communication with the housing L.
• the housing L has a window Fe open towards the ambient medium, facing the sensitive surface S B constituted by the radiative fluxmeter.
• the pressure chamber Ch and the orifice S then make it possible to generate, in the vicinity of the sensitive surface S B , a blade of gas LA making it possible to ensure the protection of the sensitive surface at high temperatures.
• a cover denoted Co, is provided so that, thanks to the existence of an opening opposite the window Fe , engen ⁇ drer the air gap or gas previously mentioned.
• the base 3 also includes a heat transfer fluid intake system fc, the base 3 being able to be provided with conduits 30 constituting a heat exchanger, which makes it possible to stabilize the temperature of the base 3 and thus to fix the temperature. initial of the radiative flux meter thus formed.
• the radiative fluxmeter described above can be implemented using microelectronic technology in thin layers.
• it may further comprise a selective radiation filter of a determined range of wavelengths of the exchanged radiative flux.
• the spectral absorptivity of the deposit covering the hot junctions as well as the spectral reflectivity of the reflectors covering the cold junctions can have specific transmission / reflection characteristics in a particular wavelength domain of the exchanged radiative flux.
• a judicious choice of the materials used makes it possible, for example, to produce a sensitive radiative fluxmeter in a determined range of wavelengths, in the ultraviolet or far infrared range (at long wavelengths).
• These types of filters could, for example, be implemented by virtue of the specific spectral properties of deposits in thin layers, of specific materials, such as silicon nitride for example.
• the radiative fluxmeter as shown in Figures 2cl and 2c2 is particularly advantageous for producing an infrared radiation detector in direct vision
• the gas used to form the gas layer can be air or an inert gas.
• the radiative fluxmè ⁇ be can be provided from a microcontroller, a control system for periodic measurement of the sensitivity S BC of the radiative fluxmeter under conditions compara ⁇ ble to those described in connection with Figure ldl.
• the microcontroller can be provided with a module for comparing the sensitivity value measured with a determined threshold value.
• This threshold value is representative of the loss of sensitivity equal to the self-calibrated sensitivity of the radiation fluxmeter in the vapor phase of the ambient medium during the appearance and deposition of the liquid phase on the sensitive surface of the radiation fluxmeter. which makes it possible to generate a signal for the appearance of the liquid phase of the aforementioned ambient medium.
• the sensitivity diagram has thus been represented as a function of the so-called humidity percentage, the concept of humidity being that of percentage of liquid phase relative to the vapor phase for a given medium.
• the notion of humidity is naturally not limited to the condensation of water vapor but can be extended to any ambient medium in which a vapor phase is liable to condense in the liquid phase, whatever the nature of the liquid considered.
• the corresponding humidity percentage is that of the dew point, which varies with the temperature noted T 0 for which the transition from the vapor phase to the liquid phase occurs.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Radiation Pyrometers (AREA)
• Investigating Or Analyzing Materials Using Thermal Means (AREA)
• Measuring Temperature Or Quantity Of Heat (AREA)

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• 1995
  • 1995-05-04 FR FR9505346A patent/FR2733828B1/fr not_active Expired - Fee Related
• 1996
  • 1996-04-30 EP EP96914265A patent/EP0826247A1/de not_active Ceased
  • 1996-04-30 JP JP8533073A patent/JPH11509923A/ja active Pending
  • 1996-04-30 WO PCT/FR1996/000657 patent/WO1996035237A1/fr not_active Ceased

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