Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
  • G01P5/10—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring thermal variables
  • G01P5/12—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring thermal variables using variation of resistance of a heated conductor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
  • G01P5/10—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring thermal variables
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49117—Conductor or circuit manufacturing
  • Y10T29/49174—Assembling terminal to elongated conductor
  • Y10T29/49179—Assembling terminal to elongated conductor by metal fusion bonding

Definitions

• It relates more particularly to probes or devices of the type anemometer hot wire or cold wire.
• It also relates to a method of manufacturing such a probe.
• It also relates to a device for regulating the supply and the measurement of such a probe.
• the electrical power generated at the level of the wire and consequently exchanged between the latter and the surrounding medium may be provided from different by an electronic circuit, which makes it possible to define three types of anemometers:
• a known probe described in the document by Ligrani and Bradshaw, 1987, and illustrated in Figure 1, comprises a wire 201 (hot wire diameter 0, 625 microns) in a platinum alloy and 10% rhodium.
• This wire is traversed by an electric current in its active portion 600 (heated length) and has a shape "U".
• This wire is attached to the end of two points 400, 600 held between them by an araldite adhesive 450. The attachment is obtained by two solders (tin) 221 of the wire on the tips.
• the spacing e between the ends of the two pins is of the order of 0.5 mm.
• the wire defines a plane which is inclined at an angle ⁇ of approximately 15 ° with respect to the plane defined by the tips 400, 600.
• the blocking effect is a disturbance on the flow, caused by the too close proximity of the ends of the pins. This disturbance affects any measurement made at the active part 600.
• a problem is therefore to be able to make a probe that improves the performance of such a probe.
• a probe of the type of that of Figure 1 has problems of vibration resistance and sensitivity.
• Another aspect of the type of measures envisaged is the filtering effect. This effect occurs when the active area is too large, providing an averaged or integrated measurement, and not a one-off measure.
• the known probes including commercial anemometer assemblies (typically 2.5 ⁇ m diameter probe associated with a constant temperature anemometer), are therefore largely insufficient for the measurement of small scales of turbulence, and totally unsuitable for measurements in close proximity. wall like the ones we want to make.
• multi-wire probes are required whose volume defined by the set of wires is very small, in order to be able to consider that all the wires is in the smallest possible volume and that, therefore, the speed is the same for all the wires.
• the realization of a probe of this type poses many technological problems, most of which are not solved.
• One of the problems posed by the invention is in particular to find a production method which makes it possible, in a reproducible manner, to obtain a probe having excellent performances.
• such a method should make it possible to produce single-wire probes as well as multi-wire, "X" or parallel-wire probes.
• the invention makes it possible in particular to produce a probe comprising very small diameter wires, associated with a large spacing between pins, in particular to limit the blocking effect.
• the invention makes it possible, in particular, to reproducibly produce probes using wires of 0.35 ⁇ m to 0.625 ⁇ m in diameter, for example 0.5 ⁇ m in diameter.
• the invention relates first of all to an anemometric probe with n wires (n1> 1), arranged in parallel or in X, for a measurement in the vicinity of a wall, comprising, for each wire: a) two pins of maintaining the wire, the end of each pin comprising a positioning and fixing zone of the wire, b) a straight portion of wire brazed to said positioning and fixing areas of the wire.
• the ends of the pins can be spaced apart by a distance of at least 4 mm.
• the wire comprises a central core made of a rhodium-platinum alloy, with a diameter of between 0.35 and 0.6 ⁇ m, and a silver sheath, eliminated on a portion of wire, called a sensitive or active zone. , of length between 0.4 mm and 0.5 mm.
• the wire can be soldered to the pins using a tin-lead type solder.
• a probe according to the invention can comprise n (n> _ 2) son, parallel or in "X", n> 2. For example it comprises 2 or 3 or 4 son parallel to each other or arranged in "X".
• the invention also relates to a method for producing an n-wire (n1> 1 or 2) anemometric probe, in particular a probe as defined above, for a measurement in the vicinity of a wall, having, for at least one of the yarns: a) positioning and holding a straight portion of the yarn, having a metal core surrounded by a protective sheath, on two surfaces, for example polished surfaces, b) then the elimination of a portion of the sheath, so as to highlight an active zone for measuring the wire, c) then brazing the wire on two pins of the probe.
• a wire previously stripped or pickled is mounted on the pins (step c).
• the wire is positioned on a structure or surfaces (step a), which allows, before it is brazed on the pins of the probe, a local stripping or stripping of the active part of the wire (step b). ). With this technique, it becomes possible to make very complex configuration probes, n parallel son or "X".
• the surfaces on which the wire comes to rest are previously aligned surfaces, so as to offer the wire a horizontal support and a line alignment as accurate as possible.
• the above steps can be repeated for each wire of a multi-wire probe.
• the invention also relates to a method as described above, for the production of an airspeed probe with at least two wires, comprising the implementation of steps a) -c) for a first of at least one of said son then the implementation of steps a) - c) for a second of said son.
• Step b) may comprise, for at least one of the wires:
• the wire can be held by means making it possible to avoid bending the wire relative to the first fixing point; such bending may indeed occur during the second positioning and fixing step.
• a method according to the invention may comprise, for example after step a) or b), the formation of a curvature of the wire, for example by bringing the two surfaces together.
• step b) comprises etching the sheath of the wire to form an active measurement zone, for example:
• a wire resistance measurement can be made to determine the etched length.
• the etching can be carried out using a loop formed by a wire on which a drop of pickling liquid can be maintained.
• an annealing step at a temperature substantially greater than the temperature at which the yarn is intended to be used may be provided.
• the brazing it can be performed by hot air gun, or by laser impact.
• a preliminary step of straightening the wire makes it possible to obtain the straight part of the wire, for example by elongation, resulting from an axial axial tension on the wire.
• it is held fixed to the ends of two studs, one of which is movable.
• This movable stud may be connected to a micrometric table of movement along at least one direction, preferably in 2 or 3 directions.
• the invention also relates to a method for measuring anemometric quantities, in particular in the vicinity of a wall, comprising the implementation of a probe according to the invention.
• the invention also relates to a device for regulating a constant-current wire anemometer, comprising:
• This regulating device can be applied to a probe according to the invention, described above, or to another type of airspeed sensor. But particularly interesting results are obtained with a probe according to the invention.
• the wire and the reference resistor are for example mounted in current mirror.
• the means for regulating a supply current preferably comprise a diode-mounted control transistor and a potentiometer.
• the invention also relates to a cold wire thermoanemometer comprising:
• an anemometer for example having the structure already described above in the context of the invention
• the invention also relates to a method for measuring a temperature in a fluid in flow, comprising the implementation of a thermo - anemometer as above, without additional thermocouple.
• FIG. 1 is a hot-wire probe, of known type
• FIGS. 2A-2E and 14 represent aspects of an "X" wire probe, according to the invention.
• FIGS. 3A-3B show other types of probe according to the invention, with two wires or more than two wires,
• FIGS. 4-10 show steps for producing a probe according to the invention
• FIG. 11 represents a supply and measurement circuit that can be used in the context of the present invention
• - Figures 12 and 13 are measurement curves according to the invention for a thermo-anemometer according to the invention
• Figures 15A and 15B show another configuration of an "X" son probe, according to the invention.
• FIG. 2A-2E An example of a probe according to the invention is illustrated in Figures 2A-2E and 14. It is a particular configuration, many others being possible.
• the probe comprises a wire 2 stretched between the tapered ends of two metal pins 4, 6, which extend in an insulating body 10 of cylindrical shape, preferably a ceramic.
• the two wires 2, 20 are arranged with an angle ⁇ between them (see FIG. 14 which represents a front view of the device) even if they are located in two distinct planes, parallel to each other and perpendicular to an axis of the device, substantially identified by the axis of the insulating body 10. These parallel planes containing them are separated by a distance less than or equal to 0.8 mm, or between 0.2 mm and 1 mm or between 0.3 mm and 0, 8 mm.
• the angle ⁇ can be 90 °, so the two wires can perpendicular to each other in the front view of FIG. 14.
• These structures are described as "X" structures because of the relative position of the wires, as illustrated in FIG. 14.
• the invention also relates to, and also allows to realize, devices with parallel son as illustrated in Figures 3A and 3B.
• the son are separated by a distance ⁇ less than or equal to 0.8 mm, or between 0.2 mm and 1 mm or between 0.3 mm and 0.8 mm.
• this maximum gap between the planes in which the wires are located contributes to the possibility of making spot measurements, making it possible to have an extremely fine representation of the phenomena observed.
• FIGS. 15A and 15B Another X configuration is shown in FIGS. 15A and 15B. It also comprises two son 2,20, each having a central detection zone as shown in Figure 2E described below. Each wire is held by two pins 4, 6, 40, 60 disposed in the probe body as described above. We see in this figure that the form "X" appears this time when we look at the probe from the side. Multiple other "X" configurations are possible. The configuration performed depends on the environment and the conditions under which a measurement is to be made.
• the probe body 10 is for example constituted by a ceramic cylinder of diameter which can be understood between 2 and 4 mm, in which are implanted as pins 4, 6, 40, 60 (case of Figures 2A and 2B, but this is also applicable to other cases, such as those of Figures 3A, 3B) of the needles stainless steel diameter for example between 0.2 mm and 0.4 mm.
• the wire 2 (and possibly another wire, or any other wire, used in a probe prepared according to the invention) is positioned on the pins 4, 6.
• An example of the shape of one of these pins, the pin 4, is shown in Figure 2C in side view.
• the reference 43 designates the part of the pin 4, on which one end of the wire 2 will be brazed.
• the other pin 6 has the same structure.
• Each pin therefore has a substantially cylindrical section body along a direction AA ', for example the axis AA' is an axis of symmetry of revolution of the spindle in the case where it has a cylindrical shape (FIG. 2C ).
• the wire 2 also has an extremely precise alignment, of the order of a hundredth of a millimeter. Unlike the known probe structure (as explained above in connection with FIG. 1), a straight portion of the wire 2 is positioned on the pins 4, 6. There is no need, as in FIG. case of Figure 1, bending the wire in the form of "U”, such a curvature affecting the accuracy and reproducibility of the device.
• the solder of the wire 2 on the pins 4, 6 is a tin-lead alloy solder.
• the emerging length of the pins will depend on the configurations, but it can be approximately of the order of 15 mm. For the "X" structure of FIGS. 2A and 2B, this length is less for the wires which are situated behind the lead wire in front of the probe, this is the case for wire 20 of FIG. over 2.
• the distance D which separates the ends of two pins intended to carry the same wire, may be substantially equal to or greater than 5 mm, and preferably between 5 mm and 8 mm, for boundary layer flows up to at vein speeds less than or slightly greater than 12 m / s.
• good behavior is obtained only when the spacing between the pins does not exceed 4 mm.
• the shear excitation can induce large amplitude oscillations at the wire scale. oscillations that lead to the rupture of the latter.
• the probe body is sheathed with a tube 12 of elastomer, which will absorb the waves or vibrations that can propagate towards the wire 2, the part of which active is very fragile.
• the yarn 2 (or possibly another yarn, or any other yarn, used in a probe prepared according to the invention) is preferably a yarn comprising a central portion 21 made of platinum or a platinum-rhodium alloy, surrounded by a sheath 22 in silver, which may be of diameter between 50 and 80 ⁇ m, as shown in Figure 2D.
• the diameter of the central portion 21 is very small, less than 0.635 microns or 0.6 microns, for example 0.35 microns or 0.5 microns.
• the wire used is preferably a "Wollaston wire” type wire made of a platinum-rhodium alloy (Pt-10% Rh). It is impossible to directly handle a wire of this diameter without risk.
• the silver sheath, with a diameter of 30 to 50 ⁇ m, which surrounds the wire ( Figure 2D) allows this manipulation.
• Such a wire offers measurement punctuality greater than that obtained in known devices, because it is possible to define a measuring zone 14 by locally eliminating the sheath of the wire, as shown in FIG. 2E. This results in an active length 1 of between 0.4 mm and 0.5 mm. A lower active length would be detrimental to the measurement because the edge effects due to the ends 22 ', 22' 'of the sheath at the boundaries of the measuring zone 14 would then be too great. This aspect is illustrated in FIG. 2E, where the active part 14 and the silver sheath 22 are clearly visible.
• the active part 14 is not visible in FIG. 2A, since the width of this active part (between 0.4 mm and 0.5 mm) is small relative to the distance E between the ends of the pins 4, 6. (at least 5 mm).
• the ratio 1 / d of the active length of the wire to its diameter, is substantially between 600 and 1500. Beyond, the punctual character of the measurement disappears: one then finds the effects of filtering or averaged measurement already mentioned. With a ratio between 600 and 1500 (600 ⁇ 1 / d ⁇ 1500), the hypothesis of two-dimensionality, therefore of a very flat temperature profile in the active zone, is satisfied. For a ratio of less than 600, the appearance of end effects means that the temperature profile along the wire can no longer be likened to a "gate" profile (that is, a constant temperature along the wire) this profile is closer to a parabolic profile.
• this situation results in a loss of sensitivity of the wire and a deterioration of the signal-to-noise ratio. Physically, this means that we can not capture phenomena of low amplitude.
• the wire 2 is connected to the pins 4, 6 by brazing the silver sheath 22 on these pins.
• a probe according to the invention has properties of location of the measurement, without filtering effect (due to punctuality on the measurement reached by the very small width of the measuring zone 14), without blocking effect (due to distance of the ends of the pins from each other). This probe is also resistant to vibrations.
• a probe according to the invention therefore makes it possible to measure physical quantities as close as possible to a wall, without bias, and therefore without a correction being necessary.
• y + is defined as the product of the velocity of friction by the distance to the wall divided by the kinematic viscosity.
• the invention also relates to a single wire probe, but also a parallel multi-wire probe, as illustrated in FIGS. 3A and 3B.
• a double probe for example which associates a hot wire 2 and a parallel cold wire 2 ', with a spacing between the two wires of the order of 0.3 mm (or more generally between 0.2 mm and 1 mm), is also object of the present invention and is shown, in side view, in Figure 3A (we see the son only by the side, so each wire 2, 2 'is likened to a point in this figure and in Figure 3B ).
• the other references are those of FIGS. 2A-2E and designate the same elements.
• two pairs of pins are provided, the pair 4, 6 already described above, on which is brazed the wire 2, and another pair 4 ', 6' (of which only the pin 4 'is visible in Figure 3A) on which is brazed the wire 2 '.
• the references are those of Figures 2A-2E and denote the same elements, the maximum distance between the son being between 0.2 mm and 1 mm, preferably between 0.3 mm and 0.8 mm.
• three pairs of pins are provided, the pair 4, 6 already described above, on which is brazed the wire 2, and another pair 4 ', 6' (only pin 4 'is visible in FIG. 3B) on which the wire 2 'is soldered, a third pair 4'',6''(of which only the pin 4''is visible in FIG. 3B) on which the wire is brazed 2 ''.
• Such a triple probe preferably operates with a hot wire, in the center (the wire 2 ') and two cold wires, on both sides (the wires 2 and 2''), which give information on the direction of the 'flow.
• a double probe or, more generally, with n wires, at least one of the wires, or each of the wires, has the characteristics indicated above, and is fixed in the manner indicated above, on a pair of pin.
• each wire having a denuded area such that the ratio 1 / d is between 600 and 1500, it was possible to carry out measurements of speed and temperature.
• This probe is composed of two pairs of wires, each pair being arranged in "X", and contained in a plane perpendicular to that of the other pair, and an additional wire (cold) for measuring the temperature.
• This configuration allows the simultaneous measurement of the three velocity components in a non-isothermal flow.
• the volume delimited by the two pairs of wires is approximately 0.4 3 mm 3 , while the ratio 1 / d of each of the wires is approximately 1000.
• a method of manufacturing a probe according to the invention will now be described. It relates to the realization of a single-wire probe, and can be applied to the realization of a probe to any number of son, unless otherwise specified.
• All operations are preferably performed under a binocular loupe, given the size of the elements and the required accuracy.
• This magnifying glass, or other visualization means selected or equivalent, is used to display with an accuracy of l / 100th mm.
• the pins 4, 6, 40, 60 are secured to the probe body 10, 12. In the latter, holes were made or grooves were dug to precisely position these pins.
• the pins are inserted into the probe body using a template so that they protrude from the probe body of equal length.
• the soldered connection between the electric supply cables 19, 19 '(FIG. 2A) arrives and the pins 4, 6 can be located in the groove or holes of the body 10 or outside.
• the welding of this connection is performed during this preparation step.
• These connections and cables, or other connections and cables, can be used for other pins.
• the sealing of the pins in the support can be provided by coating a concrete whose grip is compatible with the ceramic. Tests show that an adhesive, for example Araldite type can also very well provide this sealing function, while retaining some elasticity that is interesting for vibration absorption and saving the probe.
• the probe body once provided with its pins 4, 6, 40, 60, is inserted into an elastomer damping sheath 12, in order to limit the vibrations that can break the active part of the wire 20, which is very fine.
• FIG. 4 shows the probe body 10, 12, with its pins 4, 6 ready to receive the wire 2 of the probe.
• the body of the probe is mounted on a set of micrometer tables, not visible in the figure, which will make it possible to achieve highly accurate movements in two or three dimensions, to the hundredth of a millimeter.
• wire 2 itself, one generally starts from a wound wire in the form of a coil.
• a first operation is therefore a straightening operation of the wire, in order to erase the memory that the wire has of its winding on the coil.
• the diameter of the central core of which is less than 0.5 ⁇ m, for example 0.35 ⁇ m, during the straightening phase of the rolling wire on a marble, there is a risk of a rupture of the core central of the wire.
• a suitable rectification step implements an elongation that causes an axial axial tension to the wire.
• the wire is brazed at its two ends on a system comprising two studs 49, 51, one of which (the stud 49) is mobile thanks to its implantation on the plate of a micrometric table 69 moving in two dimensions X, Y as shown in Figure 5.
• This table will allow to perform extremely precise movements, in each of two dimensions, to the hundredth of a millimeter.
• the rectification operation it is preferable, for the rectification operation to be optimal, that the two points of the studs 49, 51 are in the same horizontal plane.
• the mechanical tension allowing straightening of the yarn is not quantified accurately. Nevertheless, the following procedure can be given.
• the displacements of the mobile stud 49 are measured using the micrometer table.
• the origin of the displacements is taken when the tension of the wire makes start the bending of a needle (for example of length 50 mm and diameter 0.2 mm) in support on the wire and held by an operator (one recalls that the operations are led under observation at high magnification, for example with a binocular loupe).
• a displacement of 0.4 mm of the mobile pad 49 is sufficient to obtain good straightness and increased rigidity of the wire.
• FIG. 1 represents globally the whole system, with two sets 81, 83 each comprising three micrometric tables 81 '(for a displacement along X), 81''(for a displacement along Y), 81''' ( for a displacement according to Z) and 83 '(for a displacement according to X), 83''(for a displacement according to Y), 83''' (for a displacement according to Z).
• Each table will allow an extremely precise displacement, to the nearest hundredth of a millimeter.
• To each of these two assemblies 81, 83 is fixed an L-shaped beam 61, 63 (see also FIGS. 6 and 7).
• the largest portion of the "L" of the beam 61 is directed substantially in the same direction as the largest portion of the "L” of the beam 63 (see Figure 9 which gives a top view of the two beams), in made in a direction substantially at 45 ° to each of the X and Z axes in Figure 8.
• Figure 9 shows the position of the two beams 61, 63 in plan view.
• Each of the ends of the wire 2 will be put in place on this system which comprises these two beams 61, 63. More particularly each wire end 2 is positioned against a surface of the corresponding beam, which surface has been machined by polishing.
• the distances d, d (FIG.
• offset between the perpendicular axes X and Z, between the ends of the two beams (for an "x" probe), are in particular functions of the spacing between the pins 4, 6 of the probe to which the wire is to be attached.
• These two beams 61, 63 are previously positioned in the same horizontal plane.
• the two beams are "straddled” by straightened wire.
• the two beams are considered at the same altitude when the wire is uniformly in contact on the face 61 ', 63' of each beam. To realize this condition, one plays on the displacement in "Y" (vertical axis) of the micrometric tables.
• the lead of the probe is then immobilized on each beam by means of a drop 71, 73 of a material of the glue or cement type, for example refractory cement (of the Degussa mark), as illustrated in FIG. .
• a material of the glue or cement type for example refractory cement (of the Degussa mark)
• the etching is carried out by a point dissolution of the sheath 22 of silver, by chemical or electrochemical etching.
• This sheath is attacked with nitric acid.
• the length 1 to be stripped is determined according to the diameter d of the wire knowing that, if one wants to ensure a temperature profile as uniform as possible on the wire during its use in hot wire, a ratio 1 / d greater than 250 allows to limit the impact on the measurement of the conduction at the ends of the active part (for a given material and therefore a given cold length).
• a ratio 1 / d greater than 250 allows to limit the impact on the measurement of the conduction at the ends of the active part (for a given material and therefore a given cold length).
• the system used here for pickling can be composed of a wire 101 of a few hundredths of a millimeter in stainless steel. This wire 101 is shown in FIG. 10, near the wire 2 to be etched, itself in position between the two beams 61, 63.
• this wire 101 forms a loop which allows the retention of the drop 102.
• the latter consisting of pure nitric acid, is deposited on the loop using a syringe. Then approach the loop and the drop using micromanipulators to bring the latter into contact with the wire 2 to strip.
• a back and forth motion is made to dissolve the silver of the sheath 22. Once the drop is saturated with silver, remove it from the wire and replace it with another drop of nitric acid. The procedure is the same until the platinum-rhodium wire 21 appears and the resistance of this wire begins to evolve.
• the etched length is adjusted according to the resistance of the probe. Typically, there is a resistance of 500 ⁇ for wire of 0.5 ⁇ m in diameter and 1 k ⁇ for wire of 0.35 ⁇ m, which corresponds to a stripped length of 5 to 6 tenths of a millimeter, corresponding to a ratio 1 / d of the order of 1100 and 1600 respectively.
• the 0.5 ⁇ m yarn is used, which makes it possible to obtain a 1 / d ratio of 1100.
• a probe with a 1 / d ratio greater than 1500 does not have the punctuality required for the measurement: we then find the effects of filtering or averaged measurement already mentioned.
• a simple electrical circuit consisting of a battery, a potentiometer and a switch is thus connected to the metal loop carrying the drop and to the wire 2 (as illustrated in FIG. 10).
• a drop 102 is formed for stripping, but this time consisting of nitric acid diluted to 5%. It is approached in the same way as the previous drops, so that the yarn is wetted inside the drop.
• the switch is then actuated, briefly because degassing is very fast and violent at the wire scale.
• the wire is rinsed with a drop of demineralized water so as to eliminate any residual trace of acid on the wire.
• To implement the previous method is formed a drop whose size is constrained by the size of the loop and the surface tension forces.
• a slight curvature is applied to the wire 2 at this time of manufacture, as has just been explained.
• the wire 2 then has a slight curvature, or an arrow, of the order of a few hundredths of mm, for example less than 2/100 th of a mm or 4/100 th of a millimeter, for example in a plane substantially perpendicular to plane the axis of the body 10 of the probe.
• This curvature will have no influence on the anemometric measurements made thereafter and gives the yarn flexibility to absorb mechanical stresses or vibrations.
• This set of operations performed one can solder the wire on the pins 4, 6, 40, 60 of the probe. So we bring these pins near the wire
• the wire 2 and a first pin are degreased with acetone.
• the solder is then melted, for example with the aid of a hot-air iron.
• the wire 2 is secured to the pin 4, and it is then soldered on its second pin 6.
• the curvature or curvature previously conferred on the wire allows this operation without risk of breakage.
• wire 2 When soldering, wire 2 adopts retains a slight curvature, or an arrow, of the order of a few hundredths of mm, for example less than 2/100 th of a mm or 4/100 th mm.
• the yarn 2 is then cut with a razor blade flush with the pins so that the wire holder assembly can be removed and the remaining wire ends can be removed from the wire holder assembly.
• Another technique implements a very localized power supply by laser beam, whose punctuality has the advantage of not polluting the environment thermally.
• the laser used is pulse mode, YAG type with a maximum power of 3OW.
• the frequency and duration of the pulses are adjustable.
• the beam is focussed on the point of soldering at the end of the pin thanks to a camera coupled to the laser, and a firing is carried out which causes the solder to melt and couples the wire to the pin.
• the implementation of this technique ensures the brazing operation regardless of the degree of miniaturization of the probe and the number of son it contains.
• the wire 2 is passed through a current calculated according to the resistance of the probe.
• the wire is thus brought to a temperature substantially greater than the temperature at which it is intended to work.
• the difference in temperature between the wire and the ambient air is given by the following relation:
• R “-R AT f " aR 0
• Ro the resistance of the probe at room temperature
• ⁇ the coefficient of evolution of the resistance with temperature (1.6 ⁇ 10 -3 ⁇ -1 for Pt-10% Rh)
• R fl1 the resistance of the wire brought to the temperature T + ⁇ T, given by Ohm's law.
• the optimal solution for protecting the wire consisted in inserting the ceramic probe body, once provided with its pins, into a damping sheath 12 of very low hardness (of the order of 25 A shores).
• a probe according to the invention is used with current supply means, and means for measuring variations in electrical resistance of the wire or wires. It is these variations that reflect the variations in speed and / or temperature of a fluid carried by a flow in which the probe is immersed.
• the system is decoupled from the electrical network, whose potentials can fluctuate (for example, by starting or stopping neighboring installations).
• the currents and / or the voltages that occur at the sensor are very small and can be easily disturbed by these network fluctuations, however small.
• installations such as a wind tunnel, it is difficult to put correctly at the same potential the different points of mass. This results in loop currents between these different ground points, driven by the potential fluctuations of the network, currents which also disturb the measurements significantly.
• This solution also makes it possible to supply all the circuits, which thus have a fixed ground potential and no longer fluctuate as may be the case when they are connected to electronic voltage regulators.
• the circuits are preferably placed in a box, for example copper, which constitutes a ground plane, connected to the ground of the battery. To this ground plane is also connected a braid surrounding the connection wires of the probe.
• EMC electromagnetic compatibility
• a particular operation is the so-called "cold wire” operation. This is a constant current mode of operation, in which the current with which the wire is fed is very low.
• Cold wire anemometers are already known.
• the power supply has a large resistance R placed in series with the wire to maintain a constant current Iw current in this wire when the flow velocity varies.
• the wire is integrated with a Wheatstone bridge to accurately measure its Rw resistance; the output signal is collected at the top of the bridge.
• the constant current anemometer has advantages. We have the choice of overheating, which is very appreciated for the study of temperature fluctuations.
• the background noise can also be measured by substituting a fixed resistance for the wire and then making the necessary corrections to the measurements. In return, the output signals are amplified significantly. The bandwidth of this measurement principle is imposed by the thermal inertia of the wire.
• R wire R 0 [I + a (TT 0 )] where RO is the resistance of the probe at a reference temperature and ⁇ the coefficient of evolution of the resistance with temperature.
• the temperature difference is small and the current with which the wire is fed is very small. It just serves to measure a voltage across the wire in order to go back to the value of its resistance. It is generally of the order of 50 to 200 ⁇ A. Thus, the heating of the wire by Joule effect is negligible, which is worth to this anemometer the name of cold wire thermometer.
• thermocouple A problem with this type of operation is as follows: the measured temperature drifts, it is necessary to associate the probe with a thermocouple to have a measurement of the average temperature.
• the invention proposes a solution to this problem.
• FIG. 11 Electronic means associated with a constant current anemometer are shown in FIG. 11, in which the wire is always designated by the reference 2.
• the circuit represented also comprises:
• - Power supply means 110 preferably a battery as explained above,
• a reference resistor 112 a potentiometer 114 for adjusting the current.
• the supply of the circuit Ve is provided by a voltage regulator (MAX 6325).
• the two resistors 2, 112 are mounted in current mirror. The adjustment of the current flowing through the two branches of the mirror, each of the branches comprising one of these two resistors, is effected by the voltage Vbe of a diode-mounted control transistor 116 via the potentiometer 114.
• the potential difference between the probe 2 and the reference resistor 112 is applied to a Operational amplifier of instrumentation 120.
• the amplifier amplification provides a measured signal which reflects the variations of the resistance of the wire 2.
• the signal is amplified at the terminals of the probe 2.
• this amplification is not too important (we try take into account the voltage resolution of the acquisition card).
• an airspeed sensor 2 has a high resistance, and the variations in output of the anemometer, after amplification, may exceed the ranges of use of the cards. This is why we choose to center on about zero the output signal of the thermometer; this also allows you to take full advantage of the measuring range and thus adjust the gain accordingly. To do this, a subtraction is performed between the signal at the terminals of the probe 2 and the signal at the terminals of a reference resistor 112.
• the current mirror arrangement makes it possible to have a stable signal crossing the reference resistance, as well as a stable current passing through the probe 2.
• Such a device has been implemented in the context of test campaigns in a wind tunnel, the probe being a single-wire probe operating in cold wire.
• the reference resistor 112 has been replaced by a metal resistor whose coefficient of variation with temperature is much lower (0.6 ppm / ° C.) and negligible.
• thermometer components the probe and its supply and measurement means
• the power of a heating mat placed in the housing of the anemometer is electronically regulated.
• thermometer The electronic circuit of the thermometer is thus maintained at a temperature greater than that of the room in which it is located.
• This temperature at which the circuit is maintained is regulated to plus or minus one-tenth of a degree.
• This device allows, after a single calibration of the entire airspeed chain, to measure in the flow not only the fluctuations of the temperature, but also its average value, which is an unprecedented result. Indeed, even in the case of known devices for which particular care is given to metrology and measurement (this is particularly the case of temperature measurements at the outlet of a jet reported by Andreopoulos in "experimental investigation of jets in a cross flow, Journal of Fluid Mechanics, 1983), temperature fluctuations are measured by a cold wire while the average value is given by other means such as a thermistor or a thermocouple.
• the circuit described in this part is applicable to a multi-wire probe. We can make as many circuits as necessary.
• Calibrations are performed in a wind tunnel.
• the air passes successively in a heating box and a water exchanger whose power and flow can be independently adjusted to obtain the desired temperature levels, between room temperature and 150 ° C.
• the cold wire probe 2 is placed in the calibration vein (surrounded by a heat guard ring) in the center of the outlet of an air injection nozzle.
• the temperature of the enclosure is given with a precision of the tenth of a degree by a reference PtIOO probe associated with an electronic measurement unit (reference: Sfere DGN75T).
• thermometer For each calibration point, an operating point of the heating box and the heat exchanger is selected. The thermal equilibrium is then allowed to settle between the air and the walls of the blower, an operation that takes several hours (typically 4). The voltage delivered by the thermometer is then measured for about thirty seconds, a value that is largely sufficient to obtain a convergence of the measurement.
• thermometer Between the largest scales captured by the thermometer and the noise of the latter, we can observe on this plot a difference of 7 decades, a ratio in this case between large and small scales discernable of the order of 3000. In d ' other words, the resolution of the thermometer in this case is about 5.10-3o C.
• the probe according to the invention makes it possible to perform measurements without correction.
• thermo-anemometer having a signal-to-noise ratio of several thousand (3500 for the thermometer and 10000 for the constant-voltage anemometer) when it is associated with a small diameter wire probe according to the invention.
• the invention makes it possible to operate a cold wire anemometer without a thermocouple to obtain a measurement of the average temperature.
• the proposed regulation circuit makes it possible to compensate the drift and to get rid of a thermocouple.
• control circuit proposed here can be applied to a probe according to the invention, described above in connection with FIGS. 2A-10 and 14, or to another type of airspeed sensor.

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• Aviation & Aerospace Engineering (AREA)
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• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
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