EP1844325A2 - Device for measuring the mechanical load exerted by a fluid using an electromechanical transducer - Google Patents

Device for measuring the mechanical load exerted by a fluid using an electromechanical transducer

Info

Publication number
EP1844325A2
EP1844325A2 EP05825869A EP05825869A EP1844325A2 EP 1844325 A2 EP1844325 A2 EP 1844325A2 EP 05825869 A EP05825869 A EP 05825869A EP 05825869 A EP05825869 A EP 05825869A EP 1844325 A2 EP1844325 A2 EP 1844325A2
Authority
EP
European Patent Office
Prior art keywords
measuring device
sensor
free space
transducer
product
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05825869A
Other languages
German (de)
French (fr)
Inventor
Bernard Hamonic
Max Mastail
Yves Mevel
Roland Person
Jean-Yves Ragon
Alain Loussert
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Institut Superieur De L' Electronique Et Du Numerique De Lille
Institut Francais de Recherche pour lExploitation de la Mer (IFREMER)
Original Assignee
Institut Superieur De L' Electronique Et Du Numerique De Lille
Institut Francais de Recherche pour lExploitation de la Mer (IFREMER)
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 Institut Superieur De L' Electronique Et Du Numerique De Lille, Institut Francais de Recherche pour lExploitation de la Mer (IFREMER) filed Critical Institut Superieur De L' Electronique Et Du Numerique De Lille
Publication of EP1844325A2 publication Critical patent/EP1844325A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/028—Analysing fluids by measuring mechanical or acoustic impedance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/222—Constructional or flow details for analysing fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/10—Scanning
    • G01N2201/102—Video camera
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02466—Biological material, e.g. blood
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02483—Other human or animal parts, e.g. bones
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02818—Density, viscosity

Definitions

  • the invention relates to a measuring device of the type comprising: a sensor with at least one electromechanical transducer; at least one electrical generator connected to said transducer; and means for determining the electrical impedance at the input of the transducer.
  • the invention also relates to a measuring apparatus equipped with such a device.
  • Such a measuring apparatus serves, in particular, to determine the density p of a liquid or pasty product flowing continuously inside a pipe and can find applications in the field of food processing, cosmetics, or plastics, allowing a better characterization of the product directly at the level of the production line and thus a better control of the quality of this product.
  • French patent application FR 2763687 describes an apparatus of this type for determining the density p of a fish paste, consisting essentially of a mixture of water, air, salt and fish fibers. at the exit of an extruder.
  • This apparatus is used in a pipe located downstream of the extruder and inside which circulates the fish paste.
  • the apparatus comprises a piezoelectric pellet serving as an electromechanical transducer disposed within the pipe, in a plane containing the axis thereof.
  • the use of the apparatus of FR 2763687 poses the following problems: it is found that the piezoelectric pellet (and its connections) disrupts the flow of the fish paste because it obstructs the pipe and separates the flow of dough in two parts. In addition, this pellet fouls very quickly which leads, on the one hand, errors in estimating the density p of the dough and, on the other hand, problems of bacterial contamination.
  • the invention aims to remedy these problems, or at least to mitigate them.
  • the invention relates to a measuring device of the aforementioned type, characterized in that said sensor is traversed by a free space within which a product is likely to flow, and in that said transducer is located on the outskirts of the said free space so as to be subjected to a mechanical load characteristic of the product flowing in said space, the measured electrical impedance being a function of said load.
  • said transducer (and therefore its connector) is located at the periphery of the free space in which the product flows.
  • the flow of the product is therefore less disturbed than by the piezoelectric pellet of FR 2763687 and the transducer is less subject to fouling.
  • the transducer does not, or little, protrude within the free space, it may even be slightly set back with respect to this space.
  • the connector of the transducer is preferably predominantly made on an unexposed face, called second face.
  • the transducer or transducers are not necessarily arranged all around the free space: they can be arranged only on one side of this space. When they are distributed all around the free space, the transducers can be distributed regularly or not.
  • said free space is of tubular general shape (i.e. it is not bent) in order to disturb as little as possible the flow of the product passing through it.
  • a tubular free space does not necessarily have a circular section.
  • the free space can indeed have rectangular, square, polygonal, ellipsoidal sections ...
  • the axial length of the tubular space is not necessarily greater than the largest dimension of its section.
  • the free space is of substantially identical section to that of the pipe on which the device is connected, in order to disturb the flow as little as possible.
  • the general operating principle of such a measuring device is as follows: the mechanical load exerted on the transducer, by the product circulating inside the tube, prevents this transducer from vibrating freely and thus modifies the electrical behavior of the latter. This then varies the value of the electrical impedance input of this transducer, which is measured. The value of this electrical impedance then makes it possible to determine by calculation the density of the product concerned, on the condition of knowing, moreover, the celerity of a stream of waves passing through this product.
  • the senor comprises a plurality of transducers distributed around the tubular space.
  • transducers can be connected in series or in parallel. In both cases, they are electrically dependent and equivalent to a single transducer measuring a mean mechanical load.
  • the transducers may be electrically independent, that is to say each be connected to their own generator, or may be connected to a common generator via a multiplexer or any other system for successively feeding each transducer.
  • said impedance measuring means measure the impedance for each independent circuit.
  • Electromechanical transducers make it possible to multiply the measurement points, and thus to characterize the product flowing in the pipe in different radial directions.
  • radial direction is meant herein a direction perpendicular to the main axis of the tubular space.
  • the electromechanical transducers are distributed regularly, in different radial directions, at the periphery of the tubular space.
  • the transducer or transducers comprise a sensitive element made of piezoelectric material, hereinafter referred to as a piezoelectric element, which makes it possible to obtain sensors of simple and compact structure.
  • a piezoelectric element which makes it possible to obtain sensors of simple and compact structure.
  • the transducers are of this type.
  • electromechanical transducer that is to say capable of receiving energy from an electrical system and supplying power to a mechanical system, or vice versa, could be envisaged.
  • the first face of the transducer (s) defines the tubular space: it is a wall of this space.
  • the first face is substantially neither recessed nor protruding with respect to said space and the risks of fouling are reduced.
  • a non-stick coating such as polytetrafluoroethylene, or PTFE (better known under the trademark "Teflon”), or a similar material.
  • PTFE also has the advantage of being compatible with agri-food standards.
  • the first face of the transducer is covered with a membrane.
  • this membrane that defines the tubular space. It must be sufficiently flexible so that the transducer can detect the mechanical load exerted by the product circulating in said space. In addition, this membrane must not prevent the transducer from vibrating.
  • the invention also relates to a measuring apparatus, comprising: a measuring device according to any one of the preceding claims; means for measuring the speed of a wave train traversing the product circulating in said free space or in a pipe portion located upstream or downstream of this space; and a calculation unit for determining the density of this product from the measured velocity and impedance.
  • This measuring device is intended to be installed on an existing pipe, the free space of said sensor being placed between two portions of this pipe and connecting these two pipe portions, upstream and downstream, via said tubular space.
  • the measuring device may comprise one or two portions of pipe, collateral (s) to said sensor and the assembly formed by the sensor and the portion (s) of pipe is installed in place of a section of the existing pipe.
  • FIG. 1 is a perspective view of a first example of a sensor that can be fitted to a measuring device according to the invention
  • - Figure 2 is a section along the plane IHI of the sensor of Figure 1;
  • - Figure 3 is a section along the plane III-III of the sensor of Figure 1;
  • FIG. 4 is a perspective view of a second example of a sensor that can equip a measuring device according to the invention.
  • FIG. 6 is a perspective view of a third example of a sensor that can equip a measuring device according to the invention.
  • FIG. 7 is a schematic representation of an exemplary measuring apparatus according to the invention
  • FIGS. 8a to 8c represent the equivalent electrical diagrams of a "vacuum” and “charging” transducer according to the invention, as well as the calculation formulas relating to the input impedance of this transducer;
  • FIG. 9 is a schematic representation of a fourth example of a sensor according to the invention.
  • FIGS. 10 to 12 schematically represent several examples of devices comprising a sensor of the type of that of FIG. 9.
  • Figures 1, 2 and 3 show a first example of a sensor 1 comprising a plurality of transducers formed of piezoelectric elements 10 in the form of platelets, such as ceramics.
  • transducers also include the connector, not shown, associated with the elements 10.
  • the type of ceramic used for the piezoelectric elements 10 is chosen according to the mechanical load of the product that these elements are intended to support (this mechanical load depends on the density p of the product).
  • this mechanical load depends on the density p of the product.
  • a ceramic of the "PZ35" type marketed by the company "Ferroperm”.
  • the elements 10, six in number in the example shown, are joined edge to edge and define between them a tubular free space 12, hexagonal section, intended to be traversed by a liquid or pasty product 14 flowing along the arrow F.
  • seals 16 are arranged between two elements
  • the elements 10 are held using two sleeves 18 which surround the ends of the sensor 1. Fingerprints 20 may be formed in the sleeves 18 to facilitate the positioning of the elements 10. These elements 10 must in all cases remain free of vibrate. Also, the sleeves are preferably made of elastomer.
  • a seal 17, for example made of silicone, may be placed around the elements 10, between the latter and the sleeves 18.
  • rods 22 are used connecting the sleeves 18. These rods are threaded on an end portion to allow screwing / unscrewing. a nut 22a to bring or move the sleeves 18 away from each other, which more or less clamp the elements 10 along the main axis of the tubular space. Note that it is mainly desired to obtain a radial loading of the elements 10 (that is to say oriented according to the thickness of these elements). This slight radial loading is obtained thanks to the aforementioned pinching, which causes a very slight radial deformation of the elements.
  • the rods 22 also have a role of maintaining the sleeves around the elements 10.
  • the sleeves 18 are produced in an elastomeric insulating material and this temperature-resistant material is selected from the products intended to circulate in the space 12.
  • this temperature-resistant material is selected from the products intended to circulate in the space 12.
  • an acetal resin such as "Delrin” (registered trademark) can be used, withstand temperatures up to 200 0 C.
  • the first faces 80 of the elements 10 are the faces oriented towards the interior of the space 12. These faces are subjected to the mechanical load exerted by the product 14.
  • the outer faces, or second faces 82, opposite the first 80, are mechanically free.
  • a conductive wire (not shown) is connected to each face 80, 82. The connection of these wires does not pose any particular problem given the nature of the ceramic material retained for the elements 10.
  • the conductor son of each element are connected to a generator specific to the element or to a common generator via a multiplexer or a system of switches actuated successively.
  • the first faces 80, as well as the second faces 82 are electrically connected to each other and connected to the generator.
  • FIGS. 4 and 5 show a second example of sensor 3, comprising a plurality of piezoelectric elements 30 in the form of rods, embedded in a matrix 31.
  • This matrix 31 may be made of epoxy resin and molded around said elements 30.
  • the elements 30 may be completely embedded in the matrix 31, as shown in Figure 5, or be only partially.
  • the material of the die 31 is chosen so that it is sufficiently flexible to allow the members 30 to vibrate and be responsive to the mechanical load exerted by the product 14.
  • a tubular space 32 passes through the sensor 3. The walls 32a of this space are formed by the matrix 31.
  • the elements 30 are evenly distributed around the periphery of this space and can be electrically independent or dependent, as explained above.
  • Their first faces 80 are separated from the walls 32a by a portion of the matrix 31 comparable to a membrane 33 covering the faces 80.
  • the composite structure (matrix 31 / elements 30) of this second exemplary sensor makes it easy to manufacture transducers of various shapes.
  • the sensor 3 may have at its ends sleeves 38 which will be used to connect the sensor 3 to a pipe. These sleeves 38 may be molded with the composite body of the sensor, or be inserts thereon, as is the case here. Stems 22 similar to those previously described are found.
  • FIG. 6 represents a third example of a sensor comprising a single piezoelectric element 50 wound on itself, so as to define a tubular space 52.
  • the piezoelectric element 50 is for example made of polyvinylidene fluoride or PVDF.
  • Two son drivers (not shown) are respectively connected to the first face 80 (ie the inner face) of the element 50 which defines the space 52 (the face 80 is a wall of the space 52), and the second face 82 (ie the outer face) of the sensor 5. These conductive son are connected to a generator, and means for measuring the impedance output of this generator.
  • the second and third examples of sensors 3 and 5 have the advantage of having a perfectly cylindrical revolution that avoids product retention.
  • FIG. 7 schematically represents an example of measuring apparatus 50 according to the invention mounted at the exit of an extruder 62.
  • the extruder 62 comprises a cylindrical body 63 inside which rotates an extrusion screw 64 driven by a motor 65.
  • the raw materials enter the body 63 through the feed hopper 66 and come out as an elaborate product 14 by the output 67.
  • This product 14 may be a fish paste, or any other liquid or pasty mixture, agri-food or not.
  • the measuring apparatus 50 comprises a measuring device according to the invention equipped with a sensor 1, 3 or 5 of the type of those described above, an electric generator 54 connected to the transducer (s) of the sensor 1, 3 Via two leads 53 and means 55 for determining the electrical impedance Ze at the output of the generator, such as an impedance bridge or other impedance measuring system.
  • an impedance meter 55 for simplicity, hereinafter, reference will be made to an impedance meter 55.
  • the senor With respect to the direction of flow of the product stream F, the sensor is connected with upstream pipe portions 51 and downstream pipe 52.
  • the generator 54 is connected directly to the transducer (s) of the sensor 1, 3, 5 by the conducting wires 53. 7, the flow direction of the current i is represented during the positive half-wave of the sinusoidal signal emitted by the generator 54, corresponding to the + and - signs represented on the latter.
  • the impedance meter 55 measures the impedance at the input of the transducer (s), which corresponds to the impedance at the output of the generator. In general, it will be noted that, whatever the components placed between the output of the generator and the input of the transducer (s), these impedances are linked and that the measurement of one makes it possible to determine the other by calculation. .
  • the same system 56 includes the generator 54 and the impedance meter 55, and thus ensures both the electrical current emission function and the impedance measurement function.
  • the upstream portion 51 is connected to the outlet mouth 67 of the extruder 62 and the two pipe portions 51 and 52, preferably of the same size, are connected by said sensor 1, 3 or 5 via the tubular space passing through this last 12, 32 or 52.
  • the sleeves 18, 38 or 58 disposed at each of the ends of the sensor 1, 3 or 5 facilitate connection to the pipe portions 51 and 52 and advantageously, the section of the tubular space 12, 32 and 52 is substantially identical to that of the lines 51 and 52.
  • the fact of choosing a substantially identical section makes it possible not to form a bottleneck that would disturb the flow of the product 14 or a widening within which this product could accumulate and stagnate. This does not exclude the possibility of choosing the section of the tubular space slightly greater or slightly smaller than that of the pipes 51 and 52. Such a situation occurs more particularly when the section of the tubular space is polygonal whereas that of the pipes is circular, as is the case in Figures 1 to 3.
  • the senor 1, 3 or 5 can be separated from the pipe portions 51 and 52 so that it can be cleaned more easily.
  • the lines 51 and 52 are nested only in the sleeves 18, 38 or 58.
  • the measuring apparatus 50 further comprises means 70 for measuring the velocity CL of a wave train traversing the product 14 flowing in the free space 12, 32 or 52 of the sensor 1, 3, 5 or in one of the pipe portions 51, 52, the wave train traversing the product 14 in a transverse direction T perpendicular to the main axis of the portions 51 or 52 or said free space.
  • these means 70 comprise an ultrasonic transmitter 71 and an ultrasound receiver disposed facing each other, at the periphery of the free space or of a pipe portion 51, 52 located upstream or downstream of this space.
  • the transmitter 71 and the receiver 72 are arranged on the upstream portion 51.
  • the means 70 also comprise a computing unit 77 connected to the receiver 72 and to a transmitter 71 via a transmission and reception device 79. signal.
  • the unit 79 sends commands for transmitting a sound wave to the transmitter 71 and calculates the delay time between the emission and the reception of the sound wave. Knowing the distance separating the transmitter 71 and the receiver 72, the member 79 can determine the celerity CL of the sound wave passing through the product 14 in the direction T.
  • the means 70 for determining the speed CL include two piezoelectric elements 10 of the sensor 1 located opposite one another. With reference to FIG. 1, these may be elements 10a and 10b.
  • One of the elements 10a, dedicated to the emission, is subjected to a variable voltage of high frequency, so as to emit an ultrasonic wave, and the other element 10b is dedicated to the reception of this wave.
  • the elements 10a and 10b, fulfilling functions similar to those of the transmitter 71 and the receiver 72, are connected to a computing unit and to a signal transmitting and receiving element fulfilling functions similar to those of the elements 77. and 79 previously described.
  • the transducer is considered equivalent to the circuit shown in FIG. 8b and the electrical impedance Ze of the transducer is given by formula B of Figure 8c.
  • This impedance depends on Z which characterizes the product 14.
  • the measurement of the electrical impedance Ze makes it possible to calculate the acoustic impedance Za of the product 14 which covers the transducer.
  • Za, CL and S thus makes it possible to know the density p of the product 14.
  • the measuring device 50 is mounted downstream of an extruder 62, during the manufacture of a mixture, depending on the value of the measured density p, it is possible to immediately act on the rotational speed of the screw 64, so as to maintain constant the density p of the mixture leaving the extruder 62.
  • the calculation unit 77 is connected to a control device 66 for adjusting the speed of the motor 65 causing the screw 64.
  • FIG. 9 represents another example of a sensor 9 according to the invention of the type comprising a frame 93 defining inside said free space 92 and in which is provided at least one lateral opening 91 covered by a sensitive plate 90 of piezoelectric material.
  • the senor 9 comprises a frame 93 defining in its interior a free space 92 within which the product 14 to be characterized is likely to circulate.
  • the arrows F represent the flow of this product 14.
  • a lateral opening 91 is formed in the frame 93.
  • the term "lateral opening” designates an opening other than the inlet 92a and outlet 92b 92 of the free space 92.
  • the free space 92 is tubular axis A.
  • the inlet and outlet openings 92a, 92b are aligned with respect to the axis A and perpendicular to it.
  • the lateral opening 91 is, in turn, parallel to the axis A.
  • the lateral opening 91 is covered by a stacked structure comprising: a sensitive plate 90 of piezoelectric material having a first face 80, facing said free space 92 , and a second face 82, opposite; a support plate 94 located on the side of the second face 82; and fixing means 95 for fixing the support plate relative to the frame 93.
  • the sensitive plate 90 When the stacked structure is assembled, the sensitive plate 90 is between the edges of the lateral opening 91 and the support plate 94.
  • the fixing means 95 make it possible to maintain the assembled structure and fix it on the frame 93. These fixing means 95 must also allow the vibration of the sensitive plate 90.
  • these fixing means are clamping screws 95 disposed at the periphery of the support plate 94, which cooperate with threaded housings formed on the frame 93, around the lateral opening 91. These clamping screws 95 must be sufficiently loosened to allow the plate 90 to be vibrated.
  • these screws 95 also make it possible to lightly load the sensitive plate 90, this load being radial. , that is to say, oriented according to the thickness of the plate 90. To control the intensity of this load, which must remain low, it serves more or less the screws of serra age 95 by checking the tightening, for example, using a torque wrench.
  • the sensitive plate 90 is made of piezoelectric polymer, in particular polyvinylidene fluoride, denoted PVDF or PVF 2 , or else a copolymer of polyvinylidene fluoride and trifluoroethylene, denoted by P (VF 2 -VF 3 ) or P (VDF-TrFE ).
  • the piezoelectric polymer plate 90 forms an electromechanical transducer able to generate a potential difference following a deformation in the direction of its thickness.
  • Piezoelectric polymer materials, such as PVDF and its copolymers have less piezoelectric properties than ceramics but have several advantages: they can be made of large-area film and / or thin, they have some flexibility in shaping and they can be molded or thermoformed. Furthermore, since these polymers are more robust in nature than ceramics, it is possible to use higher voltages serenely and thus not only the representative properties of the product layer 14 are obtained in the vicinity of the sensor 9, but an image of the properties more in depth of the vein of the product.
  • first and second faces 80 and 82 are covered with a conductive surface coating. They are for example metallized with a metal such as copper, nickel, silver, gold or a nickel-aluminum alloy. Such a coating can, for example, be obtained by vacuum metallization. Depending on the quality of the metallization, a more or less good polarization is obtained. A silver coating provides, generally, a good polarization.
  • the stacked structure further comprises first and second electrical connection means for connecting (directly or indirectly) said first and second faces, 80 and 82, of the sensitive plate 90 to the electric generator 54.
  • the first connection means comprise a conductive plate 96 covering the second face 82 of the plate 90.
  • This plate 96 may, for example, be made of copper and, advantageously, completely cover the second face 82.
  • the conductive plate 96 makes it possible to promote the homogeneity and the quality impedance measurements made by overcoming local resistance variations on the second face 82.
  • the plate 96 is electrically connected to a terminal of the generator 54.
  • the first face 80 is, in turn, in electrical contact with the frame 93 using conductive strips 97, for example copper, placed between the frame 93 and the plate 90 at the edges of the open 91.
  • the frame 93, the plate 90, the support plate 94 and the clamping screws 95 are in electrical contact and all connected to the other terminal of the generator 54.
  • said stacked structure comprises at least one PTFE plate 98 covering the first face 80 of the sensitive plate 90 and acting as a non-stick coating, in order to limit the fouling of this face 80.
  • An insulating plate 99 is disposed between the support plate and the conductive plate 96 in order to isolate the support plate 94 from the conductive plate 96.
  • This insulating plate 99 may, for example, be made of PTFE.
  • the structure of the sensor of Figure 9 is, as a whole, quite simple and allows for reliable measurements.
  • the frame 93 is installed between two upstream pipe 51 and downstream pipe portions 52, the product to be characterized circulating inside the free space 92 defined by the interior of the frame.
  • Figures 10 to 12 show several examples of devices that take these considerations into account.
  • the example of Figure 10 comprises a frame 93 having the general shape of a hollow cylinder of circular section.
  • the different plates 90, 94 of the sensor 9 are curved so as to fit the outer curvature of the frame 93 when it covers the lateral opening 91 formed therein. Note that it is easy to give a curved shape to the sensitive plate 90 of the sensor when it is made of polymer material.
  • the frame 93 has the general shape of a cylinder, of circular section, and has on its wall a flat part 100. The junction between the upstream and downstream edges of this flat and the wall of the frame 93 is made by chamfers 102. 91 lateral opening of the frame 93 is formed in the flat 100 and the plates 90, 94 of the sensor are stacked on this flat 100.
  • the frame 93 is formed by the joining of two hollow cylinders 93a and 93b, of circular section, the first cylinder 93a is crossed along its axis X by the product 14 and the second cylinder 93b cut the first cylinder 93a, the Y axis of the second cylinder 106 being perpendicular to the axis X of the first.
  • Some sensor plates, including the sensitive plate 90, are housed inside the second cylinder 93b.
  • the support plate 94 may be housed in the cylinder 93b or cover the outer opening thereof as shown. It should be noted that in all the examples of devices of FIGS. 10 to 12, the transducer of the sensor 9 (that is to say the sensitive plate 90) is located at the periphery of the free space 92 passing through the sensor 9, in accordance with FIG. to the invention.

Abstract

The invention concerns a measuring device comprising: a sensor (1) with at least one electromechanical transducer (10); at least one electric generator connected to said transducer; and means for determining the electrical impedance at the generator output. Said sensor (1) is run through by a tubular gap (12) inside which a product (14) is capable of circulating, and said electromechanical transducer (10) is located at the periphery of said tubular gap (12), so as to be subjected to a characteristic mechanical load of the product (14) circulating in said gap (12), said impedance representing said load. The inventive device is designed for use in a measuring apparatus for determining the density of the product (14) circulating inside said tubular gap (12).

Description

Dispositif de mesure Measuring device
L'invention concerne un dispositif de mesure du type comprenant : un capteur avec au moins un transducteur électromécanique ; au moins un générateur électrique connecté audit transducteur ; et des moyens pour déterminer l'impédance électrique en entrée du transducteur. L'invention concerne également un appareil de mesure équipé d'un tel dispositif.The invention relates to a measuring device of the type comprising: a sensor with at least one electromechanical transducer; at least one electrical generator connected to said transducer; and means for determining the electrical impedance at the input of the transducer. The invention also relates to a measuring apparatus equipped with such a device.
Un tel appareil de mesure sert, en particulier, à déterminer la masse volumique p d'un produit liquide ou pâteux s'écoulant en continu à l'intérieur d'une conduite et peut trouver des applications dans le domaine de l'agroalimentaire, des cosmétiques, ou de la plasturgie, en permettant une meilleure caractérisation du produit directement au niveau de la ligne de fabrication et donc une meilleure maîtrise de la qualité de ce produit. La demande de brevet français FR 2763687, décrit un appareil de ce type, permettant de déterminer la masse volumique p d'une pâte de poisson, constituée essentiellement d'un mélange d'eau, d'air, de sel et de fibres de poisson, à la sortie d'une extrudeuse. Cet appareil est utilisé au niveau d'une conduite située en aval de l'extrudeuse et à l'intérieur de laquelle circule la pâte de poisson. L'appareil comprend une pastille piézoélectrique faisant office de transducteur électromécanique disposée à l'intérieur de la conduite, dans un plan contenant l'axe de celle-ci.Such a measuring apparatus serves, in particular, to determine the density p of a liquid or pasty product flowing continuously inside a pipe and can find applications in the field of food processing, cosmetics, or plastics, allowing a better characterization of the product directly at the level of the production line and thus a better control of the quality of this product. French patent application FR 2763687 describes an apparatus of this type for determining the density p of a fish paste, consisting essentially of a mixture of water, air, salt and fish fibers. at the exit of an extruder. This apparatus is used in a pipe located downstream of the extruder and inside which circulates the fish paste. The apparatus comprises a piezoelectric pellet serving as an electromechanical transducer disposed within the pipe, in a plane containing the axis thereof.
Or, dans la pratique, l'utilisation de l'appareil de FR 2763687 pose les problèmes suivants : on constate que la pastille piézoélectrique (et sa connectique) perturbe l'écoulement de la pâte de poisson car elle obstrue la conduite et sépare le flux de pâte en deux parties. En outre, cette pastille s'encrasse très vite ce qui entraîne, d'une part, des erreurs d'estimation de la masse volumique p de la pâte et, d'autre part, des problèmes de contamination bactérienne. L'invention vise à remédier à ces problèmes, ou tout au moins à les atténuer.However, in practice, the use of the apparatus of FR 2763687 poses the following problems: it is found that the piezoelectric pellet (and its connections) disrupts the flow of the fish paste because it obstructs the pipe and separates the flow of dough in two parts. In addition, this pellet fouls very quickly which leads, on the one hand, errors in estimating the density p of the dough and, on the other hand, problems of bacterial contamination. The invention aims to remedy these problems, or at least to mitigate them.
Pour atteindre ce but, l'invention a pour objet un dispositif de mesure du type précité, caractérisé en ce que ledit capteur est traversé par un espace libre à l'intérieur duquel un produit est susceptible de circuler, et en ce que ledit transducteur est situé à la périphérie dudit espace libre de manière à être soumis à une charge mécanique caractéristique du produit circulant dans ledit espace, l'impédance électrique mesurée étant fonction de ladite charge.To achieve this object, the invention relates to a measuring device of the aforementioned type, characterized in that said sensor is traversed by a free space within which a product is likely to flow, and in that said transducer is located on the outskirts of the said free space so as to be subjected to a mechanical load characteristic of the product flowing in said space, the measured electrical impedance being a function of said load.
Grâce à l'invention, ledit transducteur (et donc sa connectique) se situe à la périphérie de l'espace libre dans lequel circule le produit.Thanks to the invention, said transducer (and therefore its connector) is located at the periphery of the free space in which the product flows.
L'écoulement du produit est donc moins perturbé que par la pastille piézoélectrique de FR 2763687 et le transducteur est moins sujet à l'encrassement.The flow of the product is therefore less disturbed than by the piezoelectric pellet of FR 2763687 and the transducer is less subject to fouling.
De préférence, pour perturber le moins possible l'écoulement du produit, le transducteur ne fait pas, ou peu, saillie à l'intérieur de l'espace libre, il peut même être légèrement en retrait par rapport à cet espace.Preferably, to disturb the flow of the product as little as possible, the transducer does not, or little, protrude within the free space, it may even be slightly set back with respect to this space.
Une seule des faces du transducteur est exposée au produit et soumise directement à ladite charge mécanique. Dans la présente demande, cette face exposée est nommée première face du transducteur. Avantageusement, la connectique du transducteur est, de préférence, majoritairement réalisée sur une face non exposée, nommée deuxième face.Only one of the transducer faces is exposed to the product and subjected directly to said mechanical load. In the present application, this exposed face is called the first face of the transducer. Advantageously, the connector of the transducer is preferably predominantly made on an unexposed face, called second face.
On notera que le ou les transducteurs ne sont pas nécessairement disposés tout autour de l'espace libre : ils peuvent être disposés uniquement sur un côté de cet espace. Lorsqu'ils sont répartis tout autour de l'espace libre, les transducteurs peuvent l'être de façon régulière ou non.Note that the transducer or transducers are not necessarily arranged all around the free space: they can be arranged only on one side of this space. When they are distributed all around the free space, the transducers can be distributed regularly or not.
Avantageusement, ledit espace libre est de forme générale tubulaire (i.e. il n'est pas coudé) afin de perturber le moins possible l'écoulement du produit qui le traverse.Advantageously, said free space is of tubular general shape (i.e. it is not bent) in order to disturb as little as possible the flow of the product passing through it.
On notera qu'un espace libre tubulaire n'a pas nécessairement une section circulaire. L'espace libre peut en effet avoir des sections rectangulaire, carrée, polygonale, ellipsoïdale... De même, la longueur axiale de l'espace tubulaire n'est pas nécessairement supérieure à la plus grande dimension de sa section. Avantageusement, l'espace libre est de section sensiblement identique à celle de la conduite sur laquelle le dispositif est branché, afin de perturber le moins possible l'écoulement.Note that a tubular free space does not necessarily have a circular section. The free space can indeed have rectangular, square, polygonal, ellipsoidal sections ... Similarly, the axial length of the tubular space is not necessarily greater than the largest dimension of its section. Advantageously, the free space is of substantially identical section to that of the pipe on which the device is connected, in order to disturb the flow as little as possible.
Le principe général de fonctionnement d'un tel dispositif de mesure est le suivant : la charge mécanique exercée sur le transducteur, par le produit circulant à l'intérieur du tube, empêche ce transducteur de vibrer librement et modifie ainsi le comportement électrique de ce dernier. Ceci fait alors varier la valeur de l'impédance électrique en entrée de ce transducteur, que l'on mesure. La valeur de cette impédance électrique permet ensuite de déterminer par calcul la masse volumique du produit concerné, à condition de connaître, par ailleurs, la célérité d'un train d'ondes traversant ce produit.The general operating principle of such a measuring device is as follows: the mechanical load exerted on the transducer, by the product circulating inside the tube, prevents this transducer from vibrating freely and thus modifies the electrical behavior of the latter. This then varies the value of the electrical impedance input of this transducer, which is measured. The value of this electrical impedance then makes it possible to determine by calculation the density of the product concerned, on the condition of knowing, moreover, the celerity of a stream of waves passing through this product.
Avantageusement, le capteur comprend une pluralité de transducteurs répartis autour de l'espace tubulaire.Advantageously, the sensor comprises a plurality of transducers distributed around the tubular space.
Ces transducteurs peuvent être montés en série ou en parallèle. Dans ces deux cas, ils sont électriquement dépendants et équivalent à un unique transducteur mesurant une charge mécanique moyenne.These transducers can be connected in series or in parallel. In both cases, they are electrically dependent and equivalent to a single transducer measuring a mean mechanical load.
Alternativement, les transducteurs peuvent être électriquement indépendants, c'est-à-dire être reliés chacun à leur propre générateur, ou encore être reliés à un générateur commun par l'intermédiaire d'un multiplexeur ou tout autre système permettant d'alimenter successivement chaque transducteur. Dans ce cas lesdits moyens de mesure d'impédance mesurent l'impédance pour chaque circuit indépendant.Alternatively, the transducers may be electrically independent, that is to say each be connected to their own generator, or may be connected to a common generator via a multiplexer or any other system for successively feeding each transducer. In this case, said impedance measuring means measure the impedance for each independent circuit.
Des transducteurs électriquement indépendants permettent de multiplier les points de mesure, et donc de caractériser le produit circulant dans la conduite selon différentes directions radiales. Par direction radiale, on entend désigner dans le présent mémoire une direction perpendiculaire à l'axe principal de l'espace tubulaire. Ainsi, lorsque la conduite est placée à l'horizontal, il devient possible de caractériser séparément la partie de produit circulant dans la partie haute de la conduite, et celle circulant dans la partie basse. Aussi, avantageusement, les transducteurs électromécaniques sont répartis régulièrement, selon différentes directions radiales, à la périphérie de l'espace tubulaire.Electrically independent transducers make it possible to multiply the measurement points, and thus to characterize the product flowing in the pipe in different radial directions. By radial direction is meant herein a direction perpendicular to the main axis of the tubular space. Thus, when the pipe is placed horizontally, it becomes possible to characterize separately the portion of product flowing in the upper part of the pipe, and that flowing in the lower part. Also, advantageously, the electromechanical transducers are distributed regularly, in different radial directions, at the periphery of the tubular space.
Avantageusement encore, le ou les transducteurs comprennent un élément sensible réalisé en matériau piézoélectrique, ci-après dénommé élément piézoélectrique, ce qui permet d'obtenir des capteurs de structure simple et compacte. Dans la description qui suit, on envisage uniquement le cas où les transducteurs sont de ce type. Néanmoins, d'autres types de transducteur électromécanique, c'est-à-dire capable de recevoir de l'énergie d'un système électrique et de fournir de l'énergie à un système mécanique, ou inversement, pourraient être envisagés. Selon un mode de réalisation de l'invention, la première face du ou des transducteurs définit l'espace tubulaire : c'est une paroi de cet espace. Ainsi, la première face n'est sensiblement ni en retrait ni en saillie par rapport audit espace et les risques d'encrassement sont diminués. Pour diminuer encore les risques d'encrassement et faciliter le nettoyage de cette première face, celle-ci peut être recouverte par un revêtement antiadhésif comme le polytétrafluoroéthylène, ou PTFE (plus connu sous la marque « Téflon »), ou une matière analogue. Le PTFE présente l'avantage, par ailleurs, d'être compatible avec les normes de l'agroalimentaire.Advantageously, the transducer or transducers comprise a sensitive element made of piezoelectric material, hereinafter referred to as a piezoelectric element, which makes it possible to obtain sensors of simple and compact structure. In the following description, only the case where the transducers are of this type is considered. Nevertheless, other types of electromechanical transducer, that is to say capable of receiving energy from an electrical system and supplying power to a mechanical system, or vice versa, could be envisaged. According to one embodiment of the invention, the first face of the transducer (s) defines the tubular space: it is a wall of this space. Thus, the first face is substantially neither recessed nor protruding with respect to said space and the risks of fouling are reduced. To further reduce the risk of fouling and facilitate the cleaning of this first face, it can be covered by a non-stick coating such as polytetrafluoroethylene, or PTFE (better known under the trademark "Teflon"), or a similar material. PTFE also has the advantage of being compatible with agri-food standards.
Selon un autre mode de réalisation, la première face du transducteur est recouverte d'une membrane. Dans ce cas, c'est cette membrane qui définit l'espace tubulaire. Elle doit être suffisamment souple pour que le transducteur puisse détecter la charge mécanique exercée par le produit circulant dans ledit espace. Par ailleurs, cette membrane ne doit pas empêcher le transducteur de vibrer.According to another embodiment, the first face of the transducer is covered with a membrane. In this case, it is this membrane that defines the tubular space. It must be sufficiently flexible so that the transducer can detect the mechanical load exerted by the product circulating in said space. In addition, this membrane must not prevent the transducer from vibrating.
L'invention a également pour objet un appareil de mesure, comprenant : un dispositif de mesure selon l'une quelconque des revendications précédentes ; des moyens pour mesurer la célérité d'un train d'onde traversant le produit circulant dans ledit espace libre ou dans une portions de conduite située en amont ou en aval de cet espace ; et une unité de calcul permettant de déterminer la masse volumique de ce produit à partir de la célérité et de l'impédance mesurées.The invention also relates to a measuring apparatus, comprising: a measuring device according to any one of the preceding claims; means for measuring the speed of a wave train traversing the product circulating in said free space or in a pipe portion located upstream or downstream of this space; and a calculation unit for determining the density of this product from the measured velocity and impedance.
Cet appareil de mesure est destiné à être installé sur une conduite existante, l'espace libre dudit capteur étant placé entre deux portions de cette conduite et raccordant ces deux portions de conduite, amont et aval, via ledit espace tubulaire. Alternativement, l'appareil de mesure peut comprendre une ou deux portion(s) de conduite, collatérale(s) audit capteur et l'ensemble formé par le capteur et les portion(s) de conduite est installé à la place d'un tronçon de la conduite existante.This measuring device is intended to be installed on an existing pipe, the free space of said sensor being placed between two portions of this pipe and connecting these two pipe portions, upstream and downstream, via said tubular space. Alternatively, the measuring device may comprise one or two portions of pipe, collateral (s) to said sensor and the assembly formed by the sensor and the portion (s) of pipe is installed in place of a section of the existing pipe.
L'invention et ses avantages seront mieux compris à lecture de la description détaillée qui suit d'exemples de l'invention, donnés à titre non limitatif. Cette description fait référence aux planches de figures annexées sur lesquelles : - la figure 1 est une vue en perspective d'un premier exemple de capteur pouvant équiper un dispositif de mesure selon l'invention ;The invention and its advantages will be better understood on reading the following detailed description of examples of the invention given in a non-limiting manner. This description refers to the plates of annexed figures in which: FIG. 1 is a perspective view of a first example of a sensor that can be fitted to a measuring device according to the invention;
- la figure 2 est une coupe selon le plan IHI du capteur de la figure 1 ; - la figure 3 est une coupe selon le plan III-III du capteur de la figure 1 ;- Figure 2 is a section along the plane IHI of the sensor of Figure 1; - Figure 3 is a section along the plane III-III of the sensor of Figure 1;
- la figure 4 est une vue en perspective d'un deuxième exemple de capteur pouvant équiper un dispositif de mesure selon l'invention ;FIG. 4 is a perspective view of a second example of a sensor that can equip a measuring device according to the invention;
- la figure 5 est une coupe selon le plan V-V d'une partie du capteur de la figure 4 ;- Figure 5 is a section along the plane V-V of a portion of the sensor of Figure 4;
- la figure 6 est une vue en perspective d'un troisième exemple de capteur pouvant équiper un dispositif de mesure selon l'invention ;FIG. 6 is a perspective view of a third example of a sensor that can equip a measuring device according to the invention;
- la figure 7 est une représentation schématique d'un exemple d'appareil de mesure selon l'invention ; - les figure 8a à 8c représentent les schémas électriques équivalents d'un transducteur "à vide" et "en charge" selon l'invention, ainsi que les formules de calcul relatives à l'impédance en entrée de ce transducteur ;FIG. 7 is a schematic representation of an exemplary measuring apparatus according to the invention; FIGS. 8a to 8c represent the equivalent electrical diagrams of a "vacuum" and "charging" transducer according to the invention, as well as the calculation formulas relating to the input impedance of this transducer;
- la figure 9 est une représentation schématique d'un quatrième exemple de capteur selon l'invention ; et - les figures 10 à 12 représentent schématiquement plusieurs exemples de dispositifs comprenant un capteur du type de celui la figure 9.FIG. 9 is a schematic representation of a fourth example of a sensor according to the invention; and FIGS. 10 to 12 schematically represent several examples of devices comprising a sensor of the type of that of FIG. 9.
Les figures 1, 2 et 3 représentent un premier exemple de capteur 1 comprenant une pluralité de transducteurs formés d'éléments piézoélectriques 10 sous forme de plaquettes, comme des céramiques.Figures 1, 2 and 3 show a first example of a sensor 1 comprising a plurality of transducers formed of piezoelectric elements 10 in the form of platelets, such as ceramics.
Ces transducteurs comprennent également la connectique, non représentée, associée aux éléments 10.These transducers also include the connector, not shown, associated with the elements 10.
Le type de céramique utilisé pour les éléments piézoélectriques 10 est choisi en fonction de la charge mécanique du produit que ces éléments sont destinés à supporter (cette charge mécanique dépend de la masse volumique p du produit). Pour un produit agroalimentaire comme une pâte de poisson, on peut, par exemple, utiliser une céramique de type « PZ35 » commercialisée par la société « Ferroperm ».The type of ceramic used for the piezoelectric elements 10 is chosen according to the mechanical load of the product that these elements are intended to support (this mechanical load depends on the density p of the product). For an agri-food product such as a fish paste, it is possible, for example, to use a ceramic of the "PZ35" type marketed by the company "Ferroperm".
Les éléments 10, au nombre de six dans l'exemple représenté, sont joints bord à bord et définissent entre eux un espace libre tubulaire 12, de section hexagonale, destiné à être traversé par un produit 14 liquide ou pâteux circulant suivant la flèche F. De manière à garantir l'étanchéité de l'espace 12, des joints d'étanchéité 16 sont disposés entre deux élémentsThe elements 10, six in number in the example shown, are joined edge to edge and define between them a tubular free space 12, hexagonal section, intended to be traversed by a liquid or pasty product 14 flowing along the arrow F. In order to ensure the sealing of the space 12, seals 16 are arranged between two elements
10 adjacents. Les éléments 10 sont maintenus à l'aide de deux manchons 18 qui entourent les extrémités du capteur 1. Des empreintes 20 peuvent être ménagées dans les manchons 18 pour faciliter le positionnement des éléments 10. Ces éléments 10 doivent dans tous les cas rester libres de vibrer. Aussi, les manchons sont, de préférence, réalisés en élastomère.10 adjacent. The elements 10 are held using two sleeves 18 which surround the ends of the sensor 1. Fingerprints 20 may be formed in the sleeves 18 to facilitate the positioning of the elements 10. These elements 10 must in all cases remain free of vibrate. Also, the sleeves are preferably made of elastomer.
Comme représenté figure 2, un joint d'étanchéité 17, par exemple en silicone, peut être disposé autour des éléments 10, entre ces derniers et les manchons 18.As shown in FIG. 2, a seal 17, for example made of silicone, may be placed around the elements 10, between the latter and the sleeves 18.
Habituellement, pour se placer dans de bonnes conditions opératoires il est préférable de mettre légèrement en charge les éléments 10. Aussi, on utilise des tiges 22 reliant les manchons 18. Ces tiges sont filetées sur une portion d'extrémité pour permettre de visser/dévisser un écrou 22a afin de rapprocher ou d'écarter les manchons 18 l'un de l'autre, ce qui pince plus ou moins les éléments 10, suivant l'axe principal de l'espace tubulaire. On notera que l'on souhaite principalement obtenir une mise en charge radiale des éléments 10 (c'est-à-dire orientée suivant l'épaisseur de ces éléments). Cette légère mise en charge radiale est obtenue grâce au pincement précité, qui provoque une très légère déformation radiale des éléments. Les tiges 22 ont également un rôle de maintien des manchons autour des éléments 10.Usually, to be placed in good operating conditions it is preferable to lightly load the elements 10. Also, rods 22 are used connecting the sleeves 18. These rods are threaded on an end portion to allow screwing / unscrewing. a nut 22a to bring or move the sleeves 18 away from each other, which more or less clamp the elements 10 along the main axis of the tubular space. Note that it is mainly desired to obtain a radial loading of the elements 10 (that is to say oriented according to the thickness of these elements). This slight radial loading is obtained thanks to the aforementioned pinching, which causes a very slight radial deformation of the elements. The rods 22 also have a role of maintaining the sleeves around the elements 10.
Avantageusement, on réalise les manchons 18 dans une matière isolante élastomère et on choisit cette matière résistante aux températures des produits destinés à circuler dans l'espace 12. Par exemple, on peut utiliser une résine acétale comme le « Delrin » (marque déposée), supportant des températures allant jusqu'à 2000C.Advantageously, the sleeves 18 are produced in an elastomeric insulating material and this temperature-resistant material is selected from the products intended to circulate in the space 12. For example, an acetal resin such as "Delrin" (registered trademark) can be used, withstand temperatures up to 200 0 C.
Les premières faces 80 des éléments 10 sont les faces orientées vers l'intérieur de l'espace 12. Ces faces sont soumises à la charge mécanique exercée par le produit 14. Les faces extérieures, ou deuxièmes faces 82, opposées aux premières 80, sont libres mécaniquement. Un fil conducteur (non représenté) est relié à chaque face 80, 82. La connexion de ces fils ne pose pas de problème particulier compte tenu de la nature du matériau céramique retenu pour les éléments 10. Lorsque les éléments 10 sont électriquement indépendants, les fils conducteurs de chaque élément sont reliés à un générateur propre à l'élément ou à un générateur commun via un multiplexeur ou un système d'interrupteurs actionnés successivement. Lorsqu'ils sont électriquement dépendants, les premières faces 80, de même que les deuxièmes faces 82, sont reliées électriquement entre elles et connectées au générateur.The first faces 80 of the elements 10 are the faces oriented towards the interior of the space 12. These faces are subjected to the mechanical load exerted by the product 14. The outer faces, or second faces 82, opposite the first 80, are mechanically free. A conductive wire (not shown) is connected to each face 80, 82. The connection of these wires does not pose any particular problem given the nature of the ceramic material retained for the elements 10. When the elements 10 are electrically independent, the conductor son of each element are connected to a generator specific to the element or to a common generator via a multiplexer or a system of switches actuated successively. When they are electrically dependent, the first faces 80, as well as the second faces 82, are electrically connected to each other and connected to the generator.
Les figures 4 et 5 représentent un deuxième exemple de capteur 3, comprenant une pluralité d'éléments piézoélectriques 30 sous forme de bâtonnets, noyés dans une matrice 31. Cette matrice 31 peut être réalisée en résine époxy et moulée autour desdits éléments 30. Les éléments 30 peuvent être totalement noyés dans la matrice 31, comme représenté figure 5, ou l'être seulement partiellement. Le matériau de la matrice 31 est choisi de sorte qu'il soit suffisamment flexible pour permettre aux éléments 30 de vibrer et d'être sensibles à la charge mécanique exercée par le produit 14. Un espace tubulaire 32 traverse le capteur 3. Les parois 32a de cet espace sont formées par la matrice 31.FIGS. 4 and 5 show a second example of sensor 3, comprising a plurality of piezoelectric elements 30 in the form of rods, embedded in a matrix 31. This matrix 31 may be made of epoxy resin and molded around said elements 30. The elements 30 may be completely embedded in the matrix 31, as shown in Figure 5, or be only partially. The material of the die 31 is chosen so that it is sufficiently flexible to allow the members 30 to vibrate and be responsive to the mechanical load exerted by the product 14. A tubular space 32 passes through the sensor 3. The walls 32a of this space are formed by the matrix 31.
Les éléments 30 sont répartis régulièrement à la périphérie de cet espace et peuvent être électriquement indépendants ou dépendants, comme expliqué plus haut. Leurs premières faces 80 sont séparées des parois 32a par une partie de la matrice 31 assimilable à une membrane 33 recouvrant les faces 80.The elements 30 are evenly distributed around the periphery of this space and can be electrically independent or dependent, as explained above. Their first faces 80 are separated from the walls 32a by a portion of the matrix 31 comparable to a membrane 33 covering the faces 80.
La structure composite (matrice 31/éléments 30) de ce deuxième exemple de capteur permet de fabriquer facilement des transducteurs aux formes variées. Le capteur 3 peut présenter à ses extrémités des manchons 38 qui serviront pour raccorder le capteur 3 à une conduite. Ces manchons 38 peuvent être moulés avec le corps composite du capteur, ou être des pièces rapportées sur ce corps, comme c'est le cas ici. On retrouve des tiges 22 analogues à celles précédemment décrites. La figure 6 représente un troisième exemple de capteur comprenant un unique élément piézoélectrique 50 enroulé sur lui-même, de manière à définir un espace tubulaire 52. L'élément piézoélectrique 50 est par exemple en polyfluorure de vinylidène ou PVDF. Il peut être réalisé sous forme de plaque puis être déformé (courbé), les bords de la plaque étant joints de manière à former un tube cylindrique, comme dans l'exemple (un joint d'étanchéité peut être disposé entre ces bords). On peut également réaliser un capteur en PVDF directement à la forme désirée. Dans les deux cas, des manchons 58 peuvent être disposés aux extrémités du capteur, soit pour maintenir l'élément 50 dans sa position déformée, soit pour faciliter le raccordement du capteur entre deux conduites. On notera qu'un unique manchon central entourant les éléments 10 pourrait être utilisé à la place des deux manchons d'extrémité 18.The composite structure (matrix 31 / elements 30) of this second exemplary sensor makes it easy to manufacture transducers of various shapes. The sensor 3 may have at its ends sleeves 38 which will be used to connect the sensor 3 to a pipe. These sleeves 38 may be molded with the composite body of the sensor, or be inserts thereon, as is the case here. Stems 22 similar to those previously described are found. FIG. 6 represents a third example of a sensor comprising a single piezoelectric element 50 wound on itself, so as to define a tubular space 52. The piezoelectric element 50 is for example made of polyvinylidene fluoride or PVDF. It can be made in the form of a plate and then be deformed (curved), the edges of the plate being joined so as to form a cylindrical tube, as in the example (a seal can be placed between these edges). It is also possible to make a PVDF sensor directly to the desired shape. In both cases, sleeves 58 may be arranged at the ends of the sensor, either to hold the element 50 in its deformed position, or to facilitate the connection of the sensor between two pipes. Note that a single central sleeve surrounding the elements 10 could be used in place of the two end sleeves 18.
Deux fils conducteurs (non représentés) sont reliés respectivement à la première face 80 (i.e. la face intérieure) de l'élément 50 qui définit l'espace 52 (la face 80 est une paroi de l'espace 52), et à la deuxième face 82 (i.e. la face extérieure) du capteur 5. Ces fils conducteurs sont reliés à un générateur, et à des moyens pour mesurer l'impédance en sortie de ce générateur.Two son drivers (not shown) are respectively connected to the first face 80 (ie the inner face) of the element 50 which defines the space 52 (the face 80 is a wall of the space 52), and the second face 82 (ie the outer face) of the sensor 5. These conductive son are connected to a generator, and means for measuring the impedance output of this generator.
Les deuxième et troisième exemples de capteur 3 et 5, ont pour avantage de présenter une cylindricité de révolution parfaite qui permet d'éviter les retenues de produit.The second and third examples of sensors 3 and 5 have the advantage of having a perfectly cylindrical revolution that avoids product retention.
La figure 7 représente schématiquement un exemple d'appareil de mesure 50 selon l'invention, monté à la sortie d'une extrudeuse 62.FIG. 7 schematically represents an example of measuring apparatus 50 according to the invention mounted at the exit of an extruder 62.
L'extrudeuse 62 comporte un corps cylindrique 63 à l'intérieur duquel tourne une vis d'extrusion 64 entraînée par un moteur 65. Les matières premières entrent dans le corps 63 par la trémie d'alimentation 66 et en ressortent sous forme de produit élaboré 14 par la sortie 67. Ce produit 14 peut être une pâte de poisson, ou tout autre mélange liquide ou pâteux, agroalimentaire ou non. L'appareil de mesure 50 comprend un dispositif de mesure selon l'invention équipé d'un capteur 1, 3 ou 5 du type de ceux précédemment décrits, un générateur électrique 54 relié au(x) transducteurs(s) du capteur 1, 3, 5 via deux fils conducteurs 53 et des moyens 55 pour déterminer l'impédance électrique Ze à la sortie du générateur, comme un pont d'impédance ou tout autre système de mesure d'impédance. Pour simplifier on parlera ci-après d'impédancemètre 55.The extruder 62 comprises a cylindrical body 63 inside which rotates an extrusion screw 64 driven by a motor 65. The raw materials enter the body 63 through the feed hopper 66 and come out as an elaborate product 14 by the output 67. This product 14 may be a fish paste, or any other liquid or pasty mixture, agri-food or not. The measuring apparatus 50 comprises a measuring device according to the invention equipped with a sensor 1, 3 or 5 of the type of those described above, an electric generator 54 connected to the transducer (s) of the sensor 1, 3 Via two leads 53 and means 55 for determining the electrical impedance Ze at the output of the generator, such as an impedance bridge or other impedance measuring system. For simplicity, hereinafter, reference will be made to an impedance meter 55.
Par rapport au sens d'écoulement du flux F de produit, le capteur est relié avec des portions de conduite amont 51 et aval 52.With respect to the direction of flow of the product stream F, the sensor is connected with upstream pipe portions 51 and downstream pipe 52.
On notera que le générateur 54 est relié directement au(x) transducteur(s) du capteur 1, 3, 5 par les fils conducteurs 53. Sur la figure 7, Ie sens de circulation du courant i est représenté lors de l'alternance positive du signal sinusoïdal émis par le générateur 54, correspondant aux signes + et - représentés sur ce dernier. L'impédancemètre 55, mesure l'impédance en entrée du (des) transducteur(s), qui correspond à l'impédance en sortie du générateur. De manière générale, on notera que quelques soient les composants placés entre la sortie du générateur et l'entrée du (des) transducteur(s), ces impédances sont liées et que la mesure de l'une permet de déterminer l'autre par calcul. En outre, selon un mode de réalisation particulier, un même système 56 inclut le générateur 54 et l'impédancemètre 55, et assure, ainsi, à la fois la fonction d'émission de courant électrique et celle de mesure d'impédance.It will be noted that the generator 54 is connected directly to the transducer (s) of the sensor 1, 3, 5 by the conducting wires 53. 7, the flow direction of the current i is represented during the positive half-wave of the sinusoidal signal emitted by the generator 54, corresponding to the + and - signs represented on the latter. The impedance meter 55 measures the impedance at the input of the transducer (s), which corresponds to the impedance at the output of the generator. In general, it will be noted that, whatever the components placed between the output of the generator and the input of the transducer (s), these impedances are linked and that the measurement of one makes it possible to determine the other by calculation. . In addition, according to a particular embodiment, the same system 56 includes the generator 54 and the impedance meter 55, and thus ensures both the electrical current emission function and the impedance measurement function.
La portion amont 51 est reliée à la bouche de sortie 67 de l'extrudeuse 62 et les deux portions de conduite 51 et 52, de préférence de même dimension, sont raccordées par ledit capteur 1, 3 ou 5 via l'espace tubulaire traversant ce dernier 12, 32 ou 52.The upstream portion 51 is connected to the outlet mouth 67 of the extruder 62 and the two pipe portions 51 and 52, preferably of the same size, are connected by said sensor 1, 3 or 5 via the tubular space passing through this last 12, 32 or 52.
Les manchons 18, 38 ou 58 disposés à chacune des extrémités du capteur 1, 3 ou 5 permettent de faciliter le raccordement aux portions de conduite 51 et 52 et avantageusement, la section de l'espace tubulaire 12, 32 et 52 est sensiblement identique à celle des conduites 51 et 52. Le fait de choisir une section sensiblement identique permet de ne pas former un goulot d'étranglement qui perturberait l'écoulement du produit 14 ou un élargissement à l'intérieur duquel ce produit pourrait s'accumuler et stagner. Ceci n'exclut pas la possibilité de choisir la section de l'espace tubulaire légèrement supérieure ou légèrement inférieure à celle des conduites 51 et 52. Une telle situation intervient plus particulièrement lorsque la section de l'espace tubulaire est polygonale alors que celle des conduites est circulaire, comme c'est le cas sur les figures 1 à 3.The sleeves 18, 38 or 58 disposed at each of the ends of the sensor 1, 3 or 5 facilitate connection to the pipe portions 51 and 52 and advantageously, the section of the tubular space 12, 32 and 52 is substantially identical to that of the lines 51 and 52. The fact of choosing a substantially identical section makes it possible not to form a bottleneck that would disturb the flow of the product 14 or a widening within which this product could accumulate and stagnate. This does not exclude the possibility of choosing the section of the tubular space slightly greater or slightly smaller than that of the pipes 51 and 52. Such a situation occurs more particularly when the section of the tubular space is polygonal whereas that of the pipes is circular, as is the case in Figures 1 to 3.
Comme expliqué précédemment, aucune partie du capteur 1, 3 ou 5 ne se situe à l'intérieur du flux F de produit 14 qui circule dans les portions de conduite 51 et 52.As explained above, no part of the sensor 1, 3 or 5 is located inside the product flow F 14 which flows in the pipe portions 51 and 52.
Avantageusement, le capteur 1, 3 ou 5 peut être séparé des portions de conduite 51 et 52 pour pouvoir être nettoyé plus facilement. Par exemple, les conduites 51 et 52 sont uniquement emboîtées dans les manchons 18, 38 ou 58. L'appareil de mesure 50 comprend, en outre, des moyens 70 pour mesurer la célérité CL d'un train d'onde traversant le produit 14 circulant dans l'espace libre 12, 32 ou 52 du capteur 1, 3, 5 ou dans l'une des portions de conduite 51, 52, ce train d'onde traversant le produit 14 dans une direction T transversale, perpendiculaire à l'axe principal des portions 51 ou 52 ou dudit espace libre.Advantageously, the sensor 1, 3 or 5 can be separated from the pipe portions 51 and 52 so that it can be cleaned more easily. For example, the lines 51 and 52 are nested only in the sleeves 18, 38 or 58. The measuring apparatus 50 further comprises means 70 for measuring the velocity CL of a wave train traversing the product 14 flowing in the free space 12, 32 or 52 of the sensor 1, 3, 5 or in one of the pipe portions 51, 52, the wave train traversing the product 14 in a transverse direction T perpendicular to the main axis of the portions 51 or 52 or said free space.
Selon un mode de réalisation, ces moyens 70 comprennent un émetteur d'ultrasons 71 et un récepteur d'ultrasons disposé en regard l'un de l'autre, à la périphérie de l'espace libre ou d'une portion de conduite 51, 52 située en amont ou en aval de cet espace. Sur la figure, l'émetteur 71 et le récepteur 72 sont disposés sur la portion amont 51. Les moyens 70 comprennent également une unité de calcul 77 reliée au récepteur 72 et à un émetteur 71 via un organe 79 d'émission et de réception de signal. L'organe 79 émet des ordres d'émission d'une onde sonore à l'émetteur 71 et calcule le temps de retard entre l'émission et la réception de l'onde sonore. Connaissant la distance séparant l'émetteur 71 et le récepteur 72, l'organe 79 peut déterminer la célérité CL de l'onde sonore traversant le produit 14 suivant la direction T. Cette célérité CL est communiquée à l'unité de calcul 77. Selon un autre mode de réalisation qui utilise le premier exemple de capteur 1 précité, les moyens 70 pour déterminer la célérité CL comprennent deux éléments piézoélectriques 10 du capteur 1 situés en regard l'un de l'autre. En référence à la figure 1, il peut s'agir des éléments 10a et 10b. L'un des éléments 10a, dédié à l'émission, est soumis à une tension variable de fréquence élevée, de manière à émettre une onde ultrasonore, et l'autre élément 10b est dédié à la réception de cette onde. Les éléments 10a et 10b, remplissant des fonctions analogues à celles de l'émetteur 71 et du récepteur 72, sont reliés à une unité de calcul et à un organe d'émission et de réception de signal remplissant des fonctions analogues à celles des organes 77 et 79 précédemment décrits.According to one embodiment, these means 70 comprise an ultrasonic transmitter 71 and an ultrasound receiver disposed facing each other, at the periphery of the free space or of a pipe portion 51, 52 located upstream or downstream of this space. In the figure, the transmitter 71 and the receiver 72 are arranged on the upstream portion 51. The means 70 also comprise a computing unit 77 connected to the receiver 72 and to a transmitter 71 via a transmission and reception device 79. signal. The unit 79 sends commands for transmitting a sound wave to the transmitter 71 and calculates the delay time between the emission and the reception of the sound wave. Knowing the distance separating the transmitter 71 and the receiver 72, the member 79 can determine the celerity CL of the sound wave passing through the product 14 in the direction T. This celerity CL is communicated to the calculation unit 77. Another embodiment that uses the first example of the aforementioned sensor 1, the means 70 for determining the speed CL include two piezoelectric elements 10 of the sensor 1 located opposite one another. With reference to FIG. 1, these may be elements 10a and 10b. One of the elements 10a, dedicated to the emission, is subjected to a variable voltage of high frequency, so as to emit an ultrasonic wave, and the other element 10b is dedicated to the reception of this wave. The elements 10a and 10b, fulfilling functions similar to those of the transmitter 71 and the receiver 72, are connected to a computing unit and to a signal transmitting and receiving element fulfilling functions similar to those of the elements 77. and 79 previously described.
Comme expliqué dans la demande de brevet français publiée FR 2763687, de la ligne 10 page 5 à la ligne 15 page 6, ainsi que dans la publication scientifique "Y. Mével, M. Mastail, R. Baron. Measurement of acoustic impédance to estimate the fish sol density, SENSORAL 98, Montpellier Narbonne, 23 27 février 98", lorsque le (ou les) transducteur du dispositif de l'invention est "à vide" (c'est à dire lorsqu'il n'est pas soumis à la charge mécanique caractéristique du produit 14) il est considéré comme équivalent électriquement à un circuit RLC série en parallèle avec un élément capacitif Co tel que représenté sur la figure 8a. L'impédance électrique Ze du transducteur est alors donnée par la formule A de la figure 8c. Une fois "en charge" (c'est à dire lorsqu'il est soumis à la charge mécanique caractéristique du produit 14) le transducteur est considéré comme équivalent au circuit représenté sur la figure 8b et l'impédance électrique Ze du transducteur est donnée par la formule B de la figure 8c. Cette impédance dépend de Z qui caractérise le produit 14. La mesure de l'impédance électrique Ze permet de calculer l'impédance acoustique Za du produit 14 qui recouvre le transducteur. Or, l'impédance Za du produit est telle que Za = p x CL x S, ou S est la surface de la première face 80 du transducteur (c'est-à-dire la surface exposée de l'élément piézoélectrique). La connaissance de Za, CL et S permet donc de connaître la masse volumique p du produit 14.As explained in the published French patent application FR 2763687, from line 10 page 5 to line 15 page 6, as well as in the scientific publication "Y. Mével, M. Mastail, R. Baron." Measurement of acoustic impedance to estimate the fish sol density, SENSORAL 98, Narbonne Montpellier, 23 February 27, 98 ", when the (or) transducer of the device of the invention is "empty" (that is to say when it is not subjected to the mechanical load characteristic of the product 14) it is considered as electrically equivalent to a series RLC circuit in parallel with an element capacitive Co as shown in Figure 8a. The electrical impedance Ze of the transducer is then given by the formula A of FIG. 8c. Once "in charge" (that is to say when subjected to the characteristic mechanical load of the product 14) the transducer is considered equivalent to the circuit shown in FIG. 8b and the electrical impedance Ze of the transducer is given by formula B of Figure 8c. This impedance depends on Z which characterizes the product 14. The measurement of the electrical impedance Ze makes it possible to calculate the acoustic impedance Za of the product 14 which covers the transducer. However, the impedance Za of the product is such that Za = px CL x S, where S is the surface of the first face 80 of the transducer (that is to say the exposed surface of the piezoelectric element). The knowledge of Za, CL and S thus makes it possible to know the density p of the product 14.
Dans le cas où l'appareil de mesure 50 est monté en aval d'une extrudeuse 62, durant la fabrication d'un mélange, on peut en fonction de la valeur de la masse volumique p mesurée, immédiatement agir sur la vitesse de rotation de la vis 64, de manière à maintenir constante la masse volumique p du mélange sortant de l'extrudeuse 62. Pour ce faire, l'unité de calcul 77 est relié à un dispositif de commande 66 permettant de régler la vitesse du moteur 65 entraînant la vis 64.In the case where the measuring device 50 is mounted downstream of an extruder 62, during the manufacture of a mixture, depending on the value of the measured density p, it is possible to immediately act on the rotational speed of the screw 64, so as to maintain constant the density p of the mixture leaving the extruder 62. To do this, the calculation unit 77 is connected to a control device 66 for adjusting the speed of the motor 65 causing the screw 64.
La figure 9 représente un autre exemple de capteur 9 selon l'invention du type comprenant un bâti 93 définissant en son intérieur ledit espace libre 92 et dans lequel est ménagée au moins une ouverture latérale 91 recouverte par une plaque sensible 90 en matériau piézoélectrique.FIG. 9 represents another example of a sensor 9 according to the invention of the type comprising a frame 93 defining inside said free space 92 and in which is provided at least one lateral opening 91 covered by a sensitive plate 90 of piezoelectric material.
Plus particulièrement, le capteur 9 comprend un bâti 93 définissant en son intérieur un espace libre 92 à l'intérieur duquel le produit 14 à caractériser est susceptible de circuler. Sur la figure 9, les flèches F représentent le flux de ce produit 14.More particularly, the sensor 9 comprises a frame 93 defining in its interior a free space 92 within which the product 14 to be characterized is likely to circulate. In FIG. 9, the arrows F represent the flow of this product 14.
Une ouverture latérale 91 est ménagée dans le bâti 93. Dans la présente demande, on désigne par ouverture latérale une ouverture autre que les ouvertures d'entrée 92a et de sortie 92b de l'espace libre 92. Dans l'exemple représenté, l'espace libre 92 est tubulaire d'axe A. Les ouvertures d'entrée et de sortie 92a, 92b sont alignées par rapport à l'axe A et perpendiculaires à celui-ci. L'ouverture latérale 91 est, quant à elle, parallèle à l'axe A. L'ouverture latérale 91 est recouverte par une structure empilée comportant : une plaque sensible 90 en matériau piézoélectrique ayant une première face 80, tournée vers ledit espace libre 92, et une deuxième face 82, opposée ; une plaque support 94 située du côté de la deuxième face 82 ; et des moyens de fixation 95 pour fixer la plaque support par rapport au bâti 93.A lateral opening 91 is formed in the frame 93. In the present application, the term "lateral opening" designates an opening other than the inlet 92a and outlet 92b 92 of the free space 92. the example shown, the free space 92 is tubular axis A. The inlet and outlet openings 92a, 92b are aligned with respect to the axis A and perpendicular to it. The lateral opening 91 is, in turn, parallel to the axis A. The lateral opening 91 is covered by a stacked structure comprising: a sensitive plate 90 of piezoelectric material having a first face 80, facing said free space 92 , and a second face 82, opposite; a support plate 94 located on the side of the second face 82; and fixing means 95 for fixing the support plate relative to the frame 93.
Lorsque la structure empilée est assemblée, la plaque sensible 90 est comprise entre les bords de l'ouverture latérale 91 et la plaque support 94. Les moyens de fixation 95 permettent de maintenir la structure assemblée et de fixer celle-ci sur le bâti 93. Ces moyens de fixation 95 doivent également autoriser la vibration de la plaque sensible 90. Dans l'exemple, ces moyens de fixation sont des vis de serrage 95 disposées à la périphérie de la plaque support 94, qui coopèrent avec des logements filetés formés sur le bâti 93, autour de l'ouverture latérale 91. Ces vis de serrage 95 doivent être suffisamment desserrées pour autoriser la vibration de la plaque 90. Avantageusement, ces vis 95 permettent également de mettre légèrement en charge la plaque sensible 90, cette charge étant radiale, c'est-à-dire orientée suivant l'épaisseur de la plaque 90. Pour contrôler l'intensité de cette mise en charge, qui doit rester faible, on sert plus ou moins les vis de serrage 95 en contrôlant le serrage, par exemple, à l'aide d'une clé dynamométrique.When the stacked structure is assembled, the sensitive plate 90 is between the edges of the lateral opening 91 and the support plate 94. The fixing means 95 make it possible to maintain the assembled structure and fix it on the frame 93. These fixing means 95 must also allow the vibration of the sensitive plate 90. In the example, these fixing means are clamping screws 95 disposed at the periphery of the support plate 94, which cooperate with threaded housings formed on the frame 93, around the lateral opening 91. These clamping screws 95 must be sufficiently loosened to allow the plate 90 to be vibrated. Advantageously, these screws 95 also make it possible to lightly load the sensitive plate 90, this load being radial. , that is to say, oriented according to the thickness of the plate 90. To control the intensity of this load, which must remain low, it serves more or less the screws of serra age 95 by checking the tightening, for example, using a torque wrench.
Avantageusement, la plaque sensible 90 est en polymère piézoélectrique, notamment en polyfluorure de vinylidène, noté PVDF ou PVF2, ou bien en copolymère de polyfluorure de vinylidène et de trifluoroethylène, noté P(VF2-VF3) ou P(VDF-TrFE). La plaque 90 en polymère piézoélectrique forme un transducteur électromécanique apte à générer une différence de potentiel suite à une déformation dans le sens de son épaisseur. Les matériaux polymères piézoélectriques, comme le PVDF et ses copolymères ont des propriétés piézoélectriques moins importantes que les céramiques mais présentent plusieurs avantages : ils peuvent être réalisés en film de grande surface et/ou de faible épaisseur, ils présentent une certaine souplesse de mise en forme et ils peuvent être moulés ou thermoformés. En outre, ces polymères étant de nature plus robuste que les céramiques, il est possible d'employer sereinement des tensions plus élevées et ainsi, on n'obtient pas uniquement les propriétés représentatives de la couche de produits 14 à proximité du capteur 9, mais une image des propriétés plus en profondeur de la veine du produit.Advantageously, the sensitive plate 90 is made of piezoelectric polymer, in particular polyvinylidene fluoride, denoted PVDF or PVF 2 , or else a copolymer of polyvinylidene fluoride and trifluoroethylene, denoted by P (VF 2 -VF 3 ) or P (VDF-TrFE ). The piezoelectric polymer plate 90 forms an electromechanical transducer able to generate a potential difference following a deformation in the direction of its thickness. Piezoelectric polymer materials, such as PVDF and its copolymers have less piezoelectric properties than ceramics but have several advantages: they can be made of large-area film and / or thin, they have some flexibility in shaping and they can be molded or thermoformed. Furthermore, since these polymers are more robust in nature than ceramics, it is possible to use higher voltages serenely and thus not only the representative properties of the product layer 14 are obtained in the vicinity of the sensor 9, but an image of the properties more in depth of the vein of the product.
Afin de polariser la plaque sensible 90, ses premières et deuxièmes faces 80 et 82 sont recouvertes d'un revêtement de surface conducteur. Elles sont par exemple métallisées avec un métal comme le cuivre, le nickel, l'argent, l'or ou un alliage nickel-aluminium. Un tel revêtement peut, par exemple, être obtenu par métallisation sous vide. En fonction de la qualité de la métallisation, on obtient une polarisation plus ou moins bonne. Un revêtement en argent permet d'obtenir, généralement, une bonne polarisation. La structure empilée comprend, en outre, des premier et deuxième moyens de connexion électrique pour relier (directement ou indirectement) lesdites première et deuxième faces, 80 et 82, de la plaque sensible 90 au générateur électrique 54. Avantageusement, les premiers moyens de connexion comprennent une plaque conductrice 96 couvrant la deuxième face 82 de la plaque 90. Cette plaque 96 peut, par exemple, être réalisée en cuivre et, avantageusement, couvrir entièrement la deuxième face 82. La plaque conductrice 96 permet de favoriser l'homogénéité et la qualité des mesures d'impédance effectuées en s'affranchissant des variations locales de résistance sur la deuxième face 82. la plaque 96 est reliée électriquement à une borne du générateur 54. La première face 80 est, quant à elle, mise en contact électrique avec le bâti 93 à l'aide de bandes conductrices 97, par exemple en cuivre, placée entre le bâti 93 et la plaque 90 au niveau des bords de l'ouverture 91. Le bâti 93, la plaque 90, la plaque support 94 et les vis de serrage 95 sont en contact électrique et tous reliés à l'autre borne du générateur 54.In order to polarize the sensitive plate 90, its first and second faces 80 and 82 are covered with a conductive surface coating. They are for example metallized with a metal such as copper, nickel, silver, gold or a nickel-aluminum alloy. Such a coating can, for example, be obtained by vacuum metallization. Depending on the quality of the metallization, a more or less good polarization is obtained. A silver coating provides, generally, a good polarization. The stacked structure further comprises first and second electrical connection means for connecting (directly or indirectly) said first and second faces, 80 and 82, of the sensitive plate 90 to the electric generator 54. Advantageously, the first connection means comprise a conductive plate 96 covering the second face 82 of the plate 90. This plate 96 may, for example, be made of copper and, advantageously, completely cover the second face 82. The conductive plate 96 makes it possible to promote the homogeneity and the quality impedance measurements made by overcoming local resistance variations on the second face 82. the plate 96 is electrically connected to a terminal of the generator 54. The first face 80 is, in turn, in electrical contact with the frame 93 using conductive strips 97, for example copper, placed between the frame 93 and the plate 90 at the edges of the open 91. The frame 93, the plate 90, the support plate 94 and the clamping screws 95 are in electrical contact and all connected to the other terminal of the generator 54.
Avantageusement encore, ladite structure empilée comprend au moins une plaque de PTFE 98 couvrant la première face 80 de la plaque sensible 90 et faisant office de revêtement antiadhésif, afin de limiter l'encrassement de cette face 80. Une plaque isolante 99 est disposée entre la plaque support et la plaque conductrice 96 afin d'isoler la plaque support 94 de la plaque conductrice 96. Cette plaque isolante 99 peut, par exemple, être en PTFE.Advantageously, said stacked structure comprises at least one PTFE plate 98 covering the first face 80 of the sensitive plate 90 and acting as a non-stick coating, in order to limit the fouling of this face 80. An insulating plate 99 is disposed between the support plate and the conductive plate 96 in order to isolate the support plate 94 from the conductive plate 96. This insulating plate 99 may, for example, be made of PTFE.
La structure du capteur de la figure 9 est, dans son ensemble, assez simple et permet d'effectuer des mesures fiables.The structure of the sensor of Figure 9 is, as a whole, quite simple and allows for reliable measurements.
En pratique, on installe le bâti 93 entre deux portions de conduite amont 51 et aval 52, le produit à caractériser circulant à l'intérieur de l'espace libre 92 définit par l'intérieur du bâti.In practice, the frame 93 is installed between two upstream pipe 51 and downstream pipe portions 52, the product to be characterized circulating inside the free space 92 defined by the interior of the frame.
Bien entendu, il est préférable de perturber le moins possible l'écoulement du produit 14 et d'éviter de créer des espaces où ce produit pourrait s'agglomérer, notamment par soucis d'hygiène. Les figures 10 à 12 représentent plusieurs exemples de dispositifs tenant compte de ces considérations.Of course, it is preferable to disturb the flow of the product as little as possible and to avoid creating spaces where this product could agglomerate, especially for reasons of hygiene. Figures 10 to 12 show several examples of devices that take these considerations into account.
L'exemple de la figure 10 comprend un bâti 93 ayant la forme générale d'un cylindre creux de section circulaire. Les différentes plaques 90, 94 du capteur 9 sont incurvées de manière à venir épouser la courbure extérieure du bâti 93 lorsqu'elle recouvre l'ouverture latérale 91 ménagée dans celui-ci. On notera qu'il est facile de donner une forme incurvée à la plaque sensible 90 du capteur lorsque celle-ci est réalisée en matériau polymère.The example of Figure 10 comprises a frame 93 having the general shape of a hollow cylinder of circular section. The different plates 90, 94 of the sensor 9 are curved so as to fit the outer curvature of the frame 93 when it covers the lateral opening 91 formed therein. Note that it is easy to give a curved shape to the sensitive plate 90 of the sensor when it is made of polymer material.
Dans l'exemple de la figure 11, on a conservé une forme générale plane pour les différentes plaques 90, 94 du capteur. Le bâti 93 a la forme générale d'un cylindre, de section circulaire, et présente sur sa paroi un méplat 100. La jonction entre les bords amont et aval de ce méplat et la paroi du bâti 93 est réalisée par des chanfreins 102. L'ouverture latérale 91 du bâti 93 est pratiquée dans le méplat 100 et les plaques 90, 94 du capteur sont empilées sur ce méplat 100.In the example of FIG. 11, a generally flat shape has been retained for the various plates 90, 94 of the sensor. The frame 93 has the general shape of a cylinder, of circular section, and has on its wall a flat part 100. The junction between the upstream and downstream edges of this flat and the wall of the frame 93 is made by chamfers 102. 91 lateral opening of the frame 93 is formed in the flat 100 and the plates 90, 94 of the sensor are stacked on this flat 100.
Enfin, dans l'exemple de la figure 12, le bâti 93 est formé par la réunion de deux cylindres creux 93a et 93b, de section circulaire, le premier cylindre 93a est traversé suivant son axe X par le produit 14 et le second cylindre 93b coupe le premier cylindre 93a, l'axe Y du second cylindre 106 étant perpendiculaire à l'axe X du premier. Certaines plaques du capteur, dont la plaque sensible 90, sont logées à l'intérieur du second cylindre 93b. La plaque support 94 peut être logée dans le cylindre 93b ou couvrir l'ouverture extérieure de celui-ci, comme représenté. On notera que dans tous les exemples de dispositifs des figures 10 à 12, le transducteur du capteur 9 (c'est-à-dire la plaque sensible 90) se situe à la périphérie de l'espace libre 92 traversant le capteur 9, conformément à l'invention. Finally, in the example of FIG. 12, the frame 93 is formed by the joining of two hollow cylinders 93a and 93b, of circular section, the first cylinder 93a is crossed along its axis X by the product 14 and the second cylinder 93b cut the first cylinder 93a, the Y axis of the second cylinder 106 being perpendicular to the axis X of the first. Some sensor plates, including the sensitive plate 90, are housed inside the second cylinder 93b. The support plate 94 may be housed in the cylinder 93b or cover the outer opening thereof as shown. It should be noted that in all the examples of devices of FIGS. 10 to 12, the transducer of the sensor 9 (that is to say the sensitive plate 90) is located at the periphery of the free space 92 passing through the sensor 9, in accordance with FIG. to the invention.

Claims

REVENDICATIONS
1. Dispositif de mesure comprenant : un capteur (1, 3, 5, 9) avec au moins un transducteur électromécanique (10, 30, 50, 90) ; au moins un générateur électrique (54) connecté audit transducteur ; et des moyens (55) pour mesurer l'impédance électrique en entrée du transducteur (10, 30, 50, 90), caractérisé en ce que ledit capteur (1, 3, 5, 9) est traversé par un espace libre (12, 32, 52, 92) à l'intérieur duquel un produit (14) est susceptible de circuler, et en ce que ledit transducteur (10, 30, 50, 90) est situé à la périphérie dudit espace libre (12, 32, 52, 92) de manière à être soumis à une charge mécanique caractéristique du produit (14) circulant dans ledit espace, l'impédance électrique mesurée étant fonction de ladite charge.A measuring device comprising: a sensor (1, 3, 5, 9) with at least one electromechanical transducer (10, 30, 50, 90); at least one electrical generator (54) connected to said transducer; and means (55) for measuring the electrical input impedance of the transducer (10, 30, 50, 90), characterized in that said sensor (1, 3, 5, 9) is traversed by a free space (12, 32, 52, 92) within which a product (14) is circulating, and in that said transducer (10, 30, 50, 90) is located at the periphery of said free space (12, 32, 52 , 92) so as to be subjected to a characteristic mechanical load of the product (14) flowing in said space, the measured electrical impedance being a function of said load.
2. Dispositif de mesure selon la revendication 1, caractérisé en ce que ledit espace libre (12, 32, 52, 92) est de forme générale tubulaire,2. Measuring device according to claim 1, characterized in that said free space (12, 32, 52, 92) is of tubular general shape,
3. Dispositif de mesure selon la revendication 1 ou 2, caractérisé en ce que ledit au moins un transducteur (10, 30, 50, 90) comprend un élément sensible réalisé en matériau piézoélectrique.3. Measuring device according to claim 1 or 2, characterized in that said at least one transducer (10, 30, 50, 90) comprises a sensitive element made of piezoelectric material.
4. Dispositif de mesure selon l'une quelconque des revendications 1 à 3, caractérisé en ce que ledit capteur (1, 3, 9) comprend une pluralité de transducteurs (10, 30, 90) répartis autour dudit espace libre (12, 32, 92).4. Measuring device according to any one of claims 1 to 3, characterized in that said sensor (1, 3, 9) comprises a plurality of transducers (10, 30, 90) distributed around said free space (12, 32 , 92).
5. Dispositif de mesure selon la revendication 4, caractérisé en ce que ledit capteur (1) comprend une pluralité de transducteurs (10) réunis bord à bord, qui définissent entre eux ledit espace tubulaire (12), un joint d'étanchéité (16) étant avantageusement disposé entre deux transducteurs (10) adjacents.5. Measuring device according to claim 4, characterized in that said sensor (1) comprises a plurality of transducers (10) joined edge to edge, which define between them said tubular space (12), a seal (16). ) being advantageously disposed between two adjacent transducers (10).
6. Dispositif de mesure selon la revendication 4 ou 5, caractérisé en ce que lesdits transducteurs (10) sont maintenus en position par au moins un manchon (18). 6. Measuring device according to claim 4 or 5, characterized in that said transducers (10) are held in position by at least one sleeve (18).
7. Dispositif de mesure selon l'une quelconque des revendications 1 à 3, caractérisé en ce que ledit capteur (5) comprend un unique transducteur (50) enroulé sur lui-même, de manière à définir ledit espace libre (52).7. Measuring device according to claim 1, wherein said sensor comprises a single transducer wound on itself, so as to define said free space.
8. Dispositif de mesure selon l'une quelconque des revendications 1 à 4, caractérisé en ce que ledit capteur (3) comprend une pluralité de transducteurs (30) noyés dans une matrice (31) moulée autour d'eux, ladite matrice définissant ledit espace libre (32).8. Measuring device according to any one of claims 1 to 4, characterized in that said sensor (3) comprises a plurality of transducers (30) embedded in a matrix (31) molded around them, said matrix defining said free space (32).
9. Dispositif de mesure selon l'une quelconque des revendications 1 à 4 caractérisé en ce que ledit capteur (9) comprend : un bâti (93) définissant en son intérieur ledit espace libre (92) et dans lequel est ménagée au moins une ouverture latérale (91); et une plaque sensible (90) en matériau piézoélectrique recouvrant ladite ouverture latérale (91).9. Measuring device according to any one of claims 1 to 4 characterized in that said sensor (9) comprises: a frame (93) defining in its interior said free space (92) and in which is formed at least one opening lateral (91); and a sensitive plate (90) of piezoelectric material covering said lateral opening (91).
10. Dispositif de mesure selon la revendication 9 caractérisé en ce que ladite ouverture latérale (91) est recouverte par une structure empilée comportant : ladite plaque sensible (90) en matériau piézoélectrique ayant une première face (80), tournée vers ledit espace libre, et une deuxième face (82), opposée à la première ; une plaque support (94) située du côté de cette deuxième face (82) ; et des moyens pour fixer la plaque support (94) par rapport au bâti (93).10. Measuring device according to claim 9 characterized in that said lateral opening (91) is covered by a stacked structure comprising: said sensitive plate (90) of piezoelectric material having a first face (80) facing said free space, and a second face (82), opposite to the first; a support plate (94) located on the side of this second face (82); and means for securing the support plate (94) relative to the frame (93).
11. Dispositif de mesure selon la revendication 9 ou 10, caractérisé en ce que ladite plaque sensible (90) a une première face (80), tournée vers ledit espace libre, et une deuxième face (82), opposée à la première, en ce que cette plaque sensible est en PVDF, ou en copolymère P(VDF- TrFE), et en ce que ses première et deuxième faces (80, 82) sont recouvertes d'un revêtement de surface conducteur.11. Measuring device according to claim 9 or 10, characterized in that said sensitive plate (90) has a first face (80), facing said free space, and a second face (82), opposite to the first, this sensitive plate is made of PVDF, or copolymer P (VDF-TrFE), and in that its first and second faces (80, 82) are covered with a conductive surface coating.
12. Dispositif de mesure selon la revendication 10 ou 11, caractérisé en ce que ladite structure empilée comprend des premier et deuxième moyens de connexion électrique pour relier respectivement lesdites première et deuxième faces de la plaque sensible au générateur, les premiers moyens de connection comprenant une plaque conductrice (96) couvrant la deuxième face (82) de ladite plaque sensible (90).12. Measuring device according to claim 10 or 11, characterized in that said stacked structure comprises first and second electrical connection means for respectively connecting said first and second faces of the generator-responsive plate, the first connection means including a conductive plate (96) covering the second face (82) of said sensitive plate (90).
13. Dispositif de mesure selon l'une quelconque des revendicationsMeasuring device according to one of the claims
10 à 12, caractérisé en ce que ladite structure empilée comprend, en outre, au moins une plaque de PTFE (98), cette plaque couvrant la première face (80) de la plaque sensible.10 to 12, characterized in that said stacked structure further comprises at least one PTFE plate (98), this plate covering the first face (80) of the sensitive plate.
14. Appareil de mesure, caractérisé en ce qu'il comprend : un dispositif de mesure selon l'une quelconque des revendications précédentes ; des moyens (70) pour mesurer la célérité d'un train d'onde traversant le produit (14) circulant dans ledit espace libre ou dans une portion de conduite (51, 52) située en amont ou en aval de cet espace ; et une unité de calcul (77) permettant de déterminer la masse volumique de ce produit à partir de la célérité et de l'impédance mesurées.14. Measuring apparatus, characterized in that it comprises: a measuring device according to any one of the preceding claims; means (70) for measuring the speed of a wave train traversing the product (14) flowing in said free space or in a pipe portion (51, 52) located upstream or downstream of this space; and a computing unit (77) for determining the density of this product from the measured velocity and impedance.
15. Appareil de mesure selon la revendication 14, caractérisé en ce que lesdits moyens pour mesurer la célérité comprennent un émetteur (71) et un récepteur d'ultrasons (72) disposés en regard l'un de l'autre, à la périphérie dudit espace libre (12) ou de ladite portion de conduite (51, 52).Measuring apparatus according to claim 14, characterized in that said means for measuring the celerity comprise an emitter (71) and an ultrasound receiver (72) disposed opposite one another, at the periphery of said free space (12) or said pipe portion (51, 52).
16. Appareil de mesure selon la revendication 14 ou 15, caractérisé en ce que lesdits moyens pour mesurer la célérité comprennent deux transducteurs (10a, 10b) du dispositif de mesure, disposés en regard l'un de l'autre. 16. Measuring apparatus according to claim 14 or 15, characterized in that said means for measuring the celerity comprise two transducers (10a, 10b) of the measuring device, arranged facing one another.
EP05825869A 2004-12-21 2005-12-20 Device for measuring the mechanical load exerted by a fluid using an electromechanical transducer Withdrawn EP1844325A2 (en)

Applications Claiming Priority (2)

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FR0413632A FR2879745B1 (en) 2004-12-21 2004-12-21 MEASURING DEVICE
PCT/FR2005/051113 WO2006067357A2 (en) 2004-12-21 2005-12-20 Device for measuring the mechanical load exerted by a fluid using an electromechanical transducer

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EP1844325A2 true EP1844325A2 (en) 2007-10-17

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CH711008A1 (en) * 2015-04-30 2016-10-31 Kistler Holding Ag Contact force testing apparatus, use of such a contact force testing apparatus, and a method of manufacturing such a contact force testing apparatus.

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US4210028A (en) * 1978-05-30 1980-07-01 Electric Power Research Institute, Inc. Method and apparatus for ultrasonically measuring concentrations of stress
DE2827423A1 (en) * 1978-06-22 1980-01-10 Philips Patentverwaltung METHOD AND DEVICE FOR DETERMINING THE INNER STRUCTURE OF A BODY BY MEANS OF SOUND BEAMS
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FR2879745A1 (en) 2006-06-23
US20080190215A1 (en) 2008-08-14
US7698953B2 (en) 2010-04-20
FR2879745B1 (en) 2007-04-27
WO2006067357A3 (en) 2006-08-31

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