ULTRASONIC DEVICE AND ULTRASONIC-ASSISTED SIEVE INTENDED FOR OPERATION IN AN ATMOSPHERE CONTAINING EXPLOSIVE DUST

Abstract

ULTRASONIC DEVICE AND ULTRASONIC-ASSISTED SIEVE FOR OPERATION IN AN ATMOSPHERE COMPRISING EXPLOSIVE DUST The invention relates to an ultrasonic device (1000) comprising: an ultrasonic transmitter (1200), configured to convert an electric current into an ultrasonic vibration; an electrical circuit (1300), configured to supply the electric current to the ultrasonic transmitter; a sealed casing (1400), delimiting an interior volume (1420) isolated from the outside, a part of the ultrasonic transmitter and a part (1320) of the electrical circuit being positioned in the interior volume, the sealed casing comprising an exterior surface configured to be in contact with an explosive atmosphere;the ultrasonic device being characterized in that it comprises a protection means (1310, 1500) configured to open the electrical circuit when a parameter representative of a failure in the operation of said ultrasonic device is greater than a threshold. Figure to be published with the abstract: Figure 2;

Description

Title of the invention: ULTRASONIC DEVICE AND ULTRASONIC-ASSISTED SIEVE INTENDED TO BE OPERATED IN AN ATMOSPHERE COMPRISING EXTREME DUST PLOSIVES TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of ultrasonic devices and more particularly ultrasonic transmitters intended to be operated in an atmosphere comprising explosive dust. The technical field also relates to ultrasonic-assisted sieves intended to be operated in an explosive atmosphere. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] The sieving of fine powders benefits particularly from the use of ultrasonic vibrations. Indeed, ultrasonic vibrations applied to a sieve tend to reduce the clogging of powder particles with each other or with the filter cloth of the sieve and thus improve the filtering of the powders and the processing flow rate.

[0003] However, sieving dry powders can load the atmosphere with a density of fine particles. Some types of fine particles, such as metal particles, pollens or agri-food particles, can have a low ignition temperature. When the density of these flammable particles exceeds a minimum explosion concentration, the use of ultrasonic devices, dissipating a large amount of heat, becomes extremely risky. The temperature on the surface of an ultrasonic transmitter can reach, during normal operation, around a hundred degrees.

[0004] To address these industrial risks, the European Union has adopted two directives relating to explosive atmospheres, known as ATEX directives. These directives define or suggest explosion protection measures depending on the level of explosion risk. For example, a device implemented in an area where an explosive atmosphere is frequently present, known as ATEX zone 20, requires protection such as encapsulation or enclosure protection. In the first case, the elements that could ignite the explosive atmosphere by sparks or by heating are enclosed in a resin in such a way that this explosive atmosphere cannot penetrate and therefore ignite. In the second case, protection is ensured by sealing the elements at risk from dust as well as by measures aimed at limiting the maximum surface temperatures during normal operation.

[0005] However, the protections described above show their limits when a normal operation is no longer ensured. There is therefore a need to provide an ultrasonic device that meets the requirements of the ATEX directives, particularly in the event of failure of the said ultrasonic device. Summary of the invention

[0006] The invention provides a solution to the problems mentioned above, by proposing an ultrasonic device protected by an enclosure and comprising an additional protection means intended to stop the device automatically when a fault is detected.

[0007] For this, the invention relates to an ultrasonic device comprising: • an ultrasonic transmitter, configured to convert an electric current into an ultrasonic vibration; • an electrical circuit, configured to supply the electrical current to the ultrasonic transmitter; • a sealed enclosure, delimiting an interior volume isolated from the exterior, a part of the ultrasonic transmitter and a part of the electrical circuit being positioned in the interior volume, the sealed enclosure comprising an exterior surface configured to be in contact with an explosive atmosphere; the ultrasonic device being remarkable in that it comprises a protection means configured to open the electrical circuit when a parameter representative of a failure in the operation of said ultrasonic device is greater than a threshold.

[0008] The term "watertight enclosure" means an enclosure that is completely protected against dust, for example, with an IP 6X protection rating.

[0009] By the term "open the electrical circuit" is meant interrupting the flow of electric current in the electrical circuit.

[0010] By the term "exterior surface" is meant a surface opposite an interior surface, the interior surface being opposite the interior volume.

[0011] The ultrasonic transmitter makes it possible to generate an ultrasonic vibration which can be implemented by a receiving system such as an ultrasonic-assisted sieve.

[0012] Thanks to its sealed casing, the ultrasonic device offers a first level of protection against explosive atmospheres, the latter preventing dust from the explosive atmosphere from coming into contact with hot elements such as the ultrasonic transmitter.

[0013] The sealed enclosure also prevents the explosive atmosphere from coming into contact with part of the electrical circuit. The intensity of the electric current which can flow in the electrical circuit during normal operation can reach 1 A to 2 A. Dissipation by Joule effect within an ohmic element in the circuit electrical circuit can cause a hot spot that can reach several hundred degrees. Thus, the enclosure prevents a hot spot in the portion of the electrical circuit from initiating an explosion of the explosive atmosphere.

[0014] The protection means provides an additional level of protection, in particular allowing the circuit to be cut off when the ultrasonic device deviates from the expected normal operation. Thus, there is no risk of the device running away or one of its components overheating.

[0015] In addition to the characteristics which have just been mentioned in the preceding paragraph, the ultrasonic device according to the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • the ultrasonic transmitter is configured to convert an electric current into an ultrasonic vibration having a frequency between 20 kHz and 100 kHz, preferably between 20 kHz and 40 kHz; • the protection means comprises a cut-off system configured to open the electrical circuit when an effective intensity of the electric current is greater than a threshold intensity for a duration called "overcurrent duration"; • the threshold intensity corresponds to a maximum average power transported by the electric current; • the electrical circuit is configured to supply the electrical current to the ultrasonic transmitter intermittently, alternating a period of generation of the electrical current at a nominal intensity and a pause period; • the cut-off system has a threshold intensity and an overcurrent duration depending on an intrinsic parameter of the cut-off system called "calibre"; • the caliber is chosen lower than the nominal intensity and the overcurrent duration is greater than or equal to the period of generation of the electric current; • the cut-off system has a cut-off capacity greater than the threshold intensity, preferably greater than 20 times the threshold intensity and preferably greater than 1000 times the threshold intensity; • the protection means comprises a plurality of cut-off systems, each cut-off system being configured to open the electrical circuit when the effective intensity of the electric current is greater than a threshold intensity for an overcurrent duration; • the protection means comprises a means for measuring a temperature of a portion to be controlled, the measuring means being configured to open the electrical circuit when the temperature of the portion to be controlled is above below a threshold temperature, the threshold temperature preferably being below a flammability temperature of the explosive atmosphere; • the ultrasonic device is configured to transmit an ultrasonic vibration to a receiving system and the portion to be controlled is a portion of the receiving system; • the portion to be checked is a portion of the waterproof envelope; • the temperature measuring means comprises a thermocouple or a pyrometer or thermal camera or radiometer; • the temperature measuring means is in thermal contact with the portion to be controlled; • the temperature measuring means is without contact with the portion to be controlled; • the temperature measuring means comprises a thermocouple preferably in thermal contact with the portion to be controlled; • the temperature measuring means comprises a pyrometer or a thermal camera or a radiometer; • the temperature measuring means comprises a gas screen arranged between the explosive atmosphere and a sensitive part of said measuring means; • the ultrasonic transmitter comprises an active part and a horn, the horn being fixed on the active part, and in that the sealed casing comprises: a sealed chamber delimiting a first portion of the interior volume, fixed on a vibration node of the ultrasonic transmitter so as to isolate the first portion of the interior volume from the exterior and position the active part of the ultrasonic transmitter in the interior volume; a sealed sheath delimiting a second portion of the interior volume enveloping the part of the electrical circuit; • the ultrasonic device comprises a coupling means fixed on the horn and configured to be coupled by screwing to a receiving system, the screwing being carried out along a first axis, the sealed chamber comprising: a body, on which the horn is fixed; and a cover, on which one end of the sealed sheath is fixed; the cover being fixed on the body by means of a sealed connection allowing rotation of the cover along a second axis, the second axis being preferably substantially aligned with the first axis; • the waterproof sheath comprises a smooth outer surface, the outer surface preferably having an effective roughness of less than 0.8.

[0016] The term "a nominal average power carried by the electric current" means an average power delivered by an electrical energy source and consumed by the ultrasonic transmitter during normal operation of the device. ultrasound.

[0017] By the term "a second axis substantially aligned with a first axis" is meant that the first and second axes are aligned at plus or minus 20°.

[0018] The term "vibration node" means a position where the amplitude of the vibration is minimal, or even zero. Conversely, the term "vibration antinode" means a position where the amplitude of the vibration is non-zero and more particularly significant, or even maximum in certain cases.

[0019] The term "radiometer" means a device configured to measure the intensity of electromagnetic radiation whose wavelength is in the infrared range. It may, for example, be a bolometer.

[0020] The invention also relates to a method of using an ultrasonic device according to the invention in which the electric current is generated intermittently.

[0021] During periods when the electric current is not generated, called pause periods, the heat dissipated by the electrical circuit and the ultrasonic transmitter is zero, making it possible to limit the increase in temperature of the ultrasonic device.

[0022] The invention also relates to an ultrasonic-assisted sieve comprising a frame and a resonator, the resonator being coupled to the frame so as to be able to transmit an ultrasonic vibration to the frame, the sieve being characterized in that it comprises an ultrasonic device according to one of the preceding claims coupled to the resonator so as to transmit an ultrasonic vibration to the frame.

[0023] According to one embodiment, the portion to be monitored comprises a surface of the chassis in the vicinity of the resonator. By the term in the vicinity of the resonator, we mean a surface extending less than a distance from the resonator, a distance over which a thermal gradient can be established. The resonator and the chassis in contact with the resonator can have large temperature variations, so monitoring their temperatures can make it possible to open the electrical circuit of the ultrasonic device and stop the generation of ultrasonic vibration. In this way, the increase in temperature of the sieve is slowed. BRIEF DESCRIPTION OF THE FIGURES

[0024] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures.

[0025] The figures are presented for information purposes only and in no way limit the invention.

[0026] [Fig-1] schematically represents a first embodiment of the ultrasonic device according to the invention.

[0027] [Fig.2] schematically represents a second embodiment of the ultrasonic device according to the invention.

[0028] [Fig.3] schematically represents a partial section along a plane AA a third embodiment of the ultrasonic device according to the invention.

[0029] [Fig.4] schematically represents a partial section along a plane BB of the third embodiment of the ultrasonic device according to the invention.

[0030] [Fig.5] schematically represents a section along a CC plane of a mode of rea use of an ultrasound-assisted sieve according to the invention

[0031] [Fig.6] schematically represents a partial section along a plane DD of the sieve ultrasound-assisted [Fig.5].

[0032] [Fig.7] schematically represents an abacus of an embodiment of a cutting system according to the invention.

[0033] Unless otherwise specified, the same element appearing in different figures has a single reference. The figures are presented for information purposes only and in no way limit the invention. DETAILED DESCRIPTION

[0034] An explosive atmosphere may comprise, intermittently or continuously, a cloud of combustible dust. The dust cloud is, for example, characterizable by its concentration of combustible dust, which may be greater than or equal to a minimum flammability concentration, and its flammability temperature. The implementation of processes or devices capable of producing combustible dust, such as ultrasound-assisted screening, is advantageously carried out in an area which will be called the confinement zone 210, illustrated in [Fig.l] and [Fig.2]. The confinement zone 210 is advantageously isolated from an external zone 220, illustrated in [Fig.l] and [Fig.2], which will also be called the neutral zone. In order to minimize the risk of an accident, the confinement zone 210 preferably only comprises non-remote means necessary for carrying out the processes or implementing the devices.The neutral zone 220 advantageously comprises means which can be moved away from the confinement zone 210. A means which can be moved into the neutral zone is for example an electrical cabinet 30.

[0035] Some devices located in the containment zone also include an enclosure 200, illustrated in [Fig.l] and [Fig.2], in which the processes that can generate dust are carried out. For example, an ultrasonic-assisted sieve may include an enclosure 200 in which the ultrasonic-assisted filtering is carried out.

[0036] European directives relating to explosive atmospheres, known as ATEX directives, classify the containment zone according to three levels, depending in particular on the frequency of occurrence of an explosive atmosphere. The invention is advantageously implemented in a zone classified 20 or 21 according to the ATEX directives, i.e. comprising an explosive atmosphere for long periods or frequently. The enclosure 200 of an ultrasonic-assisted sieve may be classified 20. The containment zone 210, in the immediate vicinity of the sieve, is likely to occasionally present an explosive atmosphere and may be classified 21. The neutral zone 220 is not likely to present an explosive atmosphere.

[0037] [Fig. 1] schematically represents a first embodiment of an ultrasonic device 1000 according to the invention. The ultrasonic device 1000 makes it possible, for example, to provide an ultrasonic vibration in order to assist the sieving of powders. According to this first embodiment, the ultrasonic device 1000 comprises an ultrasonic transmitter 1200 and an electrical circuit 1300.

[0038] The ultrasonic transmitter 1200 is intended to be coupled to a receiving system, such as an ultrasound-assisted sieve, the latter being preferably positioned in a confinement zone 210. In the example of [Fig.l], the sieve also comprises an enclosure 200 in which the ultrasonic transmitter is positioned. The electrical circuit 1300 is configured to supply an electric current to the ultrasonic transmitter 1200. For this, a first portion 1320 of the electrical circuit 1300 is intended to be preferably positioned in the enclosure 200. The ultrasonic transmitter 1200 is configured to convert the electric current into an ultrasonic vibration, said ultrasonic vibration being able to be transmitted to the ultrasonic-assisted sieve.

[0039] The electrical circuit 1300 may also comprise a second portion 1330 not intended to be operated in the confinement zone 210. The second portion 1330 of the electrical circuit 1300 is then preferably arranged outside the enclosure 200, i.e. in the confinement zone 210 and / or in the neutral zone 220. In this case, the first portion 1320 of the electrical circuit 1300 provides the link between the ultrasonic transmitter 1200 and the second portion 1330 of the electrical circuit 1300. The first portion 1320 of the electrical circuit 1300, as shown in [Fig.l], comprises an electrical conductor connected to the ultrasonic transmitter 1200. The second portion 1330 of the electrical circuit 1300, as shown, comprises an electrical conductor, a generator 1340, a cut-off system 1310 and an electrical power source 1350, such as an electrical cabinet.

[0040] The ultrasonic device 1000 comprises a first mode of protection against an explosive atmosphere, called the first ATEX protection mode, comprising a sealed enclosure 1400. The sealed enclosure 1400 is configured to seal the ultrasonic transmitter 1200 and the first portion 1320 of the electrical circuit 1300 so as to isolate them from the explosive atmosphere, in this case the atmosphere of the enclosure 200 in [Fig. 1] and [Fig. 2]. In this way, the dust from the explosive atmosphere cannot come into contact with a surface that can present a high temperature. The sealed envelope 1400 advantageously envelops all the elements of the ultrasonic device 1000 likely to present a high temperature and arranged in an area comprising the explosive atmosphere, that is to say at least the enclosure 200. The sealed envelope 1400 delimits an interior volume within which the ultrasonic transmitter 1200 and the first portion 1320 of the electrical circuit 1300 are arranged.

[0041] The ultrasonic device 1000 offers an additional level of protection in that it comprises a protection means configured to open the electrical circuit when a parameter representative of a failure in the operation of said ultrasonic device is greater than a threshold. In this way, the protection means makes it possible to cut off the flow of an electric current when the ultrasonic device deviates from the expected normal operation. Thus, there is no risk of the device running away or of one of its components overheating.

[0042] A cause of failure of an ultrasonic device according to the prior art may be poor coupling, unexpected decoupling of the receiver system or degradation of piezoelectric ceramics belonging to the ultrasonic transmitter. Overheating of the ultrasonic device according to the prior art may be observed, the overheating being able to be proportional to the intensity of the electric current and more particularly the effective intensity of the electric current, also called RMS intensity for "Root Mean Square" in English. According to this example, the parameter representative of an operating failure is an effective intensity of the electric current. In order to prevent this scenario, the means of protection of the ultrasonic device 1000 according to the invention may comprise a cut-off system 1310.The cut-off system 1310 is configured to open the electrical circuit 1300 when an effective intensity of the electrical current is greater than a threshold intensity for a duration called the "overcurrent duration". The term "opening the electrical circuit" means interrupting the flow of the electrical current in the electrical circuit. Thus, when the electrical circuit 1300 is open, the electrical current stops flowing in the electrical circuit 1300 and no more electrical power is transmitted to the transmitter 1200. The cut-off system 1310 can be arranged in any position allowing it to correctly open the electrical circuit 1300. For this, it can belong to the first portion 1320 or to the second portion 1330 of the electrical circuit 1300. However, it is preferable for the cut-off system 1310 to belong to the second portion 1330 of the electrical circuit 1300.It is also preferably positioned outside the containment zone so that it can be checked or changed easily.

[0043] When the second portion 1330 of the electrical circuit 1300 comprises a generator 1340 and an energy source 1350, the cut-off system 1310 is preferably inserted between the generator 1340 and the electrical energy source 1350. Thus, after opening of the electrical circuit 1300, the ultrasonic transmitter 1200 and the generator 1340 are no longer supplied with electrical energy. If the generator 1340 is the cause of a failure involving the opening of the electrical circuit, then the generator 1340 is made safe and no longer risks igniting the explosive atmosphere. The effective intensity of the current between the transmitter 1200 and the generator 1340 is also likely to vary more strongly as a function of time than between the generator 1340 and the electrical energy source 1350. These strong variations in effective intensity may for example result from a variation in load during the sieving of a powder and may be independent of a failure of the device 1000. The generator 1340 can dampen these strong variations so that they are not perceptible between the generator 1340 and the energy source 1350.On the other hand, if a strong variation in electrical intensity is observed between the generator 1340 and the electrical energy source 1350, it is likely to be caused by a failure of the ultrasonic device 1000 and an opening of the circuit 1300 is necessary. It is thus preferable to insert the cut-off system 1310 between the generator 1340 and the electrical energy source 1350.

[0044] The cut-off system 1310 may be a fuse, as illustrated in [Fig.l], configured to open the electrical circuit 1300 when the effective intensity of the electric current is greater than the threshold intensity during the overcurrent duration. A fuse is understood to mean an electrical conductor sized to melt when it has stored a given quantity of energy, corresponding to the effective intensity greater than the threshold intensity during the overcurrent duration. A fuse may have the advantage of opening the electrical circuit in a non-reversible manner, thus avoiding inadvertent resetting of the circuit 1300.

[0045] The cut-off system 1310 may be an electromechanical circuit breaker, as illustrated in [Fig. 2], configured to mechanically open the electrical circuit 1300 when the effective intensity of the electric current is greater than the threshold intensity during the overcurrent duration. The circuit breaker preferably comprises a means for measuring the effective intensity of the electric current of the electrical circuit 1300 and a means for opening the circuit 1300, the measuring means actuating the opening means when it has stored a given quantity of energy, also corresponding to the effective intensity exceeding the threshold intensity during the overcurrent duration.

[0046] An uncontrolled opening of the electrical circuit 1300 may present a risk of initiating an explosion of the explosive atmosphere. Indeed, a cut-off system, when it is traversed by a very high current, may present a risk of explosion or creation of electric arcs when the circuit 1300 is opened. The effective intensity that a cut-off system can withstand without degrading or without creating electric arcs is called breaking capacity. Thus, the cut-off system 1310 advantageously has a breaking capacity much higher than the threshold current, for example higher than 20 times the threshold current and preferably higher than 1000 times the threshold current. For example, for a threshold current of 1.25 A, the breaking capacity is higher than 25 A. A breaking system having a breaking capacity of 35 A can therefore be implemented. Preferably, the breaking capacity is higher than 1250 A. Thus, a breaking system having a breaking capacity of 1500 A can be implemented. The electrical circuit 1300 can be opened without the breaking system 1310 being able to cause a failure or initiate an explosion of the atmosphere.

[0047]

[0048] The overcurrent duration d can vary depending on the threshold current (Is) considered, as illustrated by [Fig.7]. Indeed, the higher the effective current circulating in the circuit, the lower the overcurrent duration d required to enable the cut-off system 1310 to open the circuit 1300. The overcurrent duration d and the threshold current Is can be linked by an intrinsic parameter of the cut-off system 1310 called rating Kl, K2. Rating Kl, K2 is expressed in Amperes and corresponds to the minimum effective current allowing the cut-off system 1310 to be triggered for a very long, theoretically infinite, overcurrent duration d. As an example, illustrated by curve K2 in [Fig.7], a 1310 cut-off system with a rating of 0.5 A can have an overcurrent duration d: • less than 30 min when the effective current circulating in the fuse is equal to approximately 2 times its rating; • less than 2 s when the effective intensity is equal to approximately 3 times its caliber; and • less than 100 ms when the effective intensity is equal to approximately 10 times its caliber.

[0049] Thus, if said cut-off system has a rating of 1.25 A, it can open the circuit in less than 2 seconds, when the effective current flowing in the circuit 1300 is greater than or equal to 3.75 A. In order to open the electrical circuit 1300 with a low opening time, much less than 1 s, it may be advantageous to implement a cut-off system having a rating K1, K2 greater than a nominal current of the electrical circuit 1300 while being as close as possible to this nominal current, so that the overcurrent duration d is as short as possible. By the term "nominal current", we mean an average current flowing in the electrical circuit during normal operation of the ultrasonic device. Thus, we will preferably choose a rating K1, K2 significantly greater than the nominal current.If, for example, the nominal current is equal to 0.45 A, a K2 rating equal to 0.5 A allows the circuit to be opened when the effective current is higher. at a threshold current Is of 1.5 A for an overcurrent duration of at least 2 seconds or greater than a threshold current of 5 A for an overcurrent duration of at least 100 ms

[0050] In order to regulate the temperature of the ultrasonic device, the generation of ultrasonic vibrations is preferably carried out in a pulsed manner, alternating for example a period of generation of a vibration and a pause period. For example, the generation period may occupy 50% of the total working time of the device. For example, the generation and pause periods may each be equal to 0.8 s. The pause period allows the ultrasonic device to limit heating. Thus, the temperature of the ultrasonic device may have a small variation, for example less than 2°C per hour, or even less than or equal to 1°K per 24 hours. The pulsed operation of the ultrasonic device may be obtained thanks to the electrical circuit which may be configured to supply the electric current to the ultrasonic transmitter intermittently.

[0051] Another advantage of generating a vibration intermittently is the possibility of lowering the rating of the cut-off system so that the threshold intensity Is is closer to the nominal intensity of the electric current during the period of generation of a vibration. It is particularly advantageous to choose a cut-off system having a rating Kl lower than the nominal intensity of the electric current during the generation period by choosing an overcurrent duration equal to the duration of the generation period. For example, if the nominal intensity of the electric current is equal to 0.45 A for a generation period duration of 0.8 s, it is then advantageous to choose a cut-off system having a rating Kl of 0.25 A rather than 0.5 A. Indeed, the example of an abacus illustrated by [Fig.7] makes it possible to determine that a cut-off system with a rating Kl of 0.25 A can have a threshold intensity of 0.5 A for an overcurrent duration of 0.8 s.Thus chosen, the cut-off system makes it possible to detect an operating failure materialized by a small variation in the effective intensity (of the order of 10%) of the electric current compared to the expected nominal intensity.

[0052] Furthermore, choosing a rating Kl lower than the nominal intensity of the electric current during the period of generation of a vibration also makes it possible to detect an operating failure where the period of generation of a vibration is greater than the overcurrent duration d. For example, if the generation of the vibration is carried out continuously rather than intermittently, then the example of the abacus of [Fig.7] of the cut-off system makes it possible to determine that said cut-off system of rating Kl equal to 0.25 A can have a threshold intensity of 0.45 A for an overcurrent duration of 6 s.

[0053] The cut-off system 1310 is preferably non-resettable. By the term "non- "resettable" means making an irreversible opening of the electrical circuit 1300. For example, when the cut-off system is a fuse, the melting of the fuse wire is irreversible and definitive. It is therefore necessary to replace the cut-off system following an opening of the circuit 1300 to allow the device to be restarted. The non-resettable system thus makes it possible to avoid mistakenly resetting the circuit and further improves the safety of the device.

[0054] The cut-off system 1310 may advantageously be configured to open the circuit 1300 when another parameter of the electric current exceeds a threshold. This may for example be an active or reactive power of the electric current exceeding a threshold power. The cut-off system 1310 is advantageously configured to open the circuit when a parameter of the electric current making it possible to report a failure of the ultrasonic device 1000 exceeds a threshold value.

[0055] Finally, to reduce a failure of the cut-off system 1310, it is advantageous to implement a redundancy of the cut-off system 1310 by inserting a plurality of cut-off systems 1310 in series in the electrical circuit 1300. Each cut-off system 1310 is advantageously configured to open the circuit 1300 when the effective intensity of the electric current is greater than a threshold intensity for an overcurrent duration among a plurality of threshold intensities and overcurrent durations. Redundancy is notably ensured when all the threshold intensities and all the overcurrent durations of the plurality are identical. When the threshold intensity and the overcurrent duration are linked by a rating, then a plurality of cut-off systems 1310 having the same rating will advantageously be chosen.

[0056] It is also conceivable that at least some of the threshold intensities and overcurrent durations among the plurality of threshold intensities and overcurrent durations are different. A plurality of cut-off systems 1310 will then advantageously be chosen having different ratings K1, K2, K3 and preferably ratings K1, K2, K3 showing different trends as a function of the threshold intensity Is and the overcurrent duration d, as illustrated by [Fig.7]. Thus, one of the cut-off systems implemented (e.g. curve K3) ensures the protection of the installation for a given overcurrent duration d, for example d = 1000s, when another cut-off system implemented, for example (curve K2) ensures the protection of the installation for another given overcurrent duration d, for example d = 0.1 s.

[0057] Each cut-off system 1310 of the plurality of cut-off systems advantageously has an identical and high cut-off power, for example greater than 20 times the highest threshold intensity, or even greater than 1000 times the highest threshold intensity. Thus, whatever the effective intensity circulating in the circuit 1300 before it opens, no damage is to be expected for the plurality of cut-off systems.

[0058] The threshold intensity of the electric current can be dimensioned according to a maximum average power usable during normal operation of the ultrasonic device 1000. The maximum average power can also be defined in relation to a nominal average power. By "nominal average power", we mean an average power delivered by an electrical energy source and consumed by the ultrasonic transmitter during normal operation of the ultrasonic device 1000. The maximum average power can be defined as equal to 125% of the nominal average power. According to an example of the device 1000 implemented by the inventors, in normal operation, the nominal average power is estimated at 120 W. According to this example, the maximum average power is therefore defined at 150 W and the effective intensity circulating between the generator 1340 and the energy source 1350 is estimated at 0.5 A.

[0059] The generator 1340 can be controlled by an automaton so that the power delivered by said generator 1340 cannot exceed an upper limit. The upper limit is a function of the amplitude and frequency of the ultrasonic vibration to be generated by the device 100.

[0060] In order to anticipate the initiation of an explosion of the explosive atmosphere, monitoring of the quantities having a direct impact on said initiation can be implemented. The quantities that can have a direct impact on the initiation of an explosion are, for example, the concentration of dust in the atmosphere and the presence of a hot spot whose temperature could exceed a flammability temperature. If the concentration of dust in the atmosphere cannot be controlled by the ultrasonic device, it may, however, be relevant to measure and / or control the temperature of elements that may have a temperature likely to exceed a flammability temperature. The vibrating elements are, for example, a part of the ultrasonic device or a part of the receiving system.

[0061] The ultrasonic transmitter 1200 may have a high temperature because it may dissipate a portion of the electric current in the form of heat. The constituent elements of the transmitter 1200, for example piezoelectric ceramics, may also dissipate a portion of the ultrasonic vibrations in the form of heat. The resonant parts of the receiver system subjected to an ultrasonic vibration may also have a high temperature. This may, for example, be a resonator of an ultrasonic-assisted sieve or the vicinity of a resonator of an ultrasonic-assisted sieve. The resonator is a solid metal part on which the ultrasonic device is fixed so as to transmit an ultrasonic vibration. A portion of the ultrasonic vibration may dissipate in the resonator or the parts in contact with the resonator or even the welds or glue points in the vicinity of the resonator and cause it to heat up.For example, the temperature of a resonator and / or . its direct vicinity during normal operation can easily reach 200°C.

[0062] [Fig. 2] schematically represents a second embodiment of the ultrasonic device 1000 according to the invention. It differs from the first embodiment in that the protection means comprises a means 1500 for measuring the temperature of a portion to be controlled. The measuring means 1500 is configured to open the electrical circuit 1300 when the temperature of said portion to be controlled is higher than a threshold temperature. The portion to be controlled may be a portion of the ultrasonic device 1000, for example a surface of the ultrasonic transmitter, or a portion of the receiver system, for example a surface in the vicinity of a resonator.Thus, when the temperature of the surface of the transmitter, or of the surface of the resonator or of the parts in contact with said resonator or of the welds or glue points in the vicinity of the resonator, exceeds the threshold temperature, the heat sources, which are the circulation of the current and / or the generation of an ultrasonic vibration, are interrupted. Thus, the increase in temperature of the assembly is slowed down and the device 1000 and / or the receiver system can cool down.

[0063] The temperature measuring means 1500 may comprise an opening device 1520, inserted into the circuit 1300, and allowing the opening of the circuit 1300. In the embodiment of [Fig.2], the opening device 1520 is inserted into the second portion 1330 of the electrical circuit 1300 but it may also be inserted into the first portion 1320 of the circuit 1300.

[0064] The temperature measuring means 1500 may also comprise a measuring probe 1510 and a converter 1530. The measuring probe 1510 and the converter 1530 are configured to measure the temperature of the portion to be controlled. The probe 1510 may generate a quantity proportional to the measured temperature and the converter is advantageously configured to convert the quantity generated by the probe 1510 into a usable temperature. The converter is also preferably configured to compare the measured temperature with the threshold temperature and actuate the cut-off device 1520 when the measured temperature is higher than the threshold temperature.

[0065] In order to carry out the temperature measurement, several measurement methods can be implemented, for example implementing a measurement by thermal conduction, or even a measurement of thermal radiation. In both cases, a measurement method insensitive to ultrasonic vibrations is to be preferred, comprising for example shielded cables.

[0066] To illustrate the first case, the measuring probe 1510 can be a thermocouple, for example of type K or type PT 100. A sensitive part of the thermocouple is positioned on the portion to be controlled.

[0067] The comparator is preferably an electronic card which can have a power source. In order to avoid the initiation of an explosion due to a failure of the comparator, it is preferably arranged outside the enclosure 200 and even more preferably outside the confinement zone 210. A Zener diode barrier can also be inserted between the sensitive part of the thermocouple and the converter 1530 so that an overvoltage from the converter 1530 cannot propagate towards the enclosure 200 or the confinement zone 210.

[0068] The measuring probe 1510 may also be a pyrometric device. By pyrometric device, or simply pyrometer, is meant any device configured to measure thermal radiation. It may for example be a photodetector, a radiometer or even an infrared camera. Most pyrometers capture thermal radiation in a solid angle, in which case the pyrometer is preferably oriented so that the solid angle of detection includes the portion to be controlled. If a pyrometer seems more complex to implement than a thermocouple, it does however allow the temperature of the portion to be controlled to be measured by being positioned at a distance from said portion. It is thus easy to measure the temperature of a vibrating surface.In addition, when the portion to be inspected is a large area, for example not entirely within the solid angle of detection of the pyrometer, the pyrometer is preferably configured so that the solid angle of detection sweeps the portion to be inspected. For example, the orientation of the pyrometer may be changed periodically. A mirror on an optical path between the portion to be inspected and the pyrometer may also be tilted periodically.

[0069] The measuring means 1500 may comprise a gaseous screen configured to keep dust from the explosive atmosphere away from the measuring means 1500 and more particularly from the measuring probe 1510. Indeed, the accumulation of dust on the measuring probe 1510 can distort the temperature measurement. This is for example the case when the measuring probe 1510 is a thermal camera comprising a lens for collecting infrared radiation. The accumulation of dust obscures the lens and can reduce the measurement accuracy. Thus the gaseous screen comprises a circulation of gas around the measuring probe 1510, the circulation of gas being configured to expel dust from the explosive atmosphere from the measuring probe 1510. In order to reduce the risk of reaction between the gas of the gaseous screen and the explosive atmosphere, the gas is an inert gas also called "neutral gas", such as nitrogen.

[0070] The measuring means 1500 advantageously has intrinsic protection that can be materialized by a level of protection of the equipment called "Equipment Protection Level" in English or otherwise known as "ATEX marking". The ATEX marking of the measuring means 1500 is advantageously compatible with the level of risk present in the enclosure 200 and at least in the confinement zone 210. The measuring means 1500 advantageously has an ATEX "IIIA" marking.

[0071] The portion to be controlled may be a portion of the sealed envelope 1400 and preferably the portion to be controlled is a portion of the outer surface of the sealed envelope 1400. The thermal transfers implemented, such as thermal conduction, thermal convection, or thermal radiation, may induce temperature gradients between different portions of the outer surfaces of the sealed envelope 1400. It is then advantageous to measure the temperature of the surfaces of the envelope 1400 in contact with the explosive atmosphere and which may have a high temperature.

[0072] The portion to be controlled may be a surface of the ultrasonic transmitter 1200. This is the element that may exhibit the greatest temperature variations. It therefore seems judicious to directly measure a temperature of said transmitter 1200.

[0073] The portion to be controlled may be a portion of the receiving system on which the ultrasonic device 1000 is fixed, for example a portion of a resonator. It may also be parts belonging to the receiving system and being in contact with the resonator. Indeed, the ultrasonic vibration propagating in the parts in contact with the resonator can cause a strong heat dissipation giving rise to a strong rise in temperature. For example, the resonator may be enclosed in a metal chassis. A layer of glue may be present between the resonator and the metal chassis. The ultrasonic vibrations tend to dissipate in the metal chassis, in particular in the vicinity of the resonator, or in the layer of glue.

[0074] Care will be taken, in the implementation of the temperature measuring means 1500, to prevent possible failures. For example, when the measuring means 1500 comprises a thermocouple, the vibration of the portion to be controlled can cause the thermocouple to detach, in particular when the latter is located on a vibration antinode. The detachment of the thermocouple prevents a temperature measurement from being carried out and therefore prevents the opening of the electrical circuit when the measured temperature exceeds the threshold temperature. So that the ultrasonic vibrations do not decouple the thermocouple from the portion to be controlled, it is preferable to fix the thermocouple to a non-vibrating element. For example, the thermocouple can be positioned close to the portion to be controlled in which case a correction is made to the temperature measurement made by the thermocouple.The thermocouple may also be positioned on a zone that vibrates little, or not at all, such as a vibration node. The term "vibration node" means a position where the amplitude of the ultrasonic vibration is low, or even zero. The ultrasonic transmitter 1200 may for example be tuned in half-wavelength to the ultrasonic vibration, in which case the central zone of the ultrasonic transmitter 1200 comprises a vibration node. It is also preferentially at this vibration node that the envelope 1400 is fixed to the transmitter. The thermocouple may then be fixed or clamped at the zone. 1200 ultrasonic transmitter central unit.

[0075] The thermocouple may also be fixed in such a way as to avoid decoupling, for example by brazing onto the portion to be tested. However, in order to avoid damaging the sensitive part of the thermocouple during brazing, said thermocouple may be encapsulated or enclosed in a thermal conductor welded or brazed onto the part to be tested.

[0076] The protection means may advantageously comprise a plurality of measuring means 1500, thus making it possible to obtain redundancy in the measurement of a temperature and the opening of the circuit 1300. Each measuring means 1500 may also measure the temperature of a different portion to be controlled among a plurality of portions to be controlled. In this way, the temperature of the ultrasonic device 1000 and / or of the receiver system may be mapped. In this case, each measuring means 1500 is advantageously configured to open the electrical circuit 1300 when the temperature of the portion to be controlled is greater than a threshold temperature relating to said portion to be controlled. Indeed, the failure of the ultrasonic device 1000 and / or of the receiver system may cause a different temperature increase, whether it is a portion of the ultrasonic transmitter 1200 or a sieve resonator.

[0077] The protection means may advantageously comprise at least one means 1500 for measuring the temperature of a portion to be controlled and at least one cut-off system 1310, making it possible to improve the detection of an operating failure of the ultrasonic device 1000 and / or the receiving system.

[0078] The sealed enclosure 1400 prevents dust from the explosive atmosphere from coming into contact with hot elements such as the ultrasonic transmitter 1200. The diameter of the dust particles can be of the order of ten micrometers to a few millimeters. It is therefore advantageous for the sealed enclosure 1400 to have a protection index at least equal to IP 6X. The IP protection index is an international standard of the International Electrotechnical Commission relating to the intrusion of solids and sealing. A protection index of IP 6X means that the enclosure 1440 is completely protected against the intrusion of dust and microscopic particles.

[0079] [Fig.3] and [Fig.4] schematically represent a third embodiment of the ultrasonic device 1000 according to two section planes AA and BB. In this embodiment, the ultrasonic device 1000 is configured to transmit an ultrasonic vibration to a receiving system, such as an ultrasound-assisted sieve. Reference will be made to the term "sieve" to designate more broadly any receiving system that can be vibrated by the ultrasonic device 1000 and more particularly the ultrasound-assisted receiving systems implemented in an atmosphere comprising explosive dust.

[0080] The [Fig.3] represent in particular a containment wall 10 separating the enclosure 200 and the containment zone 210. The ultrasonic-assisted sieve as well as the ul- emitter The second portion of the electrical circuit 1300 is preferably located in the enclosure 200. The second portion of the electrical circuit 1300 is preferably located in the confinement zone 210 and the neutral zone 220.

[0081] In order to isolate the ultrasonic transmitter 1200 from the explosive atmosphere, the sealed casing 1400 advantageously comprises a sealed chamber 1410 and a sealed sheath 1450. The sealed sheath 1450, in the example of [Fig.3] and [Fig.4] connects the sealed chamber 1410 to the wall 10 of the enclosure 200.

[0082] The sealed chamber 1410 surrounds a first portion 1421 of the interior volume. The ultrasonic transmitter 1200 comprises an active part 1210 and a horn 1220. By active part, we mean a part of the transmitter which may comprise piezoelectric ceramics. The active part 1210 is positioned within the sealed chamber 1410, in the first portion 1421 of the interior volume. The sealed chamber 1410 comprises a body 1430 and a cover 1440. The body 1430 and the cover 1440, according to the embodiment of [Fig. 3], surround the first portion of the interior volume. The cover 1440 is fixed on the body 1430 so as to close the first portion of the interior volume 1421 from the outside.

[0083] In the embodiment of [Fig.3] and [Fig.4], the body 1430 is a hollow solid having a cylinder shape aligned along a first axis Z. According to this embodiment, the internal diameter of the body 1430 is advantageously chosen so that the internal surfaces of the body 1430 are not in contact with the surfaces of the active part 1210 of the emitter 1200. The body 1430 also comprises a first opening 1433 adapted to cooperate with a part of the emitter 1200 so that the latter can be fixed, for example by screwing, on the body 1430 by making a sealed connection. The emitter 1200 is preferably tuned in half-wavelength on the ultrasonic vibration to be generated. Thus, the ultrasonic emitter 1200 in vibration can have a vibration node on a central portion, preferably annular.The body 1430 is advantageously fixed at the vibration node, that is to say at the central portion of the transmitter 1200, so that the ultrasonic vibration of the latter does not damage the body 1430. The ultrasonic transmitter 1200 is advantageously configured so that the active part 1210 is arranged on a first half of the transmitter 1200. Thus, the active part of the transmitter 1210 is arranged in a hollow volume delimited by the body 1430, the cover 1440 and the horn 1220.

[0084] The sealed sheath 1450 surrounds a second portion of the interior volume 1422. The first portion of the electrical circuit 1300 is positioned in the second portion of the interior volume. The electrical circuit 1300 is partially shown in [Fig. 3]. In this figure, only the second portion 1330 of the electrical circuit 1300 appears in the confinement zone 210, entering the sealed sheath 1450 through a press- tow 1456.

[0085] The sealed sheath 1450 also comprises a first end 1452 fixed to the sealed chamber 1410, and in particular to the cover 1440, making it possible to connect the first and second portions of the interior volume and thus allow the passage of the electrical circuit 1300 from the sealed sheath 1450 to the sealed chamber 1410. The sealed sheath 1450 makes it possible to protect the electrical circuit 1300 so that it can reach the sealed chamber 1410 without the dust from the explosive atmosphere coming into direct contact with the electrical circuit 1300. The sealed chamber 1410 advantageously has a second opening 1437 adapted to be connected to the first end 1452 of the sheath 1450 in a sealed manner. This may for example be a screw connection.

[0086] The sealed sheath 1450 also comprises a second end 1453 fixed to the containment wall 10 so that the electrical circuit 1300 can pass from the containment zone 210 to the enclosure 200. For this, the second end 1453 of the sheath may comprise two elements 1454, 1455 making it possible to enclose the containment wall 10 on either side by creating a sealed through connection between the two zones 200, 210. A cable gland 1456 makes it possible to hold a portion of the electrical circuit 1300 in place and / or to isolate the second portion from the interior volume of the containment zone 210.

[0087] The waterproof sheath 1450 is preferably flexible in order to facilitate the assembly / disassembly of the device 1000 on the ultrasonic sieve. It is however preferable that the waterproof sheath 1450 also has good resistance to shear stresses in order to protect the portion of the electrical circuit running through said sheath from shear stresses. For example, the waterproof sheath 1450 may comprise a braided layer, for example made of stainless steel.

[0088] The sealed sheath 1450 advantageously comprises an electrically insulating outer surface 1451, in order to reduce any risk of electrical charging around its periphery. For this purpose, said outer surface 1451 may comprise an outer layer made from ethylene-propylene-diene monomer (also called EPDM). EPDM also has the advantage of being compatible with the requirements of the food and pharmaceutical industries. Thus, the device 1000 can be used in the filtering of powders intended for the food or pharmaceutical industries.

[0089] The outer surface 1451 of the sealed sheath 1450 advantageously has good resistance to abrasion which may occur between said sheath 1451 and a vibrating chassis.

[0090]

[0091] The electric current may have a nominal effective voltage at the input of the ultrasonic transmitter greater than 350 V RMS. Also, in order to ensure good safety of the device, the thickness and / or the materials belonging to the outer surface 1451 of the sheath 1450 are preferably chosen to allow the insulating properties of the sealed sheath 1450 to be preserved even when a voltage greater than 10 times the nominal effective voltage is applied on either side of the sealed sheath 1450. In addition, the thickness of the outer layer, for example made of EPDM, is advantageously sized to minimize the occurrence of sliding discharges between the sheath 1450 and an electrically charged element in the vicinity of the sheath 1450. By sliding discharges, we mean an electric discharge evolving in a gas flow. The length of the sheath 1450 can also be limited to reduce the occurrence of sliding discharges. For this, the sheath 1450 advantageously has a length less than or equal to 2 m.

[0092] The accumulation of dust on the ultrasonic device 1000 can present a risk. The dust can become electrically charged due to friction with vibrating parts of the device 1000. This can result in an electrical discharge initiating an explosion. The device 1000 can be cleaned easily in order to remove all traces of dust on its surface. Thus, the exterior surfaces of the device 1000, including the exterior surface 1451 of the sealed sheath 1450, are advantageously smooth. By smooth, we mean an effective roughness advantageously less than 0.8. An effective roughness less than 0.8 is moreover compatible with the requirements of the pharmaceutical field.

[0093] The sealed sheath 1450 advantageously comprises a shield lined on an interior surface of said sheath 1450 and surrounding the electrical circuit 1300. In this way, the electromagnetic compatibility of the ultrasonic device 1000 is improved. The shield is advantageously connected to a fixed potential, such as a ground or earth in order to reduce the risk of electrostatic charging of a vibrating part of the device 1000.

[0094] The ultrasonic transmitter 1200 is configured to generate an ultrasonic vibration with a vibration frequency, for example, between 20 kHz and 100 kHz. The ultrasonic transmitter 1200 may be configured to generate an ultrasonic vibration in a restricted range between 20 kHz and 40 kHz, making it possible to effectively assist in the sieving of powder.

[0095] The ultrasonic transmitter 1200 and in particular the active part 1210 of the transmitter 1200 may comprise a plurality of piezoelectric ceramics pre-stressed between at least two metallic elements to form an assembly called a Langevin triplet. The ceramics used preferably have good thermal stability because the transmitter 1200 should be able to operate correctly in the absence of active cooling. These are, for example, ceramics comprising Lead, Zirconium and Titanium, called PZT. The preferred ceramics preferably have typically a depolarization temperature, called the Curie temperature, greater than 200°C and more preferably greater than or equal to 300°C, or even 350°C. The mechanical quality factor may also be of interest in the choice of ceramics used since it makes it possible to limit intrinsic heating of the ceramics during the operating phases. Ceramics with a mechanical quality factor greater than 500 and more preferably greater than or equal to 800 will preferably be chosen. In order to ensure the reliability and longevity of the ceramics, a heat treatment configured to age the ceramics may be carried out before the implementation of said ceramics in the ultrasonic device 1000. By aging, we mean stabilizing the acoustic properties of the ceramics, for example by increasing the vibration amplitude of the ceramics for a given electric current.

[0096] The horn 1220 is advantageously configured to efficiently transmit the ultrasonic vibration from the active portion 1210 of the ultrasonic transmitter 1200 to the receiving system.

[0097] In the embodiment of [Fig. 3], the transmitter 1200 has a symmetry of revolution along the first axis Z, which is in particular the preferred propagation axis of the ultrasonic vibrations. The active part 1210 of the transmitter 1200 is fixed on a first face of the horn 1220. A vibration node is advantageously positioned at the level of the horn 1220. In this way, the horn 1220 is fixed on the sealed chamber 1410, the active part of the transmitter 1200 is positioned within the sealed chamber 1410 and a part of the horn 122 is positioned outside the sealed chamber 1410.

[0098] The 1220 horn is advantageously made of titanium alloy in order to provide good acoustic characteristics, good robustness and low thermal conductivity.

[0099] The device 1000 advantageously comprises a coupling means 1221 to the receiving system, said connecting means 1221 being fixed to the pavilion. This is for example a stud. The coupling means 1221 makes it possible to couple the device 1000 to the receiving system and efficiently transfer the ultrasonic vibrations to the receiving system. The coupling means 1221 is advantageously aligned along the first Z axis in order to allow efficient propagation of the ultrasonic vibration. The connection with the receiving system is made by screwing and preferably along the first Z axis.

[0100] The robustness of the device 1000 depends heavily on the reliability of the horn 1220 and in particular of the coupling means 1221. Indeed, a fracture of the coupling means 1221 can separate the ultrasonic device 1000 from the receiver system. The undamped vibration of the horn 1220 in the explosive atmosphere 200 can create a heating of the horn 1220 and greatly increases the risk of initiating an explosion. The detached horn 1220 can also hammer a portion of the receiver system at very high frequency, also creating localized heating and greatly increasing the risk of initiating an explosion. The rupture of the coupling means 1221 can also cause the electrical contact between the ultrasonic device 1000 and the receiver system to open. Thus, a drift in the electrical potentials of the device 1000 and the receiver system can cause an electrical discharge in the explosive atmosphere 200. To prevent the occurrence of failures by rupture, the horn 1220 and in particular the coupling means 1221 are preferably made of titanium alloy.The titanium alloy offers very good resistance to longitudinal vibrations, i.e. to tensile / compression deformations, and thus significantly reduces the risk of failure by rupture.

[0101] The sieves used for the filtration of powders, for example agri-food, can be made of stainless steel. In this case the difference in Young's modulus between the titanium alloy of the horn 1220 and the coupling means 1221 and the sieve is sufficiently small so that the ultrasonic vibrations propagate from one material to the other with a minimum of reflections.

[0102] The risk of loosening of the coupling means 1221 or a poor quality interface between the horn and the receiving system can also present the same risks as a breakage as described previously. It is therefore advantageous that the tightening of the coupling means 1221 on the receiving system is of good quality. For this, the horn 1220 can also comprise a flat support 1222 also called a bearing surface, the bearing surface 1222 forming the base of the coupling means 1221. The coupling of the device 1000 with the receiving system can be achieved by screwing the coupling means 1221 into the screen and tightening until the bearing surface 1222 is in contact with a portion of the surface of the receiving system. The mechanical coupling thus achieved allows the propagation of ultrasonic vibrations within the receiving system in an efficient manner. The bearing surface 1222, in contact with a portion of the receiving system, participates in the propagation of the ultrasonic vibration within the screen.However, it is preferable to choose a small bearing surface 1222. Indeed, the assembly and disassembly of the ultrasonic device 1000 can damage the surface condition of the surface portion of the sieve in contact with the bearing surface 1222. A non-planar surface condition or one having a high roughness can increase the reflection of the ultrasonic vibration, which can cause local heating or heating of the ceramics. It is therefore preferable to reduce the contact surface between the bearing surface 1222 and the receiving system so as to reduce the energy which is dissipated. The external diameter d[222 of the bearing surface 1222 is preferably greater than or equal to the diameter di22i of the coupling means 1221. In an exemplary embodiment, the bearing surface . 1222 surrounding the base of the coupling means 1221 has an external diameter of 20 mm and the coupling means 1221 has a nominal diameter of 10 mm.

[0103] In order to provide a high and constant level of dust tightness, it is necessary to preserve the integrity of the sealed casing 1400. However, the operation of a receiving system, such as an ultrasound-assisted sieve, requires frequent handling operations, such as frequent disassembly and assembly of the ultrasonic device 1000 to, for example, replace worn filter cloths or modify the filtration diameter of the cloths. These frequent handling operations may present a risk of weakening the sealed casing. For example, during the handling of the ultrasonic device 1000 and in particular during the assembly / disassembly phases, the horn 1220 can be coupled / decoupled from the receiving system by screwing / unscrewing the coupling means 1221. The screwing / unscrewing causes a rotation of the horn 1220 and the body 1430 around the first axis Z.If the sealed sheath 1450 is fixed to the body 1430, then the rotation causes said sheath 1450 to move with a large amplitude around the first axis Z, which can cause impacts with other elements such as the ground or other equipment or a tearing off of one of the ends of the sheath 1450. The screwing / unscrewing in this case can also apply a torsional torque to the sheath 1450.

[0104] In order to solve the problem set out above, one end of the sealed sheath 1450 is advantageously fixed to the cover 1440 and the cover 1440 is advantageously fixed to the body 1430 by means of a sealed connection allowing rotation of the cover 1440 around a second axis R. Thus, the coupling means 1221 can be screwed / unscrewed onto the screen without the body 1430 causing the sheath 1450 to rotate or twist. The first and second axes Z, R are preferably aligned so that the sonotrode 1600 can be screwed while allowing the cover 1432 to remain stationary. Thus, no movement is applied to the sheath 1450. The mechanical integrity of the sealed sheath 1450 is therefore ensured. The sealed connection between the cover 1440 and the body 1430 prevents dust from reaching the interior of the sealed chamber 1410.

[0105] The cover 1432 advantageously comprises a second opening 1437 configured so that the waterproof sheath 1450 can be fixed there.

[0106] [Fig. 3] and [Fig. 4] schematically represent an example of a connection between the body 1430 and the cover 1440 according to two section planes AA and BB. In this example, the body 1430 comprises a groove 1434 on its outer periphery and the cover 1440, mounted on the body 1430, covers the groove 1434. A plurality of pins 1435, fixed on the cover 1432 and partially penetrating into the groove 1434, prevent the removal of the cover 1432 while allowing the rotation of the body 1430 in the cover 1432. The seal between the body 1430 and the cover 1432 can be ensured by O-rings 1436 placed at the level of the throat 1434.

[0107] The body 1430 and the cover 1440 preferably have a high resistance to corrosion so as not to contaminate the powders to be treated and to offer good reliability over time. They can be made from a grade of stainless steel comprising Molybdenum offering good resistance to corrosion, such as 316L stainless steel. 316L stainless steel elegantly has the advantage of being a poor thermal conductor since its conductivity is close to 15 W / m / K. The body 1430 and the cover 1440 can also be made from a titanium alloy. The latter is also a poor thermal conductor since it has a thermal conductivity close to 20 W / m / K. The sealed chamber 1410 thus constitutes a good thermal barrier between the explosive atmosphere and the active part 1210 of the ultrasonic transmitter 1200.

[0108] [Fig.5] and [Fig.6] schematically represent an embodiment of a receiver system 2000 according to the invention, in particular an ultrasound-assisted sieve. The sieve 2000 comprises: • a 2200 non-resonant chassis; and • an ultrasonic device 1000 according to the invention.

[0109] A filter cloth may be fixed on the non-resonant frame 2200 and allows the screening of the powders to be treated. The ultrasonic device 1000 is intended to transmit an ultrasonic vibration to the non-resonant frame 2200 in order to assist the ultrasonic screening. The non-resonant frame is not tuned to the frequency of the ultrasonic vibration.

[0110] In order to allow the propagation of an ultrasonic vibration towards the non-resonant chassis 2200, the sieve 2000 can advantageously comprise: • an inner ring 2100; • 2300 fixing lugs; and • a 2400 resonator. The inner ring 2100 is fixed to the non-resonant chassis 2200 by means of the fixing lugs 2300. In this case, the ultrasonic device 1000 is advantageously coupled to the resonator 2400, the latter being fixed, or even welded to the inner ring 2100. The latter is tuned to the frequency of the ultrasonic vibration and its stationary vibration is transmitted to the resonant chassis 2200 by the inner ring and the fixing lugs 2300. The ultrasonic device 1000 is preferentially coupled to the resonator 2400 by screwing, in particular by means of the coupling means 1221 and the bearing surface 1222 as described previously.

[0111] The sieve 2000 may also include an unbalanced motor for applying low frequency vibration to the non-resonant chassis in addition to the ultrasonic vibration.

[0112] The non-resonant chassis 2200 is in contact with the powders to be treated, it may be necessary to control its temperature, or even take action when its temperature is likely to reach a flammability temperature of the atmosphere. However, the non-resonant chassis 2200 is not necessarily the part that can show the greatest temperature variation. The resonator 2400 and the elements in contact with the resonator are more likely to show a strong temperature variation, the latter being the entry point of the ultrasonic vibrations at the sieve 2000. Thus, when the ultrasonic device 1000 comprises a means 1500 for measuring a temperature of a portion to be controlled, the portion to be controlled advantageously comprises these elements.For example, the portion to be controlled comprises the resonator 2400 and / or a portion of the inner ring 2100, the portion of the inner ring 2100 being preferably in the vicinity of the resonator and even more preferably in contact with the resonator 2400. The measuring means 1500 advantageously implements an indirect measuring means, which can for example measure thermal radiation. This may be a pyrometer or a thermal camera. It may also be a plurality of thermocouples dispersed on the sieve. The measuring means 1500 is advantageously configured to open the electrical circuit 1300 of the ultrasonic device 1000 when the temperature of one of the elements belonging to the portion to be controlled is higher than the threshold temperature.Thus, when the temperature of a part belonging to the portion to be controlled, for example a portion of the inner ring 2100, reaches the threshold temperature, the ultrasonic device 1000 is stopped and the ultrasonic vibration is stopped, thus allowing the sieve 2000 to cool.

[0113] [Fig.6] schematically represents an example of coupling between the resonator 2400 of the sieve 2000 and the horn 1220 of the ultrasonic device 1000. In this example, the horn is screwed onto the resonator 2400 using the coupling means 1221. The resonator 2400 comprises, for example, a threaded hole, adapted to the coupling means 1221 of the horn 1220.

Claims

1. Claims Ultrasonic device (1000) comprising: - an ultrasonic transmitter (1200), configured to convert an electric current into an ultrasonic vibration, the transmitter comprising an active part (1210) and a horn (1220), the horn being fixed on the active part; - an electrical circuit (1300), configured to supply the electrical current to the ultrasonic transmitter; - a sealed envelope (1400), delimiting an interior volume (1420) isolated from the exterior, a part (1210) of the ultrasonic transmitter and a part (1320) of the electrical circuit being positioned in the interior volume, the sealed envelope comprising an exterior surface configured to be in contact with an explosive atmosphere; the sealed envelope (1400) comprising: - a sealed chamber (1410) delimiting a first portion of the interior volume (1420), fixed on a vibration node of the ultrasonic transmitter so as to isolate the first portion of the interior volume from the exterior and position the active part of the ultrasonic transmitter in the interior volume, the sealed chamber (1410) comprising: a body (1430), on which the horn is fixed; and a cover (1440); - a coupling means (1221) fixed on the transmitter horn and configured to be coupled by screwing to a receiver system, the screwing being carried out along a first axis (Z), the ultrasonic device being characterized in that it comprises a protection means (1310, 1500) configured to open the electrical circuit when a parameter representative of a failure in the operation of said ultrasonic device is greater than a threshold; and in that the sealed casing (1440) comprises a sealed sheath (1450) delimiting a second portion of the interior volume enveloping the part (1320) of the electrical circuit; and in that one end of the sealed sheath is fixed to the cover (1440); and in that the cover is fixed to the body by means of a sealed connection (1434, 1435) allowing rotation of the cover along a second axis (R) while maintaining the sealing of the connection.

2. Ultrasonic device (1000) according to the preceding claim, characterized in that the ultrasonic transmitter is configured to convert an electric current into an ultrasonic vibration having a frequency between 20 kHz and 100 kHz, preferably between 20 kHz and 40 kHz.

3. Ultrasonic device (1000) according to one of the preceding claims, characterized in that the protection means comprises a cut-off system (1310) configured to open the electrical circuit when an effective intensity of the electric current is greater than a threshold intensity (Is) for a duration (d) called "overcurrent duration".

4. Ultrasonic device (1000) according to the preceding claim, characterized in that the threshold intensity corresponds to a maximum average power transported by the electric current.

5. Ultrasonic device (1000) according to one of the two preceding claims, characterized in that the cut-off system has a cut-off power greater than the threshold intensity, preferably greater than 20 times the threshold intensity and preferably greater than 1000 times the threshold intensity.

6. Ultrasonic device (1000) according to one of the three preceding claims, characterized in that the protection means comprises a plurality of cut-off systems, each cut-off system being configured to open the electrical circuit when the effective intensity of the electric current is greater than a threshold intensity (Is) for an overcurrent duration (d).

7. Ultrasonic device (1000) according to one of the preceding claims, characterized in that the protection means comprises a means (1500) for measuring a temperature of a portion to be controlled, the measuring means being configured to open the electrical circuit when the temperature of the portion to be controlled is higher than a threshold temperature, the threshold temperature preferably being lower than a flammability temperature of the explosive atmosphere.

8. Ultrasonic device (1000) according to the preceding claim, characterized in that the temperature measuring means comprises a thermocouple or a pyrometer or a thermal camera or a radiometer.

9. Ultrasonic device (1000) according to one of the two preceding claims, characterized in that it is configured to transmit an ultrasonic vibration to a receiving system and the portion to be controlled is a portion of the receiving system.

10. Ultrasonic device (1000) according to one of the two preceding claims, characterized in that the sealed sheath comprises a smooth outer surface (1451), the outer surface preferably having an effective roughness of less than 0.

8.

11. An ultrasonic-assisted sieve (2000) comprising a frame (2200) and a resonator (2400), the resonator being coupled to the frame so as to be capable of transmitting an ultrasonic vibration to the frame, the sieve being characterized in that it comprises an ultrasonic device (1000) according to one of the preceding claims coupled to the resonator so as to transmit an ultrasonic vibration to the frame.

12. Sieve (2000) according to the preceding claim, characterized in that the ultrasonic device (1000) is an ultrasonic device according to claim 9 and in that the portion to be controlled comprises a surface of the chassis in the vicinity of the resonator.

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