METHOD FOR DETERMINING THE GAIN OF AN ACOUSTIC TRANSDUCER

Abstract

A method for adjusting the gain of an ultrasonic probe, the method employing a probe (1) comprising: a measuring transmitter (11) configured to emit an ultrasonic wave incident in the liquid metal; a receiver (21) configured to detect an ultrasonic wave reflected or diffracted by the liquid metal following the emission of the incident ultrasonic wave; and a processing unit (32) configured to amplify the detection signal to a gain of α. The measuring transmitter and receiver are immersed or positioned facing a reference medium (6), the reference medium comprising a target (7). The method involves moving the target relative to the probe to different measurement positions. The gain is adjusted according to a number of positions for which the amplitude of the detection signal is within a predetermined range. Figure 4B.

Description

Title of the invention: METHOD FOR DETERMINING THE GAIN OF AN ACOUSTIC TRANSDUCER Technical field

[0001] The technical field of the invention is the characterization, by ultrasound, of a casting of liquid metal, for example a casting of an aluminum alloy. Prior art

[0002] In the field of metal casting, it is necessary to control the quality of the liquid metal, in order to detect inclusions. This is particularly the case for aluminum. Some aluminum alloy products, for example strip for casing applications, have high requirements in terms of inclusion health. These inclusions are generated during the melting, production and casting of these alloys when they are in the liquid phase. The quality of the molten metal is determined by a quantity of inclusions present in the metal. These may be oxides, nitrides, carbides, fluorides or borides. Inclusions usually encountered in molten aluminum are, for example, particles of Al2O3, MgAl2O4, A14C3, MgO, CaO, CaF2, TiB2, TiVB2, SiO2. Their size ranges from a few microns to a few hundred microns.

[0003] It is possible to monitor, online, the quality of a casting by ultrasonic measurement techniques. According to this type of measurement, an ultrasonic acoustic wave propagates through liquid metal. The acoustic wave propagates through the liquid metal. In the presence of inclusions, a part of the emitted acoustic wave is reflected and can be detected. The reflected or diffracted Fonde amplitude makes it possible to trace the size of inclusions in the metal. The ultrasonic technique allows a characterization of a part of the cast liquid metal, typically 2%, when the control is carried out in the chute transporting the liquid metal from the furnace to the casting pit.

[0004] Probes for carrying out measurements, by ultrasound, on castings, have been described in patents EP3204764B1, EP3204763B1.

[0005] Document EPI 194772B1 describes a method for calibrating a probe, in which reflectors are placed at the end of rods, the latter being placed in liquid metal. The reflectors can be of different sizes. It is thus possible to establish a correlation between the size of each reflector and the amplitude of the detected acoustic background. Such a method needs to be applied for each probe. In addition, it assumes the placement of calibrated reflectors in a liquid metal, which can be complex.

[0006] Another possibility to estimate the size of inclusions is to use a curve of correlation between measurements resulting from an ultrasonic probe and measurements resulting from a method considered to be a reference method. The reference method may, for example, be a “LIMCA” (Liquid Metal Cleanliness Analysis) type analysis method, based on an analysis of the electrical resistance of a sample of liquid metal. It may also be the method described in EPI 194772B1, using calibrated reflectors. It is thus possible to establish a correlation function between the size of inclusions, measured by the reference method, and the amplitude of the ultrasonic signal.

[0007] A difficulty linked to the use of ultrasonic probes is that their response can vary from one probe to another. However, it is difficult to envisage calibrating each probe with a reference method, such as LIMCA or as described in EPI 194772B1. Indeed, whatever the reference method chosen, such calibration requires time.

[0008] The variability of the response between two probes, of identical structures, is due in particular to differences which may affect the electronic circuits, or the materials used. Faced with identical inclusions, two different probes, of identical design, can generate detection signals of different amplitudes, due to the variability of the response of the probes.

[0009] It is preferable, even necessary, to take such variability into account, for example if one wishes to apply the same correlation curve to measurements resulting from different ultrasonic probes.

[0010] The inventors propose a method allowing for the variability of responses from different probes to be taken into account. The objective is that probes of identical design generate identical signals, or signals that can be considered as such, in the presence of an identical inclusion. Statement of the invention

[0011] A first object of the invention is a method for adjusting a gain of an ultrasonic probe, the probe comprising: - a measuring transmitter configured to emit an incident ultrasonic wave into the liquid metal; - a receiver configured to detect an ultrasonic wave reflected or diffracted by an inclusion in the liquid metal, following the emission of the incident ultrasonic wave, and to form a detection signal from the detected ultrasonic wave; - a processing unit, configured to amplify the detection signal according to said gain;

[0012] the method comprising the following steps: (a) arrangement of the probe, such that the measuring transmitter and the receiver are immersed in a reference medium, or arranged facing the reference medium, the reference medium taking the form of a liquid or a gel, the reference medium comprising a target arranged at a measuring position, the target being formed of a solid material; b) power supply to the measuring transmitter, so that the measuring transmitter emits an incident ultrasonic wave propagating in the reference medium; c) detection, by the receiver, of a detection signal representative of an ultrasonic wave reflected by the reference medium under the effect of the incident wave;

[0013] the method being characterized in that it also comprises: d) repeating steps a) to c) during different measurement times, so that at each measurement time, the target is respectively moved to different measurement positions forming a mesh in the reference medium; e) from each signal respectively detected during each step c), determination of a measurement amplitude for each measurement position; f) selection of measuring positions for which the measuring amplitude extends within a predetermined amplitude range; g) counting the number of measuring positions selected in step f) and comparing the number of positions counted with a predetermined reference value, then adjusting the gain, so that • when the number of selected measurement positions is less than the reference value, the gain is increased; • when the number of selected measurement positions is greater than the reference value, the gain is reduced.

[0014] According to one possibility: - following step e), the measured amplitudes are between a minimum amplitude and a maximum amplitude; - the predetermined amplitude range extends between a first fraction of the maximum amplitude and a second fraction of the maximum amplitude, the second fraction of the maximum amplitude being strictly less than the first fraction of the maximum amplitude.

[0015] The first fraction of the maximum amplitude can be equal to 1.

[0016] The second fraction of the maximum amplitude can be between 0.2 and 0.8.

[0017] Preferably, following step g), when the number of selected measurement positions is different from the reference value, steps a) to g) are repeated after adjusting the gain.

[0018] The method may comprise, prior to step g), an implementation of steps a) to f) with a reference probe, so that the number of measurement positions resulting from step f) implemented with the reference probe corresponds to the reference value taken into account in step g).

[0019] According to one possibility, the target is a ball with a diameter between 1 mm and 10 mm.

[0020] According to one possibility, the reference medium is water or comprises water.

[0021] According to one possibility, - the measuring transmitter is coupled to a first waveguide, immersed in the reference medium; - the receiver is coupled to a second waveguide, immersed in the reference medium.

[0022] The mesh can define different measurement positions distributed along a longitudinal axis, a lateral axis, and a transverse axis, the lateral, longitudinal and transverse axes being orthogonal two by two. During step d), the target can be translated along the longitudinal axis, for different coordinates along the lateral axis and the transverse axis.

[0023] According to one possibility: - each translation along the longitudinal axis, for the same coordinates respectively along the lateral axis and the transverse axis, is carried out in a forward direction and in a return direction; - at each coordinate respectively along the lateral axis and the transverse axis, at least one measurement amplitude is determined, which corresponds to a maximum amplitude measured during translation in the forward and / or return direction.

[0024] Another object of the invention is an ultrasonic probe, comprising: - a measuring transmitter configured to emit an incident ultrasonic wave into the liquid metal; - a receiver configured to detect an ultrasonic wave reflected or diffracted by the liquid metal, following the emission of the incident ultrasonic wave, and to form a detection signal dependent on the detected ultrasonic wave; - a processing unit, configured to amplify the detection signal according to a gain and to determine a measurement amplitude from the detection signal resulting from the receiver; - the device being characterized in that the processing unit is configured to implement steps e) to g) of a method according to the first subject of the invention from measurement amplitudes respectively determined when a target, formed of a solid material, is placed facing the probe, in different measurement positions, in a reference medium.

[0025] The probe may comprise a control unit, configured to control a movement of the target between the different measurement positions, and to transmit said measurement positions to the processing unit.

[0026] The invention will be better understood upon reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. Figures

[0027] [Fig. 1A] represents a first embodiment of a probe allowing implementation of the invention.

[0028] [Fig.1B] represents another embodiment of a probe allowing an implementation of the invention.

[0029] [Fig.2] shows a diagram of acoustic waves detected at a measurement time.

[0030] [Fig.3] shows schematically the main steps of a method according to the invention.

[0031] [Fig.4A] illustrates a target, in the form of a ball, arranged facing a probe during the implementation of a method according to the invention.

[0032] [Fig.4B] shows diagrammatically different measurement positions to which the target is successively moved.

[0033] [Fig.4C] represents amplitudes measured at different measurement positions of the target.

[0034] [Fig.4D] is a detail of [Fig.4C].

[0035] [Fig.4E] is a detail of [Fig.4D].

[0036] Figure 5 represents a correlation curve between measured amplitudes A and known inclusion dimensions. Presentation of specific embodiments

[0037] A first example of an ultrasonic probe has been shown, in connection with [Fig. 1A], allowing an implementation of the invention. The probe comprises a measurement transmitter 11 and a receiver 21. In this example, the measurement transmitter 11 and the receiver 21 are formed by the same acoustic transducer. The acoustic transducer is for example a piezoelectric transducer, known to those skilled in the art.

[0038] The transducer is for example a pellet of piezoelectric material emitting an acoustic wave at a frequency of 15 MHz. Generally, the frequency of the emitted acoustic wave is preferably between 1 MHz and 20 MHz.

[0039] The probe is intended for detecting inclusions 4 in a liquid medium 2 to be analyzed, and more precisely in a liquid metal, the metal being for example an aluminum alloy. In Figures 1A and 1B, the dotted horizontal line represents an interface between the liquid metal 2 and an ambient medium 3, the latter being for example air.

[0040] The probe 1 comprises a waveguide 13, intended to be immersed in the liquid metal 2. The waveguide is configured to facilitate propagation of an acoustic wave between the transducer, acting as a transmitter-receiver, and the liquid metal 2. The waveguide 13 is for example formed from a material of the silicon nitride or silicon oxynitride (SiAlON) type, or more generally a material, of the refractory metal or ceramic type, considered to be inert with respect to the liquid metal 2. The use of such a waveguide has been described in EP3204763B1 or in EP1194772B1.

[0041] In Figures 1A and 1B, an ultrasonic field 5 is shown diagrammatically, which corresponds to a part of the liquid metal inspected by the probe 1. When an inclusion 4 passes through the ultrasonic field, a part of the acoustic wave emitted by the measuring transmitter 11 is reflected or diffracted towards the receiver 21. The characteristics of the reflected field, in particular its amplitude, allow the detection of an inclusion and its characterization, for example an estimation of its size.

[0042] Preferably, the probe may comprise a power emitter 12, configured to emit an acoustic wave of power, i.e. greater than 10W, and preferably greater than 100W, for example 120W, as described in EP3204764. Indeed, the application of a high-power acoustic wave makes it possible to obtain the wetting of the first waveguide 13 by the liquid metal 2. The power emitter 12 is activated at regular intervals, so as to allow continuous maintenance of good wetting of the waveguide 13 by the liquid metal 2.

[0043] [Fig.1B] represents a preferred configuration, in which the probe comprises a measurement transmitter 11 and a receiver 21. The measurement transmitter 11 is connected to a first waveguide 13. The receiver 21 is connected to a second waveguide 23, preferably identical to the first waveguide 13 (same material, same dimensions), but distinct from the latter. The length of each waveguide is for example between 10 cm and 50 cm. The first and second waveguides are preferably rectilinear, and extend respectively around a first central axis A1 and a second central axis A2. The central axes A1 and A2 are intersecting, and inclined relative to each other at an angle a. The angle is for example between 25° and 35°. The angle a is for example equal to 28°. Such a configuration has been described in EP3204764B1.

[0044] In this embodiment, the probe may comprise a first power emitter 12, and a second power emitter 22, as described in connection with the first embodiment. The first and second power emitters are activated periodically, so as to improve the wetting of the first waveguide 13 and the second waveguide 23, respectively, by the liquid metal 2.

[0045] The probe comprises a control unit 31, configured to allow a control of the emission of an acoustic wave by the measurement transmitter 11, and to allow control of the emission of a power acoustic wave by the power transmitter 12 when the probe comprises such a transmitter.

[0046] Regarding the acoustic waves emitted by the measuring transmitter 11, they are generally emitted in series. In practice, each series of acoustic waves is emitted by the measuring transmitter 11 at a regular frequency, for example 10 Hz. A series comprises at least one acoustic wave, and preferably several successive acoustic waves. Within the same series, the emission frequency of the acoustic waves can be between 100 Hz and 300 Hz, which corresponds to the excitation frequency of the piezoelectric transducer of the measuring transmitter. In [Fig. 2], three waves detected by the receiver 21 are shown diagrammatically, following the emission of a series of three waves by the measuring transmitter 11. The bracket indicates that the three waves belong to the same series. In [Fig.2], the ordinate axis corresponds to the signal detected S(t) by the receiver 21 while the abscissa axis corresponds to time t.

[0047] The probe comprises a processing unit 32, configured to process the detection signal S(t) resulting from the receiver 21. The processing unit 32 comprises an amplifier, intended to amplify the detection signal resulting from the receiver 21, and whose amplification gain Go is generally set in the factory, following the manufacture of the probe. The gain Go can be adjusted as described below. The gain Go is a multiplicative term applied to the detection signal.

[0048] The processing unit 32 is configured to calculate an amplitude of the detection signal, after amplification of the latter. The calculated amplitude can be an average of the maximum amplitudes of each detected acoustic wave, or the maximum amplitude of all the acoustic waves detected following the emission of a series of waves. Subsequently, the calculated amplitude is noted A(fm). tm designates a measurement instant, which corresponds to the detection of a series of acoustic waves by the receiver 21.

[0049] The processing unit may comprise one or more microprocessors or electronic circuits. Each microprocessor or electronic circuit is configured to process the detection signal, and perform an operation chosen from: determination of the measured amplitude, amplification of the signal, or one of the steps described below.

[0050] The presence of an inclusion 4, of significant size, in the liquid metal, causes the amplitude A(tm) to vary. ■ The amplitude A(tm) can make it possible to estimate an inclusion size, from a correlation curve established experimentally, using a reference method, for example the LIMCA method or the method based on the use of calibrated reflectors, these methods being described in connection with the prior art.

[0051] The same correlation curve can be used on different ul- probes trasonic probes, of identical design, provided that the amplitudes resulting from said ultrasonic probes are comparable. However, as previously indicated, it is necessary to take into account the variability of the probes, even if the latter are similar to each other: same dimensions and same materials used.

[0052] The probe 1 is intended to be immersed in a liquid metal 2. The liquid metal may, for example, flow from a furnace, or be present in a ladle or a crucible. For example, the liquid metal flows into a chute. The waveguide(s) of the probe are immersed in the chute. The probe may be placed directly at the outlet of the furnace, or further downstream, at the outlet of a filter or a degasser. This may be a gravel bed filter (Deep Bed filter) or a CFF (Ceramic Foam Filter) type filter or any other type of filter.

[0053] For reasons of cost and time, it is not realistic to produce, for each probe, a correlation curve with a reference method. However, it is necessary to take into account the variability of the response of each probe. The inventor proposes a method making it possible to obtain a comparable response for several probes, so as to be able to use a correlation curve as described below, in connection with [Fig.3].

[0054] The main steps of the process are illustrated in [Fig.3].

[0055] Step 100: arrangement of a target in a reference medium, in an initial measurement position.

[0056] During this step, a target 7 is placed in a reference medium 6, in an initial measurement position Pq predetermined relative to the probe.

[0057] The target 7 is intended to reflect an incident acoustic wave, emitted by the measuring transmitter of the probe, towards the receiver 21. The target 7 is formed of a solid material, for example a metal or a ceramic, for example of the artificial sapphire type. The target can be a solid spherical ball, with a diameter less than 15 mm or 10 mm, for example equal to 4 mm. It is considered that, taking into account the difference in acoustic impedances between water and aluminum, a diameter of 4 mm corresponds to an ultrasonic signal equivalent to a diameter of 100 μm in liquid aluminum. However, the dimension of 100 μm corresponds to a typical dimension of an inclusion to be detected in liquid aluminum.

[0058] Generally, the target 7 is contained in a spherical volume with a diameter less than or equal to 15 mm or 10 mm. The target can be held at the end of a rod 8. Preferably, the rod is thin and formed from a weakly echogenic material. The materials forming the target 7 or the rod 8 respectively are advantageously compatible with implementation in liquid metal, for example alumina.

[0059] The target is arranged in the focal zone 9 of the probe, in the reference medium. The focal zone 9 corresponds to a zone in which, under the effect of an acoustic wave emitted by the transmitter 11, a detectable acoustic wave reaches the receiver 21. The focal zone depends on the medium to be analyzed: it is different from the focal zone 4 shown in [Fig. 1B]. In [Fig. 4A], the focal zone 9 is shown diagrammatically by a dotted outline.

[0060] An advantage of the invention is that the reference medium 6 may be other than a liquid metal. It may, for example, be a liquid medium at room temperature, for example water. It may also be a medium having a gel consistency, knowing that it is preferable for the reference medium to be liquid. An advantage of the invention is that the liquid medium and the target are simple to handle. The liquid medium is preferably left at room temperature, or at a temperature that is not restrictive from the point of view of use, preferably below 80°C.

[0061] Step 110: taking a measurement.

[0062] A measurement is carried out at a measurement instant which corresponds to the measurement position Pm occupied by the target at the measurement instant. m is a natural integer indexing each measurement instant. At the initial measurement position, m = 0. A measurement corresponds to the emission of an acoustic wave, or a series of acoustic waves, by the transmitter 11 and to the formation of a detection signal S(f) by the receiver 21. An example of a detection signal has been described in connection with FIG. 2. The processing unit 32 determines a measured amplitude A(tm) from the amplified detection signal.

[0063] Step 120: moving the target.

[0064] During step 120, the target 7 is moved to another measurement position of index m+l. Then step 110 is repeated, so that during the reiterations of steps 110 and 120, the target 7 is successively arranged in different predetermined measurement positions Pm. The measurement positions Pm describe a spatial mesh, for example a regular mesh, in the reference medium 6. The mesh is preferably a three-dimensional mesh. In FIG. 4B, different measurement positions Pm are shown distributed regularly according to a three-dimensional mesh describing a parallelepiped. The mesh is defined along a longitudinal axis X, a lateral axis Y and a transverse axis Z.

[0065] The movement of the target 7 is preferably controlled by a control unit 33, programmed to control the movement of the ball according to the predefined spatial mesh. The control unit is preferably connected to the processing unit 32, so as to provide the different positions of the target.

[0066] Step 130: collection of the amplitudes measured at each measurement time.

[0067] During step 130, the amplitudes A(tm) measured at each measurement position Pm are collected. The amplitudes A(t„^ extend between a maximum amplitude Amax and a minimum amplitude, which corresponds here to a noise level Anoise. In Figure 4C, different amplitudes A(tm) measured during a scan of a target according to a three-dimensional mesh as shown in [Fig.4B] are represented. The target was moved in the plane defined by the X and Y axes, by successive translations parallel to the longitudinal axis X, at a speed of 10 mm / s, the measurements being acquired at a frequency of 50 Hz. During each translation parallel to the longitudinal axis X, the amplitude measured, at a frequency of 50 Hz, corresponds to an average of three successive pulses detected at a frequency of 500 Hz. In [Fig.4B], the dotted lines diagrammatically represent the translations along the X axis.

[0068] The mesh extended along 100 mm parallel to the longitudinal axis X, 30 mm along the lateral axis Y and 50 mm along the transverse axis Z. In the XY plane, the translations were carried out parallel to the X axis, along a back and forth along the same line. During each translation parallel to the longitudinal axis X, the maximum amplitude measured was retained. Thus, during a back and forth along the same line, parallel to the X axis, two amplitude values ​​were extracted, which correspond respectively to the maximum amplitudes measured during the outward and return movements. The two maximum amplitudes extracted were assigned to the Y and Z coordinates at which the translation is carried out. Two successive translations along the X axis were offset by 1 mm along the Y axis. Each scan in the XY plane was carried out according to a constant coordinate along the Z axis.Following each scan in the same XY plane along the Z axis, the target was moved along the Z axis with a spatial step of 6 mm.

[0069] In Figure 4C, there are 7 lobes identified by a brace, which correspond respectively to amplitudes A(tm) measured during a scan in the XY plane at 10 different coordinates along the Z axis: Zb Z2, Z3, Z4, Z5, Z6, Z7, Z8, Z9, Zi0. The successive coordinates, along Z, are spaced 6 mm apart from each other. Each lobe is formed of amplitudes A(îni) exceeding a noise value Anoise and measured along a scan along the X and Y axes.

[0070] In Figure 4C, the ordinate axis corresponds to the measured amplitudes, normalized so that the maximum measured amplitude Amax is close to the value 80. The abscissa axis corresponds to the measurement times.

[0071] Figure 4D is a detail of Figure 4C, representing the lobe corresponding to the coordinate Z4. In Figure 4D, the measured amplitudes A^tn^ are represented, according to measurement instants distributed according to a frequency of 50 Hz, along a round trip parallel to the X axis, along coordinates Yb Y2, Y3, Y4, Y5, Y6, Y7, Y8 Y9 spaced 1 mm from each other on the Y axis. At each coordinate along the Y axis, the two maximum values ​​recorded respectively during the round trip are retained. and return.

[0072] [Fig.4E] is a detail of [Fig.4D], which corresponds to a round trip, along the X axis, at the Y5 coordinate. Two peaks can be distinguished, which correspond to the passage of the target in the most central part of the focal zone 9, in which the amplitude of the detected signal is maximum. The first peak corresponds to the outward journey and the second peak corresponds to the return of the target during the translation parallel to the X axis. As previously indicated, the values ​​of each peak are extracted and are considered as representative of the measurement position corresponding to the Y5, Z4 coordinate. Thus, in this particular embodiment, for each coordinate along the Y axis and the Z axis, two measurement amplitudes are assigned, which correspond respectively to the maximum values ​​of the amplitude detected respectively during the outward translation and the return translation.

[0073] Step 140: Selection of measurement positions.

[0074] During step 140, the measurement positions are selected for which the measured amplitudes A(^„), during the three-dimensional scanning, are included in a predetermined amplitude range AA. For example, the amplitude range AA is set between a first fraction of the maximum amplitude Amax and a second fraction of the maximum amplitude Amax. By fraction, we mean a positive real number less than or equal to 1. The first fraction is strictly greater than the second fraction. For example, the first fraction is equal to 1 and the second fraction is equal to 0.5. The amplitude range AA then corresponds to the amplitudes between the maximum amplitude Amax and 50% of the maximum amplitude Amax. Generally, the first fraction is between 0.8 and 1 and the second fraction is between 0.2 and 0.8.

[0075] The selected measurement positions Pm are then counted, for which the measurement amplitude A(f,„) is included in the amplitude range A A.

[0076] Step 150: Comparison of the number of selected measurement positions Pm with a reference value Nref.

[0077] During this step, the number N of measurement positions Pm selected during step 140 is compared with a reference value Nref.

[0078] The reference value Nref may have been previously established experimentally, by implementing steps 100 to 140, according to the same scanning parameters, using one or more reference probes. Preferably, the reference probe is of identical structure to the probe whose gain is to be adjusted. When the number N of measurement positions Pm selected during step 140 is less than the reference value Nref, that is to say when N < Nref, the gain Gq of the probe is increased.

[0079] When the number N of measurement positions Pri! selected during step 140 is greater than the reference value Nref, i.e. when N > Nref, the gain Go of the probe is reduced.

[0080] Step 160: Reiteration

[0081] After the gain has been increased or decreased, steps 100 to 150 are preferably repeated, taking into account the value of the gain Go updated during the previous iteration.

[0082] When the number N of selected measurement positions Pm corresponds to the reference number Nref, the value of the gain GQ is considered to be correct. The number of selected measurement positions then corresponds to the reference number, possibly considering a predetermined uncertainty, for example N = Nref or N = Nref ± 8. £ is for example equal to 10% of Nref.

[0083] The selections or calculations described in connection with steps 130 to 150 are carried out by the processing unit 32. The term processing unit is to be considered in the broad sense. The processing unit designates the calculation means allowing an implementation of the invention. It can consist of a single microprocessor or of different microprocessors, each microprocessor being dedicated to one or more tasks.

[0084] The processing unit 32 may be connected to a control unit 33, the latter making it possible to control the movements of the target. In this case, the control unit transmits the positions of the target to the processing unit 32.

[0085] After implementing the invention, all the probes are considered to have the same response. The response of one of them can be correlated with a usual method of the LIMCA type or the method described in EPI 194772B1.

[0086] The steps described in connection with Figure 3 were implemented by performing five consecutive scans with the same reference probe. Thus, steps 110 to 120 were repeated by performing the five scans referenced T1, T2, T3, T4 and T5. During each scan, the maximum amplitude Amax was normalized to a value of 55% and the number N of measurement positions for which the measurement amplitude was between the maximum amplitude and half the maximum amplitude was determined. Following the scans, an average of the number of measurement positions N selected during each scan was taken.

[0087] Table 1 shows the results obtained. The last column corresponds to the number of measurement positions N selected during each scan. Scan Tl T2 T3 T4 T5 Average N 30 30 30 29 32 30.2

[0088] The average value of 30.2 was then considered as a reference value. N f 1 ' ref ■

[0089] Another probe, different from the reference probe, was then implemented. For different values ​​of gain Go, 5 scans were carried out, identical to those carried out for the reference probe. The average N of measurement positions for which the measurement amplitude was between the maximum amplitude and half the maximum amplitude was then calculated. The gain Gü of the probe was adjusted so that the number N corresponded to the reference number Nref determined with the reference probe.

[0090] Table 2 shows the results obtained. GB 57.9 dB 57.6 dB 57.4 dB 56.9 dB N 34 33 30 26

[0091] We observe that for the number N to be considered equal to Nref, within a predetermined uncertainty range, the gain Go must be equal to 57.4 dB.

[0092] Adjusting the gain GQ as previously makes it possible to use a correlation curve as shown diagrammatically in Figure 5. The correlation curve is established experimentally with the reference probe. Thus, the ordinate axis corresponds to measured amplitudes Am correlated with known inclusion dimensions. The abscissa axis corresponds to a dimension, for example the diameter.

[0093] When implementing the probe on a liquid metal, the probe is arranged such that the longitudinal axis X, taken into account in steps 120 and 130, corresponds to an axis along which the liquid metal flows.

[0094] In [Fig.5], points are shown, each point corresponding to an experimental measurement. A correlation curve, in dotted lines, obtained by fitting the experimental points, is also drawn.

[0095] The correlation function thus established can be applied to amplitudes from different probes whose gain has been adjusted as previously described, so that the response of each probe is comparable to the response of the reference probe.

[0096] The invention can be applied by implementing ultrasonic probes of the same type as the reference probe, i.e. having the same structure, the same implementation and the same manufacturing method.

Claims

1. Claims Method for adjusting the gain of an ultrasonic probe, the probe comprising: - a measuring transmitter (11) configured to emit an incident ultrasonic wave into the liquid metal; - a receiver (21) configured to detect an ultrasonic wave reflected or diffracted by an inclusion in the liquid metal, following the emission of the incident ultrasonic wave, and to form a detection signal (S(t)) from the detected ultrasonic wave; - a processing unit (32), configured to amplify the detection signal according to said gain (Go); The method comprising the following steps: a) arrangement of the probe, such that the measuring transmitter and the receiver are immersed in a reference medium (6), or arranged facing the reference medium, the reference medium taking the form of a liquid or a gel, the reference medium comprising a target (7) arranged at a measuring position (P1T!), the target being formed of a solid material; b) powering the measuring transmitter (11), so that the measuring transmitter emits an incident ultrasonic wave propagating in the reference medium; c) detection, by the receiver, of a detection signal representative of an ultrasonic wave reflected by the reference medium under the effect of the incident wave; The method being characterized in that it also comprises: d) repeating steps a) to c) during different measurement times (f«), so that at each measurement time, the target (7) is respectively moved to different measurement positions (Pltl) forming a mesh in the reference medium; e) from each signal respectively detected during each step c), determination of a measurement amplitude (A(rm)) for each measurement position (Pmy, f) selection of measuring positions (Pm) for which the measuring amplitude extends within a predetermined amplitude range (AA); g) counting the number of measuring positions (N) selected in step f) and comparing the number of positions counted with a predetermined reference value (Nref), then adjusting the gain, so that: • when the number of measuring positions selected is less than the reference value, the gain is increased; • when the number of measuring positions selected is greater than the reference value, the gain is decreased.

2. Method according to claim 1, in which - following step e), the measured amplitudes are between a minimum amplitude and a maximum amplitude; - the predetermined amplitude range extends between a first fraction of the maximum amplitude and a second fraction of the maximum amplitude, the second fraction of the maximum amplitude being strictly less than the first fraction of the maximum amplitude.

3. The method of claim 2 wherein the first fraction of the maximum amplitude is equal to 1.

4. The method of claim 3, wherein the second fraction of the maximum amplitude is between 0.2 and 0.

8.

5. Method according to any one of the preceding claims, wherein following step g), when the number of selected measurement positions is different from the reference value, steps a) to g) are repeated after adjusting the gain.

6. Method according to any one of the preceding claims, comprising, prior to step g), an implementation of steps a) to f) with a reference probe, so that the number of measurement positions resulting from step f) implemented with the reference probe corresponds to the reference value (Nref) taken into account in step

7. gl- Method according to any one of the preceding claims, in which the target (7) is a ball with a diameter between 1 mm and 10 mm.

8. A method according to any preceding claim, in in which the reference medium (6) is water or comprises water.

9. Method according to any one of the preceding claims, in which - the measurement transmitter is coupled to a first waveguide (13), immersed in the reference medium; - the receiver is coupled to a second waveguide (23), immersed in the reference medium.

10. Method according to any one of the preceding claims, in which the mesh defines different measurement positions distributed along a longitudinal axis (X), a lateral axis (Y), and a transverse axis (Z), the lateral, longitudinal and transverse axes being orthogonal two by two.

11. Method according to claim 10, wherein during step d), the target is translated along the longitudinal axis (X), for different coordinates along the lateral axis and the transverse axis.

12. Method according to claim 11, in which: - each translation along the longitudinal axis, for the same coordinates respectively along the lateral axis and the transverse axis, is carried out in a forward direction and in a return direction; - at each coordinate respectively along the lateral axis and the transverse axis, at least one measurement amplitude is determined, which corresponds to a maximum amplitude measured during the translation in the forward direction and / or in the return direction.

13. Ultrasonic probe, comprising: - a measuring transmitter (11) configured to emit an incident ultrasonic wave into the liquid metal; - a receiver (21) configured to detect an ultrasonic wave reflected or diffracted by the liquid metal, following the emission of the incident ultrasonic wave, and to form a detection signal dependent on the detected ultrasonic wave; - a processing unit (32), configured to amplify the detection signal according to a gain (Go) and to determine a measurement amplitude from the resulting detection signal of the receiver; - the device being characterized in that the processing unit is configured to implement steps e) to g) of a method according to any one of the preceding claims from measurement amplitudes respectively determined when a target, formed of a solid material, is arranged facing the probe, in different measurement positions, in a reference medium.

14. An ultrasonic probe according to claim 13, comprising a control unit (33), configured to control a movement of the target between the different measurement positions, and to transmit said measurement positions to the processing unit (32).

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