Device and method for identifying gaseous contamination

Abstract

The invention relates to a device for detecting and identifying contamination of a gaseous medium by a contaminating gas. The detection and identification device (1) comprises at least one ultrasonic transmitter (10), at least one ultrasonic receiver (20), and a processing unit (30). The processing unit (30) is capable of determining a first and a second attenuation value from a first and a second characteristic signal, respectively, provided by the ultrasonic receiver (20) for a first and a second ultrasonic wave at a first and a second frequency, respectively. The processing unit is configured to identify at least one contaminating gas from the first and second attenuation values. (See Figure 1 for abbreviations.)

Description

Title of the invention: device and method for identifying gaseous contamination Technical field

[0001] The invention relates to the field of detecting gaseous contamination in a gaseous medium, such as the atmosphere of a confined space of a storage location for chemical and / or radioactive products or a fuel tank.

[0002] The invention thus relates more particularly to a device and a method for identifying gaseous contamination. State of the prior art

[0003] As demonstrated by the inventors in their work presented by L. Iglesias et. al as part of the conference "16,h International Workshop on Nanomechanical Sensors" which took place between June 19 and 21, 2019 in Lausanne, Switzerland, it is possible to use ultrasound to monitor the composition of a gaseous medium. Indeed, since the composition of the gaseous medium directly influences the propagation speed of the ultrasonic waves of the latter, it is possible to obtain information on the composition of the gaseous medium from time-of-flight measurements of the ultrasonic waves.

[0004] Thus, the inventors were able to demonstrate that with such time-of-flight measurements, it is possible, when the gaseous medium has a binary composition whose components are known, to determine the respective proportion of the components of the gaseous medium. It would therefore be conceivable, for a relatively simple composition of a gaseous medium to be monitored, to use such measurements to detect contamination of the gaseous medium.

[0005] Nevertheless, in the context of monitoring a gaseous environment, such as the atmosphere of a confined space of a storage location for chemical and / or radioactive products or a fuel tank, the gaseous composition can be relatively complex. Therefore, the use of ultrasound as proposed by the inventors in their work presented in Lausanne in 2019 does not seem suitable due to this complexity for identifying possible contamination (with this method proposed by the inventors, it is difficult to decorrelate the nature of the contaminating gas and its quantity).

[0006] It is also known from the work of A. Petculescu and his co-authors which was published in the scientific journal "Journal of Acoustical Society of America" ​​number 120 volume 4 pages 1779 to 1782 the possibility of identifying a contamination of the gaseous medium from a measurement of attenuation of the ultrasonic waves in this medium. To do this, A. Petculescu and his co-authors teach that it would be possible to determine the binary composition of a gas on the basis of a measurement of the variation in attenuation as a function of the gas pressure in a measuring chamber (more precisely of a normalized attenuation (noted aX) as a function of the ultrasonic Fonde frequency on the pressure (f / p)). Indeed, when measuring the variation in attenuation, the variation in attenuation presents an absorption peak whose amplitude and position would be characteristic of the gas composition and therefore of the contaminant. From this absorption peak, it therefore seems possible to identify the contaminant and the quantity introduced.

[0007] It will be noted that in the context of their work, A. Petculescu and his co-authors demonstrated, by Figures 3 and 4, that this absorption peak did not show any dependence on the frequency of the ultrasonic wave as such and, by Figure 5, that the identification of the contaminating gas can be obtained on the basis of measurement at only one frequency of the ultrasonic wave.

[0008] Thus, if the device proposed by A. Petculescu and his co-authors seems to allow the detection and identification of a contaminating gas, this identification requires a large number of measurements and a system for pressurizing the measuring chamber. The device taught by A. Petculescu and his co-authors is therefore relatively complex to implement and does not allow, due to this need to pressurize the measuring chamber at each identification attempt, continuous monitoring due to the measurement time.

[0009] As a result, there are no devices for detecting and identifying contamination in a gaseous medium that are truly suitable for enabling the identification of a contaminant in the context of a relatively complex composition, with monitoring that can be implemented continuously. Statement of the invention

[0010] The invention aims to remedy this drawback and thus aims to provide a device for detecting and identifying the contamination of a gaseous medium which allows the detection and identification of contamination in a gaseous medium having a relatively complex composition, said identification being able to be carried out continuously.

[0011] The invention relates to this end to a device for detecting and identifying contamination of a gaseous medium by at least one contaminating gas, the detection and identification device comprising: - at least one ultrasonic transmitter for emitting at least a first ultrasonic wave at a first frequency and at least a second ultrasonic wave at a second frequency, the first and second frequencies being distinct from each other the other, - at least one ultrasonic receiver for providing at least a first and a second signal characteristic of the first ultrasonic wave and the second ultrasonic wave respectively, the ultrasonic transmitter and the ultrasonic receiver being arranged so as to define a measurement space and so that an ultrasonic wave emitted by the ultrasonic transmitter is received by the ultrasonic receiver after passing through the measurement space, - a processing unit capable of determining a first and a second attenuation value from respectively the first and second characteristic signals supplied by the ultrasonic receiver, the processing unit being configured to calculate at least one characteristic value of the attenuation evolution between the first and the second attenuation value, and to identify the contaminating gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and the second attenuation values.

[0012] Indeed, by requiring the use of only two attenuation measurements, one at the first frequency, the other at the second frequency, the identification of the contaminating gas is simpler than the method of the prior art, even with a complex composition of the gaseous medium. It will be noted, moreover, that since these two measurements can be carried out substantially simultaneously, such a device is suitable for allowing continuous monitoring of the gaseous medium.

[0013] The processing unit may further be configured to determine, once the contaminating gas has been identified, a quantity of said gas present in the gaseous medium from the first and / or second attenuation value.

[0014] Thus, since the nature and quantity of the contaminating gas are known, it is easy to identify the risks linked to such contamination.

[0015] The processing unit may further be configured to determine, from the identity of the identified contaminating gas, a suitable frequency from at least the first and second frequencies, the determination of the quantity of said contaminating gas being calculated from the attenuation value corresponding to said suitable frequency.

[0016] In this way it is possible to obtain a particularly precise estimate of the quantity of contaminating gas.

[0017] The at least one ultrasonic transmitter may be configured to emit at least one third ultrasonic wave at a third frequency distinct from the first and second frequencies, the at least one ultrasonic receiver being configured to provide at least one third signal characteristic of the third ultrasonic wave, and in which the matched frequency is one of at least the first frequency at the third ultrasonic frequency.

[0018] In this way, it is possible to obtain a particularly precise estimate of the quantity of contaminating gas even in the case where the detection device is adapted to detect a large number of contaminating gases.

[0019] The first attenuation value can be determined from a ratio between a characteristic amplitude value of the first wave and a characteristic amplitude value previously determined in the absence of contaminating gas in the measurement space for at least one ultrasonic wave having the first frequency, the second attenuation value being determined from a ratio between a characteristic amplitude value of the second wave and a characteristic amplitude value previously determined in the absence of contaminating gas in the measurement space for at least one ultrasonic wave having the second frequency.

[0020] The use of such ratios makes it possible to avoid having to take into account the influence of the different measuring elements of the device.

[0021] Each of the first and second attenuation values ​​may be a frequency-normalized attenuation value, the characteristic value of the evolution being a difference in normalized attenuation values ​​between the first and second attenuation values.

[0022] Such a standardized attenuation value is particularly suitable for highlighting the specificities of each of the contaminating gases.

[0023] To identify the contaminant gas based on the characteristic value of the attenuation evolution and at least one of the first and second attenuation values, the processing unit may be configured to determine a sign of the characteristic value of the evolution and a sign of at least one of the first and second attenuation values.

[0024] The processing unit may be configured to identify a predetermined number of contaminating gases, this predetermined number of contaminating gases preferably comprising hydrogen, methane and carbon dioxide.

[0025] In this way, the detection and identification device can be perfectly adapted to the risks of contamination likely to appear in gaseous environments whatever this gaseous environment.

[0026] At least one of the ultrasonic transmitter and the ultrasonic receiver may include at least one capacitive micromachined transducer (cMUT).

[0027] Such micro-machined capacitive transducers are particularly advantageous in the context of the invention, in particular when they comply with the teaching of document FR 2962926, since they provide access to a large operating frequency range, both for the emission and reception of ultrasonic waves, with particularly optimized integration. Thus, the industrialization of a device according to the invention is made particularly easy.

[0028] The invention further relates to a method for detecting and identifying contamination of a gaseous medium by a contaminating gas using a detection and identification device, the detection and identification device comprising: - at least one ultrasound transmitter for emitting at least one first ultrasound wave at a first frequency and at least one second ultrasound wave at a second frequency, the first and second frequencies being distinct from each other, - at least one ultrasonic receiver for providing at least a first and a second signal characteristic of the first ultrasonic wave and the second ultrasonic wave respectively, the ultrasonic transmitter and the ultrasonic receiver being arranged so as to define a measurement space and so that an ultrasonic wave emitted by the ultrasonic transmitter is received by the ultrasonic receiver after passing through the measurement space, - a processing unit (30) capable of determining a first and a second attenuation value from respectively the first and the second characteristic signal supplied by the ultrasonic receiver, The method comprising the following steps: - emission of the first and second ultrasonic waves by the ultrasonic transmitter, - supply, by the ultrasonic receiver upon reception of the first and second ultrasonic waves, of the first and second signals characteristic of the first ultrasonic wave and the second ultrasonic wave respectively, - determination by the processing unit of a first and a second attenuation value from respectively the first and second characteristic signals provided by the ultrasonic receiver, - calculation by the processing unit of at least one characteristic value of the attenuation evolution between the first and the second attenuation value, and to identify the contaminating gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and the second attenuation values, - identification by the processing unit of at least one contaminating gas, said identification being carried out on the basis of the characteristic value of the attenuation evolution and at least one of the first and second attenuation values.

[0029] Such a method, which can be implemented with a device according to the invention, incorporates the advantages thereof.

[0030] A step of: - determination by the processing unit and from the first and / or second attenuation value of a quantity of said identified contaminating gas. Brief description of the drawings

[0031] The present invention will be better understood on reading the description of exemplary embodiments, given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0032] [fig.l] Figure 1 illustrates a hydrogen detection device according to the invention.

[0033] [fig.2] Figure 2 graphically illustrates the evolution of the variation of the coefficient attenuation AaGaz of an ultrasonic wave as a function of the ultrasonic frequency obtained for a hydrogen detection device according to the invention, this for hydrogen, carbon dioxide and methane.

[0034] [fig.3] Figure 3 graphically illustrates the evolution of the variation of the coefficient attenuation AaGaz of an ultrasonic wave this for a gaseous medium consisting of nitrogen into which hydrogen has been intermittently introduced.

[0035] [fig.4] Figure 4 graphically illustrates the evolution of the variation of the coefficient attenuation AaGaz of an ultrasonic wave this for a gaseous medium consisting of nitrogen into which carbon dioxide has been intermittently introduced.

[0036] [fig.5] Figure 5 graphically illustrates the evolution of the variation of the coefficient attenuation AaGaz of an ultrasonic wave this for a gaseous medium consisting of nitrogen into which methane has been intermittently introduced.

[0037] [fig.6] Figure 6 graphically illustrates the evolution of the variation of the coefficient attenuation illustrated in Figure 2 after frequency normalization, said variation of the normalized attenuation coefficient being noted Aan.

[0038] [fig.7] Figure 7 graphically illustrates the evolution of the variation of the coefficient attenuation AaGaz of an ultrasonic wave for a gaseous medium consisting of nitrogen into which hydrogen has been intermittently introduced, the detection device comprising for these measurements ultrasonic transducers, for the ultrasonic transmitter and receiver, the transduction surface of which is, for the first and second curves, 27 pm by 37 pm, and, for the third curve, 27 pm by 27 pm.

[0039] Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the transition from one figure to another.

[0040] The different parts represented in the figures are not necessarily on a uniform scale, in order to make the figures more readable.

[0041] The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other. Description of the embodiments

[0042] Figure 1 illustrates a device 1 for detecting and identifying contamination of a gaseous medium by a contaminating gas according to the invention, such a device detection and identification system being adapted to provide detection and identification of contamination based on an attenuation measurement of ultrasonic waves 45 as they pass through a space to be monitored 40.

[0043] It will be noted that in the context of this document and this first embodiment, the inventors were interested in the contaminating gases which are most likely to contaminate a storage location for chemical and / or radioactive products, namely hydrogen, methane and carbon dioxide. Of course, on the basis of routine calibration operations, those skilled in the art are able to adapt the present teaching to other contaminating gases without departing from the scope of the invention.

[0044] The detection and identification device according to the invention

[0045] Such a hydrogen detection device 1 comprises: - at least one ultrasound transmitter 10 capable of emitting ultrasound waves 45, - at least one ultrasonic receiver 20 capable of providing a signal characteristic of an ultrasonic wave 45, the ultrasonic transmitter 10 and the ultrasonic receiver 20 being arranged so as to define the space to be monitored 40 and so that an ultrasonic wave 45 emitted by the ultrasonic transmitter 10 is received by the ultrasonic receiver 20 after passing through the measurement space 40, - a processing unit 30 capable of determining, from at least one characteristic signal provided by the ultrasound receiver 20 upon reception of an ultrasound wave 45 emitted by the ultrasound transmitter, an attenuation value.

[0046] When setting up the detection device 1 in the context of monitoring a gaseous medium, the detection of the contamination of the gaseous medium can be carried out by placing the detection device 1 with its measuring space 40 in fluid communication with the gaseous medium. In this way, the measuring space and the gaseous medium are able to share the same atmosphere with an identical gaseous composition.

[0047] More precisely and as illustrated in FIG. 1, the ultrasound transmitter 10 according to this first embodiment comprises: - a plurality of first ultrasonic transducers 11 capable of emitting ultrasound, - a first support 12 on which the plurality of ultrasonic transducers 11 are arranged and, - a first amplification unit 15 configured to generate, from a control signal of the processing unit 30, a supply voltage for the plurality of ultrasonic transducers 11.

[0048] According to an advantageous possibility of the invention, the first ultrasonic transducers 11 are cMUT transducers, for micro-machined capacitive transducers, as described in document FR 2962926. In accordance with the teaching of this document, the first cMUT transducers according to this embodiment of the invention each comprise a membrane and have a resonance frequency of this membrane. The resonance frequency of the membrane is chosen to be higher than the frequency of the ultrasonic waves to be generated. This resonance frequency can thus be 125% to 200% of the maximum frequency of the ultrasonic waves to be generated.

[0049] Thus, for example, for a maximum frequency of the ultrasonic waves to be generated equal to 3 MHz, the ultrasonic transducers according to this first embodiment can have a resonance frequency which is between 3.75 MHz and 6 MHz.

[0050] According to the invention, the ultrasound transmitter 10 is configured to emit ultrasonic waves at a first and a second frequency distinct from each other with a respective or identical given amplitude Ao.

[0051] Such first ultrasonic transducers 11 are particularly advantageous in the present embodiment since they allow the generation of ultrasonic waves over a relatively large frequency range.

[0052] Of course, such a configuration is provided only by way of example and other types of ultrasonic transducers can be used without departing from the scope of the invention. It will be noted in particular that it is possible, as a variant and without departing from the scope of the invention, for the ultrasonic transmitter 10 to comprise at least two types of ultrasonic transducers, a first type adapted to the first frequency and a second type adapted to the second frequency.

[0053] The first ultrasonic transducers 11 are arranged on the first support 12 so as to define a first wall of the space to be monitored 40.

[0054] As shown in Figure 1, the ultrasonic receiver 20 comprises: - a plurality of second ultrasonic transducers 21 capable of receiving ultrasonic waves and of generating from said ultrasonic waves, a measurement signal corresponding to the ultrasonic waves received, - a second support 22 on which the plurality of ultrasonic transducers 21 are arranged and, - a continuous power supply 23, capable of supplying the second ultrasonic transducers 21 with a continuous voltage, - a second amplification unit 25 configured to amplify the measurement signal provided by the plurality of second ultrasonic transducers 21.

[0055] According to one possibility of the invention, the second ultrasonic transducers 21 may be of a type identical to the first ultrasonic transducers 11. Thus, in the present embodiment, and as shown in FIG. 1, the second ultrasonic transducers 11 are cMUTs, for micro-machined capacitive transducers, in accordance with the teaching of document FR 2962926.

[0056] Of course, as a variant and without departing from the scope of the invention, the second ultrasonic transducers 21 may be of another type. In the same way as for the ultrasonic transmitter 10, it is conceivable as a variant and without departing from the scope of the invention that the ultrasonic receiver 20 comprises at least two types of ultrasonic transducers 21, a first type adapted to the first frequency and a second type adapted to the second frequency.

[0057] The second ultrasonic transducers 21 are arranged on the second support 22 opposite the first ultrasonic transducers 11 so that the second support 22 defines a second wall of the space to be monitored 40. Thus the first and second supports 12, 22 together define, by the space that they delimit between them, the space to be monitored 40.

[0058] Of course, such an arrangement of the ultrasonic transmitter 10 and the ultrasonic receiver 20 is provided only as an example and is in no way limiting. Other arrangements are perfectly conceivable as long as the ultrasonic transmitter and the ultrasonic receiver 20 are arranged to define the measurement space 40 and as long as an ultrasonic wave emitted by the ultrasonic transmitter is received by the ultrasonic receiver after passing through the measurement space 40.

[0059] The second ultrasonic transducers 21 are supplied with voltage by the DC power supply 23 and the measurement signal generated by the second transducers upon receipt of an ultrasonic wave is amplified by the second amplification unit 25. This measurement signal thus amplified forms a signal characteristic of the ultrasonic wave emitted by the ultrasonic transmitter 10.

[0060] The measurement signal is supplied by the second amplifier 25 to the processing unit 30.

[0061] The processing unit 30 is more precisely capable of determining a first and a second attenuation value from respectively the first and the second characteristic signal provided by the ultrasonic receiver 20.

[0062] The processing unit is also configured to calculate at least one characteristic value of the attenuation evolution between the first and the second attenuation value, and to identify the contaminating gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and the second attenuation values.

[0063] In order to better understand the principle of identification of the contaminating gas implemented by the processing unit, the measurement principle developed by the inventors within the framework of the invention is explained below.

[0064] Measuring principle implemented within the framework of the invention

[0065] Figure 1 illustrates the principle of such identification. The processing unit 30 providing the control signal to the first amplification unit 15 which in turn supplies the first ultrasonic transducers 11, an ultrasonic wave 45 which is emitted will have an amplitude Ao corresponding to the following equation:

[0066] [Math.l] Ao = 5x HAmp} x HEmet

[0067] With S the amplitude of the control signal, HAmpi the transfer function of the first amplification unit 15, HEmet the transfer function of the first ultrasonic transducers 11.

[0068] The ultrasonic wave 45 during its transit in the measurement space 40 will present an attenuation H Gaz directly proportional to the distance d traveled and dependent on the composition of the gas found in the measurement space 40. Such an attenuation H Gaz can be calculated with the following equation:

[0069] [Math.2] H ^A ^Ga^ Gas A {} 6

[0070] With aGaz a gas attenuation coefficient corresponding to the composition of the gas located in the measurement space 40 and A the amplitude of the ultrasonic wave received by the second ultrasonic transducers 21.

[0071] Thus, the amplitude A of the ultrasonic wave received by the second ultrasonic transducers will therefore be equal to:

[0072] [Math.3] H AmpA x H Emet x

[0073] Concerning the detector, the characteristic signal supplied by the ultrasonic receiver to the processing unit will be dependent both on the transfer function Hrecept of the second ultrasonic transducers 21 and on the transfer function HAmp2 of the second amplification unit. The characteristic signal SCaract therefore corresponds to the following equation:

[0074] [Math.4] s c , r =SxH, . x H E t xed aGazd xH xH. = S x Catact Ampl ™and recept Amp2 1

[0075] In other words, from the characteristic signal SGaract and a given control signal S, and knowing all the transfer functions of each of the elements 11, 15, 21, 25 of the detection device 1, it is possible to determine the attenuation H GiZ=e~aGaA of the ultrasonic wave 45 during its transit in the measurement space 40.

[0076] [Math.5] „aG«zd = _________________________ H Amp 1

[0077] Nevertheless, according to one possibility of the invention, in order to avoid the need to characterize the transfer function of each of the elements 11, 15, 21, 25 of the detection device 1, it is possible to use a reference measurement, S Ref beforehand with a reference gas, such as the atmosphere of the gaseous medium free from gaseous contamination. According to this possibility, the variation of the attenuation coefficient AaGaz =aGaz - aRef between the gas and the reference gas can be obtained with the following formula:

[0078] [Math.6] / \ / 5 \ n — a zz — 1 n I Early | — — 1 n II aGas (lRef cl111 \SCa,.acJ

[0079] SRef being the characteristic signal recovered by the processing unit 30 during the prior reference measurement, and is the reference measurement.

[0080] Thus, with such a detection device 1 and by using a prior reference measurement, it is easy to determine a variation of the attenuation coefficient AaGaz=aGaz - aRef as an attenuation value.

[0081] Based on this principle and within the scope of the invention, the inventors have demonstrated that the attenuation measured in the presence of a contaminating gas exhibits a variation with the ultrasound frequencies which is a function of the contaminating gas. Thus, if we take the example of hydrogen, we observe that for ultrasonic wave frequencies greater than or equal to 2 MHz, or even greater than or equal to 2.5 MHz, the variation in the attenuation coefficient AaGaz measured is mainly related to the hydrogen concentration, the inventors having identified that this variation was low for carbon dioxide and methane. To obtain such a result, as illustrated in FIG. 2, the inventors studied the evolution of the variation in the attenuation coefficient AaGaz for different gases likely to contaminate the measurement space as a function of the frequency of the ultrasonic wave 45.

[0082] For this demonstration, the inventors used the following configuration: - an AGILENT™ E5061B network analyzer as a first amplifier 15 for generating an electrical excitation of 800 mV peak-to-peak which is amplified with a gain of 100 to reach 80 V peak-to-peak and to which a DC component of 40 V is added, - a DC power supply 23 configured to apply a DC voltage of 70 V to the second ultrasonic transducers 21, - a second amplifier 25 supplied by a COOKNELL™ charge amplifier, the network analyzer making it possible to measure the characteristic signal supplied by the second amplifier 25.

[0083] In this demonstrator used by the inventors to illustrate the principle of the invention, the AGILENT™ E5061B network analyzer provides part of the functions of the processing unit 30.

[0084] Thus, Figure 2 shows the evolution of the variation AaGaz for a nitrogen gas into which 1% of hydrogen (curve 101), 1% of carbon dioxide (curve 102) and 1% of methane (curve 103) have been respectively introduced and, the reference measurement having been carried out for an uncontaminated nitrogen gas, i.e. substantially pure nitrogen. For a 2 MHz ultrasonic wave, the variation of the attenuation coefficient Aa Gas is of the order of 7 m1 for hydrogen, 101, while it is lower, in absolute value, than 3 m 1 for carbon dioxide, 102, and methane, 103. For a 2.5 MHz ultrasonic wave, the variation of the attenuation coefficient Aa Gas is of the order of 10 m' for hydrogen, 101, while this same variation remains lower than 3 m ', in absolute value, for carbon dioxide, 102, and methane, 103.We can see in Figure 2 that this selectivity to hydrogen increases with frequency, particularly for frequencies above 3 MHz, or even 3.5 MHz, or even 4 MHz.

[0085] It should be noted that, unless otherwise specified, all of the gas proportion values ​​provided above and in the rest of this document are molar proportions, such a molar gas proportion corresponding directly to the same volume proportion value.

[0086] During this same study, at the origin of the invention, the inventors also demonstrated that, as illustrated in Figure 3, the variation of the attenuation coefficient AaGaz varies linearly with the presence of hydrogen, regardless of the frequency of the ultrasonic wave. To do this, the inventors introduced into an atmosphere consisting of nitrogen in turn 4% hydrogen, 3% hydrogen, 2% hydrogen, 1% hydrogen, and once again 4%, this over a given time range, the nitrogen atmosphere of the measurement space 40 being reestablished between two introductions. During these introductions, the evolution of the variation of the attenuation coefficient AaGaz was determined for three ultrasonic wave frequencies, 2 MHz (curve 111), 3.6 MHz (curve 112) and 4.1 MHz (curve 113) throughout these hydrogen introductions.

[0087] It can thus be seen that the variation of the attenuation coefficient AaGaz evolves linearly with the quantity of hydrogen introduced, regardless of the ultrasonic wave frequency selected. Indeed, from these measurements, the inventors measured a sensitivity of 0.062 cm '.% 1 at 2 MHz, a sensitivity of 0.175 cm '.% 1 at 3.6 MHz and a sensitivity of 0.211 cm '.% 1 at 4.1 MHz.

[0088] Furthermore, as shown in Figures 4 and 5, the inventors have also discovered that if the variation of the attenuation coefficient AaGaz changes preponderantly with the proportion of hydrogen in the measurement space 40 for the ultrasonic wave frequencies above 2 MHz, the evolution of the variation of this attenuation coefficient AaGaz with the frequency of the ultrasonic wave is characteristic of the contaminating gas added in the measurement space 40.

[0089] This can thus be seen in Figure 4, which shows the result of measurements during which the inventors introduced into an atmosphere consisting of nitrogen in turn 4% carbon dioxide, 3% carbon dioxide, 2% carbon dioxide, 1% carbon dioxide, and once again 4% carbon dioxide over a given time range, the nitrogen atmosphere of the measurement space 40 being re-established between two introductions. During these introductions, the evolution of the variation of the attenuation coefficient AaGaz was determined for three ultrasonic wave frequencies, 2 MHz (curve 121), 3.6 MHz (curve 122) and 4.1 MHz (curve 123) throughout these introductions of carbon dioxide.

[0090] For carbon dioxide, the inventors have thus identified that the variation of the attenuation coefficient AaGaz evolves linearly with the quantity of carbon dioxide found in the measurement space 40, this with a positive directing coefficient, and that, as for hydrogen, this same variation of the attenuation coefficient AaGaz increases, when the frequency of the ultrasonic wave 45 increases.

[0091] Concerning methane, as shown in Figure 5 which illustrates the result of measurements during which the inventors introduced into an atmosphere consisting of nitrogen in turn 4% methane, 3% methane, 2% methane, 1% methane, and once again 4% methane over a given time range, the nitrogen atmosphere of the measurement space 40 being re-established between two introductions. During these introductions, the evolution of the variation of the attenuation coefficient AaGaz was once again determined for three ultrasonic wave frequencies, 2 MHz (curve 131), 3.6 MHz (curve 132) and 4.1 MHz (curve 133) throughout these introductions of methane.

[0092] For methane, the variation of the attenuation coefficient AaGaz also varies linearly with the quantity of methane, the leading coefficient being negative unlike hydrogen and carbon dioxide (the attenuation decreases when more methane is introduced), and that, as for carbon dioxide, this same variation of the attenuation coefficient AaGaz increases, in absolute value, when the frequency of the ultrasonic wave 45 increases.

[0093] The result of all these measurements is summarized in the following table which presents the sensitivity of the variation of the attenuation coefficient with respect to the proportion of hydrogen, carbon dioxide and methane, this for the three frequencies of ultrasonic waves studied. [Tables 1] h2 in cm '.%1 co2 in cm '.%1 ch4 in cm '.%1 Fl=2 MHz 0.062 0.0195 -0.0073 F2=3.6MHz 0.175 0.024 -0.015 F3=4.l MHz 0.211 0.0335 -0.0195

[0095] From this principle, the processing unit 30 is therefore able to determine, from the characteristic signal SCaract, a first and a second attenuation value for respectively the first and second ultrasonic waves, such as for example the variation of the attenuation coefficient AaGaz or the variation of the attenuation coefficient AaGaz multiplied by d, and to determine from said first and second attenuation values ​​characteristic values ​​of a contamination of the gaseous medium by at least one contaminating gas.

[0096] Such an evolution of the variation of the attenuation coefficient AaGaz with the frequency of the ultrasonic wave and with the quantity of gas which is therefore characteristic of the contaminating gas, can therefore be used for the identification of the contaminating gas at the origin of contamination of the gaseous medium. Identification of the nature of the contamination

[0097] Thus, from the results presented above in the section “measuring principle implemented within the framework of the invention”, the inventors have developed a method for identifying the contaminating gas based on the fact that the evolution of the variation of this attenuation coefficient AaGaz with the frequency of the ultrasonic wave is characteristic of the contaminating gas.

[0098] In the context of this identification of a contamination, the inventors have retained the variation of the frequency-normalized attenuation Aan as an attenuation value, with respect to the “non-frequency-normalized” attenuation variation, which makes it possible to better highlight the specificities of each of the gases considered (hydrogen, methane and carbon dioxide). This attenuation value, called frequency-normalized Aan, is equal to the value of the variation of the attenuation coefficient AaGaz divided by the frequency f. Of course, the use of the frequency-normalized attenuation variation Aan as an attenuation value in the context of the invention is provided only as an example and other attenuation values, such as the attenuation variation AaGaz, which is therefore “non-frequency-normalized”, can of course also be used in the context of an identification method according to the invention.

[0099] Indeed, Figure 6, which illustrates the evolution of the variation of the normalized attenuation coefficient in frequency Aan as a function of the frequency (curves 141, 142 and 143 corresponding to an introduction of respectively 1% of hydrogen, 4% of carbon dioxide and 4% of methane), shows that, with the variation of the normalized attenuation coefficient in frequency Aan as attenuation value, we obtain for a first and a second frequency at 2 MHz and 3.6 MHz: - for hydrogen, curve 141 shows an attenuation value, the normalized attenuation variation in frequency Aan, presenting a positive sign (both at 2 MHz and at 3.6 MHz) and a positive variation of this same attenuation value when passing from the first to the second frequency, - for carbon dioxide, curve 142 shows an attenuation value, the normalized attenuation variation in frequency Aan, presenting a positive sign (both at 2 MHz and at 3.6 MHz) and a negative variation of this same attenuation value when passing from the first to the second frequency, - for methane, curve 143 shows an attenuation value, the normalized attenuation variation in frequency Aan, presenting a negative sign (both at 2 MHz and at 3.6 MHz) and a negative variation of this same attenuation value when passing from the first to the second frequency.

[0100] Thus, in the event of observation of a variation in the attenuation of an ultrasonic wave in the measuring chamber and therefore of a potential contamination of the gaseous medium by a contaminating gas, from two attenuation parameters alone, the sign of the variation in attenuation normalized in frequency Aan (both at the first frequency and at the second frequency) and the sign of the evolution of the variation in attenuation normalized in frequency Aan between the first and second frequencies, it is easy to determine the nature of the contaminating gas present in the gaseous medium.

[0101] According to this possibility, the processing unit 30 can be configured to authorize the implementation of an identification method comprising the following steps: - emission by the ultrasonic transmitter 10 of the first and second ultrasonic waves at the first and second frequencies respectively, - measurement of a first and a second characteristic signal by the ultrasonic receiver 20 of the first and second ultrasonic waves respectively, - determination of a first and a second attenuation value, here the normalized attenuation variations at the first and second frequencies Aan(fl) and Aan(f2), respectively from the first and second measured characteristic signals respectively, - calculation of at least one characteristic value of the attenuation evolution between the first and second attenuation values, here a difference between the normalized attenuation variations at the first and second frequencies, - identification of the nature of the possible contaminating gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and second attenuation values ​​(Aan(f2)-Aan(fl)), this for example from attenuation parameters, - determination of a characteristic value of the presence of the possible identified gas.

[0102] In order to allow the identification of the nature of the possible contaminating gas, the processing unit 30 can thus be configured to determine at least two attenuation parameters, including: - a sign of the attenuation value determined for one of the first and second frequencies, here the sign of the normalized attenuation variation in frequency Aan either at the first frequency or at the second frequency Sign(Aan(blur f2), - a sign of the difference between the attenuation value determined for the first frequency and the normalized attenuation value determined for the second frequency, said difference corresponding to a value characteristic of the attenuation evolution between the first and second attenuation values ​​which are here the normalized attenuation variations Aan, Sign(Aan(f2) - Aan(fl)).

[0103] Of course, these two parameters are provided only as examples, other attenuation parameters can be envisaged without departing from the scope of the invention, knowing that these parameters must, according to the principle of the invention, be determined from the characteristic value of the attenuation evolution and at least one of the first and second attenuation values. It will be noted in particular, in the case where a larger number of contaminating gases are of interest, that it is perfectly possible to use a slope value at the first frequency or, when a leak is proven, a variation ratio between the attenuation variation normalized in frequency at the first frequency Aan(fl) and the attenuation variation normalized in frequency at the second frequency Aan(f2).

[0104] Once a contaminating gas has been identified, the processing unit 30 may further be configured to determine a characteristic value of the presence of the identified contaminating gas. Such a characteristic value of the presence of the contaminating gas may be determined from at least one of the attenuation value determined for the first frequency and the attenuation value determined for the second frequency. Advantageously, the attenuation value used to determine the characteristic value of the presence of the contaminating gas may be the attenuation value among the attenuation value determined for the first and second frequencies which is expected to have the greatest sensitivity for the identified contaminating gas, the corresponding frequency is called the adapted frequency.It will be noted that in the present embodiment, an attenuation value at a third frequency equal to 4.1 MHz has also been determined, the selection being made. thus between the attenuation values ​​determined for the first to the third frequency.

[0105] Thus, according to this variant of the invention, the ultrasound transmitter 10 can be configured to emit at least one third ultrasound wave at a third frequency distinct from the first and second frequencies. The ultrasound receiver 20 is configured to provide at least one third signal characteristic of the third ultrasound wave respectively, and the adapted frequency is one of at least the first to the third ultrasound frequency.

[0106] In order to illustrate such a possibility, the inventors implemented the operating principle of such a method for monitoring a measurement space for contamination with hydrogen, carbon dioxide and methane from the measurements presented in the context of figures 3, 4 and 5. Thus, from these measurements, it was possible to show the result of such a method in the context of respective introductions of 1%, 2%, 3% and 4% of hydrogen, carbon dioxide and methane into the measurement space 40 which has a nitrogen atmosphere.

[0107] For each quantity of contaminant gas, based on the results illustrated in Figures 3, 4 and 5, the attenuation values ​​of the first ultrasonic wave are those corresponding to ultrasonic waves whose frequency is equal to 2 MHz, and those of the second ultrasonic wave are those corresponding to ultrasonic waves whose frequency is equal to 3.6 MHz. The first frequency is thus 2 MHz and the second frequency is 3.6 MHz.

[0108] From these attenuation values, the inventors were able to determine for each quantity of contaminating gas: - a first sign of the attenuation value at the first frequency (in other words, whether the normalized attenuation variation in frequency Aan(fl) at the first frequency increases or decreases when the contaminating gas is introduced), and - a second sign of the difference Aan(f2)- Aan(fl) between the attenuation value (here the variation of the attenuation coefficient normalized in frequency Aan) determined for the second frequency and for the first frequency.

[0109] As previously indicated, the expected signs for each of the three contaminating gases were determined from Figure 6, namely: - a first and second positive sign for hydrogen, - a first positive sign and a second negative sign for carbon dioxide, - a first and second negative sign for methane.

[0110] In the same way, on the basis of Table 1, the frequency suitable for determining the characteristic value of the presence of said contaminating gas, here the proportion of gas in the measurement space 40, has been defined for each of the contaminating gases. Thus for hydrogen, it is the third frequency which is 4.1 MHz and for methane, it is the second frequency 3.6 MHz and for carbon dioxide it is the first frequency which is 2 MHz.

[0111] It will be noted that within the framework of the invention, it would have been perfectly conceivable to use a frequency lower than 2 MHz in order to promote sensitivity to carbon dioxide and methane.

[0112] [T ableaux2] Mixture introduced Measure Determination by 30 Gas Quantity (%) Sign of Au n (fl) Sign of Au n (f2)-Aan(fl) adapted frequency MHz Gas identified Estimated quantity (%) h2 1 + + 4.1 h2 0.98 2 + + 4.1 1.99 3 + + 4.1 2.98 4 + + 4.1 4.04 CO2 1 + - 2 CO2 1.18 2 + - 2 1.94 3 + - 2 3.15 4 + - 2 3.88 CH 4 1 - - 3.6 CH 4 1.02 2 - - 3.6 1.79 3 - - 3.6 3.24 4 - - 3.6 3.93

[0113] It can be seen that by applying the method according to this possibility compatible with the invention, each of the contaminating gases has been correctly identified and the proportions determined are close to the expected values ​​showing the correct functioning of the method.

[0114] Of course, such an implementation of the identification method is provided only as an example of this possibility compatible with the invention and is therefore in no way limiting. Thus, it is conceivable, without departing from the scope of the invention, to use more than two ultrasonic wave frequencies in order to determine the attenuation parameters making it possible to discriminate the nature of the contaminating gas, or to use other types of variations than those described above (in particular using an attenuation value or attenuation difference (or even difference of attenuation variation) as such rather than signs as used in Table 2).

[0115] It will also be noted that it is perfectly conceivable, on the basis of the present teaching and using algorithms of the deep learning type (better known by its English name “deep learning”), to be able to identify a significant number of contaminating gases likely to contaminate, and even simultaneous contaminations by several contaminating gases.

[0116] Furthermore, if the present document focuses on the identification of a contaminating gas in a gaseous medium to be monitored and on the determination of the quantity of said gas found in this same gaseous medium, in the context of the practical implementation of such a device for detecting and identifying contamination, the processing unit 30 may be configured to detect such contamination or a suspicion of contamination from the detection of a variation in attenuation of at least one ultrasonic wave, such as the first and the second ultrasonic wave. According to this possibility, some, or all, of the steps of identifying the contaminating gas may be implemented only in the case of the detection of such contamination or a suspicion of contamination of the gaseous medium to be monitored (the implementation of these steps not being necessary in the case where there is no contamination).Similarly, some of the steps in detecting contamination or suspected contamination may be common to that of identifying the contaminating gas causing this contamination (in particular those concerning the emission of the first and second ultrasonic waves and the measurement of the first and second characteristic signals).

[0117] As shown above, the measurement principle discovered by the inventors based on the variation of the attenuation of the ultrasonic waves with the frequency of the ultrasonic wave and as a function of the composition of the atmosphere located in the measurement space 40 is particularly reliable. In order to demonstrate the reliability provided by the invention and to show the reproducibility of such an attenuation value, in accordance with what is shown in Figure 7, the inventors reproduced a measurement of attenuation variation AaGaz in the context of an introduction of hydrogen in accordance with the measurement shown in Figure 3 a first time with an ultrasound emitter having a surface area of ​​27 pm by 37 pm, as shown in curve 151, with an ultrasound emitter having a surface area of ​​27 pm by 27 pm, curve 152, and a second time with an ultrasound emitter having a surface area of ​​27 pm by 27 pm, curve 153.It can be seen that these curves overlap and therefore show the reliability of this measurement whether within the framework of the invention or the possibility compatible with the invention. Such reliability is perfectly compatible with the field of securing buildings and workers in. which the invention is registered.

[0118] It will further be noted that in the present embodiment, the ultrasound transmitter 10 and the ultrasound receiver 20 have a configuration in which they are opposite each other in order to define the measurement space 40. Of course, other configurations are conceivable without departing from the scope of the invention, as long as in these configurations, the arrangement of the ultrasound transmitter 10 and the ultrasound receiver 20 makes it possible to define the measurement space 40. It will be noted in particular that it is conceivable to use one or more walls capable of reflecting the ultrasound waves in order to use other configurations.

[0119] Thus, according to a variant of the invention and the possibility compatible with the invention, the ultrasound transmitter 10 and the ultrasound receiver 20 can use the same ultrasound transducer(s) in combination with a wall capable of reflecting ultrasound, the ultrasound transducers making it possible, within the framework of the ultrasound transmitter 10, to emit the ultrasound wave(s) 45 in the form of wave trains, and making it possible, after reflection of said wave trains by said wall, to measure a signal characteristic of said wave trains. It will be noted that in this configuration, the ultrasound wave travels through the measurement space twice and therefore presents, as a result, a double attenuation to which are added the losses linked to the reflection on the wall.

[0120] Similarly, according to another similar variant based on the use of a reflective wall, the transducers of each of the ultrasound transmitter 10 and the ultrasound receiver 20 can be arranged on the same support. Here too, with such a configuration, the ultrasound wave travels through the measurement space twice and therefore presents, as a result, a double attenuation to which are added the losses linked to the reflection on the wall.

Claims

Claims

1. Device for detecting and identifying (1) a contamination of a gaseous medium by at least one contaminating gas, the detection and identification device (1) comprising: - at least one ultrasound transmitter (10) for emitting at least a first ultrasound wave at a first frequency and at least a second ultrasound wave at a second frequency, the first and second frequencies being distinct from each other, - at least one ultrasound receiver (20) for providing at least a first and a second signal characteristic of the first ultrasound wave and the second ultrasound wave respectively, the ultrasound transmitter (10) and the ultrasound receiver (20) being arranged so as to define a measurement space (40) and so that an ultrasound wave (45) emitted by the ultrasound transmitter (10) is received by the ultrasound receiver (20) after passing through the measurement space (40),- a processing unit (30) capable of determining a first and a second attenuation value from respectively the first and the second characteristic signal supplied by the ultrasonic receiver (20), The detection and identification device being characterized in that the processing unit is configured to calculate at least one characteristic value of the attenuation evolution between the first and the second attenuation value, and to identify the contaminating gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and the second attenuation value.,

2. Detection and identification device (1) according to claim 1, wherein the processing unit (30) is further configured to determine, once the contaminating gas has been identified, a quantity of said gas present in the gaseous medium from the first and / or second attenuation value.

3. Detection and identification device (1) according to claim 1 or 2, wherein the processing unit (30) is further configured to determine from the identity of the identified contaminating gas, a suitable frequency from at least the first and second frequencies, the determination of the quantity of said contaminating gas being calculated from the attenuation value corresponding to said suitable frequency.

4. Detection and identification device (1) according to claim 3, wherein the at least one ultrasound transmitter (10) is configured to emit at least one third ultrasound wave at a third frequency distinct from the first and second frequencies, the at least one ultrasound receiver (20) being configured to provide at least one third signal characteristic of the third ultrasound wave respectively, and wherein the adapted frequency is one of at least the first to the third ultrasound frequency.

5. Detection and identification device (1) according to any one of claims 1 to 4, wherein the first attenuation value is determined from a ratio between a characteristic amplitude value of the first wave and a characteristic amplitude value previously determined in the absence of contaminating gas in the measurement space (40) for at least one ultrasonic wave having the first frequency, the second attenuation value being determined from a ratio between a characteristic amplitude value of the second wave and a characteristic amplitude value previously determined in the absence of contaminating gas in the measurement space (40) for at least one ultrasonic wave having the second frequency.

6. A detection and identification device (1) according to any one of claims 1 to 5, wherein each of the first and second attenuation values ​​is a frequency-normalized attenuation value, and wherein the characteristic value of the evolution is a difference in normalized attenuation values ​​between the first and second attenuation values.

7. A detection and identification device (1) according to any one of claims 1 to 6, wherein to identify the contaminant gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and second attenuation values, the processing unit (30) is configured to determine a sign of the characteristic value of the evolution and a sign of at least one of the first and second attenuation values.

8. Detection and identification device (1) according to any one of claims 1 to 7, wherein the processing unit (30) is configured to identify a predetermined number of contaminating gases, this predetermined number of contaminating gases preferably comprising- mainly hydrogen, methane and carbon dioxide.

9. Method for detecting and identifying contamination of a gaseous medium by a contaminating gas from a detection and identification device (1), the detection and identification device (1), comprising: - at least one ultrasonic transmitter (10) for emitting at least a first ultrasonic wave at a first frequency and at least a second ultrasonic wave at a second frequency, the first and second frequencies being distinct from each other, - at least one ultrasonic receiver (20) for providing at least a first and a second signal characteristic of respectively the first ultrasonic wave and the second ultrasonic wave, the ultrasonic transmitter (10) and the ultrasonic receiver (20) being arranged so as to define a measurement space (40) and so that an ultrasonic wave (45) emitted by the ultrasonic transmitter (10) is received by the ultrasonic receiver (20) after having passed through the measurement space (40), - a processing unit (30) capable of determining a first and a second attenuation value from respectively the first and the second characteristic signal provided by the ultrasonic receiver (20), The method comprising the following steps: - emission of the first and second ultrasonic waves (45) by the ultrasonic transmitter (10), - supply, by the ultrasonic receiver (20) upon reception of the first and second ultrasonic waves, of the first and second signals characteristic of the first ultrasonic wave and the second ultrasonic wave respectively, - determination by the processing unit (30) of a first and a second attenuation value from respectively the first and the second characteristic signal supplied by the ultrasonic receiver (20), - calculation by the processing unit (30) of at least one characteristic value of the attenuation evolution between the first and the second attenuation value, - identification by the processing unit (30) of at least one contaminating gas, said identification being carried out on the basis of the characteristic value of the attenuation evolution and at least one of the first and second attenuation values.

10. Method for detecting and identifying contamination according to claim 9, in which there is further provided a step of: -determination by the processing unit (30) and from the first and / or second attenuation value of a quantity of said identified contaminating gas.

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