Device for measuring at least one characteristic of a gaseous mixture in a conduit

Abstract

The invention relates to a device (10) for measuring at least one characteristic of a gaseous mixture (M) flowing within a conduit (20). The device (10) comprises a solid body (11) provided with a channel (14), a multilayer printed circuit (30) fixed to one face of the body (11) so as to close the channel at one end (14b) and a sensor (70) adapted to measure the at least one characteristic of the mixture (M).

Description

[0001] DESCRIPTION

[0002] DEVICE FOR MEASURING AT LEAST ONE CHARACTERISTIC OF A GASEOUS MIXTURE IN A CONDUIT

[0003] The present invention relates to a device for measuring at least one characteristic of a gaseous mixture flowing within a conduit.

[0004] The use of such devices in applications where it is necessary to detect or control the composition of a mixture of air and fuel within a conduit, for example in heating systems using premixing burners, is known. Devices of this type are described, for example, in the international application published under number WO 2015 / 036725 A1 and can be fixed to a wall of a conduit provided with an opening, in order to measure one or more characteristics of the gases flowing within the conduit. The device described in application WO 2015 / 036725 A1 comprises a hollow body inside which the actual sensor is arranged.

[0005] Due to the environment in which these sensors perform their function, in particular in the case of sensors that carry out the measurement directly in the mixture flowing in a conduit, as in the case of the cited document WO 2015 / 036725 A1, the proper functioning of the devices and the precision of the measurements carried out by them may be adversely affected by dirt, for example soot particles, present in the mixture or in the conduit. Additional factors that may alter the proper functioning of the sensors in question are represented by the turbulence of the mixture flowing near such sensors within a conduit and the temperature variations that may occur in the conduit during the transit of the mixture. Another critical aspect, which occurs in particular when the sensors are applied to a conduit so as to carry out the measurement directly in the mixture flowing within said conduit, is the gas tightness of the junction between the device that comprises the sensor and the conduit itself: in particular in the case of mixtures comprising highly reactive gases such as hydrogen, a high tightness of the junction is of fundamental importance from the safety point of view. Finally, the possibility of flashbacks occurring within a conduit in which a sensor for detecting the composition of a mixture has been applied exposes the sensor to significant risks of malfunction.

[0006] Aim of the present invention is to provide a device for measuring at least one characteristic of a gaseous mixture flowing in a conduit that overcomes the drawbacks of the aforementioned prior art.

[0007] In particular, it is an aim of the present invention to provide a device of the type described that is capable of effectively protecting the sensor from dirt present in the measurement environment, from turbulence of the mixture, from temperature variations in said environment and from flashbacks.

[0008] It is a further aim of the present invention to provide a device of the type described having a high gas tightness.

[0009] Said aims are fully achieved by the sensor according to the present invention, which is characterized by what is contained in the claims below.

[0010] The device forming the subject matter of the present invention comprises a solid body, i.e., not hollow, provided with a first and a second face arranged one in front of the other, i.e. opposite to each other, along an axis perpendicular to the faces. The device further comprises a channel passing through the solid body completely, i.e. from side to side; the channel is directed along said axis and has one end on the first face and the other end on the second face of the solid body. In use, the device is mounted on the conduit into which the gaseous mixture to be measured flows, so that the first face of the solid body faces towards the side wall of the conduit on which the device is fixed for the measurement to be carried out. It should be pointed out that the body of the device according to the present invention differs from that described in the aforementioned international application WO 2015 / 036725 A1 from a constructive point of view: in the application WO 2015 / 036725 A1 , the body is hollow inside and has two opposed faces closed by a steel disc and by a back plate, respectively; in the device according to the present invention, the body is solid and is completely crossed by a channel whose opposite ends are open at the opposite faces of the channel. The use of a solid body, preferably made of a metallic material with high thermal conductivity such as, for example, stainless steel and aluminium, gives strength to the device and allows to effectively stabilise the operating temperature of the device and, consequently, of the sensor, thereby contributing to improving the measurement precision of the device itself.

[0011] The device according to the present invention further comprises a multilayer printed circuit. Such a printed circuit comprises a plurality of electrically conductive and insulating layers arranged alternately between a first flat surface and a second flat surface. The two layers constituting the first and second flat surface of the printed circuit are electrically conductive layers and are preferably protected with a paint based on a generally photosensitive resin, called solder mask, which covers said electrically conductive layers except in the areas in which any electrical components must be mounted. The solder resin, if present, protects the electrically conductive layers, which are typically made of copper and comprise a plurality of conductive tracks, from oxidation and prevents accidental short circuits that could be caused by the fall of the material used for soldering electrical components on the conductive tracks.

[0012] The first flat surface of the multilayer printed circuit is mounted on the second face of the solid body (by suitable fixing means in combination with a first gasket or by adhesive, as explained below) so that the multilayer printed circuit closes the end of the channel located on the second face of the solid body: in other words, the first flat surface of the printed circuit faces towards the second face of the solid body and, since it is arranged in a way that it covers the end of the channel, said first flat surface of the printed circuit faces onto the latter at said end. Since the materials typically used to make the electrically conductive and insulating layers of the printed circuit and the soldering resin generally have a very low gas permeability, the positioning of the fixed printed circuit on the second face of the solid body, so as to close the end of the channel on the second face of the solid body, makes it possible to prevent the gaseous mixture that enters the channel through the opposite end of the channel and thus reaches the sensor from reaching the environment outside the conduit: in other words, the positioning of the printed circuit to close the end of the channel on the second face of the solid body ensures an at least partial gas tightness of the device, when it is applied to a conduit to carry out the measurement of at least one characteristic of a gaseous mixture flowing in the conduit itself.

[0013] The device comprises a sensor adapted to measure at least one characteristic of a gaseous mixture; the sensor is the component that carries out the actual detection of said at least one characteristic, for example of a physical or chemical quantity of the mixture whose value is proportional to the ratio between the amount of air and the amount of combustible gas present in the mixture. In the device according to the present invention, the sensor is mounted on the first flat surface of the printed circuit in a position facing the end of the channel on the first face of the solid body and opposite the end of the channel that is on the first face of the solid body: in other words, the sensor is mounted on the first flat surface of the printed circuit near the second flat face of the solid body, i.e. at the end of the channel that is farther from the conduit in which the gaseous mixture to be measured flows. In this way, the sensor faces onto the channel, so as to detect at least one characteristic of the mixture that diffuses into the channel from the conduit, but thanks to the positioning of the sensor at the end of the channel that is farther from the conduit, any turbulence and pressure waves generated within the conduit do not significantly affect the operation of the sensor, because they are strongly attenuated by the channel itself. In fact, the channel, when the device according to the present invention is applied to a conduit, introduces significant pressure drops for the mixture which, from the conduit, penetrates the channel and therefore attenuates the aforementioned turbulences and pressure waves present within the conduit. The damping effect of such oscillations can be amplified by suitably choosing the dimensions of the channel: in a particularly preferable embodiment, the channel has a circular cross-section with a predetermined diameter or a square cross-section with a predetermined side length and a length, measured between the opposite ends of the channel, chosen in such a way that the ratio between the length and the diameter (or the side length of the square cross-section) is preferably at least equal to one and, even more preferably, at least equal to two. In this embodiment the gaseous mixture fraction penetrating the channel from the main conduit is thus forced to propagate in a secondary conduit (the channel) which forms a narrowing and therefore introduces strong charge losses for this gaseous mixture fraction. As a result, any oscillations or turbulences in the gaseous mixture at the inlet of the channel are attenuated in the propagation within the channel itself and the fraction of mixture reaching the sensor does not, as a result, exhibit oscillations such as to jeopardise the precision of the sensor located at the end of the channel that is farther from the inlet of the channel. The described effect is particularly pronounced when the diameter of the channel (or the side length of the square cross-section) is less than 10 mm and, even more preferably, less than 5 mm.

[0014] The positioning of the sensor at the end of the channel farther from the conduit also allows to reduce any precision losses of the sensor due to the presence of dirt within the conduit and protects the sensor from temperature oscillations or flame returns in the conduit itself. The protection of the sensor from dirt, from temperature oscillations and from any flame returns within the conduit is amplified by the choice of the channel dimensions described above in relation to the embodiment in which the length L of the channel is at least equal to once the diameter D of the channel (or the side length of the square cross-section) and preferably the double (i.e. L / D at least equal to 2), where said diameter (or the side length of the square cross-section) is preferably less than 10 mm and, even more preferably, less than 5 mm.

[0015] The device further comprises a first gasket made of gas-impermeable material, preferably elastomeric, provided with a hole with dimensions substantially identical to those of the end of the channel on the first face of the solid body and fixed on said first face so as to completely cover the latter except for the end of the channel on the first face. The first gasket therefore covers the first face of the solid body, i.e. the face of the solid body opposite to that on which the multilayer printed circuit is mounted and closest to the conduit, in use, except for the end of the channel arranged on this first face: consequently, the first gasket and the hole it is provided with are arranged in a position opposite the sensor which, as indicated above, is mounted on the first flat surface of the printed circuit. Since the sensor is arranged in a position facing the end of the channel on the first face of the solid body, near the second flat face of the solid body, the sensor and the hole in the first gasket are arranged one in front of the other, on opposite sides of the channel. Thanks to this arrangement, the gaseous mixture to be measured can flow into the channel through the hole in the first gasket and the end of the channel on the first face of the solid body and can be guided by the channel itself from the first face until it reaches the sensor facing onto the channel from the side of the second flat face of the solid body.

[0016] The device comprises first fixing means adapted to fix the solid body to the conduit so that the first gasket is in direct contact with said conduit. The fixing means makes it possible to secure the body of the device to the conduit in which the mixture flows and of which at least one characteristic is to be measured so that the first gasket is interposed between the first face of the solid body and the outer wall of the conduit and is firmly kept in contact with said wall, preferably so as to be compressed by the solid body against the wall. The fixing means preferably comprises a plurality of screws and a corresponding plurality of threaded through holes in the solid body, arranged concentrically around the axis of said body, preferably at the periphery of the body itself. Each screw can be inserted in a corresponding hole of the solid body and has a length greater than the height of said body, i.e. the distance between the first and second face of the body itself: in this way, the portion of each screw housed in a through hole and protruding from the first face of the solid body can reach the wall of the conduit so as to secure the body to the wall of the conduit so that the solid body compresses the first gasket against the wall, thereby ensuring the hermetical gas tightness of the junction between the solid body and the conduit.

[0017] Preferably, the device according to the present invention further comprises a porous protection barrier permeable to gases and at least partially impermeable to the passage of solid particles, arranged inside the channel at a position comprised between the sensor and the end of said channel on the first face. The protection barrier allows the passage of the gaseous mixture from the end of the channel open on the first face of the solid body, i.e. the one closer to the conduit, up to the sensor located near the opposite end of the channel itself; at the same time, the barrier at least partially prevents the passage of solid particles (for example dirt present within the conduit in which the mixture to be measured flows) in the channel, thereby protecting the sensor from dirt and thus helping to maintain the measurement precision of the device. The use of the porous protection barrier permeable to gases and at least partially impermeable to the passage of solid particles is not essential to achieve the purposes of the present invention, since the protection of the sensor from dirt, from temperature oscillations and from turbulence and pressure waves is already guaranteed by placing the sensor at the end of the channel that is farther from the conduit; however, the use of the porous protection barrier permeable to gases and at least partially impermeable to the passage of solid particles is particularly preferable and can be advantageously provided in all the embodiments described, as said barrier allows to increase and regulate the pressure drops for the fraction of mixture that penetrates into the channel from the conduit. This barrier also allows the filtering of solid particles with predetermined dimensions.

[0018] The barrier is porous, that is, it has a plurality of orifices or openings that put opposed faces of the barrier in fluid-dynamic communication, and it exerts a filtering function that allows to inhibit the passage of solid particles of average size greater than the average size of the pores of the barrier; an example of average size is represented by the diameter, in the case of approximately circular pores. The barrier can advantageously be made by means of one or more layers of synthetic fibres, preferably polyester or cellulose fibres, having openings between the fibres with an average size (understood as the average distance between the fibres delimiting each opening, measured on one of the outer surfaces of the layer) comprised between 0.5 and 200 micrometres. Alternatively, it is possible to use at least one layer of sintered metallic material, preferably steel or bronze, provided with pores with an average size comprised between 1 and 200 micrometres. It is also possible to make the porous barrier by means of one or more layers of woven metal mesh or metal fibre, preferably made of steel, having openings with an average size comprised between 20 and 500 micrometres. The filtering power of the porous protection barrier, i.e. the ability to prevent the passage of solid particles through the barrier itself, is determined by the average size of the orifices.

[0019] In addition to protecting the sensor from dirt, the porous protection barrier allows to limit or eliminate reductions in the measurement precision of the sensor due to turbulence or fluctuations in the flow of mixture or caused by pressure waves in the conduit. This advantageous technical effect is achieved thanks to the fact that the barrier, being porous and therefore permeable to gases, introduces a local pressure drop in the conduit, by means of which oscillations and turbulences of the flow within the conduit are attenuated by the barrier. Since the barrier is formed by one or more layers of material with good thermal conductivity and thus exhibits considerable thermal inertia, the barrier also performs a function of protecting the sensor from temperature oscillations in the conduit. Barriers made of woven metal mesh or metal fibre and those made of sintered metallic material have a higher thermal capacity than the barriers made of synthetic fibres and offer a higher level of sensor protection from temperature oscillations.

[0020] The sensor preferably comprises a transducer adapted to detect the at least one characteristic of the gaseous mixture being measured. Preferably, the transducer is of the type that carries out a measurement of thermal conductivity of the mixture and generates, as a result, an electrical signal whose amplitude is proportional to the measured thermal conductivity. The sensor preferably comprises an electronic processing unit configured to obtain the value of the at least one characteristic of the gaseous mixture to be measured on the basis of the amplitude of said output signal of the transducer. The electronic processing unit is preferably configured to obtain said value of the at least one characteristic by means of a comparison between the value measured by the transducer (expressed as amplitude of said electrical output signal) and a calibration curve stored within said unit. In the case of sensors comprising a thermal conductivity transducer, the calibration curve relates thermal conductivity values to the values of a physicochemical characteristic of a gaseous mixture of known composition; an example of such a characteristic is the concentration of a specific gas in the mixture. In the case of a gaseous mixture of air and hydrogen, the calibration curve is obtained by measuring the thermal conductivity of a series of air and hydrogen mixture samples having a composition known a priori. An example of a commercially available transducer that carries out a thermal conductivity measurement is the transducer marketed by the company Sensirion under the name SLF3C-1300F. This transducer allows to carry out concentration measurements of hydrogen or oxygen in binary mixtures comprising hydrogen or oxygen in combination with air, for example.

[0021] The multilayer printed circuit on whose first flat surface the sensor is mounted in a position facing onto the channel preferably comprises at least three electrically conductive layers, separated from each other by a first and a second electrically insulating layer and provided with via holes that electrically connect the first electrically conductive layer to the second electrically conductive layer and the latter to the third electrically conductive layer: in this way, the first electrically conductive layer is electrically connected to the third electrically conductive layer by means of the second electrically conductive layer. The first electrically conductive layer defines the first flat surface of the circuit, i.e. the surface of the printed circuit that closes the channel and on which the sensor is mounted. The third electrically conductive layer defines the second flat face of the printed circuit, that is, the one placed at the interface between the device and the environment outside the conduit in which the measurement is carried out.

[0022] Advantageously, all via holes are made as blind via holes, that is, they have the form of channels passing through at least a part of the multilayer printed circuit in a direction perpendicular to the layers and have only one open end on an electrically conductive layer; each of the channels that constitutes a respective blind via hole ends on an electrically conductive layer and therefore has one end, opposite to said open end, closed by the electrically conductive layer on which the via hole ends. The multilayer printed circuit preferably has at least a first blind via hole formed through the first electrically conductive layer and the first electrically insulating layer, so as to electrically connect the first electrically conductive layer with the second electrically conductive layer, and at least a second blind via hole formed through the second electrically insulating layer and the third electrically conductive layer, so as to electrically connect the second electrically conductive layer with the third electrically conductive layer. In this embodiment, the first blind via hole has the open end on the first electrically conductive layer and the closed end on the second electrically conductive layer, while the second blind via hole has the open end on the third electrically conductive layer and the closed end on the second electrically conductive layer. Since the closed ends of the at least one first blind via hole and of the at least one second blind via hole are both located in the second electrically conductive layer, said ends are electrically connected to each other through the second electrically conductive layer and, through the respective via holes, the first flat surface of the printed circuit is thus electrically connected with the second flat surface. In this way the sensor, which is arranged on the first flat surface of the printed circuit in a position facing onto the channel in which a part of the mixture present within a conduit can flow, can be electrically connected with the electrical conductors present on the second flat surface of the circuit and so transmit outside the conduit the signals representative of the measurements made by the sensor within said conduit.

[0023] To this end, the device according to the present invention may advantageously comprise an electrical connector arranged on the second flat surface of the multilayer printed circuit, i.e. the surface at the interface with the environment outside the conduit; the electrical connector is preferably connected to the second blind via hole on said second flat surface to receive an electrical signal generated by the transducer and may advantageously be provided with a communication interface adapted to transmit the electrical signal to an external device, for example to a processing device or to an electronic board in a heating system.

[0024] Alternatively, the sensor of the device according to the present invention can be provided with at least one antenna, preferably of the flat type, for the transmission of an electrical signal (generated by the transducer) by means of electromagnetic waves, for example radio waves or microwaves, to an external device, for example a processing device or an electronic board in a heating system. In this case, the antenna can be electrically connected to the first blind via hole located on the first flat surface of the multilayer printed circuit: in other words, the antenna is mounted on the surface of the printed circuit facing onto the channel and therefore onto the conduit in which the mixture to be measured flows. The use of an antenna for the transmission to the outside of measurement signals is particularly advantageous in applications where, for reasons of space or safety, it is not possible to place electrical cables near the conduit.

[0025] In the embodiment described above, in which all via holes are made as blind via holes, it is particularly preferable to arrange the closed end of the first via hole and the closed end of the second via hole so that they are offset, i.e. misaligned with respect to each other on the second electrically conductive layer: in other words, the closed end on which the first blind via hole ends and the closed end on which the second blind via hole ends are both arranged at a non-zero distance from each other in the plane of the second electrically conductive layer. Thanks to the offset positioning of the at least one first via hole with respect to the at least one second blind via hole, it is possible to prevent the gaseous mixture present in the conduit from escaping from the conduit itself through the second via hole and the first via hole. The misalignment or offset of the at least one first via hole with respect to the at least one second via hole ensures that, in the multilayer printed circuit, there is no continuous channel between the second flat surface and the first flat surface of the printed circuit that would allow the gaseous mixture to pass through the printed circuit from the conduit until reaching the environment outside the conduit itself. Of course, the same offset or misaligned arrangement of the blind via holes can also be advantageously adopted in the case where the multilayer printed circuit comprises a number of via holes greater than two, as is typically the case, and / or a number of electrically conductive layers greater than three. The offset or misaligned arrangement of the blind via holes therefore guarantees a high gas tightness of the multilayer printed circuit and of the device according to the present invention.

[0026] The gas tightness of the multilayer printed circuit and of the device according to the present invention can be further improved by applying, on the second flat surface of the printed circuit (i.e. the surface at the interface with the external environment), a barrier layer consisting of an electrically insulating material impermeable to gases, in particular to hydrogen, and applied in such a way as to cover said second flat surface; the barrier layer may advantageously comprise an epoxy resin. The barrier layer can advantageously be used in combination with the offset arrangement of the blind via holes; the use of the barrier layer is however not limited to this embodiment: a barrier layer can be included in the device according to the invention in a general manner, to ensure gas tightness at least at the second flat surface of the printed circuit placed at the interface between the device according to the invention and the external environment. It is also possible to use the barrier layer in combination with the electrical connector, already described above, arranged on the second flat surface of the multilayer printed circuit: in this case, the barrier layer, for example a layer of epoxy resin, is applied on the second flat surface except for the region in which the electrical connector is located. The gas tightness of the device can be further improved by applying the barrier layer on the peripheral walls of the electrical connector, so as to prevent the passage of gas between the second flat surface and said peripheral walls.

[0027] A further measure that can advantageously be used in the device according to the present invention to improve gas tightness, i.e. to prevent the escape of gas from the conduit to the external environment through the device, consists in the use of a second gasket made of gas-impermeable material, preferably elastomeric, provided with a hole with dimensions substantially identical to those of the end of the channel placed on the second face of the solid body; the second gasket is advantageously arranged between the first surface of the printed circuit and the second face of the solid body so as to completely cover the latter except for the end of the channel on said second face of the solid body. The second gasket is therefore arranged on the side of the multilayer printed circuit facing towards the channel, that is, on the first flat surface on which the sensor is also arranged, interposed between the multilayer printed circuit and the solid body; the hole in the second gasket allows the second gasket to be arranged around the sensor and the end of the channel onto which the sensor faces so that the latter can freely detect one or more characteristics of the mixture present in the channel, without the second gasket interfering with the operation of the sensor. If the second gasket is used, it can advantageously be fixed to the second flat face of the solid body, together with the multilayer printed circuit, by second mechanical fixing means. Such second mechanical fixing means may comprise a plurality of screws, a plurality of threaded through holes made through the second flat face of the solid body, arranged concentrically around the axis of the body, preferably the periphery of the body itself, and a plurality of through holes made at the periphery of the printed circuit. The use of the second gasket allows to improve the gas tightness of the device according to the present invention at the interface between the multilayer printed circuit and the second face of the solid body: thanks to the second gasket, it is possible to significantly limit the passage of gas through interstices that may be present at the interface between the printed circuit and the solid body.

[0028] Alternatively, the multilayer printed circuit may be fixed to the second face of the solid body by means of a layer of adhesive material arranged between the first surface of the multilayer printed circuit and the second face of the solid body. In this embodiment, there is no second gasket between the printed circuit and the solid body and it is not necessary to use second fixing means. The use of adhesive to fix the multilayer printed circuit to the solid body, although it guarantees a gas tightness at the interface between the printed circuit and the solid body that is of lower quality, allows to create a device that is constructively simpler and cheaper than the embodiment that provides for the use of a second gasket.

[0029] In a particularly preferred embodiment, the first face of the solid body (i.e. the one closest to the conduit, in use) comprises a protruding portion, the second face of the solid body (i.e. the one at the interface with the external environment) comprises a recessed portion in a position opposite to the protruding portion and the channel passing through the solid body extends between the protruding portion of the first face and the recessed portion of the second face, the opposite ends of the channel being arranged respectively in the protruding portion and in the recessed portion. In this embodiment, the multilayer printed circuit is advantageously arranged in the recessed portion of the second face of the solid body. The solid body according to this embodiment therefore has, at the recessed portion, an embedded seat in the second face of the solid body in which the printed circuit can be housed, while the face of the solid body that comes into contact with the mixture in the conduit, i.e. the first face, has a protruding portion that can be advantageously inserted into an opening of the conduit in such a way as to guarantee the anchoring of the solid body to the conduit itself; the channel extends between the recessed portion and the protruding portion, in the direction of the axis of the solid body. The recessed portion that creates the embedded seat in the second face of the solid body allows the printed circuit to be mounted in said seat so that it is surrounded by the remaining raised part of the same second face, thus allowing the printed circuit to be protected from the action of external agents that could cause it to detach from the solid body. The protruding portion on the first face of the solid body instead allows to create on this face a protuberance that can advantageously be inserted into a corresponding opening in the side wall of the conduit and held firmly in place by shape coupling, so as to create a firm junction between the device and the conduit. This embodiment can be used both in combination with the second gasket described above, and in the case where an adhesive is used to connect the printed circuit to the solid body. It is also evident that the solid body according to this embodiment, i.e. provided with a recessed portion and with a corresponding protruding portion in a position opposite to the recessed portion, can advantageously be used in combination with a multilayer printed circuit according to any one of the embodiments described above and, in particular, with a multilayer printed circuit provided with offset blind via holes.

[0030] The device according to the present invention is used in combination with fluiddynamic conduits provided with a side wall defining an internal passage for the transport of a gaseous mixture and provided with a side opening, made in said wall, in which the device can be placed to measure at least one characteristic of the gaseous mixture. Particularly advantageous is the embodiment of the device described above and provided with a protruding portion on the first face of the solid body, as this protruding portion allows the device to be firmly fixed in the side opening by shape coupling between the protruding portion and the opening, thereby ensuring a stable mounting of the device on the conduit and a high gas tightness of the junction between the aforementioned protruding portion and the opening in the wall of the conduit. The tightness of the junction can advantageously be increased by using a suitable gasket between the solid body of the device for measuring at least one characteristic of said gaseous mixture and side opening of the conduit, so that the solid body is hermetically fixed to the side opening made in the wall of the conduit.

[0031] The device according to the present invention can be advantageously used in an apparatus for the combustion of a gaseous mixture preferably comprising air and hydrogen and comprising a fluid-dynamic conduit of the type described, i.e. with a side opening for fixing the device, as well as a gas burner provided with a wall defining a combustion chamber and with an injection opening for the injection of the gaseous mixture into said combustion chamber. The fluid-dynamic conduit to which the device can be applied can be a conduit for injecting the gaseous mixture into the combustion chamber of the burner: in this case, the device according to the present invention can be advantageously used to measure one or more characteristics of the mixture entering the burner. The device can also be applied in an opening made in the wall of the burner so that the sensor faces inside the combustion chamber of the burner itself: in this case, the device can be advantageously used to measure one or more characteristics of the mixture inside the combustion chamber of the burner. Finally, the device according to the present invention can be applied to a conduit for the emission of the combustion products of the burner, to measure one or more characteristics of said products. It is of course possible to use the sensors in the three configurations described also in combination, for example to measure the concentration of the gaseous mixture entering the burner and the composition of the combustion products emitted by the burner.

[0032] This described characteristics will be more apparent from the following description of some embodiments illustrated by way of mere non-limiting example in the accompanying drawings, in which:

[0033] - figure 1 schematically illustrates a device according to a first embodiment of the invention, placed in an opening made in a side wall of a conduit;

[0034] - figure 2 illustrates an enlarged portion of the device of figure 1;

[0035] - figure 3 illustrates a device according to a second embodiment of the invention;

[0036] - figure 4 illustrates a multilayer printed circuit that can be used in the devices according to the invention;

[0037] - figures 5(A) and 5(B) illustrate two different positions of a porous protection barrier in a device according to the invention; - figure 6 illustrates an apparatus comprising a gas burner in combination with a plurality of devices according to the invention;

[0038] - figure 7 illustrates a further embodiment in which the device according to the invention does not have a protruding portion.

[0039] Figure 1 schematically illustrates a device (10) according to a first embodiment of the invention. The device (10) is illustrated in a condition of use and is placed in an opening (22) made in the side wall (21) of a conduit (20) inside which a gaseous mixture (M) flows, for example comprising air and hydrogen. The device

[0040] (10) comprises a solid body (11) having a first face or lower face (13), arranged near the wall (21) of the conduit (20), and a second face or upper face (12), placed at the interface between the device (20) and the external environment, in a position opposite to the first face (13). Between the first face (13) and the second face (12) there extends a channel (14) that passes through the solid body

[0041] (11) from side to side, thus putting the inside of the conduit (20) in communication with the upper face (12) of the solid body (11) placed at the interface with the environment external to the conduit (20) itself. The channel extends orthogonally to the faces (12) and (13) of the solid body along an axis which, in the illustrated embodiment, constitutes an axis of rotation symmetry for the solid body (11). The channel may advantageously have a circular cross-section with a predetermined diameter or, alternatively, a square cross-section with a predetermined side length. In a particularly preferred embodiment, the channel has a circular crosssection with a predetermined diameter or a square cross-section with a predetermined side length and a length, measured between the opposite ends of the channel, chosen in such a way that the ratio between the length and the diameter (or the side length of the square cross-section) is at least equal to 1 ; the diameter (or the side length of the square cross-section) is preferably equal to, or less than, 10 mm and even more preferably equal to, or less than 5 mm. The indicated dimensional ratio and the choice of a diameter (or of the side length of the square cross-section) not greater than 10 mm and, even more preferably equal to, or less than, 5 mm make it possible to significantly reduce the effect of any turbulence and pressure waves as well as dirt present in the conduit (20) on the measurement precision of the sensor (70).

[0042] In the illustrated embodiment, the upper face (12) of the solid body (11) has, at a position corresponding to the axis, a recess defining a seat (15) on said face (12), inside which a multilayer printed circuit (30) is fixed. Figure 4 illustrates, by way of example, a multilayer printed circuit (30) usable in the present invention: as can be seen from the figure, the multilayer printed circuit (30) comprises a plurality of electrically conductive flat layers (32a, 32c, 32e), for example made of copper, separated from each other by electrically insulating flat layers (32a, 32d), for example in glass fibre impregnated with epoxy resin. The printed circuit (30) has a first flat surface (31), formed in the figure by the lower conductive layer (32a) facing onto the channel (20), and a second flat surface (33), formed by the upper conductive layer (32e) in contact with the environment outside the conduit (20). The multilayer printed circuit (30) further comprises a plurality of blind via holes (34a, 34b), described in more detail below. In the example of figure 4, the multilayer printed circuit (30) comprises three electrically conductive flat layers (32a, 32c, 32e) and two electrically insulating flat layers (32a, 32d); the multilayer printed circuit (30) may comprise a greater number of electrically conductive and insulating layers. The first flat surface (31) and the second flat surface (33) are preferably covered by a protective layer (32f, 32g) made of insulating material, called solder mask, consisting of a paint based on a generally photosensitive resin. The solder mask (32f, 32g) covers each of the flat surfaces (31, 33) of the printed circuit (30) except for the regions where electrical components are to be mounted.

[0043] In the embodiment illustrated in figures 1 and 2, the second face (12) of the solid body (11) comprises a recessed portion (15) defining a seat in which the multilayer printed circuit (30) is housed and fixed, while the first face (13) of the solid body (11) comprises a protruding portion (17) by means of which the device (10) can be advantageously anchored to the side wall (21) of the conduit (20). As can be seen from figures 1 and 2, the seat defined by the recessed portion (15) in the second face (12) of the solid body (11) is delimited by raised portions (16) at the periphery of the second face (12). The raised portions (16) of the solid body that define the seat (15) in the second face (12) of the solid body (11) and allow the multilayer printed circuit (30) to be protected from the action of external agents that could cause the circuit itself to detach from the second face (12). The first face or lower face (13) of the solid body (11) has, in a position opposite to the seat (15), the aforementioned protruding portion (17) by means of which the device (10) can be firmly fixed in the opening (22) made in the side wall (21) of the conduit (20). The protruding portion (17) has the same shape as the opening (22) and slightly smaller dimensions than those of the opening (22), so as to allow a firm shape coupling between the protruding portion (17) and the opening (22).

[0044] In all embodiments of the device according to the present invention, the device (10) is fixed to the conduit (20) in which the mixture (M) flows, in which at least one characteristic is intended to be measured by means of first fixing means (400). As can be seen, for example, from figures 1 and 2, said first fixing means can comprise a plurality of screws and a corresponding plurality of threaded through holes made in the solid body (11), arranged concentrically around the axis of said body (11), preferably at the periphery of the body itself. The screws can be inserted into the threaded through holes and reach the side wall (21) of the conduit (20) so as to firmly fix the device (10) itself to the conduit (20).

[0045] Although the formation of a protruding portion (17) in the first face (13) of the solid body (11) and of a recessed portion (15) in the second face (12) of the same body (11) is particularly preferred, the use of a protruding portion (17) and of a recessed portion (15) is not essential for the present invention. In an embodiment not illustrated, both the first face (13) and the second face (12) of the solid body (11) can be made as flat surfaces; in this case, the anchoring of the device (10) to the side wall (21) of the conduit (20) is ensured by the first fixing means (400) described above. Alternatively, the device (10) can be made according to the embodiment illustrated in figure 7: in this embodiment, the device (10) has only a recessed portion (15) that defines a corresponding seat (15) in the second face (1) of the solid body (11) but does not have a recessed portion (17) in the first face (13). In the embodiment illustrated in figure 7, the multilayer printed circuit (30) is housed in the seat (15) and is fixed to the solid body (11) by second fixing means (500), described in more detail below; alternatively, the multilayer printed circuit (30) can be fixed to the solid body (11) by means of an adhesive layer (51), as explained below in relation to figure 3. Also in the embodiment of figure 7, the device (10) is anchored to the side wall (21) of the conduit (20) by the aforementioned first fixing means (400).

[0046] As illustrated in figure 2, which shows an enlarged portion of the device of figure 1 , the multilayer printed circuit (30) can be fixed inside the seat (15) to the second face (12) by suitable second fixing means (500) which, in the device of figure 2, have the form of screws that can be inserted through corresponding holes in the printed circuit (30) and threaded through holes in the solid body (11) until reaching the wall (21) of the conduit (20) and thus fix the body (11) itself, together with the multilayer printed circuit (30), to the conduit (20).

[0047] Between the device (10) according to the present invention and the conduit (20) on whose wall (21) the device (10) is fixed, there is a first gasket (40), arranged between the lower face (13) of the body (11) and the wall (21) of the conduit (20); said first gasket (40) guarantees the gas tightness of the junction between the solid body (11) and the wall (21) of the conduit (20). In the event that the multilayer printed circuit (30) is fixed to the solid body (11) by means of screws (400), it is also preferable to use a second gasket (50), arranged between the lower face of the multilayer printed circuit (30), i.e. the first flat surface (31), and the upper face (12) of the solid body (11), to ensure a good gas tightness of the device (10) at the interface between the multilayer printed circuit (30) and the solid body (11). The first gasket (40) and the second gasket (50) are preferably made of elastomeric material. The second gasket (50) is not essential for the present invention: as already mentioned above in the discussion of the device illustrated in figure 7, in an alternative embodiment illustrated in figure 3 and described in more detail below, the multilayer printed circuit (30) can be glued to the upper face (12) of the solid body (11) by means of an adhesive layer (51). In this alternative embodiment illustrated in figure 3, no second fixing means (500) is required.

[0048] On the lower face of the multilayer printed circuit (30), i.e. on the first flat surface (31) of the circuit (30) facing onto the channel (14), a sensor (70) is mounted comprising a transducer, not illustrated in the figures, adapted to detect at least one characteristic of the gaseous mixture (M) present within the conduit (20); the transducer is preferably of the type that carries out a thermal conductivity measurement of the mixture (M), for example the transducer sold under the name SLF3C-1300F by the company Sensirion. The sensor (70) comprises in its inside several electronic components, including a processing unit configured to obtain at least one characteristic of the gaseous mixture (M) based on the measurement made by the transducer. In the case of binary gaseous mixtures, for example based on air and hydrogen, the sensor (70) may advantageously be configured to obtain the concentration of one of the components of the binary mixture, for example the concentration of hydrogen. The sensor (70) is electrically connected to the electrically conductive layer (32a) of the multilayer printed circuit (30) on which it is mounted; moreover, as explained in detail below, the sensor (70) is also electrically connected to the electrically conductive layer (32e) that constitutes the upper face of the circuit (30) (see figure 3 in this regard), i.e. the second flat surface (33) in contact with the environment outside the conduit (30), by means of appropriate via holes (34a, 34b). In this way, the sensor (70) can transmit to an external device (600) one or more signals representative of the measurement made by the transducer; to this end, the device (10) can advantageously comprise a special electrical connector arranged on the second flat surface (33) of the printed circuit (30), electrically connected to the sensor (70) through said via holes (34a, 34b) and provided with a communication interface adapted to transmit the measurement signals received from the sensor (70) to an external device (600), for example to an electronic control board of a burner or of a boiler in which the device (10) according to the present invention is used. Examples of electrical connectors provided with a communication interface usable in the device (10) are USB, RS232 and GPIB connectors. As an alternative to the use of an electrical connector mounted on the second flat surface (33) of the multilayer printed circuit (30), it is possible to transfer the measurement signals received from the sensor (70) to an external device (600) by means of an antenna, preferably consisting of a flat pitch (patch antenna) and mounted on the same side of the sensor (70), i.e. on the first flat surface (31) of the printed circuit (30) facing onto the channel (14). An example of a device (10) that uses an antenna (80) of the flat type to transmit to an external device (600) is illustrated in figure (3). The antenna (80) may advantageously operate in the radio frequency or microwave band. The embodiment that uses an antenna (80) for the transmission of the measurement signals generated by the sensor (70) has the advantage of greater compactness compared to the embodiment that uses an electrical connector mounted on the first flat surface (31) of the printed circuit (30); the use of an electrical connector instead has the advantage of greater immunity of the sensor to electromagnetic interference. Advantageously, the embodiment that uses an antenna (80) for the transmission of the measurement signals generated by the sensor (70) may also comprise a cover made of dielectric material transparent to the electromagnetic radiation emitted by the antenna (80) in the frequency range in which the latter operates. The cover, not illustrated in figure 3, can be mounted on the second face (12) of the solid body (11), i.e. on the upper face, for example by means of adhesive applied along the edge of said face (12), so as to protect the multilayer printed circuit (3) and further prevent the escape of gas.

[0049] Returning to figure 1, the device (10) according to the present invention advantageously comprises a porous protection barrier (60) arranged inside the channel (14) in a position comprised between the sensor (70) and the end (14a) of the channel (14) located on the first face (13), i.e. on the lower face of the solid body (11). The barrier (60) is permeable to gases, so as to allow at least a part of the gaseous mixture (M) to flow from the conduit (20) to the sensor (70), but it is at least partially impermeable to the passage of solid particles, for example dirt present in the conduit (20). The barrier (60) thus shields the sensor (70) from the action of solid particles that could jeopardize the precision and proper functioning of the sensor (70), thereby exerting a filtering action. For this purpose, the porous protection barrier (60) is made of one or more layers of materials having a plurality of orifices that put opposite faces of the barrier in communication. Examples of materials that can be used to make the barrier (60) are represented by woven metal meshes or metal fibres, preferably made of steel, by sintered metal powders preferably based on steel or bronze or, again, by synthetic fibres, for example in polyester or cellulose. The term porous is used in the present description to indicate any type of orifice, opening or channel that puts in fluiddynamic communication opposite faces of a layer of material; in the case of materials that use fibres or meshes, the term pore designates the openings created by intertwining fibres or threads that form said meshes, while in the case of materials based on sintered powders the term pore refers to the channels formed by the interstices existing between the particles that make up said powders. The average sizes of the pores of the barrier (60) determine the filtering power of the barrier itself, i.e. its ability to prevent the passage of solid particles from one face to an opposite face of the barrier (60): in general terms, a porous barrier (60) made with one or more layers of a material with pores having a certain average size is able to filter and therefore inhibit the passage of solid particles with an average size greater than the average pore size. In the case of materials such as sintered powders, an example of average pore size is the average diameter of each pore, while in the case of materials made of meshes of fibres or metal meshes, an example of average pore size is the average distance between the fibres or the threads that define each of the openings that define the mesh of fibres or the mesh of threads.

[0050] Materials based on synthetic fibres generally have openings with an average size comprised between 0.5 and 200 micrometres and are particularly suitable for filtering fine solid particles, while materials using sintered metal powders usually have pores with an average diameter greater than one micrometre; materials made by woven metal mesh or metal fibres have openings with an average size comprised between 20 and 500 micrometres and are more suitable for filtering coarser solid particles.

[0051] As can be seen in figure 5(A), the porous protection barrier (60) can be placed inside the channel (14) in an intermediate position between the sensor (70) and the end (14a) of the channel (14) closest to the opening (22) made in the wall (21) of the conduit (22). Alternatively, the barrier (60) may be located in the immediate vicinity of the sensor (70), as shown in figure 5(B), or at the end (14a) of the channel adjacent to the opening (22) in the wall (21) of the conduit (22), as illustrated in figure 1 and figure 7. The barrier (60) may have a flat shape, as illustrated in figures 1, 5(A) and 7, or be shaped like a hemispherical cap, as illustrated in figure 5(B). Thanks to its positioning in the channel (14) between the sensor (70) and the opening (22) in the wall (21) of the conduit (20) from which a part of the gaseous mixture (M) penetrates into the channel (14) itself and reaches the sensor (70), the porous protection barrier (60) protects the sensor (70) from turbulence and flow oscillations of the mixture (M) as well as from pressure waves that may form within the conduit (20). The protection barrier (60), being provided with pores with generally micrometric or sub-micrometric dimensions that allow the passage of the gaseous mixture from the conduit (20) to the sensor (70), introduces pressure drops in the flow through the conduit (20); such pressure drops dampen the aforementioned turbulences, oscillations and pressure waves. In this way, the barrier (60) helps to ensure that the precision of the sensor (70) is not affected by the aforementioned fluid-dynamic phenomena. Finally, the barrier (60), being made up of one or more layers of materials with a good thermal conductivity, has a thermal mass or inertia that allows to attenuate the effect of any temperature variations in the conduit (20) on the precision of the sensor (70); from this point of view, barriers that use interwoven metal meshes, metal fibres or sintered metal powders have, compared to materials based on synthetic fibres such as polyester and cellulose, a higher thermal inertia and are more effective in protecting the sensor (70) from temperature variations. The barriers using interwoven metal meshes, metal fibres or sintered metal powders also protect the sensor (70) from any flame return within the conduit (20). As already indicated above, the use of the porous protection barrier (60) is not essential to achieve the purposes of the present invention, since the protection of the sensor from dirt, from temperature oscillations and from turbulence and pressure waves is guaranteed by placing the sensor at the end of the channel that is farther from the conduit; however, the use of the porous protection barrier permeable to gases and at least partially impermeable to the passage of solid particles is particularly preferable and can be advantageously provided in all embodiments of the invention.

[0052] Since the device (10) according to the present invention detects one or more characteristics of a gaseous mixture (M) that flows within a conduit (20) by means of a measurement carried out directly within the conduit itself, it is essential that the device (10) guarantees a high gas tightness, when it is fixed to an opening (22) made in a side wall (21) of a conduit (20), so as to prevent leaks or escapes of gas through the device itself. Gas tightness of the junction by means of which the device (10) is connected to a conduit (20) to carry out the measurement is particularly important in the event that the gaseous mixture (M) of which one or more characteristics are to be detected comprises a highly reactive gas, such as for example hydrogen, because the escape of such gases poses serious safety problems.

[0053] An advantageous aspect of the invention that contributes particularly effectively to ensuring a high gas tightness of the device is the arrangement of the via holes used in the multilayer printed circuit to electrically connect together the electrically conductive layers of the printed circuit. Figure 4 illustrates, by way of example, the arrangement of two via holes (34a, 34b) in a multilayer printed circuit (30) according to the present invention. The printed circuit (30) represented in figure 4 comprises three electrically conductive layers (32a, 32c, 32e) alternated with two electrically insulating layers (32b, 32d); the electrically conductive layer (32a) forms the first flat surface (31) of the printed circuit (30), i.e. the lower face on which the sensor (70) is mounted, while the electrically conductive layer (32e) forms the second flat surface (31) of the printed circuit (30), i.e. the upper face adjacent to the environment outside the conduit (20). As can be seen from figure 4, the via holes (34a, 34b) are made as blind via holes, i.e. they have the form of channels passing through at least a part of the multilayer printed circuit in a direction perpendicular to the layers (32a-32e) and have only one open end (34ao, 34bo) on an electrically conductive layer (32a, 32e); each of the channels that constitute a respective blind via hole (34a, 34b) ends on an electrically conductive layer (32c) and therefore has the opposite end (34ac, 34bc) closed by said electrically conductive layer (32c). In the printed circuit (30) of figure 4, for example, the first blind via hole (34a) extends between the first electrically conductive layer (32a) and the second electrically conductive layer (32c), has an open end (34ao) on the first electrically conductive layer (32e) that forms the lower face (33) of the printed circuit (30) and ends on the second electrically conductive layer (32c), thus closing the end (34ac) of the first via hole (34a). Similarly, the second blind via hole (34b) extends between the third electrically conductive layer (32e) and the second electrically conductive layer (32c), has an open end (34bo) on the third electrically conductive layer (32e) and ends, like the first blind via hole (34a), on the second electrically conductive layer (32c), thus closing the end (34bc) of the second via hole (34b). As can be clearly seen from figure 4, the first blind via hole (34a) and the second blind via hole (34b) are offset, i.e. misaligned with respect to each other: the closed end (34ac) of the first blind via hole (34a) and the closed end (34bc) of the second blind via hole (34b) are located on the same electrically conductive layer, i.e. on the second electrically conductive layer (32c), but are placed at a non-zero distance from each other. In this way, the gaseous mixture (M) that reaches the lower face of the printed circuit (30), i.e. the first flat surface (31), cannot penetrate through the printed circuit (30) by means of the via holes (34a, 34b), because between these via holes there is no fluid-dynamic continuity: the gaseous mixture (M) that can penetrate inside the first blind via hole (34a) from the conduit (30) during the measurement cannot reach the opposite side, i.e. the second flat surface (33) of the printed circuit (30), because the second electrically conductive layer (32c) closes the passage to the mixture and, due to the offset of the second blind via hole (34b) with respect to the first blind via hole (34a), the gaseous mixture cannot proceed from the second electrically conductive layer (32c) through the second blind via hole (34b) up to the first flat surface (33) of the circuit adjacent to the external environment. It is also evident that the via holes (34a, 34b) are electrically connected to each other by means of the second electrically conductive layer (32c) of the printed circuit (30) and thus allow to transmit an electrical signal, for example a measurement signal generated by the sensor (70), from the first flat surface (33) of the circuit (30) facing onto the channel (14) to the second flat surface (31) of the circuit (30) in contact with the environment outside the conduit (30).

[0054] The offset arrangement of the blind via holes (34a, 34b), illustrated in figure 4 by way of example with only two holes, is also applicable to multilayer printed circuits provided with a plurality of via holes and comprising a number of layers greater than five and allows to ensure a high gas tightness of the multilayer printed circuit (30).

[0055] The offset arrangement of the via holes can be advantageously used both in the first embodiment illustrated in figure 1 and in the second embodiment illustrated in figure 3 or in that of figure 7.

[0056] The gas tightness of the device (10) according to the present invention can be further improved by the application of a barrier layer (90) consisting of an electrically insulating material impermeable to gases, in particular hydrogen, and arranged on the second flat surface (33) of the printed circuit so as to cover the latter. By way of example, the barrier layer (90) may advantageously be made of an epoxy resin; such a layer may be used in the embodiments illustrated in figures 1 , 3, 5(A), 5(B) and 7. In the event that the device (10) uses an electrical connector mounted on the second flat surface (33) of the printed circuit (30) to transmit to an external device (600) the signals generated by the sensor (70), the resin can be advantageously applied on the peripheral walls of the connector and on the portion of said second flat surface (33) not occupied by the connector, so as to hermetically seal any interstices present between the connector itself and the second flat surface (33) and in this way prevent the accidental escape of gas from the device (10).

[0057] Figure 6 illustrates, by way of example, an application of the device according to the present invention in a combustion system comprising a premixing burner (100) placed inside a chamber (200). A first device (10a) according to the present invention can be advantageously applied on the side wall of a first conduit (20a) for the injection, into the burner (100), of a gaseous mixture (M) comprising, for example, air and hydrogen; said first device (10a) can be advantageously used to control the concentration of hydrogen in the mixture entering the burner (100). A second device (10b) according to the present invention can be advantageously used inside the chamber (200) to monitor a characteristic of the gaseous mixture (M) that is inside the burner (100); said second device (10b) can be applied on a wall of the burner (100), preferably in a portion of said wall free of flames, for example to measure the concentration of air with respect to that of the combustible gas, in order to prevent the onset of flame return phenomena or to carry out a regulation of the composition of the mixture (M) itself. Finally, a third device (10c) according to the present invention can be advantageously applied on a second conduit (20b) intended to emit the combustion products of the burner (100), to measure a characteristic of such products: by way of example, the third device (10c) can be used to measure the concentration of nitrogen oxides present in the combustion products. Each of the sensors (70) used in the devices (10a, 10b, 10c) must be previously calibrated and programmed for measuring the characteristics to be detected; this calibration can be made before the in situ application of each device (10a, 10b, 10c), by measuring gaseous mixtures having composition known a priori and recording the values detected by the sensor, for example in a memory placed inside the sensor itself, so as to build a calibration curve that uniquely associates the measurement values detected by the transducer placed inside the sensor with values of the characteristic to be measured.

[0058] The signals detected by each of the sensors inside each device (10a, 10b, 10c) can then be transmitted, for example by means of an electrical connector of the type described above or an antenna (80) located inside the device, to an external device (600), for example to an electronic board for the control of the operation of the combustion system, as illustrated by way of example in figure 3.

Claims

CLAIMS1. A device (10) for measuring at least one characteristic of a gaseous mixture (M) flowing within a conduit (20), comprising: a solid body (11) having a first (13) and a second face (12) opposite to each other along an axis perpendicular to said faces; a channel (14) passing through said solid body, directed along said axis and having one end (14a) on the first face (13) and the other end (14b) on the second face (12) of said solid body (11); a multilayer printed circuit (30) comprising a plurality of electrically conductive (32a, 32c, 32e) and insulating (32b, 32d) layers arranged alternately between a first flat surface (31) and a second flat surface (33), the first flat surface (31) of the multilayer printed circuit being fixed on the second face (12) of the solid body (11) so that said multilayer printed circuit (30) closes the end (14b) of the channel (14) on the second face (12) of the solid body (11); a sensor (70) adapted to measure said at least one characteristic, mounted on the first flat surface (31) of the printed circuit (30) in a position facing the channel (14) and opposite to the end (14a) of said channel (14) located on the first face (13) of the solid body (11); a first gasket (40) made of gas-impermeable material, preferably elastomeric, provided with a hole with dimensions substantially identical to those of the end (14a) of the channel on the first face (13) of the solid body (11) and fixed on said first face (13) so as to completely cover the latter except for the end (14a) of the channel (14) on the first face (13); first mechanical fixing means (400) adapted to fix the device (10) to the conduit (20) so that the first gasket (40) is maintained between the first face (13) of the solid body (10) and the conduit (20) in direct contact with said conduit (20).

2. The device (10) according to claim 1 , wherein the sensor (70) comprises a transducer adapted to detect said at least one characteristic of the gaseous mixture (M), preferably by means of a thermal conductivity measurement, and configured to generate at least one electrical signal representative of said at least one characteristic of the gaseous mixture (M), the transducer being preferably adapted to detect the concentration of hydrogen and / or oxygen in said gaseous mixture.

3. The device (10) according to claim 2, wherein the multilayer printed circuit (30) comprises at least:- a first electrically conductive layer (32a) defining the first surface (31) of said printed circuit,- a first electrically insulating layer (32b),- a second electrically conductive layer (32c), separated from the first electrically conductive layer (32a) by the first electrically insulating layer (32b),- a second electrically insulating layer (32d)- and a third electrically conductive layer (32e) defining the second flat surface (33) of said printed circuit, the third electrically conductive layer (32e) being separated from the second electrically conductive layer (32c) by the second electrically insulating layer (32d), the multilayer printed circuit (30) further comprising at least- a first blind via hole (34a) formed through the first electrically conductive layer (32a) and the first electrically insulating layer (32b) so as to electrically connect the first electrically conductive layer (32a) with the second electrically conductive layer (32c), the first blind via hole (34a) having an open end on the first electrically conductive layer (32a) and a closed end on the second electrically conductive layer (32c),- and a second blind via hole (34b) formed through the second electrically insulating layer (32c) and the third electrically conductive layer (32e) so as to electrically connect the second electrically conductive layer (32c) with the third electrically conductive layer (32e), the second blind via hole (34b) having an open end on the third electrically conductive layer (32e) and a closed end on the second electrically conductive layer (32c); the closed end of the first via hole (34a) and the closed end of the second via hole (34b) being staggered from each other on the second electrically conductive layer (32c).

4. The device (10) according to claim 2 or 3, comprising an electrical connector arranged on the second flat surface (33) of the multilayer printed circuit (30) and connected, by means of the multilayer printed circuit (30), to the sensor (70) which is mounted on the first flat surface (31) so as to receive the at leastone electrical signal generated by the transducer, said connector being provided with a communication interface adapted to transmit the at least one electrical signal to an external device (600).

5. The device (10) according to claim 4, wherein the electrical connector is electrically connected to the second blind via hole (34b) of the multilayer printed circuit (30).

6. The device (10) according to claim 2 or 3, wherein the sensor (70) is provided with at least one antenna (80), preferably of the flat type, configured to receive the at least one electrical signal generated by the transducer and to transmit said electrical signal to an external device (600) by means of electromagnetic waves, the antenna (80) being arranged on the first flat surface (31) of the multilayer printed circuit (30).

7. The device (10) according to claim 6, wherein the antenna (80) is electrically connected to the first blind via hole (34a) of the multilayer printed circuit (30).

8. The device (10) according to claim 6 or 7, wherein the multilayer printed circuit (30) is fixed to the second face (12) of the solid body (11) by means of a layer of adhesive material (51) arranged between the first flat surface (31) of said multilayer printed circuit (30) and said second face (12) of the solid body.

9. The device (10) according to claim 8, comprising a protective cover made of dielectric material transparent to the electromagnetic waves emitted by the antenna (80), said protective cover being fixed to the second face (12) of the solid body (11).

10. The device (10) according to any one of claims 1 to 7, comprising a second gasket (50) made of gas-impermeable material, preferably elastomeric, provided with a hole with dimensions substantially identical to those of the end (14b) of the channel on the second face (12) of the solid body (11) and arranged between the first flat surface (31) of the printed circuit (30) and said second face(12) of the solid body (11) so as to completely cover the latter except for the end (14b) of the channel on said second face (12), the device (10) further comprising second mechanical fixing means (500) adapted to fix the printed circuit (30) and the second gasket (50) to the second face (12) of the solid body (11).

11. The device (10) according to any one of the preceding claims, wherein the channel (14) has a length (L), equal to the distance between the opposite ends (14a, 14b) of the channel (14), and a circular cross-section with a predetermined diameter (D) or, alternatively, a square cross-section with a predetermined side length (S), the ratio between said length (L) of the channel (14) and the diameter (D) or the side length (S) being at least equal to 1 and preferably at least equal to 2, the diameter (D) or the side length (S) being preferably less than 10 mm and even more preferably less than 5 mm.

12. The device (10) according to any one of the preceding claims, comprising a porous protection barrier (60) permeable to gases and at least partially impermeable to the passage of solid particles, arranged inside the channel (14) at a position comprised between the sensor (70) and the end (14a) of said channel on the first face (13).

13. The device (10) according to claim 12, wherein the porous protection barrier (60) is arranged on the first face (13) of the solid body (11) in the hole of the first gasket (40) so as to completely cover the opening (14a) of the channel (14) on said first face (13).

14. The device (10) according to claim 12, wherein the porous protection barrier (60) is arranged near the opening (14b) of the channel (14) on the second face (12) of the solid body (11) between the sensor (70) and the other opening (14a) of the channel placed on the first face (13).

15. The device (10) according to any one of claims 12 to 14, wherein the porous protection barrier (60) comprises at least one layer of woven metal mesh or metal fibre, preferably made of steel, having openings with an average size comprised between 20 and 500 micrometres.

16. The device (10) according to any one of claims 12 to 14, wherein the porous protection barrier (60) consists of at least one layer of sintered metallic material, preferably steel or bronze, having pores with an average size comprised between 1 and 200 micrometres.

17. The device (10) according to any one of claims 12 to 14, wherein the porous protection barrier (60) consists of at least one layer of synthetic fibres, preferably polyester fibres or cellulose fibres, having openings with an average size comprised between 0.5 and 200 micrometres.

18. The device (10) according to any one of the preceding claims, wherein the first face (13) of the solid body (11) comprises a protruding portion (17), the second face (12) of the solid body comprises a recessed portion (15) in a position opposite to the protruding portion (17) and the channel (14) passing through said solid body (11) extends between the protruding portion (17) of the first face and the recessed portion (17) of the second face, the opposite ends (14a, 14b) of the channel being arranged respectively in the protruding portion (17) and in the recessed portion (15), in which device the multilayer printed circuit is arranged in said recessed portion (15) of the second face (12).

19. The device (10) according to any one of the preceding claims, comprising a barrier layer (90) consisting of an electrically insulating material impermeable to gases, in particular to hydrogen, and arranged on the second flat surface (33) of the printed circuit so as to cover said second flat surface (33).

20. A fluid-dynamic conduit (20, 20a, 20b) having a side wall (21) defining an internal passage, an inlet opening for the introduction of a gaseous mixture (M) into the internal passage and an outlet opening for the outflow of the gaseous mixture from the internal passage, the side wall (21) being provided with a side opening (22) in which there is arranged a device (10a, 10c) for measuring at least one characteristic of said gaseous mixture (M) according to any one of the preceding claims, the solid body (11) of said device (10a, 10b) being mounted in the side opening (22) so that the sensor (70) faces onto the internal passage ofthe conduit (20a, 20b).

21. The fluid-dynamic conduit (20, 20a, 20b) according to claim 20, provided with a gasket positioned between the solid body (11) of the device (10a, 10c) for measuring at least one characteristic of said gaseous mixture (M) and the side wall (21) of the conduit (20, 20a, 20b) so that said solid body (11) is hermetically fixed to the side opening (22).

22. An apparatus for the combustion of a gaseous mixture (M) preferably comprising air and hydrogen, the apparatus comprising a fluid-dynamic conduit (20a) according to claim 20 or 21 and a gas burner (100), said burner (100) being provided with a wall defining a combustion chamber (101) and with an injection opening for the injection of the gaseous mixture (M) into said combustion chamber (101), said injection opening for the injection of the gaseous mixture (M) being connected to the outlet opening of the fluid-dynamic conduit (20a).

23. The apparatus according to claim 22, wherein the gas burner (100) is provided with a device (10b) for measuring at least one characteristic of the gaseous mixture (M) according to any one of claims 1 to 19, said device (10b) being mounted in an opening in the wall of the gas burner (100) so as to carry out said measurement in the gaseous mixture (M) present inside the combustion chamber (101) of the burner (100).

24. The apparatus according to claim 22 or 23, wherein the gas burner (100) is arranged inside a chamber (200) and said chamber (200) is provided with walls and comprises a further fluid-dynamic conduit (20b) according to claim 19 or 20, said further fluid-dynamic conduit (20b) being configured to allow the combustion products of the burner (100) to outflow from said chamber (200), the chamber (200) preferably comprising a further device (10) according to any one of claims 1 to 19, said further device (10) being placed on a wall of said chamber (200) so as to measure at least one characteristic of the gaseous mixture (M) present inside said chamber (200).

25. The apparatus according to any one of claims 22 to 24, comprising acontrol unit configured to receive the at least one characteristic of the gaseous mixture (M) detected by each of the devices (10a, 10b, 10c) for measuring at least one characteristic of said gaseous mixture present in said apparatus.

26. The apparatus according to claim 25, wherein the control unit is configured to adjust the composition of the gaseous mixture (M) to be injected into the burner (100) through the injection opening of said burner (100) as a function of the values of the characteristics received from each of the devices (10a, 10b, 10c) for measuring at least one characteristic of said gaseous mixture present in said apparatus.

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