Sound speed sensor

Abstract

The invention relates to a sound velocity sensor (10) for a fluid (FL), with at least one measuring chamber (11) in which at least one sound transducer (14, 15) is arranged, wherein at least one inlet opening (12) and at least one outlet opening (13) lead to the measuring chamber (11) and the measuring chamber (11) can be filled / flowed through by the fluid (FL) in order to carry out a measurement, wherein the sound velocity sensor (10) is arranged in a fluid line (1) through which the fluid (FL) flows and around which fluid (FL) flows.

Description

The invention relates to a sound velocity sensor according to the preamble of the first claim.DE 10 2011 121 867 A1 describes a method for measuring thermodynamic state variables of gases or liquids. The method has a receiver and / or transmitter device, an electromagnetic oscillator and / or resonator (sound transducer) and a piezoelectric element arrangement which generates the sound. The measuring system is suitable for temperatures clearly above 200° C. The resonator is formed by a cylindrical body, on the rear wall of which the sound transducer is attached. The sound transducer detects the respective reflected wave and transmits a corresponding electrical signal, which is evaluated.DE 10 2011 102 641 A1 describes a device or a method for quantitatively detecting at least one physical variable of a gas or liquid. The method has two measuring chambers which are connected to one another by a separating wall. The measuring chambers are equipped with sound transducers. The measurement is carried out by zeroing a known reference medium and the unknown sample medium. The method has a piezoelectric oscillator which couples simultaneously into the reference and sample medium.EP 3 612 829 B1 describes an acoustic sensor which has a side wall and a second end wall around a fluid-filled cylindrical cavity. The sensor uses the different acoustic resonances of gases for the underlying measurement principle in order to infer characterizing speeds of sound (linear proportionality).DE 10 2008 014 300 A1 describes a method for determining changes in state of substance mixtures by measuring the speed of sound by means of a sound transducer. These changes in state are determined by damping the introduced ultrasound or the speed of sound.DE 10 2005 051 876 B3 describes a fluidic-acoustic oscillator in whose resonant chambers acoustic waves are generated, which are converted into electrical signals by means of dynamic pressure transducers. This oscillator is preferably used for binary gas mixtures at temperatures up to 300° C.DE 36 13 125 A1 describes a planar acoustic gas composition sensor which can be used for contaminated gases at temperatures up to 100° C. The sensor is made up of five planar plates (two vibrating plates, a partition plate and two enveloping plates). This construction is distinguished by simple assembly and disassembly.EP 2 788 748 B1 describes an acoustic sensor which consists essentially of a disc-shaped acoustic cavity and circular end walls. The end walls are equipped with sound transducers which convert the pressure fluctuations generated into oscillating electrical signals.The decisive disadvantage of these sensors is that they are not space-saving and are usually arranged outside the fluid lines.The publications U.S. Pat. No. 5,060,506 A, DE 690 17 376 T2, U.S. Pat. No. 6,468,222 B1 and DE 692 19 316 T2 disclose acoustic velocity sensors for fluid lines which are arranged in the fluid line and have a complicated structural design.The object of the invention is therefore to develop a sound velocity sensor which is arranged in a space-saving manner and has a simple structural design. In addition, a process integration for process monitoring should be realizable.This object is achieved according to the invention with the features of the first claim.Advantageous embodiments are evident from the dependent claims.The acoustic velocity sensor according to the invention for a fluid has at least one measuring chamber in which at least one acoustic transducer is arranged, wherein at least one inlet opening and at least one outlet opening lead to the measuring chamber and the fluid can fill / flow through the measuring chamber for the purpose of carrying out a measurement, wherein the acoustic velocity sensor is arranged in a fluid line through which the fluid flows and fluid preferably flows uniformly around it, and wherein the measuring chamber is arranged in a casing surrounding the circumferential side in an axially displaceable and rotationally fixed manner and the casing is positioned in a fixed manner on the frame in the fluid line.This in-line arrangement of the speed-of-sound sensor directly in the fluid line allows a space-saving configuration and reliable measurements can be realized.Preferably, the measuring chamber is arranged with at least one first sound transducer and at least one second sound transducer, wherein the first and the second sound transducer are each connected to a measurement / evaluation unit.The sound transducers are preferably separated from the measuring chamber by a cover in the form of a diaphragm. A counterbore is in the cover, the bottom of the counterbore acts as a diaphragm with the sonic transducer bonded thereto. In this cover there are the holes, laterally of the sound transducer and laterally to the counterbore through which the fluid can flow.Advantageously, the jacket is preferably positioned centrally in the fluid line for a low flow loss.When the inlet and outlet openings are open, the fluid flows through the measuring chamber.To carry out a measurement, the inlet opening / s of the measuring chamber can be closed. For this purpose, at least one radially inwardly pointing stop is provided on the jacket, for example, with which the at least one inlet opening / s can / are closable.Furthermore, in order to carry out the measurements, the outlet openings of the measuring chamber are also closed.To realize the closed first position, in which a measurement is carried out, the measuring chamber abuts the radially inwardly facing stop of the jacket and the inlet openings are closed. Furthermore, the jacket circumferentially closes the outlet openings.The measuring chamber is spaced apart from the stop in a second position, in which preferably no measurement takes place, so that the at least one inlet opening is free. In this second position, the jacket also released the at least one outlet opening of the measuring chamber. Fluid now enters the measuring chamber from the line through the at least one inlet opening and exits the measuring chamber from the at least one outlet opening into the line.In order to realize an axial movement of the measuring chamber for its displacement with respect to the jacket for opening and closing the inlet and outlet opening / s, the measuring chamber is operatively connected to an electromagnet, the measuring chamber being axially displaceable within the jacket counter to a spring force of a spring (preferably a compression spring) during the actuation of said electromagnet from the closed first (measuring) position into the open second (throughflow) position.The measuring chamber has a housing with a cavity and at its two ends closure elements which are formed on their outer sides, for example, flat (for resonance). The flat outer side with a thin partition wall towards the measuring chamber is necessary for resonance measurement.Alternatively, at least the outer side of the closure element positioned in the inflow direction of the fluid can also be designed correspondingly for reducing the flow resistance, for example with a spherically curved surface, in particular spherically or in the form of a cone. In this case, the first closure element arranged in the inflow direction has the inlet openings.The outlet openings preferably lead axially or at an angle through the second closure element and / or preferably radially through the housing.The first and second closure elements have the first and second sound transducers in the direction of the cavity of the measuring chamber. Preferably, a respective recess is provided in the direction of the cavity in each closure element, in which a sound transducer is positioned in each case.In order to guarantee good flow even in the event of possible soiling of the fluid, the outlet openings advantageously have a larger diameter than the inlet openings.The first and the second sound transducer are preferably made of materials that have a piezoelectric effect. These can be, for example, piezocrystals, piezoceramic, for example technical ceramic such as lead zirconate titanate (PZT) or else quartz crystal. The sound transducers are designed in particular for measurement and excitation.The acoustic velocity sensor integrated into a fluid line can be used, for example, for determining the density and / or heat capacity of a fluid. The fluid can be, for example, a heat carrier or a refrigerant in a heat carrier circuit or refrigerant circuit (or also gas pipelines, etc.).The solution according to the invention is preferably used for single-phase, in particular gaseous, mediaBy measuring the media by means of the acoustic velocity sensor according to the invention as an inline variant in the fluid line, it is possible to infer the heat capacity of the fluid in a simple and elegant manner by means of the density of the fluid. This is in turn an important value for the calculation of the energy balance in a heat carrier circuit or refrigerant circuit.An access for a temperature and / or pressure sensor (not shown) can additionally be integrated in the line.Against the spring force, an electromagnet wound from the outside (winding not shown) is actuated and the measuring chamber is thereby opened after a measuring process has ended, so that the fluid can flow through the latter.The measuring chamber with conical ends makes it possible to reduce its flow resistance.The inlet preferably comprises six axially running inlet openings, in particular with a diameter of 1.5 mm. On the outlet side, preferably ten radial holes are arranged which are uniformly distributed over the circumference (at an angle of 36°), the diameter of which is, for example, 2 mm.The fluid conduit may be mechanically connected to a system through which the fluid flows by flanges or other suitable connections.The front cone has axially symmetrical holes through which the fluid can flow in.Both sound transducers are connected via fine cables (e.g. IEC 60228 Class 6, VDE 0295) to a lock-in amplifier, not shown, which is used as an oscillator and for frequency measurement.In the open state of the acoustic velocity sensor, the fluid flow runs through the front cone toward the radial outlet holes in front of the rear cone.When the electromagnet is deactivated, the restoring force of the spring closes the measuring chamber without generating electric interference fields or signals.The appropriately designed electromagnet (depending on density and speed opens the measuring chamber upon its actuation against the spring force of the restoring spring before a measuring process. The spring is designed according to density and speed and the electromagnet corresponding to the spring is designed with a greater force than the force of the spring.It is possible, for adjusting the spring force, to integrate a spindle in addition to the spring when the density of the fluid is variable, as already used in safety valves.The measuring chamber is mounted in the (tubular) jacket for realizing the axial movement for the opening process and the closing process, so that the radially inwardly pointing stop is also used for sealing the inlet openings during the measuring process.The measuring principle is explained below:The sound transducers are preferably identical piezoceramics with fixed dimensions. Both sound transducers can be used for measurement as well as for excitation.When the measuring chamber is filled with fluid and closed, the first sound transducer is subjected to high-frequency voltages in the mV range and excites the diaphragm (not shown of the first sound transducer. The sound transducers have, for example, the following specification: K350 PZT Disc Diameter 10 mm x 0.4 mm thick gold plated.The diaphragm is preferably made of a conductive metallic material which is corrosion-resistant in accordance with the fluid so that the material does not lose its surface quality, in particular of stainless steel. However, another material, preferably a conductive metallic material, is also possible, which is corrosion-resistant in accordance with the fluid, so that the material does not lose its surface quality.The oscillations are transmitted to the fluid (e.g. gas) in the measuring chamber between the sound transducers. The oscillations cause a resonant frequency in the fluid that depends on the composition of the fluid (e.g., gas). Due to the low voltage at the level of only 1 V, for example, voltage peaks in the second sound transducer are measured and evaluated explicitly at resonant frequencies that manifest themselves in vibration modes.The specific ratio of length to diameter of the interior (cavity, e.g. 4 / 3 for gases) of the measuring chamber enables the isolation of the second longitudinal mode, so that no interference with other modes or resonances occurs. (For example, with a selected inner diameter of 24 mm, an inner length of 32 mm of the cavity of the measuring chamber results.) Consequently, only the resonant frequency of the isolated mode can be measured. The noise floor can thereby be clearly differentiated from the peak.A minimization of the noise floor would be effected if interference variables such as holes become smaller or polyphases are avoided.The frequency measurement and evaluation can be adapted in accordance with the required uncertainty.The frequency is in direct physical mathematically writable relationship to the speed of sound.Description of the Measurement Procedure:When it is actuated against the spring force of the restoring spring, the electromagnet opens the inlet openings and the outlet openings by corresponding displacement of the measuring chamber. As a result, the fluid can flow through the measuring chamber.If the electromagnet is deactivated, the force of the restoring spring acts and the measuring chamber is pushed back into its closed position, in which the inlet openings and preferably also the outlet openings are closed. The fluid is now enclosed in the measuring chamber.The entered oscillation via the first sound transducer now generates a standing wave which has a peak in the sought longitudinal mode. For this purpose, the frequency is entered over a broad spectrum and measured continuously at the second sound transducer.The lock-in amplifier coupled to the first and second sound transducers amplifies the signal or signals obtained and compares / locks this / these with a reference signal of the excitation signal (e.g. of the excitation signal of the first sound transducer), so that the sought frequency can also be measured in a phase-shifted manner.In: Jonas Herick, "Construction of an F-Praktice Trial: Lock-In Amplifier with Computer Assisted Signal Processing in LabVIEW, Bachelor Work at the Faculty of Physics and Astronomy of the Rühr-University of Bochum, 2007", page 8 is presented: "Lock-In Metrology is an extremely effective method which was first applied by the U.S. Physicker Robert Henry Dicht for examining extremely weak microwave radiation. It is possible to measure both the amplitude, i.e. the signal strength, and the phase of noisy harmonic signals. The principle of the lock-in amplifier is based on the modulation of the variable to be measured by means of a reference signal of the same frequency. The name already describes the useful and reference signals in this circuit "locked", i.e. to a certain extent kept closed with one another."The measured resonant frequency is evaluated by calculation in order to determine the speed of sound.The invention is explained in more detail below with reference to exemplary embodiments. The following are shown: FIG. 1 shows a schematic diagram of the arrangement of the speed of sound sensor, FIG. 2 shows a schematic diagram of a sound velocity sensor which is arranged in a line in a closed position (measurement position), FIG. 3 shows the speed of sound sensor according to FIG. 2 in the closed position, FIG. 4 shows a representation of a further embodiment of a sound velocity sensor in a line.FIG. 1 shows a schematic diagram of a solution according to the invention, in which a sound velocity sensor 10 is integrated into a fluid line 1, which is located here in a closed (measurement) position. Fluid FL flows around the speed sensor 10 in the fluid line 1.The speed-of-sound sensor 10 (see also FIGS. 2 to 4 ) has a measuring chamber 11 with a substantially cylindrically formed housing 11.1, in which a cavity 11.2 is formed. The housing 11.1 (shown in dashed lines) is provided on the end side with a first closure element 11.3 in the inflow direction AN of a fluid FL and with a second closure element 11.4 in the outflow direction AB of the fluid FL (see thick arrows in the fluid line 1). In the first closure element 11.3, a plurality of axially running inlet openings 12 are present, which lead to the cavity 11.2, and radially running outlet openings 13 are present in front of the second closure element 11.4, in the direction in the housing 11.1.A first sound transducer 14 (not shown in more detail) is arranged in or on the first closure element 11.3 in the direction of the cavity 11.2, and a second sound transducer 15 is arranged in or on the second closure element 11.4 likewise in the direction of the cavity 11.2 (likewise not shown in more detail). The measuring chamber 11 is mounted axially displaceably and non-rotatably in a preferably cylindrical jacket 16. The jacket 16 has, on the side of the first closure element 11.3, a radially inwardly pointing stop 16.1, which closes the inlet openings 12 in the closed position shown. Furthermore, the jacket 16 has a length by which it closes the radial outlet openings 13 present in the housing 11.1 in the position shown.To realize the axial movement for opening and closing the inlet and outlet openings 12, 13, the measuring chamber 11 has, on its second closure element 11.4, a plunger 17 which is arranged substantially in the direction of the longitudinal axis A of the measuring chamber 11 and projects outwards. This is firmly connected at the end to an electromagnet 18, of which only the iron core is shown here, which is referred to below as electromagnet 18, against which a spring 19 (in particular a compression spring) acts. In the deactivated state of the electromagnet 18, the latter, and also the measuring chamber 11 via the plunger 17, is pressed in the direction of the radially inwardly pointing stop 16.1 of the jacket 16 (here to the left). When the first closure element 11.3 abuts the radially inwardly facing stop 16.1 of the jacket 16, the inlet openings 12 of the first closure element are closed and the axially extending jacket 16 also engages over the outlet openings 13 of the housing 11.1 of the measuring chamber 11. The fluid FL is enclosed in the measuring chamber 11 in this first position in the form of the measuring position and the required measurements can now be carried out using the first and second sound transducers 14, 15 (see also FIGS. 3 and 4 ).To open the inlet openings 12 and the outlet openings 13, the iron core / electromagnet 18 is activated, so that the latter moves to the right here counter to the spring force of the spring 19. As a result, the measuring chamber 11 is also moved to the right via the plunger 17 in the jacket 16 and the inlet openings 12 and the outlet openings 13 are released (see FIG. 2 ).The electromagnet 18 and the spring 19 are seated, for example, in a protuberance 20 of the fluid line 1.The moving core of the electromagnet 18 is preferably a core of an externally wound electromagnet 18, the windings not being shown here.Although only the core of the electromagnet 18 is shown, the designation electromagnet 18 will be used further for this purpose below.The electromagnet 18 or its core and the spring 19 cause the opening and closing of the measuring chamber 11 by axially displacing it according to the double arrow (FIG. 1 ). The jacket 16 is fixed (axially and rotationally fixed) in the fluid line 1 by indicated fastening means 21 (see FIGS. 1 and 4 ).The rotationally fixed axial displaceability of the measuring chamber 11 in the casing 16 is realized, for example, by interlocking shaped elements (not shown). For example, a radially outward-pointing protrusion can be provided on the cylinder-like housing 11.1, which engages in a groove in the jacket 16, or the jacket 16 has a radially inward-pointing protrusion, which corresponds to a groove in the housing 11.1 (not shown).In the variants according to FIGS. 1 to 3, the first and second closure elements 11.3, 11.4 have straight surfaces on their outer sides.In the variants of FIG. 4, the outer surfaces of the closure elements 11.3, 11.4 are each designed in the form of a cone 22, resulting in a lower flow resistance.According to FIGS. 1 to 4, the fluid line 1 has, in the upper region here, a first access 2, through which a first cable guide K 1 leads to the first sound transducer 14, and a second access 3, through which a second cable guide K 2 leads to the second sound transducer 15. The accesses 2 and 3 are of course closed in a fluid-tight manner.Furthermore, a third access 4, for example for a pressure sensor (not shown) and / or a fourth access 5, for example for a temperature sensor (not shown), can lead to the fluid line 1 according to FIGS. 1 and 4.FIGS. 2 and 3 show the schematic diagrams of a sound velocity sensor 10, which is arranged in a fluid line 1 in an open second position of the measuring chamber 11 (FIG. 2 ) and in a closed second position (measuring position) of the measuring chamber 11 (FIG. 3 ) in an enlarged representation in longitudinal section.It can be seen from FIG. 2 that the measuring chamber 11 of the acoustic velocity sensor 10 is displaced by the electromagnet 18 activated here, which compresses the spring 19 against its spring force, by a displacement path s (here to the right), whereby the first closure element 11.3 is spaced apart by the displacement path s from the radially inwardly facing stop 16.1 of the casing 16.As a result, the inlet openings 12 and the outlet openings 13 are exposed and the fluid FL flows from the fluid line 1 through the inlet openings 12 into the measuring chamber 11 and through the outlet openings 13 from the measuring chamber 11 into the fluid line 1. In this position, preferably no measurement takes place.According to FIG. 3, the measuring chamber 11 has been moved by the adjustment distance s into the first position, in which a measurement can be carried out by means of the sound transducers 14, 15. The first closure element 11.3 abuts the radially inwardly facing stop 16.1 of the jacket 16, so that the inlet openings 12 are closed. The outlet openings 13 in the housing 11.1 of the measuring chamber 11 were likewise closed by the jacket 16, since the housing 11.1 was pushed into the jacket 16 to a corresponding extent.The fluid FL is now enclosed in the measuring chamber 11. The enclosed fluid FL is shaded obliquely here in short lines for clarity.FIG. 4 shows the embodiment of a sound velocity sensor 10 in the first position (measurement position), which, in contrast to the variants in FIGS. 1 to 3, has closure elements 11.3, 11.4 at the end, the outer sides of which are designed in the form of a cone 22.The stop 16.1 is also designed accordingly. In addition, a seal 25 is provided between the cone 22 of the first closure element 11.3 and the stop 16.1.Otherwise, the construction of the acoustic velocity sensor according to FIG. 4 substantially corresponds to the embodiments of FIGS. 1 to 3.According to FIG. 4, the sound velocity sensor 10 is provided in a line 1 with a first fastening flange 6 with bores 7 and a second fastening flange 8 with bores 9 for fastening in a line system.It can also be seen from FIGS. 2 to 4 that a first recess 23 is present in the first closure element 11.3 in the direction of the cavity 11.2 of the measuring chamber 11, in which recess the first sound transducer 14 is fixed to the diaphragm in a vibration-proof manner. In the opposite second closure element 11.4 of the measuring chamber 11, a recess 24 is likewise provided in the direction of the cavity 11.2, in which recess the second sound transducer 15 is fixed in a vibration-proof manner by means of the diaphragm.The sound transducers 14, 15 are each mounted on a cover, not designated, which is fastened to the end face (not designated) of the respective closure element 11.3, 11.4 facing in the direction of the cavity 11.2 of the measuring chamber 11, so that the sound transducers 14, 15 protrude into the recesses 23, 24.Further, it is important to note that the fixed contact with the metal (diaphragm) is used as an electric line so that an electric signal can be applied. The measuring chamber serves as a conductor.The electrically conductive and vibration-proof connection of the sound transducers to the measuring chamber via the cavity or the depression in the cover is important.The PZTs (piezoelectric ultrasonic transducers) are pressed on in such a way that very fine surface peaks in the metal / diaphragm come into contact with the conductive gold-coated surface of the piezoceramic material (PZT) as a result of the roughness.If the covers extend up to the undesignated outer diameter of the closure elements 11.3, holes are also integrated into the cover on the inlet side of the fluid, which holes allow the flow of the fluid FL.Between the recesses 23, 24 of the closure elements 11.3, 11.4, a thin separating wall is present in the direction of the cavity 11.2 of the measuring chamber 11, which serves to form the measuring chamber or the cavity of the measuring chamber.This thin separating wall is a diaphragm as a boundary to the cavity 11.2 of the measuring chamber 11, which diaphragm preferably consists of stainless steel or another suitable conductive material.In this case, a first diaphragm 23.1 is located between the first recess 23 and the cavity 11.2 of the measuring chamber 11 and a second diaphragm 24.1 is located between the second recess 24 and the cavity 11.2 of the measuring chamber 11. These are fastened to covers. The covers are not shown in FIGS. 1 to 3, but are visible from FIG. 4, but are not designated.Through-openings, not designated, in the closure elements 11.3, 11.4 lead the connecting lines (likewise not designated) through the cable guides K1, K2 to the sound transducers 14, 15 in the recesses 23, 24 (see likewise FIGS. 2 to 4 ). The closure elements 11.3, 11.4 are preferably embodied in two parts; this can be seen in FIG. 4.The use of the acoustic velocity sensor as an in-line sensor within a fluid line results in only slight pressure losses. Fluids in the form of gas mixtures, pure gases and, if appropriate, also multi-phase mixtures can be tested therewith. The solution according to the invention also enables individual mechanical integration into pipe systems, for example via suitable flange connections such as special industrial flanges. The solution according to the invention has a robust construction and is protected from external mechanical damage by the in-line arrangement. The acoustic velocity sensor according to the invention can advantageously also be used for high and low temperatures.

Claims

Acoustic velocity sensor (10) for a fluid (FL), having at least one measuring chamber (11), in which at least one acoustic transducer (14, 15) is arranged, wherein at least one inlet opening (12) and at least one outlet opening (13) lead to the measuring chamber (11), and the fluid (FL) can fill / flow through the measuring chamber (11), in order to carry out a measurement, wherein the acoustic velocity sensor (10) is arranged in a fluid line (1) through which the fluid (FL) flows and fluid (FL) flows around it, wherein the measuring chamber (11) is arranged in an axially displaceable and rotationally fixed manner in a casing (16) surrounding the latter on the circumferential side, and the casing (16) is positioned fixed to the frame in the fluid line (1).The acoustic velocity sensor (10) according to claim 1, characterized in that at least one first acoustic transducer (14) is arranged in the measuring chamber (11) downstream of the inlet opening (12) and at least one second acoustic transducer (15) is arranged upstream and / or downstream of the outlet opening (13), wherein the first and the second acoustic transducer (14, 15) are connected to a measurement / evaluation unit.The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the at least one inlet opening (12) of the measuring chamber (11) and / or the at least one outlet opening (13) is / are closable for carrying out a measurement.The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that at least one radially inwardly facing stop (16.1) is provided on the jacket (16), with which stop the at least one inlet opening (12) can be closed and / or that the at least one outlet opening (13) of the measuring chamber (11) can be closed by a cylindrical region of the jacket (16).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that - in a first position in which a measurement is made, the measuring chamber (11) abuts against the radially inwardly facing stop (16.1) and the inlet opening (12) is closed, and that the outlet opening (13) is closed by the jacket (16), and - in a second position in which no measurement is made, the measuring chamber (11) is spaced apart from the stop (16.1) and the at least one inlet opening (12) is free and the jacket (16) releases the outlet opening (13), so that fluid (FL) from the line (1) enters the measuring chamber (11) through the inlet opening (12) and exits from the outlet opening (13) from the measuring chamber (11) into the fluid line (1).The acoustic velocity sensor (10) according to claim 5, characterized in that the measuring chamber (11) is operatively connected to an electromagnet (18), the measuring chamber (11) being axially displaceable by an adjustment path (s) from the first position into the second position within the jacket (16) counter to a spring force of a spring (19).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the inlet openings (12) and / or the outlet openings (13) lead axially and / or radially and parallel or at an angle to the longitudinal axis (A) of the acoustic velocity sensor (10) from the cavity (11.2) of the measuring chamber (11) outwards into the fluid line (1).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the measuring chamber (11) comprises a substantially cylindrical housing (11.1) with a cavity (11.2) and at both ends of the housing (11.1) closure elements (11.3, 11.4) which are formed flat or in the form of a cone (22) on their outer sides, wherein the first closure element (11.3) comprises axially extending inlet openings (12) and radially extending outlet openings (13) are arranged in front of the second closure element (11.4) in the housing (11.1).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the outlet openings (13) lead through the second closure element (11.4).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the first closure element (11.3) has the first acoustic transducer (14) in the direction of the cavity (11.2) of the measuring chamber (11) and the second closure element (11.4) has the second acoustic transducer (15) in the direction of the cavity (11.2) of the measuring chamber (11).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the outlet openings (13) have a larger diameter than the inlet openings (12).The acoustic velocity sensor (10) according to any one of the preceding claims, characterized in that the first and second acoustic transducers (14, 15) consist of identical piezoceramics and that both acoustic transducers (14, 15) are designed for measuring and for exciting.

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