DE202023107020U1 - Sound speed sensor - Google Patents

Abstract

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) to realize 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.

In EN 10 2011 121 867 A1 A method for measuring thermodynamic state variables of gases or liquids is described. The method has a receiver and/or transmitter, an electromagnetic oscillator and/or resonator (sound transducer) and a piezo element arrangement that generates the sound. The measuring system is suitable for temperatures well above 200°C. The resonator is formed by a cylindrical body, on the back 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.

In EN 10 2011 102 641 A1 A device or a method for quantitatively recording at least one physical quantity of a gas or liquid is described. The method has two measuring chambers that are connected to each other via a partition 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 that couples into the reference and sample medium at the same time.

In EP 3 612 829 B1 describes an acoustic sensor that 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 measuring principle in order to determine characteristic sound velocities (linear proportionality).

In EN 10 2008 014 300 A1 A method is described for determining changes in the state of mixtures of substances by measuring the speed of sound using a sound transducer. These changes in state are determined by the attenuation of the introduced ultrasound and/or the speed of sound.

In EN 10 2005 051 876 B3 A fluidic-acoustic oscillator is described in whose resonance chambers sound 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.

In EN 36 13 125 A1 A planar acoustic gas composition sensor is described that can be used for contaminated gases at temperatures up to 100°C. The sensor consists of five planar plates (two vibrating plates, one separating plate and two enveloping plates). This design is characterized by easy assembly and disassembly.

In EP 2 788 748 B1 describes an acoustic sensor that essentially consists of a disk-shaped acoustic cavity and circular end walls. The end walls are equipped with sound transducers that convert the generated pressure fluctuations into oscillating electrical signals.

The decisive disadvantage of these sensors is that they do not save space and are usually arranged outside the fluid lines.

The object of the invention is therefore to develop a sound velocity sensor that is arranged in a space-saving manner. In addition, process integration for process monitoring should be possible.

This object is achieved according to the invention with the features of the first claim.

Advantageous embodiments emerge from the subclaims.

The sound velocity sensor for a fluid according to the invention has at least one measuring chamber in which at least one sound transducer is arranged, wherein at least one inlet opening and at least one outlet opening lead to the measuring chamber and the measuring chamber can be filled/flowed through by the fluid in order to realize a measurement, wherein the sound velocity sensor is arranged in a fluid line through which the fluid flows and is preferably evenly flowed around by the fluid.

This in-line arrangement of the sound velocity sensor directly in the fluid line enables a space-saving design and reliable measurements can be realized.

Preferably, at least one first sound transducer and at least one second sound transducer are arranged in the measuring chamber, wherein the first and the second sound transducer are each connected to a measuring/evaluation unit.

The separation of the sound transducers from the measuring chamber is preferably done by a cover in the form of a diaphragm. In the cover there is a sensor kung, the bottom of the depression acts as a diaphragm with the sound transducer glued to it. In this cover are the holes, to the side of the sound transducer and to the side of the depression, through which the fluid can flow.

Advantageously, the measuring chamber is arranged in a casing that surrounds it on the circumference so that it can be axially displaced and is rotationally fixed, and the casing is fixed to the frame in the fluid line and is preferably positioned centrally to minimize 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, for example, there is at least one radially inward-pointing stop on the casing, with which the at least one inlet opening(s) can be closed.

Furthermore, the outlet openings of the measuring chamber are also closed in order to carry out the measurements.

To achieve the closed first position in which a measurement is carried out, the measuring chamber rests against the radially inward-facing stop of the casing and the inlet openings are closed. The casing also closes the outlet openings on the circumference.

In a second position, in which preferably no measurement is carried out, the measuring chamber is spaced from the stop so that the at least one inlet opening is free. In this second position, the at least one outlet opening of the measuring chamber is also freed up by the casing. Fluid now enters the measuring chamber from the line through the at least one inlet opening and exits the measuring chamber into the line through the at least one outlet opening.

In order to realize an axial movement of the measuring chamber to move it in relation to the casing for opening and closing the inlet and outlet opening(s), the measuring chamber is operatively connected to an electromagnet, upon actuation of which the measuring chamber can be axially displaced against a spring force of a spring (preferably a compression spring) from the closed first (measuring) position to the open second (flow-through) position within the casing.

The measuring chamber has a housing with a cavity and closure elements at both ends, which are designed to be flat on their outer sides (for resonance). The flat outer side with a thin partition wall towards the measuring chamber is necessary for resonance measurement.

Alternatively, at least the outside of the closure element positioned in the flow direction, which is arranged in the flow direction of the fluid, can be designed accordingly to reduce the flow resistance, for example with a spherically curved surface, in particular spherical or in the shape of a cone. The first closure element arranged in the flow 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 recess is provided in the direction of the cavity in each closure element, in which a sound transducer is positioned.

In order to guarantee good flow even if the fluid is contaminated, the outlet openings advantageously have a larger diameter than the inlet openings.

The first and second sound transducers are preferably made of materials that have a piezoelectric effect. These can be, for example, piezo crystals, piezo ceramics, e.g. technical ceramics such as lead zirconate titanate (PZT) or quartz oscillators. The sound transducers are designed in particular for measuring and for excitation.

The sound velocity sensor integrated into a fluid line can be used, for example, to determine the density and/or heat capacity of a fluid. The fluid can, for example, be a heat transfer medium or a coolant in a heat transfer medium circuit or coolant circuit (or gas pipelines, etc.).

The solution according to the invention is preferably used for single-phase, in particular gaseous media

By measuring the media using the sound velocity sensor according to the invention as an inline variant in the fluid line, the density of the fluid can be used to determine its heat capacity in a simple and elegant way. This is in turn an important value for the calculation Calculation of the energy balance in a heat transfer medium circuit or refrigerant circuit.

An additional access for a temperature and/or pressure sensor (not shown) can be integrated into the line.

An electromagnet wound from the outside (winding not shown) is actuated against the spring force, thereby opening the measuring chamber after completion of a measuring process so that the fluid can flow through it.

The measuring chamber with conical ends makes it possible to reduce its flow resistance.

The inlet preferably comprises six axially extending inlet openings, in particular with a diameter of 1.5 mm. On the outlet side, ten radial holes are preferably arranged, evenly distributed over the circumference (at an angle of 36°), the diameter of which is, for example, 2 mm.

The fluid line can be mechanically connected to a system through which the fluid flows by means of flanges or other suitable connections.

The front cone has axially symmetrical holes through which the fluid can flow.

Both 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.

When the sound velocity sensor is open, the fluid flow passes through the front cone to the radial outlet holes in front of the rear cone.

When an electromagnet is deactivated, the restoring force of the spring closes the measuring chamber without generating electrical interference fields or signals.

The appropriately designed electromagnet (depending on density and speed) opens the measuring chamber when it is activated against the spring force of the return spring before a measuring process. The spring is designed according to density and speed and the electromagnet corresponds to the spring with a force greater than the force of the spring.

It is possible to integrate a spindle in addition to the spring to adjust the spring force when the density of the fluid changes, as is already done with safety valves.

The measuring chamber is mounted in the (tubular) casing to realize the axial movement for the opening and closing process, so that the radially inward-pointing stop is also used to seal the inlet openings during the measuring process.

The measuring principle is explained below:

The transducers are preferably identical piezoceramics with fixed dimensions. Both transducers can be used for measuring and for excitation. The first transducer is subjected to high-frequency voltages in the mV range in a closed measuring chamber filled with fluid and excites the diaphragm (not shown) of the first transducer. The transducers have the following specifications, for example: K350 PZT Disc Diameter 10mm x 0.4mm thick gold plated.

The diaphragm preferably consists of a conductive metallic material that is corrosion-resistant according to the fluid so that the material does not lose its surface quality, in particular stainless steel. However, another material is also possible, preferably a conductive metallic material that is corrosion-resistant according to the fluid so that the material does not lose its surface quality.

The vibrations are transmitted to the fluid (e.g. gas) in the measuring chamber between the transducers. The vibrations cause a resonance frequency in the fluid, which depends on the composition of the fluid (e.g. gas). Due to the low voltage of only 1V, for example, voltage peaks in the second transducer are explicitly measured and evaluated at resonance frequencies, which 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 second longitudinal mode to be isolated so that no interference with other modes or resonances occurs. (For example, with a selected inner diameter of 24mm, the inner length of the cavity of the measuring chamber is 32mm.) Consequently, only the resonance frequency of the isolated mode can be measured. The background noise can thus be clearly distinguished from the peak.

The background noise would be minimized if disturbances such as boreholes were made smaller or multiphases were avoided.

The frequency measurement and evaluation can be adapted according to the required uncertainty.

The frequency is in direct physical and mathematically describable relationship to the speed of sound.

Description of the measuring process:

When the electromagnet is activated, it opens the inlet and outlet openings by moving the measuring chamber against the spring force of the return spring. This allows the fluid to flow through the measuring chamber. If the electromagnet is deactivated, the force of the return spring takes effect 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 vibration introduced via the first transducer now generates a standing wave that has a peak in the desired longitudinal mode. To do this, the frequency is introduced over a broad spectrum and continuously measured at the second transducer.

The lock-in amplifier coupled to the first and second transducers amplifies the received signal or signals and compares/locks them with a reference signal of the excitation signal (e.g. the excitation signal of the first transducer) so that the desired frequency can also be measured with a phase shift. In: Jonas Herick “Setting up an F-practical experiment: Lock-in amplifier with computer-aided signal processing in Lab VIEW, Bachelor thesis at the Faculty of Physics and Astronomy at the Ruhr University Bochum, 2007” is on page 8 explained: "Lock-in measurement technology is an extremely effective method that was first used by the US physicist Robert Henry Dicke to investigate 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 quantity to be measured using a reference signal of the same frequency. The name already describes the fact that the useful and reference signals in this circuit are "locked", i.e. remain closed to one another in a certain sense."

The measured resonance frequency is mathematically evaluated to determine the speed of sound.

The invention is explained in more detail below using exemplary embodiments.

• 1 Prinzipskizze der Anordnung des Schallgeschwindigkeitssensors,
• 2 Prinzipskizze eines Schallgeschwindigkeitssensors, der in einer Leitung angeordnet ist in einer geschlossenen Position (Messposition),
• 3 Schallgeschwindigkeitssensor gemäß 2 in geschlossener Position,
• 4 Darstellung einer weiteren Ausführung eines Schallgeschwindigkeitssensors in einer Leitung.

Show it:

• 1 Schematic diagram of the arrangement of the sound velocity sensor,
• 2 Schematic diagram of a sound velocity sensor arranged in a pipe in a closed position (measuring position),
• 3 Sound velocity sensor according to 2 in closed position,
• 4 Illustration of another design of a sound velocity sensor in a pipe.

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 here in a closed (measuring) position. The sound velocity sensor 10 is surrounded by fluid FL in the fluid line 1.

The sound velocity sensor 10 (see also 2 to 4 ) has a measuring chamber 11 with a substantially cylindrical housing 11.1 in which a cavity 11.2 is formed. The housing 11.1 (shown in dashed lines) is provided at the end in the inflow direction AN of a fluid FL with a first closure element 11.3 and in the outflow direction AB of the fluid FL (see thick arrows in the fluid line 1) with a second closure element 11.4. In the first closure element 11.3 there are several axially running inlet openings 12 which lead to the cavity 11.2 and in front of the second closure element 11.4 there are radially running outlet openings 13 in the housing 11.1.

In or on the first closure element 11.3, a first sound transducer 14 (not shown in detail) is arranged in the direction of the cavity 11.2 and in or on the second closure element 11.4, a second sound transducer 15 is arranged in the direction of the cavity 11.2 (also not shown in detail). The measuring chamber 11 is axially displaceable and mounted in a rotationally fixed manner in a preferably cylindrical casing 16. The casing 16 has a radially inwardly pointing stop 16.1 on the side of the first closure element 11.3, which closes the inlet openings 12 in the closed position shown. Furthermore, the casing 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 a plunger 17 on its second closure element 11.4, which is arranged essentially in the direction of the longitudinal axis 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. When the electromagnet 18 is deactivated, it, and via the plunger 17 also the measuring chamber 11, are pressed in the direction of the radially inward-pointing stop 16.1 of the casing 16 (here to the left). When the first closure element 11.3 rests against the radially inward-pointing stop 16.1 of the casing 16, the inlet openings 12 of the first closure element are closed and the axially extending casing 16 also extends over the outlet openings 13 of the housing 11.1 of the measuring chamber 11. As a result, the inlet openings 12 and the outlet openings 13 of the measuring chamber 11 are closed. 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 with the first and second sound transducers 14, 15 (see also 3 and 4 ).

To open the inlet openings 12 and the outlet openings 13, the iron core/electromagnet 18 is activated so that it moves to the right against the spring force of the spring 19. This also moves the measuring chamber 11 to the right via the plunger 17 in the casing 16 and the inlet openings 12 and the outlet openings 13 are released (see 2 ).

The electromagnet 18 and the spring 19 are located, 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 term electromagnet 18 will be used for it below.

The electromagnet 18 or its core and the spring 19 cause the opening and closing of the measuring chamber 11 by its axial displacement according to the double arrow ( 1 ). The casing 16 is secured by means of indicated fastening means 21 (see 1 and 4 ) is fixed in the fluid line 1 (axially and rotationally fixed).

The rotationally fixed axial displacement of the measuring chamber 11 in the casing 16 is achieved, for example, by interlocking shaped elements (not shown). For example, a radially outward-pointing projection can be provided on the cylinder-like housing 11.1, which engages in a groove in the casing 16, or the casing 16 has a radially inward-pointing projection that corresponds to a groove in the housing 11.1 (not shown).

For the variants according to 1 to 3 the first and second closure elements 11.3, 11.4 have straight surfaces on their outer sides.

In the variants of the 4 the outer surfaces of the closure elements 11.3, 11.4 are each designed in the form of a cone 22, which results in a lower flow resistance.

The fluid line 1 has according to the 1 to 4 in the upper area here, a first access 2 through which a first cable guide K1 leads to the first sound transducer 14 and a second access 3 through which a second cable guide K2 leads to the second sound transducer 15. The accesses 2 and 3 are of course closed fluid-tight.

Furthermore, the fluid line 1 according to the 1 and 4 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).

The 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 ( 2 ) and in a closed second position (measuring position) of the measuring chamber 11 ( 3 ) in enlarged longitudinal section.

It is out 2 It can be seen that the measuring chamber 11 of the sound velocity sensor 10 is displaced by an adjustment path s (here to the right) by the electromagnet 18 activated here, which compresses the spring 19 against its spring force, whereby the first closure element 11.3 is spaced by the adjustment path s from the radially inward-pointing 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. Furthermore, fluid FL flows around the sound velocity sensor 10. In this position, no measurement is preferably carried out.

According to 3 the measuring chamber 11 was moved by the travel distance s into the first position in which a measurement can be carried out using the sound transducers 14, 15. The first closure element 11.3 rests against the radially inward-pointing stop 16.1 of the casing 16, so that the inlet openings 12 are closed. The outlet openings 13 in the housing 11.1 of the measuring chamber 11 were also closed by the casing 16, since the housing 11.1 was pushed into the casing 16 a corresponding distance.

The fluid FL is now enclosed in the measuring chamber 11. The enclosed fluid FL is shown here diagonally hatched in short lines for clarity.

In 4 The design of a sound velocity sensor 10 in the first position (measuring position) is shown, which, in contrast to the variants in the 1 to 3 end-side closure elements 11.3, 11.4, the outer sides of which are designed in the shape 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 structure of the sound velocity sensor corresponds to 4 essentially the statements of the 1 to 3 .

The sound velocity sensor 10 is designed according to 4 in a line 1 with a first fastening flange 6 with holes 7 and a second fastening flange 8 with holes 9 for fastening in a line system.

It is from the 2 to 4 It is also apparent that in the first closure element 11.3 in the direction of the cavity 11.2 of the measuring chamber 11 there is a first recess 23 in which the first sound transducer 14 is fixed in a vibration-proof manner with the diaphragm. In the opposite second closure element 11.4 of the measuring chamber 11 there is also a recess 24 in the direction of the cavity 11.2 in which 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 front side (not designated) of the respective closure element 11.3, 11.4 pointing 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.

It is also important to mention that the solid contact with the metal (diaphragm) is used as an electrical conductor so that an electrical signal can be applied. The measuring chamber serves as a conductor.

It is important that the sound transducers are electrically conductive and vibration-resistant and that they are connected to the measuring chamber via the cavity or recess in the lid.

The PZT (piezoelectric ultrasonic transducers) are pressed so firmly that the finest surface peaks in the metal / diaphragm come into contact with the conductive gold-coated surface of the piezoceramic material (PZT) due to the roughness.

If the covers extend to the non-designated outer diameter of the closure elements 11.3, holes are also integrated into the cover on the inlet side of the fluid, which allow the fluid FL to flow through.

Between the recesses 23, 24 of the closure elements 11.3, 11.4, in the direction of the cavity 11.2 of the measuring chamber 11, there is a thin separating wall 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 is preferably made of stainless steel or another suitable conductive material.

There is a first diaphragm 23.1 between the first recess 23 and the cavity 11.2 of the measuring chamber 11 and a second diaphragm 24.1 between the second recess 24 and the cavity 11.2 of the measuring chamber 11. These are attached to covers. The covers are in the 1 to 3 not shown, but from 4 visible, but not labeled.

Unmarked through-openings in the closure elements 11.3, 11.4 lead the connecting cables (also unmarked) through the cable guides K1, K2 to the sound transducers 14, 15 in the recesses 23, 24 (see also 2 to 4 ). The closure elements 11.3, 11.4 are preferably designed in two parts, this is shown in 4 recognizable.

By using the sound velocity sensor as an in-line sensor within a fluid line, only minimal pressure losses occur. This means that fluids in the form of gas mixtures, pure gases and possibly also multi-phase mixtures can be tested. The solution according to the invention also enables individual mechanical integration into pipe systems, e.g. via suitable flange connections such as special industrial flanges. The solution according to the invention has a robust structure and is protected from external mechanical damage by the in-line arrangement. The sound velocity sensor according to the invention can also be used for high and low temperatures.

List of reference symbols

1

Fluid line

2

first access

3

second access

4

third access

5

fourth access

6

first mounting flange

7

Drilling

8th

second mounting flange

9

Drilling

10

Sound speed sensor

11

Measuring chamber

11.1

Housing of the measuring chamber

11.2

Cavity of the measuring chamber

11.3

first closure element

11.4

second locking element

12

Entrance opening

13

Outlet opening

14

first sound transducer

15

second transducer

16

Coat

16.1

radially inward pointing stop

17

Pestle

18

Electromagnet

19

Feather

20

Protrusion of fluid line 1

21

Fasteners

22

cone

23

first recess

23.1

first diaphragm

24

second recess

24.1

second diaphragm

25

Sealing ring

A

Longitudinal axis

AWAY

Flow direction

AT

Flow direction

FL

Fluid

K1

first cable routing

K2

second cable routing

s

Travel

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102011121867 A1 [0002]
• DE 102011102641 A1 [0003]
• EP 3612829 B1 [0004]
• DE 102008014300 A1 [0005]
• DE 102005051876 B3 [0006]
• DE 3613125 A1 [0007]
• EP 2788748 B1 [0008]

Cited non-patent literature

• Jonas Herick “Setting up an F-practical experiment: Lock-in amplifier with computer-aided signal processing in Lab VIEW, Bachelor thesis at the Faculty of Physics and Astronomy at the Ruhr University Bochum, 2007” is on page 8 [0054]

Claims (13)

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) to realize 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. Sound velocity sensor (10) according to Claim 1 , characterized in that in the measuring chamber (11) after the inlet opening (12) at least one first sound transducer (14) is arranged and before and/or after the outlet opening (13) at least one second sound transducer (15) is arranged, wherein the first and the second sound transducer (14, 15) are connected to a measuring/evaluation unit. Sound velocity sensor (10) according to Claim 1 or 2 , characterized in that the measuring chamber (11) is arranged axially displaceably and rotationally fixed in a casing (16) surrounding it on the circumference and that the casing (16) is positioned fixed to the frame in the fluid line (1). Sound velocity sensor (10) according to 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) can be closed to carry out a measurement. Sound velocity sensor (10) according to one of the preceding claims, characterized in that at least one radially inwardly pointing stop (16.1) is present on the casing (16), with which 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 with a cylindrical region of the casing (16). Sound velocity sensor (10) according to one of the preceding claims, characterized in that - in a first position in which a measurement is carried out, the measuring chamber (11) rests against the radially inward-pointing stop (16.1) and the inlet opening (12) is closed and that the outlet opening (13) is closed by the casing (16) and - in a second position in which no measurement is carried out, the measuring chamber (11) is spaced from the stop (16.1) and the at least one inlet opening (12) is free and the casing exposes 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 measuring chamber (11) into the fluid line (1) through the outlet opening (13). Sound velocity sensor (10) according to one of the preceding claims, characterized in that the measuring chamber (11) is operatively connected to an electromagnet (18), upon actuation of which the measuring chamber (11) is axially displaceable against a spring force of a spring (19) from the first position into the second position within the casing (16) by an adjustment path (s). Sound velocity sensor (10) according to 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 sound velocity sensor (10) from the cavity (11.2) of the measuring chamber (11) outwards into the fluid line (1). Sound velocity sensor (10) according to one of the preceding claims, characterized in that the measuring chamber (11) has 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 flat on their outer sides or in the shape of a cone (22), wherein the first closure element (11.3) has 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). Sound velocity sensor (10) according to one of the preceding claims, characterized in that the outlet openings (13) lead through the second closure element (11.4). Sound velocity sensor (10) according to one of the preceding claims, characterized in that the first closure element (11.3) has the first sound 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 sound transducer (15) in the direction of the cavity (11.2) of the measuring chamber (11). Sound velocity sensor (10) according to one of the preceding claims, characterized in that the outlet openings (13) have a larger diameter than the inlet openings (12). Sound velocity sensor (10) according to one of the preceding claims, characterized in that the first and second sound transducers (14, 15) consist of identical piezoceramics and that both sound transducers (14, 15) are designed for measuring and for excitation.

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