Measuring device for speed of sound in material samples, measuring method, computer program product, evaluation unit and simulation program product

Abstract

The invention relates to a measuring device (10) used to measure a speed of sound (35) in a material sample (25). The measuring device (10) comprises a measuring chamber (12) having a sound emitter (18), and a plurality of microphones (20) arranged at distances from one another parallel to a main axis (15) of the measuring chamber (12). The microphones (20) are used for selectively measuring a frequency (32) of a standing wave (30). The invention also relates to a method (100) for measuring a speed of sound (35) in a material sample (25) using a corresponding measuring device (10). Equally, the invention relates to a computer program product (50) of appropriate design with which such a method (100) can be carried out. The invention further relates to an evaluation unit (40) equipped with a corresponding computer program product (50). The invention also relates to a simulation program product (60) for simulating an operating behaviour of a corresponding measuring device (10).

Description

[0001] Description

[0002] Measuring device for sound speed in material samples, measuring method, computer program product, evaluation unit and simulation program product

[0003] The invention relates to a measuring device for detecting the speed of sound in a material sample. The invention also relates to a method for measuring the speed of sound in a material sample. The invention further relates to a corresponding computer program product and a corresponding evaluation unit. Furthermore, the invention relates to a simulation program product for simulating the operating behavior of such a measuring device.

[0004] From the manual "Technical Information - Model GD402 Gas Density Meter", document abbreviation TI 11T03E01- 01E from Yokogawa Electric Corporation, a gas density meter is known which is based on a measurement of a resonance frequency in a gaseous sample. The gas density meter comprises a thin-walled cylinder which is surrounded by a solid cylindrical body. A gap is formed between the thin-walled cylinder and the solid cylindrical body, over which the sample flows. A vibration of the thin-walled cylinder is recorded by means of two pairs of piezo elements.

[0005] The previously unpublished European patent application with application number 23170557. 5 shows a measuring device for measuring the speed of sound in a material sample flowing through a measuring chamber. A microphone is arranged in a central region on a wall of the measuring chamber, with which the central antinode of a harmonic oscillation is recorded. The measuring device is used in an electrolyzer.

[0006] Sound velocity measurements in material samples are increasingly being used to monitor technical processes, such as the operation of an electrolyzer. This requires increased measurement accuracy and increased robustness. Likewise, the objective is to manufacture suitable measuring devices simply and economically. The invention is based on the object of providing a method that offers an improvement in at least one of the points outlined.

[0007] The problem is solved by a measuring device according to the invention. The measuring device is designed to detect a speed of sound in a material sample, for example a gas mixture. The measuring device comprises a measuring chamber in which the material sample is at least temporarily accommodated during a measuring operation. The measuring chamber is provided with a sound emitter which is designed and arranged to induce an acoustic oscillation in the material sample. In particular, the sound emitter is designed to induce a standing wave in the material sample as an acoustic oscillation. For this purpose, the sound emitter can be controlled in a tunable manner, for example.

[0008] According to the invention, a plurality of microphones are arranged parallel to one another in relation to a main axis of the measuring chamber. The microphones are to be recorded in order to selectively record an oscillation mode of the standing wave, i.e. amplitudes which arise in the corresponding oscillation mode. The main axis of the measuring chamber corresponds to an axis along which acoustic excitations can be emitted by the sound emitter. In particular, the main axis can correspond to a direction of a maximum internal dimension of the measuring chamber. The disputed arrangement of the microphones parallel to the main axis makes it possible to specifically acoustically record positions in which, for a specific oscillation mode of the standing wave, an increased, in particular maximum, amplitude of the sound pressure present there can be expected. The oscillation mode, in turn, depends on the frequency present.This makes it possible to specifically, i.e. selectively, detect a standing wave in the measuring chamber which is present in a specific vibration mode. From this, a wavelength of the standing wave can be determined. Interference from other acoustic vibrations in the measuring chamber, in particular as a result of other vibration modes, can be suppressed in the measuring device described. The measuring device according to the invention thus enables robust and, at the same time, precise measurements. Based on the measurement of the speed of sound in the material sample, its composition, among other things, can be determined. In the case of a binary material sample, i.e. a material sample with two components, their mixing ratio can also be determined. The vibration mode to be selectively detected can be predetermined by the positioning of the microphones.

[0009] According to the invention, the measuring device has a first group of microphones for selectively detecting a frequency of a first standing wave and a second group of microphones for selectively detecting a frequency of a second standing wave, which are arranged in the measuring chamber. The first and second groups can partially comprise identical microphones, in particular a microphone arranged essentially centrally along the main axis of the measuring chamber. By means of corresponding microphones, a plurality of standing waves in the measuring chamber can be detected. With suitable control, i.e. tuning, of the sound emitter, the speed of sound in the material sample in the measuring chamber can be detected multiple times. Consequently, detection of the speed of sound by means of the first group of microphones can be made plausible by detection by means of the second group of microphones. A third, fourth, etc. group can also be used.A group of microphones can be provided on the measuring chamber for detecting a third, fourth, etc. standing wave in the material sample. The measuring chamber can therefore be adapted for operation with a plurality of material samples. The number of possible material samples is only limited by the installation space available on or in the measuring chamber. The claimed measuring device is therefore scalable in terms of versatility and is therefore also suitable for complex applications. The claimed measuring device is particularly suitable for detecting a changing concentration of hydrogen in a heavier gas. Furthermore, the first and second groups of microphones can be arranged in such a way that they detect adjacent antinodes of the standing wave which have different signs. A microphone of the second group is therefore positioned along the main axis between two microphones of the first group.The first and second groups of microphones can be arranged, in particular, on opposite walls of the measuring chamber. This allows the amplification of the combined signal to be further increased. In particular, a further increase in the SNR can be achieved.

[0010] In one embodiment of the measuring device, at least one of the microphones is connected to the sound emitter via the evaluation unit. The sound emitter and at least one of the microphones are arranged in a positive feedback loop. This allows the vibration mode to be recorded to be precisely selected during measurement. Together with the positioning of the microphones, a unique wavelength is available for a selected vibration mode. This, in turn, allows the speed of sound in the material sample to be precisely measured. Furthermore, all microphones of the claimed measuring device can be arranged in a positive feedback loop with the sound emitter. This achieves the advantages outlined above to a particular extent.

[0011] In a further embodiment of the claimed measuring device, the microphones are connected to the evaluation unit. The evaluation unit is designed to evaluate a combination of measurement signals from the microphones, for example an addition of measurement signals. The microphones can be connected to an addition unit to add the measurement signals from the connected microphones and, based on this, to form a combination signal which is designed as a sum signal. Wave antinodes of standing waves of a certain frequency or oscillation modes occur in the measuring chamber at fixed positions relative to its main axis. The microphones can be arranged such that several microphones record maximum amplitudes along the standing wave. A combination signal formed from corresponding measurement signals by addition therefore also has an increased amplitude.This increases the signal-to-noise ratio (SNR), allowing for robust measurements. Accordingly, the claimed measuring device can be manufactured using simple microphones, particularly MEMS microphones, while simultaneously providing reliable selection of a vibration mode.

[0012] Furthermore, the evaluation unit can comprise an operational amplifier. The operational amplifier is connected directly or indirectly to the microphones in such a way that the measurement signals from the microphones are combined and fed to an amplifier input of the operational amplifier. A suitable circuit can connect the microphone signal lines to one another in a node. The measurement signals can be combined with one another, i.e., added, using hardware, which ensures fast and reliable provision of the combination signal, in particular the sum signal.

[0013] In a further embodiment of the claimed measuring device, the microphones are arranged parallel to the main axis of the measuring chamber for combined, i.e. essentially simultaneous, detection of pressure antinodes. Maxima of the sound pressure of the standing wave occur periodically at the pressure antinodes of the standing wave. The pressure antinodes are evenly spaced from one another. The corresponding microphones can therefore also be arranged evenly spaced from one another, in particular in the area of ​​an expected pressure antinode. Microphones can be positioned with increased precision on or in the measuring chamber. The more precisely the microphones are positioned, the higher the achievable signal maximum of the combined signal, which in turn allows precise selection of the corresponding vibration mode and consequently also precise determination of the speed of sound in the material sample.

[0014] Furthermore, the evaluation unit belonging to the measuring device can be designed without an electronic bandpass filter. In particular, the combination signal can be sent essentially unfiltered to a phase shifter. The phase shifter belongs to the evaluation unit and is designed to shift the phase of the combination signal in such a way that positive feedback is created. Accordingly, the combination signal can have a wide range of frequencies that can be evaluated to determine the speed of sound. Because the electronic bandpass filter is omitted, the structure of the measuring device is further simplified and allows the speed of sound to be measured over a wide measuring range. The claimed measuring device is therefore suitable for measuring material samples that contain hydrogen.

[0015] In a further embodiment of the claimed measuring device, the microphones are arranged at the same circumferential position relative to the main axis of the measuring chamber. Consequently, the microphones are in the same position when viewed in a cross-section, i.e. the same circumferential position. This ensures that wave antinodes lying one after the other along the main axis reach the microphones at the same time and are thus recorded simultaneously. This eliminates the need for further temporal coordination of the measurement signals from the microphones. Furthermore, a plurality of microphones, preferably all microphones, can be mounted on a common electronic printed circuit board, for example an elongated circuit board. Such a printed circuit board can be manufactured quickly and cost-effectively with an increased degree of automation.Furthermore, the standing wave whose frequency is to be recorded can be a third or fourth harmonic longitudinal oscillation in the measuring chamber. The third and fourth harmonic longitudinal oscillations each show significant changes in their corresponding resonance frequency even with small changes in the composition of the underlying material sample. The change in the resonance frequency corresponds to a change in the speed of sound to be measured in the material sample. The third and fourth harmonic longitudinal oscillations are each advantageously suitable for monitoring the purity of the material sample. Due to the significant changes in the associated resonance frequency, which can be recorded or determined using the claimed measuring device, cost-effective microphones, for example those from consumer electronics, are sufficient for this purpose.The claimed measuring device can therefore also be manufactured cost-effectively.

[0016] Furthermore, a temperature sensor and / or a pressure sensor can be arranged in the area of ​​at least one microphone. The temperature sensor or the pressure sensor is arranged and designed to detect a temperature or a pressure present in the material sample in the measuring chamber. The detection of the speed of sound in the material sample is temperature-dependent and pressure-dependent. By means of the temperature sensor and / or pressure sensor, temperature compensation and / or pressure compensation is therefore possible when measuring the speed of sound. The accuracy of the measurement to be carried out is thereby further increased in the claimed measuring device and its potential range of use for process applications is expanded.

[0017] In one embodiment of the claimed measuring device, at least one of the microphones can be designed as a pressure microphone or as a laser microphone. Pressure microphones are designed to directly detect the sound pressure that occurs in the region of the antinodes of the standing wave to be detected. Pressure microphones offer increased robustness and are cost-effective. Likewise, a plurality of pressure microphones can be connected to form a microphone array. With such a microphone array, a plurality of frequencies of standing waves in the measuring chamber can be selectively detected simultaneously or in time-slice operation. This makes the claimed measuring device adaptable for a wide range of possible applications, for example for operation with different material samples.

[0018] Alternatively, at least one of the microphones can be designed as a laser microphone. The laser microphone can be arranged to detect a vibration of a wall of the measuring chamber. The laser microphone is positioned in such a way that it detects an area of ​​the wall in which an antinode of a given standing wave is to be expected. Laser microphones are insensitive to flow effects in the measuring chamber. Furthermore, laser microphones offer sufficient measurement accuracy even over greater distances. Accordingly, the laser microphone can be attached to or in the measuring chamber at a variety of positions. This in turn offers additional design freedom in the design of the measuring chamber and makes it possible, for example, to miniaturize the claimed measuring device.

[0019] Alternatively, several microphones can be combined to form a sound camera. The sound camera can be used to simultaneously record several positions at which antinodes of standing waves can occur in the measuring chamber. The sound camera can be adapted to a large number of standing waves of different wavelengths or frequencies without further modifications. In particular, the claimed measuring device can be set to different standing waves by appropriately parameterizing a computer program product with which the measuring device is operated. The measurement signals can also be added together if the computer program product is designed in a suitable way. The measuring device can therefore be easily adapted by updates. With increasing computing capacity, future applications of increasing complexity can also be implemented.Furthermore, the microphone can be designed as an optical microphone configured to measure a change in the refractive index of the material sample. This allows frequency ranges with increased frequencies to be detected, in particular of a few MHz, in particular of essentially 2 MHz. This allows the measuring chamber to be designed particularly compactly. For example, measuring chambers with internal dimensions of up to 20 mm along the main axis can be implemented. With such a measuring chamber and such a microphone, the speed of sound present in liquid material samples can also be measured.

[0020] The underlying problem is also solved by a method according to the invention. The method is used to measure the speed of sound in a material sample that is located in a measuring chamber of a measuring device. The material sample can remain in the measuring chamber. Alternatively, the material sample can flow through the measuring chamber. The method comprises a first step in which a standing wave is generated in the material sample. This can be done, for example, by means of a sound emitter. Furthermore, in the first step, a plurality of pressure oscillations are detected and a plurality of corresponding measurement signals are output. The pressure oscillations are caused by the standing wave. The pressure oscillations can be detected, for example, by means of a plurality of microphones.

[0021] In addition, the method according to the invention carries out a second step in which the measurement signals output in the first step are added to form a combination signal. By adding the measurement signals, their existing amplitudes are added together. In the second step, a frequency of the combination signal is also determined. The frequency of the combination signal represents a measure of the speed of sound to be measured in the material sample. On the basis of the determined frequency of the combination signal, the speed of sound present in the material sample is then determined in the second step.

[0022] Furthermore, the method according to the invention comprises a third step in which the speed of sound determined in the second step is output to a user and / or a data interface. The data interface can be designed to transmit the speed of sound to a higher-level control unit which controls a plant in which the measuring device is used. Based on this, it is in turn possible to intervene in the operation of the plant. The plant can be, for example, an electrolyzer, a chemical plant, in particular a petrochemical plant, or an energy generation plant, in particular a gas turbine.

[0023] The claimed method allows the speed of sound in the material sample to be determined precisely, reliably, and robustly. In particular, the measuring device on which the method is carried out can be designed according to one of the embodiments outlined above. The features of the measuring device are therefore readily transferable, individually or in combination, to the claimed method.

[0024] The object described above is also achieved by a computer program product according to the invention. The computer program product is designed to receive and process measurement signals sent by a plurality of microphones. The computer program product is designed according to the invention to carry out a method according to at least one of the embodiments described above. The computer program product can in particular be designed to evaluate at least the combination signal and to use this to determine the speed of sound in the material sample. Furthermore, the computer program product can be designed to operate the claimed measuring device as intended. The computer program product can be monolithic, i.e. can be executable on a single hardware platform.Alternatively, the computer program product can be modular and comprise a plurality of subprograms that can be executed on different hardware platforms and interact during operation via a communicative data connection. The computer program product can be implemented entirely or partially in the form of software. The computer program product can also be implemented entirely or partially in a hard-wired form, for example as a chip, integrated circuit, or FPGA. Likewise, the computer program product can be implemented as a combination of a hard-wired embodiment and software.

[0025] Furthermore, the problem outlined at the outset is solved by an evaluation unit according to the invention. The evaluation unit is designed to determine a speed of sound in a material sample. Furthermore, the evaluation unit is designed to evaluate a frequency of a combination signal in which measurement signals from a plurality of microphones are combined. The evaluation unit comprises a circuit which is designed according to the invention to add the measurement signals coming from the microphones. The combination signal is thus formed by the evaluation unit adding the measurement signals. The evaluation unit is designed according to the invention to carry out an embodiment of one of the methods outlined above. The evaluation unit can be designed as part of the claimed measuring device or at least be designed to be coupled to the measuring device.The features of the claimed method and the underlying measuring device can be readily transferred to the evaluation unit individually or in combination.

[0026] The object set out above is equally achieved by a simulation program product according to the invention which is designed to simulate the operating behavior of a measuring device. The simulation program product is designed to carry out a plurality of steps. In a first step, a data set is provided which is suitable for simulating the mode of operation of the measuring device to be simulated. For example, a digital image of the measuring device to be simulated can be provided to the simulation program product for this purpose. Furthermore, the simulation program product is designed to carry out a second step in which at least one operating parameter is specified which characterizes the operating behavior to be simulated.The operating parameter can be, for example, a composition of the material sample, a temperature of the material sample, its pressure and / or a flow rate through the measuring device.

[0027] Furthermore, the simulation program product is designed to carry out a third step in which a physics module is executed. The physics module is designed to determine at least one performance parameter of the measuring device based on the data set provided in the first step and the operating parameter provided in the second step. The performance parameter can be any variable that describes the functioning of the simulated measuring device in more detail. This can be, for example, the occurrence of a standing wave and / or its detection by the microphones in the measuring device. When the physics module is executed, the operating behavior of the measuring device is simulated in the third step and the performance parameter is thus determined.

[0028] The simulation program product is also designed to carry out a fourth step in which the at least one performance parameter determined in the third step is output to a user and / or a data interface. Simulation results such as the performance parameter can be transferred to other simulation-oriented computer programs via the data interface. According to the invention, the measuring device, the operating behavior of which is simulated using the simulation program product, is designed according to one of the embodiments presented above. The measuring principle implemented by the measuring device is based on the formation of standing waves in the measuring chamber, which is essentially constant in size. The measuring signals, which are a measure of the speed of sound to be measured, are amplified by addition and stand out against the acoustic backdrop present in the measuring chamber.When simulating the operating behavior, acoustic disturbances are therefore negligible. Simulating acoustic disturbances in the measuring chamber is therefore unnecessary, which reduces the required computing power. The behavior of harmonic oscillations can also be simulated easily. Overall, the simulation program has been improved in terms of real-time capability, which means that operational monitoring of such a measuring device is possible with relatively simple hardware. This in turn allows a faster response to a deviation between the simulation program and the underlying measuring device that is being simulated. This ensures safe operation of a system in which the measuring device is used.

[0029] The simulation program product can be designed as a so-called digital twin of the measuring device, as described, for example, in the document US 2017 / 286572 A1. The disclosure content of US 2017 / 286572 A1 is incorporated by reference into the present application.

[0030] The invention is explained in more detail below with reference to individual embodiments in figures. The figures are to be read as complementary to one another in that identical reference numerals in different figures have the same technical meaning. The features of the individual figures can also be combined with one another. Furthermore, the embodiments shown in the figures can be combined with the features outlined above. They show in detail:

[0031] FIG 1 shows schematically a first embodiment of the claimed measuring device in a longitudinal section; FIG 2 shows schematically a second embodiment of the claimed measuring device in a longitudinal section;

[0032] FIG 3 schematically shows a third embodiment of the claimed measuring device in a longitudinal section;

[0033] FIG 4 schematically shows a fourth embodiment of the claimed measuring device in a longitudinal section.

[0034] FIG. 1 schematically shows a first embodiment of the claimed measuring device 10 in a longitudinal section, with which an embodiment of the claimed method 100 for measuring a speed of sound 35 is carried out. The measuring device 10 comprises a measuring chamber 12 which is delimited by a wall 14 and in whose interior 16 a material sample 25 is received. The measuring chamber 12 extends essentially along a main axis 15 and is closed by opposite end faces 17. The material sample 25 is a gas mixture which comprises a first component 25. 1, a second component 25. 2 and a third component 25. 3. The composition 13 of the material sample 25 is symbolized in a diagram in FIG. 1. The measuring chamber 12 further comprises a supply line 22 and a discharge line 24 so that the substance sample 25 can flow through the measuring chamber 12 during a measuring operation.This is shown in FIG. 1 as flow direction 23. A sound emitter 18 is arranged on an end face 17 of the measuring chamber 12 and is designed to induce a predeterminable sound excitation 19 in the material sample 25. The sound emitter 21 can be controlled by control commands 21 from an evaluation unit 40, so that the sound excitation 19 has a predeterminable frequency. The sound velocity 35 to be measured is established therein as a function of the composition 13 of the material sample 25.

[0035] A plurality of microphones 20 are arranged on a wall 14 of the measuring chamber 12 and are arranged essentially parallel to the main axis 15, forming a first group 27. At least one of the microphones 20 is designed as a pressure microphone. Furthermore, one of the microphones 20 is arranged essentially centrally along the main axis 15. The microphones 20 are positioned at essentially the same distance from one another. The microphones 20 are each arranged in a region 34 in which, in the event of a corresponding sound excitation 19, an antinode 33 of a standing wave 30 occurs. The standing wave 30 shown in FIG. 1 corresponds to a sound pressure 31 which arises as a result of a longitudinal oscillation in the measuring chamber. Furthermore, the standing wave 30 has a frequency 32, via which the speed of sound 35 in the material sample 25 is to be measured.The arrangement of the microphones 20 ensures that they each record a measurement signal 36 with an increased amplitude. The microphones 20 are connected to one another via a circuit 44 which is designed to add the measurement signals 36 from the microphones 20. The addition 42 of the measurement signals 36 forms a combination signal 38 which has a correspondingly increased amplitude, wherein the combination signal 38 can be designed as a sum signal. As a result, the combination signal 38 has an increased signal-to-noise ratio, also called SNR. The evaluation unit 40 of the measuring device 10 is connected to the microphones 20 in such a way that the combination signal 38 is supplied.

[0036] The evaluation unit 40 comprises an operational amplifier 41, which is designed to amplify the combination signal 38 and feeds it to a phase shifter 43. The phase shifter 43, in turn, is designed to carry out positive feedback. Furthermore, the phase shifter 43 is connected to an amplitude control 45, whereby the amplitude of the combination signal 38, which has passed through the operational amplifier 41 and the phase shifter 43, is adjusted for further processing with a counter 46. The counter 46 is coupled to a clock generator (not shown in detail), for example a clock, and is designed to detect a frequency of the combination signal 38. The frequency detected by the counter 46 corresponds to the frequency 32 of the standing wave 30 in the measuring chamber 12.Furthermore, the evaluation unit 40 is provided with a computer program product 50 which is suitable for determining the speed of sound 35 present in the material sample 25 on the basis of the frequency 32 detected by the counter 46.

[0037] For this purpose, the measuring chamber 12 is further provided with a temperature sensor 26 and a pressure sensor 28, which are connected to the evaluation unit 40 and which are designed and arranged to record the temperature and pressure present in the material sample 25. These are also transmitted to the evaluation unit 40 in the form of measurement signals 36. Based on the frequency 32, a temperature and pressure compensated determination of the speed of sound 35 in the material sample 25 is thus possible. The evaluation unit 40 is further connected to a display unit 38, via which the speed of sound 35 can be output. Likewise, the evaluation unit 40 is coupled to a data interface 49, via which the determined speed of sound 35 in the material sample 25 can be output, for example to a higher-level control unit (not shown).

[0038] In the claimed method 100 for measuring the speed of sound 35, the standing wave 30 is generated in the material sample 25 in a first step 110. For this purpose, the sound emitter 18 is controlled in a suitable manner. The wave antinodes 33 of the standing wave 30 thus each correspond to a pressure oscillation, which is detected by the microphones 20. Due to the arrangement of the microphones 20, they are set up to each detect a pressure oscillation, i.e. a change in the sound pressure 31 at the standing wave 30. The pressure oscillations thus detected are each output by the microphones 20 as measurement signals 36 in the first step 110. Furthermore, the measurement signals 36 are added in a second step 120 to form a combination signal 38. The addition 42 is performed by a circuit 44 that connects the microphones 20 to each other. Likewise, in the second step 120, the combination signal 38 is evaluated by the evaluation unit 40.Based on the combination signal 38, the speed of sound 35 in the material sample 25 is determined. The speed of sound 35 of the material sample 25 depends, among other things, on its composition 13. The frequency 32 of the standing wave 30, in turn, depends on the speed of sound 35. As a result, the speed of sound 35 can be determined based on the frequency of the combination signal 38. This is done using the temperature sensor 26 and the pressure sensor 38 in a temperature- or pressure-compensated manner. Furthermore, a third step 130 belongs to the method 100, in which the determined speed of sound 35 is output to a user via the display unit 47 and / or via a data interface 49.

[0039] The behavior of the standing wave 30 can be simulated with reduced computational effort. For a precise simulation of the measuring device 10, simulating interference effects on the microphones 20 is essentially negligible. The measuring device 10 and its operating behavior are modeled by a simulation program product 60, which is designed as a digital twin of the measuring device 10.

[0040] FIG 2 schematically shows a second embodiment of the claimed measuring device 10 in a longitudinal section, with which an embodiment of the claimed method 100 for measuring a speed of sound 35 is carried out. The measuring device 10 comprises a measuring chamber 12 which is delimited by a wall 14 and in whose interior 16 a material sample 25 is received. The measuring chamber 12 extends essentially along a main axis 15 and is closed by opposite end faces 17. The material sample 25 is a gas mixture which comprises a first component 25.1, a second component 25.2 and a third component 25.3. The composition 13 of the material sample 25 is symbolized in a diagram in FIG 2. The measuring chamber 12 further comprises a supply line 22 and a discharge line 24 so that the substance sample 25 can flow through the measuring chamber 12 during a measuring operation.This is shown in FIG. 2 as flow direction 23. A sound emitter 18 is arranged on an end face 17 of the measuring chamber 12 and is designed to induce a predeterminable sound excitation 19 in the material sample 25. The sound emitter 21 can be controlled by control commands 21 from an evaluation unit 40, so that the sound excitation 19 has a predeterminable frequency. The sound velocity 35 to be measured is established therein as a function of the composition 13 of the material sample 25.

[0041] A plurality of microphones 20 are arranged on a wall 14 of the measuring chamber 12 and are arranged essentially parallel to the main axis 15, forming a first group 27. At least one of the microphones 20 is designed as a pressure microphone. Furthermore, one of the microphones 20 is arranged essentially centrally along the main axis 15. The microphones 20 are positioned at essentially the same distance from one another. The microphones 20 are each arranged in a region 34 in which, in the event of a corresponding sound excitation 19, a wave antinode 33 of a standing wave 30 occurs. Furthermore, a second group 29 of microphones 20 is arranged on the wall 14 of the measuring chamber 12 opposite the first group 27. The standing wave 30 shown in FIG. 2 corresponds to a sound pressure 31 which arises as a result of a longitudinal oscillation in the measuring chamber.Furthermore, the standing wave 30 has a frequency 32, at which the speed of sound 35 in the material sample 25 is to be measured. The arrangement of the microphones 20 ensures that they each record a measurement signal 36 with an increased amplitude. The microphones 20 are connected to one another via a circuit 44, which is designed to add the measurement signals 36 from the microphones 20. The microphones 20 of the second group 29 are connected to an inverter 48, which is designed to reverse the signs of the wave antinodes 33 recorded there. Accordingly, the measurement signals 36 from the microphones 20 of the first group 27 and the inversions of the measurement signals 36 from the microphones 20 of the second group 29 are added. By adding 42 the corresponding measurement signals 36 , a combination signal 38 is formed which has a correspondingly increased amplitude , wherein the combination signal 38 can be designed as a sum signal .As a result, the combined signal 38 has an increased signal-to-noise ratio, also called SNR. The evaluation unit 40 of the measuring device 10 is connected to the microphones 20 in such a way that the combined signal 38 is supplied.

[0042] The evaluation unit 40 comprises an operational amplifier 41, which is designed to amplify the combination signal 38 and feeds it to a phase shifter 43. The phase shifter 43, in turn, is designed to carry out positive feedback. Furthermore, the phase shifter 43 is connected to an amplitude control 45, whereby the amplitude of the combination signal 38, which has passed through the operational amplifier 41 and the phase shifter 43, is adjusted for further processing with a counter 46. The counter 46 is coupled to a clock generator (not shown in detail), for example a clock, and is designed to detect a frequency of the combination signal 38. The frequency detected by the counter 46 corresponds to the frequency 32 of the standing wave 30 in the measuring chamber 12.Furthermore, the evaluation unit 40 is provided with a computer program product 50 which is suitable for determining the speed of sound 35 present in the material sample 25 on the basis of the frequency 32 detected by the counter 46.

[0043] For this purpose, the measuring chamber 12 is further provided with a temperature sensor 26 and a pressure sensor 28, which are connected to the evaluation unit 40 and which are designed and arranged to record the temperature and pressure present in the material sample 25. These are also transmitted to the evaluation unit 40 in the form of measurement signals 36. Based on the frequency 32, a temperature and pressure compensated determination of the speed of sound 35 in the material sample 25 is thus possible. The evaluation unit 40 is further connected to a display unit 38, via which the speed of sound 35 can be output. Likewise, the evaluation unit 40 is coupled to a data interface 49, via which the determined speed of sound 35 in the material sample 25 can be output, for example to a higher-level control unit (not shown).

[0044] In the claimed method 100 for measuring the speed of sound 35, the standing wave 30 is generated in the material sample 25 in a first step 110. For this purpose, the sound emitter 18 is controlled in a suitable manner. The wave antinodes 33 of the standing wave 30 thus each correspond to a pressure oscillation, which is detected by the microphones 20. Due to the arrangement of the microphones 20, they are set up to each detect a pressure oscillation, i.e. a change in the sound pressure 31 at the standing wave 30. The pressure oscillations thus detected are each output by the microphones 20 as measurement signals 36 in the first step 110. Furthermore, the measurement signals 36 are added in a second step 120 to form a combination signal 38. The addition 42 is performed by a circuit 44 that connects the microphones 20 to each other. Likewise, in the second step 120, the combination signal 38 is evaluated by the evaluation unit 40.Based on the combination signal 38, the speed of sound 35 in the material sample 25 is determined. The speed of sound 35 of the material sample 25 depends, among other things, on its composition 13. The frequency 32 of the standing wave 30, in turn, depends on the speed of sound 35. As a result, the speed of sound 35 can be determined based on the frequency of the combination signal 38. This is done using the temperature sensor 26 and the pressure sensor 38 in a temperature- or pressure-compensated manner. Furthermore, a third step 130 belongs to the method 100, in which the determined speed of sound 35 is output to a user via the display unit 47 and / or via a data interface 49. The behavior of the standing wave 30 can be simulated with reduced computational effort. For a precise simulation of the measuring device 10, simulating interference influences acting on the microphones 20 is essentially negligible.The measuring device 10 and its operating behavior are represented by a simulation program product 60, which is designed as a digital twin of the measuring device 10.

[0045] A third embodiment of the claimed measuring device 20 is shown schematically in FIG 3 in a longitudinal section, on which an embodiment of the claimed method 100 for measuring a speed of sound 35 is carried out. The measuring device 10 comprises a measuring chamber 12 which is delimited by a wall 14 and in whose interior 16 a material sample 25 is received. The measuring chamber 12 extends substantially along a main axis 15 and is closed by opposing end faces 17. The material sample 25 is a gas mixture which comprises a first component 25.1, a second component 25.2 and a third component 25.3. The composition 13 of the material sample 25 is symbolized in a diagram in FIG 3. The measuring chamber 12 further comprises a supply line 22 and a discharge line 24 so that the substance sample 25 can flow through the measuring chamber 12 during a measuring operation.This is shown in FIG. 3 as flow direction 23. A sound emitter 18 is arranged on an end face 17 of the measuring chamber 12 and is designed to induce a predeterminable sound excitation 19 in the material sample 25. The sound emitter 21 can be controlled by control commands 21 from an evaluation unit 40, so that the sound excitation 19 has a predeterminable frequency. The sound velocity 35 to be measured is established therein as a function of the composition 13 of the material sample 25.

[0046] A plurality of microphones 20 are arranged on a wall 14 of the measuring chamber 12, which are arranged essentially parallel to the main axis 15 and form a first group 27. Furthermore, a plurality of microphones 20 are arranged on the wall 14 of the measuring chamber 12, which microphones form a second group 29. At least one of the microphones 20 is designed as a pressure microphone. Furthermore, one of the microphones 20 of the first and second groups 27, 29 is arranged essentially centrally along the main axis 15. The microphones 20 are positioned at essentially the same distance from one another. The microphones 20 of the first and second groups 27, 29 are each arranged in a region 34 in which, upon a corresponding sound excitation 19, an antinode 33 of a standing wave 30 occurs. The microphones 20 of the first group 27 are arranged to each detect a wave antinode 33, i.e. a pressure oscillation, on a first standing wave

[0047] 30.1. The distances between the microphones 20 of the first group 27 are determined by the frequency 32 of the first standing wave 30.1. Correspondingly, the microphones 20 of the second group 29 are configured to detect wave antinodes 33 on a second standing wave 30.2. The second standing wave 30.1 has a different frequency 32 than the first standing wave 30.1.

[0048] The first and second standing shaft 30.1 shown in FIG 3,

[0049] 30.2 each correspond to a sound pressure 31 that occurs as a result of longitudinal vibrations in the measuring chamber 12. The frequencies 32 of the first and second standing waves 30.1, 30.2 each represent a value for the speed of sound 35 in the material sample 25 to be measured. The arrangement of the microphones 20 in the first and second groups 27, 29 ensures that they each record a measurement signal 36 with an increased amplitude. The microphones 20 are connected to one another via a circuit 44 that is designed to add the measurement signals 36 from the microphones 20. The measurement signals 36 of the microphones 20 of the first and second groups 27, 29 are added in FIG. 3. Alternatively, the measurement signals 36 can also be added in groups. Alternatively, it is also possible to alternate between sampling the first and second groups 27, 29, for example in a time slice control.By adding 42 the measurement signals 36, a combination signal 38 is formed which has a correspondingly increased amplitude. As a result, the combination signal 38 has an increased signal-to-noise ratio, also called SNR. The evaluation unit 40 of the measuring device 10 is connected to the microphones 20 in such a way that the combination signal 38 is supplied. The signal components of the first group 27 and the second group 29 are separated from one another or are in separate combination signals 38 by the time-slice control of the microphones 20.

[0050] The evaluation unit 40 comprises an operational amplifier 41, which is designed to amplify the combination signal 38 and feeds it to a phase shifter 43. The phase shifter 43, in turn, is designed to carry out positive feedback. Furthermore, the phase shifter 43 is connected to an amplitude control 45, whereby the amplitude of the combination signal 38, which has passed through the operational amplifier 41 and the phase shifter 43, is adjusted for further processing with a counter 46. The counter 46 is coupled to a clock generator (not shown in detail), for example a clock, and is designed to detect a frequency of the combination signal 38. The frequency detected by the counter 46 corresponds to the frequency 32 of the standing wave 30 in the measuring chamber 12.Furthermore, the evaluation unit 40 is provided with a computer program product 50 which is suitable for determining the speed of sound 35 present in the material sample 25 on the basis of the frequency 32 of the first and / or second standing wave 30. 1, 30. 2 detected by the counter 46.

[0051] For this purpose, the measuring chamber 12 is further provided with a temperature sensor 26 and a pressure sensor 28, which are connected to the evaluation unit 40 and which are designed and arranged to record the temperature and pressure present in the material sample 25. These are also transmitted to the evaluation unit 40 in the form of measurement signals 36. Based on the frequency 32 of the first and / or second standing wave 30.1 30.2, a temperature and pressure compensated determination of the speed of sound 35 in the material sample 25 is thus possible. The speeds of sound 35 determined using the first and second standing waves 30.1, 30.2 are compared with one another for mutual plausibility check. If a difference between the speed of sound 35 determined by means of the first standing wave 30.1 and the speed of sound 35 determined by means of the second standing wave 30.2, exceeds a predefined limit value, a warning is issued.

[0052] The evaluation unit 40 is further connected to a display unit 38, via which the speed of sound 35 in the material sample 25 can be output. Likewise, the evaluation unit 40 is coupled to a data interface 49, via which the determined speed of sound 35 in the material sample 25 can be output, alternatively or additionally, for example, to a higher-level control unit (not shown).

[0053] In the claimed method 100 for measuring the speed of sound 35, the first standing wave 30.1 is generated in the material sample 25 in a first step 110. For this purpose, the sound emitter 18 is controlled in a suitable manner. The wave antinodes 33 of the first standing wave 30.1 thus each correspond to a pressure oscillation, which is detected by the microphones 20. Due to the arrangement of the microphones 20, they are configured to each detect a pressure oscillation, i.e., a change in the sound pressure 31 at the first standing wave 30.1. The pressure oscillations thus detected are each output as measurement signals 36 by the microphones 20 of the first group 27 in the first step 110. Furthermore, the measurement signals 36 are added in a second step 120, thus forming a combination signal 38. The adding 42 is carried out by a circuit 44 which connects the microphones 20 of the first group 27 to each other.Likewise, in the second step 120, the combination signal 38 is evaluated by the evaluation unit 40. Based on the combination signal 38, the speed of sound 35 in the material sample 25 is determined. The speed of sound 35 of the material sample 25 depends, among other things, on its composition 13. The frequency 32 of the first standing wave 30.1, in turn, depends on the speed of sound 35. Consequently, the speed of sound 35 can be determined based on the frequency of the combination signal 38. This is done using the temperature sensor 26 and the pressure sensor 38, respectively, with temperature and pressure compensation.

[0054] The first and second steps 110, 120 are also carried out correspondingly for the second standing wave 30.2, which has a different frequency 32 than the first standing wave

[0055] 30.1. The pressure oscillations, i.e. the wave antinodes 33, of the second standing wave 30.2 are recorded by the microphones 20 of the second group 29.

[0056] Furthermore, a third step 130 belongs to the method 100, in which the signal obtained from the first and / or second standing wave

[0057] 30.1, 30.2 is output to a user via the display unit 47 and / or via a data interface 49. The sound velocities 35, which are determined based on the first standing wave 30.1 and the second standing wave 30.2, are further compared with each other for mutual plausibility checks. If the difference between the two sound velocities 35 exceeds a predeterminable limit value, a warning is issued.

[0058] The behavior of the first and second standing waves 30.1, 30.2 can each be simulated with reduced computational effort. For a precise simulation of the measuring device 10, simulating interference that acts on the microphones 20 is essentially negligible. The measuring device 10 and its operating behavior are mapped by a simulation program product 60, which is designed as a digital twin of the measuring device 10. FIG. 4 schematically shows a third embodiment of the claimed measuring device 10 in a longitudinal section, with which an embodiment of the claimed method 100 for measuring a speed of sound 35 is carried out. The measuring device 10 comprises a measuring chamber 12, which is delimited by a wall 14 and whose interior 16 holds a material sample 25. The measuring chamber 12 extends essentially along a main axis 15 and is closed by opposite end faces 17.The substance sample 25 is a gas mixture which comprises a first component 25.1, a second component 25.2 and a third component 25.3. The composition 13 of the substance sample 25 is symbolized in a diagram in FIG. 4. The measuring chamber 12 further comprises a supply line 22 and a discharge line 24 so that the substance sample 25 can flow through the measuring chamber 12 during measuring operation. This is shown in FIG. 4 as flow direction 23. A sound emitter 18 is arranged on an end face 17 of the measuring chamber 12 and is designed to produce a predeterminable sound excitation 19 in the substance sample 25. The sound emitter 21 can be controlled by control commands 21 from an evaluation unit 40, so that the sound excitation 19 has a predeterminable frequency. The sound velocity 35 to be measured is established depending on the composition 13 of the material sample 25.

[0059] A sound camera 39, which can be read out line by line, is arranged on a wall 14 of the measuring chamber 12. The cells 37 of the sound camera 39 correspond in their function to individual microphones 20, which can also be connected together in groups and thus can be read out in groups. The cells 37 of the sound camera 39 are controlled in such a way that they record sound pressure 31, i.e. pressure oscillations, in the area 34 of wave antinodes 33 of the standing wave 30 and add these to form a combination signal 38. The positions parallel to the main axis 15 at which wave antinodes 33, i.e. pressure oscillations, are recorded, can be selected by appropriately controlling the sound camera 39. The sound camera 39 is therefore suitable for recording a large number of different standing waves 30 in the measuring chamber 12. The addition 42 of the measurement signals 36 can be carried out in the sound camera 39 by means of the computer program product 50.When using a sound camera 39, whose cells 37 serve as microphones 20, the ability to detect and evaluate standing waves 30 in the measuring chamber 12 is limited only by the dynamics of the sound emitter 18. Using the computer program product 50, it is further possible to evaluate the frequency 32 of the standing wave 30 present in the measuring chamber 12. Furthermore, the computer program product 50 on the evaluation unit 40 is suitable for determining the speed of sound 35 present in the material sample 25 based on the frequency 32.

[0060] For this purpose, the measuring chamber 12 is further provided with a temperature sensor 26 and a pressure sensor 28, which are connected to the evaluation unit 40 and which are designed and arranged to record the temperature and pressure present in the material sample 25. These are also transmitted to the evaluation unit 40 in the form of measurement signals 36. Based on the frequency 32, a temperature and pressure compensated determination of the speed of sound 35 in the material sample 25 is thus possible. The evaluation unit 40 is further connected to a display unit 38, via which the speed of sound 35 can be output. Likewise, the evaluation unit 40 is coupled to a data interface 49, via which the determined speed of sound 35 in the material sample 25 can be output, for example to a higher-level control unit (not shown).

[0061] In the claimed method 100 for measuring the speed of sound 35, the standing wave 30 is generated in the material sample 25 in a first step 110. For this purpose, the sound emitter 18 is controlled in a suitable manner. The wave antinodes 33 of the standing wave 30 thus each correspond to a pressure oscillation, which is recorded via the cells 37 of the sound camera 39, which serve as microphones 20. Predeterminable cells 37 are recorded at which pressure oscillations, i.e. changes in the sound pressure 31, are present. Cells 37 at which no pressure oscillations or weak pressure oscillations are present are not recorded and are therefore ignored. The pressure oscillations recorded in this way are output in the first step 110 by the sound camera 39 as measurement signals 36. Furthermore, the measurement signals 36 are added in a second step 120 to form a combination signal 38.The addition 42 is carried out by the computer program product 50 on the evaluation unit 40. Likewise, in the second step 120 the combination signal 38 is evaluated by the evaluation unit 40. Based on the combination signal 38, the speed of sound 35 in the material sample 25 is determined. The speed of sound 35 of the material sample 25 depends, among other things, on its composition 13. The frequency 32 of the standing wave 30, in turn, depends on the speed of sound 35. As a result, the speed of sound 35 can be determined based on the frequency of the combination signal 38. This is done using the temperature sensor 26 and the pressure sensor 38 in a temperature- or pressure-compensated manner. Furthermore, a third step 130 belongs to the method 100, in which the determined speed of sound 35 is output to a user via the display unit 47 and / or via a data interface 49.

[0062] The behavior of the standing wave 30 can be simulated with reduced computational effort. For a precise simulation of the measuring device 10, simulation of disturbances acting on the cells 37 of the acoustic camera 39 is essentially negligible. The measuring device 10 and its operating behavior are modeled by a simulation program product 60, which is designed as a digital twin of the measuring device 10.

Claims

Patent claims 1. Measuring device (10) for detecting a speed of sound (35) in a material sample (25), comprising a measuring chamber (12) with a sound emitter (18), wherein a plurality of microphones (20) for selectively detecting a frequency (32) of a standing wave (30) are arranged parallel to a main axis (15) of the measuring chamber (12) and spaced from one another, characterized in that a first group (27) of microphones (20) for selectively detecting a frequency (32) of a first standing wave (30.1) and a second group (29) of microphones (20) for selectively detecting a frequency (32) of a second standing wave (30.2) is arranged on the measuring chamber (12).

2. Measuring device (10) according to claim 1, characterized in that at least one of the microphones (20) and the sound emitter are arranged in a positive feedback circuit.

3. Measuring device (10) according to claim 1 or 2, characterized in that a plurality of microphones (20) are connected to the evaluation unit (40), which is designed to evaluate an addition (42) of measurement signals (36) of the microphones (20).

4. Measuring device (10) according to one of claims 1 to 3, characterized in that the evaluation unit (40) has an operational amplifier (41) to which the measurement signals (36) of the microphones (20) are fed in combined form at an amplifier input.

5. Measuring device (10) according to one of claims 1 to 4, characterized in that the microphones (20) are arranged parallel to the main axis (15) of the measuring chamber (12) for a combined detection of pressure antinodes (33).

6. Measuring device (10) according to one of claims 2 to 5, characterized in that the evaluation unit (40) is designed free of a bandpass filter.

7. Measuring device (10) according to one of claims 1 to 6, characterized in that the microphones (20) are arranged at the same circumferential position relative to the main axis (15) of the measuring chamber (12).

8. Measuring device (10) according to one of claims 1 to 7, characterized in that the standing wave (30) corresponds to a third or fourth harmonic longitudinal oscillation in the measuring chamber (12).

9. Measuring device (10) according to one of claims 1 to 8, characterized in that a temperature sensor (26) and / or a pressure sensor (28) is arranged in the region of at least one microphone (20).

10. Measuring device (10) according to one of claims 1 to 9, characterized in that at least one microphone (20) is designed as a pressure microphone or as a laser microphone, or several microphones (20) are combined to form a sound camera (39).

11. Method (100) for measuring a speed of sound (35) in a material sample (25) in a measuring chamber (12) a measuring device (10) comprising the steps of: a) generating a standing wave (30) in the material sample (25); detecting a plurality of pressure oscillations and Outputting a plurality of corresponding measurement signals (36); b) adding the measurement signals (36) to a combination signal (38) and determining a frequency (32) of the combination signal (38), wherein the speed of sound (35) present in the material sample (25) is determined based on the determined frequency (32) of the combination signal (38); c) outputting the speed of sound (35) in the material sample (25) determined in step b) to a user and / or a data interface (49), characterized in that the measuring device (20) is designed according to one of claims 1 to 10.

12. Computer program product (50) designed to receive and process measurement signals (36) from a plurality of microphones (20), wherein the computer program product (50) is designed to carry out a method (100) according to claim 11.

13. Evaluation unit (40) for determining a speed of sound (35) in a material sample (25), which is suitable for determining a frequency (32) of a combination signal (38), wherein the evaluation unit (40) comprises a circuit (44) which is designed to add measurement signals (36) from a plurality of microphones (20) to the combination signal (38), characterized in that the evaluation unit (40) is designed to carry out a method (100) according to claim 11.

14. A simulation program product (60) for simulating an operating behavior of a measuring device (20), which is designed to carry out the steps of: a) providing a data set suitable for simulating the functioning of the measuring device (20); b) specifying at least one operating parameter that characterizes the operating behavior to be simulated; c) executing a physics module that is designed to simulate the operating behavior of the measuring device (20) based on the data set and the at least one operating parameter and to determine a performance parameter of the measuring device (20); d) outputting the at least one performance parameter to a user and / or a data interface; characterized in that the measuring device (20) is designed according to one of claims 1 to 10.

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