Ultrasonic flow meter and method for evaluating state of medium within ultrasonic flow meter

Abstract

The invention relates to an ultrasonic flow meter (2) and to a method for evaluating the state of a medium within an ultrasonic flow meter (2), comprising a flow channel (4), at least one ultrasonic transducer (16, 18) located in or on a wall (5) of the flow channel (4), and a processing unit (14) connected to the at least one ultrasonic transducer (16, 18), the processing unit (14) is configured such that it controls the at least one ultrasonic transducer (16, 18), and wherein the processing unit (14) comprises an analysis module (36) configured such that it evaluates the state of the medium within the flow channel (4) by analyzing the attenuation behavior (i.e., damping) of the signal of the at least one ultrasonic transducer (16, 18).

Description

Technical Field

[0001] The invention relates to an ultrasonic flow meter, a fluid consumption meter comprising such an ultrasonic flow meter and a method for evaluating the state of a medium in an ultrasonic flow meter. Background Art

[0002] Ultrasonic flow meters are used in fluid consumption meters to measure the volume of fluid flowing through the meter and record water consumption at the user's site, or for energy metering in heat distribution networks.

[0003] A known problem in ultrasonic flow meters is that possible cavitation in the fluid leads to measurement errors in ultrasonic fluids. DE 10 2017 011 201 B4 discloses selectively detecting noise that may be generated by cavitation in a liquid. Summary of the invention

[0004] The object of the present invention is to provide an ultrasonic flow meter, a fluid consumption meter and a method which allow improved cavitation detection.

[0005] This object is achieved by an ultrasonic flow meter having the features defined in claim 1, by a fluid consumption meter having the features defined in claim 12 and by a method having the features defined in claim 13. Preferred embodiments are defined in the dependent claims, the following description and the drawings.

[0006] The ultrasonic flow meter comprises a flow tube or flow channel configured to receive a fluid or conduct a liquid flow. The flow channel may be connected to an inlet connector and an outlet connector of the flow meter. At least one ultrasonic transducer is located in the flow channel or on a wall of the flow channel. In a preferred embodiment, there may be two ultrasonic transducers spaced apart from each other to form an ultrasonic measurement section in the flow channel. A processing unit is connected to the at least one ultrasonic transducer, wherein the processing unit is configured so that it controls at least one ultrasonic transducer. Preferably, the processing unit is configured to perform flow measurement by using one or more ultrasonic transducers. According to the present invention, the processing unit comprises an analysis module, which is configured so that it evaluates the state of a medium in the flow channel (e.g., a liquid flowing along the flow channel). The processing unit is configured so that it analyzes the damping of at least one ultrasonic transducer to evaluate the state of the medium. This means that the analysis module is configured so that it analyzes the damping of an electrical signal of at least one ultrasonic transducer that has preferably just sent a signal. Thus, an electrical signal or a voltage signal at the transducer is analyzed. An ultrasonic transducer is an oscillator damped by its physical environment. Damping allows detection of certain conditions, such as dry running, bubbles in the liquid or cavitation that may lead to errors in the flow measurement of the ultrasonic flow meter. If such an undesirable condition is detected, the processing unit can output a fault signal and / or, for example, stop the flow measurement.

[0007] Advantageously, the analysis module is configured such that the ringdown behavior of at least one ultrasonic transducer is used to analyze the damping. Different ringing or decay behaviors are indicative of different states of the medium flowing in the flow channel. Decay analysis is a particularly good way to estimate damping. Other ways are to measure the amplitude of the oscillation relative to an undamped oscillation or to measure the shift of the resonant frequency of the oscillation relative to the natural frequency. In the following, the terms ringing or ringdown are used interchangeably.

[0008] Instead of analyzing the damping behavior, the analysis module can be configured such that another parameter can be studied. Thus, for example, the analysis module can be configured such that the shift of the oscillation frequency relative to the natural frequency can also be used to analyze the damping.

[0009] In another alternative using the decay behavior or the frequency shift, the analysis module can be configured so that when at least one ultrasonic transducer has been excited with a sinusoidal drive signal, the change in the voltage amplitude of the oscillation of the transducer can be studied. This change in amplitude is related to the damping factor of the oscillating system. An increase in damping leads to a decrease in amplitude. The advantage of this alternative is that monitoring the amplitude is relatively simple.

[0010] In a possible embodiment, the analysis module can be configured such that it samples voltage signals from at least one ultrasonic transducer and analyzes damping based on these sampled voltage signals (e.g., by studying decay behavior or ringing). The sampling can be done at periodic intervals. For example, during decay behavior or ringing, the signal considered for analyzing damping is the signal of an undriven oscillating system including an ultrasonic transducer. For example, by periodically sampling the voltage signal generated by the ultrasonic transducer, a ringing or decay curve is detected. The curve weakens over time. Depending on the state of the medium or liquid in the flow channel as part of the oscillating system, the damping characteristics are different, resulting in different ringing curves or decay curves.

[0011] In order to analyze the damping, for example by studying the decay behavior, the analysis module can be configured such that it analyzes or samples the decay over time and / or the signal strength of the voltage signal measured on the ultrasonic transducer. Preferably, the signal is determined in a state where the ultrasonic transducer is not driven, preferably after the excitation of the oscillation system has been stopped. This means that, preferably in a first step, an excitation signal is injected into the ultrasonic transducer and, immediately after stopping the excitation signal, the voltage signal on the ultrasonic transducer is sampled to determine the decay behavior or decay curve.

[0012] According to another possible embodiment, the analysis module is configured such that it calculates at least one eigenvalue representing the damping of at least one ultrasonic transducer, for example representing the attenuation behavior as a manifestation of the damping. For example, the eigenvalues ​​may be the resonant frequency and / or the quality factor Q or Q-factor of the oscillating system comprising the ultrasonic transducer, respectively. It is known in the art that the quality factor or Q-factor is used to describe an oscillating system. It is the inverse of the damping ( where ξ is the damping), and it can be defined in several ways. In the meaning of the present invention, the quality factor Q is preferably a dimensionless parameter describing how undamped an oscillator or resonator is. Thereby, a high value of the quality factor Q indicates a lower energy loss rate, so that the oscillations die out more slowly. In principle, looking at the quality factor Q enables distinguishing, for example, different states of a medium or liquid within a flow channel, which states may be, for example, filled and empty.

[0013] According to a further preferred embodiment, the analysis module is configured such that it calculates a characteristic value representing damping (e.g., decay behavior) several times, in particular a characteristic value as previously discussed, and determines the statistical dispersion of the characteristic value. By means of this statistical analysis, temperature influences can be compensated. Such temperature influences occur when the ambient temperature or the inlet fluid temperature changes. Typically, the characteristic value will be calculated at a first temperature and later at a second temperature, but this makes it difficult to correctly calculate the characteristic value if the temperature has increased, for example, between two measurements. The applicant has found that using the average value of the characteristic value is very temperature-dependent, while using the dispersion of the characteristic value around its average value is less sensitive to temperature. The discrete method advantageously eliminates this undesirable temperature influence. In addition, based on the dispersion, for example the dispersion of the quality factor Q, it is possible to accurately distinguish between different states of the medium, for example to distinguish between dry operation and cavitation. The dispersion of the characteristic value (e.g., the quality factor Q) is different for different states of the medium or liquid (such as cavitation and dry operation).

[0014] According to another possible embodiment, in order to detect cavitation of the medium in the flow channel, preferably, the analysis module is configured such that if the determined discreteness is higher than a predetermined discreteness threshold, the analysis module identifies a cavitation state. For example, the discreteness of the quality factor Q in the cavitation state is higher than the discreteness of the quality factor Q in the state of dry operation or normal operation (i.e., when the flow channel is filled with liquid, such as filled with water). In order to distinguish the state of the flow channel filled with water from the state of the flow channel dry, it may be sufficient to study only the characteristic value (e.g., the quality factor Q). In the normal operation state, when the flow channel is filled with liquid, there is a higher damping factor, i.e., a lower Q factor, than in the dry (i.e., filled with air) state. The analysis module can be configured to evaluate both the dry operation state and the cavitation state by considering both the discreteness of the characteristic value and the characteristic value itself.

[0015] According to another possible embodiment, the processing unit and the analysis module are configured so that, in order to evaluate the damping, at least one voltage signal from at least one ultrasonic transducer is sampled when the flow measurement has stopped. This means that when the flow measurement is paused, the evaluation of the damping is performed, for example, by analyzing the decay behavior. In addition, in another embodiment, the processing unit and the analysis module can be configured so that, in order to evaluate the damping, at least one voltage signal from at least one ultrasonic transducer is sampled multiple times immediately after the ultrasonic transducer has stopped sending the flow measurement signal and / or after the ultrasonic transducer has sent the oscillation test signal. This means that in the first embodiment, the measured and analyzed ringing is the ringing on the ultrasonic transducer immediately after the flow measurement signal has been sent (i.e., after the excitation by the flow measurement signal). The advantage of this embodiment is that battery power can be saved because no additional signal is required to evaluate the state of the medium. In another embodiment, a dedicated signal is used, i.e., an oscillation test signal for detecting the state of the medium (e.g., detecting cavitation). This allows the oscillation test signal to be customized for this purpose. In another possible embodiment, the ringing data from the flow measurement signal can be combined with the ringing data from the dedicated oscillation test signal. However, in all embodiments, preferably already existing electronic hardware for normal flow measurement is used to sample the ringing signal.

[0016] Preferably, the analysis module is implemented as a software module executed by the existing hardware of the processing unit. In order to execute the software program or software script, the processing unit may include, for example, a processor (CPU), memory means and other required electronic components. Preferably, these are the same hardware components used to execute the software required to perform the flow measurement.

[0017] Preferably, the ultrasonic flow meter as described above is part of a fluid consumption meter. The fluid consumption meter calculates and records fluid consumption based on the flow measurement performed by the described ultrasonic flow meter. Such a fluid consumption meter can be used, for example, to record water consumption at a user site (e.g., a building, etc.).

[0018] In addition to the described ultrasonic flowmeter and fluid consumption meter, a method is also the subject of the present invention. The method according to the present invention is provided for evaluating the state of the medium in an ultrasonic flowmeter, in particular an ultrasonic flowmeter as described above. The preferred embodiments of the ultrasonic flowmeter as described above should also be regarded as preferred embodiments of the method. Vice versa, the preferred embodiments of the method as described below should be regarded as preferred embodiments of the described ultrasonic flowmeter and fluid consumption meter. According to the method of the present invention, at least one ultrasonic transducer located in the flow channel or on the wall of the flow channel of the ultrasonic flowmeter is used to evaluate the state of the medium in the flow channel. This is done by analyzing the damping of at least one ultrasonic transducer. The damping is different for different states of the medium. Therefore, by analyzing the damping, certain states of the medium, in particular possible cavitation, can be detected. In a preferred embodiment, the attenuation behavior of at least one ultrasonic transducer can be used as a manifestation of damping.

[0019] According to a preferred embodiment of the method, at least one characteristic value representing the damping is calculated at a plurality of moments. Next, the statistical dispersion of the characteristic value can be determined. Thus, the influence of temperature variations of the inlet fluid or the ambient temperature can be compensated or eliminated. As mentioned above, the dispersion of the characteristic value (e.g. the quality factor Q) is different for different states of the medium, in particular for cavitation and for the normal state in which the flow channel is only filled with liquid.

[0020] Preferably, a cavitation state is determined if the determined dispersion is above a predetermined dispersion threshold. Compared to a state of normal operation or dry running, in a cavitation state there is a higher dispersion of characteristic values, for example a higher dispersion of the quality factor Q. The difference can be defined by a suitable dispersion threshold.

[0021] Damping (e.g., decay behavior as a manifestation of damping) can be analyzed by analyzing or evaluating the signal strength and / or the attenuation determined after the electrical excitation of the ultrasonic transducer has ceased. This ensures that the state of the medium is evaluated when the flow measurement is paused. In order to evaluate the decay behavior of the ultrasonic transducer, the flow measurement signal or a dedicated oscillation test signal used for the flow measurement can be used. The sampling of the decay signal preferably starts immediately after the excitation has been terminated. For example, the decay behavior as a manifestation of damping is analyzed between two flow measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the following, the present invention is described by way of example with reference to the accompanying drawings. In these drawings:

[0023] Figure 1 A schematic cross section of a fluid consumption meter according to the invention is shown.

[0024] Figure 2 Shown according to Figure 1 Partial view of the flow meter of a fluid consumption meter.

[0025] Figure 3 The ringing signal and the quality factor Q over time for a first state of the medium are schematically shown.

[0026] Figure 4 The ringing signal and the quality factor Q over time for the second state of the medium are schematically shown.

[0027] Figure 5 The ringing signal and the quality factor Q over time for the third state of the medium are schematically shown.

[0028] Figure 6 An example of multiple repeated calculations of the quality factor Q for three different states of the medium is shown.

[0029] Figure 7 The dispersion of the calculated quality factor Q is schematically shown.

[0030] Figure 8 The effect of temperature on the calculated Q value is shown. DETAILED DESCRIPTION

[0031] Figure 1 Schematically shown is a fluid consumption meter comprising an ultrasonic flow meter 2. The ultrasonic flow meter 2 comprises a flow channel 4 defined by a wall 5 and connecting an inlet connection 6 and an outlet connection 8. The inlet connection 6 and the outlet connection 8 are arranged for connecting the consumption meter to a pipe system, for example a water supply pipe, to record water consumption.

[0032] In this example, a valve 10 is arranged on the inlet side, ie upstream of the inlet connection 6 in the inlet pipe. Such a valve 10 may cause cavitation within the medium flowing through the flow channel 4.

[0033] In this example, an electronics housing 12 including a processing unit 14 is integrally connected to the flow channel 4. In this example, the processing unit 14 is connected to two ultrasonic transducers 16 and 18, which are arranged on the wall 5 of the flow channel 4 spaced apart from each other in the flow direction 20. Reflector elements 22 and 24 are arranged in the flow channel facing the two ultrasonic transducers 16 and 18, which guide the ultrasonic signals from the ultrasonic transducer 16 and from the reflector element 24 to the second ultrasonic transducer 18 in the flow direction. Correspondingly, a signal is sent in the opposite direction of the flow, and the flow is detected in the measuring section between the two transducers 16 and 18 by using the time-of-flight principle. Based on the ultrasonic signals received by the ultrasonic transducers 16, 18, the processing unit 14 calculates the flow and the fluid consumption.

[0034] Cavitation, for example caused by valve 10, may affect such flow measurements. It is therefore desirable to detect the state of the medium (e.g. water) within the flow channel to identify a state of the medium that does not allow a correct flow measurement. Such a state may be signaled to the consumer or, for example, a water supply facility, or the measurement may be suspended. The cavitation state may be signaled, for example, as a flashing LED on the flow meter, an alarm on an app on a smartphone, or a time-stamped entry in a register at the supply facility.

[0035] Figure 2 The processing unit 14 and the first ultrasonic transducer 16 are shown in detail. The processing unit 14 includes a microprocessor 26, a memory 28 and a power supply 30. In addition, the processing unit 14 may include a communication unit 32 (e.g., a radio unit 32) that allows information about the recorded consumption to be transmitted to the head-end system. In addition, other information can be transmitted toward an external control device via the communication unit 32, or can be received from the head-end system or the external control device. In this example, the processing unit 14 includes a flow measurement unit 34 and a cavitation analysis unit 36. The flow measurement unit 34 and the cavitation analysis unit 36 ​​can be arranged as software modules executed in the processing unit 14 by the microprocessor 26. The flow measurement unit 34 and the cavitation analysis unit 36 ​​are connected to at least one of the ultrasonic transducers (in this example, the ultrasonic transducer 16) via an electrical connection 35. The flow measurement unit 34 and the cavitation analysis unit 36 ​​are configured to send an excitation signal to the ultrasonic transducer 16 so that the ultrasonic transducer 16 outputs an ultrasonic signal. Furthermore, the flow measurement unit 34 and the cavitation analysis unit 36 ​​may receive a voltage signal from one of the ultrasonic transducers 16, 18 (in this example, the ultrasonic transducer 16). The ultrasonic transducers 16, 18 may be piezoelectric transducers. The damping and damping constant of the oscillating system including the ultrasonic transducer 16 are determined by the combined properties of the components of the oscillator. The ultrasonic transducer itself has the same oscillator properties as the fluid, but the wall 5 and backing 37 of the transducer also affect the behavior of the oscillator.

[0036] According to an embodiment of the present invention, the state of the medium in the flow channel 4 is analyzed based on the ringing or decaying signal. To this end, an excitation signal is sent from the cavitation analysis unit 36 ​​to the ultrasonic transducer 16, so that the transducer 16 outputs an ultrasonic signal toward the reflector 22. In a subsequent step, the excitation signal is stopped, and the ringing or decaying voltage signal generated by the ultrasonic transducer 16 on the electrical connection 35 is then determined and analyzed by the cavitation analysis unit 36. In order to determine the ringing signal, the voltage generated by the transmitting ultrasonic transducer 16 is periodically sampled. Thereby, the ringing or decay curve can be detected.

[0037] Based on this detected signal, the quality factor Q or Q-factor is calculated. This is done in the following manner. The area under the envelope of the ringing signal is calculated as an expression for Q. The envelope of the decaying signal is given by:

[0038] ε(t)=A0e -t / τ

[0039] Where A0 is the amplitude of the driving signal and t is time. The time constant τ of the decay signal is given by

[0040]

[0041] Among them, ω N is the natural frequency of the decaying oscillation signal, and Q is the quality factor.

[0042] The area under the envelope is proportional to the Q factor:

[0043]

[0044] Thus, by adding the sampled envelopes, a good estimate of the integral and Q factor up to an arbitrary constant can be calculated.In the meaning of the present invention, when referring to the Q factor or quality factor Q, it is this relative measurement, not the strictly true Q factor.

[0045] Figures 3 to 5Three examples of ringing signals and associated quality factors Q plotted over time t are shown. At time point t1, the excitation signal stops and ringing or decay begins. In this case, the excitation signal is formed by a rectangular pulse of amplitude A0 during this drive time period of the ultrasonic transducer 16, which ends at t1. In one embodiment, the excitation signal corresponds to a signal for measuring flow. In another embodiment, the excitation signal is customized for decay behavior analysis and, for example, has more pulses than the excitation signal in flow measurement. At t1, the undriven time period begins and the voltage signal that can be measured on the ultrasonic transducer 16 decays and becomes a sinusoidal oscillation. The ultrasonic pressure wave 11 faces an impedance consisting of the impedance of the backing 37, the wall 5 of the flow channel 4 and the medium or fluid in the flow channel 4 itself. If the fluid channel 4 is filled with a fluid (such as water), the ultrasonic transducer 16 easily removes its energy, which is radiated into the fluid. Once the drive signal or excitation signal stops at t1, the cavitation analysis unit 36 ​​starts sampling the ringing signal and calculates the quality factor Q. Depending on the state of the medium in the flow channel 4, the resulting curve of the quality factor Q is different. Figure 3 The curve of a flow channel 4 filled with water is shown. Figure 4 The curve of the flow channel 4 filled with air, i.e. the curve of the dry running state, is shown. In this state, due to the lack of water, the signal has a lower damping in the flow channel 4 and there is a slower oscillation decay. Figure 5 The cavitation case shown, with Figure 3 The main decay wave is largely unchanged compared to the water-filled flow channel 4 shown. However, there is a much larger spread in the calculated Q values, which is Figure 5 Indicated by the different dashed curves Q. By analyzing the statistical diffusion, the normal state and the cavitation state can be distinguished.

[0046] Figure 6 The quality factor Q is plotted over time for a number of measurements (e.g. 1000 measurements). Different curves of the quality factor Q can be identified for different states of the medium. Curve IV is Figure 4 The curve V is the curve of the dry running state. Figure 5 The quality factor Q curve of the cavitation state is shown. Figure 6 Compared to the normal operation curve shown by curve III in FIG. 1 , curve V has a much larger spread. Curve III for normal operation corresponds to Figure 3The ringing curve shown in FIG. 4 is a ringing curve shown in FIG. 4 . In this medium state, the flow channel 4 is filled with water without bubbles inside, i.e., a state with substantially no cavitation. The signal according to curve IV has a similar low spread, however, as shown in curve III, the quality factor Q of the dry operation is higher than the quality factor Q of the water-filled state. Therefore, by analyzing the quality factor Q and the spread of the quality factor Q, three different states of the medium or liquid flowing through the flow channel 4, i.e., normal operation, dry operation, and cavitation, can be distinguished.

[0047] In order to evaluate the spread of the quality factor Q, the dispersion σQ is calculated, for example, by using the following formula:

[0048]

[0049] Where N is the sample size.

[0050] Figure 7 The distribution of the dispersion of the Q factor calculated in this way is shown in FIG. The figure shows the dispersion for three different states of the medium, a dispersion 38 for the dry state of the flow channel 4, a dispersion 40 for the normal state (i.e., when the flow channel 4 is filled with fluid without cavitation), and a dispersion 42 for the cavitation state. It can be seen that the dispersion σ Q In the cavitation state, it is much higher. Therefore, if the discrete σ Q Above the predetermined discreteness threshold σ T , cavitation can be identified. The analysis is performed by the processing unit 14.

[0051] from Figure 7 It can be seen that the dispersion σ of the normal state and the dry state Q are similar, however, these states can be distinguished based on the different magnitudes of the quality factor Q as described above.

[0052] Figure 8 Calculated values ​​of the quality factor Q as a function of temperature are shown. The Q value of the dry meter is a function of the ambient temperature, while the Q value of the water-filled meter is a function of the inlet fluid temperature. The Q value of the water-filled flow meter 2 is strongly affected by inlet fluid temperatures of 40°C and above, and at very high temperatures the quality factor has the same value as the dry meter. Therefore, the bare quality factor is not unambiguous, as the same Q value can refer to the dry state or the water-filled state of the flow meter. Therefore, in order to reduce the influence of temperature, a method using the statistical dispersion of Q has been introduced.

[0053] A method of mathematically integrating the envelope of the oscillation after the driving force has been removed and using this as an expression for the damping of the ultrasonic transducer 16 has been described above. A different method is to measure the oscillation frequency ω relative to the natural frequency ω N Therefore, Q is obtained by the following formula

[0054]

[0055] Yet another option is to drive the oscillation of the ultrasonic transducer 16 by a sinusoidal driving force. For a driving force given by: f(t) = f0 cos(ω d t), where f(t) is the driving force, f0 is the amplitude of the driving force, ω d is the driving frequency, and the amplitude A of the oscillation of the ultrasonic transducer 16 is given by:

[0056]

[0057] Therefore, the damping β can be estimated since the amplitude A decreases as the damping increases. The methods proposed above for estimating the damping are not exhaustive and other methods are possible.

[0058] Multiple embodiments of the present invention are possible. In one embodiment, the attenuation behavior associated with one ultrasonic transducer 16, 18 is compared to the attenuation behavior of adjacent ultrasonic transducers 16, 18 in the flow meter 2. If the attenuation behaviors are different from each other, this may be an indication of a faulty or aged ultrasonic transducer 16, 18. In another embodiment, the calculated Q factor is associated with a timestamp. This enables analysis of the causes and effects of upstream pipeline events and the occurrence of cavitation in the ultrasonic flow meter. In a further embodiment, analysis of the attenuation behavior of the ultrasonic transducer is used to determine the viscosity of the medium flowing in the flow tube. A high viscosity medium will cause a lower Q factor than a low viscosity medium.

[0059] If the invention is used in an ultrasonic flow meter used in a district heating network, the decay behavior can be used as a fingerprint of the state of the heating medium. The medium is classified as industrial water because it includes additives such as, for example, corrosion inhibitors etc. If the composition of the industrial water changes over time, the decay behavior will also change and is therefore an indicator of changes in the composition of the industrial water.

[0060] Reference numerals list

[0061] 2 Ultrasonic flow meter

[0062] 4 Flow channels

[0063] 5 walls

[0064] 6 Inlet connection

[0065] 8 Outlet connection

[0066] 10 valve

[0067] 11 Ultrasonic pressure waves

[0068] 12 Electronic housing

[0069] 14 Processing Units

[0070] 16, 18 Ultrasonic transducer

[0071] 20 Flow direction

[0072] 22, 24 Reflector element

[0073] 26 Microprocessor

[0074] 28 Memory

[0075] 30 Power Supply

[0076] 32 Communication Unit

[0077] 34 Flow measurement unit

[0078] 35 Electrical connection

[0079] 36 Cavitation Analysis Unit

[0080] 37 Backing

[0081] 38 Dispersion of Q for dry state

[0082] 40 Dispersion of Q for normal state

[0083] 42 Dispersion of Q for cavitation

[0084] Q Quality Factor

[0085] σ Q Dispersion of quality factor Q

[0086] σ T Discreteness threshold

Claims

1. An ultrasonic flow meter (2), comprising a flow channel (4), at least one ultrasonic transducer (16, 18) located in the flow channel or on a wall (5) of the flow channel (4), and a processing unit (14) connected to the at least one ultrasonic transducer (16, 18), the processing unit (14) being configured such that the processing unit controls the at least one ultrasonic transducer (16, 18), Features The processing unit (14) comprises an analysis module (36) which is configured such that the analysis module evaluates the state of the medium in the flow channel (4) by analyzing the damping of the electrical signal of the at least one ultrasonic transducer (16, 18).

2. The ultrasonic flow meter (2) according to claim 1, characterized in that: The analysis module (36) is configured such that the attenuation behavior of the at least one ultrasonic transducer (16, 18) is used to analyze the damping.

3. The ultrasonic flowmeter (2) according to claim 1 or 2, characterized in that: The analysis module (36) is configured to make the oscillation frequency (ω) relative to the natural frequency (ω N ) is used to analyze the damping.

4. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The analysis module (36) is configured such that, in order to analyze the damping, the at least one ultrasonic transducer is excited with a sinusoidal drive signal (f(t)) and a change in the amplitude (A) of the electrical response signal from the at least one ultrasonic transducer (16, 18) is used to analyze the damping.

5. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The analysis module (36) is configured such that it samples a voltage signal from the at least one ultrasonic transducer (16, 18) and analyzes the damping based on the sampled signal.

6. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The analysis module (36) is configured such that the analysis module analyzes the damping by analyzing the signal strength and / or attenuation of the voltage signal from the ultrasonic transducer (16, 18).

7. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The analysis module (36) is configured such that the analysis module calculates at least one characteristic value representative of the damping, preferably the at least one characteristic value is a resonance frequency and / or a quality factor (Q) of the oscillating system.

8. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The analysis module (36) is configured such that the analysis module calculates eigenvalues ​​representing the damping at a plurality of times and determines a dispersion of the eigenvalues.

9. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The state of the medium is a cavitation state of the medium in the flow channel (4), and preferably, the analysis module is configured such that if the determined discreteness is higher than a predetermined discreteness threshold (σ T ), the analysis module determines the cavitation state.

10. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The processing unit (14) and the analysis module (36) are configured such that, for evaluating the damping, at least one signal from the at least one ultrasonic transducer (16, 18) is sampled when flow measurement has ceased.

11. Ultrasonic flow meter (2) according to one of the preceding claims, characterized in that The processing unit (14) and the analysis module (36) are configured such that, for evaluating the damping, at least one signal from the at least one ultrasonic transducer (16, 18) is sampled immediately after the ultrasonic transducer (16, 18) has stopped sending a flow measurement signal and / or after the ultrasonic transducer (16, 18) has sent an oscillation test signal.

12. A fluid consumption meter, characterized in that: The fluid consumption meter comprises an ultrasonic flow meter (2) according to one of the preceding claims.

13. A method for evaluating the state of a medium in an ultrasonic flow meter (2), the flow meter (2) comprising a flow channel (4) and at least one ultrasonic transducer (16, 18) located in the flow channel (4) or on a wall (5) of the flow channel (4), Features The damping of the at least one ultrasonic transducer (16, 18) is analyzed.

14. The method according to claim 13, characterized in that At least one eigenvalue representing the damping is calculated at a plurality of times, and a dispersion of the eigenvalues ​​is determined.

15. The method according to claim 14, characterized in that If the determined dispersion is higher than the predetermined dispersion threshold (σ T ), the cavitation state is determined.

16. The method according to one of claims 13 to 15, characterized in that The attenuation behavior of the at least one ultrasonic transducer (16, 18) is used as a representation of the damping.

17. The method according to one of claims 13 to 16, characterized in that In order to analyze the damping, preferably in order to analyze the decay behavior as a manifestation of the damping, the signal strength and / or the decay are analyzed, which are determined after the excitation of the ultrasonic transducer (16, 18) has ceased.

18. The method according to one of claims 13 to 17, characterized in that The damping is analyzed between two flow measurements, preferably the decay behavior as a manifestation of the damping is analyzed.

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