阅读说明：本技术 用于超声换能器的完整性检测系统 (Integrity detection system for ultrasonic transducer ) 是由 F·卡苏贝克 M·伦纳 S·马拉诺 G·黑尔德 于 2020-11-13 设计创作，主要内容包括：本发明涉及一种信号处理单元(150),该信号处理单元(150)配置成：使第一超声发射器在被附连到容器(102)的壁时发射第一超声测试信号；当被附连到容器的壁时从至少一个超声接收器(110”,112,114)来接收第一超声测试信号；检测所接收的第一超声测试信号的飞行时间；以及如果所检测的飞行时间对应于容器(102)的壁中从第一超声发射器(110’)到至少一个超声接收器(112,114)的路径(120)的长度,则确定第一超声发射器和第一超声接收器到容器(102)的壁的声耦合式完整的。(The invention relates to a signal processing unit (150), the signal processing unit (150) being configured to: causing a first ultrasonic transmitter to transmit a first ultrasonic test signal when attached to a wall of a container (102); receiving a first ultrasonic test signal from at least one ultrasonic receiver (110 ", 112, 114) when attached to a wall of a container; detecting a time of flight of the received first ultrasonic test signal; and determining that the acoustic coupling of the first ultrasonic transmitter and the first ultrasonic receiver to the wall of the container (102) is complete if the detected time of flight corresponds to a length of a path (120) in the wall of the container (102) from the first ultrasonic transmitter (110') to the at least one ultrasonic receiver (112, 114).)

1. A signal processing unit (150) is configured to

Causing a first ultrasonic transmitter (110') to transmit a first ultrasonic test signal when attached to a wall of a container (102);

receiving the first ultrasonic test signal from at least one ultrasonic receiver (110 ", 112, 114) when attached to the wall of the container;

detecting a time of flight of the received first ultrasonic test signal; and

determining that the acoustic coupling of the first ultrasonic transmitter and the first ultrasonic receiver to the wall of the container (102) is complete if the detected time of flight corresponds to a length of a path (120) in the wall of the container (102) from the first ultrasonic transmitter (110') to the at least one ultrasonic receiver (112, 114).

2. An integrity detection system (100) for detecting an integrity state of an acoustic coupling between an ultrasonic transducer and a wall of a container (102), comprising:

a first ultrasonic transducer (110) configured for attachment to the wall of the container (102); the first ultrasonic transducer (110) comprises a first ultrasonic transmitter (110') and a first ultrasonic receiver (110 ");

at least one ultrasonic receiver (110 ", 112, 114) configured for attachment to the wall of the vessel (102); and

the signal processing unit (150) of claim 1.

3. The integrity detection system (100) of claim 2,

wherein one of the at least one ultrasonic receiver (110 ', 112, 114) is the first ultrasonic receiver (110') of the first transducer (110).

4. The integrity detection system (100) of claim 2 or 3, comprising a further ultrasound transducer (212, 214);

wherein the further ultrasonic transducer (212, 214) is configured to emit a second ultrasonic test signal along a first path (222, 224) to the first ultrasonic receiver (110 ") and along a second path (232, 234) to the further ultrasonic transducer (212, 214) in the wall of the container (102);

wherein the first ultrasonic receiver (110 ") and the further ultrasonic transducer (212) are further configured to receive the second ultrasonic test signal and to transmit the received second ultrasonic test signal to the signal processing unit (150); and

wherein the signal processing unit (150) is further configured to detect a second time of flight of the received second ultrasonic test signal and to determine that the acoustic coupling of the first ultrasonic transducer (110) and the further ultrasonic transducer (212) is complete if the detected second time of flight corresponds to a corresponding length of the first and second paths (222, 232) of the second signal.

5. The integrity detection system (100) of any one of the preceding claims,

wherein the at least one ultrasonic receiver (110 ") is further configured to measure an excitation signal of a first ultrasonic test signal and to transmit the measured excitation signal to the signal processing unit (150);

wherein the signal processing unit (150) is further configured to: receiving the excitation signal from the at least one ultrasound receiver (110 "); determining a decay time of the measured excitation signal; and if the decay time is less than a threshold value, determining that the acoustic coupling of the first ultrasound transmitter (110') and the at least one ultrasound receiver is complete; and wherein if the signal processing unit (150) has determined that the acoustic coupling of the first ultrasound transmitter (110') and the at least one ultrasound receiver is not complete; and

the signal processing unit (150) is further configured to then detect the first time of flight and determine that the acoustic coupling between the first ultrasonic transmitter (110') and the wall of the container (102) is complete based on the first time of flight.

6. The integrity detection system (100) of claim 5, wherein the excitation signal is a signal generated by application of an excitation voltage to a piezo of the first ultrasonic test signal.

7. The integrity detection system (100) of one of the claims 5 or 6, wherein the measured excitation signal transmitted to the signal processing unit (150) is a raw signal, and the signal processing unit (150) is configured to pre-process the raw signal by applying a Hilbert transform and/or frequency filtering.

8. The integrity detection system (100) of claim 7,

wherein the signal processing unit (150) is further configured to subtract the raw signal or the pre-processed signal from a factory calibration waveform template and/or cross-correlate the raw signal with a factory calibration waveform template, wherein the factory calibration waveform template represents acoustic terminated and acoustic unterminated transducers.

9. The integrity detection system (100) of any one of claims 5 to 8, wherein the threshold is a signal-to-noise ratio or a value based on an output of an artificial intelligence algorithm or a pattern recognition algorithm.

10. The integrity detection system (100) of any of claims 4 to 8, wherein the signal processing unit (150) is further configured to compare an amplitude, a power spectrum, a spectrum and/or a temporal phase of the received excitation signal with the waveform template.

11. A method (500) for detecting a state of integrity of an acoustic coupling between an ultrasound transducer and a wall of a container (102), comprising the steps of:

transmitting (502) a first ultrasonic test signal by a first ultrasonic transmitter (110 '), wherein the first ultrasonic transmitter (110') is attached to the wall of the container (102);

receiving the first ultrasonic test signal by at least one ultrasonic receiver (110', 112, 114), wherein the at least one ultrasonic receiver (110 ", 112, 114) is attached to the wall of the container (102) and transmits the received first ultrasonic test signal to the signal processing unit (150);

detecting, by the signal processing unit (150), a time of flight of the received first ultrasonic test signal; and

determining, by the signal processing unit (150), that the acoustic coupling of the first ultrasonic transmitter (110 ') and the first ultrasonic receiver (110 ', 112, 114) to the wall of the receptacle (102) is complete if the detected time of flight corresponds to a length of a path (120) in the wall of the receptacle (102) from the first ultrasonic transmitter (110) to the at least one ultrasonic receiver (110 ', 112, 114).

12. The method (500) of claim 11, further comprising the steps of:

measuring (606) an excitation signal of the first ultrasonic test signal and transmitting the measured excitation signal to the signal processing unit (150);

determining (608) a decay time of the measured excitation signal by the signal processing unit,

determining (610), by the signal processing unit, that the acoustic coupling of the first ultrasound transmitter (110 ') and the at least one ultrasound receiver is complete if the decay time is less than a predetermined threshold value, and if the signal processing unit (150) has determined that the acoustic coupling of the first ultrasound transmitter (110') and the at least one ultrasound receiver is not complete,

detecting (506) the first time of flight and determining (508) that the acoustic coupling between the first ultrasonic transmitter (110') and the wall of the container (102) is complete based on the first time of flight.

13. A program element comprising instructions which, when executed on a processor of the signal processing unit (150), cause the integrity detection system (100) as defined in any one of claims 2 to 10 to perform the steps of the method as defined in claim 11.

14. A computer readable medium having stored thereon the program element of claim 13.

Technical Field

The invention relates to an integrity detection system for detecting an integrity state of an acoustic coupling between an ultrasound transducer and a wall of a container, a method for detecting the integrity of an acoustic coupling, a signal processing unit, a program element and a computer readable medium.

Background

A non-invasive ultrasound sensor is typically mounted outside the container and generates acoustic waves that penetrate the wall. The propagation of the wave is influenced by the properties of the container content (content), including for example the liquid level or the flow rate. Thus, the characterization of the wave outside the container after propagation allows for the measurement of the content properties. For this reason, efficient, stable and reliable coupling of acoustic waves in and out of the container is of crucial importance-especially for mobile or diagnostic applications.

Disclosure of Invention

It is an object of the invention to detect the integrity status of the ultrasound transducer coupling of an ultrasound transducer attached to a wall of a vessel.

This problem is solved by the subject matter of the independent claims. Embodiments are provided by the dependent claims, the following description and the accompanying drawings.

The embodiments similarly relate to an integrity detection system for detecting an integrity state of an acoustic coupling between an ultrasound transducer and a wall of a container, a method for detecting an integrity state, a signal processing unit, a program element and a computer-readable medium. Synergistic effects may result from different combinations of embodiments, but they may not be described in detail.

Still further, it should be noted that all embodiments of the invention relating to methods may possibly be performed with the order of the steps as described, but this is not necessarily the only and essential order of the steps of the method. The methods provided herein can be performed in another order of the disclosed steps without departing from the respective method embodiments, unless explicitly mentioned to the contrary hereinafter.

Technical terms are used according to their common sense. If a particular meaning is conveyed for certain terms, the definition of the term will be given below in the context in which the term is used.

According to a first aspect, there is provided a signal processing unit configured to: causing a first ultrasonic transmitter to transmit a first ultrasonic test signal when attached to a wall of a vessel; receiving a first ultrasonic test signal from at least one ultrasonic receiver when attached to a wall of a container; detecting a time of flight of the received first ultrasonic test signal; and determining that the acoustic coupling of the first ultrasonic transmitter and the at least one ultrasonic receiver to the wall of the vessel is complete (intact) if the detected time of flight corresponds to the length of the path in the wall of the vessel from the first ultrasonic transmitter to the at least one ultrasonic receiver.

According to a second aspect, an integrity detection system for detecting an integrity state of an acoustic coupling between an ultrasound transducer and a wall of a container is provided. The integrity detection system includes: a first ultrasonic transducer configured for attachment to a wall of a vessel; and a signal processing unit. The first ultrasonic transducer includes a first ultrasonic transmitter and a first ultrasonic receiver configured for attachment to a wall of the vessel. The first ultrasonic transmitter is configured to transmit a first ultrasonic test signal. The at least one ultrasonic receiver is configured to receive the first ultrasonic test signal and to transmit the received first ultrasonic test signal or a signal corresponding to the received second ultrasonic test signal to the signal processing unit accordingly. The signal processing unit is configured to detect a first time of flight of the received first ultrasonic test signal and to determine that the acoustic coupling between the first ultrasonic transmitter and the wall of the vessel is intact if the detected first time of flight corresponds to the length of the path in the wall of the vessel from the first ultrasonic transmitter to the at least one ultrasonic receiver.

That is, there may be one transmitter and also one or more ultrasonic receivers that receive the first test signal transmitted by the first ultrasonic transmitter. The receiver transmits the first test signal to a signal processing unit, where the signal is analyzed for significance (significance) of peaks as characteristic of e.g. the covered path. If the second test signal is not detected, no integrity is given. That is, the contact for introducing ultrasonic energy into the wall and into the container is absent. By arranging more than one receiver, redundancy is provided so that the decision as to whether integrity is given or not can be made according to a policy related to the amount of detected signal. Furthermore, a shorter path can be achieved, which may be necessary if the properties of the container wall do not allow propagation of sound waves, such as for example a long path around a full circle of the container. In addition, the variation in pulse propagation time over a longer measurement time period allows detection of transducer misplacement.

The first test signal may be a dedicated test signal used only for testing as described in this disclosure, or it may be transmitted and used for periodic ultrasonic measurements. In any case, a test signal is received and analyzed for integrity checking.

According to an embodiment, one of the at least one ultrasonic receiver is a first ultrasonic receiver of the first transducer.

Taking a cylindrical container as an example, in case of a correct acoustic contact, the acoustic pulse is expected to make one or several round trips along the circumference of the container and is in turn coupled in the transducer. The time of flight or equivalent estimated time of arrival (ToA) can be estimated from the circumference of the vessel and the speed of sound in the wall. Alternatively, the reference measurement may be performed, for example, after a successful installation, to obtain the time of flight for one round trip. In case of loss of acoustic contact, no signal can be detected near the expected ToA or in case of expected time of flight, respectively. Thus, the integrity detection system allows for detecting integrity by checking whether the transmitted ultrasonic signal arrives after traveling circumferentially around the vessel wall. The length of the path may comprise one round trip or several round trips around the container. In this example, the container is considered to be cylindrical. However, the container may have another geometry, wherein the signal may be reflected at a wall, edge, etc.

The term "first signal" is used herein for a set of single signals from the first ultrasound transducer, where each signal of the single signals may be transmitted in a different mode. To this end, the transducer may be equipped with one or several transmitter elements (which can operate at different frequencies), allowing the generation of different acoustic modes in the wall. The wave modes include, for example, lamb waves, rayleigh waves, or schottky waves.

The term "ultrasound transducer" is used in this disclosure as an ultrasound device that includes a receiving element ("receiver") and a transmitting element ("element"). An "ultrasound receiver" may be integrated in the ultrasound transducer as, for example, a first ultrasound transducer or an ultrasound device that only receives.

According to an embodiment, the integrity detection system comprises a further ultrasonic transducer configured to emit a second ultrasonic test signal along a path to the first ultrasonic receiver and along a path to the further ultrasonic transducer in the wall of the vessel. The first ultrasonic receiver and the further ultrasonic transducer are configured to receive a second ultrasonic test signal and to transmit the received second ultrasonic test signal or a signal corresponding to the further received second ultrasonic test signal to the signal processing unit accordingly. The signal processing unit is further configured to detect a second time of flight of the received second ultrasonic test signal, and to determine that the acoustic coupling of the first ultrasonic transducer and the further ultrasonic transducer is complete if the detected second time of flight corresponds to the corresponding lengths of the first and second paths of the second signal. The second signal may be transmitted independently of the second ultrasonic signal, in particular with respect to the transmission time. Note again that the time of flight is equivalent to the expected ToA, as known to the skilled person.

According to this embodiment, one or several transducers capable of transmitting and receiving test signals are attached to the wall of the vessel. Any transmit-receive configuration between transducers is possible, allowing further redundancy. In particular, it may happen that a transducer for testing the integrity of the acoustic coupling of the first transducer has insufficient contact for transmitting or receiving a test signal. An arrangement with one or several transducers, each transmitting and receiving a test signal, can minimize the risk of false decisions.

According to a further embodiment, the at least one ultrasonic receiver is further configured to measure an excitation signal of the first ultrasonic test signal and to transmit the received excitation signal to the signal processing unit. The signal processing unit is further configured to: receiving an excitation signal from at least one ultrasonic receiver; determining a decay time of the received excitation signal; and determining that the acoustic coupling of the first ultrasound transmitter and the at least one ultrasound receiver is complete if the decay time is less than a predetermined threshold. The signal processing unit is further configured to detect a first time of flight if the signal processing unit has determined that the acoustic coupling of the first ultrasonic transmitter and the at least one ultrasonic receiver is not complete, and to determine that the acoustic coupling between the first ultrasonic transmitter and the wall of the container is complete based on the first time of flight.

In other words, two different tests are performed. Since the failure of the first test still does not indicate that the coupling is not complete, a second test is performed. The second test may also be performed separately, however, the first test is easier to perform and there are occasions when it is possible to omit the second test (in case the first test passes).

The first signal used for (i) the excitation measurement and for (ii) the measurement of the time of flight may be the same transmitted signal or two subsequent signals, wherein the order in which these signals are transmitted may be (i) first and (ii) thereafter, or vice versa. Preferably, signal (ii) is transmitted only if the stimulus-based integrity check fails.

According to an embodiment, the excitation signal is a signal generated by application of a piezoelectric excitation voltage to the first ultrasonic test signal.

The received excitation signal decreases in amplitude (such as e.g. voltage or signal to noise ratio) over time during/after the excitation phase. The term "decay time" relates to the time from a starting time, e.g. when the activation of the piezo is started, to a point in time when a predefined voltage or signal to noise ratio is reached, e.g. during a de-activation phase. In exponential decrease, the decay time may be characterized by a time parameter of an exponential curve, which may in turn be denoted as "decay rate".

The acoustic excitation process involves applying a voltage of several volts to the piezo at some operating frequency, at which the piezo then begins to oscillate and emit an ultrasonic signal. The coupling agent between the piezo and the container wall significantly improves the energy transfer from the piezo to the container wall or through the medium into the medium. Similarly, if the inner container wall is wetted, the energy transfer into the medium is improved. Thus, depending on the contact at the outer side and the wetting of the inner side, more or less energy is reflected, which results in the signal. If a large portion of the energy is reflected due to insufficient contact or wetting, the decay time is significantly longer than the original decay time.

In practice, there is an overlap of the excitation and reflected signals. The attenuation of the signal comprising the echo signal is considered in this disclosure as part of the acoustic excitation process. Thus, the term "excitation signal" also includes echo signals.

The decay time may be compared to factory calibration values. As a possible implementation, factory calibration waveform templates representing acoustic terminated and unterminated transducers, which are subtracted from or cross-correlated with the measured waveforms for comparison, can be stored in the signal processing unit. By "acoustic termination" is meant that the acoustic waves are absorbed at the termination so that there is no back reflection of the piezoelectric, thereby causing a fast ring down time, as opposed to the unterminated case.

Thus, the system allows online diagnosis of the integrity of the acoustic coupling of the ultrasound sensor by measuring the decay time or decay rate of the acoustic excitation signal accordingly or another comparison method and the presence of the acoustic signal propagating along the circumference of the container. In addition to decay time and rate, other quantities characterizing the change in the excitation signal can similarly be used, some of which are described below. A single transducer with a single excitation element is suitable for performing integrity checks even during normal transducer operation (e.g. during non-invasive fluid level or flow measurements) and provides continuous validity information on the measured data. This self-diagnostic feature improves sensor reliability and enables condition monitoring, which is a key function of intelligent digital sensors.

According to a further embodiment, the excitation signal transmitted to the signal processing unit is a raw signal, and the signal processing unit is configured to pre-process the raw signal by applying a hilbert transform and/or frequency filtering. As known to the skilled person, the original signal is an analog signal as received, an appropriately amplified (or electrically pre-processed, e.g. using an analog filter) original signal or a more complex digitally sampled signal.

According to a further embodiment, the signal processing unit is further configured to subtract the raw signal or the pre-processed signal from the factory calibration waveform template and/or cross-correlate the raw signal with the factory calibration waveform template, wherein the factory calibration waveform template represents the acoustic terminated and acoustic unterminated transducers.

The signal processing unit may be further configured to determine whether the acoustic coupling of the first ultrasound transducer is complete based on the subtraction and/or cross-correlation.

The factory calibration waveform template may be stored in a memory of the signal processing unit. The template may be stored as a sample or processed sample depending on the type of comparison to be performed with the measured signal.

It is known to the skilled person that for subtraction and cross-correlation a corresponding time alignment or time shift of the reference signal with respect to the measured original signal is necessary.

According to further embodiments, the threshold used to distinguish between intact and defective acoustic couplings is a signal-to-noise ratio or a value based on the output of an artificial intelligence algorithm or a pattern recognition algorithm. For example, a reference signal-to-noise ratio may be predefined against which the measured signal-to-noise ratio is compared.

According to a further embodiment, the signal processing unit is further configured to compare the amplitude, power spectrum, spectrum and/or temporal phase of the received excitation signal with the waveform template. Thus, different further characteristics of the acoustic wave may be used for comparison of the reference waveform with the measured waveform of the excitation signal.

According to a further aspect, a method for detecting an integrity state of an acoustic coupling between an ultrasound transducer and a wall of a container is provided. The method comprises the following steps:

in a first step, a first ultrasonic test signal is emitted by a first ultrasonic emitter, wherein the first ultrasonic emitter is attached to a wall of the container. In a next step, the first ultrasonic test signal is received by at least one ultrasonic receiver attached to a wall of the container and transmitted to the signal processing unit. In a further step, the time of flight of the received first ultrasonic test signal is detected by the signal processing unit. In a further step, it is determined by the signal processing unit that the acoustic coupling of the first ultrasonic transmitter and the first ultrasonic receiver to the wall of the vessel is complete if the detected time of flight corresponds to the length of the path in the wall of the vessel from the first ultrasonic transmitter to the at least one ultrasonic receiver.

The steps described in this method may also be part of a broader method corresponding to the above description of the system, wherein the decay time of the excitation signal is first analyzed and if the integrity cannot be determined by the analysis, the above described steps may be performed as a second check-up.

Thus, according to an embodiment, the method further comprises the steps of:

an excitation signal of the first ultrasonic test signal is measured and the measured excitation signal is transmitted to the signal processing unit. The decay time of the measured excitation signal is determined by the signal processing unit. Determining, by the signal processing unit, that the acoustic coupling of the first ultrasonic transmitter and the at least one ultrasonic receiver is complete if the decay time is less than a predetermined threshold, and determining that the acoustic coupling between the first ultrasonic transmitter and the wall of the vessel is complete based on the first time of flight if the signal processing unit has determined that the acoustic coupling of the first ultrasonic transmitter and the at least one ultrasonic receiver is not complete.

Accordingly, a method for monitoring the integrity of the acoustic coupling of an ultrasound transducer is proposed, which may comprise one or two parts. For example, in the first part, the decay rate of the acoustic excitation pulse is measured at the operating frequency. An acoustic contact is considered to be present if the decay time corresponds to the decay time corresponding to the acoustic termination transducer. If the decay time is longer, in a second part of the method, a second measurement may be performed. The second part of the method may be performed as a stand-alone test (i.e. without performing the first part).

Here, a specific acoustic pattern is initiated, which propagates in the container wall and along a path such that the acoustic signal is detected by the same transducer as the corresponding transmitting transducer. Acoustic contact is considered appropriate if the pulse(s) is present at the expected time(s). The expected pulse propagation time can be estimated from the known speed of sound for the corresponding acoustic mode and the length of the propagation path. In the absence of a pulse, acoustic contact is lost, and an alert message may be generated for the user or the measurement may be marked as invalid.

The signal processing unit may comprise circuitry without programmable logic, or may be or include a microcontroller, a Field Programmable Gate Array (FPGA), an ASIC, a Complex Programmable Logic Device (CPLD), or any other programmable logic device known to those skilled in the art. The signal processing unit may further comprise communication means for receiving data from the sensors, by wire or over the air, for sending signals to the sensors, and optionally for communicating with network means. Furthermore, the signal processing unit may comprise storage means for storing codes and data, such as e.g. acoustic wave templates for terminated and unterminated transducers. The signal processing unit may be a single device inside the housing or a logical device consisting of several locally distributed hardware devices.

According to a further aspect, a program element is provided, which, when being executed on a processor of a signal processing unit, controls an integrity detection system to carry out the steps of the method.

The computer program element may be an integral part of the computer program, but it can also be a separate complete program. For example, a computer program element may be used to update an already existing computer program to achieve the present invention.

According to a further aspect, a computer readable medium is provided on which a program element is stored.

The computer-readable medium may be seen as a storage medium, such as for example a USB stick, a CD, a DVD, a data storage device, a hard disk or any other medium on which the program elements as described above can be stored.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the drawings and following description.

Drawings

Figure 1 shows a schematic view of a first example of an integrity detection system for detecting the integrity status of an acoustic coupling,

figure 2 shows a simplified diagram of a second example of an integrity detection system,

figure 3 shows a simplified diagram of the ring down of the excitation signal,

figure 4a shows an exemplary graph of a data line with a round trip peak,

fig. 4b shows a simplified diagram of a top view of a container, wherein an attached transducer emits a round trip signal,

figure 5 shows a flow diagram of a method according to an embodiment,

fig. 6 shows a further flowchart of a method according to an example.

Detailed Description

Fig. 1 shows a schematic diagram of a first example of an integrity detection system 100 for detecting an integrity state of an acoustic coupling between an ultrasonic transducer 100 and a wall of a container 102. Transducer 110 includes a transmitter 110' and a receiver 110 ", and is thus a transducer for transmitting and receiving ultrasonic signals, while devices 112 and 114 are ultrasonic receivers. Physically, the transmitter 110' and receiver 110 "can be the same component, i.e., the same piezo is used and switched from transmitter to receiver. This is usually the best solution, so that the (as then) receiving piezo has exactly the same properties (e.g. eigenfrequency). The transducer 110 transmits ultrasonic signals using different acoustic modes, creating a propagation path 122 inside the wall of the container 102 from the transducer 110 to the receiver 112 and similarly creating paths 124 and 120 to the receiver 124, the path 124 extending around the container 102 such that the transducer 110 receives the signals transmitted by itself. If the length of the path and the speed of sound inside the walls of the vessel 102 are known, the expected time of flight can be calculated and compared to the measured time difference between transmission and reception. Additional indicators may be used without measuring time of flight. For example, if the signals are detected simultaneously at the receivers 112 and 114-depending on the geometry-a complete coupling can be assumed. Furthermore, periodic repetitions of the received signal (i.e., a significant peak in amplitude as shown in fig. 4 a) corresponding to a round trip of the test signal around the vessel 102 indicate a correct connection.

Fig. 2 shows a schematic diagram of a second example of an integrity detection system. In the example shown, the first transducer 110 and two further transducers 212, 214 are attached to a wall of the container 102. The first transducer 110 transmits a first test signal to the further transducers 212, 214 and receives a second signal from each of the further transducers 212, 214, as indicated by arrows 222 and 224. In addition, the first transducer 110 transmits a first signal to itself as indicated by arrow 220. Similarly, transducers 212 and 214 each transmit signals to themselves 232, 234 and to each other 226.

FIG. 3 shows a simplified diagram of a measured ring down of a signal exciting a test signal. The thin lines show the envelope of the ultrasound signal, which is derived from the original signal of the signal comprising the echo signal, for example by applying a hilbert transform and frequency filtering. The thick lines 302, 304 are a fit to the exponential decay of the envelope signal. The straight line at the beginning is caused by the saturation of the piezo during the excitation phase when a high initial voltage is applied to the piezo or when the amplitude is still too high immediately after this phase. Line 304 is the result of the signal when there is good contact and the container wall is wet inside the transducer location, while line 302 shows the situation when there is no liquid in the container 102 or no contact at this location.

A decay constant of an exponential function representing the decay rate may be determined, which decay constant may be compared to a corresponding predetermined decay constant or decay rate of the exponential function when the wall of the container interior is wet or dry or when contact between the piezo and the container wall is present or absent.

FIG. 4a shows the received voltage u [ mV ] of the round trip signal]Envelope and time tAnd figure 4b shows a top view of a corresponding arrangement in which the transducers are attached to the container 102. The test signal in FIG. 4a is an A0 acoustic mode signal (lamb wave) at an operating frequency of 380 kHz, which travels around the vessel 102. Fig. 4b shows a top view on the container 102 and the transmitting and receiving transducers 110. Arrows 430 and 432 indicate the path of the ultrasonic test signal around the container. The first receive peak 402 is an excitation signal that includes an echo signal that echoes (echoed) at the vessel wall immediately after the transmit signal. Peak 404 is the detected signal after one run around the container. Accordingly, peaks 206 and 208 are the second and third arriving peaks of the signal, e.g., due to round trips or reflections.

Fig. 5 shows a flow diagram of a method according to an embodiment. The method 500 for detecting the integrity of the acoustic coupling of an ultrasound transducer at a wall of a vessel comprises the steps of:

a second ultrasonic test signal is transmitted 502 by the ultrasonic transmitter. The first ultrasonic test signal is received 504 by the at least one ultrasonic receiver and the received first ultrasonic test signal is transmitted to the signal processing unit 150. The time of flight of the received first ultrasonic test signal is detected 506 by the signal processing unit 150, and if the detected time of flight corresponds to the length of the path 120 around the wall of the container 102, the acoustic coupling between the first ultrasonic transducer 110 and the wall of the container 102 of ultrasonic transducers is determined 508 by the signal processing unit to be complete.

Fig. 6 shows a further flowchart 600 according to an example. After the start in 602, in a first step, a first test signal is emitted 604 by the ultrasonic transducer 110. The first test signal may be the same test signal as described for fig. 5 or a different signal. In 606, the first test signal is received by the ultrasonic transducer 110 as an excitation signal and is transmitted to the signal processing unit 150. In 608, the decay time of the received excitation signal is determined by the signal processing unit and analyzed for the integrity of the acoustic coupling of the transducer. The analysis may include pre-processing of the original signal and investigation of the delay times and characteristics of the waveforms (which may be compared to the stored waveform templates by subtraction or cross-correlation). If the analysis result is that the acoustic coupling is complete in 610, the signal processing unit sends 612 a corresponding indication to e.g. a man-machine interface or another interface, and the process ends 630. Otherwise, at 616, the method 500 described above is performed. If at 618 the analysis results in that the acoustic coupling is complete, the signal processing unit sends an indication that there is no problem with the coupling at 620 and the process ends 630. Otherwise, the coupling is not complete as indicated 624, and the process ends 630.

With proper acoustic contact and wetting of the walls, a large portion of the acoustic energy is radiated into the medium contained by the tank, which causes rapid attenuation (acoustic termination transducer). However, if the signal attenuation is closer to that of the unterminated transducer, it may be caused by a) loss of acoustic contact or b) a change in wetting of the walls (e.g., caused by a low liquid level or partial fill).

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items or steps recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems. Any reference signs in the claims shall not be construed as limiting the scope of the claims.