阅读说明：本技术 操作用于确定流体变量的测量装置的方法以及测量装置 (Method for operating a measuring device for determining a fluid variable, and measuring device ) 是由 M·梅尔 A·麦丁格 A·霍夫曼 M·施密特 于 2020-09-22 设计创作，主要内容包括：本申请涉及一种用于操作测量装置(1)的方法,测量装置包括振动换能器(5),振动换能器通过测试激励信号(13)驱动,以在流体中激励波(7),波沿传播通路(8)往回引导至振动换能器或引导至至少一个附加振动换能器(6),从而激励振动换能器或附加振动换能器振动,获取与该振动相关的输出信号(14),并确定输出信号的、位于分析间隔(16)中那一段的频率(18),一旦振动换能器激励波的驱动结束和/或一旦达到或超过振动幅值的最大值(42),分析间隔就开始,和/或在满足激发条件时,错误消息或通知(19)输出给用户和/或测量装置外部的装置,和/或测量装置处于故障状态。本申请还涉及一种用于确定流体变量的测量装置。(The application relates to a method for operating a measuring device (1) comprising a vibration transducer (5) driven by a test excitation signal (13) to excite a wave (7) in a fluid, the wave being guided back along a propagation path (8) to the vibration transducer or to at least one additional vibration transducer (6) to excite the vibration transducer or the additional vibration transducer to vibrate, an output signal (14) being obtained relating to the vibration, and the frequency (18) of the output signal in that section of the analysis interval (16) being determined, the analysis interval being started as soon as the driving of the excitation wave of the vibration transducer is ended and/or as soon as a maximum value (42) of the vibration amplitude is reached or exceeded, and/or an error message or notification (19) being output to a user and/or to a device external to the measuring device when excitation conditions are met, and/or the measuring device is in a fault state. The application also relates to a measuring device for determining a fluid variable.)

1. Method for operating a measuring device (1) for determining a fluid variable related to a fluid and/or a fluid flow of a fluid, the measuring device comprising: a measuring vessel (3), the measuring vessel (3) holding a fluid and/or a fluid flowing through the measuring vessel (3); and a vibration transducer (5), which vibration transducer (5) is arranged on the measuring vessel (3), wherein a control device (4) of the measuring device (1) drives the vibration transducer (5) by means of a test excitation signal (13) in order to excite a wave (7) in the fluid, which wave (7) is conducted back along a propagation path (8) to the vibration transducer (5) or to at least one additional vibration transducer (6) of the measuring device (1) arranged on the measuring vessel (3) in order to excite said vibration transducer (5) or additional vibration transducer (6) to vibrate, wherein the control device (4) acquires an output signal (14) related to said vibration and determines a frequency (18) of the output signal (14) in that section of the analysis interval (16), wherein, upon termination of the driving of the excitation wave (7) by the vibration transducer (5) and/or upon reaching or exceeding a maximum value (42) of the vibration amplitude, the analysis interval (16) is started, the determination of the fluid variable is performed according to the determined frequency (18), and/or an error message or notification (19) is output to a user and/or a device external to the measuring device and/or the measuring device (1) is in a fault state in which, in particular, the determination of the fluid variable is not performed when an excitation condition is fulfilled, which depends on the determined frequency (18).

2. The method of claim 1, wherein: the determination of the fluid variable depends on the determined frequency, wherein a measurement excitation signal (21) is determined from the determined frequency (18), the control device (4) outputting the measurement excitation signal (21) to the vibration transducer or the additional vibration transducer (5, 6) as part of the determination of the fluid variable.

3. The method according to claim 1 or 2, characterized in that: the control device (4) determines digital measurement data (15) from the output signal (14), said digital measurement data describing the instantaneous change of the output signal (14), wherein the frequency (18) and/or the time at which the maximum value (42) of the vibration amplitude is reached is determined from the digital measurement data (15).

4. The method of any preceding claim, wherein: the frequency (18) is determined by determining a maximum (43, 44) of the power density spectrum (17, 29-32, 36-39) of the output signal (14) in the analysis interval (16) or by analyzing the time interval between the points of intersection of the output signal (14) within the analysis interval (16) above and/or below a determined limit value.

5. The method of any preceding claim, wherein: the control device (4) determines an envelope or instantaneous signal amplitude of the output signal (14), wherein the beginning and/or the end of the analysis interval (16) is dependent on the envelope or instantaneous signal amplitude.

6. The method of any preceding claim, wherein: use of a measuring device (1), wherein for a given test excitation signal (13) amplitude, the amplitude of the output signal (14) has a local maximum (43, 44) for at least one resonance frequency (34, 35), wherein the test excitation signal (13) is a periodic signal (11) amplitude-modulated by an envelope (12), the resonance frequency (34, 35) and the excitation frequency of the periodic signal (11) differ by at least 1% or at least 3% of the resonance frequency (34, 35), and/or the excitation frequency and the envelope (12) are selected such that the minimum (25) of the power density spectrum (22, 23, 24) of the test excitation signal (13) is offset with respect to the resonance frequency (34, 35) by at least 1% or at least 3% of the resonance frequency.

7. The method according to claim 6, characterized in that: at most 25 or at most 15 or at most 10 periods of the periodic signal (11) lie within the envelope (12).

8. The method of any preceding claim, wherein: use of a measuring device (1), wherein, when white noise is used as excitation signal, the amplitude of the output signal (14) will have a local maximum for at least one additional resonance frequency or main frequency, the test excitation signal (13) being a periodic signal (11) amplitude-modulated by an envelope (12), the envelope (12) being selected such that the frequency spectrum of the test excitation signal has a local minimum at the additional resonance frequency or main frequency.

9. The method of any preceding claim, wherein: the measurement excitation frequency (20) of the measurement excitation signal (21) is read from the look-up table on the basis of the determined frequency (18).

10. Measuring device for determining a fluid variable related to a fluid and/or a fluid flow of a fluid, the measuring device comprising a measuring vessel (3) for holding the fluid and comprising a vibration transducer (5, 6) arranged on the measuring vessel and a control device (4), characterized in that the measuring device (1) is arranged to perform the method according to any of the preceding claims.

Technical Field

The invention relates to a method for operating a measuring device for determining a fluid variable relating to a fluid and/or a fluid flow of the fluid, and the measuring device comprises: a measuring vessel holding a fluid and/or a fluid flowing through the measuring vessel; and a vibration transducer arranged on the measurement volume. The invention also relates to a measuring device for determining a fluid variable relating to a fluid and/or a fluid flow of a fluid.

Background

Ultrasonic meters are one possible way to detect flow rates or other measurement variables associated with a fluid. These meters use at least one ultrasonic transducer in order to couple ultrasonic waves into the fluid flowing through the measuring tube, which ultrasonic waves are guided to a second ultrasonic transducer either along a straight path or after several reflections at walls or special reflecting elements. The flow rate through the measurement tube can be determined from the difference in transit time of the ultrasonic wave between the ultrasonic transducers when the transmitter and receiver are interchanged. For other measurement tasks, for example for identifying a fluid from the speed of sound in the fluid, it may even be sufficient to use only one ultrasonic transducer (back to which the wave is directed).

In order to be able to integrate such a measuring device easily into a fluid circuit, it is preferred that the device has a space-saving design and achieves low energy consumption, for example such that the battery can be operated over a longer time interval. When a signal with a particular frequency is used here to excite an ultrasound wave, the amplitude of the received signal is generally dependent on this frequency for a given vibration transducer size and a given excitation power, wherein particularly large signal amplitudes of the received signal can be achieved at a particular resonance frequency of the system. In order to obtain a high signal quality and thus also a high measurement accuracy, it is therefore preferred to be able to operate the vibration transducer at or at least close to the resonance frequency of the measurement system. Due to component tolerances, the relevant resonance frequency (in particular its response to changes in the measured parameter, for example to changes in temperature) may vary between measuring devices which are in principle of the same construction, or may vary as part of an aging process of the measuring device.

In order to automatically adjust the operating point of the operating frequency, document EP2725353B1 proposes to change the drive frequency of the ultrasonic sensor at intervals and to determine the intensity of the signal received by the ultrasonic receiver for each interval. The drive frequency is changed until the received signal strength reaches a maximum. Since this requires a relatively large number of measurement processes to be performed until the operating point can be determined, adjusting the operating point will require a relatively large amount of energy and no flow rate measurement, or at least no optimal flow rate measurement, can be made in this time interval.

Disclosure of Invention

It is therefore an object of the present invention to specify a method for operating a measuring device, in which an excitation signal used in the measurement, in particular the frequency of the excitation signal, can be determined with little energy and/or time consumption and/or a change in the resonance frequency can be easily detected.

According to the invention, this object is achieved by a method of the type mentioned in the introduction, wherein the control device of the measuring device drives the vibration transducer by means of a test excitation signal in order to excite a wave in the fluid, which wave is guided back to the vibration transducer along a propagation path or to at least one additional vibration transducer of the measuring device, which additional vibration transducer is arranged on the measuring vessel in order to excite the vibration transducer or the additional vibration transducer to vibrate, wherein the control device acquires an output signal relating to the vibration and determines the frequency of that section of the output signal which lies in an analysis interval, wherein the analysis interval is started as soon as the driving of the excitation wave of the vibration transducer is ended and/or as soon as a maximum value of the vibration amplitude is reached or exceeded, wherein the determination of the fluid variable is carried out according to the determined frequency and/or in case an excitation condition is fulfilled, which fulfils depending on the determined frequency, the error message or the notification is output to a user and/or a device external to the measuring device and/or the measuring device is in a fault state, wherein in particular no determination of the fluid variable is performed.

When the wave is excited by a very broadband excitation signal, the vibrations of the receiving vibrating transducer will be excited to have a main frequency equal to the resonance frequency of the system. The main frequency may be determined, for example, as a maximum of the power density spectrum, or using a frequency counter. However, in order to achieve a robust transmission of vibrations from the vibration transducer to the additional vibration transducer, or back to the same vibration transducer along the propagation path, a relatively narrow-band excitation signal should be used, e.g. a periodic signal determining the main frequency of the excitation, which periodic signal is modulated by an amplitude envelope (envelope). However, as a result of this, a corresponding spectral distribution of the excitation signal is imposed on the output signal, so that the main frequency of the excitation signal or an intermediate frequency between this frequency and the actual resonance frequency is usually determined as the distinct resonance frequency when the entire output signal is analyzed.

In the context of the present invention, it has been found that this problem can be avoided or significantly reduced by considering only the analysis interval, which begins once the driving of the excitation wave of the vibration transducer is completed or once the amplitude of the vibration reaches or exceeds a maximum value. This is due to the fact that during the excitation of the vibration by the drive of the vibration transducer or by the incident wave, i.e. before said time, a forced vibration of the vibration transducer or of the additional vibration transducer occurs, the frequency of which is determined by the frequency of the external excitation. On the other hand, once the driving of the excitation wave of the vibration transducer has ended, in particular when the expected transit time of the wave back to or to the vibration transducer can be additionally delayed, or once the maximum value of the vibration amplitude is reached, it can be assumed that the vibration transducer or the additional vibration transducer is free to vibrate, at least for most of the analysis intervals, so that the vibration spectrum is governed by the resonance frequency of the system or the vibration transducer or the additional vibration transducer. By only taking into account the output signal within the analysis interval, the influence of the frequency spectrum of the test excitation signal on the determined output signal frequency spectrum can be at least substantially eliminated, so that the frequency of the output signal within the analysis interval, in particular the resonance frequency of the system or of the vibration transducer or of the additional vibration transducer, can be determined with high accuracy by a single measurement. The excitation frequency can thus be adjusted in particular to a certain resonance frequency of the system (or in particular of the vibration transducer).

In particular, the determined frequency can be the main frequency of the output signal in the analysis interval. The various options for determining the dominant frequency will be described in more detail later. As part of the method according to the invention, in particular, the excitation frequency of the measurement excitation signal is determined from the determined frequency. The excitation frequency may be the same as the determined frequency, may be offset from the determined frequency by a fixed offset amount, may be determined using a look-up table, and the like. In particular, the frequency may be the frequency of a periodic signal, such as a sine wave or a square wave. The periodic signal can be amplitude modulated by an envelope, such as a square wave function of determined length, a cosine square window or a Blackman-Harris window, etc.

As will be described in more detail later, the determined frequency is preferably used to determine an excitation signal for the vibration transducer, which is used to determine the fluid variable. In addition or alternatively, parameters or correction factors that depend on the determination frequency can be taken into account when determining the flow variable, in particular when processing the measurement data. For example, the parameter or correction factor can be determined from a look-up table, which is obtained, for example, empirically. For example, the correction factor can be used to correct for effects due to aging of the measurement device or environmental conditions (e.g., temperature) that also affect the resonant or dominant frequency in the system.

Additionally or alternatively, in determining the fluid variable according to a determined frequency, under certain conditions, a notification can be given or an error message can be output according to the determined frequency. For example, when the determined frequency is outside the target range or the deviation from the target value is larger than the limit value, the excitation condition for giving a notification or for an error message may be satisfied. For example, the resonance frequency of the measuring device, which can be determined as the determined frequency, can change due to aging or damage of the vibration transducer or of the additional vibration transducer. Slight variations in the resonant frequency can be counteracted by adjusting the measurement excitation signal. However, when the deviation that occurs is too great, or the magnitude of the deviation indicates that the measurement accuracy may be affected (e.g. due to ageing or damage of the measuring device), this can be communicated to the user, or a suitable communication or a suitable error message can be given to a device external to the measuring device, in particular wirelessly, for example to advise repair of the measuring device or replacement of certain components. The notification can be given by a notification device mounted on the measuring device, for example by means of a loudspeaker, a display or the like. However, it is also possible, for example, to transmit a suitable signal via a radio link for the purpose of giving a notification, for example to a central device or monitoring system of the supplier or manufacturer of the measuring device, or to the user's handset. Additionally or alternatively, the measuring device can be switched to a fault state when the excitation condition is fulfilled. The measured values cannot be acquired in the fault state or the measured data acquired in the fault state is marked as an error. This can prevent the acquisition of damaged measurement data or measurement data without guaranteed accuracy when the determined frequency indicates a significant change in the characteristics of the measurement apparatus.

When the frequency is determined at a plurality of instants spaced apart in time as described above, it may also be preferred that the determined change in frequency is stored and/or analysed for diagnostic purposes. For example, a change in the frequency characteristic near the end of the period of use of the vibration transducer can be identified, or a step change in the frequency can be identified, which may indicate, for example, damage to the vibration transducer, such as a crack or the like.

In the following explanations and examples, emphasis is given to measuring devices with a vibration transducer for coupling (coupling) waves directly into a fluid and receiving waves directly from the fluid. However, the teaching according to the invention can equally be applied to measuring devices in which the coupling of waves into and/or out of the fluid takes place indirectly through the wall (e.g. pipe wall) of the measuring vessel. For example, the vibration transducer and/or the additional vibration transducer can be arranged to first excite a guided wave in the wall of the measuring vessel, which guided wave in turn causes the wave to couple into the fluid. For example, Lamb waves can be coupled as guided waves into the wall of the measuring vessel.

The determination of the fluid variable preferably depends at least to such an extent on the determined frequency, i.e. the measurement excitation signal is determined from the determined frequency, which the control device outputs to the vibration transducer or the additional vibration transducer as part of the determination of the fluid variable. In particular, the excitation frequency of the measurement excitation signal can be determined from the determined frequency and set, for example, to this frequency. Thus, for example, excitation at the resonance frequency of the vibration transducer can be achieved. This enables a sufficient signal amplitude to be obtained with a relatively small energy input, thereby ensuring a low energy consumption of the measuring device.

The control device can determine from the output signal digital measurement data which describe the instantaneous change of the output signal, wherein the frequency and/or the time at which the maximum value of the vibration amplitude is reached is determined from the digital measurement data. In this case, the output signal is preferably converted by an analog-to-digital converter with a conversion rate which is greater than the main frequency of the test excitation signal or the measurement excitation signal or greater than the determined frequency or the resonance frequency to be determined, for example at least 3 or 5 or 10 times greater. The digital processing of the measurement data makes it possible, for example, to determine the envelope of the output signal and thus the maximum value of the amplitude particularly easily. In addition, the power density spectrum of the analysis interval or of the sub-intervals of the analysis interval can be determined effortlessly, for example by means of a Fourier transform, in particular a fast Fourier transform, so that the dominant frequency (as maximum of the power density spectrum) can be easily determined. The acquisition of the digital measurement data can, for example, start at the end of the excitation of the wave or be offset relative to it at certain time intervals.

The frequency can be determined by determining the maximum of the power density spectrum of the output signal in the analysis interval or by analyzing the time interval between the output signal and an intersection (crossover) within the analysis interval above and/or below a determined limit value. As described above, the digital measurement data can be analyzed. In this case, the power density spectrum can be generated by Fourier transform. The spacing between zero or other intersections with the line above or below the limit value can also be easily determined in the digital measurement data. However, it is also possible to determine the time interval between the crossing points above and/or below a certain limit value, in particular the time interval between zero crossing points, without prior analog-to-digital conversion, for example by means of a frequency counter, periodic measurement or (usually) a time-to-digital converter.

The control device is able to determine an envelope or instantaneous signal amplitude of the output signal, wherein the start and/or end of the analysis interval is dependent on the envelope or instantaneous signal amplitude. In particular, a maximum or minimum value of the output signal or of the digital measurement data between each two intersection points with the limit value above and/or below (and therefore in particular between each two zero intersection points) can be determined as the instantaneous signal amplitude. The envelope can be determined, for example, by low-pass filtering the conditioned (squared) or otherwise rectified output signal or by processing the digital measurement data accordingly.

In particular, the analysis interval can start at a maximum value of the vibration amplitude or at a determined time after the maximum value, wherein the maximum value can be determined by the signal amplitude envelope or the instantaneous signal amplitude. The end of the analysis interval can be chosen such that the instantaneous signal amplitude or envelope at the end of the analysis interval falls below a certain limit value. As already explained, the selection of the start of the analysis interval can be such that the frequency spectrum of the test excitation signal has no or only a small influence on the determined frequency. Said selection of the end of the analysis interval can be advantageous for excluding from the frequency determination time intervals in which the output signal or the digital measurement data is dominated by noise.

Since in the method according to the invention for frequency determination only the analysis interval is taken into account, and not the entire output signal, any influence of the frequency spectrum of the test excitation signal on the determined frequency can be significantly reduced even at this stage, as already described. However, when the main frequency of the test excitation signal is very close to the frequency to be determined, the accuracy of the frequency determination may be compromised. In addition, it should be avoided that the frequency to be determined is at a minimum of the power density spectrum, as this can make it more difficult to identify the resonance frequency.

In the method according to the invention, therefore, a measuring device can be used in which, for a given test excitation signal amplitude, the amplitude of the output signal has a local maximum for at least one resonance frequency, wherein the test excitation signal is a periodic signal amplitude-modulated by an envelope, the resonance frequency and the excitation frequency of the periodic signal differing by at least 1% or at least 3% of the resonance frequency, and/or the excitation frequency and the envelope are selected such that the minimum of the power density spectrum of the test excitation signal deviates from the resonance frequency by at least 1% or at least 3% of the resonance frequency. Preferably, the resonant frequency and the excitation frequency of the periodic signal can differ by 5% or more of the resonant frequency, and/or the minimum of the power density spectrum of the test excitation signal can be offset from the resonant frequency by 5% or more of the resonant frequency.

When a measuring device is used in which the amplitude of the output signal will have a local maximum for at least one additional resonance frequency or main frequency (when white noise is used as the excitation signal) and the test excitation signal is a periodic signal amplitude modulated by an envelope, preferably the envelope can be chosen such that the frequency spectrum of the test excitation signal has a local minimum at the additional resonance frequency or main frequency. For example, for a rectangular or pulse-shaped envelope, the width of the pulse can be so selected. When the frequency spectrum of the test stimulus signal has a minimum for a frequency, that frequency is also suppressed in the output signal. It is thereby prevented that additional, undesired resonances or main frequencies cause errors in the detected or resonant frequency.

For an ultrasonic transducer, the resonant frequency may be around 1MHz, for example, can be at 1.05 MHz. Thus, the offset can be, for example, at least 10kHz, at least 30kHz, or 50kHz or greater. Preferably, the resonance frequency can be a frequency which is determined in the method according to the invention as the determination frequency. For a given test excitation signal amplitude, the amplitude of the output signal can in particular have an overall maximum at the resonance frequency. However, the measuring channel or the vibration transducer or the additional vibration transducer can also have a plurality of resonance frequencies, wherein, for example, the excitation is to take place at resonance frequencies which are not the overall maximum.

For example, a sufficient shift of the minimum of the power density spectrum of the test excitation signal from the resonance frequency can be achieved by making the main maximum of the power density spectrum of the test excitation signal relatively broad, for example with a width of the resonance frequency of at least 10% or at least 20% or at least 30%.

Up to 25 or up to 15 or up to 10 periods of the periodic signal can lie within the envelope. For example, 6 or 12 periods of the periodic signal can lie within the envelope. A large width of the main maximum of the power density spectrum of the test excitation signal can be achieved by using a relatively short envelope. In particular, the amplitude of the test excitation signal can be zero outside the specified length of the envelope. A square wave function can be used as an envelope, so that, for example, the number of periods of the periodic signal is output without additional amplitude modulation, and no signal is output before and after the number of periods. The periodic signal can be, for example, a sine wave.

The measured excitation frequency of the measured excitation signal can be read from the look-up table in dependence on the determined frequency. By determining an appropriate look-up table, systematic errors in determining the frequency (e.g., resonant frequency) can be eliminated. Also, when desired, the use of a suitable look-up table can ensure that excitation occurs at a determined location relative to the resonant frequency. Alternatively, the determined frequency can be used directly as the measurement excitation frequency, and/or the determined frequency can be scaled, and/or an offset can be added to determine the measurement excitation frequency.

In addition to the method according to the invention, the invention also relates to a measuring device for determining a fluid variable relating to a fluid and/or a fluid flow of a fluid, the measuring device comprising a measuring vessel for holding the fluid, and further comprising: a vibration transducer arranged on the measurement vessel; and a control device, wherein the measuring device is arranged to perform the method according to the invention. In particular, the vibration transducer can be arranged and disposed on the measuring vessel such that, when excited by a test excitation signal from the control device, the wave excited in the fluid is guided back along the propagation path to the vibration transducer or to at least one additional vibration transducer of the measuring device, which is disposed on the measuring vessel such that the vibration transducer or the additional vibration transducer is excited to vibrate. The control device can in particular be arranged to control the vibration transducer according to the method of the invention and to obtain an output signal of the vibration transducer or of an additional vibration transducer and to process said output signal according to the method of the invention.

The features described in relation to the method according to the invention can be used to develop the measuring device such that it has the advantages associated with the method and vice versa.

Drawings

Further advantages and details of the invention are represented in the following exemplary embodiments and in the drawings, in which:

FIG. 1 schematically shows an exemplary embodiment of a measuring device according to the present invention;

FIG. 2 shows a flow chart of an exemplary embodiment of a method according to the present invention;

FIG. 3 schematically shows power density spectra of different test stimulus signals that can be used in an exemplary embodiment of a method according to the present invention; and

fig. 4-7 schematically show measurement and processing data obtained in an exemplary embodiment of the method according to the invention.

Detailed Description

Fig. 1 shows a measuring device 1 for determining a fluid variable, in particular a fluid flow rate through a fluid-carrying measuring vessel 3. A vibration transducer 5 and an additional vibration transducer 6 are arranged on the side wall 2 of the measuring vessel 3. The control device 4 is able to supply the vibration transducers 5, 6 with associated excitation signals in order to excite the transducers to vibrate and thus in each case excite the waves 7 for vibrating the transducers 5, as shown in fig. 1. The wave 7 excited by the vibration transducer 5 is guided along the propagation path 8 to the additional vibration transducer 6 and vice versa. The special vibration transducers 5, 6, at which the waves 7 are incident, are excited to vibrate. The special vibration transducers 5, 6 thus provide output signals which are related to the vibrations and which are picked up by the control device 4. The wave 7 is guided along the propagation path 8 by the ultrasonic mirrors 9, 10. Alternatively, it is also possible, for example, to use vibration transducers 5, 6, which vibration transducers 5, 6 transmit waves 7 obliquely into the measurement container 3, so that the ultrasound mirrors 9, 10 can be omitted. In another embodiment, the vibrating transducers 5, 6 can first excite the sidewall 2 to vibrate, which sidewall 2 in turn excites the waves 7, rather than exciting the appropriate waves directly in the fluid.

The measuring device 1 shown can be used, for example, to determine the flow velocity of the fluid 3 and thus the flow rate of the fluid 3 by analyzing the propagation time difference of the wave 7 from the vibration transducer 5 to the additional vibration transducer 6 and vice versa. The process described below can also be used with measurement devices that determine other fluid properties, such as fluid type by measuring sound speed. In this case, for example, the waves 7 can also be guided from the vibration transducer 5 back to the transducer along a propagation path (not shown) without the need for an additional vibration transducer 6. In the example shown in fig. 1, this can be done, for example, by omitting the ultrasonic mirror 9, so that the wave 7 is reflected back to the vibrating transducer 5 by the opposite side wall 2.

In order to achieve a high measurement quality with low energy consumption, it is preferred that the main frequency of the measurement excitation signal used to drive the vibration transducer 5, 6 (as part of determining the fluid variable) is equal to the resonance frequency of the system or vibration transducer 5, 6, resulting in a particularly large amplitude of the output signal for a given excitation power. Since this frequency is usually dependent on operating parameters (e.g. temperature), may also differ between different measuring devices due to component tolerances, or may vary due to aging of the measuring device, it is preferred to determine the respective frequency in certain operating situations or periodically during operation of the measuring device 1. The corresponding method implemented by the control device 4 is described in more detail below with reference to fig. 2.

In step S1, a periodic signal 11, for example a sine wave, is first generated at a determined frequency. The frequency of the periodic signal is chosen such that it has a certain offset from the assumed resonance frequency, although the offset is not too large. For example, the frequency of the periodic signal may differ from the assumed resonant frequency by between 1% and 10% of the assumed resonant frequency.

In step S2, an envelope 12 is generated, which envelope 12 is used in step S3 for the amplitude modulation of the periodic signal 11 in order to provide the test stimulus signal 13. In the simplest case, the envelope 12 may be a square wave function, so that the test stimulus signal 13 can correspond to a certain number of periods of the periodic signal 11, for example. However, other envelopes 12 are also possible, which can also be referred to as window functions, such as cosine square functions, trapezoidal envelopes, etc. It is preferred to use a relatively short envelope 12. This results in a wider frequency spectrum and thus a robust excitation of the resonance frequency, even when the periodic signal is significantly detuned from the resonance frequency.

In step S4, the control device 4 outputs the test excitation signal 13 to the vibration transducer 5 so as to excite the transducer to vibrate. Thus, the wave 7 is excited in the fluid and guided along the propagation path 8 to the additional vibration transducer 6 as described above, thereby exciting the vibration of the additional vibration transducer 6.

In step S5, the control device 4 acquires an output signal 14, which output signal 14 is provided as a result of the vibration of the additional vibration transducer 6. In particular in step S6, an analog-to-digital conversion of the output signal 14 can be carried out in order to provide the digital measurement data 15. Alternatively, this step can also be omitted, however, other steps for signal processing can be performed in analog form.

In step S7, an evaluation interval 16 for the output signal 14 or for the digital measurement data 15 is determined, in particular for this interval, meaning that the above-mentioned resonance frequency is to be determined. In order to prevent the spectral composition of the test excitation signal 13 from causing errors in the frequency determination, the analysis interval 16 is chosen such that it does not start until after the excitation of the wave 7 in step S4 is completed. This can be easily achieved, for example, by the control device 4 setting a suitable time stamp. Additionally or alternatively, for the same purpose, the analysis interval 16 can be selected such that it only starts when or after the maximum value of the amplitude of the vibration or output signal 14 or the digital measurement data 15 is reached. For example, the maximum magnitude can be determined by calculating the envelope. The end of the evaluation interval 16 is preferably selected such that the amplitude or the envelope of the output signal 14 or the digital measurement data 15 falls below a certain limit value at this point in time. The time interval in which the main feature of the output signal is noise can be excluded.

In step S8, the analysis interval 16 or its sub-intervals are subjected to a Fourier transform (Fourier transform), in particular by a fast Fourier transform, in order to obtain a power density spectrum of the output signal 14 in the analysis interval 16. Then, in step S9, the frequency 18 can be specifically determined as the global or local maximum of the power density spectrum 17.

As mentioned above, the determined frequency 18 is a good measure for measuring the resonance frequency of the system or the vibration transducer 5, 6. Determining a sharp or sudden change in the frequency 18 can indicate that the vibration transducers 5, 6 or other components of the measuring device 1 are severely aged or damaged, thus requiring, for example, maintenance or repair of the measuring device 1. Therefore, a check can be performed in step S10 to confirm whether the excitation condition is satisfied, for example, when the frequency 18 is outside the determination target range, or when the deviation from the target value exceeds the limit value. Alternatively or additionally, the temporal change of the frequency 18 for a plurality of time interval determinations can also be analyzed by the excitation conditions. This can be used, for example, to identify a step change or similar change in the frequency 18, which can indicate, for example, a crack or other damage to the vibration transducer 5, 6.

When the excitation condition is satisfied in step S10, a notification 19 or an error message can be output in step S11. For this purpose, a notification device 11 of the measuring device can be used, for example a display, a loudspeaker or the like. It is particularly preferred that additionally or alternatively, notification or error messages are sent wirelessly to a system that is capable of storing, managing and visualizing all meter data from the system operator or the water supply network. An example of such a system is the IZAR entry from Diehl Metering. Alternatively, a suitable notification can also be sent, for example wirelessly, to the user's mobile communication device.

When it is confirmed in step S10 that the excitation condition is not satisfied, the measurement apparatus 1 is set to continue the operation. As an alternative to the illustrated example embodiment, in this context, it is also possible to additionally perform steps S12 to S14 described below when the excitation condition in step S10 is satisfied. For example, the measuring device 1 can first continue normal operation until maintenance can be performed.

In step S12, a measurement excitation frequency 20 is determined from the determined frequency 18. For example, a look-up table can be used for this purpose to correct for systematic errors, as part of determining the frequency 18, and/or to deliberately ensure that the measurement device operates at a frequency different from the resonant frequency. In step S13, a measurement excitation signal 21 is then generated, which has a main frequency equal to the measurement excitation frequency 20. This can be carried out, for example, by means of a measurement excitation signal 21 as a periodic signal, which measurement excitation signal 21 has a measurement excitation frequency 20 and is amplitude-modulated by an envelope.

In step S14, the vibration transducer 5 and/or 6 is driven using the measurement excitation signal 21 in order to determine the fluid variable. For example, the measured excitation signal 21 can be used to determine the individual waves 7 as part of determining the transit time difference between the vibrating transducers 5, 6, as described above, in order to determine the flow rate. The processing here can correspond to the processing known from the prior art for determining the transit time difference, except for the use of the measurement excitation signal 21 with the measurement excitation frequency 20 determined as described above, and will therefore not be described in detail.

Alternatively or additionally, the knowledge about the modified resonance frequency can also be used to determine a correction factor as part of the measurement, in particular an empirically obtained correction factor, for determining the fluid variable. This can be achieved, for example, by a look-up table.

The drive data and signals provided and/or processed by the control device 4 are described in more detail below with reference to a number of examples. Fig. 3 shows power density spectra 22, 23, 24 for three different available test stimulus signals 13. In all three cases, the periodic signal 11 of the test excitation signal 13 is a sine wave with a frequency of 1.1 MHz. In each case, a square wave function is used as envelope 12, the length of which is selected to output twenty-four oscillation periods in the case of power density spectrum 22, twelve oscillation periods in the case of power density spectrum 23 and six oscillation periods of a sine wave in the case of power density spectrum 24. Outputting fewer periods of oscillation results in broadening of the maxima of the associated power density spectra 22, 23, 24. In this respect, it is generally advantageous to use relatively few vibration cycles. When a relatively large number of vibration cycles is output, as in the example of the power density spectrum 22, a relatively large number of minima 25 may result in finding regions of the resonant frequency, which may interfere with determining the resonant frequency, as explained in more detail below.

Fig. 4 shows an example of an output signal 14 acquired by the additional vibration transducer 6 or of digital measurement data 15 representing the output signal 14. In this example, a test excitation signal 13 having a power density spectrum 23, i.e. having a main frequency of 1.1MHz and 12 vibration periods, is used. As soon as the vibration of the additional vibration transducer 6 is forcibly excited, the amplitude of the output signal 14 rises first. Since the characteristic or resonant frequency of the system is to be determined, as described above, the analysis interval 16 is selected such that it does not begin until after the maximum value 42 of the amplitude of the output signal 14.

The result of the selection of the analysis interval 16 is explained in more detail below with reference to fig. 5. Fig. 5 shows the temporal variations 26, 27, 28 of the respective main frequencies of the output signal 14 for different main frequencies of the associated test stimulus signal 13. Here, the transient variation 26 corresponds to a segment of the short-time Fourier transform of the output signal 14 shown in fig. 4, which is generated by the main frequency of the test excitation signal 13 of 1.1 MHz. The main frequency of the test excitation signal 13 is 1.05MHz for the transient variation 27 and 1.0MHz for the transient variation 28. The resonance frequency is slightly above 1.05 MHz. The relatively strong quasi-periodic oscillations of the temporal variations 26, 27, 28 clearly visible in fig. 5 are mainly produced by the relatively short window for the relevant short-time Fourier transform. For a longer transform window, a small change in the determined dominant frequency over a period of time will be obtained. Nevertheless, in fig. 5, the time interval before the maximum value 42 of the vibration amplitude is reached and therefore before the analysis interval 16 and the change in the analysis interval 16 can be clearly distinguished. Before the start of the analysis interval 16, for each variation 26, 28 of the test excitation signal 13 having a main frequency significantly different from the resonance frequency, the frequency is determined to be the main frequency between the main frequency 13 and the resonance frequency of the test excitation signal. Thus, as long as forced vibrations are detected at the vibration transducer 6, it is almost impossible to reliably determine the resonance frequency. In the region of the amplitude maximum 42 of the output signal 14, i.e. at the beginning of the analysis interval or shortly before the beginning, the instantaneous change 26, 27, 28 in the main frequency is concentrated towards the resonance frequency, so that in the analysis interval 16 the same main frequency (i.e. the resonance frequency) is determined approximately independently of the main frequency of the test excitation signal 13.

When only the main frequency is considered, care should be taken to ensure that the main frequency of the test excitation signal 13 is not too close to the other resonance frequency. When this is the case, although the resonance frequency 34 in the power density spectrum still results in a local maximum 43, as shown in fig. 6, it may be the case when the overall maximum 44 is at the additional resonance frequency 35. Fig. 6 shows by way of example: a power density spectrum 29 of the output signal 14, which results from excitation at a primary frequency of 800 kHz; a power density spectrum 30 of the output signal 14, which results from excitation at a primary frequency of 850 kHz; a power density spectrum 31 of the output signal 14, which results from excitation at a primary frequency of 900 kHz; a power density spectrum 32 of the output signal 14, which results from excitation at a primary frequency of 950 kHz; and a power density spectrum 33 of the output signal 14, which is generated by excitation at a primary frequency of 1.2 MHz. As can be seen, an overall maximum 43 is obtained at the resonant frequency 34 sought only for the power density spectra 32 and 33. The excitation main frequency for the power spectrum 29, 30, 31 is significantly closer to the additional resonance frequency 35, with the result that most of the excitation energy excites vibration at this frequency. However, it is also apparent in fig. 6 that even for these power density spectra 29, 30, 31 at least a local maximum 43 at the resonance frequency 34 results, so that even when using a test excitation signal 13 with a relatively low frequency, the resonance frequency 34 can be located by also taking into account the local maxima 43, 44 or by taking into account only the maxima 43, 44 within a particular frequency range (for example above 1 MHz).

The process, in which the frequency to be determined is determined in the analysis interval 16 in which the forced excitation of the additional vibration transducer 6 has ended, substantially eliminates the influence of the frequency spectrum of the test excitation signal 13 on the determination of the frequency 18, as described above. However, it should be avoided here that the frequency to be determined is located at a minimum of the power density spectrum of the test excitation signal 13. This will be explained in detail below with reference to fig. 7. Fig. 7 shows four power density spectra 36, 37, 38, 39 of the output signal 14 resulting from different test stimulus signals 13. In this case, the primary frequency or frequency of the periodic signal 11 of the test excitation signal 13 is 1.05MHz, i.e. very close to the resonance frequency, for each of the obtained power density spectra 36 and 37. In contrast, power density spectra 38, 39 are obtained for the excitation frequency of periodic signal 11 at 1.1 MHz. In the case of the power spectra 36, 39, the envelope is chosen such that 24 cycles of the periodic signal are output. In the acquisition of the power density spectra 37 and 38, only 6 cycles of the relevant periodic signal 11 are output in each case.

As expected, the power density spectra 36, 37, 38 all have a maximum 43 in the region of the resonant frequency 34, while the maximum 40 of the power density spectrum 39 is sharply shifted with respect to the resonant frequency 34, and it can be seen that the local minimum 41 of the power density spectrum 39 is close to the resonant frequency 34. This initially unexpected behavior will be easily explained when considering the power density spectrum 22 of the test stimulus signal 13 shown in fig. 3, which is used to obtain the power density spectrum 39 or the associated output signal 14. This also has a minimum 25 at the location of the minimum 41, so that, due to the power density spectrum 22, the test excitation signal 13 can input substantially no energy for vibrations at the resonance frequency 34.

In order to avoid this problem and thus the possibility of incorrectly identifying the sought frequency 18, it is preferred to obtain a relatively wide-band excitation or at least a relatively wide first maximum of the power spectrum of the test excitation signal 13 by using the short envelope 12, so that, for example, even a periodic signal 11 (e.g. a sine wave) is output for only 6 cycles or less.

Reference number table

1 measuring device

2 side wall

3 measuring container

4 control device

5 vibration transducer

6 vibration transducer

7 wave

8 propagation path

9 ultrasonic mirror

10 ultrasonic mirror

11 signal

12 envelope

13 test stimulus signal

14 output signal

15 measurement data

16 analysis Interval

17 power density spectrum

18 frequency

19 Notification

20 measuring the excitation frequency

21 measuring the excitation signal

22 power density spectrum

23 power density spectrum

24 power density spectrum

25 minimum value

26 variations

27 variation

28 change

29 power density spectrum

30 power density spectrum

31 power density spectrum

32 power density spectrum

33 power density spectrum

34 resonant frequency

35 resonant frequency

36 power density spectrum

37 power density spectrum

38 power density spectrum

39 power density spectrum

40 max

41 minimum value

42 maximum value

43 maximum value

44 maximum value

S1-S14 steps