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EP-4741775-A1 - METHOD FOR OPERATING AN ULTRASONIC FLOW METER AND CORRESPONDING ULTRASONIC FLOW METER

EP4741775A1EP 4741775 A1EP4741775 A1EP 4741775A1EP-4741775-A1

Abstract

A method (1) for operating an ultrasonic flowmeter (2) for measuring the flow rate through a measuring tube (4) through which a medium (3) flows is presented and described, wherein the ultrasonic flowmeter (2) comprises at least one transmitting ultrasonic transducer (5) for transmitting ultrasonic signals (6) and at least one receiving ultrasonic transducer (7) for receiving ultrasonic signals (6) and a control and evaluation unit (8), wherein the ultrasonic transducers (5, 7) are arranged such that they realize an ultrasonic measurement path (9) in the medium (3) and wherein the control and evaluation unit (8) controls the transmitting ultrasonic transducer (5) such that it emits the ultrasonic signal (6), the receiving ultrasonic transducer (7) receives the emitted ultrasonic signal (6) and the control and evaluation unit (8) in measurement mode (14) derives at least one indirect value for the flow rate (Vp) of the medium (3) through the measuring tube (4) is determined. The method can react flexibly to changing measurement conditions by having the control and evaluation unit (8) control the transmitting ultrasonic transducer (5) so that a broadband ultrasonic signal (USb,tx) is emitted, by determining an optimal measurement frequency range (M_opt) in an evaluation step (10), by frequency-filtering (11) the received broadband ultrasonic signal (USb,rx) into several measurement frequency ranges (M) of the received broadband ultrasonic signal (USb,rx), by furthermore calculating (12) at least one quality value (Q) from the frequency-filtered ultrasonic signal (USb,rx,f) of the corresponding measurement frequency range (M) for each of the measurement frequency ranges (M) and determining the measurement frequency range (M) that achieves the highest quality value (Q) as the optimal measurement frequency range (M_opt), and by using a signal propagation time (t_sig) when determining the at least indirect value for the flow rate (Vp), which after frequency filtering (11) of the received broadband ultrasound signal (USb,rx) from the optimal measurement frequency range (M_opt).

Inventors

  • Schipper, Willemijn
  • van Dijk, Eugene

Assignees

  • Krohne AG

Dates

Publication Date
20260513
Application Date
20251031

Claims (15)

  1. Method (1) for operating an ultrasonic flowmeter (2) for measuring the flow rate through a measuring tube (4) through which a medium (3) flows, wherein the ultrasonic flowmeter (2) comprises at least one transmitting ultrasonic transducer (5) for transmitting ultrasonic signals (6) and at least one receiving ultrasonic transducer (7) for receiving ultrasonic signals (6) and a control and evaluation unit (8), wherein the ultrasonic transducers (5, 7) are arranged such that they realize an ultrasonic measurement path (9) in the medium (3) and wherein the control and evaluation unit (8) controls the transmitting ultrasonic transducer (5) such that it emits the ultrasonic signal (6), the receiving ultrasonic transducer (7) receives the emitted ultrasonic signal (6) and the control and evaluation unit (8) in measurement mode (14) derives at least an indirect value for the emitted and received ultrasonic signals (6) from a determined signal transit time (t_sig) of the ultrasonic signal (6). The flow rate (Vp) of the medium (3) through the measuring tube (4) is determined. characterized by that the control and evaluation unit (8) controls the transmitting ultrasound transducer (5) in such a way that a broadband ultrasound signal (USb,tx) is emitted, that in an evaluation step (10) an optimal measurement frequency range (M_opt) is determined by frequency-filtering (11) the received broadband ultrasound signal (USb,rx) into several measurement frequency ranges (M) of the received broadband ultrasound signal (USb,rx), by furthermore calculating (12) at least one quality value (Q) from the frequency-filtered ultrasound signal (USb,rx,f) of the corresponding measurement frequency range (M) for several of the measurement frequency ranges (M), and determining the measurement frequency range (M) that achieves the highest quality value (Q) as the optimal measurement frequency range (M_opt), and that in determining the at least indirect value for the flow rate (Vp) a signal transit time (t_sig) is used which has been determined after frequency filtering (11) of the received broadband ultrasound signal (USb,rx) from the optimal measurement frequency range (M_opt).
  2. Method (1) according to claim 1, characterized in that the evaluation step (10) for determining an optimal measurement frequency range (M_opt) is carried out with each determination of the at least indirect value for the flow rate (Vp) of the medium (3), or that the evaluation step (10) for determining an optimal measurement frequency range (M_opt) is carried out after a plurality of determinations of the at least indirect value for the flow rate (Vp) of the medium (3), or that the evaluation step (10) for determining an optimal measurement frequency range (M_opt) is triggered by an external signal of the ultrasonic flow meter (2).
  3. Method (1) according to claim 1 or 2, characterized in that the broadband ultrasound signal (USb,tx) is generated by excitation of the transmitting ultrasound transducer (5) with a superposition of several periodic time signals of different frequencies, in particular wherein the periodic time signals are harmonic signals.
  4. Method (1) according to claim 1 or 2, characterized in that the broadband ultrasound signal (USb,tx) is generated by excitation of the transmitting ultrasound transducer (5) with a square wave signal or with a periodic square wave signal sequence (15), in particular wherein the fundamental frequency of the periodic square wave signal sequence (15) corresponds to a fundamental mode of an oscillation of the transmitting ultrasound transducer (5).
  5. Method (1) according to one of claims 1 to 4, characterized in that the received broadband ultrasound signal (USb,rx) is frequency-filtered (11) into several measurement frequency ranges (M) of the received broadband ultrasound signal (USb,rx) by using at least one analog or digital bandpass filter (13), in particular wherein the digital bandpass filter (13) is implemented as a Finite Impulse Response (FIR) or as an Infinite Impulse Response (IIR) filter.
  6. Method (1) according to one of claims 1 to 5, characterized in that the quality value (Q) for a measurement frequency range (M) is determined by determining a signal transit time (t_sig) of the frequency-filtered ultrasound signal (USb,rx,f) and by determining a transit time deviation (delta_t_sig) from a reference transit time (t_sig,ref), wherein a smaller transit time deviation (delta_t_sig) corresponds to a higher quality value (Q).
  7. Method (1) according to claim 6, characterized in that the comparison time (t_sig,ref) is a signal time from a predetermined measurement frequency range (M) is or the comparison propagation delay (t_sig,ref) is the mean of signal propagation delays (t_sig) from predetermined measurement frequency ranges (M), in particular the mean of signal propagation delays (t_sig) from all measurement frequency ranges (M).
  8. Method (1) according to one of claims 1 to 7, characterized in that the quality value (Q) for a measurement frequency range (M) of the received broadband ultrasound signal (USb,rx) is determined by calculating a signal deviation (delta_USb) in the considered time interval between the received, frequency-filtered broadband ultrasound signal (USb,rx,f) and a corresponding reference signal (USref), wherein a smaller signal deviation corresponds to a higher quality value (Q).
  9. Method (1) according to claim 8, characterized in that the signal deviation (delta_USb) is calculated by comparing corresponding vibration amplitudes.
  10. Method (1) according to one of claims 1 to 9, characterized in that the quality value (Q) for a measurement frequency range (M) of the received broadband ultrasound signal (USb,rx) is determined by calculating at least one frequency deviation (delta_f) in the considered time interval between the received, frequency-filtered broadband ultrasound signal (USb,rx,f) and a corresponding reference signal (USref), wherein a smaller frequency deviation (delta_f) corresponds to a higher quality value.
  11. Method (1) according to claim 10, characterized in that the instantaneous signal frequencies of the compared signals are calculated in the time domain by applying the Hilbert transform to the signals, in particular wherein the quality value (Q) is the mean value of several of the calculated frequency deviations (delta_f) in the considered time interval.
  12. Method (1) according to one of claims 1 to 11, characterized in that the quality value (Q) for a frequency range (M) of the received broadband ultrasound signal (USb,rx) is determined by calculating at least one signal-to-noise ratio (SNR) of the received broadband ultrasound signal (USb,rx) in the considered time interval, wherein a larger signal-to-noise ratio (SNR) corresponds to a higher quality value (Q).
  13. Method (1) according to claim 12, characterized in that the signal-to-noise ratio (SNR) is calculated from the peak-to-peak value of the pure noise signal (Noise) and the peak-to-peak value of the noisy useful signal (Signal+Noise).
  14. Ultrasonic flow meter (2) with a measuring tube (4) for measuring the flow rate through the measuring tube (4) through which a medium (3) flows, with at least one transmitting ultrasonic transducer (5) for transmitting ultrasonic signals (6) and at least one receiving ultrasonic transducer (7) for receiving ultrasonic signals (6) and with a control and evaluation unit (8), wherein the ultrasonic transducers (5, 7) are arranged such that they realize an ultrasonic measurement path (9) in the medium (3) and wherein the control and evaluation unit (8) controls the transmitting ultrasonic transducer (5) such that it emits the ultrasonic signal (6), the receiving ultrasonic transducer (7) receives the emitted ultrasonic signal (6) and the control and evaluation unit (8) in measurement mode (14) derives at least an indirect value for the flow rate (Vp) of the medium from a determined signal transit time (t_sig) of the ultrasonic signal (6) by evaluating emitted and received ultrasonic signals (6). (3) determined by the measuring tube (4), characterized by that the control and evaluation unit (8) controls the transmitting ultrasound transducer (5) in such a way that a broadband ultrasound signal (USb,tx) is emitted, that the control and evaluation unit (8) determines an optimal measurement frequency range (M_opt) in an evaluation step (10) by frequency-filtering (11) the received broadband ultrasound signal (USb,rx) into several measurement frequency ranges (M) of the received broadband ultrasound signal (USb,rx), by furthermore calculating (12) at least one quality value (Q) from the frequency-filtered ultrasound signal (USb,rx,f) of the corresponding measurement frequency range (M) for several of the measurement frequency ranges (M), and determining the measurement frequency range (M) that achieves the highest quality value (Q) as the optimal measurement frequency range (M_opt), and that in determining the at least indirect value for the flow rate (Vp) a signal transit time (t_sig) is used which has been determined after frequency filtering (11) of the received broadband ultrasound signal (USb,rx) from the optimal measurement frequency range (M_opt).
  15. Ultrasonic flow meter (2) according to claim 14, characterized in that the control and evaluation unit (8) performs the method (1) according to the characterizing part of at least one claim of claims 2 to 13 during the operation of the ultrasonic flow meter (2).

Description

The invention relates to a method for operating an ultrasonic flow meter for measuring the flow rate through a measuring tube through which a medium flows. The ultrasonic flow meter comprises at least one transmitting ultrasonic transducer for sending ultrasonic signals, at least one receiving ultrasonic transducer for receiving ultrasonic signals, and a control and evaluation unit. The ultrasonic transducers are arranged such that they create an ultrasonic measurement path in the medium. The control and evaluation unit controls the transmitting ultrasonic transducer such that it emits the ultrasonic signal, the receiving ultrasonic transducer receives the emitted ultrasonic signal, and the control and evaluation unit, during measurement operation, determines at least an indirect value for the flow rate of the medium through the measuring tube from a determined signal transit time of the ultrasonic signal by evaluating the emitted and received ultrasonic signals. The invention also relates to such an ultrasonic flow meter. Flow measurement using ultrasonic waves has been known for a long time. Regardless of the specific measurement method employed (e.g., transit-time measurement, transit-time difference measurement (with and against the flow direction), frequency measurement/Doppler effect), flow measurement is always based on the propagation of ultrasonic waves in the medium flowing through the measuring tube, the flow velocity of which is to be determined. The (average) flow velocity of the medium along the ultrasonic measurement path can be deduced from the signal transit time of the ultrasonic signal, and thus indirectly also the flow rate of the medium through the measuring tube. Typically, the transmitting ultrasonic transducers are excited with a very narrowband signal, preferably at a single, specific frequency. This has advantages in terms of energy consumption (eigenvalues of piezo actuators/sensors in the ultrasonic transducer) and signal processing; by selecting a specific frequency, it is also possible to selectively influence, for example, the shape and attenuation of the transmitted ultrasonic signal. This approach is problematic when... boundary conditions change under which the specific frequency was selected, for example the speed of sound in the medium. The object of the present invention is to further develop the method for operating an ultrasonic flow meter and the ultrasonic flow meter described above in such a way that it is possible to react robustly to changing operating conditions during measurement. In the previously described method, the derived problem is initially solved by the control and evaluation unit controlling the transmitting ultrasound transducer in such a way that a broadband ultrasound signal is emitted. In an evaluation step, an optimal measurement frequency range is determined by frequency-filtering the received broadband ultrasound signal into several measurement frequency ranges. Furthermore, in this evaluation step, at least one quality value is calculated for each of the frequency-filtered ultrasound signals within the corresponding measurement frequency range, and the measurement frequency range that achieves the highest quality value is determined as the optimal measurement frequency range. This step clarifies what is meant by a broadband ultrasound signal. The broadband ultrasound signal must, in any case, contain frequency components over a certain frequency range – either continuously or distributed across specific areas – so that the required frequency filtering into multiple measurement frequency ranges is meaningfully possible, meaning that frequency components can be present in the areas under investigation. When determining the at least indirect value for the flow rate, a signal transit time is used - i.e., in regular measurement operation - which has been determined from the optimal measurement frequency range after frequency filtering of the received broadband ultrasound signal. Therefore, a broadband ultrasound signal is always used, both in the evaluation step, where the optimal measurement frequency range is determined, and in normal measurement operation, where the broadband ultrasound signal is frequency-filtered to the optimal measurement frequency range and the signal propagation time is then determined from the frequency-filtered ultrasound signal. By consistently using a broadband ultrasound signal, the emitted ultrasound signal always contains a suitable frequency, which is advantageous even under changing measurement conditions. Changed measurement conditions are not reacted to with a changed ultrasound signal emitted by the transmitting ultrasound transducer, but merely with an adapted frequency filtering of the received broadband ultrasound signal, because the optimal measurement frequency range has changed. According to an advantageous embodiment of the method, the evaluation step for determining an optimal measurement frequency rang