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EP-4741776-A1 - METHOD FOR OPERATING AN ULTRASONIC FLOW METER AND ULTRASONIC FLOW METER

EP4741776A1EP 4741776 A1EP4741776 A1EP 4741776A1EP-4741776-A1

Abstract

A method (1) for operating an ultrasonic flow meter (2) for measuring the flow rate through a measuring tube (4) through which a medium (3) flows is presented and described, wherein the ultrasonic flow meter (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 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) determines at least an indirect value for the flow rate of the medium (3) through the measuring tube (4) by evaluating emitted and received ultrasonic signals (6). Consistent measurement quality is achieved by the control and evaluation unit (8) adjusting an ultrasonic signal frequency (f) of the emitted ultrasonic signal (6) in such a way that a change in the opening angle (phi) of the sound lobe (10) of the ultrasonic signal (6) caused by a change in the value of the speed of sound (v_sos) of the medium (3) is at least partially compensated.

Inventors

  • Schipper, Willemijn
  • van Dijk, Eugene

Assignees

  • Krohne AG

Dates

Publication Date
20260513
Application Date
20251031

Claims (10)

  1. Method (1) for operating an ultrasonic flow meter (2) for measuring the flow rate through a measuring tube (4) through which a medium (3) flows, wherein the ultrasonic flow meter (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) determines at least an indirect value for the flow rate of the medium (3) through the measuring tube (4) by evaluating the emitted and received ultrasonic signals (6). characterized by that the control and evaluation unit (8) controls the transmitting ultrasonic transducer (5) such that the emitted ultrasonic signal (6) is emitted with a defined ultrasonic signal frequency (f_det), so that at a defined value (v_sos,det) of the speed of sound (v_sos) of the medium (3) flowing in the measuring tube (4) the ultrasonic signal (6) is emitted with a defined opening angle (phi_det) of a sound lobe (10) of the ultrasonic signal (6), that the control and evaluation unit (8) receives a current value (v_sos,akt) for the speed of sound of the medium (3) flowing in the measuring tube (4), that when the received current value (v_sos,akt) of the speed of sound (v_sos) changes compared to the defined value (v_sos,det) of the speed of sound of the medium (3), the control and evaluation unit (8) changes the ultrasonic signal frequency (f) of the emitted ultrasonic signal (6) to a current value (f_akt) of the ultrasonic signal frequency (f), so that a change in the opening angle (phi) of the sound lobe (10) of the ultrasonic signal (6) caused by the change in the value of the speed of sound (v_sos) of the medium (3) is at least partially compensated.
  2. Method (1) according to claim 1, characterized in that the ultrasound signal frequency (f) of the emitted ultrasound signal (6) is changed in such a way as to that the opening angle (phi) of the sound lobe (10) of the emitted ultrasound signal (6) remains within a tolerance range (delta_phi) around a nominal opening angle (phi_nom).
  3. Method (1) according to claim 1 or 2, characterized in that the ultrasound signal frequency (f) is changed abruptly in a frequency jump to the changed current value (f_act) of the ultrasound signal frequency, in particular wherein the change to the changed value (f_act) of the ultrasound signal frequency jumps from one tolerance limit (phi_tol1) of the tolerance range (delta_phi) to the other tolerance limit (phi_tol2) of the tolerance range (delta_phi).
  4. Method (1) according to claim 1 or 2, characterized in that the ultrasound signal frequency (f) is continuously changed to the changed current value (f_act) of the ultrasound signal frequency (f).
  5. Method (1) according to one of claims 1 to 4, characterized in that the ultrasonic signal frequency (f) of the emitted ultrasonic signal (6) is only changed when the change in the obtained speed of sound (f_act) compared to the defined speed of sound (f_det) of the medium (3) exceeds a predetermined change threshold.
  6. Method (1) according to one of claims 1 to 5, characterized in that the current value (v_sos,akt) for the speed of sound (v_sos) of the medium (3) flowing in the measuring tube (4) is calculated by the control and evaluation unit (8) itself on the basis of a time-of-flight measurement of the emitted ultrasound signal (6) and a known propagation length of the emitted ultrasound signal (6).
  7. Method (1) according to one of claims 1 to 5, characterized in that the current value (v_sos,akt) for the speed of sound (v_sos) of the medium (3) flowing in the measuring tube (4) is specified, in particular by an external parameter input.
  8. Method (1) according to one of claims 1 to 5, characterized in that the required change in the value of the ultrasound signal frequency (f) to the current value (f_actual) of the ultrasound signal frequency (f) to compensate for the influence of the change in the speed of sound (v_sos) in the medium (3) on the opening angle (phi) of the sound lobe (10) of the ultrasound signal (6) is calculated on the basis of a physical-mathematical model of wave propagation, in particular by using an equation to describe the sound pressure (p) as a function of from a pole angle (phi) to a main radiation direction (phi_0) of the transmitting ultrasonic transducer (5).
  9. Ultrasonic flowmeter (2) for measuring the flow rate through a measuring tube (4) through which a medium (3) flows, comprising at least one transmitting ultrasonic transducer (5) for transmitting ultrasonic signals (6) and a receiving ultrasonic transducer (7) for receiving ultrasonic signals (6), 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 an ultrasonic signal (6), the receiving ultrasonic transducer (7) receives the emitted ultrasonic signal (6) and the control and evaluation unit (8) determines at least an indirect value for the flow rate of the medium (3) through the measuring tube (4) by evaluating emitted ultrasonic signals (6) and received ultrasonic signals (6). characterized by that the control and evaluation unit (8) during operation of the ultrasonic flow meter (2) controls the transmitting ultrasonic transducer (5) such that the emitted ultrasonic signal (6) is emitted with a defined ultrasonic signal frequency (f_det), so that at a defined value (v_sos,det) of the speed of sound (v_sos) of the medium (3) flowing in the measuring tube (4) the ultrasonic signal (6) is emitted with a defined opening angle (phi_det) of a sound lobe (10) of the ultrasonic signal (6), that the control and evaluation unit (8) receives a current value (v_sos,akt) for the speed of sound (v_sos) of the medium (3) flowing in the measuring tube (4), that when the received current value (v_sos,akt) of the speed of sound (v_sos) changes compared to the defined value (v_sos,det) of the speed of sound (v_sos) of the medium (3), the control and evaluation unit (8) changes the ultrasonic signal frequency (f) of the emitted ultrasonic signal (6) to a current value (f_akt) of the ultrasonic signal frequency (f), so that a change in the opening angle (phi) of the sound lobe (10) of the ultrasonic signal (6) caused by the change in the value of the speed of sound (v_sos) of the medium (3) is at least partially compensated.
  10. Ultrasonic flow meter (2) according to claim 9, characterized in that the control and evaluation unit (8) is in operation of the ultrasonic flow meter (2) performs the method (1) according to the characterizing part of at least one claim of claims 2 to 8.

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, wherein the ultrasonic flow meter comprises at least one transmitting ultrasonic transducer for sending ultrasonic signals and at least one receiving ultrasonic transducer for receiving ultrasonic signals, and a control and evaluation unit, wherein the ultrasonic transducers are arranged such that they create an ultrasonic measurement path in the medium, and wherein the control and evaluation unit controls the transmitting ultrasonic transducer such that it emits an ultrasonic signal, the receiving ultrasonic transducer receives the emitted ultrasonic signal, and the control and evaluation unit determines at least an indirect value for the flow rate of the medium through the measuring tube by evaluating the emitted and received ultrasonic signals. Furthermore, the invention also relates to such an ultrasonic flow meter. Flow measurement using ultrasonic waves has been known for decades. Regardless of the specific measurement method used (for example, transit-time measurement, transit-time difference measurement (with and against the flow direction), frequency measurement/Doppler effect), flow measurement is always based on the transmission of ultrasonic waves in the medium flowing through the measuring tube, the flow velocity of which is to be measured. In the vast majority of ultrasonic flowmeters, the characteristic dimensions of the measuring tube (in the case of the usual round measuring tubes, the measuring tube diameter) are significantly larger than the wavelength of the ultrasonic signal used for the measurement, so that the ultrasonic waves propagating in the medium can be considered free-space waves. It is known that the shape of the emitted ultrasonic signals can be influenced by various measures, for example, by a specific design of the ultrasonic transducer geometry. In this context, the opening angle of the ultrasonic lobe of the emitted ultrasonic signal is often discussed. If the maximum sound pressure is present in a main radiation direction of the transmitting ultrasonic transducer, then the angle at which the maximum sound pressure is reached is determined, deviating from the main radiation direction. For example, only half the sound pressure is present. This angle is then interpreted as the opening angle of the sound beam, although sound pressure can still be detected at larger opening angles. In any case, the opening angle of the sound beam of the ultrasound signal is a suitable measure of the focus of the ultrasound signal. A small beam angle of the ultrasonic signal is advantageous for achieving a good signal-to-noise ratio. In ultrasonic flowmeters with multiple measurement paths and several pairs of ultrasonic transducers, small beam angles can prevent or at least reduce mutual interference between the transducers. If installation situations involve components protruding into the measurement space traversed by the measurement path (other sensors, agitators, etc.), small beam angles also prevent or reduce disruptive reflections. Conversely, the beam angle must be sufficiently large to ensure that the ultrasonic signal reliably covers a sufficiently large reception area. The object of the present invention is to further develop the method for operating the ultrasonic flow meter and the corresponding ultrasonic flow meter in such a way that consistent measurement quality is ensured even in highly variable measurement situations. The derived problem in the method described at the beginning for operating an ultrasonic flow meter is initially solved by the control and evaluation unit controlling the emitting ultrasonic transducer in such a way that the emitted ultrasonic signal is emitted with a defined ultrasonic signal frequency, so that at a defined value of the speed of sound of the medium flowing in the measuring tube, the ultrasonic signal is emitted with a defined opening angle of a sound lobe of the ultrasonic signal. These defined conditions and settings of the ultrasonic flowmeter often correspond to the conditions and specifications underlying the ultrasonic flowmeter's design for a particular medium, such as water. Many processes using ultrasonic flowmeters involve relatively stable process conditions. The present invention is based on observations made in connection with gaseous media whose composition is subject to changes, which can have a significant impact on the ultrasound signal, in particular on the opening angle of the sound lobe of the emitted ultrasound signal and thus on the measurement. Especially when working with light gases (for example, hydrogen), significant differences in the propagation of sound waves can occur when the gas (for example, to natural gas) or its composition changes. This is because the speed of sound in a gaseous medium is inversely proportional to the square root of the molar mass of its