Ultrasonic flow measuring device having a wall thickness being less in the area of the phased array ultrasonic transducer contact area

Abstract

Flow velocity of a fluid is measured using a measuring sensor comprising a conduit with a conduit wall, and at least two ultrasonic transducer units (20, 22), each of which consists of an array of individual ultrasonic transducers (30-x, 32-x) and defining a measuring path (24) between them in the conduit (14). The ultrasonic transducer units emit ultrasonic signals and received ultrasonic signals are evaluated to determine the flow velocity. The individual ultrasonic transducers are driven with different phase, so that the ultrasonic transducer units provide a phased array. In order to achieve the most accurate measurement results possible, the ultrasonic transducer units contact the outside of the conduit wall (16), and the conduit wall (16) is formed in the area of the contact with a wall thickness (w) that is less than half the wavelength of the transverse wave (λ.sub.Rohr) of the ultrasound in the conduit wall.

Claims

1. Device for measuring the flow velocity of a fluid (18) having a measuring sensor (12) which has a conduit (14) for the fluid (18) with a conduit wall (16), at least two ultrasonic transducer units (20, 22), each consisting of an array of individual ultrasonic transducers (30-x, 32-x) and defining a measuring path (24) in the conduit (14) between them, a control and evaluation unit (34) for controlling the ultrasonic transducer units (20, 22) for transmitting ultrasonic signals (28) and for evaluating received ultrasonic signals (28) and determining the flow velocity (v), and the control and evaluation unit (34) is designed to drive the individual ultrasonic transducers (30-x, 32-x) with different phases, so that the ultrasonic transducer units (20, 22) are each designed as a phased array, characterized in that the ultrasonic transducer units (20, 22) contact the outside of the pipe conduit wall (16), the measuring path (24) is formed as a secant path (21) and does not lie diametrically, and wherein the conduit wall (16) is formed in the area of the contact with a wall thickness (w) that is less than half the wavelength of the transverse wave (λpipe) of the ultrasound in the conduit wall (16).

2. Device according to claim 1, characterized in that the wall thickness in the area of the contacting is less than a quarter of the wavelength of the transverse wave (λpipe) of the ultrasound in the conduit wall (16).

3. Device according to claim 1, characterized in that the dimensions of the ultrasonic transducers (30-x, 32-x) parallel to the conduit wall (16) are smaller than the ultrasonic wavelength in the fluid.

4. Device according to claim 1, characterized in that the dimensions of the ultrasonic transducer units (20,22) parallel to the conduit wall (16) are greater than twice the ultrasonic wavelength in the fluid.

5. Device according to claim 1, characterized in that at least one of the measuring paths has a secant angle of greater than 20°.

6. Device according to claim 1, characterized in that the array is a linear array and consists of one line.

7. Device according to claim 1, characterized in that the array is two-dimensional.

8. Device according to claim 1, characterized in that the area of the contacting is formed by a recess in the exterior of the conduit wall (16), the dimensions of the recess being adapted to the array.

9. Device according to claim 1, characterized in that the ultrasonic transducers are coupled to a structure-borne sound filter.

10. Device according to claim 1, characterized in that the ultrasonic transducers are glued or pressed to the conduit wall (16).

11. Device according to claim 1, characterized in that at least one of the measuring paths has a secant angle of greater than 30°.

12. Device according to claim 1, characterized in that the array is two-dimensional and the individual ultrasonic transducers are arranged in rows and columns.

13. Device for measuring the flow velocity of a fluid (18) having a measuring sensor (12) which has a conduit (14) for the fluid (18) with a conduit wall (16), at least two ultrasonic transducer units (20, 22), the ultrasonic transducers glued or pressed to the conduit wall (16), each transducer consisting of an array of individual ultrasonic transducers (30-x, 32-x) and defining a measuring path (24) in the conduit (14) between them, and a control and evaluation unit (34) for controlling the ultrasonic transducer units (20, 22) for transmitting ultrasonic signals (28) and for evaluating received ultrasonic signals (28) and determining the flow velocity (v), the control and evaluation unit (34) designed to drive the individual ultrasonic transducers (30-x, 32-x) with different phases, so that the ultrasonic transducer units (20, 22) are each designed as a phased array, wherein the ultrasonic transducer units (20, 22) contact the outside of the conduit wall (16), wherein the conduit wall (16) is formed in the area of the contact with a wall thickness (w) that is less than half the wavelength of the transverse wave (λpipe) of the ultrasound in the conduit wall (16), and wherein the control and evaluation unit is designed in such a way that the ultrasonic transducers located at the edge of the array can be controlled in such a way that active structure-borne sound suppression is thereby achieved.

14. Device for measuring the flow velocity of a fluid (18) having a measuring sensor (12) which has a conduit (14) for the fluid (18) with a conduit wall (16), at least two ultrasonic transducer units (20, 22), the ultrasonic transducers glued or pressed to the conduit wall (16), each transducer consisting of an array of individual ultrasonic transducers (30-x, 32-x) and defining a measuring path (24) in the conduit (14) between them, and a control and evaluation unit (34) for controlling the ultrasonic transducer units (20, 22) for transmitting ultrasonic signals (28) and for evaluating received ultrasonic signals (28) and determining the flow velocity (v), the control and evaluation unit (34) designed to drive the individual ultrasonic transducers (30-x, 32-x) with different phases, so that the ultrasonic transducer units (20, 22) are each designed as a phased array, wherein the ultrasonic transducer units (20, 22) contact the outside of the conduit wall (16), wherein the conduit wall (16) is formed in the area of the contact with a wall thickness (w) that is less than half the wavelength of the transverse wave (λpipe) of the ultrasound in the conduit wall (16), and wherein the control and evaluation unit is designed such that the control of the ultrasonic transducers with respect to their phase for each ultrasonic transducer is dependent on the speed of sound in the fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is described in detail by means of preferred embodiments with reference to the drawing. In the drawing the figures show:

(2) FIG. 1 to 3 a schematic representation with a measuring path in a conduit to illustrate the individual angle definitions;

(3) FIG. 4 a schematic representation of a device according to the inventive subject matter.

DETAILED DESCRIPTION

(4) A device 10 according to the inventive subject matter comprises a measuring sensor 12, which has a conduit 14 for the fluid with a conduit wall 16. The fluid, a gas or liquid, flowing through the conduit 14 is shown in FIG. 4 with a wide arrow 18.

(5) Furthermore, the device 10 has at least two ultrasonic transducer units 20 and 22, which define a measuring path 24 between them in the conduit 14, which is indicated by arrows 24 in FIG. 4. The measuring path 24 is shown in FIG. 4 as a diametrical path for easier visualization. It can also be designed as a secant path. Secant paths are the actual target of the invention. As known from the state of the art and described above, the ultrasonic transducer units 20 and 22 are arranged with a mutual offset in flow direction 18. This means that the measuring path 24 is not orthogonal to the flow direction 18. Each of the ultrasonic transducer units 20 and 22 can operate as a transmitter or receiver.

(6) From the path angle α and the distance D to the opposite channel wall, with a round conduit 14 and diametrical measuring path that would be the conduit diameter, the length L of the measuring path 24 in the fluid medium results. Ultrasonic signals 28, which are emitted and received on the measuring path 24 in opposite directions, thus have one component in the direction of the flow direction 18 and another component in the opposite direction of the flow direction 18. The ultrasonic signals 28 are emitted in pulsed form as ultrasonic wave packets 28 to determine the flow velocity v of the fluid 18 as in the state of the art according to the transit time method by the relation

(7) $\begin{array}{cc}v=\frac{t_2-t_1}{2*t_2*t_1}*\frac{L}{\cos \left(\alpha \right)}& \left(3\right)\end{array}$

(8) where t.sub.2 and t.sub.1 denote the sound travel times required by the radiated ultrasonic wave packets 28 to travel the measurement path 24 upstream and downstream, respectively.

(9) An ultrasonic transducer unit 20 or 22 consists of a group (array) of individual ultrasonic transducers 30-x or 32-x. The “x” in the reference number stands for a running index for each individual transducer. In the drawing only four ultrasonic transducers 30-1 to 30-4 or 32-1 to 32-4 are shown in one row.

(10) The individual ultrasonic transducers 30-x or 32-x are controlled by an electronic control and evaluation unit 34 to emit ultrasound in such a way that they have a phase offset within their row. The phase offset is selected in such a way that the superposition of the resulting ultrasonic waves results in the ultrasonic wave packet 28 with a wave front 26 with the path angle α. The ultrasonic transducers 30-x or 32-x of an ultrasonic transducer unit 20 or 22 are thus constructed as a phased array.

(11) The electronic control and evaluation unit 34 has electronic components (not shown), like resistors, capacitors, memories and integrated circuits and the like, preferably placed on a circuit board.

(12) In order for the ultrasonic transducers 30-x or 32-x to emit ultrasound at all through the conduit wall 16 in the described manner, the ultrasonic transducers 30-x or 32-x contact the conduit wall 16 on the outside. In contrast to known clamp-on systems, however, the conduit wall 16 is now formed in the area of the contact with a wall thickness w which is less than half, preferably less than a quarter, of the wavelength λ.sub.pipe of the transverse wave of the ultrasound in the conduit wall 16. In the case of a typical conduit wall made of steel with a typical speed of sound of the transverse wave of c.sub.L,pipe=3100 m/s, the wall thickness w would be about 0.78 mm at a typical ultrasonic frequency of f=1 MHz, corresponding to a quarter of the wavelength.

(13) The control and evaluation unit 34 controls the individual ultrasonic transducers 30-x and 32-x. This applies both to the transmission of ultrasound with the individual control with corresponding phase and to the reception with the evaluation of the incoming ultrasound wave packet 28 at each transducer. In particular, the evaluation unit 34 determines the transit time t of the ultrasonic wave packets 28, which are transmitted in one or the opposite direction along the measuring path 24. The flow velocity v is calculated from the transit times t.sub.1 and t.sub.2 of outgoing and returning ultrasonic wave packets 28 according to equation (3).

(14) Due to the inventive design of the ultrasonic transducer units 20 or 22 as phased array, the angle of radiation γ depends on the phase shift of the individual signals and on the speed of sound in the fluid. The speed of sound itself depends on environmental conditions such as temperature and pressure. It is therefore advantageous that by controlling the individual ultrasonic transducers 30-x or 32-x by means of the control and evaluation unit 34, the phase difference can be adjusted depending on the ambient conditions in such a way that the angle of radiation γ remains the same, even if the speed of sound changes. To determine the ambient conditions, an environmental detection unit 44 can be provided, which detects e.g. temperature and/or pressure in the conduit 14 and transmits it to the control and evaluation unit 34 to monitor the fluid properties and thus be able to calculate the speed of sound and density. With this knowledge, the ultrasonic transducers 30-x or 32-x can be controlled or evaluated better. The density is necessary to calculate the mass flow and can be calculated from the properties of the medium as well as temperature and pressure.

(15) In this way the device 10 in accordance with the inventive subject matter can be used for a wide range of the speed of sound.

(16) In one embodiment of the invention, the dimensions b of the individual ultrasonic transducers 30-x or 32-x parallel to the conduit wall 16 are smaller than the ultrasonic wavelength λ.sub.fluid in the fluid and preferably smaller than 0.6 times the ultrasonic wavelength λ.sub.fluid.

(17) Advantageously, the dimensions B of the ultrasonic transducer units 20 or 22 parallel to the conduit wall 16 are larger than twice the ultrasonic wavelength λ.sub.fluid in the fluid.

(18) The area of contact, i.e. the area of thinned wall thickness, is formed as shown in FIG. 4 by a recess 40, which is inserted into the conduit wall 16 from the outside. The shape of the recess is sensibly adapted to the array in its dimensions.

(19) In the embodiment shown in FIG. 4, the arrayed ultrasonic transducer units 20 and 22 consist of a line of only four ultrasonic transducers 30-x and 32-x respectively. This limitation is mainly due to the fact that the drawing should remain simple and clear. If four of such single transducers do not provide enough signal, the array may have more, for example eight, transducers. Therefore, the array is preferably designed with more transducers. The number of ultrasonic transducers is a compromise between signal strength, complexity and cost.

(20) If the array is a two-dimensional array with arrangement of the ultrasonic transducers 30-x or 32-x in rows and columns, then the beam angle γ can be changed by controlling the individual ultrasonic transducers 30-x or 32-x by means of the control and evaluation unit 34. This can counteract a drift effect, especially at high fluid flow velocities. The radiation angle γ can be adjusted so that the opposite ultrasonic transducer unit 20 or 22 is always “hit” by the emitted wave packet 28, regardless of the flow velocity.

(21) The ultrasonic transducers 30-x or 32-x of an ultrasonic transducer unit 20 or 22 are coupled with a structure-borne sound filter in a way not shown here, wherein the coupling can be realized by gluing or pressing the transducers onto the wall.

(22) In a further embodiment of the invention, the control and evaluation unit 34 is designed to control the ultrasonic transducers located at the edge of the array (in FIG. 4 these would be 30-1 and 30-4 or 32-1 and 32-4) in such a way that active structure-borne sound suppression takes place, i.e. that lateral vibration components are eliminated by interference with the ultrasound generated by the edge, so that the edge of the array transmits effectively as little vibration as possible laterally into the conduit wall.

(23) Thus, coupling of ultrasound into the conduit wall 16 can at least be reduced, if not prevented.

(24) The above description is based on a diametric measurement path 24 for the sake of simplicity, because the construction details are independent of whether the path is diametric or secant. It should be repeated, however, that the object of the invention is to achieve secant paths 21 and in particular very off-center secant paths, which is only possible in the version according to the inventive subject matter. Preferably, the control of the ultrasonic transducers 30-x or 32-x is such that at least one of the measuring paths has a secant angle greater than 20°, preferably greater than 30°. As mentioned above, secant paths and especially the consideration of secant paths located far outside of the measuring range lead to a higher resistance of the result against perturbations and thus to more accurate measurement values.