Measuring apparatus and method for determining the flow speed of a fluid flowing in a conduit

Abstract

A measuring apparatus (10) for determining the flow speed of a fluid (12) flowing in a conduit (14) using at least one ultrasonic transducer (18a-b) that is attached to the conduit wall (22) from the outside and has an oscillating body (34) that couples to a part region (32) of the conduit wall (22) that acts as a membrane of the ultrasonic transducer (18a-b) that can vibrate, characterized in that a coupling piece (36) whose cross-section is smaller than the cross-section of the oscillating body (34) is arranged between the membrane (32) and the oscillating body (34).

Claims

1. A measuring apparatus for determining the flow speed of a fluid flowing in a conduit using at least one ultrasonic transducer that is attached to a conduit wall from the outside and that has an oscillating body that couples to a part region of the conduit wall that acts as a membrane of the ultrasonic transducer that can vibrate, wherein a coupling piece whose cross-section is smaller than the cross-section of the oscillating body is arranged between the membrane and the oscillating body.

2. The measuring apparatus in accordance with claim 1, wherein the oscillating body can vibrate in longitudinal and transverse directions.

3. The measuring apparatus in accordance with claim 1, wherein the coupling piece is configured in one piece with the conduit wall.

4. The measuring apparatus in accordance with claim 1, that has a pocket that is attached in the conduit from the outside and whose base forms the membrane on which the coupling piece is arranged.

5. The measuring apparatus in accordance with claim 4, wherein the oscillating body is at least partly arranged in the pocket.

6. The measuring apparatus in accordance with claim 4, wherein the pocket is closed toward the outside by a transducer holder.

7. The measuring apparatus in accordance with claim 6, wherein the oscillating body is elastically connected to the transducer holder.

8. The measuring apparatus in accordance with claim 4, wherein the pocket has a cylindrical or frustoconical section.

9. The measuring apparatus in accordance with claim 1, wherein the oscillating body is of parallelepiped shape or cylinder shape.

10. The measuring apparatus in accordance with claim 1, wherein the coupling piece has a cylindrical or frustoconical section.

11. The measuring apparatus in accordance with claim 1, wherein the fluid is a liquid.

12. The measuring apparatus in accordance with claim 1, that has at least two ultrasonic transducers that are disposed opposite one another with the flow therebetween and with an offset in the direction of flow and that has an evaluation unit that is configured to exchange ultrasonic signals between the ultrasonic transducers and to determine the flow speed with respect to a time of flight difference of ultrasound transmitted and received again with and against the flow.

13. A method of determining the flow speed of a fluid flowing in a conduit in which an ultrasonic transducer attached to a conduit wall from the outside and having an oscillating body that couples to a part region of the conduit wall that uses the part region as a membrane that can vibrate is provided, the method comprising the step of: transmitting ultrasound between the membrane and the oscillating body by a coupling piece whose cross-section is smaller than the cross-section of the oscillating body.

14. The method in accordance with claim 13, further comprising the step of: setting the oscillating body into an oscillation in longitudinal and transverse directions.

15. The method in accordance with claim 13, further comprising the step of: transmitting the ultrasound directly between the oscillating body and the conduit wall by a coupling piece formed in one piece with the conduit wall.

Description

[0024] The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:

[0025] FIG. 1 a longitudinal sectional view of a measuring apparatus for determining the flow speed with ultrasonic transducers;

[0026] FIG. 2 a detailed view of an ultrasonic transducer region in FIG. 1;

[0027] FIG. 3 a schematic three-dimensional representation of the oscillation of an oscillating body of an ultrasonic transducer;

[0028] FIG. 4 a three-dimensional inner view of a pocket in the conduit wall for an ultrasonic transducer;

[0029] FIG. 5 an outer view of a pocket in the conduit wall for an ultrasonic transducer; and

[0030] FIG. 6 a detailed view of an ultrasonic transducer similar to FIG. 2 for a geometrical variant of a pocket.

[0031] FIG. 1 shows a simplified longitudinal section view of a measuring apparatus 10 for determining the flow speed or the throughflow calculated therefrom of a fluid 12 in a tubular conduit 14 that flows in a direction marked by an arrow 16. The determination of the flow speed takes place, for example, using the differential time of flight method described in the introduction by evaluating the times of flight on a transmission and detection of ultrasonic signals between the pair of ultrasonic transducers 18a-b and against the flow in a control and evaluation unit. The control and evaluation device is not shown itself in FIG. 1, but is rather only indicated by its connections 20a-b to the ultrasonic transducers 18a-b. The number of ultrasonic transducers 18a-b can vary in other embodiments.

[0032] The conduit 14 in the region of the ultrasound measurement forms a measurement body of the measuring apparatus 10. The representation has been selected as if this measurement body were an integral part of the existing conduit 14. This is possible in principle, but in practice the measuring apparatus 10 is manufactured with its own measurement body that replaces a corresponding section of an existing conduit after the assembly and is for this purpose, for example, inserted at both sides by flange connections.

[0033] The ultrasonic transducers 18a-b are integrated in a conduit wall 22 of the conduit 14. This first corresponds to the clamp-in assembly explained in the introduction, but with a transducer concept in accordance with the invention that will be explained in more detail further below with reference to FIGS. 2 to 6. The ultrasonic transducers 18a-b are supported from the outside by a transducer holder 24. In this exemplary embodiment, the conduit 14 or the transducer holder 24 is surrounded right at the outside in the region of the measurement body by a housing or by a cover pipe 26.

[0034] As indicated by sound propagation lines 28, the outward and inward radiation directions of the ultrasonic transducers 18a-b are perpendicular to a center axis of the conduit 14. In order nevertheless to achieve an axial offset of the two ultrasonic transducers 18a-b and thus to achieve a measurement effect in a time of flight difference process, a broad radiation characteristic of, for example, more than 20° is required. At a higher ultrasonic frequency, in particular in the high kHz or even MHz range, this means a radiation surface whose diameter is only in the order of magnitude of a millimeter.

[0035] Instead of two ultrasonic transducers 18a-b, a plurality of pairs of ultrasonic transducers can also be provided that span a plurality of measurement paths between one another for a measurement apparatus 10 having a multi-path configuration. A more exact measurement is possible with an irregular flow or with upstream disturbances using such a multi-path counter that has a plurality of measurement paths offset with respect to one another and to the pipe axis. A single-path counter implicitly requires a homogeneous flow that can be detected by the single path or thereby only measures a first approximation of a complicated flow.

[0036] FIG. 2 shows the region of an ultrasonic transducer 18a in the conduit wall 22 in an enlarged representation to more exactly illustrate the improvement and simplification by the transducer principle in accordance with the invention. A hollow space or a pocket 30 is formed in the conduit wall 22 and is closed toward the outside by the transducer holder 24. A thin-wall part region 32 of the conduit wall 22 remains toward the inside in the region of the pocket; it simultaneously serves as a membrane of the ultrasonic transducer 18a and is excited to oscillate by its oscillating body 34, for example a piezoceramic material, to transmit an ultrasonic signal; or conversely, it is excited to oscillate on an impact of an ultrasonic signal from the interior of the conduit 14 on the part region 32 of the oscillating body 34. The thin-wall part region 32 remains stable enough to withstand an internal conduit pressure to be expected. The conduit wall 22 forms an inner surface closed in itself without recesses or projections that could disturb the flow or at which depositions could settle.

[0037] The oscillating body 34 is now not directly placed onto the part region 32 acting as a membrane. A coupling piece 36 is rather provided therebetween whose cross-sectional surface is much smaller than that of the part region 32 and of the oscillating body 34. The oscillating body 34 can be formed as a piezoelectric block that is placed directly onto the coupling piece 36. Both a direction connection between the oscillating body 34 and the coupling piece 36 and an additional coupling material are conceivable. In addition, the connection can only be established by a force-transmitting coupling, for instance by a clamping force from above, but also by adhesive bonding or soldering.

[0038] The coupling piece 36 is in turn preferably an integral element of the conduit wall 22 such that additional contact points are omitted. For this purpose, the pocket 30 and the coupling piece 36 are preferably formed together in an efficient production process and the coupling piece 36 is-so-to-say left in position in so doing. It should, however, not be precluded, despite the foreseeable disadvantages in the sound transmission and in the mechanical robustness, to fasten the coupling piece 36 to the base of the pocket 30 at the part region 32 as a separate element. The oscillating body is held in a yielding manner at the wall holder 24 toward the outside, which is represented by a spring 38. An exemplary practical implementation of the spring 38 is an elastomer layer. The force of the spring 38 can also establish or stabilize the connection between the oscillating body 34 and the coupling piece 36.

[0039] The coupling piece 36 makes possible a transducer plate or a radiation surface having a small diameter with a simultaneous utilization of a larger oscillating body 34. The possible dimensions of the oscillating body 34 and of the radiation surface become independent of one another due to the coupling piece 36. A larger oscillating body 34 is functionally advantageous both for the frequency configuration and for reaching the required sensitivity. As already addressed multiple times, a small radiation surface is actually required at higher frequencies for a wide radiation characteristic. These initially contradictory demands can be simultaneously satisfied by the coupling piece 36.

[0040] FIG. 3 again separately shows a schematic three-dimensional representation of the oscillating body 34 for explaining its oscillating behavior. The specific parallelepiped-shaped or cube-shaped geometry of the oscillating body 34 and equally the specific deformation by the oscillation are to be understood as exemplary. The oscillating body 34 carries out a special oscillation in operation that is illustratively called a pillow oscillation because it is reminiscent of a strongly shaken pillow due to the only small-surface fixing to the coupling piece 36 and due to its geometrical extent in the vertical direction and lateral direction. This can be understood as a volume resonance. While the oscillating body 34 becomes shorter in the longitudinal direction, that is in the vertical direction in FIG. 3, it thickens transversely at all sides. This is particularly pronounced at the lateral edges due to the block geometry. The shortening in the longitudinal direction is also not uniform, but is rather very highly pronounced at the center, while the corners move less. This oscillation is transmitted by the coupling piece 36 to the membrane or to the part region 32 or conversely the membrane sets the oscillating body 34 into oscillation via the coupling piece 36 on incident ultrasound.

[0041] The oscillating body 34 preferably works in a frequency range of some hundred kHz up to some MHz, with, however, the principle also working from a few kHz to at least ten MHz. The specific useful frequencies are fixed by the geometry and by the material such that it is considered on the configuration of the oscillating body 34. The oscillating body 34 is preferably operated at one of its resonances; the coupling piece 36 at its resonance or beneath its resonance. The resonance of the part region 32 can also selectively be used.

[0042] FIG. 4 again shows the pocket 30 with the coupling piece 36 in a three-dimensional sectional view. The pocket 30 is cylindrical in the upper region and tapers inwardly due to a frustoconical shape. The inner contour thereby reduces in the direction of the part region 32 that thus has a smaller surface than the cross-section in the upper region of the pocket 30 that can in particular also be smaller than the oscillating body 34 due to the coupling piece 36. The coupling piece 36 is of cylindrical shape in this embodiment. FIG. 5 shows a photograph of a conduit wall 22 having a prepared pocket 30 and coupling piece 36.

[0043] FIG. 6 again shows a longitudinal section of the measuring apparatus 10 in the region of an ultrasonic transducer 18a, similar to FIG. 23, but with a different geometry of the pocket 30. While the pocket 30 previously tapered conically toward the part region 30, a stepped configuration of the pocket with a larger cylinder diameter in the region of the oscillating body 34 and a small cylinder diameter in the region of the coupling piece 36 is shown in FIG. 6. These are only examples of the pocket geometry. The pocket 30 can also be cylindrical without any cross-sectional reduction, with more steps, with other combinations of cylinder sections and cone sections or in even other geometries. This also applies very much accordingly to the coupling piece 36; however, there the condition of a cross-sectional surface noticeably smaller with respect to the oscillating body remains in force. The shape of a cube, of a parallelepiped or of a cylinder can be considered for the oscillating body, for example.