Ultrasound measuring section made from plastic and corresponding measuring method

[0001] The invention relates to a method for producing an ultrasonic measuring section according to the preamble of claim 1, an ultrasonic measuring section according to the preamble of claim 6 and a method for measuring the flow rate according to the preamble of claim 14. [0002] As an important method for determining flow in technical applications, a differentiation method has been developed flight time. The method of varying the time of flight uses the fact that the speed of propagation of the ultrasonic signal depends on the speed of flow of the medium in which it propagates. Accordingly, the ultrasonic signal travels more slowly in the opposite direction of flow than in the direction of flow. Technical implementation is obtained by using two ultrasonic transducers with possibly identical transfer function. To determine the difference in time of flight, one ultrasonic pulse is sent through the medium in the direction of flow and the other in the opposite direction. At the same time, both sensors work alternately as a transmitter and receiver.

[0003] Many known plastic measuring instruments use the so-called collinear system of ultrasonic transducers needed for measurement, i.e. electroacoustic transducers are located lying directly opposite each other. This has the effect that the flow guide cannot be rectilinear, but, for example, must be u-shaped to a collinear measuring chamber, and a removable injection mold cannot be produced for this. Rather, it must be made of two or more parts and welded together. This was proposed, for example, in the description of W0-A1-94 / 21989, where the measuring section is U-shaped. It is inconvenient that it must be connected by welding from several parts, which inevitably leads to welds in the measuring section. As they are "particle traps", they are not desirable.

[0004] From DE-A01-39 41 544, an ultrasonic measuring instrument is known in which ultrasonic waves travel in a W-shaped path between two signal converters. The sound waves are reflected first from the bottom wall of the pipe, then from the top wall of the pipe, and finally again from the bottom wall of the pipe. Some of the sound waves travel only with only one reflection from the bottom wall of the pipe. These sound waves are attenuated by attaching the silencer to the bottom wall.

[0005] EP-B1-0 521 855 describes a similar flow meter. However, the reflection surfaces are curved so that the sound waves are focused. The bottom wall of the tube has a defocusing reflection surface between the focusing surfaces. At the same time, the part of the sound waves that flows through the measuring tube through the "V" shaped path is suppressed. However, also using these means, the acoustic signal is very attenuated by the flow meter and the receiving signal converter receives a very weak signal, on which the sound waves overlap, which follow the "V" path through the pipe. When the signal converter receives a weak trip, it is sensitive to interference. This applies to both mechanical and electromagnetic noise.

[0006] EP-A1-0 538 930 describes a measuring tube whose wall has a cross-sectional elliptical profile. An ultrasonic transmitter and an ultrasonic receiver are placed in the focal points of the ellipse. In the middle of the measuring tube, the insert extends in the longitudinal direction,

EP 1 891 400 Β1 formed as an obstacle, with a profile that is either shaped as an ellipse or in the form of an ellipse, with the apex directed in the direction of flow. Using this insert, it is to be impossible to reach the ultrasound directly from the transmitter to the receiver, without being reflected by the walls of the measuring tube. The ultrasonic transmitter and ultrasonic receiver are located on the axial central axis of the measuring tube.

[0007] The disadvantage of said traditional constructions is the tendency to trap bubbles or particles. Especially in the descriptions mentioned at the beginning there are cavities or corners in which bubbles and particles can be captured and thus falsify the measurement. At the same time, many of the corner inlets, which are unfavorable from a flow technique point of view, tend to silt up due to contaminants.

[0008] DE 199 44 411 A1 shows an ultrasonic flow meter with a measuring tube in which ultrasonic transducers are embedded in holes in the pipe wall. The ultrasonic transducers are displaced in the axial direction and placed diagonally opposite each other. The measuring tube has a tubular insert, which tapers from the front of the measuring tube to a measuring channel, which has a longitudinal oval shape in cross section. The insert has thickened end areas on which are each placed diagonally opposite to the bevel transducer, in which the headlights are mounted. Accordingly, the stream is introduced by radiation into the tube through the transducer, perpendicular to the tube axis, is reflected in an oblique axial direction at an angle corresponding to the bevel and reflected from the second bevel reflector to the second reflector. The disadvantage of this system is, in particular, that it is very labor-intensive in terms of shape and production. Basically, it consists of three structural parts, except for the transducers and reflectors that must be combined or incorporated into each other. In order for the measuring section through which the fluid flows to be sealed relative to the outer pipe, attention should be paid to the tightness when installing the insert.

[0009] EP 1 413 858 A1 shows an ultrasonic flow meter in which a measuring tube can also be made of plastic. As can be seen in particular from Fig. 1, the direct transfer of the ultrasonic signal measurement must be carried out without indirect reflection being introduced from the oblique wall areas. It can be seen from the figures that - if the measuring pipe were to be made of plastic - the measuring pipe is not made of two expanding sliders that are pulled out from different sides of the measuring section, because in the measuring pipe, in the area of ​​the wall bevings, undercuts are provided in two directions. In this way, each slide, if used as such, would be locked immediately and could no longer be removed from the finished measuring section. Therefore, the measuring section must be made of two bowls, each forming a half of the measuring tube, which should be tightly connected with each other, especially by welding or gluing. However, the above-mentioned drawbacks would again arise.

[0010] The invention is based on the task of developing a method for producing an ultrasonic measuring section for measuring the flow rate, the design of which is simple and the production costs are low.

[0011] According to the invention, the task is solved first by a method for producing an ultrasonic measuring section with the characterizing feature of claim 1. Furthermore, the invention provides for ultrasonic

EP 1 891 400 Β1 measuring section with the features of claim 6 and method of measuring the flow intensity with the features of claim

14.

[0012] The shape of the measuring section in the form of one-flight steps is important. Preferred embodiments are given in the dependent claims.

[0013] The advantage of the measuring section is that the measuring section can be made of one part by injection molding, because thanks to the use of two sliders, it is possible to remove the workpiece from the mold. There are no welds, so there are no potential "particle traps". In addition, air or gas bubbles can hardly settle in liquids and pass the measuring section quickly, which largely eliminates measurement spuriousness.

Depending on the properties of the plastic used, the outer wall serves as reflectors (reflection from the air, surrounding the measuring section), internal wall (reflection from the plastic measuring section), mounted on the external wall or injected as an insert in the plastic reflector from a suitable material, for example metal, for the necessary reflection. Insofar as penetration through the plastic wall has to occur, the plastic wall to be penetrated preferably has a uniform thickness throughout the spotlights.

[0015] The invention will be explained in more detail on the basis of the attached figures. It shows or shows:

<td></td><td>fig. 1</td><td>view of the ultrasonic measuring section according to the invention, with an ultrasonic</td>

<td> 20</td><td></td><td>transmitting and receiving transducers and reflectors;</td>

<td></td><td>Fig. 2a</td><td>section through the ultrasonic measuring section according to the invention, with the sound path traveled;</td>

<td></td><td>Fig. 2b</td><td>a side view of Fig. 2a, in which the embodiment of the ultrasonic measuring section according to the invention is clearly visible, in the shape of a one-step staircase;</td>

<td> 25</td><td>Figure 3</td><td>section through the ultrasonic measuring section according to the invention, during manufacture by two sliders;</td>

<td></td><td>fig. 4</td><td>a view of both sliders that are used to produce the measuring section according to the invention;</td>

<td></td><td>figures 5a-d</td><td>four different ways of mounting the reflector on the measuring section, a</td>

<td> 30</td><td>Figs. 6a-d</td><td>correspond to Figs. 5a-d, but each embodiment is additionally provided with a radius at the place where the reflector is located.</td>

[0016] Fig. 1 shows a view of the ultrasonic measuring section 1 according to the invention with two ultrasonic transmitting and receiving transducers 2, 3, spaced apart in the direction of fluid flow. The sound emitted by the transmitting transducers 2, 3 is guided through the measuring section 1 through two reflectors before it is picked up by the second transmitting transducer 3, 2. To determine the difference in run time, and thus flow velocity, one ultrasonic pulse is sent through the medium in the direction of flow, the other in the opposite direction. At the same time, both sensors 2, 3 work alternately as transmitters and receivers. At both ends, the ultrasonic measuring section 1 has two connection parts 51, 52, which in the embodiment shown are shaped as

EP 1 891 400 Β1 round. On the connecting parts 51, 52, the measuring section is connected to external devices, not shown, which direct fluid through the measuring section 1. The ultrasonic measuring section 1 is produced from one part by injection molding. It can be made, for example, from high purity Teflon. By means of the ultrasonic measuring section 1, for example, the flow of gases or liquids can be measured. The electronic evaluation system connected to measuring section 1 will not differ from the prior art systems.

[0017] Fig. 2a shows a cross-section through the ultrasonic measuring section 1 according to the invention with the following elements: ultrasonic transmitters and receivers 2, 3 and reflectors 4. The ultrasonic path in measuring section 1 is marked with the marking 5. According to the invention, measuring section 1 it is made as a passage made in the shape of one-flight stairs. Fig. 2b is a side view of Fig. 2a, in which the stepped embodiment of the ultrasonic measuring section according to the invention is visible. The transition chamfers have at least two reflectors 4 that reflect and further direct the sound through the ultrasonic transmitting and receiving transducers 2, 3. The measuring section 1 according to the invention consists of only one injection part and has a straight passage for the fluid. Thus, in the episode, measurement this 1 there are no "bubble or particle traps" that could falsify the flow rate measurement. In this way, overlaps in the measuring signal can be ruled out. As it is clearly seen in Fig. 2a, the sound is thus transferred in a letter-shaped manner between the transmitting and receiving transducers 2, 3 through two reflectors 4 through the passage / measuring section 1 in the form of one-way stairs. At the same time, a temperature sensor 7 can be provided in the wall of the measuring section 1, which allows the joint possibility of influencing the temperature during the evaluation of the measurement data.

[0018] The method for producing the measuring section 1 according to the invention is schematically illustrated in Figs. 3 and 4. In a first step, two expanding slides 8,9 are arranged side by side. Together, the two sliders 8, 9 form the outline of the measuring section 1 in the shape of one-step stairs. The measuring section 1 is arranged around the slides 8, 9 by injection molding. Then, both sliders 8, 9 can be pulled out on different sides of the measuring section 1. 3 illustrates a cross-section through the ultrasonic measuring section 1 according to the invention during manufacture by two slides 8, 9. All elements that must be attached outside measuring section 1 can be attached in the next stage: ultrasonic transmitters and receivers 2, 3, temperature sensor 7 and optional headlights mounted from the outside 4.

[0019] In the present invention, depending on the properties of the plastic used, an external wall (Fig. 5a, reflection from the air, surrounding the measuring section), internal wall (Fig. 5b, reflection from the plastic of the measuring section) serves for reflection, mounted on the outer wall (Fig. 5c) or injected as an insert in the plastic reflector (Fig. 5d) from a suitable material, for example from metal. Of course, the appropriate metal must be individually adapted to the acoustic properties of the plastic used. Thus, the present invention does not use metal reflectors that are in contact with the environment. Insofar as penetration through the plastic wall has to occur, the plastic wall to be penetrated preferably has a uniform thickness throughout the spotlights.

EP 1 891 400 -1 [0020] In order to compensate for performance tolerances and to compensate for temperature-related changes in the length of measuring section 1, the reflectors may have a radius, which, however, leads to a weakened reception signal. The size of the radius depends on the materials used. The embodiments of Figs. 6a to 6d correspond to the embodiments of Figs. 5a to 5d, however the corresponding embodiment additionally has a radius.