Patent Grant
7647840
The invention relates to a plastic ultrasonic measurement section and a measurement method for ultrasonic measurement corresponding to the independent claims.
The transit time difference method has evolved as the most important method for measuring the flow in technical applications. The transit time difference method makes use of the fact that the propagation rate of an ultrasonic signal is dependent on the flow rate of the medium in which it propagates. Correspondingly the ultrasonic signal moves more slowly counter to than in the flow direction. Technical realization takes place through the use of two ultrasonic transducers with identical transmission function. To determine the transmit time difference an ultrasonic pulse is transmitted through the medium in the flow direction and a second pulse in the opposite direction. Both sensors operate alternately as transmitter and receiver.
The prior art, patents and patent applications disclosed numerous variants operating according to the aforementioned principle.
Many known plastic measurement devices use a so-called colinear arrangement of the ultrasonic transducers required for the measurement, i.e. the transducers are positioned directly facing one another. As a result the flow guidance cannot be straight and must instead e.g. be coupled in U-shaped manner in the measurement chamber with the colinear arrangement and it is not possible to produce a releasable injection mould for the same. It must instead be made from two or more parts, which are welded together. This has e.g. been proposed in WO-A1-94/21989, the measurement section being constructed with a U-shape. A disadvantage thereof is that it must be welded together from several parts, which inevitably leads to welding seams in the measurement section, which are undesirable because they form particle traps.
DE-A1-39 41 544 discloses an ultrasonic measurement device, in which ultrasonic waves traverse a W-shaped beam path between two signal transducers. The sound waves are firstly reflected on the lower wall of the tube, then on the upper wall and finally on the lower tube wall again. Part of the sound waves traverses a path with only a single reflection on the lower tube wall. These sound waves are damped by fitting a damper to the lower wall.
EP-B1-521 855 describes a similar flowmeter. However, the reflecting surfaces are curved, so that the sound waves are focussed. The lower tube wall has a defocussing reflecting surface between the focussing surfaces. That part of the sound waves which traverses the measurement tube in a V-shaped path is damped. However, these measures lead to a strong damping of the acoustic signal through the flowmeter and the receiving signal transducer receives a weak signal over which is superimposed the sound waves which have followed the V-shaped path through the tube. When the signal transducer receives a weak signal it is susceptible to interference. This applies both to mechanical noise and to electromagnetic noise.
EP-A1-538 930 describes a measurement tube, whose wall has in cross-section an elliptical path. At the foci of the ellipse are located an ultrasonic transmitter and an ultrasonic receiver. Longitudinally and in the centre of the measurement tube extends an insert constituting an obstacle and having a profile, which is either also in the form of an ellipse or which is ellipse-like with tips pointing in the flow direction. The aim of this insert is to ensure that ultrasound does not pass directly from transmitter to receiver without being reflected on the measurement tube walls. The ultrasonic transmitter and ultrasonic receiver are located on the axial central axis of the measurement tube.
Such known constructions to permit measurement in oblique or V-shaped manner through the measurement section cannot be used due to the characteristics of the plastic and the necessary measurement precision.
Another disadvantage of the conventional constructions is the inclination to bubble or particle trap formation. Particularly in the case of the aforementioned publications, the bulges or angles are present which can trap the bubbles and particles and thereby falsify the measurement. At the same time many of the hydraulically unfavourable, angular inlet points have a clogging tendency due to contaminants.
The object of the present invention is to provide an ultrasonic measurement section and a flow measurement method avoiding the aforementioned disadvantages and in which there are no bubble or particle traps which could falsify the flow measurement.
A further object of the invention is to provide an ultrasonic measurement section and a flow measurement method excluding interferences in the measurement signal.
Another object of the invention is to provide a method for the production of an ultrasonic measurement section, which can be made from plastic by injection moulding from one piece, having no internal welding seams or other bubble or particle traps.
According to the invention these objects are achieved through the independent claims.
In particular, these objects are achieved by a plastic ultrasonic measurement section used for the flow measurement of fluids, which has two ultrasonic transmitting and receiving transducers arranged in spaced manner in the fluid flow direction and in which the sound between the transmitting and receiving transducers, can be guided in Z-shaped manner by at least two reflectors.
These objects are more particularly achieved by a flow measurement method having an inventive ultrasonic measurement section, the sound between the transmitting and receiving transducers being guided in Z-shaped manner by at least two reflectors.
The objects are achieved by a method for the production of an inventive ultrasonic measurement section comprising the following method steps:
Advantageous embodiments are given in the subclaims.
An advantage of this measurement section is that it can be produced from one piece by injection moulding, because through the use of two sliders it is possible to release the workpiece. There are no welding seams, i.e. potential particle traps. It is also more difficult for air or gas bubbles to become fixed in liquids and rapidly traverse the measurement section, which largely avoids measurement falsifications.
Advantageously the measurement section is in stepped form and the reflectors are constituted, as a function of the characteristics of the plastics used, by the outer wall (reflection on the air surrounding the measurement section), inner wall (reflection on the plastic of the measurement section), as well as a reflector made from a suitable material, e.g. metal, fitted to the outer wall or injection moulded as an insert in the plastic, for the purpose of the necessary reflection. If the plastic wall has to be penetrated, the wall to be penetrated is advantageously of the same thickness over the entire area of the reflectors.
The invention is illustrated by the attached drawings, wherein show:
a A section through an inventive ultrasonic measurement section with the path covered by the sound.
b The side view of
a-d Four different ways of fitting a reflector to the measurement section.
a-d Corresponding to
a shows a section through an inventive ultrasonic measurement section 1 with the ultrasonic transmitting and receiving transducers 2, 3 and reflectors 4. The path of the ultrasound in measurement section 1 is indicated by reference numeral 5. According to the invention the measurement section 1 is in the form of a stepped passage.
The method for the production of the inventive measurement section 1 is diagrammatically illustrated in
As a function of the characteristics of the plastic used in the present invention, for the necessary reflection use is made of the outer wall (
To compensate production tolerances and temperature-caused length changes to the measurement section 1, the reflectors can have a radius, but this leads to an attenuated reception signal. The size of the radius is dependent on the materials used. The embodiments of
| Number | Date | Country | Kind |
|---|---|---|---|
| 01921/05 | Dec 2005 | CH | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/011123 | 11/21/2006 | WO | 00 | 6/3/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2007/065557 | 6/14/2007 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5421210 | Kobayashi et al. | Jun 1995 | A |
| 5627323 | Stern | May 1997 | A |
| 6802223 | Nakatani et al. | Oct 2004 | B2 |
| 7287435 | Ketelsen | Oct 2007 | B2 |
| Number | Date | Country |
|---|---|---|
| 39 41 544 | Jun 1991 | DE |
| WO 9114925 | Oct 1991 | DE |
| 199 44 411 | Apr 2001 | DE |
| 101 20 355 | Oct 2002 | DE |
| 0 223 123 | May 1987 | EP |
| 0 521 855 | Jan 1993 | EP |
| 1 413 858 | Apr 2004 | EP |
| 09 287989 | Nov 1997 | JP |
| WO 9421989 | Sep 1994 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20080271544 A1 | Nov 2008 | US |
