ULTRASONIC FLOWMETER "W"

Abstract: The present invention relates to an ultrasonic flowmeter for measuring flows of liquid or gas through a measuring tube which is equipped with ultrasonic transducers, where the ultrasound is reflected by the tube wall, by focussing reflecting plane. If at least one focussing reflecting plane is ellipsoid, and the transducers are placed in the focal points of the ellipse, a simple and cheap ultrasonic flowmeter can be provided, which can carry out accurate and quick measurings.

Description: Ultrasonic Flowmeter " " The present invention relates to an ultrasonic flowmeter for measuring liquid or gas flow through a measuring tube which is equipped with ultrasonic transducers, where the ultrasound is reflected by the tube wall which has at least one focussing reflecting plane. From DE 39 41 544 Al a flowmeter is known where ultrasonic waves pass a 'W beam path between two transducers. The sound waves are reflected first in the bottom of the tube, then in the top of the tube, and finally in the bottom of the tube. Some of the sound waves pass along a path with only one reflection towards the bottom of the tube. These sound waves are damped by damping material placed in the bottom of the tube. EP 0 521 855 Bl describes the same flowmeter, but the reflecting planes are curved, so that the sound waves are focussed. The tube bottom has a defocussing reflecting plane between the focussing planes. Hereby the part of the sound waves which passes a 'V path through the meter tube is damped. Even with these precautions the acoustic signal is strongly damped through the flowmeter, and the receiving transducer receives a weak signal, which is superposed by sound waves which have followed the 'V path through the tube. When the transducer receives a weak signal, it is sensitive to noise, which may be both mechanical and elec¬ tromagnetic. The object of the present invention is to provide a simple and cheap ultrasonic flowmeter, which can carry out accu¬ rate and quick measurements. The task set can be solved with a flowmeter as the one described in the introduction, whose at least one focussing reflecting plane is ellipsoid, and the transducers are placed in the focal points of an ellipse. Hereby it can be achieved that all parts of a pencil of sound waves traverse the same distance, and a pure signal is obtained. The pencil of sound waves emitted from one of the focal points of the ellipse will be reflected and concentrated in the other focal point of the ellipse. This leads to amplification of the received signal, which there¬ by becomes less sensitive to noise. The transducers can be placed in a transducer plane, which may be displaced laterally in relation to the axis of the meter tube. Hereby the same result is obtained at measurements of both turbulent and laminar flows in the meter tube. The present invention can be implemented by reflecting the ultrasound several times from the tube wall, and the ultra¬ sound passes along a 'W-shaped beam path. Hereby a reason- able time difference is obtained for measuring downstream and upstream, even though the meter tube has a small inter¬ nal diameter. The flowmeter may have several ellipsoid mirrors where the ellipses have common focal points on reflecting planes. Hereby the flowmeter can be built with many reflections between the tube walls. By alternately focussing and spreading the ultrasound, measurements can be made over a long measuring distance without critical loss of signal strength. An efficient flowmeter can be built in a small diameter tube. A long signal path in the medium means that low flow speeds can be measured. The flowmeter can be designed with at least two ellipsoid mirrors where the ellipses have a common focal point on the opposite wall of the tube, and the other focal points of the ellipses are found on the transducer surfaces. Hereby the common focal point can be made with special reflective properties, and damping of the ultrasonic signal decreases. The reflecting planes may advantageously be oblique in relation to each other and in relation to the transducers. Hereby the sound path can be mirrored out of the transducer plane. The ultrasonic flowmeter may be built so that ultrasound emitted from a first transducer falls first on a plane mirror which is turned through a first angle in relation to the transducer plane, after which the ultrasound is reflected by the ellipsoid reflecting plane, which is turned through a second angle in relation to the transducer plane, after which the ultrasound is reflected back to the transducer plane by the plane mirror before the ultrasound reaches the second transducer. Hereby ultrasonic waves can be obtained in the entire cross section of the tube. In this manner the same effect is obtained as by multi-track measuring with only one transducer set. The transducers may be placed on the same side of the meter tube, but turned through an angle in relation to each other. Hereby the ultrasonic waves may also be made to fill the cross section of the tube. The ultrasonic flowmeter may advantageously be designed so that the transducers are placed withdrawn from the medium flow on a shadow tube through which the ultrasound passes before coming into contact with the medium flow. Hereby damping and spreading can be achieved of sound waves fall¬ ing on the wall of the shadow tube. This ensures that sound waves that pass along the 'V path are reduced, and measur¬ ing errors are eliminated. The shadow tube may have internal reflecting planes which spread the ultrasound. Hereby part of the sound beam that hits the tube wall may be spread in different directions. Hereby the sound waves are transformed into a noise signal that does not disturb the measurements in the tube. In the following the invention is explained on the basis of drawings: Fig. 1 shows a section through a possible embodiment of the invention, Fig. 2 shows a section through another possible embodiment of the invention, Fig. 3 shows a cross section through a meter tube which is designed according to the invention, Fig. 4 shows a section through a possible embodiment of a shadow tube, Fig. 5 shows a section through an alternative embodiment of the invention. Fig. 1 shows a longitudinal section through a meter tube 1 with two ultrasonic transducers 2, 3. They may be magneto- strictive, electromagnetic, or electrostrictive. The trans¬ ducers may be designed piezoelectrically. The ultrasonic signal from the transducers 2, 3 are reflected in a mirror 4. The mirror 4 is designed as an ellipsoid of revolution, and the transducers are placed in the focal points 7, 8 of the ellipsoid. The ultrasonic signal is emitted from one of the trans¬ ducers 2, 3, which is placed in one of the focal points 7. The ultrasonic signal is reflected by the mirror 4 into the other focal point 8, where the signal is received by the other transducer 2, 3. Fig. 2 shows a longitudinal section through another embodi¬ ment of the invention. Like in Fig. 1, the meter tube 1 has two transducers 2, 3, which are placed on a shadow tube 6, 7 at a distance from the medium flow. The mirror 4, which is designed as an ellipsoid of revolution, is shown here in the top of the tube on the same side as the transducers. In the bottom of the tube there is a plane mirror 9. The transducers 2, 3 are held by plugs 10, 11, which are screwed into the meter tube 1. The transducers 2, 3 are protected against medium contact by diaphragms 12, 13. The diaphragms 12, 13 are fixed between the plugs 10, 11 and collars in the meter tube 1. Sealing between the plugs 10, 11 and the meter tube 1 is effected with 0-rings 14, 15. A recess 16 is shown, which may be used for a temperature sensor. Between the transducers 2, 3 is shown a box 17, which may contain an electronic circuit which may generate ultrasonic pulses and carry out signal processing of the ultrasonic signal received. The electronic circuit may contain a display for measuring parameters. A keyboard may give the user a possibility of changing between various data shown on the display. Ultrasound is emitted from one of the transducers 2, 3, which is placed in one of the focal points 7, 8 of the ellipsoid mirror 4. The ultrasound is reflected first by the plane mirror 9 up against the ellipsoid mirror 4. From here the ultrasound is reflected back towards the plane mirror 9. Here the ultrasound is reflected again, after which it is concentrated in the other focal point 7, 8 on the other transducer 2, 3. Fig. 3 shows a crosswise section through a meter tube as the one shown in Fig. 2. The plane mirror 9 is turned through an angle 21 in relation to the transverse axis 20 of the meter tube 1. The mirror 4, which is shaped like an ellipsoid of revolution, is turned through another and larger angle in relation to the transverse axis 20 of the meter tube. The transducer plane 19 is laterally displaced in relation to the centre line 18 of the meter tube. Ultrasound is emitted from one ellipsoid focal point 7 in the direction of the plane mirror 9, which is turned through an angle 21. From here the ultrasound is reflected in an oblique direction towards the ellipsoid mirror 4. The ultrasound is spread and fills the entire meter tube cross section. By reflection of the ellipsoid mirror 4 the ultrasound is concentrated and returned via the plane mirror 9 to a focal point 9 on a transducer surface. By filling the entire cross section of the tube with ultra¬ sound, a flowmeter can be built which provides for various velocities of movement in the flow profile. The flowmeter can measure accurately at laminar as well as at turbulent flows. Fig. 4 shows a section through a possible embodiment of a shadow tube. The shadow tube 6 is shown with reflecting planes 22 on the interior side of the tube. Ultrasound emitted by a transducer 2 is spread, and part of the ultra¬ sound will fall on the interior surface of the shadow tube 6. Reflections from here may influence measurements in that ultrasonic waves follow another path between the trans¬ ducers. The alternative path may be shorter or longer than the desired path. The consequence of the undesirable waves is that they arrive either earlier or later than the proper signal. The result is inaccurate measuring. By designing the interior side of the shadow tube 6 with random reflecting planes 22, the part of the ultrasound falling on the tube wall is scattered in various direc¬ tions. Hereby the ultrasound is transformed into noise which is radiated in various directions. The noise is mixed with existing noise in the meter tube, and the influence on the receiver transducer disappears. Fig. 5 shows a section through an alternative embodiment of the invention. Two ellipsoid mirrors 23, 24, which have a common focal point 27, are shown here. The other focal points 26, 28 of the ellipsoids lie on the surfaces of the transducers. The reflecting planes 27, where the sound waves are focussed, may be designed of material with good reflecting properties. Holes may be drilled in the meter tube, and the reflecting planes 27 may be mounted on a plug which fills the hole. The drilled holes may be provided with threads, and screws with polished end planes may be screwed in so that the focussed ultrasound is mirrored on the screws.

Claims: P A T E N T C L A I M S 1. An ultrasonic flowmeter for measuring flows of liquid or gas through a measuring tube which is equipped with ultrasonic transducers where the ultrasound is re¬ flected by the tube wall which has at least one focus¬ sing reflecting plane, c h a r a c t e r i s e d in that at least one focussing reflecting plane (4, 23, 24) is ellipsoid, and the transducers (2, 3) are placed in the focal points (7, 8, 26, 28) of the ellipse. 2. An ultrasonic flowmeter according to claim 1, c h a r a c t e r i s e d in that the transducers (2, 3) are placed in a transducer plane (19) , which is laterally displaced in relation to the axis (18) of the meter tube. 3. An ultrasonic flowmeter according to claim 1 or 2, c h a r a c t e r i s e d in that the ultrasound is reflected several times by the tube wall, and the ultrasound passes along a 'W-shaped beam path. 4. An ultrasonic flowmeter according to claim 1 or 2 , c h a r a c t e r i s e d in that the flowmeter has several ellipsoid mirrors (24, 25), where the ellipses have common focal points on reflecting planes (27) . 5. An ultrasonic flowmeter according to claim 4, c h a r a c t e r i s e' in that the flowmeter has at least two ellipsoid mirrors (24, 25) , where the ellipses have a common focal point (27) on the opposite wall of the tube, and the other focal points (26, 28) of the ellipses are found on the transducer surfaces. 6. An ultrasonic flowmeter according to one of the claims 1-5, c h a r a c t e r i s e d in that the reflect¬ ing planes (4, 9, 23, 24, 27) are oblique in relation to each other and in relation to the transducer plane (19) . 7. An ultrasonic flowmeter according to one of the claims 1-6, c h a r a c t e r i s e d in that ultrasound emitted from a first transducer (2) falls first on a plane mirror (9) , which is turned through a first angle in relation to the transducer plane (19) , after which the ultrasound is reflected by the ellipsoid reflecting plane (4) , which is turned through a second angle in relation to the transducer plane (19) , after which the ultrasound is reflected back to the transducer plane (19) by the plane mirror (9) before the ultrasound reaches the second transducer (3) . 8. An ultrasonic flowmeter according to one of the claims 1-7, c h a r a c t e r i s e d in that the trans¬ ducers (2, 3) are placed on the same side of the meter tube, but turned through an angle in relation to each other. 9. An ultrasonic flowmeter according to one of the claims 1-8, c h a r a c t e r i s e d in that the trans¬ ducers (2, 3) are placed withdrawn from the medium flow on a shadow tube (5, 6) , through which the ultrasound passes before coming into contact with the medium flow. 10. An ultrasonic flowmeter according to one of the claims 1-9, c h a r a c t e r i s e d in that the shadow tube (5, 6) has internal reflecting planes (22) which scatter the ultrasound.

Inventors: HANSEN HENNING MAX, LOLK SOEREN, HANSEN, HENNING, MAX, LOLK, SOEREN
Applicants: DANFOSS AS, HANSEN HENNING MAX, LOLK SOEREN, DANFOSS A/S, HANSEN, HENNING, MAX, LOLK, SOEREN
Application year: 1996
Main classification: G01F1
IPC codes: G01F1