ULTRASONIC FLOWMETER "W"

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 reflected by the tube wall which has at least one focussing reflecting plane, characterised 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, wherein 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. 2. An ultrasonic flowmeter according to Claim 1, characterized in that the ultrasound is reflected several times by the tube wall, and the ultrasound passes along a 'W-shaped beam path. 3. An ultrasonic flowmeter according to Claim 1 or 2, characterized in that the flowmeter has several ellipsoid mirrors, where the ellipses have common focal points on reflecting planes (27). 4. An ultrasonic flowmeter according to Claim 3, characterized in that the flowmeter has at least two ellipsoid mirrors (23, 24), 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. 5. An ultrasonic flowmeter according to one of the Claims 1-4, characterized in that the reflecting planes (4, 9, 23, 24, 27) are oblique in relation to each other and in relation to the transducer plane, passing through the transdusers symmetry axis. 6. An ultrasonic flowmeter according to one of the Claims 1-5, characterized 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). 7. An ultrasonic flowmeter according to one of the Claims 167, characterized in that the transducers (2, 3) are placed on the same side of the meter tube, but turned through an angle in relation to each other. 8. An ultrasonic flowmeter according to one of the Claims 1-7, characterized in that the transducers (2, 3) are placed withdrawn from the medium flow on a shadow tube (5, 6), through which the ultrasound passes before coming into con