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Abstract

In a method for measuring the mass flow M of a fluid flowing through a pipe having a cross-sectional area A, the sound velocity c.sub.2 in the fluid is determined as well as the flow velocity v of the fluid by sing-around technique. Further, reflection technique is used which comprises measuring the amplitude both of an ultrasonic pulse which has been reflected in a boundary between a first and a second material having different acoustic impedances, and of an ultrasonic pulse which has been reflected in the boundary between the second material and the fluid, it being possible to determine the density of the fluid on the basis of the measured amplitudes, the sound velocity c.sub.2 in the fluid and the acoustic impedances of the first and the second material. The mass flow M is then obtainable as M=v.times.A.times..rho..sub.2. A mass flowmeter especially has a transducer with a piezoelectric crystal (5), a first block (6) of a first material disposed adjacent said crystal, and a second block (7) of a second material disposed between the first block and the fluid, and calculating and amplitude metering means (10 and 12).

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