Ultrasonic technique for fluid flow speed measurement - using three sound converters fixed to prisms, two on one side of flow tube and electronic circuit to compensate for time delays

摘要

In one example of the ultrasonic pick-up unit, two acoustic converters (1a, 1b) are mounted on an oblique face of a corresponding prism (2a, 2b) on either side of a hollow tube (3). The converters are typically of the Pb-Zr-Ti type. A fluid (4) flowing through the tube with a velocity V at an angle THETA to the normal to the light path, leads to a sound transit time, in addition to the delay time in the prisms, of T1(T2) = D/cost (C+Vsin THETA), where C is the sound velocity and the positive (negative) sign is taken for T1(T2) depending on the direction of fluid flow. Improved accuracy is obtained by adding a third prism abutting against the first (2a) so that an additional signal is obtained from reflection from the internal face of the hollow tube. The compensation signal is fed into the external electronic circuit, with a delay unit, a compensation circuit and an integrator.