| 摘要 |
<p>Ultrasonic flow meter of the clamp-on type for the measurement of the flow rate of a liquid in a pipeline, provided with two piezoelectric transmitting-receiving transducers, each accommodated in a housing, which are clamped at both sides of the pipeline axially offset with respect to each other thereon and which alternately transmit ultrasonic pulses into the pipeline and receive them therefrom in order to determine the flow rate from the transit time of the source pulses in the upstream and downstream direction. The transducers each consist of a row of adjacent subtransducers, the pulse emission face of which row is coupled over its entire length in the axial direction to the pipe wall. The substransducers are activated by control signals, the phase difference between the control signals at every two adjacent subtransducers and the distance between the centres thereof being matched to each other such that the transducer deforms approximately sinusoidally with a periodic length which corresponds to the wavelength lambda of Lamb surface waves to be generated in the pipe wall in the A o mode. Said waves propagate in the axial direction along the pipe wall and, on the inside thereof, are converted into longitudinal waves in the adjacent liquid.</p> |
