| 摘要 |
An apparatus for determining a characteristic such as sound speed for a fluid in a tube comprises means for applying a force to cause a change in a transverse dimension of a segment of the tube, wherein the change in the transverse dimension is reversible, and means for launching and receiving ultrasonic signals. Ultrasonic signals propagate through the tube along paths of different lengths. At least one of the paths is located entirely within the segment having the changed transverse dimension. The applied force may cause the transverse dimension to change continuously or in discrete steps. Path length differences between the paths are determined, and transit times are determined for each of the ultrasonic signals. The characteristic is determined based on information comprising the path length differences and the transit times.
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