| 摘要 |
A signal transducer (T1, T2) mounts to a straight tube (25) to measure the flow velocity of fluid flowing therein. The transducer operates above cut-off and is coupled with a wedge (22) angled to launch a signal into the fluid at an acceptance angle that sends the lowest order mode acoustic signal axially through the fluid so it is readily detected by a receiving transducer (T2, T1) located along the conduit. A vertically polarized shear wave couples through wedge and tube wall, launching into the fluid at an angle larger than the wedge angle, preferably about 75 to 80 degrees. The system is particularly useful for metering ultrapure fluids, slurries, emulsions and biological or pharmaceutical process fluids. A prototype embodiment operates with a signal burst of four cycles at a frequency of one megahertz for launching and receiving a signal in a ten millimeter OD conduit. The wedge may be formed of hard plastic such as an acrylic, PVC or PEI having a shear wave velocity less than 1400 meters per second, and is coupled, e.g., via a silicone rubber sheet, into a conduit having a comparable sound speed, passing through the conduit wall into the fluid to produce an interrogation signal with a Gaussian envelope. At the receiving end, a comparable crystal and wedge pick up the first arriving signal through the pipe wall, a reconverted shear wavesignal at the frequency of interest.
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