| 摘要 |
A pipe (10) contains a flowing fluid, say, oil. The oil includes particulate material (12) which, for example, may be metal and or carbon particles (16). A transmitter (14) fixed to the pipe exterior for the purpose of projecting ultrasonic signals through the wall of pipe (14) onto the particles (12). The signals are deflected by the particles (12) onto a receiver (18) at a reduced frequency brought about by the Doppler effect. A spectrum analyser (not shown) is utilised to count the Doppler signals which represent the quantity of particles.
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