| 摘要 |
A method of measuring the velocity of particles in a fluid flow comprises: directing at the fluid flow a pair of light beams spaced apart by a predetermined distance, the beams carrying respectively first and second modulations and being directed in a direction generally transverse to the direction of flow; detecting at a common detector means (3) light reflected from or scattered by particles passing through the two beams to produce a detector signal; separating said detector signal into a first signal carrying the first modulation and a second signal carrying the second modulation; comparing the pattern of variations in amplitude in the first and second signals to establish a correlation between the patterns and measuring the temporal displacement in the correlation; and calculating from the temporal displacement and the known distance between the beams the velocity of the particles in the fluid flow. <IMAGE> |
