Processing of phase Doppler velocimetry using a fast digital signal processor.

A signal processing system using laser Doppler velocimetry to simultaneously measure size and velocity in a denser dispersed two phase flow is described. A fast Fourier transform method was adopted to detect both Doppler frequency for velocimetry detecting and phase shift of Doppler signals for particle sizing. Particle diameter was proportional to the phase among Doppler signals observed at different positions. The signal processor comprised a fast analogue to digital converted, a digital signal processor and a microcomputer for fast spectral analysis. This system is simpler and more flexible than those based on zero crossings of Doppler burst signals. The optical system was made of optical fibre to stabilize it and make it compact. The system was applied to glass spherical particles and water spray flow. The results confirmed a high resolution in measuring particle size and velocity even for a noisy signal in a higher concentration of dispersed phase.