THE PULSE DISPLACEMENT TECHNIQUE - A SINGLE-PARTICLE COUNTER WITH A SIZE RANGE LARGER THAN 1000-1

This paper describes the pulse displacement technique (PDT) to simulta neously measure particle size and velocity in applications characteriz ed by a large size range and high particle concentration. PDT is based on the detection of scattered refraction and reflection pulses which sweep past a detector at different times as a particle traverses a nar row probe volume. Basic analytical relationships are presented which a llow the calculation of the spatial and temporal widths and separation s of the reflection and refraction pulses as a function of particle di ameter and velocity. Two implementations of PDT are discussed using on e or two receivers with two laser sheets having the same or different wavelengths. This paper also discusses several methods to measure part icle velocity with PDT, discusses the limitations associated with sign al broadening in practical systems, and briefly presents experimental results which show that the temporal separation between the refraction and reflection pulse maxima is independent of collecting lens f-numbe r from f/3 to f/20 for particle sizes ranging from 250 to 2000 mum.