| 摘要 |
An aerodynamic particle size measuring device includes a laser energy source and beam splitting, shaping and polarizing optics for forming two parallel, peripherally overlapping beams. The beams are caused to intersect a gas stream perpendicular to the direction of gas flow, thus to form a measuring volume at the intersection of the beams and flow. Single particles are carried through the measuring volume with the gas flow, each particle scattering and extinguishing light according to the beam profile, as predetermined by the degree of beam overlap and the Gaussian intensity distribution of each beam. A photodetector, responsive either to scattered light or light extinction, generates a time-dependent voltage profile that tends to replicate the intensity profile. The resulting electrical signal is processed to determine an amplitude, set a threshold for minimally acceptable amplitudes, and to derive two negative-going zero crossings for an unambiguous time/velocity determination. Logic circuitry employs the threshold in combination with the zero crossings to reject velocity readings based on single trigger or coincidence events.
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