Response Characteristics Of Laser Diffraction Particle Size Analyzers: Optical Sample Volume Extent And Lens Effects

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Abstract
The response characteristics of laser diffraction particle sizing instruments were studied theoretically and experimentally. In particular, the extent of optical sample volume and the effects of receiving lens properties were investigated in detail. The experimental work was performed with a Malvern Instruments Ltd. Model 2200 particle size analyzer using a calibration reticle containing a two-dimensional array of opaque circular disks on a glass substrate. The calibration slide simulated the forward-scattering characteristics of a Rosin-Rammler droplet size dis-tribution. The reticle was analyzed with collection lenses of 63 mm, 100 mm, and 300 mm focal lengths using scattering inversion software that determined best-fit Rosin-Rammler size distribution parameters. The Malvern 2200 data differed from the predicted response for the reticle by about 10%. The discrepancies are attributed to nonideal effects in the detector elements and the lenses. A set of calibration factors for the detector elements was determined here that corrected for the nonideal response of the instrument. The response of the instrument was also measured as a function of reticle position, and the results confirmed a theoretical optical sample volume model presented here.

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