Laser Obscuration Time


The Ankersmid “EyeTech” Particle Size & Shape systems (Lab Systems, On-Line/In-Situ Probes) are both based on a well-founded principle of Light Obscuration, also known as the Laser Obscuration Time (LOT) technology. Stationary or moving particles can be measured by a scanning and rotating laser beam (= PSA, Particle Size Analysis) and/or Characterized/visualized (optical) (= DSA/DSC, Dynamic Shape Analysis/Characterization) using a CCD (video) camera. All controlled and automated using a powerful 21 CFR -11 (image) analysis software, which entails capabilities like pre-processing, filter options, re-run analysis data, etc. 
A He-Ne laser beam passes through a rotating wedge prism and is focused down to a small spot. The result is a circular movement of a focused laser beam. The laser beam scans the individual particles in the measurement zone. As the particles within the sample volume are individually bisected by the laser spot, interaction signals are generated. These signals are then detected by a photodiode.

Since the beam rotates at a constant speed, the duration of interaction (obscuration) provides a direct measurement of the individual particle''s size. The interaction signals are collected and analyzed in 600 discrete size intervals.
Sophisticated pulse analysis algorithms are employed to reject out-of-focus and off-center interactions.

The strength of the Laser Obscuration Time principle is that it relates solely and directly to particle size, rather than to secondary properties from which size may be inferred. This eliminates inconsistencies due to sample refractive index, viscosity variations, Brownian Motion and thermal convection.
Routine calibration is not required, and to a large degree, results are not dependent on the optical properties of the particulates or the medium. Problems of coincidence and orifice clogging are avoided by using interaction pulse analysis to provide an optically defined measurement zone, rather than a mechanically defined orifice.
Simultaneously offering high resolution and wide dynamic range, the Laser Obscuration Time analysis generates the most accurate one-dimensional sizing of particles.


Ankersmid M&C bvba,         Neerlandweg 21, B-2610 Wilrijk,        :,  : (32) - 3/820 80 01,