Particle size distribution analyzers based on measuring the phenomenon of Brownian motion can be broadly classified as being based on either autocorrelators or on power spectrums. For the purpose of this document, systems using autocorrelators will be called Photon Correlation Spectroscopy (PCS) systems. Power spectrum analyzers such as the HORIBA LB-550 are designed to examine the differences in frequency of light scattered off particles.
The LB-550 technique is designed to analyze fluctuations in the intensity of any
scattered light from a body in relation to the incident light. This method is also
referred to as the frequency analysis method. PCS analyzers are based on the method in which the number of photons per time unit is counted, assuming that light consists of a series of photons.
As described above, the PCS instrument is designed to count moving particles
in terms of the number of photons. Therefore, it must simultaneously measure particles which are moving at both fast and slow speeds. The simultaneous measurement requires that fast-moving particles be determined at high speeds, and slow-moving ones over extended periods of time. In actual practice, however, it is very difficult to create an instrument that combines the above functions with continuous data multiplication capability.
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