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PI Overview

Particle Insight Principles of Operation

How does the system work?

Principles of operation; plumbing diagram
General diagram of the recirculation system

Recirculation vs. single-pass analysis

Recirculation vs. single pass analysis

•  Recirculation gives particles the chance to present themselves in more than one orientation, resulting in more accurate characterization.
•  Recirculation of the aliquot is a must for process optimization.
•  Repeated, random orientation of particles has been cited numerous times as a preferred or required method.
•  Laser diffraction has employed sample recirculation for 40+ years to ensure accuracy.
•  In a single-pass sytem, only a fraction of particles present are seen and analyzed, given the dimensions of the sensing zone and camera speed.
•  Single-pass systems generally use hydrodynamic focusing that require expensive sheath fluids.

Image capture and analysis

Capture of a particle silhouette on a camera sensor

Images are captured containing two-dimensional silhouettes of particles. The image is turned into a binary (black and white) representation, using the Threshold parameter.
•  pixel intensities in the image can range from 0 (black) to 255 (white).
•  the threshold is a value between 0 and 255, typically about 75% of the background average.
•  all pixels darker than the threshold are counted as belong to a particle; lighter than the threshold is background.
•  the threshold is an adjustable parameter, since different values work best under different image conditions.

From the resulting particle shapes, various size and shape measures are calculated.

Pixel resolution is important

How camera pixel resolution affects accuracy

For proper analysis of particles an adequate pixel density is needed.

Calculating size measures from the particle silhouette

Calculating a size measure from the silhouette

From the silhouette area and perimeter, size and shape measures may be calculated.
•  the red outline is a circle having the same area as the silhouette. This diameter is a commonly-used single measure of size. It is called the "equivalent circular area" diamter.
•  the "equivalent circular perimeter" diameter (not shown) is another measure of size, and is calculated from the perimeter instead of the area.
•  from the original area and perimeter, a "circularity" figure may be determined:   circ = 4πA / P2
•  these measures are appropriate for particles that have low aspect ratio (width similar to height).
•  other measures are available for other kinds of particle shapes.