The Coulter Counter Multisizer 2e determines distributions of silt and clay-
sized particles suspended in a conductive liquid by forcing the suspension to
flow through a small aperture.
As a particle passes through the aperture, it changes the resistance between
the internal and external electrodes. This produces a current pulse of short
duration having a magnitude proportional to the particle volume.
To minimize coincidence, or measuring more than one particle at a time, the
concentration of the suspension may be adjusted. Acceptable
concentrations limit the number of particles passing through the aperture to
less than 1,000 per second.
During analysis of a sample, the series of pulses is electronically classified by size and counted.
After an analysis is completed, the data is logged on a computer.
The silt and clay fractions of geological samples usually have a large particle
diameter range. If this diameter range exceeds 20:1, more than
one size aperture tube must be used.
The first analysis is performed with a 200-micron aperture tube; a 30-micron
aperture tube is used during the second analysis. The analyst first performs
all of the 200-micron aperture analyses, then swaps aperture tubes and
changes the machine settings.
Before the 30-micron aperture analyses are run, the analyst must split each
sample with a 20-micron sieve. When an individual sample is run as part of a
group, a typical time for each multi-aperture analysis is approximately 5
minutes.