C Resolution comparable to LALLS; adjacent narrow peaks that differ by
about 15%-20% can be resolved.
Disadvantages
C Dynamic size range is limited to about 30 in a single run (from about 2%
of the orifice size to about 60% of the orifice size). Analysis of broader
distributions requires pre-separation of samples according to size (for
example, via sieves), so that the individual fractions can be run using
different orifices. This makes analysis of broad distributions more difficult
and the results more doubtful.
C Samples must be suspended in a conductive fluid; saline water may not
be convenient for many kinds of samples.
C The particles must normally be electrical insulators.
C While the minimum size for the method is about 0.5 micron, experience
has shown that measurements below 2 - 3 microns are often very difficult
due to stray oversize particles that get trapped in the orifice and cause
plugging. Particles below 0.5 micron can’t be measured by this technique
under any circumstances.
C Resolution near the lower limit of the instrument is often not as good as in
the middle of the measurable range.
The Light Counter
How it Works
The light counter is very much the optical equivalent of the electrozone counter.
Particles are forced through a counting chamber, where a focused laser beam is
partially blocked as the particle passes. The reduction in light intensity reaching
a detector is related to the optical cross section of the particle, and this is
converted to a size distribution.
Advantages
C Suitable for a relatively broad range of sizes (~0.5 micron to >2,000
microns, using different size sensors).
C Simple in concept, and easy to calibrate with known size standards.
C Quick analysis time - normally less than 3 minutes
C Gives repeatable results with many kinds of samples.
C Resolution comparable to LALLS (at least for larger spherical particles);
adjacent narrow peaks that differ by about 15%-20% can be resolved.
Disadvantages
C Dynamic size range is limited to about 100-200 for a single run. Analysis
of broader distributions requires measurement using two different size
sensors.
C Resolution appears to suffer with smaller particles.
C Non-spherical particles reduce resolution, because the cross section of
the particle is evaluated rather than it’s volume. The cross section for a
given particle weight will depend on both particle shape and orientation
as it passes through the detector. A second detector beam perpendicular
to the first would allow a better measurement of volume, but to this
author’s knowledge, only single beam instruments are produced.
C It is impossible to measure particles below 0.5 micron, and measurements
below 1 - 2 microns may be of lower accuracy than over the rest of the
measurement range.
about 15%-20% can be resolved.
Disadvantages
C Dynamic size range is limited to about 30 in a single run (from about 2%
of the orifice size to about 60% of the orifice size). Analysis of broader
distributions requires pre-separation of samples according to size (for
example, via sieves), so that the individual fractions can be run using
different orifices. This makes analysis of broad distributions more difficult
and the results more doubtful.
C Samples must be suspended in a conductive fluid; saline water may not
be convenient for many kinds of samples.
C The particles must normally be electrical insulators.
C While the minimum size for the method is about 0.5 micron, experience
has shown that measurements below 2 - 3 microns are often very difficult
due to stray oversize particles that get trapped in the orifice and cause
plugging. Particles below 0.5 micron can’t be measured by this technique
under any circumstances.
C Resolution near the lower limit of the instrument is often not as good as in
the middle of the measurable range.
The Light Counter
How it Works
The light counter is very much the optical equivalent of the electrozone counter.
Particles are forced through a counting chamber, where a focused laser beam is
partially blocked as the particle passes. The reduction in light intensity reaching
a detector is related to the optical cross section of the particle, and this is
converted to a size distribution.
Advantages
C Suitable for a relatively broad range of sizes (~0.5 micron to >2,000
microns, using different size sensors).
C Simple in concept, and easy to calibrate with known size standards.
C Quick analysis time - normally less than 3 minutes
C Gives repeatable results with many kinds of samples.
C Resolution comparable to LALLS (at least for larger spherical particles);
adjacent narrow peaks that differ by about 15%-20% can be resolved.
Disadvantages
C Dynamic size range is limited to about 100-200 for a single run. Analysis
of broader distributions requires measurement using two different size
sensors.
C Resolution appears to suffer with smaller particles.
C Non-spherical particles reduce resolution, because the cross section of
the particle is evaluated rather than it’s volume. The cross section for a
given particle weight will depend on both particle shape and orientation
as it passes through the detector. A second detector beam perpendicular
to the first would allow a better measurement of volume, but to this
author’s knowledge, only single beam instruments are produced.
C It is impossible to measure particles below 0.5 micron, and measurements
below 1 - 2 microns may be of lower accuracy than over the rest of the
measurement range.
