In the Coulter Principle instrumentation, the change in electric resistance due to passages of particles through the aperture is determined using fast electronic circuitry. The detected signals are instantaneously digitized at a rate of a few million times per second into digital signals. The digital signal is then recorded for every pulse in the form of pulse parameters, i.e., timing, height, width of pulses, etc. Since most measurements aim at obtaining particle counting or size distribution, the recorded pulse height is converted to particle size using the calibration constant and placed into one of the pre-set size bins. The particle size distribution and counting are the cumulative result of all pulses measured.
All recorded parameters
of pulses are still available for purposes
other than standard, full-range particle
size distribution. These parameters
can be subtracted or sorted, i.e., reprocessed
differently according to various applications.
For example, if one wants to have a
zoom-in size distribution showing every
detail of the distribution, then a narrower
size range can be chosen and all pulses
can be sorted and placed into the new
set of finer bins. Another example is
that when the pulse heights (or sizes)
are sorted in a time sequence, for samples
of narrow size distribution, such a
plot can be used to monitor sample change
during measurement. Yet still another
example is that one may plot pulse height
as a function of pulse width to find
information of particle shape.
In summary, the digitized pulse information has made many new applications of the Coulter Principle measurement possible and many more applications are being discovered.
