Factors Determining Measurement Result

Lecture on Partical Analysis - Hands-on Course -

Table 1 lists the factors that determine measurement results in the order of measurement process progression when measuring particle size distribution using a laser diffraction particle size analyzer (i.e. particle size analyzer that operates based on the laser diffraction/scattering method).

Table 1 Factors Determining Measurement Results When Using a Laser Diffraction Particle Size Analyzer

Measurement Target (Sample) and Operator Technique Related Factors
(1) Pretreatment
   Dispersion medium, dispersant, dispersing conditions
(2) Sampling
   Sampling of measurement target (sample) and pouring method into dispersing bath (sample bath)
Analyzer-Related Factors
(3) Circulation of suspension between sampler and flow cell
   Circulation pump, ultrasonic transducer, stirring mechanism
(4) Detection of diffracted/scattered light
   Optical system (light source, shape of diffracted light/scattered light sensor, number of elements,
   location of components), signal transmission system (amplifier, A/D converter)
(5) Calculation of particle size distribution
   Particle size distribution algorithm (calculation method), computer (only calculation time is influenced)

Of these steps (measurement processes), (1) and (2) are related to the measurement target (sample) and operator technique, and steps (3) to (5) are analyzer-related.

Though these factors are independent of each other, the order in which they affect the measurement result is fixed, and problems that occur in a previous step cannot be remedied at a later step.

Problems caused by the measurement target (sample) and operator technique are almost impossible to correct by proper means on the analyzer. Variance will naturally increase if an unstable sample is measured. Problems related to the measurement target (sample) itself cannot be solved at all even by lowering the sensitivity of the analyzer to output more stable data with less variance. Sometimes such a way of solution will even cause measurement to deviate from its original objective.

Moreover, though hardware performance could be brought out to its maximum by the software (particle size distribution calculation algorithm), it would be impossible to expect more beyond that.
For example, on small-power circulation pumps, it is difficult to sufficiently circulate particles having a large particle size and heavy specific gravity. This sometimes results in the particle size distribution shifting in the smaller direction. Moreover, the particle size distribution resolution drops if a diffracted/scattered light sensor with a small number of sensing elements is used. Improvements in resolution cannot be expected even if the number of divisions on the particle size range is ostensibly increased by the software. And, there also exists limitations in resolution due to the diffraction/scattering phenomenon itself even if the number of diffracted/scattered light sensor elements is increased beyond the necessary number.

For Research Use Only. Not for use in diagnostic procedures.

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