Particle sizing data: How to correlate results of different measuring instruments
Whether you ship or receive a dry bulk material, its particle size and shape must meet the application spec. This requires verifying that these properties are identical when the material is shipped [from you or another vendor] and received [by you or another user]. When measurements differ, it could mean that the powder has changed -- such as by compacting during shipping or by forming agglomerates resulting from excess humidity. But often, the particles are identical; the sizing instruments at the shipping and receiving ends just give different results. This article explains why different instruments yield different sizing results, how to minimize the differences, and how to correlate results from different instruments. Special problems with optical instrument sizing results are also discussed.
Instruments that measure particle properties operate in one of two ways: by directly observing and measuring the particles or by measuring the way energy interacts with the particles. The results produced by the latter type can be strongly affected by particle size, shape, and other properties. Thus, depending on which instruments are used, interfacility data [results measured at different facilities] and intrafacility data [results measured in the same facility by different instruments or by the same instrument using different techniques] can differ markedly.