How is particle size (100--1000 µm) used to design a Knapp challenge kit?

Particle size is the backbone of Knapp kit design because detectability depends on size: a challenge kit uses a graded range, typically 100--1000 µm, to establish the probability of detection (PoD) across the inspection process.

The human eye reliably detects visible particulates down to roughly 100--150 µm under controlled lighting, with smaller particles detected less consistently --- so a kit that spans 100 µm, 200 µm, 300 µm, 500 µm, 800 µm and 1000 µm maps the full PoD curve from "rarely seen" to "almost always seen." The Knapp method compares an inspection process against a manually established baseline using these known-probability units: a qualification (POD) set typically runs 10--15% defect units with the remainder certified defect-free "blank" units, and includes several sizes of each contaminant so the result is statistically meaningful. FTI's particulate defect matrix, for example, places each particle and fibre type across the size columns, totalling 160 defective and 60 defect-free components.

FTI designs challenge sets and probability-of-detection kits around this sizing logic so manual, semi-automated, and automated systems are qualified across the real range of detectability under USP <1790>.