Primary standards
Measurement and particle-counter sources
- ISO 21501-2:2019. Light-scattering liquid-borne particle counter calibration and verification. Official ISO page.
- ISO 21501-3:2019. Light-extinction liquid-borne particle counter calibration and verification. Official ISO page.
- ISO 21501-4:2018. Light-scattering airborne particle counter for clean spaces. Official ISO page.
- NIST Policy on Metrological Traceability. Definition, responsibilities and claim boundaries. NIST policy.
- NIST Metrological Traceability FAQ. Clarifies that only measurement results are traceable and that NIST does not endorse products. NIST FAQ.
- NIST SRM listings. Includes polystyrene sphere reference materials such as SRM 1691 and SRM 1961. NIST SRM page.
Applied Physics product sources
Current manufacturer pages used in this release
- 20–900 nm PSL sphere family
- Approximately 1–160 µm PSL sphere family
- HEPA Test PSL particles
- Ezy-Cal count precision standards
- Particle size standards portfolio
- Applied Physics microspheres overview
Known limitation: the Applied Physics website contains legacy duplicates and occasional conflicting values. The current quote, controlled document and lot certificate must govern the transaction.
Use of sources
No source replaces the complete procedure
These links support educational summaries and claim controls. Users must obtain the full applicable standard, instrument documentation and current product documentation needed for their work.
Applied Physics technical pathway
Match the standard to the measurement—not the other way around.
Send the instrument, medium, target size, concentration, certificate and packaging requirements to Applied Physics for a technical recommendation.