Size setting error
Compares reported size with the reference response.
Crosswalk
Which ISO 21501 part applies?
| Standard | Instrument method | Typical size range described by ISO | Application context |
|---|---|---|---|
| ISO 21501-2:2019 | Light-scattering liquid-borne particle counter | 0.1–10 µm | Pure water, chemicals and particles in liquids |
| ISO 21501-3:2019 | Light-extinction liquid-borne particle counter | 1–100 µm | Pharmaceutical liquids and other liquid-particle applications |
| ISO 21501-4:2018 | Light-scattering airborne particle counter | 0.1–10 µm | Clean-space classification and airborne particle measurement |
Parameters
Calibration is more than a single size point
Counting efficiency
Evaluates count response at defined size conditions.
Size resolution
Assesses the ability to distinguish particle populations.
Flow and sample volume
Connects count results to the actual volume sampled.
False count
Assesses background or instrument-generated events where applicable.
Maximum concentration
Identifies coincidence or saturation limitations.
PSL selection
Why refractive index matters
ISO 21501-2 notes that a light-scattering liquid counter’s measured particle size depends on the refractive indices of the particles and medium; the result is therefore equivalent to calibration particles in pure water. That is a critical reason not to treat optical size as a geometry-only measurement.
Procedure control: use the exact reference material, medium, preparation and settings required by the applicable method and instrument manufacturer.
Applied Physics pathway
Build the node plan
- Identify ISO part, instrument model and detector method.
- Confirm useful size range and required calibration nodes.
- Choose the correct PSL family and available certified means.
- Confirm concentration and sample preparation.
- Review certificate uncertainty and distribution.
- Run calibration or verification under the controlled procedure.
Source control: Official ISO abstracts define the current scope and typical ranges. ISO 21501-2 ISO 21501-3 ISO 21501-4
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.