How to choose a laser particle counter for cleanrooms
A laser particle counter classifies cleanroom air quality by counting particles by size. This guide explains the key selection criteria: sample flow rate, smallest detectable particle size, number of channels, and compliance with ISO 14644-1 and ISO 21501-4.
View particle countersHow does a laser particle counter work?
A laser particle counter draws in a defined volume of air and passes it through a measuring cell where a focused laser beam illuminates the flow. Each particle scatters the light, and the intensity of that scattered light is used to derive the particle size and count it (light-scattering principle).
Counted particles are sorted by size into channels and scaled to a reference volume (usually 1 m³ or 1 ft³). This yields the cleanroom class per ISO 14644‑1, from ISO Class 1 (extremely clean) to ISO Class 9.
How ISO classes 1 to 9 are defined and how to measure correctly.
Read the guideSample volume and smallest particle size
Two figures decide suitability: the flow rate and the smallest detectable particle size. Classifying the cleaner classes requires evaluating a larger air volume, because statistically only very few particles are present there.
Portable instruments typically run at 28.3 l/min (1 cfm) and draw a 1 m³ sample in about 35 minutes per point. Very clean classes (ISO 1‑3) need instruments sensitive down to 0.1 µm; routine monitoring is often covered by counters from 0.3 or 0.5 µm.
- A higher flow rate clearly shortens the measuring time per point.
- A smaller detectable size raises price and calibration effort.
- The number of sample points depends on cleanroom area (the ISO 14644‑1 square-root rule).
Channels and ISO 21501-4 compliance
Channels are the size classes into which the counter sorts particles simultaneously. Typical instruments offer 4, 6 or 8 channels, for example 0.3 / 0.5 / 1.0 / 5.0 µm. More channels give a finer size spectrum and make trend analysis and troubleshooting easier.
For reliable results the counter must be calibrated to ISO 21501‑4. This standard defines the calibration and testing of light-scattering particle counters, including counting efficiency, size resolution, false-count rate and flow-rate accuracy. Only then are measurements accepted for ISO 14644‑1 classification.
- 4 channels are enough for simple classification and cleaning control.
- 6 to 8 channels help with root-cause analysis and contamination sources.
- Data storage, printer output and interfaces ease GMP documentation.
Frequently asked questions
What flow rate does a particle counter need for ISO 14644-1?
The established standard is 28.3 l/min, that is one cubic foot per minute (1 cfm). This lets the counter draw the 1 m³ sample volume needed per point for classification within a reasonable time.
What does smallest detectable particle size mean?
It states the diameter above which the counter reliably detects particles, typically 0.1, 0.3 or 0.5 µm. Very clean classes such as ISO 1 to 3 require sensitivity down to 0.1 µm, while standard classes are often covered by 0.5 µm.
Why does ISO 21501-4 matter?
This standard governs the calibration of light-scattering particle counters, including counting efficiency, size resolution and flow-rate accuracy. Only an instrument calibrated to ISO 21501‑4 delivers results accepted for ISO 14644‑1 classification.
How many channels should a particle counter have?
For pure classification 4 channels are often enough. For trend analysis, troubleshooting and identifying contamination sources, 6 to 8 channels are advantageous because they provide a finer size spectrum.
Looking for the right particle counter?
We supply portable and fixed laser particle counters with ISO 21501-4 calibration, matched to your target cleanroom class per ISO 14644-1.
Calibrated to standard
Instruments with a valid ISO 21501-4 certificate.
Reliable classification
Suited to ISO 14644-1, class 1 to 9.
Right sensitivity
From 0.1 to 5 µm for every target class.
Expert advice
Cleanroom specialists support your selection.