Particle Counter Terminology and Standards
Your need to find the best particle counter for your application depends on monitoring environment, communications, desired flow rate, and the particle sizes of interest. Don’t know where to start? Read on for an overview of the basics for choosing the method to monitor your process air.
Common Specs: Flow rate and Sample Volume
All airborne particle counters sample air at a specified volumetric flow rate, or the speed of air being pulled through the particle counter. Flow rate units are usually in cubic-feet-per-minute (CFM) or liters-per-minute (LPM). Particle counters are calibrated to sample at their specified flow rates, and sizing accuracy is dependent on that flow rate.
To meet classification standards, particle counters sample defined volumes of air. This provides qualified, statistical significance to particle count data. For example, to meet ISO 14644-1:2015 requirements, particle counters need to sample 1 cubic meter. If a particle counter has a flow rate of 1 CFM, the sampling time will be 35 minutes to pull in enough air to equal 1 cubic meter. Faster flow rates can achieve ISO specifications in less time. A particle counter with a flow rate of 50 LPM can sample one cubic meter in only 20 minutes.
What is ISO?
The International Organization for Standardization (ISO) provides standards for industrial and commercial systems. The ISO 14644-1 standard is for classifying air cleanliness in cleanrooms, and ISO 14644-2 for monitoring air cleanliness in cleanrooms. They ensure everyone has the same frame of reference when looking at their monitoring data.
To meet ISO cleanroom classifications, the particle counter’s maximum concentration must be capable of exceeding ISO limits. For example, monitoring 0.1 µm particles in Class 5 requires the particle counter to have a maximum concentration greater than 100,000 particles per cubic meter (2,841 particles per cubic foot). For 0.3 µm particles, the counter needs a maximum concentration greater than 10,200 particles per cubic meter (290 particles per cubic foot). These limits are easily achieved with most modern particle counters. Note that there is no ISO specification for 0.1 µm particle counts higher than ISO Class 6, so a 0.1 µm particle counter is not required for those applications.
Solutions to aid in attaining cleanroom certification are listed in the following table.
Cleanroom Certifying Solutions
|0.1 µm||1.0 CFM||Lasair® III 110 Aerosol Particle Counter|
|0.3 µm||1.0 CFM||Lasair III 310C Aerosol Particle Counter|
|0.5 µm||3.56 CFM||Lasair III 5100 Aerosol Particle Counter|
Curious about other considerations when looking for an airborne particle counter? Download the full paper here.
Want to read more? Jump to other released posts in this series:
- Part 2 of 4: Types of Monitoring
- Part 3 of 4: Number of Monitoring Locations
- Part 4 of 4: Particles in Process Gasses