Particle counter
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A particle counter is an instrument that detects and measures individual particles in a fluid. Particle counters are used to determine the quality of the fluid being sampled. Applications of particle counters are separated into two primary categories:
- Aerosol particle counters
- Liquid particle counters
Aerosol particle counters
Aerosol Particle Counters are used to determine the air quality by counting and sizing the number of particles in the air. This information is useful in determining the amount of pollutants inside a building or in the ambient air. It also is useful in understanding the cleanliness level in a controlled environment. A common controlled environment aerosol particle counters are used is a cleanroom. Cleanrooms are used extensively in semiconductor manufacturing, biotechnology, pharmaceutical, disk drive, aerospace and other fields that are very sensitive to environmental contamination. Cleanrooms have defined particle count limits. Aerosol particle counters are used to test and classify a cleanroom to insure its performance is up to a specific cleanroom classification standard. Several standards exist for cleanroom classification. The most frequently referred to classification is from the United States. Though originating in the United States, the standard Federal Standard 209E was the first and most commonly referred to. This standard was replaced in 1999 by an international standard, however it remains today the most widely referenced standard in the world.
US FED STD 209E cleanroom standards
| Class | 0.1 µm | 0.2 µm | 0.3 µm | 0.5 µm | 1 µm | 5 µm |
| 1 | 35 | 7 | 3 | 1 | ||
| 10 | 350 | 75 | 30 | 10 | 1 | |
| 100 | 3500 | 750 | 300 | 100 | 10 | 1 |
| 1,000 | 1,000 | 100 | 10 | |||
| 10,000 | 10,000 | 1,000 | 100 | |||
| 100,000 | 100,000 | 10,000 | 1,000 |
The Replacement standard is ISO 14644-1 and is meant to completely replace Federal Standard 209E. Each of these standards represents the maximum allowable number of particles in a unit of air. The typical unit is either cubic feet or cubic meters. The particle counts are always listed as cumulative.
ISO 14644-1 cleanroom standards
| particle/m³ | ||||||
| Class | 0.1 µm | 0.2 µm | 0.3 µm | 0.5 µm | 1.0 µm | 5.0 µm |
| ISO 1 | 10 | 2 | ||||
| ISO 2 | 100 | 24 | 10 | 4 | ||
| ISO 3 | 1,000 | 237 | 102 | 35 | 8 | |
| ISO 4 | 10,000 | 2,370 | 1,020 | 352 | 83 | |
| ISO 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | 29 |
| ISO 6 | 1,000,000 | 237,000 | 102,000 | 35,200 | 8,320 | 293 |
| ISO 7 | 352,000 | 83,200 | 2,930 | |||
| ISO 8 | 3,520,000 | 832,000 | 29,300 | |||
| ISO 9 | 35,200,000 | 8,320,000 | 293,000 | |||
Cleanroom class comparison
| ISO 14644-1
| FED STD 209E |
| ISO 3
| 1 |
| ISO 4
| 10 |
| ISO 5
| 100 |
| ISO 6
| 1,000 |
| ISO 7
| 10,000 |
| ISO 8
| 100,000 |
Liquid particle counters
Liquid Particle Counters are used to determine the quality of the liquid passing through them. The size and number of particles can determine if the liquid is clean enough to be used for the designed application. Liquid particle counters can be used:
Quality of drinking water
Cleaning solutions
Cleanliness of power generation equipment
Determine the cleanliness of parts prior to manufacturing
Cleanliness of injectable drugs
Detection methods
Two methods are used for detecting and measuring particles. Light Blocking and Light Scattering. The Light Blocking method is useful for detecting and sizing particles greater then 1 micrometre in size and is based upon the amount of light a particle blocks when passing through the detection area of the particle counter.
The Light Scattering Method is used for detecting and sizing particles from 0.05 micrometres and larger. This technique is based upon the amount of light that is redirected by a particle passing through the detection area of the particle counter. This redirection is referred to as light scattering.
Terms
Particle:''' Solid Material Ranging in Size from 5nm to 100µm
Particle Counter: Device Used to Count and Size Individual Particles
Sample Time: Duration of Sample
Sample Flow Rate: Volume of Fluid Passing Through the Particle Counter per Unit Time ''Cubic foot / minute Milliliter / minute''
View Volume (Percentage): Percentage of Sample Measured
Sample Volume: Sample Flow Rate X View Volume X Sample Time
Counting Efficiency: Comparison of Particle Counter Under test to More Sensitive Instrument
Sensitivity: Minimum Detectable Particle Size
Zero Count Level (False Count): Number of False Counts When Inlet Fluid Stream is Particle Free
Concentration Limits: Maximum Particle Concentration Permitted for Particle Counter Operation allowing no more than a 5% Coincidence Error
Coincidence Error: Counting Error from more than one particle entering view volume at the same time
Channels: Particle Sizing Bins
Cumulative: Mode of Particle Counter Operation Indicating Particle Counts for the Particle Channel Size of Interest and all Particles Larger
Differential: Mode of Particle Counter Operation Indicating Particle Counts for the Particle Channel Size of Interest up Until The Next Larger Particle Size Channel
Other types of particle counters:
Remote Particle Counters
Small particle counters that are used to monitor a fixed location typically inside a cleanroom or Minienvironment to continuously monitor particle levels 24 hours / day seven days a week. These smaller counters typically do not have a local display and are connected to a network of other particle counters and other types of sensors to monitoring the overall cleanroom performance. This network of sensors is typically connected to a Facility Monitoring System (FMS), Data Acquisition System or [Programmable Logic Controller].
This computer based system can integrate into a database, alarming and may have e-mail capability to notify facility or process personnel when conditions inside the cleanroom have exceeded predetermined environmental limits. Remote particle counters are available in several different configurations, from single channel to models that detect up to 8 channels simultaneously. Remote particle counters generally have a particle size detection range from 0.1 to 10 micrometres and may feature one of a variety of output options including; [mA 4-20 mA], [RS-485] [Modbus] and pulse output.
Manifold particle counters
Modified aerosol portable particle counter that has been attached to a sequencing sampling system. The sequencing sampling system allows for one particle counter to sample multiple locations, via a series of tubes drawing air from up to 32 locations inside a cleanroom. Typically less expensive then utilizing remote particle counters, however each tube is monitored in sequence.
Handheld particle counters
Small self contained particle counter that is easily transported and used. Though lower flow rates of 0.1 ft³/min (one 10th of a cubic foot) (0.2 m³/h) than larger portables with 1 ft³/m (2 m³/h), handhelds are useful for most of the same applications.
External links
- [Controlled Environments Magazine]
- [BPA - Particle Counters]
- [Choosing a Handheld Particle Counter (blog)]
- [How to Select a Particle Counter]
- [Lighthouse Worldwide Solutions]
- [cleanrooms Magazine]
- [IEST]
- [Kanomax USA Inc]
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