If your cleanroom process, testing, or lab requires monitoring airborne particles down to .1 micron, the best solution is to use a He-Ne laser based particle counter, which offers increased accuracy in the .1-10 micron particle size range over traditional laser diode based particle counters.
The Helium-Neon (HeNe) gas laser produces an extremely bright red <!–[if gte vml 1]>
Choosing the best particle counter for a cleanroom can be a daunting task. However, there are a number of areas you can consider to ensure an optimal choice for your cleanroom environment.
Understanding How a Particle Counter Works
The first step to choosing a particle counter is understanding how the instrument works. An aerosol particle counter, for example, works on the principal of either light scattering or light blocking. An aerosol stream is drawn through a chamber with laser-based or white light. Then when the light source illuminates the particle, the light is rerouted or absorbed. Light scattered by a single particle in a specific direction in relation to the original direction creates a unique signature relating to the particle’s size. And this is what enables the sizing and counting of individual particles.
Generally, particle counters are comprised of four distinct components. One of the main elements is a light source, such as a helium-neon laser, solid state laser diode and high intensity light. The other components are photo detection electronics, sample flow system and counting electronics.
These components may be positioned completely within the particle counter or in a remote location. During the particle counting process, the light is collimated to beam on the sample volume. Then as particles are transmitted through this volume, they scatter the light. The amount of light that scatters is measured by the photo detection system. And the sizes of the particles are determined by the concentration of the scattered light.
Usage an Important Consideration
Next, it’s also important to factor in how the particle counter will be used when choosing a device suitable for your situation. Here are some essential questions to explore:
Particle Counter Specifications
Particle counters are often selected based on their unique specifications. Most manufacturers use the same design principles, but their counters differ according to the specific details of the design.
Therefore, it’s important to consider major specifications like sample sensitivity and flow rate. Sensitivity relates to the smallest size particle that can be detected by the counter. Flow rate is the amount of air that passes through the particle counter. This rate is normally represented in cubic feet, with common flow rates being 1.cfm and o.1cfm. The greater the flow rate, the larger the pump required to pull the air—which translates into the need for a bigger particle counter.
Other important specifications to evaluate when choosing a particle counter include size range, number of counting channels, the durability of the laser or laser diode, the lifetime of the light source, and the ability to hold calibration.
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Many people are confused about the difference between cleanroom certification and cleanroom monitoring. But their requirements and standards make them distinctly dissimilar/different.
A cleanroom is essentially a modular environment in which various factors are kept under strict control, including airborne contaminants, the temperature, relative humidity, differential pressure and static electricity. In addition, cleanrooms are evaluated based on several levels of cleanliness referred to as classes. When a cleanroom is certified to a certain class, it must operate according to standards that meet or exceed the performance of that class under a specific occupancy status.
Certification vs. Monitoring Cleanroom certification, essentially, involves checking the room for various parameters to ensure that it is built to a specific set of requirements. The room is also routinely retested to the same factors to ensure the standards have not changed. On the other hand, cleanroom monitoring applies a broader approach. The monitoring of a cleanroom is done to ensure that:
Cleanroom classification and class limits are established in ISO 14644-1. However, specifications for testing and monitoring to prove continued compliance are covered in ISO 14644-2. More specifically, ISO 14644-2 determines the type and frequency of testing required to conform to the standard. Some tests are mandatory; others are optional.
Compliance Demonstration ISO 14644-2 also dictates that cleanroom particle classifications in areas cleaner than ISO class 5 require a time interval of at least six months between demonstrations of adherence to ISO 14644-1. And any areas that are less clean than ISO Class 5 require a 12-month maximum interval between displays of compliance.
In practical terms, demonstrations of compliance may be done more frequently than the maximum intervals specified in ISO 14644-2. The more often a show of compliance takes place, the smaller the loss of time and materials in the case of compliance failure. But if a cleanroom does not meet its designated standard, this can create a problematic situation. The quality of all products or processes performed in that area since the last demonstration of compliance will be suspect. Maintaining a Constant Monitoring Plan If an ongoing monitoring plan is developed for airborne particles and air pressure differential, changes can be made to the schedule of the particle counting certification testing. The monitoring plan should be determined by a risk assessment based on the type of facility, possible causes of contamination and impact of corruption on the product or process performed in the facility.
Keep in mind that it’s impractical and expensive to create minimum monitoring points based solely on the area of room in square meters. This approach works in certification, but coverage and testing guidelines must be established regardless of process and risk assessment. However, in a monitoring program, risk assessment is critical to determining what and where to monitor. To make better choices about what and where particle monitoring should be performed, you should enhance your experience with different tooling and facilities, as well as your understanding of particle generation and cleanroom particle counters. If you have additional questions or feedback on this topic, please click on the comments button below or call us at 877-688-2703 |
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