What is the best particle counter in a clean room?
Clean room particle counters can vary greatly depending on particle threshold, cost, and characteristics. How do you know if you need a particle counter or what type of particle counter you need to buy? This article covers the basics and facts of particle counters to help you determine the best particle counter for clean room applications.
What is a particle counter?
Particle counter is a device that can detect and count particles separately. There are three main types of particle counters: aerosol, liquid and solid, but only aerosol particle counters directly related to the clean room. So we're going to focus on that. Aerosol particle counters determine air quality by counting particles in the air and determining their size. They are primarily used for cleanroom applications. Because clean rooms have defined particle number limits, use aerosol particle counters to test and classify clean rooms to ensure that they are up to standard.
Type of particle counter
Aerosol particle counters are of two types: optical and condensing. In an optical particle counter, particles pass through a high-energy light source, measure the amplitude of the scattered or blocked light and count the particles. Optical particle counter provides many options for detecting and measuring particles. They are shading, light scattering and direct imaging. The method of blocking light is based on the amount of light that can be captured when particles are larger than microns and the amount of light that can be captured when particles pass through the source. Light scattering techniques can detect smaller particles based on the amount of light that is redirected through the light source. Direct imaging USES light from the laser as a source, illuminating the passing particles like an automatic microscope and measuring their area.
What is the Condensed Particle counter (CPC)?
Condensing particle counters count aerosol particles by first expanding them and using them as nucleating centers to generate droplets in the supersaturated gas. The condensate particle counter can measure 2 nm particles, but the optical particle counter cannot. Particle counters come in different sizes. There is a handheld foam, a small, portable stand-alone model. Manual particle counters typically have low flow rates, making them ideal for sample testing and small air certification in a clean room. Large portable devices are located in fixed locations and monitor the air 24 hours a day, 7 days a week. The high flow rates of these portable devices make them ideal for sampling large amounts of air.
Considerations when selecting a particle counter
The first is the particle size that needs to be monitored. This is determined by the ISO rating of the clean room. Make sure that the displayed particle counter measures all the particle sizes you need to monitor. For example, particle counters have a size range of 0.3/0.5/5.0 m.
Particle countercurrent and position sensing
The second factor is the flow of the particle counter. To do this, we need the following formula: Vs = 20 / Cnm) x1000. Vs is the minimum single sample size per location. Cnm is the maximum size grade limit assigned to the clean room grade. 20 is a predefined number of particles that can be counted in the clean room category. It calculates the number of liters of air that must be pumped in the clean room. For example, if a grade 4 clean room is required, the maximum particle size is 1.0 m and the maximum concentration is 83 particles/m3 according to the ISO 14644-1 clean room standard. Insert it into the equation Vs = (20/83) x 1000 and Vs = 240.96. Therefore, 240.96 litres of air should be cleared. So if you choose a small handheld particle counter with a flow rate of 2 liters per meter, air sampling takes approximately 120 minutes or 2 hours. Therefore, in this example, it is recommended to find a larger portable particle counter with a higher flow rate.