How Particle Counters Work?

Different than what we assume, particle counters are not counting particles. They are all light-scattering airborne particle counters and they focus on light that is scattered from the particles. Instead of a camera that "sees" particles, particle counters have a laser to scatter light and a photodiode to "define" equivalent diameter. Let's see how...

How Light Scattered Airborne Particle Counter (LSAPC) Work?

The light-scattered particle counter is an instrument based on the principle of light scattering from particles. In order to meet current standards such as ISO 14644-1:2015, particle counters can count 0.1 microns up to 5 microns. Depending on application this size can go up to 100 microns.

Air enters the chamber inside the particle counter called the laser block, which is the main part of the particle counter.? Like an item shining in front of a headlight during the night, particles that are passing in front of a laser beam illuminate.

Depending on the mechanism, this light is redirected or absorbed. As a factor of illumination, particles can be identified by size and total numbers. The light that meets the particle is scattered in specific directions in relation to the original direction and has a unique signature that relates to the size of the particle and allows the particle counter to determine the size and quantity of individual particles.

What if a piece of fiber enters a particle counter laser block, vertical size as 100 microns or just a section less than 1 micron?

That's the most critical question! In reality, particles are not always sphere-like. They have different dimensions in different cross-sections. So better to know "Equalent Area Size";

Equivalent Size Area

A particle is a 3-dimensional object, and only if it is spherical can its exact size be determined by its diameter. Equivalent diameter is normally based on the physical properties measured, such as light scattering, where the amount of light scattered by a particle is related to the size of the particle. In order to ensure particle sizes in particle counters, synthetic particles such as PSLs (polystyrene latex) are widely used in industry (this is what we used in our calibration labs! perfect spherical particles) With exact diameter, PSLs are helping us to simulate particle light scattering so we can get particle counters calibrated based on this data and set equivalent particle diameter as reference diameter.

There are two mechanisms that particle counters work; light blocking and light scattering. Both methods have similarities such as using flow path, light sources /mostly laser) and detectors such as photodiodes. When a particle is illuminated with a laser, the radiation is scattered at a frequency like that of the illuminated light. Scattered lights from each particle are controlled by lenses and collected by a concave mirror. This beam directly focused on the photodiode to convert photonics to electric pulses.

Light scattering airborne particle counters are the required technology for non-viable particle counting used in the testing, validation and environmental monitoring of cleanrooms and clean spaces. Light-blocking systems are using “particle shadow” to define particle size. Parallel to particle size, shadow size changes over the photodiode and light-blocking technology can define particle size based on the photodiode electric signal.

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