Instant Air Quality Insights: Portable Particle Counters Are Here!

Handheld particle counters or Portable particle counters are designed to quickly count and measure contaminant particles in cleanroom air, controlled environments, and liquids like chemicals and water. Users often view these devices as simple tools that display results instantly when a button is pressed. However, it's crucial to understand the technology inside the instrument to grasp the significance of the data it produces (what particles are being counted) and to contextualize how particle counters work. Below, we offer a comprehensive explanation of the functioning of laser particle counters.

Particle Counter Light Source

Handheld particle counters commonly used in clean rooms rely on the principle of light scattering. This means they use a very bright light source, typically a laser diode nowadays, to illuminate particles. In the past, they used gas lasers or halogen bulbs emitting white light.

The bright light passes through an optical block containing mirrors and photodetectors. Air samples are drawn through the optical path by a small vacuum pump. When the laser interacts with particles in the air, it causes the light to scatter in various directions. By scattering, we mean the light changes direction unpredictably. (See the image below)

In a handheld particle counter, the elliptical clam shapes shown in the diagram function as mirrors. These mirrors are silvered, positioning the reflecting surface on the interior. When light scatters and contacts these mirrors, they concentrate the scattered light onto one or multiple photodetectors.

Photodetectors

The photodetector transforms the burst of light energy emitted by each particle into an electrical pulse. Measuring the amplitude of this signal and comparing it against a calibration curve allows us to determine the particle's size. Additionally, by tallying the number of pulses, we can establish the quantity of particles, which are categorized into size groups.

The Principle of Handheld Particle Counters 

The concept of light scattering encompasses various physical phenomena. These include:

Additionally, there may be instances of absorption, where particles retain a portion of the light energy. Some particle types may also exhibit effects like phosphorescence. As such, light scattering involves a combination of physical properties related to light and its interaction with particles. This interaction is influenced by factors such as particle composition, refractive index, and the contrast between the particle and its surrounding medium, such as air.

The Accuracy of A Handheld Particle Counters

During operation, the particle counter compares the response it receives from the particle signal to a calibration curve generated using latex spheres. Essentially, it assesses how particles interact with laser light and relates this to an idealized scenario involving latex spheres in the air. It's important to note that particles with different scattering characteristics may appear either smaller or larger compared to the latex standard.

For instance, silicon particles have high reflectivity relative to latex, resulting in significant light scattering and larger sizing. Conversely, particles that absorb light or scatter minimally will appear smaller relative to the latex standard. This highlights the lack of absolute measurement, as particles may fall into larger or smaller size categories based on their differences from the latex standard.

Furthermore, the orientation of particles as they pass through the laser beam impacts their sizing. For instance, a rod-shaped particle presenting its full length to the beam will scatter more light, resulting in larger sizing. Conversely, if the rod exposes only one end, its smaller cross-sectional area will lead to smaller particle sizing.

Here’s What A Sample Results Would Look Like

1. The highest concentration of particles was observed in the 0.3 μm size range, with 207,391  particles per cubic foot.
2. Particle counts decrease as particle size increases, following the expected trend for clean room environments.
3. Overall, the facility maintains acceptable particle levels within specified limits.

Concluding All

Particle counters are great at giving you instant info about how many particles are in a room or near an important process. Other methods, like using filters or microscopes, take a lot longer and are harder.

Handheld particle counters have been really important for making clean room production better. They're fast, clear, and easy to use. Today's machines are really reliable and simple. They work by using light and comparing it to known standards, so you always get accurate results.