Laser Particle Counter

A particle counter is an instrument that detects and counts particles. By its very nature a particle counter is a single particle counter, meaning it detects and counts particles one at a time. The nature of particle counting is based upon either light scattering, light obscuration, or direct imaging.

A high energy light source is used to illuminate the particle as it passes through the detection chamber. The particle passes through the light source (typically a laser or halogen light) and if light scattering is used, then the redirected light is detected by a photo detector. If direct imaging is used, a halogen light illuminates particles from the back within a cell while a high definition, high magnification camera records passing particles.

Recorded video is then analyzed by computer software to measure particle attributes. If light blocking (obscuration) is used the loss of light is detected. The amplitude of the light scattered or light blocked is measured and the particle is counted and tabulated into standardized counting bins.


Fig - The laser beam passes through the walls of a glass container or a flow-thru cell

Particle counter uses as its basic light source a laser diode (650nm wavelength). The beam from this laser is spatially filtered and focused by a lens assembly to form a small and well-defined illuminated volume within the liquid being inspected. A scanning mechanism provides a circular displacement of this illuminated volume at a constant rate of speed. As the illuminated volume moves across a particle suspended in the liquid, some light from the beam will be scattered. This is known as Fraunhofer diffraction.

Most of this scattered light is in the near-forward direction and is collected by the optical system of the photodetector assembly. The flash of light striking the photodetector will cause an electrical pulse in the preamplifier connected to the photodetector. The amplitude and width of this pulse are a function of the size of the particles, The analog signals generated by the light pulses are routed to a computer and digitized.

Applications :

  • Quality control of hydraulic fluids and oils.
  • De-ionized water and acid testing for semiconductor manufacturing.
  • Vial and ampule inspection for pharmaceuticals.
  • Silt and sediment sizing.
  • Oceanographic particles.
  • Sizing for corrosive chemicals and solvents.
  • Cell counting where physical force would damage particles.
  • Particle agglomeration studies.
  • Water treatment plants.
  • Filter efficiency control.
  • Powdered solids manufacturing.