Particle Size Distribution Measurement by the Laser Diffraction/Scattering Method Part2

Particle Size Distribution with Laser Diffracted/Scattered Light

Mechanism for Detecting Diffracted/Scattered Light in Detector

  1. The laser beam emitted from the light source is converted to a slightly thicker beam by the collimator.
  2. This beam is irradiated on the sample particle group to be measured.
  3. Diffracted/scattered light is emitted from all particles irradiated by the laser beam, and a light intensity distribution pattern is formed as a result of overlaying these lights.
  4. The light intensity distribution pattern of the forward scattered light is condensed by the lens, and a concentrically-shaped diffracted/scattered image is formed on the detecting plane positioned at a distance equal to the focal distance.
  5. This diffracted/scattered image is detected by the forward diffracted/scattered light sensor (Wing sensor) which is made up of concentrically-placed light-receiving elements.
  6. In addition to the forward scattered light, side and back scattered light also is detected by side and back scattered light sensors.

Sensor for Detecting the Light Intensity Distribution Pattern

This is the Wing sensor used on the SALD Series (3100/2100/7000).

Despite its unique shape, very much like the wings of a bird, it actually functions as an extremely large concentrically shaped sensor for detecting light over a wide range.

This sensor is used to detect the light intensity distribution pattern in the forward direction (laser beam travel direction).

The center section of the Wing sensor comprises 54 element, while the two "wing" sections comprise 11 elements each.

A side scattered light sensor and multiple back scattered light sensors also are used.

All of the sensing elements of the Wing sensor and side/back scattered light sensors are used to accurately detect the spatial light intensity distribution pattern of diffracted/scattered light.

Light Intensity Distribution Data of Diffracted/Scattered Light Detected by the Sensor

The following shows light intensity distribution data actually obtained by the sensors that detect the light intensity distribution pattern of diffracted/scattered light emitted from a particle group.

The overall light pattern and NOT just the intensity detected by each individual sensor element is important.