Light scattering particle counter

Inventors

SHIMMURA, Masaki • Imai, Takehiro • TABUCHI, Takuya

Assignees

Rion Co Ltd

Abstract

A light scattering particle counter that improves the signal-to-noise ratio by attenuating the high frequency noise component while suppressing the attenuation of the signal component by irradiating a sample fluid with a laser beam La to form a particle detection area, detecting a particle with a multi-channel light detecting element that receives scattered light Ls from a particle passing through the particle detection area, and with low pass filters having time constants τc, τm, τe that are set to depend on beam diameter of the laser beam La and flow velocity of the fluid which flows through each divided area, to count particles in the sample fluid.

Core Innovation

The invention is a light scattering particle counter designed to improve the signal-to-noise (SN) ratio by attenuating the high frequency noise component while suppressing attenuation of the signal component. This is achieved by irradiating a sample fluid with a laser beam to form a particle detection area and detecting particles passing through this area with a multi-channel light detecting element that receives scattered light from the particles. The invention employs low pass filters with time constants set based on the beam diameter of the laser beam and the flow velocity of the fluid in each divided detection area, enabling particle counting in the sample fluid.

The problem addressed relates to conventional light scattering particle counters where scattered light from the sample fluid itself generates high frequency noise that overlaps the output signal from particles. Additionally, the flow velocity of the sample liquid and the beam diameter of the laser differ across the particle detection area, resulting in variation in signal peak height and duration. When conventional low pass filters have a single time constant, optimizing between noise attenuation and signal preservation for all areas is challenging, leading to reduced detection sensitivity and SN ratio especially near the wall surfaces where flow velocity is slower and signal pulses are broader and weaker.

The invention solves this by using a multi-channel light detecting element to divide the particle detection area into multiple sections, each corresponding to a detector element, and by setting the time constant of low pass filters processing each channel's output signal to values that correspond to local beam diameter and flow velocity. This individualized filtering allows for minimal attenuation of signal components regardless of position in the detection area while sufficiently reducing high frequency noise. As a consequence, the SN ratio and particle detection sensitivity are improved across the entire particle detection area compared to conventional counters.

Claims Coverage

The patent discloses two independent claims covering key inventive features related to a light scattering particle counter configured for improved noise filtering and particle detection.

These inventive features enable adaptive filtering of the high frequency noise in the output signals from divided detection areas based on their specific characteristics, enhancing signal preservation and thereby improving the particle detection sensitivity and signal-to-noise ratio throughout the particle detection area.

Stated Advantages

Documented Applications