Particle Counting Method Using Voltage Wave Pattern Time Difference
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Solution Overview
Problem
Existing particle counting methods in clean rooms, such as those in the semiconductor industry, face issues with false counting due to floating particles and interference from radiation and light intensity changes, which are not accurately distinguished from normal particles, leading to miscalculations.
Innovation Solution
The method involves using a photoelectric conversion device to detect scattered light from particles, calculating time differences in output voltage wave patterns to differentiate between normal particles and floating particles or light interference, with adjustable parameters to refine counting accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light scattering type particle counter is used to count particles in clean rooms, then particle detection capability is provided, but false counting occurs due to floating particles and radiation interference
Solution Approach 1:
The system dynamically adjusts the baseline level and detection thresholds based on real-time monitoring of the detection output signal. The baseline is continuously updated during periods without particle detection, allowing the system to adapt to changing environmental conditions such as radiation intensity and light source fluctuations, thereby reducing false counting while maintaining detection sensitivity
Solution Approach 2:
The invention changes the parameters used for particle identification from simple threshold-based detection to a combination of threshold level, continuance time, and rate of change analysis. By monitoring how long a signal exceeds the threshold and how rapidly it changes, the system can distinguish between genuine particle signals and false signals from radiation or floating particles
2Reliability
If the continuance time of wave pattern is used to identify floating particles, then false counting from floating particles is reduced, but duplicated wave patterns of normal particles cannot be distinguished
Solution Approach 1:
The system uses multiple criteria (threshold level, continuance time, and rate of change) rather than relying solely on continuance time. By requiring signals to meet multiple conditions simultaneously, the system avoids the pitfall of misidentifying normal particles with prolonged detection as floating particles, while still effectively filtering out false signals
3Device complexity
If radiation and light intensity changes are not considered, then particle counting is simplified, but false counting occurs from these interference sources
Solution Approach 1:
The system performs self-calibration by continuously monitoring the detection output signal and automatically updating the baseline level without external intervention. This self-adjusting mechanism allows the system to compensate for radiation interference and light intensity changes autonomously, maintaining counting accuracy without adding complex external calibration equipment or procedures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise counting of particles by distinguishing normal particles from floating particles and light interference, ensuring accurate particle size division and reducing false counting errors.
Implementation Method 1
detects a scattered light from a particle included in the sample gas by a photoelectric conversion device
Implementation Method 2
irradiating a sample gas with light and detecting a scattered light from every particle contained in the sample gas
Data Source
AI summary
A particle counting method that can count the number of the particles precisely. The method discriminates a wave pattern of the scattered light from a normal particle (subject of the counting) and a wave pattern of the light scattered by the agitation such as a floating particle, a radiation or changes in the intensity of the light. In one embodiment, a method for counting particles is disclosed which irradiates a light to a sample gas, detects a scattered light from a particle included in the sample gas by a photoelectric conversion device, counts the number of the particles of every particle size division by the output voltage wave pattern of the photoelectric conversion device, calculate a time difference (Ta−T1) from a point (T1) being a peak of output voltage wave pattern and a point (Ta) being a falling detection threshold (A), when the time difference (Ta−T1) is beyond counting cancellation time (B), the output voltage wave pattern is not counted as a particle.