Particle counting method
Inventors
Imai, Takehiro • Matsuda, Tomonobu • Abe, Toshiyuki • Nakajima, Tsutomu
Assignees
Publication Number
US-8497989-B2
Publication Date
2013-07-30
Expiration Date
2031-11-30
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Abstract
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.
Core Innovation
The invention provides a particle counting method that precisely counts the number of particles by irradiating a sample gas with light and detecting scattered light from particles using a photoelectric conversion device. It distinguishes between output voltage wave patterns originating from normal particles and those caused by agitation such as floating particles, radiation, or changes in light intensity. The method uses thresholds and timing to discriminate false counts from actual particles.
The problem solved is that conventional particle counters can mistakenly count floating particles drifting in the sensor block or signals caused by radiation and intensity changes of the irradiation light, resulting in false counting. Prior art methods either cannot distinguish overlapping wave patterns of multiple normal particles from floating particles or fail to consider effects from radiation and changes in light intensity, leading to miscounting.
To address these issues, the invention calculates the time difference between the peak of the output voltage wave pattern and a falling detection threshold. If this time difference exceeds a predetermined counting cancellation time, the pattern is not counted as a particle. For wave patterns with multiple peaks, the method also compares the voltage difference between each peak and the preceding dip to a predetermined voltage value, applying similar timing-based discrimination to decide if the pattern represents normal particles or false signals.
Claims Coverage
The patent includes three independent claims covering methods of particle counting incorporating specific timing and voltage difference analyses to discriminate normal particles from false signals.
Time difference calculation for single peak wave patterns
Irradiate sample gas with light and detect scattered light using a photoelectric conversion device. Count particles by size division from the output voltage wave pattern. Calculate a time difference (Ta−T1) between the peak of the voltage wave pattern and a falling detection threshold (A). When this time difference exceeds a counting cancellation time (B), the wave pattern is not counted as a particle.
Time difference and voltage difference calculation for multiple peak wave patterns
Irradiate sample gas with light and detect scattered light with a photoelectric conversion device. Count particles by size division from the output voltage wave pattern which has multiple peaks. For each peak (Px), evaluate if the voltage value difference with the preceding dip (Dx−1) exceeds a predetermined voltage value (C). Calculate a time difference (Ta−Txm) between the falling detection threshold (A) and the point just before a selected peak (Pxm). If this time difference exceeds the counting cancellation time (B), the wave pattern is not counted as a particle.
Voltage difference threshold to identify valid peaks
When the voltage value difference between each peak (Px) and the preceding dip (Dx−1) does not exceed the predetermined voltage value (C), the peak is not considered a particle-generated peak and is thus not counted.
Modifiable threshold parameters
The falling detection threshold (A), the counting cancellation time (B), and the predetermined voltage value (C) used for discrimination are modifiable.
The claims define a particle counting method based on discriminating normal particles from false counts by analyzing timing and voltage characteristics of the output voltage wave pattern, including single and multiple peak scenarios, with modifiable threshold parameters enhancing counting accuracy.
Stated Advantages
Enables precise counting of normal particles by differentiating their output voltage wave patterns from those of floating particles, radiation, or changes in light intensity.
Capable of distinguishing normal particles even when the output voltage wave pattern comprises multiple peaks.
Documented Applications
Management and monitoring of clean rooms in industries requiring controlled clean spaces, such as semiconductor or electronic device manufacturing.
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