CFC False Count Reduction via Drain Segmentation
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Solution Overview
Problem
Contemporary Condensation Particle Counters (CPCs) experience false-particle counts due to the drainage of working fluid, which creates bubbles and are detected as particles, especially at higher volumetric sample flow rates, leading to performance issues in clean environments like semiconductor clean rooms where stringent false count rates are required.
Innovation Solution
The design incorporates techniques and structures to reduce or eliminate false-particle counts by managing the drainage of working fluid, including the use of a removable wick cartridge with a drain sidecar and water sensors to prevent excess water from forming bubbles or empty droplets, and optional electronic filtering to differentiate actual particles from false counts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If gravity-based drainage is used for working fluid, then device complexity is reduced, but false-particle counts increase due to bubble formation at higher flow rates
Solution Approach 1:
The CPC is divided into separate functional sections: a growth tube section and a drainage section. The drainage section includes a drain reservoir positioned below the growth tube, allowing working fluid to drain separately from the particle detection zone. This segmentation prevents bubbles formed during drainage from entering the optical detection path, reducing false counts while maintaining simple gravity-based drainage.
Solution Approach 2:
The drainage system utilizes vertical positioning (dimensional change) by placing the drain reservoir at a lower elevation than the growth tube. This height difference creates a separate drainage dimension that isolates the bubble formation zone from the horizontal particle detection path, allowing gravity drainage without compromising measurement reliability.
2Productivity
If volumetric sample flow rate is increased, then particle detection speed is improved, but bubble formation increases leading to higher false counts
Solution Approach 1:
The harmful effect of bubble formation is extracted and isolated from the particle detection process. By directing working fluid drainage into a separate reservoir positioned below the growth tube, bubbles form and accumulate in the drainage section rather than the detection section. This allows high flow rates for productivity without proportionally increasing false counts in the measurement zone.
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 significantly reduces false-particle counts, enhancing the performance of CPCs to meet stringent clean room requirements by minimizing internally generated counts, thereby improving the accuracy of particle detection in clean environments.
Implementation Method 1
Condensation Particle Counters (CPCs) have different mechanisms to drain the working fluid out of the growth tube or wick
Implementation Method 2
Most contemporary CPCs rely on gravity to drain the working fluid
Data Source
AI summary
Various embodiments include methods of reducing false-particle counts in a water-based condensation particle counter (CPC). One embodiment of a method includes delivering water into one or more wicks, sensing an excess volume of water delivered to the wicks, collecting the excess volume of water into a collection reservoir, and draining the excess volume of water from the collection reservoir. Other methods and apparatuses are disclosed.