Optical Particle Counter Velocity Measurement
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Solution Overview
Problem
Existing optical particle counters are complex and costly due to the need for precise control of air flow velocity to detect particles accurately, which often requires pumps or fans, and suffer from edge effects that lead to unreliable particle sizing.
Innovation Solution
The apparatus calculates a parameter related to particle velocity by processing the intensity and time of flight of scattered radiation, allowing for accurate measurement of particle velocity and concentration without the need for precise air flow control, using a processing circuit to determine the velocity of particles and adjust the gas flow generator accordingly, or eliminating the need for one.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pumps or fans are used to control air flow velocity, then particle detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical flow control system (pumps or fans) with an optical measurement system. The particle velocity is determined by measuring the time of flight of particles through the detection zone and combining this with light scattering intensity measurements. This substitution eliminates the need for complex mechanical flow control while maintaining measurement accuracy.
Solution Approach 2:
The system uses the particles themselves as tracers to measure flow velocity. By tracking the time it takes for particles to traverse the known detection zone and measuring their light scattering properties, the system self-determines the air flow velocity without requiring external flow control devices. The particles provide the information needed to compensate for velocity variations.
2Measurement precision
If pumps or fans are used to control air flow velocity, then particle detection accuracy is improved, but cost increases
Solution Approach 1:
The patent replaces expensive mechanical flow control equipment with a cost-effective optical measurement approach. The velocity determination is achieved through processing light scattering signals and time of flight measurements, which uses standard optical components and signal processing rather than costly pumps or precision flow controllers.
Solution Approach 2:
The system uses inexpensive particles from the air sample itself as measurement tracers, rather than requiring expensive flow control infrastructure. The particles naturally present in the air stream serve as the measurement medium, eliminating the need for costly flow generation and control equipment.
3Measurement precision
If a narrow column of air is used for particle detection, then particle sizing accuracy is improved, but edge effects cause unreliable measurements at the boundaries
Solution Approach 1:
The system uses feedback from the light scattering intensity measurements to correct for edge effects. By measuring the intensity of scattered light and combining this with time of flight data, the system can identify and compensate for particles passing through edge regions of the detection zone, ensuring reliable sizing across the entire field of view.
Solution Approach 2:
The patent changes the parameters used for particle characterization from relying solely on spatial position to using a combination of time of flight and light scattering intensity. This parameter change allows the system to accurately size particles regardless of their position in the detection zone, overcoming the edge effects that plague traditional narrow-column systems.
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 reduces the complexity and cost of optical particle counters by enabling accurate particle sizing and concentration measurement without requiring expensive flow control systems, while maintaining reliable particle detection and concentration calculations.
Implementation Method 1
a radiation source configured to generate a beam of radiation
Implementation Method 2
detect particles individually from light scattered as they pass through a relatively shallow light beam
Data Source
Figure 1
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Figure 5
AI summary
An optical particle counter determines the velocity of particles passing through a particle detection zone, and thereby the velocity of gas flow, from both the measured time of flight of discrete particles and also the size of intensity peaks of scattered light. This is used to determine particle concentration and may be used to control an optional fan.