Smoke Detector External Sampling Multi-Wavelength Ambient Light Correction
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Solution Overview
Problem
Smoke detectors with external sampling volumes face challenges in distinguishing smoke particles from ambient light and nuisance particles, leading to false alarms or missed responses due to difficulties in isolating signals and distinguishing particle types.
Innovation Solution
A smoke detector employing a proximity sensor with light emitters and detectors that emit and measure light at different wavelengths, combined with an ambient-light sensor, to differentiate between smoke and nuisance particles by analyzing the scattering behavior and ambient light corrections, allowing for accurate identification of smoke particles and obstructions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an external sampling volume is used to eliminate internal sensing chamber and reduce lag time, then the Available Safe Egress Time is increased and response speed is improved, but the difficulty of isolating scattered light signal from ambient light signal increases
Solution Approach 1:
The detection system is segmented into multiple independent optical paths: a first optical path for detecting scattered light from smoke particles and a second optical path for detecting ambient light. This segmentation allows the system to separately measure and process signals from different sources, resolving the contradiction between fast response and signal isolation.
Solution Approach 2:
An ambient light sensor acts as an intermediary device that measures ambient light levels and provides correction data to the smoke detection algorithm. This intermediary enables the system to compensate for ambient light interference while maintaining fast response to smoke particles.
2Device complexity
If external sampling volume is used to enable flush mounting and aesthetic appearance, then the device complexity is reduced and installation is simplified, but the difficulty of distinguishing smoke particles from nuisance particles increases
Solution Approach 1:
Different wavelengths of light are used to probe particles with different local optical properties. The system measures light scattering at multiple wavelengths (e.g., blue and red) to capture the wavelength-dependent scattering characteristics that differ between smoke particles and nuisance particles, enabling precise distinction.
Solution Approach 2:
The system changes the optical parameters by using multiple wavelengths and measuring both scattered light intensity and wavelength distribution. This parameter expansion provides additional discrimination dimensions beyond simple light detection, allowing accurate distinction between particle types.
3Device complexity
If single wavelength light detection is used to simplify the device structure, then the device complexity is reduced, but the ability to distinguish smoke particles from nuisance particles deteriorates
Solution Approach 1:
The system transitions from single-wavelength detection to multi-wavelength detection, adding the wavelength dimension to the measurement space. This dimensional expansion enables the system to capture spectral scattering characteristics that provide particle type discrimination while maintaining relatively simple optical components.
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 solution reduces false alarms and response delays by accurately distinguishing smoke particles from nuisance particles and ambient light, enhancing the detection efficiency and reliability of smoke detectors with external sampling volumes.
Implementation Method 1
emitting light outside its housing and detecting light scattered back into the housing by smoke particles located within the sampling volume
Implementation Method 2
uses an ambient-light sensor to measure and compensate for the ambient light level
Data Source
AI summary
In accordance with certain embodiments, a smoke detector determines the presence of smoke particles outside its housing based on measurements of light detected at different wavelengths and corrected based on an ambient light level.