Optical Hazard Detector Scattered-Light Signal Normalization
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Solution Overview
Problem
Existing optical hazard detectors using the scattered-light principle face challenges in accurately distinguishing between smoke and dust particles, leading to potential false alarms and inadequate detection of high dust or steam densities, which can indicate safety risks such as fire acceleration or hot water leaks.
Innovation Solution
The method involves irradiating particles with both infrared and blue light, normalizing and comparing the scattered-light signals to determine an amplitude ratio, which allows for the evaluation of either the first scattered-light signal for dust/steam density or the second for smoke density, enabling separate signaling for dust/steam warnings and fire alarms based on predefined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the detector uses scattered-light principle to detect particles, then it can detect both smoke and dust, but it cannot accurately distinguish between them leading to false alarms
Solution Approach 1:
The detection system is segmented into multiple evaluation paths based on particle size. The evaluation unit divides the detection process into distinct branches: one for smoke particles (smaller size) and one for dust/steam particles (larger size), using wavelength-specific scattering characteristics to separate the detection paths and eliminate false alarms.
Solution Approach 2:
The system changes the wavelength parameter of incident light to differentiate particle types. By using at least two different wavelengths (e.g., visible and infrared), the system exploits the wavelength-dependent scattering properties to accurately distinguish between smoke and dust/steam particles, improving measurement precision.
2Loss of information
If the detector only evaluates one scattered-light signal, then the device complexity is reduced, but it cannot provide separate dust/steam and smoke density information
Solution Approach 1:
The evaluation unit dynamically switches between evaluating different scattered-light signals based on the detected particle type. When dust/steam particles are detected, the system dynamically evaluates the first scattered-light signal for dust/steam density; when smoke particles are detected, it dynamically evaluates the second scattered-light signal for smoke density, providing appropriate information without requiring constant complex multi-signal processing.
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 effectively suppresses false alarms by distinguishing between smoke and dust/steam, providing accurate density signals for both, thereby enhancing fire safety monitoring and identifying potential hazards like high dust or steam levels.
Implementation Method 1
an optical hazard detector with a detection unit operating in accordance with the scattered-light principle
Data Source
AI summary
Particles to be detected are irradiated by first wavelength light and second wavelength light. The light that is scattered by the particles is converted into a first and second scattered-light signals. The two scattered-light signals are normalized with respect to one another such that the amplitude profile thereof approximately corresponds to larger particles such as dust and steam. Furthermore, an amplitude ratio is formed between the two scattered-light signals and an amplitude comparison value (90%) is set, which corresponds to a predeterminable particle dimension in the cross-over region between smoke and dust/steam. Mainly the first scattered-light signal is evaluated if the amplitude ratio exceeds the amplitude comparison value (90%) and a dust/steam-density signal is emitted. In the other case, mainly the second scattered-light signal that is evaluated and a smoke-density signal is emitted.