Backscatter Smoke Detector Angular Geometry
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Solution Overview
Problem
Conventional photo-electric smoke detectors produce false alarms due to their inability to differentiate between large-size hazardous particles and small-size non-smoke particles, failing to meet Underwriter Laboratories (UL) 217-8 and 268-7 standards, which require accurate discrimination between 'broiling hamburger' and 'flaming foam fire' scenarios.
Innovation Solution
A photo-electric smoke detector with a single emitter and receiver configured at an angular distance of less than 90°, generating a back scatter effect to minimize detection of small particles during non-hazardous events while accurately detecting larger particles, using a controller to determine alarm thresholds based on a time increment between specific obscuration levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photo-electric smoke detectors use standard forward light scattering configuration, then they can detect large-size particles from hazardous fires, but they produce false alarms for small-size particles from non-hazardous events like cooking
Solution Approach 1:
The patent changes the optical geometry parameter by positioning the light receiver at an angular distance of less than 90 degrees from the light emitter, creating a backscatter configuration. This geometric parameter change enables the detector to distinguish between particle sizes based on their light scattering characteristics, thereby reducing false alarms while maintaining detection accuracy for hazardous fires.
Solution Approach 2:
The patent introduces a new spatial dimension by measuring the angular distance between the emitter and receiver. This angular dimension provides an additional parameter for particle characterization, allowing the system to differentiate between small non-hazardous particles and large hazardous particles based on their distinct light scattering patterns in the backscatter configuration.
2Reliability
If smoke detectors use multiple emitters and receivers to improve particle discrimination, then detection accuracy improves, but device complexity and cost increase
Solution Approach 1:
Instead of adding multiple emitters and receivers, the patent achieves particle discrimination by changing the geometric parameters of a single emitter-receiver pair. By positioning the receiver at less than 90 degrees from the emitter and using specific obscuration thresholds, the system achieves the same discrimination capability with reduced component count, thereby lowering device complexity and cost.
Solution Approach 2:
The single emitter-receiver pair is designed to perform multiple functions: detecting particle presence, characterizing particle size through light scattering patterns, and triggering appropriate alarms. This multi-functional design eliminates the need for separate detection systems for different particle types, reducing overall device complexity while maintaining comprehensive detection capability.
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
The solution reduces false alarms by accurately distinguishing between small and large particles, ensuring compliance with UL 217-8 and 268-7 standards without increasing complexity or cost, allowing for timely and appropriate alarm triggering during hazardous fires.
Implementation Method 1
A photo-electric smoke detector is a type of smoke detector that works based on light reflection principles
Implementation Method 2
generating a back scatter effect to minimize detection of small particles during non-hazardous events
Data Source
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AI summary
A smoke detector (100) with an emitter (120) and a receiver (130) defining an angular distance there between less than 90°, the angular distance between the emitter and the receiver generating a back scatter effect, and a method of operating the smoke detector are provided. The smoke detector (100) includes a housing (110) defining a chamber (111) for receiving ambient materials, an emitter (120) configured to emit light (ex. infrared light or any light in the visible spectrum, such as blue light) into the chamber, a receiver (130) configured to receive light reflected from the ambient materials in the chamber and generate output signals, and a controller (140) configured to receive output signals from the receiver and determine whether a current condition of the chamber indicates a need to trigger an alarm.