Surface Mount Smoke Detector Back Scatter Geometry
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Solution Overview
Problem
Conventional photo-electric smoke detectors face manufacturing complexity and cost issues due to manual component insertion and are prone to false alarms, failing to meet UL 217-8 and 268-7 standards, as they cannot distinguish between hazardous and non-hazardous particle sizes.
Innovation Solution
A smoke detector design featuring a surface-mounted emitter and receiver configured to emit and receive light vertically, with a back scatter effect at an angular distance less than 90°, using surface-mount technology to simplify manufacturing and reduce complexity, and a controller to differentiate between fast and slow fires based on obscuration thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If manual insertion of emitters and receivers through PCB holes is used, then precise angular placement for reliable detection is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical insertion method (manual placement through PCB holes at specific angles) with a surface-mount configuration where emitters and receivers are mounted vertically on the PCB surface. This eliminates the need for precise angular placement through holes and simplifies the manufacturing process while maintaining detection reliability through the back-scatter optical geometry.
Solution Approach 2:
The patent transitions from a two-dimensional angular placement problem (placing components at specific angles through PCB holes) to a three-dimensional solution by mounting components vertically on the PCB surface. This dimensional change allows the emitters and receivers to be positioned perpendicular to the PCB plane, eliminating angular placement complexity while enabling back-scatter detection geometry.
2Reliability
If conventional forward light scattering arrangement is used, then detection of mid-size particles is achieved, but false alarms occur with small-size and large-size non-smoke particles
Solution Approach 1:
The patent changes the detection parameter from forward light scattering to back-scatter light reflection by positioning the receiver to detect light reflected at angles greater than 90 degrees from the emitter direction. This parameter change in optical geometry enables discrimination between smoke particles and non-smoke particles based on their different back-scatter characteristics, reducing false alarms while maintaining detection accuracy.
3Measurement precision
If multiple emitters and receivers at various angles are used, then particle discrimination capability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent makes the single emitter and receiver configuration universal by designing them to work together in a back-scatter geometry that inherently provides particle discrimination capability. The receiver positioned to detect back-scattered light performs multiple functions: detecting smoke particles, discriminating particle sizes, and rejecting non-smoke particles, eliminating the need for multiple component assemblies.
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 design simplifies manufacturing, reduces false alarms by accurately discriminating between particle sizes, and meets UL standards by triggering alarms appropriately, avoiding false positives during non-hazardous events while detecting hazardous fires effectively.
Implementation Method 1
The receiver is configured to receive light at an angular distance less than 90° reflected by the ambient materials in the chamber. The angular distance generates a back scatter effect.
Implementation Method 2
photo-electric smoke detectors work based on light reflection principles
Data Source
AI summary
A smoke detector with a surface mounted emitter configured to emit light substantially vertically and a surface mounted receiver configured to receive light at an angular distance less than 90° reflected by ambient materials, and a method of operating the smoke detector are provided. The angular distance at which the light is reflected by the ambient materials generates a back scatter effect. The smoke detector includes a housing defining a chamber for receiving the ambient materials, a supporting structure (e.g., a printed circuit board (PCB)) disposed adjacent to the housing, an emitter mounted substantially vertically to an upper surface of the supporting structure, and a receiver mounted substantially vertically to the upper surface of the supporting structure. The smoke detector may also include a controller configured to receive output signals from the receiver (to determine whether a current condition of the chamber indicates a need to trigger an alarm).