Dual Sensor Fire Detector Using Shared Light Source
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Solution Overview
Problem
Existing fire detectors face challenges in efficiently detecting both smoldering and flaming fires, with photoelectric sensors being better for smoldering fires and ionization sensors for flaming fires, while MOS gas sensors consume high power and lack selectivity, limiting their application in battery-powered systems.
Innovation Solution
A dual-sensor fire detector using a blue or UV light source for both smoke and gas sensing, where the light source enhances the operation of an MOS gas sensor, potentially heating it intermittently, and utilizing different oxides for NO2 and CO detection, with radiant energy divided into beams for both scattering volume and gas sensor activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If MOS gas sensors are heated to 200-400°C using a resistance heater for proper operation, then the sensor sensitivity and response are improved, but the power consumption increases significantly (up to 500 mW for thick film sensors)
Solution Approach 1:
The patent combines the light source function with the heating function. The blue or UV LED serves dual purposes: detecting smoke particles through light scattering and providing radiant energy to heat the MOS gas sensor. This merging eliminates the need for a separate resistance heater, significantly reducing power consumption while maintaining sensor sensitivity.
Solution Approach 2:
The light source is designed to perform multiple functions simultaneously: smoke detection via forward scattering, MOS sensor heating through radiant energy, and potential enhancement of sensor response. This multi-functionality resolves the contradiction by eliminating dedicated heating infrastructure that would consume additional power.
2Device complexity
If a single light source is used for both smoke detection and MOS sensor heating, then device complexity is reduced and power consumption is lowered, but the light intensity must be optimized to serve both functions effectively
Solution Approach 1:
The patent optimizes specific parameters of the blue or UV LED to achieve dual functionality. By selecting appropriate wavelengths (blue or UV range) and adjusting operational characteristics, the light source effectively performs both smoke detection and sensor heating. This parameter optimization resolves the contradiction by enabling a single component to meet multiple performance requirements.
3Measurement precision
If MOS gas sensors are used for gas detection, then sensitivity to oxidizing gases is improved, but selectivity to specific gases is reduced as they respond to a whole class of oxidizing gases
Solution Approach 1:
The patent employs multiple MOS sensors, each with different selective oxide coatings, to detect different gas types. This segmentation allows the system to maintain high sensitivity to oxidizing gases while achieving selectivity through the combination of multiple specialized sensors. Each sensor targets specific gases (e.g., NO2, CO) while the overall system provides comprehensive gas 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
This approach allows for efficient detection of both smoldering and flaming fires with reduced power consumption and improved selectivity, enabling effective fire detection in battery-powered systems.
Implementation Method 1
This is predicted by the Mie scattering theory, which says that particles will preferentially scatter light in the forward direction when the wavelength of light approaches the particle size.
Implementation Method 2
Radiant energy can be directed onto such sensors to increase their sensitivity instead of heating them. Doing so reduces the amount of power required to operate them.
Implementation Method 3
Most detectors use only forward scattering detectors with a light source in the near infrared.
Data Source
AI summary
A dual sensor fire detector includes a smoke sensor and a gas sensor. A source of radiant energy emits a primary beam that is formed into first and second beams. One beam is directed into a smoke sensing chamber. The other is directed to the gas sensor. Outputs from the smoke sensor and the gas sensor are combined to make a fire determination.