Long-Wave Pass IR Filters for Flame Discrimination
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Solution Overview
Problem
Existing optical flame detectors face challenges in reliably distinguishing between actual flames and false alarm sources due to their inability to effectively discriminate between infrared radiation from flames and other sources, leading to increased costs and sensitivity issues with the use of multiple bandpass filters and pyroelectric detectors.
Innovation Solution
A flame detection apparatus utilizing a plurality of optical sensors with long-wave pass (LWP) infrared filters, where each filter is responsive to different wavelengths with no long-wave cutoff, allowing for enhanced discrimination and reduced costs by using fewer and less expensive filters, along with a protective covering providing a common cutoff wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple bandpass filters are used to improve flame discrimination, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention divides the infrared spectrum into multiple wavelength bands using multiple optical sensors, each equipped with a long-wave pass filter. This segmentation allows the system to capture spectral information at different wavelengths (e.g., 3.9 μm, 4.3 μm, 4.8 μm) independently, enabling flame discrimination through comparative analysis of signals from different bands while using simpler long-wave pass filters instead of multiple complex bandpass filters
Solution Approach 2:
Instead of using bandpass filters that block most wavelengths and pass only a narrow range (which increases complexity and cost), the invention inverts the approach by using long-wave pass filters that block only short wavelengths and pass a broad range of long wavelengths. This inversion allows each sensor to receive abundant infrared energy across a wide spectrum while still enabling discrimination through multi-wavelength comparison
2Measurement precision
If narrow bandwidth filters are used to enhance flame discrimination, then measurement precision is improved, but sensor cost and sensitivity requirements increase
Solution Approach 1:
The system segments the spectral detection across multiple sensors with different long-wave pass filter cutoff wavelengths, allowing each sensor to operate with a broad bandwidth while the collective array achieves spectral discrimination. This avoids the need for any single sensor to use a narrow bandwidth filter, maintaining high signal-to-noise ratios
Solution Approach 2:
The invention changes the filter parameter from narrow bandpass to broad long-wave pass characteristics. By adjusting the cutoff wavelength parameter of each long-wave pass filter (e.g., 3.5 μm, 4.0 μm, 4.5 μm), the system achieves spectral discrimination through parameter variation rather than bandwidth restriction, maintaining high photon flux and signal-to-noise ratio
3Measurement precision
If multiple sensors with different filters are used to improve discrimination, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The invention inverts the conventional approach by using long-wave pass filters instead of bandpass filters. Long-wave pass filters are simpler and less expensive to manufacture because they require fewer optical layers and can be made from common materials like germanium or silicon with appropriate coatings. Multiple sensors with these simpler filters are more cost-effective than fewer sensors with complex narrow bandpass filters
Solution Approach 2:
Each optical sensor in the array serves multiple functions: it detects infrared radiation across a broad wavelength range, provides spectral information at its specific cutoff wavelength, and contributes to flame discrimination through comparative analysis with other sensors. This multi-functionality reduces the need for specialized expensive components for each sensor
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 provides improved discrimination between flames and false alarms, reduces the overall cost of the detector, and enhances the signal-to-noise ratio by allowing more light to pass through, while being less sensitive to angle of incidence effects, thus offering a more reliable and cost-effective flame detection system.
Implementation Method 1
a first optical sensor configured with a first long-wave pass infrared filter and responsive to a first wavelength range and a second optical sensor configured with a second long-wave pass infrared filter and responsive to a second wavelength range
Implementation Method 2
Some system engineers have sought to alleviate some of the cost of adding more bandpass filters to the system by utilizing pyroelectric detectors such as lithium tantalate (LiTaO3)
Data Source
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AI summary
A flame detection apparatus is provided that provides low cost fire detection with improved false alarm discrimination and that includes at least two optical sensors, each configured with a Long Wave Pass IR filter with distinct minimum responsive wavelengths and arrayed to broadly sample the MWIR band.