Open Path Gas Detector WDM Filter Misalignment Tolerance
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Solution Overview
Problem
Current open path gas detectors are sensitive to slight misalignments and partial beam blockages between the transmitter and receiver, leading to incorrect gas determinations and false alarms due to the imaging optical system's 50% signal loss and sensitivity to alignment changes.
Innovation Solution
The open path gas detection system employs a wavelength-division multiplexing (WDM) filter and non-imaging Kohler lens arrangement, which separates radiation by wavelength, providing equal intensities to photodiodes and allowing for misalignments of up to ±1.5 degrees, reducing signal instability and false alarms through 'Top Hat Illumination' and adjustable field stops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an imaging optical system with beam splitter is used to provide separate signals for each detector, then wavelength separation is achieved, but signal loss is 50% in each channel and the system is sensitive to misalignment
Solution Approach 1:
The optical system is segmented into multiple non-imaging optical channels, each dedicated to a specific wavelength detection path. This segmentation eliminates the need for beam splitting and allows each channel to collect and transmit light independently to its corresponding detector, thereby avoiding 50% signal loss per channel while maintaining wavelength separation capability
Solution Approach 2:
A diffuser is introduced as an intermediary optical element between the light source and the non-imaging optical channels. The diffuser creates uniform illumination distribution across all channels, ensuring stable detection signals even when there are misalignments or beam blockages, thus acting as a mediator that decouples the system from alignment sensitivity
2Measurement precision
If an imaging optical system is used with dedicated band-pass filters for each detector, then accurate gas detection is achieved, but the system is sensitive to slight misalignment between dual optical channels
Solution Approach 1:
Instead of using imaging optics that require precise alignment between channels, the patent inverts the approach by using non-imaging optics that are inherently tolerant of misalignment. The optical design is fundamentally reversed from image-based to illumination-based, where uniform light distribution is achieved through diffusers rather than precise optical channel alignment
Solution Approach 2:
The patent changes the optical parameters by transitioning from imaging optics with narrow field-of-view requirements to non-imaging optics with wide acceptance angles. This parameter change allows the system to tolerate larger misalignments while maintaining detection accuracy, as the non-imaging channels can accept light from a broader angular range
3Quantity of substance
If separate transmitter and receiver units are used at opposite ends of a straight beam path, then open path gas detection is achieved, but the system is vulnerable to partial beam blockage and misalignment
Solution Approach 1:
The patent transitions from a one-dimensional linear optical path to a multi-dimensional illumination pattern using non-imaging optics. The diffuser creates light propagation in multiple directions and dimensions, so that partial blockage in one dimension does not completely obstruct the detection path, providing redundancy and robustness against beam blockage
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 configuration doubles signal strength, tolerates larger misalignments, and reduces false alarms by maintaining stable detection signals even under conditions of optical axis instability, such as in marine vessels, and extends maintenance intervals by allowing larger beam misalignments.
Implementation Method 1
an optical element, such as a wavelength-division multiplexing, WDM, filter operable to separate incident beam into a first wavelength portion and a second wavelength portion
Implementation Method 2
a first photodiode and a second photodiode arranged to receive the first and second wavelength portions respectively
Implementation Method 3
the wavelength of the infrared radiation is chosen so that it is absorbed by the gas of interest
Data Source
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AI summary
In implementations, an open path gas detector is disclosed that can include imaging or non-imaging optical components. The detector can include components that allow for misalignment of radiation received by the detector of about 1 without causing false alarms. In implementations, the detector can include a beam splitter or a wavelength-division multiplexing filter to allow for more of the radiation received by the detector to be detected by the sensors.