Smoke Detector LED Optical Feedback Circuit
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Solution Overview
Problem
High sensitivity aspirated smoke detectors often lack a quiescent level of optical measurement, making it difficult to determine the operational status of the optical source, such as a light emitting diode (LED), which can lead to issues in maintaining proper operation and detecting potential failures like burnout.
Innovation Solution
Implementing a feedback system using a photo diode to measure reflected light from the LED, which adjusts the optical output and provides feedback to maintain the LED within its linear region, and includes a detection circuit to generate maintenance signals when the LED is not operating correctly, along with an aspiration unit to control the smoke chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high sensitivity photo sensor is used in an aspirated smoke detector, then the detection sensitivity is improved, but the quiescent level of optical measurement becomes too low or nonexistent, making it difficult to determine source operational status
Solution Approach 1:
A non-smoke particulate material is introduced as an intermediary into the sensing chamber to provide a quiescent background scattering level. This allows the high sensitivity photo sensor to have something to measure when no smoke is present, enabling determination of source operational status while maintaining high detection sensitivity for actual smoke events.
Solution Approach 2:
The system creates an artificial quiescent optical environment by introducing non-smoke particles that simulate the light scattering properties needed for measurement. This copied scattering environment enables the photo sensor to operate in its optimal high-sensitivity range while still providing a measurable baseline for source status determination.
2Measurement precision
If the optical source operates at high intensity to ensure detection sensitivity, then smoke detection capability is improved, but the risk of LED burnout or degradation increases
Solution Approach 1:
The photo sensor continuously monitors the light scattering from non-smoke particles in the chamber, providing feedback about the actual optical source intensity. This feedback mechanism enables real-time detection of LED degradation or burnout conditions, allowing the system to maintain reliable operation and alert users to source failures before they affect smoke detection capability.
Solution Approach 2:
The system performs preliminary monitoring of the optical source status by continuously measuring the quiescent scattering level. This preliminary detection of source degradation allows for proactive maintenance or replacement before the LED fails completely, ensuring continuous reliable operation.
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
Ensures the optical source operates within its linear range, providing reliable feedback for maintenance and ensuring continuous detection of smoke concentrations, while preventing LED burnout or degradation by adjusting the optical output and monitoring its status effectively.
Implementation Method 1
Some of the light from the LED is reflected off the lens. An optical sensor, such as a photo diode detects the reflected light.
Implementation Method 2
An optical sensor, such as a photo diode detects the reflected light. The current produced by the photo diode can be used to provide feedback
Implementation Method 3
monitoring of output of a source light emitting diode (LED) can be implemented
Implementation Method 4
measuring reflected or scattered light from a lens that is used to focus the LED light into a smoke chamber
Implementation Method 5
an aspiration unit, a fan or blower for example, can be coupled to the detector's smoke chamber to inject fluid into or draw fluid from that chamber
Data Source
AI summary
A photo-electric smoke detector includes a source of radiant energy and a closed loop control circuit which responds to a radiant energy feedback signal to adjust an output characteristic of the emitted radiant energy and which evaluates a quality characteristic of the emitted radiant energy. The feedback circuit and the source can be intermittently activated. Emitted radiant energy is directed toward a lens. The feedback signal is proportional to radiant energy reflected or scattered off of the lens.