Photoelectric Smoke Detector Noise Filtering With Dual Light Sensors
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Solution Overview
Problem
Photoelectric smoke detectors face challenges in distinguishing extraneous ambient light from the transmitted light pulse, especially in open room detectors, leading to noise interference and reduced sensitivity to smoke particles, which violates UL standards.
Innovation Solution
Implementing multiple light sensors, including a first light sensor to detect reflected light and a second light sensor to detect noise, with a control circuit to subtract or filter out noise signals using techniques like Weiner or Kalman filters, improving the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the tripping point of the smoke detector is moved closer to the noise floor to increase sensitivity to smoldering fires, then sensitivity to smoke particles is improved, but noise interference from ambient light becomes greater
Solution Approach 1:
The detection function is segmented into two independent light sensors: one optimized for detecting scattered light from smoke particles, and another for measuring ambient noise light. This segmentation allows each sensor to be specialized for its specific function, enabling the system to maintain high sensitivity while separately measuring and compensating for noise interference.
Solution Approach 2:
The second light sensor acts as an intermediary that measures the ambient noise light level, which then serves as a reference signal for the control circuit to subtract from the first sensor's output. This intermediary measurement enables the system to compensate for noise without directly affecting the primary detection function.
2Measurement precision
If multiple light sensors are added to detect and subtract noise signals, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The control circuit performs multiple functions: it processes the signal from the first light sensor, measures the noise level from the second light sensor, subtracts the noise component, and triggers the alarm when appropriate. By making the control circuit multi-functional, the patent reduces the need for separate dedicated components for each function, thereby managing complexity while achieving noise suppression.
3Ease of manufacture
If open room detector design is used to eliminate chamber, then manufacturing cost and complexity are reduced, but ability to distinguish transmitted light pulse from ambient light becomes more difficult
Solution Approach 1:
The detection system is segmented into two independent sensing channels: one for smoke detection and one for ambient light measurement. This segmentation removes the need for a light-tight chamber while maintaining the ability to distinguish signal from noise through electronic separation of the detection functions.
Solution Approach 2:
The control circuit continuously monitors the ambient light level through the second sensor and uses this feedback to dynamically adjust the noise compensation applied to the first sensor's signal. This feedback mechanism enables the open-room design to maintain accurate smoke detection despite varying ambient light conditions.
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
Enhances the detector's performance by reducing noise interference, allowing for chamberless designs and improved sensitivity to smoke particles, meeting UL standards while reducing energy costs.
Implementation Method 1
When smoke particles are present, the smoke particles scatter the light beam. A light sensor in the smoke detector detects the scattered light to allow an alarm to be triggered. The light source and light sensor may be positioned off angle such that when smoke is present, the smoke reflects the light and causes the receiver to receive the reflected light.
Implementation Method 2
Extraneous ambient light (e.g., from the sun or lighting in a room) may be difficult to distinguish from the transmitted light pulse, especially if the photoelectric smoke detector is an open room detector.
Data Source
AI summary
A system and method for the use of digital analysis to filter out extraneous light are disclosed. The system may include a light source to emit a light beam in a smoke detector. The system may include a first light sensor in the smoke detector to receive a reflected light beam corresponding to the light beam reflecting off a smoke particle. The system may include a second light sensor in the smoke detector to receive a noise light corresponding to ambient light in the smoke detector. The system may include a control circuit. The control circuit may be to receive the reflected light signal from a first light sensor indicative of the reflected light beam and to receive a noise signal from the second light sensor indicative of the noise light. The control circuit may be to reduce noise from the reflected light signal based on the noise signal.