Synchronous Sampling for Fluorescent Light Immunity in Microwave Detectors
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Solution Overview
Problem
Microwave Doppler transceivers in security systems are prone to false alarms due to sensitivity to fluorescent lights, and existing solutions like hardware notch filters are impractical for high-volume, low-cost manufacturing and may remove too much of the desired signal, while DIP switches for frequency selection are cumbersome and error-prone.
Innovation Solution
A system and method that automatically detects and synchronizes with ambient line frequencies to isolate and filter noise from fluorescent light flicker, using amplifiers, filters, and controllers to adjust interrogation timing, eliminating the need for installer intervention and addressing frequency variations between 50 Hz and 60 Hz regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware notch filters are used to block fluorescent light frequencies, then false alarms from fluorescent lights are reduced, but the desired signal may be removed and manufacturing complexity increases
Solution Approach 1:
The patent replaces hardware notch filters (mechanical/electrical filtering system) with a software-based synchronous sampling approach. The controller adjusts the sampling rate to match the line frequency, creating a digital comb filter that eliminates fluorescent light interference without requiring physical filtering components. This substitution reduces device complexity while maintaining reliability.
Solution Approach 2:
The patent dynamically changes the sampling rate parameter to match the detected line frequency (50 Hz or 60 Hz). By adjusting this key parameter, the system creates notches at the line frequency and its harmonics in the frequency domain, effectively blocking fluorescent light interference without removing desired motion detection signals. This parameter-based solution is simpler than hardware filtering.
2Adaptability or versatility
If DIP switches are used for frequency selection, then the system can adapt to different line frequencies, but installation time increases and error potential increases
Solution Approach 1:
The patent implements automatic line frequency detection and adaptation. The controller measures the ambient electromagnetic environment to detect the local line frequency (50 Hz or 60 Hz) and automatically adjusts the sampling rate accordingly. This self-service approach eliminates the need for installer intervention with DIP switches, reducing installation time and error potential while maintaining full adaptability to different frequency regions.
Solution Approach 2:
The system performs preliminary automatic frequency detection during initialization before the user needs to operate it. By proactively detecting and adapting to the local line frequency beforehand, the system ensures optimal performance without requiring the installer to manually configure DIP switches, thus improving ease of operation while preserving adaptability.
3Reliability
If sampling is performed at fixed 50 Hz, then line noise rejection is achieved, but the system fails in 60 Hz regions and produces aliases when line frequency varies
Solution Approach 1:
The patent transforms the static fixed 50 Hz sampling rate into a dynamic sampling rate that adapts to the actual line frequency. The controller continuously monitors and adjusts the sampling rate to match the detected line frequency (50 Hz, 60 Hz, or intermediate values). This dynamic approach maintains reliable line noise rejection while providing universal compatibility across different frequency regions and conditions, eliminating the aliases problem that occurs with fixed sampling rates.
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 solution provides fluorescent light immunity by synchronizing the intrusion detection system with the line frequency, reducing false alarms and ensuring accurate motion detection without requiring manual frequency setting, thus enhancing the reliability and ease of use of security systems.
Implementation Method 1
an object that is in motion, towards or away, from the Microwave Doppler transceivers will shift the original frequency and reflect a return signal at a frequency that is offset by a particular frequency, based on the speed and direction of the object relative to the microwave Doppler source. This phenomenon is known as a Doppler shift.
Implementation Method 2
Fluorescent lights operate by supplying a high voltage pulse across a space filled with a gas that, once excited by the pulse, causes phosphor particles to fluoresce, thus emitting light.
Implementation Method 3
The transceiver also amplifies the return pulse
Data Source
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AI summary
A system and method for reducing interference caused by fluorescent light on alarm system components using synchronous sampling is provided. The system incorporates a detector for detecting the line frequency of a power line and synchronizes the security system to the detected line frequency. The detector employed may be a light emitting diode configured as a photodetector, an antenna tuned for frequencies near 55 Hz, or a filter connected to an output of a Microwave channel.