AC Zero-Crossing Detection with Counter Gating for Noise Rejection
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Solution Overview
Problem
Existing zero crossing detection circuits are ineffective in preventing false zero crossing identifications, leading to inaccurate RMS voltage calculations, inappropriate switch transfers, phase rotation errors, and potential equipment damage due to noise transients in alternating voltage power sources.
Innovation Solution
A method and system that utilize a signal status counter and a processor to detect zero crossings by decrementing or incrementing the counter based on signal logic values, setting a flag to enable detection only when specific conditions are met, thereby distinguishing true zero crossings from noise-induced false detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional zero crossing detection circuits are used, then zero crossing points can be detected, but false zero crossing identifications occur due to noise pulses
Solution Approach 1:
The system performs preliminary validation by checking signal conditions (positive polarity, above threshold voltage, minimum pulse width) before confirming a zero crossing event. This preliminary action filters out noise pulses that don't meet the criteria, preventing false zero crossing identifications while maintaining accurate detection of true zero crossings
Solution Approach 2:
The patent introduces an intermediary validation process between signal detection and zero crossing confirmation. This intermediary layer checks multiple parameters (polarity, voltage threshold, pulse width) and only allows true zero crossings to pass through to the detection output, effectively blocking noise-induced false detections
2Reliability
If noise filtering is applied to prevent false detections, then reliability improves, but detection response time increases
Solution Approach 1:
The system applies partial filtering by implementing minimum pulse width requirements and voltage threshold checks only when necessary to distinguish noise from true zero crossings. This selective application of filtering criteria prevents excessive delay while still achieving reliable false detection prevention
Solution Approach 2:
The patent dynamically adjusts detection parameters such as voltage thresholds and pulse width requirements based on signal characteristics. By changing these parameters adaptively, the system maintains fast response time for true zero crossings while applying sufficient filtering to prevent false detections from noise pulses
3Reliability
If multiple validation conditions are implemented, then false zero crossing detections are prevented, but device complexity increases
Solution Approach 1:
The validation process is segmented into distinct functional blocks: polarity detection, voltage threshold checking, pulse width measurement, and zero crossing confirmation. Each segment handles a specific validation aspect independently, making the complex multi-condition system more manageable and implementable while maintaining high reliability
Data Source
AI summary
Methods and systems for detection of zero crossings in a signal are described. For example, true zero crossings in an alternating voltage power source signal can be detected in the presence of noise pulses. The zero crossing detections are performed by establishing a value of a signal status counter, and at a repeating interval if the signal is a logic low value, the value of the signal status counter is decremented if the signal status counter is greater than a first value otherwise a flag is set to enable detection of a zero crossing in the signal. In addition, at the repeating interval, if the signal is a logic high value, the value of the signal status counter is incremented, and if after incrementing the signal status counter is equal to a second value and the flag is set, a zero crossing of the signal is declared.